Behavior of glass in the sintering of metal-glass materials
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In this investigation, a study was made of the migration of glass in metal-glass specimens during sintering. It is shown that window-pane glass exhibits appreciable softening at 600‡C, while at 800–900‡C its viscosity is so low that it can freely penetrate into pores (when interconnecting pores are present). Pyrex glass maintains a higher viscosity up to temperatures of 1000–1100‡C. Thus, compared with windowpane glass, pyrex glass is less susceptible to impregnation with metal oxides.
In shrinkage studies, it is possible to detect two stages of size variation, associated with essentially different processes. In the first stage of shrinkage, brought about by surface tension forces at the metal/molten glass interface, the glass promotes shrinkage. In the second stage, caused by diffusion processes in the metallic skeleton, the glass hinders shrinkage by exerting an internal pressure within the metallic skeleton. Depending on the glass grade and the material of the metallic skeleton, the dividing line between these two processes shifts.
With increasing porosity of specimens, the internal pressure exerted by the glass decreases.
The presence of oxygen in the heating zone intensifies the shrinkage of metal-glass specimens.
The precipitation of minerals as a result of glass migration at temperatures of 1000–1100‡C depends on the material of the metallic skeleton. In iron-glass specimens, minerals are precipitated at the wetting boundary of the glass drop on the metal surface. In nickel-glass specimens, minerals crystallize over the whole surface covered by the molten drop.
KeywordsViscosity Porosity Migration Surface Tension Shrinkage
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