Rapid sonochemical preparation of shape-selective lead iodide

Lead iodide (PbI₂) films/crystals with various nano/micro morphologies (e.g., Nanoflake, block and microrod) were rapidly synthesized by taking advantage of a simple sonochemical method. The PbI₂ crystals with uniform nanoflake structures could be fabricated directly on lead foils with the irradiation time as short as 36 s via interfacial reaction between lead foils and elemental iodine in ethanol at ambient temperature. It was found experimentally that the morphologies of the resulting thin films/crystals could be well controlled by the adjustment of several parameters including irradiation time, reaction solvents, iodine concentration, ultrasonic power, and reaction temperature. Most importantly, the resultant PbI₂ films are stable enough to resist rolling under the drastic ultrasound irradiation in a liquid media. This method is believed to be the fastest way for in situ fabrication of morphology-controlled semiconductor films on various metal substrates for subsequent applications related to the other metal iodide or metal sulfide semiconductor films.     

Low temperature preparation of stabilized zirconia

The preparation of stabilized zirconia by thermal decomposition of metal alkoxides is reported. Formation of stabilized zirconia takes place at 400° C. The a.c. conductivity of the samples has been measured from 400 to 1000°C. The best conductivity is found in ZrO₂doped with 15 per cent CaO, which at 400° C is 2.37×10⁻⁶ Ω⁻¹ cm⁻¹ and at 1000°C is 1.26×10⁻² Ω⁻¹ cm⁻¹, with an activation energy of 1.16eV. Transport number measurements show that stabilized zirconia prepared by this method is purely an oxygen ion conductor.     

Automatic metallographic preparation of low-concentration, directionally solidified lead-tin alloys

The preparation for metallographic examination of lead and lead alloys, especially of low alloy concentrations, is very difficult to accomplish. The problems that occur are not common to most other materials. Lead alloys tend to deform, smear, and even recrystallize during preparation. Embedded particles and scratches are common problems. The slightest deformation will be hardly detectable in other materials but will be very obvious in lead. Because of these problems, careful attention must be given to the abrasive process. A successful method has been developed for obtaining clean metallographic specimens of low tin concentration alloys.     

Low temperature vapor-phase preparation of TiO2 nanopowders

The preparation of TiO₂ nanopowders by vapor-phase hydrolysis of TiCl₄ below 600°C is studied in this paper. Influences of preparation variables, such as preparative temperature, residence time, reactant concentration, and H₂O/TiCl₄ mole ratio, on TiO₂ particle size, morphology and chlorine contamination are investigated, followed by discussion. It shows that the hydrolysis temperature exerts greatest influences, while the residence time hardly have impact on product particles below 400°C, among the hydrolysis variables investigated. The chlorine contamination on nanopowders occurs during the preparation which can be greatly reduced by proper control on preparation variables. Unlike the high temperature gas-phase processes such as oxidation route and flame synthesis, low-temperature route shows the ready control on product powders, and thus obtains titania powders with small size, narrow size distribution and very weak agglomeration. In addition, the decreased energy consumption, retarded corrosion on the reactor and the reduced operation problems would be expected for the low temperature processes.     

全氟乙基碘制备新工艺

简要介绍了全氟乙基碘合成技术中催化剂、工艺方法、原料路线等方面的进展。     

Low temperature preparation and characterization of CdTiO3 nanoplates

An alternative low cost method was proposed for the low temperature (600 °C) preparation of CdTiO₃ nanoplates, using low-melting-point Cd(NO₃)₂ · 4H₂O and high-reactive-activity TiO₂ nanocrystals as the reactants. The structure, composition, specific surface area, thermal stability and optical properties of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, Brunauer–Emmett–Teller surface area analysis, UV–vis absorption and room temperature photoluminescence spectra. The as-synthesized CdTiO₃ nanoplates were thermally stable at temperatures ≤ 900 °C, and their phase changed from ilmenite to perovskite when heated in air at 1000 °C for 2 h. Besides, they exhibited a strong and broad visible light emission in the range of about 470–750 nm upon laser excitation at 325 nm, enabling their use as a luminescent material.     

Magnetic flux pinning and flux jumps in polycrystalline MgB2

MgB₂ polycrystalline samples were fabricated under varying conditions of isostatic pressing in argon gas. The critical current densities (J_C) were determined through measurements of hysteresis loops, and the highest value of J_C at 10 K was 1.9 × 10⁴ A/cm² at 4.8 T. The depinning temperatures were measured at various magnetic fields using the vibrating reed technique. Flux jumps appeared below 7.4 K. The hysteresis loops were carefully examined to determine the temperature and magnetic field range where flux jumps appeared.     

Low temperature preparation ofβ-alumina by an alkoxide route

β-alumina has been prepared by the thermal decomposition of a mixture of sodium and aluminium isopropoxides followed by heating up to 1000°C. It has been found necessary to use sodium isopropoxide in excess (25–30%) for the complete formation ofβ-alumina at 1000°C. On the other hand one obtains a mixture ofβ-alumina andα-alumina when the starting materials are taken in the stoichiometric ratio Na₂O:11Al₂O₃. DTA, TG and DTG studies of a mixture of sodium and aluminium isopropoxide showedβ-alumina formation at 1000°C. NCL Communication No. 4446.     

Low temperature Ni-nanocrystals-assisted hybrid polycrystalline silicon thin film transistor for non-volatile memory applications

The nickel-nanocrystals (Ni-NCs)-embedded silicon nitride acting as a trapping layer has been successfully demonstrated to manipulate the charging and discharging of electrons in a thin film transistor (TFT) for non-volatile memory (NVM) applications. Regarding device performance, with and without Ni-NCs in the stack and under a programming/erasing condition of +/−18 V for 1 s, a better threshold voltage shift of 3.2 V can be reached compared to a shift of 2.0 V for a stack without Ni-NCs. The shift is an index representing the value required to differentiate “0” or “1” states during operation. In this case, the diameter range and number density of Ni-NCs are 5-13 nm and 5.3 × 10¹¹ cm⁻², respectively.     

PVD法制备多晶碘化汞膜的光电特性研究

用热壁物理气相沉积法(Hot-Wall PVD)制备出晶体质量较好的多晶HgI2膜,研究了生长参数对沉积膜质量的影响,对多晶HgI2膜用金相显微镜、XRD、红外光谱进行了表征观察及对用多晶HgI2膜制备的探测器采用了暗电流测试;结果表明PVD法制备的多晶HgI2膜纯度高,结构完整性好,均匀性好,并且其相应器件有低的暗电流(电场0.2V/μ m时,为25pA/mm2).     

High temperature fatigue of a polycrystalline nickel base superalloy

Abstract

A high temperature fatigue crack growth study on an experimental disc alloy of approximate composition Ni-14.75Cr-14-19Co-4.75Mo-3Al-3.75Ti-1.75Ta-0.7Hf-0.06Zr-0.02C-0.0175B wt- has been undertaken. Comparison of constant load fatigue crack growth tests conducted in air and a vacuum at 725C and in air at room temperature indicate that an oxidising environment has a major influence on crack growth rates over a wide range of applied stress intensity range. In particular it contributes to enhanced embrittlement of grain boundary regions, promoting an early transition to intergranular failure along with a concomitant increase in growth rate. Constant stress intensity factor range tests at high R ratio showed that a decrease in frequency at 725C in both air and a vacuum caused an increase in the crack growth rate per cycle due to time dependent crack growth. This was most significant in air at 725C rather than in vacuo, although in both instances low frequency tests were accompanied by wholly intergranular crack growth. At lower R ratios the influence of time dependent processes is less pronounced, especially in a vacuum. For the purposes of prediction a straightforward linear summation model using sustained load crack growth results combined with high frequency growth rates was found to model reasonably the influence of frequency on crack growth rates for the air tests at 725C. This can be rationalised by the observation that in air intergranular failure proceeds by linking of prior cracked or embrittled grains some distance ahead of the crack tip. At lower values of stress intensity range a slight under prediction of growth rates was evident, but improvements could be made through the use of triangular waveform data. For the vacuum tests, the linear summation model was consistently found to over predict growth rates due to the transitory nature of the sustained load crack growth rates under repeated loading and was not generally deemed suitable. Under these conditions damage occurs close to the crack tip and direct interaction between time dependent and time independent mechanisms will occur. This is not taken into account by a summation approach and more accurate modelling of damage formation in the varying strain fields ahead of the crack tip is required to predict this.     

多晶莫来石纤维的制备研究

以水为溶剂,采用铝粉、Al Cl3·H2O、酸性硅溶胶为原料,通过溶胶-凝胶法制备了多晶莫来石纤维。借助X射线小角散射(SAXS)测试了Al3+的聚集形态,采用XRD、SEM、HRTEM等测试手段分析不同热处理温度下纤维的物相组成,纤维形貌,晶型结构等。X射线小角散射的结果表明,Al3+主要以Al13(OH)25Cl15的形态存在于聚合氯化铝溶胶中。纤维前驱体经1 050℃热处理后主晶相为莫来石,随着温度升高至1200℃,晶相结构趋于完整,HRTEM分析结果说明了纤维的多晶结构。     

Preparation of lead iodide films by iodination of chemically deposited lead sulphide films

A method of preparation of PbI₂ films by iodination of chemically deposited PbS films is described. The X-ray characterization of these films show that they are poly-crystalline in nature and the crystallites are preferentially oriented with c-axis perpendicular to the plane of the substrates. The analysis of the diffuse reflectance measurements performed on material scraped off the substrates yielded a forbidden energy gap of 2.34 eV in conformation with the results of pure PbI₂ powder. The transmittance spectra of these films, in the wavelength range 400 to 600 nm, revealed a characteristic strong absorption edge at about 510 nm and a hump at about 490 nm. On the basis of the changes in conductance of PbS film during iodine treatment a mechanism of iodination has been proposed.     

Pattern of flux tubes in superconducting lead films

At low magnetic fields the intermediate-state structure of type I superconducting films can consist of multiquantum flux tubes arranged in an ordered or disordered configuration. We have studied the number of flux tubes in small, rectangular, lead films of 6–8 µm thickness as a function of the magnetic field applied perpendicular to the films, using a high-resolution magnetooptical method. In order to facilitate the establishment of the equilibrium flux distribution and to minimize the influence of the Gibbs free energy barrier against magnetic flux penetration, the specimens were cooled at constant field from aboveT _c to 4.2 K. From the results the average flux tube diameter was calculated using flux conservation. The flux tube diameter was found to be larger by a factor of 2–3 than the value expected from the Goren-Tinkham model.Based on work performed under the auspices of the U.S. Atomic Energy Commission.     

Influence of solution rate and substrate temperature on the properties of lead iodide films deposited by spray pyrolysis

Polycrystalline lead iodide (PbI₂) thin films have been deposited by spray pyrolysis method using N,N-dimethylformamide (DMF) as solvent as a function of several deposition parameters. DMF is used as an alternative to water due to the larger solubility limit of PbI₂ in this solvent. In this work, the solution rate during the deposition time of 3 h was varied in the range of 0.11 cm³/min up to 0.30 cm³/min. A growth rate varying from 19 Å s^?1 up to 47 Å s^?1 was obtained as a function of solution rate. Dark current as a function of temperature for the final films reveals that for larger solution rates smaller values of electrical resistivity is obtained. For a solution rate of 0.30 cm³/min, an electrical transport activation energy (E _a) of about 0.65 eV was measured for the whole temperature range. On the other hand, for the sample deposited with a solution rate of 0.11 cm³/min, two main transport mechanisms can be observed with an activation energy of about 1.23 eV for temperatures above 50 °C. The effect of substrate temperature is also discussed. Samples were deposited in the temperature range of 170 °C up to 250 °C with a fixed solution rate of 0.16 cm³/min. In addition, the films were exposed to X-ray irradiation in the mammography diagnosis region, using a molybdenum (Mo) anode and a peak tube potential between 26 and 36 kV (equivalent photon energies between 10 keV and 15 keV).     

High temperature creep in polycrystalline AIN-SiC ceramics

Polycrystalline dense ceramic specimens containing 75 mol % AIN-25 mol % SiC and 60 mol % AIN-40 mol % SiC were subjected to creep deformation in bending at elevated temperatures. Over the range of temperatures and stresses investigated, the creep rate was found to vary linearly with stress indicative of diffusional creep. Creep was found to be thermally activated with activation energy in the range from 175 kcal mol⁻¹ to 219 kcal mol⁻¹. Electron microscopic observation indicated that crack like cavities formed near the tensile surfaces during creep.