No abstract

Factors influencing the concentration and distribution of elemental silicon codeposited during chemical vapor deposition (CVD) of SiC from MTS (CH3SiCl3) and hydrogen diluted by argon are reported. The experiments were carried out in both hot‐ and cold‐wall reactors at 1383–1473 K at atmospheric pressure. Codeposition of free silicon was detected even at very low excess hydrogen, contrary to the prediction of thermochemical calculations. In the hot‐wall reactor, under conditions of high exchange rate of the feed gases, deposits of uniform composition were obtained, containing 0%–90% free silicon, depending upon feed gas composition. The deposits of pure silicon carbide consisted of β‐SiC with a microhardness of 2400 kg/mm2 at a typical formation rate of 30 μm/h. Microhardness decreased to 800 kg/mm2 with increasing silicon concentration. In the cold‐wall reactor, under impinging gas flow conditions, nonuni‐form deposition occurred: a local gradient of Si/SiC was obtained with free silicon concentrations varying gradually between 0% and 35%. Si/SiC ratios in the deposits were determined by a combination of XRD, scanning AES, and SMP.

This study is aimed at developing a simulation model of a solar volumetric reactor for hydrocarbon reforming, operating at high temperature and pressure. It will then be used to optimize the reactor design and analyze its performance. The model development utilizes previous and on-going experimental work on volumetric receiver and catalyst development. The reaction’s kinetics are computed, using the CHEMKIN II simulation package. The chemical kinetic modeling of the relevant C-H-O system is based on: (i) Definition of the relevant computation domain and parameters: temperature, pressure, reactant compositions, residence time, and catalyst load, (ii) Utilizing laboratory measurements at 700–1400 K and 1–4 bar. to quantify the kinetic parameters for both, H2O, and CO2 reforming of CH4 and for the Reverse Water Shift reaction. Calculated and measured data are compared for three representative cases, showing a good agreement. The results indicate that the Arrhenius method can be a viable and practical way to predict the behavior of steam and CO2 reforming over a range of temperatures and pressures. Furthermore, it is shown that the present approach can provide a method for estimating the desirable dimensions of the reactor for reforming of CH4. Additional, on-going computational and experimental work, which would provide a more accurate simulation, can easily be implemented using the present numerical model.

This study is aimed at developing a simulation model of a solar Volumetric reactor for hydrocarbon reforming, operating at high temperature and pressure. It will then be used to optimize the reactor design and analyze its performance. The model development utilizes previous and on-going experimental work on Volumetric receiver and catalyst development. The reaction’s kinetics are computed, using the CHEMKIN II simulation package. The chemical kinetic modeling of the relevant C-H-O system is based on: (i) Definition of the relevant computation domain and parameters: temperature, pressure, reactant compositions, residence time, and catalyst load, (ii) Utilizing laboratory measurements at 700–1400K and 1–4 bar. to quantify the kinetic parameters for both, H2O, and CO2 reforming of CH4 and for the Reverse Water Shift reaction. Calculated and measured data are compared for three representative cases, showing a good agreement. The results indicate that the Arrhenius method can be a viable and practical way to predict the behavior of steam and CO2 reforming over a range of temperatures and pressures. Furthermore, it is shown that the present approach can provide a method for estimating the desirable dimensions of the reactor for reforming of CH4. Additional, on-going computational and experimental work, which would provide a more accurate simulation, can easily be implemented using the present numerical model.