纳米铜粉在乙醇溶液中的团聚规律

研究了纳米铜粉在乙醇溶液中团聚的影响因素及其规律。结果表明:随着静止时间的延长,纳米铜粉的团聚粒径逐渐增大,粒径的分布范围先是增大,当团聚达到动态平衡后又逐渐变小;当团聚达平衡状态时,纳米铜粉的平均粒径随其质量分数的增加而增大,但当质量分数达到一定值时平均团聚粒径就达到极限;纳米铜粉在悬浊液中的团聚速率随纳米铜粉质量分数的增大而增大。     

Ballistic behaviour of gun powder and flash powder for firework chemicals as a function of particle sizes

In this paper, analysis of ballistic behaviour of gun powder and flash powder of firework chemicals with different particle size have been carried out in a closed vessel to find out the maximum pressure when ignited. The experiment was carried out by changing the variables like sample composition, particle size, vessel volume. Works were carried out to synthesis of nanoflash powders and the particle sizes are 139.7 nm for KNO₃, 94.5 nm for Al and 92.36 nm for S. The nanoflash powders are mixed with micron powders in different ratios and crackers are manufactured. The maximum pressure during the combustion of different samples and explosivity of the crackers are analysed. Results show that peak pressure is increased by 21.6% and explosive impulse is increased by 60% when burning of 100% nfp compared to 10% nfp cracker.     

Particle size effect on abrasion resistance of mottled cast iron with different retained austenite contents

Effects of particle abrasive sizes on wear resistance of mottled cast iron with different retained austenite contents were studied. Abrasive wear tests using a pin test on alumina paper were carried out, using abrasive sizes between 16 μm and 192 μm. Retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of samples and the alumina paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results show that at lower abrasive sizes the mass loss was similar for the iron with different austenite contents. However, at higher abrasive sizes the samples with higher retained austenite content presented higher abrasion resistance. For lower abrasive sizes tested, samples with higher and lower retained austenite content both presented microcutting. On the other hand, the main wear micromechanism for the samples with higher retained austenite content and higher abrasive sizes was microploughing. The samples with lower retained austenite content presented microcutting and wedge formation at higher abrasive sizes. Higher abrasive size induced more microcutting in samples with lower retained austenite. The iron with lower retained austenite content presented wider grooves for the different abrasive sizes measured. SEM on the abrasive paper used on samples with higher retained austenite showed continuous and discontinuous microchips and the samples with lower retained austenite showed discontinuous microchips at 66 and 141 μm. This research demonstrates the relation between abrasive size, wear resistance, groove width and wear micromechanism for mottled cast iron with different retained austenite contents.     

On the compressive behavior of sintered porous coppers with low-to-medium porosities—Part II: Preparation and microstructure

A polymer space-holder method was used in this study to prepare porous coppers with low-to-medium porosity within the range 5–50%. This provides the possibility to control the pore size, distribution and structure. Optical microscopy and scanning electron microscopy (SEM) with energy dispersion spectrum (EDS) were utilized to characterize the porous samples. Two different sizes of copper powders, 5 and 45 μm, were used to investigate the effect of raw materials powder size. Microstructure results have shown that there exist two different types of pore in the sintered samples: round-shaped macro-pores left over by the burnout of the space holder and irregular micro-pores or the intervals among metal powders. No matter which size powder was used, the size of the macro-pore falls into a range 200–500 μm, but the pore structures are different in the two cases, interconnected or open pores for the 45 μm raw powders and closed pore for the 5 μm powders. The sizes of the micro-pores among the copper powders in the two cases are also different, several microns for the 5 μm powders and 10–20 μm for the 45 μm powders, though all micro-pores are interconnected for both powder sizes. From the viewpoint of pore structure, it is concluded that the 45 μm powder is more appropriate for use to prepare the porous metal. In addition, the effect of the binder was also investigated. It is suggested that a binder that can be easily and completely removed should be used in order to induce the residue. This paper, as Part II of the publication, focuses on the fabrication of the porous samples where Part I [Lemons JE, editor. Quantitative characterization and performance of porous implants for hard tissue application. ASTM STP 953; 1985] has been published earlier for the mechanical properties of the material.     

水雾化铁粉轧制试验研究

对自制的设备进行控制系统的改装,使得轧制参数便于调整.进行水雾化铁粉轧制试验,确定了随机轧制时带材相对密度和粉末松装相对密度及厚度的关系,分析了初始辊缝大小和摩擦系数对带材性能的影响.试验表明,对于150mm轧辊,当初始辊缝为0.475mm时,可轧制出最厚为1.22mm带材.     

球墨铸铁摩擦副激光熔覆处理层摩擦磨损研究

采用激光熔覆技术在球墨铸铁表面制备了原位析出颗粒增强金属基复合材料表层.以激光强化的球墨铸铁为上试样、灰铸铁为下试样,进行了标准的SRV快速磨损试验.结果表明:熔覆层致密,冶金结合良好,与灰铸铁配副,磨损深度分别为0.84μm、1.79μm,摩擦系数在0.065-0.078内变化,摩擦系数随摩擦时间的增加呈逐渐降低的趋...     

Erosion-corrosion of chromium steel in a rotating cylinder electrode system: some comments on particle size effects

The effect of particle size on the erosion-corrosion response of a Cr containing steel in NaOH was studied in a rotating cylinder electrode system. The results showed that for the same addition of particles by weight, the corrosion rate in the presence of erosion was independent of particle size. However, the erosion-corrosion rate appeared to be dependent on particle sizes for size ranges from 50 to 100 μm but above this value, this dependence was reduced. Erosion-corrosion mechanism and wastage maps were constructed based on the results showing the variation in erosion-corrosion regimes, as a function of particle size and electrochemical potential.     

锐钛矿型二氧化钛纳米颗粒的制备及其粒径控制

采用水解-均相沉淀法在加入相同体积、不同浓度沉淀剂的溶液中,以四氯化钛为主要原料,制备了不同粒径的二氧化钛纳米颗粒.用透射电镜、X射线衍射仪、比表面积分析仪、差热分析和紫外-可见光谱分析仪等,对所制备的纳米颗粒进行了表征.结果表明:随着沉淀剂浓度的不同,可制备出不同粒径的二氧化钛纳米颗粒,其粒径均匀,尺寸分布较窄,纯度高,晶型皆为单一的锐钛矿型.     

PIM粉末颗粒的分形特征及其分形维数

分析了粉末注射成形几种常用粉末颗粒形状、投影边界、表面的分形特征。介绍了一种适用于粉末颗粒的分维测量方法。根据民镜图片，用“数盒子”法测算了羰基铁和羰基镍粉投影边界图形的分形维数，它们分别在1.068-1.080、1.225-1.235之间，说明羰基镍粉末颗粒的形状特征有可能用Koch曲线分形性质来进行描述和分析，分形理论的引入可为研究粉末注射成形提供更准确的定量描述原料特征的方法，为粉末注射成形过程的控制提供了更精确的工艺参数。     

自蔓延燃烧合成多孔NiTi形状记忆合金的显微组织和孔隙结构

以镍粉和钛粉为原料,采用自蔓延燃烧合成技术制备了多孔NiTi形状记忆合金,研究了压坯压力、镍含量、钛粉粒径等参数对合金孔隙尺寸、孔隙均匀性和显微组织的影响。结果表明:自蔓延燃烧合成的NiTi合金为螺旋分层结构;压坯压力在100~200 MPa范围内再经自蔓延燃烧合成的NiTi合金的孔隙均匀,且为三维连通结构,比较理想;镍质量分数为40%左右时,孔隙的分布和三维贯通性均较理想;当钛粉粒径较大时,出现了大量的液相和NiTi2、Ni3Ti等杂质相,反应很不充分,钛粉粒径在50~100μm之间为好。     

Acoustic emissions for particle sizing of powders through signal processing techniques

The present work introduces an innovative method for measuring particle size distribution of an airborne powder, based on the application of signal processing techniques to the acoustic emission signals produced by the impacts of the powder with specific metallic surfaces. The basic idea of the proposed methodology lies on the identification of the unknown relation between the acquired acoustic emission signals and the powder particle size distribution, by means of a multi-step procedure. In the first step, wavelet packet decomposition is used to extract useful features from the acoustic emission signals; the dimensionality of feature space is further reduced through multivariate data analysis techniques. As a final step, a neural network is properly trained to map the feature vector into the particle size distribution.The proposed solution has several advantages, such as low cost and low invasiveness which allow the system based on this technique to be easily integrated in pre-existing plants. It has been successfully applied to the PSD measurement of coal powder produced by grinding mills in a coal-fired power station, and the experimental results are reported in the paper. The measurement principle can also be applied to different particle sizing applications, whenever a solid powder is carried in air or in other gases.     

316不锈钢粉末直接激光烧结的球化效应

采用直接金属激光烧结的方法,对316不锈钢粉末进行了一系列激光烧结实验。实验发现,由于液相粘度较高、表面张力大以及熔体材料不浸润固相颗粒和基板等因素的影响,导致烧结过程中出现球化现象。球化的出现,一方面导致形成球形的液滴表面和不连续的烧结线,妨碍下一粉末层的铺放,不利于烧结的顺利进行,严重时还将会导致无法烧结成形;另一方面也使得烧结层留有大量孔隙,强度很低,成形质量不高。分析了316不锈钢粉末球化效应产生的原因,讨论了工艺参数对316不锈钢金属粉末烧结成形的影响。     

Adhesive wear of stir cast hypereutectic Al–Si–Mg alloy under reciprocating sliding conditions

This paper describes an attempt to enhance the wear properties of hypereutectic cast aluminium–silicon alloys produced by semi-solid metal (SSM) processing technique. The rheological experiments on SSM slurries were performed under continuous cooling condition from liquidus temperature. Wear characteristics of alloy under investigation were studied using pin on flat wear system over a range of normal load (10–40 N) at constant average sliding speed (0.2 m/s) against cast iron and stainless steel counter surface. Stir cast alloy showed lesser weight loss compared to conventional cast alloy. Stir cast and conventional cast alloys showed higher weight loss against the stainless steel as compared to that against cast iron counter surface. Optical microscopy of the conventional cast and stir cast hypereutectic alloy has shown that stir casting causes refinement of primary silicon particles and modification of eutectic silicon compared to conventional cast alloy. The scanning electron microscopy of wear surfaces was carried out to investigate the mode of wear.     

Preparation of Ultrafine SiO2 Powder from Rice Husk and Properties of Its Infrared Spectrum

This paper discussed impact of temperature on the size distribution in preparing ultrafine silica from rice husk.The samples prepared were analyzed with infrared spectrum,and the relation between the particle size and intensity of characteristic absorption peak of IR at center around 1 100 cm-1 was disscussed with the baseline method.Results show that when the temperature is 650 ℃ and roasting time is 11 h,at optimal reaction conditions,the size distribution of the ultrafine silica powder prepared is relatively concentrated,and the average particle size is 199.5 nm.Moreover,the characteristic absorption band of IR is broadening gradually along with particle size decreasing.     

热重分析仪在研究纳米铁粉熔融特性中的应用

利用比表面积测试仪（BET ）和电子扫描电镜（SEM ）对纳米铁粉表面特性进行测定,利用热重分析仪（TGA）对50nm、100nm、500nm和20000nm铁粉在10℃· min-1、20℃· min-1、30℃· min-1和40℃· min-1升温速率下进行了热分析实验,得到纳米铁粉的表面微观结构、差示扫描量热曲线（DSC ）和热重曲线（T G ）,结果发现：粒径为50nm和100nm的铁粉在较低的温度下可能发生了相变,相变温度区间为260～350℃,而粒径为500nm和20000nm的铁粉在燃烧过程中则没有发生熔融,纳米金属粒径越小,越容易熔化。     

Model for compaction of metal powders

A new yield criterion for metal powder compaction based on continuum mechanics has been proposed. It includes three parameters to characterize the geometric hardening of powder compact and strain hardening of incompressible metal matrix. The elasto-plastic finite element method to describe compaction of metal powders has been formulated using the new yield criterion. The values of parameters in the yield criterion could be determined through cold isostatic pressing (CIP). The finite-element method was used to simulate compaction behaviour of copper powders of different shape and mean particle size.     

制备工艺对掺铕ATO纳米粉体性能的影响

采用化学共沉淀法制备了掺杂稀土铕的ATO纳米粉体。运用X射线衍射（XRD）测试方法对ATO粉体的结构进行表征,研究了滴定终点pH值、反应温度和热处理温度对粉体晶型结构、粒径和导电性能的影响,发现pH值为9、反应温度为60℃、600-700℃热处理温度下得到粉体的性能最佳。此温度下制备的ATO粉体的晶型结构较完整,粉体的电阻率为280Ω.cm,颗粒尺寸为33-34 nm。     

Ball-cratering abrasion tests with large abrasive particles

The application of a ball-cratering method to test three-body abrasive wear of bulk materials in the presence of large abrasive particles has been investigated. Four types of abrasive particles of different sharpness were used to make slurries: glass beads, silica sand, crushed quartz and alumina. All the particles were sieved to a size of 250–300 μm. Two common industrial materials, mild steel and 27% Cr white cast iron, were used as wear samples. Wear rates of metallic samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.It was found that the surface roughness of the ball significantly affects the wear rates and the wear mechanisms of the metallic samples. The surface roughness of the ball steadily increased with testing time and was mainly affected by the angularity of abrasive particles. More angular particles generated higher ball surface roughness. It was found that the gradual increase in the ball surface roughness was responsible for non-linearity of wear rates with sliding time. The increasing depth of the wear craters also contributed to this non-linearity as deeper craters facilitate particle entrainment. Three-body rolling wear dominated when the ball was smooth and the contribution of two-body grooving wear increased with increasing the ball roughness. Softer mild steel samples were more affected by the ball roughness changes than the harder white cast iron samples. Wear surface morphology was also affected by the angularity of particles and by the material properties of wear samples. Particle fracture was found in all four groups of abrasives and the angularity of the particles was slightly altered. Therefore, the ball-cratering test, under the testing conditions used, can be considered as a high-stress abrasion test.     

Effect of Sintering Temperature and Atmosphere on Nonlubricated Sliding Wear of Nano-Yttria-Dispersed and Yttria-Free Duplex and Ferritic Stainless Steel Fabricated by Powder Metallurgy

The nonlubricated sliding wear behavior of nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel against a diamond tip was studied. The stainless steel samples were fabricated by a conventional powder metallurgy route in which nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel powders were cold compacted and then conventionally sintered at either 1000, 1200, or 1400°C in an argon atmosphere. For comparison, another set of samples was sintered at 1000°C in a nitrogen atmosphere. The wear behavior of sintered stainless steel samples against a diamond indenter was investigated using a pin-on-disc apparatus at 10 and 20 N loads and at a constant speed of 0.0041 m/s. It is proposed that yttria-dispersed stainless steels showed higher wear resistance compared to yttria-free stainless steel due to their improved hardness and density. Stainless steel sintered in a nitrogen atmosphere exhibited better wear resistance than those sintered in an argon atmosphere due to the formation of hard and brittle Cr₂N. The wear mechanisms of stainless steels against diamond were found to be mainly abrasive and oxidative. Semiquantitative analysis of the worn surfaces and wear debris confirmed the occurrence of oxidation processes during wear.     

Feasibility study of a new rapid tooling process

The requirements for faster product development cycles, lower product cost and environmental sustainability are ever increasing in today’s globally competitive market. Tooling is a very important phase in the product manufacturing cycle. To overcome the shortcomings of long lead-time and high cost associated with conventional tooling processes, new tooling methods with shorter lead-time and lower cost are strongly under demand. In this study, the feasibility of the proposed new rapid tooling process based on back support of a metal shell with packed metal powders is examined. First, the effect of metal powder properties, such as powder shape, size, and size distributions, on powder-packing behaviour is investigated experimentally. Then, the compressive behaviours of the metal shell and the shell-powder assembly are analysed numerically with different compressive loading. The study indicates that the proposed new rapid tooling method can potentially be used for injection moulding applications.