Cr2O3微粉加入量对Al2O3-Cr2O3质耐火材料性能的影响

以电熔铬刚玉和白刚玉为主要原料,用Cr₂O₃微粉部分替代电熔铬刚玉细粉,研究了Cr₂O₃微粉加入量对Al₂O₃-Cr₂O₃质耐火材料常温和高温性能、物相组成和显微结构的影响。结果表明,随着Cr₂O₃微粉加入量的增加,原位形成了(Al_1-xCr_x)₂O₃固溶体,促进了烧结,材料的显气孔率先降低后升高,且(Al_1-xCr_x)₂O₃固溶体的晶格常数呈线性增加,符合Vegard定律。材料的常温抗折强度和常温耐压强度随Cr₂O₃微粉加入量的增加先升高后降低,在Cr₂O₃微粉加入量为15%(质量分数)时强度达到最大值。而当Cr₂O₃微粉加入量为20%(质量分数)时,由于有挥发现象,材料显气孔率上升,强度下降。材料高温抗折强度随Cr₂O₃微粉加入量的增加而增加,材料的残余强度保持率呈先降低后升高的趋势。     

YCrO3/Al2O3 Core‐Shell Design: The Effect of the Nanometric Al2O3‐Shell on Dielectric Properties

We report a novel strategy to improve the dielectric properties of the biferroic YCrO₃ ceramic compound through interface conduction control by means of an insulating Al₂O₃ using a core‐shell design. The YCrO₃ particles were covered with several layers of insulating Al₂O₃ using the atomic layer deposition technique to produce the core‐shell structure. TEM images reveal homogeneous and well‐defined Al₂O₃ coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al₂O₃‐shell to be amorphous. The dielectric characteristics of the sintered nano‐composite were investigated in the 100 Hz–1 MHz frequency range and temperature between 300 and 580 K. As the Al₂O₃‐shell thickness covering the YCrO₃ particles is increased, a decrease of the dielectric permittivity, loss tangent and AC conductivity values was found in the whole range of temperatures and frequencies. Furthermore, the rounded hysteresis loop, typical of conductive ceramic is restored as the insulating Al₂O₃ layer becomes thicker. This behavior is explained because the insulating Al₂O₃‐shell acts as internal barrier layer localizing the surface charges on the sintered grain boundaries. This fact was confirmed by Electron Beam Induced Current technique where a clear contrast at the grain boundaries confirms the charge localization at the YCrO₃/Al₂O₃ interface. These results also reveal that the Al₂O₃‐shell induces another conductive mechanism when the insulating Al₂O₃ layer becomes thicker. Nonetheless, this new strategy is an effective approach to suppress the parasitic conductivity in polycrystalline multiferroic ceramics and increasing thus the multifuncionality.     

Effect of Zircon Addition on Properties of Low Carbon Al2O3-C Refractories

Using tabular alumina as aggregate,tabular alumina fines, reactive alumina ultra-fines, aluminum powders,silicon powders,carbon black,flake graphite,B4C and zircon fines as matrix,low carbon Al2O3- C refractories were prepared. Influences of zircon powders additions( 0,3%,5% and 7%,in mass,the same hereinafter) on properties,phase composition and microstructure were investigated. The results show that the ZrO2- nitride can be in-situ formed through carbothermal reduction and nitridation in Al2O3- C refractories.With the increase of zircon powder,the oxidation resistance of the Al2O3- C refractories improves obviously,the oxidized layer thickness decreases from 7. 94 mm without zircon to 2. 71 mm with 5% zircon. HMOR at 1 400 ℃of the Al2O3- C refractories reaches the maximum 14. 9MPa when zircon addition is 5%. With the increase of zircon powder,the apparent porosity and bulk density change a little,CMOR and CCS increase.     

加入SiC、SiAlON对刚玉-SiC-SiAlON材料组成、结构和力学性能的影响

以刚玉和8%Si粉为原料,1500℃埋碳烧后得刚玉-SiC-SiAlON复合材料.本文研究在加入8%Si粉基础上,另加入0～10%SiC或SiAlON粉对刚玉-SiC-SiAlON复合材料组成、结构和力学性能的影响.结果表明:加入SiC或SiAlON首先可促进Si反应完全,生成更多非氧化物使试样微膨胀量增加,重量增加;同时使试样的显气孔率提高,常温抗折强度降低;加入SiC使试样的结构疏松,高温力学性能下降;但由于生成较多O-SiAlON以及气孔率提高使试样的抗热震性明显提高;加入SiAlON,试样中生成较多的SiC,并有粒状的β-SiAlON存在,可明显提高试样的高温力学性能.     

The Effect of the Addition of Re and Ge on the Properties of Pt/Al2O3

The effect of Re and Ge addition to Pt/Al₂O₃ was studied. Mono-, bi- and a trimetallic catalysts were prepared and characterized by TPR, XPS, TPO and by the n-pentane, cyclohexane (CH) and n-octane reactions. It was found that the trimetallic was the most active and stable catalyst and showed selectivities to aromatics and isomers very similar to the bimetallic germanium-based catalyst.     

稀土助剂Gd2O3对W/Al2O3复合陶瓷烧结性能、力学性能和屏蔽性能的影响

以微米钨粉和α-Al2O3粉为基体,Gd2O3-MgO-SiO2为改性剂,采用常压烧结方式制备了W/Al2O3屏蔽复合陶瓷,并研究了Gd2O3含量及烧结温度对复合陶瓷烧结性能、微观结构、力学性能和屏蔽性能的影响.结果表明:烧结温度为1550℃,引入1.5wt％的Gd2O3可明显提高陶瓷的致密化程度,其力学强度高达276.44 MPa,较未改性陶瓷提高了38％.并且该陶瓷对y射线有优异的屏蔽性能,半衰减厚度值仅为1.49 cm.     

Effect of CeO2 and Al2O3 contents on Ce‐ZrO2/Al2O3 composites

Effect of CeO₂ and Al₂O₃ contents on phase composition, microstructures, and mechanical properties of Ce–ZrO₂/Al₂O₃ composites was studied. The CeO₂ content in CeO₂–ZrO₂ varied from 7 to 16 mol%, and the Al₂O₃ content in Ce‐ZrO₂/Al₂O₃ composites were 7 and 22 wt%. When CeO₂ content was ≤10 mol%, high Al₂O₃ content contributed to hinder the tetragonal‐to‐monoclinic ZrO₂ phase transformation during cooling and decrease the density of microcracks in the composites. Tetragonal ZrO₂ single‐phase was obtained in the composites with ≥12 mol% CeO₂, regardless of the Al₂O₃ content. Hardness, flexural strength, and toughness were dependent on CeO₂ and Al₂O₃ contents which were related to the microcracks, grain size, and phase transformation. The high flexural strength and toughness of the composites with 7wt% Al₂O₃ could be obtained at an optimum CeO₂ content of 12 mol%, whereas those of the composites with 22 wt% Al₂O₃ could be achieved in the wide CeO₂ content range of 8.5‐12 mol%.     

Effect of Polyacrylic Acid Addition on Rheology of SiC‐Al2O3‐ZrO2(3Y) Mixed Suspensions

A suspension with good rheology and high stability is crucial for slip casting and gelcasting technology. However, a mixed suspension from two or more different powders usually has bad rheology because of the easy agglomeration of mixed powders caused by the attractive force between the powders with heterocharges. We studied the surface modification of the each single‐component powders (SiC, Al₂O₃, ZrO₂(3Y) powders) and the SiC‐Al₂O₃‐ZrO₂(3Y) mixed powders to increase the repulsive force by adjusting the pH value and adding polyacrylic acid (PAA) as dispersant. The PAA addition effects on the SiC‐Al₂O₃‐ZrO₂(3Y) mixture were investigated in terms of zeta potential, pH range for heterocharge region, dispersion of the mixed powders and rheology of the mixed slurry based on the study of each unary suspensions. The results show that before surface modification the SiC‐Al₂O₃‐ZrO₂(3Y) mixed powders were agglomerated severely because they were in the heterocharge region with a broad pH range from 3.5 to 8.25, while after surface modification (pH = 10.5, PAA = 0.8wt%) the heterocharge region was narrowed with a relatively narrower pH range from 2.6 to 3.7. The mixed powders with homocharges were dispersed well because of the great electrostatic repulsive force and steric hindrance offered by PAA and the mixed suspensions had favorable rheology.     

Al2O3-ZrO2-CeO2系陶瓷的微观组织结构及强度性能

列出了对在Al_2O_3-ZrO_2-CeO_2(Al_2O_3 50%克分子)系中在粉料早期产物凝胶体合成的过程中,各组份的沉淀顺序对相关陶瓷材料的形态及微观组织结构的影响的研究结果。表明了陶瓷的强度和操作使用性能与微观组织结构尺寸因素之间的依存关系。查明,利用早期产物各组份同时沉淀的方法合成的粉料制造的刀具拥有更高的切削寿命。     

Effect of Al_2O_3-SiC Composite Powder on Properties of Al_2O_3-SiC一C Bricks

Al2O3- SiC- C specimens were prepared using white fused corundum( 3- 1,≤1 and ≤0. 044 mm),Al2O3- SiC composite powders( d50≤5 μm),α-Al2O3micropowder( d50= 1. 2 μm),SiC powder( ≤0. 044mm),flake graphite( ≤0. 088 mm),Si powder( d50= 42. 8 μm) and B4C powder( d50≤10 μm) as main starting materials,and thermosetting phenolic resin as binder. 4%,8%,12% and 16%( in mass,the same hereinafter) of Al2O3- SiC composite powders substituted the same quantity of α-Al2O3micropowder + SiC powder.Effects of composite powder additions on apparent porosity,bulk density,cold modulus of rupture,cold crushing strength,hot modulus of rupture( 1 400 ℃),therma shock resistance( 1 100 ℃,water quenching) and oxidation resistance( 1 000 and 1 500 ℃) of Al2O3- SiC- C specimens after 180 ℃ curing,1 000 ℃ 3 h carbon-embedded firing and 1 500 ℃ 3 h carbon-embedded firing,respectively,were researched. The results indicate that:( 1) with the increase of Al2O3- SiC composite powder,cold strengths of the cured specimens decline,those of the specimens fired at 1 000 ℃ change a little,and those of the specimens fired at 1 500 ℃ change a little except for an obvious improvement of cold crushing strength;( 2) with the increase of Al2O3- SiC composite powder,hot modulus of rupture at 1 400 ℃ decreasesand thermal shock resistance enhances significantly;( 3) when Al2O3- SiC composite powder addition is4%,the oxidation resistance at 1 500 ℃ is the best,and the reason may be the composite powder is finer and more active,which is beneficial to form dense mullite protective layer to retard the O2diffusion into the specimens.     

低Cr2O3含量Al2O3-MgO浇注料物理性能及物相变化研究

本文研究了低Cr2O3含量Al2O3-MgO浇注料的物理性能,采用X射线衍射仪和扫描电子显微镜对浇注料的物相变化和显微结构进行了分析.结果发现:镁铝尖晶石含量可控制浇注料的显气孔率、体积密度、线变化率及强度.高温下Cr2O3消失是因为其固溶于新生成的MgAl2O4相中,固溶的存在提高了浇注料的物理性能.采用硅微粉结合时,高温下会产生一定的镁橄榄石相.     

Effect of Alumina Reactivity on the Densification and Properties of Al2O3–Cr2O3 Refractories

Alumina‐chrome (Al₂O₃–Cr₂O₃) refractories with Al₂O₃:Cr₂O₃ molar ratio 1:1 were synthesized in the temperature range of 1400–1700°C by conventional solid–oxide reaction route. The effect of different aluminas (viz., hydrated and calcined) on the densification, microstructure, and properties of Al₂O₃–Cr₂O₃ refractories was investigated without changing the Cr₂O₃ source. The starting materials were analyzed to determine the chemical composition, mineralogy, density, surface area, and particle size. Sintered materials were characterized in terms of densification, phase assemblage, and mechanical strength at room temperature and at higher temperatures. Microstructural evolution at different sintering temperature was correlated with sintering characteristics. It can be concluded that the Al₂O₃–Cr₂O₃ refractories prepared with hydrated alumina as Al₂O₃ source show better densification and hot mechanical strength than corresponding calcined variety.     

Al粉加入量对凝胶粉结合铝镁不烧砖力学性能的影响

以各种粒径的棕刚玉、白刚玉(<0.047 mm)、镁砂细粉和α-Al2O3为主要原料,铝凝胶粉为结合剂,研究了铝粉加入量对精炼钢包铝镁不烧砖线变化率、抗折强度、耐压强度、显气孔率、体积密度和高温抗折强度的影响,并借助XRD和SEM研究了不烧砖的物相组成和显微结构.结果表明:随着铝粉量的增加,借助于塑性相成型,不烧砖烘干后的显气孔率减小、体积密度增大,抗折、耐压强度增大;在热处理过程中,铝粉一方面促进烧结,另一方面由于铝粉被氧化导致体积膨胀,并占主导地位,使得不烧砖显气孔率增大,体积密度减小,强度先增大后减小.高温抗折强度随铝粉加入量的增加而增大.     

High‐temperature Bending Strength of Self‐Healing Ni/Al2O3 Nanocomposites

Bending strength of 5 vol.% Ni/Al₂O₃ composites as a function of testing temperature is investigated at temperatures ranging from room temperature to 1200°C. Self‐healing performance at high temperatures of the composites is evaluated by conducting high‐temperature bending tests for as‐sintered, as‐cracked, and as‐healed specimens. Bending strength of as‐sintered specimens dramatically decreases from 995 MPa at room temperature to 205 MPa at 1200°C. Additionally, the plastic deformation of the as‐sintered specimens occurs when the testing temperature reaches to 1200°C. The values of high‐temperature bending strength of as‐healed specimens are comparable with those of as‐sintered specimens. Similar to that of as‐sintered specimens, bending strength of as‐healed specimens degrades when the testing temperature increases. Results of the present study indicate that the recovery of bending strength by the self‐healing function is able to achieve at temperatures as high as 1200°C. Unlike the mechanical behaviors at high temperatures of as‐sintered and as‐healed specimens, the bending strength of as‐cracked specimens slightly increases with the increase of testing temperature. This phenomenon is attributed to the effect of the self‐healing mechanism during high‐temperature bending tests.     

纳米ZrO2对Al2O3陶瓷性能的影响

以纳米ZrO2,微米Al2O3为原料,采用无压烧结方式制备了ZTA复相陶瓷.结果表明:纳米ZrO2的加入有利于制备细晶ZTA复相陶瓷.此外,nano-ZrO2的加入对Al2O3陶瓷的显微结构也产生影响,ZrO2颗粒以"晶内型"和晶界型2种形式存在.合理的配方组成及制备工艺有利于ZrO2以四方亚稳相存在.ZrO2质量分数为30%时,其四方相质量分数可达69%,有利于应力诱导相变增韧,该ZTA复相陶瓷的抗弯强度、断裂韧性分别达到604MPa,6.87MPa·m1/2.     

Al2 O3对硼硅酸盐玻璃结构和性能的影响

硼硅酸盐玻璃具有优良的抗热冲击性能和优异的光学性能。主要探讨了Al2 O3对硼硅酸盐玻璃的结构和性能的影响。通过红外光谱测试分析了Al2 O3含量不同时玻璃的结构变化,测试了玻璃的热膨胀系数,转变温度、膨胀软化温度、粘度和化学稳定性。研究结果表明：Al2 O3的加入使得玻璃结构中[ BO4]减少,[ BO3]相应增加,从而使得玻璃结构疏松。玻璃的热膨胀系数增大,Tg 和膨胀软化点Td 降低,化学稳定性减弱;但玻璃的软化点Tf 在Al2 O3含量小于3%时,随Al2 O3含量增加有降低趋势,大于3%时随Al2 O3含量增加有增大的趋势。玻璃的高温粘度随Al2 O3的加入增大,但低温粘度减小。     

Al-Mg合金加入量对低碳Al2O3-Al-C不烧滑板材料低温性能的影响

以板状刚玉、α-Al2O3微粉、石墨、Al粉、Al-Mg合金粉为原料,以酚醛树脂为结合剂,研究了铝镁合金的加入量对Al2O3-Al-C不烧滑板材料500-700℃埋碳和氧化气氛烧后抗折强度和抗氧化性能的影响.结果表明:Al-Mg合金加入量不宜超过6％;引入适量Al-Mg合金,500℃埋碳条件和氧化气氛烧后试样的常温抗折强度和抗氧化性均未改善,但600℃和700℃埋碳条件和氧化气氛烧后的常温抗折强度均提高;随温度升高,试样的常温抗折强度和抗氧化性均提高;试样常温强度和抗氧化性提高的原因在于:Al-Mg合金活性高,可保护树脂碳不被氧化,且Al-Mg合金有部分与CO反应生成MgO和Al2O3陶瓷相对材料起增强作用.     

CaO含量对Al2O3-MgO-CaO系浇注料性能的影响

高纯度的Al2O3-MgO-CaO系浇注料正广泛应用于精炼钢包的透气砖、座砖、工作衬及包壁修补料等,纯铝酸钙水泥既是Al2O3-MgO-CaO系统浇注料的结合剂,同时又是浇注料中CaO的主要来源.本试验通过改变纯铝酸钙水泥的加入量来改变CaO的含量,探究高温下形成的CA6等矿相对体系性能的影响.结果发现:氧化钙以本研究中的纯铝酸水泥形式引入时,随其引入量的增加,材料经110 ℃处理后的物理性能呈现优化的趋势;CA6形成产生的体积膨胀在促进结构的致密化的同时,当达到一定程度时,会导致材料结构劣化,因此材料经1550 ℃处理及5次热循环后,其物理性能呈现先提高后降低的趋势.综合各项性能认为,纯铝酸钙水泥加入量在5wt%~8wt%时其高温强度及抗热震性能较为优异.     

SiCW对Al2O3基陶瓷浓悬浮体流变性能的影响

研究了SiCW加入至Al2O3基体中注凝成型料浆的流变特性.研究结果表明:该体系表现出剪切增厚的胀流型流变特性.料浆流变性能与SiCW掺量、SiCW平均长度和SiCW与浆料的混合时间有关;但随着SiCW掺量的增加,剪切应力迅速增加,系统出现中断剪切现象;为了改善含SiCW料浆的流变性能,通过在晶须表面覆盖了一层钛酸酯的憎水膜,降低了料浆的表观粘度和剪切应力,并相应提高了晶须的掺量.