# Fabrication of Nano-CeO2 and Application of Nano-CeO2 in Fe Matrix Composites

Authors: Wang Tiebao; Cui Chunxiang; Wang Xiaodong; Li Guobin
Journal: Journal of Nanomaterials
 (2010)

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## Abstract

It is expatiated that nano-CeO2 is fabricated by the direct sedimentation method. The
components and particles diameter of nano-CeO2 powders are analyzed by XRD and SEM . The thermodynamic analysis and acting mechanism of nano-CeO2 with Al in Fe matrix composites are researched, which
shows that the reaction is generated between CeO2 and Al in the composite, that is,  3CeO2+4Al→2Al2O3+3[Ce], which obtains Al2O3 and active [Ce] during the sintering process. The
active [Ce] can improve the performance of CeO2/Fe matrix composites. The suitable amount of CeO2 is about 0.05% in CeO2/Fe matrix composites. SEM fracture analysis shows that
the toughness sockets in nano-CeO2/Fe matrix composites are more than those in no-added nano-CeO2 composites, which can explain that adding nano-CeO2 into Fe matrix composite, the toughness of the
composite is improved significantly. Applied nano-CeO2 to Fe matrix diamond saw blades shows that Fe matrix
diamond saw blade is sharper and of longer  cutting life than that with
no-added nano-CeO2.


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## Body

## 1. Foreword

Nanometer particle is physical dimensions of particle in 1~100 nm whose possessive space is between an atom and a macroscopical substance. The scientific researches of nanometer material have been one of the interesting researches in chemistry, physics, and material science fields. Due to the surface effect, the less size effect, the quanta size effect, the tunnel effect and so on, nanocomposites have many especial characteristics, which has extensive applied foreground.In China there are resourceful rare-earth elements which possess 43% of world reserves. In the rare-earth elements the prices of cerium are lower, and its applications are the most comprehensive.In this paper, preparation method ofCeO2 nanopowder is investigated. And the intention is that CeO2 nanopowder is applied to diamond saw blades.


## 2. Preparation Method of CeO2 Nanopowder

So far preparation method ofCeO2 nanopowder includes mainly flux method [1], solid state reaction method [2], direct sedimentation or agglomerating method [3], sonochemical synthesis method [4], sol-gel method [5], microemulsion method [6, 7], gas condensation method [8], and so on.


### 2.1. Preparation Principium of CeO2 Nanopowder

The investigation has used agglomerating method to prepareCeO2 nanopowder. Preparation principium of CeO2 nanopowder is as follows.The deionized water solution with 0.1 mol ·L-1  Ce(NO3)3·6H2O is prepared, whereafter the deposition solvent of 0.1 mol·L-1(NH4)2CO3·H2O is acceded to the mother solution which reacts as follows: (1)3(NH4)2CO3·H2O+2Ce(NO3)3·6H2O=Ce2(CO3)3·8H2O↓+6NH4NO3+7H2OTo get hold of colloid solution by the reaction, the colloid solution is filtrated in vacuum. For the sake of wiping off impurities and preventing conglomeration of nanopowder in later heat treatment, the filtrated cake is washed repeatedly with deionized water or ethanol. The deionized water solution or ethanol solution is dispersed by ultrasonic, which gets quadratic colloid solution. The quadratic colloid solution is filtrated, which obtains prophase powder. The prophase powder is dried at300°C for 1 hour in drying machinery, in which the reaction is as follows: (2)2Ce2(CO3)3+O2=4CeO2+6CO2↑TherebyCeO2 nanopowder is acquired.


### 2.2. Analysis of Components and Grains Size on CeO2 Nanopowder

Figure1 is the analyse result of prepared nanopowder by X-ray diffraction. Figure 1 shows that prepared nanopowder is CeO2.Figure 1
X-ray diffraction analysis of fabricatedCeO2 nanopowder.Preparing powder desired to obtain nanometer size, two essential conditions must be satisfied.(1)
In the processes of nucleation and growth, nucleation velocity as well as growth speed must be controlled.(2)
In prepared solution process, the convergence effect of grain must be controlled. The method is as follows.Adding PEG600 in the solution, formedCe2(CO3)3 grains are enwrapped by PEG600 molecules, which avoids the aggregation of Ce2(CO3)3 grains.In addition the effect parameters of preparedCeO2 nanopowder involve yet reaction temperature and times, drying temperature and times, and the kinds of added surface activing agent.Figure2 is the analysis result of TEM on prepared CeO2 nanopowder.Figure 2
TEM photograph ofCeO2 nanopowder.From Figure1 it can be descried that CeO2 nanopowder is batt shape, whose size is about 20 nm.


## 2.1. Preparation Principium of CeO2 Nanopowder

The investigation has used agglomerating method to prepareCeO2 nanopowder. Preparation principium of CeO2 nanopowder is as follows.The deionized water solution with 0.1 mol ·L-1  Ce(NO3)3·6H2O is prepared, whereafter the deposition solvent of 0.1 mol·L-1(NH4)2CO3·H2O is acceded to the mother solution which reacts as follows: (1)3(NH4)2CO3·H2O+2Ce(NO3)3·6H2O=Ce2(CO3)3·8H2O↓+6NH4NO3+7H2OTo get hold of colloid solution by the reaction, the colloid solution is filtrated in vacuum. For the sake of wiping off impurities and preventing conglomeration of nanopowder in later heat treatment, the filtrated cake is washed repeatedly with deionized water or ethanol. The deionized water solution or ethanol solution is dispersed by ultrasonic, which gets quadratic colloid solution. The quadratic colloid solution is filtrated, which obtains prophase powder. The prophase powder is dried at300°C for 1 hour in drying machinery, in which the reaction is as follows: (2)2Ce2(CO3)3+O2=4CeO2+6CO2↑TherebyCeO2 nanopowder is acquired.


## 2.2. Analysis of Components and Grains Size on CeO2 Nanopowder

Figure1 is the analyse result of prepared nanopowder by X-ray diffraction. Figure 1 shows that prepared nanopowder is CeO2.Figure 1
X-ray diffraction analysis of fabricatedCeO2 nanopowder.Preparing powder desired to obtain nanometer size, two essential conditions must be satisfied.(1)
In the processes of nucleation and growth, nucleation velocity as well as growth speed must be controlled.(2)
In prepared solution process, the convergence effect of grain must be controlled. The method is as follows.Adding PEG600 in the solution, formedCe2(CO3)3 grains are enwrapped by PEG600 molecules, which avoids the aggregation of Ce2(CO3)3 grains.In addition the effect parameters of preparedCeO2 nanopowder involve yet reaction temperature and times, drying temperature and times, and the kinds of added surface activing agent.Figure2 is the analysis result of TEM on prepared CeO2 nanopowder.Figure 2
TEM photograph ofCeO2 nanopowder.From Figure1 it can be descried that CeO2 nanopowder is batt shape, whose size is about 20 nm.


## 3. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

### 3.1. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

CeO2nanopowder glue water solution (or ethanol solution) must be dispersed by ultrasonic before CeO2/Fe matrix composites are fabricated. Whereafter Fe, Cu, Al, Sn, and CeO2 nanopowder are mixed by design content. The powders are grinded by ball milling into symmetrical powder, so composite samples are finally pressed and sintered by hot-press.The sintering ofCeO2/Fe matrix composites can be divided into five stages.(1)
In the first stage, sintering temperature is less than 400°C. In this stage, laigh melting-point metals begin to melt. The surface oxides of metal grain are deoxidized by aluminum, and the adsorbent gas around metal grain begins to be eliminated at one time. In this stage, squeeze play is too large to prevent spilling of laigh melting point metals. The squeeze play to samples is popularly 0.8 MPa in the stage.(2)
In the second stage, the sintering is at400°C by squeeze play 1.2 MPa. The intent added squeeze play is mainly to eliminate the volatilization gas of liquid olefin.(3)
In the third stage,400°C up to sintering temperature (800°C), the content of liquid phase increases along with the temperature raise. The fine grains and raised part of grains will be melted. Solid grains will arrange renewedly and remanent gas will be eliminated ulteriorly. In this stage, squeeze play to samples is 1.2 MPa to 2 MPa.(4)
Fourth stage, that is, heat preservation stage in which squeeze play to samples keeps at 2 MPa all the way. In this stage, alloy elements want to diffuse and dissolve reciprocally, which forms solid solution. And the reaction betweenCeO2 and Al is as follows:
(3)3CeO2+4Al=2Al2O3+3[Ce].CeO2 reacts with aluminum to produce active [Ce] and nano-Al2O3 during the sintering. The active [Ce] can be adsorbed at surface of solid grain, which debases interfacial tension of grains to increase the adhesional wetting between solid grains and liquid state metal, to  enhance hardness and strength of materials.(5)
In the fifth stage, that is, cooling stage, sintered samples are air cooling. When samples temperature is lower than300°C, the sintered samples can be taken out from the mold of hot-press.


### 3.2. The Properties of CeO2/Fe Matrix Composite

Figure3 shows the effect of CeO2 content on the hardness (HRB) and bending strength of Fe matrix composites. From Figure 3 it can be seen that the hardness and bending strength of Fe matrix composites attain the most value when the CeO2 content is 0.05%wt, whose content is clearly less. Because CeO2 can react with aluminum to produce active [Ce], such as front depiction, [Ce] can increase felting strength among grains. The remnant less CeO2 can play a complementarity strength part. But more CeO2 is able to become impure, which can cause brittleness increasing of material.Figure 3
The effect ofCeO2 content on the hardness and bending strength of Fe matrix composites. (The samples size of bending test is 40 mm×10 mm×3 mm.)


### 3.3. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

The relation betweenΔG0 of oxides such as CuO, FeO, NiO, Al2O3,CeO2, and Ce2O3 and temperature are shown in Figure 4, whose test condition is at 800°C for 5 minutes and squeeze play to samples is 2 MPa.Figure 4
Relationship betweenΔG0 and T.Figure4 shows that the standard creating free enthalpy ΔG0 of Ce2O3 is the lowest at the same temperature. ΔG0 of Al2O3 is higher than that of Ce2O3 but is lower than that of CeO2, which indicates that CeO2 can be deoxidized by aluminium to form active [Ce] and Al2O3 as formula (3).


### 3.4. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

Figure5 shows the elements distributing in CeO2/Fe matrix composite, whose distributing is not symmetrical because the composites are fabricated by powder metallurgy process. It is important to note that there is no oxygen with Ce displaying at the peak value, indicating that CeO2  can reacts with aluminium to produce active [Ce].Figure 5
The liner distribution analysis of elements on Fe matrix composite to which 0.5%wt nano-CeO2 was added.Figure6 shows X-ray analysis result. There are Al2O3 and Ce in CeO2/Fe matrix composite, which explains that the reaction between CeO2 and aluminum is capable of occurring, that reaction is shown in formula (3).Figure 6
X-ray analysis of nano-CeO2/Fe matrix composite.For workout, the moreCeO2 (0.5%wt) is added to CeO2/Fe matrix composite, so there is CeO2 in Figure 6.


### 3.5. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

Figure7 is SEM photograph of samples fracture on CeO2/Fe matrix composites. Figures 7(a) and 7(b) show that there are more dimples in added CeO2Fe matrix composite than in no-added CeO2one, which shows that CeO2/Fe matrix composite has higher toughness than Fe matrix composite. It is perhaps because CeO2 can be deoxidized by aluminium to form active [Ce] which can nail on the dislocation, which can obtain the fine crystalline grin under sintering.SEM photograph of samples fracture.
(a)
no-addedCeO2(b)
addedCeO2 (0.05%wt)


## 3.1. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

CeO2nanopowder glue water solution (or ethanol solution) must be dispersed by ultrasonic before CeO2/Fe matrix composites are fabricated. Whereafter Fe, Cu, Al, Sn, and CeO2 nanopowder are mixed by design content. The powders are grinded by ball milling into symmetrical powder, so composite samples are finally pressed and sintered by hot-press.The sintering ofCeO2/Fe matrix composites can be divided into five stages.(1)
In the first stage, sintering temperature is less than 400°C. In this stage, laigh melting-point metals begin to melt. The surface oxides of metal grain are deoxidized by aluminum, and the adsorbent gas around metal grain begins to be eliminated at one time. In this stage, squeeze play is too large to prevent spilling of laigh melting point metals. The squeeze play to samples is popularly 0.8 MPa in the stage.(2)
In the second stage, the sintering is at400°C by squeeze play 1.2 MPa. The intent added squeeze play is mainly to eliminate the volatilization gas of liquid olefin.(3)
In the third stage,400°C up to sintering temperature (800°C), the content of liquid phase increases along with the temperature raise. The fine grains and raised part of grains will be melted. Solid grains will arrange renewedly and remanent gas will be eliminated ulteriorly. In this stage, squeeze play to samples is 1.2 MPa to 2 MPa.(4)
Fourth stage, that is, heat preservation stage in which squeeze play to samples keeps at 2 MPa all the way. In this stage, alloy elements want to diffuse and dissolve reciprocally, which forms solid solution. And the reaction betweenCeO2 and Al is as follows:
(3)3CeO2+4Al=2Al2O3+3[Ce].CeO2 reacts with aluminum to produce active [Ce] and nano-Al2O3 during the sintering. The active [Ce] can be adsorbed at surface of solid grain, which debases interfacial tension of grains to increase the adhesional wetting between solid grains and liquid state metal, to  enhance hardness and strength of materials.(5)
In the fifth stage, that is, cooling stage, sintered samples are air cooling. When samples temperature is lower than300°C, the sintered samples can be taken out from the mold of hot-press.


## 3.2. The Properties of CeO2/Fe Matrix Composite

Figure3 shows the effect of CeO2 content on the hardness (HRB) and bending strength of Fe matrix composites. From Figure 3 it can be seen that the hardness and bending strength of Fe matrix composites attain the most value when the CeO2 content is 0.05%wt, whose content is clearly less. Because CeO2 can react with aluminum to produce active [Ce], such as front depiction, [Ce] can increase felting strength among grains. The remnant less CeO2 can play a complementarity strength part. But more CeO2 is able to become impure, which can cause brittleness increasing of material.Figure 3
The effect ofCeO2 content on the hardness and bending strength of Fe matrix composites. (The samples size of bending test is 40 mm×10 mm×3 mm.)


## 3.3. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

The relation betweenΔG0 of oxides such as CuO, FeO, NiO, Al2O3,CeO2, and Ce2O3 and temperature are shown in Figure 4, whose test condition is at 800°C for 5 minutes and squeeze play to samples is 2 MPa.Figure 4
Relationship betweenΔG0 and T.Figure4 shows that the standard creating free enthalpy ΔG0 of Ce2O3 is the lowest at the same temperature. ΔG0 of Al2O3 is higher than that of Ce2O3 but is lower than that of CeO2, which indicates that CeO2 can be deoxidized by aluminium to form active [Ce] and Al2O3 as formula (3).


## 3.4. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

Figure5 shows the elements distributing in CeO2/Fe matrix composite, whose distributing is not symmetrical because the composites are fabricated by powder metallurgy process. It is important to note that there is no oxygen with Ce displaying at the peak value, indicating that CeO2  can reacts with aluminium to produce active [Ce].Figure 5
The liner distribution analysis of elements on Fe matrix composite to which 0.5%wt nano-CeO2 was added.Figure6 shows X-ray analysis result. There are Al2O3 and Ce in CeO2/Fe matrix composite, which explains that the reaction between CeO2 and aluminum is capable of occurring, that reaction is shown in formula (3).Figure 6
X-ray analysis of nano-CeO2/Fe matrix composite.For workout, the moreCeO2 (0.5%wt) is added to CeO2/Fe matrix composite, so there is CeO2 in Figure 6.


## 3.5. Fabrication and Properties Analysis of CeO2/Fe Matrix Composite

Figure7 is SEM photograph of samples fracture on CeO2/Fe matrix composites. Figures 7(a) and 7(b) show that there are more dimples in added CeO2Fe matrix composite than in no-added CeO2one, which shows that CeO2/Fe matrix composite has higher toughness than Fe matrix composite. It is perhaps because CeO2 can be deoxidized by aluminium to form active [Ce] which can nail on the dislocation, which can obtain the fine crystalline grin under sintering.SEM photograph of samples fracture.
(a)
no-addedCeO2(b)
addedCeO2 (0.05%wt)


## 4. The Application of Nano-CeO2/Fe Matrix Composite on Diamond Saw Blade

Figure8 is the out-edge height of diamond. Applying nano-CeO2 to Fe matrix diamond saw blades, the result obtained from Figure 8 shows that the out-edge height of diamond added nano-CeO2 is higher than that of no-adding nano-CeO2 in edges of diamond saw blade. And so the diamond saw blade added nano-CeO2 is sharper.The out-edge height of diamond.
(a)
no-addedCeO2(b)
addedCeO2The characteristics of different diamond saw blades are shown in Table1. Investigation shows that the holding strength of matrix to diamond for adding nano-CeO2 is 58 MPa higher than that for no-adding nano-CeO2. So under the same condition of cutting life, added nano-CeO2 diamond saw blade is clearly sharper than the no-adding nano-CeO2one.Table 1
The characteristics of different diamond saw blades.
Kind of diamond saw bladesHolding strength (MPa)Cutting speed (m/minute)Cuting life (m)No-added nano-CeO256630.53450Added nano-CeO262439.83475


## 5. Conclusions

(1)
The investigation used agglomerating method to prepareCeO2 nanopowder. Preparation principium of CeO2 nanopowder is as follows:
(4)3(NH4)2CO3·H2O+2Ce(NO3)3·6H2O=Ce2(CO3)3·8H2O↓+6NH4NO3+7H2O
In the dryness process at 300°C for 1 hour, the reaction creates CeO2 nanopowder as follows:
(5)2Ce2(CO3)3+O2=4CeO2+6CO2↑
CeO2 nanopowder is of batt shape, whose size is about 20 nm.(2)
In the sintering process at800°C for 5 minutes, CeO2 in the matrix is deoxidized by aluminium which creates active [Ce]. The reaction is as follows:
(6)3CeO2+4Al→2Al2O3+3[Ce]
to produce active [Ce] and nano-Al2O3.(3)
Applied nano-CeO2 to Fe matrix diamond saw blades shows that Fe matrix diamond saw blades is sharper and of longer cutting life than on-adding nano-CeO2.



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*Source: 768251-2010-09-26.xml*