A Plane Source Method for Measuring Interdiffusion Coefficients of Transparent Liquids

a constant coefficient of thermal expansion, ( 2 2 + 1) x 10~6 degr. 1 , is obtained over the range 200 — 550 °C, and it appears as if the coefficient might be slightly lower in the region between 200 °C and room temperature. The thermal expansion of monoclinic lithium sulphate has been estimated previously by P I S T O R I U S 6, who measured the powder diffraction pattern at 500 C. From a comparison with the somewhat inaccurate room-temperature values of the unit-cell constants, he concluded that the thermal expansion takes place mainly along the c-axis. The difference between the quoted unit cell volumes at 500 °C and room temperature corresponds to an average coefficient of (linear) thermal expansion of 39 x 1 0 6 degr. 1 , which is higher than our result given above. For cubic lithium sulphate the contraction measurements give a coefficient of thermal expansion of (43 ± 3) x 1 0 6 degr . 1 for the range 600 750 °C.