An expression for the accurate prediction of the viscosities of various indvstrial slags has been derived using a model based on the concept of network structure. The equation is expressed in terms of slag componentsand some basic physical quantities. The viscosity predictions closely fit with the experimental data for a large number of blast furnace type slags.

We examined sintering additives for alumina. When using CuO-TiO2-Nb2O5 additive, dense sintered alumina was obtained by firing at 1000°C or below, even though additive content was at most 10 mass%. It is considered that the formation of mixed oxide consists of CuO, TiO2 and Nb2O5 has an important role for low temperature sintering of alumina. Thermal conductivity of the above sample was 15 W/mK, which was the highest value yet reported within LTCC (Low Temperature Co-fired Ceramics) materials.

For the purpose of enabling the low-temperature sintering of alumina, the addition of Ag 2 O to CuO-TiO 2 -Nb 2 O 5 type sintering additive was examined. The use of CuO-TiO 2 -Nb 2 O 5 -Ag 2 O type sintering additive by 5 wt% enabled the low-temperature sintering of alumina at 860 • C. It is presumed that the formation of Cu 4 TiNb 4 O x solid solution has an important role for low temperature sintering of alumina. The obtained sintered material showed high thermal conductivity of 18 W/mK, higher than that of conventional LTCC materials, and that the material could be co-fired with silver electrodes.

CuO-TiO2-Nb2O5 was utilized as additive (5 wt%) to obtain densified alumina using the firing temperature of 885 °C for 96 h. Densification started at ~835 °C, which was lower than the melting point of the additive (~967 °C). The melting temperature of the powder mixture consisting of the additive and alumina was measured, but no significant changes were observed compared with the melting temperature of the additive. Furthermore, the lattice constants measurements of the alumina sample obtained after heat treatment at 885 °C revealed an increase in unit cell volume, which suggested the incorporation of Cu and Ti components into alumina according to the TEM-EDS analysis. In addition, the timing of the increase in alumina lattice constant and that of the rapid increase in the sintered density of the additive-containing alumina coincided. These results indicated that the densification of the sample occurred in solid state (solid-state-activated sintering). The sample fired at 935 °C for 6 h exhibited the thermal conductivity of 22 W/mK, which was higher than that of conventional low-temperature co-fired ceramic materials (~2-7 W/mK), the relative dielectric constant (εr) of 10.2, the quality factor multiplied by the resonant frequency (Q × f) value of 47000 GHz, and the temperature coefficient of resonant frequency (τf) of-50 ppm/K.

For the purpose of lowering the sintering temperature of alumina with a CuO-TiO 2-Nb 2 O 5 additive, effects induced by changes in the firing atmosphere, in particular, oxygen partial pressure (pO 2), were studied. It was confirmed that sintering was promoted in regions where the pO 2 was lower than that in the air atmosphere, 0.21 atm. Our analysis of the additive using TG-DTA and XRD methods indicated that both the melting temperature and compositions of the produced compound vary with the change in firing atmosphere. These changes were presumed to affect the sintering performance. By lowering the pO 2 to 0.05 atm, a dense sintered sample with good dielectric properties was obtained at a firing temperature of 925 °C.