Measurements of the thermal diffusivity of Li₂SiO₃ by the modulated-electron-beam technique and discovery of some electric phenomena

The properties of three kinds of specimens have been measured between approximately 500 °C and 1000 °C with the modulated-electron-beam thermal diffusivity equipment. The three types are: nearly stoichiometric specimens, specimens containing small amounts of lithium orthosilicate (Li₄SiO₄), and specimens containing 0.3% and 6.6% of lithium disilicate (Li₂Si₂O₅). Thermal diffusivity and thermal conductivity increase with increasing degree of hypostoichiometry (more disilicate), and presumably also with density. Unfortunately, exact values for the hyperstoichiometric samples (those which contain orthosilicate) cannot be given, since in these samples a hysteresis effect occurs which is only partly reversible. Above approximately 900-950°C all specimens undergo an irreversible, steep increase of thermal diffusivity and thermal conductivity. Some parameters affecting the behaviour of the different specimens as a function of temperature are discussed. An investigation to find a reason for the unstable results obtained with some specimens led to the discovery of unexpected electric phenomena, which the paper also discusses.