SHOCK-TUBE STUDY OF SILICON ATOM OXIDATION BY CO AND CO2

In the present study the very fast high;temperature thermal decomposit ion of silane was used as a Si atom source to initiate its reactions w ith either CO or CO2. The experiments were performed behind reflected shock waves by applying atomic resonance absorption spectroscopy (ARAS ) for detecting Si and C atoms. In the first part initial mixtures of 0.75-20 ppm SiH4 and 0.2-5% CO in Ar were used to perform experiments in the temperature range 2720 K less than or equal to T less than or e qual to 5190 K at pressures 0.6 bar less than or equal to p less than or equal to 1.0 bar. From the measured Si atom absorption profiles the rate coefficient for the reaction Si + CO --> (k3) SiO + C (R3) was d etermined by applying the first-order method. The results were summari zed by the following Arrhenius expression: k(3) = 7.8 X 10(14) exp(-34 510K/T) cm(3) mol(-1) s(-1) +/- 20% The evaluation of measured dopes o f C atom formation results in rate coefficients k(3) close to the valu es found from Si atom measurements. This demonstrates SiO and C to be the dominant products. In the second part Si atom measurements in SiH4 /CO2/Ar mixtures were performed to study its reaction with CO2. Initia l mixtures of 0.5-0.75 ppm SiH4 and 200 ppm CO2 were used to carry out experiments in the temperature range 2100 K less than or equal to T l ess than or equal to 3160 K at pressures 0.4 bar less than or equal to p less than or equal to 1.4 bar. From the Si atom concentration profi les the rate coefficient of the reaction Si + CO2 --> (k4) SiO + CO (R 4) was determined by applying again the first-order method. The result s of the data interpretation can be summarized by the following Arrhen ius expression: k(4) = 6.0 X 10(14) exp(-9420K/T) cm(3) mol(-1) s(-1) +/- 25% Although it was not possible to observe any reaction product, the formation of SiO and CO is obviously reasonable due to energetic r easons.