Effect of Al Powder and Si Powder Additions on Structure and Properties of Unburned Magnesium Aluminate Spinel Refractories

Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material,phenolic resin as the binder,aluminum powder(2%,4%,and 6%by mass)and silicon powder(when Al powder addition is 4%,Si powder addition varies:1%and 2%,by mass)as additives.The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures(1000,1400,and 1600℃for 3 h)were studied.The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1000 or 1400℃,and meanwhile AlN reinforcement phase forms in the matrix,which greatly improves the hot modulus of rupture of the samples at 1400℃;however,the heat treatment at 1600℃has little influence on the strength;the addition of Al powder and Si powder results in the formation of low melting point phases,greatly reducing the hot modulus of rupture.However,the low melting point phases promote sintering,which enhances the density and the cold modulus of rupture,and decreases the volume change during heating.The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.

Effect of Sc_2O_3 addition on densification and microstructure of different spinelized magnesium aluminate spinels

The densification and microstructure of different spinelized magnesium aluminate spinels（MAS） were studied adding Sc_2O_3 as additive. Sintered products were then characterized in terms of densification, phase analysis, quantitative elemental analysis and microstructure. The results show that Sc_2O_3 is found to be beneficial for the densification of MAS. Sc_2O_3 has a more significant effect on the densification of partially spinelized MAS batch than that of fully spinelized MAS batch. At the sintering temperature of 1650 °C, the bulk density of sintered products of partially spinelized powders increases by 0.243 g/cm3 as the Sc_2O_3 content increases from 0 to 4%（mass fraction） and that of fully spinelized powder increases by 0.14 g/cm3. Compared with the sintered samples prepared from the fully spinelized powder, the sintered samples using the partially spinelized powders as raw materials have more compact microstructures.

Two-step sintering of magnesium aluminate spinels and their corrosion in Na_3AlF_6-AlF_3-CaF_2-Al_2O_3 bath

New types of refractory materials need to be developed for designing the man-made ledge of the Hall-Heroult cell for aluminum electrolysis, which are currently constructed by frozen ledge.Magnesium aluminate spinel （MAS） as potential candidate materials was prepared by two-step sintering. The densification and grain growth of the MAS wereinvestigatedbytheArchimedes drainage method and scanning electron microscope （SEM）. All the specimens were corroded in aNa3AlF6-AlF3-CaF2-Al2O3bath to assess the corrosion resistance. The results show that a MAS material with a high relative density of 99.2% and ahomogeneous microstructure is achieved under two-step sintering conditions. The corrosion mechanisms of MAS inNa3AlF6-AlF3-CaF2-Al2O3 bathare mainly proposed by dissolution of MAS, formation of aluminum oxide, and diffusion of fluorides. The MAS prepared by two-step sintering exhibits good corrosion resistance to theNa3AlF6-AlF3-CaF2-Al2O3bath.

Development of Magnesium Aluminate Spinel Castable for Roof of EAF with High Molten Iron Charging Ratio

Specimens of magnesium aluminate spinel castable and calcium aluminate cement bonded bauxite based castable were prepared using special bauxite （particle size ≤8 mm ） and sintered magnesia as aggregates, SiO2 micropowder, α-alumina micropowder and calcium aluminate cement as binders, drying, firing at 1 350 ℃ and 1 500 ℃ for 3 h, respectively. The bulk density, cold modulus of rupture, cold crushing strength, permanent change in dimensions on heating, thermal shock resistance and slag resistanee were determined. The results show that compared with calcium aluminate cement bonded bauxite based castable, the magnesium aluminate spinel castable has higher cold crushing strength after drying, better slag resistance but worse thermal shock resistance. Magnesium aluminate spinel based roof of EAF with high molten iron charging ratio has a longer service life.

Synthesis of Magnesium Aluminate Spinel-corundum Composite with Waste Slide Plate and Magnesia Carbon Brick

Magnesium aluminate spinel -corundum composite was prepared with waste slide plate and magnesia carbon brick. Microstructure and sintering ability of as-prepared magnesium aluminate spinel -corundum composite were investigated with XRD, SEM, and DSC/TG. With the addition of waste slide plate increasing or synthesis tem- perature rising, the bulk density of the specimen increases and the apparent porosity decreases, but the crystallinity of the specimen decreases and the magnesium alaminate spinel phase increases. The obtained composite contains 72% spinel and 26% corundum. Primary phase and secondary phase are bonded by glass phase. The results show that it is feasible to synthesis magnesium aluminate spinel - corundum material with waste slide plate and magnesia carbon brick.

Chinese Standards on Refractories Magnesium Aluminate Spinel

1 Scope This standard specifies the terms, definitions, classifications, technical requirements, test methods, inspection rules, packing, marking, transportation, storage, and quality certificate of magnesium aluminate spinel. This standard is applicable to the magnesium alu- minate spinel prepared by sintering method or electric mehing method with raw materials of industrial alumina or bauxite, and light burnt magnesia.

Feasibility of aluminum recovery and MgAl_2O_4 spinel synthesis from secondary aluminum dross

The feasibility of aluminum recovery from secondary aluminum dross by extraction with NaOH solution and the subsequent synthesis of MgAl_2O_4 spinel by sintering the extracted slag were studied. The extraction percentage of soluble aluminum from the dross reached 80% at a temperature of 353 K, liquid-to-solid ratio of 12 mL·g^(-1), stirring speed of 300 r·min^(-1), and an extraction time of 15 min; the hydrolysis percentage of AlN reached 40% with an extraction time of 30 min. The activation energies of the soluble aluminum and AlN extracted from the dross were 7.15 and 8.98 kJ·mol^(-1), respectively, indicating that their kinetics were controlled by outer diffusion without a product layer. The extracted slag was sintered in the temperature range 1373–1773 K; MgAl_2O_4 spinel with a compressive strength as high as 69.4 MPa was produced in the sample sintered at 1673 K for 3 h. This value exceeds the threshold(40 MPa) prescribed by the National Standard for the Magnesia and Magnesia-alumina Refractory Bricks of China(GB/T 2275-2007). These results establish the effectiveness of aluminum recovery from secondary aluminum dross and subsequent MgAl_2O_4 spinel synthesis.

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.

莫来石-刚玉-镁铝尖晶石复相材料的抗碱侵蚀性能研究

为了提高莫来石-刚玉质匣钵的抗碱侵蚀性能,以煤矸石、工业氧化铝和工业氧化镁为原料,采用二步煅烧法制备了莫来石-刚玉-镁铝尖晶石复相材料,研究了工业氧化镁加入量(加入质量分数分别为1%、2%、3%、4%和5%)对试样物相组成、显微结构及物理性能的影响,并探究了试样抗钠离子电池正极材料的侵蚀机制。结果表明:1)氧化镁可促进莫来石晶体生长和试样烧结致密化,且由于莫来石晶体直接结合及微晶镁铝尖晶石颗粒增韧,所有试样均具有高的常温耐压强度,≥248 MPa;2)以不同形态分布于试样中的镁铝尖晶石可形成物理屏障,阻止Na^(+)渗透,阻隔其与莫来石和刚玉反应,提高试样的抗碱侵蚀性能;3)综合试样的物理性能和抗碱侵蚀性能,工业氧化镁的最佳加入量为4%(w)。

水泥回转窑过渡带用尖晶石-方镁石-铝酸钙耐火材料的制备

水泥回转窑过渡带由于难以结窑皮和所用耐火材料热导率较高,使得窑体表面温度高,散热损失大。本工作以菱镁矿、白云石和煅烧氧化铝为原料合成了尖晶石-铝酸钙复相轻量骨料,以此为颗粒,以烧结镁砂细粉为基质制备出尖晶石-方镁石-铝酸钙耐火材料。借助扫描电子显微镜、X射线衍射仪等手段研究了合成原料物相组成对耐火材料常温物理性能、荷重软化温度和抗水泥物料侵蚀性能的影响,结果表明:利用菱镁矿、白云石和煅烧氧化铝为原料在1650℃保温4 h可以合成吸水率较低的尖晶石-铝酸钙复相轻量耐火原料。以合成尖晶石-铝酸钙复相材料为骨料可以制备出常温耐压强度较高的尖晶石-方镁石-铝酸钙耐火材料,其高强度得益于合成骨料与方镁石基质的良好结合。尖晶石-方镁石-铝酸钙耐火材料具有较好的抗水泥物料侵蚀性能,可用于水泥回转窑过渡带。

镁铝尖晶石对全抛釉陶瓷釉面性能的影响

为提升全抛釉陶瓷产品的耐磨性能,在全抛釉中引入耐磨强化组元—镁铝尖晶石,探究了镁铝尖晶石掺量对全抛釉陶瓷光泽度、硬度、耐磨性、物相与微观结构的影响规律。研究结果表明:在全抛釉陶瓷产品制造工况下(低温快烧,辊道窑烧成温度1220℃,烧成周期40 min),随着镁铝尖晶石掺量的增加,全抛釉层中镁铝尖晶石含量逐渐提升,继而可有效提升全抛釉的硬度与耐磨性;但是镁铝尖晶石的引入,会增大全抛釉的烧成温度,导致全抛釉层中气孔含量与尺寸增加,不利于提升全抛釉的光泽度、发色性能以及防污性能;此外,控制适宜的镁铝尖晶石掺量可制得综合性能优异的全抛釉产品:当镁铝尖晶石的添加量为12wt%时,釉层综合性能最优,产品维氏硬度达到7.42 GPa,莫氏硬度5级,耐磨性达到4级(6000转),同时抛光后产品具有较高的光泽度(94°)和优良的发色(蓝黄黑色差值<3.2)与防污性能(5级),完全能够满足全抛釉陶瓷产品的使用需求。

羧甲基纤维素钠加入量对镁铝尖晶石质多孔隔热材料性能的影响

为提高热工窑炉的能源利用效率,首先将质量比为35∶65的中档镁砂细粉与煅烧氧化铝粉混合、烘干、破碎至d_(50)=2.3μm的混合粉;然后分别引入不同量的稳泡剂羧甲基纤维素钠(CMC)和0.6%(w)的发泡剂油酸钾,制得泡沫料浆;最后将泡沫料浆注入40 mm×40 mm×40 mm模具中,脱模,经110℃保温24 h干燥,再经1500℃保温3 h烧后,制备了镁铝尖晶石质多孔隔热材料。研究了CMC加入量(外加质量分数分别为0、0.1%、0.2%、0.3%、0.4%、0.5%)对料浆和烧后试样性能的影响。结果表明:1)当CMC加入量大于0.1%(w)后,料浆膨胀比降低,黏度增大,气泡数量减少,气泡平均直径变小。2)当CMC加入量为0.2%(w)时,料浆的Zeta电位绝对值最大,为18.3 mV,此时料浆最稳定;烧后试样内部的气孔为球形封闭气孔,数量最多,此时试样的显气孔率为73.5%,体积密度为0.95 g·cm^(-3),常温耐压强度为13.1 MPa。

发泡-自发凝固浇注法制备镁铝尖晶石质多孔材料

为了提高热工窑炉的热效率,降低热能损耗,以工业级中档镁砂细粉(d50=34.2μm)、煅烧氧化铝粉(d50=3.4μm)为原料,油酸钾为发泡剂,羧甲基纤维素钠为稳泡剂,异丁烯与马来酸酐交替共聚物(ISOBAM-104,简称“IB”)为固化剂,采用发泡-自发凝固浇注法制备镁铝尖晶石质多孔材料,研究了IB加入量(外加质量分数分别为0、0.1%、0.2%、0.3%和0.4%)对料浆和1500℃保温3 h烧后试样性能的影响。结果表明:1)随IB加入量增加,料浆的膨胀比减小,Zeta电位的绝对值先增大后减小,烧后试样的显气孔率减小,体积密度增大,常温耐压强度先升高后降低,气孔分布由紧密堆积变为独立分散,孔壁增厚,热导率先增大后减小。2)当IB加入量为0.3%(w)时,Zeta电位为-52.6 mV,料浆最稳定;烧后试样的常温耐压强度最大,为32.7 MPa,显气孔率为54.4%,体积密度为1.63 g·cm^(-3),热导率为0.205 W·m^(-1)·K^(-1)(350℃);平均气孔尺寸最小,为46.8μm,综合性能最佳。

Preparation of Light-weight Spinel Refractories by Foaming-gel Process

Light-weight magnesium -aluminate spinel materi- als were prepared by foaming-gel process with polyalumi- nium chloride （PAC） as gel. Effect of solid loading in initial slurry on microstructure, porosity, pore size distri- bution, thermal conductivity and mechanical properties was investigated. The results show that the bulk density of the light-weight magnesium -aluminate spinel mate- rials is in the range of O. 7 1.2 g cm-3 ; pore size distribution curves show single-peak characteristics and the mean pore size is in the range of 30. 83 - 61.37 μm ; with the increase of solid loading, the linear shrinkage of the green body during firing and the permanent change in dimensions on heating at l 600 ℃ for 3 h de- crease, but the bulk density increases, the mechanical properties increase obviously; the maximum compressive strength and bending strength reach 35. 25 MPa and 9. 92 MPa, respectively, while the bulk density is 1. 16 g · cm ; and the thermal conductivity at 1 000 ℃ tea- ches 0. 371 W · m-1 . K-1 while the bulk density is O. 7 -3 g · cm

Effect of Y_2O_3 Addition on Sintering Properties and Microstructure of Spinel Materials

The effect of Y2O3 addition on the sintering proper- ties and microstructure of spinel was investigated using alumina-rich spinel as the raw material. The phase con- stitution and microstructure of the specimens were charac- terized by XRD and SEM, and the pore structure of the specimens was measured by a mercury porosimeter. The results indicate that a viscous melt forms wrapping around spinel crystals by adding a little Y2O3 powders （1 mass% ）, yttrium alumina garnet will crystallize around spinel crystals by adding more Y2O3 powders （ 3 mass% ） ; the sintering properties of the spinel are sig- nificantly improved by adding Y2O3 powders less than 3 mass%, while they will be relatively weakened by adding Y2O3 powders more than 3 mass%.

Effect of Spinels on Properties of MgO-Al_(2)O_(3) Refractories for RH Snorkels

With satisfactory high temperature properties,thermal shock resistance and mechanical properties,refractories in the MgO-Al_(2)O_(3) system have become promising alternative to MgO-Cr_(2)O_(3) counterpart used as RH snorkel lining.High purity dead burned magnesia,fused magnesia and sintered spinel were used as raw materials and sulfite pulp waste as the binder,specimens of the refractories in the Mg0-Al_(2)O_(3) system were prepared for the purpose of investigating the influences in terms of the addition of three kinds of spinels,with Al_(2)O_(3) 50%,66% and 78%,by mass,respectively,and the size of MA50 spinel on properties of the specimens.Relatively superior comprehensive properties can be achieved when 16%of MA50 spinel with sizes under 1mm is adopted.

Effect of Al-Si Alloy Addition on Properties of Fused Spinel Carbon Materials

Fused magnesium aluminate spinel carbon materials were prepared using fused magnesium aluminate spinel and flake graphite as the main raw materials and phenolic resin as the binder.The effects of the Al-Si alloy addition(0,2%,4%,6%,8%and 10%,by mass)on the properties of fused magnesium aluminate spinel carbon materials were studied.The results show that fiber materials are generated in the samples with Al-Si alloy addition,which can significantly improve the cold and hot modulus of rupture,the cold elastic modulus,and the thermal shock resistance of the samples.When the addition of Al-Si alloy is 6%-8%,the comprehensive performance of the sample is the optimum.

固溶反应对MA-Al_(2)O_(3)材料结构和性能的影响

以电熔镁铝尖晶石为主要原料并加入少量烧结刚玉细粉部分替代尖晶石细粉,或以白刚玉为主要原料并加入少量电熔镁铝尖晶石细粉替代白刚玉细粉,制备了两组MA-Al_(2)O_(3)材料。研究刚玉与镁铝尖晶石之间的固溶反应对材料性能及显微结构的影响。结果表明:1)在两组材料中均发生了固溶反应,使得镁铝尖晶石的富铝程度增大,镁铝尖晶石中的氧化铝含量(w)由约76%增加到80%以上,从而加强了试样骨料与基质的结合,减少结构缺陷,改善了材料的高温性能;2)在以镁铝尖晶石为主要原料的MA-Al_(2)O_(3)材料中,加入烧结刚玉可使其常温耐压强度增大,改善其高温抗蠕变性和抗热震性;3)在以白刚玉为主要原料的MA-Al_(2)O_(3)材料中,加入镁铝尖晶石细粉,其常温耐压强度、高温抗蠕变性和高温抗折强度均有大幅度提高。

活性镁铝尖晶石的合成及其抗铜熔炼渣侵蚀机理

为寻找无铬化耐火材料在铜冶金领域的替代材料,制备高致密度镁铝尖晶石材料,探究镁铝尖晶石材料抗铜熔炼渣侵蚀机理。采用轻烧氧化镁与工业氧化铝为主要原料,经不同轻烧温度合成活性镁铝尖晶石,并对其烧结性能进行表征,利用静态坩埚法,研究镁铝尖晶石材料抗铜熔炼渣侵蚀能力。研究结果表明:合成的活性镁铝尖晶石原料的晶粒粒径小,烧结活性高的标准活性镁铝尖晶石原料的最适宜轻烧温度为1 400℃。所合成活性尖晶石原料在1 750℃保温3 h后可烧结合成致密尖晶石材料,致密尖晶石材料中尖晶石晶粒发育良好,呈致密镶嵌结构,晶粒分布均匀,平均粒径在7.26μm左右,材料密度达3.29 g/cm^(3),显气孔率为3.53%。镁铝尖晶石与铜熔炼渣反应可形成液相与Mg(Fe^(2+))Al(Fe^(3+))_(2)O_(4)尖晶石相;且材料致密化程度对抗渣渗透起关键作用,对比传统工业上应用的电熔尖晶石原料,所合成出的活性尖晶石表现出较高烧结活性,可提高材料致密化程度,从而提高材料抗渣渗透能力。

镁铝尖晶石透明陶瓷的研究进展

镁铝尖晶石(MgAl2O4)作为先进的透明陶瓷材料,具有透过波段宽、透过率高、各向同性,高熔点、高硬度、高强度、高电阻率、高热导率、高抗热震,耐腐蚀和耐高温等优异性能,可广泛应用于红外制导窗口、高马赫航空器的整流罩、透明装甲和极端环境下的光电设备窗口等关系国防安全与高性能关键设备领域。本文简要介绍了镁铝尖晶石透明陶瓷的基本性能和国内外研制情况,重点介绍中材人工晶体研究院有限公司三十余年在镁铝尖晶石高纯粉体合成、镁铝尖晶石透明陶瓷成型烧结工艺和性能研究及应用开发方面所做工作,分析了材料研制中遇到的困难与在应用开发过程中面临的竞争和挑战,思考材料的研究方向、方法,并对其应用和发展予以展望。