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121.
《中国稀土学报(英文版)》2019,37(7):760-766
A novel process of calcification-leaching for bastnaesite concentrate(REFCO_3) was proposed. The prior calcification was carried out in the system of NaOH-CaO-H_2O and the lgC-pH pattern for Ce-F-Ca-C-H_2O system was drawn. The thermodynamics result indicates that decomposition for bastnaesite requires certain alkaline condition, but excessive alkalinity also causes decomposition of CaF_2. XRD and SEM-EDS analyses on the calcification-leaching process reveal that bastnaesite first decomposes into RE(OH)_3 and CaF_2. Then, by HCl leaching rare earths were extracted,while CaF_2 was left in the leaching residue. In addition, effects of temperature, time, NaOH and CaO on the calcification were investigated. The results show that the leaching rate of rare earths(REs)reaches 72.5 wt%, at the same time 99.2 wt% of F is left in leaching residue with 20 wt% NaOH and 38 wt% CaO at 493 K for 180 min. 相似文献
122.
《Materials Research Bulletin》1987,22(10):1341-1345
Stabilization factors of the high and low temperature phases of TaSe3 are investigated. The low temperature phase is stabilized by zirconium or titanium impurity. The high temperature phase is stabilized by oxygen impurity. Without oxygen impurity, the low temperature phase is stable up to decomposition temperature and the phase transition is completely suppressed by zirconium impurity. 相似文献
123.
《Surface & coatings technology》1987,30(2):207-214
A high activity aluminide coating was formed on the γ phase Inconel 625 superalloy by the pack cementation process. Transmission electron microscopy was used to investigate the structure of the transient oxides formed on the aluminide coating. The transient oxides formed on the coating after exposure in air at 1200 °C for 250 s were found to consist of highly oriented NiO, Ni(Al, Cr)2O4 and α-(Al, Cr)2O3. 相似文献
124.
《Calphad》1987,11(2):135-142
Experimental information on the thermochemistry and phase equilibria in the Cu-Si system have been combined to calculate a set of coefficients representing the thermodynamic properties of the pure components, stoichiometric phases and solution phases of the system considered. With these coefficients, the thermodynamic functions and the phase diagram have been calculated. The calculated results agree well with the experimental results, except for the chemical potential of Si in liquid Cu-Si at low Si contents. 相似文献
125.
《Journal of the European Ceramic Society》2022,42(8):3634-3643
Novel AlN-SiC-C refractories were fabricated by nitrogen gas-pressure sintering using single Al4SiC4 as raw-material. The high nitrogen pressure is essential and effective for the nitridation because it contributes to the diffusion of the nitrogen atoms into the interior matrix of Al4SiC4 specimen. Different from traditional carbon-containing refractories and ceramic bonded carbon materials (CBCs), the resulted products possess a honeycomb microstructure consisting of interlocked structure of worm-like SiC and C particles with a AlN ceramic boundary. AlN-SiC nanoparticles and aluminum carbonitride particles (Al-C-Ns) were formed at the interface between AlN-rich and C/SiC-rich area, which acted as transition phases that make these two areas combined tightly. The as-prepared AlN-SiC-C refractories at 1700 ℃ by a 20 atm pressure showed a relative density of 75.8%, combining a bulk density of 2.20 g/cm3 with a flexural strength of 120.9 MPa. Furthermore, the potential reaction mechanism responsible for fabrication of AlN-SiC-C refractories was revealed. 相似文献
126.
《Ceramics International》2015,41(4):5807-5811
In this paper, porous ceramic aggregates were prepared by electrical insulators waste (EIW). Effects of sintering temperature and content of EIW on the aggregates’ properties such as bulk density, and apparent porosity, total porosity, and cold crushing strength were investigated. With increasing sintering temperature and content of EIW, bulk density and cold crushing strength of the aggregates increased, apparent porosity and total porosity decreased. Based on these results, total porosity of specimens in group B sintered at 1200 °C is 62.0%, cold crushing strength is 35.3 N, and thermal conductivity is 0.165 W/(m K) at 300 °C. Comprehensive properties of specimens can be optimized by adjusting sintering temperature. Meanwhile, strength variation resulted from the combined effects of phase transformation and matrix densification under different sintering temperatures. 相似文献
127.
《Ceramics International》2017,43(2):1895-1903
This paper examined theoretically and experimentally packing behavior, sintering behavior and compressive mechanical properties of sintered bodies of the bimodal particle size system of 80 vol% large particles (351 nm diameter)–20 vol% small particles (156 nm diameter). The increased packing density as compared with the mono size system was explained by the packing of small particles in 6-coordinated pore spaces among large particles owing to the similar size relation between 6-coordinated spherical pore and small particle. The sintering between adjacent large particles dominated the whole shrinkage of the powder compact of the bimodal particle size system. However, the bimodal particle size system has a high grain growth rate because of the different curvatures of adjacent small and large particles. The derived theoretical equations for the compressive strengths of both mono size system and bimodal particle size system suggest that the increase in the grain boundary area and relative density by sintering dominate the compressive strength of a sintered porous alumina. The experimental compressive strengths were well explained by the proposed theoretical models. The strength of the bimodal particle size system was high at low sintering temperatures but was low at high sintering temperatures as compared with that of mono size system of large particles. This was explained by mainly the change of grain boundary area with grain growth. The stress–strain relationship of the bimodal particle size system showed an unique pseudo-ductile property. This was well explained by the curved inside stress distribution along the sample height. The inside stress decreases toward the bottom layer. The fracture of one layer of sintered grains over the top surface proceeds continuously with compressive time along the sample height when an applied stress reaches the critical fracture strength. 相似文献
128.
《Ceramics International》2017,43(4):3465-3474
This study investigated the effect of elemental crystal Ge or/and GeO2 doping on the microstructure and varistor properties of TiO2–Ta2O5–CaCO3 varistor ceramics, which were prepared via the traditional ball milling–molding–sintering process. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy demonstrated that co-doping with Ge and GeO2 changed the microstructure of TiO2–Ta2O5–CaCO3 ceramics, thereby increasing the nonlinear coefficient and decreasing the breakdown voltage. The optimum doping concentrations of Ta2O5, CaCO3, Ge, and GeO2 exhibited the highest nonlinear coefficient (α=14.6), a lower breakdown voltage (EB=18.7 V mm−1), the least leakage current (JL=10.5 μA cm−2), and the highest grain boundary barrier (ΦB=1.05 eV). In addition, Ge and GeO2 function as sintering aids, which reduce the sintering temperature because of their low melting points. 相似文献
129.
《Ceramics International》2019,45(12):14675-14683
In this work, the relationships between the composition-driven phase boundary, ferroelectricity and strain properties of the (1-x)(K0.48Na0.52)(Nb1-ySby)O3-xBi0.5(Na0.82K0.18)0.5ZrO3 (abbreviated as (1-x)KNN1-ySy-xBNKZ) ceramics were investigated. A giant electric field-induced strain of 0.3% (d331 = 750 p.m./V) and a low hysteresis (16.4%) were obtained in the 0.97KNN0.98S0.02-0.03BNKZ ceramics. The giant strain is attributed to the enhanced piezoelectricity induced by the appearance of the O-T phase boundary and the electric-field-induced phase transition from the relaxor phase to the ferroelectric phase. Furthermore, the 0.97KNN0.98S0.02-0.03BNKZ ceramics exhibit good thermal stability in the temperature range from 25 °C to 150 °C. Hence, this work can promote the practical applications of KNN-based lead-free piezoelectric ceramics in highly sensitive and precise piezoelectric actuators. 相似文献
130.
《Journal of the European Ceramic Society》2022,42(15):7063-7071
Metallic doping can stabilize cubic phase Li7La3Zr2O12 (LLZO) solid electrolyte for high conductivity, due to the enhanced vacancies and disordered Li-site. However, the understanding of metallic doping in the crystal lattice during the high-temperature sintering process is still not clear. In present study, a gradient series of Fe doped LLZO are formulated via solid-phase reaction, and then investigated through crystal analysis and morphological characterization. Pair distribution function essay implies that doped Fe3+ promotes random distribution of Li+ over the available sites in the located crystal. Additionally, the ceramic morphology confirms that the particles sizes in LLZO pellets suddenly grow above 1000 ℃, and Fe doping can obviously suppress Li loss above 600 ℃. As a result, the LLZF0.15 exhibits the relatively high ionic conductivity of 1.99 × 10–5 S cm–1 at 45 ℃. 相似文献