Atomic Layer Deposited Ti2O3 Thin Films

Ti₂O₃ thin films have been prepared through atomic layer deposition and subjected to electrical resistivity measurements as a function of temperature. The as-prepared films were stable for up to three weeks. In Ti₂O₃ thin films, the insulator-metal transition is observed at ∼80 K, with nearly 3–4 orders of magnitude change in resistivity. The anomalous increase in electrical resistivity in the films is in accordance with the two-band model. However, the energy interval between the bands depending on the crystallographic c/a ratio leads to a change in electrical resistivity as a function of temperature.     

Preparation and Characterization of Al8.31Si1.91Mg3.78O20/Al4.8Si1.2O9.6/Mg2.0Al4.02Si4.98O18 Multiphase Material

A two-step sintering method was used to prepare Al8.31Si1.91Mg3.78O20 (corundum solid solution)/Al4.8Si1.2O9.6 (mullite solid solution)/Mg2.0Al4.02Si4.98O18 (cordierite solid solution) multiphase material, for the purposes of making these three crystal structures have point defects which could help the particles diffuse and transfer at high temperature, accelerate the sintering efficiently and enhance the material strength as well as the bulk density. The impacts of different formulas on the structure and properties of the multiphase material were investigated. With XRD and SEM analyses, for each sample, the crystal structure and microstructure were characterized, the crystalline phase content and cell parameters were determined with Rietveld Quantification software, and the properties were tested. The comparative optimal formula determined was calcinated chamotte of 80wt% and calcinated sludge of 20wt%; and its corresponding bending strength and retention rate of bending strength after a thermal shock were 29.74 MPa and 80.15%, respectively.     

着靶速度对刚玉块石混凝土抗侵彻性能的影响

着重对不同着靶速度下,弹体在刚玉块石混凝土中的侵彻情况进行了试验。研究结果表明,弹体的侵彻深度不随靶速度的提高而增加。这与弹体在普通混凝土和岩石中的侵彻现象明显不同,主要是由侵彻弹体发生破坏失去了继续侵彻能力造成的。而且,与普通混凝土或岩石相比,着靶速度越高,刚玉块石混凝土的抗侵彻性能越强。     

环境气氛作用下煤灰在刚玉质耐火板上的表面结渣行为

采用了扫描电镜、能谱分析仪、X射线衍射等方法对不同环境气氛下熔融煤灰在刚玉耐火板上煅烧渣样进行了测试，并就渣样的形貌、成分分布及与刚玉质耐火板之间的高温烧结特性进行了分析研究。研究结果表明，氧化性气氛下，碱性氧化物促进了煤灰在刚玉耐火板上的黏结作用，特别是Al含量较高的耐火板更有利于促进其发生共晶反应。还原性条件下，煤灰中生成的FeO具有很强的助熔效果，促使矿物之间产生低熔点的共熔物，同时Fe、Cr、Ti的扩散偏析减弱，加强了熔融煤灰对耐火板的黏结作用。     

刚玉块石粒径对刚玉块石砼抗侵彻性能影响的试验研究

对刚玉块石粒径对刚玉块石砼抗侵彻性能的影响进行了试验研究,结果表明,刚玉块石粒径越大,布置越紧密,刚玉块石砼的抗侵彻性能越强;在提高材料遮弹性能上,设法使弹体破坏比使其偏转效果更佳。     

Preparation, characterization and gas-sensitive properties of nano-crystalline Cr_2O_3-Fe_2O_3 mixed oxides

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Influence of the exchange‐correlation functional in all‐electron calculations of the vibrational frequencies of corundum (α‐Al2O3)

The equilibrium structural parameters, high‐ and low‐frequency dielectric tensors, Born effective charges, and Γ‐point vibrational frequencies of bulk Al₂O₃ corundum are calculated by using the periodic, ab initio program CRYSTAL, which adopts an all‐electron Gaussian‐type basis set. The effect of basis set and the performance of three different functionals, i.e., LDA, PW91, and B3LYP, are discussed. The mean absolute deviation from the measured frequencies is as small as 7 cm^?1 for both the LDA and B3LYP functionals, indicating that these functionals perform extremely well in this case. The mean absolute deviation increases to 18 cm^?1 when the PW91 functional is used. All three functionals reproduce the equilibrium geometry of corundum to a high level of accuracy, with LDA and B3LYP outperforming PW91 slightly. The comparison of the current all‐electron calculations with previous plane‐wave, pseudo‐potential calculations shows an overall similar performance. The results of isotopic substitution for both Al and O are also presented. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

High-pressure single-crystal studies of MnTiO3

Abstract

Recent high-pressure single-crystal x-ray diffraction experiments have provided new information on the crystal chemistry of MnTiO₃ and have provided insight into polymorphic transitions among phases of this composition. The stable polymorph of MnTiO₃ at room P and T has the ilmenite structure. At high P and T, MnTiO₃ ilmenite (MnTiO₃ II) transforms to a LiNbO₃ structure through a cation reordering process, and the quenched LiNbO₃-structure phase transforms to a perovskite structure as the pressure is again increased. This transition is unique in that twinned MnTiO₃ II crystals transform under pressure to untwinned crystals having the perovskite structure. The back-transformation of perovskite to the LiNbO₃ structure as pressure is released is similar to that observed previously for the rutile-type dioxides TiO₂ and SnO₂.     

Theoretical evaluation of the electron paramagnetic resonance spin Hamiltonian parameters for the impurity displacements for Fe3+ and Ru3+ in corundum

The impurity displacements for Fe³⁺ and Ru³⁺ in corundum (Al₂O₃) are theoretically studied using the perturbation formulas of the spin Hamiltonian parameters (zero-field splitting and anisotropic g factors) for a 3d⁵ (with high spin S = 5/2) and a 4d⁵ (with low spin S = 1/2) ion in trigonal symmetry, respectively. According to the investigations, the nd⁵ (n = 3 and 4) impurity ions may not locate at the ideal Al³⁺ site but undergo axial displacements by about 0.132 Å and 0.170 Å for Fe³⁺ and Ru³⁺, respectively, away from the center of the ligand octahedron along the C₃ axis. The calculated spin Hamiltonian parameters based on the above axial displacements show good agreement with the observed values. The validity of the results is discussed.     

刚玉块石砼抗侵彻特性试验研究

刚玉材料具有特殊的物理力学性能,硬度高,强度大,用混凝土作粘结剂,将大小不一、形状不规则的刚玉块石紧密粘结成具有一定厚度的平面板状,然后将其和混凝土共同浇注,这样的复合整体称为刚玉块石混凝土,这是一种新型防护遮弹材料,为研究其防护遮弹性能及效果,本文对普通钢筋混凝土和刚玉块石混凝土同时进行了抗侵彻模拟试验研究,试验中设计弹速340m/s,测定了侵彻深度,对弹体和靶体的破坏现象进行了描述,通过两者的试验结果的对比分析与研究,可以发现,与普通钢筋混凝土相比,刚玉块石混凝土能够有效的使弹体破坏,并阻止其侵彻,具有较强的抗侵彻能力。本文的研究结果可以为刚玉块石混凝土抗侵彻性能的机理探索提供参考。