Papers by Keyword: Ultra-Fine Powder

Abstract: YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by co-precipitation method and hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that the precursor powder prepared via the co-precipitation method is mainly from amorphous to crystalline transition with the increasing calcination temperature, the precursor agglomeration is more serious, In the process of increasing the calcination temperature, the dispersibility of the roasted powder is greatly improved, which is favorable for the growth of the crystal grains, so that the particle size of the powder is gradually increased, the YAG precursor prepared by the co-precipitation method is transformed into YAG crystals, the phase transition occurs mainly between 900 and 1100°C. When the molar ratio of salt to alkali is Y³⁺: OH^-=1: 8 via the hydrothermal reaction, the YAG particles with homogeneous morphology can be obtained. When the molar ratio of salt and alkali is increased continuously, the morphology of YAG particles is not obviously changed. The co-precipitation method is easy to control the particle size, the hydrothermal method is easy to control the particle morphology.

Abstract: YAG materials has a number of unique properties, the application is very extensive. In this paper, the superfine YAG powder materials were prepared by hydrothermal precipitation method. The influence of synthesis process on the morphology of the powder was investigated. The results showed that when the molar ratio of salt to alkali that Y³⁺: OH^- is 1:8, the more uniform morphology of the particles can be prepared, when the molar ratio of salt to alkali is increased, the morphology of the particles will not change. The reaction time is longer, the particle size will be thicker. The smaller the concentration of Y³⁺ ions is, the larger the particle size will be small. The experimental results show that the rod-like particles have a poly-crystal structure at the reaction temperature of 200°C, reaction time of 2 days and the molar ratio of salt to alkali of 1:8. The diameter of the rod-like particles is most of the powders have a particle size of 1000 nm and a small amount of powder has a particle size of about 5000 nm. The purity of powder is higher through the test of XRD.

Abstract: As a new candidate material for the ceramic layer in thermal barrier coatings (TBCs) system, La₃NbO₇ was synthesized with La₂O₃ powder and Nb₂O₅ powder by solid state reaction. The stating powders with a mole ratio of La to Nb of 3:1 were mixed and then the mixture was calcined under the different temperatures(800°C, 1000°C, 1200°C) and dwell times(2h, 6h, 10h). The phase structure of the powder was observed by X–ray diffraction(XRD), and the microstructure of the sample was observed by scanning electron microscope(SEM). The effect of calcination temperature and dwell Time on the phase formation were examined. The results indicate that the La₃NbO₇ powder with single phase can be synthesized successfully at 1200°C for 10h in air, and the La₃NbOsub>7 powders synthesized have an ultra-fine particle size of 0.5˜1µm with a granular particle shape. With the temperature increasing, LaNbO_{4/sub> was synthesized firstly and then La3}NbO₇ was synthesized with a mole ratio of La₂O₃ to LaNbO₄ of 1:1.

Abstract: Al(OH)3 ultrafine powder was extracted from fly ash with the method of dispersing agent-carbonizating. Fly ash is activated by the method of sintering with limestone, so the inert mullite can be convert into C₁₂A₇ which can be dissolved in Na₂CO₃ liquor. The conversion of β-C₂S to γ-C₂S is accompanied by an increase in volume and results in the self-pulverization of the sintering feed, and the diameter of the self-pulverized powder is below 1μm. Na₂CO₃ liquor was used to leach Al₂O₃ in the form of NaAlO₂ from the self-pulverized powder. High performance dispersing agent is added in the carbonation process to control the crystal and aggregation of Al(OH)₃, and the ultrafine powder of Al(OH)₃ is prepared, which diameter is less than 0.4μm.

Abstract: The particle diameter and luminous intensity of aluminum powder were measured by laser analyzer and photo-effect tester. The luminous intensity of [Ba(NO3)2＋Al] illuminant were studied for different shape and diameter of aluminum powder as well as ultra-fine powder prepared by chemical method. The results show that the luminous intensity increases with particle size reduced, and luminous intensity of non-spherical aluminum is more than that of spherical aluminum. The change rate of luminous intensity increases rapidly when particle diameter was less than 2μm. It’s change rate in [0.6，2.13] is 4.37 times that in [2.13，4.24] interval.The ultra-fine aluminum powder and the submicron aluminum powder can effectively enhance the luminous performance of pyrotechnics.

Abstract: The rheological behavior of sub-micron zinc oxide and alumina mixture powders aqueous suspension has been investigated over a wide range of volumetric solids loading (Ø = 0.2–0.55), in which polyacrylic acid (PAA) was used as a dispersant. The dependence of relative viscosity (η_r)–solids loading (Ø) determined experimentally was compared with models. The experimental results showed that the suspension apparent viscosity (η) reached a minimum as the dispersant addition reached 0.2 wt%, the viscosity increased with the solids loading and the rheological behavior of the suspension was content basically with the model proposed by Liu. From η_r–Ø relationship the maximum solid loading (Ø_m) was estimated to be 0.55, which was in accord with our experimental results.

Abstract: The effect of carrier gas temperature on entrainment characteristics of Geldart group C powder from solid mixtures (groups A and C) were investigated in a fluidized bed, which was 40mm in inner diameter and 150mm in height. Silicon powder of mean size 2.2μm was adopted as entrained material (group C), hollow alumina pellets of mean size 775μm were used as coarse particles (Group A), and industrial nitrogen (99.5%) was applied as carrier gas. mixture of silicon powder (50g) and alumina pellets (50g) were used as bed materials. The nitrogen flow rate varied from 1.5m³/h to 2.5m³/h, and the nitrogen temperature varied from 60°C to 120°C. The experimental results revealed that the bed materials were in good fluidizaton state at all of the experimental conditions. At given nitrogen flow rate, the entrainment rate constant and powder gas ratio increased at the same rate as the nitrogen temperature increased. When nitrogen temperature increased from 60°C to 120°C, the entrainment rate constant and powder gas ratio increased over 140%. The phenomena indicted that increasing carrier gas temperature was an effective method to improve entrainment characteristics of ultrafine powders.

Abstract: In order to prepare ultrafine La₃NbO₇ powder, a potential material for thermal barrier coatings, the calcination process of La₃NbO₇ was studied in this paper.The precursor of La₃NbO₇ was synthesized by using a citric acid complex method. A calcination process had been systematically investigated. The reaction temperature was determined by differential scanning calorimetry (DSC). The phase composition of powders was characterized by X-ray diffraction (XRD), and the morphology was obtained by scanning electron microscope (SEM). The results revealed that the single-phase La₃NbO₇ powder could be successfully prepared while the calcination temperature exceeded 800°C and a better morphology could be maintained at 800°C for 4 hours. Considering all above, an optimum calcination scheme was adopted at 800°C for 4 hours. The as-prepared La₃NbO₇ powders had a grain size of about 50nm and an average particle size of about 300nm.

Abstract: The ultrafine bio-glass powder of Si-Al-Ca-P-F^- polynary system was prepared by sol-gel method with organic and inorganic compounds such as Si (OC₂H₅)₄, (C₂H₅)₃PO₄, Ca (NO₃)₂·4H₂O, Al (NO₃)₃·9H₂O and NH₄F. The powder was heat-treated at the different temperature in the range from 200 to 900°C and its crystallized transition was ascertained. The morphology, composition, structure state and crystallized behavior of the glassy powder were characterized by means of TEM, XRD, EDS, DSC-TG, FT-IR etc methods and compared with the glassy powder of the same system by melting-quenching and liquid precipitation. The results show that the powder containing elements Si, Al, Ca, P, F and O belongs to typical amorphous state, and is composed of the near spherical particles with the size from 100 to 400nm; The transition temperature of glass was about 580°C, and the crystallized phase CaF₂ precipitate firstly above 600°C; A series of crystallized phases Ca₅(PO₄)₃F and Ca₅(PO₄)₂SiO₄ were separated sequentially with increasing temperature; The network structure of glass is similar to that of melt-quenching or liquid precipitation glass.

Abstract: Micron, sub-micron and nanometer sized MgO•Al2O3 ultra-fine powders were prepared by gel precipitation, solid-phase synthesis, sol-gel and flame throwing pyrogenation methods. XRD analysis showed that all of the ultra-fine powder is pure with the single MgO•Al2O3 spinel phase. The powder size was measured by laser granularity analyzer and the average size is 1780, 505 and 60 nm with a quite uniform distribution of particle size. MgO•Al2O3 spinel powder with different granularity were sprayed into molten low carbon steel in MgO crucible and MoSi2 furnace at 1873 K. Quantitative microscopic examination showed that big particle inclusions reduce and small particle inclusions increase, as a result, the average size reduce. Data comparison from spraying powders with different size showed that spraying MgO•Al2O3 of nanometer tends to cause more small inclusions in molten steel. The sprayed steel samples were rolled and heat treated for the mechanical properties tests, which showed spraying nanometer MgO•Al2O3 is the best way to improve mechanical property of steel.