THERMAL-DECOMPOSITION OF TETRAETHOXYSILAN E STUDIED BY ATMOSPHERIC MASS-SPECTROMETER

was pursued as functions of temperature, TEOS concentration and reside nce time where the gaseous reaction products identified by the atmosph eric mass-spectrometer are C2H5 and C2H5OH, from which the following r eaction scheme can be proposed: (1) The overall thermal decomposition reaction of TEOS to precipitate SiO2(s) can be expressed as follows: O C2H5)(4)(g)-->SiO2(s)+2C(2)H(4)(g)+2C(2)H(5)OH(g) (2)The gaseous react ion intermediate species observed is SiO(OC2H5)(2), which may be produ ced by the following reaction: (OC2H5)(4)(g)-->SiO(OC2H5)(2)(g)+C2H4(g )+C2H5OH(g) (3) The oder of reaction with respect to the TEOS concentr ation obtained experimentally is from 0.2 to 0.5, (4) The above-mentio ned experimental observation, in which the step(c) is the rate control ling step and the oder of reaction is (1/3), leads to (a) the thermal decomposition of TEOS to produce the intermediate: (OC2H5)(4)(g)-->SiO (OC2H5)(2)(g)+C2H4(g)+C2H5OH(g) (b) the adsorption reaction of the int ermediate: SiO(OC2H5)(2)(g)+-->SiO(OC2H5)* (c) the SiO2(s) precipitat ion from the adsorpted speciees: SiO(OC2H5)(2)-->SiO2(s)+C2H4(g)+C2H5 OH(g)