Abstract
Factors affecting cracking of porous glasses during leaching have been confirmed experimentally for two different composition glasses under leaching condition in which only leached or unleached layer shows cracking, When a glass exhibits swelling during leaching, cracks are developed in the unleached layer due to the generation of tensile stress in it. In contrast, when a glass shows shrinkage, the tensile stress generated in leached layer leads to cracking of this layer. To reduce this tensile stress, it is assumed to be very important that Na2O in the SiO2-rich phase is not be extracted and that SiO2-gels in pores are removed. Experimental results showed that H2O-leaching satisfies these requirements even for glasses which showed cracking due to swelling or shrinkage during typical acid leaching. In fact, a large amount of SiO2-gels did not stay in pores and Na2O was not extracted by H2O leaching. It was noticed, however, that in further leaching with acid solution sometimes cracks developed in leached layer, depending on the glass compositions and heating conditions.
