Papers by Keyword: Powder

Abstract: Fine powder of Zn₃Nb₂O₈ was prepared by chemical co-precipitation using KOH, Nb₂O₅ and ZnSO₄·7H₂O as raw materials. Laser particle analyzer was used to investigate the precursor. It showed that the average size (D50) was 3.13μm, and the particle distribution ranged from 1.82µm to 4.47µm. TG-DTA and XRD showed that, the precursor yielded Zn₃Nb₂O₈ ceramics by calcined at 850°C, which was much lower than 1100°C, at which Zn₃Nb₂O₈ ceramics could be obtained by traditional solid state method. The sintering of as-obtained powers with Cuo-Bi₂O₃-V₂O₅ sintering aids results in producing Zn₃Nb₂O₈ ceramics with s density 94.20% of the theoretical, and a product up to 19.83 (at 30MHz) at sintering temperature 950°C.

Abstract: Two observation techniques of internal microstructure, including hole and second particle, of micron scale powders have been established and applied to frangible and tough powders. One is that powders were embedded in epoxy resin, sectioned by an ultramicrotome, then observed by using the transmission electron microscopy (TEM) in turn; another is that the fracture of powders were observed by using the scanning electron microscopy (SEM).

Abstract: La-doped barium titanate ceramics with 0~1.0 at.% La₂O₃ were prepared by conventional solid state reaction method. The crystal structure and dielectric properties of La-doped barium titanate ceramics were investigated. Lanthanum ions have entered the unit cell and substituted for Ba²⁺ ions on the A sites of perovskite structure. The a-axis lattice constant increases and the c-axis lattice constant decreases as lanthanum content increases. Addition of lanthanum leads to the fall of the Curie temperature of La-doped BTO ceramics. There are two different doping mechanisms for La-doped BTO ceramics. The dielectric loss of BTO ceramics with 0.3 at.% La₂O₃ is higher than that of pure BTO ceramics. When lanthanum content is above 0.5 at.%, the dielectric loss of La-doped BTO ceramics decrease with the increasing of lanthanum content. The result of dielectric constant as a function of temperature at different frequencies indicates that La-doped BTO ceramics are not relaxor ferroelectrics but ferroelectrics with diffuse phase transition.

Abstract: The sol - gel method is the effective technique to prepare high purity ultrafine alumina powder. Laser particle size analyzer and scanning electron microscopy were used to study the inflence of pH, leaching of precursor sol, surface modification of alumina powder on the secondary particle size. The impact of leaching sol on powder crystal was tested with X-ray diffraction. The results show that: aluminum nitrate solution showed different appearance with different pH values during titration aluminum nitrate solution with ammonia. When pH=3~5.5, the solution occur through no precipitation to the white precipitate, then the solution becomes relatively thin paste; when the pH was from 6.0 to 6.5, the solution becomes more thick paste. When the pH increased from 7.0 to 8.0, the solution has turned into a more dilute paste. The impact of pH on the particle size is: When the pH increased from 5.5 to 7.0, aluminum powder particle size gradually become thicker and larger. When the pH continues to rise, powder particle size is reduced, when the sol pH value is 8.0, it can get the smallest particle size for alumina powder, up to 548nm. Powder average particle size when adding TEA surfactant to sol is less than the sol without any surfactant particle size from the micrograph. Moreover, particle size is more uniform with TEA surfactant, but powder particle size which did not add surfactant to the sol is clear size differences and the dispersion is poor. When the sol containing surfactant, the effect of surface modification is not obvious. In the case of sol without surfactant powder particle size reduced after the surface modification, then powder surface modification is necessary, it can prevent the powder from congregating. The crystal type is relatively perfect and single α-Al2O3 after filtration, the crystal type without leaching is α-Al2O3 and γ-Al2O3, with a smaller particle size, crystal grain size is relatively smaller. If alumina sol isn’t be leached it contains ammonium nitrate, ammonium nitrate will decompose and release various gases during sintering, the gas emission has an crushed effect on the sintered powder.

Abstract: Characterization of feedstocks for powder injection molding of SiC_p-reinforced aluminium composite, as potential use for automotive and light-weight applications, has been studied in this research. Al-4.5 wt.% Cu powder, SiC_p and polymeric binder were pre-mixed and compounded using a twin screw extruder at 170oC prior to powder injection molding at 170 oC. Effects of varied solid loadings at 52, 55 and 58% on green properties of the feedstocks have been investigated. Experimental results showed that compounding followed by powder injection molding allowed uniform distribution of SiC_p surrounding the aluminium powder. It was found that higher solid loading improved bulk density while hardness values were observed to be similar. Molded specimens of 55% solid loading provided the optimum bend strength and strain at failure. Moreover, it was observed that the opposing abrasive property with angular shape of SiC_p resulted in SiC_p scratching effect, leading to irregular surface of aluminium powder after injection molding. This consequence and molding porosity were expected to be responsible for relatively low density of the molded specimens, giving the difficulty in molding at higher solid loading.

Abstract: Surface modifications using the powder mixed electric discharge machining (PMEDM) process has gained a lot of research interest in recent few years. The present paper investigates the material transfer from the powder suspended in dielectric, electrode and dielectric material for enhancing the surface properties measured in terms of the microhardness of the machined surface for two kinds of die steels (H11 and H13). Four different powder materials aluminium, copper, graphite and tungsten were mixed with dielectric during machining with three different dielectric materials namely kerosene, EDM oil and refined mineral oil. Other process parameters were varied at suitable levels. Maximum increase in microhardness was observed with addition of tungsten powder and with tungsten-copper electrode even at lower current. Current significantly affected the transfer mechanism of material on the machined surface but was dwarfed by the very significant affect of powder which had the largest contribution. A relative comparison of microhardness between deposited and non-deposited regions showed an increase of 37% for H11 and 56% for H13 due to addition of powder. The photomicrographs of the machined surface also supported the material transfer from powder, electrode as well as dielectric forming compounds that suitably improve the surface properties of H11 and H13 die steel.

Abstract: This paper investigates the effect of electric discharge machining (EDM) process parameters and powder mixed in dielectric on surface properties of three die steel work materials; namely High Carbon High Chromium (HCHCr), EN 31 and Hot Die Steel (HDS). The mechanism of material deposition from the suspended powder and/or tool electrode is reported. Current emerged as the most significant factor affecting the microhardness along with powder mixed in the dielectric and electrode material. Amongst the two electrode materials, copper-tungsten along with tungsten powder had the best microhardness. Selected samples were analyzed for X-ray Diffraction (XRD) followed by microstructure analysis using a Scanning Electron Microscope (SEM). The results showed significant material transfer from the electrode as well as powder either in free form or in compound form. It was concluded that surface modification of die steels can be done by incorporating simple modifications in the EDM set-up resulting in higher microhardness and superior wear resistance of the machined surface.

Abstract: Dense and submicron-sized hydroxyapatite powders were synthesized through spray pyrolysis of calcium phosphate solution with polyethylene glycol (PEG). Irregular shaped and fragile hydroxyapatite aggregates, and spherical and hollow hydroxyapatite particles were obtained after spray pyrolysis at 1100 °C when using calcium phosphate solution with and without PEG, respectively. After dewaxing at 650 °C for 3 hours, the hydroxyapatite aggregates were broken into submicron-sized particles whereas micron-sized spherical hollow particles were almost intact. The relative densities of hydroxyapatite disks made by submicron and micron sized hydroxyapatite particles were about 90% and 81%, respectively, after sintering at 1110 °C for 3 hours. The results were explained in terms of the disintegrating function of carbon which was previously formed among the hydroxyapatite aggregates by the decomposition of PEG during spray pyrolysis.

Abstract: The novel lithium enriched lithium tantalate (LiTaO₃) targets were papered by employing the sol-gel process and the high temperature sintered process. The sol of LiTaO₃ was firstly prepared through reacting lithium ethoxide with tantalum ethoxide. The LiTaO₃ powder was fabricated by presintered LiTaO₃ dry gel 4 hour, at 800°C. The 11cm13cm1cm lithium enriched LiTaO₃ target samples were prepared by sintered the pressed LiTaO₃ powder billet 4 hour in the 850°C muffle furnace. The density of the 5% overdose lithium enriched LiTaO₃ target is measured 5.96g/cm³. The XRD measured results show that the ion beam enhanced deposited (IBED) thin film samples using the prepared 5% overdose lithium enriched LiTaO₃ target have the polycrystal structure of LiTaO₃, but there has remanent Ta₂O₅ existed in the IBED thin film samples. The main reason for the remanent Ta₂O₅ growth was due to the stoichiometric proportion mismatch between Li and Ta in the IBED thin film samples during the high temperature annealed process, which caused the lithium oxide evaporation loss from the IBED thin film samples and made the proportion of Ta₂O₅ increase. After multipule repeated target prepared experiments, the 8.76% overdose lithium enriched LiTaO₃ target is suitable for fabricating the 550°C annealed IBED LiTaO₃ thin film. After the repeated process experiments, the suitable deposited process parameters of the IBED-C600M instrument for the 8.76% overdose lithium enriched LiTaO₃ target were obtained. The SEM micrographs of the 550°C annealed IBED LiTaO₃ thin films prepared by the 8.76% overdose lithium enriched LiTaO₃ target reveal the prepared thin films are uniform, smooth and crack-free on the surface, and the perfect adhesion between the thin film and the substrate. The successfully fabricated LiTaO₃ thin film samples verify the prepared processes of novel LiTaO₃ sputtering target are effective.

Abstract: The cement powder materials are evaluated by fractal theory. Fractal characteristic parameters are analysed and evaluated by the method of laser particle size analyzer, microscope, transmission electron microscope. In this paper, cement powder materials has good self-similarity. Fractal dimension of grading is tested and evaluated by laser particle size analyzer, fractal dimension of cluster is tested by microscope, fractal characteristic of particle distribution is tested by transmission electron microscope. Compared with traditional weight of screen residue and specific surface area, those methods are more careful. Fineness fractal parameters and activity of ultra fine fly ash and pulverized slag have good linear dependence relation that is evaluated by fractal dimensions. Fractal characteristics provide an important basis to further explore the inherent relation of cement powder materials and concrete material density effect.