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61.
Cubic boron nitride is synthesized by the reaction of Li3N and B203 under high pressure and high temperature (4.0-5.0 GPa, 1350-1500℃). The minimum pressure of cBN formation is 4.0 GPa. The present condition of cBN formation is clearly lower than the eutectic temperature of Li3BN2 and BN in the Li3N-hBN system (5.5 GPa, 1610℃). The content of cBN in the sample increases, while the content of hBN decreases with the temperature and pressure. The maximum conversion rate (5.0 GPa, 1500℃) is about 34%, which is higher than that in the hBN-Li3N system. The cBN crystals are octahedral or tetrahedral in shape and approximately 20 μm in diameter. 相似文献
62.
Ceramic components manufacturing by selective laser sintering 总被引:2,自引:0,他引:2
In the present paper, technology of selective laser sintering/melting is applied to manufacture net shaped objects from pure yttria-zirconia powders. Experiments are carried out on Phenix Systems PM100 machine with 50 W fibre laser. Powder is spread by a roller over the surface of 100 mm diameter alumina cylinder. Design of experiments is applied to identify influent process parameters (powder characteristics, powder layering and laser manufacturing strategy) to obtain high-quality ceramic components (density and micro-structure).The influence of the yttria-zirconia particle size and morphology onto powder layering process is analysed. The influence of the powder layer thickness on laser sintering/melting is studied for different laser beam velocity V (V = 1250-2000 mm/s), defocalisation (−6 to 12 mm), distance between two neighbour melted lines (so-called “vectors”) (20-40 μm), vector length and temperature in the furnace. The powder bed density before laser sintering/melting also has significant influence on the manufactured samples density.Different manufacturing strategies are applied and compared: (a) different laser beam scanning paths to fill the sliced surfaces of the manufactured object, (b) variation of vector length (c) different strategies of powder layering, (d) temperature in the furnace and (e) post heat treatment in conventional furnace. Performance and limitations of different strategies are analysed applying the following criteria: geometrical accuracy of the manufactured samples, porosity. The process stability is proved by fabrication of 1 cm3 volume cube. 相似文献
63.
Low energy single nucleon transfer reactions are proposed as a tool to investigate the structure of nuclei far off stability.
Experimental concepts and conditions are discussed, in particular high resolution γ-ray spectroscopy after single nucleon
pickup reactions. Nuclear structure is described by Skyrme Hartree-Fock calculations including pairing. As representative
examples, binding energies, radii and wave functions for Mg and Sn isotopes are calculated. In the neutron deficient Mg isotopes
a proton skin is found. At the neutron driplines the Mg and Sn isotopes develop extended neutron skins. The nuclear structure
results are used in DWBA and EFR-DWBA transfer calculations. Single nucleon transfer reactions of 32,36Mg and exotic Sn beams on targets ranging from 2H to 24Mg in inverse kinematics are explored. The one-nucleon transfer cross sections decrease strongly for high-Z targets. An impact
parameter analysis shows that the transfer process is selective on the tails of the wave functions. The largest cross sections
are obtained for 2H and 9Be targets at incident energies of E
lab
= 2-5 MeV/u. The energy-momentum dependence is closely related to the special properties of wave functions of weakly bound
states. Two-neutron (p,t) stripping reactions are studied for a 6He projectile. A strong competition of sequential and direct processes is found at low energies.
Received: 1 October 1997 / Revised version: 25 November 1997 相似文献
64.
A. De Bonis R. Teghil J.V. RauA. Galasso S. OrlandoA. Santagata 《Applied Surface Science》2011,257(12):5315-5318
The plasma produced by ultra-short laser ablation of ZrB2 and ReB2 has been studied by ICCD imaging and time and space resolved optical emission spectroscopy. The aim was to clarify the mechanism of deposition leading to the morphology and composition found in the deposited films. The results indicate that for all systems the film characteristics are compatible with a deposition mechanism involving a growth from nanoparticles, ejected directly from the target, whose composition can be interpreted in terms of equilibrium vaporization during the flight from the target to the substrate. 相似文献
65.
本文研究了Je(s)manowicz于1956年提出的关于丢番图方程(1.1)解的猜想.利用数论中的一些方法,得到了丢番图方程(1.2)的所有正整数解,证明了Je(s)manowicz猜想在这类情况下的正确性. 相似文献
66.
The nanoindentation technique is used to analyze the depth dependence of the hardness and the reduced elastic modulus of bulk glasses and glass wool fibers (4-12 μm in diameter) of calcium aluminosilicate composition. In spite of the fiber geometry and the delicate sample mounting-technique, nanoindentation proves to be a relatively accurate method that provides reproducible data for both hardness (H) and reduced elastic modulus (Er) of thin glass fibers. It is found that H and Er are generally lower for the fiber than for the bulk sample. Within a given fiber, both H and Er are approximately constant with increasing indentation depth. However, both of these parameters decrease with diminishing fiber diameter. This trend is attributed to an increase of the free volume of the fibers with decreasing fiber diameter, i.e. to an increase of the fictive temperature. 相似文献
67.
Ultrathin La2O3 gate dielectric films were prepared on Si substrate by ion assistant electron-beam evaporation. The growth processing, interfacial structure and electrical properties were investigated by various techniques. From XRD results, we found that the La2O3 films maintained the amorphous state up to a high annealing temperature of 900 °C for 5 min. From XPS results, we also discovered that the La atoms of the La2O3 films did not react with silicon substrate to form any La-compound at the interfacial layer. However, a SiO2 interfacial layer was formed by the diffusion of O atoms of the La2O3 films to the silicon substrate. From the atomic force microscopy image, we disclosed that the surface of the amorphous La2O3 film was very flat. Moreover, the La2O3 film showed a dielectric constant of 15.5 at 1 MHz, and the leakage current density of the La2O3 film was 7.56 × 10−6 A/cm2 at a gate bias voltage of 1 V. 相似文献
68.
Effects of Raw Material Content on Efficiency of TiN Synthesized by Reactive Ball Milling Ti and Urea
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Ti and urea mixed according to the molar ratios of 2:1, 3:1 and 4:1 axe milled under the same condition. The structures of the as-synthesized powders are analyzed by an x-ray diffractometer (XRD). The decomposed temperature of the urea and the products decomposed are characterized by differential scanning calorimetry (DSC) and thermogravimetry analysis-Fourier transform infrared (TG-FTIR) spectrometry. The results show that the reaction progress is a diffusion reaction. The efficiency of TiN synthesized by reactive ball milling can be increased by increasing the content of Ti. The reactive ball milling time decreases from more than 90 h to 40 h correspond- ing to the content ratio between Ti and urea increasing from 2:1 to 4:1. Ammonia gas (NH3) and cyanic acid (HNCO), the decomposed products of urea, react with the refined Ti to form TiN. The grain refinement of Ti has a significant effect on the efficiency of reactive ball milling. 相似文献
69.
Guodong Wei Weiping Qin Ryongjin Kim Guofeng Wang Peifen Zhu Daisheng Zhang Kezhi Zheng Lili Wang 《Applied Physics A: Materials Science & Processing》2009,96(2):521-527
By using a novel and low-cost microwave method, three-dimensional SiC networks have been synthesized in large-scale. The composition
and structural features of the product were characterized by X-ray diffraction, field emission scanning electron microscopy,
and transmission electron microscopy. The results show that the SiC networks consist of nanocable X-junction and Y-junction.
Some nanocables are composed of 3C–SiC multicore encapsulated in single amorphous SiO2 shell. The SiC networks emitted stable violet–blue light around 380 nm under 325-nm excitation. Compared to the emission
peak of the SiC networks after etched and the reported results of 3C–SiC nanowires, the emission peak of the SiC networks
shows significant blueshift. The origin of the photoluminescence for the SiC networks could be due to two possible reasons:
the central crystalline SiC nanowires and amorphous SiO2 shell. A two-step growth mechanism of the SiC networks was proposed based on the experimental characterizations. The successful
synthesis of SiC networks is an important step in the development of SiC-based electronic devices and circuits. 相似文献
70.
The reactive ion beam mixing (IBM) of V/Al interfaces by low-energy N2+ ions at room temperature leads to the formation of V–Al–N ternary nitride thin films. The kinetics, growth mechanisms, composition
and electronic structure of those films have been studied using X-ray photoelectron spectroscopy, ultraviolet photoelectron
spectroscopy, Factor Analysis and Monte Carlo TRIDYN simulations. The comparison of experimental results with those obtained
from TRIDYN simulations suggests that the chemical reaction with the nitrogen partial pressure and processes driven by residual
defects are the rate-controlling mechanisms during the reactive IBM of V/Al interfaces. The kinetics of mixing is characterized
by two stages. During the first stage (≤4×1016 ions/cm2), the formation of vanadium nitride is observed. In the second stage, vanadium nitride is transformed into a V–Al–N ternary
nitride due to Al incorporation in the near surface region. Moreover, the V/Al ratio can be varied in a broad range, whereas
the nitrogen concentration slightly decreases with increasing the aluminium content of the film. 相似文献