Deoxidation of Liquid Copper with Reducing O<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Flames

The rate of deoxidation of molten copper during top blowing with various reducing gases has been investigated using thermogravimetry. It was observed that the rate of deoxidation increases with an increasing flow rate of H₂ or CO and that H₂ is a more effective reducing reagent than CO. The rate of deoxidation using methane was measured for O₂/CH₄ ratios from 1.5 to 2.0. As expected, the deoxidation rate decreased with an increasing O₂/CH₄ feed ratio because the flame became less reducing. For all tests, initially there is a linear decrease in mass as oxygen is removed. However, for some experiments, after some time, a sudden acceleration in the rate of mass loss occurs. Using video and X-ray imaging, it was found that this pattern corresponded to gas evolution from within the molten copper. This finding can be explained by the sudden water vapor evolution because the hydrogen dissolved in the copper reacts with the remaining oxygen, and “boiling” takes place, leading to an enhanced stirring of the copper.     

Kinetics of deoxidation of liquid copper by graphite particles during submerged injection

Liquid copper can be deoxidized by submerged injection of inert gas in the presence of graphite particles. This paper describes the results of experiments in which approximately 20 kg copper melts were deoxidized by injection of N₂, CO₂, and air in the presence of low sulfur graphite particles. The apparent kinetics of the deoxidation process are first order with respect to the concentration of dissolved oxygen, and the concentration of oxygen in the melt could be reduced to less than 10 ppm by weight after less than 30 minutes of injection. The kinetics are consistent with mixed rate control with both mass transfer and chemical reaction rate affecting the rate of deoxidation. In these experiments, the rate of deoxidation under a graphite covering was slower when particles were injected with the gas stream than when gas was injected alone, although this result may have been influenced by the small size of the melt. Y. W. Chang, formerly Graduate Student with the Department of Civil Engineering, Mechanics, and Metallurgy, University of Illinois at Chicago 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.     

采用石油液化气进行钢液脱氧

在实验室利用石油液化气对钢中氧进行去除.研究结果表明:利用石油液化气对钢液脱氧是可行的,配合VD真空冶炼,可用于生产高碳、高质量洁净钢.钢液脱氧时,通入氩气和液化气两者的混合气体的脱氧效果优于单纯通入单一气体,钢中氧含量下降更明显,碳含量增加幅度更低.混合气体对钢液脱氧操作8 min后,钢中脱氧减慢,氧含量下降不明显.钢液脱氧的起始阶段,钢中碳含量增加较为缓慢,当钢中氧含量降低到一定水平后,钢中碳含量迅速增加.通入氩气,加强了钢液搅拌,在一定程度上抑制钢中氢含量的增加速度,促进了钢中氢的去除.     

Deoxidation of a Copper Melt by CO Gas Bubbling to Produce Oxygen Free Copper

In this study, gas bubbling was used to deoxidise a copper melt. Prior to the deoxidation of copper, a water model was developed and evaluated to investigate the characteristics of bubbles produced by air injection with nozzles of different shapes and sizes. Bubble frequency, floating velocity and diameter were measured by a high speed video camera and were compared to theoretical results. Approximately 500 g of 99.9 % pure copper was melted in a graphite crucible by induction melting under an argon atmosphere. After samples were completely melted, CO gas was introduced from the nozzle into the copper melt to achieve deoxidisation. Oxygen concentrations in the melt were reduced to less than 6 ppm by CO gas bubbling. Electrical conductivities of the samples produced by CO bubbling were between 101.6 and 102.3 % IACS.     

Deoxidatlon rate of copper droplet levitated in Ar-H2 gas stream

Levitated copper droplets, 5 mm in diameter with initial oxygen contents of 0.036 to 1.9 wt pct, were deoxidized at about 1970 K in an Ar-H₂ gas stream. The Ar-H₂ gas mixture having hydrogen partial pressure less than 4 kPa was introduced into a silica reaction tube of 11-mm ID at gas flow rates up to 2 x 10^-4 Nm³s^-1. The effects of initial oxygen content of the droplets, hydrogen partial pressure, and gas flow rate on the deoxidation process were examined. A mixed control model for the deoxidation rate involving both gas and liquid film mass-transfer resistances was combined with a thermodynamic relationship for the dissolved species in molten copper. The value of 2 × 10^-4 m 73x00D7; s^-1 was assigned to the liquid film mass-transfer coefficient of dissolved oxygen throughout all experimental conditions. Under the experimental conditions of low initial oxygen content and high hydrogen partial pressure, the liquid film mass-transfer resistance was significant. When a droplet of high initial oxygen content was deoxidized, transition phenomena from gas to liquid film mass-transfer control were noticed in the later stage of reaction. It was deduced from the present model that the accumulation of dissolved hydrogen was indispensable to these phenomena. Formerly Student     

Electrochemical deoxidation of titanium

Removal of oxygen in titanium using an electrochemical technique was examined at temperatures around 1223 K with the purpose of obtaining nearly oxygen-free titanium. Titanium and carbon electrodes, immersed in molten CaCl₂, served as cathode and anode, respectively, with an external DC source. CaCl₂ was employed to produce the deoxidant calcium and to facilitate the reaction by decreasing the activity of the by-product CaO. By applying about 3 V between the electrodes, the calcium potential in CaCl₂ was increased at the titanium cathode surface and titanium samples of the cathode could be deoxidized by the electrolytically produced deoxidant calcium or by calcium of high activity in the CaCl₂ flux. Resulting O²⁻ species, mainly present as the deoxidation product CaO in the flux, reacted at the carbon anode to form CO (or CO₂) gas which was removed from the system. Titanium wires containing 1400 mass ppm oxygen were deoxidized to less than 100 mass ppm, whereas the carbon concentration increased by about 50 mass ppm. In some cases, the oxygen concentration in titanium samples was lowered to a level less than 10 mass ppm that could be determined by conventional inert gas fusion analysis. The behavior of contaminants, such as carbon and nitrogen, is also discussed.     

“Chemical vacuum”—A concept to be refined

The concept “chemical vacuum” is discussed, as applied to the carbon deoxidation of metallic melts. Melting in an argon atmosphere, which is chemical vacuum for the reaction of carbon-oxygen interaction in a metallic melt, is shown not to be equivalent to melting in physical vacuum. For melting in an argon atmosphere, the total gas-phase pressure over a melt is important, and the fact that an unmixed gas layer is likely to exist over the molten metal surface should be taken into account. The CO content in this layer is determined by the carbon and oxygen contents in the melt.     

Effects of BOF top blowing and bottom stirring conditions on suppressing excessive oxidation

Abstract

The effects of top blowing and bottom stirring conditions during steelmaking in a 6 t basic oxygen furnace (BOF) were investigated in studies with the aim of suppressing excessive oxidation. With low oxygen feed rate and high stirring energy, the apparent partial pressure of CO P′_CO was calculated from the equilibrium of carbon and oxygen in molten steel as being <1 atm. The relationship between top blowing/bottom stirring conditions and mass transfer at the slag/metal interface was analysed. It is proposed that mass transfer at the hot spot is significantly affected by the reaching rate of oxygen to the steel bath and bottom stirring. Mass transfer at the slag/metal interface, outside the hot spot, is sufficient to allow equilibrium to be attained in combined blowing BOF processes. Thus, the oxygen that is not consumed for decarburisation is distributed between steel and slag, i.e. deoxidation from steel to slag takes place, which makes it possible to obtain P′_CO <1 atm under atmospheric conditions. The decarburisation model developed based on the analysis reproduces the suppression of excessive oxidation under a decreased, top blown oxygen feed rate and is in good agreement with results from both 6 t BOF experiments and 350 t commercial BOF operation.     

The rate of antimony elimination from molten copper by the use of Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> slag

The rate of Sb elimination from molten copper by the use of Na₂CO₃ slag was measured at 1523 K. The results obtained under the present experimental conditions show that Sb in molten copper is eliminated in a tri-valent or a penta-valent form, depending on the oxygen concentration at the slag-metal interface, and its elimination rate increases with increasing initial oxygen concentration in molten copper. The overall elimination rate of Sb is affected by the stirring condition of the molten copper, which indicates a rate control by mass transfer in that phase. The mass-transfer coefficients of Sb and oxygen in molten copper at 1523 K without external stirring were determined, respectively, to be

Desulfurization and deoxidation of Cu-S-O alloy in induction melting and solidification under argon and their rates of elimination in vacuum induction melting

Solid Cu-S-O alloy (about 150 g) containing 0.05 pct S and 0.04 pct O (by weight) was heated to 1473 or 1573 K under argon at 6.5 to 101 kPa. Desulfurization of 64 to 80 pct and deoxidation of 75 to 82 pct were observed. The extent did not depend on argon pressure, and this desulfurization and deoxidation probably occurred during melting. In the course of solidification and remelting of molten Cu-S-O alloys containing sulfur and oxygen at approximately the same concentration,i.e., 0.027 pct S and 0.026 pct O, and 0.0456 pct S and 0.0416 pct O under argon at 1.33 to 102 kPa, the percentage of sulfur removed was 49 to 75, the percentage of oxygen removed was 63 to 81, and the extent did not depend on argon pressure. The alloys containing more oxygen than sulfur before cooling,i.e., 0.0216 pct S and 0.081 pct O and 0.0185 pct S and 0.15 pct O, 73 to 90 pct of the sulfur was eliminated. Most desulfurization and deoxidation probably occurred in the course of solidification, because vigorous boiling was observed at this stage. The rates of removal of oxygen and sulfur from molten Cu-S-O alloys maintained at 1373, 1473, and 1573 K under vacuum were expressed by a first-order rate equation, and the dependence of their rate constants on the reciprocal of temperature was determined. In alloys in which pct S ≃pct O before evacuation and pct S ranges from 0.0202 to 0.042 and pct O ranges from 0.023 to 0.048, 79 to 96 pct desulfurization and 66 to 87 pct deoxidation were observed. For the alloys with pct O > pct S initially,i.e., 0.081 pct O and 0.0216 pct S, and 0.15 pct O and 0.0176 pct S, 85 to 94 pct desulfurization was observed and was close to the observed levels of desulfurization in solidification and remelting of the alloys with pct O > pct S under argon.     

Electronically driven transport of oxygen from liquid iron to CO + CO2 gas mixtures through stabilized zirconia

Transport of oxygen in the following electrochemical system was investigated;O (liquid iron) Oⁱⁿ²⁻ (in ZrO₂2−CaO) O₂ (CO + CO₂) An alumina crucible was charged with liquid iron containing 580 ± 10 ppm oxygen. A calcia-stabilized zirconia tube (closed at one end) was immersed in the liquid iron. The inside of the zirconia tube was flushed with a stream of CO + CO2 gas mixture. Oxygen was removed from liquid iron to the CO + COO₂ gas mixture without application of an external current. Kinetics of oxygen transport in this system are discussed in terms of mixed ionic and electronic conduction of the zirconia, and also diffusion of oxygen in liquid iron. The rate controlling step for this oxygen removal process was found to be transport of oxygen across a boundary layer in the melt at the melt/electrolyte interface. M. IWASE, on leave from the Department of Metallurgy, Kyoto University, Kyoto, Japan M. TANIDA, Formerly Graduate Student at Kyoto University     

熔盐中CaO浓度对O~(2-)放电过程的影响

为研究熔盐中CaO浓度对O~(2-)在石墨阳极放电过程的影响,以钛铁矿为电解阴极、石墨为阳极,以添加有摩尔百分数0～2%CaO的CaCl_2-NaCl熔盐为电解质,采用气相色谱法测试阳极气体成分。结果表明,当采用石墨为电解阳极时,阳极气体为CO和CO_2混合气。改变CaO的浓度对O~(2-)的放电路径影响显著,当CaO浓度为0～0.5%时,O~(2-)放电主要生成CO;当CaO浓度增加至1%时,O~(2-)放电主要生成CO_2;当继续增加CaO浓度至1.5%～2%时,O~(2-)放电主要生成CO。     

A Study on the Electrochemical Deoxidation Using ZrO2 Based Solid Electrolyte and a Periodic DC Voltage

An electrochemical deoxidation using a ZrO₂ based solid electrolyte was investigated to control the interfacial oxygen concentration between the molten steel and ZrO₂. The electrochemical deoxidation cell consisted of an MgO stabilized ZrO₂ and an external power supply. In a previous study with constant external DC voltage, the oxygen concentration at the interface between the solid electrolyte and the molten steel was decreased to 2.2 ppm, which was the limit caused by the cathodic over‐potential when a constant external DC voltage was applied. In the present study, a novel process of using a periodic or cyclic voltage for the electrochemical deoxidation cell was developed, to surpass this limitation caused by the over‐optential of the electrochemical cell and thus decreasing the oxygen concentration to sub‐ppm levels at the interface between the molten Fe and the solid electrolyte.     

The kinetics of deoxidation of copper and copper alloys by carbon monoxide

The kinetics of deoxidation of molten copper, Cu-50 pct Ag and Cu-60 pct Sn alloys were studied. The solid electrolyte EMF technique was used to measure the oxygen content as a function of time. The gas was introduced as bubbles emitted from various-sized orifices placed in the melt. Liquid phase mass transfer control is implied by the results for deoxidation in the range 0.05 pct oxygen down to 0.005 pct, where the chemical reaction rate is inferred to become significant in controlling the overall rate. Hughmark’s mass transfer correlation is tested and found to be useful in predicting the liquid phase mass transfer coefficient. This paper is based on a portion of the Dissertation submitted by C. R. NANDA to the Graduate School of the University of Wisconsin in partial filfillment of the requirements for the Ph.D, degree. The research was conducted while the authors were, respectively, Research Assistant and Associate Professor in the Department of Minerals and Metals Engineering, University of Wisconsin, Madison, Wis.     

CO_2替代Ar净化钢液工艺研究

通过实验室试验和工业性试验,对比在CO2、Ar作为保护性气体和搅拌用气体条件下钢中氧含量和氮含量的变化。试验结果表明,CO2作为搅拌用气体,可以降低钢中氧含量,均匀成分,降低钢中夹杂物含量。     

转炉超音速氧枪喷头磨损后的吹炼特性变化

 转炉氧枪喷头会随枪龄的增加发生不同程度的侵蚀,为了探究氧枪喷头侵蚀程度对超音速气体射流吹炼特性的影响,建立了120 t转炉及超音速氧枪的三维全尺寸几何模型,研究了氧枪喷头不同磨损角度对气体射流特性、熔池速度及壁面侵蚀的影响。发现随着磨损角度增加,射流速度衰减加快,射流核心区长度缩短,同一等速线长度缩短,射流中心最大速度和最大速度点距中心距离增大。射流动压衰减速度随磨损角度增加而加快,磨损角度由0增至20°,距喷头端面1.5 m处最大动压减小了14.84%,14 000 Pa等压线包围面积由0.038 m2减小至0.002 m2。钢液面处高速区面积随着磨损角度增加而减小,死区面积随着磨损角度增加而增大。熔池纵截面高速区域主要分布在冲击凹坑和底吹元件附近,低速区域主要分布在熔池底部,死区主要分布在熔池底部中心和炉壁下部区域。当熔池深度小于0.6 m时,顶吹气流对熔池的搅拌起主要作用,磨损角度增加,熔池搅拌能力变弱,熔池横截面高速区面积减小,低速区和死区面积增大;当熔池深度大于0.6 m时,底吹气流对熔池搅拌起主要作用,高速区面积基本不变。渣-金作用区域和底吹流股附近流体湍动能较大、壁面剪切应力较为集中,该部位耐火材料侵蚀严重。熔池壁面附近流体湍动能和壁面剪切力随磨损角度增加而降低,转炉炉衬侵蚀速度减小。     

A model for the silicon-manganese deoxidation of steel weld metals

From an analytical and theoretical study of flat and out-of-position gas metal arc (GMA) C-Mn steel welds containing varying additions of silicon and manganese, we conclude that the buoyancy effect (flotation obeying Stokes’ law) does not play a significant role in the separation of oxide inclusions during weld metal deoxidation. Consequently, the separation rate of the particles is controlled solely by the fluid flow pattern in the weld pool. A proposed two-step model for the weld metal deoxidation reactions suggests that inclusions formed in the hot, turbulent-flow region of the weld pool are rapidly brought to the upper surface behind the arc because of the high-velocity flow fields set up within the liquid metal. In contrast, those formed in the cooler, less-turbulent flow regions of the weld pool are to a large extent trapped in the weld metal as finely dispersed particles as a result of inadequate melt stirring. The boundary between “hot” and “cold” parts for possible inclusion removal is not well defined, but depends on the applied welding parameters, flux, and shielding gas composition. As a result of the intricate mechanism of inclusion separation, the final weld metal oxygen content depends on complex interactions among the following three main factors: (1) the operational conditions applied, (2) the total amount of silicon and manganese present, and (3) the resulting manganeseto-silicon ratio. The combined effect of the latter two contributions has been included in a new deoxidation parameter, ([pct Si][pct Mn])^−0.25. The small, negative exponent in the deoxidation parameter indicates that control of the weld metal oxygen concentrations through additions of silicon and manganese is limited and that choice of operational conditions in many instances is the primary factor in determining the final degree of deoxidation to be achieved.     

Copper deoxidation kinetics utilizing carbon monoxide

Gaseous deoxidation of liquid copper with carbon monoxide as the reducing gas has been examined. The reducing gas was introduced at a submerged orifice so that well characterized, single bubbles were formed. The deoxidation kinetics are determined primarily by the mass transport of oxygen in liquid copper. No effect of sulfur over the range of 10 to 200 ppm was observed. Increasing the temperature from 1113 to 1173°C slightly inhibit the kinetics of oxygen removal. Formerly Graduate Students, Michigan Technological University, Houghton, MI 49931 This paper is based on a portion of the dissertation submitted by R. J. Andreini in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Michigan Technological University.     

Mass transfer between a horizontal,submerged gas jet and a liquid

The rate of reaction between a horizontal, submerged gas jet and a liquid has been measured in a model system under conditions where mass transfer in the gas phase is rate limiting. The gas was 1 pct SO₂ in air, and the liquid was a 0.3 pct solution of hydrogen peroxide in water. SO₂ absorption rates were measured as a function of jet Reynolds number (10,000 < N_Re < 40,000) and jet orifice diameter (0.238 < d₀ < 0.476 cm). The product of the gas phase mass transfer coefficient and the interfacial area per unit length of jet trajectory, k_SO2 α was found to increase linearly with increasing Reynolds number and to be a strong function of the orifice diameter. The ratio of k_so2 α to volumetric gas flow rate was shown to be independent of Reynolds number for a given orifice diameter. Extrapolated values of k_so2 α are lower than the coefficients measured for vertical CO jets blown upward through liquid copper. Extrapolation of the measured mass transfer data to the jet conditions in copper matte converting and in the gaseous deoxidation of copper has indicated that the gas utilization efficiencies in these processes should approach 100 pct if gas phase mass transport is rate controlling.     

Copper deoxidation kinetics utilizing carbon monoxide

Gaseous deoxidation of liquid copper with carbon monoxide as the reducing gas has been examined. The reducing gas was introduced at a submerged orifice so that well characterized, single bubbles were formed. The deoxidation kinetics are determined primarily by the mass transport of oxygen in liquid copper. No effect of sulfur over the range of 10 to 200 ppm was observed. Increasing the temperature from 1113 to 1173°C slightly inhibit the kinetics of oxygen removal. R. J. ANDREINI and R. B. PHILLIPS, Formerly Graduate Students, Michigan Technological University, Houghton, MI 49931, This paper is based on a portion of the dissertation submitted by R. J. Andreini in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Michigan Technological University.