Physical and mathematical modelling of boron carbide manufacturing process

Abstract

Boron carbide is produced in a heat?resistance furnace using boric oxide and petroleum coke as the raw materials. In this process, a large current is passed through the graphite rod located at the center of the cylindrical furnace, which is surrounded by the coke and boron oxide mixture. Heat is generated at the surface of the electrode, due to which boron oxide reacts with the coke to produce boron carbide. The process is inefficient in terms of the production of boron carbide as only 30% charge gets converted into boron carbide. No published attempt has been made to optimize the process using mathematical modelling. Also, experimentally not much work has been done. Therefore, in this study both mathematical and physical modelling has been carried out. In mathematical modelling, a simultaneous heat and mass transfer model has been developed for the resistance?heating furnace, considering boron carbide formation as a typical carbothermal reduction. Coupled transient, partial differential equations have been worked out. These equations have been solved numerically, using the implicit finite volume method in their non?dimensional form, to obtain the profiles of temperature and volume fraction reacted in the furnace. Mathematical model has been developed both in one and two dimensions. One?dimension model has been made time and grid?size independent. Only preliminary results of the two?dimensional model have been presented as it is still under the development stage. A laboratory?scale physical model of the process has been fabricated and installed with necessary accessories, such as powder supply unit and electrode cooling unit. The furnace is made of stainless steel body and high?temperature ceramic wool insulation. In order to validate the mathematical model, temperature has been measured at various locations in the furnace. Similarly, the product has been collected from the various locations, at the end of each experiment, to analyze them for various species. Temperature inside the furnace, during the run, ranges from 2500°C (near the core) to 900°C (near the outer surface of the charge). Temperatures have been measured using pyrometer, C, B and K type thermocouple. A special device has been made to measure the core temperature more precisely. Also, experiments have been conducted to correlate emissivity of graphite with temperature in order to get correct measurement of the core temperatures using pyrometer. Experiments were performed to measure the porosity of the mixture/product at various temperatures, as it is an important parameter which can affect the simulation results significantly. Model developed in the present study has been validated with laboratory?scale experiments. A reasonable agreement has been found between the two. A sensitivity analysis has been done in order to optimize the process. Further improvement is needed both in experiments and modelling.