SYNTHESIS OF ZnO NANOPARTICLES WITH NARROW SIZE DISTRIBUTION UNDER PULSED MICROWAVE HEATING

ZnO nanoparticles with very narrow size distribution were synthesized by coupling homogeneous precipitation with microemulsion under pulsed microwave heating. The conditions of preparing ZnO nanoparticles were investigated. The products were characterized with DTA, TGA, XRD, TEM and UV-Vis. The synthesized ZnO nanopartices had much stronger ultraviolet absorptivity than normal ZnO powders; the average size of products was sensitive to the variation of the power or duration of microwave irradiation.     

TEMPERATURE SENSITIVITY AND PREDICTION OF THE MECHANICAL BEHAVIORS OF ULTRAFINE GRAINED ALUMINUM UNDER UNIAXIAL COMPRESSION

In the present work, we explore the strain hardening behaviors as well as the effect of temperature on the plastic deformation of ultrafine grained aluminum. The temperature sensitivity is determined and compared with that of coarse grained material. The results indicate that the flow stress of ultrafine grained aluminum displays enhanced sensitivity to temperature. The reduction in activation volume is suggested to be the major reason for the enhanced temperature sensitivity as grain size is refined into the sub-micrometer regime. Finally, a phenomenological constitutive model is proposed to describe the post-yield response of ultrafine grained aluminum.     

SYNTHESIS OF NICKEL NANOPOWDERS IN MICROEMULSION

IntroductionNanometer-scalecrystallitesofvariousmetalsandnonmetalshaveattractedagreatdealofattentionoverthepastdecade.Forsuchcrystallites,thephysicalandchemicalpropertiesareheavilydependentonparticlesizeandshape,and,asaresult,thesematerialshaveawiderangeofapplications(Ai&Kang,2003).Monodispersefinenickelparticlesarerequiredforhightechnologyapplicationsinalkalinerechargeablebatteries,magneticrecordingmediaandchemicalcatalysts,etc.,suchasconductingandmagneticinks,andferrofluids(Glicksman,1984).…     

MoO3-ZnO/镍基复合涂层制备及其摩擦学性能研究

利用等离子喷涂工艺制备了含氧化物(MoO₃-ZnO)的镍基复合涂层,通过UMT-3球盘式高温摩擦试验机评价了复合涂层在室温、400和800 ℃下的摩擦学性能,并采用扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)以及拉曼光谱仪(Raman)等分析手段研究了涂层微观组织、物相组成以及磨损机理. 结果表明:在室温和400 ℃,复合涂层的摩擦系数和磨损率均高于Ni-5%Al金属基底,且随着氧化物含量的增加,润滑和耐磨性能均被削弱,主要表现为磨粒磨损和黏着磨损. 在800 ℃,MoO₃和ZnO的添加可以有效改善复合涂层的摩擦性能,随着其含量的增加,摩擦系数变化不明显,而磨损率逐渐增加. 特别是添加5%MoO₃和5%ZnO的复合涂层在800 ℃摩擦系数低至0.28,磨损率低至4.22×10?5 mm3/(N·m),其良好的高温润滑耐磨性能得益于摩擦表面二元氧化物(NiO、MoO₃和ZnO)和三元氧化物(ZnMoO₄和NiMoO₄)的协同作用.      

等离子喷涂Al2O3/TiO2纳米复合涂层的制备、结构及摩擦学性能

采用喷雾干燥法对溶胶-凝胶法合成的系列A l2O3/TiO2纳米复合粉体进行造粒,使用等离子喷涂技术制备系列A l2O3/TiO2纳米复合涂层.对涂层结构和形貌分析表明所制备的A l2O3/TiO2纳米复合涂层形成了具有熔融区和半熔融区的双区形态的纳米复合结构.使用UMT-2MT试验机研究了复合涂层的摩擦磨损性能,结果表明复合涂层的磨损率随TiO2含量的增加表现出先降低而后增大的趋势,TiO2质量百分数为10%的纳米复合涂层的磨损率最低;而涂层的摩擦系数随TiO2含量的增加变化不大.复合涂层的磨损机制为裂纹扩展导致的磨损剥落.     

超细二氧化硅粉体对淀粉火焰抑制的实验研究

为了探究不同粒径二氧化硅粉体抑制效果上的差异,采用小尺寸竖直燃烧管道系统,研究添加10 μm和30 nm二氧化硅粉体时,不同粒径小麦淀粉燃烧的火焰传播、温度、速度等参数特性的变化。实验结果表明:超细二氧化硅粉体能减弱小麦淀粉燃烧反应强度;30 nm二氧化硅粉体抑制效果优于10 μm二氧化硅,当小麦淀粉粒径小于25 μm时,质量浓度为0.43 kg/m3、粒径30 nm的超细二氧化硅粉体可使小麦淀粉火焰亮度明显下降,最高温度下降38.07%,最大速度和平均速度分别下降42.25%、65.59%;超细二氧化硅粉体主要起物理抑制作用,抑制效果与小麦粒径成反比关系,小麦粒径越小,二氧化硅抑制效果越好。     

Direct reduction of hematite powders in a fluidized bed reactor

Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar–50%H₂ atmosphere at 450–550 °C in a fluidized bed reactor. The ultrafine hematite powder shows the typical agglomerating fluidization behavior with large agglomerates fluidized at the bottom of the bed and small agglomerates fluidized at the upper part of the bed. It was found that defluidization occurred even at the low temperature of 450 °C with low metallization rate. Defluidization was attributed mainly to the sintering of the newly formed iron particles. Granuation was employed to improve the fluidization quality and to tackle the defluidization problem, where granules fluidized like a Geldart's group A powder. Granulation was found to effectively reduce defluidization during reduction, without however sacrificing reduction speed. The as-reduced iron powders from both the ultrafine and the granulated hematite exhibited excellent sintering activity, that is, fast sintering at temperature of as low as ～580 °C, which is much superior as compared to that of nano/ultrafine iron powders made by other processes.     

微纳米晶金属的应变率敏感性及应变硬化行为分析

基于亚微米、纳米晶粒组织塑性变形过程中多种变形机制(位错机制、扩散机制及晶界滑动机制)共存,建立了理论模型,用于定量研究亚微米、纳米晶粒组织的塑性变形行为.以铜为模型材料,计算分析了晶粒尺度、应变率以及温度对亚微米、纳米晶粒组织塑性变形行为的影响.结果表明:相比粗晶铜,亚微米晶铜表现出明显的应变率敏感性,并且应变率敏感系数随晶粒尺度及变形速率的减小而增大;同时,增大变形速率或降低变形温度都能提高材料的应变硬化能力,延缓颈缩发生,进而提高材料的延性.计算分析结果与实验报道吻合.     

碳化钨几何形状对碳化钨增强镍基合金火焰喷涂涂层的摩擦性能影响

采用火焰喷涂/重熔(Flame spray/fusion)技术,制备碳化钨(20wt%)增强镍基合金涂层,其中碳化钨采用不同几何形状,探讨碳化钨几何形状对涂层显微组织、组成相、微硬度以及摩擦磨损性能的影响.结果显示,碳化钨几何形状的确是影响各项性能的重大因素,就抗磨损性能而言,大直径的圆形碳化钨增强效果最佳,而小直径的圆形碳化钨增强效果最差.     

多巴胺改性UHMWPE粉末对环氧涂层韧性及摩擦性能的影响

利用多巴胺氧化自聚合性质改性超高分子量聚乙烯(UHMWPE)粉末惰性表面,制备得到改性粉末,并添加于环氧树脂中制备成耐磨环氧涂层,同时与添加未改性UHMWPE粉末的环氧涂层对比.采用扫描电镜(SEM)、X射线光电子能谱(XPS)和红外光谱(IR)表征改性粉末表面形貌和化学元素状态,利用摩擦磨损试验机测试环氧涂层表面的摩擦系数和磨损率.结果表明:改性粉末表面黏附1层含极性基团的聚多巴胺,能够与环氧树脂发生反应而固化在涂层中,相容性增强.改性粉末表面O,C元素相对含量比较O/C和N/C值随改性时间延长而增大,在5 h时趋于稳定.当改性粉末添加量从6.7%增至20%时,环氧涂层的抗冲击性能增强,摩擦系数和磨损率随之降低,改善了涂层的摩擦学性能,而且效果优于添加未改性粉末的涂层.     

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALUMINA COATINGS PLASMA-SPRAYED AT DIFFERENT SUBSTRATE TEMPERATURES

Alumina coatings are prepared by atmospheric plasma spraying through controlling the substrate temperature during spraying. The changes in microstructure and mechanical properties of the coatings prepared at different substrate temperatures are examined. The hardness and the elastic modulus of the coatings are measured by indentation methods. The results show that interlamellar bonding in the coatings is significantly improved with increasing the substrate temperature. Moreover, long through-thickness colum...     

MICROSTRUCTURE AND CHARACTERISTICS OF MECHANICALLY ACTIVATED W-Cu POWDER

Introduction Tungsten-copper alloy powders are used in many fields on account of the high electric and thermal conductivities of copper and high melting point of tungsten. W-Cu pow-ders, as prepared conventionally by means of infiltration, has the disadvantage of inhomogeneity in microstructure, and are difficult to work with after sintering. Increasing the particle activity of these powders tends to accelerate the sintering process, lower the sintering temperature and improve their properties…     

HVOF制备的多峰WC-12Co涂层摩擦磨损特性

本文采用超音速火焰喷涂(HVOF)工艺制备了2种多峰结构和1种亚微米结构WC-12Co涂层,并采用SEM、XRD等方法对3种涂层进行了显微组织、孔隙率、相结构及显微硬度分析;在进行涂层球盘摩擦磨损试验的基础上,探讨了多峰WC-12Co涂层的磨损机理.研究结果表明:由含30% 纳米WC-12Co的粉末制备的多峰涂层WC氧化脱碳程度最低,显微硬度最高;采用含50%纳米WC-12Co的粉末制备的多峰涂层孔隙率最低、耐磨损性能最为优良.     

含WC陶瓷相电弧喷涂层耐磨粒磨损性能的研究

采用电弧喷涂含WC-CoNi金属陶瓷粉末的粉芯丝材,在低碳钢基体上制备铁基复合涂层,采用MLS-225型湿砂橡胶轮磨损试验机评价铁基复合涂层的耐磨粒磨损性能,利用光学显微镜、扫描电子显微镜和X射线衍射仪对涂层的显微组织结构、磨损表面及其相组成进行分析.结果表明:含WC陶瓷相涂层的耐磨粒磨损性能较好,相对Q235钢提高约9倍;当粉芯中WC质量分数低于25%时,随着WC含量增加,涂层的硬度和耐磨性增加;当粉芯中WC质量分数超过25%后,涂层的耐磨性有所下降;电弧喷涂含WC陶瓷相涂层的磨损机制主要为硬质相的脆性剥离和轻微的塑性切削,在磨粒磨损条件下硬度较低的金属基体先磨损,硬度较高的WC和Fe3B硬质相起到阻止石英砂磨损的作用,从而降低了涂层的磨损.     

DISPERSION AND NUCLEATION FOR ULTRAFINE PARTICLES OF SILICA AND SILICATE IN POLY（ETHYLENE TEREPHTHALATE） BASED COMPOSITES

In this paper,the dispersion and nucleation behavior of ultrafine particles of silica and layered silicate (LS) in poly(ethylene terephthalate) (PET) matrix are investigated and characterized by Transmission Electron Microscopy (TEM),Wide Angle X-ray Diffraction (WAXD),Dynamic Scanning Calorimetry (DSC),and Atomic Force Microscopy (AFM).The solid precursors based on silica and LS are suggested originally for preparing nanocomposites with good dispersion morphology.Results show that the initial sub-micron (1000-500nm) LS particles are exfoliated or dispersed into nanometer-scale particles (30-70nm) during their polymerization with PET monomers.These dispersed nanoparticles form an ordered morphology in their nucleation and growth during annealing nanocomposites.DSC patterns reveal that the double melting peaks of annealed PET-LS nanocomposites disappear,while they have shrunken in PET-silica ones.These findings strongly demonstrate that the dispersed nanoparticles accelerate the crystallization of PET.The dispersed LS particles have higher percolation and nucleation performance than those of silica.The homogeneous distribution morphology of ultrafine particles is easily obtained by controlling the load of their corresponding precursors.Such a dispersion obviously improves PET properties in that its heat distortion temperature (HDT)increases from 76℃ to 103℃, and crystallization increases 2-4 times more than that of PET.Especially,the nanocomposite films keep themselves transparent when particle load is within 2 wt.% though there are 3 wt.% or so of agglomerated particles in the nanocomposites.     

蛇纹石热处理产物作为润滑油添加剂的摩擦学性能

考察了表面修饰蛇纹石超细粉体及其热处理产物作为液体石蜡添加剂的摩擦学性能,研究了热处理温度对蛇纹石添加剂抗磨、减摩性能的影响,通过测量摩擦表面接触电阻,监测了摩擦化学反应膜的动态形成过程,利用扫描电镜、能谱仪等分析了摩擦表面形貌及元素分布.结果表明:蛇纹石粉体在摩擦表面释放氧原子,形成氧化物颗粒增强氧化膜,显著降低摩擦,改善液体石蜡的润滑性能.300~600 ℃的热处理在提高粉体活性的同时,保持蛇纹石的层状结构,增强其解理释氧和对摩擦表面的吸附能力,从而促进摩擦化学反应膜的形成,进一步改善蛇纹石的摩擦学性能.当热处理温度高于850 ℃后,蛇纹石粉体的层状结构被破坏,形成大量镁橄榄石和顽火辉石硬质相,加重磨损.     

SURFACE METALLIZATION OF CENOSPHERES AND PRECIPITATORS BY ELECTROLESS PLATING

This paper reports the use of a colloidal Pd^0 catalysis system to metallize the surface of precipitators separated from coal fly-ash, and metals such as Cu, Ni etc. are deposited on the precipitators surface. Alternatively, according to the characteristic surface of cenospheres, an Ag coating catalysis system is adopted to first deposit Ag on the cenospheres surface, followed, if necessary, by the deposition of other metals such as Cu, Ni, etc. on the Ag coating to produce monolayer and multilayer metal-coated cenospheres. The surface characteristics and the morphologies of the metal coatings are examined in detail with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. It can be shown that the quality of metal coatings derived from the Aa coatina catalysis system, is better than that of the colloidal Pd^0 catalysis system.     

WC-Co-Cr涂层的孔率和层状结构对冲蚀行为的影响

用3种高速火焰热喷涂设备将6种商业粉末喷涂在0Cr13Ni5Mo不锈钢基材上,制成结构不同的WC-Co-Cr涂层。用自行研制的料浆罐冲蚀试验机对9种涂层和基材的冲蚀行为进行研究,重点分析气孔率和层状结构对涂层耐冲蚀性能的影响。结果表明：气孔率和层状结构均降低了涂层的耐冲蚀性能,低速低料浆浓度时,气孔率对涂层耐冲蚀能力的影响较层状结构严重,气孔率高的涂层耐冲蚀性能甚至不如基材;高速和高料浆浓度时,层状结构明显的涂层耐冲蚀性能更差。本文探讨了利用单摆冲击划痕法测定涂层比能耗来定量表征层状结构的有效性,讨论了利用涂层气孔率和比能耗的测量结果推测其耐冲蚀性能的可能性。     

利用水下爆炸法评价火炸药爆炸危险性的研究

本文提供了一种测定火炸药冲击感度,并根据测定值判定其冲击爆炸危险性的新方法测定水下爆炸气泡能法。通过对30几种炸药的试用,判定的结果与文献报道的用其他方法判定的结果相当好的一致。而且本法的优点还在于同时可得到试样的动、静态威力,操作简便、安全、噪音小。此外,利用本试验法还探讨了炸药形态、惰性介质(水)对冲击感度的影响。这些对于处理炸药时应如何采取安全对策具有指导意义。     

SYNTHESIS OF STRONTIUM-AND MAGNESIUM-DOPED LANTHANUM GALLATE BY GLYCINE-NITRATE COMBUSTION METHOD

Sr- and Mg-doped lanthanum gallate powders with the composition of La0.55Sr0.15Ga0.85Mg0.15O2.85were synthesized by a glycine-nitrate combustion method. Powders prepared under different fuel combustion conditions were investigated by XRD and TEM. The results show that, under slightly rich fuel condition, the product powders contain less impurity phases, and powders prepared by the glycine-nitrate combustion contain far less impurity phases and have smaller particle sizes than those prepared by solid-state reaction method or acrylamide polymerization technique.