As an emerging preparation technology,wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys,owing to its unique technical advantages.Ascertaining the synthesis m...As an emerging preparation technology,wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys,owing to its unique technical advantages.Ascertaining the synthesis mechanism behind wet chemical method is indispensable for controlled synthesis of highquality W-Y2 O3 composite powder precursor.The co-deposition mechanism of yttrium and tungsten component behind the wet chemical method of preparing yttrium-doped tungsten composite nanopowder was investigated systematically in this work.A series of co-deposited composite powders fabricated under different acidity conditions were used as research targets for investigating the effect of surface composition and structure on co-deposition efficiency.It was found that white tungstic acid has more W-OH bonds and much higher co-deposition efficiency with Y^3+ions than yellow tungstic acid.It is illustrated that the coordination reaction between W-OH bonds on tungstic acid particles and Y^3+ions brings the co-deposition of yttrium and tungsten component into being.Through displacing H^+ions in W-OH bonds,Y^3+ions can be adsorbed on the surface of or incorporated into tungstic acid particles in form of ligand.Consequently,to control and regulate Y2 O3 content in powder precursor accurately,H^+ion concentration in wet chemical reaction should be in range of 0.55-2.82 mol L^-1 to obtain white tungstic acid.Besides,H^+ion concentration also has prominent effect on the grain size and morphology of reduced powder precursor.The optimal value should be around 1.58 mol L^-1,which can lead to minimum W grain size(about 17 nm) without bimodal structure.The chemical mechanism proposed in this work could produce great sense to preparation of high-quality precursor for sintering high-performance Y2 O3 dispersion strengthened W based alloys.Our work may also shed light on the approach to exploit analogous synthesis mechanism in other alloy systems.展开更多
In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low tempe...In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.展开更多
W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characteriz...W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The XRD showed that the W-2 wt.%Y2O3 composite powder, including tungsten matrix and Y2O3 particles, was refined to nanometer sizes during the MA process. The SEM and TEM micrographs showed that the MA produced composite powder presented a lamellar morphology and contained many dislocations and microcracks. The EDS showed that the Y and O elements were uniformly distributed in the W matrix after mechanically alloying for 15 h. The W-2 wt.%Y2O3 composite material with uniform distribution of yttrium was obtained by sintering of the MA produced composite powder.展开更多
W-Y2O3 composite nanopowders prepared via wet chemical method exhibit unique morphologies and micro structures.The yttrium addition during chemical reaction process affects not only the composition of tungsten acid hy...W-Y2O3 composite nanopowders prepared via wet chemical method exhibit unique morphologies and micro structures.The yttrium addition during chemical reaction process affects not only the composition of tungsten acid hydrate precursors,but also the reduction property of tungsten oxide transformed from precursors.In this study,the morphology evolution of the samples with and without yttrium during reduction process has been studied,and it is found that the addition of yttrium can exert a strong influence on the reduction route of tungsten oxide and the final morphology of tungsten particles.The cause of the difference of reduction route and tungsten particle morphology is also analyzed.It is suggested that the composition of the samples with yttrium at the beginning of reduction is pure cubic system WO3(c-WO3),and the c-WO3 particles have c-WO3 whiskers attached to the surface.This kind of whiskers is essential for c-WO3 to be reduced directly to tungsten and also helpful to obtain W-Y2O3 powders with small size and good uniformity.展开更多
基金supported financially by the National Natural Science Foundation of China(Nos.51574178 and 51822404)the Natural Science Foundation of Tianjin(No.18JCYBJC17900)the Seed Foundation of Tianjin University(No.2018XRX-0005)。
文摘As an emerging preparation technology,wet chemical method has been employed widely to produce lots of alloy materials such as W and Mo based alloys,owing to its unique technical advantages.Ascertaining the synthesis mechanism behind wet chemical method is indispensable for controlled synthesis of highquality W-Y2 O3 composite powder precursor.The co-deposition mechanism of yttrium and tungsten component behind the wet chemical method of preparing yttrium-doped tungsten composite nanopowder was investigated systematically in this work.A series of co-deposited composite powders fabricated under different acidity conditions were used as research targets for investigating the effect of surface composition and structure on co-deposition efficiency.It was found that white tungstic acid has more W-OH bonds and much higher co-deposition efficiency with Y^3+ions than yellow tungstic acid.It is illustrated that the coordination reaction between W-OH bonds on tungstic acid particles and Y^3+ions brings the co-deposition of yttrium and tungsten component into being.Through displacing H^+ions in W-OH bonds,Y^3+ions can be adsorbed on the surface of or incorporated into tungstic acid particles in form of ligand.Consequently,to control and regulate Y2 O3 content in powder precursor accurately,H^+ion concentration in wet chemical reaction should be in range of 0.55-2.82 mol L^-1 to obtain white tungstic acid.Besides,H^+ion concentration also has prominent effect on the grain size and morphology of reduced powder precursor.The optimal value should be around 1.58 mol L^-1,which can lead to minimum W grain size(about 17 nm) without bimodal structure.The chemical mechanism proposed in this work could produce great sense to preparation of high-quality precursor for sintering high-performance Y2 O3 dispersion strengthened W based alloys.Our work may also shed light on the approach to exploit analogous synthesis mechanism in other alloy systems.
基金supported by the National Natural Science Foundation of China(Nos.51822404 and 51574178)the Science and Technology Program of Tianjin(No.18YFZCGX00070)+1 种基金the Natural Science Foundation of Tianjin(No.18JCYBJC17900)the Seed Foundation of Tianjin University(Nos.2018XRX-0005 and 2019XYF-0066)。
文摘In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.
文摘W-2 wt.%Y2O3 composite material with uniform distribution of yttrium element was fabricated through processes of mechanical alloying （MA） and spark plasma sintering （SPS）. The relevant productions were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. The XRD showed that the W-2 wt.%Y2O3 composite powder, including tungsten matrix and Y2O3 particles, was refined to nanometer sizes during the MA process. The SEM and TEM micrographs showed that the MA produced composite powder presented a lamellar morphology and contained many dislocations and microcracks. The EDS showed that the Y and O elements were uniformly distributed in the W matrix after mechanically alloying for 15 h. The W-2 wt.%Y2O3 composite material with uniform distribution of yttrium was obtained by sintering of the MA produced composite powder.
基金financially supported by the National Natural Science Foundation of China(Nos.51822404 and 51574178)the Science and Technology Program of Tianjin(No.18YFZCGX00070)+1 种基金the Natural Science Foundation of Tianjin(No.18JCYBJC17900)the Seed Foundation of Tianjin University(Nos.2018XRX-0005 and 2019XYF-0066).
文摘W-Y2O3 composite nanopowders prepared via wet chemical method exhibit unique morphologies and micro structures.The yttrium addition during chemical reaction process affects not only the composition of tungsten acid hydrate precursors,but also the reduction property of tungsten oxide transformed from precursors.In this study,the morphology evolution of the samples with and without yttrium during reduction process has been studied,and it is found that the addition of yttrium can exert a strong influence on the reduction route of tungsten oxide and the final morphology of tungsten particles.The cause of the difference of reduction route and tungsten particle morphology is also analyzed.It is suggested that the composition of the samples with yttrium at the beginning of reduction is pure cubic system WO3(c-WO3),and the c-WO3 particles have c-WO3 whiskers attached to the surface.This kind of whiskers is essential for c-WO3 to be reduced directly to tungsten and also helpful to obtain W-Y2O3 powders with small size and good uniformity.
