Characterization of Trichlorosilane Release and Combustion Hazards

Chen*, Jenq-Renn; Tsai, Hsiao-Yun; Ngai, Eugene Y.
(National Kaohsiung First University of Science & Tech., Taiwan)

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Trichlorosilane (TCS) is one of the key raw materials in manufacturing of PV grade polysilicon and silane gas. It is also been used directly in the semiconductor process as an alternative silicon source gas. TCS has a boiling point of 31.85 degree C and a flash point of -27.3 degree C with flammability limits of 1.2%~90.5%, rendering TCS a flammable liquid. The major hazard of TCS is however not lies on its flammability but rather on its water reactivity and combustion by-product hydrogen chloride (HCl). Burning of TCS in air does not create a noticeable flame but instead, a very thick white smoke. Pure TCS vapor in the air will also react with moisture and form light smoke. The white smoke contains silicon dioxide and HCl which could cause significant impact on the environment and nearby community. To date, there exist very little information on how to assess the impact from TCS release and combustion. In this work, we will attempt to address these issues by performing direct field tests of TCS release and combustion. Three sizes of square test pans, 0.3m0.3m, 0.5m0.5m, and 1m1m, with height of 0.1 m are used for TCS release and combustion tests. Five thermocouples are attached to the bottom of the pans to measure the liquid temperature. A fixed amount of TCS is filled into the test pan that is placed on a digital balance to measure the vaporization rate. For combustion tests, the TCS is ignited by a torch and the burning rates are measured. An open-path FTIR is used to identify the pollutant in the downwind ambient air. Pollutants identified were silicon dioxide and HCl for TCS combustion, and TCS and HCl for TCS release. Direct reading gas detectors were used to monitoring hydrogen chloride concentration in downwind locations. A dense gas dispersion model is used to verify the source model from burning rate and the measured downwind HCl concentration. The results will be useful in the emergency planning and risk assessment for TCS release.

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