Papers by Keyword: Ultra-Fine Powder

Abstract: The ultrafine glassy powder of Al-Si-Ca-P-O-F polynary system was prepared by liquid precipitation method with several inorganic compounds as reactants containing the ions such as Al3+, SiO32-, P3O105-, Ca2+, F-, respectively. The powder was heat-treated in the range of temperature from 773 to 1173K and its crystallized processes were ascertained. The morphology, composition, bonding state and structure, crystallized behavior of the glassy powder were characterized by means of TEM, XRD, EDAX, IR, DSC etc methods. The results show that the powder containing Al, Si, Ca, P, O, F elements belongs to typical amorphous state, and the particles appeared hollow and near spherical morphology with the size from 30 to 70nm. The hollow particles collapsed as plate like conglutination state and a series of crystallized phases CaF2, Al2SiO5, Ca2SiO4, and Ca3(PO4)2 were separated sequentially during heat treatment in the range of temperature above. The characteristics of the glassy powder are similar to those of popular melting-quenched glass of the system. The network structure of the glass was mainly formed by the tetrahedrons of [SiO4], [AlO4] and [PO4], which were linked by the oxygen atoms of the angle in the tetrahedrons.

Abstract: The preparation and characterization of silver powders with spheric shape and different sizes by chemical reduction of silver ions in the presence of ethanol amine using hydrochinone (C6H6O2) as the reducing agent are described. The size distribution, microstructure, and the phase composition of the obtained Ag Powders were characterized by the Laser Particle Size Analyzer, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the X-ray diffraction (XRD). The Ag powder was in face-centered cubic crystal structure with spheric morphology. The average tap density of silver powders is up to 4.0g/cm3. It was also found that the size of the Ag particles can be adjusted conveniently to a certain degree by varying the silver ions content, the addition amount of dispersing agent, the aging time, the temperature of the reaction, and the concentration ratio of hydrochinone to Ag+.

Abstract: Steady alkalescence monodispersed silicasol were obtained from sodium metasilicate by using chemical precipitation. The process employed low Zeta electric potential controlled growth to achieve big grain diameter 130nm. In this work, the best conditions of grain diameter growth were optimized, which included pH, reaction temperature, digestion time, and so on. The performances of the product have been studied by XRD, IR, Nano Particle Analyzer, ζ electric potential and SEM. Sphericity silica nanoparticles with good stability and high dispersion were obtained, which attained the standard of manufacturing production.

Abstract: Ultrafine NiFe2O4 particles with spinel structure were prepared in the system of water-in-oil microemulsion of water/Triton X–100/n-hexanol/cyclohexane. The effects of calcining temperature and the other operation conditions were systematically discussed based on the techniques of SEM, XRD, VSM and so on. The result showed that NiFe2O4 nanoparticles, with a narrow size distribution(30-70nm), could be obtained by microemulsion method. The crystal grain diameter of the ultrafine NiFe2O4 particles could be enhanced with the improvement of the calcining temperature, the molar ratio of water to surfactant (w=[H2O]/ [surfactant]) and the concentration of Fe3+(or Ni2+), respectively. The VSM plots showed that the ferrimagnetic behavior was expected for this type of magnetic material. The XRD patterns and DTA-TG curves revealed that the optimal calcining temperature of NiFe2O4 sample was at around 500°C. The relation between the average particle size (D) and the value of w could be expressed as D=13.911+0.2628w. Moreover, it was indicated that low concentration of Fe3+(or Ni2+) was beneficial to the formation of small and regular NiFe2O4 particles.

Abstract: Ultrafine MgAl2O4 powders have been successfully synthesized by solid-state reaction from the mixture of AlOOH and MgO at the lower temperature. The samples were investigated by DTA/TG、XRD and SEM analyses. The results showed that AlOOH can be decomposed into γ-Al2O3 from DG/TDA curves, which can improve the activity of Al2O3 and promote the process of solid-state reaction. The XRD analysis showed the single-phase MgAl2O4 was formed at 1400°C. Meanwhile it was detected by ICP-MS that the purity of powders was 99.995%. The SEM images showed that the mineralizer containing fluoride such as AlF3, NH4F can promote the resultant to grow into regular octahedrons and disperse the particles. The XRD analysis indicated the mixture containing 5% AlF3 can transform the integrated MgAl2O4 powders at 1200°C, nearly 200°C lower than general solid-state reaction. Furthermore, The SEM images showed that fluoride can crystal the fine particles into the larger MgAl2O4 crystals, about 0.5～1.5µm.

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

Abstract: [1] Chen Li, Wang Li-Ping, Zeng Zhi-Xiang, Xu Tao. Surf Coat Technol, 2006,201:599-605. doi:10.1016/j.surfcoat.2005.12.008 [2] Wei X Y, Zhu Z G, Prewett P D, Jiang K. Microelectron Eng, 2007,84:1256-1259. doi:10.1016/j.mee.2007.01.218 [3] Thiemig Denny, Lange Ronny, Bund Andreas. Electrochim Acta, 2007,52:7362-7371. doi:10.1016/j.electacta.2007.06.009 [4] Chang L M, An M Z, Guo H F, Shi S Y. Appl Surf Sci, 2006,53:2132-2137. doi:10.1016/j.apsusc.2006.04.018 [5] Feng Q Y, Li T J, Zhang Z T, Zhang J, Liu M, Jin J Z. Surf Coat Technol, 2007,201:6247-6252. doi:10.1016/j.surfcoat.2006.11.019 [6] Du L Z, Xu B S, Dong S Y. Wear, 2004,257:1058–1063. doi:10.1016/j.wear.2004.07.003

Abstract: The two cutting tools obtained from ultra-fine grade Ti (C,N)-based cermets were tested in the dry cutting of a medium carbon steel (AISI1045). Microstructure and mechanical properties were studied. Wear mechanisms (mainly diffusion and oxidation) were investigated in detail and compared each other in order to better understand key aspects due to thermal wear mechanisms. Comparing tool A with B, under the adopted cutting conditions, the tool A has a better resistance to oxidation deformation in machining medium carbon steel due to the higher hardness, although tool B has higher bending strength and fracture toughness.

Abstract: Ultrafine MgAl2O4 powders were synthesized by a nitrate-citrate sol-gel combustion process using Al(NO3)3·9H2O, Mg(NO3)2·6H2O and C6H8O7·H2O as initial materials. The result of X-ray diffraction (XRD) analysis indicated that single-phase MgAl2O4 powder could be obtained at 850 oC, which is much lower than that needed in solid-state reactions. Transmission electron microscopy image showed that the as-prepared powder was in the nano scale and little agglomerate exited. It is concluded that this process need shorter time, lower temperature, and simple equipments.

Abstract: The paper is dedicated to the study of the interdependence of structure and properties of sintered heterophase ceramic composition based on ultra-fine (nanosized) powders. The compositions based on brittle oxygen-free high-strength compounds under certain conditions are able to demonstrate micro-plasticity. Microstructure of such materials typically features homogeneous fine grains with certain critical maximum grain size. The substantial contribution of interphase boundaries and their dislocation structure to the non-trivial mechanical properties is discussed. Special features of interphase boundaries are demonstrated to contribute to the change in rupture resistance of the heterophase ceramics. Correlations between strength and elastic properties and results of tribological tests using «pin and disk» arrangement were studied. Increased fracture resistance, wear resistance, and micro-plasticity of heterophase ceramics is found to be due to the modification microstructure size parameters and distinctive features of interphase boundaries. The generally formulated purpose of the present study is a search for the solution to the problem of production of the advanced structural ceramic materials based upon oxygen-free refractory compounds with improved physical and mechanical properties.