CRYSTALLIZATION OF COPPER METAPHOSPHATE GLASS

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3), independent of the [Cu2+]/[Cu(total)] ratio in the glass. However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the [Cu2+]/[Cu(total)] ratio in the glass. The crystal formed in the reduced glass is oriented and needle-shaped and less aligned at higher crystallization temperature. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, but small at high temperature. The glass transition temperature of the glass increases as the [Cu2+]/[Cu(total)] ratio is raised. This dependence may be used to explain the relative crystallization rates. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.