Silicon surface etching and its dominant rate process are studied using hydrogen chloride gas in a wide concentration range of 1 -100% in ambient hydrogen at atmospheric pressure in a temperature range of 1023 -1423 K, linked with the numerical calculation accounting for the transport phenomena and the surface chemical reaction in the entire reactor. The etch rate, the gaseous products and the surface morphology are experimentally evaluated. The dominant rate equation accounting for the first-order successive reactions at silicon surface by hydrogen chloride gas is shown to be valid. The activation energy of the dominant surface process is evaluated to be 1.5 Â 10 5 J mol À 1 . The silicon deposition by the gaseous by-product, trichlorosilane, is shown to have a negligible influence on the silicon etch rate. D

Acceleration tests were done using the small-scale microporous membrane (MF) module to predict the increase in transmembrane pressure at the constant flow rate dead-end filtration in a pilot plant for treating the river water or dam water. The kaolin suspension, solution of humic acid and the mixture of kaolin and humic acid were used as feed water in the acceleration tests. The conventional equations of medium blocking filtration were applied to predict the pressure increase for both pilot plant tests and small-scale ones. The experimental results are summarized as follows: (1) The pilot plant tests: The time course of transmembrane pressure was expressed by the complete blocking filtration equation or the standard one when the unstable time at the beginning of operation was excluded. (2) The acceleration tests using small-scale membrane module:(a) No increase in transmembrane pressure was observed when the kaolin suspension and the bentonite one were used as feed water, (b) The increasing rate of transmembrane pressure was lowered by the addition of coagulant into the humic acid solution, (c) The humic acid had a great influence on the increasing rate of transmembrane pressure in the filtration of water containing kaolin or no kaolin and (d) Similar curves of filtration time vs. transmembrane pressure were obtained in the acceleration tests as were obtained in pilot plant tests.