Effect of inorganic-organic composite coating on the dispersion of silicon carbide nanoparticles in non-aqueous medium

In order to disperse silicon carbide (SiC) nanoparticles homogeneously in a non-aqueous medium, the surface of SiC nanoparticles needs to be modified via surface organic functionalization. A method of SiC nanoparticle surface modification by grafting of polyacetals via inorganic-organic composite coating was developed. The resulting graft percentage of up to 10.5% was much higher than that of direct grafting. The inorganic-organic composite coating on a SiC nanoparticle surface led to an almost complete decomposition of the secondary structure of the agglomerates and the formation of the primary structure. Dispersibility of the modified version was studied by using a transmission electron microscope (TEM) and size distribution analyser. The sedimentation experiments showed that the coated SiC nanoparticles exhibited good suspension stability in butanone. The composition of the inorganic-organic composite coating on the SiC nanoparticles was investigated by energy dispersive x-ray analyses (EDX), hydrogen nuclear magnetic resonance ((1)H NMR) and Fourier-transformed infrared spectroscopy (FT-IR). This work provides a novel concept of surface grafting modification for non-oxide nanoparticles to improve their dispersibility in non-aqueous medium.     

One-step mechanical synthesis of the nanocomposite granule of LiMnPO4 nanoparticles and carbon

The nanocomposite granule of LiMnPO₄ nanoparticles and carbon were directly and rapidly created from the starting powder materials by one-step mechanical method without extra heat assistance. The primary particle size and the granule particle size obtained by this method were less than 20 nm and around 20 μm, respectively. The granules could be compacted easily to be the electrode for high packing density. The cathode electrode made by the granules also consisted of the network structure of LiMnPO₄ and that of carbon, thus reduced the lithium ion diffusion path and achieved high electron conductivity. Although, the specific capacity was still 60% of the theoretical capacity, it is expected to be innovative energy-saving process for manufacturing lithium ion batteries by better control of the granule structure in future.     

Ultrasonic assisted fabrication of particle reinforced bonds joining aluminum metal matrix composites

This paper presents a method of producing uniform particle strengthened bonds between pieces of aluminum metal matrix composite (Al-MMCs), of strength equal to that of the substrate material. SiC particle reinforced Zn-based filler metals were fabricated by mechanical stir casting and ultrasonic treatment, and then used to join pieces of SiC_p/A356 composite with the aid of ultrasonic vibration. The filler metals made by mechanical stirring were porous and contained many particle clusters. Ultrasonic vibration was used to disperse the agglomerates and prevent further coagulation of SiC particles during joining, but the method failed to eliminate the porosity, resulting in a highly porous bond. The filler metal treated by ultrasonic vibration was free of defects and produced a non-porous bond strengthened with uniform particles between pieces of SiC_p/A356 composite. The presence of surface oxide films at the bonding interface significantly degraded the performance of SiC particle reinforced bond. Removal of this oxide film by at least 4 s of ultrasonic vibration significantly increased the bond strength, reaching a value equal to that of the substrate metal.     

歧化反应及置换反应制备Cu/纳米SiC复合粉体

为了实现Cu对纳米SiC的表面包覆改性,分别采用歧化反应和置换反应两种方法制备了Cu/纳米SiC复合粉体.利用扫描电子显微镜、透射电子显微镜和能谱仪研究了Cu/纳米SiC复合粉体的微观形貌、聚集状态、粒径以及Cu和纳米SiC的质量分数.实验结果表明:单个复合粒子的粒径约为100 nm;针对随机选择的两种方法制备的复合粉体的两个不同区域进行的分析表明,歧化反应条件下Cu的质量分数分别为37%和35%,成分均匀;置换反应条件下Cu的质量分数分别为79%和25%,成分差异大.歧化反应法比置换反应法的包覆效果好,实现了Cu对纳米SiC的均匀性包覆.     

Physical aspects of wet granulation III. effect of wet granulation on granule porosity

Abstract

The porosity of granules produced by wet granulation has been studied using mercury porosimetry. Granule pore size distribution appears to be bimodal, with a population of micropores and macropores. Pore surface area varies with kneading time, going through a maxima at a point where physical properties such as flow and bulk density also exhibit a maxima. True granule density displays a direct relationship to rate of flow. The information in general supports the postulate that equilibrium microporous granules are formed first in the wet granulation process, followed by consolidation with subsequent formation of microporous twins and agglomerates.     

The effect of foam polystyrene granules on cement composite properties

Crumbled recycled foam polystyrene waste as well as spherical large and fine blown polystyrene waste is used to produce the filler for a light thermo-insulating composite, the matrix of which is light foam cement. For better cohesion, fillers are hydrophilizated with foam cement surfactant solution.Polystyrene granules and foam cement concrete interaction schemes are discussed. The investigation of foam cement concrete and polystyrene granule contact zone showed that the contact of these two materials is very close, without any fractures or microcracks. Adherence of the two components depends on the size and shape of granules used.When a polystyrene granule is ripped out of foam cement concrete, the emerged “hole” closely repeats the structure of the granule and there is some polystyrene residue left in it. This proves the fact that foam cement concrete contact zone is stronger than the polystyrene granule material. When fine polystyrene granules are used, it disintegrates along the contact zone. Such composite has the lowest adhesion strength, however, it is stronger in comparison with a composite, made with different foam polystyrene granules, provided by better macrostructure. Strength and thermal conductivity of the composite depend on its density, the filler, its sort and amount used, and is defined by regression equations.     

Ni-金刚石复合涂层的结构优化及基础磨削性能

采用电沉积技术在304不锈钢基体上制备了Ni-金刚石复合涂层。通过金刚石掺入量、加厚镀时间优化了金刚石复合涂层结构,利用球-盘式摩擦磨损试验仪研究了优化后的金刚石复合涂层对不同材料偶件(GCr15、SiC、304不锈钢)的磨削性能。结果表明:金刚石掺入量为1.5g/L时,金刚石上砂均匀且密集;加厚镀15min时,金刚石埋入率约为2/3,附着强度较好,适合磨削加工;GCr15、SiC、304不锈钢3种材料偶件的磨损体积依次减小,分别为:0.353 76mm~3、0.315 90 mm~3、0.194 01 mm~3,金刚石复合涂层对GCr15有较好的磨削性能;金刚石复合涂层磨削GCr15、SiC、304不锈钢均发生了磨粒磨损,此外,GCr15还发生了微弱的化学磨损,不锈钢发生了较明显的化学磨损和粘着磨损。     

Fabrication of titania/hydroxyapatite composite granules for photo-catalyst

The titania/hydroxyapatite composite granular photo-catalyst with novel microstructure was fabricated by the process based on the liquid immiscibility effect and followed by precalcination and hydrothermal treatment from commercially available powders of α-Tri-calcium phosphate and TiO₂. XRD, SEM, BET, optical microscopy and UV-vis spectrophotometer were applied to characterize the prepared photo-catalyst. Microstructure analysis indicated that the granule was weaved by rod-shaped hydroxyapatite crystals whose surface was covered by nano-sized TiO₂. In the composite granules, the active surface of anatase was retained effectively. With the hybridization of TiO₂ and HAp, a 16-nm blue-shift of absorption edge could be observed and the crystallinity of anatase could be enhanced by precalcination. The granules with the rod-shaped hydroxyapatite crystals performing as scaffold work as three-dimensional high porous, size-controllable small reactor. The phase and microstructure transformation of the granule before and after hydrothermal treatment was investigated and its decomposition ability was evaluated by using Methylene blue as a target pollutant compound.     

Physical aspects of wet granulation III. effect of wet granulation on granule porosity

The porosity of granules produced by wet granulation has been studied using mercury porosimetry. Granule pore size distribution appears to be bimodal, with a population of micropores and macropores. Pore surface area varies with kneading time, going through a maxima at a point where physical properties such as flow and bulk density also exhibit a maxima. True granule density displays a direct relationship to rate of flow. The information in general supports the postulate that equilibrium microporous granules are formed first in the wet granulation process, followed by consolidation with subsequent formation of microporous twins and agglomerates.     

Influence of SiC, Si3N4 and Al2O3 particles on the structure and properties of electrodeposited Ni

The structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si₃N₄ and Al₂O₃ were compared. A comparison was made with respect to structure, morphology, microhardness and tribological behaviour. The coatings were characterized with optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) technique. The cross-sectional microscopy studies revealed that the particles were uniformly distributed in all the composites. However, a difference in the surface morphology was revealed from SEM studies. The microhardness studies revealed that Si₃N₄ reinforced composite showed higher hardness compared to SiC and Al₂O₃ composite. This was attributed to the reduced crystallite size of Ni — 12 nm compared to 16 nm (SiC) and 23 nm (Al₂O₃) in the composite coating. The tribological performance of these coatings studied using a Pin-on-disk wear tester, revealed that Si₃N₄ reinforced composite exhibited better wear resistance compared to SiC and Al₂O₃ composites. However, no significant variation in the coefficient of friction was observed for all the three composites.     

Evaluation of Binder Activities on the Physical Properties and Compression Characteristics of Granules Prepared by Two Different Modes

Abstract

The effects of various binders and binder concentrations in production of granules by two different granulation modes were first investigated on the basis of the granule size distribution. Increasing the amount of binder produced larger and less friable granules associated with a decrease in flow rate and an increase in angle of repose. The strength of granules prepared by either the wet conventional or the fluidized bed was a function of its mean particle diameter and of binder-content with the later factor being more predominant. The inclusion of paracetamol into the placebo formula decreased the granule crushing strength. The effect was more pronounced with smaller granules and decreased with increasing granule size.

The rank order of the paracetamol-PVP granules crushing strength was reversed for the tensile strength of their corresponding tablets, viz., the paracetamol-PVP tablets prepared from fluidized granulation exhibited a higher tensile strength than that compressed from wet granules. A new parameter index “ø_b index” which combines tablet characteristics is presented. The index proposed allowed an overall simpler quantitative evaluation of a binder activity. Incorporated into this index are four tablet parameters, viz., tensile strength, percent porosity, median dissolution time, and percent friability. A higher “ø_b, index” infers better physical properties of tablets. Binders used in this study are then classified according to this index: PVP > gelatin > PEG 6000.     

Role of dispersion conditions on grindability of yttria stabilized zirconia (YSZ) powders

A precursor for zirconia - 8 mole% yttria (YSZ-ZrO₂-8 m% Y₂O₃) powder was prepared by coprecipitation and the calcination temperature was fixed as 900°C from TG-DTA and XRD studies. The calcined powder could be dry ground only to a mean particle size (D₅₀) of 6 Μm containing substantial amount of coarse agglomerates in the size range 10–100 Μm. The dispersion conditions for its wet grinding were evaluated through zeta-potential and viscosity studies. The zeta-potential variation with pH of the aqueous suspensions of the powder exhibited maximum numerical values at 3 and 11 pH, exhibiting the ideal pHs for dispersion stability through electrostatic columbic repulsion mechanism. Slurries of dry ground powders with solid concentration in the range 15–30 vol.% exhibited pseudo-plastic flow characteristics, indicating presence of flocculates. With progress of grinding, the increase in viscosity of the slurries became less significant with decreasing solid concentration. Even though the particle size of the ground slurries decreased with decreasing solid content, there was little change in it for slurries with solid content < 20 vol.%. Grinding conditions for formation of sinter-active powders of YSZ with sub-micron size (D ₅₀ ∼ 0.7 Μm free of agglomerates of size > 5 Μm) were established. Compacts from this powder could be sintered at 1400°C to translucent bodies with 99% theoretical density.     

Ball milling-induced reduction of MoS2 with Al

The ball milling-induced reduction of MoS₂ by Al has been investigated. Although this is a highly exothermic reaction that, based on its thermodynamic properties, should progress as a self-sustaining process, ignition could not be achieved by ball milling. In order to identify the reason, XRD, particle size distribution, SEM, and DTA measurements were carried out on a series of samples milled for different durations. It was found that the largest composite agglomerates broke up due to the presence of a fine dispersion of MoS₂ particles. SEM also revealed that the grains are packed rather loosely within the agglomerates. These results indicate that a self-sustaining process can take place only if large and well-compacted composite particles are present.     

Development of Al356/SiCp cast composites by injection of SiCp containing composite powders

One of the great challenges of producing cast metal matrix composites is the agglomeration tendency of the reinforcements. This would normally result in poor distribution of the particles, high porosity content, and low mechanical properties. In the present work, a new method for uniform distribution of very fine SiC particles with average size of less than 3 μm was employed. The key idea was to allow for gradual in situ release of properly wetted SiC particles in the liquid metal. For this purpose, SiC particles were injected into the melt in three different forms, i.e., untreated SiC_p, milled particulate Al–SiC_p composite powder, and milled particulate Al–SiC_p–Mg composite powder. The resultant composite slurries were then cast from either fully liquid (stir casting) or semisolid (compocasting) state. Consequently, the effects of the casting method and the type of the injected powder on the microstructural characteristics as well as the mechanical properties of the cast composites were investigated. The results showed that the distribution of SiC particles in the matrix and the porosity content of the composites were greatly improved by injecting milled composite powders instead of untreated-SiC particles into the melt. Casting from semisolid state instead of fully liquid state had similar effects. The average size of SiC particles incorporated into the matrix was also significantly reduced from about 8 to 3 μm by injecting milled composite powders. The ultimate tensile strength, yield strength and elongation of Al356/5 vol.%SiC_p composite manufactured by compocasting of the (Al–SiC_p–Mg)_cp injected melt were increased by 90%, 103% and 135%, respectively, compared to those of the composite manufactured by stir casting of the untreated-SiC_p injected melt.     

Thermal analysis and mechanical properties of Sn–1.0Ag–0.5Cu solder alloy after modification with SiC nano-sized particles

The size and morphology of intermetallic compounds (IMCs) of Sn–1.0Ag–0.5Cu (SAC105) solder alloys can have a significant influence on the mechanical strength of solder joints. The aim of the present study is to investigate the influence of SiC nano-particles addition on the microstructure, thermal behavior, and corresponding mechanical properties of SAC(105) solder alloys. Results show that the addition of SiC nanoparticles into the SAC(105) alloy melt prompts the formation of primary β-Sn phase with small sub-grain size in the solidified structure. The SiC nanoparticles can offer an additional nucleation sites for the formation of refined Ag₃Sn and Cu₆Sn₅ IMCs. The hard SiC particles and refined IMCs with small spacing could obstruct the dislocation slipping and thus, lead to a strong dispersion strengthening mechanism in the composite solder. As a result, the composite SAC(105)/SiC solder displayed a higher ultimate tensile strength and 0.2 % yield strength (0.2 %YS) than that of plain SAC(105) solder. The addition of SiC nano-sized particles can also effectively reduce the undercooling and pasty range, while the melting temperature is maintained at the SAC(105) level, indicating that the novel composite solder is fit for existing soldering process.     

Effect of calcinations of starting powder on mechanical properties of hydroxyapatite–alumina bioceramic composite

The effect of calcinations of starting powder on the mechanical properties of hydroxyapatite (HA)-based bioceramic composite was investigated. The calcinations of HA powder in air at 900 °C increased the crystallinity as well as the size of the powder. Ball milling after the calcinations was effective in eliminating large agglomerates in the powder. When the powder was mixed with reinforcing Al₂O₃ powder, the mixture became fine and homogeneous. The flexural strength of HA–Al₂O₃ composite was increased by the calcinations processes at all the Al₂O₃ concentration. However, the fracture toughness was not much influenced by the calcinations. These results lead to the conclusion that the calcinations process effectively reduced the critical flaw size in the body by removing the agglomerates in the HA powder.     

Electric discharge hole grinding in hybrid metal matrix composite

Moving toward a hybrid approach, a hybrid process, electric discharge hole grinding (EDHG) was used to machine a hybrid metal matrix composite (MMC) (Al6063/SiC/Al₂O₃/Gr). Here, holes were drilled and ground in a single step process (EDHG) using a novel tool electrode. The experiments were designed using response surface methodology (RSM). The objective of this study was to investigate the effect of electric discharge diamond hole grinding operation on the surface roughness (SR) of the hole. The input process parameters were current, duty factor, tool speed and flushing pressure. It was found that the process is very effective in producing a finished hole. A comparison of surface roughness was made between electric discharge drilling (EDD) and electric discharge diamond hole grinding, thereby showing the effectiveness of the electric discharge diamond hole grinding process. The grinding action of the process is clearly visible in the scanning electron microscopic (SEM) image. It was observed that the craters, globules of resolidified material and micro cracks, which are normally seen on surfaces machined by electric discharge machining (EDM), are completely ground off by electric discharge diamond hole grinding.     

Thermal and grinding induced residual stresses in a silicon carbide particle-reinforced aluminium metal matrix composite

The residual stresses in a silicon carbide particle-reinforced aluminium (SiC_p/Al) metal matrix composite (MMC) were measured using the X-ray diffraction method. The thermal residual stresses induced by annealing were found to be hydrostatic tension for the Al matrix and hydrostatic compression for the SiC reinforcement. After grinding treatment, the force equilibrium between these hydrostatic stresses was disturbed and compressive stresses were measured in both constituents. The effect of grinding extended into the bulk, and depth profiles of the residual stresses in both constituents were obtained by layer removal. The behaviour exhibited in these depth profiles is explained and their usefulness is indicated.     

Effect of fiber orientation on surface microscopic characteristics of surface grinding of unidirectional C/SiC composites

Ceramic matrix composites have complex structures. For exploring the impact factors of machined surface quality and material removal mechanism, its internal structure must be decoupled, and then a unidirectional C/SiC composite was designed and fabricated in this paper. Through a series of representative surface grinding experiments, the machined surface of the composites was characterized by 3D profile test, and the microscopic characteristics and material removal mechanism of the grinding surface were discussed in detail. The results showed that the fiber orientation had a significant effect on the surface quality, and the order of 3D surface roughness was longitudinal > normal > transverse. On the basis of the systematic analysis of the microscopic characteristics of the machined surface, the brittle fracture was the dominant form of material removal in grinding process. Further, combined with 3D surface profile and surface micromorphology, the effect of fiber orientation on the removal mechanism of composites was revealed. The results not only enrich the machinability and improve the surface quality of unidirectional C/SiC composites, but also provide some guidance for grinding of the woven composites.     

Incorporation of new technique for processing of Al/SiCp composites based on evaporative pattern casting (EPC) method

Abstract

A336 Al matrix composites containing different volume fraction and mean mass particle size of SiC particles as the reinforcing phase were synthesised by evaporative pattern casting (EPC) route. The process consisted of fabricating of EPS/SiC_p composite pattern followed by EPC of A336 Al alloy. The EPS/SiC_p pattern was made by blending SiC particles with expandable polystyrene (EPS) beads and placing them in expanding mould heating with steam until EPS beads expand completely. Uniform distributed SiC particles around the EPS beads and locally movement of them during pouring and degradation leads to homogenous distribution of particles in final Al/SiC_p composite. Higher modulus, strength and hardness were observed in the composites than the unreinforced Al alloy part. The fracture surfaces of the composite samples exhibited dimple surfaces and fracture in SiC particles.