No description available.

No description available.

A dissertation submitted to the faculty of Engineering, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science in Engineering. / The role of chromite dissolution in the smelting of ferrochromium was investigated with the object of improving the throughput and chromium recovery of the process. The solubility of a typical Transvaal chromite in silicate slags with cao/si02 ratios from 0,03 to 0,55 at 1550·C and 1650·C was determined. Synthetic slags were melted in porous chromite crucibles and the slag underwent repeated reactions with the chromite grains as it penetrated the crucible wall. Finally the slag came into equilibrium with -''the ,original chromite towards the outer part of the crucible wall. Microprobe analysis of this slag yielded the maximum or saturated solubilities of the chromite constituents in the slag. The solubility of cr203 was found to be low (-1 per cent) while the remaining components' solubilities (A1203 -16 per cent, FeO)T 12 per cent and MgO-8 per cent) were significantly higher. CaO/Sio2 ratios greater than 0,1 lowered the solubility of Mg0 significantly (e.g. from 14,1 per cent to 5,8 per cent at 1650·C). The complete dissolution of this chromite in these slags requires the slag to contain less than the solubility limits of each of these species simultaneously. It was recommended that the best way to achieve this in practice would be a well-stirred slag bath containing suspended carbon particles, in which a cao/Sio2 ratio of less -than 0,1 was maintained. Further work to investigate the effect of slag composition (including Na20 and CaF2) on the kinetics of chromite reduction in such a system was recommended. / AC 2018

No description available.

Cheung, Hoi Cheung = Fe₈₁C₁₄Si₅旋節合金的變形 / 張凱翔. / "December 2010" / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Cheung, Hoi Cheung = Fe₈₁C₁₄Si₅ xuan jie he jin de bian xing / Zhang Kaixiang. / Abstract --- p.i / Acknowledgements --- p.iii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Spinodal Decomposition --- p.1 / Chapter 1.3 --- Theory of Elasticity --- p.5 / Chapter 1.4 --- Deformation of Metals --- p.9 / Chapter 1.5 --- Fracture Mechanics --- p.10 / Chapter 1.6 --- Contact Mechanics --- p.12 / Chapter 1.7 --- Indentation Fracture --- p.16 / Chapter 1.8 --- Deformation and Failure of Tungsten Carbide --- p.20 / References --- p.22 / Figures --- p.25 / Chapter Chapter 2 --- Experiment / Chapter 2.1 --- Sample Preparation --- p.40 / Chapter 2.2 --- Indentation --- p.42 / Chapter 2.3 --- Analysis Method --- p.43 / References --- p.46 / Figures --- p.47 / Chapter Chapter 3 --- Result and Discussion / Chapter 3.1 --- Introduction --- p.50 / Chapter 3.2 --- Deformation on the Top Surfaces --- p.50 / Chapter 3.3 --- Deformation on the Side Surfaces --- p.52 / Chapter 3.4 --- A comparison with Tungsten Carbide (WC/Co) --- p.59 / Chapter 3.5 --- Discussion --- p.60 / Chapter 3.6 --- Conclusion --- p.63 / References --- p.64 / Figures --- p.67

The internal oxidation behaviour of Ni-base and Fe-base alloys containing approximately 5 at% Al and both with and without low concentration Cr additions in flowing low-oxygen atmospheres at 1273 K was studied. There were two groups of Febase alloys; ferritic alloys that were Fe-Al-Cr and others that also contained approximately 9.3 at% Ni in order to make them austenitic. Ni?base alloys were oxidised in oxygen partial pressures of either 4.6 ?? 10-11 atm or 9.8 ?? 10-13 atm and Febase alloys were oxidised in an oxygen partial pressure of 1.2 ?? 10-16 atm The aim of this investigation was to examine the effect of internal oxidation on Fe- and Ni-base alloys containing Al or Al with Cr. The morphology of the precipitates formed and rates of reaction were of interest. Oxidation of the ferritic Fe-base alloys produced internal oxidation only at lower solute concentrations. In these alloys steady state diffusion-controlled precipitation was prevented from occurring due to the formation of an oxide barrier at the reaction front, and cracking off of the internal oxidation zone. In all of the austenitic alloys (Ni-base and y-Fe-base) internal oxidation was observed after all exposures. In y-Fe-base alloys and in Ni-base alloys oxidised at the higher oxygen partial pressure (4.6 ?? 10-11 atm) precipitation zones were found to widen according to parabolic kinetics, indicating diffusion control. In Ni-base alloys oxidised at 9.8 ?? 10-13 atm, precipitation zones were observed to widen according to parabolic kinetics up to 40.9 hours. However, the rate slowed for longer reaction times due to coalescence of precipitates at the reaction front. The rate of internal oxidation decreased with increasing Cr, and thus total solute, concentration. The parabolic rate constants measured for internal oxidation were higher than predicted by Wagner's theory of internal oxidation, which is consistent with observations in previous studies. Kinetics were accelerated by the presence of elongated precipitates, aligned approximately normal to the alloy surface. Chromium alloy additions led to precipitate coarsening, and at lower oxygen partial pressures, to loss of elongated morphology. The precipitates formed were found to be a mixture of M2O3 and AM2O4, where M represents either Al or Cr, and A represents either Fe or Ni. Both oxide forms were detected at all depths within the internal oxidation zone. However, Cr-containing oxides were limited to the part of the internal oxidation zone closer to the alloy surface, while Al-containing oxides were present at all depths. This is consistent with thermodynamic predictions.

No description available.

Amorphous alloys have a range of desirable ferromagnetic, electrical, mechanical and chemical properties. For instance, the application of Fe-based soft ferromagnetic amorphous alloys as transformer core materials can cut the transformer core losses to about 1/4, with considerable energy saving. However, during manufacture, heat treatment and in service, amorphous alloys may need to be exposed to moderately high temperatures for a period of time, with possible degradation caused by oxidation and crystallisation. There has been almost no previous study of oxidation behaviour and the relationship between oxidation and crystallisation in amorphous alloys. Eight important amorphous alloys and an industrial crystalline silicon steel have been studied in the present work; amorphous Fe78Si9Bl3, Fe40Ni40B20, Fe40Ni40P14B6, Co58NilOFe5SillB16, Fe32Ni36Crl4P12B6, Co66Fe4NilSil5B14, Co76Fe2Mn4Si6B12 and Ni78Si8B14, and crystalline Fe94Si6. A combination of thermogravimetry, optical and electron microscopy, electron probe microanalysis, X-ray diffractometry and differential scanning calorimetry has been used to investigate the oxidation and crystallisation kinetics, oxide structure and composition, oxidation and crystallisation mechanisms and the effect of crystallisation on the oxidation behaviour. The results show that the oxidation resistance at 350 C in air increases in the order Fe40Ni40- P14B6 < Fe94Si6 < Co66Fe4NilSil5B14 < Co58NilOFe5SillB16 < Co76MnFe2- Si6B12 < Fe40Ni40B20 < Si78Si9B13 < Ni78Si8B14 < Fe32Ni36Crl4P12B6. Most of the amorphous alloys obey a parabolic oxidation rate law, but the oxidation kinetics, oxide growth mechanism and resulting oxide structure change sharply when crystallisation takes place in the amorphous alloys. Amorphous Fe78Si9B13 and Fe40Ni40B20 have better oxidation resistance than the corresponding crystalline alloys, while amorphous Fe40Ni40P14B6 and Co58NilOFe5Sil1B16 have poorer oxidation resistance than the crystalline counterparts. Most of the crystalline alloys also obey a parabolic oxidation rate law, except for the crystalline Co based alloys and Fe40Ni40B20, which obey a logarithmic rate law. In most cases, the amorphous and crystalline alloys oxidise to form a fine-scale multiphase oxide scale, except for amorphous Fe40Ni40P14B6, which oxidises to form a whisker-like thick layer of Fe203- In general, ion diffusion through fast transport paths such as grain boundaries and dislocations is the rate controlling process for oxide growth. Different oxidation kinetics and oxide growth mechanisms in amorphous and crystalline alloys of the same composition are caused by micro-chemical segregation of the alloying elements during crystallisation.

The internal oxidation behaviour of Ni-base and Fe-base alloys containing approximately 5 at% Al and both with and without low concentration Cr additions in flowing low-oxygen atmospheres at 1273 K was studied. There were two groups of Febase alloys; ferritic alloys that were Fe-Al-Cr and others that also contained approximately 9.3 at% Ni in order to make them austenitic. Ni?base alloys were oxidised in oxygen partial pressures of either 4.6 ?? 10-11 atm or 9.8 ?? 10-13 atm and Febase alloys were oxidised in an oxygen partial pressure of 1.2 ?? 10-16 atm The aim of this investigation was to examine the effect of internal oxidation on Fe- and Ni-base alloys containing Al or Al with Cr. The morphology of the precipitates formed and rates of reaction were of interest. Oxidation of the ferritic Fe-base alloys produced internal oxidation only at lower solute concentrations. In these alloys steady state diffusion-controlled precipitation was prevented from occurring due to the formation of an oxide barrier at the reaction front, and cracking off of the internal oxidation zone. In all of the austenitic alloys (Ni-base and y-Fe-base) internal oxidation was observed after all exposures. In y-Fe-base alloys and in Ni-base alloys oxidised at the higher oxygen partial pressure (4.6 ?? 10-11 atm) precipitation zones were found to widen according to parabolic kinetics, indicating diffusion control. In Ni-base alloys oxidised at 9.8 ?? 10-13 atm, precipitation zones were observed to widen according to parabolic kinetics up to 40.9 hours. However, the rate slowed for longer reaction times due to coalescence of precipitates at the reaction front. The rate of internal oxidation decreased with increasing Cr, and thus total solute, concentration. The parabolic rate constants measured for internal oxidation were higher than predicted by Wagner's theory of internal oxidation, which is consistent with observations in previous studies. Kinetics were accelerated by the presence of elongated precipitates, aligned approximately normal to the alloy surface. Chromium alloy additions led to precipitate coarsening, and at lower oxygen partial pressures, to loss of elongated morphology. The precipitates formed were found to be a mixture of M2O3 and AM2O4, where M represents either Al or Cr, and A represents either Fe or Ni. Both oxide forms were detected at all depths within the internal oxidation zone. However, Cr-containing oxides were limited to the part of the internal oxidation zone closer to the alloy surface, while Al-containing oxides were present at all depths. This is consistent with thermodynamic predictions.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Bibliography: leaves 342-356.