Thickness Of SiC Layer Research Articles

High-Rate Thermal Plasma CVD of SiC

Using a hybrid thermal plasma reactor for a new CVD process, thick SiC layers were successfully deposited at a rate of {approx}500 {mu}m/h on a graphite substrate from SiCl{sub 4} and CH{sub 4} under soft vacuum ({approx}2.7 {times} 10{sup 4} Pa). The process is performed typically under flow rates of SiCl{sub 4} = 1.5 g/min and CH{sub 4} = 300 cm{sup 3}/min and deposition temperatures of 1,000{degree} to 1,100{degree}C. The effects of deposition conditions on certain characteristics of the deposited layers were investigated. SEM revealed that the appearance of the deposited layers strongly depended on the substrate position. The prepared layers were dense and nearly stoichiometric {beta}-SiC with (100) preferred orientation. A new method for measuring substrate temperature is also reported, and grown characteristics are discussed.

R.f.-sputtered SiC coatings on carbon fibres

R.f. sputtering as a new method for the deposition of SiC layers onto carbon fibre substrates was applied at temperatures below 400°C and deposition rates higher than 1 μm h -1. Optimum conditions for high quality SiC films were selected by variation in the r.f. power, r.f. peak voltage, substrate temperature and gas pressure. The SiC layers were characterized using electron probe microanalysis, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, transmission high energy electron diffraction, IR and UV transmission spectroscopy as well as Vickers' hardness measurements. Amorphous SiC layers were obtained. In the case of discontinuous SiC deposition onto carbon monofilaments the film thickness precalculated from the sputtering parameters was achieved, whereas the continuous process results in film thickness of about one-third of the precalculated value. When fibre bundles with different numbers of monofilaments were used no influence on the resulting SiC layer thickness could be observed. Increasing the SiC film thickness, however, led to a strong decrease in the fibre tensile strength for layers more than 50 nm thick.

SiC‐Fission Product Reactions in HTGR TRISO UC2 and UCxOy Fissile Fuel: I, Kinetics of Reactions in a Thermal Gradient

The potential for SiC‐lanthanide fission product reactions on the cool side of TRISO‐coated UC2 and UC4.3O1.3 fuel particles was studied in postirradiation thermal‐gradient heating experiments. The kinetics of the reactions were obtained by determining the rate of decrease in SiC thickness as‐a function of temperature and fission density. Reaction rates are independent of the fission density for UC2 kernel burnups >5% FIMA. The rate of change in SiC thickness for TRISO UC2 in a temperature gradient isX (μm/h) = 4.2×107 exp(‐3.283×105/8.313T). No reduction in SiC thickness was observed in TRISO UC4.3O1.3fuel; the rates of SiC fission product reactions are at least an order of magnitude slower than those observed in UC2. No metallic fission product release from TRISO particles was indicated until the SiC layer thickness was reduced by 50%.

Considerations on PyC and SiC coated oxide particles for gas cooled fast reactor application

Recently, coated particles with a SiC outer coating layer have been proposed for Gas Cooled Fast Reactor application. SiC is a very fragile material. Although under fast irradiation it can creep at relatively low temperatures, a very low strain (⪢ 0.3%) can produce hairline cracks. A SiC coating layer can therefore withstand only moderate overpressures when subjected to large fast neutron exposures. In the present paper the pressure inside the particle due to gas fission products and CO-CO 2 is calculated. The operation temperature of the particle due to the condition strain ⩽ 0.3% is given as a function of SiC layer thickness in conditions typical for GCFR's application