Synthesis of boron carbide (B4c) powder via dynamic / thermochemical method

There are many methods for the production of boron carbide (B4C) in powder form. Each method contains differences in terms of the characteristics of the material produced and the cost of the method. Commercially, carbothermal reduction (CR) has been the method preferably used for the B4C powder production. Dynamic Carbothermal Reduction (DCR) is a new method, patented as "Advanced Technical Ceramics' Powder Synthesis via Rotating Tube Furnace in a Controlled Atmosphere" (Patent No: TR 2011 02804 B, 2011). This method was deemed successful in synthesizing nitride based ceramic powders, nevertheless, a study which investigate its efficiency in obtaining carbide based ceramic powders has not been carried out yet. Therefore, this thesis focuses on the optimization of DCR method with the possibility of synthesising B4C powders. In the study, boron oxide (B2O3), carbon black and some minor additives were used as starting raw materials. Mixtures from raw materials were prepared in appropriate stoichiometry and their conversion to B4C by DCR process was examined. As an additive, silicon carbide (SiC), silicon dioxide (SiO2) and calcium carbonate (CaCO3) were used and their effects on final product (powder) properties and on the DCR process were investigated. In addition, small amounts of B4C powders were added to the starting materials as nucleates. The raw materials / powders used were mixed and granulated manually or using a device. The prepared granules were reacted under argon gas atmosphere in the DCR system and the products obtained were analysed. The effects of pretreatments (such as initial boron oxide powder size, additives and their quantities, recipes used, and the speed of the granulator in the granule preparation) and DCR processes (such as reaction duration and temperature, static or dynamic of the system and the heating regime) on the obtained product properties were examined. In this study, B2O3 starting powders having average grain size of 160 µm have been brought to about 8 - 10 µm in size by mechanical grinding. With the addition of 0.03 mol commercial B4C powder in the mixture of carbon and boron oxide (with C / B2O3 mole ratio of 2) was mixed with a rotational speed of 4000 rpm and millimeter size granules were produced. Afterwards, these granules were subjected to DCR process at 1500oC for 1 hour at a reactor rotation speed of 4 rpm under 1 L/min Ar-gas flow yielding B4C powders in micron and submicron size range. The product obtained is over 98% B4C and its conversion efficiency was over 90%. These values are the first in the literature and patent application of the system has been made (Patent application nu: 2019-GE-596299).