Progress in Powder Metallurgy

Abstract: A hyrdrothermal reaction process has been developed to prepare rod-like crystals of copper oxide using copper nitrate trihydrate as a function of synthesis temperature, stirring speed and solution pH value. The properties of the fabricated crystals were studied using scanning electron microscopy, X-ray diffraction and particle size analysis. The morphology of the synthesized CuO was dependent on both the pH value of the solution and the morphology of the seed materials. Synthesized particles have regular morphologies and a uniform size distribution.

Abstract: TiO2 nanoparticle was synthesized by the flame method using a metal organic precursor of titanium tetraisopropoxide (TTIP, Ti(OC3H7)4), which was controlled by varying the ratio and flow rate of gas mixtures consisting of oxygen (oxidizer), methane (fuel) and nitrogen (carrier gas). The morphology and the size distribution of nanoparticles were observed with TEM and FESEM, and the phase evolution was analyzed by XRD measurement using a monochromator. The crystalline phases of TiO2 nanoparticle depended strongly on the temperature distribution in the flame, whereas the morphology was not sensitive. During the flame synthesis of TiO2 nanoparticle, anatase TiO2 nanoparticle was predominantly synthesized at the high flame temperature and rapid flame cooling condition. The low flame temperature and long flame length enabled to form almost rutile TiO2 nanoparticle (>95%). The anatase nanoparticle was formed by a homogeneous nucleation and has finally kept the anatase phase without the phase transformation any more in the flame. However, the rutile TiO2 nanoparticle was not formed directly and homogeneously in flame, and was manufactured by the phase transformation such as amorphous
anatase
rutile. It was proved that the rutile phase was nucleated heterogeneously from the amorphous or anatase particles.

Abstract: Laser pyrolysis is a very suitable gas-phase process for the synthesis of a wide range of nanoparticles at laboratory scale. The principle of the method is based on the decomposition of gaseous or liquid reactants by a high power CO2 laser followed by a quenching effect. The literature reports the possibility to produce carbides, nitrides, oxides, metals and composites nanoparticles by this process. This paper reports a study of the effect of the laser intensity (using an innovative optical system) and of the gas flow rates on the characteristics (size and structure) of silicon carbide (SiC) nanoparticles produced at pilot scale (up to 1.13 kg/h) by using a mixture of silane (SiH4) and acetylene (C2H2). It has been shown that the decrease of the gas flow rate favors the increase of the mean grain size of the particles and that the increase of the laser intensity seems to provoke an increase of the mean crystal size and/or crystal number.

Abstract: This works deals with the deposition of Ti-Zr-Ni icosahedral quasicrystalline powders by low vacuum plasma spray technique and the performances of the resulting coating layers. The microstructure of the coatings, as analyzed by X-ray diffraction and TEM techniques, consisted of nanometer-sized W-Ti50Zr35Ni15 1/1 cubic approximant and TiZrNi Laves phases as well as a low volume fraction of submicrometer-sized ZrO2 phase. The absence of the icosahedral phase in the coating layers was explained by the loss of Ti during plasma spraying. The shift in the composition and the presence of the ZrO2 phase within the coating layers are believed to be responsible for the reduced microhardness and corrosion performances evaluated by electrochemical tests in a Hanks’ Balance Salt Solution at 37oC.

Abstract: The reaction-sintered alumina ceramics with low firing shrinkage were prepared from Al/Al2O3 powder mixture by attrition milling and the effect of milling characteristics of raw powders on reaction sintering was investigated. Powder mixtures of flaky shape Al with coarse alumina was much more effectively comminuted by the attrition milling than the mixtures of globular shape Al with coarse alumina powders. Furthermore the coarse alumina was much more useful in pulverizing and grinding the ductile Al particles than fine alumina. After attrition milling and isopressing at 400MPa, the Al/Al2O3 specimen was oxidized at 1200°C for 8 hours followed by sintering at 1550°C for 3 hours. Because mixed powder of coarse alumina with flaky Al was much more effectively comminuted than the globular Al, sintered body of more than 97% theoretical density was achieved, but low contents of Al leads to relatively higher shrinkage of about 8%. As the coarse alumina particles are much more useful in cutting and reducing the ductile Al particles, the use of the coarse alumina powder was much more effective in reaction-sintering.

Abstract: Novel bisphenol-based wholly aromatic sulfonated poly(ether sulfone-ketone) copolymer and organic-inorganic composite membranes were prepared for operation 80°C in polymer electrolyte membrane fuel cell (PEMFCs). The copolymer were synthesized by direct aromatic nucleophilic substitution polycondensation of 4,4-difluorobenzophenone, 2,2’-disodiumsulfonyl- 4,4’-fluorophenylsulfone (40mole% of bisphenol A) and bisphenol A. Polymerization proceeded quantitatively to high molecular weight in N-methyl-2-pyrrolidinone at 180°C. Organic-inorganic composite membranes were obtained by mixing organic polymers with hydrophilic SiO2 obtained by sol-gel process. The polymer and a series of composite membranes were studied by FT-IR, 1HNMR, differential scanning calorimetry (DSC) and thermal stability. The proton conductivity as a function of temperature decreased as SiO2 content increased, but methanol permeability decreased. The nano composite membranes were found to poses all requisite properties; Ion exchange capacity (1.2meq./g), glass transition temperatures (164-183), and low affinity towards methanol (4.63-1.08x10-7 cm2/S).

Abstract: The particle size distribution is one of the important parameters for characterisation of quality of metal powders. Specific material properties such as ability to flow, reactivity as well as compressibility and its hardening potentials – hence the most important characteristics of sintered metals - are determined by the size distribution. The correct particle size distribution is the key to best product quality in atomisation processes of aluminium, milling of pure metals and other processes.

Abstract: The Ag/TiO2-xNx nanoparticles were synthesized by photochemical deposition with irradiation of visible light in a TiO2-XNX suspension system. The prepared products were characterized by means of XRD, Uv-vis, and FEM. Its photocatalytic activity was investigated by the decomposition of methylene blue (MB) solution under illumination of visible and ultraviolet light, respectively. Compared to TiO2-xNx, the photocatalytic activity of as–prepared Ag/TiO2-xNx is obviously enhanced due to the decreasing recombination of a photoexcited electron-hole pair. The mechanism in which photocatalytic activity is enhanced is discussed in detail.

Abstract: Monodispersed and nano-sized Cu powders were synthesized from copper sulfate pentahydrate (CuSO4ㆍ5H2O) inside a nonionic polymer matrix by using wet chemical reduction process. The sucrose was used as a nonionic polymer network source. The influences of a nonionic polymer matrix on the particle size of the prepared Cu powders were characterized by means of Xray diffraction (XRD), scanning electron microscopy (SEM), and particle size analysis (PSA). The smallen Cu powders with size of approximately 100㎚ was obtained with adding of 0.04M sucrose at reaction temperature of 60°C. The particle size of the Cu powders prepared by the reduction inside polymer network was strongly dependent of the sucrose content and reaction temperature.

Abstract: Monosized germanium micro particles are prepared by a newly developed Pulsated Orifice Ejection Method (POEM). The obtained particles are categorized into two kinds of the microstructures as refined and coarse ones. The morphological difference is estimated to be determined by the undercooling level during nucleation. Actually, the increase in the temperature of the melt was effective in coarsening the microstructure, because the temperature of the melt intensely relates to the undercooling level. The transition temperature of coarse and refined microstructures is found to be 1300-1350K. Furthermore, a triggered nucleation could improve the crystallinity of the particles in the short separation.