MgWO_4:Nd~(3+)的水热合成及近红外发光性能研究

采用水热法制备MgWO_4:Nd~(3+)近红外发光材料.通过XRD,SEM和发光光谱等手段对样品的物相、形貌、发光性质进行表征.XRD测试结果表明:水热法制备MgWO_4:Nd~(3+)在850℃以上煅烧时,四方晶系转变为单斜晶系;1050℃煅烧后,sEM显示样品形貌由片状变为棒状且分散良好;激发和发射光谱的对比研究表明,MgWO_4:Nd~(3+)中WO_4~(2-)对Nd~(3+)存在有效的能量传递.研究了Nd~(3+)的掺杂量、煅烧温度、煅烧时间对材料近红外发光的影响.结果表明:在1050℃煅烧时,Nd~(3+)掺杂量为0.5%时发光最强;随着煅烧温度的升高,MgWO_4:Nd~(3+)的近红外发光强度先增强后减弱,而煅烧时间对发光强度影响很小.     

Influence of Gas Type on the Thermal Efficiency of Microwave Plasmas for the Sintering of Metal Powders

Microwave plasmas have enormous potential as a rapid and energy efficient sintering technology. This paper evaluates the influence of both plasma atmosphere and metal powder type on the sintering temperatures achieved and the properties of the sintered powder metal compacts. The sintering is carried out using a 2.45 GHz microwave-plasma process called rapid discharge sintering (RDS). The sintering of three types of metal powder are evaluated in this study: nickel (Ni), copper (Cu) and 316L stainless steel (SS). An in-depth study of the effects of the plasma processing parameters on the sintered powder compacts are investigated. These parameters are correlated with the mechanical performance of the sintered compacts to help understand the effect of the plasma heating process. The substrate materials are sintered in four different gas discharges, namely hydrogen, nitrogen oxygen and argon. Thermocouple, pyrometer and emission spectroscopy measurements were taken to determine the substrate and the discharge temperatures. The morphology and structure were examined using scanning electron microscopy and X-ray diffraction. The density and hardness of the sintered compacts were correlated with the plasma processing conditions. As expected higher densities were obtained with powders with lower sintering temperatures i.e. nickel and copper when compared with stainless steel. Under the power input and pressure conditions used, the highest substrate temperature attained was 1,100°C for Cu powder sintered in a nitrogen atmosphere. In contrast under the same processing conditions but in an argon plasma, the temperature achieved with SS was only 500°C. The effect of the plasma gas type on the sintered powder compact chemistry was also monitored, both hydrogen and nitrogen yielded a reducing effect for the metal in contrast with the oxidising effect observed in an oxygen plasma.     

The effect of processing conditions on the mechanical properties of polyethylene produced by selective laser sintering

A study was performed to explore the feasibility of processing a polyethylene by selective laser sintering. The polyethylene powder was characterised by scanning electron microscopy, particle size analysis and differential scanning calorimetry. The laser sintering processing conditions, especially powder bed temperature, laser power and laser scan counts, were studied. Well defined tensile testing specimens of the polyethylene were produced successfully by double laser scanning. The effect of the thermal history during the laser sintering process on the mechanical properties of the laser sintered parts is discussed for the first time.     

TiO2超细粉热稳定性的研究

本实验以ＴｉＣｌ４为原料，采用超临界流体干燥法地出ＴｉＯ气凝胶超细粉，在６２３－９２３Ｋ温度范围内考察了其织构和结构的热稳定性。实验发现，随着焙烧温度的提高，样吕的比表面和孔体积减小表面堆积密度增大，同时伴随颗粒烧结长大并连成链状。对ＴｉＯ２气胶超细粉的烧结机理研究表明，其烧结为表面扩散控制过程，烧结活化能为２２２．６ｋＪ／ｍｏｌ。     

Characteristics of the hydrous titanium dioxide-anatase phase transformation during hydrothermal treatment in aqueous solutions

The transformations of hydrous titanium dioxide, prepared by thermal hydrolysis of titanium(IV) compounds in sulfuric acid solutions, during hydrothermal treatment (150–240°C) in water were studied. The dispersivity and the chemical compositions of the samples obtained determined depending on the synthesis conditions (the composition) of hydrous titanium dioxide and the heat treatment temperature.     

水热法合成纳米TiO2及其在Grtzel电池中的应用

By varying the hydrolysis and hydrothermal processing parameters in preparing TiO2 nanoparticles different sizes of TiO2 nanoparticles are obtained.(1) At higher autoclaving temperature,lower pH and longer autoclaving period,larger sizes of TiO2 nanoparticles are prepared.(2) The nanoporous electrodes made from sintering smaller TiO2 nanoparticles show relatively poor IPCE and low absorption in UV Vis spectrum,(3) Higher IPCE can be achieved with TiO2 nanoporous electrodes made from sintering larger TiO2 nanoparticles.These electrodes are suitable for studying behavior of the photoelectrochemistry of dye sensitized nanoporous electrodes.     

水热法合成纳米TiO_2及其在Grtzel电池中的应用

By varying the hydrolysis and hydrothermal processing parameters in preparing TiO2 nanoparticles different sizes of TiO2 nanoparticles are obtained.(1) At higher autoclaving temperature,lower pH and longer autoclaving period,larger sizes of TiO2 nanoparticles are prepared.(2) The nanoporous electrodes made from sintering smaller TiO2 nanoparticles show relatively poor IPCE and low absorption in UV-Vis spectrum,(3) Higher IPCE can be achieved with TiO2 nanoporous electrodes made from sintering larger TiO2 nanoparticles.These electrodes are suitable for studying behavior of the photoelectrochemistry of dye sensitized nanoporous electrodes.     

A novel low temperature synthesis technique of sol–gel derived nanocrystalline alumina abrasive

The effect of ball milling process, co-doped seed and two step sintering technique on the properties of sol–gel derived alumina abrasive sintered at low temperature was investigated. The results showed that ball milling time with 10 h can be effective in enhancing the activity of the precursor and the microstructural uniformity of sintered alumina abrasive. A small amount of Al₂O₃–(NH₄)₃AlF₆ co-doped seed addition had potential synergistic effects for reducing α-Al₂O₃ phase transformation temperature and improving the mechanical property of alumina abrasive. A remarkable suppression of grain growth was achieved by controlling sintering temperature with two-step sintering method. Therefore, by using ball milling process, co-doping α-Al₂O₃–(NH₄)₃AlF₆ seed and two-step sintering technique, the sol–gel derived uniform nanocrystalline alumina abrasive is easily achieved at low temperature. Nanocrystalline alumina abrasive prepared at these conditions exhibited excellent mechanical properties and wear resistance compared to fused corundum abrasive and those sol–gel derived corundum abrasive with conventional sintering methods.     

Al2O3 @ TiO2—A simple sol-gel strategy to the synthesis of low temperature sintered alumina-aluminium titanate composites through a core-shell approach

A simple sol-gel based core-shell approach for the synthesis of alumina-aluminium titanate composite is reported. Alumina is the core and titania is the shell. The coating of titania has been performed in aqueous medium on alumina particle by means of heterocoagulation of titanyl chloride. Further heat treatment results in low temperature formation of aluminium titanate as well as low temperature sintering of alumina-aluminium titanate composites. The lowering of the reaction temperature can be attributed to the maximisation of the contact surface between the reactants due to the core-shell approach involving nanoparticles. The mechanism of formation of aluminium titanate and the observations on densification features in the present process are compared with that of mixture of oxides under identical conditions. The sintered alumina-aluminium titanate composite has an average grain size of 2 μm.     

Effect of sintering temperature on mechanical and microstructural properties of bovine hydroxyapatite (BHA)

The influence of sintering temperature on densification, microstructure and the mechanical properties of bovine hydroxyapatite (BHA), produced by a calcination method, was investigated. Densification and mechanical properties improved with increasing sintering temperature in the range between 1000°C and 1300°C, with optimum properties being obtained at a sintering temperature of 1200°C. The measured mechanical properties indicate that sintered BHA bodies are interesting biomaterials for further investigation in biomedical applications.     

Thermal behavior of nickel–metal hydride battery during charging at a wide range of ambient temperatures

In this study, hydoxyapatite (HA) prepared from calcined bovine bone was studied. Two methods were used for HA sintering: conventional sintering (CS) and microwave sintering (MS). HA was obtained by calcination of bovine bone at 800 °C for 4 h followed by wet ball milling. Afterwards, the powder was compacted under 75 MPa and sintered for 2 h at different temperatures, from 1050 to 1200 °C. It has been found that the bulk density of HA increases by increasing sintering temperature when both CS and MS were used. Nevertheless, at the same temperature and for a shorter time (15 min), the HA sintered by microwave were characterised by a density relatively higher than that of sintered by conventional furnace. For example, at 1100 °C the bulk densities of samples using CS and MS were about 2.49 (for 120 min) and 2.93 (for 15 min) g/cm³, respectively. Furthermore, a near theoretical density (98.6%) was obtained when HA samples were sintered at 1200 °C for 15 min only but using the proposed MS, which was much higher than that (89.7%) of HA samples sintered at the same temperature for longer holding time (120 min). Besides this, the X-ray analyses have shown that heat-treatment, using these two processes, has lead to HA decomposition into tricalcium phosphate and/or tetracalcium phosphate.     

Preparation of nanocrystalline TiO2 thin film at low temperature and its application in dye-sensitized solar cell

The electrophoretic deposition combined with common pressure hydrothermal treatment was employed to prepare nanocrystalline TiO₂ thin film from suspension of tetra-n-butyl titanate and P25 at low temperature. The tetra-n-butyl titanate was hydrolyzed and crystallized into anatase to interconnect nanocrystalline TiO₂ particles and to stick them to a conductive substrate by common pressure hydrothermal treatment to improve the electron transport properties of the deposited thin film. A dye-sensitized solar cell based on TiO₂ thin film prepared by the low temperature method yielded the conversion efficiency of 6.12%. Due to the relative slower electron transport rate in the deposited film, its conversion efficiency was slightly lower than that of the cell with TiO₂ thin film prepared by the conventional high temperature sintering method. Since it is free of high temperature sintering step, this method can be used to prepare nanocrystalline TiO₂ thin film on plastic polymer conductive substrate for fabrication of flexible dye-sensitized solar cell.     

BaCe_(0.8)Y_(0.2)O_(3-α)的溶胶-凝胶法合成及其电性能

用溶胶-凝胶法合成了BaCe_(0.8)Y_(0.2)O_(3-α)固体电解质前驱体，并以低 于通常固相反应150～250 ℃的温度（即1400～1500 ℃）进行了烧结。以烧结体样 品为固体电解质、多孔性铂为电极，组成氢及氧浓差电池、氢-空气燃料电池，测 定了BaCe_(0.8)Y_(0.2)O_(3-α)烧结体的质子和氧离子迁移数以及燃料电池的性 能，并与高温固相反应法合成的样品进行了比较。结果表明，烧结温度能显著影响 溶胶-凝胶法合成样品的质子迁移数及燃料电池性能。烧结温度≥ 1450 ℃时，质 子迁移数近似为1，燃料电池性能亦较高，烧结温度< 1450 ℃时，质子迁移数< 1 ，燃料电池性能亦较低。在1400～1500 ℃烧结的样品中，1450 ℃下烧结的样品具 有最高的电池性能，接近于高温固相反应法合成的样品。     

水解对MCM-41分子筛的结构破坏作用

详细考察了ＳｉＭＣＭ－４１、ＡｌＭＣＭ－４１和ＨＡｌＭＣＭ－４１在不同环境中的水解和结构破坏情况．空气和水蒸汽中短期高温焙烧对全硅型ＳｉＭＣＭ－４１的结构影响较小,但在潮湿空气中长期放置可因Ｓｉ—Ｏ—Ｓｉ键发生水解而造成结构的严重破坏．ＡｌＭＣＭ－４１的抗水解能力优于ＳｉＭＣＭ－４１的,但因其结构中包含一定量的Ｎａ＋离子,降低了高温焙烧时结构的热稳定性和水热稳定性．ＨＡｌＭＣＭ－４１的热稳定性和水热稳定性均优于ＡｌＭＣＭ－４１．分子筛水热晶化过程中的盐析效应被证实是导致ＡｌＭＣＭ－４１和ＨＡｌＭＣＭ－４１抗水解能力增强的原因,因此在合成原料中加盐可显著改善ＭＣＭ－４１分子筛的抗水解能力和稳定性     

Effect of co-sintering temperature on the performance of SOFC with YSZ electrolyte thin films fabricated by dip-coating method

Anode-supported yttria-stabilized zirconia (YSZ) electrolyte thin films were fabricated by the dip-coating method using the simple methylethylketone/ethanol-based YSZ suspension. Influences of the sintering temperature on the performance of solid oxide fuel cells were studied. Fully dense YSZ electrolyte thin films were obtained after being sintered at 1,300 °C as well as at 1,400 or 1,500 °C through SEM observation. The open circuit voltages of the cells all reached above 1.10 V at the testing temperatures. The testing results proved that both the anode performance and the electrolyte conductivity sintered at 1,300 °C were superior to those sintered at 1,400 or 1,500 °C. Investigation on the cell voltage drop under operation condition revealed, that the sintering temperature has more significant effect on the performance of the electrodes than on the electrolyte.     

用湿化学法制备Sm0.5Sr0.5CoO3-La0.8Sr0.2Ga0.8Mg0.15Co0.05O3复合阴极及其性能表征

用湿化学法制备了Sm0.5Sr0.5CoO3(SSC)－La0.8Sr0.2Ga0.8Mg0.15Co0.05O3(LSGMC5)中温固体氧化物燃料电池复合阴极材料，其中SSC用甘氨酸－硝酸盐法合成，LSGMC5用柠檬酸盐法合成。XRD结果表明，甘氨酸－硝酸盐法制备的SSC在焙烧温度大于1223K即表现为单一的钙钛矿结构。随焙烧温度的升高，SSC粉末颗粒增大,导致含有高温烧结SSC的电极与电解质界面结合变差。采用多种技术考察了利用不同温度（1173－1373K）预烧的SSC粉末制备的SSC-LSGMC5阴极上进行的氧还原反应。结果表明，SSC-LSGMC5复合电极的性能显著依赖于电极中SSC粉末的预烧温度，当SSC粉末焙烧温度在1223K附近时，具有最小的欧姆电阻以及氧还原反应极化电阻，1A· cm-2电流密度下的极化过电位为0.077 V。     

Preparation and hydrogen permeation properties of BaCe0.95Nd0.0503-δ membranes

Dense mixed proton and electron conducting membrane made of BaCe0.95Nd0.05O3-δ(BCNd5)was prepared by pressing followed by sintering.X-ray diffraction(XRD)was used to characterize the phase structure of both the powder and the sintered membranes.The microstructure of the sintered membranes was studied by scanning electron microscopy(SEM).Hydrogen permeation through the BCNd5 membrane was studied using a high temperature permeator.The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions,which is due to H hopping via surface OH groups.At 925℃,a hydrogen permeation flux of 0.02 mL/min cm2 was obtained under wet condition.which recommends BCNd5 as a potential material for hydrogen-selective membranes.     

吸附相反应技术制备TiO2的结晶过程以及光降解气相甲苯

研究了吸附相反应技术制备纳米TiO2的结晶过程, 并探讨了该过程对TiO2光催化活性的影响. 利用XRD测定了不同温度和时间焙烧后TiO2的晶型以及晶粒粒径的变化, 发现即使焙烧温度高达900 ℃, TiO2仍维持纯锐钛矿晶型. 随着焙烧温度的增加, TiO2的晶粒粒径变化不大, 均在7 nm以下, 在焙烧温度高于700 ℃时, 锐钛矿结晶峰的峰面积随温度增加, 峰面积保持不变. 改变焙烧时间基本不影响TiO2的晶型和晶粒粒径, 因而其光催化活性变化也较小. 光降解气相甲苯实验表明, 700 ℃焙烧后样品的催化活性最高, 且优于商用P25光催化剂.     

Preparation of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> by thermal hydrolysis of iron(III) basic sulfate

Features of the hydrolytic transformation of iron(III) basic sulfate under hydrothermal conditions at 140–200°C were studied. The influence of the conditions of the hydrothermal treatment of iron(III) basic sulfate on the rate and degree of its hydrolysis was examined. The chemical and phase composition of metastable intermediates was ascertained, and conditions for the formation of the final product of thermal hydrolysis, hematite of high phase purity, were determined.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1416–1420.Original Russian Text Copyright © 2004 by Eshchenko, Salonikov.     

Preparation and Crystallization of Magnetic Glass-Ceramics from the Residues after Sulfur Release and Iron Recovery from Copper Ore Tailings with Varied CaO Content

To comprehensively reuse copper ore tailings (COT), the fabrication of glass-ceramics by the direct sintering method was investigated, where the residues after sulfur release and iron recovery from copper ore tailings were used as raw materials. The effect of the CaO added on the fabrication of glass-ceramics was emphasized. After analysis of chemical composition and thermodynamics, crystallization kinetics were analyzed by Differential Scanning Calorimetry (DSC) and fitted to the Kissinger equation. The crystal phase and microstructure of sintered glass-ceramics heated between 1080 °C and 1100 °C were estimated by X-Ray diffraction analysis (XRD) and Scanning Electron Microscopy (SEM), respectively. Furthermore, the effects of the addition of CaO on the properties of the sintered glass-ceramics have been discussed. The results showed that the magnetic glass-ceramics were sintered by the residues successfully, the color of which was lighter than that of glass-ceramics sintered by raw materials before iron recovery. According to the XRD analysis, hedenbergite, wollastonite and sekaninaite were formed with traces of maghemite and quartz. In terms of crystallization kinetics and sintering results, a decrease in the activation energies of crystallization and in sintering temperature were observed for an increase in the addition of CaO of up to 10 wt.%. Moreover, the properties of the sintered glass-ceramics, including bulk density, linear shrinkage and flexural strength, were enhanced, while water absorption and true density were reduced with the increase of the amount of CaO added.