Pressure sintering of copper-glass mixtures

In order to enhance the thermal conductivity of the glass containing high-level radioactive waste oxides, copper-glass composite compacts were fabricated as a model. The compacts were prepared by pressure sintering of the mixtures of electrolytic copper and Pyrex glass powders at 200 kg/cm2 in graphite dies. Thermal conductivity of the compact was measured by a laserflash method. The compacts of the copper powder showed the relative densities over 0.95 by sintering at the temperatures higher than 5000C, but the density was observed to decrease slightly as the increase of temperature by the release of the adsorbed gas to form the entrapped pores. The compacts of the glass powder were fully densified at the temperatures higher than the yield point of the glass, 6250C. The composite compacts could be successfully prepared at 6500C or above. Linear relationships were observed between the density or the thermal expansion coefficient of the compact and the volume fraction of copper. The thermal conductivity increased as the copper content increased. It was found that the conductivity followed the so-called logarithmic rule, one of the mixture rules of thermal conductivity, up to the copper content of about 20 vol%. Over this content, the conductivity increased remarkably apart from the rule as copper formed a continuous phase in the compact. (auth.)