Materials Science Forum Vols. 534-536

Abstract: The performance of an in-house designed mechanofusion process and the preparation of composite powders for plasma spraying are investigated in a variety of powdered mixtures including metal/oxide, carbide/oxide, carbide/metal and metal/oxide/carbide. Scanning electron microscopy shows that dry particle coating depends on the thermo-mechanical and chemical properties of the powdered system. In the metal/oxide, carbide/oxide and metal/oxide/carbide powder mixtures, fine ceramic particles coat the surface of the metallic or ceramic coarser particles with no need of binders or solvents. However with the carbide/metal powdered system, an intimate mixture of components is achieved with an incipient dry particle coating. A nearly rounded shape of the final composite particles is induced by the mechanical energy input with no formation of new phases as confirmed by XRD analysis. It is suggested that the coating mechanism is governed by agglomeration and rolling phenomena. Finally these types of powders feature characteristics to be plasma sprayed in air.

Abstract: This paper described the preparation method for composing high-grade synthetic diamond by water atomizing using FeNi30 powder catalyst.The FeNi30 powder was corroded by the 100Mpa super high-pressure water atomizing technique and selecting organic RY corrosion inhibitor. Contrast test of the original FeNi30 powder and the treated FeNi30 powder on synthetic diamonds were conducted under super high-temperature and high-pressure using cubic press. The result shows that after the FeNi30 powder was corroded,the FeO phase and Fe3O4 phase could not longer be found by X-Ray analysis.Furthermore,the oxygen content of the powder increased up to 100PPM under the natural condition for one year. After the powder was mixed with graphite powder, diamond could be made by isostatic pressing method. Its color became darker and its TTI value increased slightly. However, its penetrability was still different from the high-grade synthetic diamond made by gas atomizing FeNi30 powder catalyst.

Abstract: Several titanate powders (Al2TiO5, SrTiO3, etc.) were synthesized by an ethylene glycol solution route. Titanium isopropoxide and nitrate salts were dissolved in stoichiometric proportions in liquid-type ethylene glycol without any precipitation. The parent precursor sols were dried to porous gels, and then the gels were calcined and crystallized. All synthesized titanate powders had stable crystallization behavior at low temperature and high specific surface area after a simple ball-milling process. A three-component PZT (Pb(Zr0.52·Ti0.48)O3) powder was also synthesized successfully by the ethylene glycol method. In this study, the characteristics of the multi-component titanate powders by the ethylene glycol method are examined.

Abstract: Using microwave synthesized HAp nano powder and polymethyl methacrylate (PMMA) as a pore-forming agent, the porous biphasic calcium phosphate (BCP) ceramics were fabricated depending on the sintering temperature. The synthesized HAp powders was about 70-90 nm in diameter. In the porous sintered bodies, the pores having 150-180 μm were homogeneously dispersed in the BCP matrix. Some amounts of pores interconnected due the necking of PMMA powders which will increase the osteoconductivity and ingrowth of bone-tissues while using as a bone substrate. As the sintering temperature increased, the relative density increased and showed the maximum value of 79.6%. From the SBF experiment, the maximum resorption of Ca2+ ion was observed in the sample sintered at 1000°C.

Abstract: The purpose of this paper is to investigate the possibility of rod-like Al2TiO5 formation via a mechanical activation process. A QM-ISP-4 Planetary Mill was employed to activate mechanically the mixtures of anatase and corundum in air at room temperature for different times. The milled powder mixtures were then sintered in air at 1300°C for 1 h. The XRD results showed that the milled powder mixtures were completely transformed into Al2TiO5 after sintering, except the mixtures milled for 5 and 10 hours. The SEM observations showed the typical morphology of rod-like Al2TiO5 vary in the range: widths from 0.6 to 1.2 μm, and lengths from 3.0 to 6.0 μm. The rod-like Al2TiO5 formation was attributed to the positive effects caused by the mechanical activation.

Abstract: The most important parameter for production of fine powders efficiently is the velocity of the atomizing gas. This can be achieved by increasing the pressure, but this way will not be economic. For that reason, to achieve supersonic velocities different nozzle designs are used in close coupled configuration for an efficient atomization. In this study, a new laval type nozzle was designed and manufactured. Using this nozzle tin powder was produced in close coupled system by using nitrogen gas at different operating conditions. The results showed that the increasing the gas pressure up to 1.47 MPa reduced the mean powder size down to 11.39 microns with a gas/melt mass flow rate ratio of 2.0. Powders are spherical in shape and have smooth surfaces.

Abstract: Nanostructured CeO2 powder was synthesized by a thermochemical process and its applicability as an oxygen gas sensor was investigated. An amorphous precursor was prepared by spray drying a cerium-nitrate solution and then heat-treated in air to induce evaporation of volatile components from the precursor powder, which then forms nanostructured ceria. The powder produced possessed a loose agglomerated structure with extremely fine CeO2 particles about 15 nm in size, resulting in a very high specific surface area (110 m2/g). The average grain size of a specimen sintered from the ceria powder at 1000 oC was about 40 nm, and its oxygen sensitivity n (logσ
log(PO2 /Po)-n) was about 1/4 at 600 oC. The response time t90, time for responding to a change of oxygen partial pressure, of the specimens sintered at 800 ~ 1100 oC was very short, i.e., 3 ~ 5 seconds: The signal output was almost identical and uniformly repeated in a stable manner.

Abstract: The spherical anatase TiO2 nanoparticle of 50 nm in diameter was manufactured by flame method and was subsequently heat-treated to investigate the transformation behavior from anatase to rutile using TEM observation. The anatase particle was facetted at the free surface and a neck formed between the anatase particles prior to the phase transformation. This resulted in the severe lattice distortion at the region of the interface. Unfortunately, we could not find the rutile grain nucleated in the anatase particle due to very fast grain growth. All the phase boundaries observed in HRTEM images existed in the contact between anatase and rutile particles. The nucleation of rutile phase in anatase particle was suppressed at the low heat-treated temperature but the grain growth of rutile particles after the phase transformation grew very fast by the sweeping phenomena of grain boundary. It leaded to the microstructure without the rutile phase traped in anatase particle.

Abstract: Hybrid atomization is a new atomization technique that combines gas atomization with centrifugal atomization. This process can produce fine, spherical powders economically with a mean size of about 10 μm diameter and a tight size distribution. Experiments on the process were carried out using a Sn-9 mass% Zn alloy to investigate the influence of processing parameters on powder characteristics in hybrid atomization. The primary atomization mechanism under normal hybrid atomization conditions is predicted to be direct drop formation mode.

Abstract: The disintegration of 6 different Nb-Zr-Fe alloys and their hydrogen storage properties due to hydrogenation have been investigated. The hydrogenation was performed in a 0.1MPa hydrogen pressure held at room temperature in arc melting chamber without exposure to air atmosphere. The thermal stability of hydrogen dissolved in disintegrated powder was measured in the temperature range from room temperature to 600°C by using the thermal analysis equipment. Hydrogen contents in alloys were evaluated from the mass difference of TG curve and chemical determinations for hydrogen gas analysis. The values of hydrogen content are in accordance with both chemical and mass difference methods. The hydrogen contents of disintegrated alloys synthesized were in the range of 1.2-2.0 wt% which depend on the composition of alloys.