SHS Technology for Composite Ferroalloys. 2. Synthesis of Ferrosilicon Nitride and Ferrotitanium Boride

The combustion of ferrosilicon in nitrogen is very similar to the combustion of metallic silicon. With increase in silicon content in the initial ferrosilicon, its reaction rate with nitrogen increases, as is clear from the considerably more vigorous combustion. The nitrogen concentration in the combustion products increases here. Over the whole range of initial parameters (nitrogen pressure, grain size of the powder, batch composition), the combustion products consist mainly of β-Si₃N₄. No large quantity of α-Si₃N₄ is observed. In practice, FS75 and FS90 ferrosilicon is optimal for refractory production, while FS65 and FS75 ferrosilicon, with lower impurity content, is best for the production of components used in steel production. The introduction of iron in the Ti–B system (T_ad = 3190 K) considerably restricts the combustion concentration range. A mixture with 16.9% B burns in a narrow Ti:B concentration range close to 0.86. In combustion of the Fe–B + Ti mixture, increase in the initial temperature considerably expands the concentration range for synthesis. In all cases, increase in the initial temperature considerably boosts the combustion rate. Heating to T₀ ≥ 300°C permits the use of mixtures with titanium powder containing larger grains (r_me.Ti ≥ 0.4 mm) in self-propagating high-temperature synthesis (SHS). A wide range of B:Ti ratios may be used. The combustion of such mixtures permits the production of an alloy with 6–14% B and 30–60% Ti. Specialized industrial equipment has been constructed: a series of SHS reactors with working volumes of 0.06, 0.15, and 0.3 m³, permitting the large-scale production of materials based on refractory inorganic compounds for use in metallurgy. The industrial production of composites based on oxygen-free compounds by self-propagating hightemperature synthesis has been introduced.