The temperature dependence of the reactions of halogen atoms Cl and Br with SiH4 and (CH3)3SiH have been investigated with the flash photolysis-resonance fluorescence technique. CCI4 and CH2Br2 were used as precursors to produce Cl and Br atoms, respectively. Experiments gave {k(Cl + SiH4) (295 - 472 K)} = (1.56 +0.11) x 10-1 exp[(2.0 + 0.2) kJ mol'/RT] cm3 s4, {k(Br + SiH4)(295 - 575 K)} = (9.0 + 1.5) x 10-" exp[-(17.0 + 0.6) Id mol'/RT] cm3 s', {k(Cl + (CH3)3SiH)(295 - 468 K)} = (1.24 0.35) x 104 exp[(1.3 + 0.8) Id mol4/RT] cm3 s', and {k(Br + (CH3)3SiH)(295 - 456 K)} = (7.6 + 3.3) x 1010 exp[-(28.4 + 1.3) Id mol'/RT] cm3 s'. The results were compared with values from earlier work.

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The kinetics of the Cu⁺⁺ catalysed reduction of dichromate by hydrogen in aqueous perchlorate solutions were investigated between 160° and 200°C. A significant dependence of rates on Cr[superscript](VI) was observed. The mechanism proposed to account for the kinetics gave rise to a rate law of the form [formula omitted] where the rate constant for the hydrogen activation step, k₁, is given by [formula omitted]. The rate constant ratios k₋₁/k₂ and k₋₁/k₃ are believed to be temperature independent in the temperature range under consideration, and have approximate values of 0.38 and 0.02 respectively. As a consequence of these studies a similar mechanism was proposed for the Cu⁺⁺ catalysed hydrogen-oxygen recombination reaction investigated by McDuffie and co-workers. According to this mechanism an apparent discrepancy between the observations of Halpern et al and those of the former workers can be explained. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

The kinetics of the reduction of silver amine complexes in aqueous solutions were investigated and found to be second order overall, the rate being proportional to silver complex and hydrogen concentrations. These systems were studied under conditions of essentially complete complexing and therefore the rates were independent of amine concentration. The rates were also shown to be independent of amine perchlorate concentration and thus of pH within a limited range. Enthalpies and entropies of activation were determined for each system and an attempt was made to correlate kinetic data with information on complex stability constants and amine basicities. The most prominent trend in the results was the inverse dependence of rate on complex stability constant. Two mechanisms are proposed both involving heterolytic cleavage of the hydrogen molecule. In the first mechanism, the proton released in the rate determining step is taken up by the basic ligand directly. In the second mechanism, a water molecule replaces the amine ligand and acts as the proton acceptor. The strength of the silver-ligand bond and the difficulty of ligand replacement by water account for the inverse dependence of rate on complex stability for each mechanism respectively. Arguments are presented to support both mechanisms. In general dibasic amine complexes activated hydrogen more readily and displayed a more negative entropy of activation than do the monoamine complexes. These observations are attributed to the presence of a free basic group in the ligand aiding the cleavage of the hydrogen molecule in the rate determining step. The proximity of the second basic group to the central silver atom also appears to be important. These effects and the possible role of the free basic group in the ligand are discussed. / Science, Faculty of / Chemistry, Department of / Graduate

D.Ed. (Didactics) / This study focused on the misconceptions which exist among standerd ten pupils in the field of chemical equilibrium and the rate of chemical reactions. Although the teacher Is confident that meaningful teaching occurs In the classroom situation, misconceptions do materialise frequently. Several factors concerning the pupil, the teacher as well as the subject content Itself were Investigated. The main objective of this study Is to Investigate the nature and extent of the misconceptions regarding the rate of chemical reactions and the chemical equilibrium experienced by standard ten pupils. Following this, pupils are exposed to a computer program which has been complied to eliminate the misconceptions regarding these two themes...

The reaction of 1-(diphenylphosphino)-2-(diphenylphosphito)benzene (PP*) and Os3(CO)10(ACN) has been investigated. A combined experimental and computational study on the isomerization of 1,2-Os3(CO)10[μ-1,2-Ph2P(C6H4)P(OPh)2] (A) and 1,1-Os3(CO)10[μ-1,2-Ph2P(C6H4)P(OPh)2] (B) and reversible ortho-metalation exhibited by the triosmium cluster B are reported. The subsequent conversion of cluster B to the hydrido cluster HOs3(CO)9[μ-1,2-PhP(C6H4-η1)C6H4P(OPh)2] (E) and the benzyne-substituted cluster HOs3(CO)8(µ3-C6H4)[μ-1,2-PhP(C6H4)P(OPh)2] (N) has been established. All of these new clusters have been isolated and fully characterized in solution by IR and NMR spectroscopy; in addition, X-ray diffraction analyses have been performed on the clusters A, B, J, and N. The ortho-metalation reaction that gives cluster E is shown to be reversible, and the mechanism has been probed using selectively deuterated PP* isotopomers. Kinetic and thermodynamic isotope data, in conjunction with DFT calculations, are presented that support the existence of an intermediate unsaturated cluster in the ortho-metalation reaction. Due to interest in the coordination chemistry of formamidines, the non-symmetric amidine ligands PhNC(Me)NHPri, PhNC(Et)NHPri, and (2,4,6-Me3C6H2)NC(Me)NHPri, have been synthesized, and their reaction with Os3(CO)10(MeCN)2 has been investigated. Of the twelve new clusters prepared in section, seven have been structurally characterized by X-ray crystallography.

Future thrusts for gasoline engine development can be broadly summarized into two categories: (i) efficiency improvements in conventional spark ignition engines, and (ii) development of advance compression ignition (ACI) concepts. Efficiency improvements in conventional spark ignition engines requires downsizing (and turbocharging) which may be achieved by using high octane gasolines, whereas, low octane gasolines fuels are anticipated for ACI concepts. The current work provides the essential combustion kinetic data, targeting both thrusts, that is needed to develop high fidelity gasoline surrogate mechanisms and surrogate complexity guidelines. Ignition delay times of a wide range of certified gasolines and surrogates are reported here. These measurements were performed in shock tubes and rapid compression machines over a wide range of experimental conditions (650 – 1250 K, 10 – 40 bar) relevant to internal combustion engines. Using the measured the data and chemical kinetic analyses, the surrogate complexity requirements for these gasolines in homogeneous environments are specified. For the discussions presented here, gasolines are classified into three categories: (i) Low octane gasolines including Saudi Aramco’s light naphtha fuel (anti-knock index, AKI = (RON + MON)/2 = 64; Sensitivity (S) = RON – MON = 1), certified FACE (Fuels for Advanced Combustion Engines) gasoline I and J (AKI ~ 70, S = 0.7 and 3 respectively), and their Primary Reference Fuels (PRF, mixtures of n-heptane and iso-octane) and multi-component surrogates. (ii) Mid octane gasolines including FACE A and C (AKI ~ 84, S ~ 0 and 1 respectively) and their PRF surrogates. Laser absorption measurements of intermediate and product species formed during gasoline/surrogate oxidation are also reported. (iii) A wide range of n-heptane/iso-octane/toluene (TPRF) blends to adequately represent the octane and sensitivity requirements of high octane gasolines including FACE gasoline F and G (AKI ~ 91, S = 5.6 and 11 respectively) and certified Haltermann (AKI ~ 87, S = 7.6) and Coryton (AKI ~ 92, S = 10.9) gasolines. To assess conditions where shock tubes may not be ideal devices for ignition delay measurements, this work also presents a detailed discussion on shock tube pre-ignition affected ignition data and the ignition regimes in homogeneous environments. The shock tube studies on pre-ignition and associated bulk ignition advance may help engines research community understand and control super-knock events.

The purpose of this thesis was to determine the kinetics and stoichiometry for the aquation of the pentaaquomonobromonmethylchromium(III) complex. The complex was prepared by the reduction of dibromomethane by chromium(II). The products of aquation, in the absence of oxygen, were found to be hexaaquachromium(III), methanol, and bromide. The balanced net ionic reaction can be written: 2H2O + (H2O)5CrCH2Br2+ → (H2O)6Cr3+ + CH3OH + Br-

Gas phase kinetics and thermochemistry of several halogenated species relevant to atmospheric, combustion and plasma chemistry were studied using experimental and ab initio theoretical techniques.

Semicrystalline polymers constitute the majority of the commercially manufactured polymers, mostly known as commodities with low modulus and inferior properties. A robust approach used in tailoring such commodity’s properties for more advanced applications is through the incorporation of inorganic nanoparticles (NPs). Over the past half century, polymer nanocomposites (PNCs) have attracted extensive interest in fundamental research and technological applications. However, NPs have been found to result in complicated alterations in the semicrystalline polymer crystallization kinetics, and their crystalline morphology, which could either synergistically or adversely affect the final composite properties. A comprehensive understanding of this topic is still lacking, which with one could tune the final polymer properties for various cutting-edge applications. In this dissertation, we focus on the crystallization kinetics of semicrystalline PNCs and the connection between the morphology and the mechanical (and rheological) properties of such hybrid systems. First, we control the NP dispersion and self-assembly in a semicrystalline poly(ethylene oxide) (PEO) matrix using both bare and polymer-grafted NPs. We show that bare NPs (with different sizes) and unimodal poly(methyl methacrylate) (PMMA)-g-SiO2 NPs uniformly disperse in a PEO matrix because of the favorable interaction between the matrix and the NP surface (or the PMMA brush). Grafting the latter NPs with a short dense polystyrene brush that is immiscible with PEO while varying the PMMA grafting parameters induces self-assembly and leads to various NP structures: well-dispersed, connected sheets, strings, and large aggregates. Next, we systematically investigate the role of bare and self-assembled grafted NPs on the spherulitic growth kinetics of semicrystalline polymers. In all cases, the incorporation of spherical NPs suppresses the polymer growth kinetics. Using rheological measurements, we show that the reduction in growth is mainly attributed to the NPs increasing the melt viscosity; whereas, they minimally alter the secondary nucleation process. Surprisingly, the PNC growth kinetics is suppressed in two apparently universal manners when plotted as a function of confinement: NP dominated and brush-controlled regimes. Bare NPs and large aggregates of polymer-grafted NPs appear to nearly follow the same dependence for the role of additives on polymer viscosity, weakly suppressing the growth kinetics. On the other hand, all the other self-assembled NP structures showed much stronger growth reductions because of the larger increase in the melt viscosity by the chemically bonded brush. Given our prior knowledge of the PNC growth kinetics, we then draw generalized trends for the role of bare and grafted NPs in nucleating semicrystalline polymers. This is achieved by comparing the polymer crystallization kinetics in the presence of large, asymmetric, immobile fillers (selected from the well-established literature) to those smaller, spherical, mobile NPs (examined throughout this thesis). Generally, NPs serve as heterogenous nucleation sites when incorporated at smaller amounts, leading to accelerated crystallization kinetics. At larger filler contents, NPs confine the polymer chains into smaller domains and become more susceptible to aggregation, which results in antinucleating effects and suppressing the crystallization rate. Such competing effects result in a maximum nucleation efficiency at moderate filler contents. It is also worth noting that the degree of nucleation enhancement and subsequent suppression depends on the system and is controlled by NP dispersion, geometry, and surface chemistry. For example, one- and two-dimensional NPs usually result in a higher nucleation power compared to spherical NPs. Another major difference between mobile and immobile fillers is that when slowly crystallizing from the melt, the smaller diffusive NPs can be segregated and ordered into hierarchal structures (interlamellar sheets and interfibrillar and interspherulitic aggregates). This provides a much richer class of materials with a kinetics route in controlling NP assemblies. Finally, we create robustly toughened semicrystalline polymers by confining the PEO crystallization using a densely grafted PMMA brush (i.e., PMMA-g-SiO₂) with different molecular weights. For comparison, we prepare linear PMMA/PEO blends with equivalent PMMA molecular weights and volume fractions to those of the nanocomposites. We show that PMMA-g¬-SiO₂ NPs surpass linear PMMA homopolymers in terms of toughening the PEO matrix, with the grafted system experiencing relatively higher connectivity and lower crystallinity. At moderate confinement, the nanocomposite sustains a maximum modulus increase of 42%, with around a 200-fold increase in the PEO toughness. This provides a novel route for toughening semicrystalline polymers using noncrystallizable polymer-grafted NPs.