INFLUENCE OF ATMOSPHERE ON MOLTEN SILICON DENSITY

The influence of atmosphere on the density of molten silicon has been studied. The density was measured by an improved Archimedean method with the accuracy of 1.1%. The density under argon gas mixed with hydrogen 7.15% is found to be equivalent to that under pure argon gas at the melting; point, but showed higher values at higher temperatures (1430-1500 degrees C) with the thermal volume expansion coefficient of about 8.8 x 10(-5) K-1. The density under the hydrogen-containing argon also shows a time-dependent variation over 5 h after melting. The solubility of hydrogen in molten silicon is estimated to be below 3 x 10(18) atoms cm(-3). This result suggests that the increase of the density in the presence of hydrogen is caused by the change of the arrangement of the silicon atoms.