Structural Features of（Ce,La or Sr）（Mn or Co）O_3 NanoPerovskites as a Catalyst for Carbon Monoxide Oxidation

The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considered to be Mn or Co cations.XRD analysis and Fourier transform infrared spectroscopy results confirm the formation of perovskite structure for catalysts in which La3？and Sr2？are considered as the cations of site A.Ceria is detected as the main crystalline phase when Ce4？is selected to be cation of site A.It is found that the octahedral factor（rB/rO） takes the same important role as the tolerance factor to form cubic perovskite.Average crystallite size of the products was calculated by data of the XRD and measured by the TEM analysis.Results of the XRD and TEM studies were supported by the study of the particles size distribution,which was carried out in a particle size analyzer.The perovskite samples were also used for stoichiometric oxidation of carbon monoxide with air.     

Influence of Yb2O3 addition on microstructure and corrosion resistance of 10Cu/（10NiO-NiFe2O4） cermets

10Cu/(10NiO-NiFe₂O₄) cermets doped with Yb₂O₃ were prepared by conventional powder metallurgy technique. The effects of Yb₂O₃ content and sintering temperature on the relative density, phase composition, microstructure of the sintered cermets and the corrosion resistance to Na₃AlF₆-Al₂O₃ melts were investigated by sintered density test, XRD analysis and SEM. YbFeO₃ phase, which distributes in the ceramics grain boundary as particles or film, is produced by the reaction between Yb₂O₃ and ceramics. The addition of Yb₂O₃ accelerates the sintering process of ceramics matrix, eliminates pores in the boundary and results in coarsened crystalline grain. The relative density of the cermets with about 1% (mass fraction) Yb₂O₃ sintered at 1275 °C increases to above 95%. Addition of about 1.0% Yb₂O₃ can inhibit obviously the corrosion of NiFe₂O₄ grain boundary and Cu phase in Na₃AlF₆-Al₂O₃ melts.     

Novel thermal expansion of lead titanate

Lattice parameters of lead titanate were precisely re-determined in the temperature range of -150-950℃ by high precision XRPD measurements. It was clarified that there was no any evidence for a new phase transition at low tempera-tures. Tetragonal distortion strain decreases with temperature increasing. A novel thermal expansion was observed, positive thermal expansion from -150℃ to room temperature (RT) and above 490℃, and the negative thermal expansion in the temperature range of RT-490℃. A big jump of thermal expansion coefficient is attributed to the tetragonal-cubic phase transition. A rationalization for the negative thermal expansion of PbTiO3 is due to the decrease of anion-anion repulsion as polyhedra become more regular at heating. The mechanisms of positive and negative thermal expansions were elucidated as the same nature in the homogenous tetragonal phase at present case.     

Pb(1-x)SrxTiO3固溶化合物及其热膨胀性

通过高温固相合成法合成Pb1-xSrxTiO3固溶化合物,用X射线衍射测定其固溶范围为O≤x≤1,晶胞参数随固溶度z连续变化,呈非线形关系;高温X射线衍射测定了x=0．0,O．15,0．20,O．50,0．90,1．O固溶化合物的结构,得出晶格常数与温度的关系,计算出相应的本征热膨胀系数．DSC分析表明,Pb0．8Sr0．2TiO3热力学性质稳定．     

立方氮化硼的热膨胀性

通过高温高压方法合成了目前制作c-BN工具的最常用的琥珀色c-BN磨料,利用超大功率高温X射线衍射仪精确测定c-BN的晶格常数,得出晶格常数随温度变化的关系,从而精确计算c-BN的本征热膨胀系数.从室温到1000℃温度范围内,c-BN的平均线膨胀系数α=4.92×10~(-6)/℃,平均体膨胀系数万β=1.47×10~(-5)/℃.     

选择性激光烧结成形温度场的研究进展

选择性激光烧结技术与传统铸造工艺相结合,为快速制造某些难以用传统方法获得的铸件提供了有利途径.对于各种粉末材料在选择性激光烧结成形过程中温度场的模拟与预测,是合理选择其烧结工艺参数的基础.本文中综述了聚合物粉末、聚合物覆膜金属/陶瓷粉末和金属粉末在选择性激光烧结过程中的热物性参数变化规律及其相应的成形温度场分布,以利于激光选择性烧结各类粉末材料而精确成形零部件.     

铸态GCr15钢在连续加热过程中的奥氏体化动力学特征与组织演变

利用DIL805A热膨胀仪记录了铸态GCr15钢在不同的加热速率下(0.5、3、5、30、100 ℃/s)的线膨胀量,获得了不同加热速率下的热膨胀曲线和奥氏体体积转变分数曲线,研究了加热速率对奥氏体化的影响。采用高温光学显微镜对该钢在连续加热过程中的奥氏体转变过程进行了观察分析。研究表明:GC15钢在连续加热过程中的奥氏体转变可分为3个阶段:在760~790 ℃为珠光体向奥氏体的转变、(Fe, Cr)₃C_II向奥氏体中的溶解和奥氏体的成分均匀化温度分别为790~890 ℃及890 ℃以上。并且随着加热速率提高,相变临界温度提高,相变速率提高。在连续加热过程中,铸态GCr15钢的奥氏体转变是一个形核和长大交替进行的过程。     

Fe-6.5Si�߹������������D03��Ķ�������

 Fe-6.5Si高硅钢是一种具有高磁导率、低矫顽力和低铁损等优异性能的软磁材料。但有序相B2和D03,尤其是D03相的出现会使高硅钢的硬度和脆性急剧升高,并对薄板的轧制加工产生非常不利的影响。由于该合金中同时存在A2、B2和D03三相,且X射线衍射峰大量重叠,给D03相的定量分析带来困难。采用直接比较法定量分析D03相的体积分数,结果表明,h+k+l为偶数时A2与B2相{hkl}晶面衍射的结构因子相同。若将A2与B2合并成一相处理,适当调整X射线衍射直接比较法的关系式,进而对D03相的特征衍射峰与三相重叠的衍射峰进行直接比较,即可计算出D03相的体积分数。     

Crystal structure and negative thermal expansion properties of solid solution Er2W3-xMoxO12

A series of solid solutions Er₂W_3?xMo_xO₁₂ (0.5≤x≤2.5) were successfully synthesized by the solid state method. Their crystal structures and negative thermal expansion properties were studied by high temperature X-ray powder diffraction and the Rietveld method. All samples with rare earth tungstates and molybdates crystallize in the same orthorhombic structure with space group Pnca, and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TECs) of Er₂W_3?xMo_xO₁₂ were determined as ?16.2×10^?6 K^?1 for x=0.5 and ?16.5×10^?6 K^?1 for x=2.5 while ?20.2×10^?6 K^?1 and ?18.4×10^?6 K^?1 for unsubstituted Er₂W₃O₁₂ and Er₂Mo₃O₁₂ in the identical temperature range of 200?800 °C. High temperature XRD data and bond length analysis suggest that the difference between W—O and Mo—O is responsible for the change of TECs after the element substitution in the series of solid solutions.     

Coefficients of thermal expansion of thin metal films investigated by non-ambient X-ray diffraction stress analysis

Cu, Ni and Pd layers were deposited by DC-magnetron sputtering on Si wafer substrates. The mechanical stresses and the coefficients of linear thermal expansion (CTEs) were investigated by non-ambient (in-situ) X-ray diffraction measurements employing the sin²ψ crystallite group method. It was found that, in the as-produced state, the CTEs were larger than expected on the basis of literature values for the Cu and Ni layers, but not for the Pd layer. Upon annealing of the layers grain growth and decrease of the crystalline imperfection, monitored by in-situ X-ray diffraction measurements of the diffraction line broadening, occurred. The increase of the crystallite size was paralleled by a decrease of the CTE values for the Cu and Ni films. The grain-size dependence of the CTE is discussed in terms of the coordination (state of bonding) of atoms at grain boundaries and surfaces.     

The Heusler Phase Ti25(Fe50 − x Ni x )Al25 (0 ≤ x ≤ 50); Structure and Constitution

Alloys with composition Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50) were investigated employing electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD). For TiFe₂Al, in situ neutron powder diffraction (ND) was used for the inspection of phase constitution covering the temperature range from 27 °C (300 K) to 1277 °C (1550 K). Combined Rietveld refinement of ND and XPD data for TiFe₂Al revealed that Fe atoms occupy the 8c site in space group Ti with a small amount of Al sharing the 4a site, and the remaining Ti and Al atoms adopting the 4b site. This structural model was successfully applied in the refinement of all alloys Ti₂₅(Fe_50 − x Ni _x )Al₂₅ (0 ≤ x ≤ 50). Partial atom order exists on the Fe-rich side while complete order is observed for the Ni-rich side. Profiles recorded by in situ neutron powder diffraction for TiFe₂Al in the range of investigated temperatures show two phases, namely Heusler phase and MgZn₂-type Laves phase. Diffraction peaks from the Heusler phase dominate the profiles at lower temperatures but at higher temperatures the MgZn₂-type Laves phase is the main phase. No CsCl-type phase was found in the alloy in the investigated temperature range. The thermal expansion coefficient of TiFe₂Al is 1.4552 × 10⁻⁵ K⁻¹.