Control of the manganese-oxygen reaction in pure iron melts

EMF sensor measurements using ZrO₂(CaO) or ThO₂(Y₂O₃) plug-type sensors with a Cr-Cr₂O₃ reference were performed to redetermine the Mn-O equilibrium reaction. In these experiments a strong effect of deoxidation of manganese was ascertained at saturation with solid deoxidation products. The measuring interval of the sensors at MnO saturation was limited to about 12 min due to chemical corrosion of the used Al₂O₃ sheaths. In the case of double saturation with solid MnO · Al₂O₃ (MA) and Al₂O₃ (A) the sensors could be used as long as desirable. Moreover, the combined deoxidation of the iron melt with Mn and Al was investigated. An auxiliary electrode at the tip of the sensor ensured rapid saturation of the iron melt with solid MnO or MnO · Al₂O₃ + Al₂O₃.     

Control of the aluminium-oxygen reaction in pure iron melts

Modified electrochemical oxygen sensors based on CaO-doped ZrO₂ and Y₂O₃-doped ThO₂ were developed and applied to study the aluminium-oxygen reaction in pure liquid iron with special regard to the provision of reliable experimental conditions and the attainment of true chemical equilibrium. The sensors represent valuable tools particularly for EMF long-term measurements over several hours. At 1600 °C, values of the constant and of the interaction parameters and were determined. When Fe-O-Al melts are covered with a slag phase at an activity a(Al₂O₃) < 1, e.g., CaO-saturated CaO-Al₂O₃ slag, the Al-O relationship in the iron may nevertheless be controlled by an equilibrium oxide phase at an activity a(Al₂O₃) = 1, presumably represented by inclusion particles consisting of pure Al₂O₃.     

Control of the chromium-oxygen reaction in pure iron melts

Oxygen activities in Fe-O-Cr melts, equilibrated with chromium oxide, were determined as a function of chromium content by EMF measurements using ZrO₂(CaO) plug-type sensors with a Cr-Cr₂O₃ reference. Plug-type sensors with or without Cr₂O₃ saturator were used in the experiments. From the experimental results values for the activity coefficient f_O and the interaction parameters and were evaluated. Raoultian chromium activity features a slight positive deviation from ideal solution behaviour in the temperature range from 1550 to 1650°C. Taking into account the calculated interaction parameters, the equilibrium constant K_Cr-O was redetermined at 1550 to 1650°C. In comparison with previous studies a better agreement was obtained with existing thermochemical data.     

Desulfurizing iron-carbon melts with lime under reduced pressures

Experiments were carried out to compare the rates of formation of CaS on CaO crystals which were either immersed in a sulfur-bearing, carbon-saturated iron melt or held in the effluent gases just above the melt. Temperatures ranged from 1375°C to 1600°C, and times ranged from one to twelve hours. The CaS layers were measured both metallo-graphically and with an electron microprobe. Data on the time and temperature dependence of the layer thickness are presented. These layers were about 15 microns thick after 6 h at 1460°C, independent of whether or not the crystal was immersed in molten iron. The role of lime in the desulfurization process is to act as a getter for removal of sulfur from the gas stream. W. C. PHELPS, JR., Deceased, formerly with the Department of Metallurgy and Materials Science, Purdue University, Lafayette, Ind. 47907.     

Denitrogenation of steel melts with oxygen and sulphur by injection of argon under reduced pressure

Denitrogenation of steel melts with oxygen and sulphur was studied under reduced pressure by injection of argon. The rate of nitrogen desorption was found to obey a reaction of second order. The macrokinetic rate increases with increasing Ar flowrate until bubble coalescence occurs in the melts. The effects of sulphur and oxygen on nitrogen desorption were evaluated from the experimental data. The dimensionless rate constant for nitrogen is described by . A reasonable agreement was obtained in comparison with the results of other investigators.     

Rate of nitrogen desorption from CaO-Al2O3 melts to gas phase

There is a limit to lowering the nitrogen level in steel, because of pickup from the atmosphere during and after degassing. Therefore, the nitride capacity of various fluxes has been measured in order to examine the possibility of nitrogen removal by using slag. It is necessary to take into account the nitrogen reaction rate between the gas and slag phases for the efficient removal of nitrogen in practical steelmaking processes. In this study, the nitrogen desorption rate from CaO-Al₂O₃ melts to gas phase has been examined at 1873 K. The mass-transfer coefficient of nitrogen in the melts increases as the CaO content increases, and the dependence is related to the viscosity of the melts. The reaction-rate constant of nitrogen desorption is found to be proportional to the 3/2 power of the oxygen partial pressure and increases as the CaO content increases under constant oxygen partial pressure.     

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.     

Selective removal of iron contaminations from zinc-chloride melts by cementation with zinc

An investigation into the cementation of iron chloride from a zinc-chloride melt at 400 °C has been carried out with zinc powder. The variables studied include preparation of the chloride melt and the amount of zinc added. The effect of lead, copper, and cadmium on cementation of iron has also been investigated. According to the results, it is possible to reduce the iron concentration in zinc-chloride melts to 20 ppm with a small excess of zinc. The preparation of the melt proved to be very important. Insufficient purification of the melt with respect to oxides, hydroxides, and water resulted in a low reaction rate and high residual iron concentration.     

Settling of undissolved zirconium particles in pure magnesium melts

Zirconium is a remarkable grain refiner for magnesium alloys and is currently introduced into magnesium alloys primarily in the form of a Mg–Zr master alloy (Zirmax^® a Mg–33.3Zr alloy supplied by Magnesium Elektron). Owing to the difficulties of attaining complete dissolution, undissolved zirconium particles are often observed in Zirmax^® alloyed magnesium microstructures in the form of both isolated individual particles varying from submicrometre to greater than 10 μm, and various sizes of clusters that contain a number of zirconium particles. Aimed at improving the alloying efficiency with Zirmax^® and eliminating these undesirable large zirconium inclusions prior to pouring, this paper provides a detailed theoretical and experimental study of the settling behaviour of undissolved zirconium particles in pure magnesium melts. Various characteristics of the settling behaviour of zirconium particles are clarified based on the good agreement achieved between the experimental observations and theoretical predictions. In addition, it is also shown that wet chemical analysis of the total zirconium content in samples taken after different settling times at temperature can be an effective approach for evaluating the settling behaviour of undissolved zirconium particles in pure magnesium melts.     

Vaporization of iron and phosphorus from iron-phosphorus melts in oxygen-bearing gas streams

Experiments have been made to demonstrate that when an oxygen-bearing gas is blown on the surface of iron-phosphorus melts, iron and phosphorus vaporize at rates enhanced by vapor-gas phase reactions. These findings are in accord with the theoretical predictions. The reaction mechanism considered is based on the concept of vaporization of phosphorus at the surface of iron as volatile PO and PO₂, which then react with iron vapor and oxygen in the gas close to the surface of the melt. If powdered lime were present, as in the Q-BOP, a relatively stable calcium phosphate would form, thus bringing about dephosphrization. From the available thermodynamic data and reaction-equilibrium data, equilibrium constants have been derived for the reaction of PO and PO₂ with liquid iron.     

Some properties of reduced iron powder manufactured from Mill-scale

Conclusions Some key data are presented on the properties of iron powder reduced with a solid reducing agent from low-carbon steel mill-scale and on the mechanical characteristics of specimens pressed from this powder and sintered in hydrogen and dissociated ammonia atmospheres. The properties of iron powder manufactured by the process described meet the requirements of powder metallurgy.Translated from Poroshkovaya Metallurgiya, No. 3 (135), pp. 102–106, March, 1974.     

载金炭常压、无氰、乙醇蒸馏解吸工艺的改进

针对载金炭经常压、无氰、乙醇蒸馏解吸工艺处理后,解吸炭品位仍较高的问题,通过工业试验,找出了载金炭解吸过程中最有效的时间段,提出了把一次完整的解吸过程分成两段的新方法。对新方法中两次解吸条件的异同做了讨论,在此基础上对常规常压、无氰、乙醇蒸馏解吸工艺进行了改进。工艺改进后,单筐载金炭解吸时间从12~16h缩短到9h,尾炭品位从150g/t左右普遍降至30~50g/t,单塔日解吸载金炭量从200kg上升到300kg。该工艺已应用于云南某金矿的实际生产,效果良好。     

A new interpretation of mechanisms of nitrogen desorption from liquid iron

Mechanisms of nitrogen desorption from liquid iron were discussed in detail. It is proposed that association of nitrogen atoms at the surface to form a molecule occurs by two separate mechanisms operating in parallel: single site mechanism meaning that an adsorbed atom reacts with an atom coming from the bulk using one adsorption site, and dual site mechanism meaning that two adsorbed atoms diffuse to and react with each other over two adsorption sites, and that association via these two parallel mechanisms is rate controlling for the interfacial reaction of nitrogen desorption. A model for the second order rate constant of nitrogen desorption from liquid iron was theoretically derived, and was found to be in close agreement with the results reported in literature, for both normal pressure and reduced pressures.     

Contact reaction of graphite with liquid iron and iron base melts

Conclusions A study was made, by a sessile drop technique involving simultaneous heating of the specimen and the base plate, of the interfacial reactions at the melt/graphite interfaces in the systems iron/graphite, iron-carbon-containing melt/graphite, iron-copper/graphite, iron-tin/graphite, iron-germanium/graphite, iron-gallium/graphite, and iron-aluminum/graphite. It is shown that the strength of the bond between the phase in contact in the systems investigated (except the system iron-aluminum/graphite) is determined by the work of adhesion linked with the departure of the system from a state of equilibrium. A relationship has been found between isotherms of wetting of graphite by the melts investigated and the effects of tin, germanium, gallium, and copper on the solubility of carbon in the relevant ternary systems. It is demonstrated that, for systems characterized by carbide formation (the system iron-aluminum/graphite), an isotherm of wetting of graphite by melts represents a complex dependence on melt composition.Translated from Poroshkovaya Metallurgiya, No. 6 (138), pp. 64–71, June, 1974.