Ferrosilicon Nitride Research Articles

Performance of silica bricks with ferrosilicon nitride as the mineralizer

Novel silica bricks were made of crystalline silica with ferrosilicon nitride as the mineralizer. The phase, microstructure, pore characteristics and high-temperature properties of the novel silica bricks prepared by adding 1%, 1.5% and 2% ferrosilicon nitride were characterized. The results showed that, compared to conventional silica bricks (with mineralizers of calcium hydroxide and iron scale), the novel silica bricks with the addition of ferrosilicon nitride contained less calcium oxide, less residual quartz and more tridymite. The ferrosilicon nitride was gradually oxidized to form SiO2 and Fe2SiO4 during the firing stage of the silica bricks. After adding ferrosilicon nitride, the degree of particle breakage was reduced, and the pore size of interconnected pores increased. With the increase in ferrosilicon nitride content, the silica brick structure gradually densified. The silica brick sample with 2% ferrosilicon nitride achieved better creep resistance at high temperature (1550 °C, 0.2 MPa), but the refractoriness under load of the bricks was slightly reduced by using ferrosilicon nitride as a mineralizer. An optimization model of ferrosilicon nitride as a mineralizer was established.

Development and Application of SHS Ferrosilicon Nitride to Increase the Resistance of Taphole Clays for Blast Furnaces

Development and Application of SHS Ferrosilicon Nitride to Increase the Resistance of Taphole Clays for Blast Furnaces

Cost-effective manufacture and synthesis mechanism of ferrosilicon nitride porous ceramic with interlocking structure

To realize cost-effectively manufacture of high-performance Si3N4 porous ceramic, a ferrosilicon nitride porous ceramic with an optimized interlocking structure was synthesized by flash combustion synthesis using FeSi75 powder as raw material. And the technology has been improved in many ways to ensure stable industrial production. The theoretical combustion temperature of FeSi75 in N2(g) is up to 4608K, while Si3N4 is unstable. Both adding diluent and designing the preheat temperature of nitrogen are taken to control synthesis temperature below 1600 °C. During synthesis, the Fe–Si liquid phase and SiO(g), which are essential for the selective growth of elongated columnar β-Si3N4 and whisker α-Si3N4 respectively, are formed firstly. Then, nitriding proceed in multiple ways. N diffuses through Fe–Si(l) and reacts with Si to form β-Si3N4, and the growth of elongated β-Si3N4 in Fe–Si liquid follows the dynamic ripening model, which is very fast and effective. Thus, an interlocking structure composed of elongated β-Si3N4 with an aspect ratio above 20 is reached. There is also an indirect nitridation reaction, that is, FeSi75 preferentially reacts with trace O2 in atmosphere to form SiO(g), which is further nitrided to form needle-like α-Si3N4. Needle-like α-Si3N4 is interspersed in the well-developed columnar β-Si3N4, making the structure stronger. Fe finally exists in the form of Fe3Si, which binds the surrounding elongated Si3N4 to form a sea-urchin like unit, making the structure more stable and strengthened. Through control of these reactions, optimizations in microstructure are reached, and the annual output of has reached 25,000 tons. The reaction model is established.

Kinetic Study of the Ferrosilicon Nitriding Process

The ferrosilicon nitride used for steelmaking has been synthesized by direct nitriding. The relationship between the reaction temperature and nitriding effect was investigated. The results show that the initial reaction temperature between FeSi75 and nitrogen is approximately 900°C. Increasing holding temperature or prolonging holding time is beneficial to increase the nitrogen content in the nitrided product. At 1400°C, the nitrogen content in ferrosilicon nitride reached 30.28% when the holding time was 4 h. With the increase of nitriding reaction temperature, the phase of α-Si3N4 transferred to β-Si3N4 gradually. Pore diffusion was identified as the dominant restrictive link during the ferrosilicon nitriding process.

Nitrided Ferroalloy Production By Metallurgical SHS Process: Scientific Foundations and Technology

.

Formation mechanism of Sialon in alumina-ferro-silicon-nitride composite under nitrogen atmosphere at high temperatures

Sialon bonded Al2O3 composites were successfully synthesized using ferro-silicon nitride and different alumina sources at 1500 °C and 1600 °C under N2 atmosphere. Fused corundum, sintered alumina and the mixture of both were used as different alumina sources to evaluate their effects on the formation of Sialon phases. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDAS). The results show that the Sialons (β-Sialon (Si2Al4O4N4) and 15R-Sialon (SiAl4O2N4)) contents are dependent on the sintering temperature and alumina sources. Formation mechanism of Sialon in samples prepared with different alumina sources is different. Sintered alumina can react with Si3N4 directly to form Sialon. In sample prepared with fused corundum, AlON is formed first and then it reacts with Si to form Sialon. Sintered alumina exhibits better reactivity than fused corundum. Sialon is more stable than AlON under N2 atmosphere at high temperature with the existence of carbon.

Reaction mechanism between porous ferrosilicon nitride ceramic and molten steel

A novel porous ferrosilicon nitride (Fe3Si–Si3N4) ceramic sliding gate was prepared and applied in a ladle in a steel mill; it was characterised by X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive spectroscopy. The results showed that after use, the sliding gate consisted of a reaction layer (0–1.5 mm), a transition layer (1.5–2.2 mm), a gradient layer (2.2–20 mm), and an unaltered layer. In the reaction layer, Si3N4 is decomposed, and the structure is damaged; in the transition layer, Si3N4 is stable, and the structure shows no obvious change; in the gradient layer, Si3N4 is oxidised slightly. The reaction mechanism is as follows. The structure of the original porous ferrosilicon nitride resembles a sea urchin, and β-Si3N4 columns are bundled together by Fe3Si. During operation, Fe3Si reacts with molten steel to form an Fe/FeSi melt, which attacks the structure, whereas Si3N4 decomposes to the product N2(g) [Si3N4(s)+Fe(l)→FeSi(l)+N2(g)]. N2(g) forms a high-pressure gas cushion that blocks the molten steel, protecting the inner part of the sliding gate, so Si3N4 remains stable in the transition layer. Further inward, Si3N4 is oxidised slightly by trace [O] from the molten steel to generate silicon oxynitride. The reaction model was established.

Role of the vapour phases in the formation mechanism of 15R-SiAlON in FexSiy-Si3N4-Al2O3 composites at 1800 °C

The synthesis of 15R-SiAlON in FexSiy-Si3N4-Al2O3 composites was carried out at 1800 °C in flowing nitrogen. The role of the vapour phases from ferrosilicon nitride (FexSiy-Si3N4) and Al2O3 was studied by phase evolution, microstructure, and thermodynamic analyses. The results show that the formation of 15R-SiAlON is highly related to SiO(g), Si(g), Al2O(g) and Al(g) from FexSiy-Si3N4-Al2O3 composites. At 1800 °C in flowing nitrogen, SiO(g) and Si(g) are generated from ferrosilicon nitride. Al2O(g) and Al(g) are released from Al2O3, and their pressures depend on that of oxygen. The increase of ferrosilicon nitride promotes the generation of vapour phases. The diffusion of Al2O(g) and Al(g) into Si3N4, and of SiO(g) and Si(g) into Al2O3 particles enable the growth of 15R-SiAlON flakes based on both the Si3N4 and Al2O3 substrates by solid-gas reaction. In the presence of the Fe-Si liquid, 15R-SiAlON whiskers with Fe-Si sphere on the top are generated by the liquid-solid-gas mechanism. The reactions between Al2O(g)/Al(g) and SiO(g)/Si(g) in nitrogen generate large amounts of 15R-SiAlON whiskers by the gas-gas mechanism.

Silicon nitridation mechanism in reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride

AbstractReaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride, with Si powder, SiC particles and Fe3Si–Si3N4 particles as raw materials, respectively, are prepared in flame‐isolation nitridation shuttle kiln with flowing N2 at 1723K. There is columnar β‐Si3N4 in both Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride. However, fibrous α‐Si3N4 is only observed in Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride contains much more Si2N2O than Si3N4–SiC. By analyzing the oxidation thermodynamics of Si and Si3N4, it is known that in the process of producing Si3N4–SiC, Si is oxidized first to gaseous SiO and fibrous α‐Si3N4 is generated with SiO and N2. The existence of SiO is the reason of low silicon nitridation rate. But in the process of producing Si3N4‐bonded ferrosilicon nitride, Si3N4 is easier to be oxidized than Si and Si2N2O is generated on the surface of Si3N4 hexagonal prisms in ferrosilicon nitride particles. Meanwhile, Si in raw materials forms new ferrosilicon alloys with Fe3Si, which decreases the temperature of liquid appearance and blocks some open pores in the samples, which stops the matter loss of nitridation. Liquid ferrosilicon alloys favors β‐Si3N4 generation from Si direct nitridation and fibrous α‐Si3N4 transformation, which used to exist in ferrosilicon nitride raw materials.

Oxidation Resistance and Mechanical Enhancement of Ferro-Silicon Nitride on Silica Sol Bonded SiC Castable

Silica sol bonded SiC castable have obvious advantages of slag resistance and thermal stress damage resistance. However, they are not widely used due to their weak oxidation resistance at high temperature. Ferro-silicon nitride is added to improve the oxidation resistance of SiC castable. The efficiency of SiC castable in the presence of different contents of ferro-silicon nitride was evaluated through sintered properties, isothermal oxidation behaviors and microstructural analysis. The results show that sample with 5wt% ferro-silicon nitride possessed good mechanical behavior after heat treatment due to its acceleration for the formation of SiC whiskers. At 1500 °C, Isothermal oxdation curve indicated that the oxidation progress performed two-stage model controlled by chemical reaction at the earlier period and diffusion at the later period. Sample with 5wt% ferro-silicon nitride present faster oxidation rate (kc) at the earlier stage versus the contrast sample (0.025 mg·cm-2·min-1 vs 0.087 mg·cm-2·min-1), and slower oxidation rate (kd) at the later stage (0.145 mg·cm-2·min-1 vs 0.137 mg·cm-2·min-1). After 470 min isothermal oxidation test, the weigh gain of sample with 0 wt% ferro-silicon nitride exceeded the sample with 5wt% ferro-silicon nitride.

In situ synthesis mechanism of 15R–SiAlON reinforced Al2O3 refractories by Fe–Si liquid phase sintering

Abstract15R–SiAlON bonded Al2O3 refractories were successfully synthesized using ferrosilicon nitride and alumina by liquid phase sintering. The phase composition and morphology were analyzed by means of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show that 15R–SiAlON reinforcement can be in situ obtained in the specimens with 5 wt% ferrosilicon nitride at 1500°C to 1700°C in flowing N2 of 0.1 MPa. The morphology of 15R–SiAlON is strongly dependent on the morphology of intermediate AlON phases formed at different temperatures. Fe–Si alloys from ferrosilicon nitride form liquid phase and accelerate the formation of 15R‐SiAlON, in which process the wettability of Fe–Si alloys is improved by the increase in Si content, carbon coating on particle, solution process and reactions. The 15R–SiAlON reinforced Al2O3 refractory materials possess high cold crushing strength of 138‐171 MPa.

Performance investigation of resin bonded ferro-silicon nitride-corundum refractories after creep at 1300 °C

Novel tempered resin bonded ferro-silicon nitride-corundum refractories containing 0wt%, 15wt% and 25wt% ferro-silicon nitride were prepared respectively. Creep tests were performed under a load of 0.2MPa at a temperature of 1300°C for 50h in air. The results showed that creep performance was significantly improved by the addition of ferro-silicon nitride. Ferro-silicon nitride-corundum containing 15wt% ferro-silicon nitride initially presented a steady-state stage and was able to remain stable from the beginning of the holding time until 50h of creep testing. All the specimens exhibited cold crushing strength more than 100MPa both before and after creep testing. Phase composition and microstructure were analyzed following the creep experiments. The results showed that Si2N2O and O’-sialon crystals formed in situ during creep testing, in addition to the conversion of α-Si3N4 to β-Si3N4. Liquid Fe3Si from the ferro-silicon nitride component accelerated the formation of the O’-sialon and prolonged the growth of β-Si3N4, which improved the creep performance significantly. Fe3Si liquid migrated into the pores, and some Fe3Si coexisted with residual carbon from the resin, which filled a part of pores and protected the specimens from severe oxidation.

Reaction mechanism for in-situ β-SiAlON formation in Fe3Si–Si3N4–Al2O3 composites

In this work, Fe3Si–Si3N4–Al2O3 composites were prepared at 1300°C in an N2 atmosphere using fused corundum and tabular alumina particles, Al2O3 fine powder, and ferrosilicon nitride (Fe3Si–Si3N4) as raw materials and thermosetting phenolic resin as a binder. The effect of ferrosilicon nitride with different concentrations (0wt%, 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%) on the properties of Fe3Si–Si3N4–Al2O3 composites was investigated. The results show that the apparent porosity varies between 10.3% and 17.3%, the bulk density varies from 2.94 g/cm3 and 3.30 g/cm3, and the cold crushing strength ranges from 67 MPa to 93 MPa. Under the experimental conditions, ferrosilicon nitride, whose content decreases substantially, is unstable; part of the ferrosilicon nitride is converted into Fe2C, whereas the remainder is retained, eventually forming the ferrosilicon alloy. Thermodynamic assessment of the Si5AlON7 indicated that the ferrosilicon alloy accelerated the reactions between Si3N4 and α-Al2O3 fine powder and that Si in the ferrosilicon alloy was nitrided directly, forming β-SiAlON simultaneously. In addition, fused corundum did not react directly with Si3N4 because of its low reactivity.

Distribution Status of Trace Oxygen in Fe<sub>3</sub>Si-Si<sub>3</sub>N<sub>4</sub>

The distribution status of trace oxygen in the ferro-silicon nitride (Fe3Si-Si3N4) was investigated at the present, which was prepared by flash combustion synthesis method from FeSi75. The results showed that while the grain size of FeSi75 used in preparing Fe3Si-Si3N4 was less than0.074 mm, “active oxidation” occurred firstly, silicon was oxidized to form gaseous SiO(g), oxygen partial pressure was reduced in the system, silicon reacted with nitrogen directly to form Si3N4 while the system oxygen partial pressure approached less than 10-19MPa (T=1823K). O2(g) promoted the formation of Si3N4, Gaseous SiO(g) finally reacted with nitrogen and Si to form Si2N2O. The ferro silicon nitride was characterized by X-ray diffractometer and scanning electron microscope, the distribution of Si2N2O was uneven in the silicon nitride, and Si2N2O mainly distributed around Fe3Si or near the hole.

SHS Ferrosilicon Nitride NITRO-FESIL®TL as a New TAP-Hole Clay Refractory Component for Blast Furnaces1

The scientific and technical manufacturing firm Etalon developed and perfected industrial technology for manufacturing SHS ferrosilicon nitride NITRO-FESIL® TL, which is a composite consisting of silicon nitride, iron silicide, and free iron. On an industrial scale together with OAO MMK and ZAO Metallurgremont test tap-hole clays are provided containing ferrosilicon nitride NITRO-FESIL® TL. Taphole clays with the new component demonstrate higher corrosion and erosion resistance, and oxidation resistance, and also better sintering capacity. As a result of this reliable sealing of iron tap-holes, a smooth, more prolonged iron and slag flow regime with stable discharge parameters is provided. The clay is recommended for introduction.

Effect of dilution and additive on direct nitridation of ferrosilicon

Abstract Ferrosilicon nitrides were fabricated by direct nitridation of ferrosilicon, and the effects of ferrosilicon nitride and α-Si3N4 dilution and ammonium chloride (NH4Cl) additive on characteristics of the nitride products were investigated. The phases of final nitride products consist of α-Si3N4, β-Si3N4 and iron silicides with various compositions. Long columnar crystals, equiaxed crystals and flower-like crystals were observed in the final products, and fiber or whisker-like crystals with a low degree of crystallization were also found in the nitrides. Both the diluents and additive can improve the nitridation degree, but only the additive can increase the content of α-Si3N4 in the nitride products. As a diluent, ferrosilicon nitride can decrease the cost of nitride products, and increase their nitridation degree more than α-Si3N4. NH4Cl made the products fluffy and expansive, while the dimensions of the compact without addition of NH4Cl remain unchanged during nitridation.

Effect of Si-SiC Additives on Properties of Tap Hole Clay

Non-water taphole clay was prepared by using high alumina ((Al2O3)>85%,Particle Size is 3~1, ≤1 mm),coke, clay, kyanite, Ferrosilicon Nitride Powder and Corundum powder, adding more 15% tar as the binder and Si-SiC (0,4%,8%,12%) to replace Ferrosilicon Nitride. Specimens with dimensions of φ50mm × 50mm and 125mm × 25mm × 25mm were prepared under a uniaxial pressure of 5MPa. The microstructure, high temperature bending strength (600oC,800 oC,1000 oC,1200 oC,1400 oC) and apparent porosity and sinter ability of the tap hole clay were studied. The influence of the substitution content of Si-SiC of the tap hole Clay was also investigated. The results showed that the high temperature bending strength of the samples decreased with the increasing of Si-SiC and apparent porosity almost no changing, but it could still met the need of the actual requirement. The Si-SiC substitution content within 5% of the tap hole clay has also good performance. Through the analysis of the microscopic structure of the tap hole clay, the tap hole clay with Si-SiC has good sinter ability.

Using ferrosilicon nitride of nitro-fesil grade in gate and spout components

Development results are presented for the new NITRO-FESIL strengthening additive, which is intended for gate and spout parts in blast furnace production. Researches on the high-temperature process in the ferrosilicon-nitrogen system have provided a new industrial technology for making materials based on silicon nitride. The technology is characterized by the absence of energy consumption, complete ecological safety, and a product distinguished by good working properties.

Self-propagating high-temperature synthesis of ferrosilicon nitride

Self-propagating high-temperature synthesis of ferrosilicon nitride

Experience of preparing and using water-free tap-hole mixes in OAO MMK

In the OAO MMK blast furnace plant water-free tap-hole mixes have been introduced with a carbon-containing concentrate, with a ferrosilicon nitride tap-hole product from Spetsremstroi OOO, and a Chinese product. In the first (traditional) composition instead of the coke portion there is use of a carbon-containing concentrate (CCC). Presence of silicon carbide and carbon in the CCC promotes and increase in the slag and iron resistance of the tap-hole mix. Testing a mix of the second composition has shown that in a number of parameters it is at the level of imported mixes and even surpasses them, only being inferior in specific consumption.