Production of semiconductor grade high-purity iron

Semiconductor grade high-purity Fe will be required in practical use of β-FeSi₂. However, high-purity Fe with more than 99.9999% in purity has not been produced commercially. Then, a process consisting of anion exchange in a HCl solution, hydrogen reduction and plasma arc melting has been developed for the production of high-purity Fe. All metallic impurities can be virtually removed from Fe by the two anion-exchange steps, in which some elements such as Cu and Mo are separated efficiently under reducing conditions by the addition of Fe powder at the 1st step, and the rest of impurities are surely separated under oxidizing conditions at the 2nd step. Non-metallic impurities such as oxygen, carbon and nitrogen also can be eliminated to very low levels by the hydrogen reduction and the hydrogen plasma arc melting steps.     

Refining effect of hydrogen plasma arc melting on titanium sponges

Hydrogen plasma arc melting (HPAM) of commercial Ti sponges (> 99.7%) was examined. Ti sponges had main impurities such as Fe, Al, Cl and Mn. These main impurities could be reduced more efficiently by HPAM than by Ar PAM. Other small amount of impurities also had a tendency of reduction by HPAM. In addition, it was found that each removal degree is attributable to a differential refining effect caused by the difference of initial impurity concentration. For the unique refining effect of HPAM, dissociated and activated hydrogen atoms involved in the high temperature plasma arc are considered to play an important role in the melting process.     

Preparation of silica coated iron oxide nanoparticles using non-transferred arc plasma

Silica coated iron oxide nanoparticles were prepared using non-transferred arc plasma. The plasma was discharged with argon. Vapors of iron pentacarbonyl (Fe(CO)₅) and tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) were injected into a plasma torch with carrier gas and reacted in the plasma chamber. In addition, two types of reaction chambers that are a hot wall reactor and a cold wall reactor were used to investigate the effect of temperature gradient on the synthesis of silica coated iron oxide nanoparticles. The synthesized nanoparticles were collected on the chamber wall and bottom. Phase compositions of the obtained nanoparticles were characterized by X-ray diffractometer (XRD) and the morphologies and the size distributions of the synthesized particles were analyzed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Additionally, elements mapping of the coated particles was performed by energy dispersive spectroscopy (EDS). The phase composition of the prepared particles was mainly composed of amorphous silica and polycrystalline Fe₃O₄. It was confirmed that the silica was adsorbed on iron oxide particles or encapsulated iron oxide particles. Furthermore, the mechanism of the formation of silica coated iron oxide in the plasma chamber was predicted.     

A single target RF magnetron co-sputtered iron doped tin oxide films with pillars

The SnO₂ gas sensors and catalytic surfaces are produced by different techniques with a wide range of dopants improving their selectivity and sensitivities. The surface topology is important because the active surface area can be enlarged dramatically by employing nanostructures. Many reported techniques for the tin oxide nanostructures preparation require fine powders or liquid precursors together with high temperatures above 500 °C. But the nanostructures can be formed by the RF off-axis magnetron sputtering technique at room temperature from a bulk target. The single target co-sputtering of SnO₂ target with Fe inset was used to deposit SnO₂ film doped by iron.The 400 nm diameter pillars were successfully deposited in controllable density on polished Si substrates at low pressure 0.3 Pa of argon and oxygen gas mixture. The pillars were not formatted at the beginning of deposition process but certain SnO₂ film was required. The surface around the pillars was flat without any significant texture.The iron in form of the iron oxide was found to be the doping in deposited coatings when the stannic oxide was sub-stoichiometry with oxygen vacancies.     

The effect of Si and microstructure evolution on the thermal expansion properties of Fe–42Ni–Si alloy strips

An alloying element of 0–1.5 wt.% Si was added to an Fe–42%Ni system, and alloy strips were fabricated using a melt drag casting process. The effects of the Si and annealing treatments on the thermal expansion properties of Fe–42Ni alloy were investigated. The addition of Si enlarged the coexisting temperature region of the solid–liquid phase and reduced the melting point, which improved the formability of the alloy strip. An alloy containing 0.6 wt.% Si had a lower thermal expansion coefficient than any other alloy in the temperature range from 20 to 350 °C. The grain size increased with the rolling reduction ratio and annealing temperature, which caused an increase in magnetostriction and consequently a decrease in the thermal expansion coefficient of the strip. The alloy strip containing 1.5 wt.% Si had a higher thermal expansion coefficient than the alloy containing 0.6 wt.% Si because of grain refining caused by the precipitation of Ni₃Fe.     

Annealing effects on the structural and magnetic properties of Fe–Al silica nanocomposites prepared by sequential ion implantation

The nanostructural and magnetic properties of FeAl–SiO₂ granular solids prepared by sequential ion implantation have been investigated as a function of the annealing atmosphere (either oxidizing or reducing) and implantation order. Nanoscopic particles with a bcc structure were found in both as-implanted samples. In the sample Al–Fe prepared by implanting first the Al ions and later the Fe ions, the lattice parameter indicates the presence of practically pure iron nanoparticles. On the other hand, in sample Fe–Al with the implantation order inverted, the lattice parameter is consistent with the presence of an iron rich iron–silicon alloy. The magnetic data confirm the presence of the pure Fe and the Fe–Si alloy in the as-implanted samples and the absence of FeAl intermetallic compounds. The annealing in Ar/H₂ promotes the growth of the clusters and increases the Si content in the particles in both samples. In Fe–Al sample, this induces a disorder–order phase transition from the disordered Fe–Si solid solution to the Fe₃Si phase and the coprecipitation of the ordered FeSi phase. The magnetic moment increases after the annealing in Ar/H₂ due to the incorporation of the iron atoms dispersed in the matrix and to the higher crystalline order. The annealing in air is responsible essentially of the growth of the Fe–Si clusters in both samples. On the other hand, in sample Al–Fe the oxygen interacts with the pure iron clusters by promoting the Fe₂O₃ formation.     

Structure and mechanical properties of as-cast Ti–5Nb–xFe alloys

In this study, as-cast Ti–5Nb and a series of Ti–5Nb–xFe alloys were investigated and compared with commercially pure titanium (c.p. Ti) in order to determine their structure and mechanical properties. The series of Ti–5Nb–xFe alloys contained an iron content ranging from 1 to 5 mass% and were prepared by using a commercial arc-melting vacuum-pressure casting system. Additionally, X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer, and three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys possessed a range of different structures and mechanical properties dependent upon the various additions of Fe. With an addition of 1 mass% Fe, retention of the metastable β phase began. However, when 4 mass% Fe or greater was added, the β phase was entirely retained with a bcc crystal structure. Moreover, the ω phase was only detected in the Ti–5Nb–2Fe, Ti–5Nb–3Fe and Ti–5Nb–4Fe alloys. The largest quantity of ω phase and the highest bending modulus were found in the Ti–5Nb–3Fe alloy. The Ti–5Nb–2Fe alloy had the lowest bending modulus, which was lower than that of c.p. Ti by 20%. This alloy exhibited the highest bending strength/modulus ratio of 26.7, which was higher than that of c.p. Ti by 214%, and of the Ti–5Nb alloy (14.4 ) by 85%. Additionally, the elastically recoverable angles of the ductile Ti–5Nb–1Fe (19.9°) and Ti–5Nb–5Fe (29.5°) alloys were greater than that of c.p. Ti (2.7°) by as much as 637% and 993%, respectively. Furthermore, the preliminary cell culturing results revealed that the Ti–5Nb–xFe alloys were not only biocompatible, but also supported cell attachment.     

Surface phenomena during the early stages of sintering in steels modified with Fe–Mn–Si–C master alloys

The characteristics of the metallic powder surface play a critical role in the development of strong bonds between particles during sintering, especially when introducing elements with a high affinity for oxygen. In this study, Mn and Si have been combined in a Fe–Mn–Si–C master alloy powder in order to reduce their chemical activity and prevent oxidation during the heating stage of the sintering process. However, when this master alloy powder is mixed with an iron base powder, differences in chemical activity between both components can lead to an oxygen transfer from the iron base powder to the surface of the master alloy particles. The present research is focused on studying the evolution of the master alloy particle surface during the early stages of sintering. Surface characterization by X-ray Photoelectron Spectroscopy (XPS) shows that the master alloy powder surface is mostly covered by a thin easily reducible iron oxide layer (~ 1 nm). Mn–Si particulate oxides are found as inclusions in specific areas of the surface. Evolution of oxides during sintering was studied on green compacts containing iron powder, graphite and Fe–Mn–Si–C master alloy powder that were heat treated in vacuum (10^− 6 mbar) at different temperatures (from 400, 600, 800 to 1000 °C) and analyzed by means of XPS. Vacuum sintering provides the necessary conditions to remove manganese and silicon oxides from the powder surface in the range of temperatures between 600 °C and 1000 °C. When sintering in vacuum, since the gaseous products from reduction processes are continuously eliminated, oxidation of master alloy particles due to oxygen transfer through the atmosphere is minimized.     

Refining effect of hydrogen plasma arc melting on hafnium metal

Removal of metallic impurities from Hf metal by hydrogen plasma arc melting (HPAM) has been examined. Several impurities such as Al, Ti, Cr, Fe, and Cu were efficiently removed when only Ar plasma gas was used. Furthermore, the addition of H₂ to Ar plasma gas remarkably improved the removal degrees of Si, Ni, Ge, and Sn as well as above impurities. It was found that HPAM has an excellent effect to eliminate impurities with higher vapor pressures than that of Hf metal.     

Structure and oxidation resistance of plasma sprayed Ni–Si coatings on carbon steel

Ni–Si coatings consisting of mainly NiSi₂ and NiSi were deposited on a carbon steel by air plasma spraying. Isothermal oxidation tests of the carbon steel substrates with the Ni–Si coatings at 500–800 °C have been carried out. The result indicated that a protective SiO₂-based oxide scale was formed on the surface of the coatings after oxidation. On the other hand, during oxidation, phase transformation occurred among the NiSi₂, NiSi and Ni₂Si phases constructing the Ni–Si coatings. This was caused by the extraction of silicon from the silicides and the reformation of silicides at the silcide/Si-blocks interface. Above 700 °C, the outward diffusion of iron and carbon became very fast and consequently decarburization happened at the coating/substrates interface, which induced the formation of pores in the substrates near the interface. In addition, grain boundary oxidation of Cr in the steel substrate was observed above 700 °C.     

Formation phenomena of iron oxide-silica composite in microwave plasma and DC thermal plasma

Iron oxide-silica composite was synthesized using atmospheric microwave plasma and DC thermal plasma. There has recently been increasing interest in predicting the final product during vapor phase synthesis using plasma because of difficulty obtaining desirable product. In this study, vapor phase synthesis of iron oxide-silica composite from iron pentacarbonyl (Fe(CO)₅) and tetraethyl orthosilicate (SiC₈H₂₀O₄, TEOS) was conducted using various Fe/Si ratios and different types of plasma to identify the formation mechanism in the Fe-Si-O multi-component system. The morphologies and phase compositions of the synthesized particles were analyzed and compared. The results showed that the Fe/Si ratio and the type of plasma influenced the morphologies and the phase composition. A thermodynamic consideration was introduced to investigate the particle formation phenomena, which could explain the differences induced by varying the Fe/Si ratio and type of plasma. The particle formation mechanism was divided into a condensation step and a diffusion step. At the condensation step, the Fe/Si ratio determined the condensation temperature, which is related to the morphology. At the diffusion step, the quenching rate of the plasma determined the degree of diffusion, which was related to the phase composition and formation of the external layer.     

Effects of processing parameters on the refinement of primary Si in A390 alloys with a new Al–Si–P master alloy

In this study, a new Al–17Si–2.5P master alloy has been successfully prepared to refine primary Si in hypereutectic A390 alloys. By means of electron probe microanalyzer (EPMA), a large number of AlP particles can be found in the Al–17Si–2.5P master alloy. An orthogonal L₉(3³) test was designed to investigate the integrated effects of refining factors including phosphorus addition level, melting temperature and holding time, and subsequently to optimize the processing parameters. It is found that under the optimized conditions, i.e., phosphorus addition of 375 ppm, melting temperature of 800 °C, and holding time of 30 min, the average sizes of primary Si can be most remarkably decreased from 116 μm to 14 μm with sphere-like morphology. Meanwhile, the Brinell hardness and tensile strength can be significantly increased by 14.1 and 27.8%, respectively. In addition, thermal analysis is also performed with differential scanning calorimeter (DSC) to analyze the solidification process of Al–18Si alloys.     

Dry sliding wear behaviour of hypereutectic Al–Si piston alloys containing iron-rich intermetallics

The effect of iron-rich intermetallics on the wear behaviour of Al–Si hypereutectic alloys has been studied. Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 18, 51, 74 and 100 N and at a constant sliding speed of 0.3 m/s. The addition of 1.2 wt.% Fe to the LM28 alloy increased the wear rate due to the formation of needle beta intermetallics. Introducing 0.6 wt.% Mn to the iron-rich alloy changed the beta intermetallics into the modified alpha phases, and therefore reduced the detrimental effect of iron. TIG welding method as a surface melting process was applied on the iron and manganese containing alloy and led to a fine microstructure and increased the wear resistance.     

O/sub 2/ sensing properties of Zn- and Au-doped Fe/sub 2/O/sub 3/ thin films

Zn- and Au-doped iron oxide thin films have been prepared by liquid phase deposition. These films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their performance as oxygen gas sensors has been measured. It has been shown that both the Zn and Au dopants increase the oxygen response of the pure iron oxide films. The XRD and SEM results show that Zn changes both the microstructure and the particles size of the sensing layer through the formation of a solid solution with iron oxide. However, the strong increase in sensitivity to oxygen of the Au-doped Fe/sub 2/O/sub 3/ film has been related to the more favorable chemisorption of oxygen on the small gold particles at the interface with the semiconductor oxide. The results show that Au-doped iron oxide sensors are most promising for oxygen gas sensing.     

Microstructure and mechanical performance of depositing CuSi3 Cu alloy onto 30CrMnSi steel plate by the novel consumable and non-consumable electrodes indirect arc welding

A novel consumable and non-consumable electrodes indirect arc welding (CNC-IAW) with low heat input was successfully applied in depositing CuSi₃ Cu alloy onto 30CrMnSi steel plate. The indirect arc was generated between the consumable and non-consumable welding torch. The microstructure of the deposited weld was analyzed by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and optical microscopy (OM). The results showed that the dilution ratio of the bead-on-plate weld was controlled no higher than 5% and the deleterious iron picking up was effectively restrained. The deposited metal mainly consisted of ε-Cu solid solution and a small amount of Fe₂Si phase. In the interfacial zone between the deposited metal and base metal, the thickness of the zone changed from thick to thin and the microstructure changed from complex to simple from the middle to both sides. In the middle of the interfacial zone, the microstructure presented three sub-layers consisting of Fe₃Si (L)/Fe₃Si (S) + ε-Cu/α-Fe. In the both sides of the interfacial zone, the microstructure presented single α-Fe layer. The formation mechanism of the interfacial zone could be successfully explained by the formation of the Fe liquid–solid phase zone adjacent to the Fe base metal and the interfusion between Fe and Si. The average compressive shear strength reached 321 MPa and its fracture morphology mainly belonged to ductile fracture.     

The effect of Fe addition on processing and mechanical properties of reaction infiltrated boron carbide-based composites

Dense metal-ceramic composites based on boron carbide were fabricated using boron carbide and Fe powders as starting materials. The addition of 3.5–5.5 vol% of Fe leads to enhanced sintering due to the formation of a liquid phase at high temperature. Preforms, with about 20 vol% porosity were obtained by sintering at 2,050 °C even from an initial boron carbide powder with very low sinterability. Successful infiltration of the preforms was carried out under vacuum (10⁻⁴ torr) at 1,480 °C. The infiltrated composite consists of four phases: B₁₂(C, Si, B)₃, SiC, FeSi₂ and residual Si. The decrease of residual Si is due to formation of the FeSi₂ phase and leads to improved mechanical properties of the composites. The hardness value, the Young modulus and the bending strength of the composites fabricated form a powder mixture containing 3.5 vol% Fe are 2,400 HV, 410 GPa and 390 MPa, while these values for the composites prepared form iron free B₄C powder are 1,900 HV, 320 GPa and 300 MPa, respectively. The specific density of the composite was about 2.75 g/cm³. The experimental results regarding the sintering behavior and chemical interaction between B₄C and Fe are well accounted for by a thermodynamic analysis of the Fe–B–C system.

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Cr/Al复合合金化Fe_3Si基有序合金及其有序度研究

基于合金化的改性原理,以调整材料的长程有序度为改性思想,采用真空电弧熔炼/热压退火制备了四种Cr/Al复合合金化Fe3Si基有序合金。通过XRD,SEM,EPMA等对合金进行了表征,并采用长程有序参数定量表征了退火得到的有序相的有序程度。结果表明:四种不同成分的有序合金,具有不同的显微组织。随着Si含量降低合金有序度下降,且Cr/Al的复合效应对这一趋势起到了促进作用,使得具有相同Si含量的Fe65Si25Cr5Al5有序合金的有序度低于Fe3Si,分别为0.658和0.796。     

Intermetallic phases in Al-Mn alloys

The intermetallic phases present in high-purity and commercial purity Al-Mn alloys (up to 2% Mn) in as-cast and heat-treated conditions were extracted electrolytically in 10% HCl in methanol solution and identified by X-ray diffraction. As iron is known to increase the coarse cast-intermetallic particles and to cause refinement of the grain size after recrystallization, different amounts of iron (up to 0.5%) were added and the resulting intermetallic phases were extracted and identified with and without heat treatment. The unidentified phase -Al (Mn, Fe)Si, reported by Sperry and others, was recognized as corresponding for ASTM card number 6-0669 and the conditions favourable for its formation were determined. This phase may be responsible for refining the grain size after recrystallization in commercial purity alloys as compared to high-purity Al-Mn alloys and may therefore be tried as an inoculant (by adding powdered compound to liquid alloys) for grain refining.     

真空感应熔炼中的碳脱氧

应用热力学稳定性好的氧化钙耐火材料,提高精炼温度,强化碳脱氧的热力学和动力学条件,实现了几种金属材料氧的高纯净。     

Silicon effects on formation of EPO oxide coatings on aluminum alloys

Electrolytic plasma processes (EPP) can be used for cleaning, metal-coating, carburizing, nitriding, and oxidizing. Electrolytic plasma oxidizing (EPO) is an advanced technique to deposit thick and hard ceramic coatings on a number of aluminum alloys. However, the EPO treatment on Al–Si alloys with a high Si content has rarely been reported. In this research, an investigation was conducted to clarify the effects of silicon contents on the EPO coating formation, morphology, and composition. Cast hypereutectic 390 alloys (∼ 17% Si) and hypoeutectic 319 alloys (∼ 7% Si) were chosen as substrates. The coating morphology, composition, and microstructure of the EPO coatings on those substrates were investigated using scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD). A stylus roughness tester was used for surface roughness measurement. It was found that the EPO process had four stages where each stage was corresponding to various coating surface morphology, composition, and phase structures, characterised by different coating growth mechanisms.