A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / The synthesis and applications of carbon nanomaterials (CNMs) such as carbon nanofibres (CNFs), carbon nanotubes (CNTs) and carbon nanospheres (CNSs) have attracted a lot of attention due to their unique chemical and physical properties. For the synthesis of CNMs with desired morphology to occur, one needs to consider three components, namely, the catalyst, carbon source and source of power. However, the cost of the catalysts involved in making CNMs is one of the challenging factors. Due to properties such as high aspect ratio, CNM use as fillers in polymer nanocomposites has been on the forefront to improve the mechanical strength of polymer materials such as polyesters. Due to their hydrophobic nature, the interaction between the filler and matrix tends to be problematic. In this study, we investigated the use of a waste material, coal fly ash as a catalyst for the synthesis of CNMs using the chemical vapour deposition method. The use of CO2 and C2H2 as carbon sources, either independently or together, was also employed. A comparison of two different ashes was also investigated. Lastly, the use of these synthesized and acid treated CNMs as fillers was examined. The catalysts and synthesized CNMs were characterised using SEM, TEM, EDS, laser Raman spectroscopy, XRD, BET, TGA and Mössbauer spectroscopy. The mechanical properties were investigated by testing the tensile, flexural and impact properties. The synthesis of CNMs using fly ash as a catalyst without pre-treatment or impregnating with other metals was achieved. Optimum yields and uniform morphology was obtained at 650 oC, at a flow rate of 100 ml/min using H2 as a carrier gas and C2H2 as a carbon source. Mössbauer spectroscopy revealed that cementite (Fe3C) was the compound responsible for CNF formation. Further, CNMs were formed over fly ash as a catalyst, using CO2 as a sole carbon source, an additive and a carbon source before reacting with C2H2. Duvha was Page | iii found to be a better fly ash catalyst compared to Grootvlei and an optimum loading was achieved at 0.25%. Treating the CNFs with HCl/HNO3 resulted in the highest tensile, flexural and impact strengths. This study / GR 2016

Geopolymer concretes synthesised from composite class F fly ashes and a mixed alkaline activator were optimised by use of Taguchi orthogonal design method. The optimised mix achieved a compressive strength at the age of 28 days of 70 and 58 MPa after initial curing at 70??C for 12 hours and at 23??C for 24 hours, respectively. The resultant Geopolymer has an amorphous aluminosilicate structure. Efflorescence and the potential risk of alkali-silica reaction for the Geopolymer used in this study are both very low. The research confirmed that the Geopolymer concrete developed in this study is far superior to Portland cement concrete when exposed in a sulphuric acid environment. The standard immersion tests finally selected for this research were in 10% sulphuric acid for 56 days and in 1% sulphuric acid for one year. Geopolymer concrete samples retained their shape without softening though they experienced a mass loss of about 5% and a strength loss of some 30%. Portland cement concrete recorded a mass loss of some 40% in a 10% sulphuric acid for 28 days. The penetration rate of sulphuric acid into the Geopolymer concrete was found to approximately follow Fick’s first law of diffusion and a linear relationship between the neutralisation depth and the square root of immersion time (in day) was established. The degradation processes of Geopolymer concrete in sulphuric acid environments were intensively studied. The first stage involved the preferential liberation of alkali ions. The tetrahedral aluminium in the Si-O-Al configuration was removed and converted to octahedral aluminium. Consequently, the original units of Si(1Al) degraded to a silica polymorph structure in the corroded Geopolymer, which continued to serve a cementitious role. In contrast, in the case of Portland cement concrete, the acid solution dissolved the hydration products of the cement paste. The residual reaction products were found to be soft and have no structural strength. Geopolymers with alkaline activators of mixed sodium hydroxide and sodium silicate did not exhibit any cracking problems. Class F fly ash with low calcium content was found to be suitable for developing a Geopolymer binder able to withstand sulphuric acid attack.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 160-165).

Thesis (M.S.)--University of Florida, 2003. / Title from title page of source document. Includes vita. Includes bibliographical references.

No description available.

Cabbage root fly passes through three generations a year in the south of England. The first generation peaks in late April to early May having overwintered in diapause. Recently, populations have been discovered in which the emergence of first generation flies was protracted, lasting until mid-July. The project aimed to investigate the incidence of late emergence in Devon and to examine the ways in which late emergers differed from early emergers in their progress through diapause. A new emergence trap was developed and used in conjunction with yellow water traps to monitor the emergence of cabbage root fly populations at locations of contrasting agricultural practice. Late emergence was widespread in Devon, occurring later (up to September), and in a greater proportion of some populations than any previously reported. The phenomenon appears to be a response to the planting of brassicas in June, as flies emerging at the normal time may not be able to locate a host crop. Emergence in a substantial proportion of one population was delayed for a year. This has not been been previously reported in cabbage root fly and represents a 'sit and wait' strategy associated with short-lived habitats, occurring in patches often separated by considerable distances but which frequently reappear in approximately the same location. A gas chromatography technique was developed which is capable of individually monitoring the respiration rates of large numbers of pupae. The results suggested that the temperature optimum for diapause development may r1se in late emergers, possibly above the threshold for postdiapause development. There was considerable 1ntrapopulat1on variation in temperature responses. Overall, the results suggest that the level of variation in temperature response and emergence times between and within populations will require careful local investigation with continuous reassessment of selection pressures, for an accurate prediction of cabbage root fly emergence.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1991. / Includes bibliographical references (leaves 100-107) / Microfiche. / xiii, 107 leaves, bound ill. 29 cm

Geopolymer concretes synthesised from composite class F fly ashes and a mixed alkaline activator were optimised by use of Taguchi orthogonal design method. The optimised mix achieved a compressive strength at the age of 28 days of 70 and 58 MPa after initial curing at 70??C for 12 hours and at 23??C for 24 hours, respectively. The resultant Geopolymer has an amorphous aluminosilicate structure. Efflorescence and the potential risk of alkali-silica reaction for the Geopolymer used in this study are both very low. The research confirmed that the Geopolymer concrete developed in this study is far superior to Portland cement concrete when exposed in a sulphuric acid environment. The standard immersion tests finally selected for this research were in 10% sulphuric acid for 56 days and in 1% sulphuric acid for one year. Geopolymer concrete samples retained their shape without softening though they experienced a mass loss of about 5% and a strength loss of some 30%. Portland cement concrete recorded a mass loss of some 40% in a 10% sulphuric acid for 28 days. The penetration rate of sulphuric acid into the Geopolymer concrete was found to approximately follow Fick’s first law of diffusion and a linear relationship between the neutralisation depth and the square root of immersion time (in day) was established. The degradation processes of Geopolymer concrete in sulphuric acid environments were intensively studied. The first stage involved the preferential liberation of alkali ions. The tetrahedral aluminium in the Si-O-Al configuration was removed and converted to octahedral aluminium. Consequently, the original units of Si(1Al) degraded to a silica polymorph structure in the corroded Geopolymer, which continued to serve a cementitious role. In contrast, in the case of Portland cement concrete, the acid solution dissolved the hydration products of the cement paste. The residual reaction products were found to be soft and have no structural strength. Geopolymers with alkaline activators of mixed sodium hydroxide and sodium silicate did not exhibit any cracking problems. Class F fly ash with low calcium content was found to be suitable for developing a Geopolymer binder able to withstand sulphuric acid attack.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemical Engineering, 2007. / Includes bibliographical references (p. 161-168).

Thesis (Ph. D.)--University of Missouri--Rolla, 2007. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed January 28, 2008) Includes bibliographical references.