Interfacial phenomena between molten metals and sapphire substrate

Interfacial energies and contact angles for liquid Cu-sapphire and liquid Ag-sapphire systems as a function of O₂ partial pressure were experimentally determined using the sessile drop technique. For very low values of P_o2the variation of γ_lg is small, but at P_o2, values high enough to establish a monolayer on the liquid metal, γ_lg decreases linearly with increasing logP _o2. The slope of this line is related to the surface concentration of oxygen through Gibb's absorption equation. For various metal-sapphire systems, γ_lg is found to be a cosine function of the contact angle (θ) whereas γ_sl seems to be a linear function of (θ). A theoretical model has been developed to predict this behavior. One empirical constant relating to the free energy of formation of an interfacial compound was employed. The validity of the model has been tested for the Cu, Ag, Fe, and Ni-sapphire systems. The model has also been used to predict the effect ofP _o2on the interfacial energies and contact angle for the Co-sapphire system.     

Interfacial reaction between CO2-CO gas and molten iron oxide containing P2O5

The interfacial reaction between CO₂-CO gas and molten iron oxide containing P₂O₅ was investigated by the ¹³CO₂-CO isotope exchange technique at 1773 K with CO₂/CO=1.0. The apparent rate constant rapidly decreased with the addition of P₂O₅ up to 2.86 mol pct PO_2.5 and the Fe³⁺/Fe²⁺ ratio kept constant at approximately 0.2. By the classic site blockage model, in which the reaction only occurs on the vacant sites, and the modified site blockage model, in which the reaction occurs on the vacant sites and the sites occupied by phosphorus simultaneously, the effect of the addition of P₂O₅ was analyzed and the reaction mechanism of CO₂ dissociation was discussed. It may be concluded that the dissociation of the adsorbed CO₂ molecule is reasonable as a rate-determining step and that the effect of phosphorus on the interfacial reaction is caused by the decrease in the number of active sites with the increase of phosphorus content as a surface active element in molten iron oxide.     

Interfacial tension between aluminum and NaCl-KCl-based salt systems

Aluminum scrap is frequently remelted under a NaCl-KCl based salt flux cover to prevent oxidation, to aid in the stripping of oxide films, and to improve drop coalescence. In this process, the interfacial tension between the aluminum metal and the salt flux plays an important role. However, the measurement of interfacial tensions at high temperature is difficult and prone to errors. Therefore, an interfacial tension model, presented in this article, has been developed. The interfacial tension between aluminum and NaCl-KCl based melts does not change with the addition of chlorides or with variations in the composition of the NaCl-KCl melt. On the other hand, the addition of fluorides decreases the interfacial tension to various extents due to the adsorption of sodium and/or potassium at the interface. Addition of AlF₃ is the least effective; additions of LiF, MgF₂, CaF₂, BaF₂, or SrF₂ are moderately effective; and additions of NaF or KF are the most effective in lowering the interfacial tension.     

Cell survival at low oxygen tension and dose build-up in argon

Mammalian cells were exposed to 250 kVp X-irradiation in air, argon and nitrogen to determine whether cells irradiated when severely hypoxic have survival curves with lower extrapolation numbers (n) than their aerobic counterparts. Cells irradiated suspended in liquid showed no significant differences between values of 'n' irrespective of the gas used, neither was the sensitivity of cells irradiated in argon any greater than that of cells irradiated in nitrogen. In contrast, cells attached to glass dishes irradiated with the medium withdrawn were apparently much more sensitive in argon than in nitrogen. It has been demonstrated that the lower survival of cells irradiated in argon could have been caused by the greater photoelectric absorption in argon compared with nitrogen. When the dosimetric discrepancy was removed either by absorption of photoelectrons in liquid or by use of high energy radiations, there was no evidence that severe hypoxia during irradiation could lead to reduced values of 'n'.     

铜渣熔融氧化提铁的试验研究

某铜厂炼铜副产品铜渣中铁的含量高于40%,铁在铜渣中主要以铁橄榄石(2FeO·SiO2)和Fe3O4的形式存在,很难直接利用.本文进行了高温熔融氧化铜渣富集提取铁的研究,先将铁橄榄石中的铁组分转化为Fe3O4,再通过磁选工艺回收得到铁精矿.所得的铁精矿品位在61%以上,能够满足高炉炼铁原料的要求.     

Effect of carbon and sulphur on the surface tension of molten iron

Surface tensions of Fe‐4%C‐S alloys were measured at 1623 and 1823 K using the sessile drop technique. Thermodynamic models based on Butler's equation for surface tension of liquid alloys have been compared with experimental results. Calculated values are found to be in good agreement with those of the experimental data of the system. At the same sulphur activity, the effect of carbon on the surface tension of Fe‐C‐S alloys was found to extrude only when the sulphur content was less than 0.005 %.     

Equilibria between cerium or neodymium and oxygen in molten iron

Autoradiographs show that there is an obvious reaction between Ce and Nd in liquid iron and the MgO/CaO crucible wall. For reaching the Ce-O, Nd-O equilibrium, a long melting period and the addition of rare earth elements (RE’s) in several batches were needed to ensure the full reaction between the RE’s in the melt and crucible wall. The dissolved Ce or Nd content in iron was measured by means of radioactive isotopes¹⁴¹Ce or¹⁴⁷Nd and electrolysis in the organic electrolyte. The oxygen activity was measured by solid electrolyte sensors made of ZrO₂(MgO) tube. The relationships between the equilibrium constants and the temperatures for reactions Ce₂O₃ (s) = 2[Ce] + 3[O], CeO₂ (s) = [Ce] + 2[O], and Nd₂O₃ (s) = 2[Nd] + 3[O], as well as the corresponding thermodynamic parameters, have been determined. Formerly Graduate Student at the University of Science and Technology Beijing     

Kinetics of reactions between gases and molten alloys of iron

Abstract

Under conditions where transport in the gas phase is rate determiiling, a unified concept of reactions between gases and solutes dissolved in liquid metals may be based on the equilibrium constant for the reaction. Examples are given for reactions between the gases hydrogen or oxygen and the solutes carbon, sulphur and oxygen dissolved in liquid iron.

Résumé

Quand le transport en phase gazeuse détermine le taux de réaction, un concept unifié de réactions entre des gaz et des solutés dissouts dans un métal liquide peut être basé sur les constants d'équilibre de la réaction. Nous présentons des exemples pour la réaction de l'oxygène ou de l'hydrogène gazeux avec du carbone, du soufre ou de l'oxygène dissouts dans du fer liquide.     

Equilibria between rare earth elements and sulfur in molten iron

The equilibrium constants of Ce-S, La-S, and Nd-S in molten iron and the related interaction coefficients were determined experimentally and the following results obtained: K_CeS = 2.80 × 10^-6 e_S ^Ce = −1.88 K_LaS = 7.41 × 10^-7 e_S ^La= −1.51 K_NdS = 2.57 × 10^-6 e_Nd ^S= −1.51 In these experiments a radioactive isotope technique was used to determine the extremely low contents of the rare earth elements in the metal phase at equilibrium. In order to avoid errors caused by any partial inclusion of RE content of nonmetallic inclusions in the analytical results for the dissolved RE, the metal samples were electrolyzed in an organic electrolyte at low temperature, and the dissolved rare earth contents determined by measuring the radioactivity of the electrolyte. The dependence of the equilibrium values (concentration products) Ce-S on [pct C] in the system Fe-Ce-S-C was also determined. The interaction coefficient e_Ce ^C was determined to be −0.43. Earlier workers have obtained higher values for the Ce-S and La-S equilibrium constants than the present authors. Some explanation is offered for the difference.     

冶金用耐火材料与铁水相际间运动的电现象

钢铁冶炼过程中,耐火材料与钢液(铁水)界面间存在的电场将影响两相间的润湿、溶解以及化学反应等界面作用.为明确钢液(铁水)与耐火材料间因相对运动所引起的摩擦起电行为,进行低温流体流动带电试验和热态模拟试验.由低温流体流动带电试验可知,随着搅拌速度的增加,流体与石墨容器因摩擦起电所产生的静电电压逐渐增大;不同种类的流体因其...     

Interfacial reactions in molten Sn/Cu and molten In/Cu couples

The interfacial reactions of molten Sn and molten In with solid Cu substrate were determined by studying their reaction couples. The annealing temperature was 300 °C. The phases formed at the interface were examined by optical microscopy, scanning electron microscopy, and electron probe microscopy analysis (EPMA). The thickness of the reaction layers was measured using an image analyzer. For Cu/Sn couples, two phases, ε and η, were found. Only the Cu₁₁In₉ phase was observed at the interface of the Cu/In couples. In comparison with the results of couples of solid Sn and solid In with solid Cu substrate, their phase formation sequences were similar; however, the interfacial morphology and the reaction rates were different. For the liquid/solid couples, the reaction rate was much faster and the interface was nonplanar. A mathematic model was also proposed to describe the dissolution of the Cu substrate and the growth of the intermetallic compounds. Fast dissolution of the substrate was observed in the beginning of the reaction and was followed by a relatively slow growth of the intermetallic compounds at the interface.     

Kinetics of the reactions between silica and alumino-silicate refractories and molten iron

The rate of corrosion of silica and alumlno-silicate refractories in Armco iron melts at 1600°C was measured. A standard “immersion” technique was used under both static and dynamic conditions. It was found that the corrosion of the refractories in Armco iron melts was initially controlled by a chemical reaction process but changed rapidly to a steadystate, diffusion-controlled process. A liquid silicate product layer built up at the interface during the induction period. The steady-state rate of corrosion was independent of the oxygen content of the melt and was also found to be a linear function of the peripheral velocity of the refractory specimen. The rate of corrosion for the various refractories was measured and found to be controlled by diffusion of iron and oxygen in the silicate layer.     

Arsenic activities in molten copper and copper sulfide melts

In recent years, the concentration of the group Va elements such as arsenic, antimony, and bismuth has been increasing in copper concentrates. The elimination and recovery of these elements during the copper smelting process have presented serious problems. While the distribution of minor elements has been studied extensively, very little knowledge exists on the activities of these minor elements in copper mattes. Consequently, in this study the activities of arsenic were measured to determine activity coefficients of arsenic in the dilute solution region of molten copper, in Cu₂S saturated copper, and in copper mattes equilibrated with copper at 1423 K by a mass spectrometric Knudsen effusion technique. Formerly with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada     

The kinetics of nitrogen absorption and desorption from a plasma arc by molten iron

A plasma torch and refractory-lined furnace with a 10 kg capacity were used to study the kinetics of nitrogen absorption and desorption in molten iron. In this study, melts containing both oxygen and sulfur were used. In accord with earlier studies, a limiting rate constant of 0.020 cm/s-pct was observed at high oxygen and/or sulfur contents. At lower oxygen and/or sulfur contents, the measured desorption rates are smaller than most of the reported values and appear to be limited by mixed melt, mass transfer chemical control. Absorption of nitrogen from the plasma arc is limited by mass transfer in the melt. The dominant form of convection in the vicinity of jet impingement is surface tension driven flow. The reaction N(g)=N(pct) appears to be responsible for the enhanced nitrogen content of the melt. The nitrogen content of a melt in equilibrium with the atomic nitrogen content of an Ar-5 pct N₂ plasma jet was determined to be 0.30 wt pct or thirty times the equilibrium value. T. B. KING, formerly Professor of Metallurgy at the Massachusetts Institute of Technology, Cambridge, MA, is deceased. This paper is based on a presentation made in the T.B. King Memorial Symposium on “Physical Chemistry in Metals Processing” presented at the Annual Meeting of The Metallurgical Society, Denver, CO, February, 1987, under the auspices of the Physical Chemistry Committee and the PTD/ISS.     

低压氩气氛火花放电等离子体中铜的时间分辨发射光谱及其激发机理(英文)

抽真空充氩激发条件下,测定了Cu元素的单次火花脉冲放电时的几种原子线和离子线的放电强度随着氩气气氛压力变化的情况。它的原子谱线和离子谱线的放电信号随时间变化的峰形有很大差异。原子共振线CuⅠ324.75 nm的峰宽要大于离子线CuⅡ213.60 nm的峰宽。对于CuⅠ324.75 nm谱线,其单次放电寿命几乎与氩气压力无关,在随时间变化的峰形中包含一个初始峰和一个较大的后端拖尾峰,在氩气压力增大时拖尾峰更加明显。对于CuⅡ213.60 nm谱线,其单次放电寿命在不同氩气压力条件下有一定变化,在随时间变化的     

Elimination of copper from the molten steel by NH3 blowing under reduced pressure

Based on the finding that blowing of NH₃ gas onto molten pure copper at atmospheric pressure causes an evaporation of an enormously high rate, attempts have been made to eliminate copper dissolved in molten steel by NH₃ gas blowing under reduced pressure. Typical behaviours of molten steel when attacked by NH₃ gas are boiling, splashing and, in a violent case, slopping from the crucible. These phenomena are accompanied by an immense increase in the surface area from which volatile species are able to evaporate and may be useful for vacuum metallurgical processes. In this investigation, the decuprization experiments have been conducted to measure the rate at which the copper level in the molten steel is reduced using a vacuum induction furnace and blowing NH₃ gas through a vertical water-cooled copper nozzle. The data were represented in terms of the amount of copper transferred from the melt to the gaseous phase per unit surface area and time. According to these experiments, complete decuprization was attainable confirming selective evaporation of copper from molten steel under reduced pressure. So far as the mechanism of copper elimination by NH₃ gas, besides the enhanced vacuum evaporation of metal by the cooling effect of endothermic decomposition of NH₃, the formation of volatile copper compound was suggested from the fact that the copper could be removed down to an extra-low level of several ppm, even under a residual gas pressure of the order of 10 Torr.     

Direct reduction of iron in low temperature hydrogen plasma

Abstract

This paper describes the effects of various parameters on the reduction of hematite in the presence of microwave assisted non-thermal hydrogen plasma. The parameters include microwave power, hydrogen flowrate, pressure, microwave power density and temperature. It has been shown that hydrogen flowrate, pressure and microwave power are interrelated to effect the microwave power density that controls the plasma temperature. The experimental conditions encounter three temperatures: surrounding the sample, associated with the plasma and at the plasma/substrate interface. It has been deduced that the third one is the most effective in determining the rate of the reaction, and in the present case, activation energy of 20 kJ mol^?1 is reported.