Preparation of pressureless-sintered SiC-Y2O3-Al2O3

Sintering additives were prepared from aluminium hydroxide and yttrium hydroxide. These additives were soluble in water and resulted in a binder. A -SiC powder was mixed with the additive solution and sintered at 2150° C without pressure. The oxides formed from the additive promoted sintering. The sintered body contained no pores. Aluminium, silicon, and yttrium oxide were precipitated in the sintered body.     

Synthesis and photoluminescence study of La1.8Eu0.2O3 coating on nanometric α-Al2O3

In this work the La_1.8Eu_0.2O₃ coating on nanometric alpha-alumina, α-Al₂O₃@La_1.8Eu_0.2O₃, was prepared for the first time by a soft chemical method. The powder was heat-treated at 100, 400, 800 and 1200 °C for 2 h. X-ray powder diffraction patterns (XRD), transmission electronic microscopy (TEM), emission and excitation spectra, as well as Eu³⁺ lifetime were used to characterize the material and to follow the changes in structure as the heating temperature increases. The Eu³⁺ luminescence data revealed the characteristic transitions ⁵D₀ → ⁷F_J (J = 0, 1 and 3) of Eu³⁺ at around 580, 591 and 613 nm, respectively, when the powders were excited by 393 nm. The red color of the samples changed to yellow when the powder was annealed at 1200 °C. The decrease in the (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) ratio from around 5.0 for samples heated at lower temperatures to 3.1 for samples annealed at 1200 °C is consistent with a higher symmetry of the Eu³⁺ at higher temperature. The excitation spectra of the samples also confirms this change by the presence of a more intense and broad band at around 317 nm, instead of the presence of the characteristic peak at 393 nm, which corresponds to the ⁷F₀ → ⁵L₆ transition of the Eu³⁺. The lifetimes of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ for the samples heat-treated at 100, 400, 800 and 1200 °C was evaluated as 0.57, 0.72, 0.43 and 0.31 ms, respectively.     

B2O3-Al2O3-SiO2透明玻璃陶瓷研究

玻璃陶瓷属于一类多晶陶瓷材料.通过调整玻璃基质和晶相组成可以制备出具有良好的力学、热学、电学和光学性能的玻璃陶瓷材料.采用传统的熔融和退火技术制备出含B2O3-Al2O3-SiO2-Li2O-K2O组分的硼铝硅玻璃,并通过成核和长晶工艺最终制备出透明玻璃陶瓷.配合料在铂金坩埚中于1450℃下熔融2h,然后经两步热处理制度控制晶核的生成和晶粒的长大.采用差热分析技术确定成核和长晶温度.采用X射线衍射技术对不同热处理制度下的玻璃陶瓷样品进行分析,以确定最佳成核和长晶条件.采用扫描电子显微镜分析玻璃陶瓷形态,晶粒尺寸及其在残余玻璃相中的分布.采用UV-Vis-Nir分光光度计测定玻璃陶瓷样品的透过率.     

B2O3-Al2O3-SiO2系微晶玻璃析晶动力学研究

采用差示扫描量热（DSC）分析法对B2O3-Al2O3-SiO2系统微晶玻璃的析晶动力学参数进行了测定，研究了该系统微晶玻璃的析晶动力学。结果表明：随着B2O3/SiO2比的降低，该系统玻璃的析晶活化能E呈先升高后降低的变化趋势，当B2O3/SiO2比为11：5时，析晶活化能最小，Emin=375．4kJ／mol，晶化指数n则先减小后增大，但均〉4，表明该系统玻璃可整体析晶。     

Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-CaSO4 systems

Mixtures of CaO, amorphous SiO₂ and kaolinite in the presence or absence of SO ₄ ^2– ions (added as CaSO₄·2H₂O) were treated in suspension under hydrothermal conditions at temperatures of 80–200 °C. Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO₂ mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO ₄ ^2– ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and -C₂SH by increasing the autoclaving temperature. In the C-S-A-C¯s system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-alumirtate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, -C₂SH and anhydrite II are formed. In both systems the excess Al₂O₃ appeared as a hydrogarnet phase, C₃ASH₄.Cement Notations used are C CaO - S SiO₂ - A Al₂O₃ - H H₂O - CH Ca(OH)₂ - C¯s CaSO₄     

The crystallization of Gd2 3 -Al2O3 glasses

Glasses of Gd₂O₃ · x Al₂O₃ compositions where x represents 5/3, 4 and 6, were prepared using a rapid quenching apparatus and a laser beam. The crystallization process of the glasses was studied by means of differential thermal analysis (DTA), X-ray diffraction analysis and electron microscopy. The crystallizations of Gd₂O₃ · 5/3Al₂O₃, Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · 6Al₂O₃ are complex and exhibit one, two and three exothermic peaks in DTA measurement with increasing Al₂O₃ concentration, respectively. The crystallization process of Gd₂O₃ · 5/3Al₂O₃ glass involved the direct formation of the gadolinium aluminium garnet, 3Gd₂O₃ · 5l_{2 3} (GdAG), which is not obtained by the ordinary solid phase reaction. After crystallization of Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · l_{2 3} glass, both phases become a mixture of Gd₂O₃ · Al₂O₃ (perovskite type) and -Al₂O₃.     

Physical and Thermal Properties of P2O5-Al2O3-BaO-La2O3 Glasses

The physical and thermal properties of P2O5-Al2O3-BaO-La2O3 glasses were investigated. The effects of glass compositions on the transition temperature, thermal expansion coefficient, density, hardness and refractive index of glasses were studied. The highest hardness of the glasses is 4143.891 MPa and the lowest thermal expansion coefficient of the glasses is 71.770×10-7/℃. A phosphate glass with high mechanical strength and good thermal characteristic is obtained.     

Sinterability of Y2O3-Al2O3 particulate stainless steel matrix composites

P/M 316L austenitic stainless steel has been reinforced with yttria and alumina particles. In order to improve the sintering behaviour of these composite materials, chromium diboride and boron nitride were added. The sinterability of the different materials has been characterised through dilatometry and sintering curves (sintered density vs. sintering temperature). A metallographic study by SEM coupled with microprobe has also been performed. Composites materials present a good densification. Chromium diboride and boron nitride react with the matrix in different manners, but they both greatly improve the sinterability of reinforced materials. The optimum sintering temperature for these composites materials is 1250 °C.     

An investigation of phase stability in the Y2O3-Al2O3 system

The stability of the three known phases in the Y₂O₃-Al₂O₃ pseudo-binary system has been investigated. YAlO₃ (YAP) and Y₄Al₂O₉ (YAM) decompose at elevated temperatures, the products of the reaction being the third compound Y₃Al₅O₁₂ (YAG) and an unknown phase (designated X). The decomposition is most evident in powders but can also be initiated on the surface of bulk single crystals. X-ray diffraction studies have been performed in an attempt to identify the structure and composition of the unknown phase. The thermal decomposition has been found to be surface controlled and an optical and scanning electron microscope study of the associated morphological changes in YAlO₃ indicates that the reaction involves localized surface melting, probably with the loss of oxygen which effectively moves the composition off the binary join.     

Oxidation behaviour of the sintered Si3N4-Y2O3-Al2O3 system

The oxidation behaviour of silicon nitride composed of Si₃N₄, Y₂O₃, Al₂O₃, AlN and TiO₂ was investigated in dry and wet air at 1100–1400 °C. The oxidation rates were confirmed to obey the parabolic law. An activation energy of 255 kJ mol^–1 was calculated from the Arrhenius plots of the results of oxidation in an air flow. In still air the oxidation rate was larger than that in an air flow, but the oxidation rate in flowing air was not affected by the air flow rate. -cristobalite and Y₂O₃·2SiO₂ were formed in oxidized surface layers. These crystal phases increased with increasing oxidation temperature. In particular, a higher content of -cristobalite was obtained in still air oxidation. The existence of water vapour in flowing air greatly promoted the oxidation.Concurrent with Kanagawa Academy of Science and Technology.     

Phase changes at abraded surfaces of ZrO2-Sc2O3-Al2O3 solid electrolyte

Diamond grinding drastically lowered the surface monoclinic concentration in a ZrO₂-Sc₂O₃-Al₂O₃ solid electrolyte and caused asymmetric broadening of the X-ray diffraction peaks. Annealing in air eliminated the broadening and partly restored the monoclinic concentration, in a manner which suggests that the grinding had converted surface monoclinic to a metastable tetragonal structure.     

爆轰法合成纳米α-Al_2O_3粉体

利用硝酸铝、尿素和炸药为原料,通过研究配比出一种类似塑性炸药的混合炸药,引爆此混合炸药,爆轰完毕得到了纳米-αAl2O3粉体。对收集到的实验粉体分别进行了高分辨率透射电镜分析、衍射分析和热分析。分析结果表明,用此法所得到的纳米-αAl2O3呈球形,颗粒尺寸分布非常均匀,每个颗粒的大小为35nm左右,晶型为单一的α型。爆轰法合成纳米-αAl2O3具有合成反应速度快、设备简单和易放大产量的优点。     

阳极支撑型ITSOFC密封材料SrO-La2O3-Al2O3-B2O3-SiO2微晶玻璃的研究

研究了应用于阳极支撑型的中温固体氧化物燃料电池(ITSOFC)密封的SrO-La2O3-Al2O3-B2O3-SiO2体系微晶玻璃不同组分的线膨胀率,结果表明当微晶玻璃粉组成SrCO3 28.14%(摩尔分数),La2O3 21.17%(摩尔分数),Al2O3 7.22%(摩尔分数),H2BO3 41.72%(摩尔分数),SiO2 1.76%(摩尔分数)(SLABS3) 时,最符合ITSOFC密封要求.差热分析结果表明SLABS3的玻璃转变温度在670℃～760℃之间,结晶温度在813～840℃之间,玻璃软化点约在900℃,XRD测试表明微晶玻璃与Ni-La0.3Ce0.7O1.85(Ni-LDC)阳极化学相容性好,将微晶玻璃和Ni-LDC在850℃烧结100h后,SEM观察界面粘附性好,EPMA测试界面的元素含量结果表明,虽然阳极的Ce会向微晶玻璃扩散10μm的深度,但观察不到微晶玻璃的元素向Ni-LDC扩散现象.用SLABS3密封模拟电池,测试开路电压结果表明SLABS3的密封效果和稳定性良好.     

Preparation and characterisation ofβ″-Al2O3

Beta alumina solid electrolyte is a potential candidate in the fabrication of Na-S batteries. In the present study, it has been prepared in the form of discs by uniaxially as well as isostatically pressing and sintering in the temperature range 1585–1630°C, the highest sintered density of 3·25 g/cm³ has been achieved in the samples isostatically pressed and sintered at 1630°C. X-ray analysis of the samples shows formation ofβ″-phase. Microstructure of the sintered samples reveals some darker regions which are attributed to low soda content. Resistivity at 300°C measured by the two-probe method at a frequency of 1 MHz on samples having vacuum-deposited silver electrodes is 15 ohm-cm, which is slightly higher than the value of 5–13 ohm-cm reported in literature using molten sodium electrodes. The activation energy of conductivity is 0·24 eV which is comparable to the literature value of 0·24–0·35 eV.     

Creep features of Al2O3-Al alloy composites

Creep features of two cast aluminium alloy composites reinforced by Al₂O₃ short fibres randomly oriented in the matrices have been studied at 300 °C and several stress levels. The presence of short-term negative creep in primary creep is an important feature for the composites, which resulted from randomly oriented fibres strongly resisting dislocation creep in the matrix. However, the negative creep magnitude depended on both the applied stress and the nature of the material. There was a critical stress for the presence of the short-term negative creep. When the applied stress had exceeded the critical value, the negative creep disappeared. Fibres traversing grain boundaries can reinforce and resist grain boundary sliding at elevated temperature. The effect of stress on creep rate for the composites is not so strong as that for unidirectional metallic matrix composites. During the creep, some intermetallic phases in the Al₂O₃/Al-5Si-3Cu-1 Mg composite were precipitated and most of them were segregated at grain boundaries, leading to a small increase of the creep rate.