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1.
Silicon nitridation mechanism in reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride
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Menglong Long Yong Li Xiuming Jin Guisheng Yao Jialin Sun Ramachandran V. Kumar 《Journal of the American Ceramic Society》2018,101(9):4350-4356
Reaction‐bonded Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride, with Si powder, SiC particles and Fe3Si–Si3N4 particles as raw materials, respectively, are prepared in flame‐isolation nitridation shuttle kiln with flowing N2 at 1723K. There is columnar β‐Si3N4 in both Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride. However, fibrous α‐Si3N4 is only observed in Si3N4–SiC and Si3N4‐bonded ferrosilicon nitride contains much more Si2N2O than Si3N4–SiC. By analyzing the oxidation thermodynamics of Si and Si3N4, it is known that in the process of producing Si3N4–SiC, Si is oxidized first to gaseous SiO and fibrous α‐Si3N4 is generated with SiO and N2. The existence of SiO is the reason of low silicon nitridation rate. But in the process of producing Si3N4‐bonded ferrosilicon nitride, Si3N4 is easier to be oxidized than Si and Si2N2O is generated on the surface of Si3N4 hexagonal prisms in ferrosilicon nitride particles. Meanwhile, Si in raw materials forms new ferrosilicon alloys with Fe3Si, which decreases the temperature of liquid appearance and blocks some open pores in the samples, which stops the matter loss of nitridation. Liquid ferrosilicon alloys favors β‐Si3N4 generation from Si direct nitridation and fibrous α‐Si3N4 transformation, which used to exist in ferrosilicon nitride raw materials. 相似文献
2.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures
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Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
3.
Synthesis and growth mechanism of single crystal β‐Si3N4 particles with a quasi‐spherical morphology
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Si‐Yuan Sun Yi‐Yao Ge Qi Wang Zhao‐Bo Tian Jie Zhang Wei Cui Guang‐hua Liu Ke‐Xin Chen 《Journal of the American Ceramic Society》2018,101(10):4526-4537
Single‐crystal β‐Si3N4 particles with a quasi‐spherical morphology were synthesized via an efficient carbothermal reduction‐nitridation (CRN) strategy. The β‐Si3N4 particles synthesized under an N2 pressure of 0.3 MPa, at 1450°C and with 10 mol% unique CaF2 additives showed good dispersity and an average size of about 650 nm. X‐ray photoelectron spectroscopy analysis revealed that there was no SiC or Si–C–N compounds in the β‐Si3N4 products. Selected‐area electron‐diffraction pattern and high‐resolution image indicated single crystalline structure of the typical β‐Si3N4 particles without an obvious amorphous oxidation layer on the surface. The growth mechanism of the quasi‐spherical β‐Si3N4 particles was proposed based on the transmission electron microscopy and energy dispersive X‐ray spectroscopy characterization, which was helpful for controllable synthesis of β‐Si3N4 particles by CRN method. Owing to the quasi‐spherical morphology, good dispersity, high purity, and single‐crystal structure, the submicro‐sized β‐Si3N4 particles were promising fillers for preparing resin‐based composites with high thermal conductivity. 相似文献
4.
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
5.
Zhaoyun Xu Bo Wang Jianfeng Yang Zhongjian Zhao 《Journal of the American Ceramic Society》2014,97(11):3392-3395
Porous silicon nitride ceramics with various porosities were fabricated by liquid phase sintering of mixtures containing fibrous and equiaxed α‐Si3N4 powder with a various content ratios. The effects of the contents of the fibrous α‐Si3N4 powder (0%–100%) on the microstructure and mechanical properties of porous Si3N4 ceramics were studied. As the increase of the fibrous α‐Si3N4 powder content, both the density of green bodies and the linear shrinkage decreased, resulting in increased porosity due to the inhibited densification by the fibrous Si3N4 particle. XRD analysis proved the complete formation of single β‐Si3N4 phase. SEM analysis revealed that the microstructure of the low content of fibrous α‐Si3N4 porous ceramics was almost composed of fine elongated β‐Si3N4 grains with high aspect ratio while numerous coarse elongated β‐Si3N4 grains with low aspect ratio surrounding fine grains were formed as the content of the fibrous α‐Si3N4 powder increased. With the increase in content of the fibrous α‐Si3N4 powder from 0% to 100%, the porosity changed from 47.8% to 56.6%, and the flexural strength decreased from 146 to 62 MPa correspondingly, indicating a flexural adjustment of the porosity and mechanical properties. 相似文献
6.
A new macromolecular coupling agent butyl acrylate (BA)‐methyl methacrylate (MMA)‐vinyl triethoxy silane (VTES) tercopolymer was synthesized using solution polymerization initiated by free radical initiator benzoyl peroxide (BPO) and dicumyl peroxide (DCP). Dodecylthiol is choosed as the chain transfer to control the molecule weight of this tercopolymer. The terpolymer's molecular structure was confirmed by FTIR and NMR, and its average molecular weight was determined by GPC. In this work, the tercopolymer BA–MMA–VTES is used for surface modification of silicon nitride (Si3N4) nanopowder. The structure surface properties and thermal stability of modified nano‐Si3N4 were systematically investigated by FTIR, TGA, TEM, and size distribution analyzer. The results show that the macromolecular coupling agent bonds covalently on the surface of nano‐sized Si3N4 particles and an organic coating layer is formed. The optimum loading of this macromolecular coupling agent BA–MMA–VTES tercopolymer is 5% (wt %) of nano‐sized Si3N4. TEM also reveals that modified nano‐Si3N4 possesses good dispersibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
7.
《Journal of the European Ceramic Society》2006,26(15):3459-3466
Si3N4 ceramic was jointed with itself by active brazing with a Cu–Pd–Ti filler alloy. Interfacial microstructure of the Si3N4/Si3N4 joint was analyzed by EPMA, TEM and X-ray diffract meter. The results indicate that a TiN reaction layer with a thickness about 5 μm is formed at the interface between Si3N4 ceramic and filler alloy. The TiN reaction layer is composed of two zones: one next to the Si3N4 ceramic with grains of 100 nm and the other zone that connects with the filler alloy and has grains of 1 μm. The microstructure of the joint can be described as: Si3N4 ceramic/TiN layer with fine grains/TiN layer with coarsen grains/Cu[Pd] solid solution. Some new phases, such as Pd2Si, PdTiSi, Ti5Si3 and TiN, were formed in the Cu[Pd] solid solution interlayer. With increasing brazing temperature from 1100 °C to 1200 °C, the thickness of the TiN reaction layer is not changed. Meanwhile, the amount and size of the TiN and Pd2Si phases in the Cu[Pd] solid solution increase, while, the amount of the PdTiSi phase decreases. 相似文献
8.
In this article, three kinds of surface‐modified methods were used to treat β‐Si3N4 whiskers before being incorporated into Bis‐GMA/TEGDMA dental resin matrix in order to improve the whiskers' reinforcing effect. The experimental results showed that composites with directly heat‐treated and then silanized β‐Si3N4 whiskers had the best reinforcing effect. They had flexural strength of 160 ± 7.0 MPa (mean ± SD; n = 6), compressive strength of 371 ± 1.4 MPa (mean ± SD; n = 5) and HRA of 48.4 ± 0.5(mean ± SD; n = 5), respectively. In addition, water sorption and solubility test demonstrated that the composites were reliable to use as the dental restoration materials. Therefore, the directly heat‐treated and then silanized β‐Si3N4 whiskers (better than β‐Si3N4 whiskers mixed with SiO2 nanoparticles or SiO2 sols) were most suitable fillers to reinforce dental resin composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
9.
Jimei Xue Xiaowei Yin Fang Ye Litong Zhang Laifei Cheng 《Journal of the American Ceramic Society》2013,96(3):979-986
A thermodynamic calculation on the chemical vapor deposition of the SiCl4–NH3–CH4–H2–Ar system was performed using the FactSage thermochemical software databases. Predominant condensed phases at equilibrium were SiC, Si3N4, graphite, and Si. The equilibrium conditions for the deposition of condensed phases in this system were determined as a function of the deposition temperature, dilution ratio (δ), and reactant ratios of CH4/SiCl4 and NH3/SiCl4. The CVD phase diagrams were used to understand the reactions occurring during the formation of Si–C–N from the gas species and determine the area of SiC–Si3N4. The concentration of condensed‐phase products was used to determine the deposition conditions of CVD SiC–Si3N4. The present work was helpful for further experimental investigation on CVD Si–C–N. 相似文献
10.
Ru Xia Yuchuan Zhang Qingren Zhu Jiasheng Qian Qiannian Dong Fangshan Li 《应用聚合物科学杂志》2008,107(1):562-570
In this work, a macromolecular coupling agent (BA‐MAA‐AN tercopolymer) was used for surface modification of native nano‐sized silicon nitride (Si3N4) powder. This modification strategy was designed for preparing nano‐Si3N4/NBR composites. The structure and surface properties of modified nano‐Si3N4 were systematically investigated by FTIR, XPS, TGA, TEM, Size Distributions Analyzer, and Contact Angle Measurement. It was found that, the optimum loading of BA‐MAA‐AN tercopolymer coated on the surface of nano‐sized Si3N4 is 10% of nano‐Si3N4. According to the spectra of FTIR, XPS and TGA, it can be inferred that this macromolecular coupling agent covalently bonds on the surface of nano‐sized Si3N4 particles and an organic coating layer is formed. The contact angle experiments show that the hydrophobic property of nano‐sized Si3N4 modified with macromolecular coupling agent is improved obviously. TEM reveals that modified nano‐Si3N4 possesses good dispersibility and the average diameter in NBR is less than 100 nm. It has also been found that the oil resistance of NBR based nanocomposites is improved greatly due to the modified nano‐Si3N4. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
11.
Xinmei Hou Ziyou Yu Zhiyuan Chen Kuo‐Chih Chou Baojun Zhao 《Journal of the American Ceramic Society》2013,96(6):1877-1882
The reaction behavior of α‐Boron nitride (BN) powder in wet air was investigated at 1273 K using thermogravimetric (TG) analysis, X‐ray diffraction (XRD), and mass spectrometry. Scanning electron microscopy and electron probe X‐ray microanalysis (EPMA) were used to analyze the morphological and elemental development of the sample. The results show that the reaction process consists of two stages: the oxidation of BN powder to form B2O3 and the further reaction of B2O3 with H2O. In the first stage, the oxidation reaction occurs very quickly and can be described by Chou's model. In the second stage, the reaction rate followed the linear rate law. 相似文献
12.
Crystal Growth in the Combustion Synthesis of α‐Si3N4 Using Si with Different Particle Sizes
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Yiyao Ge Qi Wang Wei Cui Yifeng Zou Zhipeng Xie Kexin Chen 《Journal of the American Ceramic Society》2015,98(10):3398-3403
In this present work, Si3N4 powders with high α‐phase contents and distinct crystal morphologies were prepared via a promising approach of combustion synthesis (CS), using Si powders with different particle sizes as reactants. The influence of Si particle size on phase composition and crystal morphologies in the products was systematically investigated. Two unique crystal morphologies, radial‐spheroidal‐cluster and flowerlike, were observed in the Si3N4 products. The crystal growth mechanisms of Si3N4 granules in the CS system with disparate Si have been proposed based on experiments and thermokinetic calculations. As conclusion, the α‐phase content in the final product was synergetically dominated by the vaporization process of Si particles and the α–β phase transformation of Si3N4 during the after‐burn period. Si3N4 powders with high α‐phase content can be obtained from Si powders with an appropriate particle size. 相似文献
13.
Synthesis of well‐dispersed β‐Si3N4 with equiaxed structures using carbothermal reduction–nitridation method
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Si‐Yuan Sun Yi‐Yao Ge Zhao‐Bo Tian Jie Zhang Ke‐Xin Chen Zhi‐peng Xie 《Journal of the American Ceramic Society》2017,100(12):5363-5366
Well‐dispersed β‐Si3N4 powders with a novel equiaxed structure and eminent crystal integrity were prepared by carbothermal reduction–nitridation (CRN) strategy with the assistance of CaF2 additive. The growth mechanism of Si3N4 particles in the CRN process was elucidated. It is proposed that the liquid phase formed by SiO2 and CaF2 additive is crucial to the formation of equiaxed β‐Si3N4, and with an appropriate content of CaF2, Si3N4 powders with pure β phase, superior dispersity and crystal integrity can be obtained. 相似文献
14.
The Si3N4 ceramic was joined to 42CrMo steel using Ag–Cu–Ti + Mo composite filler. Effect of Mo particles content on the microstructure and mechanical properties of the joints were investigated. Defect-free joints were received when the Si3N4/42CrMo steel joints were brazed with Ag–Cu–Ti + Mo composite filler. The results show that a continuous reaction layer which is composed of TiN and Ti5Si3 was formed near the Si3N4 ceramic. A double reaction layer which consists of Fe2Ti and FeTi was also formed adjacent to 42CrMo steel, with Fe2Ti being located near the steel. The central part of the joint is composed of Ag based solid solution, Cu based solid solution, Mo particles and some Cu–Ti intermetallic compounds. The maximal bending strength reached 587.3 MPa with 10 vol.% Mo particles in the joint, at which the joint strength was 414.3% higher than the average strength for the case without Mo particles addition. 相似文献
15.
Effect of Fe‐Contained Species on the Preparation of α‐Si3N4 Fibers in Combustion Synthesis
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Yiyao Ge Siyuan Sun Qi Wang Wei Cui Yifeng Zou Zhipeng Xie Kexin Chen 《Journal of the American Ceramic Society》2016,99(4):1464-1471
Herein, Si3N4 powders of comparatively high α‐phase but with distinct morphologies, especially α‐Si3N4 fibers, were successfully prepared by a developed combustion synthesis (CS) strategy. Different proportions of Fe and Fe2O3 were innovatively doped in reactants as additives to control the phase constitution and their relative percentage, as well as morphologies of final microstructures. One step further, the effects of Fe‐contained impurities on the CS process were rationally proposed and verified based on a series of meticulous designed experiments. It turns out that two contradictory effects of metal Fe on the formation of α‐Si3N4 synergistically play vital roles in the CS reaction. The existence of metal Fe can accelerate the crystallization of the amorphous SiO2, which act as protection layer outside the Si powders and subsequently promote the generation of gaseous SiO. These gaseous SiO easily reacts with N2 and eventually form α‐Si3N4. On the other hand, the formation of β‐Si3N4 will be promoted by the assistance of some liquid phases, and in this case, they mainly come from the reaction between Fe and Si. For this study, when the content of doped Fe is below 2 mol%, the prior effect on promoting α‐phase content is pronounced. Otherwise, the latter dominates the CS process as the content of Fe additive is further increased above 2 mol%. In a different way, Fe2O3 mainly encourages the formation of β phase through the large amount of newly generated liquid phases, although the reduced SiO2 and Fe may still promote the α/β ratio on some extent. 相似文献
16.
Liangbo Sun Qingjing Wei Jian Fang Chunfeng Liu Jie Zhang 《Ceramics International》2021,47(2):2068-2076
Porous Si3N4 (P–Si3N4) ceramic was successfully joined to Invar alloy using a Cu–Ti active brazing alloy for the first time. The interfacial reactions between the Cu–Ti filler and two dissimilar substrates were studied. The influence of brazing process on the microstructure evolution of the joint was revealed, along with the formation of an infiltration layer that permitted the bonding of P–Si3N4 substrate. Ti reacted with Si3N4 to form TiN and Ti5Si3 compounds, resulting in the decomposition of Si3N4. In addition, the reaction and diffusion dual-layer formed at the Cu–Ti/Invar interface, which was attributed to the interaction of alloy elements between the braze filler and the Invar alloy. Fe–Ti and Ni–Ti intermetallics together with Cu solid solution (s,s) constituted the microstructure of the brazing seam. In addition, the optimal shear strength of the brazed joint was 20 MPa and the fracture propagation occurred in the P–Si3N4 ceramic substrate adjacent to the infiltration layer during the shearing tests. 相似文献
17.
《Ceramics International》2017,43(5):4344-4352
The corrosion behavior of silicon nitride (Si3N4) ceramics with a porosity of 46% at 1200–1500 °C under different conditions including dry O2, O2 containing 20 vol% H2O and Ar containing 20 vol% H2O is compared. The results show that porous Si3N4 ceramics exhibit good oxidation resistance up to 1200 °C. Their corrosion behavior varies depending on the temperature and atmosphere. Water vapor can obviously affect the morphology of the reaction product and thus accelerate the corrosion rate due to its specific inward diffusion mechanism and devitrified effect at high temperature. In view of the reaction kinetics, it proceeds in a diffusion-controlled manner in dry O2 while follows the parabolic-linear law at water-containing atmosphere. Furthermore, a new model considering both oxidation and volatilization reactions is established. These provide a baseline for expanding the application fields of non-oxide porous ceramics such as Si3N4 and silicon carbide (SiC) etc. 相似文献
18.
Wei‐Ming Guo Shang‐Xian Gu Yang You Qiang‐Guo Jiang Shang‐Hua Wu Hua‐Tay Lin 《Journal of the American Ceramic Society》2015,98(12):3651-3654
Densification and thermal stability of hot‐pressed Si3N4–ZrB2 ceramics with and without additives were investigated in N2 atmosphere. The addition of MgO–Yb2O3, MgO–Y2O3, and Al2O3–Yb2O3 resulted in significant increase in relative density of the ceramics hot‐pressed at 1500°C from 48.5% to 98.0%, 97.3%, and 95.6%, respectively. There was weak reaction of ZrB2 with N2 to form ZrN in hot‐pressed ceramics. Then heat treatment at 1550°C resulted in the further reactions to produce ZrN, ZrSi2, and BN. The Si3N4–ZrB2 ceramics with MgO–Yb2O3 showed much better thermal stability as compared to the ceramics with Al2O3–Yb2O3. The small difference in density led to the obvious difference in thermal stability. Therefore, Si3N4–ZrB2 ceramics should be densified to full density, to obtain high thermal stability. 相似文献
19.
Martin Studer Hans‐Ulrich Blaser Stephan Burkhardt 《Advanced Synthesis \u0026amp; Catalysis》2002,344(5):511-515
The first successful example of the asymmetric hydrogenation of substituted α‐keto ethers with Cinchona‐modified Pt/Al2O3 is reported. In the absence of an additional base, kinetic resolution of the racemic starting material was observed with high diastereoselectivity and ee's up to 98% at conversions of <50%. Addition of KOH gave a strong reaction acceleration but racemic product. Immobilization of OH – on solid ion exchangers resulted in the desired dynamic kinetic resolution, and ee's of >80% were obtained at >95% conversion. These effects are rationalized on the basis of a simple kinetic and structural model. 相似文献
20.
Siqi Ma Shuai Fu Qikun Wang Hualong Yang Wanlin Li Peigang He Meirong Wang Delong Cai Xiaoming Duan Dechang Jia Hua-Tay Lin Yu Zhou 《International Journal of Applied Ceramic Technology》2023,20(4):2239-2248
In this paper, a honeycomb Si3N4 ceramic was fabricated by 3D printing with a well-preserved structure. The effects of Si3N4 content on the rheological properties of Si3N4/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si3N4 to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si3N4 ceramics tended to be non-catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si3N4 content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering. 相似文献