Faceting of High-Angle Grain Boundaries in Titanium-Excess BaTiO3

The grain boundaries in BaTiO₃ with excess Ti of 0.5, 0.3, and 0.1 at.% sintered at 1300° or 1250°C have been examined by scanning electron microscopy (SEM), electron backscattered diffraction pattern (EBSP), and transmission electron microscopy (TEM). In the 0.1% Ti-excess specimen, large grains growing abnormally form high-angle grain boundaries when they impinge on each other as verified by EBSP. A large fraction of these grain boundaries are faceted with hill-and-valley shapes. In the 0.5% Ti-excess specimen, large grains growing abnormally are elongated in the directions of their {111} double twins. These grains often form flat grain boundaries parallel to their {111} planes with the fine matrix grains, and the grain-boundary segments between the large impinging grains with high misorientation angles are often also parallel to the {111} planes of one of the grains. These grain boundaries are expected to be singular. Most of the grain boundaries between the randomly oriented fine-matrix grains in the 0.3 at.% Ti-excess specimen are also faceted with hill-and-valley shapes at finer scales when observed under TEM. The facet planes are parallel to {111}, {011}, and {012} planes of one of the grain pairs and are also expected to be singular. These high-angle grain boundaries lying on low index planes of one of the grain pairs are similar to those observed in other oxides and metals.     

Reducing the Sintering Temperature for MgO–Al2O3Mixtures by Addition of Cryolite (Na3AlF6)

The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al₂O₃and MgO powders with the addition of Na₃AlF₆up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al₂O₃can be produced from the mixture of 72 wt% (50 at.%) Al₂O₃+ 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na₃AlF₆fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al₂O₃can be produced from either the mixture of 90 wt% (78 at.%) Al₂O₃+ 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al₂O₃+ 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na₃AlF₆in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al₂O₃. Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water.     

Pulsed Electric Current Sintering of Silicon Nitride

Pulsed electric current sintering (PECS) has been used to densify α-Si₃N₄ powder doped with oxide additives of Y₂O₃ and Al₂O₃. A full density (>99%) was achieved with virtually no transformation to β-phase, resulting in a microstructure with fine equiaxed grains. With further holding at the sintering temperature, the α-to-β phase transformation took place, concurrent with an exaggerated grain growth of a limited number of elongated β-grains in a fine-grained matrix, leading to a distinct bimodal grain size distribution. The average grain size was found to obey a cubic growth law, indicating that the growth is diffusion-controlled. In contrast, the densification by hot pressing was accompanied by a significant degree of the phase transformation, and the subsequent grain growth gave a broad normal size distribution. The apparent activation energy for the phase transformation was as high as 1000 kJ/mol for PECS, almost twice the value for hot pressing (∼500 kJ/mol), thereby causing the retention of α-phase during the densification by PECS.     

Densification and Sintering Kinetics in Sintered Silicon Nitride

The sintering sequence of Y₂O₃-Al₂O₃-doped Si₃N₄ was investigated with respect to the relationship between densification, α→β transformation, and microstructural development. Quenching studies were performed to reveal these interactions during a complete sintering cycle. Isothermal studies were conducted to examine the sintering kinetics and compared to Kingery's liquid-phase sintering model. The bulk density increased to ≥90% of theoretical density with only minor transformation taking place. Major transformation occurred in a late sintering stage and was accompanied by the development of elongated grains. The kinetic order of the densification process, taking into account an appropriate correction, was larger than any of the rate exponents predicted by the Kingery model, indicating that other single or mixed mechanisms were active.     

Sintering-driven effects on the band gap of (Pb,La)(Ti,Ni)O3 photovoltaic ceramics

In this work, the influence of the sintering temperature on the physical properties of (Pb_0.8La_0.2)(Ti_0.9Ni_0.1)O₃ (PLT-Ni) ceramics is reported. The experimental data revealed that the energy band gap of PLT-Ni ceramics could be tailored from approximately 2.7 to 2.0 eV by changing the sintering temperature from 1100°C to 1250°C. It is demonstrated that the simple substitution of Ti⁴⁺ by Ni²⁺ cations is effective to decrease the intrinsic band gap while increasing the tetragonality factor and the spontaneous polarization. However, the additional red-shift observed in the absorption edge of the PLT-Ni with increasing the sintering temperature was associated with a continuous increase in the oxygen vacancies () amount. It is believed that the impact of the creation of these thermally induced is manifold. The presence of and Ni²⁺ ions generate the Ni²⁺- defect-pairs that promoted both a decrease in the intrinsic band gap and an additional increase of the tetragonality factor, consequently, increasing the spontaneous polarization. The creation of Ni²⁺- defects also changed the local symmetry of Ni²⁺ ions from octahedral to a square pyramid, thus lifting the degeneracy of the Ni²⁺ 3d orbitals. With the increase in the sintering temperature, lower-energy absorbing intraband states were also formed due to an excess of , being responsible for an add-on shoulder in the absorption edge, extending the light absorption curve to longer wavelengths and leading to an additional absorption in “all investigated” spectrum as well.     

口腔修复用Y-TZP陶瓷材料制备工艺研究

采用国产3Y-TZP亚微米粉体，通过双向模压结合等静压成形有效克服了条形试样的烧结弯曲，探讨了24h排胶工艺对预烧试样力学性能的影响，通过对预烧试样热膨胀曲线的测定、不同烧结温度试样力学性能和密度的比较及XRD定量分析确定了适宜的烧结工艺。结果表明，牙科支架用陶瓷，将预烧试样升至1550℃保温0．5h，排胶工艺对预烧试样的抗弯强度和断裂韧性并无显著影响，对于即可获得足够的抗弯强度，提高其断裂韧性。     

烧结工艺对纳米AgSnO2复合材料致密度的影响

对化学镀法制备的纳米AgSnO2粉末分别采用常压、热压和真空烧结的方法制成AgSnO2复合材料，研究了烧结方法及工艺对致密度的影响。结果表明，采用常压烧结，虽然成型压力、烧结温度和时间对致密度有一定的影响，但复压、复烧后，材料的致密度十分接近。热压能在短时间内获得96％以上的致密度，但复烧时膨胀严重，甚至出现鼓泡。真空烧结对去除吸附物有利，但仍会有少量残留并导致复烧时出现膨胀。在较低的压力下成型并采用分段保温烧结，不但能消除吸附物的影响，复烧后还可以得到94％的致密度。研究表明，纳米粉末表面大量的吸附物以及由此造成的封闭在压坯中的气体是阻碍烧结致密化的根本原因。     

炼铁原、燃料检、实验系统的建立与应用

介绍了济钢炼铁原、燃料检、实验系统的构成，主要性能特点，使用过程中的经验教训。此系统使用后年节省检、实验费用95．64万元。     

Y_2O_3-MgO共稳定ZrO_2的相研究

通过化学组成和相含量设计,采用湿混法制备了MgO和Y2O3共同稳定ZrO2粉末,在不同的温度下烧结,获得了室温下单斜相和四方相含量不同的烧结样品,用X射线峰宽化法测定并计算了粒子尺寸。结果表明:随着Y2O3含量的增加,单斜相含量降低,四方相含量增加。温度对相含量的影响较小,而晶粒尺寸受Y2O3和温度的影响并不明显。     

基于线性规划和神经网络的优化烧结配料系统开发

合理经济地确定烧结配料问题，具有十分重要的意义。本文从技术要求和经济效益两方面综合考虑烧结配矿的最佳经济性问题。根据线性规划法的思路。以生产实践为基础，建立目标函数，确定约束条件，对烧结所用铁矿粉进行优化配料。同时，利用神经网络模型预测烧结矿的性能指标，依据其结果调整线性规划的约束条件，从而得到满足烧结矿质量要求的最佳配矿比。