热等静压法制备多孔NiTi形状记忆合金

运用热等静压法(hot isostatic pressing,HIP),制备出多孔的NiTi形状记忆合金.制备出的多孔NiTi合金具有接近球状的孔,孔径在50～200μm,孔的分布均匀且各向同性.本文研究了多孔NiTi形状记忆合金在不同时效条件下的微观结构和马氏体相变行为,发现富Ni的多孔NiTi形状记忆合金的相变机制与富Ni致密NiTi合金相类似,时效后的冷却曲线出现两个峰,表示母相B2→R的转变和R→B19'的转变过程.     

等静压技术在粉末冶金材料生产中的应用

介绍了等静压技术的发展概况、原理与类别,并着重评述了该技术在粉末冶金材料生产中的应用及对材料组织性能的影响。     

热等静压制备亚微米细晶氧化铝陶瓷的研究

采用商业氧化铝粉体为原料,MgO为烧结助剂,采用干压结合冷等静压成型素坯,再经适当温度预烧得到具有一定密度的预烧体,对预烧体的晶粒生长与致密化过程进行了研究.素坯在1275℃/160MPa下热等静压烧结2h后得到了平均晶粒尺寸为650～850nm的氧化铝陶瓷.通过万能材料试验机、显微硬度仪测试抛光样品力学性能,得到其三点抗弯强度为(620±30) MPa,硬度HV10为(19.7±0.4)GPa,断裂韧性约2.52MPa·m1/2.     

热等静压法制备TiNiNb合金管工艺及其微观组织研究

利用热等静压法将TiNiNb预合金粉末制备成了大尺寸TiNiNb合金管(外径35 mm,内径15 mm,高为100 mm)。对制备出的TiNiNb合金管的微观组织、力学性能及马氏体相变行为进行了探究。结果表明,热等静压工艺参数为1 100℃、110 MPa、保温保压3 h时,可制备出微观组织较均匀的大尺寸TiNiNb合金管。热等静压TiNiNb合金管微观组织主要有TiNi基体相、β-Nb相、少量的(Ti,Nb)_2Ni相及TiC相。热等静压态TiNiNb合金管硬度高于锻态TiNiNb合金这可能是存在TiC相导致。在研究其马氏体相变行为时,发现该合金马氏体相变为两步相变,但其马氏体逆相变行为并不明显。     

热处理对热等静压SiP/Al-Cu复合材料显微组织和力学性能的影响

采用元素粉作为原料, 通过热等静压技术(HIP)制备出50%Si_P/Al-Cu和70%Si_P/Al-Cu(体积分数)复合材料, 研究固溶处理和峰值时效处理对复合材料显微组织、 Al₂Cu相溶解过程及力学性能的影响。结果表明: 热等静压技术制备的Si_P/Al-Cu复合材料完全致密, 组织均匀细小, 材料由Si相、 Al相和Al₂Cu组成, 白色Al₂Cu相产生于原始的Cu粉与Al粉界面处。在516 ℃固溶处理2 h后, 70%Si_P/Al-Cu复合材料中的Al₂Cu相全部溶入Al基体中, 而50%Si_P/Al-Cu复合材料中还残留少量Al₂Cu相。经过峰值时效处理后, 50%Si_P/Al-Cu和70%Si_P/Al-Cu复合材料的抗弯强度为548 MPa和404 MPa, 相对于热等静压态分别提高了38.81%和13.51%, 复合材料的强度显著增强。     

AlN-BN复相陶瓷的热等静压制备与性能研究

以氮化铝(AlN)和氮化硼(BN)为原料, 无烧结助剂、热等静压烧结制备了AlN-BN复相陶瓷, 研究了热等静压温度和压强对两种不同原料配比(摩尔比)烧结试样的微观结构和性能的影响。结果表明: 增加BN的添加量对复相陶瓷的烧结致密化影响较小, 但逐渐降低硬度和热导率、增大体积电阻率。相同原料配比下, 复相陶瓷的密度越高, 其热导率、体积电阻率、硬度越高。热导率和体积电阻率的实测值与两相复合模型方程较为符合。当n_AlN:n_BN=75:25时, 在温度为1600℃、压强为90 MPa、保温3 h的热等静压工艺下可以制备出相对密度达98.03%、热导率为77.29 W/(m·K)、体积电阻率为1.35×10¹⁵ Ω·cm的复相陶瓷。     

耐蚀合金/碳钢热等静压扩散焊接反应层元素互扩散规律研究

利用动力学软件Dictra中的单相扩散模型模拟计算耐蚀合金与碳钢热等静压扩散焊接结合界面附近的元素浓度分布,并根据热力学相图计算建立获得扩散反应层内微观组织与界面元素浓度分布之间的关系.计算结果表明:该模拟方法能够准确描述热等静压扩散焊接过程中的元素浓度分布规律,同时能够预测扩散反应层内的微观组织变化.在此基础上,利用这一模型计算得出温度和时间对扩散焊接过程中元素互扩散规律的影响,结合元素扩散距离与界面结合质量之间的关系,得到耐蚀合金与碳钢可以实现界面良好结合的工艺条件:1050℃/200MPa/2.5～3h,1100℃/200MPa/1h,1150℃/200MPa/0.5h等.     

致密 TiC-Al2O3复合陶瓷材料的自蔓延高温合成

本文通过自蔓延高温合成结合准热等静压法(     

热等静压对DD3单晶高温合金组织与性能的影响

选用两种热等静压工艺对DD3合金进行热等静压实验,研究了热等静压对DD3单晶高温合金组织与性能的影响.观察、分析了热等静压及完全热处理后组织,测试了经热等静压并热处理后合金的持久、蠕变及拉伸性能.结果表明:热等静压工艺可部分或完全消除DD3合金的铸造疏松或缩孔,但导致合金γ'强化相的回溶和不规则长大,热处理后γ'相粗大且立方化和规则性差,合金的中、高温持久和蠕变性能有所降低,对900℃拉伸性能无明显影响.     

热等静压烧结制备细晶粒Ce,Y:SrHfO3闪烁陶瓷

Ce:SrHfO₃陶瓷因具有高密度和高有效原子序数, 对高能射线具有很强的阻止能力。同时, Ce:SrHfO₃陶瓷还具有快衰减和高能量分辨率等优异的闪烁性能, 引起了研究人员的广泛关注。由于传统的烧结方法难以实现非立方结构Ce:SrHfO₃陶瓷的透明化, 本研究采用真空长时烧结和短时真空预烧结合热等静压烧结(Hot Isostatic Pressing, HIP)方法制备Ce,Y:SrHfO₃陶瓷。以金属氧化物和碳酸盐为原料, 1200 ℃下煅烧8 h可以获得平均粒径为152 nm的纯相Ce,Y:SrHfO₃粉体。1800 ℃真空烧结20 h获得平均晶粒尺寸为28.6 μm的不透明的Ce,Y:SrHfO₃陶瓷, 而两步烧结法可以制备光学透过率良好的Ce,Y:SrHfO₃陶瓷。本研究详细分析了陶瓷致密化过程中微结构的演变, 探究了预烧结温度对Ce,Y:SrHfO₃陶瓷密度、显微结构和光学透过率的影响。真空预烧(1500 ℃×2 h)结合HIP后处理(1800 ℃×3 h, 200 MPa Ar)所获得的Ce,Y:SrHfO₃陶瓷在800 nm处的最高直线透过率为21.6%, 平均晶粒尺寸仅为3.4 μm。在X射线激发下, Ce,Y:SrHfO₃陶瓷在400 nm处产生Ce³⁺ 5d-4f发射峰, 其XEL积分强度比商用锗酸铋(BGO)晶体高3.3倍, Ce,Y:SrHfO₃陶瓷在1 μs门宽下的光产额约为3700 ph/MeV。良好的光学和闪烁性能可以拓宽Ce,Y:SrHfO₃陶瓷在闪烁探测领域的应用。     

The blue bronze Tl0.30MoO3 structure and physical properties

Crystals of the so-called blue bronze Tl_0.30MoO₃ were prepared by tempering molten mixtures. The structure was refined in the space group C2/m from 2171 reflections corrected for absorption. The R and R_w factors obtained from the last refinement cycle are 0.030 and 0.036 respectively for 114 refined parameters. The Zachariasen method enabled the 4d distribution over the three independent sites Mo1, Mo2 and Mo3 to be determined and gave 16.6 %, 39.7 % and 43.7 % respectively.For each octahedron a close correlation appears between the number of shared edges, the formal molybdenum charge and its eccentricity within the polyhedron. It is found that the molybdenum Mo1 has the highest formal charge ; this site does not seem to participate in the electrical conductivity which takes place mainly in the slabs thanks to the molybdenum sites Mo2 and Mo3 which represent 83.4 % of the electron density.Tl_0.30MoO₃ shows a metal-to-semiconductor transition at 185 K, probably of Peierls type. We propose that the non-linear effects and metastability phenomena observed below 180 K, in the non-ohmic regime are very likely due to the depinning of a charge density wave, as it has been found in the blue bronze K_0.30MoO₃     

A structural study of the hexagonal potassium tungsten bronze,K0.26WO3

The crystal structure of the hexagonal potassium tungsten bronze, K_XWO₃, has been investigated by single crystal X-ray and powder neutron diffraction techniques. The space group is P6₃22. The new structural feature found in this study is the puckering of the ring of 6 oxygen atoms forming the “windows” in the hexagonal tunnels. The potassium ions appear to be disordered over two sites in the tunnel, towards one of the two sets of window oxygen atoms.     

Electronic structure and transport properties of K-doped blue bronze Rb0.15K0.15MoO3

Single crystals of K-doped blue bronze Rb_0.15K_0.15MoO₃ and Rb_0.3MoO₃ have been investigated by measurements of the X-ray photoemission spectrum (XPS), electrical resistivity and thermoelectric power, respectively. Analysis of the XPS data reveals that two final states representing alternate screening channels coexist in Rb_0.15K_0.15MoO₃. Compared with the pure bronze, the Mo sites of the doped sample contain less 4d electrons which reflected in the movement of Mo3d spectrum. Due to the discrepancy of electronic structure, the K ion doping results in the notable increase of the single particle activation energy and decrease of the thermoelectric power in the charge density wave state.     

Preparation of hexagonal WO3 from hexagonal ammonium tungsten bronze for sensing NH3

Hexagonal tungsten oxide (h-WO₃) was prepared by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95. The structure, composition and morphology of h-WO₃ were studied by XRD, XPS, Raman, ¹H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N₂ specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO₃ sample was built up by 50-100 nm particles, had an average specific surface area of 8.3 m²/g and was thermally stable up to 450 °C. Gas sensing tests showed that h-WO₃ was sensitive to various levels (10-50 ppm) of NH₃, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH₃. To this NH₃ concentration, the sensor had significantly higher sensitivity than h-WO₃ samples prepared by wet chemical methods.     

Preparation and characterization of nano-sized Sr0.7Ca0.3TiO3 crystallines by low temperature aqueous synthesis method

Nano-sized calcium strontium titanate (Sr_0.7Ca_0.3TiO₃) particles were prepared by low temperature aqueous synthesis method at temperature as low as 90 °C and under ambient pressure. To improve the morphology and crystallinity of the particles, the hydrothermal treatment was used. The lattice structure, particle size, particle morphology, and hydroxyl defects of Sr_0.7Ca_0.3TiO₃ particles were investigated by using XRD, TEM, FE-SEM, TG and FT-IR measurements. The as-prepared particles with size about 100 nm were single cubic phase crystallines which consist of aggregates of small rounded nanocrystals about 10 nm in diameter. However, in as-prepared crystallines, a hydroxyl group was detected as a lattice defect. After the hydrothermal treatment, the hydroxyl groups in Sr_0.7Ca_0.3TiO₃ nanoparticles were partially released from the perovskite lattice. The morphology and crystallinity of the hydrothermally treated particles were observably improved.     

Evidence for the non-existence of a bragg reflection superlattice in K2Pt(CN)4Br0.3·3H2O and K2Pt(CN)4Cl0.3·3H2O

An extensive and careful search for superlattice reflections in K₂Pt(CN)₄Br_0.3·3H₂O and K₂Pt(CN)₄Cl_0.3·3H₂O has yielded no evidence for an enlarged cell. Six individual crystals obtained via different preparative methods, from solutions at several pH values from 2 to 10, and subjected to a variety of conditions of temperature and humidity have been examined. All samples gave identical cells and nearly identical diffraction patterns. Two samples gave a single weak non-integral 00l neutron reflection which is not explainable by order contamination or double diffraction.     

Al2O3/CuSn6Pb6Zn3青铜复合材料的摩擦学性能研究

研究了粉末冶金法制备的Al2O3/CuSn6Pb6Zn3青铜复合材料的摩擦学性能.试验结果表明该复合材料的耐磨性较CuSn6Pb6Zn3青铜有较大的提高,并且Al2O3颗粒的粒径和体积含量均对复合材料的耐磨性有影响.     

The preparation and growth of pure single crystals of K2Pt(CN)4Br0.3·3H2O and K2Pt(CN)4Cl0.3·3H2O

The preparation of pure single crystals of K₂Pt(CN)₄Br_0.3·3H₂O and K₂Pt(CN)₄Cl_0.3·3H₂O has been investigated. Crystals with reproducible d.c. conductivity and dielectric constants were obtained only when the mixed valence platinum salt contained one halide. The bromide complex was particularly susceptible to contamination by chloride, and a preparation scheme is presented which excludes the unwanted halide. The best quality crystals were grown by slow evaporation of solutions which were 1 molar in urea and 0.1 molar in the appropriate potassium halide.     

Preparation of polycrystalline BaTi2O5 by pressureless sintering

Polycrystalline BaTi₂O₅ (BT₂) was prepared by pressureless sintering in air using BaCO₃ and TiO₂ as starting materials. XRD results of the calcined powder showed BaCO₃ and TiO₂ reacted completely after being calcined above 950 °C, showing a mixture of BaTiO₃ (BT), BT₂, BaTi₄O₉ and Ba₄Ti₁₃O₃₀. A small amount of ZrO₂ (less than 0.1 wt%) was effective to prepare BT₂ in a single phase and the second phase of BT and B₆T₁₇ increased with ZrO₂ content. BT₂ sintered body in a single phase was obtained at 1175-1300 °C when ZrO₂ content was 0.08 wt%. The maximum permittivity of BT₂ sintered body was 340 at the Curie temperature (T_c) of 463 °C and the frequency of 100 kHz.     

Production of single-crystal K3C60

A simplified technique for synthesizing high-quality millimeter-sized single-crystals of K₃C₆₀ is reported. The preparation method consists of a two-step process where pure C₆₀ crystals are first grown and later doped with potassium vapor. The undoped crystals are grown using an open-tube vapor transport with a flowing helium gas carrier. Doping occurs in a highvacuum environment inside a specialized quartz tube which allows phase purity to be monitored via magnetization measurements of the superconducting state. Utilizing the aforementioned procedure, one can attain samples with magnetically determined superconducting transition widths (10–90% diamagnetic shielding) of less than 1 K.