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1.
Preparation and Properties of Sintering Additives Coated Si3N4 from Heterogeneous Nucleation Processing 总被引:1,自引:0,他引:1
The sintering additives such as Al2O3 and /or Y2O3 were coated on the surfaces of Si3N4 particles via heterogeneous nucleation processing using a buffered pH solution as the precipitation reagent .They nucleated and grew only on the surfaces of Si3N4 and did not form sol particles in solution by TEM observation .The isoelectric point(IEP) of coated Si3N4 was different from that of as-received Si3N4.The IEP of Al(OH)3-coated Si3N4 occurred at pH8.4, which is close to that of alumina .When Al(OH)3-coated Si3N4 particles were coated with Y(OH)3,the IEP of coated Si3N4 powder shifted from pH8.4 to pH9.2 ,similar to that of yttria.In addition ,the rheological data showed that Al2O3 and /or Y2O3 coated Si3N4 suspension is nearly Newtonian and that added Si3N4 suspension shows a shear rate thinning behavior. 相似文献
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In this work, an efficient process by diluting the nano-SiCp/Al composite granules in the molten matrix under ultrasonic vibration(UV) was developed to prepare metal matrix nano-composites(MMNCs).Millimeter-sized composite granules with high content of SiC particle(8 wt%) were specially fabricated by dry high-energy ball milling(HBM) without process control agent, and then remelted and diluted in molten Al alloy under UV. The MMNCs melt was finally squeeze cast under a squeeze pressure of 200 MPa, Microstructure of the composite granules during dry HBM was investigated, and the effect of UV on microstructure and mechanical properties of the MMNCs was discussed. The results indicate that nano-SiC particles are uniformly distributed in the nano-SiCp/Al composite granules, which are covered by vestures of pure Al. During diluting, nano-SiC particles released from the composite granules are quickly dispersed in the molten matrix by UV within 4 min. Microstructure of MMNCs is significantly refined under UV and squeeze casting, eutectic Si phase modified to fine islands with an average length of 1.4 μm. Tensile strength of the squeeze cast MMNCs with 1 wt% of nano-SiC particles is 269 MPa, which is improved by 25% compared with the A356 alloy matrix. 相似文献
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Al2O3/Al2O3 joints were brazed with a new kind of filler materials,which were formed by adding Al2O3 particulates into Ag-Cu-Ti active filler metal.The results showed that the material parameters (the Ti content,Al2O3 particulate volume fraction) of the composite filler materials affected the shear strength of brazed joints.When the Ti content was 2 wt pct in the filler metal, the shear strength of brazing joints decreased with the increasing the volume ratio of Al2O3 particulate .When the Ti content was 3 wt pct in the filler metal, the shear strength of joints increased from 93.75 MPa(Al2O3 pOvol pct) to 135.32 MPa(Al2O3 p15 vol.pct). 相似文献
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《材料科学技术学报》2012,(3):234-240
A method of preparing continuous(Al+Al2O3)-coated SiC fiber reinforced nickel matrix composite was presented,in which the diffusion between SiC fiber and nickel matrix could be prevented.Magnetron sputtering is used to deposit Ni coating on the surface of the(Al+Al2O3)-coated SiC fiber in preparation of the precursor wires.It is shown that the deposited Ni coating combines well with the(Al+Al2O3) coating and has little negative effect on the tensile strength of(Al+Al2O3)-coated SiC fiber.Solid-state diffusion bonding process is employed to prepare the(Al+Al2O3)-coated SiC fiber reinforced nickel matrix with 37% fibers in volume.The solid-state diffusion bonding process is optimized and the optimum parameters are temperature of 870,pressure of 50 MPa and holding time of 2 h.Under this condition,the precursor wires can diffuse well,composite of full density can be formed and the(Al+Al2O3) coating is effective to restrict the reaction between SiC fiber and nickel matrix. 相似文献
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The synthesis of TiN and Al2O3 by in situ injection of reactive nitrogen gas into molten Al alloys has been evaluated over the temperature range from 1000 to 1600℃. It is shown that TiN and Al2O3 can be formed in melt with nitrogen and surplus oxygen (in vacuum room of the induction furnace) as the reactive gases over 1000℃. Up to 2.1 wt pct Al2O3 and 5.2 wt pct of TiN in situ phases in an Al alloy has been formed in a range of size from 0.8 to 5 μm. The formation mechanism of TiN and Al2O3 is discussed in this paper. 相似文献
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Ankur Gupta ;Swetha Barkam ;Debrupa Lahiri ;R.Balasubramaniam ;Kantesh Balani 《材料科学技术学报》2014,30(8):808-813
Nickel-gamma alumina(Ni—γAI2O3) composite coatings were synthesized by pulsed electrodeposition technique with different concentrations of alumina(0,10,20 and 50 g/L) in Watt’s bath.Both ultrasonic vibration and magnetic-stirring were utilized to disperse Al2O3 and to achieve its optimum loading.Microstructure shows that agglomerates occur at higher loadings,but 10 g/L Al2O3 addition in bath has shown uniform dispersion of alumina with improved mechanical properties such as hardness,Young’s modulus and yield strength by 40%,46%and 35%,respectively,when compared to that of pure Ni coating.Further,elasto-plastic indentation mechanics has shown that strength at 29%strain is enhanced to 110.5 GPa for 10 g/L Al2O3electrophoretically deposited Ni—yAI2O3 coating when compared to that of electrodeposited Ni(81.8 GPa). 相似文献
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Multi-walled carbon nanotubes (MWNTs) were coated with nanometer sized SiC layer by magnetron sputtering, and their corrosion resistances in oxygen and gaseous silicon were studied, respectively. X-ray diffraction (XRD) reveals that the as-coated MWNTs are comprised of the amorphous SiC and the phase could transfer from amorphous to polycrystalline SiC by annealing at 1360 °C. Scanning electron microscopy (SEM) observation indicates that SiC nanoparticles are uniformly coated on the MWNTs, forming a continuous SiC coating. Thermogravimetric analysis (TGA) confirms that the onset temperature of oxidation increases from 540 to 700 ~C with the SiC coating. The morphologies of non-coated and SiC-coated MWNTs after corrosion by oxygen and gaseous silicon were also characterized by SEM. The results revealed that SiC coating could protect MWNTs from the corrosion with qaseous silicon effectivelv. 相似文献
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In situ Al2O3 decomposed from Al2(SO4)3 reinforced aluminum matrix composites was fabricated through stirring cast by adding Al2(SO4)3 to the molten alloy which is the raw and processed materials from which industrial high purity Al2O3 is made. Not only production cost may be reduced but also SO3 decomposed from Al2(SO4)3 may refine and remove the gas from the molten composites by the way stated before. As a result, Al2O3 and matrix bonded well, no cast defects being found, such as gas hole, porosity and particles segregation in in situ Al2O3 decomposed from Al2(SO4)3 reinforced aluminum matrix composites It is considered the key fact of particulate reinforced aluminum matrix composites really being produced in industrial that SO3 decomposed from Al2(SO4)3 may refine and remove the gas from the molten composites. 相似文献
9.
JianguoYANG JingweiWU HongyuanFANG 《材料科学技术学报》2003,19(5):509-510
In order to understand the rate-controlling process for the interracial layer growth of brazing joints brazed with active composite filler materials, the thickness of brazing joints brazed with conventional active filler metal and active composite filler materials with different volume fraction of AI203 particulate was studied. The experimental results indicate although there are Al2O3 particulates added into active filler metals, the time dependence of interracial layer growth is t^2 as described by Fickian law for the joints brazed with conventional active filler metal. It also shows that the key factor affecting the interracial layer growth is the volume fraction of alumina in the composite filler material compared with the titanium weight fraction in the filler material. 相似文献
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本文通过在纳米SiC颗粒表面包覆一层Al2O3,使包覆型SiC与Al2O3具有相似的表面化学性质,从而包覆型SiC-Al2O3混合粉悬浮液具有相似于单相Al2O3悬浮液的流变性质。研究了分散剂、颗粒匹配及温度对包覆型SiC-Al2O3混合粉悬浮液流变性质的影响。结果表明,对于亚微米粉,尤其纳米粉,高聚物电解质分散剂不能改善其流变性;合适的颗粒匹配及温度可以改善悬浮液的流动性。,The surface chemical property of SiC was similar to that of Al2O3 by coating SiC with Al2O3,so that the rheological behavior of coated SiC-Al2O3 suspension was like to that of single phase Al2O3 suspension.The effect of dispersant,size distribution and temperature on rheological behavior of coated SiC-Al2O3 suspension were studied.Results indicated that polyelectrolyte did not improve rheological behavior for fine powder suspension,especially for nanosized powder suspension,but proper size distribution and temperature could. 相似文献
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Aluminum oxide (Al2O3) matrix have been reinforced by the multi-walled carbon nanotubes (MWCNTs) to overcome the inherent brittleness of Al2O3 matrix. In order to increase mechanical properties of MWCNTs-Al2O3 composites, MWCNTs need to be well dispersed and individually incorporated in Al2O3 matrix. In this work, aluminum hydroxide (Al(OH)3) used as a Al2O3 precursor and MWCNTs were mixed in an aqueous solution for the homogeneous mixing of hetero-particles, as functions of the content of MWCNTs and the potential hydrogen (pH) of Al(OH)3 suspension. Firstly, MWCNTs were purified and modified by an acid reagent, inducing that the dispersibility of MWCNTs is increased in an aqueous solution by carboxylic group given on the surface of MWCNTs. The modified MWCNTs were added in the Al(OH)3 suspension, and then the mixture was filtered at room temperature. The filtered powders were formed using an uniaxial pressing and then densified by a pressureless heat treatment. As the pH is decreased the Al(OH)3 particles are well dispersed in an aqueous solution, due to the increment of repulsive force between particles with a same surface charge. MWCNTs are individually incorporated into Al2O3 matrix up to 1 vol.% MWCNTs, whereas MWCNTs are aggregated at the composite with 3 vol.% MWCNTs. Therefore, control of the pH and the MWCNTs content are key factors to be considered for the fabrication of MWCNTs-Al2O3 composites with high functional properties. 相似文献
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Nanoscale ISFET (ion sensitive field-effect transistor) pH sensors are presented that produce the well-known sub-nernstian pH-response for silicon dioxide (SiO(2)) surfaces and near ideal nernstian sensitivity for alumina (Al(2)O(3)) surfaces. Titration experiments of SiO(2) surfaces resulted in a varying pH sensitivity ~20 mV/pH for pH near 2 and >45 mV/pH for pH > 5. Measured pH responses from titrations of thin (15 nm) atomic layer deposited (ALD) alumina (Al(2)O(3)) surfaces on the nanoISFETs resulted in near ideal nernstian pH sensitivity of 57.8 ± 1.2 mV/pH (pH range: 2-10; T = 22 °C) and temperature sensitivity of 0.19 mV/pH °C (22 °C ≤ T ≤ 40 °C). A comprehensive analytical model of the nanoISFET sensor, which is based on the combined Gouy-Chapman-Stern and Site-Binding (GCS-SB) model, accompanies the experimental results and an extracted ΔpK ≈ 1.5 from the measured responses further supports the near ideal nernstian pH sensitivity. 相似文献
15.
SANDEEP KUMAR VIKRAM JAYARAM T. V MANI K. G. K WARRIER 《Journal of Materials Science》1997,32(17):4719-4722
Composites of Al2O3–SiC–Al have been prepared by the oxidative infiltration of Si-free aluminium alloys into SiC particulate that were coated
with spray-pyrolysed alumina. Moisture degradation studies were carried out to evaluate the extent of formation of aluminium
carbide, the formation of which was also inferred by the determination of the residual silicon content in the composite. The
efficiency of the coating technique in protecting the SiC from attack by the melt was evaluated at 1000 and 1200 °C.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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Jianguo YANG Hongyuan FANG Xin WANNational Key Laboratory of Advanced Welding Production Technology Harbin Institute of Technology Harbin China 《材料科学技术学报》2002,18(4)
Al2O3l2O3 joints were brazed with a new kind of filler materials, which were formed by adding AI203 particulates into Ag-Cu-Ti active filler metal. The results showed that the material parameters (the Ti content, Al2O3 particulate volume fraction) of the composite filler materials affected the shear strength of brazed joints. When the Ti content was 2 wt pct in the filler metal, the shear strength of brazing joints decreased with the increasing the volume ratio of Al2O3 particulate. When the Ti content was 3 wt pct in the filler metal, the shear strength of joints increased from 93.75 MPa(AI203p 0 vol. pct) to 135.32 MPa(AI203p 15 vol. pct). 相似文献