Wettability of silicon carbide ceramic by Al2O3/Dy2O3 and Al2O3/Yb2O3 systems

Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al₂O₃ /Dy₂O₃ and Al₂O₃ /Yb₂O₃, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al₂O₃ and RE₂O₃ reacted and formed the Dy₃Al₅O₁₂ (DyAg) and Yb₃Al₅O₁₂ (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics.     

Microstructural observations of pressure cast Ni3Al/Al2O3 and Ni/Al2O3 composites

Pressure castings of Ni₃Al(IC218)/Al₂O₃ and Ni/Al₂O₃ composites, made with continuous DuPont FP α-Al₂O₃ and DuPont PRD166 α-Al₂O₃+20 wt pct partially stabilized ZrO₂ 20 μm diameter fibers, were examined by optical, scanning electron microscope (SEM), and transmission electron microscope (TEM) techniques. According to optical magnifications, excellent infiltration took place. However, in SEM and TEM magnifications, small gaps were found adjacent to regions where bonding had taken place between fibers. On the basis of available evidence, the gap formation was attributed to trapped gases and microshrinkage. Titanium was added to the metal to promote infiltration. Diffusion of Ti into the fibers of the Ni/Al₂O₃ composites occurred, but similar diffusion into the fibers of the IC218/Al₂O₃ composites did not take place. The qualitatively higher bond strength of the interfaces of the Ni/Al₂O₃ composites was ascribed to the diffusion of Ti into Al₂O₃. No interface reaction layer was found in any of the composites. Very little grain growth was found to take place in either the FP or PRD 166 fibers after casting and after a subsequent ten day anneal at 1150 °C.     

Al2O3对烧结矿RDI的影响规律

采用断裂韧性的方法并结合电子显微分析技术,研究了Ａｌ２Ｏ３对烧结矿的低温还原粉化率（ＲＤＩ）的影响规律。研究结果表明：Ａｌ２Ｏ３主要分布在烧结矿的玻璃相中,并以硅铝酸铁和硅铝酸钙的形式存在;烧结矿中Ａｌ２Ｏ３的增加导致玻璃相的断裂韧性降低。作认为,玻璃相断裂韧性的降低是引起烧结矿的ＲＤＩ增大的主要原因,并确定了烧结矿综合断裂韧性与ＲＤＩ良好的对应关系。     

Influence of Al2O3 Level in CaO-SiO2-MgO-Al2O3 Refining Slags on Slag/Magnesia-Doloma Refractory Interactions

Metallurgical and Materials Transactions B - The influence of the Al2O3 level in CaO-SiO2-MgO-Al2O3 (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was...     

Influence of MgO addition on the properties of porous Al2O3 refractory containing TiO2 and Al2O3 in the matrix

The properties of porous Al₂O₃ refractory containing TiO₂/Al₂O₃ with a molar ratio of 0.96 in the matrix were studied with different amounts of MgO additives. Bright glossy areas were observed around and inside the Al₂O₃ particles. These were determined as Al₂O₃ · TiO₂ from the results of X-ray diffraction and EPMA analyses. The addition of MgO generated the dark glossy areas the compound of which was Na₂O · 4 MgO · 15 Al₂O₃. But for high MgO contents, Al₂O₃ · TiO₂, MgO · Al₂O₃ and Na₂O · 4 MgO · 15 Al₂O₃ coexisted in the dark glossy areas. These products prevented TiO₂ from invading the grain boundary, consequently grain-boundary cracks in the particles decreased and the physical properties, especially compressive and bending strength, were extremely improved. Thermal shock resistance was also improved by the rise of strength and fracture energy due to the addition of MgO. Corrosion resistance increased as the content of MgO increased. This was considered to be generated by the occlusion of FeO into MgO. Particularly, the fact that the penetration thickness decreased by the addition of MgO will contribute not only to the stable operation in actual use but also eliminating the procedure during which the porous plugs are cleaned by O₂ after every usage.     

Influence of the Ratio of Ethanol to Water on the Agglomeration of Al2O3/Y2O3-ZrO2 Nanoparticles

A method of heating ethanol-aqueous salt solution combined with co-precipitation was used to synthesize Al2O3/ZrO2 nanoparticles. The analysis of DSC and XRD revealed that the transformation temperature from amorphous to crystal phase was about 850℃. The grain size was increased with the raising of calcine temperature. The alcohol-water ratio did not affect the formation of main crystal phases, but affected the agglomeration of nanoparticles based on the results of TEM. When alcohol-water ratio was 51, the dispersion of nanoparticles was good. When there was not alcohol, the dispersion of nanoparticles was poor because there was only pure co-precipitation reaction and the speed of co-precipitation reaction was too high to have enough time of PEG. dispersing particles.     

Al含量对Al_2O_3/Al金属陶瓷性能影响研究

金属陶瓷既保持了陶瓷材料优异特性,又具备金属材料优势,是一种重要的新型工程材料。本文利用粉末冶金方法制备氧化铝-铝金属陶瓷材料,研究其致密化机理,为制备高性能金属陶瓷材料提供参考。研究表明,随着Al含量的降低,金属陶瓷材料的致密度逐渐降低。在扫描电镜图片中,颗粒呈连续分布且较大的为金属Al颗粒,颗粒呈不连续分布较细小的为Al2O3颗粒。随着Al含量的降低,金属陶瓷材料的晶界数量逐渐增多。随着Al含量由75%(质量分数,下同)减至25%时,硬度依次下降,Al含量高,易熔融相多,Al2O3粉末相对少,Al能较好较充分的将Al2O3粉末包裹住,且致密化效果好,故样品整体有较高的硬度。随着Al含量的降低,样品的导电性逐渐变差。     

Influence of Al2O3 on the reoxidation of aluminum in molten cryolite

The influence of Al₂O₃ content on the reoxidation reaction at 1293 K between CO₂ and Al dissolved in molten cryolite was examined. The rate and extent of the reaction were evaluated as the concentration of Al₂O₃ was varied from 0 to 12 wt pct at 4 pct intervals. The cryolite, under an argon atmosphere, was saturated with Al before CO₂ was introduced. High initial reaction rates were observed with a quasisteady state condition established 30 to 60 min after beginning an experiment. Increasing the Al₂O₃ content of the melt significantly reduced the initial rate, but it was not found to alter the steady rate for a given flow system. This phenomenon was observed for systems where CO₂ was passed over or bubbled through the molten cryolite. Bubbling the CO₂ through the molten cryolite led to increases in both the initial and steady state rates. M. K. Han, formerly a Graduate Fellow with the University of Washington.     

Thermodynamic analysis of aluminate formation at Fe/Al2O3 and Cu/Al2O3 interfaces

Subsolidus ternary phase relationships in the systems FeAlO and CuAlO are reviewed in order to provide a basis for thermodynamic analysis of aluminate formation at Fe/α-Al₂O₃ and Cu/α-Al₂O₃ interfaces. Expressions for the critical oxygen activity in the Fe-rich and Cu-rich solid solutions necessary to stabilize the equilibrium aluminate phases (FeAl₂O₄ and CuAlO₂, respectively) in the presence of α-Al₂O₃ are derived using data available in the literature. As in previous work in the NiαAl₂O₃ system, aluminate formation by solid state reaction of Fe and Cu with α-Al₂O₃ was calculated to require a threshold concentration of oxygen in the metal, which is of the order of 1/5 the solubility limit. The sults are presented in stability diagrams and compared with previous results on the Ni/α-Al₂O₃ system in terms of the free energies of formation of the aluminates and the relative free energes of solution of oxygen in the metals. The results are also compared with available experimental observations on Fe/α-Al₂O₃ and Cu/α-Al₂O₃ interfaces.     

过程控制剂对Al2O3/Mo复合粉末细化的影响

采用溶胶一凝胶技术制备Al2O3/Mo复合粉末,研究了过程控制剂(PCA)——硬脂酸和无水乙醇对Al2O3/Mo复合粉末细化的影响.利用X射线衍射仪和扫描电镜对复合粉末进行物相和形貌分析,利用激光粒度分布测试仪测试了粉末的粒度分布.结果表明:添加过程控制剂可以有效降低粉末粘球和结块的现象,提高出粉率;不添加过程控制剂时,粉末颗粒大小极不均匀;以硬脂酸和无水乙醇作PCA时,随着球磨时间的延长,Al2O3/Mo复合粉末逐渐被细化,颗粒大小相对均匀,颗粒形态经历了从球状向片状再到球形的转化,其中以无水乙醇作PCA时,粉末被细化的速率较高.以硬脂酸作PCA最终制得的粉末较以无水乙醇作PCA最终得到的粉末,粒度分布较为均匀,且细小颗粒的粒径分布较多.     

Influence of MgO,Al2O3 and CaO/SiO2 on the viscosity of blast furnace type slag with high Al2O3 and 5 wt-% TiO2

The effect of MgO, Al₂O₃ and CaO/SiO₂ on the viscosity of CaO–SiO₂–Al₂O₃–MgO–5 wt-% TiO₂ slag was studied in the temperature range of 1673–1773?K. At a fixed CaO/SiO₂ ratio of 1·17 and 12 wt-% Al₂O₃, the viscosity of the slag decreased with increasing MgO content because of depolymerisation of the silicate structures. At a fixed CaO/SiO₂ ratio of 1·17 and 8 wt-% MgO, the viscosity of the slag increased with increasing Al₂O₃ content. At 8 wt-% MgO and 12 wt-% Al₂O₃ wt-%, increasing the CaO/SiO₂ ratio from 1·07 to 1·50 resulted in lower slag viscosity. The temperature dependencies of the viscosity on MgO addition, Al₂O₃ addition, and CaO/SiO₂ ratio were analyzed, and the apparent activation energies of each system were found to be between 178 and 232?kJ/mol, 273 and 360?kJ/mol, and 204 and 233?kJ/mol, respectively. Five different viscosity models were employed to predict slag viscosity, and the Riboud model was found to be the best for predicting this parameter.     

Al2O3含量对ZrO2/Al2O3陶瓷材料微观结构和力学性能的影响

以陶瓷纺织剪刀为应用目标。开发成功ZrO2／Al2O3复相陶瓷材料，并对其微观结构和力学性能进行了研究。结果表明。随着Al2O3含量的增加，材料晶粒逐渐减小，材料中t相ZrO2的含量呈上升趋势。这有利于材料断裂韧度和横向断裂强度的提高；当Al2O3含量（质量分数）为20％左右时，ZrCh／Al2O3复相陶瓷材料的综合力学性能最佳。     

烧结矿不同MgO/Al2O3比对烧结性能及冶金性能影响的试验研究

为了研究MgO/Al2 O3比对烧结矿的烧结性能和冶金性能的影响,开展不同MgO/Al2 O3比烧结杯及冶金性能试验,结果表明:随MgO/Al2 O3比逐步升高,烧结矿的烧结性能、还原度及软熔滴落性能等指标逐步变差,且MgO/Al2O3比超过1.83后变差程度明显.主要原因是随着MgO/Al2O3比的增加,烧结矿中含镁...     

Catalytic Synthesis of Tert-Butyl Acetate by Nd2O3/Al2O3-Nd2O3/ZnO

Nd2O3 was used to support Al2O3 and ZnO to prepare a supported solid base catalyst and investigate the effect of catalyst and reaction conditions on the synthesis of tert-butyl acetate. The composited oxide of Nd2O3/Al2O3-Nd2O3/ZnO exhibited excellent catalytic activity for the synthsis of tert-butyl acetate. The molar ratio of tert-butanol to acetic anhydride is 31, the catalyst in total amount of reactant nearly 0.5%, and reaction time 6 h. With the above conditions, yield of the reaction could reach to 65%. The structure of product were verified by the FT-IR, Element analysis, and MS, which proved that the product was tert-butyl acetate.     

复合材料Al/Al4C3/Al2O3的组织结构与力学性能

采用机械合金化（ＭＡ）球磨和热压烧结工艺制备了复合材料Ａｌ／Ａｌ４Ｃ３／Ａｌ２Ｏ３，对其组织结构和力学性能进行了研究。结果表明，发育良好的Ａｌ４Ｃ３棒状单晶体和等轴状γＡｌ２Ｏ３均匀分布在铝晶界或晶粒内部，二者体积含量约为６６ｖ％。Ａｌ／Ａｌ４Ｃ３和Ａｌ／Ａｌ２Ｏ３界面洁净，为直接的原子结合，但不存在确定的位向关系。复合材料的室温、高温强度及刚度比粉末冶金纯铝（Ｐ／ＭＡｌ）显著提高。     

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

Al_2O_3La_2O_3Y_2O_3/Cu复合材料的电弧侵蚀特性研究

采用喷射沉积和内氧化法制备出Al2O3La2O3Y2O3/Cu复合材料,研究该材料在直流20 V/20 A的工作条件下触点的电弧侵蚀特性,并与Al2O3/Cu材料进行了对比分析.利用电子天平、扫描电镜等方法分析电弧侵蚀后触点的质量变化和表面微观结构.结果表明,通过添加Y2O3、La2O3稀土氧化物颗粒,可有效降低触头材料的材料转移量.Al2O3La2O3Y2O3/Cu材料的抗熔焊性和抗烧损性优于Al2O3/Cu材料的性能.在直流阻性负载条件下Al2O3La2O3Y2O3/Cu阳极触头表面形成凹坑,阴极触头表面形成凸起,触点表面显示出浆糊状凝固物和喷发坑等电弧侵蚀形貌特征.     

m(MgO)/m(Al_2O_3)对铁矿粉烧结矿相组成的影响

在准化学平衡条件下,通过相平衡实验研究了不同的m(MgO)/m(Al_2O_3)对含两种类型的Al_2O_3的铁矿粉烧结矿相组成的影响。利用X射线衍射及扫描电镜分别对试样进行了矿相组成分析和显微结构观察。实验结果表明:当温度为1300℃、二元碱度R=2.0时,含两种类型的Al_2O_3的铁矿粉主要矿相组成相近;随着m(MgO)/m(Al_2O_3)的增大,磁铁矿(Fe_3O_4)、硅酸盐(Ca_2SiO_4)、铁酸一钙(CaO·Fe_2O_3)等矿相含量有所升高;同时铁酸钙中固溶Al减少,铁酸钙形态由板片状向针状转变,并且产生富Mg的复合铁酸钙(SFCAM)。