High-pressure sintering study of a novel hard material (W0.5Al0.5)C-0.5 without binder metal

A novel hard material of (W0.5Al0.5)C-0.5 has been successfully sintered under high-pressure (4.5 GPa). The influence of sintering time and temperature on the microstructure, Vickers microhardness and density of the as-prepared specimens are well described. Interestingly, sintering temperature has an amazing influence on the hardness, density and microstructure of the specimen while the sintering time does not. It is found that the most suitable sintering condition from our work is 1600 degrees C and 10 min under pressure of 4.5 GPa. The hardness and relative density of the as-prepared sample can reach 2340 kg mm(-2) and 98.62%, respectively. The cell parameters of the sintered specimen is found to be little smaller than that of the powder, which we propose is related to the high pressure.

Fabrication, microstructure and mechanical properties of novel cemented hard alloy obtained by mechanical alloying and hot-pressing sintering

A novel cemented carbides alloy (W0.4Al0.6)C-0.65-Co were prepared by mechanical alloying and hot-pressing sintering in this work. Hot-pressing (HP) as a common technique was performed to fabricate the bulk bodies of the hard alloys. The hardness, bending strength, density of the novel hard alloy are also tested, and it has superior mechanical properties. The hardness of (W0.4Al0.6)C-0.65-Co hard alloy was very high, and the density, operate cost of the novel material were much lower than WC-Co, more important is the aluminum dissolving is not decrease the strength compared with the WC-Co system. There is almost no eta-phase in the (W0.4Al0.6)C-0.65-Co cemented carbides system even the carbon deficient reaches the astonishing value of 35%. This novel property will give us more choice to design and gain new materials that we needed.

Microwave-assisted synthesis of high-molecular-weight poly(ether imide)s by phase-transfer catalysis

A facile and rapid polycondensation reaction of disodium bisphenol A with bis(chlorophthalimide)s was preformed with a domestic microwave oven in o-dichlorobenzene by phase-transfer catalysis. The polymerization reactions, in comparison with conventional heating polycondensation, proceeded rapidly and were completed within 25 min. The polymerizations gave the corresponding poly(ether imide)s with inherent viscosities of 0.55-0.92 dL g(-1). The effects of various factors on the polymerization, such as the amount of the catalyst, the reaction time, and the microwave power were studied. The properties of the polymers were briefly characterized.

Lanthanum zirconate nanofibers with high sintering-resistance

The PVP/lanthanum nitrate/zirconium oxychloride (PVP-precursor) nanofiber was prepared by electrospinning technique. Lanthanum zirconate (La2Zr2O7, LZ) in the nanofiber is formed after calcination at 800 degrees C and the nanofiber with pyrochlore structure and a diameter of 100-500 nm can be obtained by calcination of the above precursor fiber at 1000 degrees C for 12 h. The surface of the fiber is rough but the continuous microstructure is still maintained after calcination. LZ fibers stack randomly, resulting in a structure with a low contact area between the fibers. This special structure makes the fiber to have a high resistance to sintering at elevated temperatures. The BET (Brunauer-Emmett-Teller) specific surface areas of the LZ fiber and powder calcined at different temperatures are shown in this paper, and the fiber was characterized by TG-DTA (thermal gravimetry-differential thermal analysis), XRD (X-ray diffraction), N-2 absorption-desorption porosimetry and SEM (scanning electron microscopy).

Sintering of nanopowders of amorphous silicon nitride under ultrahigh pressure

Nanopowders of amorphous silicon nitride were densified and sintered without additives under ultrahigh pressure (1.0-5.0 GPa) between room temperature and 1600 degrees C. The powders had a mean diameter of 18 nm and contained similar to 5.0 wt% oxygen that came from air-exposure oxidation, Sintering results at different temperatures were characterized in terms of sintering density, hardness, phase structure, and grain size. It was observed that the nanopowders can be pressed to a high density (87%) even at room temperature under the high pressure. Bulk Si3N4 amorphous and crystalline ceramics (relative density: 95-98%) were obtained at temperatures slightly below the onset of crystallization (1000-1100 degrees C and above 1420 degrees C, respectively. Rapid grain growth occurred during the crystallization leading to a grain size (>160 nm) almost 1 order of magnitude greater than the starting particulate diameters, With the rise of sintering temperature, a final density was reached between 1350 and 1420 degrees C, which seemed to be independent of the pressure applied (1.0-5.0 GPa), The densification temperature observed under the high pressure is lower by 580 degrees C than that by hot isostatic pressing sintering, suggesting a significantly enhanced low-temperature sintering of the nanopowders under a high external pressure.

A microwave emissivity model of sea surface under wave breaking

With the effective medium approximation theory of composites, a remedial model is proposed for estimating the microwave emissivity of sea surface under wave breaking driven by strong wind on the basis of an empirical model given by Pandey and Kakar. In our model, the effects of the shapes of seawater droplets and the thickness of whitecap layer (i.e. a composite layer of air and sea water droplets) over the sea surface on the microwave emissivity are investigated by calculating the effective dielectric constant of whitecaps layer. The wind speed is included in our model, and the responses of water droplets shapes, such as sphere and ellipsoid, to the emissivity are also discussed at different microwave frequencies. The model is in good agreement with the experimental data of microwave emissivity of sea surface at microwave frequencies of 6.6, 10.7 and 37GHz.

Determination of trace arsenic and selenium in jellyfish by microwave digestion-hydride generation-atomic fluorescence spectrometry

A method of hydride generation-atomic fluorescence spectrometry was proposed in the present paper for the determination of trace arsenic and selenium in jellyfish. The samples were treated by the combination of microwave digestion and lyophilization. The optimal conditions for treating and analyzing samples were established. The problem of the effect of the superfluous acid in the digesting solution on the results was solved, and the influence of coexisting foreign ions on the determination of arsenic and selenium was investigated. The accuracy of the method was confirmed by the method of standard additions. This method proved to be simple, rapid and repeatable, and is suitable for the analysis of biologic samples containing water.

Salt-assisted acid hydrolysis of chitosan to oligomers under microwave irradiation

The effect of inorganic salts such as sodium chloride on the hydrolysis of chitosan in a microwave field was investigated. While it is known that microwave heating is a convenient way to obtain a wide range of products of different molecular weights only by changing the reaction time and/or the radiation power, the addition of some inorganic salts was shown to effectively accelerate the degradation of chitosan under microwave irradiation. The molecular weight of the degraded chitosan obtained by microwave irradiation was considerably lower than that obtained by traditional heating. Moreover, the molecular weight of degraded chitosan obtained by microwave irradiation assisted under the conditions of added salt was considerably lower than that obtained by microwave irradiation without added salt. Furthermore, the effect of ionic strength of the added salts was not linked with the change of molecular weight. FTIR spectral analyses demonstrated that a significantly shorter time was required to obtain a satisfactory molecular weight by the microwave irradiation-assisted inorganic salt method than by microwave irradiation without inorganic salts and conventional technology. (C) 2005 Elsevier Ltd. All rights reserved.

Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a thigh degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and C-13 NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32mg/mL, respectively. It is a potential antioxidant in vitro. (C) 2004 Published by Elsevier Ltd.

Effect of microwave treatment on chemical composition and in sacco digestibility of wheat straw in yak cow

Wheat straw was treated with microwave for 4 min and 8 min at a power of 750 W and frequency of 2,450 MHz. Chemical compositions of untreated, 4 min treated and 8 min treated Straws were analyzed and in sacco degradabilities of all these straws in yak rumens were measured. Microwave treatment didn't significantly (p > 0.05) affect the chemical composition of the straw. In sacco dry matter (DM) degradability of the straw after 18 h incubation in rumen was significantly (p < 0.01) improved by microwave treatment. In sacco crude protein (CP) degradability of the straw was not (p > 0.05) affected by microwave treatment. In sacco organic matter (OM) degradability of the straw was increased (p < 0.01) by around 20% for both the 4 min and 8 min microwave treatment, that of acid detergent fibre (ADF) was increased (p < 0.01) by 61.6% and 62.8%, and that of ash free ADF was enhanced by 72.1% and 69.6% for the 4 min and 8 min microwave treatment respectively. No significant difference was observed between the 4 min and 8 min microwave treatment on the degradability of DM, OM, CP, ADF and ash-free ADF of the straw.