Si在纯Fe及低硅钢中扩散行为

采用磁控溅射方法,分别在纯Fe以及低硅钢基片上沉积富Si膜,并对其进行真空扩散热处理.通过能谱分析及X射线衍射研究了Si在纯Fe与低硅钢基体中的扩散特征,运用DICTRA软件建立了扩散模型.研究发现Si在纯Fe基体中扩散时发生γ-Fe(Si)→α-Fe(Si)相转变,扩散速率受控于相界面的迁移.当沿截面Si含量梯度不足以驱动相界面正向迁移时,延长扩散时间会发生相界面回迁现象,最终趋于单一相内均匀化扩散过程.Si在低硅钢基体中的扩散符合Fick扩散第二定律.     

Kinetics of iron oxide reduction from CaO-MgO-FeOn-SiO2 slags by silicon dissolved in liquid iron

At steelmaking temperatures, the kinetics of slag-metal reactions is usually determined by mass transfer. This occurs in two ways: normal mass transfer which is induced by stirring, and mass transfer by interfacial convection induced by interfacially active elements like oxygen and sulphur. In the present work, mass transfer during the reduction of iron oxide from a basic slag by silicon dissolved in liquid iron was studied under defined conditions of gas stirring by argon in MgO crucibles with 1500 g iron and 250 g slag. The variations of the FeO content in the slag and the silicon content in the iron during the reaction were measured by sampling. Trials were carried out with stirring gas flow rates between 1 and 20.4 l/h(STP). The experimental data were evaluated with the multi-component transport model in order to determine the mass transfer coefficients of the reaction components. Simultaneously, the coefficients of normal mass transfer were calculated with the boundary layer theory of liquid-liquid mass transfer for non-turbulent flow conditions. The measured mass transfer coefficients were by a factor 2.5 larger than the theoretically calculated. The difference indicates the presence of mass transfer by interfacial convection. Mass transfer by interfacial convection is superimposed to normal mass transfer.     

Diffusion of silicon in aluminum

Interdiffusion coefficients in Al-Si alloys were determined by Matano’s method in the tem-perature range from 753 to 893 K with the couple consisting of pure aluminum and an Al-Si alloy. Temperature dependence of the impurity diffusion coefficients of Si in Al, obtained by extrapolation of the concentration dependence of the interdiffusion coeffi-cient to zero mole fraction of Si, is given by the following equation: DSi/Al = (2.02^+0.97 _-0.66 × 10^-4 exp [-(136 ±3) kJ mol^-1/RT] m²/s. p ] The Kirkendall marker was found to move toward the Si-rich side, indicating that the Si atom diffuses faster than the Al atom in Al-Si alloys. From the interdiffusion coeffi-cient and the marker shift, the intrinsic diffusion coefficients were calculated. The difference in the activation energies (ΔQ) between the impurity diffusion of Si in Al and the self-diffusion of Al was estimated by means of the asymptotic oscillating po-tential and the Le Claire theory. The calculated value of ΔQ is in fair agreement with the experimental value. The vacancy-solute binding energy for Si in Al was also dis-cussed based on the diffusion data. formerly Undergraduate Student, Tohoku University     

Kinetics of mass transfer of manganese and silicon between liquid iron and slags

The kinetics of mass transfer of Mn and Si between liquid iron and slags were investigated in laboratory experiments at 1600°C in MgO crucibles with 1500 g iron and 250 g slag. Three different slags consisting of CaO-MgO-MnO-SiO₂, MgO-MnO-SiO₂ and MgO-MnO-Al₂O₃-SiO₂ were used. The concentration-vs.-time curves, experimentally measured under defined flow conditions generated by gas stirring, were evaluated by application of a multi-component transport model in order to obtain the mass transfer coefficients. The numerical values of the thus determined measured mass transfer coefficients were compared with values calculated by a theory of mass transfer at liquid-liquid interfaces. The measured and theoretical values were in good agreement with each other in the case of reduction of MnO from the slag by Si in the metal, provided that the measurements had been carried out below a critical stirring intensity, above which metal droplets were emulsified in the slag. Experiments, where sulphur was dissolved in the metal melt and where the sulphur contents were systematically varied, showed no changes of the mass transfer coefficient in comparison to sulphur-free melts. The experimental mass transfer coefficients for the reduction of silica from the slag by manganese in the metal were smaller than those calculated by the mentioned mass transfer theory. This could be explained by inhibition of surface renewal under the influence of solid reaction products precipitated at the interface.     

Rates of dissolution of solid iron,cobalt, nickel,and silicon in liquid copper and diffusion rate of iron from liquid Cu-Fe alloy into liquid copper

Consideration is given to the previously reported data on the observed dissolution rate of the vertical peripheries of cylindrical iron, cobalt, and nickel in liquid copper at temperatures in the range of 1468 to 1653 K under natural convection. The observed steady-state rate is close to the rate calculated from an equation expressed in terms of the activity of solute for dissolution rate controlled by mass transfer through a boundary layer in the liquid. The dissolution rate of the horizontal bottom face of cylindrical cobalt in liquid copper is determined at 1573 to 1574 (±6) K in the absence of fluid flow. The decrease in height of the cylinder, z(m), obeys z = α √t where t is time (s) and α is 4.18 × 10⁻⁶ m · s^−1/2. This value is in close agreement with the calculated one based on an equation expressed in terms of the activity of solute for dissolution rate controlled by non-steady-state diffusion in the liquid. Experiments have been carried out to explore the dissolution rates of one vertical edge of a square silicon plate and the horizontal bottom face of a silicon disk in liquid copper at ∼1473 K. The rate at the lowest part of the vertical edge ranges from 39 to 69 mol · m⁻² · s⁻¹, and the calculated rate based on the former equation is close to the average of the maximum and minimum observed values. The ratios of these observed dissolution rates to those of iron, cobalt, or nickel under natural convection are in the range of 74 to 910. In the dissolution of the horizontal bottom face, the value of α is estimated from another equation in which the densities of solid and liquid different from each other and the activity of solute are taken into account. This estimated value is in the range of the observed ones. The total amounts of iron diffused from liquid Cu-Fe alloy into liquid copper within capillaries at 1574 K are determined. Their average is expressed as a function of the activity of iron.     

Diffusion of hydrogen in iron

A mass spectrometer was used to study hydrogen diffusion and trapping phenomena in fullyannealed and slightly cold-worked pure iron specimens which were in contact with distilled water or dilute acidic Buffer solutions. In the case of fully-annealed iron and slightly coldworked iron, hydrogen can diffuse into iron only when the iron contacts water directly. This diffusion phenomenon of hydrogen increased markedly with temperature and was accelerated by abrasion and hydrogen ion concentration in dilute acid. Abrasion and hydrogen ions in a dilute acidic Buffer solution did not affect the diffusion coefficient of hydrogen,D, but increased the hydrogen concentration at the iron surface contacting water or Buffer solution,C _s . The permeability of hydrogen in fully-annealed iron in contact with distilled water and the diffusion coefficient of hydrogen in fully-annealed and slightly cold-worked iron for the temperature range 10° to 100°C were measured. Trapping parameters in the slightly cold-worked iron were calculated.     

Influence of iron and silicon on the phase composition and structure of heat-resistant casting nikalines strengthened by nanoparticles

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system is analyzed as applied to heat-resistant nikalines (aluminum alloys of a new generation based on Ni-containing eutectic), which are strengthened by the Al₃Zr (L1₂) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat-resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).     

二溴对硝基偶氮氯膦光度法测定硅铁中铁

在0.072 mol/L的盐酸介质中,显色剂二溴对硝基偶氮氯膦与铁发生显色反应,形成了摩尔比为2∶1的络合物。该络合物的最大吸收波长位于610 nm处,铁量在0.14~0.80μg/mL范围内符合比尔定律,测得络合物的表观摩尔吸光系数为1.63×104L.mol-1.cm-1。所拟方法用于硅铁标样中铁的测定,测定值与认定值相符,RSD在1.4%~2.1%之间(n=6)。     

Diffusion bonding of silicon nitride to

In this article, the results are presented of an investigation dealing with diffusion bonding of hot-pressed silicon nitride to austenitic stainless steel AISI 316 without the use of a metallic interlayer. Experiments were carried out in vacuum, and it was found that under specific con- ditions, permanent joints can be obtained. Optical microscopy and electron probe microanalysis (EPMA) reveal that the reaction layer formed during the diffusion bonding process consists of a porous zone extending into the ceramic and a diffusion zone extending into the steel. Both zones are similar in chemical composition and contain mainly Fe, Ni, Cr, and Si, whereas the pores appear to contain molecular nitrogen. The formation of the reaction layer can be explained in terms of the decomposition of the silicon nitride, which is promoted under diffusion bonding conditions in vacuum. The free silicon generated by the decomposition reaction diffuses into the steel, whereas the nitrogen is trapped in pores. It appears that the strength of the joint is determined by the residual stresses which develop as a result of the thermal mismatch between the ceramic and the steel. The porous zone has a beneficial influence on the strength, because it partly accommodates the residual stresses.     

Diffusion in Bcc iron base alloys

Using radiotracer techniques, volume diffusion measurements have been carried out in the bcc phases of the following systems: Iron containing 0 to 20 wt pct Cr, Iron containing 0 to 20 wt pct V, and Iron containing 0 to 6 wt pct Ti The activation energies and frequency factors were found to decrease with increasing solute content. A comparison is made between the experimental results and theoretical calculations in terms of the various relationships between activation energy, entrogy, and frequency factor.     

基于神经网络的高炉铁水硅含量预报模型的研究

根据RBF神经网络具有收敛速度快和全局优化的特点,建立了RBF网络模型,并将其应用对高炉铁水硅含量预报。监于铁水硅含量与炉缸温度之间的密切相关性,通过铁水硅含量来间接地反映炉内温度变化。采用MATLAB中的Newrbe函数进行函数逼近,对高炉一段连续时期内正常生产的数据的归一化处理后进行训练和仿真,提高了铁水硅含量预报的命中率。高炉冶炼运用先进的RBF人工神经网络预报模型,能预报铁水硅含量的高低,判断炉温走势,实现炉温调控,有利于节能降耗,并可监测多个主要控制对象,为高炉操作提供指导。     

Kinetics of chromium oxide reduction from a basic steelmaking slag by silicon dissolved in liquid iron

The reduction of chromium oxide from a basic steelmaking slag (45 wt pct CaO, 35 wt pct SiO₂, 10 wt pct MgO, 10 wt pct A1₂O₃) by silicon dissolved in liquid iron at steelmaking temperatures was studied to determine the rate-limiting steps. The reduction is described by the reactions: (Cr₂O₃) + Si = (SiO₂) + (CrO) + Cr [1] and 2 (CrO) +Si = (SiO₂) + 2 Cr [2] The experiments were carried out under an argon atmosphere in a vertical resistance-heated tube furnace. The slag and metal phases were held in zirconia crucibles. The course of the reactions was followed by periodically sampling the slag phase and analyzing for total chromium, divalent chromium, and iron. Results obtained by varying stirring rate, temperature, and composition defined the rate-limiting mechanism for each reaction. The rate of reduction of trivalent chromium (reaction [1] above) increases with moderate increases in stirring of the slag, and increases markedly with increases in temperature. The effects of changes in composition identified the rate-limiting step for Cr⁺³ reduction as diffusion of Cr⁺³ from the bulk slag to the slag-metal interface. The rate of reduction of divalent chromium does not vary with changes in stirring of the slag, but increases in temperature markedly increase the reaction rate. Thus, this reaction is limited by the rate of an interfacial chemical reaction. The reduction of divalent chromium is linearly dependent on concentration of divalent chromium, but is independent of silicon content of the metal phase.     

Dielectric characteristics of silicon nitride powders in the SHF range

Conclusions The dielectric properties of silicon nitride are strongly affected by the presence of impurities, in particular oxygen. The dielectric permittivity of silicon nitride, calculated from data yielded by measurements at a frequency of 9.5 GHz, is 6.3–7.1, and the tangent of its dielectric loss angle, (5.3–9.7) · 10^–3.Translated from Poroshkovaya Metallurgiya, No. 9(213), pp. 62–70, September, 1980.     

The effects of silicon on the reaction between solid iron and liquid 55 wt pct Al−Zn baths

The effect of various silicon levels on the reaction between iron panels and Al-Zn-Si liquid baths during hot dipping at 610°C was studied. Five different baths were used: 55Al−0.7Si−Zn, 55Al−1.7Si−Zn, 55Al−3.0Si−Zn, 55Al−5.0Si−Zn, and 55Al−6.88Si−Zn (in wt pct). The phases which formed as a result of this reaction were identified as Fe₂Al5 and FeAl3 (binary Fe−Al phases with less than 2 wt pct Si and Zn in solution),T1, T2, T4, T8, andT _5H (ternary Fe−Al−Si phases), andT _5C (a quaternary Fe−Al−Si−Zn phase). Compositional variations through the reaction zone were determined. The phase sequence in the reaction zone of the panel dipped for 3600 seconds in the 1.7 wt pct Si bath was iron panel/(Fe₂Al₅+T ₁)/FeAl₃/(T _5H+T _5C)/overlay. In the panel dipped for 1800 seconds in the 3.0 wt pct Si bath the reaction zone consisted of iron panel/Fe₂Al₅/(Fe₂Al₅+T ₁)/T ₁/FeAl₃/(FeAl₃+T ₂)/T _5H/overlay. In the panel dipped for 3600 seconds in the 6.88 wt pct Si bath the phase sequence was iron panel/Fe₂Al₅/(Fe₂Al₅+T1)/(T1+FeAl3)/(T1+T2)/T2/T8/T4/overlay. The growth kinetics of the reaction zone were also studied. A minimum growth rate for the reaction zone which formed from a reaction between the iron panel and molten Al−Zn−Si bath was found in the 3.0 wt pct Si bath. The growth kinetics of the reaction layers were found to be diffusion controlled in the 0.7, 1.7, and 6.88 wt pct Si baths, and interface controlled in the 3.0 and 5.0 wt pct Si baths. The presence of the interface between theT2/T5H, Fe2Al5/T ₁, orT ₁/FeAl₃ phases is believed responsible for the interface controlled growth kinetics exhibited in the 3.0 and 5.0 wt pct Si baths.