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Laser Rapid synthesis La_2 (MoO_4) _3 and Ce_2 (WO_4) _3 material and its thermal expansion

Author: WangZheng
Tutor: ZuoMingJu；LiangErJun
School: Zhengzhou University
Course: Optics
Keywords: Laser Rapid Synthesis A2 MO4 3 Thermal expansion of Tungstate and molybdate
CLC: TF124.5
Type: Master's thesis
Year: 2007
Downloads: 65
Quote: 0
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Abstract


Aroused widespread concern in recent years, the negative thermal expansion material. The emerging negative thermal expansion material is generally of W, Mo, V and P salts. Where A 2 (the MO 4 ) 3 series tungstate and molybdate materials, the negative thermal expansion coefficient and easily through the component The change of the thermal expansion coefficient to be adjusted. Currently, the methods of synthesis of such materials for the solid phase synthesis method and the wet-chemical method, but there are obvious drawbacks. Wherein the solid-phase synthesis method due the feedstock in WO 3 of MoO 3 and other high temperature volatile, difficult to control the ratio of raw materials, so the purity of the final product is not high; requires repeated and sintering, a long preparation time, the large energy consumption. Complex reaction process of the wet chemical method, the range of equipment needed, and technological requirements. Considering the traditional synthetic methods, low efficiency, high cost, difficult to mass production, there is an urgent demand for the development of new synthetic methods. Laser synthesis of functional ceramics is a new technology developed in recent years. Laser as a new heat source, because it has the energy is highly concentrated, directivity of good characteristics, so that the laser synthesis of materials and traditional sintering material, there are significant differences in the physical properties and microstructure. Laser synthesis method of high cooling rate, the shortening sample firing time, so it can effectively inhibit 3 is the raw material of WO of MoO 3 powder volatiles; synthesis process easy control sintering power and scanning time, so the process is relatively simple and easy to operate, high repeatability, and easiest to implement large-scale production. Some studies have shown is (MO 4 ) 3 series tungstates and molybdates material A and for A 2 3 ionic radius of its negative thermal expansion will have a significant impact A 3 ion radius larger material negative thermal expansion coefficient is also large. This work introduces a large radius of the rare earth ion laser synthesis method first successful synthesis of single-phase La 2 (MoO 4 ) 3 molybdate the salt and Ce 2 the (WO 4 ), 3 TUNGSTATE. Using XRD, Raman spectroscopy and scanning electron microscopy analysis means a systematic analysis of the samples found the synthesized La 2 (the MoO 4 ) 3 2 (WO to 4 ) 3 forming somewhat less composition uniformity is monoclinic structure, lattice constant a = 0.7830nm b = 1.1736nm, c = 1.2037nm, β = 110.83 °; oriented in a direction along the laser incident surface of small grain aggregates, formed inside a large number of bunched whisker crystals, due to the heat conduction direction determines the direction of crystal growth, crystal approximation growth. The lateral size of the dendrite in 10μm, and the grain size of 1μm to 2μm. The structural stability of the sample at room temperature. With CO 2 laser sintering the rapid synthesis tungstate and molybdate material method is feasible, it is possible to effectively suppress the volatilization of the raw material, to obtain high purity product, for fast and effective synthesis of other types of tungsten formate and molybdate materials useful exploration. This new approach to improve efficiency, reduce costs, not only for scientific research purposes, a small amount of synthetic, also suitable for large-scale production for industrial use.

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CLC: > Industrial Technology > Metallurgical Industry > Metallurgical Technology > Powder metallurgy (metal ceramic technology ) > Powder molding, sintering and post-processing > Sintering process
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