Fabrication and Properties of Closed-pore Al_2O_3-based Refractory Aggregates

A novel Al_2O_3-based refractory aggregate with closed-pore structure was fabricated utilizing superplasticity with submicro-sized Al_2O_3 and MgO as raw materials,and SiC as a high temperature pore-forming agent.The effect of MgO on porosity,phase composition and microstructure of the refractory aggregate has been investigated. For comparison,the common Al_2O_3-based refractory aggregates and porous ones with open-pore structure were also prepared. The results indicate that the closed porosity of Al_2O_3-based refractory aggregate increases as the content of MgO increases. When the content of MgO is 15 mass%,the closed and apparent porosities are 14. 5% and 1. 1%,respectively. The main phase compositions are Al_2O_3 and MgAl_2O_4. The formation mechanism of closed pores is that the fine-crystallinegrain Al_2O_3 ceramic possesses superplastic deformation ability after adding MgO at high temperatures. When SiC powder is added to the Al_2O_3 ceramic,the generated gases by the reaction of SiC at the sintering temperature can provide a pressure to make grain boundaries slide. Then,the gases are enclosed by crystalline grains to form the closed pores. The slag corrosion resistance of the fabricated closed-pore Al_2O_3-based refractory aggregate is better than the common refractory aggregate and porous ones.     

溶胶-凝胶法制备镍锌铁氧体及其电磁损耗性能

以Zn(NO3)2×6H2O, Ni(NO3)2×6H2O, Fe(NO3)3×9H2O及柠檬酸为原料,采用溶胶-凝胶法制备前驱体,在1200℃下对其煅烧3 h,合成了NixZn1-xFe2O4(x=0, 0.3, 0.5, 0.7)铁氧体. 产品表征结果表明,所有NixZn1-xFe2O4均属立方晶系尖晶石结构,结晶完整,在580 cm-1附近均具有铁氧体的红外吸收特征峰,晶粒大小均在100 nm左右. 在0.2~1.8 GHz测试频率范围内,Ni0.7Zn0.3Fe2O4和Ni0.5Zn0.5Fe2O4铁氧体对电磁波的吸收损耗性能相对较好,Ni0.7Zn0.3Fe2O4的电磁损耗角正切值tgd为0.67~1.59, Ni0.5Zn0.5Fe2O4为0.37~1.51,随Ni含量增加,其电磁损耗逐渐增强.     

铬酸盐对镁合金微弧氧化膜耐蚀性的影响

研究在硅酸盐溶液中添加K2CrO4对AZ91D镁合金微弧氧化膜耐蚀性的影响。结果表明：在含有K2CrO4的硅酸盐系溶液中进行微弧氧化处理的镁合金表面能够获得黄绿色的氧化膜层,主要由MgO、Mg2SiO4、MgAl2O4及MgCr2O4等耐蚀物相组成,其中具有尖晶石结构的MgCr2O4对提高膜层耐蚀性有极大的促进作用,同...     

Synthesis and Properties of Fusion-Cast Refractories in the MgO – Al2O3 System

Results of a study of fusion-cast refractories in the MgO – Al₂O₃ high-alumina system are reported. A casting technology for spinelide refractories is proposed. The materials synthesized are analyzed for phase composition by x-ray diffractometry and petrography and are shown to consist of corundum, MgAl₂O₄ spinel and their solid solutions. The materials are tested for corrosion resistance in industrial glass melts, and a corundum spinelide material with 5% Mg is recognized as the most promising for practical use.     

添加磁性纳米粒子制备气体分离功能炭膜

以聚酰胺酸为炭膜前驱体,分别以Fe_3O_4、γ-Fe_2O_3、Zn_(0.5)Ni_(0.5)Fe_2O_4以及二茂铁为掺杂物,经高温热解制备了4种Fe系物质掺杂的气体分离功能炭膜,对所制备的功能炭膜微结构及磁性能进行了表征.结果表明,各掺杂物在热解炭化过程中发生了物相结构的变化,其中Fe_3O_4和Zn_(0.5)Ni_(0.5)Fe_2O_4纳米粒子对前驱体起到了催化石墨化的作用.气体渗透测试结果表明,各掺杂物所制备的功能炭膜以分子筛分机理为主导进行气体分离,且气体渗透性能都有了显著的提高,特别是小分子气体H2渗透性最大提高了近48倍,Fe3O4掺杂所制备的功能炭膜,其H_2、CO_2、O_2、N_2和CH_4等单组分气体的渗透系数分别达到了12 194、3 433、1 175、136和74 Barters[1Barter=1×10~(-10)cm~3(STP)·cm/cm~2·s·cmHg].经FeO_4、γ-Fe_2O_3和Zn_(0.5)Ni_(0.5)Fe_2O_4掺杂制备的功能炭膜更是提高了H_2/CO_2的分离选择性.     

含ZrO_2添加剂对方镁石-尖晶石耐火材料抗渣性能的影响

采用电熔镁砂、电熔镁铝尖晶石为主要原料,用坩埚法研究了三种含ＺｒＯ２ 添加剂对方镁石－ 尖晶石耐火材料抗渣性能的影响。结果表明：引入的ＺｒＯ２ 能有效吸收渣中的ＣａＯ,形成高熔点的ＣａＺｒＯ３ 固相堵塞在气孔中,阻止了炉渣的进一步渗透,又有效地降低了ＣａＯ 对尖晶石的分解作用及ＣａＯ、ＳｉＯ２ 等对主晶相方镁石的侵蚀作用;同时,ＺｒＯ２ 的引入能促进烧结,提高高温固相直接结合率,对提高抗渣性也有着十分重要的意义。     

溶胶-凝胶法制备不锈钢表面SiO2-TiO2-Al2O3-ZrO2涂层

在乙醇中,分别以盐酸、醋酸为催化剂,以正硅酸乙酯、钛酸正丁酯、硝酸铝、氧氯化锆为金属醇盐前躯体,通过分步水解法制备了SiO2-TiO2-Al2O3-ZrO2复合溶胶,利用浸渍法将陈化后的复合溶胶涂覆到不锈钢表面制得透明的复合涂层。对SiO2-TiO2-Al2O3-ZrO2复合涂层进行了差热分析(DTA)、失重分析(TG)、红外光谱(IR)、X射线衍射分析(XRD)以及耐HCl、CuSO4和FeCl3溶液浸泡腐蚀实验。结果表明,涂层中存在TiO、SiO、AlO键的氧化物网状结构,其XRD图中出现了锐钛矿和板钛矿的相结构。该涂层致密,具有良好的耐蚀性能。     

α-Al_2O_3微粉对低碳MgO-C材料性能的影响

以电熔镁砂及鳞片石墨为主要原料,热塑性酚醛树脂为结合剂,研究了α-Al_2O_3微粉对低碳MgO-C材料性能的影响.结果表明:(1)Al_2O_3微粉的加入提高了低碳MgO-C材料的体积密度,降低了显气孔率,提高了强度,显著改善了MgO-C砖的抗氧化性;(2)高温下Al_2O_3微粉与MgO原位反应生成连续的尖晶石相,改善了材料基质的显微结构,增强了陶瓷结合,将MgO颗粒与鳞片石墨紧密地结合起来,提高了组织结构的整体性,从而提高了材料的致密度和强度;(3)高温下原位反应生成连续的尖晶石相堵塞脱碳层中的部分气孔,降低了氧的扩散速度,同时提高了MgO的沉积速度,使加入Al_2O_3微粉的低碳MgO-C材料抗氧化性能得以提高.     

The Structure of Fusion-Cast High-Chrome Oxide Refractories in the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> - MgO - Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System

The phase composition and structure of fusion-cast refractories composed of 57.0 – 84.2% Cr₂O₃, 4.3 – 36.1% MgO, 2.0 – 9.7% Al₂O₃, and 2.4 – 6.9% SiO₂ have been studied by petrographic and x-ray spectral microprobe analysis methods. Refractories high in MgO with modulus M = (Cr₂O₃ +Al₂O₃)/MgO = 1.64 – 3.1 are shown to consist of spinel phase Mg(Cr, Al)₂O₄ and silicate glass. Refractory materials (80.8 – 84.2% Cr₂O₃, 4.3 – 4.7% MgO, 2.0 – 9.7% Al₂O₃, and 2.7 – 6.9% SiO₂ with M = 18.7 – 20.2) are three-phase systems composed of spinel, escolaite, and glass phase. These materials, owing to their high corrosion resistance, have promising potentiality for practical applications.__________Translated from Novye Ogneupory, No. 12, pp. 69 – 74, December, 2004.     

氮化硼/二硼化锆对氧化镁-氧 化铝-碳材料性能影响

以电熔镁砂、用后镁碳砖、α-氧化铝和石墨为原料,引入复合添加剂氮化硼/二硼化锆（BN/ZrB2）,经共磨、加酚醛树脂结合剂混炼、成型及热处理工艺制备氧化镁-氧化铝-碳耐火材料,研究复合添加剂BN/ZrB2及煅烧温度对烧后试样烧结性、抗氧化性、显微结构和矿物相组成的影响。结果表明： BN/ZrB2添加剂在氧化镁-氧化铝-碳耐火材料中的优先氧化顺序为二硼化锆>氮化硼>碳,添加剂BN/ZrB2氧化生成三氧化二硼,三氧化二硼与基质中电熔镁砂及用后镁碳砖中的氧化镁反应生成低熔点相Mg3B2O6,液相Mg3B2O6有利于提高氧化镁-氧化铝-碳耐火材料的烧结性和抗氧化性。烧后试样矿物相组成为方镁石、镁铝尖晶石和少量Mg3B2O6相。     

Formation and leachability of hexavalent chromium in the Al2O3-CaO-MgO-Cr2O3 system

The Al₂O₃-CaO-MgO-Cr₂O₃ system has immense potential for refractory castables applications. However, Cr(III) can potentially be oxidized to carcinogenic Cr(VI) during the usage, which can cause subsequent problems with disposal. Equilibrium experiments on the Al₂O₃-CaO-MgO-4wt%Cr₂O₃ system were performed at 1500?°C in air. The effect of MgO addition (0 and 20?wt%) on the formation and leachability of hexavalent chromium was investigated using XPS, XRD, SEM-EDS, the TRGS 613 standard Cr(VI) leaching test and multiple leaching tests. A Cr(VI)-containing phase Ca₄Al₆CrO₁₆ predominantly formed in the samples with 0 and 5?wt% MgO, while the Cr(III)-containing Mg(Al, Cr)₂O₄ spinel phase formed in the samples with 10 and 20?wt% MgO. Addition of MgO suppressed the formation of Cr(VI) while favored the formation of spinel phase. Concentrations of Cr(VI) in the leachates from TRGS 613 tests exceeded the European limit of 0.0002?wt% in all samples, although decreased significantly with 20?wt% MgO addition.     

Kinetics of the formation of protective slag layers on MgO–MgAl2O4–C ladle bricks determined in laboratory

Carbon-bonded magnesia and magnesia-alumina bricks are the state of the art lining materials of the sidewalls and the bottom of steel ladles. Industrial trial tests revealed, that a new generation of MgO–MgAl₂O₄–C bricks, where pre-reacted spinel is added in form of a new calcium magnesium aluminate (CMA) raw material, exhibit a longer service life caused by an enhanced corrosion resistance due to the formation of a protective slag layer. In terms of this work, laboratory corrosion tests have been performed in order to mimic the protective slag layer formation and to study the kinetics of the formation. It has been found that the formation highly depends on the amount of iron present in the melt, which leads to the precipitation of the brownmillerite-phase. Furthermore, the study was extended to force the formation of protective slag layers of different composition which are reliable at higher temperatures and wider temperature ranges by targeted adaption of the brick composition. Cup tests showed that there is a potential to manipulate the composition of a protective slag layer by targeted adaption of the brick composition. Especially MgO, Al₂O₃, Fe_xO_y, and SiO₂ from the brick or slag enrich at the slag/refractory-interface.     

普碳钢用陶瓷基高温防护涂层制备及其性能表征

采用机械混合法制备了一种针对碳钢的新型Al2O3-MgO-TiO2-CaO体系陶瓷基高温防护涂料,1300℃下可在Q235B钢表面形成致密保护层,提高钢抗氧化烧损性能.结果表明,在涂料粒度48～75μm、涂层厚度0.5mm的条件下,涂层防护性能优良.涂层的防护温度范围为900～1300℃,1300℃时比原样可降低氧化烧损59.36%,防护寿命长于8h.涂层的应用将氧化层由经典的Fe2O3/Fe3O4/FeO三层结构转变为一层尖晶石结构,同时减薄了氧化层厚度,显著降低了Fe元素的高温扩散速率.     

不同氧化物(ZnO、Fe2O3、ZrO2)对SiO2-MgO-Al2O3-F玻璃陶瓷析晶的影响

应用扫描电子显微镜（SEM）和X射线衍射（XRD）等技术研究了ZnO、Fe2O3、ZrO2对SiO2-MgO-Al2O3-F玻璃陶瓷析晶组织形态的影响。结果表明：在所研究的玻璃体系中，不同氧化物加入后都促进了主晶相氟云母晶体的析出。但不同氧化物对析出晶体的形貌影响不同，当基础玻璃中添加了质量分数为2．0％的ZnO时，形成片状氟云母晶体和颗粒状莫来石相；当添加2．0％的Fe2O3后，大量均匀细小的针状氟云母晶体和块状FeFeO4晶体析出；而当添加4．0％的ZrO2后，除了氟云母和莫来石析出外，粒状ZrO2晶体夹杂在氟云母晶体之间均匀析出。     

Effect of Al_2O_3-ZrO_2 Composite Powder on Thermal Shock Resistance of ZrO_2 Sizing Nozzles

ZrO_2 sizing nozzles with a basic formulation were prepared using 45%( by mass,the same hereinafter)( Mg,Y)- PSZ aggregate,55%( Mg,Y)- PSZ fines and 5% PVA binder. Al_2O_3-ZrO_2 composite powders( 3%,6%,9% and 12%) prepared by sol- gel method were added to replace the equal amount of( Mg,Y)- PSZ fines. Effects of Al_2O_3- ZrO_2 composite powders on physical properties,phase composition and microstructure of the ZrO_2 sizing nozzles were studied.The results show that: the performances of the modified sizing nozzles with 3% Al_2O_3-ZrO_2 composite powder are better than those of the nozzles without composite powder used in current production process,and the thermal shock resistance of the former nozzles is six times of that of the latter one.     

A Retrospective Review of Alumina-magnesia-carbon Refractories

The residual expansion of in-situ spinel formation in using of alumina-magnesia-carbon(AMC)bricks monolizes the lining of steel-making ladles with the closure of their joints,which has been an effective solution avoiding washing out of the joints in ladle lining by the reduction of the penetration of liquid slag and molten steel.Alumina-magnesiacarbon refractories are overall reviewed,in terms of major raw materials,thermal evolution,corrosion and oxidation,and thermomechanical behavior,as well as type,addition and fraction of magnesia used.General commercial products contain 5%-10%MgO and 5%-10%C with a certain amount of metallic aluminum powder,which is believed to facilitate spinel formation at early stage of heating-up,although high magnesia containing AMC bricks are studied and used sometimes.With low ratio of Al₂O₃/C=12.9 and the carbon content of 6.4%C,AMC brick exhibits the highest corrosion resistance.It is important to determine the type,addition and fraction of magnesia used in AMC refractories for demonstrating high corrosion resistance and superior thermomechanical behavior.     

电磁场作用下高铁渣对MgO-C耐火材料的侵蚀

电磁场会促使熔渣中的铁、锰离子与MgO-C耐火材料反应形成锰掺杂镁铁尖晶石相,为进一步研究锰掺杂镁铁尖晶石的生成形貌及特征,采用Fe2O3质量分数为53.62%、CaO与SiO2质量比为0.8的高铁渣,分别在有、无电磁场环境下,对碳质量分数为14%的MgO-C耐火材料进行渣蚀试验。结果表明:感应炉存在电磁场,使熔渣中部分Fe2+/Fe3+与镁砂中Mg2+发生置换形成镁铁尖晶石,其含有少量Mn2+离子;镁铁尖晶石中铁含量从渣蚀层到渗透层急剧降低,锰含量几乎维持不变;侵蚀后试样渗透层较明显。电阻炉无电磁场,则侵蚀后试样没有形成镁铁尖晶石,熔渣中Si、Ca渗透到方镁石晶格中,形成钙镁榄橄石低熔相,将镁砂溶解到熔渣中;渣蚀层有明显的MgAl2O4生成。     

浮区法生长Yb3Fe5O12晶体及其磁光特性

用移动熔剂浮区法研究从Yb_2O_3-Fe_2O_3体系中生长Yb_3Fe_5O_(12)的可能性,分析了Yb_3Fe_5O_(12)为唯一固相区域内的大致相关系。找出了合适的助熔剂配比(Yb_2O_3: Fe_2O_3=20:80)及晶体的生长条件。并生长出了Yb_3Fe_5O_(12)单晶。测量了诙晶体的磁光性能,在λ>1.3μm时,其Faraday旋转角θ_F不随波长增加而改变。同时,在Y_3Fe_5O_(12)中掺入Yb可得到θ_F的温度系数为零的晶体。     

Effects of Firing and Operating Atmospheres on Microstructure and Properties of Phosphate Bonded Cr_2O_3-Al_2O_3-ZrO_2 Bricks

The microstructure and properties of phosphate bonded Cr_2O_3-Al_2O_3-ZrO_2 specimens fired in air or coke bed were investigated firstly. Then property change of the Cr_2O_3-Al_2O_3-ZrO_2 bricks after secondary treatment in simulation environment was studied. Finally,corrosion resistances of the Cr_2O_3-Al_2O_3-ZrO_2 bricks in air and simulation environment were compared; and microstructure of on-site used Cr_2O_3-Al_2O_3-ZrO_2 bricks in slagging gasifiers was analyzed. The results show that the atmosphere has significant effect on the microstructure and properties of the phosphate bonded Cr_2O_3-Al_2O_3-ZrO_2 bricks. As the specimens are fired in air,the phosphate forms a composite solid solution with Cr_2O_3 and Al_2O_3,therefore,strength of the specimens is enhanced. For specimens fired in coke bed,a certain amount of gases are generated owing to the reduction of phosphate and part of Cr_2O_3,which results in the increasing number and size of the pores,bad interfacial bonding between Cr_2O_3 aggregates and matrix as well as low strength of the specimens. During service process in reducing atmosphere,the phosphate binder and part of Cr_2O_3 in edge of the specimens are also reduced,leading to significant increase of number and size of the pores in the edge of the specimens; as a result,inreducing atmosphere,the specimens show much worse corrosion resistance than in air.     

Innovative Lining of Unburnt Al_2O_3-MgO Brick for 300t Steel Ladle in Baosteel

The manufacture of clean steel needs high performance carbon-free bricks for ladle lining.Based on long term application experiences of the prefab Al₂O₃-MgO blocks,unburnt Al₂O₃-MgO brick has been developed by pressing a mix of alumina,spinel and magnesia as major raw materials and Al₂O₃-MgO gel powder as binder.In addition to low open porosity and high strength,the unburnt Al₂O₃-MgO brick shows superior corrosion resistance and thermal shock resistance to the prefab block.Field trials in a 300t steel ladle have indicated the residual lining of unburnt Al₂O₃-MgO bricks showed smooth surface without large spalling and seldom steel infiltration,consequently longer service life than the prefab blocks.The reliable,unburnt Al₂O₃-MgO bricks have more advantages of high efficiency,energy-saving and eco-friendly production.It will be one of the best options for ladle lining in the manufacture of high-purity steel.