- Email: [email protected]
CuO couple by high-energy ball milling
Journal of Alloys and Compounds 268 (1998) 211–214
L
Solid-state reaction of Al / CuO couple by high-energy ball milling a, a b b a b Xi Shengqi *, Qu Xiaoyan , Ma Mingliang , Zhou Jingen , Zheng Xiulin , Wang Xiaotian a
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’ an 710072, P.R. China b School of Materials Science and Engineering, Xi’ an Jiaotong University, Xi’ an 710049, P.R. China Received 7 July 1997; received in revised form 3 November 1997
Abstract The solid state reaction of Al / CuO induced by high-energy ball milling was studied systematically. When the amount of Al was 20 wt%, only reduction occurred. When the amount of Al exceeded 20 wt%, along with the reduction, a synthesis reaction occurred simultaneously. As the amount of Al increased, the reaction products were Cu 9 Al 4 , CuAl 2 or a Al(Cu) solid solution, respectively. The mechanism of these two types of reactions occurring during ball milling is discussed. 1998 Elsevier Science S.A. Keywords: Al / CuO; Solid state reaction; High-energy ball milling
1. Introduction In recent studies, high-energy ball milling was recognized as a solid state reaction process [1,2]. Much research efforts were spent on the reaction occurring during ball milling which led to the synthesis of amorphous alloys and metallic compounds. Also redox reactions occurring during ball milling were studied [3,4]. The purpose of the present paper is to study the composite reaction when the redox and synthesis reactions occur simultaneously during ball milling. The Al / CuO couple was chosen for this study. For this couple it can be expected that different results are attained when the amount of Al is changed .
2. Experimental A stirred ball mill was used in this study. The details of the equipment and experiment have been described elsewhere [4]. The ball to powder weight ratio (CR ) was 80. Chemically pure elemental Al and CuO powders with an Al weight percentage of 20, 35, 57,70 and 85 were milled respectively. After the predetermined milling time, the ball milled powders were removed from the vial and analyzed using X-ray diffractometry (XRD) and differential scanning calorimeter (DSC). All X-ray diffraction experiments were performed in a Rigaku diffractometer (D-max / C *Corresponding author. 0925-8388 / 98 / $19.00 1998 Elsevier Science S.A. All rights reserved. PII S0925-8388( 97 )00566-5
type) using Cu Ka radiation. The DSC experiments were performed in a Perkin-Elmer DSC7 instrument under a dynamic high purity Ar atmosphere with a heating rate of 60 K min 21 .
3. Results and discussion
3.1. The solid state reduction reaction The results of mixed Al / CuO powder with 20 wt% Al during ball milling at different milling time is shown in Fig. 1. After milling for 2.5 h, the pure mixed powders of Cu and Al 2 O 3 were present. This shows that a reduction reaction has been induced by ball milling. For milling times up to 2 h, there were no apparent changes in the mixed powders. The grain size of the constituents was refined. Fig. 2 shows the DSC results of milled powders at different milling times. Powders milled for 0.5 to 2 h showed an exothermic effect in the temperature range 280|3608C. For powders with increased milling time, the exothermic effect also increased. The powder milled for 2 h was heated to 4008C in the DSC analysis. Fig. 3 shows the X-ray analysis of this powder before and after heating. The reaction taking place in this powder involved the transformation of CuO into Cu 2 O. No pure Cu existed in this heated powders. From the above results, it can be deduced that the grain
212
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
Fig. 1. s, Al; d, Cu; h, CuO; x, Al 2 O 3 , a, 0.5 h; b, 1.0 h; c, 1.5 h; d, 2.0 h; e, 2.5 h. The XRD pattern of mixed Al / CuO powder with 20 wt% Al milled for different times.
size of the constituents was refined continuously during ball milling and a large amount of the Al / CuO couple was formed. The reaction occurring in powders during milling was different from that occurring during heating of powders milled for a short time. It showed that some of the Al / CuO couple in mixed powders trapped in the balls could attain the ignition condition during ball impact. A local reduction reaction occurred. As this reaction has a
Fig. 3. s, Al; h, CuO; j, Cu 2 O. The XRD pattern of powders with 20 wt% Al milled for 2.0 h before (a) and after (b) heating.
significant heat effect, a reduction reaction of the trapped powder was induced.
3.2. Composite solid state reaction According to composite reaction of Al1CuO→CuAl 2 1 Al 2 O 3 , the amount of Al should exceed 48 wt%. Fig. 4 shows the results of the Al / CuO mixed powder with 57 wt% Al at different milling times. As milling time
Fig. 2. a, 0 h; b, 0.5 h; c, 2.0 h. The DSC pattern of powder with 20 wt% Al milled for different times.
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
Fig. 4. s, Al; h, CuO; n, CuAl 2 ; x, Al 2 O 3 ; a, 1 h; b, 2 h; c, 4 h. The XRD pattern of Al / CuO powder with 57 wt% Al milled for different times.
increased, the constituents were mixed and refined. After up to 6 h, the composite reaction took place and CuAl 2 was formed in the mixed powders. The DSC results of this powder milled for different times are shown in Fig. 5. Exothermic effect occurred in the temperature range 120| 3008C. The powder milled for 2 h showed the maximum exothermic effect. The X-ray diffraction pattern of this powder after heating to 3008C in the DSC is shown in Fig.
213
Fig. 6. s, Al; h, CuO; n, CuAl 2 ; x, Al 2 O 3 ; j, Cu 2 O. The XRD pattern of powder with 57 wt% Al milled for 2 h before (a) and after (b) heating.
6. As can be seen, Al 2 O 3 , CuAl 2 , Cu 2 O, CuO and Al were present in this heated powder. It proved that for short milling times the milled powder can be present in different states. Similar to the reduction reaction, CuAl 2 1Al 2 O 3 was directly formed during ball milling. This was also different from the results of heated powder milled for short time. In general, the temperature of milled powder could rise 100–300 K during ball milling [5]. No Cu 2 O is formed during ball milling. The temperature is not the only
Fig. 5. The DSC pattern of Al / CuO powder with 57 wt% Al milled for different times (a) 0 h (b) 1 h (c) 2 h (d) 4 h.
214
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
important factor. The impact time between balls during milling is shorter (about 10 25 s) compared to the heating time in the DSC [6]. This may cause the different results. When the reaction occurred, the pure Cu formed by reduction from CuO combined with the refined Al and the CuAl 2 compound formed directly.
3.3. Results obtained with different Al content As the amount of Al increased, along with the reduction reaction, the synthesis reaction occurred simultaneously. Fig. 7 shows the results of the reactant Al / CuO with different Al contents. The products were Cu, Cu 9 Al 4 , CuAl 2 or Al(Cu) solid solution respectively as the Al content increased. Comparing Figs. 2 and 5, as the Al content increased,
the reaction temperature of the heated powder decreased and the exothermic temperature range was broadened. This may be explained by the fact that as the Al content increased the grain size of Al / CuO became much finer, which could be supported by the results shown in Figs. 1 and 4. The effect of the reaction heat also decreased simultaneously. The composite reaction occurred at a comparatively low temperature in the form of a diffusion reaction.
4. Conclusions (1) CuO could be reduced by Al during ball milling. A local reduction reaction occurred when ignition conditions were reached during ball milling. (2) With increasing Al content a composite reaction took place with the main character of a diffusion reaction. (3) With increasing Al content the end products of the composite reaction were Cu1Al 2 O 3 , Cu 9 Al 4 1Al 2 O 3 , CuAl 2 1Al 2 O 3 or Al 2 O 3 1Al(Cu) solid solution, respectively.
References
Fig. 7. s, Al; d, Cu; m, Cu 9 Al 4 , n, CuAl 2 ; x, Al 2 O 3 ; a, 20 wt% Al; b, 35 wt%Al; c, 57 wt% Al; d, 70 wt% Al; e, 85 wt% Al. The XRD pattern of Al / CuO powder with different Al content milled for 6 h.
[1] C.C. Koch, Annu. Rev. Mater. Sci. 19 (1989) 221. [2] G.B. Schaffer, P.G. McCormick, Mater. Forum 16 (1992) 91. [3] G.B. Schaffer, P.G. McCormick, Mater. Sci. Forum 89-90 (1992) 779. [4] Shengqi Xi, Jingen Zhou, Dongwen Zhang, Xiaotian Wang, J. Mater. Sci. Lett. 15 (1996) 634. [5] R.M. Davis, B. McDermott, C.C. Koch, Metall. Trans. 19A (1988) 2867. [6] D.R. Maurice, T.H. Courtney, Metall. Trans. 21A (1990) 289.
L
Solid-state reaction of Al / CuO couple by high-energy ball milling a, a b b a b Xi Shengqi *, Qu Xiaoyan , Ma Mingliang , Zhou Jingen , Zheng Xiulin , Wang Xiaotian a
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’ an 710072, P.R. China b School of Materials Science and Engineering, Xi’ an Jiaotong University, Xi’ an 710049, P.R. China Received 7 July 1997; received in revised form 3 November 1997
Abstract The solid state reaction of Al / CuO induced by high-energy ball milling was studied systematically. When the amount of Al was 20 wt%, only reduction occurred. When the amount of Al exceeded 20 wt%, along with the reduction, a synthesis reaction occurred simultaneously. As the amount of Al increased, the reaction products were Cu 9 Al 4 , CuAl 2 or a Al(Cu) solid solution, respectively. The mechanism of these two types of reactions occurring during ball milling is discussed. 1998 Elsevier Science S.A. Keywords: Al / CuO; Solid state reaction; High-energy ball milling
1. Introduction In recent studies, high-energy ball milling was recognized as a solid state reaction process [1,2]. Much research efforts were spent on the reaction occurring during ball milling which led to the synthesis of amorphous alloys and metallic compounds. Also redox reactions occurring during ball milling were studied [3,4]. The purpose of the present paper is to study the composite reaction when the redox and synthesis reactions occur simultaneously during ball milling. The Al / CuO couple was chosen for this study. For this couple it can be expected that different results are attained when the amount of Al is changed .
2. Experimental A stirred ball mill was used in this study. The details of the equipment and experiment have been described elsewhere [4]. The ball to powder weight ratio (CR ) was 80. Chemically pure elemental Al and CuO powders with an Al weight percentage of 20, 35, 57,70 and 85 were milled respectively. After the predetermined milling time, the ball milled powders were removed from the vial and analyzed using X-ray diffractometry (XRD) and differential scanning calorimeter (DSC). All X-ray diffraction experiments were performed in a Rigaku diffractometer (D-max / C *Corresponding author. 0925-8388 / 98 / $19.00 1998 Elsevier Science S.A. All rights reserved. PII S0925-8388( 97 )00566-5
type) using Cu Ka radiation. The DSC experiments were performed in a Perkin-Elmer DSC7 instrument under a dynamic high purity Ar atmosphere with a heating rate of 60 K min 21 .
3. Results and discussion
3.1. The solid state reduction reaction The results of mixed Al / CuO powder with 20 wt% Al during ball milling at different milling time is shown in Fig. 1. After milling for 2.5 h, the pure mixed powders of Cu and Al 2 O 3 were present. This shows that a reduction reaction has been induced by ball milling. For milling times up to 2 h, there were no apparent changes in the mixed powders. The grain size of the constituents was refined. Fig. 2 shows the DSC results of milled powders at different milling times. Powders milled for 0.5 to 2 h showed an exothermic effect in the temperature range 280|3608C. For powders with increased milling time, the exothermic effect also increased. The powder milled for 2 h was heated to 4008C in the DSC analysis. Fig. 3 shows the X-ray analysis of this powder before and after heating. The reaction taking place in this powder involved the transformation of CuO into Cu 2 O. No pure Cu existed in this heated powders. From the above results, it can be deduced that the grain
212
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
Fig. 1. s, Al; d, Cu; h, CuO; x, Al 2 O 3 , a, 0.5 h; b, 1.0 h; c, 1.5 h; d, 2.0 h; e, 2.5 h. The XRD pattern of mixed Al / CuO powder with 20 wt% Al milled for different times.
size of the constituents was refined continuously during ball milling and a large amount of the Al / CuO couple was formed. The reaction occurring in powders during milling was different from that occurring during heating of powders milled for a short time. It showed that some of the Al / CuO couple in mixed powders trapped in the balls could attain the ignition condition during ball impact. A local reduction reaction occurred. As this reaction has a
Fig. 3. s, Al; h, CuO; j, Cu 2 O. The XRD pattern of powders with 20 wt% Al milled for 2.0 h before (a) and after (b) heating.
significant heat effect, a reduction reaction of the trapped powder was induced.
3.2. Composite solid state reaction According to composite reaction of Al1CuO→CuAl 2 1 Al 2 O 3 , the amount of Al should exceed 48 wt%. Fig. 4 shows the results of the Al / CuO mixed powder with 57 wt% Al at different milling times. As milling time
Fig. 2. a, 0 h; b, 0.5 h; c, 2.0 h. The DSC pattern of powder with 20 wt% Al milled for different times.
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
Fig. 4. s, Al; h, CuO; n, CuAl 2 ; x, Al 2 O 3 ; a, 1 h; b, 2 h; c, 4 h. The XRD pattern of Al / CuO powder with 57 wt% Al milled for different times.
increased, the constituents were mixed and refined. After up to 6 h, the composite reaction took place and CuAl 2 was formed in the mixed powders. The DSC results of this powder milled for different times are shown in Fig. 5. Exothermic effect occurred in the temperature range 120| 3008C. The powder milled for 2 h showed the maximum exothermic effect. The X-ray diffraction pattern of this powder after heating to 3008C in the DSC is shown in Fig.
213
Fig. 6. s, Al; h, CuO; n, CuAl 2 ; x, Al 2 O 3 ; j, Cu 2 O. The XRD pattern of powder with 57 wt% Al milled for 2 h before (a) and after (b) heating.
6. As can be seen, Al 2 O 3 , CuAl 2 , Cu 2 O, CuO and Al were present in this heated powder. It proved that for short milling times the milled powder can be present in different states. Similar to the reduction reaction, CuAl 2 1Al 2 O 3 was directly formed during ball milling. This was also different from the results of heated powder milled for short time. In general, the temperature of milled powder could rise 100–300 K during ball milling [5]. No Cu 2 O is formed during ball milling. The temperature is not the only
Fig. 5. The DSC pattern of Al / CuO powder with 57 wt% Al milled for different times (a) 0 h (b) 1 h (c) 2 h (d) 4 h.
214
X. Shengqi et al. / Journal of Alloys and Compounds 268 (1998) 211 – 214
important factor. The impact time between balls during milling is shorter (about 10 25 s) compared to the heating time in the DSC [6]. This may cause the different results. When the reaction occurred, the pure Cu formed by reduction from CuO combined with the refined Al and the CuAl 2 compound formed directly.
3.3. Results obtained with different Al content As the amount of Al increased, along with the reduction reaction, the synthesis reaction occurred simultaneously. Fig. 7 shows the results of the reactant Al / CuO with different Al contents. The products were Cu, Cu 9 Al 4 , CuAl 2 or Al(Cu) solid solution respectively as the Al content increased. Comparing Figs. 2 and 5, as the Al content increased,
the reaction temperature of the heated powder decreased and the exothermic temperature range was broadened. This may be explained by the fact that as the Al content increased the grain size of Al / CuO became much finer, which could be supported by the results shown in Figs. 1 and 4. The effect of the reaction heat also decreased simultaneously. The composite reaction occurred at a comparatively low temperature in the form of a diffusion reaction.
4. Conclusions (1) CuO could be reduced by Al during ball milling. A local reduction reaction occurred when ignition conditions were reached during ball milling. (2) With increasing Al content a composite reaction took place with the main character of a diffusion reaction. (3) With increasing Al content the end products of the composite reaction were Cu1Al 2 O 3 , Cu 9 Al 4 1Al 2 O 3 , CuAl 2 1Al 2 O 3 or Al 2 O 3 1Al(Cu) solid solution, respectively.
References
Fig. 7. s, Al; d, Cu; m, Cu 9 Al 4 , n, CuAl 2 ; x, Al 2 O 3 ; a, 20 wt% Al; b, 35 wt%Al; c, 57 wt% Al; d, 70 wt% Al; e, 85 wt% Al. The XRD pattern of Al / CuO powder with different Al content milled for 6 h.
[1] C.C. Koch, Annu. Rev. Mater. Sci. 19 (1989) 221. [2] G.B. Schaffer, P.G. McCormick, Mater. Forum 16 (1992) 91. [3] G.B. Schaffer, P.G. McCormick, Mater. Sci. Forum 89-90 (1992) 779. [4] Shengqi Xi, Jingen Zhou, Dongwen Zhang, Xiaotian Wang, J. Mater. Sci. Lett. 15 (1996) 634. [5] R.M. Davis, B. McDermott, C.C. Koch, Metall. Trans. 19A (1988) 2867. [6] D.R. Maurice, T.H. Courtney, Metall. Trans. 21A (1990) 289.