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1.
Jiangbo Wen Hongjie Wang Lei Fan Liting Wei Min Niu Hongfei Gao Zhixin Cai 《Journal of the American Ceramic Society》2019,102(1):136-143
Here we prepared porous silicon oxynitride (Si2N2O) ceramics by reaction sintering of SiO2 and Si3N4 using five different rare-earth oxides (RE2O3, RE = Lu, Yb, Y, Sm, and La) as sintering aids. The influences of RE2O3 on the formation, densification, microstructure, and mechanical properties of Si2N2O ceramics have been investigated in detail. The results have indicated that with the increase in RE ionic radius, the formation temperature of Si2N2O decreases, and the densification process could be promoted by RE2O3 with larger RE3+ ionic radius. In addition, microstructures and mechanical properties are highly dependent on the RE2O3 additives. With the increase in RE3+ ionic radius, Si2N2O changes from platelike crystals to elongated crystals. The samples doped with La2O3 and Sm2O3 with elongated crystals exhibit higher flexural strength and higher Vickers hardness. 相似文献
2.
Moritz Kindelmann Ke Ran Wolfgang Rheinheimer Koji Morita Joachim Mayer Martin Bram Olivier Guillon 《Journal of the American Ceramic Society》2021,104(10):4946-4959
Cation doping of Y2O3 is an established approach for tailoring densification and grain growth during sintering. However, the segregation of doped cations to the grain boundary and their impact on processing are still not completely understood. Segregation can be driven by electrostatic effects due to charge mismatch with the host lattice or elastic effects induced by ion size mismatch. While segregation is caused by thermodynamics, it impacts diffusion and the kinetics of grain boundaries during densification and microstructure evolution. In this study, we utilize two isovalent dopants (La3+ and Gd3+), that is we focus on the elastic component of segregation. We investigate the densification as well as the grain growth kinetics of both doped and undoped Y2O3 during field-assisted sintering/spark plasma sintering (FAST/SPS). While Gd3+ is showing no significant effect on densification, La3+ resulted in a strongly reduced sintering activity. Furthermore, the analysis of the grain growth behavior during sintering and on predensified samples revealed a decrease in the grain growth coefficient, with La3+ having the strongest impact. The structure and chemistry at the grain boundary were observed by aberration-corrected TEM. While no structural change was caused by doping, the chemical analysis showed a strong segregation of La3+ to the grain boundary, which could not be observed for Gd3+. The results indicate that segregated La3+ causes a drastic decrease in grain boundary migration rates through solute drag as well as much slower sintering kinetics, likely caused by a decrease in the grain boundary self-diffusion due to segregation. This study further underlines the importance of the elastic contribution to cation segregation and establishes a clear relationship to grain growth and sintering kinetics, which are both decreased by segregation. 相似文献
3.
《Journal of the European Ceramic Society》2003,23(2):371-378
Porous Si3N4 ceramics were fabricated by liquid-phase sintering with a Yb2O3 sintering additive, and the microstructure and mechanical properties of the ceramics were investigated, as a function of porosity. Low densification was achieved using a lower Yb2O3 additive content. Fibrous β-Si3N4 grains developed in the porous microstructure, and the grain morphology and size were affected by different sintering conditions. A high porosity, ∼40–60%, with β-Si3N4 grain development, was obtained by adjusting the additive content. Superior mechanical properties, as well as strain tolerance, were obtained for porous ceramics with a microstructure of fine, fibrous grains of a bimodal size distribution. 相似文献
4.
《Journal of the European Ceramic Society》2006,26(6):1059-1067
The densification behaviors (include α–β transformation) and high-temperature characteristics (especially oxidation resistance and high-temperature strength properties) of Si3N4 sintered bodies using Al2O3–Yb2O3 based sintering additive are investigated.Densification and α–β transformation behaviors were investigated by varying the compositions of Al2O3–Yb2O3 additives. In terms of the influence of the Y2O3/Al2O3 ratio on densification behavior, a greater Yb2O3/Al2O3 ratio tends to inhibit densification. The α–β transformation tended to be delayed in sintered bodies with a small additive amount of 3.4 mass%. Compared with the transformation behaviors of the sintered bodies using Al2O3–Y2O3 additives, those using Al2O3–Yb2O3 additives exhibited a narrower temperature zone for α–β transformation, which attributed to the finer structure for the sintered body using Al2O3–Yb2O3 additives. This is affected by the difference in solubility of Si3N4 in the two kinds of glass phase.High room temperature strength of 900–1000 MPa was obtained for sintered bodies with a 10.0 mass% addition of additives, and this is considered to be due to the finer micro-structure. Precipitation of a Yb4Si2N2O7 phase at the grain boundary glass phase, as induced by crystallization processing, enables the improvement of 1300 °C strength to about 650–720 MPa. Crystallization processing resulted in a 30% reduction in the amount of weight change during oxidation (from 3.42 to 2.46 mg/cm2), demonstrating the effectiveness in improving oxidation resistance. 相似文献
5.
Biljana Mikijelj Zubair Nawaz Jamie J. Kruzic Juan Idrobo Jeffrey J. Swab Husseyin Özcoban Hans Jelitto Gerold A. Schneider Theo Fett Yi Liu 《Journal of the American Ceramic Society》2015,98(5):1650-1657
Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE2O3 additions (RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La–Lu additions, but surprisingly were progressively lower for Y‐ and Lu‐doped samples. The lower strength and toughness were associated with fewer visible crack deflections and grain bridges. Detailed microstructural analysis of the Lu‐doped material revealed a complex intergranular nanostructure with variable Lu content and Si3N4 nanocrystals. Furthermore, the Lu‐rich areas showed an extra Lu‐adsorption site on the Si3N4 prismatic planes not previously observed in other studies. This inhomogeneous structure was attributed to grain growth impingement and higher viscosity of the Lu‐doped oxynitride glass that slows homogenization. The Y‐doped material with nearly identical glass viscosity demonstrates intermediate behavior. Finally, substituting half of the Lu2O3 with La2O3 resulted in a homogenous intergranular structure, attributed to a lower viscosity of the oxynitride glass phase, and high mechanical properties. Overall, care must be taken when adapting Si3N4 processing parameters for the smaller ionic radius rare earth dopants such as Lu and Y. 相似文献
6.
Ye Zhang Dongxu Yao Kaihui Zuo Yongfeng Xia Jinwei Yin Hanqin Liang Yu-Ping Zeng 《Ceramics International》2021,47(16):22461-22467
Porous silicon nitride (Si3N4) ceramics were fabricated by self-propagating high temperature synthesis (SHS) using Si, Si3N4 and sintering additive as raw materials. Effects of different types of sintering additives with varied ionic radius (La2O3, Sm2O3, Y2O3, and Lu2O3) on the phase compositions, development of Si3N4 grains and flexural strength (especially high-temperature flexural strength) were researched. Si3N4 ceramics doped with sintering additive of higher ionic radius had higher average aspect ratio, improved room-temperature flexural strength but degraded high-temperature flexural strength. Besides, post-heat treatment (PHT) was conducted to crystallize amorphous grain boundary phase thus improving the creep resistance and high-temperature flexural strength of SHS-fabricated Si3N4 ceramics. Excellent high-temperature flexural strength of 140 MPa~159 MPa and improved strength retention were achieved after PHT at 1400 °C. 相似文献
7.
Andre A. Bernardes Lorena B. Caliman Andre L. da Silva Jefferson Bettini Kleber L. Guimarães Douglas Gouvea 《Journal of the American Ceramic Society》2020,103(4):2835-2844
Manufacturing nanoceramics is challenging owing to the instability of the grain size resulting from the high driving force toward growth associated with the interfaces. Nanometric ceramics of some oxides have exceptional mechanical and optical properties, eg, magnesium aluminate spinel (MgAl2O4). The production of these fully conformed ceramics requires a precursor powder, which generally contains sintering-promoting additives. Li salts are typically used as sintering promoters for MgAl2O4, but the interface stability associated with the segregation of the additive is poorly understood. In this study, MgAl2O4 samples containing 0-2.86 mol% Li ions were synthesized via a simultaneous-precipitation method in an ethylic medium and subsequently calcined at 800°C in air. The nanopowders exhibited only the MgAl2O4 phase, and the crystallite size was determined by the Li2O concentration. The crystallite size was changed via the chemical modification of the interfaces by the segregation of Li ions. The solubility in the bulk material was very low at the fabrication temperature, and small amounts of Li ions saturated the bulk material and segregated to the grain boundaries (GBs), significantly stabilizing the grain–grain interface compared with the surface. The resulting powder was then aggregated further owing to the initial stage of sintering. The surface excess obtained via the selective lixiviation method confirmed that the segregation to the GBs was greater than that to the surface. Energetics calculations confirmed these results, indicating a high enthalpy of segregation at the GBs () compared with that at the surfaces (). The enthalpy of segregation together with the interface excess allowed us to estimate the reduction in the interface energy with Li+ segregation of 0.8% to the surface and 11.2% to the GBs. The Li+ segregation to the surfaces started by Al3+ substitution, and for powders with ≥1.8 mol% Li ions, Mg+2 was preferentially substituted at the surfaces. 相似文献
8.
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
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.
Lei Fan Meng Zhou Zhongqi Shi Xuefeng Lu Chao Wang 《Journal of the American Ceramic Society》2014,97(5):1371-1374
Porous β‐Si3N4 ceramics are sintered at 1600°C in N2 and postheat treated at 1500°C under vacuum using Li2O and Y2O3 as the sintering additives. The partial sintering and phase transformation are promoted at low temperature by the addition of Li2O. The addition of Y2O3 is advantageous for the formation of high aspect ratio β‐Si3N4 grains. After postheat treatment, a large amount of intergranular glassy phase is removed, and the Li content in the samples is decreased. By this method, the β‐Si3N4 porous ceramic with a porosity of 54.1% and high flexural strength of 110 ± 8.1 MPa can be prepared with a small amount of sintering additives, 0.66 wt% Li2O and 0.33 wt% Y2O3, and it is suitable for high‐temperature applications. 相似文献
11.
Equiaxed β–Si3N4 ceramics prepared by rapid reaction‐bonding and post‐sintering using TiO2–Y2O3–Al2O3 additives
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Li‐Xiang Wu Wei‐Ming Guo Ling‐Yong Zeng Hua‐Tay Lin 《Journal of the American Ceramic Society》2017,100(12):5353-5357
Sintered reaction‐bonded Si3N4 ceramics with equiaxed microstructure were prepared with TiO2–Y2O3–Al2O3 additions by rapid nitridation at 1400°C for 2 hours and subsequent post‐sintering at 1850°C for 2 hours under N2 pressure of 3 MPa. It was found that α–Si3N4, β–Si3N4, Si2N2O, and TiN phases were formed by rapid nitridation of Si powders with single TiO2 additives. However, the combination of TiO2 and Y2O3–Al2O3 additives led to the formation of 100% β–Si3N4 phase from the nitridation of Si powders at such low temperature (1400°C), and the removal of Si2N2O phase. As a result, dense β–Si3N4 ceramics with equiaxed microstructure were obtained after post‐sintering at high temperature. 相似文献
12.
Minzhong Huang Yao Huang Jun Ou Yangyang Wu Junye Wang Shanghua Wu 《International Journal of Applied Ceramic Technology》2022,19(6):3403-3409
Enhancement of the thermal conductivity of silicon nitride is usually achieved by sacrificing its mechanical properties (bending strength). In this study, β-Si3N4 ceramics were prepared using self-synthesized Y3Si2C2 and MgO as sintering additives. It was found that the thermal conductivity of the Si3N4 ceramics was remarkably improved without sacrificing their mechanical properties. The microstructure and properties of the Si3N4 ceramics were analyzed and compared with those of the Y2O3-MgO additives. The addition of Y3Si2C2 eliminated the inherent SiO2 and introduced nitrogen to increase the N/O ratio of the grain-boundary phase, inducing Si3N4 grain growth, increasing Si3N4 grain contiguity, and reducing lattice oxygen content in Si3N4. Therefore, by replacing Y2O3 with Y3Si2C2, the thermal conductivity of the Si3N4 ceramics was significantly increased by 31.5% from 85 to 111.8Wm−1K−1, but the bending strength only slightly decreased from 704 ± 63MPa to 669 ± 33MPa. 相似文献
13.
《应用陶瓷进展》2013,112(1):20-24
AbstractAbstractLow temperature sintering of α‐Si3N4 matrix ceramics was developed in the present study using 4?wt‐%MgO together with Al2O3 or AlPO4 as the sintering additives and spark plasma sintering technique. The results suggested that α‐Si3N4 ceramics could be densified at low sintering temperature by adjusting both the sintering temperature and sintering additive content. For low temperature sintered α‐Si3N4 ceramics, using MgO and Al2O3 as the sintering additives, the densification is not complete at a temperature lower than 1600°C, and the mechanical strength is <200?MPa. When MgO and AlPO4 were used as the sintering additives, the increase in AlPO4 content not only declines the sintering temperature but also promotes the mechanical property of the sintered Si3N4 ceramics. It was the AlPO4 phosphate binder that played a significant role in low temperature sintering of Si3N4 ceramics. 相似文献
14.
Yinsheng Li Ha-Neul Kim Haibo Wu Mi-Ju Kim Jae-Woong Ko Young-Jo Park Zhengren Huang Hai-Doo Kim 《Journal of the European Ceramic Society》2021,41(1):274-283
Si3N4 ceramics were sintered at 1900 °C under a nitrogen pressure of 1 MPa using Y2O3-MgO additives. The effects of Y2O3 content (0.5-4 mol%) on microstructure and thermal conductivity were systematically investigated. The increasing Y2O3 content led to increases in amount and viscosity of liquid phase during sintering, which induced a “bimodal to normal” transition in distribution of grain size, decreased Si3N4/Si3N4 contiguity and enhanced devitrification degree of intergranular phase in sintered bulks. Moreover, the decreasing Y2O3 content was found to improve the elimination efficiency of SiO2 impurity during sintering, resulting in lower lattice oxygen content in densified specimens. The microstructure had a strong effect on thermal conductivity. The samples sintered for 3 h gained an increase of thermal conductivity from 65 to 73 W·m-1 K-1 with increasing Y2O3 content, while the samples sintered for 12 h obtained a substantial increase of thermal conductivity from 87 to 132 W·m-1 K-1 with decreasing Y2O3 content. 相似文献
15.
《Ceramics International》2022,48(13):18615-18624
To enhance the thermal conductivity of Si3N4, a polydopamine (PDA) coating was creatively introduced into ceramics sintered with different additive contents through a two-step sintering process consisting of a first treatment at 1500 °C for 8 h followed by 12 h at 1900 °C under 1 MPa nitrogen pressure. After the first-step sintering, the PDA-coated sample exhibited a higher elimination effect of the liquid phase and an increase in the N/O ratio, which allowed the additives to directly interact with the Si3N4 grains, resulting in a microstructure with more and larger rod-shaped grains. After the second-step sintering, the densified samples of the PDA-coating attained slightly coarser rod-shaped grains, lower O content, higher N/O ratio and peak intensity (XRD) of the Y2Si3O3N4 phase, thicker grain boundary film, and secondary phases mainly residing in multigrain junctions. Consequently, the thermal conductivity of all the PDA-coated samples typically showed a 10–12% increment in comparison to the PDA-free samples for each additive content. 相似文献
16.
《Journal of the European Ceramic Society》2005,25(1):19-28
Sintering additives containing Y2O3 influence the microstructure and the crystalline-state of Si3N4-ceramics produced via pressureless sintering, and determine their response towards oxidation. Y2SiO5 and Y2Si2O7 were formed after sintering and oxidation, respectively. The superficial layers formed after oxidation are thinner and formed faster on the surface of the compositions 90Si3N4–5Y2O3–5Al2O3 and 90Si3N4–5Y2O3–5AlN than on 90Si3N4–5Y2O3–2.5Al2O3–2.5AlN (in wt.%). The 90Si3N4–5Y2O3–5Al2O3/liquid Al interface features strong interfacial adhesion while mild diffusion should govern the interfacial interactions. Compounds, whose formation results from the yttria-containing sintering aids, such as yttrium aluminates, should act as diffusion barriers at the ceramic/liquid metal interface. The experimental results indicate attractive features for applications in both Al-foundry industry and production of Si3N4–Al composites. 相似文献
17.
18.
Bernard Haochih Liu Po-Jui Su Ching-Huan Lee Jow-Lay Huang 《Ceramics International》2013,39(4):4205-4212
We proposed a novel approach to investigate the three-dimensional microstructures and sintering behaviors of Si3N4-based ceramic nanocomposites by electrochemical impedance spectroscopy. Si3N4/TiC and Si3N4/TiN with various weight percentages of conductive phases were prepared by spark plasma sintering (SPS) at different temperatures and dwell times. The incorporation of TiC and TiN into β-Si3N4 provides pulse current paths inside the ceramics due to their higher conductivity. These paths enable the localized Joule heating and mass transport, facilitating the densification and grain growth of ceramic compact. The electrochemical study of such nanocomposites has revealed three-dimensional information of the evolution of their microstructures, and the capacitive and resistive characteristics of the nanocomposites reflect the densification, grain growth, and element distribution in the compact. The impedance model presented in this work suggests isolated distribution of TiN in Si3N4 while Si3N4/TiC of the same amount of additives at the same sintering conditions formed conductive network. This impedance analysis further explained the differences in densification mechanism of SPS in Si3N4/TiN and Si3N4/TiC. 相似文献
19.
《Ceramics International》2016,42(16):18641-18647
Silicon nitride (Si3N4) ceramics offer excellent thermal, mechanical and dielectric properties, which make Si3N4 a good candidate material for an application as electronic packaging material. For an application as a heat dissipation substrate, most studies focused on achieving a high thermal conductivity through long-time heat preservation and different kinds of heat treatments. Very few studies also considered the mechanical and dielectric properties. In addition, there have not been systematic researches about influence of additives concentration and type on the combination properties of Si3N4. Therefore, in this study, Si3N4 ceramic samples were prepared via hot pressing at 1800 °C with a relatively short heat preservation step (2 h), with different amounts of Y2O3 added as sintering additive. The effect of the initial concentration of the rare earth oxide on the chemical composition, microstructure, thermal conductivity, as well as the mechanical and dielectric properties of the Si3N4 ceramic samples was systematically studied. 相似文献
20.
Weide Wang Dongxu Yao Huanbei Chen Yongfeng Xia Kaihui Zuo Jinwei Yin Hanqin Liang Yu-Ping Zeng 《Journal of the American Ceramic Society》2020,103(3):2090-2100
A novel ZrSi2–MgO system was used as sintering additive for fabricating high thermal conductivity silicon nitride ceramics by gas pressure sintering at 1900°C for 12 hours. By keeping the total amount of additives at 7 mol% and adjusting the amount of ZrSi2 in the range of 0-7 mol%, the effect of ZrSi2 addition on sintering behaviors and thermal conductivity of silicon nitride were investigated. It was found that binary additives ZrSi2–MgO were effective for the densification of Si3N4 ceramics. XRD observations demonstrated that ZrSi2 reacted with native silica on the Si3N4 surface to generate ZrO2 and β-Si3N4 grains. TEM and in situ dilatometry confirmed that the as formed ZrO2 collaborated with MgO and Si3N4 to form Si–Zr–Mg–O–N liquid phase promoting the densification of Si3N4. Abnormal grain growth was promoted by in situ generated β-Si3N4 grains. Consequently, compared to ZrO2-doped materials, the addition of ZrSi2 led to enlarged grains, extremely thin grain boundary film and high contiguity of Si3N4–Si3N4 grains. Ultimately, the thermal conductivity increased by 34.6% from 84.58 to 113.91 W·(m·K)−1 when ZrO2 was substituted by ZrSi2. 相似文献