Warm compaction behaviors of iron-based powder lubricated by different kinds of graphite

1　INTRODUCTIONConventionalpowdermetallurgy(PM ) process ingcanproduceiron basedPM partswithadensitylessthan 7.1g/cm3(arelativedensityofapproxi mately 90 % ) .Theirmechanicalpropertiesaresub stantiallylessthanthoseoftheirfulldensitycounter part.IncreasingdensityisthebestwaytoincreasetheperformanceofthePM parts .Therearemanyprocessesthatcanproduceiron basedPM partswithhighdensitysuchaspowderforging ,doublepress/doublesinter(DP/DS)andCuinfiltration ,butwarmcompactionisthemosteconomical…     

Joining mechanism of field-assisted diffusion bonding of solid electrolyte ceramic to metals

1　INTRODUCTIONField assisteddiffusionbonding(FDB) ,asaspe cialmethodofsolid statediffusionbonding ,hasbeeninvestigatedwidelyinthefieldofbondingofceramicsandmetals .Appliedinastaticelectricfield ,itcanbeproceededatlowtemperatureandpressureandinshorttime.FDBissuitableforassemblysealingofmetal oxidesimeconductor(MOS) ,suchasminiatureinstruments ,sensorsandsoon .Nowlotsofphysicalcharactersduringbondinghavebeenreported[13] ,andinordertomeettherequirementofmicroelectromechanicalsystems(MEM…     

Effects of electromagnetic stirring on microstructures of solidified aluminum alloys

1　INTRODUCTIONPractically ,mechanicalstirringandelectromag neticstirring (EMS)arewidelyusedtogenerateforcedflowinsolidificationandcastingofmetalsandalloys,resultingin greatchangesofthesolidifiedstructures,segregationsand propertiesofthecast ings .Muchattentionhasbeenpaidtosolidificationofdendriticalloyssuperposedwithforcedflow ,andmanypreviousworkshavebeenfocusedontheeffectsoffluidflowonthestructuraltransitions,suchascolumnar equiaxedtransitions(CET)ormacro segre gationinthealloys[13] .…     

Decomposition of supersaturated sodium aluminate solution

1　INTRODUCTIONThecrystallizationofgibbsite(Al(OH) 3)fromsu persaturatedsodiumaluminatesolutionisanimportantpartofcommercialalumina production .However ,longperiodandlargeburdenoftheprocessmakeitbecomebottleneckofalumina production .Thede compositionofsupersaturatedsodiumaluminatesolu tionintogibbsite ,whichinvolvesinthetransforma tionoftetrahydroxy ,Al(Ⅲ ) containingspeciesinso lutionintooctahedralcoordinateAl(OH) 3inthepres enceofNa+andOH- ions ,areasyetunknown .Specially ,intensi…     

Microstructure and strength of brazed joints of TiB2 cermet to TiAl-based alloys

In this study, TiB2 cermet and TiAl-based alloy are vacuum brazed successfully by using Ag-Cu-Ti filler metal.The microstructural analyses indicate that two reaction products, Ti ( Cu, Al ) 2 and Ag bused solid solution ( Ag ( s. s ) ) , are present in the brazing seam, and the iuterface structure of the brazed joint is TiB2/TiB2 Ag ( s. s ) /Ag ( s. s ) Ti ( Cu,Al)2/Ti( Cu, Al)2/TiAl. The experimental results show that the shear strength of the brazed TiB2/TiAl joints decreases us thebrazing time increases at a definite brazing temperature. When the joint is brazed at 1 223 K for 5 min, a joint strength up to 173 MPa is achieved.     

Chemical Thermodynamic Analysis of Silicon Doping in MOCVD of GaAs System

With chemical thermodynamic method,enthalpies,entropies and heat capacities of(SiH_3)_nAsH_(3-n)(1≤n≤3),(CH_3)_mSiH_(4-m)(1≤m≤4)and their radicals were calculated.Homogeneous reactions equilibrium of 65gas phase species in SiH_4(or Si_2H_6)doped MOCVD GaAs by TMG and AsH_3 system was analyzed,the re-lations of gas phase partial pressures with growth temperatures and input partial pressures were calculated.When the gas phase is saturated with a GaAs:Si solid,the gas phase partial pressures and solid phase siliconimpurity(Si_(Ga)-As,Ga-Si_(As),Si_(Ga)-Si_(As))concentrations were calculated under different growth temperatures andinput partial pressures.With the above results,some of the Si doping behavior in MOCVD of GaAs are ex-plained.     

Measurement of surface crystallinity of PAA and PAANa coatings and its effect on hydrophilicity of coatings

1　INTRODUCTIONAsanimportantwater solublemacromoleculecompound,poly (acrylicacid) (PAA)anditssaltshavebeenwidelyused[1] .Utilizingitsfinefilm form ingcapacityandhydrophilicity ,Okoroaforetal[2 ] ,andPanetal[3] developedanewhydrophilicpaintforaluminiumfin[2 ,3] .Hydrophilic paintforheat ex changerofairconditioningdemandslittlesurfacecon tactangle ,sothatcontinuoushomogeneouswaterfilmcanformeasily ,andcandrainoffcondensedwa teronthesurfaceoffintimely[4 6 ] .Hydrophilicityofcoatingsisaffec…     

Effect of Addition of Polytetrafluoroethylene （PTFE） and Silicon Carbide （SIC） on Properties of Electroless Nickel AHoy Coatings

Electroless nickel (copper)-phosphorus-silicon carbide (SiC)-polytetrafluorocthylene(PTFE) composite coatigs were prepared by adding SiC and PTFE into electroless nickel(copper)-phosphorus alloy baths.The effects of addition of SiC and PTFE on depositing rate.microhardness.wear resistance and anti-fiction of the resulted composite coatings were studied.The results indicated that electroless nickel(copper).phosphorus alloy coatings were grealty improved in depositing rate,microhardness,wear resistance and antifriction by co-deposited proper amount of SiC and PTFE.     

Effect of borate coating on corrosion resistance of pure nickel in molten LiCl-Li2O

1　INTRODUCTIONAttheendofthetwentiethcentury ,alithiumreductiontechniquewasdevelopedtodisposeofnucle arfuel(UO2 )used[1] .Inthis process ,theoxide(UO2 )isreducedtothemetallicform(U)byreactionwithlithiumdissolvedinmoltenLiClat 75 0℃ .Thetechniquecaneffectivelyreducethevolumeandradia tionofspentnuclearfuel,whichisconvenienttostoreandmanage .Unfortunately ,thecontainmentmaterialsusedinthetechniqueundertakeseverecor rosionowingtothestrongbasicoxideLi2 OformedanddissolvedinmoltenLiCl.Sev…     

Prices of Castings, Foundry Raw and Auxiliary Materials in Some Regions of China

(Time range: Nov. 2004-Mar. 2005)Prices of foundry materials for investment casting in Shenyang region in 2003-2004Name Price (RMB yuan /t) Range of price rise (%)UreaZircon flourGangue flour (sand)Fuel oilFerrochromiumStainless steel scrapCoalNickel plateAluminum ingotFerromolybdenum*The information is provided by Shoushan SUN, Shenyang Sidanli Co. Ltd.Prices of foundry materials and castings of Beipiao city, Liaoning in the end of Dec. 2004Name Price (RMB yuan /t) Name Price (…     

Preparation of highly dispersed antimony-doped tin oxide nanopowders by azeotropic drying with isoamyl acetate

Antimony-doped tin hydroxide colloid precipitates were prepared by hydrolysis of SnCl4·5H2O and SbCl3 ethanol solutions. Isoamyl acetate was selected as azeotropic drying solvent and was compared with the most commonly used n-butanol solvent on treating precipitate for low hard agglomeration precursor powders. The FT-IR, BET, XRD, and TEM results of the precursor powders and calcinated antimony-doped tin oxide powders were recorded. The results demonstrate that isoamyl acetate is an excellent azeotropic drying solvent that can effectively prevent the agglomeration of particles and greatly improve the fluffiness of the obtained dried powders. After these precursor powders are calcined, antimony-doped tin oxide nanopowders with tetragonal futile structure and high dispersivity can be obtained.     

PREPARATION OF NANOMETER ZrO2-8%Y2O3 POWDERS BY AZEOTROPIC DISTILLATION PROCESSING

１ＩＮＴＲＯＤＵＣＴＩＯＮＩｔｉｓｗｅｌｋｎｏｗｎｔｈａｔｓｉｎｔｅｒｉｎｇｔｅｍｐｅｒａｔｕｒｅｗｉｌｂｅｇｒｅａｔｌｙｄｅｃｒｅａｓｅｄｄｕｅｔｏｐｒｅｐａｒａｔｉｏｎｏｆｕｌｔｒａｆｉｎｅａｎｄｈｏｍｏｇｅｎｅｏｕｓｐｏｗｄｅｒｓ．Ａｓａｒｅ...     

微乳法制备氧化锆纳米粉体

以可溶性锆盐溶液—环己烷—聚乙二醇辛基苯醚—正戊醇体系的微乳液反应为基础 ,以氨水为沉淀剂 ,在微乳液中发生化学反应产生凝胶状沉淀 ,经洗涤、焙烧得到超细分散 Zr O2 纳米粒子。本文在微乳液法的基础上加入了一种较新的脱水工艺—共沸蒸馏制备了纳米 Zr O2 粉末。通过比表面积 (BET)、透射电镜 (TEM)、X-射线衍射 (XRD)对样品进行了形态表征和物相分析 ,结果表明通过本方法制备的 Zr O2 纳米粉末尺寸可控制在小于 4 0 nm的范围内 ,并具有良好的分散性。共沸蒸馏能充分地脱去凝胶中残余的水分 ,防止因含水胶体干燥过程引起的粉末硬团聚 ,从而显著地提高了粉末的性能     

纳米γ-Al2O3的溶胶-凝胶法制备及表征

异丙醇铝为先驱体,异丙醇为溶剂,乙酰乙酸乙酯为螯合剂,聚乙二醇(PEG1000)为分散剂,硝酸为胶溶剂,采用溶胶-凝胶法制备了纳米γ-Al2O3.并采用DTA/TG,XRD,TEM等测试技术对纳米γ-Al2O3粉体进行表征.结果表明,通过溶剂、螯合剂、分散剂和胶溶剂的协同效应,在750℃煅烧条件下,γ-Al2O3粒子形貌为针状结构,长度为20～30 nm;在900℃煅烧条件下,γ-Al2O3粒子形貌为颗粒状,平均晶粒尺寸为10 nm左右;纳米γ-Al2O3粒子尺寸均一、分散性良好.     

纳米氧化铝粉体的绿色合成

以廉价的铝锭和异丙醇为起始原料,采用独特的分离提纯、回收再利用技术和溶胶凝胶工艺,合成高性能纳米氧化铝粉体,并利用TEM,XRD和石墨炉原子吸收法等对粉体的相组成、形貌和杂质含量进行分析研究.得出原料对粉体的形貌和组成没有影响,两种不同的Al源均制备出了粒径为10～20nm,球形γ-Al2O3粉体;而原料和蒸馏工艺对纳米氧化铝粉体的纯度有影响,随铝锭纯度的增加,所制备的纳米氧化铝所含的微量杂质含量明显下降.和一次蒸馏相比,二次蒸馏所得产物的主要微量杂质明显下降.利用重熔铝锭为原料,采用二次蒸馏工艺,制得了纯度高达99.99%的纳米氧化铝,且在制备过程中没有废液,废气排出,实现了高纯纳米氧化铝粉体的低成本、环保型生产.     

Hydro/solvo-thermal synthesis of ZnO crystallite with particular morphology

ZnO with controllable morphologies of hexangular pillars, tubes, tablets and tube-structured needles was hydro/ solvo-thermally synthesized by simply changing solvents among H2O, H2O2, alcohol and olefin, using Zn(NO3)2-6H2O and NaOH as the starting materials. The products were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence (PL) measurement. The growth mechanism of differently structured ZnO was discussed. The results reveal that the synthesized ZnO crystals possess a wurtzite structure, the solvent kind has very different influence on the morphology of ZnO, and the hexangular pillars, tablets, short pillars and needles of ZnO are easily obtained in solvent of H2O, C2H5OH+H2O, wet olefin, and H2O2.     

正交设计法优化高分散超细银粉的制备工艺

以AgNO3为银源,抗坏血酸为还原剂,通过液相还原法制备了超细银粉。运用L25(56)的正交试验设计,考察了AgNO3浓度、抗坏血酸浓度、分散剂种类、分散剂用量、溶液pH值及反应温度对超细银粉的分散性及粒度的影响。分析得出制备超细银粉的优化条件:AgNO3浓度为0.15mol.L-1,抗坏血酸浓度为0.40mol.L-1,油酸为分散剂,分散剂用量为8%(相对AgNO3质量),pH值为4,反应温度为50℃。在优化的实验条件下,制备出高分散近球形的超细银粉,其平均粒度为0.89μm。并运用SEM、XRD对其进行了表征。     

Hydridation and oxidation behaviors of tantalum hydride during milling process

The effect of ethanol addition during milling on the milling performances of Ta-hydride powders was investigated for hydride and dehydride processes during Ta recycling process. As the Ta-hydride was milled in a conventional dry atmosphere, Ta₂O was dominantly formed due to the increased temperature of the Ta-hydride pieces because they were rubbed against each other and crushed by the ring mill system. However, with the addition of ethanol solvent, the ratio of the Ta₂H phase increased compared to the Ta₂O phase, and the size of the powders reduced and became more uniform. These were attributed to the enhanced hydride formation and reduced contact between the Ta-hydride powders and air by wetting them. Therefore, an optimum amount of ethanol addition and milling time can enhance the formation of additional Ta-hydrides, while preventing oxidation during milling.     

Effect of processing parameters on the microstructure and thermal conductivity of diamond/Ag composites fabricated by spark plasma sintering

Diamond/metal composites with 50 vol.% diamond have been produced by spark plasma sintering (SPS) using pure Ag as a matrix and diamond particles as reinforcement. Three kinds of powder mixing processes were used to prepare the mixture of diamond/Ag powders: dry mixing without milling medium, wet mixing and magnetic blending. Subsequently, they were all consolidated by SPS at various processing parameters to produce bulk diamond/Ag composites. Then samples were heat treated in order to obtain a higher thermal conductivity. The effect of processing parameters on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated by comparing the experimental data. It reveals that particles were easy to agglomerate and the distribution of mixed powders was inhomogeneous by dry mixing method, and wet mixing method is too complex. The most favorable mixing process is magnetic blending by which the powders can be homogenously mixed and the composites prepared by optimized SPS processing parameters can obtain the highest relative density and the best thermal conductivity among the composites prepared by different processes. The magnetic blending diamond/Ag composites even have a 23% increase in thermal conductivity compared with pure silver sintered by SPS.     

CNTs/SiC/Cu复合材料制备及性能

以碳纳米管(CNTs)、碳化硅(SiC)粉体、锌(Zn)粉和CuSO_4·5H_2O为主要原料,用化学镀的方法制备CNTs /Cu复合粉体,再采用非均相沉淀法制备CNTs/SiC/Cu复合粉体.在750 ℃、100 MPa的制度下进行真空热压烧结后制得CNTs/SiC/Cu复合材料,其中Cu的含量(体积分数,下同)为70%,CNTs的含量(体积分数, 下同)分别为0,3%,5%,8%,12%.利用XRD、SEM分析样品的物相组成和显微结构;利用阿基米德排水法、显微硬度计、三点弯曲法测试了复合材料的密度、显微硬度和抗弯强度.结果表明,随着碳纳米管含量的增加,CNTs/SiC/Cu复合材料的密度、显微硬度和抗弯强度等性能发生相应变化,其中,抗弯强度呈现逐渐升高趋势.与未添加碳纳米管的30SiC/70Cu复合材料相比,添加12%CNTs的12CNTs/18SiC/70Cu 样品,抗弯强度提高了21.45 MPa.