This thesis is submitted as a portfolio of peer-reviewed publications. / For many geochemical systems, reaction kinetics determines the system's current status and evolution. It might also be the key to unraveling their thermal history. In metal sulfide systems, kinetic studies have been carried out on four sets of solid-state transitions/transformations in Fe-Ni-S and Ni-S systems. In this work, a new kinetic model, the Refined Avrami method, has been developed to account for reactions involving changes in reaction mechanisms. Nonstoichiometric compounds are commonly present in these reactions. The exsolution of pentladite from the monosulfide solid solution (mss) is an important reaction in the formation of nickel ores. For near equimolar mss compositions, the reaction rate is rapid even in the low temperature ranges. For bulk composition Fe₀.₇₇ Ni₀.₁₉ S, the experimental results show the reaction rates ( mss → pentlandite ) vary from 1.6x10⁻⁵ to 5.0x10⁻⁷ s⁻¹ at 200 °C and from 9.4x10⁻⁵ to 4.1x10⁻⁷ s⁻¹ at 300 °C. The activation energy, E [subscript a], varies during the course of reaction from 49.6 kJ.mol⁻¹ at the beginning of reaction (nucleation mechanism is dominant) to 20.7 kJ.mol⁻¹ at the end (crystal growth mechanism is dominant). Monosulfide solid solution (mss) is a common intermediate phase observed during the oxidation of nickel ores, such as violarite and pentlandite. The investigation of mss oxidation is of benefit in understanding the thermal behavior of economically important metal sulfides during smelting. The oxidation products of mss vary in our samples depending on their compositions. Apart from the common oxidation products hematite and Ni₁ ₇ S₁₈, Fe₂ (SO₄) ₃ was observed during the oxidation of Fe₇ . ₉ S₈ and pentlandite for Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ . The activation energy was determined using a model-free method. The oxidation of Fe₆.₄ Ni₁.₆ S₈ exhibited a higher E [subscript a] than Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ over the course of the reaction. The E [subscript a] increases with reaction extent (y) from 67.1 to 103.3 kJ.mol⁻¹ for mss composition Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ and from 76.1 to 195.0 kJ.mol⁻¹ for Fe₆.₄ Ni₁.₆ S₈ . The kinetic study of the α - Ni₁₋ ₓ S → β - NiS transition shows that initial compositions of α - Ni₁₋ ₓ S plays an important role in the kinetics of the transition. The activation energy ( E [subscript a] ) for this α - to β - phase transition is 16.0 ( ± 0.5 ) kJ.mol⁻¹ for NiS in the temperature range 70 to 150 °C, and 13.0 (± 0.5) kJ.mol⁻¹ in the temperature range 250 to 350 °C. For Ni₀. ₉₇ S, however, E [subscript a] deceases from 73.0 ( ± 0.5 ) to 17.0 ( ± 0.5 ) kJ.mol⁻¹ over the course of the reaction in the temperature range 300 to 320 °C. The relationship between E [subscript a] and extent of transition (y) for the initial bulk Ni₀. ₉₇ S was derived using the Refined Avrami method. For Ni deficient compositions, α - Ni₁₋ₓ S, the transformation to β-NiS is accompanied by the exsolution of either a progressively more Ni deficient α-Ni₁₋ₓ S and Ni₃ S₄ , and the reactions become more sluggish for more metal deficient compositions. The study of oxidation kinetics of α-NiS is of metallurgical interest, as α-NiS related phases may occur when nickel ores are flash smelted to produce nickel matte. In an open air environment, the oxidation mechanisms of α-NiS are constant at 670 and 680 °C, dominated by the direct oxidation of α-NiS → NiO. The dominant oxidation mechanism changes to a chain reaction : α-NiS → [superscript k] ₁ Ni₃ S₂ → [superscript k] ₂ NiO at 700 °C. Therefore, different kinetic models need to be applied to these two distinct reaction mechanisms. Activation energy for the oxidation, α-NiS → NiO, in the temperature range 670 to 680 °C was calculated to be 868.2 kJ.mol⁻¹ using Avrami/Arrhenius method. Rate constant k₁ and k₂ are approximated to be 3 x 10⁻⁴ s⁻¹ and 5 x 10⁻⁴ s⁻¹ for the first part and second part of the chain reaction respectively at 700 ° C. The study of the variation in reaction rate with oxidation time illustrates the optimum oxidation time zone for each temperature, where NiO can be produced at the fastest rate. / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2005.

This thesis is submitted as a portfolio of peer-reviewed publications. / For many geochemical systems, reaction kinetics determines the system's current status and evolution. It might also be the key to unraveling their thermal history. In metal sulfide systems, kinetic studies have been carried out on four sets of solid-state transitions/transformations in Fe-Ni-S and Ni-S systems. In this work, a new kinetic model, the Refined Avrami method, has been developed to account for reactions involving changes in reaction mechanisms. Nonstoichiometric compounds are commonly present in these reactions. The exsolution of pentladite from the monosulfide solid solution (mss) is an important reaction in the formation of nickel ores. For near equimolar mss compositions, the reaction rate is rapid even in the low temperature ranges. For bulk composition Fe₀.₇₇ Ni₀.₁₉ S, the experimental results show the reaction rates ( mss → pentlandite ) vary from 1.6x10⁻⁵ to 5.0x10⁻⁷ s⁻¹ at 200 °C and from 9.4x10⁻⁵ to 4.1x10⁻⁷ s⁻¹ at 300 °C. The activation energy, E [subscript a], varies during the course of reaction from 49.6 kJ.mol⁻¹ at the beginning of reaction (nucleation mechanism is dominant) to 20.7 kJ.mol⁻¹ at the end (crystal growth mechanism is dominant). Monosulfide solid solution (mss) is a common intermediate phase observed during the oxidation of nickel ores, such as violarite and pentlandite. The investigation of mss oxidation is of benefit in understanding the thermal behavior of economically important metal sulfides during smelting. The oxidation products of mss vary in our samples depending on their compositions. Apart from the common oxidation products hematite and Ni₁ ₇ S₁₈, Fe₂ (SO₄) ₃ was observed during the oxidation of Fe₇ . ₉ S₈ and pentlandite for Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ . The activation energy was determined using a model-free method. The oxidation of Fe₆.₄ Ni₁.₆ S₈ exhibited a higher E [subscript a] than Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ over the course of the reaction. The E [subscript a] increases with reaction extent (y) from 67.1 to 103.3 kJ.mol⁻¹ for mss composition Fe₆ . ₁ ₅Ni₁ . ₅₄ S₈ and from 76.1 to 195.0 kJ.mol⁻¹ for Fe₆.₄ Ni₁.₆ S₈ . The kinetic study of the α - Ni₁₋ ₓ S → β - NiS transition shows that initial compositions of α - Ni₁₋ ₓ S plays an important role in the kinetics of the transition. The activation energy ( E [subscript a] ) for this α - to β - phase transition is 16.0 ( ± 0.5 ) kJ.mol⁻¹ for NiS in the temperature range 70 to 150 °C, and 13.0 (± 0.5) kJ.mol⁻¹ in the temperature range 250 to 350 °C. For Ni₀. ₉₇ S, however, E [subscript a] deceases from 73.0 ( ± 0.5 ) to 17.0 ( ± 0.5 ) kJ.mol⁻¹ over the course of the reaction in the temperature range 300 to 320 °C. The relationship between E [subscript a] and extent of transition (y) for the initial bulk Ni₀. ₉₇ S was derived using the Refined Avrami method. For Ni deficient compositions, α - Ni₁₋ₓ S, the transformation to β-NiS is accompanied by the exsolution of either a progressively more Ni deficient α-Ni₁₋ₓ S and Ni₃ S₄ , and the reactions become more sluggish for more metal deficient compositions. The study of oxidation kinetics of α-NiS is of metallurgical interest, as α-NiS related phases may occur when nickel ores are flash smelted to produce nickel matte. In an open air environment, the oxidation mechanisms of α-NiS are constant at 670 and 680 °C, dominated by the direct oxidation of α-NiS → NiO. The dominant oxidation mechanism changes to a chain reaction : α-NiS → [superscript k] ₁ Ni₃ S₂ → [superscript k] ₂ NiO at 700 °C. Therefore, different kinetic models need to be applied to these two distinct reaction mechanisms. Activation energy for the oxidation, α-NiS → NiO, in the temperature range 670 to 680 °C was calculated to be 868.2 kJ.mol⁻¹ using Avrami/Arrhenius method. Rate constant k₁ and k₂ are approximated to be 3 x 10⁻⁴ s⁻¹ and 5 x 10⁻⁴ s⁻¹ for the first part and second part of the chain reaction respectively at 700 ° C. The study of the variation in reaction rate with oxidation time illustrates the optimum oxidation time zone for each temperature, where NiO can be produced at the fastest rate. / Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2005.

Thesis (M.S.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 70-76)

Application of high pressure and high temperature has been used to synthesize a new compound: boron monosulfide. Two polymorphs have been made by varying the temperature. A cubic phase was formed at 60 kilobars pressure and 1500° C., and an orthorhombic phase was formed at 60 kilobars and 1400° C. The synthesis procedure has been optimized and the best results were obtained at these conditions using water as a mineralizer. Without the water, it is necessary to use higher temperatures to form the cubic phase. The cubic material is very stable at atmospheric conditions and does not react with common acids or bases. Its density was measured to be 2.52 gm/cm 3 in the powder form with some of the larger crystals measuring at 2.58 gm/cm^3 It is a light olive color in the powder form and the larger crystals are transparent with a deep yellow color. The orthorhombic material is a light tan color and its density was measured to be 2.53 gm/cm^3. The crystal systems of the two polymorphs were determined by X-ray diffraction. It was not possible to determine the space group to which the cubic system belongs due to the imperfections in the crystals. Attempts to grow single crystals large enough to analyze properly by single crystal diffraction were not successful. The crystallite size was determined roughly by line broadening of the X-ray diffraction pattern to be 120 A. in the cubic material. The cell parameter, as measured from the X-ray diffraction pattern, was found to be 4.39 A.

No description available.