感应等离子体技术制备球形铸造碳化钨粉体及其性能表征

球形碳化钨增强金属基复合涂层具有高硬度、高韧性和优异的耐磨、耐蚀性等特点,可以对材料表面起到有效保护作用。传统铸造碳化钨粉体多呈不规则的片状或多角状,流动性差且硬度低,难以满足高性能涂层材料的要求。本文以多角状铸造碳化钨粉体为原料,采用感应等离子体技术制备球形碳化钨粉体,研究感应等离子体技术工艺参数对碳化钨粉体球化效果的影响规律。采用扫描电子显微镜、X射线衍射仪、霍尔流速计、激光粒度分析仪等对球化处理前后碳化钨粉体的形貌、物相、松装密度、粒度分布进行表征。结果表明:送粉率为110 g/min、载气流量为5.0 L/min时,采用感应等离子体技术可制备颗粒饱满、表面光滑、分散性良好,球化率高达99%以上,且球形度较好的球形碳化钨粉体。球化后碳化钨粉体无孔洞等缺陷,内部组织为典型的细针状WC和W₂C的共晶,组织结构均匀细密。球化后碳化钨粉体的硬度高达3 258HV,提高了408HV;球化后碳化钨粉体的松装密度由8.01 g/cm³提高到9.75 g/cm³,霍尔流速由10.30 s/50 g降低到6.80 s/50 g,粉体的流动性提高。     

Effect of powder characteristics on the sinterability of hydroxyapatite powders

The effect of different sintering conditions on the sintered density and microstructure of two different hydroxyapatite (HA) powders was examined. The powder characteristics of a laboratory synthesized HA powder (Lab HA) were low crystallinity, a bimodal particle size distribution, a median particle size of 22 m and a high specific surface area (SSA) of 63 m²/g. By contrast, a commercial calcined HA (commercial HA) was crystalline and had a median particle size of 5 m and a low SSA of 16 m²/g. The different powder characteristics affected the compactability and the sinterability of the two HA powders. Lab HA did not compact as efficiently as commercial HA, resulting in a lower green density, but the onset of sintering of powder compacts of the former was approximately 150 °C lower than the later. The effect of compaction pressure, sintering temperature, time and heating rate on the sintered densities of the two materials was studied. Varying all these sintering conditions significantly affected the sintered density of commercial HA, whereas the sintered density of Lab HA was only affected significantly by increasing the sintering temperature. The Vickers hardness, H_v, of Lab HA was greater than commercial HA for low sintering temperatures, below 1200 °C, whereas for higher sintering temperatures the commercial HA produced ceramics with greater values of hardness. These trends can be related to the sinterability of the two materials.     

Investigation of erosive wear behavior and physical properties of SGF and/or calcite reinforced ABS/PA6 composites

The aim of this study was to investigate the erosive wear behavior of glass fiber, CaCO₃ particle and glass fiber/CaCO₃ hybrid reinforced ABS/PA6 blend based composites. The samples were prepared by using melt mixing and injection molding techniques. The mechanical, thermal, morphological properties and erosive wear behavior were investigated in terms of reinforcing agent type and composition. It was observed that the tensile strength and modulus values of hybrid composites gave a value between tensile strength and modulus values of only fiber reinforced composites and only particle reinforced composites. From DSC analysis it was revealed that T_g and T_m of composites were not significantly affected by reinforcement; however, degree of crystallinity was found to be sensitive to reinforcement type and composition. The impingement angle was found to have a significant effect on the erosive wear behavior. The results indicated that composite materials exhibited maximum erosion rate at impact angle of 30° conforming their ductile erosion behavior. In order to investigate wear mechanisms, eroded surface analysis was done by scanning electron microscopy. Surface analysis showed that repeated impact of hard silica sand particles caused a local removal of the matrix from the fiber surface and led to form craters on the surface of the composite material.     

Synthesis and Ag Recovery of Nanosized ZnO Powder by Solution Combustion Process for Photocatalytic Applications

Nanometer-sized ZnO powders for photocatalytic applications were prepared by a solution combustion method with various starting materials and fuels. It was easy to obtain single-phase ZnO powders using the solution combustion method regardless of the starting materials and fuels. However, the particle size and shape of the synthesized ZnO powders were different than the used fuel. Using glycine as a fuel, the particle shape of ZnO powders was spherical with uniform nanosize. On the other hand, using carbohydrazide as a fuel, the particle shape was platelike. The ZnO powder synthesized using Zn(OH)₂ and glycine as starting material and fuel, respectively, showed good powder characteristics, such as average grain size of 75 nm and the specific surface area of 94 m²/g. The average particle size and specific surface area were greatly dependent on the types of oxidants and fuels. Removal of silver ions from a used photo-film developing solution was attempted to examine the photocatalytic activity of the prepared ZnO powders. It also showed excellent photocatalytic properties in that the silver ions were completely removed from the solution within 3 min.     

A computer simulation of the time dependence of the erosion of Pyrex glass by glass beads

With the aid of scanning electron microscopy (SEM) observations of the surface of Pyrex glass, eroded by spherical glass beads, a recursive algorithm has been formulated which predicts the weight-loss from the specimen as a function of time. This method takes into account three mechanisms of material removal: material chipped off when cone cracks form on the surface; materials removed due to interaction of cone cracks on the flat surface; and materials removed due to chipping of exposed cone frustrums and the underlying rough surface. Multi-particle erosion tests were performed on the Pyrex glass target material employing spherical glass beads as impacting particles. Four different particle velocities and average particle sizes were employed as the varaibles in the experiments. An analysis of the experimental results in conjunction with the mathematical model showed a very good agreement between experimental results and theoretical prediction.     

Improvements of the microstructure and erosion resistance of boron carbide with additives

A series of test materials were produced from boron carbide (B₄C) powders with additions of either boron in amounts up to 60 wt.%, silicon (4 wt.%) or silicon and silicon carbide (4 wt.% and 30 wt.%, respectively). The powder mixtures were densified by encapsulation hot-isostatic pressing. The test materials where evaluated in dry particle erosion tests with silicon carbide grits. Particular attention was given to the relation between the microstructure and the composition.It was found that boron additions up to 20 wt.%, decreased the average grain size and reduced the porosity of the boron carbide. A material with 60 wt.% boron exhibited very low porosity and supreme resistance to particle erosion. The erosion resistance was also significantly improved by additions of silicon and silicon carbide.The favorable effects of boron, silicon and silicon carbide are discussed in terms of their influence on microstructural parameters, such as grain size, porosity, grain boundaries and reduction of free carbon.     

Co-precipitation synthesis in the presence of surfactant and characterization of nanosized CaRuO3 powders and its application in fired thick film resistors in nanoelectronics

In this paper, we are presenting the co-precipitation synthesis of CaRuO₃ from the solutions of CaCl₂·2H₂O and RuCl₃·xH₂O in the presence of CTAB as the surfactant at pH 9.41 and dried at 100 °C in air and at 250 °C in vacuum. The resultant powders were characterized by TGA/DTA, SEM-EDX, XRD, and TEM-SAED techniques. The transmission electron micro-structural studies of powders revealed that the average particle size is around 12 nm. The particle size of CaRuO₃ powder prepared by this solution route without CTAB is around 150–250 nm and solid-state route is 300–400 nm. The resistor paste was formulated by using nano-powders of CaRuO₃ and lead borosilicate glass admixtures pre-heated at 600 °C and peak firing at 850 °C. The electrical studies (sheet resistance and hot/cold temperature coefficient of resistance) of fired thick film resistors prepared from these powders are presented in this paper. We are also presenting the investigation of cross sectional microstructures of above fired thick film resistors. The hot and cold TCR values are higher than the expected values due to the processing of the paste in less than 1 g and non-exchange reactions between Ca²⁺ and Pb²⁺ of functional material and glass respectively due to ionic radii difference of these two metal ions.     

Heat conductivity,physico-mechanical properties and interrelations of them and structures of pressureless sintered composites produced of Si3N4-Al2O3-Y2O3(-ZrO2) nanodispersed system

The microstructures and properties of high-density materials produced by a pressureless sintering of nanodispersed powders of composition Si₃N₄-Al₂O₃-Y₂O₃(-ZrO₂) have been studied. It has been found that these self-reinforced materials of low glass phase content exhibit the bending strength R _bm = 720–850 MPa, Vickers hardness = 15.3–15.7 GPa, fracture toughness = 6.0–6.1 MPa·m^1/2, and heat conductivity = 15–25 W(m·K). The factors affecting physico-mechanical properties and heat conductivity of silicon-nitride materials have been discussed.     

Messung von Rayleighwellen zur Untersuchung der Erosion an der Oberfläche kristalliner Werkstoffe mit Hilfe der Doppelpuls-Holographie

Measuring Rayleigh Waves to Investigate the Erosion at the Surface of Crystalline Materials by Means Double-Pulse Holographic Interferometry The repeated impact of solid particles on a material surface results in erosion. For technical applications as the pneumatic transport the particle diameters are varying between 10^?610^?3 m, the mean particle velocities are up to 30 m/s. In order to investigate experimentally the mechanism of erosion for crystalline materials, planar plates of austenitic steel are damaged due to the repeated impact of spherical particles. The elastic and plastic deformations, which are produced by this impact, result in propagation of longitudinal and transverse elastic waves into the material and of Rayleigh waves along the material surface. The amplitude of the surface deflection due to a single impacting particle is only 10^?810^?7 m. At different states of damage the surface deflection which is caused by such an impact is measured by means of double-pulse holographic interferometry. Because of the small amplitude of the Rayleigh waves two-reference-beam holographic interferometry is required. The initial wear of the material is recognized by the disturbed propagation of the surface wave.     

Influence of powder characteristics and powder processing routes on microstructure and properties of hot pressed silicon nitride materials

Four different commercial Si₃N₄ powders were hot pressed with the addition of La₂O₃ and Y₂O₃ as sintering aids. Two powder processing routes were set up: addition of sintering aid powders by ultrasonic dispersion, addition of nanodispersed amorphous additive species by chemical coprecipitation. The following aspects were analyzed: characteristics of starting powders and powder mixtures, with reference to surface modification (electrokinetic behaviour and surface properties) induced by the powder treatment; sintering behaviour of the powder mixtures; influence of raw powders characteristics and processing route on microstructure and properties of dense materials. The microstructural characteristics of hot pressed materials (grain size, aspect ratio, grain boundary phases) were found to be dependent on powder characteristics and its process history. Significant variation of the mechanical properties (Young modulus, hardness, toughness and strength) were related to microstructural features. Strength, for example, ranges from 600 to 1200 MPa at room temperature and from 400 to 1000 MPa at 1200°C; toughness ranges from about 4 to about 6 MPam^1/2.     

Slip casting of sol–gel-synthesized barium strontium zirconium titanate ceramics

The sol–gel method was used to synthesize two different Ba_0.75Sr_0.25Ti_0.95Zr_0.05O₃ powders: one of high purity and the other of low purity. These two sol–gel-synthesized powders show two distinct particle sizes and surface areas. The slip casting method was applied to these two sol–gel powders followed by a pressureless sintering, which shows large differences in sintered density and grain size for the pressureless sintered disks. Neutron powder diffraction shows a transition to the nonpolar cubic Pm–3m space group at higher temperatures for both materials. Pair distribution function analysis was used to examine the local displacements of the Ti⁴⁺ and Zr⁴⁺ cations. The dielectric constant, loss tangent, and bias were measured on these two materials.     

内嵌式钨铜粉末爆炸复合结构材料的研究

为满足托克马克核聚变装置内壁材料对W-Cu复合材料的需求,提出了内嵌式粉体爆炸复合方法和技术工艺。先用该方法制备内嵌式W-Cu粉复合材料,其实验粉末分别采用粒径3μm与23μm的纯钨粉和添加10%铜粉的W-Cu混合粉末(质量分数)。然后利用扫描电子显微镜、显微硬度计对内嵌式W-Cu粉复合材料进行表征、分析。结果显示,实验粉末经过爆炸烧结压实后能达到90%以上该密实材料的密度。添加10%铜粉后制备的W-Cu粉复合结构材料结合界面更加规则均匀理想,结合界面附近几乎没有孔隙,粉末压实部分孔隙度更小且孔隙的尺寸更小,均匀致密性更好,但粉末压实层硬度更低。使用粒径3μm的混合粉末与23μm的混合粉末,后者制备的W-Cu粉复合材料,粉末压实部分均匀致密性更好,孔隙度更小且孔隙的尺寸更小,粉末压实层密度更大,但硬度更低。     

内嵌式钨铜粉末爆炸复合结构材料的研究

为满足托克马克核聚变装置内壁材料对 W-Cu复合材料的需求,提出了内嵌式粉体爆炸复合方法和技术工艺。先用该方法制备内嵌式W-Cu粉复合材料,其实验粉末分别采用粒径3μm与23μm的纯钨粉和添加10%铜粉的W-Cu混合粉末(质量分数)。然后利用扫描电子显微镜、显微硬度计对内嵌式 W-Cu粉复合材料进行表征、分析。结果显示,实验粉末经过爆炸烧结压实后能达到90%以上该密实材料的密度。添加10%铜粉后制备的 W-Cu粉复合结构材料结合界面更加规则均匀理想,结合界面附近几乎没有孔隙,粉末压实部分孔隙度更小且孔隙的尺寸更小,均匀致密性更好,但粉末压实层硬度更低。使用粒径3μm的混合粉末与23μm的混合粉末,后者制备的 W-Cu粉复合材料,粉末压实部分均匀致密性更好,孔隙度更小且孔隙的尺寸更小,粉末压实层密度更大,但硬度更低。     

Explosive consolidation of 316L stainless steel powder – Effect of phase composition

Two stainless steel (SS) AISI 316L powders have been processed by explosive consolidation using a cylindrical configuration. Powders with d₅₀ of 9 and 5 μm and a phasic structure consisting of fcc and bcc are used. After shock processing (3.5 up to 4.9 mm/μs) hardness was evaluated. Powders with the lowest particle size and processed with the highest detonation velocities (4.9 and 4.1 mm/μs) gave rise to a bulk material where in the centre occurred a phase transformation of bcc to fcc phase. Nevertheless, the hardness values were dissimilar along the cross section depending on the macrodefects (centre hole and cracks) produced by detonation. After a pre-heating treatment (900 °C), this powder was full austenitic (fcc) and when submitted to explosive consolidation, it led a monolithic solid without cracks, with a density of 99% TMD (theoretical maximum density) and a hardness of 3.1 GPa. This value is lower than others measured, particularly when a centre hole is not present, revealing hardening by plastic deformation. Concerning powder with higher particle size (d₅₀ = 9 μm), the presence of mainly austenite induces after shock processing function of detonation parameters and localisation hardness values from 3.9 up to 5.0 GPa. The homogeneity of hardness reflex of absence of defects and low stress are almost achieved only for low particle size powders, using the lowest detonation velocities (3.4 GPa).     

Soft chemical synthesis of nanosized zinc aluminate spinel from the thermolysis of different organic precursors

A new method of preparation of nanocrystalline zinc aluminate (ZnAl₂O₄) powder is described in this paper. Different organic acids are used as template material and nitric acid as an oxidant. Single phase ZnAl₂O₄ spinel can be formed at a much lower temperature through this route which gives nanocrystalline powder with uniform particle size and morphology. The powders are characterized by thermo gravimetric analysis (TGA), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT-IR), BET surface area analysis and field emission scanning electron microscopy (FE-SEM). The average crystallite size of the single phase material was of 20 to 30 nm and the surface area was found to be 21 to 27 m²g^?1.     

Effect of microstructure on the erosion and impact damage of sintered silicon nitride

The erosion rates and impact damage of two sintered silicon nitride materials with identical compositions but different microstructures were determined as a function of impacting particle (SiC) kinetic energy and temperature (25–1000° C) using a slinger-type erosion apparatus. The coarse-grained silicon nitride had significantly better resistance to impact damage than the fine-grained material. Crack-microstructure interactions were characterized using scanning electron microscopy and showed that crack-bridging was an important toughening mechanism in the coarse-grained material. Post-impact strength data were significantly less than those predicted from the indentation-strength data, due to impact flaws linking up prior to fracture. Consistent with its greater fracture resistance, the erosion rate of the coarse-grained material was less than that of the fine-grained material for erosion at 25 deg, and was independent of erosion temperature.     

Fabrication of cellular structure composite material from recycled soda-lime glass and phlogopite mica powders

A homogeneous composite material with different physical structures has been fabricated from recycled colourless soda-lime glass powders and phlogopite-type mica powders by mixing the two powder components and sintering the mixture at a temperature above 850° C for a period of 30 min or longer. The physical structure of the composite material can be fabricated into either a cellular structure consisting of both closed and open cells or a highly densified ceramic body. The cellular structure composite material is found to have a compressive strength of about 0.877 MN m^–2 and thermal conductivity values in the range of 0.290 to 0.306 W m^–1 °C^–1 when measured at temperatures in the range of 25 to 100° C. The highly densified composite material, on the other hand, is found to have a compressive strength of about 53.0 MN m^–2 and thermal conductivity values in the range of 0.198 to 0.250 W m^–1 °C^–1. The composite material, when compared with other common building materials, is found to be potential material for construction applications because of its superior mechanical and thermal properties.     

Effect of calcium phosphate glass on bone formation in calvarial defects of Sprague-Dawley rats

The purpose of this study was to investigate the bone regenerative effect of calcium phosphate glass in vivo. We prepared two different sizes of calcium phosphate glass powder using the system CaO-CaF₂-P₂O₅-MgO-ZnO; the particle size of the powders were 400 μm and 40 μm. 8 mm calvarial critical-sized defects were created in 60 male Sprague-Dawley rats. The animals were divided into 3 groups of 20 animals each. Each defect was filled with a constant weight of 0.5 g calcium phosphate glass powder mixed with saline. As controls, the defect was left empty. The rats were sacrificed 2 or 8 weeks after postsurgery, and the results were evaluated using radiodensitometric and histological studies; they were also examined histomorphometrically. When the bigger powders with 400 μm particle were grafted, the defects were nearly completely filled with new-formed bone in a clean healing condition after 8 week. When smaller powders with 40 μm particle were transplanted, new bone formation was even lower than the control group due to a lot of inflammatory cell infiltration. It was concluded that the prepared calcium phosphate glass enhanced the new bone formation in the calvarial defect of Sprague-Dawley rats and it is expected to be a good potential materials for hard tissue regeneration. The particle size of the calcium phosphate was crucial; 400 μm particles promoted new bone formation, while 40 μm particles inhibited it because of severe inflammation.     

Re‐Use of Marble Stone Powders in Producing Unsaturated Polyester Composites

The main goal of this study is to evaluate the potential of waste stone powders as filler in composite materials with a matrix of unsaturated polyester. These wastes are generated in the form of stone fragments and stone‐cutting sludge. Ground marble wastes are thoroughly characterized with the aim to use them as fillers: Mineralogical and chemical composition, particle size distribution, and morphology of these waste stone powders are investigated. Unsaturated polyester resin composites with the different stone powder fillers are prepared. The influence of powder type on the composites’ mechanical properties (tensile, bending, impact, and hardness characteristics), water resistance, thermal stability as well as surface fracture morphology of composites are studied. The moduli of the composites increase by 100%, the hardness of the composites may be improved by 80% upon loading with the “waste” filler, leading to an economical material and helping to reduce waste.

     

Erosion of polymers and polymer composites surfaces by particles

Surface erosion due to solid particle impact is a major concern in engineering applications of handling solid-particulate flow. A semi-empirical model is developed for numerical erosion simulation of polymers and polymer composites. The novelty of the developed model is the correct capturing of the angle of maximum erosion for different erosion modes of polymeric materials and relating it to measurable mechanical properties of the target materials. The model incorporates both the material removal due to elastic–plastic collision of the particles at oblique and normal impact angles. The oblique impact model is derived for ploughing and fracture governed mechanisms of material removal. A simplified correlation is used to consider the relative effect of each mechanism on the total erosion at oblique impact angles. The model indicates the variation in velocity exponent to the mechanism of material removal. The theoretically derived model for single-particle impact is correlated to the available experimental results of multi-particle impacts through the empirical coefficients. The predictions are in good agreement with the extensive literature data for polymers and polymer composites. Further, to propose a single model of erosion for polymer and its composite, the relationship between the empirical coefficients in the developed model and the target material properties is established.