共查询到20条相似文献,搜索用时 140 毫秒
1.
Effects of Y2O3–RE2O3 (RE = Sm,Gd, Lu) Additives on Electrical and Thermal Properties of Silicon Carbide Ceramics 下载免费PDF全文
Seung Hoon Jang Kwang Joo Kim Seoung‐Jae Lee Kwang‐Young Lim 《Journal of the American Ceramic Society》2016,99(1):265-272
In this study, we investigated the electrical and thermal properties of SiC ceramics with 2 vol% equimolar Y2O3–RE2O3 (RE = Sm, Gd, Lu) additives. The three SiC ceramics with 2 vol% equimolar Y2O3–RE2O3 additives showed electrical conductivities on the order of ~103 (Ω·m)?1, which is one order of magnitude higher than that of the SiC ceramics sintered with 2 vol% Y2O3 only. The increase in electrical conductivity is attributed to the growth of heavily nitrogen‐doped SiC grains during sintering and the confinement of oxide additives in the junction area. The thermal conductivities of the SiC ceramics were in the 176–198 W·(m·K)?1 range at room temperature. The new additive systems, equimolar Y2O3–RE2O3, are beneficial for achieving both high electrical conductivity and high thermal conductivity in SiC ceramics. 相似文献
2.
Semchenko G. D. Shmygarev Yu. M. Starolat E. E. Katin V. V. D'yakonenko N. L. 《Refractories and Industrial Ceramics》2004,45(1):36-41
Technological factors capable of influencing the structure, physicomechanical properties, and crack resistance of silicon nitride ceramics intended for fabrication of component of complex shape are considered. The effect of a composite sintering aid Al2O3 + Y2O3 and an ethyl silicate binder on strength and crack resistance of raw and sintered ceramics subjected to hydrostatic compression is discussed. It is shown that the ceramics in question can be tested for crack resistance by the indentation method. 相似文献
3.
You Zhou Hideki Hyuga Dai Kusano Chika Matsunaga Kiyoshi Hirao 《Journal of the American Ceramic Society》2019,102(4):1579-1588
A variety of combinations of Y2O3 and MgO were used as additives in preparing Si3N4 ceramics by the sintering of reaction-bonded silicon nitride (SRBSN) method. By varying the amount of Y2O3 in the range of 0-5 mol% and that of MgO in the range of 0-8 mol%, the effects of Y2O3 and MgO additives on nitridation and sintering behaviors as well as thermal conductivity were studied. It was found that appropriate amount and combination of Y2O3 and MgO additives were essential for attaining full densification and achieving high thermal conductivity. The sample doped with 2.5 mol% of Y2O3 and 5 mol% of MgO attained a thermal conductivity of 128 Wm−1K−1 when sintered at 1900°C for 6 hours, and the sample doped with 2 mol% of Y2O3 and 4 mol% of MgO achieved a thermal conductivity of 156 Wm−1K−1 when sintered for 24 hours. 相似文献
4.
You Zhou Tatsuki Ohji Hideki Hyuga Yu‐ichi Yoshizawa Norimitsu Murayama Kiyoshi Hirao 《International Journal of Applied Ceramic Technology》2014,11(5):872-882
Silicon nitride ceramics were prepared from a high‐purity silicon powder doped with 2 mol% Y2O3 and 5 mol% MgO as sintering additives via a route of sintering of reaction‐bonded silicon nitride (SRBSN). The materials sintered at 1900°C for 3, 6, 12, and 24 h had thermal conductivities of 109, 125, 146, and 154 W/m/K, and four‐point bending strengths of 786, 676, 608, and 505 MPa, respectively. The fracture toughness values, determined by the single‐edge‐precracked‐beam (SEPB) method, were 8.4, 8.6, 9.7, and 10.7 MPa m1/2 for the materials sintered for 3, 6, 12, and 24 h, respectively, which were similar to the results measured by the chevron‐notched‐beam (CNB) test method. The materials sintered for longer times (12 and 24 h) showed stronger R‐curve behaviors over longer range of crack extension, in comparison with the materials sintered for shorter times (3 and 6 h). 相似文献
5.
Shishuai Li Yongfeng Xia Dongxu Yao Hanqin Liang Yu-Ping Zeng 《International Journal of Applied Ceramic Technology》2023,20(1):465-474
Sintered reaction-bonded silicon nitride (SRBSN) with high thermal conductivity was obtained using (Y0.96Eu0.04)2O3 and MgO as sintering additives. Green compacts were nitrided at 1400°C for 4 h. Post-sintering was carried out at 1850 and 1900°C for 4 h, respectively. In reaction-bonded silicon nitride (RBSN) doped with Y2O3 and MgO, the β-Si3N4 content and nitridation degree were 51.1% and 93.8%, respectively. However, the β-Si3N4 content and nitridation degree were 72.6% and 96.7% in a nitrided compact doped with (Y0.96Eu0.04)2O3 and MgO. After post-sintering, the phase composition, microstructure, mechanical properties, and thermal conductivity were investigated. After sintering at 1900°C for 4 h, the thermal conductivity of SRBSN doped with (Y0.96Eu0.04)2O3 and MgO was increased by 16.5% compared to that of the samples doped with Y2O3 and MgO. The highest hardness of 1639 HV and the good flexural strength of 776.4 MPa were also achieved in the sample doped with 2-mol.% (Y0.96Eu0.04)2O3 and 5-mol.% MgO. 相似文献
6.
Zhuo Zhang Xiaoming Duan Baofu Qiu Zhihua Yang Delong Cai Peigang He Dechang Jia Yu Zhou 《Journal of the European Ceramic Society》2019,39(5):1788-1795
Textured hexagonal boron nitride (h-BN) matrix composite ceramics were prepared by hot pressing using 3Y2O3-5Al2O3 (mole ratio of 3:5) and 3Y2O3-5Al2O3-4MgO (mole ratio of 3:5:4) as liquid phase sintering additives, respectively. During the sintering process with liquid phase environments, platelike h-BN grains were rotated to be perpendicular to the sintering pressure, forming the preferred orientation with the c-axis parallel to the sintering pressure. Both h-BN matrix ceramic specimens show significant texture microstructures and anisotropic mechanical and thermal properties. The h-BN matrix ceramics prepared with 3Y2O3-5Al2O3-4MgO possess higher texture degree and better mechanical properties. While the anisotropy of thermal conductivities of that prepared with 3Y2O3-5Al2O3 is more significant. The phase compositions and degree of grain orientation are the key factors that affect their anisotropic properties. 相似文献
7.
Influence of sintering additives on densification kinetics and high‐temperature strength in γ‐Y2Si2O7 ceramics 下载免费PDF全文
Xingyu Fan Hongjie Wang Min Niu Lei Su Jun Zhou Jinpeng Fan Dahai Zhang 《Journal of the American Ceramic Society》2017,100(3):1195-1201
Pressureless sintering of pure γ‐Y2Si2O7 powders that had been synthesized by a solid‐liquid reaction method using Y2O3 and SiO2 powders with Li2O, MgO, and Al2O3 additives was reported. The sintering kinetics of γ‐Y2Si2O7 powders was analyzed to track details of densification evolution. Apparent activation energies of the densification of γ‐Y2Si2O7 powders were reported for the first time, which was 57.1, 96.6, and 100.2 kJ/mol for the powders with Li2O, MgO, and Al2O3 additives, respectively, indicating that Li2O could promote the densification behavior effectively. The flexural strengths as a function of temperature for the γ‐Y2Si2O7 ceramics with different additives were also investigated. The degradation of high‐temperature flexural strength was mainly ascribed to the softening of grain‐boundary glassy phase. γ‐Y2Si2O7 specimens fabricated using the powders with MgO or Al2O3 additives exhibited better high‐temperature mechanical properties. 相似文献
8.
《Ceramics International》2023,49(12):19806-19816
Aluminium titanate (Al2TiO5, AT) flexible ceramics were prepared from Al2O3–TiO2 powder system with MgO and Fe2O3 as additives through solid-state method. The effects of addition level of MgO and Fe2O3 on phase compositions, sintering behavior, microstructure and fracture properties of AT flexible ceramics were systematically investigated. The experimental results show that the introduction of additives can promote the formation of AT and improve the densification by forming solid solution. The addition of MgO could effectively refine AT grains since the formed MgAl2O4 spinel grains could pin at the AT grain boundary and inhibit the growth of AT grains. Conversely, the addition of Fe2O3 could promote the AT grain growth. And the simultaneous addition of MgO and Fe2O3 is beneficial to develop elongated rod-like AT grains. With that, the improved fracture properties can be obtained. Due to pining effect of spinel and better densification, the flexural strength of modified AT flexible ceramics is about 34 times higher than that of virgin. In addition, thanks to the microcracked structure and high grain aspect ratio, events of crack deflection, crack branching, grains pull-out and grains bridging are more likely to occur, leading to an increase in the flexibility by about 133%. 相似文献
9.
《Ceramics International》2020,46(17):27175-27183
The fabrication of silicon nitride (Si3N4) ceramics with a high thermal conductivity was investigated by pressureless sintering at 1800 °C for 4 h in a nitrogen atmosphere with MgO and Y2O3 as sintering additives. The phase compositions, relative densities, microstructures, and thermal conductivities of the obtained Si3N4 ceramics were investigated systemically. It was found that at the optimal MgO/Y2O3 ratio of 3/6, the relative density and thermal conductivity of the obtained Si3N4 ceramic doped with 9 wt% sintering aids reached 98.2% and 71.51 W/(m·K), respectively. EDS element mapping showed the distributions of yttrium, magnesium and oxygen elements. The Si3N4 ceramics containing rod-like grains and grain boundaries were fabricated by focused ion beam technique. TEM observations revealed that magnesium existed as an amorphous phase and that yttrium produced a new secondary phase. 相似文献
10.
Effects of Sintering Aids on the Transparency and Conversion Efficiency of Cr4+ Ions in Cr: YAG Transparent Ceramics 下载免费PDF全文
Tianyuan Zhou Le Zhang Hao Yang Xuebin Qiao Peng Liu Dingyuan Tang Jian Zhang 《Journal of the American Ceramic Society》2015,98(8):2459-2464
Tetravalent chromium‐doped Y3Al5O12 ceramics were fabricated by solid‐state reactive sintering method using high‐purity Y2O3, α‐ Al2O3, and Cr2O3 powders as the starting materials. CaO and MgO were co‐doped as the sintering aids. The effects of TEOS and divalent dopants (CaO and MgO) on the optical qualities, the conversion efficiency of Cr4+ ions, and the microstructure evolutions of 0.1 at.% Cr4+: YAG ceramics were investigated. Fully dense, dark brown colored Cr4+: YAG ceramics with an average grain size of 3.1 μm were achieved. The in‐line transmittance of the as‐prepared ceramic at 2000 nm was 85.3% (4 mm thick), and the absorption coefficient at 1030 nm (the characteristic absorption peak of Cr4+ ions) was as high as 3.7 cm?1, which was higher than that of corresponding single crystals fabricated by Czochralski method. 相似文献
11.
S. Fünfschilling T. Fett S.E. Gallops J.J. Kruzic R. Oberacker M.J. Hoffmann 《Journal of the European Ceramic Society》2010,30(6):1229-1236
A procedure is presented that allows the simple estimation of bridging stresses from crack growth resistance curve (R-curve) data. The first-order approximation results by taking the derivative of the R-curve. For an increased degree of accuracy a second-order solution is suggested. This step includes straight-forward integration of the first-order results. The procedure is outlined in detail and applied to fatigue threshold R-curve results for a MgO + Y2O3-doped silicon nitride (MgY-SN) and an 99.5% pure alumina obtained with compact tension specimens, and fracture toughness R-curve results for a MgO + La2O3-doped silicon nitride (MgLa-SN) obtained with notched bending bars. The approximate bridging stresses are compared with the “full solutions” computed with much more effort by solving a system of integral equations. 相似文献
12.
《Journal of the European Ceramic Society》2021,41(14):6971-6982
Silicon nitride (Si3N4) ceramics were fabricated by gas pressure sintering (GPS) using four sintering additives: Y2O3–MgO, Y2O3–MgF2, YF3–MgO, and YF3–MgF2. The phase composition, grain growth kinetics, mechanical properties, and thermal conductivities of the Si3N4 ceramics were compared. The results indicated that the reduction of YF3 on SiO2, induced a high Y2O3/SiO2 secondary phase ratio, which improved the thermal conductivity of the Si3N4 ceramics. The depolymerization of F atom reduces the diffusion energy barrier of solute atom and weakens the viscous resistance of anion group, which was beneficial to grain boundary migration. Besides exhibiting a lower grain growth exponent(n = 2.5)and growth activation energy (Q = 587.94 ± 15.35 kJ/mol), samples doped with binary fluorides showed excellent properties, including appreciable thermal conductivity (69 W m−1 K−1), hardness (14.63 ± 0.12 GPa), and fracture toughness (8.75 ± 0.18 MPa m1/2), as well as desirable bending strength (751 ± 14 MPa). 相似文献
13.
Yumi Fukuda Koichi Harada Maki Yonetsu Ariane K. Albessard Yasushi Hattori Kenji Essaki Yasuhiro Goto Tomohiro Suetsuna 《Journal of the American Ceramic Society》2021,104(12):6563-6571
When reaction-bonded silicon nitride containing MgO/Y2O3 additives is sintered at three different temperatures to form sintered reaction-bonded silicon nitride (SRBSN), the thermal conductivity increases with sintering temperature. The β-Si3N4 (silicon nitride) crystals of SRBSN ceramics were synthesized and characterized to investigate the relation between the crystal structure and the lattice oxygen content. The hot-gas extraction measurement result and the crystal structure obtained using Rietveld analysis suggested that the unit cell size of the β-Si3N4 crystal increases with the decrease in the lattice oxygen content. This result is reasonable considering that the lattice oxygen with the smaller covalent radius substitutes nitrogen with the larger one in the β-Si3N4 crystals. The lattice oxygen content decreased with increasing sintering temperature which also correlated with increase in thermal conductivity. Moreover, it is noteworthy from the viewpoint that it may be possible to apply the lattice constant analysis for the nondestructive and simple measurement of the lattice oxygen content that deteriorates the thermal conductivity of the β-Si3N4 ceramics. 相似文献
14.
Martin Härtelt Stefan Fünfschilling Thomas Schwind Heinz Riesch‐Oppermann Theo Fett Jamie J. Kruzic 《Journal of the American Ceramic Society》2013,96(8):2593-2597
Fatigue failure is a concern when high‐strength, high‐toughness silicon nitride ceramics are used in mechanical components and the growth of natural flaws will determine the usable upper bound strength. In this study a fracture resistance curve (R‐curve) model is incorporated into an established method for deducing natural flaw growth rates from a combination of strength and fatigue life data for smooth specimens. Experimental data for a commercial silicon nitride, SL200, were examined. When compared with results deduced using a constant fracture toughness model, the new method gives more physically realistic growth rate results. Specifically, by incorporating the R‐curve the deduced fatigue threshold is equal to the reported intrinsic toughness for crack propagation of 2.2 MPa√m, whereas the constant fracture toughness model gives a physically unrealistic threshold value. Furthermore, much better agreement is achieved with the growth rates measured using macroscopic compact‐tension specimens. Overall, it is concluded that the R‐curve effect should not be ignored when deducing the fatigue crack growth rates of natural flaws in high‐toughness silicon nitride ceramics. 相似文献
15.
Yusen Duan Jingxian Zhang Xiaoguang Li Hainan Bai Pavol Sajgalik Dongliang Jiang 《International Journal of Applied Ceramic Technology》2019,16(4):1399-1406
Silicon nitride ceramics were pressureless sintered at low temperature using ternary sintering additives (TiO2, MgO and Y2O3), and the effects of sintering aids on thermal conductivity and mechanical properties were studied. TiO2–Y2O3–MgO sintering additives will react with the surface silica present on the silicon nitride particles to form a low melting temperature liquid phase which allows liquid phase sintering to occur and densification of the Si3N4. The highest flexural strength was 791(±20) MPa with 12 wt% additives sintered at 1780°C for 2 hours, comparable to the samples prepared by gas pressure sintering. Fracture toughness of all the specimens was higher than 7.2 MPa·m1/2 as the sintering temperature was increased to 1810°C. Thermal conductivity was improved by prolonging the dwelling time and adopting the annealing process. The highest thermal conductivity of 74 W/(m∙K) was achieved with 9 wt% sintering additives sintered at 1810°C with 4 hours holding followed by postannealing. 相似文献
16.
《Journal of the European Ceramic Society》2002,22(11):1897-1904
The impulse excitation technique (IET) and high temperature X-ray diffraction (HTXRD) were used to investigate the intergranular glass phase and its crystallisation behaviour in four hot-pressed silicon nitrides. The internal friction or damping peak height measured with IET near the glass transition temperature, Tg, is used as a qualitative indicator for the amount of residual intergranular amorphous phase after sintering. Silicon nitride powder was hot-pressed with different sintering additives. The silicon nitride containing 4 wt.% Al2O3 does not reveal an internal friction peak at Tg, i.e. it does not contain a significant amount of intergranular glass phase. Three other silicon nitrides, containing either 8 wt.% Y2O3, 6 wt.% Y2O3+2 wt.% Al2O3, or 2 wt.% Y2O3+4 wt.% Al2O3+2 wt.% TiN, do show an internal friction peak near Tg. This “Tg-peak” is nearly unaffected by heating up to 1400 °C in the silicon nitride with Y2O3+Al2O3+TiN sintering aids, whereas the amount of intergranular glass in the ceramics containing either Y2O3+Al2O3 or Y2O3 as a sintering aid is strongly reduced by subsequent heating. As observed from HTXRD, the onset temperature of crystallisation of the intergranular glass in the ceramic containing Y2O3+Al2O3 sintering aids is about 1100 °C, with the formation of Y–N-apatite (Y20N4Si12O48) and O-sialon (Al0.04Si1.96N1.96O1.04). The O-sialon phase in the yttria and alumina containing ceramics, formed either during sintering or during heat treatment, is not stable at elevated temperatures and dissolves in the intergranular glass phase between 1300 and 1400 °C. The O-sialon phase in the ceramic without Y2O3 sintering additive, however, is thermally stable. The presence of Ti4+ ions in the intergranular glass phase is suggested to inhibit its crystallisation, resulting in a stable high temperature damping behaviour. 相似文献
17.
Beiyue Ma Yandong Tang Chengji Deng 《International Journal of Applied Ceramic Technology》2022,19(5):2523-2532
Silicon nitride (Si3N4) ceramics doped with two different sintering additive systems (Al2O3–Y2O3 and Al2O3–Yb2O3) were prepared by hot-pressing sintering at 1800℃ for 2 h and 30 MPa. The microstructures, nano-indentation test, and mechanical properties of the as-prepared Si3N4 ceramics were systematically investigated. The X-ray diffraction analyses of the as-prepared Si3N4 ceramics doped with the two sintering additives showed a large number of phase transformations of α-Si3N4 to β-Si3N4. Grain size distributions and aspect ratios as well as their effects on mechanical properties are presented in this study. The specimen doped with the Al2O3–Yb2O3 sintering additive has a larger aspect ratio and higher fracture toughness, while the Vickers hardness is relatively lower. It can be seen from the nano-indentation tests that the stronger the elastic deformation ability of the specimens, the higher the fracture toughness. At the same time, the mechanical properties are greatly enhanced by specific interlocking microstructures formed by the high aspect ratio β-Si3N4 grains. In addition, the density, relative density, and flexural strength of the as-prepared Si3N4 ceramics doped with Al2O3–Y2O3 were 3.25 g/cm3, 99.9%, and 1053 ± 53 MPa, respectively. When Al2O3–Yb2O3 additives were introduced, the above properties reached 3.33 g/cm3, 99.9%, and 1150 ± 106 MPa, respectively. It reveals that microstructure control and mechanical property optimization for Si3N4 ceramics are feasible by tailoring sintering additives. 相似文献
18.
High Nonlinearity and High Voltage Gradient ZnO Varistor Ceramics Tailored by Combining Ga2O3, Al2O3, and Y2O3 Dopants 下载免费PDF全文
Hongfeng Zhao Jun Hu Shuiming Chen Qingyun Xie Jinliang He 《Journal of the American Ceramic Society》2016,99(3):769-772
This paper deals with the electrical characteristics of rare‐earth‐doped ZnO varistor ceramics. Multiple donor dopants (Al3+, Ga3+, and Y3+) were employed to improve the comprehensive performance of ZnO varistor ceramics. The leakage current of rare‐earth‐doped ZnO varistor ceramics decreased noticeably with Ga2O3 dopants. The Ga3+ dopant occupies the defect sites of grain boundaries and increases the barrier potential of ZnO varistor ceramics, so the leakage current is effectively inhibited. Y2O3 is primarily located around the grains, which restrains ZnO grain growth, increasing the voltage gradient. The Al3+ goes into the lattices of ZnO grains, decreasing the grain resistance; thus, the residual voltage ratio can be controlled at low levels under a high impulse current. With the combined incorporation of Al3+, Ga3+, and Y3, excellent electrical properties of ZnO varistor ceramics can be acquired with a nonlinearity coefficient of 87, voltage gradient of 517 V/mm, leakage current of 0.96 μA/cm2, and residual voltage ratio of 1.60. These rare multiple donor dopants can aid in engineering high‐quality ZnO varistors. 相似文献
19.
Bensheng Huang Sheng Fu Shunshun Zhang Anna Lin Zhongyi Guan 《International Journal of Applied Ceramic Technology》2020,17(3):1183-1193
The effects of zirconia and yttrium oxide addition on microstructure, bulk density, microhardness, flexural strength, and wear resistance of high alumina ceramics (>97 wt% Al2O3, MSA ceramics) composed of MgO–SiO2–Al2O3 system have been investigated. The results show that the addition of zirconia makes the mechanical properties and wear properties of ceramics composed of MgO–SiO2–Al2O3–ZrO2 (MSAZ ceramics) system have been greatly improved compared with MSA ceramics. In addition, the ceramics composed of MgO–SiO2–Al2O3–ZrO2–Y2O3 (MSAZY ceramics) system have better mechanical properties and wear properties than MSAZ ceramics. With the contents of zirconia and yttrium oxide increase, the bulk density, microhardness, and flexural strength of MSAZ and MSAZY ceramics increased at first and then decreased. However, the wear rate shows the opposite. When 0.4 wt% ZrO2 and 0.6 wt% Y2O3 were added to the matrix, the wear rate of MSAZY ceramics reached a minimum of 0.042%, and the wear resistance was improved by about 73.8% compared with MSA ceramics with a wear rate of 0.16%. In addition, the optimum additions of zirconia and yttria are 0.4% and 0.6%, respectively. 相似文献
20.
Xiao-Tong Jia Zhao-Hui Zhang Tian-Hao Xu Luo-Jin Liu Yuan-Hao Sun Xian-Yu Li Qiang Wang Zhao-Hu Jia Yang-Yu He Xing-Wang Cheng 《Journal of the American Ceramic Society》2023,106(10):6301-6316
Aluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO. The addition of La3+ and Mg2+ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y3+ facilitates liquid-phase sintering of AlON ceramics. Moreover, the addition of Mg2+ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties. 相似文献