Papers by Keyword: Nanocrystalline Powder

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Authors: A.P. Newbery, Byung Ahn, P. Pao, S.R. Nutt, Enrique J. Lavernia
Abstract: Mechanical milling of Al alloy powder in liquid nitrogen leads to a large reduction in the scale of the microstructure and results in material with high thermal stability and strength. However, it is important to consolidate the powder and achieve bulk material with sufficient toughness and ductility for structural applications. In this investigation, hot isostatic pressing, followed by quasiisostatic forging and hot rolling, were performed to fabricate Al 5083 plate with a predominantly ultra-fine grained microstructure. Plate produced in this way possessed enhanced tensile strength and ductility, exceeding that of conventionally processed material.
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Authors: Hyoung Seop Kim, Min Hong Seo, Won Sun Ryu, Seung Chae Yoon, Hong Rho Lee, Jai Sung Lee, Chang Kyu Rhee
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Authors: C.A. Cunha, A.G.F. Padial, Nelson Batista de Lima, J.R. Martinelli, Olandir Vercino Correa, Lalgudi Venkataraman Ramanathan
Abstract: Cr3C2-NiCr coatings have been used for corrosion and wear resistant applications. In the last decade, thermal sprayed coatings using nanostructured feed stock of other materials has exhibited higher hardness, strength and corrosion resistance. Hence, it is anticipated that nanostructured Cr3C2-NiCr coatings will also exhibit these properties and therefore posses improved performance characteristics. Preparation of nanostructured feed stock powders is the first step in the synthesis of nanostructured coatings and mechanical milling is an effective process to obtain the powders. Preliminary studies in which commercial Cr3C2-NiCr powders were milled in hexane and gaseous nitrogen revealed that particle and crystallite size were significantly smaller in powders milled in nitrogen. This paper presents the effect of hexane content and milling parameters on Cr3C2-Ni20Cr powder characteristics. Use of just sufficient hexane as the milling media reduced significantly the particle and crystallite sizes.
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Authors: Torsten Rabe, Rolf Prümmer, Rolf Waesche
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Authors: Cheng Peng, Zhen Zhang, Dong Lin Huang, Yan Li Liu
Abstract: Pr2O3-doped ceria nanopowders were synthesized by a nitrate-citrate combustion process. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. XRD analysis showed that no impurity were observed up to x=0.3 in Ce1-xPrxO2-δ systems. The influence of ignition temperature on the characteristics of the powders was studied. The change of the crystal structure with the content of doped Pr was investigated. The highest ionic conductivity, σ600°C=2.45×10-3S/cm, was found for the composition of x=0.15.
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Authors: Karima Belaroui, G. Rapillard, Paul Bowen, H. Hofmann, V. Shklover
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Authors: M. Jachimowicz, V.I. Fadeeva, Henryk Matyja, Agnieszka Grabias
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Authors: Marcin Rosiński, Andrzej Michalski
Abstract: The paper presents the results of the examination of nanocrystalline NiAl-TiC composites with 25 wt.% and 40 wt.% of TiC. The starting materials were coarse-grained powders which were subjected to mechanical refining to obtain a nano-crystalline grain size. These powders were then sintered using the pulse plasma method. After sintering the NiAl-TiC composites have a density of 99.9% of the theoretical value. The grain size, determined by X-ray diffraction using the Hall-Williamson method; density; hardness and fracture toughness of the composites were investigated. The results obtained showed that the pulse plasma sintered NiAl-TiC have a density very close to the theoretical value and that the nano-crystalline microstructure was maintained. The NiAl-TiC composites containing 25wt.% of TiC have a hardness of 750 HV1 and a stress intensity factor KIC of 7 MPa⋅m1/2, whereas those containing 40 wt.% of TiC have a hardness of 1070 HV1 and KIC of 11.8 MPa⋅m1/2.
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Authors: Traian Florin Marinca, Ionel Chicinaş, Virgiliu Călin Prică, Florin Popa
Abstract: Nanocrystalline nickel ferrite powder was obtained using high energy reactive ball milling technique. Nickel oxide (NiO) and iron oxide (Fe2O3) powders were used as starting material. Milling was performed in air atmosphere using a planetary ball mill. Milling time was up to 30 hours. The product of milling was annealed at 350 oC for 4 hours in order to eliminate the internal stresses and finish the solid state reaction. X-ray diffraction analysis was used to study the nickel ferrite formation. A nanocrystallite mean size of 10 nm was found after 24 hours of milling. Using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDX) the particle morphology and the chemical homogeneity were studied. It was found that the obtained product has particle size in range of micron and submicron.
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Authors: Grzegorz Kalisz, Anna Swiderska-Sroda, Stanislaw Gierlotka, Ewa Grzanka, Bogdan F. Palosz, Svetlana Stelmakh
Abstract: Thermal surface purification in an inert gas flow and densification processes of SiC and diamond nanocrystalline powders with specific surface in the range of 60 – 300 m2/g and average grain sizes from 5 to 15 nm in diameter were examined. Termogravimetric Analysis (TGA) linked with mass spectrometry of outgassing products show that surface impurities desorb at up to 450°C. Further heating above 450°C leads to oxidation of the powder surface. Small Angle X-Ray Scattering (SAXS) and gas porosimetry (ASAP) was applied to investigate densification of the nanocrystalline powders. Compaction under 1GPa or higher pressure was found necessary for obtaining the ceramic matrix with porosity in the nanometer range.
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