超细粉末材料粒度测试技术研究

Considered actual development in the field of ultramicron material and present situation of particle analysis technology, improvement of microscopy and laser particle analyzer in surveying ultramicron material was discussed.It was presented in this paper why microscopy,laser particle analyzer and microprobe analysis technology have a chance of development,and how to develop particle analysis technology.

石墨粒度对C/Cu复合材料载流摩擦磨损性能的影响

分别采用45、150μm两种粒度的镀铜石墨经粉末冶金法制得C/Cu复合材料,借助销-盘式载流摩擦磨损试验机研究了石墨粒度对C/Cu复合材料载流摩擦磨损性能的影响,利用电镜对磨擦表面进行微观分析。结果表明,45μm石墨颗粒较150μm石墨颗粒能够减少电弧发生,并提高该复合材料的力学性能和增强摩擦面润滑膜的形成,能有效降低该复合材料的摩擦系数和磨损率。

Arc erosion behaviors of AgSnO_2 contact materials prepared with different SnO_2 particle sizes

To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag?4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag?4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag?4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag?4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag?4%SnO2contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.

掺杂钨中微量元素钾行为的研究

对掺杂微量元素钾的钨粉进行粒度分级后,发现钾的浓度是对粉末粒度敏感的因素,随粉末粒度减小,钾含量(PPM级)是增加的,几乎呈线性关系。由不同粒度钨粉分别制成的制品,钾的浓度依然遵循着粉末中的规律,但由于钾的微量差别引起制品许多物理性能的明显差异,也存在着较好的规律。俄歇分析表明钾可能存在于粉末颗粒表层的100A范围。在坯条中主要富集于晶界和气孔内,在棒丝中,晶界及解理面均存在有钾,经高温处理后,钾主要的钾泡形式沿丝轴排列。

Studies on Spinel LiMn_2O_4 Cathode Material Synthesized from Different Mn Sources

The spinel LiMn2O4 cathode material was synthesized with the solid-state reaction method. Four manganese compounds including electrolytic manganese dioxide (EMD), MnCO3, Mn3O4 and nano-EMD were used as Mn sources while LiOH·H2O was used as the uniform Li source. The crystal structure characteristics of these samples produced were investigated by means of XRD, SEM, particle size distribution analysis and specific surface area testing. Their electrochemical properties were also studied by comparing their specific capacity, charge and discharge efficiency and cycle performance.

Utilization of municipal solid waste incineration fly ash in lightweight aggregates

Washing pre-treatrnent of municipal solid waste incineration （MSWI） fly ash blended with shale and sludge was utilized in the manufacture of light-weight aggregates and processed to form ceramic pellets. A formula uniform design was performed to arrange the mixture ratio of the materials. The optimal mixture ratio of the materials was determined by measuring the bulk density, granule strength, and 1 h water absorption of the pellets. It is shown that the optimal mixture ratios of materials, MSWI fly ash, shale, and sludge, are 23.16%, 62.58%, and 14.25% （mass fraction）, respectively. The performance testing indicators of light-weight aggregates are obtained under the optimum mixture ratio： bulk density of 613 kg/m3, granule strength of 821N, and 1 h water absorption of 11.6%, meeting 700 grade light-aggregate of GB/T 17431.2--1998 standard. The results suggest that utilization of MSWI fly ash in light-weight aggregates is an effective method and a potential means to create much more values.

Probabilistic analysis of geomembrane puncture from granular material under liquid pressure

A simplified probabilistic analysis of geomembrane punctures from granular material was presented when subjected to liquid pressure.The probability distribution of contact force between geomembrane and granular material was obtained based on the principle of equal probability and assumptions that grains are spheres with constant size.A particle flow code PFC3Dwas employed to simulate the contact process which indicates a good agreement with the theoretical probabilistic analysis.The odds of geomembrane puncture from grains of constant size were obtained by evaluating the puncture force which should not exceed the puncture resistance of geomembrane.The effects of grain radius,grain rigidity and liquid pressure were studied in more detail and displayed in graphs.Both high-level of liquid pressure and large grain can result in high risk of geomembrane puncture.The influence of grain rigidity on the geomembrane puncture odds is significant.For granular material with a grain size distribution,the geomembrane puncture odds can be estimated by the grain size distribution,served as weight function and it is a cautious design if the largest grain is chosen as the design grain size.

Microstructure and mechanical properties of TA15/TC11 graded structural material by wire arc additive manufacturing process

A graded structural material(GSM)with a material transition from TA15 to TC11 was fabricated by wire arc additive manufacturing(WAAM)method.The grain morphology,chemical composition,microstructure and mechanical properties of the as-deposited GSM were all characterized to investigate their variations along the deposition direction.The results indicate that from TA15 to TC11,the grain size decreases and a transition from columnar grains to equiaxed grains occurs.The content of alloy element alters greatly within a short distance,and the width of the mutation zone is 800μm.Both TA15 and TC11 regions exhibit basketweave microstructure withα-phase andβ-phase.However,during the transition from TA15 to TC11,theα-lath becomes fine,which leads to an increase in microhardness.The tensile test shows that the bonding strength at the interface is higher than the longitudinal strength of TA15,and the lateral elongation at the interface is higher than that of TA15 and TC11.

Multilayer aluminum composites prepared by rolling of pure and anodized aluminum foils

Experimental results on processing,structural and mechanical characterization of a multilayer composite based on commercially pure aluminum foils were presented.A multilayer composite was produced by hot-rolling of anodized and non-anodized aluminum foils alternately sandwiched.In addition,the same process was applied for bonding of non-anodized foils.In both cases,obtained multilayer composites were compact and sound.In order to study composites microstructural evolution and mechanical properties,optical and scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),X-ray diffraction(XRD)analysis,hardness,tensile and three-point flexural tests were performed.Microstructural characterization confirmed that the rod-like particles distributed in parallel rows in the composite aluminum matrix with anodized foils correspond to Al2O3.Maximum and minimum peaks of oxygen and aluminum,respectively,suggest that after the final hot-rolling of composite with non-anodized foils,a small amount of coarser particles were formed at boundaries between foils.Hardness,strength,modulus of elasticity and flexural strength of both multilayer composites were much higher than those of pure aluminum,whereas ductility was significantly less.The composite with anodized foils exhibited the highest strength and modulus of elasticity,but lower ductility compared to composite processed from non-anodized foils.Fracture failure corresponded to the change of ductility.

Characteristics of two Al based functionally gradient composites reinforced by primary Si particles and Si/in situ Mg_2Si particles in centrifugal casting

Two kinds of Al based functionally gradient composite tubes reinforced by primary Si particles alone and primary Si/in situ Mg2Si particles jointly were successfully prepared by centrifugal casting,and their structural and mechanical characters were compared.It is found that the composite reinforced with primary Si particles takes a characteristic of particles distribution both in the inner and outer layers.However,composite reinforced with primary Si/Mg2Si particles jointly takes a characteristic of particles distribution only in the inner layer and shows a sudden change of particles distribution across the section of inner and outer layers.The hardness and wear resistance of Al-19Si-5Mg tube in the inner layer are greatly higher than that in the other layers of Al-19Si-5Mg tube and Al-19Si tube.Theoretical analysis reveals that the existence of Mg2Si particles is the key factor to form this sudden change of gradient distribution of two kinds of particles.Because Mg2Si particles with a lower density have a higher centripetal moving velocity than primary Si particles,in a field of centrifugal force,they would collide with primary Si particles and then impel the later to move together forward to the inner layer of the tube.

Microstructural and abrasive wear properties of SiC reinforced aluminum-based composite produced by compocasting

The effect of SiC particles reinforcement with average size of 1, 5, 20 and 50 μm and volume fraction of 5%, 10% and 15% on the microstructure and tribological properties of Al-based composite was investigated. Composites were produced by applying compocasting process. Tribological properties of the unreinforced alloy and composites were studied using pin-on-disc wear tester, under dry sliding conditions at different specific loads. The influence of secondary mechanical processing with different rolling reductions on the dry sliding wear characteristics of Al matrix composites was also assessed. Hardness measurement and scanning electron microscopy were used for microstructural characterization and investigation of worn surfaces and wear debris. The proper selection of process parameter such as pouring temperature, stirring speed, stirring time, pre-heated temperature of reinforcement can all influence the quality of the fabricated composites. The porosity level of composite should be minimized and the chemical reaction between the reinforcement and matrix should be avoided.

Experimental study on remodeling strength of granular materials under different loads and lengths of time

Remodeled clay and sand rock specimens were prepared by designing lateral confinement and water drainage experiments based on the stress exerted on granular materials in a waste dump.An in situ test was conducted in an internal waste dump;the physical and mechanical parameters of the remodeled rock mass dumped at different time and depths were measured.Based on statistics,regression analysis was performed with regard to the shearing stress parameters acquired from the two tests.Other factors,such as remodeling pressure(burial depth),remodeling time(amount of time since waste was dumped),and the corresponding functional relationship,were determined.Analysis indicates that the cohesion of the remodeled clay and its remodeling pressure are correlated by a quadratic function but are not correlated with remodeling time length.In situ experimental results indicate that the shear strength of reshaped granular materials in the internal dump is positively correlated with burial depth but poorly correlated with time length.Cohesion Cand burial depth H follow a quadratic function,specifically for a short time since waste has been dumped.As revealed by both in situ and laboratory experiments,the remodeling strength of granular materials varies in a certain pattern.The consistency of such materials verifies the reliability of the remodeling experimental program.

New double yield surface model for coarse granular materials incorporating nonlinear unified failure criterion

A new double-yield-sarface （DYS） model was developed to characterize the strength and deformation behaviors of coarse granular materials （CGMs）. Two kinds of deformation mechanisms, including the shear and compressive plastic deformation, were taken into account in this model, These two deformation mechanisms were described by the shear and compressive yield functions, respectively. The Lode angle dependent formulations of proposed model were deduced by incorporating a 3D nonlinear unified failure criterion. Some comparisons were presented between the numerical predictions of proposed model and test data of true triaxial tests on the modeled rockfills. The model predictions are in good agreement with the test data and capture the strain hardening and plastic volumetric dilation of CGMs. These findings verify the reasonability of current DYS model, and indicate that this model is well suited to reproduce the stress-strain-volume change behavior of CGMs in general.

Si_3N_4/Ni nanocomposite formed by electroplating: Effect of average size of nanoparticulates

Properties of Si3N4/Ni electroplated nanocomposite such as corrosion current density after long time immersion,roughness of obtained layer and distribution of nanometric particulates were studied.Other effective factors for fabrication of nanocomposite coatings were fixed for better studying the effect of the average size of nanoparticulates.The effects of the different average size of nanometric particulates(ASNP)from submicron scale(less than 1μm)to nanometric scale(less than 10 nm)were studied.The nanostructures of surfaces were examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and atomic force microscopy(AFM).Corrosion rates of the coatings were determined using the Tafel polarization test.It is seen that decreasing the ASNP will lead to lower corrosion current densities;however,in some cases,pitting phenomena are observed.The roughness illustrates a minimum level while the distribution of nanometric particulates is more uniform by decreasing the ASNP.The effects of pulsed current on electrodeposition(frequency,duty cycle)and concentration of nanoparticulates in electrodeposition bath on trend of obtained curves have been discussed.Response surface methodology was applied for optimizing the effective operating conditions of coatings.The levels studied were frequency range between 1 000 and 9 000 Hz,duty cycle between 10%and 90%and concentration of nanoparticulates of 10-90 g/L.

Research on Preparation of the Composite Materials LiFePO4-Li3V2（PO4）3

The article developed a lithium iron phosphate - composite cathode material of lithium vanadium phosphate. Using X-ray diffraction （XRD）, electronic scanning electron microscopy surface （SEM）, laser particle size analyzer, carbon and sulfur analyzer, and X-ray photoelectron spectroscopy, etc. for the prepared composites were characterized and found the material is mainly crystalline structure of lithium iron phosphate, and lithium vanadium, wherein a small amount of impurities; finer particle size of the material, the particle size distribution is narrow and uniform, smooth particle surface, wrapping in good carbon composite with other materials prepared in comparison the case has a carbon content of about optimum conductivity. To assemble the material into a cell after the 0.1C, IC, 2C when and 5C, the first discharge capacity were 160,145,127 and 109 mA·h·g^-1, after 50 cycles, the discharge capacity of 162, respectively, 144,126 and 106 mA·h·g^-1, which showed good rate characteristics and cycle characteristics.

Evaluation of the effective thermal conductivity of composite polymers by considering the filler size distribution law

We present an empirical model for the effective thermal conductivity (ETC) of a polymer composite that includes dependency on the filler size distribution-chosen as the Rosin-Rammler distribution. The ETC is determined based on certain hypotheses that connect the behavior of a real composite material A, to that of a model composite material B, filled with mono-dimensional filler. The application of these hypotheses to the Maxwell model for ETC is presented. The validation of the new model and its characteristic equation was carried out using experimental data from the reference. The comparison showed that by using the size distribution law a very good fit between the equation of the new model (the size distribution model for the ETC) and the reference experimental results is obtained, even for high volume fractions, up to about 50%.

Analytical investigations and fuzzy logic-based modeling of the impact resistance of aluminum-epoxy laminated composites

In the present paper, Charpy impact resistance of aluminum-epoxy laminated composites in both crack divider and crack ar-rester configurations has been investigated. In both configurations, an analytical investigation has been carried out to evaluate the effects of layers thickness on impact resistance of the specimens. A model based on fuzzy logic for predicting impact re-sistance of the specimens has been presented. For purpose of building the model, training and testing using experimental re-sults from 126 specimens produced from two basic composites were conducted. The data used for the input data in fuzzy logic models are arranged in a format of 7 input parameters that cover the thickness of layers, the number of layers, the adhesive type, the crack tip configuration, the content of SiC particles, the content of methacrylated butadiene-styrene particles and the number of test trial. According to these input parameters, in the fuzzy logic model, the impact resistance of each specimen was predicted. The training and testing results in the fuzzy logic model have shown a strong potential for predicting impact resis-tance of aluminum-epoxy laminated composites.

One-Dimensional Analysis of Supersonic Two-Stage HVOF Process

The one-dimensional calculation of the gas/particle flows of a supersonic two-stage high-velocity oxy-fuel(HVOF) thermal spray process was performed. The internal gas flow was solved by numerically integrating theequations of the quasi-one-dimensional flow including the effects of pipe friction and heat transfer. As for the supersonicjet flow, semi-empirical equations were used to obtain the gas velocity and temperature along the centerline. The velocity and temperature of the particle were obtained by an one-way coupling method. The material ofthe spray particle selected in this study is ultra high molecular weight polyethylene (UHMWPE). The temperaturedistributions in the spherical UHMWPE particles of 50 and 150 m accelerated and heated by the supersonic gasflow was clarified.