Optical and Electrical Properties of Polycrystalline ZnSe:Li

ZnSe:Li ceramics were prepared by hot-pressing powder mixtures of ZnSe and LiOH at 1050°C under a pressure of 30 MPa. The luminescence spectra of the ceramics are dominated by a red emission centered at 630 nm. With increasing Li concentration, the intensity and width of the red band increase, and the band shifts to shorter wavelengths. The nature of the emission centers and the effect of the doping level on their parameters are discussed. The electrical properties of the ZnSe:Li ceramics can be understood in terms of percolation in heterogeneous systems.     

Aqueous synthesis of internally doped Cu:ZnSe/ZnS core-shell nanocrystals with good stability

To prepare biologically available Zn-based NCs in aqueous solution, we herein reported the synthesis of aqueous Cu:ZnSe/ZnS NCs with internally doped aqueous Cu:ZnSe NCs as the core template. Due to the dual protection of Cu impurities by the ZnSe core and ZnS shells, the as-prepared Cu:ZnSe/ZnS NCs show excellent stability in the open air, which overcomes the intrinsic instability of traditional aqueous Cu:ZnSe NCs. The as-prepared Cu:ZnSe/ZnS NCs possess extremely good stability, good biocompatibility and lower cytotoxicity, and thus can be used as a promising candidate for fluorescent NC-based biological applications.     

Cu掺杂ZnSe高效量子点的合成及其光学特性研究

采用生长掺杂方式制备了Cu掺杂ZnSe高效量子点, 探索了不同Zn、Se前驱体配比对ZnSe晶核以及ZnSe:Cu量子点质量的影响, 并研究了Cu离子掺杂过程中的光谱特征。研究表明, 进一步通过在表面掺杂的ZnSe:Cu量子点上同质包覆ZnSe壳层, 能够实现其发光效率和稳定性的有效提高; 采用配体交换能够实现ZnSe:Cu量子点由油溶性到水溶性的转变。这种新型的掺杂量子点有望替代传统含Cd量子点应用于环境友好型固体发光器件和生物标记。     

The fabrication of light-emitting devices from hot-pressed ZnSe powders

A hot-pressing process was developed to synthesize fine ZnSe powders into compacts with high bulk density. The hot-pressed ZnSe powder compacts after an annealing treatment in the Zn-Al alloy melt were readily processed into light-emitting devices based on a metal-semiconductor (M-S) device structure. The fabricated devices are found to emit light in the orange region of the visible spectrum and have a room temperature quantum efficiency of the order of 10^–6 photons/electron in the reverse direction. The photoluminescence and electroluminescence characteristics of the hot-pressed ZnSe powder compacts are also found to be very similar to those observed in single crystal material.     

Piezoelectric properties of hot-pressed 18PMN-41PZ-41PT ceramics

Piezoelectric ceramics of 18PMN-41PZ-41PT were sintered by hot-pressing and normal sintering methods. The microstructure, density, P-E curve and S-E curve were also compared. The best hot-pressing condition for 18PMN-41PZ-41PT material was obtained at a temperature of 1000 °C and a pressure of 700 kg cm⁻²; it could achieve 99.66% theoretical density and a fine, uniform microstructure as a result of a 200–300 °C decrease in the sintering temperature. A higher coercivity was attained with the density increase. The fine, uniform microstructure also enhanced the increase in polarization and strain.     

Densification of W-Ni-Cu and W-Fe-Cu Alloys at 1573 K

Anewkindoffunctionallygradedmaterials(FGM)withdensitygradientcanbeusedindynamichigh-pressuretechnology['].Recently,theresearchonsuchFGMofAl-Cusystemhasbeenreportedl2],butitisstillnecessarytoinvestigatesuchmaterialsinhigherdensityrange,e.g.,W-MosystemFGM.OnlywhenhighrelativedensityofeverytransientlayerofsuchFGMisensuredcangoodeffectbeob-tainedinfactualapplication.Theliquid-phasesin-teringmethodisusuallyappliedtoacquiretungstenheavyalloyswithfulldensity,butthecorrespond-ingsinteringtempera…     

热压烧结TiB2陶瓷的显微结构和力学性能研究

以Y₂O₃－Al₂O₃为烧结助剂,通过热压制备了TiB₂陶瓷,研究了烧结温度、烧结时间和晶化处理对材料的显微结构和力学性能的影响．实验结果表明,随着烧结温度的升高,烧结体失重增加,其抗弯强度和断裂韧性降低;烧结时间延长,其显微结构的均匀性降低,对力学性能不利．晶粒直径对TiB₂陶瓷的力学性能有重要影响．晶化处理能够导致晶界拆出YAG相,从而提高TiB₂陶瓷的高温抗弯强度．     

ZnSe<Cu> Luminescence at High Doping Levels

ZnSe was doped with Cu via thermal diffusion from Cu foil in the course of chemical vapor deposition. The Cu distribution over the deposit was studied, and the Cu solubility in ZnSe was determined as a function of temperature. Copper was shown to prevent oxygen incorporation from the gas phase. The microstructure and homogeneity of ZnSe were studied by scanning electron microscopy. The cathodoluminescence (CL) spectra were measured on fracture surfaces in order to elucidate the origin of the Cu-related emission centers. Heavy doping with Cu was shown to gives rise to a long-wavelength CL band, which shifts from 525 to 550 nm as the temperature is raised from 80 to 300 K. The associated changes in oxygen-related self-activated luminescence were correlated with the Cu and O concentrations. To gain more detailed insight into the origin of the green Cu-related emission in p-type ZnSe, we examined its photoexcitation spectrum, temperature-dependent peak position, quenching, and variation with excitation intensity. The conclusion is drawn that the longer wavelength CL bands are due to electron transitions from the Zn_i ^·· donor level to the impurity band. The CL spectrum of heavily doped ZnSe shows no emissions between 800 and 1400 nm, related to the V _Se and V _Zn vacancies.     

Development and cytotoxicity evaluation of SiAlONs ceramics

SiAlONs are ceramics with high potential as biomaterials due to their chemical stability, associated with suitable mechanical properties, such as high fracture toughness and fracture resistance. The objective of this work was to investigate the mechanical properties and the cytotoxicity of these ceramic materials. Three different compositions were prepared, using silicon nitride, aluminum nitride and a rare earth oxide mixture as starting powders, yielding Si₃N₄–SiAlON composites or pure SiAlON ceramics, after hot-pressing at 1750 °C, for 30 min. The sintered samples were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Furthermore, hardness and fracture toughness were determined using the Vicker's indentation method. The biological compatibility was evaluated by in vitro cytotoxicity tests. Ceramic with elevated hardness, ranging between 17 and 21 GPa, and high fracture toughness of 5 to 6 MPa m^1/2 were obtained. Since a nontoxic behavior was observed in the cytotoxicity tests, it may be assumed that SiAlON-based ceramics are viable materials for clinical applications.     

Super-lyophobicity of porous Si3N4/BN ceramics with nanopores and nanowires by molten copper

Porous Si₃N₄/BN ceramics (PSBC) with a microstructure containing nanopores and nanowires were prepared by reaction bonding of silicon nitride (RBSN) technique. The phase composition and microstructure of PSBC were characterized by X-ray diffractometry (XRD) and field emission scanning electronic microscope (FE-SEM). The porosity of PSBC was 52.6%, the pore size was in the range of 60 to 300 nm. The wettability of PSBC by molten Cu at 1300 °C was investigated by the sessile drop method. The ceramics exhibit super-lyophobicity by molten Cu. The nanopores and nanowires embodied in PSBC increased the heterogeneity and surface roughness, resulting in the super-lyophobicity of the ceramics by molten Cu.     

SiC—WC复合陶瓷材料的研究

本文对亚微细SiC—WC复合陶瓷粉末的制备及热压烧结性能进行了研究。在探讨烧结体密度、强度随热压条件变化的基础上得出了适合于SiC—WC复合陶瓷的热压工艺条件。在此条件下烧结体的相对密度达99％以上,弯曲强度达1019MN/m~2。研究表明,在SiC中加入5～25Vol.％的WC,能改善材料的烧结性能,加快致密化速率,并能提高烧结体的强度与韧性。     

TiB2-TiC复相陶瓷的结构与性能研究

TiB₂-TiC复合粉制备的TiB₂-TiC复相陶瓷的相对密度达99.8%,硬度为 93.2HRA,断裂韧性为5.53MPa·m1/2。显微结构研究表明:TiB₂-TiC烧结体体内的位错和残余气孔影响材料性能。复合粉烧结体晶粒尺寸细小,大小分布均匀,晶粒之间界面干净,无杂质沉积,烧结体中TiB₂和TiC两相界面接合处元素B,C,Ti的含量存在梯度变化,都有利于烧结体性能提高。TiB₂晶粒生长存在取向性。     

New concept bioceramics composed of octacalcium phosphate (OCP) and dicarboxylic acid-intercalated OCP via hydrothermal hot-pressing

Octacalcium phosphate (OCP) and adipic acid-intercalated complexed OCP (Adi-OCP) were synthesized. Moreover, we made ceramic bodies out of them through a hydrothermal hot-pressing (HHP) method. Characteristic features of both the powder and ceramics were investigated by the X-ray diffraction method (XRD). Surface morphology of the ceramics was observed by scanning electron microscopy (SEM). Density, compressive strength and pore size distribution of the ceramics were measured. Crystalline structure of the newly developed OCP ceramics had no phase transformation from the starting materials. Moreover, the newly developed OCP ceramics had good mechanical properties only through the HHP treatment with a temperature as low as 110 °C. In order to evaluate bioactivity, the ceramics were immersed in simulating body fluid (SBF). It was predicted that OCP and Adi-OCP had better bioactivity than that of conventional HAp ceramics.     

热压烧结TiB2陶瓷的显微结构和力学性能研究

以Ｙ２Ｏ３－Ａｌ２Ｏ３为烧结助剂,通过热压制备了ＴｉＢ２陶瓷,研究了烧结温度,烧结时间和晶化处理对材料的显微结构和力学性能的影响。实验结果表明,随着烧结温度的升高,烧结体失重增加,其抗弯强度和断裂韧性降低,烧结时间延长,其显微结构的均匀性降低,对力学性能不利。晶粒直径对ＴｉＢ２陶瓷的力学性能有重要影响,晶化处理能够导致晶界析出ＹＡＧ相,从而提高ＴｉＢ２陶瓷的高温抗弯强度。     

Improvement in the mechanical properties of polycrystalline beta-alumina via the use of zirconia particles containing stabilizing oxide additions

Polycrystalline beta-alumina ceramics containing yttria-doped zirconia particles have been produced by hot-pressing and “two-peak” sintering schedules. With the former fabrication process, both a chemical reaction involving sodium metazirconate and α-alumina, and a direct mixing route were employed. The mechanical properties of the ceramics produced by the direct mixing route were superior to those produced by the chemical route. The maximum amount of tetragonal zirconia retention, and thus fracture toughness, obtained using direct mixing occurred for additions of 4wt% yttria-doped zirconia. An increase of ∼ 124% in the fracture toughness was obtained compared with the pure beta-alumina ceramic. Transfer of this fabrication route to a pressureless sintering schedule was less successful owing to difficulties in attaining full densification. The increases in strength observed with introduction of second phase zirconia could be attributed to an improvement in the degree of densification achieved, and the maximum increase in toughness was only ∼27%.     

Permeability, porosity and pore geometry of hot-pressed calcite

Permeability may be altered in the Earth by plastic flow of the rock matrix. In order to better understand the relation between plastic flow and pore geometry, we measured the permeability of a suite of hot-pressed calcite samples with differing porosities. We found that the permeability dramatically decreased with decreasing porosity, particularly in the range of 10 to 4% total porosity. These results agree with a model for pore geometry changes during hot-pressing as previously developed for ceramics. Measurements of unconnected and interconnected porosity showed that the interconnected porosity virtually disappeared in samples with a total porosity of 4% or less. Scanning electron microscope observations showed that the porosity of samples above 10% total porosity were composed of large ‘spheroidal’ pores which were often connected by ‘tubular’ pores. During the last stage of hot-pressing, these ‘tubes’ are thought to collapse making the pore network disconnected.     

Effects of titanium surface modifications on bonding behavior of hydroxyapatite ceramics and titanium by hydrothermal hot-pressing

In order to improve the interface strength in the bonded body of hydroxyapatite (HA) ceramics and Ti disks prepared by a hydrothermal hot-pressing (HHP) method, the effects of Ti surface modification on the bonding behavior were investigated. The reaction layer composed of titanium dioxide and sodium titanate was formed on the Ti surface using a 5 M NaOH solution with the objective of increasing the interface strength between the Ti substrate and HA ceramics to be formed by the HHP method. Three conditions with different temperature and treatment times were tested to modify the Ti surface. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HA. Solidification of HA and its bonding with Ti were achieved simultaneously by using the HHP method at the low temperature as low as 323 K. 3-point bending tests were conducted to obtain an estimate of the interface fracture toughness of HA/Ti. The Ti surface modification conducted at 323 K for 2 h using the hydrothermal NaOH solution was shown to be most effective among the three conditions tested. The hydrothermal Ti surface modification enabled us to increase significantly the interface fracture toughness. The enhancement of the interface fracture toughness was possibly due to the presence of anatase formed on the Ti surface and the good adhesion in the bioactive layer.     

不同烧结工艺对K0.5Na0.5NbO3陶瓷微结构的影响

采用普通烧结方法和热压烧结方法制备了K0.5Na0.5NbO3(KNN)无铅压电陶瓷.着重研究了两种烧结工艺对陶瓷的微观结构、晶粒形貌及致密度的影响.研究结果表明,两种烧结方法制备的陶瓷样品都具有单一的正交钙钛矿结构,与普通烧结工艺相比,利用热压烧结工艺制备的样品呈现较高的相对密度(大于98%)、较小的晶粒尺寸(0.6μm左右)及较低的介电损耗(1 kHz,tanδ≤2.8%).实验中发现对于热压烧结的样品,通过改变后期退火温度,样品的晶粒尺寸,致密度可以有规律地变化.     

Machinable Al2O3/BN composite ceramics with strong mechanical properties

Al₂O₃/BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing α-Al₂O₃ powders with turbostratic BN (t-BN) coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal BN (h-BN) particulates were homogeneously dispersed within Al₂O₃ grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al₂O₃ monolithic ceramics. The nanocomposite ceramics with BN content more than 20 vol.% exhibited excellent machinability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary information on the relationship between microstructures and properties are provided. The mechanism of material removal is also discussed.     

Chemical preparation of PLZT powder from aqueous solution

A new method for preparing homogeneous lanthanum-modified lead zirconate-titanate (PLZT) powder from aqueous salt solution containing hydrogen peroxide by precipitation is described. Inorganic salts such as zirconium oxychloride and titanium tetrachloride instead of organo-metallic salts can be available as raw materials which attain well reactioned and fine-grained PLZT powder processed by decomposing the dried product at 650°C. PLZT ceramics formed by hot-pressing the powder show considerable improvements in the qualities such as optical transparency and homogeneity.