Process design and production of boron trichloride from native boron carbide in lab-scale

Turkiye owns the biggest boron mine reserves of the world, so it is a necessity to research the possibilities of obtaining high-tech products of boron. This study is oriented to provide one of two main inputs, boron trichloride (BCl₃) gas and carbon/tungsten core, for production of boron fiber manufactured by well-hidden hot filament CVD method. In this study, the production of BCl₃ from native boron carbide (B₄C) was aimed. In the production process, two different originally designed set-ups were used. In the set-ups, the reaction occurred by passing chlorine gas (Cl₂) through B₄C layer (10-110 g) which has different heap heights. The reactor was a vertical quartz tube heated up to 850°C by a tube furnace with silicon carbide (SiC) heating element. Chlorine as reaction gas and nitrogen as purging gas were dried in two different columns with calcium chloride (CaCl₂) and molecular sieve package. Flow rates of Cl ₂, pressure and temperature changes in the set-ups were controlled respectively by rotameter, mass-flow controller (MFC), mercury U-tube manometer, thermocouple and thermometers which were placed in different zones. The product gases were separated in consecutive distillation columns and waste gases were conveyed to a rashing ring packaged gas scrubber. In pipelines, traps and condensers, various metal (i.e. Fe, Al, W, Si, and Cr) halides depending on the impurities of B₄C were detected in different phases. The products in form of gas, liquid and solid were analyzed with FTIR, AAS, XRD and SEM/EDS. Production efficiencies (up to 85 %) and consumption rate of Cl₂ (up to 91 %) were assigned.