# Effect of Rare Earth Y on Properties of  Nanosized    90W-7Ni-3Fe Composite Powder  Fabricated by Spray   Drying-Hydrogen Reduction

Authors: Y.-Z. Ma; Liu Wensheng; Huang Baiyun; Fan Jinglian
Journal: Journal of Nanomaterials
 (2008)

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## Abstract

(W,Ni,Fe) composite oxide powder synthesized by spray drying was reduced at 700∘C for 90 minutes in H2 atmosphere. The effect of rare earth Y on H2 reduction of (W,Ni,Fe) composite oxide powder was studied. Phase composition, crystalline size, and particle morphology of the reduced powder have been measured by X-ray diffraction and scanning electron microscope (SEM). Fsss particle size and special surface area of the reduced powder were also measured and analyzed. The result showed that new phase Y(Ni0.75W0.25)O3
appeared in the reduced powder and particle morphology was nearly spherical or polyhedron by Y additions. The higher the rare earth element content was, the bigger the influencing on particle morphology was. When the rare earth Y content was under 0.8%, with the increase of the rare earth element content, dBET, Fsss, and crystal sizes of the reduced powder decreased greatly.


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## Body

## 1. Introduction

Tungsten-based heavy alloys,  which are used as kinetic energy penetrators, counter weights, radiation shields, and electrical contacts due to their high density, strength, and ductility, are two-phase composites produced by liquid phase sintering mixed elemental tungsten, nickel, and iron powders. Typical compositions have 90 wt% tungsten with the balance nickel and iron, usually in the ratio of7:3 [1].Nanostructured tungsten-based alloys possess very high properties, which put high demands on the manufacture process for both powders and bulk alloys. High-energy ball milling, which is a well-known process for preparing amorphous alloyed powders, has been considered as a powderful technique due to relative inexpensive equipment [2]. However, it takes tens of hours to fabricate nanosized W-Ni-Fe composite powder for high-energy milling technique     [3], so the milling efficiency is very low. Meanwhile, high-energy milling could bring inclusions. Spray drying process is a useful technique for synthesizing numerous nanostructured materials due to its simplicity and various elements homogeneous dispersibility [4, 5]. Previous studies have discussed preparation and reduction mechanisms of (W,Ni,Fe) composite oxide powder by spray drying      [6–8]. In this paper, effects on the reduced powder properties with Y additions were studied by previous reduced conditions optimized at 700°C for 90 minutes.


## 2. Experimental

The  raw materials in this experiment included the(NH4)6H2W12O40⋅xH2O,           Ni(NO3)2⋅6H2O,   Fe(NO3)3⋅9H2O,  Y(NO3)2⋅6H2O, and surfactant PEG-1000. First, the  (NH4)6H2W12O40⋅xH2O, Ni(NO3)2⋅6H2O, and Fe(NO3)3⋅9H2O were added in distilled water
by a composition ratio of 90 wt%W-7 wt%Ni-3 wt%Fe and produced solution with 0.2, 0.4, 0.6, 0.8 wt% Y additions by  Y(NO3)2⋅6H2O   (theoretical content calculation), respectively. Secondly, the solution was changed into
solution colloid by adjusting pH value, and  0.5g⋅L−1  PEG-1000 was added. Finally,
the (W,Ni,Fe) precursor oxide powder was fabricated by drying spraying of solution colloid, then the nanosized 90W-7Ni-3Fe composite powder including different Y additions was fabricated by reduction of the (W,Ni,Fe) precursor oxide powder in the hydrogen-atmosphere at 700°C for 90 minutes.Special  surface areas  of the reduced powder were measured by the nitrogen adsorption method. The Fsss sizes of the reduced powder
were measured by the Fisher testing
method. The phase compositions and crystal sizes of the reduced powder were
tested and analyzed with Rigaku D/max2550VB+18 Kw X-ray diffraction
made in Japan. The reduced powders were dispersed by ultrasonic wave for 30 minutes, whose morphology images were observed with the JSM-5600LV
type scanning electron microscope (SEM) made by JEOL cop.


## 3. Results and Discussion

### 3.1. Effect of Rare Earth Y on Phase Composition of 90W-7Ni-3Fe Composite Powder

Figure1 showed curves between the Y additions and phase
compositions of the reduced composite powder at 700°C   for 90 minutes.  It was seen from Figure 1 that the phase
compositions of the reduced powder were W and γ-(Ni,Fe) without the rare earth Y addition,
new phase Y(Ni0.75W0.25)O3 was appeared when
adding 0.4 wt% Y. With the increase of Y additions from 0.4 wt% to 0.8 wt%,
intensity of new phase Y(Ni0.75W0.25)O3 raised
in X-ray diffraction graph.X-ray
diffraction images of W-Ni-Fe composite powder
reduced: (a) no Y addition;  (b) 0.4 wt% Y;  (c) 0.8 wt% Y.
(a)(b)(c)


### 3.2. Effect of Rare Earth Y on Properties of 90W-7Ni- 3Fe Composite Powder

Figure2 showed curves between the dBET particle sizes,
Fsss particle sizes, and crystal sizes of the reduced powder and the Y
additions. The crystal sizes of the reduced powder were decreased with increase
of the Y additions from Figure 2(a). High Y addition has better effect on
inhibition for crystal size than low Y addition. The dBET  and
Fsss particle sizes of the reduced powder with some Y additions were much
smaller than those of the reduced powder without Y addition from Figures 2(b) and 2(c). Even if 0.2 wt% Y was added, the dBET
and Fsss particle sizes of the reduced
powder declined obviously. With the increase of water vapor produced during
reduction process, tungsten oxide and water vapor synthesized volatiling  WOx⋅H2O,    that is WO2(OH)2,
which deposited on the surface of metal tungsten powder by vapor transference,
and led to growth of particles [9].  The process sequenced asProperties curves of the reduced powder for different   Y additions: (a) crystal sizes; (b)dBET; (c) Fsss.
(a)(b)(c)When rare
earth Y was added, new phase Y(Ni0.75W0.25)O3 formed and
adsorbed on the surface of tungsten particles. Meanwhile, new phase Y(Ni0.75W0.25)O3 can effectively prevent WO2(OH)2 from producing and decreasing vapor transference, which inhibited effectively W particles from growing
up.


### 3.3. Effect of Rare Earth Y on Morphology Images of 90W-7Ni-3Fe Composite Powder

SEM
morphology images of the reduced composite powder were listed in Figure3. From
Figure 3, the reduced W-Ni-Fe composite powder by rare earth Y additions was more homogeneous dispersibility
than that of no Y addition. Meanwhile, with the increase of Y addition, effect
of rare earth on dispersibility of the reduced powder enlarged obviously. It
was also seen clearly from Figure 3 that,  powder particle morphology with rare
earth Y addition has changed, the particle morphology was spherical without rare earth Y, but the
powder particle morphology was nearly spherical with 0.4 wt% Y and polyhedral
with 0.8 wt% Y. The higher the Y additions were, the greater the effect on powder
particle morphology was. Because energy state of some crystal interface has changed
when some rare earth Y were added, which forced crystal quickly growth up at
some directions and inhibited other directions from growthing up.   With the increase of rare earth Y,  tendency of preferential
orientation growthing
was more obvious [10, 11].Morphology images of the reduced powder for different Y additions
(SEM): (a) no Y addition; (b) 0.4 wt% Y; (c) 0.8 wt.% Y.
(a)(b)(c)


## 3.1. Effect of Rare Earth Y on Phase Composition of 90W-7Ni-3Fe Composite Powder

Figure1 showed curves between the Y additions and phase
compositions of the reduced composite powder at 700°C   for 90 minutes.  It was seen from Figure 1 that the phase
compositions of the reduced powder were W and γ-(Ni,Fe) without the rare earth Y addition,
new phase Y(Ni0.75W0.25)O3 was appeared when
adding 0.4 wt% Y. With the increase of Y additions from 0.4 wt% to 0.8 wt%,
intensity of new phase Y(Ni0.75W0.25)O3 raised
in X-ray diffraction graph.X-ray
diffraction images of W-Ni-Fe composite powder
reduced: (a) no Y addition;  (b) 0.4 wt% Y;  (c) 0.8 wt% Y.
(a)(b)(c)


## 3.2. Effect of Rare Earth Y on Properties of 90W-7Ni- 3Fe Composite Powder

Figure2 showed curves between the dBET particle sizes,
Fsss particle sizes, and crystal sizes of the reduced powder and the Y
additions. The crystal sizes of the reduced powder were decreased with increase
of the Y additions from Figure 2(a). High Y addition has better effect on
inhibition for crystal size than low Y addition. The dBET  and
Fsss particle sizes of the reduced powder with some Y additions were much
smaller than those of the reduced powder without Y addition from Figures 2(b) and 2(c). Even if 0.2 wt% Y was added, the dBET
and Fsss particle sizes of the reduced
powder declined obviously. With the increase of water vapor produced during
reduction process, tungsten oxide and water vapor synthesized volatiling  WOx⋅H2O,    that is WO2(OH)2,
which deposited on the surface of metal tungsten powder by vapor transference,
and led to growth of particles [9].  The process sequenced asProperties curves of the reduced powder for different   Y additions: (a) crystal sizes; (b)dBET; (c) Fsss.
(a)(b)(c)When rare
earth Y was added, new phase Y(Ni0.75W0.25)O3 formed and
adsorbed on the surface of tungsten particles. Meanwhile, new phase Y(Ni0.75W0.25)O3 can effectively prevent WO2(OH)2 from producing and decreasing vapor transference, which inhibited effectively W particles from growing
up.


## 3.3. Effect of Rare Earth Y on Morphology Images of 90W-7Ni-3Fe Composite Powder

SEM
morphology images of the reduced composite powder were listed in Figure3. From
Figure 3, the reduced W-Ni-Fe composite powder by rare earth Y additions was more homogeneous dispersibility
than that of no Y addition. Meanwhile, with the increase of Y addition, effect
of rare earth on dispersibility of the reduced powder enlarged obviously. It
was also seen clearly from Figure 3 that,  powder particle morphology with rare
earth Y addition has changed, the particle morphology was spherical without rare earth Y, but the
powder particle morphology was nearly spherical with 0.4 wt% Y and polyhedral
with 0.8 wt% Y. The higher the Y additions were, the greater the effect on powder
particle morphology was. Because energy state of some crystal interface has changed
when some rare earth Y were added, which forced crystal quickly growth up at
some directions and inhibited other directions from growthing up.   With the increase of rare earth Y,  tendency of preferential
orientation growthing
was more obvious [10, 11].Morphology images of the reduced powder for different Y additions
(SEM): (a) no Y addition; (b) 0.4 wt% Y; (c) 0.8 wt.% Y.
(a)(b)(c)


## 4. Conclusion

(1)
The phase compositions of
the reduced powder were W andγ-(Ni,Fe) without the rare earth Y addition, but
new phase Y(Ni0.75W0.25)O3 was appeared by adding
0.4 wt%      Y. With the increase of Y additions from 0.4 wt% to 0.8 wt%,
intensity of new phase Y(Ni0.75W0.25)O3 raised
in X-ray diffraction graph.(2)
With
increase of Y additions in the range of 0.8 wt%, the crystal,dBET, and Fsss sizes of the reduced
W-Ni-Fe composite powder were decreased from 26.1 nm, 96.6 nm, 0.64 μm to 19.8 nm, 45.2 nm, 0.28 μm, respectively.(3)
Rare
earth Y possessed great influence on powder particle morphology. The particle morphology is
spherical without rare earth Y, but the particle morphology is nearly
spherical by adding 0.4 wt% Y or polyhedron with 0.8 wt% Y addition. The higher
rare earth content is, the bigger influencing on particle morphology is.



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*Source: 459093-2008-04-14.xml*