State-of-the-art alumino-silicate refractories for al electrolysis cells

The refractory material of choice for aluminum cell bottom linings worldwide is alumino-silicates, due to high availability, relatively low cost, and empirically good performance. During operation of aluminum electrolysis cells, the alumino-silicates are subjected to infiltration and attack by molten electrolyte components. The penetration of sodium and molten fluorides through the cathode causes significant mineralogical transformation in the refractory, and, in extreme situations, it may terminate the pot life. This paper reviews the current understanding of deterioration mechanisms for refractory materials used in bottom lining of aluminum reduction cells. The silica content of the alumino-silicate refractories is the major single factor affecting deterioration rates through the formation of viscous melts and a glass-like barrier in the reacted lining. In addition, reactions between metallic sodium and alumino-silicate refractories may cause volume expansions in the exposed lining. The present review concludes that firebricks with an optimum silica content are probably still the best penetration barriers available.     

小型铁液包的保温设计

国内铸造厂使用的小型铁液包通常使用单层耐火材料包衬,铁液在这种铁液包中温度下降很快。为了减缓铁液在浇注过程中的温降,设计了一种新的小型铁液包包衬结构,使用3种导热系数耐火材料制作包衬。结果表明,3层耐火材料包衬设计,减缓了铁液在浇注过程中的温降,对浇铸温度提高和节能减排效果显著。在相同工况下,3层包衬的铁液最终浇铸温度比单层包衬高29℃。     

高铬刚玉涂料及防粘砂机理研究

试验了醇基高铬刚玉粉涂料并在铸钢生产中应用,采用电子探针分析了高温钢液作用过的涂层断面结构,探讨了其防粘砂机理。结果表明,这种涂料有较好的防粘砂效果;发现了钢液表面的FeO和砂型中的水玻璃向涂层中渗透,涂层中耐火骨料颗粒表面熔融,烧结成彼此相连的大块状,骨料间隙填充硅酸铝、铁、钠玻璃相,形成一定厚度的致密隔离层,有效地防止了钢液的渗透。     

The effect of the addition of fine andalusite particles in refractory bricks on gaseous corrosion

In the past, the mechanisms of corrosion in refractory materials used in the flue wall of anode baking furnaces have been poorly understood. To better understand the processes of degradation, a study of corroded refractories from anode baking furnaces was conducted. This study found that all refractory bricks contain fine andalusite particles in the matrix and fireclay as aggregates. The first stage of corrosion is the penetration of gaseous sodium, coming from recycled anodes, through the porosity of materials. Then, at high temperature, sodium becomes oxidized and is included in the liquid phase. The sodium-rich liquid phase corrodes the refractory material, in particular mullite networks. To understand why the andalusite mineral is used in the refractory materials, a corrosion test able to simulate the gaseous corrosion of materials at laboratory scale was developed. Several recipes, composed of andalusite or fireclay, were submitted to the corrosion test. The microstructural observations showed that the matrix is more sensitive to corrosion. Thus, the use of a raw material such as andalusite in the matrix is advised in order to reduce the gaseous sodium corrosion of fireclay based bricks.     

The technological properties of molten slag an-ShT2

Conclusion Heating in molten slag AN-ShT2 with no iron oxide at 780–880°C has the following advantages as compared with heating in molten chlorides: decarburizing and corrosion of the parts is prevented, and distortion due to quenching is substantially reduced; cold and wet parts can be placed in the bath without danger of spatter from the hot slag.Certain disadvantages of slag AN-ShT2 as an agent for heating parts should also be noted. The high viscosity and low fluidity increase the carryout as compared with molten salts; the heating rate in the slag bath, and consequently its throughput, is lower. The intensity of the attack of slag AN-ShT2 on refractory materials excludes its use in electrode baths with refractory linings. Since iron oxide sharply impairs the properties of the slag, the crucibles, thermocouple jackets, quenching apparatus, and molds for pouring off the slag must be manufactured from heat resistant steel. The molten slag has a narrower range of operating temperatures (780–880°C) than the chlorides used in medium-temperature salt baths (700–950°C).All-Union Scientific-Research Tool Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 2–6, December, 1971.     

Corrosion in potlining refractories: Effect of cathode material interpreted using a unified approach

The corrosion chemistry of aluminosilicate potlining refractories has been studied using a post-mortem approach that considers both metallic sodium and molten bath as the corrosive agents. This article describes the results, which show that the cathode block material has a significant influence on the type of corrosion involved. Cells containing semi-graphitized cathode blocks are more susceptible to the attack of their refractory potlining by the action of the molten bath. The use of amorphous blocks in such cells promotes the corrosion of their potlining refractories mostly by the action of the metallic sodium. For more information, contact C. Allaire, école Polytechnique (CRIQ campus), Department of Engineering Physics and Materials Engineering, 8475 Christophe-Colomb Street, Montréal, QC, H2M 2N9, Canada; claude.allaire@polymtl.ca.     

Sodium-beta alumina batteries: Status and challenges

This paper provides a review of materials and designs for sodium-beta alumina battery technology and discusses the challenges ahead for further technology improvement. Sodium-beta alumina batteries have been extensively developed in recent years and encouraging progress in performance and cycle life has been achieved. The battery is composed of an anode, typically molten sodium, and a cathode that can be molten sulfur (Na-S battery) or a transition metal halide incorporated with a liquid phase secondary electrolyte (e.g., ZEBRA battery). In most cases the electrolyte is a dense solid β″-Al₂O₃ sodium ion-conducting membrane. The issues prohibiting widespread commercialization of sodium-beta alumina technology are related to the materials and methods of manufacturing that impact cost, safety, and performance characteristics.     

锆英石对镁钙质耐火材料性能的影响

镁钙质耐火材料是一种强碱性耐火材料,对碱性炉渣和钢液具有良好的化学稳定性,且有利于钢液的脱磷、脱硫,以及钢液的净化,但由于CaO的易水化性使镁钙质耐火材料的使用受到了限制。实验选用6种不同锆英石的加入量,采用两种不同的烧结方案,对添加锆英石后的镁钙质耐火材料的性能进行了研究。结果表明,添加锆英石后的镁钙质耐火材料烧结性能提高,显气孔率降低,体积密度增大,荷重软化温度提高,抗渣性增强。     

91W-6Ni-3Fe难熔合金、TiAl合金和铁基合金在熔铝中的耐腐蚀行为(英文)

采用静态浸没腐蚀试验研究91W-6Ni-3Fe难熔合金(91W)、TiAl金属间化合物和两种常用铁基合金(QT700和H13 钢)在750℃铝液当中的腐蚀性能。通过3D光学显微镜、SEM、EDS 和XRD研究样品的表面形貌,腐蚀界面和相组成。结果表明:91W具有最好的耐铝液腐蚀性能,QT700次之,H13再次之,TiAl合金的耐铝液腐蚀性能最差。四种金属材料的腐蚀失重均符合抛物线规律,材料在经过一开始的加速腐蚀阶段后,腐蚀速率趋于稳定。材料在铝液当中溶解遵循扩散-反应机制,91W材料在铝液当中的腐蚀主要由扩散这一速控步骤所决定,而TiAl合金的腐蚀性能差主要是由于TiAl-(TiAl3)-Al扩散偶反应具有较低的激活能。     

Metal-Mould Reactions in casting Aluminium-Lithium Alloys in Sodium-silicate-bonded Sand Moulds

Abstract

Metal-mould reactions in casting Al-Li alloys in sodium-silicate-bonded sand moulds have been studied by the modified Gertsman technique. Molten Al-2.7% Li alloy was poured into a bottom-gated vertical cylindrical mould cavity (150 mm x 50 mm dia) made from no-bake organic-binder-based sands. At the bottom of the mould cavity, a standard AFS three-ram sodium-silicate-bonded sand sample (the test sample) was placed vertically to provide the necessary interface for investigation. After cooling, the reaction products formed at the interface and samples from the bottom portion of the castings were collected for investigation. These were analysed to find Li loss from the casting as a result of metal-mould reactions. The casting was vertically sectioned and visually observed for appearance of blow holes, if any, while the sub-surface was studied for microhardness variation. The as-cast surface and the reaction products were also studied by SEM and X-ray diffraction analysis.

The study reveals that the Li in the molten alloy enters into vigorous chemical reaction with the sodium silicate resulting in the release of metallic sodium and formation of reaction products containing αLithium aluminium meta silicate. Li is thus lost from near the surface of the casting. Probably, the sodium released causes the gas blow holes in the sub-surface of castings due to its high vapour pressure at the working temperature.     

Bi2S3-ZnO-Na2CO3体系热力学分析及应用

对Bi2S3-ZnO-Na2CO3低温熔盐体系进行热力学分析,计算了在700～1 500 K温度下体系中各反应的标准吉布斯自由能变化值(ΔG TΘ),并绘制了相应的ΔG TΘ—T图。热力学分析结果表明,在700～1 100 K温度范围内,Bi2S3中的Bi会被C还原成金属Bi进入金属相中,S将以ZnS形式进入固体物渣中。根据分析结果,在700～1 100 K温度下,以Na2CO3等钠盐为熔剂、ZnO为固硫剂、粉煤为还原剂,开展了验证试验。试验得到了直收率达98%的粗铋,S几乎100%以ZnS的形式固定在渣中,与热力学分析结果一致。     

Interactions between TiAl alloys and yttria refractory material in casting process

In this work, U-shaped yttria ceramic crucibles have been prepared to melt Ti–47Al (at.%) alloy in a vacuum induction furnace, in order to simulate the worst practical situation with respect to the interactions between TiAl alloy and yttria refractory material. The effects of superheating temperature and cooling media on the metal–crucible interface, microstructure, chemical composition and microhardness have been evaluated. The investigation demonstrates that interactions between the yttria crucible and the molten TiAl consist of slight chemical dissolution and some physical erosion and the extent of the dissolution and erosion depend on the superheating temperature. The thermodynamics of TiAl–Y₂O₃ reactions have been investigated according to the calculation of the Gibbs free energy change of the yttria dissolution reaction. The possibilities of melting and casting TiAl alloys by the use of yttria refractory material are also discussed.     

Zirconia sol-gel coatings on alumina-silica refractory material for improved corrosion resistance

The corrosion resistance of a simple zirconia (ZrO₂) sol-gel coating deposited from a highly dilute sol on an alumina-silica (Al₂O₃-SiO₂) refractory crucible material to molten borosilicate glass was investigated. The bulk density and porosity of the Al₂O₃-SiO₂ refractory substrate material measured by mercury intrusion porosimetery (MIP) were 3.3 g/ml and 38%, respectively. The porosity measurements were verified by electron microscopic image analysis, revealing that the porosity was appreciably decreased to a value of 18% for the ZrO₂ coated refractory. The corrosion loss of an uncoated refractory in molten borosilicate glass held at 1400 °C for 168 h was 27%, as measured by ASTM C621-84. A lower corrosion loss of 16% was observed for ZrO₂ coated refractory. Nanoscratch testing indicated strong adhesion of the zirconia film to the refractory materials. Microstructural analysis performed at the corroded interface regions by optical microscope and SEM/EDS suggested that the corrosion loss of the Al₂O₃-SiO₂ refractory was governed by the decomposition of the SiO₂ phase and diffusion of Al₂O₃ crystals into the molten borosilicate glass. The crystal phases present in the corroded interface regions were characterized using X-ray diffraction (XRD). The improved corrosion resistance of the ZrO₂ coated refractory to molten borosilicate glass was correlated to the reduced surface porosity and may be aided by the presence of zircon (ZrSiO₄) in the surface layer.     

Corrosion behaviour of Y2O3-ZrO2 coatings on IN713LC in a LiCl-Li2O molten salt

Hot corrosion studies were performed on superalloy specimens. The IN713LC superalloy were sprayed with an aluminized NiCrAlY-bond coat and then with an yttria-zirconia top coat. The bare superalloy reveals an obvious weight loss due to spalling of the scales by the rapid scale growth and thermal stress. The top coatings showed a much better hot corrosion resistance in the presence of LiCl-3 wt.% Li₂O molten salt when compared with those of the bare superalloy and the aluminized bond coatings. These coatings have been found to be beneficial for increasing hot corrosion resistance of structural materials for lithium molten salts.     

Der Einfluß von pH-Wert und Sauerstoffgehalt von Pufferlösungen auf das Korrosionsverhalten metallischer Werkstoffe

Influence of pH and oxygen content of buffer solutions on the corrosion behaviour of metallic materials The application of solutions to the decontamination of materials in nuclear installations is based on the condition that their corrosion behaviour is clearly understood. Since electrochemical corrosion is due to cathodic and anodic partial reactions which are influenced in different ways by the pH of hte solution and the oxygen content it is suggested that the results of electrochemical experiments with buffer solutions be used as a model for predicting the corrosion behaviour of materials in other solutions. In the tests described here potentiocinetic current-potential-curves have been traced and galvanic corrosion tests have been made. The results obtained in ascorbic acid, postassium hydrogen phthalate, ammonium citrate and acetate, sodium and potassium tartrate, ammonium hydrogen phosphate, sodium carbonate, hexamethylene tetramin, ethylene diamine enable – on the basis of summarized current-potential-curves – the metals studied to be classified in four groups characterized by clear differences concerning the influence of pH on the corrosino behaviour.     

THERMODYNAMIC CALCULATION OF INTERFACE REACTIONS BETWEEN TITANIUM MELT AND SPECIAL MOLD MATERIALS

１ＩＮＴＲＯＤＵＣＴＩＯＮＴｉｔａｎｉｕｍｃａｓｔｉｎｇｓｈａｖｅｂｅｎｗｉｄｅｌｙａｐｐｌｉｅｄｉｎｍａｎｙｒｅｇｉｏｎｓｓｕｃｈａｓａｅｒｏｎａｕｔｉｃｓ,ａｅｒｏｓｐａｃｅａｎｄｓｏｆｏｒｔｈ．Ｂｕｔｔｈｅｄｒａｗｂａｃｋｏｆｔｈｅｈｉｇｈｒｅ...     

Catalytic properties of metallic fibers fabricated by tempering of melt on a rotating heat-receiver

Metallic fibers fabricated by the method of directly suspended melt-droplet extraction are promising for application in catalysis as carriers of catalytically active compounds and as catalytic systems themselves due to their physicochemical properties, structure, surface defects, and low hydrodynamic resistance of porous permeable materials formed from them. The catalytic activity of fibers based on copper, nickel, iron, aluminum, and titanium, also containing noble, transition, refractory, and rare-earth metals, in the reaction of CO oxidation has been estimated. Among the studied samples, fibers based on copper, copper–nickel alloy, and Nichrome with addition of noble metals have been found promising to perform further studies for their application as catalysts of oxidation–reduction reactions.     

The mystery of molten metal

Recent advances in scientific understanding of high-temperature materials processing using novel experimental methodologies have shed light on the complex role of surface and interface phenomena.New in-situ studies on molten metal/solid ceramic interactions using a unique experimental complex at the Foundry Research Institute,Krakow,have revealed a number of unusual observations in materials processing at high temperatures.We present some such unusual observations and their explanation with reference to liquid metal processing of AI,Ni,and Ti,and their alloys in contact with oxide ceramics.In particular,we focus on the following aspects:primary oxidation of AI from residual water vapor or oxygen,capillary purification to remove surface oxide,substrate protection by CVD carbon,roughening due to spinel whisker formation,inclusions in castings due to mechanical detachment,floatation due to buoyancy forces,and segregation due to directional solidification,modification of the solid surface morphology by metal vapor ahead of the liquid,and the complication due to multi-component alloys melted in crucibles made from complex oxide-based ceramics.In the case of Ti,rapid reactions with oxides result in undesirable volumetric changes that create difficulty in casting high-quality Ti parts,particularly by investment casting.Nanoscale(e.g.,colloidal)coatings based on Y2O3 protect crucibles and hold ladles against such attack.Practical insights and recommendations for materials processing emerging from the fundamental studies on high-temperature interfacial phenomena have been described.     

铝及铝合金在熔融纳中的腐蚀行为

研究了纯铝、Al-Si和AL-Mg合金在350～450℃熔融钠中的腐蚀行为。采用OM、XRD、EDAX和EPMA分析了腐蚀产物的组织形貌和合金元素的分布。实验结果表明高纯铝受到轻微的腐蚀,并非完全“免蚀”。工业纯铝的腐蚀较明显,主要发生在杂质偏聚的晶界附近。铝合金的腐蚀程度取决于杂质元素尤其是硅的含量。铝中添加一定量的镁并用微量锆细化晶粒可改善合金对熔融钠的耐蚀性。铝和铝合金的腐蚀产物经测定为AINaSi相。     

钢包周转的优化研究

通过对炼钢过程中钢包周转的优化控制,缩短了钢包周转周期,确定了合理的钢包使用数量,并且加快了空包运行速度,基本上能保证红包出钢。钢包周转的优化对降低转炉出钢温度,减少钢包炉衬损耗,减少炉后后吹,特别是稳定钢水温度、保证连铸工艺的顺行、提高钢水质量和降低吨钢成本都有着重要的意义。