Fe Si Melt Research Articles

Effects and function mechanism of Fe‐containing additives on SiC synthesis with silicon cutting waste

AbstractWith the rapid development of the photovoltaic industry, a great amount of silicon cutting waste (SCW) are being generated, which lead to a heavy environmental burden as well as a high cost of the photovoltaic industry. In this paper, the effects of Fe‐containing additives and their function mechanism on recycling SCW to synthesize high‐purity SiC were studied. The results show that Fe‐containing additives, including Fe, Fe2O3, and Fe(NO3)3, have obvious effect on recycling SCW to synthesize SiC. And Fe(NO3)3 additive achieves the best effect. Fe(NO3)3 can effectively destroy the SiO2 film wrapped on the Si particles, so that expose the inner Si to C at lower temperatures than that of the reaction between C and SiO2. Besides, Fe(NO3)3 additive can effectively reduce the activation energy both for Si and C reactions and SiO2 and C reactions, and contribute to the transport of the raw materials as well as the dissolution and precipitation of Si and C due to the formation of the FeSi melt at low temperatures. The optimal processing conditions are determined as Fe(NO3)3 addition of 1–3 wt.% and smelting temperature of 1200–1300℃.

Reaction and formation mechanism of Fe-Si3N4 composite prepared by flash combustion synthesis

In this paper, in order to improve the performance of Fe–Si3N4 composite synthesized by flash combustion, the detailed nitridation mechanism and formation process were discussed. In the process of high temperature nitriding, ξ phase rapidly melted to form Fe-Si melt and the cycle of rapid surface nitriding → rupture of nitridation shells → new melt exposing and nitriding occurred continually on the surface of Fe-Si melt. Since ions have different activities on the surface and internal, Fe ions near the surface migrated inwards and Si ions inside moved out; meanwhile, the Fe-Si melt kept shrinking. The nitriding reaction of the Fe-Si melt finished till the overall activity aSi approached 0, leaving the atom ratio of [Fe] to [Si] at 3:1. During the falling of the formed Si3N4 and Fe3Si melt in the N2 flow, the surface of Si3N4 was oxidized to form a SiO2 film. The nitridation product fell into the product pool, loosely stacking and adhering together by the SiO2 film. α-Si3N4 dissolved and precipitated to form β-Si3N4 crystals, and the β-Si3N4 crystals kept growing to form radioactive elongated crystals. As the temperature decreased, the Fe3Si melt cooled down; the Si-N-O melt, α-Si3N4 and the roots of elongated β-Si3N4 crystals formed the dense areas.

Viscosity of liquid amorphizing alloys of iron with boron and silicon

The temperature and concentration dependences of the kinematic viscosity of melts of the binary FeSi system with a silicon content from 3 to 45at.% and melts FeXBYSi(100−X−Y) (x=70 and 80at.%; y=0−(100−x)) have been investigated in the paper. Nonmonotonic concentration dependence of the viscosity and the activation energy of viscous flow of FeSi melts have been obtained. Almost monotonic increase in the viscosity values is observed in concentration dependences of quasi-binary systems of Fe70B30Fe70Si30 and Fe80B20Fe80Si20 when replacing silicon atoms by boron atoms.

The influence of Si concentration on undercooling of liquid Fe

Concentration dependences of undercooling ability, (ΔТ), of Fe–Si melts with Si concentration up to 30at.% have been studied in this paper. It has been shown that the crystallization ability of the α-Fe(Si) solid solution rises sharply within the range from 5 to 10at.% Si. The obtained ΔТ(х) dependence is accounted for by the change of the geometrical and chemical short-range order of the atomic arrangement. The numeric description of ΔТ(х) in the composition range up to 30at.% Si has been carried out by the probabilistic approach used to determine various short-range ordering configurations and experimental undercooling ability values with the 2.5 and 2.7at.% Si concentrations.

Phase relations in the carbon-saturated C–Mg–Fe–Si–O system and C and Si solubility in liquid Fe at high pressure and temperature: implications for planetary interiors

The phase and melting relations of the C-saturated C–Mg–Fe–Si–O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = −1.7 to −1.2, where ΔIW is the deviation of the oxygen fugacity (fO2) from an iron-wustite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < −3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe–Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO2, whereas the solubility of Si decreased with increasing fO2. The carbon-bearing phases were graphite, Fe3C, SiC, and Fe alloy melt (Fe–C or Fe–Si–C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < −6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe–Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth’s core.

Effect of Fe Addition on the Activity Coefficient of Si in Cu–Fe–Si Melt at 1623 K

Effect of Fe Addition on the Activity Coefficient of Si in Cu–Fe–Si Melt at 1623 K

Thermodynamics of Phosphorus Removal from Silicon in Solvent Refining of Silicon

AbstractRefining of silicon for solar applications using metallurgical approaches has attracted a considerable attention in the recent years. The present study involves employing solvent refining as a purification technique in which silicon recrystallization takes place from an iron-silicon alloy melt. It is believed that iron will perform as the impurity “getter” and purified silicon crystals grow from the alloy melt, while the impurities are segregated to the liquid alloy. The focus of this article is on removal of phosphorus, as a critical impurity in solar silicon. In order to assess the feasibility and efficiency of phosphorus removal through solvent refining, the distribution of phosphorus between solid Si and Fe-Si melt at 1483–1583 K (1210–1310 °C) was measured. Interaction parameter between phosphorus and iron was calculated by varying the concentration of phosphorus at each temperature.

Influence of cooling rate and composition on formation of intermetallic phases in solidifying Al–Fe–Si melts

Aluminium alloys containing 0·3%Fe and 0·05%Si, 0·3%Fe and 0·15%Si, 0·3%Fe and 0·45%Si, and 0·5%Fe and 0·2%Si were solidified with different cooling rates. Shapes of intermetallic particles and their spatial distribution in the alloys were characterised by optical and scanning electron microscopy. X-ray diffraction analysis was used to establish the types of intermetallic phases extracted from the alloys by dissolving the FCC matrix in boiling phenol. The influence of melt superheating on the microstructure was analysed by comparing phase portraits of alloys solidified from melts whose temperatures before casting were 100 and 350°C above the liquidus.On a solidifié des alliages d’aluminium contenant 0·3%Fe et 0·05%Si, 0·3%Fe et 0·15%Si, 0·3%Fe et 0·45%Si et 0·5%Fe et 0·2%Si, à différentes vitesses de refroidissement. On a caractérisé la forme des particules intermétalliques et leur distribution spatiale dans les alliages, au moyen de la microscopie optique et de la microscopie électronique à balayage. On a utilisé l’analyse de la diffraction des rayons X pour établir les types de phases intermétalliques extraites des alliages par dissolution de la matrice FCC dans du phénol en ébullition. On a analysé l’influence de la surchauffe du bain sur la microstructure en comparant les images de phase des alliages solidifiés à partir des bains dont les températures avant le moulage étaient de 100 et de 350°C au-dessus du liquidus.

Fundamental study for solvent growth of silicon carbide utilizing Fe-Si melt

Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was investigated at 1523 K by the phase equilibration technique, and was further studied with the thermodynamic calculation. It was found that Fe- 36 mol% Si melt equilibrates with SiC at the temperature and possesses the higher carbon solubility than silicon-based melt. The first trial of the SiC crystal growth experiment was then carried out with Fe- 36 mol% Si melt by means of temperature difference method, and formation of SiC layer was obtained on the graphite substrate. Accordingly, it was found possibility for rapid growth of SiC by the solvent growth method with Fe- 36 mol% Si melt.

Equilibrium Phase Relationship between SiC and a Liquid Phase in the Fe-Si-C System at 1523&amp;ndash;1723 K

Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was studied to determine the optimal composition of a high SiC content solvent. The solubility of carbon in molten silicon was examined and the thermodynamic properties of the liquid phase in the Si-C system were reassessed. The phase relationship between SiC and Fe-Si melt was investigated by the equilibration technique at 1523–1723 K. It was found that Fe-36 mol% Si alloy equilibrates with SiC at the corresponding temperatures. The equilibrium phase relationship between SiC and various compositions of Fe-Si melts was studied by using thermodynamic calculations. The results indicated that SiC is far more soluble in iron-rich Fe-Si melt than in silicon-rich melt. The Fe-Si melt of Fe-36 mol% Si composition possessing high SiC solubility should be a suitable solvent for rapid liquid phase growth of SiC. [doi:10.2320/matertrans.MRA2008404]

Solubility of oxygen in iron-silicon melts

The oxygen solubility in Fe-Si melts in equilibrium with SiO2 at 1873 K has been determined in a whole concentration range. The isotherm of oxygen solubility exhibits both intermediate minimum and maximum at 20 and 85 mass% Si, respectively. The corresponding values of oxygen saturated contents are as follows: 1.4 and 94 ppm. The following values of Wagner interaction parameters were calculated: ϵO(Fe)Si = 129 ± 2.7 and ϵO(Si)Fe = -6.5 ± 2.0.

Growth of SiC nanowires/nanorods using a Fe–Si solution method

A new solution technique to grow SiC nanowires/nanorods was developedby simply heating Fe–Si melt on a graphite plate in argon atmosphere to1600 °C for 3 and 6 h. SiC nanowires/nanorods with diameters of 100 nm and lengths of several tens ofmicrometres were grown on the surface of the melt. The prototype of the nanowires/nanorods is 3C-SiC(β-SiC), and the growth direction is [111] for 3C-SiC. Taking into consideration theaction of Fe in Fe–Si melt and the possible participation of oxygen, the growthmechanism of the SiC nanowires is proposed. It is believed that the formationof SiC nanowires is a combination of the solid–liquid–solid (SLS) reaction fornucleation and the vapour–liquid–solid (VLS) process for nanowire growth. In the SLSreaction, graphite carbon (solid) dissolved in the Fe–Si melt (liquid), and thenreacted with the silicon in the melt to form SiC nuclei (solid). In the VLS reaction,SiO and CO (vapours) dissolved in the melt droplets (liquid) attached to the tipof the growing SiC nanowires (solid), and reacted to make them grow further.

Deoxidation with silicon and the control of oxide inclusions in electrical steels

The oxygen solubility in Fe-Si melts in equilibrium with SiO2 at 1873 K has been determined in a concentration range of 0.1–70 wt % Si. Model alloys are melted in quartz crucibles in an argon atmosphere. The oxygen content in analytical samples is determined by the inert-gas reducing-fusion method after careful sample preparation. The results obtained have been processed using a thermodynamic model that can calculate the oxygen activity and solubility in Fe-Si melts up to 100 wt % Si. The effects of the heating rate and the silicon content on the carbon concentration in carbonyl iron and Fe-Si alloys are studied using the inert-gas reducing-fusion method in the temperature range 1673–2373 K. Oriented electrical steels are investigated using fractional gas analysis. The main forms of oxygen in these steels are found to be silicates, Al2O3, and MgAl2O4.

Thermodynamics of Titanium and Nitrogen in Fe-Si Melt

The thermodynamics of titanium and TiN formation in Fe-Si-Ti-N melts was studied. A metal-nitride-gas equilibration technique was used to measure the activities of titanium and nitrogen in the presence of pure solid TiN under various nitrogen pressures in the temperature range of 1843-1923 K. The activity coefficients of titanium and nitrogen relative to 1 mass% standard state in liquid iron were calculated from the experimental results for Fe-Si alloys of silicon content up to 2.26 mass%. The first- and second order interaction parameters of silicon on titanium, eSiTi and rSiTi, were determined as -0.0256 and 0 at 1873 K, respectively. Similarly, the interaction parameters of silicon on nitrogen, eSiN and rSiN, were determined as 0.0491 and 0 at 1873 K, respectively. The temperature dependence of these interaction parameters was also determined. The validity of thermodynamic parameters determined in the present study was examined by observing the formation of TiN precipitates in a Fe-1%Si-Ti-N melt of controlled titanium and nitrogen contents at 1873 K.

Closure of the Fe–S–Si liquid miscibility gap at high pressure

A high pressure investigation of melting relationships in the Fe–S–Si system has been conducted in a multi-anvil apparatus from 10 to 27 GPa and up to 2343 K. At 1 atm, the Fe–S–Si ternary system exhibits a vast miscibility gap [Raghavan, V., 1988. Phase diagrams of ternary iron alloys. Part 2: Ternary systems containing iron and sulphur. Indian Institute of Metals, Calcutta]. Quenched samples from experiments conducted at 10 and 12 GPa show an emulsion of immiscible liquids (an Fe–S melt and an Fe–Si melt). The liquid miscibility gap persists to at least 2343 K at 10 GPa. At 15 GPa, only one liquid is quenched, with a fine homogeneous dendritic texture. The results provide a mechanism to incorporate both S and Si as the light elements into the Earth’s core during a moderately high-pressure differentiation, consistent with geochemical models predicting up to 15 wt.% of light elements in the Earth’s core with 2–5 wt.% S and 7–10 wt.% Si. In contrast, for small planets such as Mars and Ganymede, differentiation took place within the pressure range of the miscibility gap. The composition of these cores is likely to be S-rich but Si-poor.

Infiltration of SiC preforms with iron silicide melts: microstructures and properties

Spontaneous infiltration of SiC preforms with Fe X Si Y (=Fe 3Si, Fe 5Si 3 and FeSi) melts produced SiC/Fe X Si Y composites with nearly full density (≥96.5% theoretical density). The phases, microstructures and mechanical properties have been studied with conventional materials characterization techniques including X-ray diffraction, optical microscopy, scanning electron microscopy etc. A key issue behind these studies is dissolution of SiC in Fe X Si Y melts during infiltration. The dissolution of SiC in Fe 3Si melt led to carbon precipitation and phase changes (Fe 3Si disappeared and Fe 5Si 3 and FeSi formed). However, Fe 5Si 3 and FeSi infiltration gave no carbon precipitation, but SiC sintering, particle coalesce and grain growth instead. Extra-large SiC grains and SiC single crystals were found in fine SiC (0.5 μm) infiltrated by Fe 5Si 3. Phase equilibrium calculations for Fe–Si–C system were performed at 1873 K using chemsage in order to study SiC solubility and the condition for the precipitation of SiC rather than C in Fe–Si melt. Mechanical properties including micro-hardness, bending strength and Weibull modulus of all infiltrated samples were tested and analyzed on the basis of phase and microstructure observations.

Phase-field simulation of semisolid metal processing under conditions of laminar and turbulent flow

Interface stability theory predicts that the effect of stirring during solidification will decrease the stability of the solid–liquid interface and promote dendrite formation. In contrast, during semi-solid metal processing, non-dendritic particles form when stirring a casting. This apparent conflict has been resolved in the present work by taking into account the effect of turbulence. A model of stagnant diffusion boundary layer, developed by Vogel & Cantor, has been used to describe the effects of laminar flow, and has been modified to allow for the effects of turbulence. The growing of an Al 5Fe 2 spherical seed from an Al–Fe–Si melt under conditions of both laminar and turbulent flow has been simulated by means of a phase-field model. In pure laminar flow, the phase-field simulations agree well with the interface stability theory predictions. Under conditions of increased turbulence, the particles change from dendritic to rosettes and then to spherical morphologies as the extent of stirring increases; this result agrees well with experimental observations of semi-solid metal processing. The relative viscosities of slurries with such different particle morphologies were calculated and showed good agreement with experimental data. The effect of turbulence was explained in terms of constitutional undercooling and classical particle growth theory.

Synthesis of β-FeSi2 by Splat Solidification in Short-Duration Microgravity

We synthesized β-FeSi2 by splat solidification in microgravity. When the Fe–Si melt was solidified in microgravity on a copper chill block with a tin layer, the solidified sample had a uniform structure and composition. Though this Fe–Si alloy was identified as a mixture of ε-FeSi and α-FeSi2 by X-ray diffraction analysis, single-phase β-FeSi2 was obtained by heat treatment at 1123 K for 0 s at a heating rate of 10 K/min. When the Fe–Si melt was solidified in microgravity on a copper chill block without a tin layer, the solidified sample had many small precipitants of ε-FeSi because of poor heat transfer between the melt and copper chill block. When the Fe–Si melt was solidified using argon gas pressure (4×105 Pa) on a copper chill block with a tin layer, the solidified sample had many precipitants of ε-FeSi. Furthermore, some parts had a uniform structure, but the composition ratio continuously shifted in the solidification direction.

Structural properties of liquid Fe–Si alloys

The atomic structure of liquid Fe–Si alloys within the whole concentration range (including pure components) was investigated at the temperature of 1550 °C by means of X-ray diffraction. Analysis of the reported data on physical properties of Fe–Si melts has been carried out. Interrelation between liquid-state structure and solid-state properties was considered. Fe–Si alloys in the liquid state are shown to be micro-inhomogeneous and they contain atomic micro-formations (clusters) that differ by atomic composition and packing. There are five types of clusters: two of them consist of atoms of one kind (Fe or Al); the composition of the other clusters depends on the stoichiometry of solid Fe 3Si, FeSi and Fe 2Si 5 phases. The entire concentration range of the Fe–Si system consists of four concentration intervals. Within each interval melts are constituted of the clusters of two kinds. The variation of the component concentrations in Fe–Si alloys results in changing of volume fraction of each type clusters, whereas the atomic composition and arrangement inside the clusters remains constant.

Solidification Parameters and Microstructures of Rapidly Solidified Fe-Si and Fe-C Melt Spun Ribbons

Solidification Parameters and Microstructures of Rapidly Solidified Fe-Si and Fe-C Melt Spun Ribbons