Chemical and morphological changes of porous hydrated calcium silicate in paddy soil

The chemical and morphological changes of porous hydrated calcium silicate material (PS) during the dissolution process in paddy soil were investigate d by using both a scanning electron microscope (SEM) and an energy dispersi ve X-ray (EDS) analysis. The results showed that original PS consisted of a gglomerate of various sizes with almost the same elemental composition. The SEM images at a high magnification showed that the original PS consisted o f agglomerates of small platelike crystals (less than or equal to 1 mu m) o f tobermorite [Ca-5(Si6O18-H-2). 4H(2)O]. On the other hand, elemental comp osition showed that the PS agglomerates in paddy soil altered to Si- and Ca -rich agglomerates after incubation for 53 d, The morphological differences between the two types of agglomerates were observed by SEM at a high magni fication, The Si-rich agglomerates were similar to the original PS in morph ology, whereas the Ca-rich agglomerate appeared as a large crystal. The X-r ay diffraction patterns obtained in a previous study suggested the presence of quartz and calcite in PS after incubation for 53 d (Saigusa et al, 2000 : Soil Sci, Plant Nutr., 46, 89-95), Si- and Ca-rich agglomerates were iden tified as silica skeletons of PS and calcite, respectively. It was suggeste d that the silica skeletons of PS remained as a silicon source for rice pla nts even after the disappearance of tobermorite revealed by the X-ray diffr actogram.