Papers by Keyword: Powder

Abstract: Beta-spodumene glass-ceramic powder was prepared by Sol–gel route. Tetraethyl orthosilicate (TOES), aluminum nitrate, lithium carbonate were used as starting materials. X-ray powder diffraction (XRD), thermal expansion coefficient (TEC), scanning electron microscope (SEM) and transmission electron microscope (TEM) were utilized to characterize the dried LAS gels and glass-ceramic blocks. The results suggest beta-spodumene is the only crystals phase in the prepared LAS glass-ceramics powder when sintering temperature is 950 °C. The average particle size of the beta-spodumene crystal is about 30 nm with a narrow size distribution both in prepared LAS glass-ceramics powder and block. The thermal expansion coefficient of moulding pressed blocky LAS glass-ceramics is lower than 0.6×10^{-6 o}C^-1.

Abstract: In order to study temperature distribution of metal powder stream in laser fabricating, its thermal radiation in visible region was detected by CCD. Based on Planck’s radiation law, the relation between molten powder temperature and its visible thermal radiation could be set up. The thermal radiation image signal of powder stream was transformed to digital signal which was used to analyzing its temperature distribution. It was shown that crosswise dimension of molten powder was about 2.5mm in diameter at the distance of 5mm from power nozzle. The powder out from powder nozzle was heated rapidly by laser. Temperature of powder in central axis regions was the highest which was nearly 2000K at the power of 1100w. The temperature gradient of powder at the edge of laser stream was greatly. The measurement results could be used to optimize the design of powder nozzle and processing parameters of laser fabricating.

Abstract: The subject of the research was an alloy AlZnMg and AlCuMg with addition of Zr and Ag manufactured of powders by hot plastic consolidation in process of direct extrusion. Paper also presents results of research of structure evolution and mechanical properties for different tempers of precipitation strengthening and further plastic deformation, including hydrostatic extrusion. Obtained results R_m above 700MPa (for AlZnMg alloy) and above 500MPa (for AlCuMg alloy) shows significant possibilities of manufacturing from Al alloys powders products with ultrafine grain and nanometric structure which properties exceeding alloys manufactured with standard methods.

Abstract: Compare investigate physicochemical properties of fine powder and two ultrafine powders of Dragon’s Blood, and then to determinate particle size distribution for ultrafine powders of Dragon’s Blood. Specific surface area and porosity, surface morphology and moisture absorption of Dragon’s Blood powders were investigated. The content and the in vitro dissolution of dracorhodin in Dragon’s Blood powders were determined by HPLC. The results showed that the content of dracorhodin had no significant difference among three Dragon’s Blood powders. With the decreasing of particle size the degree of moisture decreased. The dissolution of dracorhodin in the order of: ultrafine powder I > ultrafine powder II > fine powder. An appropriate degree of superfine grinding can improve moisture absorption of Dragon’s Blood powders and dissolution of dracorhodin. Particle size distribution of Dragon’s Blood ultrafine powder should be controlled about 40 μm.

Abstract: This paper uses centrifugal spray drying process to prepare powder polycarboxylate superplasticizer. The best spray drying process: speed of centrifugal atomizer is 16000r/min, feed liquid temperature is 30°C, import / export air temperature of drying chamber is 200°C/80°C. It achieves a high concentration of polycarboxylate superplasticizer to prepare powder product. It solves the problem of sticky and low-performance of powder polycarboxylate superplasticizer during traditional preparation. Analyzing the structure of polycarboxylate superplasticizer before and after spray-drying by infrared spectroscopy, and verifying the conclusion through macroeconomic performance experiments.

Abstract: Pyrite nano-powder was synthetized in a high-pressure solvothermal process in the ethanediol solvent, with Fe(NO₃)₃·9H₂O and NH₂CSNH₂ as the raw materials. The sample was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the results show that the product has a pure phase in a typical cubic crystal. The effects of temperature, aging time and surfactant on the shape of the crystallites were investigated systematically. The nano-powder synthetized shows itself in various micro-shapes such as granule, globular and flake, with its diameter ranging from hundreds of nanometers to one micrometer.

Abstract: This paper investigates characteristics of heat transfer in Fe micrometer and nanometer powder. The understanding for thermal properties of the powder is advantageous to the advancement of the processing technologies such as laser cladding, laser sintering, powder metallurgy and its other applications. Nanosized particles possess characteristic physical and chemical properties different from those of bulk materials due to the confinement of electrons, excitons, and photons into small volumes. Therefore it is valuable to discuss the thermal behaviours of powders constituted by nanometer-sized particles. The powder is wrapped up in the slender tube. One end of the slender tube filled with powder is connected to the low constant-temperature reservoir and the other end is kept at room temperature. The temperature histories at the 1cm location of the slender tube from the low constant-temperature reservoir are recorded using thermalcouples. Powders of particles with the diameter sizes 20nm and 5000nm are employed in this experiment. The results show that the thermal diffusion in the 20nm Fe powder is faster than that in the 5000nm Fe powder.

Abstract: Li₄Ti₅O₁₂ powders were synthesized by solid state reaction of Li₂CO₃ and spherical composite powders of carbon and TiO₂ (denoted as C/TiO₂). C/TiO₂ powders were synthesized by spray pyrolysis of using lactic acid aqueous solution. The particle characteristics of Li₄Ti₅O₁₂ powders were determined by SEM, XRD and DTA-TG. DTA-TG showed that the carbon content was around 8 wt% in Li₄Ti₅O₁₂ powders. XRD revealed that the spinel structure (Fd3m) was obtained by heating at 750 °C under N₂ atmosphere. The first rechargeable capacity of Li₄Ti₅O₁₂ anode was about 160 mAh/g at 1 C. That of Li₄Ti₅O₁₂ anode decreased to 90 mAh/g at 20 C. The rechargeable capacity of Li₄Ti₅O₁₂ anode decreased with increasing the rechargeable rate, but 81% of initial discharge capacity of Li₄Ti₅O₁₂ anode was retained after 200 cycles at 1C

Abstract: The paper presents test results concerning characteristics of the selected thermal properties of ceramic powders based on rare earth zirconates with a pyrochlore structure of RE2Zr2O7 type, intended for thermal spraying of TBCs. Gadolinium, lanthanum, samarium and neodymium based powders were tested. The scope of the tests encompassed thermal diffusivity analysis of the powders in a compressed pellets form within temperature range 25-1500°C, and also tests of specific heat and thermal expansion coefficient within similar temperature range. Standard powder of 8YSZ type on the basis of zirconium oxide modified with yttrium oxide was used as a reference material. Specific heat measurements of the powders showed that the highest values within the entire test temperature range were obtained for the standard YSZ type powder. In the case of new type of powders, the results obtained are very similar and only slightly lower in comparison with YSZ powder. The lowest values were obtained for the samarium based powder (temperature range corresponding to operating temperature). Character of the curves obtained do not show course of strong reactions connected with phase changes. Dilatometric tests of materials made it possible to determine thermal expansion coefficient. Mean coefficient values are included within the range from 5.5 x 106mm/°C to 10.0 x 106mm/°C. The highest mean value of thermal expansion coefficient was obtained for Nd2Zr2O7 powder and the lowest one for La2Zr2O7 powder. The lowest thermal diffusivity value at room temperature was shown by Nd2Zr2O7 powder, and the highest one by 8YSZ powder (0.215 mm2/s).

Abstract: The specific properties of material, such as resistance, the cost and the weight, become key factors in the decision making and the choice of vulgarization of material in its industrial and technological aspect. The choice of a resinous system used like stamps in the design of composites, depends on the mechanical performances and the cost of the resin. Currently the prohibitory cost of composite materials slows down the rise of their applications in certain technical fields. In this study, the physical and the mechanical characterization is presented, bearing on the resin of the type RESOW 55 E reinforced out of powders of different nature at different rate. The results of the mechanical tests carried out, show clearly, that the fracture is strongly influenced by the type and the rate of powder added in the matrix. In reinforcement, according to the results obtained with x-rays, one notes that there are no new chemical compounds formed in elaborate materials. The presence of powder does not modify the structure of polymer and that is confirmed by the x-rays analysis and spectrometric analysis. Based on experimental results, a model of Weibull strength distribution function has been established for each specimen. Finally, a confrontation of the theoretical and experimental results is carried out, based on probabilistic models.