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Study on Fraction of Rare Earth-molybdenum Alloy by Liquid-liquid Doping Method

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Tutor: LiJiWen
School: Henan University of Science and Technology
Course: Non-ferrous metallurgy
Keywords: Mo-RE alloy,Hydrothermal method,Liquid-Liquid doping,Hightemperature performance
CLC: TF841.2
Type: Master's thesis
Year:  2013
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Molybdenum and its alloys have the properties of high melting point, high boilingpoint, excellent electrical conductivity, favorable elasticity modulus and small linearexpansion coefficient under high temperature. Based on these high performances, theyare more and more used in chemical industry, aerospace technology and nuclearindustry and so on. Hydrothermal synthesis has quickly became the main method ofpreparing fabrication powder using hydrometallurgy based on the advantages that thepowder rules of the sample morphology, particle uniformity£¬high purity and clearfabrication environment and so on. In the paper, the rare earth molybdenum trioxidewas fabricated by methods of hydrothermal and liquid-liquid doped to analyze theeffect that technological parameter of hydrothermal synthesis method has on theappearance of molybdenum trioxide power, and the rare earth molybdenum alloy wasprepared by process of molybdenum trioxide reduction, pressing, sintering and rolling,by which the effect that the rare earth doping has on thermodynamic property andmicro-structure of molybdenum alloy at high temperature was studied. With theadvanced technology application of XRD, SEM, TEM, the shape of coarse grain andproperties of alloy structure was analyzed. The main research findings as follows:(1). The optimum experiment conditions of fabrication the molybdenum trioxideusing hydrothermal method were: the optimum pH value is0.5, the optimum time is25h, the optimal reaction temperature is180¡æ, and the optimal reaction fill rate is90%. The fabricated powders were one-dimensional with hexastyle structure, thediameter of grain is about5¦Ìm and length is about10¦Ìm.(2). The preparation of molybdenum trioxide by using aged treated precursormakes the average particle-degree smaller, around4¦Ìm. The molybdenum trioxideprepared by using the ion-exchange resin treated precursor easily reunion, however,there are many nanometer-sized one-dimensional molybdenum trioxide with diameterof150nm, length of5¦Ìm. (3). The molybdenum trioxide particles is fine fabricated by lanthanum nitrateliquid-liquid doped. During hydrothermal reaction, lanthanum oxide could be gainedafter decomposition of lanthanum nitrate and ammonium molybdate, and added intoMoO3powder. The amount is added inversely with the particle size of molybdenumtrioxide.(4). After the reduction, the particle size of the molybdenum powders doped withrare earth is smaller than that of the pure molybdenum powders. Meanwhile, themolybdenum powder is very fine and reaches nano size. But the size of the nano-doped molybdenum powders changed little compared with the molybdenum trioxidewithout reduction.(5). The high temperature mechanical behavior of molybdenum alloy doped withthe rate earth oxide is improved sharply when the temperature is1400-1700¡æ. Thetensile strength and yield strength of the doped molybdenum alloy can reach97.264¡«153.25MPa and87.9¡«113.84MPa respectively. It is increased by17.77%¡«29.23%and8.03%¡«22.10%respectively compared with the non-doped molybdenum alloy,and the elongation increased by1.52%~2.19%.
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