Thermodynamic domains of the various solid deposits in the B--C--H--Cl vapor system

Calculations were made of the equilibrium conditions under which chemical deposition of B4C from BCl3--CH4--H2 mixtures takes place. Pure B4C is mainly obtained for gas phase mixtures in which BCl3/CH4 greater than 1 and H2/BCl3 greater than 1. The maximum yield is obtained in the range 1675--2075K for the initial composition BCl3 = 0,1; CH4 = 0.02; H2 = 0.88. The dependence of the hydrogen partial pressure on the equilibrium composition is discussed. At high temperatures with a large excess of hydrogen, the tendency is to form gaseous BH2 and BH3 instead of condensed species. By decreasing the amount of hydrogen, graphite begins to deposit under CH4/BCl3 much less than 1/4 ratios. At lower temperatures the equilibrium content of BCl2H increases as the H2/BCl3 ratio falls. Results of the calculations are confirmed by experimental data