Characterization of the heat source of thermal aquifers within the Soutpansberg Basin in the Limpopo Province, South Africa: Evidence from geophysical and geological investigations
- Authors: Nyabeze, Peter Kushara
- Date: 2019
- Subjects: Basins (Geology) -- Analysis Geology, Structural -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Geology)
- Identifier: http://hdl.handle.net/10353/15167 , vital:40192
- Description: The research was conducted to contribute towards the knowledge base on the potential for geothermal energy in the Soutpansberg Basin, located in the Limpopo Province of South Africa. The focus area was Siloam, an area that hosts a hottest spring with the highest recorded temperature of 67.5°C. The research involved visits to the Soutpansberg Basin, water sampling, carrying out ground geophysical surveys, and high-level processing of airborne magnetic data to determine depths and temperatures of magnetic sources. The water samples from the hot springs were found to be enriched in sodium, bicarbonate and chlorine with very low concentrations of other element species. The chemical composition of the spring water indicated a source chemistry comprising of the Na-ClHCO3 water assemblage that is a typical signature for deep circulating groundwater of meteoric origin. The circulation depth was inferred to be 2.0 km. The increased resolution of the ground magnetic, electrical resistivity tomography, and electromagnetic conductivity methods data made it possible to delineate subsurface structures at the spring such as dykes, sills, faults and fractures from generated depth models. Modelling of ground magnetic data showed that the Siloam hot spring occurred between two interpreted north dipping dykes approximately 150 m apart. The minimum depth extent of the dykes was interpreted to be 650 m. The magnetic susceptibility values determined from rock measurements and modelling of magnetic data indicated the presence of volcanic and metamorphic rocks. Electromagnetic profiling data showed that there were three main high conductivity zones in the study area with values above 100 mS/m; A central zone associated with the spring; A zone to the south of the spring and a north zone associated with the Siloam Fault. Ground geophysics survey results confirmed the existence of the Siloam Fault. Two artesian boreholes with water warmer than 40 °C were identified to the south of the Siloam hot spring. Both electromagnetic conductivity and electrical resistivity tomography surveys delineated lateral and vertical variation in the bedrock to depths of 40 m to 60 m. Water bearing structures that could be faults, or fractures were identified. Layering due to weathering and water content was found to be in the depth range of 20 m to 40 m. The depths of the potential heat sources were computed from the radially averaged power spectrum of airborne magnetic data for square blocks with side dimensions L of 51 km, 103 km, and 129 km. Spectral analysis based approaches namely Centroid method, Spectral peak method, and the Fractal based approach were used for computing depth and temperatures to heat sources. Airborne magnetic data sets with larger window sizes were preferred for depth computations, as they preserved spectral signatures of deeper sources and reduced the contribution of shallower sources. The size of the data windows did not have a marked effect of depth and temperature values. Shallower magnetic sources depths of approximately 2.0 km were delineated using the Euler deconvolution method. An anticlinal feature at depths of 2.0 to 4.5 km was 4 Final Submission of Thesis, Dissertation or Research Report/Project, Conference or Exam Paper delineated in the central part of the basin. Spectral analysis results indicated that the depth to the top of magnetic sources was at 3.5 km to 6.2 km; the centroid of the basement at 7.92 km to 13.41 km, and the basal below 11.09 km and 14.08 km. The lower end depth spectrum was determined from application of the Centroid method with the deeper being results from the Fractal based approach. The Spectral peak method was useful for determining the depth to the top of magnetic sources. The temperature of the top of magnetic sources and basement centroid were computed to be in the range 234.00 °C to 281.34 °C. Magnetic source depths and basal temperatures that were in the Curie point range within which rocks lose magnetism due to heat were determined, using a computation approach that utilised fractal parameters, to be 21.39 km and 577.42 °C, respectively. Increasing the value of the fractal parameter β from 0 to 4, had an effect of retaining deeper depths and higher temperatures. The fractal parameter β range of 3 to 4 that gave the Curie point parameters indicated basal rock types with an igneous predisposition. The research highlighted evidence for the existence of the Soutpansberg Basin Geothermal Field (SBGF). The area around Siloam is a potential target for drilling exploration geothermal energy boreholes based on the occurrence of hot springs, shallow heat source depths, anticlinal structure, high formation temperatures, deep circulating water and the achieved Curie point temperature.
- Full Text:
- Date Issued: 2019
- Authors: Nyabeze, Peter Kushara
- Date: 2019
- Subjects: Basins (Geology) -- Analysis Geology, Structural -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Geology)
- Identifier: http://hdl.handle.net/10353/15167 , vital:40192
- Description: The research was conducted to contribute towards the knowledge base on the potential for geothermal energy in the Soutpansberg Basin, located in the Limpopo Province of South Africa. The focus area was Siloam, an area that hosts a hottest spring with the highest recorded temperature of 67.5°C. The research involved visits to the Soutpansberg Basin, water sampling, carrying out ground geophysical surveys, and high-level processing of airborne magnetic data to determine depths and temperatures of magnetic sources. The water samples from the hot springs were found to be enriched in sodium, bicarbonate and chlorine with very low concentrations of other element species. The chemical composition of the spring water indicated a source chemistry comprising of the Na-ClHCO3 water assemblage that is a typical signature for deep circulating groundwater of meteoric origin. The circulation depth was inferred to be 2.0 km. The increased resolution of the ground magnetic, electrical resistivity tomography, and electromagnetic conductivity methods data made it possible to delineate subsurface structures at the spring such as dykes, sills, faults and fractures from generated depth models. Modelling of ground magnetic data showed that the Siloam hot spring occurred between two interpreted north dipping dykes approximately 150 m apart. The minimum depth extent of the dykes was interpreted to be 650 m. The magnetic susceptibility values determined from rock measurements and modelling of magnetic data indicated the presence of volcanic and metamorphic rocks. Electromagnetic profiling data showed that there were three main high conductivity zones in the study area with values above 100 mS/m; A central zone associated with the spring; A zone to the south of the spring and a north zone associated with the Siloam Fault. Ground geophysics survey results confirmed the existence of the Siloam Fault. Two artesian boreholes with water warmer than 40 °C were identified to the south of the Siloam hot spring. Both electromagnetic conductivity and electrical resistivity tomography surveys delineated lateral and vertical variation in the bedrock to depths of 40 m to 60 m. Water bearing structures that could be faults, or fractures were identified. Layering due to weathering and water content was found to be in the depth range of 20 m to 40 m. The depths of the potential heat sources were computed from the radially averaged power spectrum of airborne magnetic data for square blocks with side dimensions L of 51 km, 103 km, and 129 km. Spectral analysis based approaches namely Centroid method, Spectral peak method, and the Fractal based approach were used for computing depth and temperatures to heat sources. Airborne magnetic data sets with larger window sizes were preferred for depth computations, as they preserved spectral signatures of deeper sources and reduced the contribution of shallower sources. The size of the data windows did not have a marked effect of depth and temperature values. Shallower magnetic sources depths of approximately 2.0 km were delineated using the Euler deconvolution method. An anticlinal feature at depths of 2.0 to 4.5 km was 4 Final Submission of Thesis, Dissertation or Research Report/Project, Conference or Exam Paper delineated in the central part of the basin. Spectral analysis results indicated that the depth to the top of magnetic sources was at 3.5 km to 6.2 km; the centroid of the basement at 7.92 km to 13.41 km, and the basal below 11.09 km and 14.08 km. The lower end depth spectrum was determined from application of the Centroid method with the deeper being results from the Fractal based approach. The Spectral peak method was useful for determining the depth to the top of magnetic sources. The temperature of the top of magnetic sources and basement centroid were computed to be in the range 234.00 °C to 281.34 °C. Magnetic source depths and basal temperatures that were in the Curie point range within which rocks lose magnetism due to heat were determined, using a computation approach that utilised fractal parameters, to be 21.39 km and 577.42 °C, respectively. Increasing the value of the fractal parameter β from 0 to 4, had an effect of retaining deeper depths and higher temperatures. The fractal parameter β range of 3 to 4 that gave the Curie point parameters indicated basal rock types with an igneous predisposition. The research highlighted evidence for the existence of the Soutpansberg Basin Geothermal Field (SBGF). The area around Siloam is a potential target for drilling exploration geothermal energy boreholes based on the occurrence of hot springs, shallow heat source depths, anticlinal structure, high formation temperatures, deep circulating water and the achieved Curie point temperature.
- Full Text:
- Date Issued: 2019
Sedimentology and shale gas potential of the Ecca Group, Karoo Supergroup in the Eastern Cape, South Africa
- Authors: Nemanashi , Tshisikhaiwe
- Date: 2019
- Subjects: Sedimentology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14616 , vital:40023
- Description: The aim of the study was to establish a deeper understanding on the stratigraphy, sedimentology, petrology, organic geochemistry and diagenesis of the Ecca Group, and to provide new insight on the shale gas occurrence and potential of the Ecca Group, Karoo Supergroup in the southern Karoo Basin. The Ecca Group stratigraphy is divided into five formations from the bottom upwards, namely the Prince Albert, Whitehill, Collingham, Ripon and the Fort Brown Formations. The stratigraphy of the five studied stratigraphy’s formations is now sub-divided into two new different members each. These subdivision was based on field investigation of lithological features, sedimentary structures, facies characteristics and stratigraphic correlation points. Each member has been assigned a lithological name. Sixteen sedimentary facies have been identified in the study area and were subdivided into six distinctive facies associations (FA 1, FA 2, FA 3, FA 4, FA 5 and FA 6). Sedimentological characteristics of facies associations identified indicate that the Ecca Group sediments initially accumulated in a deep marine environment, progressed through turbidite, shallow marine and ended in lacustrine and deltaic environments. The stratigraphic succession of the Ecca Group constitutes a perfect regression sequence, indicating that the marine water gradually retreated and the sea-level gradually dropped. Grain size analysis was performed on twenty four Ecca Group sandstone samples. Statistical parameters of grain-size statistical parameters, linear discriminate functions, passega diagrams and bivariate analysis were used to reveal the hydrodynamic conditions and depositional environments. The results indicated that the Ecca Group sandstones are mostly fine to very fine grained, near-symmetrical, mesokurtic and indicative of dominance of low energy environments. The linear discriminate function analysis for the Prince Albert, Whitehill, Collingham and Ripon Formations samples indicates that the majority of the deposits were by turbidity currents all in a deep marine environment; whilst of the Fort Brown Formation samples are lacustrine/deltaic deposits. The depositional mechanism C-M plot indicates that majority of the Ecca Group sediments clustered in the PQ and QR field suggesting deposition mainly by suspension, rolling or saltation as well as graded suspension. Modal mineral composition analysis indicates that the main framework grains of the Ecca Group sandstones are quartz, feldspar as well as lithic fragments derived from metamorphic, igneous and sedimentary rocks with a few from volcanic origin. The Ecca Group sandstones iii are immature compositionally and can be classified as feldspathic wackes and lithic wackes. The QFL ternary diagram revealed a dissected and recycled orogen arc provenance; whereas QmFLt ternary diagram point to dissected arc and transitional arc sources to an active continental margin as well as recycled provenance. These provenance characteristics suggest a metamorphic and plutonic terrains influence as the main source rock with minor debris derived from recycled sedimentary rocks. The weathering diagram and semi-quantitative weathering index suggests that the sandstones from the Ecca are mostly from a plutonic source area under arid to humid climatic conditions. The detrital modal compositions of these Ecca Group sandstones are related to a strike-slip setting, back arc to continental margin setting. Diagenetic features of the Ecca sandstones and shales are subdivided into early, late (burial) and uplift-related diagenetic stages. Mechanical compaction, recrystallization, cementation, replacement and the dissolution of framework grains or cements are some of the main diagenetic processes that largely affected the Ecca sediments. Early diagenetic processes include cementation, point/planar contact, formation of pyrite, hematite cements and mineral inversions. Recrystallization, replacement, compaction, overgrowth, albitization, seritisation, illitization, concave-convex and suture contacts as well as dissolution took place mostly in the later diagenetic stage due to increase of temperature and pressure as burial depth increased. The uplift-related diagenetic stage was mostly affected by deformation and fracturing, calcitization, dissolution, erosion and weathering. Diagenetic processes largely affected the porosity and permeability of the reservoir rock properties of the Ecca Group. Organic geochemistry results indicate that the sediments were highly weathered and the TOC values ranging from 0.10 to 7.35 wt% with mostly less than 0.5%, which indicate the source rocks have poor oil potential. The majority of the Ecca Shales have HI values less than 50 mg HC/g, TOC indicating Type-IV kerogen mostly derived from reworked organic matter with very little hydrocarbon generation potential. The relatively high Tmax (oC) and vitrinite reflective values indicate that most shales are thermally over-matured thus they have low hydrocarbon pontential.
- Full Text:
- Date Issued: 2019
- Authors: Nemanashi , Tshisikhaiwe
- Date: 2019
- Subjects: Sedimentology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14616 , vital:40023
- Description: The aim of the study was to establish a deeper understanding on the stratigraphy, sedimentology, petrology, organic geochemistry and diagenesis of the Ecca Group, and to provide new insight on the shale gas occurrence and potential of the Ecca Group, Karoo Supergroup in the southern Karoo Basin. The Ecca Group stratigraphy is divided into five formations from the bottom upwards, namely the Prince Albert, Whitehill, Collingham, Ripon and the Fort Brown Formations. The stratigraphy of the five studied stratigraphy’s formations is now sub-divided into two new different members each. These subdivision was based on field investigation of lithological features, sedimentary structures, facies characteristics and stratigraphic correlation points. Each member has been assigned a lithological name. Sixteen sedimentary facies have been identified in the study area and were subdivided into six distinctive facies associations (FA 1, FA 2, FA 3, FA 4, FA 5 and FA 6). Sedimentological characteristics of facies associations identified indicate that the Ecca Group sediments initially accumulated in a deep marine environment, progressed through turbidite, shallow marine and ended in lacustrine and deltaic environments. The stratigraphic succession of the Ecca Group constitutes a perfect regression sequence, indicating that the marine water gradually retreated and the sea-level gradually dropped. Grain size analysis was performed on twenty four Ecca Group sandstone samples. Statistical parameters of grain-size statistical parameters, linear discriminate functions, passega diagrams and bivariate analysis were used to reveal the hydrodynamic conditions and depositional environments. The results indicated that the Ecca Group sandstones are mostly fine to very fine grained, near-symmetrical, mesokurtic and indicative of dominance of low energy environments. The linear discriminate function analysis for the Prince Albert, Whitehill, Collingham and Ripon Formations samples indicates that the majority of the deposits were by turbidity currents all in a deep marine environment; whilst of the Fort Brown Formation samples are lacustrine/deltaic deposits. The depositional mechanism C-M plot indicates that majority of the Ecca Group sediments clustered in the PQ and QR field suggesting deposition mainly by suspension, rolling or saltation as well as graded suspension. Modal mineral composition analysis indicates that the main framework grains of the Ecca Group sandstones are quartz, feldspar as well as lithic fragments derived from metamorphic, igneous and sedimentary rocks with a few from volcanic origin. The Ecca Group sandstones iii are immature compositionally and can be classified as feldspathic wackes and lithic wackes. The QFL ternary diagram revealed a dissected and recycled orogen arc provenance; whereas QmFLt ternary diagram point to dissected arc and transitional arc sources to an active continental margin as well as recycled provenance. These provenance characteristics suggest a metamorphic and plutonic terrains influence as the main source rock with minor debris derived from recycled sedimentary rocks. The weathering diagram and semi-quantitative weathering index suggests that the sandstones from the Ecca are mostly from a plutonic source area under arid to humid climatic conditions. The detrital modal compositions of these Ecca Group sandstones are related to a strike-slip setting, back arc to continental margin setting. Diagenetic features of the Ecca sandstones and shales are subdivided into early, late (burial) and uplift-related diagenetic stages. Mechanical compaction, recrystallization, cementation, replacement and the dissolution of framework grains or cements are some of the main diagenetic processes that largely affected the Ecca sediments. Early diagenetic processes include cementation, point/planar contact, formation of pyrite, hematite cements and mineral inversions. Recrystallization, replacement, compaction, overgrowth, albitization, seritisation, illitization, concave-convex and suture contacts as well as dissolution took place mostly in the later diagenetic stage due to increase of temperature and pressure as burial depth increased. The uplift-related diagenetic stage was mostly affected by deformation and fracturing, calcitization, dissolution, erosion and weathering. Diagenetic processes largely affected the porosity and permeability of the reservoir rock properties of the Ecca Group. Organic geochemistry results indicate that the sediments were highly weathered and the TOC values ranging from 0.10 to 7.35 wt% with mostly less than 0.5%, which indicate the source rocks have poor oil potential. The majority of the Ecca Shales have HI values less than 50 mg HC/g, TOC indicating Type-IV kerogen mostly derived from reworked organic matter with very little hydrocarbon generation potential. The relatively high Tmax (oC) and vitrinite reflective values indicate that most shales are thermally over-matured thus they have low hydrocarbon pontential.
- Full Text:
- Date Issued: 2019
A systematic review of online child sexual abuse: victim risk and offender profile and methodologies
- Authors: Sleeman, Ananda
- Date: 2017
- Subjects: Child sexual abuse , Child pornography , Sexually abused children , Online sexual predators
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/10761 , vital:26821
- Description: The purpose of this treatise was to synthesize the current research, nationally and internationally, both qualitative and quantitative, concerning online child sexual abuse. The study focused on crimes of a sexual nature perpetrated against children, with or without consent, in an online environment. The aim was to clearly articulate the characteristics of victims, including both their vulnerabilities and their protective factors and to provide offender profiles, including their methodologies. Method: A systematic search for peer reviewed articles published between 2000 and 2006 was conducted. The final sample included 73 articles, which were arranged in order of publication, and the top and bottom interquartile range was selected for review and coding. Results: 36 articles were thematically coded in order to identify the most prominent themes in the articles. The result of this review was a typology of victims and offenders, as well as offender methodologies that reflects an aggregation of the most prominent research on the subject of online child sexual abuse. Conclusion: Much of the common knowledge concerning online child sexual offenders and their victims is incorrect. The typologies identified in this review show a much more diverse picture of both offenders and victims than is held in popular knowledge. This research has identified the damage that misinformation can do, and has highlighted the need for accurate, empirically sound information to be made available to parents, teachers, health care professionals and youth.
- Full Text:
- Date Issued: 2017
A systematic review of online child sexual abuse: victim risk and offender profile and methodologies
- Authors: Sleeman, Ananda
- Date: 2017
- Subjects: Child sexual abuse , Child pornography , Sexually abused children , Online sexual predators
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/10761 , vital:26821
- Description: The purpose of this treatise was to synthesize the current research, nationally and internationally, both qualitative and quantitative, concerning online child sexual abuse. The study focused on crimes of a sexual nature perpetrated against children, with or without consent, in an online environment. The aim was to clearly articulate the characteristics of victims, including both their vulnerabilities and their protective factors and to provide offender profiles, including their methodologies. Method: A systematic search for peer reviewed articles published between 2000 and 2006 was conducted. The final sample included 73 articles, which were arranged in order of publication, and the top and bottom interquartile range was selected for review and coding. Results: 36 articles were thematically coded in order to identify the most prominent themes in the articles. The result of this review was a typology of victims and offenders, as well as offender methodologies that reflects an aggregation of the most prominent research on the subject of online child sexual abuse. Conclusion: Much of the common knowledge concerning online child sexual offenders and their victims is incorrect. The typologies identified in this review show a much more diverse picture of both offenders and victims than is held in popular knowledge. This research has identified the damage that misinformation can do, and has highlighted the need for accurate, empirically sound information to be made available to parents, teachers, health care professionals and youth.
- Full Text:
- Date Issued: 2017
Development of an enzyme-synergy based bioreactor system for the beneficiation of apple pomace lignocellulosic waste
- Authors: Abboo, Sagaran
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/315 , vital:19947
- Description: Due to the finite supply of non-renewable fossil fuels, agro-industrial wastes are identified as alternate, renewable sources for energy supply. Large amounts of fruit waste are generated in South Africa due to fruit juice and wine processing from apples, grapes and citrus fruit. Apple pomace is the solid residue that is left over after juice, cider and wine processing and constitutes between 25-30% of the total fruit. On a global scale millions of tonnes of apple pomace are produced; between 2006-2007 over 46 million tonnes were produced. In South Africa a total production of 244 469 tonnes were produced during the 2011- 2012 season. Initially, apple pomace was regarded as a waste by-product used for animal feed and compost in soil, however presently it is considered a source of dietary fiber and natural antioxidants like polyphenols. In addition, apple pomace has a high carbohydrate content and can be enzymatically hydrolysed to produce sugar monomers which, in turn, can be fermented by yeasts to produce bioethanol. The polyphenols present in apple pomace can be used for their health properties, and the bioethanol can be used as a replacement for fossil fuel. Apple pomace is lignocellulosic in nature and consists of hemicellulose, cellulose, lignin and pectin. A combination of enzymes such as cellulases, hemicellulases, pectinases and lignases are required to operate in synergy for the degradation of lignocellulosic biomass. This is due to the recalcitrant nature of lignocellulose. This study investigated the degradation of apple pomace using a combination of commercially obtained enzyme cocktails viz. Viscozyme L , Celluclast 1.5L and Novozyme 188. The commercial enzymes Viscozyme L and Celluclast 1.5L were added in a ratio of 1:1 (50%:50%). The final concentrations of the enzymes were 0.019 mg/ml each. Novozyme 188 was added to provide a final concentration of 0.0024 mg/ml. A novel cost effective 20L bioreactor was designed, constructed and implemented for the degradation of apple pomace to produce value added products. The hydrolysis of the apple pomace was performed initially in 1 L flasks (batch fed) and, once optimized, scaled up to a 20 L bioreactor in batch mode. The bioreactors were operated at room temperature (22 ± 2ºC) and in an unbuffered system. The sugars released were detected and quantified using an optimized validated HPLC method established in this study. The sugars released in the bioreactors were mainly glucose, galactose, arabinose, cellobiose and fructose. The polyphenols released in this study were gallic acid, catechin, epicatechin, chlorogenic acid, rutin and phloridzin, which have a number of health benefits. The simultaneous analyses of the polyphenols were performed using a newly developed and validated HPLC method established in this study. This method was developed to detect nine polyphenols simultaneously. The two HPLC methods developed and validated in this study for the analysis of sugars and polyphenols demonstrated good accuracy, precision, reproducibility, linearity, robustness and sensitivity. Both analytical methods were validated according to the International Convention on Harmonization (ICH). The HPLC parameters for sugar analysis were: refractive index (RI) as the detection mode, the stationary phase was a ligand-exchange sugar column (Shodex SP0810) and an aqueous mobile phase in isocratic mode was used. The HPLC method for polyphenols employed UV diode array detection (DAD) as the detection mode, a reverse phase column as the stationary phase and a mobile phase of consisting of 0.01 M phosphoric acid in water and 100% methanol using gradient elution mode. The highest concentrations of sugars released in the novel 20 L bioreactor with 20% apple pomace (w/v) substrate loading were as follow: glucose (6.5 mg/ml), followed by galactose (2.1 mg/ml), arabinose (1.4 mg/ml), cellobiose (0.7 mg/ml) and fructose (0.5 mg/ml). The amounts of polyphenols released at 20% (w/v) apple pomace substrate were epicatechin (0.01 mg/ml), catechin (0.002 mg/ml), rutin (0.03 mg/ml), chlorogenic acid (0.002 mg/ml) and gallic acid 0.01 (mg/ml). Two mathematical models were developed in this study for kinetic analysis of lignocellulose (apple pomace) hydrolysis in the novel 20 L bioreactor, using the experimental data generated by the above HPLC analyses. The first model, modelling with regression, defines the hydrolysis of the sugars glucose, galactose, cellobiose and arabinose produced in the novel 20 L bioreactor at 5%, 10%, 15% and 20% (w/v) substrate concentrations. The regression model describes the sugars produced in the 20 L bioreactor by minimizing the error of the sugars released by finding a value for K which minimises the function which computes the sum of squares of errors between the solution curves and the data points. The second, more complex, model developed in this study used a system of differential equations model (ODE). This model solved the system by using a numerical method, such as the Runge-Kutta method, then fitted the solution curves to the data. Both models simulated (and had the ability to predict) the production of sugars in the novel 20 L bioreactor for apple pomace hydrolysis. These two models also revealed the time at which the maximum amount of sugars were released, which revealed the optimum time to run the 20 L bioreactor in order to be more cost effective. The optimum time for maximum glucose (the main sugar used in fermentation for biofuel production) release was determined to be around 60 h. The ODE model, in addition, determined the rate at which the substrate became depleted, as well as the rate at which the enzymes became deactivated for the various substrate loadings in the 20 L bioreactor. A third model was developed to determine the optimal running cost of the bioreactor which incorporated the substrate loading and the amount of glucose (g/L) produced. The novel 20 L bioreactor constructed from cost effective materials demonstrated that agro-industrial waste can be converted to value-added products by lignocellolytic enzymes. The sugars released from apple pomace can be used in biofuel production and the polyphenols as food supplements and nutraceuticals for health benefits. This novel study contributes to agro-industrial waste beneficiation via fuel production. In addition, using agro-industrial waste for the generation of value added products (instead of mere disposal) will help prevent environmental pollution.
- Full Text:
- Date Issued: 2016
- Authors: Abboo, Sagaran
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/315 , vital:19947
- Description: Due to the finite supply of non-renewable fossil fuels, agro-industrial wastes are identified as alternate, renewable sources for energy supply. Large amounts of fruit waste are generated in South Africa due to fruit juice and wine processing from apples, grapes and citrus fruit. Apple pomace is the solid residue that is left over after juice, cider and wine processing and constitutes between 25-30% of the total fruit. On a global scale millions of tonnes of apple pomace are produced; between 2006-2007 over 46 million tonnes were produced. In South Africa a total production of 244 469 tonnes were produced during the 2011- 2012 season. Initially, apple pomace was regarded as a waste by-product used for animal feed and compost in soil, however presently it is considered a source of dietary fiber and natural antioxidants like polyphenols. In addition, apple pomace has a high carbohydrate content and can be enzymatically hydrolysed to produce sugar monomers which, in turn, can be fermented by yeasts to produce bioethanol. The polyphenols present in apple pomace can be used for their health properties, and the bioethanol can be used as a replacement for fossil fuel. Apple pomace is lignocellulosic in nature and consists of hemicellulose, cellulose, lignin and pectin. A combination of enzymes such as cellulases, hemicellulases, pectinases and lignases are required to operate in synergy for the degradation of lignocellulosic biomass. This is due to the recalcitrant nature of lignocellulose. This study investigated the degradation of apple pomace using a combination of commercially obtained enzyme cocktails viz. Viscozyme L , Celluclast 1.5L and Novozyme 188. The commercial enzymes Viscozyme L and Celluclast 1.5L were added in a ratio of 1:1 (50%:50%). The final concentrations of the enzymes were 0.019 mg/ml each. Novozyme 188 was added to provide a final concentration of 0.0024 mg/ml. A novel cost effective 20L bioreactor was designed, constructed and implemented for the degradation of apple pomace to produce value added products. The hydrolysis of the apple pomace was performed initially in 1 L flasks (batch fed) and, once optimized, scaled up to a 20 L bioreactor in batch mode. The bioreactors were operated at room temperature (22 ± 2ºC) and in an unbuffered system. The sugars released were detected and quantified using an optimized validated HPLC method established in this study. The sugars released in the bioreactors were mainly glucose, galactose, arabinose, cellobiose and fructose. The polyphenols released in this study were gallic acid, catechin, epicatechin, chlorogenic acid, rutin and phloridzin, which have a number of health benefits. The simultaneous analyses of the polyphenols were performed using a newly developed and validated HPLC method established in this study. This method was developed to detect nine polyphenols simultaneously. The two HPLC methods developed and validated in this study for the analysis of sugars and polyphenols demonstrated good accuracy, precision, reproducibility, linearity, robustness and sensitivity. Both analytical methods were validated according to the International Convention on Harmonization (ICH). The HPLC parameters for sugar analysis were: refractive index (RI) as the detection mode, the stationary phase was a ligand-exchange sugar column (Shodex SP0810) and an aqueous mobile phase in isocratic mode was used. The HPLC method for polyphenols employed UV diode array detection (DAD) as the detection mode, a reverse phase column as the stationary phase and a mobile phase of consisting of 0.01 M phosphoric acid in water and 100% methanol using gradient elution mode. The highest concentrations of sugars released in the novel 20 L bioreactor with 20% apple pomace (w/v) substrate loading were as follow: glucose (6.5 mg/ml), followed by galactose (2.1 mg/ml), arabinose (1.4 mg/ml), cellobiose (0.7 mg/ml) and fructose (0.5 mg/ml). The amounts of polyphenols released at 20% (w/v) apple pomace substrate were epicatechin (0.01 mg/ml), catechin (0.002 mg/ml), rutin (0.03 mg/ml), chlorogenic acid (0.002 mg/ml) and gallic acid 0.01 (mg/ml). Two mathematical models were developed in this study for kinetic analysis of lignocellulose (apple pomace) hydrolysis in the novel 20 L bioreactor, using the experimental data generated by the above HPLC analyses. The first model, modelling with regression, defines the hydrolysis of the sugars glucose, galactose, cellobiose and arabinose produced in the novel 20 L bioreactor at 5%, 10%, 15% and 20% (w/v) substrate concentrations. The regression model describes the sugars produced in the 20 L bioreactor by minimizing the error of the sugars released by finding a value for K which minimises the function which computes the sum of squares of errors between the solution curves and the data points. The second, more complex, model developed in this study used a system of differential equations model (ODE). This model solved the system by using a numerical method, such as the Runge-Kutta method, then fitted the solution curves to the data. Both models simulated (and had the ability to predict) the production of sugars in the novel 20 L bioreactor for apple pomace hydrolysis. These two models also revealed the time at which the maximum amount of sugars were released, which revealed the optimum time to run the 20 L bioreactor in order to be more cost effective. The optimum time for maximum glucose (the main sugar used in fermentation for biofuel production) release was determined to be around 60 h. The ODE model, in addition, determined the rate at which the substrate became depleted, as well as the rate at which the enzymes became deactivated for the various substrate loadings in the 20 L bioreactor. A third model was developed to determine the optimal running cost of the bioreactor which incorporated the substrate loading and the amount of glucose (g/L) produced. The novel 20 L bioreactor constructed from cost effective materials demonstrated that agro-industrial waste can be converted to value-added products by lignocellolytic enzymes. The sugars released from apple pomace can be used in biofuel production and the polyphenols as food supplements and nutraceuticals for health benefits. This novel study contributes to agro-industrial waste beneficiation via fuel production. In addition, using agro-industrial waste for the generation of value added products (instead of mere disposal) will help prevent environmental pollution.
- Full Text:
- Date Issued: 2016
Drivers of macrophyte assemblages in South African freshwater systems
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
- Authors: Martin, Grant Douglas
- Date: 2013
- Subjects: Freshwater plants -- South Africa Aquatic weeds -- South Africa Invasive plants -- South Africa Freshwater ecology -- South Africa Biotic communities -- South Africa Maximum entropy method Lagarosiphon major -- South Africa Phytophagous insects -- South Africa Hydrellia -- South Africa Parasitoids -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5621 , http://hdl.handle.net/10962/d1004127
- Description: Potentially damaging submerged invasive freshwater macrophytes have been identified in South African freshwater systems, but have received less attention than their floating counterparts. To ascertain the changes and effects that these species may have on macrophyte ecology, an understanding of the drivers of macrophyte assemblages is essential. The aims of this thesis were to investigate select abiotic and biotic factors driving introduction, establishment and spread of submerged macrophytes in South Africa. Surveys on the status of submerged plant species in South Africa were conducted to find out the distribution and diversity of the species present, imported to, and traded in South Africa. Numerous submerged indigenous and invasive macrophyte locality records were collected during field surveys, of which many were first time records. Pet stores and aquarist trading activities were identified as potential vectors for the spread of submerged macrophytes through online surveys and personal interviews. These results highlighted the potential these species have for continuing to enter, and spread within South African water bodies. Maximum Entropy (MAXENT) is a general-purpose method used to predict or infer distributions from incomplete information, and was used here to predict areas suitable for the establishment of five of these invasive macrophytes. Many systems throughout South Africa, particularly those in the subtropical coastal regions, were found to be climatically suitable for the establishment of Elodea canadensis Michx., Egeria densa Planch., Hydrilla verticillata (L.f.) Royle (all Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae), and Cabomba caroliniana Gray (Cabombaceae). Despite the high probability of invasion, facilitated by vectors and suitable climate, South Africa’s rich indigenous submerged aquatic flora may be preventing the establishment of these submerged invasive species. Studies on the competitive interactions between a common indigenous submerged macrophytes, Lagarosiphon major (Roxb.) (Hydrocharitaceae) and M.spicatum, an invasive native to Eurasia, were conducted to ascertain which conditions influence competitive superiority. High sediment nutrient conditions significantly increased the growth rate and competitive ability of both species, while clay sediments significantly increased the competitive ability of L. major over M. spicatum, but sandy sediments improved the competitive ability of M. spicatum. These results highlighted the dynamic changes in competition between submerged species driven by abiotic factors, but did not take into consideration the effect that herbivory, a biotic factor, could have on competition between the two species. The effect of herbivory by phytophagous insects of submerged plant species has been regarded as negligible. To find out what this effect is, multiple field surveys were undertaken throughout South Africa to find natural enemies of indigenous Lagarosiphon species with the aim of identifying such species, and quantifying their influence on plant growth dynamics. Several new phytophagous species were recorded for the first time. An ephydrid fly, Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) was ascertained to be the most ubiquitous and abundant species associated with L. major in South Africa. The influence of herbivory by this fly on the competitive ability of L. major in the presence of M. spicatum was investigated using an inverse linear model, which showed that herbivory by H. lagarosiphon reduced the competitive ability of L. major by approximately five times in favour of M. spicatum. This study served to highlight the importance of herbivory as a driver of submerged aquatic plant dynamics. Current ecological theory emphasises the importance of investigating beyond plant-herbivore interactions, by including multitrophic interactions in community dynamics. Therefore, the potential of parasitism by a parasitoid wasp, Chaenusa luteostigma sp. n. Achterberg (Hymenoptera: Braconidae: Alysiinae) on H. lagarosiphon to shift the competitive interactions between the two plant species was also examined. The addition of the parasitoid reduced the effect of herbivory by the fly on L. major by half, thereby shifting the competitive balance in favour of L. major over M. spicatum. This study provides valuable insight into a selection of drivers of submerged macrophyte assemblages of South Africa. It highlights the precarious position of South African freshwater systems with regard to the potential invasion by damaging submerged invasive species. It also provides interesting insights into the effect of competition, herbivory and parasitism on the establishment and spread of species within submerged freshwater systems. Understanding the different influences could assist managers and policy makers to make validated decisions ensuring the integrity of South African freshwater systems.
- Full Text:
- Date Issued: 2013
Post-impoundment population dynamics of non-native common carp Cyprinus Carpio in relation to two large native cyprinids in Lake Gariep, South Africa
- Authors: Winker, Henning
- Date: 2011
- Subjects: Cyprinidae -- South Africa -- Gariep Dam Carp -- South Africa -- Gariep Dam Fish populations -- South Africa -- Gariep Dam Fishes -- Physiology -- South Africa -- Gariep Dam Barbus aeneus -- South Africa -- Gariep Dam Mudfishes -- South Africa -- Gariep Dam Freshwater fishes -- South Africa -- Gariep Dam
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5311 , http://hdl.handle.net/10962/d1005156
- Description: To contribute to the understanding of the invasion biology of common carp Cyprinus carpio in southern Africa, this thesis investigated the life history, relative abundance, long-term population demographics and trophic niche utilisations of non-native common carp C. carpio in relation to two endemic cyprinids, Orange River mudfish Labeo capensis and smallmouth yellowfish Labeobarbus aeneus in South Africa‟s largest impoundment, Lake Gariep. The growth zone deposition rates in astericus otoliths of the three species were validated as biannual for C. carpio and as annual for L. capensis and L. aeneus, which allowed for reliable estimation of lengths-at-age upon which growth, age-at-maturity and mortality rates could be estimated. Cyprinus carpio exhibited fast growth, matured relatively early at two years of age and attained a maximum age of seven years. Labeo capensis grew significantly slower, but attained older ages of up to 12 years. Females showed notably delayed maturation at approximately six years of age. The life history parameter estimates for L. aeneus were similar to those of L. capensis. These species-specific life history characteristics contributed to a substantially higher population growth potential of C. carpio compared to L. capensis and L. aeneus. Delta-lognormal and delta-gamma Generalized Linear Models (GLMs) were used to analyse patterns of relative abundance of L. capensis, L. aeneus and C. carpio. The application of these GLMs was necessary to account for large proportions of zeros and strong skewness in the catch-per-unit-effort (CPUE) from experimental gillnet and fisheries-dependent angler surveys. Confidence intervals around predicted abundance indices were obtained through the development of a generalised parametric bootstrap procedure. The resulting standardised abundance indices were coupled with results from analysis of stable isotope ratios of fish tissues and potential food resources and revealed that C. carpio was mainly confined to soft-bottom habitats, where it predominantly foraged on benthic invertebrates. Labeo capensis was abundant in a wide range of benthic habitats and was consumed basal food resources such as detritus. Labeobarbus aeneus was found to feed mostly on pelagic zooplankton. There were no significant interspecific differences in trophic niche space, suggesting limited resource competition among the three species. Standardised historical and contemporary gillnet CPUE data indicated slow population growth rates of L. capensis and L. aeneus during the first ten years postimpoundment, but showed high biomass levels some four decades after impoundment. These results could be corroborated by stochastic age-structured production model (ASPM) simulations. In contrast to the two endemic species, the gillnet CPUE of C. carpio showed a clear „boom and bust‟ pattern, which, based on ASPM simulations, could be best explained by increased food availability during the first five years postimpoundment, followed by suboptimal conditions thereafter. Together, these results provided evidence that the establishment of the C. carpio population did not prevent the slow but successful long-term establishment of the two large endemic cyprinids. Both endemic fishes revealed specialised feeding within the impoundment.
- Full Text:
- Date Issued: 2011
- Authors: Winker, Henning
- Date: 2011
- Subjects: Cyprinidae -- South Africa -- Gariep Dam Carp -- South Africa -- Gariep Dam Fish populations -- South Africa -- Gariep Dam Fishes -- Physiology -- South Africa -- Gariep Dam Barbus aeneus -- South Africa -- Gariep Dam Mudfishes -- South Africa -- Gariep Dam Freshwater fishes -- South Africa -- Gariep Dam
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5311 , http://hdl.handle.net/10962/d1005156
- Description: To contribute to the understanding of the invasion biology of common carp Cyprinus carpio in southern Africa, this thesis investigated the life history, relative abundance, long-term population demographics and trophic niche utilisations of non-native common carp C. carpio in relation to two endemic cyprinids, Orange River mudfish Labeo capensis and smallmouth yellowfish Labeobarbus aeneus in South Africa‟s largest impoundment, Lake Gariep. The growth zone deposition rates in astericus otoliths of the three species were validated as biannual for C. carpio and as annual for L. capensis and L. aeneus, which allowed for reliable estimation of lengths-at-age upon which growth, age-at-maturity and mortality rates could be estimated. Cyprinus carpio exhibited fast growth, matured relatively early at two years of age and attained a maximum age of seven years. Labeo capensis grew significantly slower, but attained older ages of up to 12 years. Females showed notably delayed maturation at approximately six years of age. The life history parameter estimates for L. aeneus were similar to those of L. capensis. These species-specific life history characteristics contributed to a substantially higher population growth potential of C. carpio compared to L. capensis and L. aeneus. Delta-lognormal and delta-gamma Generalized Linear Models (GLMs) were used to analyse patterns of relative abundance of L. capensis, L. aeneus and C. carpio. The application of these GLMs was necessary to account for large proportions of zeros and strong skewness in the catch-per-unit-effort (CPUE) from experimental gillnet and fisheries-dependent angler surveys. Confidence intervals around predicted abundance indices were obtained through the development of a generalised parametric bootstrap procedure. The resulting standardised abundance indices were coupled with results from analysis of stable isotope ratios of fish tissues and potential food resources and revealed that C. carpio was mainly confined to soft-bottom habitats, where it predominantly foraged on benthic invertebrates. Labeo capensis was abundant in a wide range of benthic habitats and was consumed basal food resources such as detritus. Labeobarbus aeneus was found to feed mostly on pelagic zooplankton. There were no significant interspecific differences in trophic niche space, suggesting limited resource competition among the three species. Standardised historical and contemporary gillnet CPUE data indicated slow population growth rates of L. capensis and L. aeneus during the first ten years postimpoundment, but showed high biomass levels some four decades after impoundment. These results could be corroborated by stochastic age-structured production model (ASPM) simulations. In contrast to the two endemic species, the gillnet CPUE of C. carpio showed a clear „boom and bust‟ pattern, which, based on ASPM simulations, could be best explained by increased food availability during the first five years postimpoundment, followed by suboptimal conditions thereafter. Together, these results provided evidence that the establishment of the C. carpio population did not prevent the slow but successful long-term establishment of the two large endemic cyprinids. Both endemic fishes revealed specialised feeding within the impoundment.
- Full Text:
- Date Issued: 2011
Biological generation of reactive alkaline species and their application in a sustainable bioprocess for the remediation of acid and metal contaminated wastewaters
- Authors: Van Hille, Robert Paul
- Date: 2002
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21049 , http://hdl.handle.net/10962/6129
- Description: This project focused on the development of an integrated biological system for the treatment of acidic and metal-laden effluents, based on the sustainable biological generation of reactive alkaline species. Initial studies concentrated on the binding and accumulation of heavy metals by biomass of the cyanobacteria, Spirulina sp. Metal binding was rapid, with saturation reached in 30 minutes, and followed an affinity series of Pb > Cu > Zn >>Fe. The binding capacity of the Spirulina for each of the metals was relatively low when compared to a range of other biosorbents. The toxicity thresholds of the algae was determined for copper and zinc. These were low (10umoles/g) and as such, the algae were not suitable for application in a treatment system in which they came into direct contact with the toxic metals. The algae were able to increase the pH of the surrounding medium. This occurred as a result of the accumulation of inorganic carbon, from bicarbonate, as a response to low concentrations of carbon dioxide in the medium. The resulting release of a hydroxide ion into solution led to the increase in pH. The increase in pH was shown to be due to a reduction in acidity, rather than an increase in alkalinity. The enzyme carbonic anhydrase was shown to be pivotal in this system. Attempts to determine the enzyme activity directly were unsuccessful, due to the inherent inaccuracy of the assay system. An indirect method of determining enzyme activity, by measuring changes in the carbonate species equilibrium, was developed. Under optimal conditions Spirulina was able to reduce the acidity by an amount equivalent to the addition of 3670umoles NaOH g·' h·'. Predictive modelling showed that this enhanced the potential of the medium to effect metal precipitation. For the algal system to be sustainable, a readily available source of bicarbonate was needed. This was achieved by the oxidation of organic carbon, under sulphidogenic conditions, by a bacterial consortium isolated from the anaerobic component of a facultative pond. The consortium was shown to consist of sulphate reducing (most likely Desulvovibrio and Desulfotomaculum)and acetogenic bacteria. Sulphate removal rates of 500mg 1·' day·' and 135mg 1·' day·' were achieved in a 21 agitated and 281 upflow reactor respectively. The bicarbonate generation rate in the 281 reactor was calculated as 4033umoles 1·' day·', which proved sufficient to act as a feed for the algal system. Sparging the anaerobic digester overflow with air and nitrogen resulted in a reduction in the aqueous sulphide concentration. Using nitrogen, a 70% recovery of sulphide, as H2S gas, was achieved in 60 minutes, while with air, this dropped to 40%, due to the oxidation of the aqueous sulphide. The stripping ofH2S resulted in an increase in pH. The H2S gas was used for the selective precipitation of copper and lead in the integrated system. The dynamics of metal precipitation was investigated. For simple reactions, between individual IV metal and base species, it was possible to generate an accurate predictive model and confirm the precipitating species using wavelength dispersive X-ray spectroscopy (WDS). In more complex systems, where precipitation of the artificial acid mine drainage was examined, the predictive modelling and WDS could not accurately describe the system. The addition of aqueous sulphide to copper and iron resulted in the formation of metastable, amorphous precipitates, which remained in suspension. Ageing of the copper precipitate resulted in the evolution of a stable crystalline structure (covellite) and the aggregation and settling of the precipitate. In the case of iron, the amorphous precipitate underwent oxidation before a stable iron sulphide could evolve and the settled precipitate was an iron oxide or oxyhydroxide. The artificial acid mine drainage was treated with sulphide, hydroxide, anaerobic digester overflow and algal overflow. The best metal removal was achieved with the sulphide and hydroxide, while the algal overflow outperformed the anaerobic digester overflow. The precipitate generated by the addition of sulphide was the most compact, followed by the algal overflow, the anaerobic digester overflow and the hydroxide. Efficient precipitation of all the heavy metals, except manganese, was achieved using the algal overflow at an acidity to alkalinity ratio of 1 :2. This ratio was selected for use in the pilot system. The Spirulina based pilot system was effectively used to treat an effluent from the Black Mountain base metal mine. The necessity to maintain the algae in suspension and avoid biomass washout were practical considerations which counted against this system. The replacement of the Spirulina by Oscillatoria, which adhered to a solid support, overcame these problems. The integrated biological system was able to effectively treat an artificial acid mine drainage for 90 days, reducing the concentration of all metals, except manganese, to below the acceptable environmental risk levels. The treatment of the final effluent in a second anaerobic digester reduced the manganese concentration to 4.5uM and proved that the sulphate reducing bacteria could be cultivated on enriched, partially treated acid mine drainage. The integrated biological treatment system performed well, effectively treating an effluent modelled closely on the quality of the water being discharged from the East Rand Basin. The cost of such a system would be considerably less than a "high tech" physico-chemical system. This, coupled with the potential long term sustainability of a biological system, would make it a potentially attractive option for the treatment of future acid mine drainage discharges.
- Full Text:
- Date Issued: 2002
- Authors: Van Hille, Robert Paul
- Date: 2002
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21049 , http://hdl.handle.net/10962/6129
- Description: This project focused on the development of an integrated biological system for the treatment of acidic and metal-laden effluents, based on the sustainable biological generation of reactive alkaline species. Initial studies concentrated on the binding and accumulation of heavy metals by biomass of the cyanobacteria, Spirulina sp. Metal binding was rapid, with saturation reached in 30 minutes, and followed an affinity series of Pb > Cu > Zn >>Fe. The binding capacity of the Spirulina for each of the metals was relatively low when compared to a range of other biosorbents. The toxicity thresholds of the algae was determined for copper and zinc. These were low (10umoles/g) and as such, the algae were not suitable for application in a treatment system in which they came into direct contact with the toxic metals. The algae were able to increase the pH of the surrounding medium. This occurred as a result of the accumulation of inorganic carbon, from bicarbonate, as a response to low concentrations of carbon dioxide in the medium. The resulting release of a hydroxide ion into solution led to the increase in pH. The increase in pH was shown to be due to a reduction in acidity, rather than an increase in alkalinity. The enzyme carbonic anhydrase was shown to be pivotal in this system. Attempts to determine the enzyme activity directly were unsuccessful, due to the inherent inaccuracy of the assay system. An indirect method of determining enzyme activity, by measuring changes in the carbonate species equilibrium, was developed. Under optimal conditions Spirulina was able to reduce the acidity by an amount equivalent to the addition of 3670umoles NaOH g·' h·'. Predictive modelling showed that this enhanced the potential of the medium to effect metal precipitation. For the algal system to be sustainable, a readily available source of bicarbonate was needed. This was achieved by the oxidation of organic carbon, under sulphidogenic conditions, by a bacterial consortium isolated from the anaerobic component of a facultative pond. The consortium was shown to consist of sulphate reducing (most likely Desulvovibrio and Desulfotomaculum)and acetogenic bacteria. Sulphate removal rates of 500mg 1·' day·' and 135mg 1·' day·' were achieved in a 21 agitated and 281 upflow reactor respectively. The bicarbonate generation rate in the 281 reactor was calculated as 4033umoles 1·' day·', which proved sufficient to act as a feed for the algal system. Sparging the anaerobic digester overflow with air and nitrogen resulted in a reduction in the aqueous sulphide concentration. Using nitrogen, a 70% recovery of sulphide, as H2S gas, was achieved in 60 minutes, while with air, this dropped to 40%, due to the oxidation of the aqueous sulphide. The stripping ofH2S resulted in an increase in pH. The H2S gas was used for the selective precipitation of copper and lead in the integrated system. The dynamics of metal precipitation was investigated. For simple reactions, between individual IV metal and base species, it was possible to generate an accurate predictive model and confirm the precipitating species using wavelength dispersive X-ray spectroscopy (WDS). In more complex systems, where precipitation of the artificial acid mine drainage was examined, the predictive modelling and WDS could not accurately describe the system. The addition of aqueous sulphide to copper and iron resulted in the formation of metastable, amorphous precipitates, which remained in suspension. Ageing of the copper precipitate resulted in the evolution of a stable crystalline structure (covellite) and the aggregation and settling of the precipitate. In the case of iron, the amorphous precipitate underwent oxidation before a stable iron sulphide could evolve and the settled precipitate was an iron oxide or oxyhydroxide. The artificial acid mine drainage was treated with sulphide, hydroxide, anaerobic digester overflow and algal overflow. The best metal removal was achieved with the sulphide and hydroxide, while the algal overflow outperformed the anaerobic digester overflow. The precipitate generated by the addition of sulphide was the most compact, followed by the algal overflow, the anaerobic digester overflow and the hydroxide. Efficient precipitation of all the heavy metals, except manganese, was achieved using the algal overflow at an acidity to alkalinity ratio of 1 :2. This ratio was selected for use in the pilot system. The Spirulina based pilot system was effectively used to treat an effluent from the Black Mountain base metal mine. The necessity to maintain the algae in suspension and avoid biomass washout were practical considerations which counted against this system. The replacement of the Spirulina by Oscillatoria, which adhered to a solid support, overcame these problems. The integrated biological system was able to effectively treat an artificial acid mine drainage for 90 days, reducing the concentration of all metals, except manganese, to below the acceptable environmental risk levels. The treatment of the final effluent in a second anaerobic digester reduced the manganese concentration to 4.5uM and proved that the sulphate reducing bacteria could be cultivated on enriched, partially treated acid mine drainage. The integrated biological treatment system performed well, effectively treating an effluent modelled closely on the quality of the water being discharged from the East Rand Basin. The cost of such a system would be considerably less than a "high tech" physico-chemical system. This, coupled with the potential long term sustainability of a biological system, would make it a potentially attractive option for the treatment of future acid mine drainage discharges.
- Full Text:
- Date Issued: 2002
Photocatalytic reactions of metal diphthalocyanine complexes
- Authors: Nensala, Ngudiankama
- Date: 2000
- Subjects: Metal complexes Electrochemistry Photochemistry Pentachlorophenol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4328 , http://hdl.handle.net/10962/d1004989
- Description: Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.
- Full Text:
- Date Issued: 2000
- Authors: Nensala, Ngudiankama
- Date: 2000
- Subjects: Metal complexes Electrochemistry Photochemistry Pentachlorophenol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4328 , http://hdl.handle.net/10962/d1004989
- Description: Photocatalytic reactions of tin diphthalocyanine, Sn ^IVPc₂ and anionic form of Nd^III, Dy^III, Eu^III, Tm^III and Lu^III diphthalocyanine complexes ( [Pc(-2)Nd^IIIpc(-2)]⁻ , [Pc(-2)Dy^IIIPc(-2)]⁻ , [Pc(-2)Eu^IIIPc(-2)⁻, [Pc(-2)Tm^IIlPc(-2)r and [Pc(-2)LuIIIpc(-2)]⁻ respectively) in the presence of CH₂CI₂, S0₂, pentachlorophenol (PCP), 4-chlorophenol (4-Cp) and thionyl chloride have been studied. Photoreactions involving lanthanide diphthalocyanines, filtered and unfiltered radiations were employed, whereas for photoreactions involving tin diphthalocyanine, only unfiltered radiation was employed. For lanthanide diphthalocyanine complexes, LnPce-, the photosensitization power increases with the decrease of the lanthanide ionic radii, implying that the photocatalytic activity of LnPc₂⁻ complexes is associated with the π-π interaction between both phthalocyanine rings. Thus, LuPc₂⁻ is a better photocatalyst than other lanthanide diphthalocyanine complexes. Photolysis ofSnPc₂ in an acetonitrile/dichloromethane solvent mixture, using unfiltered radiation from a tungsten lamp, results in the one-electron oxidation of this species to [Pc( -2 )Sn(IV)Pc(-1)]⁻. The relative quantum yields for the disappearance of SnPc₂ are in the order of 10⁻¹. The photoreaction of SnPc₂ is preceded by excitation to nπ* excited states, before been ,quenched by CH₂CI₂. The one-electron oxidation species, [Pc(-2)Sn(lV)pc(-1)]⁻ was also formed during the photolysis of SnPc₂ in dichloromethane containing S0₂, and with quantum yields of order of 10⁻³. Visible photolysis of [Pc( -2)Nd^IIIpc(-2)]⁻, [Pc(-2)Dy^IIIPc(-2)]⁻ and [Pc(-2)Lu^IIIpc(-2)]⁻ in N,N. dimethylformamide (DMF)/dichloromethane solvent mixture containing SO₂, results in the formation of the one-electron oxidation species, Pc(-2 )Nd^IIIpc(-1), Pc( -2) Dyi^IIIPc(-1) and Pc(-2)Lu^IIIpc(-1), respectively. The relative quantum yields are in the order of 10². The photoreactions are preceded by population of the excited triplet state,³π-π* [ LnPc₂]⁻ complex, before exchanging an electron with S0₂. The one-electron oxidation species of Dy^III and Lu^III diphthalocyanine complexes have also been formed from visible photolysis of [Pc(-2 )Dy^IIIPc(-2)]⁻and [Pc(-2)Lu^IIIpc(-2)]⁻in acetonitrile containing PCP. The PCP is reductively dechlorinated to tetra- and trichlorophenols. The quantum yields for the photosensitization reactions are in the order of 1 0⁻. Photolysis, using visible radiation from 220 W Quartzline lamp, of an aqueous solution of 4-Cp, saturated with oxygen and containing a suspension of solid [Pc(-2)Nd^IIIpc(-2)]⁻, results in the formation of benzoquinone, hydro quinone and 4-chlorocatechol. The quantum yields for the degradation of 4-Cp are in the order of 10⁻. Langmuir-Hinshelwood kinetic model shows the adsorption of 4-chlorophenol onto solid [Pc(-2)Nd^IIIpc(-2)]⁻. Lanthanide diphthalocyanine complexes ([Pc-2)Nd^IIIpc(-2)]⁻. [Pc(-2)Eu^IIIpc(-2)]⁻, (Pc(-2)Tm^IIIpc( -2)]⁻ and (Pc(-2)Lu^IIIpc(-2)]⁻) undergo one or two-electron oxidation in the presence of thionyl chloride. At low concentrations of SOCI₂(<10⁻⁴ mol dm⁻³) the visible yhotolysis of [Pc(-2 )LnPc(-2)]⁻ complexes result in the one-electron oxidation, giving neutral lanthanide diphthalocyanine species, Pc(-2)Ln^IIIpc(-1). The Pc(-2 )LnPc(-I) species undergoes one-electron photooxidation to [Pc(-I )LnPc( -I)]⁻ in dichloromethane and in the presence of SOC₁₂. At large concentrations of SOC₁₂ (>10⁻² mol dm⁻³), direct two-electron oxidation of the (Pc(-2 )LnPc - 2)]⁻ species to (Pc(-1)LnPc(-1)]⁻ occurs. Spectroelectrochemical behaviours of Sn^IVPc₂ have been also studied. The cyclic voltammetry ofSnPc₂ in CH₂CI₂/TBAP show two reduction couples at -0.56 V and -0.89 V versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE. In DMFITEAP system, the reduction couples are observed at -0.44 V and -0.81 V versus SCE whereas the oxidation couple occurred at 0.43 V versus SCE. The oxidation couple corresponds to [Pc(-2 )Sn^IVPc(-2 )]/[Pc(-2)Sn^IVPc( -I)] . and the reduction couples to [Pc(-2)Sn^IVPc( -2 )]/[Pc(-2 )Sn^IVPc( -3 )]⁻ and [Pc(-2)Snl^IVPc( -3)] ⁻/[Pc(-3 )Sn^IVPc(-3)]²⁻, respectively. The electronic absorption spectra of these reduced and oxidized species are reported.
- Full Text:
- Date Issued: 2000
Three dimensional kinetic analysis of asymmetrical lifting
- Authors: Li, Jian-Chuan
- Date: 1996
- Subjects: Lifting and carrying , Human engineering , Materials handling , Manual work
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5174 , http://hdl.handle.net/10962/d1018240
- Description: Manual lifting is dynamic in nature and involves asymmetrical loading of the human body. This study investigated kinematic and kinetic characteristics of asymmetrical lifting in three dimensions, and then constructed a 3-D biomechanical force model of the lower back which is capable of quantifying torsional stress on the human spine. Eleven healthy adult male manual workers were recruited as subjects and lifted a 1 Okg load placed at the sagittal plane (0°) and at 30°, 60° and 90° lateral planes to the right, from 150mm and 500mm initial lift heights, respectively, to an 800mm high bench in the sagittal plane. Subjects' spinal motions and the trajectorial movements of the load in three-dimensional space were monitored simultaneously by a Lumbar Motion Monitor and a V-scope Motion Analyzer. Generally, the spinal motion factors increased as a function of increasing task asymmetry and differed (p < 0.05) between the lower (150mm) and higher (500mm) levels in the sagittal plane. In all asymmetrical conditions the motion factors showed a dramatic increase at the 500mm level compared to the increase at the 150mm level. The rates of increase in the horizontal and frontal planes were greater than those in the sagittal plane. Task asymmetry had a significant effect on the spinal kinematic parameters in the frontal plane at the two lift heights, and only at the high level (500mm) in the horizontal plane, with exception of average acceleration . Initial lift height exerted a significant effect on peak velocity and acceleration in both frontal and horizontal planes and on range of motion in the horizontal plane. Kinetic characteristics of the object being lifted in three-dimensions increased with an increase in task asymmetry. The increase was more dramatic in the lateral direction in the horizontal plane. However, motion factors in the vertical direction dominated the full range of the lift, irrespective of task asymmetry and lift height. The kinetic measures differed (p < 0.05) between the lower ( 1 50mm) and the higher (500mm) levels in the vertical direction except for average force. Task asymmetry had a significant effect on dynamic measures in the anterior-posterior direction. Both task asymmetry and lift height had a significant effect on dynamic motion factors in the lateral direction. From insights gained in the empirical study a three-dimensional biomechanical force model of the lower back was constructed based on a mechanism of muscle force re-orientation in the lumbar region. Acknowledging that the lower back is designed to be able to rotate around its longitudinal axis, the proposed model accounts for compression and shear forces and a torsional moment. The model has similar predictability to Schultz and Andersson's (1981) model when the human trunk exerts only a flexion-extension moment in the sagittal plane, but additionally predicts dramatic increases in shear forces, oblique muscle forces and torsional moment under asymmetrical lifting conditions which the Schultz-Andersson model does not. The increase rates in these forces and moment are not linearly related over task asymmetric angle.
- Full Text:
- Date Issued: 1996
- Authors: Li, Jian-Chuan
- Date: 1996
- Subjects: Lifting and carrying , Human engineering , Materials handling , Manual work
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5174 , http://hdl.handle.net/10962/d1018240
- Description: Manual lifting is dynamic in nature and involves asymmetrical loading of the human body. This study investigated kinematic and kinetic characteristics of asymmetrical lifting in three dimensions, and then constructed a 3-D biomechanical force model of the lower back which is capable of quantifying torsional stress on the human spine. Eleven healthy adult male manual workers were recruited as subjects and lifted a 1 Okg load placed at the sagittal plane (0°) and at 30°, 60° and 90° lateral planes to the right, from 150mm and 500mm initial lift heights, respectively, to an 800mm high bench in the sagittal plane. Subjects' spinal motions and the trajectorial movements of the load in three-dimensional space were monitored simultaneously by a Lumbar Motion Monitor and a V-scope Motion Analyzer. Generally, the spinal motion factors increased as a function of increasing task asymmetry and differed (p < 0.05) between the lower (150mm) and higher (500mm) levels in the sagittal plane. In all asymmetrical conditions the motion factors showed a dramatic increase at the 500mm level compared to the increase at the 150mm level. The rates of increase in the horizontal and frontal planes were greater than those in the sagittal plane. Task asymmetry had a significant effect on the spinal kinematic parameters in the frontal plane at the two lift heights, and only at the high level (500mm) in the horizontal plane, with exception of average acceleration . Initial lift height exerted a significant effect on peak velocity and acceleration in both frontal and horizontal planes and on range of motion in the horizontal plane. Kinetic characteristics of the object being lifted in three-dimensions increased with an increase in task asymmetry. The increase was more dramatic in the lateral direction in the horizontal plane. However, motion factors in the vertical direction dominated the full range of the lift, irrespective of task asymmetry and lift height. The kinetic measures differed (p < 0.05) between the lower ( 1 50mm) and the higher (500mm) levels in the vertical direction except for average force. Task asymmetry had a significant effect on dynamic measures in the anterior-posterior direction. Both task asymmetry and lift height had a significant effect on dynamic motion factors in the lateral direction. From insights gained in the empirical study a three-dimensional biomechanical force model of the lower back was constructed based on a mechanism of muscle force re-orientation in the lumbar region. Acknowledging that the lower back is designed to be able to rotate around its longitudinal axis, the proposed model accounts for compression and shear forces and a torsional moment. The model has similar predictability to Schultz and Andersson's (1981) model when the human trunk exerts only a flexion-extension moment in the sagittal plane, but additionally predicts dramatic increases in shear forces, oblique muscle forces and torsional moment under asymmetrical lifting conditions which the Schultz-Andersson model does not. The increase rates in these forces and moment are not linearly related over task asymmetric angle.
- Full Text:
- Date Issued: 1996
A physico-chemical investigation of refractory hard metals
- Authors: Philip, Hamish Ian
- Date: 1973
- Subjects: Refractory materials Heat resistant alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4441 , http://hdl.handle.net/10962/d1007630
- Description: In this investigation, the resistivity of vanadium nitride at elevated temperatures has been measured using a resistance bridge based on the Dauphinée/Mooser (1955) chopper system. In general, an almost linear increase of resistivity with temperature was observed for VN, but at certain temperatures, deviations from linearity (anomalies) were observed, these have been classified into three types. Attempts have been made to correlate the anomalous behaviour and temperature coefficients of resistivity with the ambient atmospheres and with the impurities, (especially oxygen), stoichiotmetry and density of this material. Oxygen and excess nitrogen appear to be electron donors in their effects on VN and result in a decrease in the slope of resistivity vs temperature curves. Oxygen and excess nitrogen also appear to increase the overall resistivity due to an increase in defect concentration. No effects due to the ambient atmosphere have been observed in the case of hot-pressed samples. lndicating that reaction can only occur if the reacting gases can reach the interior of the samples.
- Full Text:
- Date Issued: 1973
- Authors: Philip, Hamish Ian
- Date: 1973
- Subjects: Refractory materials Heat resistant alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4441 , http://hdl.handle.net/10962/d1007630
- Description: In this investigation, the resistivity of vanadium nitride at elevated temperatures has been measured using a resistance bridge based on the Dauphinée/Mooser (1955) chopper system. In general, an almost linear increase of resistivity with temperature was observed for VN, but at certain temperatures, deviations from linearity (anomalies) were observed, these have been classified into three types. Attempts have been made to correlate the anomalous behaviour and temperature coefficients of resistivity with the ambient atmospheres and with the impurities, (especially oxygen), stoichiotmetry and density of this material. Oxygen and excess nitrogen appear to be electron donors in their effects on VN and result in a decrease in the slope of resistivity vs temperature curves. Oxygen and excess nitrogen also appear to increase the overall resistivity due to an increase in defect concentration. No effects due to the ambient atmosphere have been observed in the case of hot-pressed samples. lndicating that reaction can only occur if the reacting gases can reach the interior of the samples.
- Full Text:
- Date Issued: 1973
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