Density Measurement of Molten Silicon by a Pycnometric Method

The density of molten silicon was measured using a newly developed pycnom- eter made of boron nitride. The present method has many advantages for measuring the density of molten silicon, which has a high temperature and can be easily oxidized. The pycnometer was precisely machined, and its volume at high temperatures was acculately determined. The procedure to overflow the excess melt was carried out in a closed apparatus under a helium atmosphere. A special procedure was introduced to avoid the error generated by the volume expansion of silicon when it solidified. The total uncertainty of the measurement was estimated to be within 0.50. The measured density showed a linear rela- tionship with respect to temperature and agreed well with literature values. The expansion coefficient of molten silicon was similar to those of typical molten metals in spite of the low expansion coefficient of solid silicon. This suggested that the structural change of molten silicon was similar to those of typical metals.