还原气氛下渣-锍两相平衡反应

通过考察还原气氛下熔渣与锍相之间的平衡情况,研究了渣-锍两相反应的影响因素及机理,探讨了还原产物的分配规律。结果表明,熔渣碱度提高有利于锍相还原反应的进行,添加CaS抑制锍相的还原。由于锍相成分及密度不同出现分层现象,造成锍相在熔渣中的夹杂损失。CaS与金属铁具有互斥性,当熔渣中CaS质量分数超过0.9%之后,渣相中几乎没有金属铁的存在;在选取的实验条件下,CaS在渣、锍两相的平衡分配比维持在0.5左右。     

Oxidation of molten copper matte

An amount of 80 mg of molten copper matte of a pseudo-ternary Cu₂S-FeS-Fe system contained in a slender alumina sample tube was oxidized at 1503 and 1533 K in a mixed O₂-Ar gas stream and the oxidation path was followed, comparing the overall rate of oxidation with the gaseous diffusion in the sample tube. The following successive reactions were found to be controlled by gas diffusion. Initially, Fe was oxidized to form FeO. After the melt composition reached a pseudo-ternary Cu₂S-FeS-FeO system, FeS was oxidized to form FeO. As the amount of FeO increased, Fe₃O₄ was also formed and subsequently Cu was produced by the oxidation of Cu₂S. In the latter stage, the Cu was oxidized, and the final product under the condition of gas diffusion control was composed of Cu₂O, Fe₃O₄, and CuFeO₂. On the other hand, the rate of formation of Fe₂O₃, CuO, and CuFe₂O₄ was much slower and they were not formed during the oxidation duration where the overall rate of oxidation was controlled by gas diffusion.     

Kinetic study of the reaction of glutathione peroxidase with peroxynitrite

Glutathione peroxidases and their mimics, e.g., ebselen or diaryl tellurides, efficiently reduce peroxynitrite/peroxynitrous acid (ONOO-/ONOOH) to nitrite and protect against oxidation and nitration reactions. Here, we report the second-order rate constant for the reaction of the reduced form of glutathione peroxidase (GPx) with peroxynitrite as (8.0 +/- 0.8) x 10(6) M-1 s-1 (per GPx tetramer) at pH 7.4 and 25 degreesC. The rate constant for oxidized GPx is about 10 times lower, (0.7 +/- 0.2) x 10(6) M-1 s-1. On a selenium basis, the rate constant for reduced GPx is similar to that obtained previously for ebselen. The data support the conclusion that GPx can exhibit a biological function by acting as a peroxynitrite reductase.     

Vapor pressure determination of arsenic activity in a molten Cu-Fe-S matte

The activity of As in a molten copper smelting matte of composition 35.0 mass pct Cu, 35.8 mass pct Fe, and 29.9 mass pct S has been derived from vapor pressure measurements at 1336 K. The initial As doping level was 1.6 mass pct. Mass spectrometry showed the principal vapor phase species to be As₂; smaller amounts of AsS and S₂ were also present. The activity coefficient of As in the matte, γ (As), was found to have the value 0.7 ±0.2 (mole fraction)^-1 in the composition range studied. Activity values found in the present study were an order of magnitude smaller than those determined by an isopiestic method, and were about two orders of magnitude greater than those derived from measurements of As distribution between copper and white metal. The vapor pressure method is believed to be more direct and reliable; sources of error in the various methods are discussed.     

A Kinetic study of the reaction of zinc oxide with iron powder

Electric arc furnace (EAF) dusts contain significant quantities of zinc, mostly in the form of zinc oxide. This dust has been classified as a hazardous waste due to the presence of lead, cadmium, and hexavalent chromium. It is important that environmentally acceptable processes be developed to treat this waste. One possible alternative process would involve reacting the zinc oxide in the dust with either solid or liquid iron. In addition, in the carbothermic reduction processes, which have been designed to treat the dust, metallic iron is formed, and this iron can participate in the reduction of zinc oxide. In the present research, the reduction of zinc oxide by iron according to the reaction $ZnO_{(s)} + Fe_{(s)} = Zn_{(g)} + FeO_{(s)} $ was studied using a thermogravimetric technique. Briquettes of zinc oxide powder and electrolytic iron were reacted in the temperature range of 1073 to 1423 K in an argon atmosphere. First, a thermodynamic analysis was performed using the Facility for the Analysis of Chemical Thermodynamics (F*A*C*T) computational system, and then the effect of experimental variables on the reaction kinetics was determined. These variables included argon gas flow rate, reaction temperature, reagent particle size, iron to zinc oxide ratio, aspect ratio of the briquette, briquetting pressure, and alkali and alkaline earth additions. It was found that, initially, the reaction was chemically controlled with an activation energy of 230 kJ/mol. Additions, such as sodium chloride and calcium fluoride, promoted the reaction, and the activation energies were 172.5 and 188.7 kJ/mol, respectively. Once a product layer had formed, the reaction was limited by the diffusion of zinc gas away from the reaction interface. The experimental data were fitted to a parabolic rate law, and the parabolic rate constant was found to be $k_p = - 2.47 + 0.0021 T(K)$      

A study on the mechanism of reaction between refractory materials and aluminium deoxidised molten steel

The conditions of formation of inclusions in steel during ladle refining in MgO-C lined ladles have been investigated in laboratory experiments at 1873 K in MgO-C crucibles with 50 g iron. From both the experimental results as well those of a thermodynamic study conducted in parallel, the following conclusions can be made about the reaction mechanism between the MgO-C refractory and aluminium deoxidised molten steel: At steelmaking temperature an internal oxidation-reduction occurs in the MgO-C refractory. The formation of a thin oxide layer at the interface is due to the reaction between magnesium vapour and aluminium dissolved into the molten steel and the CO(g) generated by the reaction between MgO and C in the crucible walls. The oxide inclusions formed in the steel have been shown mainly to consist of MgO, Al₂O₃ or mixture of them. Some of the finest inclusions are considered to be formed as secondary inclusions during cooling and solidification of the steel and they are connected only with the diffusion of magnesium from the crucible to the molten steel. The thermodynamic calculations indicate that during vacuum refining, as the pressure decreases, the chemical compatibility of carbon-bonded magnesia for ladle lining decreases.     

Kinetic experiment of dissolving coke in molten iron

The liquid iron carburization in the blast furnace process can almost come to a saturation state, while, that in flash ironmaking process is unexpected, since there is no solid charge that will press the hot metal and no carburization reaction that occurs between the bottom deadman. In order to study the kinetics of coke dissolution into the molten iron in flash iron- making process, a series of experiments were carried out. Reduced iron powder and chemically pure graphite were used as raw materials, and the tubular resistance furnace was employed to heat the samples up to 1855K and melt them, and the high- purity N2 was injected as the protective gas throughout the experiments. The experimental results show that without regard to the factor kt of dissolution rate, the values of kt under natural convection condition are 4. 20??m/s in group 1, 5. 28??m/s in group 2 and 6. 50??m/s in group 3. On the contrary, when taking this factor into account, kt decreases with time increase and only can be controlled by the mass transfer. Besides, when there is sulfur in the iron- carbon melts, it shows that kt also decreases with the increase of sulfur content.     

Kinetics of the carbon-oxygen reaction in molten iron

The kinetics of carbon monoxide absorption by stagnant liquid iron has been investigated over the first 10 min or so of gas-liquid metal contact. On the basis of experiments conducted at temperatures ranging between 1580° and 1700°C (PCO= 1 atm) and carbon monoxide pressures ranging between 0.1 and 1.5 atm (at 1600†C), it was concluded that the absorption kinetics of CO in liquid iron was diffusion controlled. Mass transfer equations developed to describe the process were adapted to define an “apparent diffusion coefficient” of carbon monoxide. This coefficient is a function of carbon and oxygen binary diffusion coefficients, and also depends on the initial bulk oxygen and carbon concentrations, and on the equilibrium constant for the reaction. CO = C + O Experimental D_COvalues averaged at 9.8 10−⁵cm²s−¹, while binary carbon and oxygen diffusivities were computed to be 41.2 10−⁵ and 5.2 10−T⁵cm²s−¹ respectively. Using the data obtained, the relative influence of carbon and oxygen diffusion on the kinetics of carburization and decarburization reactions is quantitatively considered. Formerly Graduate Student, McGill University, Montreal, Quebec, Canada     

固态和液态钢的激光诱导等离子体比较

比较了产生于室温固态钢以及高温液态钢上激光诱导等离子体的特征、原子铁的激发温度以及电子密度。通过在386～400nm波长范围的中性铁原子发射谱线, 由波尔兹曼作图法确定了铁原子的激发温度。通过测量AlI394.4nm的谱线宽度, 估算了电子密度。对固体钢来说, 铁元素的激发温度从延迟时间为10μs时的10800K下降到延迟时间为80μs时的7300K。当延迟时间分别为10μs和70μs时, 产生于固态钢和液态钢上等离子体间的激发温度并没有显著差别。在铁元素和铝元素大部分的中性原子线中, 可以观察到液态钢的谱线宽度比固态钢的谱线宽度更窄。当激光脉冲的观察延迟时间均为10μs时, 产生于液态钢上等离子体的电子密度大约为(0.99±0.15)×10¹⁷/cm³, 这相当于产生在固态钢上等离子体电子密度的46%。     

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.     

Studies on the anodic dissolution of copper matte

Anodic polarisation studies on copper matte revealed that a copper matte electrode polariess abruptly in H,SO, solution but not in HCl solution. Anodic dissolution of copper matte was studied at various anodic potentials in 2 N solutions of HCl and H,SO,. It was found that at lower anodic potential (around 0.4 volt vs. saturated calomel electrode) copper dissolves preferentially (at 90% current efficiency) over iron (8–10% C.E.), in both the acid solutions. It was further observed that this preferential dissolution of copper takes place over a longer period (about 6 h) in HCl than in H₂SO₄ solution (about 3 h). Preferential dissolution of copper from copper matte was found to be independent of HCl concentration (0.5 N to 4 N). From the X-ray diffraction analysis of the original copper matte and electrolysed copper matte, it was established that digenite and bornite phases of copper matte dissolved causing preferential dissolution of copper.     

Kinetics of solid state silica fluxed reduction of chromite with coal

Abstract

Solid state reduction of an Australian chromite with black coal and silica addition was studied thermogravimetrically in the temperature range 1000–1400°C under an argon atmosphere. Reduction was found to occur in two stages. In the first stage, reduction is initiated by the nucleation of metallic iron, and the rate is likely to be controlled by the diffusion of cations in the outer zone of the chromite particles. The Zhuravlev–Lesokhin–Tempel'man equation was determined to fit closest to the experimental data, giving an activation energy of 194 kJ mol^-1. The second stage involves the reduction of chromium, iron, and some silicon ions through the slag. The rate of reduction is proposed to be controlled by dissolution of the chromite into the slag with an activation energy of 256 kJ mol^-1. Silica addition was found to enhance significantly the rate and degree of reduction at 1300 and 1400°C.     

不同脱砷剂钢液脱砷研究

为了充分利用我国含砷铁矿资源,采用CaO+CaF₂、CaC₂+CaF和Si-Ca-Ba合金+CaF₂对钢液进行脱砷研究,获得较高的脱砷率,其中Si-Ca-Ba合金+CaF₂脱砷效果最明显,其脱砷率最高可达67.7%.在相同实验操作条件下,通过实验室研究,分析比较了温度、传质系数和S含量对不同脱砷剂脱砷效果的影响.     

Dissolution of solid antimony in molten bismuth under static conditions

The dissolution of solid antimony in molten bismuth was studied under static and isothermal conditions using the reaction couple and immersion methods between 623 and 773 K. The dissolution of antimony under the antimony upper position, using reaction couple method, was governed by diffusion, and the diffusion coefficient of antimony in molten bismuth was obtained as follows:D _L = 2.08 X 10-⁸exp(-ll kJ mol^-1/RT), (m²/s). The dissolution of antimony under the immersed condition was governed by the natural convection resulting from the density difference in the melt, and the dissolving antimony was distributed uniformly by natural convection in molten bismuth. The apparent activation energy for the dissolution of solid antimony in molten bismuth was the same as that for the diffusion of antimony in the melt.     

Kinetic study of an enzyme-catalysed reaction in the presence of novel irreversible-type inhibitors that react with the product of enzymatic catalysis

In the present paper a kinetic study is made of the behaviour of a Michaelis-Menten enzyme-catalysed reaction in the presence of irreversible inhibitors rendered unstable in the medium by their reaction with the product of enzymatic catalysis. A general mechanism involving competitive, non-competitive, uncompetitive and mixed irreversible inhibition with one or two steps has been analysed. The differential equation that describes the kinetics of the reaction is non-linear and computer simulations of its dynamic behaviour are presented. The results obtained show that the systems studied here present kinetic co-operativity for a target enzyme that follows the simple Michaelis-Menten mechanism in its action on the substrate, except in the case of an uncompetitive-type inhibitor.