SHS TECHNOLOGY OF COMPOSITION FERROALLOYS. PART II. SYNTHESIS OF FERROSILICON NITRIDE AND FERROTITANIUM BORIDE

Abstract

Consistent patterns in the combustion of ferrosilicium in nitrogen are rather similar to those of metal silicon. As the concentration of silicon in initial ferrosilicium is increased, the intensity of its interac­tion with nitrogen increases as well, resulting in a significant growth of the combustion rate. The concentration of nitrogen in the combus­tion products here increases as well. In the entire investigated range of initial parameters (nitrogen pressure, powder fineness, burden mix), the main phase in the combustion products is β-Si3N4. No considerable amounts of α-Si3N4 have been observed. In practical applications, the use of FS75 and FS90 ferrosilicium is optimal for producing fire-re­sistant materials, while FS65 and FS75 (being the purest alloy grades) are optimal for obtaining alloying steel compositions. Introducing iron into the (Ti – B) ( T ad = 3190 K) system significantly narrows down the concentration limits of combustion. ((Fe – B) + Ti) mixture with 16.9 % B alloy burns in a narrow range of Ti:B concentrations close to 0.86. When a ferroboron-titanium mixture burns, an increase in the initial temperature significantly expands the synthesis concentration limits. In all the cases, an increase in the initial temperature leads to a significant increase in the combustion rate. Heating up to T 0 ≥ 300 °C allows for involving mixtures with more coarse titanium powders ( r av. Ti ≥ 0.4 mm) into the SHS process. The synthesis is implemented in a wide range of B:Ti ratios. By burning such mixtures one can ob­tain alloys with 6 – 14 % B and 30 – 60 % Ti. Specialized industrial equipment has been built: a series of SHS reactors with the operation  volume of 0.06, 0.15 and 0.3 m3 for the serial production of manufac­turing items based on hard-melting inorganic compositions (nitrides, borides, silicides, etc.) for metallurgical applications. Industrial SHS production of composite materials based on oxygenless compositions has been set up.