Mechanism and features of nitriding of ferrosilicon in the combustion regime

Чухломина, Л. Н.; Maksimov, Yu. M.; Китлер, В. Д.; Vitushkina, O. G.

doi:10.1007/s10573-006-0056-0

Cited by 18 publications

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References 3 publications

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“…The main release of heat, which gives rise to the propagation of the combustion reaction wave, occurs as a result of the interaction of silicon with nitrogen. In accordance with previous results [3], the synthesis temperature can reach 2100°C. At 850 -1000°C the topaz present ahead of the combustion front undergoes thermal decomposition with mullite 3Al 2 O 3 × 2SiO 2 , silica in the form of crystobalite, and hydrogen fluoride gas being formed [7]:…”

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Phase composition of the products of combustion of ferrosilicon in nitrogen with fluorine-containing additives present

2008

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“…As shown in [3,4], the composition Si 3 N 4 is obtained by introducing 40 -60% 2 pre-nitrided ferrosilicon or 1 -10% ammonium chloride into the initial ferrosilicon.…”

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Phase composition of the products of combustion of ferrosilicon in nitrogen with fluorine-containing additives present

2008

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“…Changing the nitrogen pressure from 3 to 7 MPa and the diameter of the sample from 60 to 35 mm results in a more uniform distribution of the phases over the cross-section of the sample, although the outer layers are once again enriched with silicon oxynitride. In addition, the products of synthesis at the center of the sample and in the surface layers contain iron monosilicide FeSi, indicating incomplete transformation of silicon into silicate nitride [5].…”

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Phase composition of the products of nitriding ferrosilicon with zircon concentrate additives

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“…The secondary silicon phase (highly disperse silicon crystallizing at the eutectic point) is present in all high-silicon alloys, including alloys FS 75 and FS 65. According to the studies in [3], nitriding of ferrosilicon in the combustion conditions is a multistage process and up to 1350°C takes place due to the reaction of free silicon with nitrogen. Above 1350°C, step dissociation of iron disilicide takes place during nitriding and ends in formation of silicon nitride and a-Fe.…”

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“…2 Tomsk Polytechnic University, Tomsk, Russia 3. Here and below unless specifically indicated otherwise, mass content.…”

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Effect of the silicon content in the initial alloy on synthesis of silicon nitride in burning ferrosilicon in nitrogen

Чухломина

Maksimov

2008

Glass Ceram

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Nitriding of the industrial alloy FS 65 in conditions of self-propagated high-temperature synthesis was investigated. The effect of the phase composition of the initial alloy on the combustion process was established. The dependence of the degree of nitriding of the products of combustion on the nitrogen pressure, sample diameter, and dilution of the initial batch with inert and activating additives was investigated. Silicon nitride with a 0.07% residual iron content was obtained by the method of acid concentration.The possibility of obtaining silicon nitride by the method of self-propagated high-temperature synthesis (SHS) using industrial ferrosilicon FS 75 or the industrial powder (PUD 75) that is obtained when this alloy is ground was previously demonstrated (RF Patent No. 2257338) [1]. Calculation of the economic effectiveness of obtaining silicon nitride from ferrosilicon powder wastes (PUD 75) showed that the cost of the silicon nitride obtained is several times lower than the stabilized market price. Ferroalloy plants currently manufacture other high-silicon alloys in addition to ferrosilicon FS 75, including ferrosilicon with a 63 -68% 3 silicon content (FS 65). When FS 65 is crushed, industrial powder with a 65 -69% silicon content is produced and must be utilized. If we consider that hundreds of tons of powdered ferrosilicon wastes are formed each year at ferroalloy plants, organization of more exhaustive processing of the wastes to obtain a valuable expensive product should be considered economically expedient.An analysis of the published data showed that the mechanisms of combustion of FS alloy FS 65 in nitrogen have not been established. RF Patent No. 2218440 showed that the product of combustion of FS 65 in nitrogen is multiphase, with a low degree of nitriding. The product obtained (nitrided ferrosilicon) is an alloying material and can be used for manufacturing high-nitrogen steels.The results of a study of the mechanisms of combustion of ferrosilicon FS 65 in gaseous nitrogen are reported and the conditions of synthesis of combustion products with the maximum possible degree of nitriding are determined in the present article.Industrial ferrosilicon FS 65 contains 66.7% silicon, and the remainder is iron and impurities (GOST 1415-93). The alloy is a two-phase material consisting of silicon and lebeauite, FeSi 2 . As the phase diagram of the Fe -Si system indicates, the FeSi 2 -Si eutectic melts at 1206°C and lebeauite melts at 1220°C. On the whole, the melting point of different brands of ferrosilicon is a function of the silicon content in them. The melting point of alloy FS 65 with a 63 -68% silicon content is 1210 -1250°C, while it is slightly higher (1210 -1315°C) for alloys FS 75 and FS 90 with a 74 -80 and over 89% silicon content. The melting point of silicon is 1415°C.The initial alloy was crushed to dispersion of less than 200 mm and poured into cylindrical tubes 40 -60 mm in diameter with gas-permeable walls. Before synthesis, the initial ferrosilicon was dried in a vacuum drying chamb...

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Mechanism and features of nitriding of ferrosilicon in the combustion regime

Cited by 18 publications

References 3 publications

Phase composition of the products of combustion of ferrosilicon in nitrogen with fluorine-containing additives present

Phase composition of the products of combustion of ferrosilicon in nitrogen with fluorine-containing additives present

Phase composition of the products of nitriding ferrosilicon with zircon concentrate additives

Effect of the silicon content in the initial alloy on synthesis of silicon nitride in burning ferrosilicon in nitrogen

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