Research and Application of New Non-burned Periclase-magnesia Alumina Spinel Bricks

To meet the needs of environmental protection and promote the application of chromium-free refractories for RH refining furnaces, research on application of new non-burned periclase-magnesia alumina spinel bricks was carried out. Through laboratory research and field application, it is concluded that the non-burned periclase-magnesia alumina spinel brick can replace magnesia-chrome material, and its service life is equivalent to that of the magnesia-chrome material with reduced cost.

Effect of MgCl2 Solution Impregnation Process on Properties of Alumina-spinel Castables

In order to improve the properties of purging plugs and to prolong their service life,this work attempted to impregnate alumina-spinel castables for purging plugs in refining ladle with saturated magnesium chloride solution under vacuum.After being impregnated for the first time,the specimens were treated in two different ways:(1)dried at 110℃for 24 h;(2)heated at 600℃for 3 h.Then they were impregnated for the second time.All specimens were heated at 1550℃for 3 h,then the cold properties and the high temperature properties were tested according to corresponding standards.Test results were compared and analyzed.The results show that:after being impregnated,the specimen have both better cold properties and high temperature properties,the microstructure analysis result proves that it is attributed to in situ formed spinel.However,because MgO produced by MgCl2-6H20 decomposing above 527℃can hydrate and destroy specimen microstructure,which can make the properties of specimens impregnated in the second way get worse.By comprehensive consideration,the first scheme way is more suitable.

Effects of Several Factors on Viscosity of Alumina-spinel Slurries

The effects of several commercial dispersants,including AN 2000,ammonium polyacrylate,sodium tripolyphosphate,sodium hexametaphosphate, and of solids loading and of electro fused magnesia on rheological properties of aqueous alumina spinel slurries were studied. The results reveal that AN 2000 is the most effective one among the selected dispersants for alumina spinel slurries. With 0.5% weight of AN 2000, the 57vol% solids loading alumina spinel slurry with viscosity of 0.37 Pa·s was obtained at shear rate of 50s 1 .

Effect of spinel content on the properties of phosphoric acid bonded high alumina castables

In order to study the effect of fused spinel on the properties of phosphoricacid bonded high alumina castables, samples with different contents of fused spinel were prepared.The results show that when the contents of the fused spinel are between 8% and 16% (mass fraction),the castables have good properties. The castables overcome the shortages of the phosphoric acidbonded high alumina castables with bauxite cement as a hardening promoter. The experimentsdemonstrate that most of the service properties of the castables with fused spinel are better thanthose of the normal phosphoric acid bonded castables which use bauxite cement as a hardeningpromoter. The examination of the materials indicates that free MgO inclusions in the spinel powdercan promote the hardening of the castables.

Effect of Ultrafine Spinel Sources on Slag Resistance and Microstructure of Alumina-spinel Castables

In order to clarify the effect of ultrafine spinel sources on slag resistance and microstructure of alumina -spinel castables,using tabular alumina and spinel as coarse aggregates,tabular alumina powders,spinel powders,calcium aluminate cement,spinel containing cement,spinel micro-powder and reactive alumina ultrafines as matrix,alumina-spinel castables used for RH snorkels were prepared by changing the particle size and sources of preformed spinel.The effects of different ultrafine spinel sources (CMA72,spinel micro-powder) on the properties of alumina-spinel castables were investigated.Thermal shock resistance and slag resistance of specimens were compared by the residual strength rate (1 100 ℃,air cooling 1 cycle) and static crucible method.The microstructure and the slag corrosion resistance mechanism of the specimens were analyzed by SEM and EDS.The result shows that slag resistance of alumina-spinel castables can be improved by adding ultrafine preformed spinel,such as CMA72,and spinel micro-powder.The introduction of ultra-fine preformed spinel has little effect on HMOR of alumina-spinel castables,but has negative effect on TSR.ultra-fine and dispersive preformed spinel in the matrix and fine microstructure are the main reasons for the improvement of slag resistance of castables.

Research on Alkali Resistance of Alumina-rich MgAl2O4 Spinel for Alkali Recovery Furnace

Chrame containing refractories are a kind of traditional material for the lining of alkali recovery furnaces, but the formation of hexavalent chrome compounds will give rise to detrimental effect on environment and human＇s health. With the gradual awakening of people＇s comciousness about environment protection, it is urgent to prepare environmental-friendly materials for alkali recovery jurnaces with high quality and long life. In this paper, alumina-rich MgAl2O4 spinel （ AR90 ） was used to replace chromite. The physical properties of dried （110 ℃ for 24 h） or fired （1 300 ℃ for 3 h） AR90 and chromite were studied, respectively. The alkali vapor method was used to determine the alkali resistance of the two materials. The results show that： （1） after drying at 110 ℃ for 24 h, AR90 specimens show higher apparent porosity and slightly lower bulk density than chromite specimens; after firing at 1 300 ℃ for 3 h, AR90 has significantly higher apparent porosity as well as higher bulk density; （2） after the alkali attack, the AR90 specimens sintered at 1 300 ℃ exhibit smaller strength change and much higher compressive strength than the chromite specimens; meanwhile, the permeability degree of alkali salt in chromite specimens is more serious than that in AR90 specimens, which indicates that AR90 possesses better alkali resistance.

MgCl_(2)·6H_(2)O溶液对方镁石-镁铝尖晶石耐火材料性能的影响

以电熔镁砂和电熔镁铝尖晶石为原料,以18°Be’、24°Be’、30°Be’三种不同浓度的MgCl_(2)·6H_(2)O溶液和酚醛树脂为结合剂,制备方镁石-镁铝尖晶石耐火材料。以酚醛树脂为对照组,通过研究MgCl_(2)·6H_(2)O溶液对材料常温抗折强度、常温耐压强度、烧结性能、抗热震性能的影响,探明MgCl_(2)·6H_(2)O溶液对材料的作用机理。结果表明,在常温下MgCl_(2)·6H_(2)O溶液能与镁砂反应生成氯氧镁水泥(MOC),MOC在微观下表现为交错互锁的晶须结构,使得耐火材料在干燥后具有非常高的机械强度。当热处理温度为1 700℃、溶液浓度为24°Be’时,材料的常温耐压强度达到79.1 MPa,相较于酚醛树脂提高了58.2%;当热处理温度为1 700℃、溶液浓度为18°Be’时,材料的显气孔率达到16.8%,相较于酚醛树脂降低了13.4%。MgCl_(2)·6H_(2)O溶液浓度的增加有利于提高材料的断裂韧性。MOC和Mg(OH)_(2)在烧成过程中会分解产生活性MgO,促进材料的烧结。此外,分解产生的活性MgO呈类球状,它们分散填充在镁砂颗粒内部裂隙处,形成微孔结构,有利于减缓热震时的热应力冲击。

不同种类铝镁尖晶石细粉对刚玉尖晶石浇注料性能的影响

以板状刚玉颗粒和电熔尖晶石颗粒为骨料,以板状刚玉细粉、烧结或电熔尖晶石细粉、活性α-Al_(2)O_(3)微粉为基质,高纯铝酸钙水泥为结合剂,振动浇注成型,经1550℃高温烧成后制备刚玉尖晶石试样。研究了不同厂家烧结尖晶石细粉和电熔尖晶石细粉的化学成分、物相组成和粒度分布对刚玉尖晶石浇注料显微结构、烧后永久线变化率、显气孔率、体积密度、常温抗折强度、高温抗折强度和常温耐压强度的影响。

活性氧化铝加入量对活性氧化镁结合刚玉-尖晶石浇注料性能的影响

为改善活性氧化镁结合刚玉-尖晶石浇注料的性能,以板状刚玉、活性氧化铝微粉、活性氧化镁微粉和乳酸铝为原料,制备了活性氧化镁结合刚玉-尖晶石浇注料,研究了活性氧化铝微粉加入量(加入质量分数分别为0、8%、13%和18%)对浇注料显微结构、物相组成、物理性能及抗渣侵蚀和渗透性能的影响。结果表明:1)活性氧化铝微粉的加入促进了活性氧化镁结合刚玉-尖晶石浇注料的烧结,提高了骨料和基质的结合程度,使浇注料显微结构更加致密;2)随着活性氧化铝微粉加入量的增加,试样体积稳定性提高,显气孔率降低,体积密度增加,常温抗折强度和耐压强度及抗渣性提高;3)当活性氧化铝微粉加入量为18%(w)时,活性氧化镁结合刚玉-尖晶石浇注料的综合性能最好(考虑到颗粒级配和原料成本的问题,没有必要再进一步增加活性氧化铝微粉),其体积密度为3.05 g·cm^(-3),显气孔率为18.5%,加热永久线变化为0.31%,常温抗折强度和耐压强度分别为13.5和73.8 MPa,抗渣性最佳。

Al_2O_3-ZrO_2-Spinel三元纳米复相陶瓷超塑性变形及组织演变

采用真空热压烧结工艺制备了三元纳米复相陶瓷并进行了超塑性压缩试验。结果表明:纳米复相陶瓷中的第二相在烧结和变形过程中有效地阻止了基体Al2O3的晶粒长大。在1650℃材料表现出良好的高应变速率超塑变形能力,变形抗力小于30MPa。微观组织观察表明由于变形过程中存在有益压应力,材料变形后晶界处未出现空洞,经变形量为60%的压缩变形后材料中存在较高密度的位错,位错主要存在于尖晶石和氧化锆第二相中,基体Al2O3的晶粒仍为等轴状,表明位错运动对晶界滑移起到了积极地协调作用。

单相掺杂稀土氧化物对镁铝尖晶石材料性能影响的研究进展

综述了单相掺杂稀土氧化物对镁铝尖晶石材料烧结性能、力学性能、抗渣侵蚀性能以及耐其他介质腐蚀性能的影响及作用机理。在此基础上,指出了镁铝尖晶石材料在制备和应用过程中存在的问题,并展望了稀土氧化物掺杂镁铝尖晶石材料的研究方向。

Thermodynamic simulation of the effect of slag chemistry on the corrosion behavior of alumina–chromia refractory

The corrosion behavior of alumina-chromia refractory against two kinds of industrial slags （coal slag and iron smelting slag） at 1550℃ was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina-chromia refractory.

Relation Between Sintering Reactivity of Matrix and Thermal Shock Resistance of Ultra-low Cement Bonded Corundum-spinel Castables for Fired Purging Plugs

Purging plugs installed in the bottom of steel ladles are widely used for the secondary refining of high quality steel grades.The dynamic service conditions and temperature gradients caused by the cold inert gas blown through the plug during stirring create a strong thermal shock impact on the materials.This can affect its service life and restrict the safety and efficiency of steel making if the plug fails during use.In this work,the influence of the particle size distribution (PSD) and amount of reactive alumina on the sintering behavior of ultra-low cement bonded corundum-spinel based castables was investigated on lab scale.The relationship between sintering reactivity of matrix and thermal shock resistance of castables was evaluated in detail.Results show that the sintering of castables can be intensified by using finer reactive alumina.However,excessive sintering of the castable through finer reactive alumina is negative for thermal shock resistance.The microstructure characterization reveals that castables with more intense sintering show denser matrix structure,which is less effective in hampering crack propagation and therefore results in decline of their thermal shock resistance.

Preliminary Study on MgO·Al_2O_3 Spinel Fiber

MgO·Al 2O 3 spinel fibers may be obtained by thermal treatment of pressed specimens composed of Mg-Al-O materials with appropriate oxide-metal ratio at high temperature under controlled atmosphere. Their phase composition and microstructure have been examined.

CeO_(2)对形成镁铝尖晶石转变温度的影响

采用固相烧结法合成镁铝尖晶石粉末,通过X射线衍射分析尖晶石的相变转变温度。结果表明:CeO_(2)对相变反应具有促进作用,添加3%CeO_(2)能够使尖晶石的相变转变温度由1500℃降低到1300℃;随着温度的升高,尖晶石生成量增加。加入稀土CeO_(2)含量大于1%时,随着CeO_(2)含量的增加,稀土CeO_(2)对尖晶石的相变温度的促进作用增强;CeO_(2)含量小于3%时,保温时间对尖晶石的形成影响不大,在1500℃下,当CeO_(2)含量为5%时,随着保温时间的延长,尖晶石的含量增加。对温度、保温时间和稀土加入量综合考虑,生产中添加3%CeO_(2),1300℃煅烧保温2h为宜。

Effect of Heredity of Raw Materials on Properties of Alumina-magnesia Refractory Castables

Regarding the morphology of alumina,effect of the heredity of raw materials on properties of aluminamagnesia refractory castables was investigated by adding platelet alumina as the specific template.In-situ spinel platelet formed derived from platelet alumina.By comparing phase evolution,apparent porosity,bulk density,permanent linear expansion and strength,it was demonstrated that the utilization of the microstructures＇ heredity of platelet alumina was a new alternative for controlling properties of alumina-magnesia refractory castables.

镁砂细粉对尖晶石轻质耐火材料结构与性能的影响

以电熔尖晶石细粉、烧结镁砂细粉和镁铝尖晶石空心球为主要原料,采用固相烧结法制备了尖晶石轻质耐火材料。借助XRD、SEM等测试手段研究了镁砂细粉和空心球对材料物相组成、显微结构、耐压强度、导热系数等方面的影响。结果表明:少量镁砂细粉(小于5%)的引入,部分固溶于尖晶石中,部分在空心球与尖晶石粉末颗粒之间产生二次尖晶石,促进了空心球与周围粉末颗粒间的结合,减小了材料的孔隙尺寸,降低了导热系数;增加镁砂细粉引入量,有利于促进烧结、提高材料的致密性与耐压强度;控制镁砂细粉引入量小于5%,可制备得到体积密度为1.85~1.98 g/cm^(3)、耐压强度为22.8~27.3 MPa、导热系数为0.256~0.524 W/(m·K)(200~1 000℃)的尖晶石轻质耐火材料。

MgAl_(2)O_(4)透明陶瓷力学性能及尖晶石基装甲抗弹性能研究进展

当前,随着对防护材料的要求越来越高,传统以防弹玻璃为主的透明装甲已难以满足使用要求,更轻更薄的陶瓷基透明装甲正在逐渐成为主流选择。MgAl_(2)O_(4)作为一种性能优异的透明陶瓷材料,具有较高的机械强度、优异的耐蚀性和耐磨性、良好的抗热震性能和抗热冲击性能。首先,介绍了近年来国内外MgAl_(2)O_(4)透明陶瓷的制备技术进展,在MgAl_(2)O_(4)透明陶瓷制备过程中,通常选用热压烧结结合热等静压后处理技术,粉体原料尺寸应控制在适合的范围内,添加LiF使其微观结构的均匀性更好。其次,介绍了MgAl_(2)O_(4)透明陶瓷微观结构和力学性能之间的联系,微观结构直接影响透明陶瓷所有力学性能,进而影响其抗弹性能;硬度随晶粒尺寸的减小而提高,致密度越高,硬度也越高;弹性模量与相对密度直接相关,与晶粒尺寸无明显关系。微观结构越均匀其断裂韧性越高。最后,解释了力学性能与装甲抗弹性能的相关性,硬度和断裂韧性之间存在反比关系,建议装甲陶瓷硬度大于弹丸硬度,断裂韧性尽可能大。断裂模式与陶瓷吸收的能量有关,穿晶断裂优于沿晶断裂。弹性模量增加了弹丸与陶瓷表面的相互作用时间,可使陶瓷吸收更多能量。高弯曲强度有助于陶瓷承受多重弹丸冲击。因此,需要将多种性能组合起来才能实现装甲陶瓷抗弹性能的最大化。

不同粒度锌铝尖晶石加入量对方镁石-锌铝尖晶石性能的影响

以高纯镁砂(5~0.074、≤0.074 mm)为主要原料,分别以烧结法合成的锌铝尖晶石颗粒(5~0.074 mm)和细粉(≤0.074 mm)取代相应粒度的高纯镁砂,制备了方镁石-锌铝尖晶石试样,分别研究了锌铝尖晶石颗粒(加入质量分数分别为10%、15%和20%)和细粉(加入质量分数分别为5%、10%和15%)的引入量对试样性能的影响,并与市售的铁铝尖晶石砖的性能作对比。结果表明:1)随锌铝尖晶石颗粒引入量的增加,试样的显气孔率增大,体积密度和常温耐压强度降低,抗热震性能稍有提高;2)随锌铝尖晶石细粉引入量的增加,试样的常温物理性能和抗热震性能均有提高;3)当锌铝尖晶石以10%(w)颗粒料或5%~10%(w)细粉料引入时,其抗侵蚀性能均优于目前水泥窑使用铁铝尖晶石砖的。综合来看,锌铝尖晶石以5%(w)细粉形式引入的试样性能最好。

浮法玻璃中镁质结石的分析

介绍了浮法玻璃生产中出现的镁质结石的形态和成分特点,结合对停产冷修的浮法玻璃窑炉内部的取样测试,分析了白云石的分解、飞散过程以及熔窑内镁铝尖晶石的形成机理,为浮法玻璃中镁质结石问题的解决提供参考依据。