Mar 4, 2020

Sublimation Studies of SiC by Using a Quadrupole Mass Spectrometer

The partial pressure of components in the gas phase in the sublimation process of SiC is of special interest for a better understanding of the Lely‐crystal growth process. It is known that at thermodynamic equilibrium the gas phase of SiC has a complex composition. We have sublimated 6H‐SiC and 3C‐SiC under equilibrium conditions in a tantalum Knudsen cell by resistance heating. Corresponding measurements with a carbon furnace show so many contaminants that no results for the composition of SiC gas phase can be evaluated. SiC powder of different polytypes (3C‐SiC and 6H‐SiC), different grain size (≤7 μm, 40–60 μm) and different Si/C ratio (addition of elemental silicon to the SiC powder) was evaporated in the temperature range 1900 to 2200°C. The beam of the sublimated Si‐C compound molecules was analyzed with a quadrupole mass spectrometer. Different Si‐C molecules were identified by the ratio of the partial pressures of their natural isotopes. Si, , and  were the dominant species. The heats of sublimation for the different molecules were evaluated using the Clausius‐Clapeyron equation.


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