Fabrication of dense albite aggregates by hot pressing

Abstract

Synthetic rocks are used in laboratories to measure the physical and chemical properties of Earth’s constituent minerals in order to understand Earth’s interior. To understand the phenomena in the middle and upper crust, dense aggregates of Na-rich plagioclase are necessary. Therefore, we explored a method of fabricating dense aggregates of albite with low porosities, homogeneous microstructures, the absence of melt and sample sizes larger than a cubic centimetre using hot pressing by solid-state sintering. We conducted multiple experiments in which we varied the particle sizes, the agglomerations of powder, the method of forming, the sintering temperature, and the pressure and duration of the hot pressing. Two particle size fractions of powder, less than two micrometres and less than a few hundred nanometres, were prepared by pulverisation and decantation of natural albite powder. Because fine-grained albite powder seems to agglomerate easily, a technique to dry and disperse the powder was also developed. Hot pressing was carried out at temperatures of 1000‒1150 °C and pressures of 40‒120 MPa. The following were found to be important in obtaining dense aggregates of albite: (1) powders with a particle size less than a few hundred nanometres; (2) powders are adequately dispersed; and (3) preparation of green bodies by slip casting, which makes hot pressing efficient. A dense albite aggregate can then be fabricated using hot pressing at a temperature of 1080 °C and pressure of 100 MPa by solid-state sintering.[Figure not available: see fulltext.].