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排序方式: 共有98条查询结果,搜索用时 437 毫秒
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2.
The aim of the present work has been to produce high-dense Si3N4 ceramics by a cheaper pressureless sintering method and then to attain vacuum heat treatment to remove residual grain boundary glass in gaseous form. LiAlO2 was used as a sintering additive rather than using Li2O, since its grain boundary glass is not stable above 1200 °C. LiAlO2 was synthesised from 42% Li2CO3 and 58% Al2O3 powder mix reacting together at 1450 °C for 3 h in a muffle furnace. X-ray analysis showed that 95% LiAlO2 was obtained. LiAlO2 was milled and added to silicon nitride powder as a sintering additive. Hot-pressing and pressureless sintering of LiAlO2 containing Si3N4 compacts were carried out at temperatures between 1450–1750 °C. The sintered samples were vacuum heat-treated at elevated temperatures under high vacuum to remove intergranular glass and to increase refractoriness of Si3N4 ceramics. Scanning electron microscope images and weight loss results showed that Li in grain boundary glass (Li–Al–Si–O–N) was successfully volatilised, and oxidation resistance of the sintered samples was increased. 相似文献
3.
Dae-Su Lee Soon-Jong Jeong Eon-Cheol Park Jea-Sung Song 《Journal of Electroceramics》2006,17(2-4):505-508
Dielectric and piezoelectric properties of grain oriented (Bi0.5Na0.5)TiO3-BaTiO3 ceramics were investigated in a process that the templated grain growth and hot pressing methods were employed. A ceramic
composition in Bi-based perovskite structure family, (Bi0.5Na0.5)TiO3-BaTiO3, was chosen as a matrix material and plate shaped SrTiO3 as a template. To examine the combined process effect on piezoelectric properties, three processes, conventional solid reaction,
templated grain growth and the combine treatment of templated grain growth and hot-pressing, were compared. Specimen processed
by templated grain growth and hot pressing methods exhibited better piezoelectric coefficient, d
31 (−79.6 pC/N) and electromechanical coefficient, k
33 (0.35) than those of the other specimens, fabricated by solid reaction and templated grain growth, respectively. The improved
properties were attributed to reduction of pore existing in matrix, which is related to abnormal grain growth from SrTiO3 template and its resultant heterogeneous shrinkage. 相似文献
4.
Feather,as a by-product of the poultry industry,has long been treated as a solid waste,which causes environmental and economic problems.In this work,the hydrolyzed feather keratin(HFK)was extracted from the chicken feather using a cost-effective method of alkali-extraction and acid-precipitation by applying urea and sodium sulfide.The aim was development and characterization of the eco-friendly films based on the HFK with variable glycerol contents by a thermoplastic process.The thermal analysis showed that high temperature and high pressure improved the compatibility between the glycerol and the HFK molecules.Also it was shown that the addition of water is necessary in the hot-pressing process of films.The FT-IR analysis indicated that the formation of the new hydrogen bonds between HFK and glycerol.By increasing the glycerol content,the film tensile strength(σ_b)decreases from 10.5 MPa to 5.7 MPa and the solubility increases from 15.3% to 20.9%,while the elongation at break(εb)achieves the maximum value of 63.8% for the film with 35% glycerol.The swelling was just below 16.9%at 25 °C for 24 h,suggesting a good stability of the films in water.The water vapor permeability(WVP)varied between 3.02 × 10~(-10)g · m~(-2)· s~(-1)· Pa~(-1)and 4.11 × 10~(-10)g · m~(-2)· s~(-1)· Pa~(-1)for the films with 20% and40% glycerol,respectively.The HFK film was uniform,translucent and tough,which could be used in packaging and agricultural field. 相似文献
5.
《Journal of the European Ceramic Society》2014,34(4):985-990
Reactive hot-pressing was scarcely applied to fabricate titanate ceramic waste forms designed for immobilizing high-level radioactive waste (HLW). However, compared with non-reactive processes, there is an advantage of producing high-density ceramics at reduced temperatures by reactive hot-pressing. CeIV-doped titanate composite ceramics with relative densities in excess of 99% were prepared by reactive hot-pressing at temperature as low as 1150 °C and pressure of 30 MPa for 1–4 h. The results show that low-temperature densification of the composite ceramics might be attributed to the plastic deformation under hot-pressing condition. In addition, aqueous stability testing was carried out using the standard MCC-1 static leach test method. The results demonstrate that the normalized elemental leach rate of Ca, Ce and Zr were fairly constant in a low value below 5 × 10−2 g m−2 d−1, 7 × 10−6 g m−2 d−1 and 6 × 10−6 g m−2 d−1 after 21 d. 相似文献
6.
Effect of milling ball size on the densification and optical properties of transparent Y2O3 ceramics
Hyeon-Myeong Oh Young-Jo Park Ha-Neul Kim Jae-Woong Ko Hyun-Kwuon Lee 《Ceramics International》2021,47(4):4681-4687
In this study, we report highly transparent Y2O3 ceramics fabricated by hot-pressing only at 1500 °C without a HIP treatment, featuring in-line transmittance levels of 77% and 84% at a wavelength of 400 and 1100 nm, respectively with the grain size suppressed to 710 nm. The effect of the ball size during the grinding of Y2O3 powders on the correlation between the thus-prepared Y2O3 powders and the optical properties of the hot-pressed samples is demonstrated for the first time. With a decrease in the diameter of the ZrO2 balls from 5 mm to 1 mm, the milling efficiency was enhanced and admirable transparency of Y2O3 was attained at a short milling time. However, several micron-sized pores remained in the transparent specimens prepared with 1 mm balls, originating from the inhomogeneously packed region of the green body. Finally, the 2 mm was found to be optimum for obtaining a fine-grained and pore-free microstructure with the best in-line transmittance of Y2O3 ceramics. 相似文献
7.
Li-Xiang Wu Lin-Lin Zhu Yang You Rui-Lin Lin Qing-Qing Liu Wei-Ming Guo Hua-Tay Lin Kevin Paul Plucknett 《Ceramics International》2021,47(1):935-942
Dense pressure-sintered reaction-bonded Si3N4 (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu2O3–MgO–Y2O3 sintering additive. The addition of Eu2O3–MgO–Y2O3 was shown to promote full nitridation of the Si powder. The nitrided Si3N4 particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu2O3–MgO–Y2O3 were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu2O3 doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m?1 K?1, significantly higher than the counterpart without Eu2O3 doping, or with ZrO2 doping by conventional methods. 相似文献
8.
《Advanced Powder Technology》2020,31(7):2833-2842
In this study, the Al–5Cu matrix composites reinforced with different boron carbide (B4C) particle volume fractions have been successfully produced by the hot-pressing method. Then, the artificially aging (T6) was applied to the composites for increasing their mechanical properties. The combined effect of the T6 heat treating and the B4C particle volume fraction on the corrosion behaviour of the composites were investigated by potentiodynamic scanning (PDS) technique under aerated and deaerated 3.5% NaCl marine environments. The effect of the T6 treating on the hardness and corrosion susceptibilities of the composites were also evaluated microstructurally to contribute to their industrial use and production processes. The microstructural characterization of the composites was carried out by using a scanning electron microscope (SEM) with an attached energy dispersive spectrum (EDS) and X-ray diffraction (XRD). It was found that the corrosion susceptibilities of the composite have been interestingly decreased with increasing the B4C particle volume fraction in the matrix while the T6 treatment enhances the pitting susceptibility of the composites. The reason of the behaviour has been discussed in details the text. 相似文献
9.
《Ceramics International》2017,43(10):7958-7962
A ceramic particulate composite composed of oxide, and carbide ceramics was found to have high strength, hardness, and fracture toughness values. A composition consisting of Al2O3 with 15 vol% SiC and 15 vol% B4C additions was produced by hot-pressing at 1650 °C for 30 min, with full density reached after ~5 min at temperature. Both WB and WB2 were observed, with the W source presumably an impurity from WC milling media, and Al18B4O33 was also detected following densification. Strength was ~880 MPa, which is greater than values reported for comparable composites of Al2O3 containing 30 vol% SiC or B4C. Vickers hardness was ~21 GPa, and fracture toughness was ~4.5 MPa m½, comparable to values reported for the binary mixtures. The calculated critical flaw size of the material was similar to the size of the SiC/B4C clusters and microcracking at grain boundaries. The latter resulting from thermal expansion mismatch between the Al2O3 matrix and SiC/B4C reinforcing phases. 相似文献
10.
《Journal of the European Ceramic Society》2017,37(5):2259-2263
Reaction sintering of MgO and Al2O3 with addition of LiF as sintering additive was used to prepare MgAl2O4 spinel ceramic by hot pressing. The process parameter (temperature, pressure, dwell time), the stoichiometric ratio of MgO to Al2O3 and the selection of the alumina raw powder are equally important for highest transparency of the spinel ceramic. With this optimization highest transparency of 86% in the visible range at λ = 640 nm together with UV transmission of 62% at 200 nm for spinel ceramic with 4 mm thickness was reached. 相似文献