Characterization of Calcined Kaolin/TiO_2 Composite Particle Material Prepared by Mechano-Chemical Method

Calcined kaolin/TiO2 composite particle material （CK/TCPM） was prepared with TiO2 coating on the surfaces of calcined kaolin particles by the mechano-chemical method. X-ray diffraction （XRD） and scanning electron microscope （SEM） were used to investigate the microstructures and morphologies, respectively. The mechanism of the mechano-chemical reaction between calcined kaolin and TiO2 was studied by infrared spectra （IR）. The results show that TiO2 coats evenly on the surfaces of calcined kaolin particles by Si-O-Ti and Al-O-Ti bonds on their interfaces. The hiding power and whiteness of CK/TCPM are 17.12 g/m^2 and 95.7%, respectively, presenting its similarity to TiO2 in pigment properties.

Study on dry friction and wear resistance of a WC-Co particle reinforced iron matrix composite material

In order to select a suitable material for the rolling mill guide application, the dry sliding friction and wear resistance of a tungsten carbide combining cobalt (WC-Co) particle reinforced chromium cast iron composite material were studied. In particular, the wear resistance was discussed in detail. The results showed that the composite material demonstrates 25 times the wear resistance of high Cr cast iron, and 9 times the wear resistance of heat resistant steel. However, the average friction factor in the stable friction stage showed a relationship of μComposites/45#steel>μHigh chromium cast iron/45#steel>μHeat resistant steel/45 # steel. The wear resistance mechanism of the composite material was associated with the reinforcing particles, which protruded from the worn surface to bear the friction load when the matrix material surface was worn, thereby reducing the abrasive and adhesive wear. In addition, the matrix material possessed suitable hardness and toughness, providing a support to the reinforcements.

Finite element simulation of the micromachining of nanosized-silicon-carbide-particle reinforced composite materials based on the cohesive zone model

A finite element method based on the cohesive zone model was used to study the micromachining process of nanosized silicon-carbide-particle(SiCp) reinforced aluminum matrix composites. As a hierarchical multiscale simulation method, the parameters for the cohesive zone model were obtained from the stress-displacement curves of the molecular dynamics simulation. The model considers the random properties of the siliconcarbide-particle distribution and the interface of bonding between the silicon carbide particles and the matrix.The machining mechanics was analyzed according to the chip morphology, stress distribution, cutting temperature, and cutting force. The simulation results revealed that the random distribution of nanosized SiCp causes non-uniform interaction between the tool and the reinforcement particles. This deformation mechanics leads to inhomogeneous stress distribution and irregular cutting force variation.

Template synthesis of copper azide primary explosive through Cu2O@HKUST-1 core-shell composite prepared by “bottle around ship” method

Copper azide(CA), as a primary explosive with high energy density, has not been practically used so far because of its high electrostatic sensitivity. The Cu2O@HKUST-1 core-shell structure hybrid material was synthesized by the “bottle around ship” methodology in this research by regulating the dissolution rate of Cu2O and the generation rate of metal-organic framework(MOF) materials. Cu2O@HKUST-1 was carbonized to form a Cu O@porous carbon(CuO@PC) composite material. CuO@PC was synthesized into a copper azide(CA) @PC composite energetic material through a gas-solid phase in-situ azidation reaction.CA is encapsulated in PC framework, which acts as a nanoscale Faraday cage, and its excellent electrical conductivity prevents electrostatic charges from accumulating on the energetic material’s surface. The CA@PC composite energetic material has a CA content of 89.6%, and its electrostatic safety is nearly 30times that of pure CA(1.47 mJ compared to 0.05 mJ). CA@PC delivers an outstanding balance of safety and energy density compared to similar materials.

Effects of silver powder particle size on the microstructure and properties of Ag-Yb_2O_3 electrical contact materials prepared by spark plasma sintering

mg-Yb203 electrical contact materials were fabricated by spark plasma sintefing （SPS）. The effects of silver powder particle size on the microstructure and properties of the samples were investigated. The surface morphologies of the sintered samples were examined by optical microscope （OM）, and the fracture morphologies were observed by scanning electron microscopy （SEM）. The physical and mechanical properties such as density, electrical resistivity, microhardness, and tensile strength were also tested. The results show that the silver powder particle size has evident effects on the sintered materials. Comparing with coarse silver powder （5 ktm）, homogeneous and fme microstmcture was obtained by fine silver powder （_〈0.5-1am）. At the same time, the electrical conductivity, microhardness, and tensile strength of the sin- tered samples with fine silver powder were higher than those of the samples with coarse silver powder. However, silver powder particle size has little influence on the relative densities, which of all samples （both by free and coarse silver powders） is more than 95%. The fracture characteristics are ductile.

Microstructure and hardness of WC-Co particle reinforced iron matrix surface composite

In this study, a high Cr cast iron surface composite material reinforced with WC-Co particles 2-6 mm in size was prepared using a pressureless sand mold infiltration casting technique. The composition, microstructure and hardness were determined by means of energy dispersive spectrometry(EDS), electron probe microanalysis(EPMA), scanning electron microscope(SEM) and Rockwell hardness measurements. It is determined that the obtained composite layer is about 15 mm thick with a WC-Co particle volumetric fraction of ～38%. During solidification, interface reaction takes place between WC-Co particles and high chromium cast iron. Melting and dissolving of prefabricated particles are also found, suggesting that local Co melting and diffusion play an important role in promoting interface metallurgical bonding. The composite layer is composed of ferrite and a series of carbides, such as(Cr, W, Fe)23C6, WC, W2C, M6C and M12C. The inhomogeneous hardness in the obtained composite material shows a gradient decrease from the particle reinforced metal matrix composite layer to the matrix layer. The maximum hardness of 86.3 HRA(69.5 HRC) is obtained on the particle reinforced surface, strongly indicating that the composite can be used as wear resistant material.

Synthesis of nano-CaCO_3 composite particles and their application

Nano-calcium carbonate composite particles were synthesized by the soapless emulsion polymerization technique of double monomers. The composite particles formation mechanism was investigated. The effects of composite particles on the mechanical properties of nano-CaCO3-ABS （acrylonitrile-butadiene-styrene copolymer） composite material were studied. It was validated that the composite particles are made up of the nano-calcium carbonate cores and the shells of alternating copolymers of butyl acrylate （BA） and styrene （St）. The shells are chemically grafted and physically wrapped on the surface of nano-calcium carbonate particles. When the composite particles were filled in ABS matrix, the CaCO3 particles are homogeneously dispersed in the composite material as nanoscales. The impact strength of the composite material is obviously enhanced after filling appropriate amounts of composite particles. It can be concluded that the soapless emulsion polymerization of double monomers is an effective method for nano-CaCO3 surface treatment. 2008 University of Science and Technology Beijing. All rights reserved.

Facile synthesis and performance of polypyrrole-coated sulfur nanocomposite as cathode materials for lithium/sulfur batteries

In situ chemical oxidation polymerization of pyrrole on the surface of sulfur particles was carried out to synthesize a sulfur/polypyrrole （SIPPy） nanocomposite with core-shell structure. The composite was characterized by elemental analysis, X-ray diffraction, scanning/transmission electron microscopy, and electrochemical measurements. XRD and FTIR results showed that sulfur well dispersed in the core-shell structure and PPy structure was successfully obtained via in situ oxidative polymerization of pyrrole on the surface of sulfur particles. TEM observation revealed that PPy was formed and fixed to the surface of sulfur nanoparticle after polymerization, developing a well-defined core-shell structure and the thickness of PPy coating layer was in the range of 20-30 nm. In the composite, PPy worked as a conducting matrix as well as a coating agent, which confined the active materials within the electrode. Consequently, the as prepared SIPPy composite cathode exhibited good cycling and rate performances for rechargeable lithium/sulfur batteries. The resulting cell containing SIPPy composite cathode yields a discharge capacity of 1039 mAh·g^-1 at the initial cycle and retains 59% of this value over 50 cycles at 0.1 C rate. At 1 C rate, the SIPPy composite showed good cycle stability, and the discharge capacity was 475 mAh·g^-1 after 50 cycles.

Review:Progress in Core-shell Rubber Particles for Efficiently Toughening Resins

Core-shell toughening particles are structured composite particles consisting of generally two different components, one at the center as a rubbery elastic core and surrounding by the second as a glassy inelastic shell. The design, preparation, and application of core-shell polymer particles have been briefly reviewed. Morphological characteristics of the core-shell particles by transmission electron microscopy(TEM) and scanning electron microscopy(SEM) are focused. The vital factors that are useful to control core-shell morphology and toughening properties including core-shell monomer species, polymerization conditions, cross-linking reagents, synthetic method, and post-processing techniques are analyzed. Distinguished properties are mainly considered as the most desirable features that endow core-shell polymer particles with various applicabilities, particularly as effectively toughening components in brittle epoxy resin and polylactide that are substrate of copper clad laminate widely used in the modern electronic world and environmentally friendly materials that are useful as packaging films, disposable tableware, biomedical equipment, and new energy vehicles.

Strain Regularity and Stiffness Tensor of Reinforcers in Dense Particle Reinforced Composites

Based on the study of strain distribution in composites reinforced with high-volume-fraction, randomly distributed particles, the quantitative relation between the average strains of matrix/reinforcers and microstructure parameters of the composite is investigated. It is revealed that besides the average strains, strain fluctuation is also an important factor affecting the stiffness modulus of the composites. The relation between the strain fluctuation and microstructure parameters of the composite is also obtained to derive the stiffness tensor. The theoretical prediction is favorably compared with experimental results.

Effect of Volume Fraction of Particle on Wear Resistance of Al_2O_3/Steel Composites at Elevated Temperature

Based on previous work, abrasive wear resistance of Al 2O 3/steel composites with different Al 2O 3 particle volume fraction (VOF) at 900 ℃ was investigated. The experimental results showed that a suitable particle VOF is important to protect the metal matrix from wear at elevated temperature. Both too high and too low particle VOF lead to a poor abrasive wear because a bulk matrix is easily worn off by grits when it exceeds the suitable VOF and also because when VOF is low, the Al 2O 3 particles are easily dug out by grits during wearing as well. When the particle VOF is 39%, the wear resistance of tested composites is excellent.

Microstructure-based three-dimensional characterization of chip formation and surface generation in the machining of particulate-reinforced metal matrix composites

Particulate-reinforced metal matrix composites(PRMMCs)are difficult to machine due to the inclusion of hard,brittle reinforcing particles.Existing experimental investigations rarely reveal the complex material removal mechanisms(MRMs)involved in the machining of PRMMCs.This paper develops a three-dimensional(3D)microstructure-based model for investigating the MRM and surface integrity of machined PRMMCs.To accurately mimic the actual microstructure of a PRMMC,polyhedrons were randomly distributed inside the matrix to represent irregular SiC particles.Particle fracture and matrix deformation and failure were taken into account.For the model’s capability comparison,a two-dimensional(2D)analysis was also conducted.Relevant cutting experiments showed that the established 3D model accurately predicted the material removal,chip morphology,machined surface finish,and cutting forces.It was found that the matrix-particle-tool interactions led to particle fractures,mainly in the primary shear and secondary deformation zones along the cutting path and beneath the machined surface.Particle fracture and dilodegment greatly influences the quality of a machined surface.It was also found that although a 2D model can reflect certain material removal features,its ability to predict microstructural variation is limited.

Anisotropic permittivity and conductivity transition of composite material embedded by non-spherical particles

When the size of inhomogeneous particles in composite material is much smaller than the incidence wavelength, the average dielectric properties can be expressed in terms of effective permittivity εeff which is treated as macroscopically homogeneous. For many years, effective permittivity was usually studied by dipole polarizability as an electrostatic problem.It did not illustrate how the scattering was omitted. Actually, a particulate material can be treated as a random medium whose dielectric constant is randomly fluctuated between particle εs and background material εb The electric properties of such materi-

Preparation and Characterization of Monodispersed Co_2O_3 Ultrafine Particle Sol

The present, paper contains a new composite material Co;O;UFP sol prepared by using W/O microemulsion method, and its size distribution, interracial and optical nonlincar properties are discussed. The method for the preparation of UFP sol is as follows: at first, CoCl;and DBS so-

Study on Particle Pushing in Front of Growing Interface During Soldification

For in situ composite materials, the interaction between the second phase particles and the solidification interface attracts more attentions of people, for concerning the final distribution of the particles on the matrix. With the conception of the local solidification time, a kinematics mechanism of particle pushing into the crystal boundary during the solidification process was assumed. Through the analysis of forces acted on the particle in front of the solid/liquid interface the critical velocity criterion for the particles pushing was given. The calculation results show when the growth rate of the interface V is less than or equals to the critical velocity V C , the particles on the solid/liquid interface is pushed into the boundary region of cellular crystals, where they are distributed as a chain like straight, which forms a particle strengthened in situ composite materials.

Particle Size Influence on the Effective Permeability of Composite Materials

The energy method, which estimates the effective permeability of composite material is proposed. We approximate the effective static magnetic permeability by energy method and Maxwell-Garnett method for spherical particles dispersing system. Considering the effect of the interface layer between the medium and the particle, we study the nanoparticles embedded in a medium exactly. The interface layer property plays a significant factor for the effective permeability of the composite material in which nano-sized particles embedded.

纤维增强树脂矿物复合材料的细观力学特性及损伤机理

纤维增强树脂矿物复合材料因优异的力学性能得到广泛应用,但有关材料损伤机理的研究仅停留在宏观层面,较少关注损伤过程中材料的细观力学特性和微裂纹演化规律。针对这一问题,基于颗粒流离散元技术建立了纤维树脂矿物复合材料的细观模型,分析了材料应力-应变曲线的变化规律,揭示了材料的微裂纹萌生扩展机制和其破坏失效形式。结果表明,相比于树脂矿物复合材料,纤维增强树脂矿物复合材料的抗压强度更高,起裂应力和损伤应力更大;骨料颗粒形状对纤维的增强增韧作用影响较小;纤维对树脂矿物复合材料具有增韧阻裂的作用。研究从细观角度揭示了纤维增强树脂矿物复合材料的损伤性能,能够为该材料的推广应用提供指导。

尾矿陶粒/正壬醛酰腙复合材料的制备、表征和相变储能性质

针对固液相变储能材料在相变过程中液体发生泄漏而缩短其使用寿命,甚至造成安全隐患问题,实验研究常压下自发浸渗法制备了一种低相变温度、高潜热的尾矿陶粒/正壬醛酰腙复合材料,通过红外光谱、紫外可见漫反射光谱、XRD和对N2吸脱附实验对复合材料进行了表征,测试了复合材料的热稳定性和相变储能稳定性。红外光谱和紫外可见漫反射光谱结果表明,尾矿陶粒与正壬醛酰腙之间作用力是氢键;XRD测试和N2吸脱附实验显示,在形成复合材料过程中,正壬醛酰腙钻入到了尾矿陶粒的孔结构中;TG和DSC测试结果表明,形成复合材料后热稳定性增强,在100次升温和降温循环试验后,复合材料的熔化潜热仅降低了1.10%,凝固潜热增加了0.40%,说明复合材料具有良好的循环稳定性和热稳定性。

金刚石粒径对金刚石/Cu-B合金复合材料热物理性能的影响

采用Cu-B合金为基体,选用粒径分别为110、230、550μm的金刚石颗粒作为增强体,利用气压熔渗工艺在1100℃、10 MPa气体压力下制备金刚石/Cu-B合金复合材料,研究金刚石颗粒粒径对复合材料组织结构、界面相分布及热物理性能的影响。结果表明,随着金刚石粒径的增大,复合材料热导率上升,热膨胀系数减小,复合材料界面处硼碳化合物含量增加,界面结合情况得到改善。由金刚石颗粒粒径为550μm时,复合材料热导率最高,可达680.3 W/(m·K),热膨胀系数最小,为4.905×10^(−6)K^(−1),符合高效热管理器件对金刚石/金属基复合材料的热物理性能要求,在电子产品散热器件方面具有良好的应用前景。