Syntheses and High-Temperature Vaporizations for Compounds in the System Li<sub>2</sub>O-WO<sub>3</sub>

Abstract

Syntheses, sinterings and vaporizations of double oxides of Li2O⋅WO3(1/1), 2Li2O⋅WO3(2/1) and 3Li2O⋅WO3(3/1) in the system Li2O-WO3 were investigated. 1/1 mixture changed to 3/2 compound at 100°C and 1/1 formed above 500°C. Sinterings of 1/1 were made at 700°C for 4h with relative density (RD) of 89-91%. 2/1 mixtume changed to α-2/1 from 100 to 700°C and β-2/1 appeared in the temperature range from 740 to 1000°C. Sinterings were made at 800 to 1000°C with RD of 45-47%. 3/1 mixture began to form 3/1 at 600-700°C and maximum yield of 3/1 compound was obtained at 1000°C. Sinterings were made at 900-950°C for 3h with RD of 62-80%. Vaporization experiments on pellets (1.37cm in dia.) were made in air flow (1cm·min-1) at temperatures from 700 to 1000°C, and straight lines with slopes from 0.2 to 1.0 were obtained on a log-log graph of both vaporization and time. These slope values increased approaching to 1 with increasing vaporization time. From the vaporization rates at early stages, an activation energy of 170kJ·mol-1 was obtained for 3/1 compound. Products after the vaporizations of 3/1 compound were mixtures of 2/1 and 3/1. The vaporization experiments for pure WO3 were also made at 700-1100°C and the slope values were almost 1. The amount of vaporization was lower than those for 3/1 and 2/1. Effect of porosity on the vaporization was confirmed using NaCl compacts with various porosities. The maximum increase of the vaporization rate against the specimen with 0% porosity was 14% for that with 30% porosity.