Effects of Chrome Oxide Concentrate Powder on Properties of Magnesia Composite Materials

The magnesia composite materials were prepared using fused magnesia,used magnesia chrome bricks, magnesium aluminate spinel, alumina powder and chrome oxide powder as starting materials. In order to improve the performance of magnesia composite material,the influence of chrome oxide concentrate powder on the properties of magnesia composite material was researched. The apparent porosity,bulk density,cold crushing strength,linear expansion and thermal shock resistance of the specimens were determined. The results show that adding chrome oxide concentrate promotes the formation of the composite phases of three kinds of spinel,which is beneficial to the thermal shock resistance. The magnesia chrome spinel can not be formed at high temperatures theoretically,but can dissolve in the magnesia composite material. Comprehensively,the optimal addition of chrome oxide concentrate is 10. 0 mass% for the magnesia composite materials.     

Progress of Environment-friendly Basic Refractories for Cement Industry

The chrome pollution from cement industry was introduced briefly,the research on chrome free basic refractories for cement kilns was reviewed,the production technologies of magnesia calcia,magnesium aluminate spinel,magnesia hercynite refractories,etc. were specified,the principles to improve thermal shock resistance and coating adhesiveness of refractories were analyzed,the measures to extend service life by improving production equipment and service conditions of refractories were put forward,the future of chrome free refractories was expected and some developing suggestions were given.     

水泥回转窑用含ZrO2耐火材料

含ZrO2耐火材料在水泥窑上的应用不断增加,水泥窑用含ZrO2耐火材料包括含锆白云石砖、含锆镁砖、含锆镁尖晶石砖、含锆高铝砖等.本文从材料的抗化学侵蚀性、热震稳定性、导热性和力学性能等方面讨论了ZrO2的引入对耐火材料使用性能的影响.     

A Short Communication on Refractories as Kiln Lining along Various Thermal Zones in Pre-calcining Cement Rotary Kiln

Modern cement rotary kiln is often large in size while rotating in high speed. Thermal condition within a rotary kiln is rather complex,exerting severe thermal and chemical attack on refractory of its kiln lining. In the present paper,the cause that leads to refractory failure was analyzed; requirements for refractory to overcome such failure was discussed. Composites and properties of different refractories most often used as kiln lining were assessed,including magnesia-chrome bricks,magnesia spinel bricks, dolomite bricks, silicon carbide mullite bricks and castables etc. Recommendation was made for refractories with suitable composites and properties to be used as kiln lining in each specific zone to best counteract the severe thermal conditions. A cost-effective configuration was presented to assemble kiln lining for rotary kiln's different zones in line with the regulation at JC/T 2196-2013 "Specifications of refractory for cement rotary kiln". Chromite-free refractories with property of high endurance to thermal attack and corrosion are required to be used in modern Pre-calcining cement rotary kilns.     

水泥回转窑烧成带用耐火材料的最新研究

对水泥回转窑烧成带用耐火材料的使用条件和要求进行了分析,并对近年来水泥窑用镁铬砖、镁尖晶石砖、镁钙锆砖的应用进行了探讨,指出所存在的缺点及改进措施。认为其发展方向为镁钙锆砖及尖晶石砖,并对其应用前景进行了展望,希望实现水泥回转窑的无铬化。     

富镁尖晶石对固体磷酸铝结合Al2O3-SiC浇注料性能的影响

采用致密电熔刚玉、氧化铝粉、黑碳化硅为主要原料,固体磷酸铝为结合剂,研究分别加入8%、10%、12%、14%和16%富镁尖晶石对Al2O3-SiC浇注料性能的影响。结果表明富镁尖晶石是固体磷酸铝结合Al2O3-SiC质浇注料较好的促凝剂,但其加入量不宜太多,最佳加入量为12%。     

Effects of different additives on properties of magnesium aluminate Spinel–Periclase castable

Bauxite- and alumina-based spinels were employed as refractory aggregates, and sintered magnesia fine powder, calcium aluminate cement, microsilica, and activated α-Al₂O₃ were utilized as matrices. The effects of alumina powder, analytically pure zinc oxide, and analytically pure zirconia on the properties of magnesium aluminate spinel–periclase castables were studied. The results demonstrated that the addition of the three additives promoted the sintering of magnesium aluminate spinel–periclase castables. Simultaneously, the three additives significantly improved the high-temperature properties of the samples. The thermal shock resistance of the alumina powder sample increased by 200%, that of the pristine zinc oxide sample by 75%, and that of the zirconia sample by 125%. The additives effectively improved the thermal shock resistance of the magnesium aluminate spinel–periclase castable. In addition, the slag resistance depths of the samples with alumina powder and zirconia were 41% lower than that of the sample without additives, which significantly improved the slag resistance of the magnesium aluminate spinel–periclase castable.     

Three bond modes of basic refractories used for Ruhrstahl Heraeus degassing process

Magnesia–spinel brick and unburnt periclase–spinel–Al brick are being employed as a substitution of traditional magnesia–chrome brick in the chromium-free campaign of lining materials in Ruhrstahl Heraeus (RH) degasser. These three materials are investigated, in terms of physical properties, corrosion resistance and flexibility by wedge splitting test. Tracking their physical alterations and chemical reactions through burning or heating, three bond modes are discovered. Magnesia–chrome brick is subject to a series of phase transformation with rising temperature to yield a liquid envelop around chromite-ore particles, to further form porous rim while liquid is gradually absorbed by surrounding magnesia and eventually to precipitate secondary chromite spinel lied between magnesia particles by thoroughly dissociating chrome ore. The precipitated chromite spinel functions as the featured bond that enhances hot strength and corrosion resistance to slag, and additionally liquid coexistence improves the flexibility. The direct bond mode of magnesia particles in magnesia–spinel brick endures slag penetration by immanent character of MgO. Spinel incorporation in magnesia effectively improves thermal shock resistance. Due to minor negative value of permanent linear change after reheating, further sintering (densifying) in using at high temperature would bring a risk of loosening and open joints of magnesia–spinel lining. While used in RH degasser, unburnt periclase–spinel–Al bricks undergo a miraculous process of metallic Al melting, gaseous AlN and AlON formation, MgAlON whiskers germination combined with gaseous Mg reduced, and micron-size whisker network bond domination in their matrix. Such a whisker-network bond renders the material a successful eco-friendly alternative to magnesia–chrome refractory.     

Improvement of Durability of Purging Plugs Using MgO Micropowder for Refining Ladles

To modulate the matrix of purging plugs, MgO micropowder was introduced as a replacement to magnesia powder in alumina–magnesia castables, and the effect of MgO micropowder on the properties of alumina–magnesia castables and the possibility of developing chrome‐free castables were investigated. Experimental results showed that the introduction of MgO micropowder resulted in an improvement in the volume stability, strength, and thermal shock resistance of alumina–magnesia castables due to its high surface energy and small particle size. However, excessive amounts of MgO micropowder led to a lower densification, and there was a slight degradation in the performance of the alumina–magnesia castables. The slag resistance of the prepared alumina–magnesia castables was significantly better than that of the alumina–chrome castables. Microstructure and energy spectrum analysis showed that the formation of a solidified reaction layer, mainly consisting of spinel and CaAl₁₂O₁₉, was the major cause of the observed difference in slag resistance. In addition, the alumina–magnesia castables had a lower linear thermal expansion coefficient than that of the alumina–chrome castables at each experimental temperature, which effectively decreased the thermal stress during its service period, thus exhibiting good thermal shock resistance.     

Effect of spinel content on slag attack resistance of high alumina refractory castables

High alumina refractory castables based on the Al₂O₃-MgO-CaO diagram ternary system were prepared using tabular alumina, white electrofused corundum, calcined alumina, synthetic spinel, dead-burned magnesia, dolomite, and calcium aluminate cement as starting raw materials. Two kinds of slags with 9.02 and 4.14 CaO/SiO₂ ratios were studied for slag resistance by means of crucible tests. The corrosion thickness increases with increase in magnesia content in all the designed compositions. The slag penetration decreases with increases in spinel content. Taking into account these results a refractory castable composition for its positioning into a steelmaking ladle was chosen.

Microstructural studies by SEM of samples taken from the slag line and wall in a steelmaking ladle were carried out. The correct amount of spinel required for practical applications was determined by the Al₂O₃-MgO-CaO-SiO₂ diagram quaternary system. A detailed model of the attack mechanisms is proposed.     

不同添加剂对镁质浇注料性能的影响

以电熔镁砂和高纯镁砂为主要原料制备了镁质浇注料,研究了不同添加剂对镁质浇注料性能的影响。研究结果表明,5种添加剂中,加入氧化铝微粉的镁质浇注料经1 100℃和1 500℃烧后的体积密度最大,浇注料基质中形成的方镁石/镁铝尖晶石复相结构有利于提高试样的抗热震性。加入氧化铬、铝铬渣和焦宝石的镁质浇注料,其抗热震性均高于未加入添加剂的镁质浇注料的该项性能。     

电熔镁砂加入量对钢包用铝镁质透气砖性能的影响

为了实现钢包用透气砖的无铬化,以板状刚玉(6～3、3～1、≤1mm)为骨料,板状刚玉细粉(≤0.044mm)、α-Al2O3微粉(≤5μm,d50=2.01μm)、镁铝尖晶石细粉(≤0.044mm)、电熔镁砂细粉(≤0.044mm)为基质,以纯铝酸盐水泥为结合剂,将骨料和基质的质量比固定为70:30,通过研究电熔镁砂细粉加入量(其质量分数1％、2％、3％、4％、5％)对铝镁质透气砖性能的影响,研制了铝镁质透气砖,与铬刚玉质透气砖的性能进行了对比.结果表明:加入质量分数2％的电熔镁砂细粉,试样的力学性能提高,抗热震性增强;进一步增大电熔镁砂细粉的加入量,由于原位镁铝尖晶石的生成量过多,微裂纹发展成为破坏性裂纹,试样的强度急剧降低,体积密度下降,试样的加热永久线变化增大,抗热震性先增强后减小,高温抗折强度下降.通过铬刚玉质透气砖和铝镁质透气砖性能及现场试用情况的对比,认为铝镁质透气砖可代替铬刚玉质透气砖使用,实现透气砖的无铬化.     

冲击参数对氧化铝基耐火材料常温耐磨性的影响

参照GB/T18301《耐火材料常温耐磨性试验方法》,分别以标准碳化硅砂(36#)、电熔白刚玉砂(36#)和石油支撑剂用陶粒为磨损介质,采用不同压力(300kPa、448kPa和600kPa)的压缩空气和不同量(1kg、2kg)的磨损介质对普通高铝砖(LZ-65和LZ-75)、高炉用高铝砖、磷酸盐结合高铝砖、高纯刚玉砖、刚玉莫来石砖、铬刚玉砖、赛隆结合刚玉砖、微孔刚玉砖和塑性相复合刚玉砖等10种氧化铝基耐火材料进行了磨损实验。结果表明:(1)随着冲击气体压力的增大,10种材料的磨损量都增加,但由于这些材料在组成和结构上的差异,其磨损量增加的幅度存在明显差异。(2)由于磨损介质的颗粒形状和体积密度不同,在相同的冲击气体压力下,磨损介质的流动速度不同,对材料的磨损量也不同,其中,采用碳化硅时磨损量最大,采用白刚玉时次之,采用陶粒时最小。(3)当磨损介质碳化硅砂用量增加1倍时,材料的磨损量增加,但不同材料的磨损量增加幅度不同,其中微孔刚玉砖和磷酸盐结合高铝砖分别增加了1.84倍和1.26倍,而高纯刚玉砖和高炉用高铝砖增加的不足0.4倍。(4)耐火材料的常温耐磨性能取决于其强度和结构的致密性,强度和致密度较高的材料耐磨性能较好。     

Chemical corrosion mechanisms of magnesia–chromite and chrome-free refractory bricks by copper metal and anode slag

The penetration and corrosion resistance to copper and anode slag of six magnesia–chromite and six chrome-free refractory brick types were tested using static finger tests at a typical copper-refining temperature (1300 °C). The microstructures of the as-delivered and tested refractory types were investigated by means of electron-probe micro-analysis (EPMA) and scanning electron microscopy (SEM) techniques. The results showed that the overall wear rate of the fingers was very low, with the exception of the alumina-based brick made of fused corundum and magnesia–alumina spinel, and the magnesia-based brick made of sintered magnesia and zircon addition. In all refractory types new phases were formed as a result of slag-refractory interactions. Apart from the samples recovered from the copper zone of the latest generation of direct-bonded magnesia–chromite bricks, all the rest were completely infiltrated by copper and slag components (copper oxide, iron oxide, alumina and silica). However, the amount of infiltrated liquid in the chrome-free types was higher than in the magnesia–chromite bricks. Explanations are provided for the distinct infiltration behaviour. The results show that economically viable chrome-free refractory alternatives are still elusive for anode furnace linings.     

水泥窑用耐火材料及其选择匹配

水泥窑用耐火材料有粘土砖、高铝砖、磷酸盐结合高铝质窑衬砖、镁砖、镁铝尖晶石砖、普通镁铬砖、直接结合镁铬砖等等，根据它们不同性能分别匹配于窑系统的不同部位。     

Corrosion of Disposing Urban Domestic Wastes on Refractories for Cement Rotary Kilns

Corrosion of burning urban domestic wastes to alkali-resistant bricks and spalling-resistant high alumina bricks was researched by static crucible method and SEM in order to choose refractories for cement rotary kilns for collaboratively disposing wastes. The result indicates that the main corrosion mechanism is slag permeation and corrosion; the emitted high temperature gases containing alkali,sulfur and chlorine during burning the wastes react with refractories forming low melting point sulfate,chloride and compound salts,which metamorphose the refractories,and the loose metamorphic layer is easy to spall under thermal stress. So,corrosion resistance and spalling resistance shall be taken into account when choosing refractories for cement rotary kilns for collaboratively disposing wastes. It is suggested that decomposition furnaces should adopt spalling resistant high alumina bricks and anti-coating Si C castables,and preheating equipment should adopt high strength alkali-resistant bricks and castables.     

Corrosion behavior of carbon,Al2O3, and MgO refractories during the preparation of a Ti–Si–Al alloy via the aluminothermic reduction of a Ti-bearing blast-furnace slag

The extraction of Ti from Ti-bearing blast-furnace slag (TBFS) via aluminothermic reduction to prepare Ti–Si–Al alloy has several promising applications. However, the refractories of the furnace lining can dissolve into the molten slag and change the composition of the slag, not only shortening the life of the refractories, but also influencing the preparation of Ti–Si–Al alloys for industrial applications. The main purpose of this study was to explore the corrosion behavior of refractories (carbon, alumina, and magnesia bricks) and determine the most suitable refractories for the aluminothermic reduction of TBFS. Herein, for the first time, the dissolution equilibrium of refractories during the aluminothermic reduction of TBFS and its effect on aluminothermic reduction were revealed. The results revealed that the alumina and magnesia bricks were more effective for obtaining bulk Ti–Si–Al alloy and avoiding high mass loss of the Ti–Si–Al alloy compared to the carbon bricks. Furthermore, the corrosion of alumina and magnesia bricks increased with an increase in the content of the added CaO; however, the corrosion of the alumina bricks was more severe compared to the magnesia bricks. In addition, the largest extraction ratio of Ti (maximum value: 99.85%) was achieved when magnesia bricks were employed. The results of this study indicate that magnesia bricks are the optimal refractory for the preparation of Ti–Si–Al alloy via the aluminothermic reduction of TBFS. This work provides important experimental information for the industrial application of the aluminothermic reduction of TBFS in the preparation of Ti–Si–Al alloys.     

Role of Ti and Sn ions in spinel formation and reactive sintering of magnesia-rich ceramics

The solid solubility of magnesia in magnesium aluminate spinel and magnesium aluminate spinel in magnesia does not change with temperature thus not creating bonds or precipitation over periclase grains in a single stage sintering process. In comparison, the precipitated spinels in magnesia-chromia refractories form complex spinel due to inversion in the position of bivalent and trivalent cations within the structure, making them more stable at high temperature than either normal or inverse spinel. Additives form low-temperature compounds that diffuse into the spinel structure and create defects that change the properties of spinel solid solution. In the present study, magnesia and alumina powders along with tetravalent oxide additives were analyzed for their role in reactive densification of spinel in a single stage firing process in order to achieve a better binding system for magnesia-based refractories. These tetravalent oxides on reaction with magnesia form spinel solid solution with MgAl₂O₄ as they have similar crystal structure. The spinel solid solution formed using oxide additives is expected to have higher solubility in magnesia than magnesium aluminate spinel, resulting in improvement of the bonding during sintering through increased in solid solubility at elevated temperatures followed by precipitation of secondary spinel phases, similar to the complex spinel in magnesia-chrome refractories. The formation of spinel during firing remains as a second phase that retards the grain growth of periclase. The changes in unit cell dimensions with temperature and amount of additive were analyzed using Reitveld method and correlated with the densification behaviour at different temperatures.     

常用耐火材料化学分析标准综述

介绍了国内外硅质、粘土质、高铝质、镁质、镁铬质、碳化硅质耐火材料以及刚玉的化学分析方法标准，论述了这些标准日常使用时的注意事项及适用范围。     

Synthesis and densification of magnesium aluminate spinel: effect of MgO reactivity

Stoichiometric magnesium aluminate spinel was synthesized by reaction sintering of alumina with caustic and sintered magnesia. The volume expansion of 5–7% during MgAl₂O₄ formation was utilized to identify the starting temperature of spinel formation and densification by high temperature dilatometry. The magnesia reactivity was determined by measurement of crystallite size and specific surface area. Caustic magnesia and sintered magnesia behave differently vis-à-vis phase formation and densification of spinel. Densification of stoichiometric Mag-Al spinel was carried out between 1650 and 1750 °C. Attempts were made to correlate the MgO reactivity with microstructure and densification of spinel.