1. Department of Chemical Engineering, Kongju National University, 182 Shinkwandong, Chungnam 314-701, Korea
2. Department of Chemistry, Kongju National University, 182 Shinkwandong, Chungnam 314-701, Korea
3. Department of Materials Development, Korea Institute of Geology, Mining and Materials, P.O. Box 14, Taedok Science Town, Taejon, Korea