Composites that show visible light transmittance, UV absorption, and moderately high refractive index, based on poly(methyl methacrylate) (PMMA) and zinc oxide (zincite, ZnO) nanoparticles, were prepared in two steps First, surface-modified ZnO nanoparticles with 22 nm average diameter were nucleated by controlled precipitation via acid-catalyzed esterification of zinc acetate dihydrate with pentan-1-ol The surface of growing crystalline particles was modified with tert-butylphosphonic acid (tBuPO3H2) in situ by monolayer coverage Particle size and graft density of −PO3H2 on the particle surface were controlled by the amount of surfactant applied to the reaction solution Second, the surface-modified particles were incorporated into PMMA by in-situ bulk polymerization Free radical polymerization was carried out in the presence of these particles using AIBN as initiator Volume fraction (φ) of the particles was varied from 010 to 776% (05 to 30 wt %) Although the particles are homogeneously dispers

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Optical properties of composites of PMMA and surface-modified zincite nanoparticles

Microorganisms: Induction and inhibition of corrosion in metals

Multi-scale modeling of chemical vapor deposition processes for thin film technology

Structures and energies of the gas-phase species produced during and after the various unimolecular decomposition reactions of methyltrichlorosilane (MTS) with the presence of H2 carrier gas were determined using second-order perturbation theory (MP2). Single point energies were obtained using singles + doubles coupled cluster theory, augmented by perturbative triples, CCSD(T). Partition functions were obtained using the harmonic oscillator-rigid rotor approximation. A 114-reaction mechanism is proposed to account for the gas-phase chemistry of MTS decompositions. Reaction enthalpies, entropies, and Gibbs free energies for these reactions were obtained at 11 temperatures ranging from 0 to 2000 K including room temperature and typical chemical vapor deposition (CVD) temperatures. Calculated and experimental thermodynamic properties such as heat capacities and entropies of various species and reaction enthalpies are compared, and theory is found to provide good agreement with experiment.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1107&context=cbe_pubs

Theoretical study of the pyrolysis of methyltrichlorosilane in the gas phase. 1. Thermodynamics.

In this study, new boroaluminide protective coatings were deposited on ferritic–martensitic steel substrates (P91) using the pack cementation technique, at moderate temperatures in order not to influence the substrates' mechanical properties. Extensive thermodynamic calculations were performed initially, using the Thermocalc Computer program, so as to optimize the process parameters. The most important gas-precursors for successful deposition of the coatings were identified. The effect of pack composition on the formation and growth of boroaluminides at 715 °C, using pack powders containing Al and B as element depositing sources, two halide salts as activators, and Al2O3 as inert filler, was investigated. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al, B and Fe and an inner layer containing mostly B, Cr and Fe. The layers were characterized by means of optical and Scanning Electron Microscopy (SEM) in terms of coating morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coatings due to the boroaluminizing process.

Boroaluminide coatings on ferritic–martensitic steel deposited by low-temperature pack cementation

A comprehensive study of the chemical vapor codeposition of silica, alumina, and aluminosilicates from SiCl{sub 4}-AlCl{sub 3}-H{sub 2}-CO{sub 2} mixtures is presented. A hot-wall reactor, coupled to an electronic microbalance, is used to investigate the dependence of the deposition rate on temperature, pressure, composition, and total flow rate over a broad range of operating conditions. The experimental observations are discussed in the context of the results obtained in independent deposition experiments of silica and alumina from mixtures of SiCl{sub 4}-H{sub 2}-CO{sub 2} and AlCl{sub 3}H{sub 2}-CO{sub 2}, respectively, in the same apparatus. The results show that the deposition of silica proceeds at very low rates that are by more than an order of magnitude lower than those of alumina deposition at the same temperature, pressure, total flow rate, and carbon dioxide and chloride mole fractions in the feed. When both chlorides (SiCl{sub 4} and AlCl{sub 3}) are fed to the reactor, that is, in the codeposition process, the rate of SiO{sub 2} deposition is much higher than that seen in the single species deposition experiments, while the opposite behavior is observed for the rate of deposition of Al{sub 2}O{sub 3}. The results of deposition experiments conducted on refractory wires, inmore » order to obtain information on the effect of the substrate position in the reactor, show that manipulation of residence time offers a way to control the composition of the codeposited films in alumina and silica. The experimental results are compared with those obtained in a past study using methyltrichlorosilane as silicon source.« less

Chemical Vapor Deposition of Aluminosilicates from Mixtures of SiCl4, AlCl3, CO 2, and H 2

Detailed homogeneous and heterogeneous chemistry models are formulated for the chemical vapor deposition (CVD) of alumina from mixtures of aluminum trichloride, hydrogen, and carbon dioxide. Since formation of the species that are required for the incorporation of oxygen atoms in the film (primarily H 2 O and OH) takes place through the pathways of the water-gas-shift reaction, a complete kinetic model for this process is incorporated as a submodel in the homogeneous chemistry model. Information obtained from the analysis of the thermodynamic equilibrium in the gas phase of the reacting mixture and from past experimental and theoretical studies is employed to determine which elementary reaction steps play an important role in the overall deposition process The kinetic model is introduced into the transport and reaction model of a tubular, hot-wall CVD reactor, and it is employed to obtain results on the effects of the operating conditions on the variation of the gas-phase composition, deposition rate, and surface species coverages with residence time, under conditions typically encountered in aluminum oxide chemical vapor deposition. Experimental data obtained in a tubular, hot-wall CVD reactor in our laboratory are used to validate the predictions of the overall model. The model is found to he capable of reproducing successfully the experimental data and the various behavior patterns observed in the experiments, such as the occurrence of a maximum in the variation of the deposition rate with parameters that affect strongly the residence time of the mixture in the reactor.

Development and Validation of a Mathematical Model for the Chemical Vapor Deposition of Alumina from Mixtures of Aluminum Trichloride, Carbon Dioxide, and Hydrogen

The co-deposition of silica, alumina, and aluminosilicates from mixtures of methyltrichlorosilane, aluminum trichloride, carbon dioxide, and hydrogen was investigated in this study In order to elucidate some aspects of the co-deposition process, the deposition of pure silica and pure alumina from mixtures of methyltrichlorosilane and aluminum trichloride, respectively, with CO2 and H2 was also investigated Kinetic data were obtained by carrying out CVD experiments on SiC substrates in a hot-wall reactor of tubular geometry, which permitted continuous monitoring of the deposition rate through the use of a microbalance Reaction rate data are presented for temperatures between 1073 and 1373 K (800–1100 °C) at 133 kPa (100 torr) pressure for various feed compositions and various positions along the axis of the deposition reactor Thermodynamic equilibrium computations were performed on the Al/Si/Cl/C/O/H, Al/Cl/C/O/H, and Si/Cl/C/O/H systems at the conditions used in the deposition experiments The experimental observations are discussed in the context of the results of the equilibrium analysis and of past studies Among the most interesting findings of this study is that the presence of AlCl3 has a catalytic effect on the incorporation of silica in the deposit, leading to co-deposition rates that are a factor of 2–3 higher than the deposition rates that are obtained when only one of the two chlorides (CH3SiCl3 or AlCl3) is present in the feed

Co‐deposition of Silica, Alumina, and Aluminosilicates from Mixtures of CH3SiCl3, AlCl3, CO2, and H2. Thermodynamic Analysis and Experimental Kinetics Investigation

A detailed kinetic model is formulated for the decomposition of chlorosilanes [e.g., silicon tetrachloride (SiCl 4 ) and methyltrichlorosilane (CH 3 SiCl 3 , MTS)] in mixtures of CO 2 and H 2 under conditions encountered when these mixtures are used to deposit SiO 2 on solid substrates or to form powders in the gas phase. A complete mechanistic model for the water gas-shift reaction is included as a subset in the overall homogeneous mechanism. The kinetic model is introduced into the transport and reaction model of a plug-flow reactor, and the overall model is used to investigate the sensitivity of gas-phase composition on the operating conditions, the residence time in the reactor, and some key steps in the pathways of the homogeneous chemistry of the process Two sources of silicon are used in the computations, namely, silicon tetrachloride and methyltrichlorosilane. The results of the computations reveal that at the same conditions the major components of the gas phase reach partial equilibrium at shorter residence times in the MTS system. In both systems, the gas phase approaches equilibrium at residence times that are much greater than those typically encountered in chemical vapor deposition reactors. The concentrations of SiCl x compounds and water vapor are much higher in the MTS system. In agreement with past experimental observations, this result suggests that silica should be deposited at higher rates from mixtures containing MTS.

Mathematical Modeling of the Gas-Phase Chemistry in the Decomposition of Chlorosilanes in Mixtures of Carbon Dioxide and Hydrogen at High Temperatures

A detailed surface reaction mechanism is formulated for the deposition of SiO 2 from SiCl 4 /CO 2 /H 2 and CH 3 SiCl 3 /CO 2 /H 2 mixtures. The heterogeneous mechanism is coupled to a homogeneous model developed in a past study for the decomposition of chlorosilanes in CO 2 and H 2 , and the overall kinetic model is introduced into the transport and reaction model of a plug-flow reactor. The model is employed to investigate the sensitivity of the predicted deposition rates, surface coverages of adsorbed species, and gas-phase composition on the residence time in the reactor and the operating conditions. It is found that the concentrations of the gas-phase species (silicon species and oxygen species) that are responsible for silica deposition are strongly influenced by the occurrence of the heterogeneous reactions, and this in turn leads to strong dependence of the deposition rate profile on the reactor geometry (deposition surface to reactor volume ratio). For comparable silicon and oxygen loadings of the feed, the concentrations of the deposition precursors are much higher when methyltrichlorosilane (MTS) is used as silicon source. As a result, the rate of silicon oxide deposition from MTS can be higher by a few orders of magnitude. Experiments on silica deposition conducted in our laboratory showed that this is indeed the case, and that the overall transport and reaction model was found to be capable of reproducing, both qualitatively and quantitatively, all results obtained in those experiments.

Development and Validation of a Mathematical Model for the Chemical Vapor Deposition of Silica from Mixtures of Chlorosilanes, Carbon Dioxide, and Hydrogen

Stephanos F. Nitodas

Papers

Chemical Vapor Deposition of Aluminosilicates from Mixtures of SiCl4, AlCl3, CO 2, and H 2

Development and Validation of a Mathematical Model for the Chemical Vapor Deposition of Alumina from Mixtures of Aluminum Trichloride, Carbon Dioxide, and Hydrogen

Co‐deposition of Silica, Alumina, and Aluminosilicates from Mixtures of CH3SiCl3, AlCl3, CO2, and H2. Thermodynamic Analysis and Experimental Kinetics Investigation

Mathematical Modeling of the Gas-Phase Chemistry in the Decomposition of Chlorosilanes in Mixtures of Carbon Dioxide and Hydrogen at High Temperatures

Development and Validation of a Mathematical Model for the Chemical Vapor Deposition of Silica from Mixtures of Chlorosilanes, Carbon Dioxide, and Hydrogen