Corrosion modeling of magnesia aggregates in contact with CaO–MgO–SiO2 slags

Ladle refining is an efficient process for improvement of quality of steel on secondary metallurgy under harsh conditions. Magnesia refractories with high purity are important raw materials for ladle lining in high-quality steel production. However, the penetration by CaO–MgO–SiO₂ slags damages magnesia refractories, which considerably limits their service life. Abundant grain boundaries in magnesia create channels for slag penetration and lead to the destruction of the structure. The effect of the microstructure on the slag corrosion behavior of magnesia aggregates requires further systematic investigation. In this study, a corrosion model was established to describe the slag penetration process of magnesia aggregates. The effects of the grain-boundary size and slag CaO/SiO₂ mass ratio (C/S ratio) on slag penetration were investigated, and the possibility of the microstructure optimization of magnesia aggregates was discussed. The results indicated that magnesia aggregates exhibited excellent slag resistance for slag with a C/S ratio above 1.5 or even 2.0. When the slag C/S ratio was lower than 1.5, the dissolution rate of magnesia decreased more rapidly with the increase in the slag C/S ratio. In addition, the much smaller grain-boundary size increased the slag penetration resistance by promoting the formation of a dense isolation layer and inhibiting further penetration processes. The calculation results agreed well with the experimental results, suggesting that the corrosion model is promising for predicting slag corrosion.     

烧结MgO在SiO2—FeO—CaO与FeS—Cu2S熔体界面区的局部侵蚀

采用坩埚法，借助自行设计的高温Ｘ射线透射影视设备，通过Ｘ射线照像主电视观察，研究了烧结ＭｇＯ材料在炉渣（ＳｉＯ２－ＦｅＯ－ＣａＯ）与冰铜（ＦｅＳ－Ｃｕ２Ｓ）界面区局部优先侵蚀过程。发现：ＭｇＯ材料在渣中ＦｅＯ形成致密的（Ｆｅ，Ｍｇ）Ｏ层，紧邻（Ｆｅ，Ｍｇ）Ｏ层形成渣膜，而界面张力流的存在使渣膜产生运动，促进渣膜层中ＭｇＯ的传质过程，加速ＭｇＯ材料的侵蚀，从而引起ＭｇＯ材料在渣－冰铜界面区局部优先侵     

Basic slag corrosion of alumina–magnesia–carbon refractory bricks containing Al and Si antioxidants

The slag-corrosion behavior of two alumina–magnesia–carbon refractories (AMC) with different antioxidants (Si and Al) has been comparatively studied by means of thermodynamic simulation and laboratory tests. A cup test (static) at 1723 K and 1873 K and dipping test (dynamic) at 1873 K were carried out using a steelmaking ladle slag. An iterative method that considers the change of the liquid's composition while it penetrates the refractory was employed for the thermodynamic calculation. The simulation as well as the static tests showed similar performance between both refractories (5% of wear at 1723 K and 6% at 1873 K). In spite of the type of antioxidant, the material with smaller particles of magnesia exhibited better performance in the dynamic test, with 55% less wear than the other AMC brick. This behavior was attributed to the faster MgAl₂O₄ spinel formation, which increased the material's cohesion, especially the matrix, during the heating stage. The Si antioxidant improved oxidation resistance, although it did not have a positive effect on the corrosion resistance of the material in any of the performed tests.     

不同熔渣对钢包铝镁铬材料渣蚀行为的影响

选取冶炼取向硅钢和铝镇静钢的精炼终渣及钢包用铝镁铬砖,采用静态坩埚法于1600 ℃×3 h下进行熔渣侵蚀试验,对渣蚀后试样作显微结构分析,并测定熔渣的化学成分和熔化温度.结果显示,随着熔渣中Al2O3含量的升高和碱度的增加,熔渣的熔点升高,粘度增加.粘度较大的熔渣与耐火材料接触后扩散较慢,对耐火材料的侵蚀和渗透减弱.并且当熔渣与耐火材料的反应产物为高熔点的CA2、CA6和MA尖晶石相且连续交错分布时,能堵塞液相扩散通道,抑制熔渣向耐火材料内部的进一步渗透.     

基于数字图像相关法的铝镁质耐火材料抗侵蚀性能研究

钢渣侵蚀是耐火材料在服役过程中的主要损毁形式之一,实际侵蚀过程难以直接观察。传统上采用蚀后分析方法来评价耐火材料的抗侵蚀能力和了解侵蚀机理,但易缺少过程信息,导致结果存在偏差。因此,本文在高温可视化系统基础上,结合数字图像相关法,选取三种典型钢渣,开展铝镁质耐火材料的渣蚀行为研究,并探讨了不同钢渣及热处理温度对材料抗侵蚀能力的影响。结果表明：碱度越低的熔渣对铝镁质耐火材料的侵蚀越严重;对铝镁质耐火材料进行1 000℃以上的热处理,可有效提高材料的抗侵蚀能力;通过数字图像相关法可以获得随时间变化的平均应变曲线和侵蚀应变云图,其中平均应变曲线可以对比铝镁质耐火材料对不同钢渣的抗侵蚀能力,侵蚀应变云图可以反映侵蚀的演变过程,两者为耐火材料渣蚀过程的表征提供了量化指标。     

Influence of Grain Phase on Slag Corrosion of Low-Cement Castable Refractories

The grain phase has a significant influence on the extent and mechanism of attack of low-cement castables with similar bond systems in a crucible corrosion test. The general corrosion mechanism, as determined by post mortem scanning electron microscopic examination of corroded samples and thermodynamic calculations for all four grain types examined (white-fused alumina (WFA), tabular alumina (TA), brown-fused alumina (BFA), and alumina-rich spinel (S)), involves initial reaction of the most penetrating slag (enriched in calcium, manganese, and iron, because these elements diffuse rapidly) with the fine alumina and calcium aluminates of the matrix. This reaction gives a CaO-rich local liquid, which can then react with each grain predominantly to form calcium hexaluminate (CA₆) and hercynitic spinel. In the WFA system, a complete CA₆ layer forms around the grain, whereas in the TA system, this layer is incomplete. In both systems, extensive penetration occurs, although corrosion is low. In the BFA system, titanates are released from the grain into the bond, leading to increased densification of the refractory, via liquid-phase sintering, and consequent low penetration. However, the resulting fluid liquid dissolves easily in the slag, so that corrosive wear is high, even though a CA₆ layer forms around the grain. In the S grain system, uptake of the rapidly diffusing cations into the spinel crystal structure leads to silica-rich and viscous local liquid, which leads to low penetration and corrosion.     

浅谈碳空比控制对合成氨系统的影响

探讨碳空比对合成氨系统的影响,认为碳空比的高低直接影响整个合成氨装置的功耗,控制适宜的碳空比在实际生产中尤为重要.进一步阐述中原大化集团有限责任公司在特殊条件下碳空比的控制.     

Corrosion Resistance Mechanism of MgO-CaO Refractories to Refining Slag

Corrosion resistance and penetration resistance of MgO-CaO materials with different CaO contents （22%, 42%, 49%, 53%, in mass）to refining AOD slag or VOD slag were investigated using static crucible technique by visual observation, SEM and XRD. The corrosion resistance and penetration resistance of speci-mens decrease with the increase of CaO content. This may be caused by the formation of C3S and C2S during the reactions between specimens and the slag. The formed C3S and C2S can restrain the further penetration to the matrix. The higher the CaO content, the more the C2S or C3S formed, the lower the porosity of the speci-mens, and the lower the penetration depth and corrosion rate. The corrosion resistance to AOD slag is better than that to VOD slag, because the reaction between AOD slag and the matrix is slighter than that between VOD slag and the matrix.     

Effect of in situ formation of Ti(C,N) on the properties of Al2O3–ZrO2–C slide plate material

Al₂O₃–ZrO₂–C slide plate was ordinarily used in sliding nozzle system because of its excellent mechanical properties and slag corrosion resistance. This study improved the slag corrosion resistance of the slide plate by the carbothermic reduction of TiO₂ and aluminothermic reduction of TiO₂ under high temperature in coke bed to generate Ti(C,N) phase in situ. The result revealed that TiC of the high melting point phase could enter into anorthite (CaAl₂Si₂O₈) of the low melting point phase, forming eutectic phase CaAl₂Si₂O₈–TiC, and improve the viscosity of the slag. Furthermore, TiC and CaAl₂Si₂O₈ captured FeO and MnO from the slag, resulting in the increase of the slag viscosity, inhibiting the penetration corrosion of the slag, and improving the slag corrosion resistance of the materials. In general, compared with the material without TiO₂ powder, the slag corrosion resistance of the material introduced 2 wt.% TiO₂ powder was increased by 24%. Meanwhile, the cold crushing strength of fired specimen at room temperature was increased by 35.6%.     

碳硫比对磷石膏分解率的影响研究

在氮气条件下,磷石膏在不同温度、碳硫比和保温时间下的分解情况不尽相同,提高煅烧温度和延长保温时间可有效的提高磷石膏的分解率。在1100℃和1150℃、碳硫比0.7、保温20 min时,磷石膏分解的分解率可达在99%以上;而在1200℃、保温5 min后,磷石膏的分解率可以达到99%以上。     

Corrosion Resistance of Fused Cr_2O_3-Al_2O_3 Grains with Different Compositions

Six kinds of Cr2O3 Al2O3 fused grains ( the mass percent of Cr2O3 was 15% ,40% ,50% ,60% ,85% and 99% ,respectively) were prepared using chrome green and Al2O3 powder as starting materials by electrofusion,named as CR15,CR40,CR50,CR60,CR85, and CR99,respectively. The corrosion resistance of the six kinds of Cr2O3 Al2O3 fused grains ( 4 1 mm) was studied using rotary slag corrosion method. The results show that: ( 1) the corrosion resistance of the fused grains increases with the Cr2O3 content and the grain size increasing; ( 2) the grains of CR99 and CR85 with higher Cr2O3 content are corroded at the slag surface layer,because FeO and Al2O3 in the slag corrode the grains; FeO reacts with Cr2O3 in the aggregates forming ( Fe,Cr) 3O4 spinel firstly,and the spinel reacts with other phases forming composite spinel; when FeO is fully consumed,Al2O3 penetrated into the grains reacts with Cr2O3 forming Al2O3 Cr2O3 solid solution on the grains surface; ( 3) for CR60,the corrosion exists both in the slag surface layer and in the penetration layer; in the penetration layer,CaO and SiO2 react with Al2O3 in Al2O3 Cr2O3 solid solution forming anorthite, gehlenite, and glass phase; the grains of CR50,CR40 and CR15 have the same corrosion mechanism with CR60 in the penetration layer.     

Translucent Polycrystalline Alumina with Improved Resistance to Sodium Attack

Reaction of sodium with polycrystalline alumina (PCA) arc tubes in high-pressure sodium lamps can limit lamp performance. The rate of degradation depends on the grain-boundary diffusion of a reaction product, aluminum, through the PCA wall. The effects of sintering aids and other dopants on the sodium resistance of PCA are investigated via accelerated lamp tests and microstructural analyses. Key material parameters for sodium resistance are the spinel (MgAl₂O₄) second phase and the grain-boundary MgO level. Eliminating spinel in the sintered body, doping with tetravalent cations to charge-compensate the Mg²⁺ solutes, and creating a second phase to absorb MgO in situ , significantly improve the resistance of PCA to sodium attack.     

FactSage热力学计算在耐火材料抗渣侵蚀性中的应用

商用热力学计算软件FactSage在耐火材料抗渣侵蚀性研究中起到重要作用,因此在耐火材料研究中应用越来越广泛。本文总结了近15年来热力学计算在耐火材料抗渣侵蚀性研究中的应用,重点介绍了耐火材料抗渣侵蚀研究中常用的热力学计算模型,分析了各种模型的原理、特点、适用情景、精确度与局限性,并给出了详细的运用实例。此外,本文介绍了热力学计算与其他方法相结合运用的实例,包含ANSYS、动力学分析、分子动力学模拟等方法,规避热力学计算的局限性,更加全面地分析熔渣对耐火材料的侵蚀行为。最后,本文对热力学计算存在的问题进行了归纳,并基于现有研究现状对其发展前景与方向进行了展望。     

熔铸AZS耐火材料的组成、性能与结构

以熔铸AZS33#、AZS36#及AZS41#为研究对象,对其化学组成、体积密度和显气孔率、气泡析出率、静态下抗玻璃液侵蚀性能和显微结构分别进行了测试.并分析了这些化学组成、物理性能和显微结构三者之间的关系.主要利用化学组成与显微结构讨论了影响熔铸AZS耐火材料的气泡析出率和静态下抗玻璃液侵蚀性能结果的原因.为熔铸AZS耐火材料在玻璃熔窑的使用提供技术参考.     

原位反应生成Sialon结合Al2O3-C材料的抗渣侵蚀机理

以电熔白刚玉、单质硅粉和石墨为主要原料,在氮气气氛下1450℃保温4h原位生成Sialon结合Al2O3-C材料,采用静态坩埚法对烧后的Sialon结合Al2O3-C材料在1600℃下进行抗渣实验.采用XRD分析氮化后Al2O3-C材料的物相组成,用SEM和EDS分别对渣蚀后材料的显微结构和成分进行分析.结果表明:Al2O3-C材料高温氮化后能够生成较多β-Sialon相和少量的SiC相;热力学分析表明,Sialon和SiC本身氧化产生的SiO2和Al2O3,溶解到渣中,降低渣的侵蚀和渗透;SEM结果表明,渣的渗透主要是沿刚玉颗粒边缘进行的,随着渗透的深入,CaO含量不断下降.