1. Shin‐Etsu Handotai Company, Limited, Isobe Research and Development Center, Annaka, Gunma 379‐01, Japan
2. Shin‐Etsu Handotai Company, Limited, Isobe Plant, Annaka, Gunma 379‐01, Japan
3. Department of Chemical Engineering, Faculty of Engineering, Hiroshima University, Higashi‐Hiroshima, Hiroshima 724, Japan