THERMAL-EXPANSION OF CHROMIUM (CR) TO MELTING TEMPERATURE

In situ x-ray data on molar volumes of chromium have been collected ov er the temperature range from 300 K to melting. The sample was heated to melting by passing an electrical current through the sample (the te chnique of electrical resistance wire heating). The sample consists of a tungsten wire as a heater and a mixture of Cr and W powder, which i s placed in a hole of 250 mu m diameter. Tungsten was used as an inter nal standard for temperature determination. In order to prevent the sp ecimen from oxidation, the experiments were carried out in an argon fl ow. Unit cell parameters of Cr at different temperatures were calculat ed using (110), (200), (211), and (220) reflections. Precision of dete rmination of lattice parameter is 10(-4) A at 300 K and 5 10(-4) A at 2000 K. Thermal expansion of Cr increases rapidly at temperatures high er than 1200 K. The linear thermal expansion (alpha) of chromium betwe en 300 and 2130 K is given by: alpha = 1.220(5) 10(-5) - 1.150(6) 10(- 8) T + 1.132(8) 10(-6) T-2 - 0.507(7)/T-2 (T, K). In our experiments, Cr melted between 2120 and 2150 K.