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991.
992.
Jingjing Liu Wenlong Huo Bo Ren Ke Gan Yuju Lu Xiaoyan Zhang Xinyue Tang Jinlong Yang 《Ceramics International》2018,44(14):16751-16757
An innovative approach for fabricating porous alumina ceramics (PACs) with improved mechanical and thermal properties using walnut shell powders as pore-forming agent combined with alumina sol impregnation is reported in the present work. It is demonstrated that uniform distribution of spherical pores can be observed in as-prepared PACs by using above technical route. The decrease of walnut shell powder sizes significantly promotes the enhancement of crushing strength and reduction of thermal conductivity of the PACs. Meanwhile, the impregnated alumina sol is favoring for the formation of spherical micro-pores, then further improves their mechanical and thermal insulation performances. The lowest thermal conductivity and highest crushing strength of resulting sample reach 0.16?W/m?K and 29.2?MPa, respectively. This novel method offers new possibilities to fabricate high-quality PACs. 相似文献
993.
Lirong Yang Xiaoyu Liu Zhigang Liu Chunmei Wang Gang Liu Qinglong Li Xiaoxin Feng 《Ceramics International》2018,44(17):20613-20619
g-C3N4 has received extensive attention because of its good chemical stability and environmental friendliness. Since g-C3N4 prepared from various precursors had different photocatalytic activities, g-C3N4 materials marked as U-gCN, D-gCN and M-gCN were synthesized from various precursors of urea, dicyandiamide and melamine, respectively. The D-gCN and M-gCN with smaller surface area were heated again to obtain exfoliated g-C3N4 with 2D nanosheet morphology and larger specific surface area named D-gCN-L and M-gCN-L, respectively. The synthesized bulk g-C3N4 and g-C3N4 2D nanosheets were characterized by XRD, SEM, BET, PL, UV–Vis diffuse reflectance spectroscopy, XPS, zeta potential and TG. The photocatalytic degradation of methylene blue (MB) was carried out on U-gCN, D-gCN, M-gCN, D-gCN-L and M-gCN-L, and D-gCN-L shows the highest photocatalytic degradation performance because of its larger specific surface area, lower electron-hole recombination and wide light absorption range. 相似文献
994.
Fei Zhao Tiezhu Ge Jinxing Gao Liugang Chen Xinhong Liu 《Ceramics International》2018,44(16):19123-19130
Porous mullite ceramics were fabricated by the transient liquid phase diffusion process, using quartz and fly-ash floating bead (FABA) particles and corundum fines as starting materials. The effects of sintering temperatures on the evolution of phase composition and microstructure, linear shrinkage, porosity and compressive strength of ceramics were investigated. It is found that a large amount of quartz and FABA particles can be transformed into SiO2-rich liquid phase during the sintering process, and the liquid phase is transient in the Al2O3-SiO2 system, which can accelerate the mullitization rate and promote the growth of mullite grains. A large number of closed pores in the mullite ceramics are formed due to the transient liquid phase diffusion at elevated temperatures. The porous mullite ceramics with high closed porosity (about 30%) and excellent compressive strength (maximum 105?MPa) have been obtained after fried at 1700?°C. 相似文献
995.
Ping Cai Qiming He Xishi Wu Xuejian Liu Yan Liu Jie Yin Yihua Huang Zhengren Huang 《Ceramics International》2018,44(16):19135-19142
The W-doped Nb4AlC3 ceramics [(Nb1-xWx)4AlC3, x?=?0–0.0375] were successfully fabricated by in-situ reactive hot-press-aided method using elemental niobium, aluminum, graphite and tungsten powders. The XRD results suggest that the matrix phase (Nb1-xWx)4AlC3 and the second phase (Nb1-xWx)C were simultaneously formed when W was added. The SEM images show that (Nb1-xWx)C is dispersed in the W-doped Nb4AlC3 ceramics matrix. The mechanical properties of Nb4AlC3 were greatly enhanced by W doping. Typically, the (Nb0.975W0.025)4AlC3 exhibits the highest flexural strength (483?±?21?MPa), fracture toughness (8.5?±?0.3?MPa?m1/2) and Young′s modulus (382?±?18?GPa) at room temperature (RT), which are increased by 59%, 15% and 30%, respectively, compared with the present Nb4AlC3. The Vickers hardness of (Nb0.9625W0.0375)4AlC3 (4.8?±?0.2?GPa) is 92% higher than that of Nb4AlC3. The (Nb0.975W0.025)4AlC3 also retains a high flexural strength of 344?±?4?MPa at 1400?°C (71% of RT value), which is much higher than the RT flexural strength (303?±?22?MPa) of the present Nb4AlC3. The strengthening effect is attributed to the solid solution of W and the incorporation of the second phase (Nb1-xWx)C. The excellent mechanical properties endow the W-doped Nb4AlC3 ceramics as promising high-temperature structural materials. 相似文献
996.
Shuangjian Li Xiaoqin Zhao Yulong An Duanduan Liu Huidi Zhou Jianmin Chen 《Ceramics International》2018,44(15):17864-17872
Thermal sprayed ceramic coatings have extensively been used in components to protect them against friction and wear. However, the poor lubricating ability severely limits their application. Herein, yttria-stabilized zirconia (YSZ)/MoS2 composite coatings were successfully fabricated on steel substrate with the combination of thermal spraying technology and hydrothermal reaction. Results show that the synthetic MoS2 powders are composed of numbers of ultra-thin sheets (about 7 ~ 8?nm), and the sheet has obvious lamellar structure. After vacuum impregnation and hydrothermal reaction, numbers of MoS2 powders, look like flowers, generate inside the plasma sprayed YSZ coating. Moreover, the growing point of the MoS2 flower is the intrinsic micro-pores of YSZ coating. The friction and wear tests under high vacuum environment indicate that the composite coating has an extremely long lifetime (>?100,000 cycles) and possesses a low friction coefficient less than 0.1, which is lower by about 0.15 times than that of YSZ coating. Meanwhile, the composite shows an extremely low wear rate (2.30?×?10?7 mm3 N?1 m?1) and causes slight wear damage to the counterpart. The excellent lubricant and wear-resistant ability are attributed to the formation of MoS2 transfer films and the ultra-smooth of the worn surfaces of hybrid coatings. 相似文献
997.
Microstructural evolution and densification behavior of porous kaolin-based mullite ceramic added with MoO3 were investigated. The results indicated that MoO3 addition not only lowered the secondary mullitization temperature to below 950?°C, but also facilitated effectively the anisotropic growth of mullite grains. Fine mullite whiskers grew and interlocked with one another in the pre-existing pore regions, in-situ forming a stiff 3D skeleton structure of mullite whiskers, which arrested further densification of the sample. On the other hand, due to the great capillary attraction of small pores, the liquid phase tended to spread over small grains, which favored the growth from small mullite grains into whiskers at the expense of the liquid phase. Consequently, competitive mechanisms of sintering and crystal growth of mullite functioned, which further limited the sample densification. As a result, the total linear shrinkage of the sample added with MoO3 after firing at 1400?°C was only ??2.75%, and its porosity was retained at as high as 67%. 相似文献
998.
Yong Chen Can-Can Zhang Lu Qin Chao-Bin Jiang Kang-Hui Liu Chao Ma Zhen-Tao Wu Rui-Kun Pan Wan-Qiang Cao Cong Ye Zhang Li 《Ceramics International》2018,44(15):18264-18270
The bismuth layer-structured Na0.5Bi4.5-xPrxTi4O15 (x?=?0, 0.1, 0.2, 0.3, 0.4, and 0.5) (NBT-xPr3+) ceramics were fabricated using the traditional solid reaction process. The effect of different Pr3+ contents on dielectric, ferroelectric and piezoelectric properties of Na0.5Bi4.5Ti4O15 ceramics were investigated. The grain size of Pr3+-doping ceramics was found to be smaller than that of pure one, the maximum dielectric constant and Curie temperature Tc gradually decreased with increasing Pr3+ contents, and the dielectric loss decreased at high temperature by Pr3+-doping. Moreover, the activation energy (Ea), resistivity (Z’), remanent polarization (2Pr) and piezoelectric constant (d33) increased by Pr3+-doping. The NBT-xPr3+ ceramics with x?=?0.3 achieved the optimal properties with the maximum dielectric constant of 1109.18, minimum loss of 0.00822 (250?kHz), Ea of 1.122?eV, Z’ of 7.9?kΩ?cm (725 ºC), d33 of 18 pC/N, 2Pr of 12.04 μC/cm2. The enhancement was due to the addition of Pr3+ which suppressed the decreasing of resistivity at high temperature and made it possible for NBT-xPr3+ ceramics to be poled in perpendicular direction, implying that it is a great improvement for Na0.5Bi4.5Ti4O15 ceramics in electrical properties. 相似文献
999.
Wenwen Xia Guodong Xia Guangsheng Tu Xin Dong Sumei Wang Rui Liu 《Ceramics International》2018,44(8):9125-9131
High-k oxide dielectric films have attracted intense interest for thin-film transistors (TFTs). However, high-quality oxide dielectrics were traditionally prepared by vacuum routes. Here, amorphous high-k alumina (Al2O3) thin films were prepared by the simple sol-gel spin-coating and post-annealing process. The microstructure and dielectric properties of Al2O3 dielectric films were systematically investigated. All the Al2O3 thin films annealed at 300–600?°C are in amorphous state with ultrasmooth surface (RMS ~ 0.2?nm) and high transparency (above 95%) in the visible range. The leakage current of Al2O3 films gradually decreases with the increase of annealing temperature. Al2O3 thin films annealed at 600?°C showed the low leakage current density down to 3.9?×?10?7 A/cm2 at 3?MV/cm. With the increase of annealing temperature, the capacitance first decreases then increases to 101.1?nF/cm2 (at 600?°C). The obtained k values of Al2O3 films are up to 8.2. The achieved dielectric properties of Al2O3 thin films are highly comparable with that by vapor and solution methods. Moreover, the fully solution-processed InZnO TFTs with Al2O3 dielectric layer exhibit high mobility of 7.23?cm2 V?1 s?1 at the low operating voltage of 3?V, which is much superior to that on SiO2 dielectrics with mobility of 1.22?cm2/V?1 s?1 at the operating voltage of 40?V. These results demonstrate that solution-processed Al2O3 thin films are promising for low-power and high-performance oxide devices. 相似文献
1000.
Bin Li Guangqi Li Junhong Chen Haiyang Chen Xinming Xing Xinmei Hou Yong Li 《Ceramics International》2018,44(8):9395-9400
Elongated β–Si3N4 crystals have a significant influence on the mechanical property of Fe–Si3N4 composite. In this paper, the formation mechanism of elongated β–Si3N4 crystals in Fe–Si3N4 composite was investigated. During the preparation process, β–Si3N4 crystals developed in a spiral and layer growth mechanism in the dense areas. They kept growing from the dense areas and formed radially distributed elongated crystals with hexagonal prismatic morphology as time went on. As for the formation mechanism, the (100) crystal plane of β–Si3N4 from Si-N-O melt is mainly the vicinal crystal planes growth with different angles from the (100) crystal plane. At the later stage, the crystallization and the diffusion forces in Si-N-O molten phase decreased. However, the short range diffusion remained active and resulted in the gradient distribution of N content near the boundary. With the temperature decreasing, the disappearance of the short range diffusion implied the end of the crystallization process of the elongated β–Si3N4 crystals. 相似文献