The Mechanism Of Controlled In-situ Preparation Of W-Y₂O₃ Nanocomposite Powders By Liquid Chemical Method

Tungsten-based materials are widely used in various field for their unique properties such as high melting points,tensile and creep strength,corrosion and wear resistance,electrical and thermal conductivity,and the preparation of tungsten based composite powders with small average particle size,good uniformity and high purity is of great importance to the preparation of tungsten based materials with excellent properties.Wet chemical method can be used to prepare tungsten based nano powders in liquid phase by chemical reaction at atomic or molecular scale,which is suitable for the synthesis of pure tungsten powder or tungsten based nanocomposite powders with controllable structure.This method can precisely control the distribution,size and shape of the doped particles on the premise of ensuring the high purity and mixing uniformity of nanocomposite powders,and has attracted extensive attention in recent years.However,the chemical reaction and hydrogen reduction process of wet chemical method still need to be controlled and optimized.Besides,in previous research,the size of the reduced powders often existed a bimodal distribution,which led to the formation of bimodal structures,and the formation mechanism and elimination methods of which still need to be studied.In this paper,W-Y₂O₃ nanocomposite powders were prepared by liquid chemical method.The effects of hydrogen ion concentration???H⁺??in the chemical reaction on the final production was analyzed firstly,following the study on the component and microstructure of the precursor and the relationship between crystalline phase fraction in the precursor and the morphology of the tungsten particles in the reduced powder.Then the The factors that cause the bimodal distribution of tungsten grain size in the prepared powder were also studied.Based on the results of these researches,the effect of temperature and reduction time on the morphology and particle size of the reduced powders and the effect of yttrium addition on the reduction characteristics of the precursors were also discussed.It was indicated that the hydrogen ion concentration has an optimum value on the premise of ensuring the content of Yttrium,which is approximately 0.16mol·L^-1.And there might be a certain relationship between the crystalline phase fraction in the precursor and the morphology of the tungsten particles in the reduced powder,which is closely related to yttrium.On top of that,the bimodal distribution of tungsten grain size might be caused by the maldistribution of Y₂O₃ during hydrogen reduction process and shall be avoided by controlling reaction conditions,especially??H+?.Besides,the reduction temperature and reduction time shall also have dramatic effects on the morphology and particle size of the reduced powders.Apart from that,the addition of yttrium can change the chemical composition of the precursor,thus changing the phase composition of the tungsten oxide resulting from the decomposition of the precursor during hydrogen reduction process,resulting in a change in the reduction route of the precursor.In conclusion,by keeping the hydrogen ion concentration during chemical reaction process and the reduction time and temperature,W-Y₂O₃ nanocomposite powders with good purities,small particle size and nice particle size uniformity can be obtained.