Thesis (M.A.) -- University of Tennessee, Knoxville, 2005. / Title from title page screen (viewed on Feb. 2, 2006). Thesis advisor: Lee Meadows Jantz. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1934. / Typescript. Includes bibliographical references.

Submitted in fulfillment of the academic requirements for the award of the degree of Master of Engineering, Durban University of Technology, Durban, South Africa, 2018. / Overdependence on fossil-based fuels and their effect on environment is a global concern by energy stake holders. Bulk of present day hydrogen comes from gasification of coal, steam reforming and partial oxidation of hydrocarbons. Steam reforming accounts for over 50% of world hydrogen production despite producing carbonaceous gases which are harmful to the environment and poisonous to both; proton exchange fuel cells and alkaline fuel cells. Natural gas is a preferred feed for hydrogen production, because it is abundantly available on earth. Catalytic decomposition of ammonia can produce clean hydrogen but ammonia itself is an air pollutant. Catalytic decomposition of methane into carbon and hydrogen is an attractive option to producing clean hydrogen because its products are carbon and hydrogen. In this work, five different catalysts comprising of varying quantities of nickel and lithium, supported on calcium oxide were synthesized by incipient wetness impregnation method and designated according to weight % as; 30%Ni/CaO, 37.5%Ni-12.5%Li/CaO, 25.0%Ni- 25.0%Li/CaO, 12.5%Ni-37.5%Li/CaO and 50%Li/CaO. The synthesized catalysts were characterized by (XRD, SEM, BET and TEM) and tested for methane decomposition. From the XRD patterns of the synthesized catalysts, distinct crystalline phases of CaO and NiO were positively identified in 50%Ni/CaO according to their reference JCPDS files. Introduction of Lithium hydroxides improved the crystalline structure of the Ni/CaO catalyst. SEM analyses of the catalyst material using Image-J software confirmed that all catalyst materials were nanoparticles ranging from 3.09-6.56nm. BET results confirmed that, all the catalysts are mesoporous with pore sizes ranging from 20.1nm to 45.3nm. Introduction of LiOH to Ni/CaO generates mesoporous structures by destructing the lattices of the CaO structure during the formation of Ni-Li/CaO species. Particle size distribution in TEM analyses revealed that, a higher nickel loading in the catalyst favours the formation of carbon nanotubes while higher lithium hydroxide loading favours the formation of carbon fibres (CF). Low yield of carbon fibres from methane decomposition on unsupported Ni catalyst in 50%Ni/CaO was attributed to the presence of large Ni particles with low index planes which were incapable of dissociating the unreactive methane molecule. The aim of this work was to synthesize a catalyst for use in decomposition of methane into carbon and hydrogen, that addresses drawbacks of traditional solid metal catalysts such as sintering and coking. From the experimental results, 37.5%Ni-12.5%Li/CaO catalyst recorded 65.7% methane conversion and 38.3%hydrogen yield while 50%Ni/CaO recorded the lowest methane conversion of 60.2% and a hydrogen yield of 35.7% at 650℃. Outstanding performance of the 37.5%Ni-12.5%Li/CaO catalyst is attributed to the incorporation of lithium hydroxide which provided more catalyst active sites and a molten environment for proper dispersion of the nickel metal. The solid 50%Ni/CaO catalyst readily deactivated due to coking unlike the supported molten 37.5%Ni-12.5%Li/CaO catalyst in which methane decomposition reaction took place by both surface reaction and chemisorption. / M

The chemical reactivity of a solid is influenced to a marked degree by the presence of imperfections or defects in the solid. Bond strengths are considerably weaker at points of imperfection than elsewhere in the solid, and hence the initiation of reaction is favoured at these sites due to the relative ease of bond rupture. Line defects, such as edge or screw dislocations, jogs, Smekul cracks etc, are of prime importance in such changes. The surface of a solid or in intergranular boundaries, where a state of strain exists, are also favourable places for the initiation of a reaction, Point defects e.g. vacancies or interstitialions or atoms also play important roles in chemical change, often in conjuction with line defects.

The thermal decomposition of silver permanganate, pre-irradiated in BEPO and in a ⁶°C₀ Ϫ 'hot spot' has been investigated in the temperature range 100 - 125°C. The results are similar to those for irradiated KMn0₄ and the mechanism proposed for the latter is again suggested. The activation energy for the migration of point defects over the induction period is 1.03 ev. The decompositions of unirradiated and irradiated crystals differ in that the latter undergo physical disintegration over the acceleratory period. X-ray studies immediately prior to disintegration show strain and fragmentation in the irradiated crystal. An explanation involving the annealing of point defects at dislocation is advanced to explain the changes produced in the p/t plots with increased dosage, and fixed decomposition temperature. Summary, p. 94.

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No description available.

Yim Wai-leung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 73-77). / Abstracts in English and Chinese. / THESIS COMMITTEE --- p.ii / ABSTRACT (English version) --- p.iii / ABSTRACT (Chinese version) --- p.v / ACKNOWLEDGEMENTS --- p.vi / TABLE OF CONTENTS --- p.vii / LIST OF FIGURES --- p.ix / LIST OF TABLES --- p.xi / Chapter CHAPTER 1. --- General Introduction / Chapter Section 1.1 --- Introduction --- p.1 / Chapter Section 1.2 --- Electronic Structure Calculation / Chapter 1.2.1 --- Density Functional Theory --- p.2 / Chapter 1.2.2 --- "Exchange, Correlation and the Local Density Approximation" --- p.4 / Chapter 1.2.3 --- Bloch's Theorem and Plane Wave Basis Set --- p.6 / Chapter 1.2.4 --- The Pseudopotential Approximation --- p.10 / Chapter Section 1.3 --- Molecular Dynamics / Chapter 1.3.1 --- Molecular Dynamics --- p.12 / Chapter 1.3.2 --- Nose Thermostat / Chapter 1.3.2.1 --- Introduction --- p.14 / Chapter 1.3.2.2 --- Feedback Method --- p.15 / Chapter Section 1.4 --- Case Studies / Chapter 1.4.1 --- Thermal properties of small silver clusters --- p.18 / Chapter 1.4.2 --- Thermal decomposition channels of NTO --- p.20 / Chapter CHAPTER 2. --- Ab Initio Molecular Dynamics Study on Agn (n=4-6) / Chapter Section 2.1 --- Introduction --- p.22 / Chapter Section 2.2 --- Computational Method --- p.24 / Chapter Section 2.3 --- Results and Discussion / Chapter 2.3.1 --- Ag2 --- p.26 / Chapter 2.3.2 --- Ag4 --- p.30 / Chapter 2.3.3 --- Ag5 --- p.36 / Chapter 2.3.4 --- Ag6 --- p.45 / Chapter Section 2.4 --- Summary --- p.49 / Chapter CHAPTER 3. --- Ab Initio Molecular Dynamics Study on Thermal Decomposition of NTO / Chapter Section 3.1 --- Introduction --- p.52 / Chapter Section 3.2 --- Computation Details --- p.55 / Chapter Section 3.3 --- Results and Discussion / Chapter 3.3.1 --- Comparison of the Quantum Calculations by VASP and Gaussian98 --- p.56 / Chapter 3.3.2 --- Exploring the Reaction Channels --- p.62 / Chapter 3.3.2.1 --- Hydrogen-transfer Activation --- p.62 / Chapter 3.3.2.2 --- Homolytic Cleavage of C-N02 Bond --- p.63 / Chapter 3.3.2.3 --- Nitro-nitrite Rearrangement --- p.64 / Chapter 3.3.2.4 --- Direct Ring Rupture --- p.64 / Chapter 3.3.3 --- Energetic Consideration --- p.65 / Chapter 3.3.4 --- Activation Barriers --- p.70 / Chapter 3.3.5 --- Summary --- p.72 / REFERENCES --- p.73

The decomposition behavior of several mining reagents (i.e., xanthate, dithiocarbamate, dithiophosphate and dithiophosphinate) used widely in mineral processing operations was studied. Decomposition has been reported to generate toxic compounds such as CS₂ (carbon disulfide) and COS (carbonyl sulfide), causing severe concerns to SHE (safety, health and environment). With the global trend of becoming sustainable/green and the increasingly strict regulations, the mining industry is facing an unprecedented pressure to handle the problematic reagents that can lead to the adverse impacts. Unfortunately, the interests of the prior research are biased on the performance of the reagents to optimize the efficiency and lower the cost, while the examination of the decomposition behavior is almost neglected. Under the circumstance of poor endeavor found in the prior investigations, the knowledge gap awaits to be filled in a systematic and integrated manner to recommend countermeasures for those problematic reagents. It can be seen from those fragmented studies collected from literature that only a limited understanding of thermal or aqueous decomposition behavior is achieved. It is far from sufficient for industrial guidance of mitigation. One key reason is the lack of robust methods to investigate decomposition under various conditions that are interesting to the mining companies (e.g., the flotation conditions). Consequently, the method development has always been considered of the utmost importance upon the start of this work to align with our overall goal of understanding the decomposition behavior under the various conditions. Three methods under a consistent strategy were designed to examine the decomposition under three conditions from Simple (in aqueous solutions alone), to Complex (in ore pulp under flotation conditions), to Specific (in solution containing metal ions). These three conditions were chosen based on the general interests from several prominent mining companies (Vale, Barrick, Freeport McMoRan and Newmont) to understand the decomposition mechanism and kinetics. The Simple is to serve as control for all other conditions. Besides, most of the prior studies in the literature are only conducted for the Simple condition. Therefore, the Simple is to resolve all discrepancies and conflicts, and provide a relatively comprehensive summary of the decomposition under the control condition. The Complex puts decomposition in a new environment that has never been explored before: the ore pulp under the simulated batch flotation conditions. Conclusions drawn from this part provide the most practical guidance for industrial mitigation. The Specific goes after the Complex to thoroughly understand the effect of a specific factor on decomposition. The decomposition responding to the variation of a certain factor is followed within a closed system with the compositional changes measured in all phases. The integrated analysis enables the correlation of the decomposition behavior to its original causes, which are the interactions of the reagent with other components in the system. Through the systematic investigation of decomposition of various reagents under various conditions, it is concluded that decomposition depends heavily on those parallel or sequential interactions that occur along with the decomposition reaction. For example, the decomposition reaction of xanthate throughout our entire study is regarded as ROCS₂⁻→CS₂. When xanthate forms xanthic acid, monothiocarbanate or dixanthogen with the change of pH, its breakup into CS₂ is altered. When xanthate interacts with Cu²⁺ forming Cu₂X₂, decomposition is depressed, but with Fe³⁺ forming FeX₃ decomposition is promoted. The CS₂ generated from decomposition could interact with OH- to form CS₃²⁻ or dissolve in solution or adsorb on minerals, leading to the decrease of CS₂ detected. The bonding properties between the –CS₂ moiety and other atoms or radicals in the molecule affect the stability of the reagents and the subsequent decomposition. The necessity to include a list of the side-interactions as complete as possible is key to understand and predict the decomposition behavior. With experimental efforts taken to develop methodologies to measure the decomposition under various conditions, the attempt to model the decomposition behavior is also initiated in this work. Based on the conclusions from experimental results, major components determining the output of the final decomposition products are identified. Unsurprisingly, the decomposition reaction together with its parallel and sequential interactions is critical. Simulation using Matlab to assess the decomposition of a simplified system containing SIBX and Cu²⁺ ions has achieved preliminary success by matching well with the experimental measurements. This establishes the groundwork for furthering the simulation of more complex systems and model development. Reagents decompose differently, although they might be applied to function similarly during an operation. As flotation collectors used for sulfide ore beneficiation, dithiocarbamate and xanthate possess some similarities in the decomposition in terms of generating CS₂. Their decomposition also decreases with the chain length. On the other hand, the decomposition of dithiophosphate and dithiophosphinate are different as the breakup of the molecule is mainly at their alkyl chain to generate moieties such as olefins. Compared to the studies carried out to understand the performance of the reagents when being used, research on decomposition requires more attention. Therefore, derivative work can be conducted based on results achieved in this work. For example, it is useful to further examine how reagents decompose after adsorbing on the mineral surfaces. It complements the knowledge to thoroughly understand decomposition at different spots within a complex system. The chemical fate studies of mining reagents with respect to the understanding the decomposition open up the window of developing methodologies to examine adverse behaviors. The experimental setups are applicable to simulate various conditions under which the reagent is being used and generating the adverse impacts. The strategy of analyzing decomposition within a complex system as shown in this study also provides insight into systematically investigating the other types of adverse behaviors.

Thesis (Ph.D.)--University of Wollongong, 2004. / Typescript. Includes bibliographical references: leaf 142-167.