Alumino-Silico-thermic synthesis of high purity ferroboron alloy and its characterization

High purity ferroboron (Fe-B) alloy is used as an alloying agent for making special grades of steels, Nd-Fe-B magnets etc. In this study, alumino-silico-thermic co-reduction of Fe2O3 and B2O3 was attempted to prepare high purity Fe-B. Extensive differential thermal analysis (DTA) studies were carried out to understand the reduction behaviour of Fe2O3 and B2O3 by Al and Si. DTA exothermic peaks indicated three step reduction of Fe2O3 (Fe2O3 -> Fe3O4 -> FeO -> Fe) when reacted with Al and Si separately. B2O3-Si system did not show exothermic peaks while heating indicating sluggish or no reduction, however, B2O3-Al DTA peaks indicated two step reduction behaviour. Differential thermal analysis of Fe2O3-B2O3-Al-Si indicated completion of reduction of oxides, and formation of different intermediate phases. Specially designed reduction reactors were used to produce ferroboron alloy in bulk quantities. Thermal analysis results suggested that the formation of aluminium and silicon borides could be avoided using sub-stoichiometric amount of Al and Si, which was further confirmed from the bulk thermit product. Si acted as reducing agent as well as forming low melting slag comprising of Al(Si)-B-O type oxides. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and Particle Induced Gamma-ray Emission (PIGE) analysis confirmed the presence of 12 wt% boron in the alloy product with lower content (<1 %) of impurity elements like Al and Si. The relationship between the chemical homogeneity with the thermit process parameters was established. Microstructure and mechanical properties confirmed the formation of Fe2B and FeB phase in the thermit alloy.

Automated summary

In this study, high purity Fe-B alloy was prepared through alumino-silico-thermic co-reduction of Fe2O3 and B2O3. Differential thermal analysis revealed the reduction behavior of Fe2O3 and B2O3 with Al and Si. The formation of aluminum and silicon borides was avoided by using sub-stoichiometric amounts of Al and Si.