Transport phenomena in some solids under hipping pressure

The effects of pressure in hot isostatic press (HIP) on the transport phenomena have been studied on the following three systems; (1) Fe–WC, (2) Ba(Zr,Ti)O3 and (3) amorphous SiO2–crystalline SiO2. In these cases, mass transports were suppressed by hipping pressure. In the Fe–WC system, WC grains reacted with surrounding Fe, and the pressure appears to suppress the diffusion. In the case of (2), thin plates of Ba(Zr,Ti)O3, having different compositions, were piled to make a functionally graded material (FGM). To suppress the diffusion between the plates, hipping pressure of 200 MPa was applied at 900°C, and then the temperature was raised to 1200°C. The hipped compact revealed a flat temperature dependence of dielectric constant, which was ca. 2000 over the temperature range of 25–120°C. The grain growth was also suppressed by the hipping pressure. In the case of (3), the crystallization of amorphous SiO2 was suppressed under the conditions of 1200°C, 200 MPa and 30 min to prepare the amorphous–crystalline composite of SiO2.