铝团簇的理论计算以及金属纳米材料制备和性能的初步研究
摘要
本文主要进行了三部分的工作，一是对于铝的2～7个原子的小团簇进行了理论计算，二是对于自悬浮定向流制备纳米金属粉进行了理论模拟，三是对于纳米金属材料的制备和性能进行的初步研究。
由于靶材料掺入金属团簇示踪材料的需要，我们对铝材料的团簇行为进行了理论计算，考虑到计算量和理论模型的缺陷，初步研究是在7个原子以内进行的。计算方法是采用Gaussia98程序的B3LYP的方法和全电子的基函数6-311+G*，对Al2—Al7小团簇的结构和能级进行了ab initio计算。我们计算的结果表明：Al_2～Al_7的铝团簇中能级分布具有一些分立的能级，不同于普通块体材料的能级分布。原子数少于5个原子时，铝团簇具有稳定的平面结构，而铝团簇从六个原子的开始具有了三维空间立体结构。在2～7个原子构成的铝团簇中，Al团簇的平均配位数随着团簇中原子个数的增加而增加，随原子个数的增加而趋近于体相的12个。就我们计算的结果来言，Al_2～Al_7的铝团簇中没有出现象碱金属那样的幻数结构。这一研究为我们今后开展多元素体系的团簇计算奠定了基础。
自悬浮定向流方法制备纳米铝粉和铜粉的过程中，通过控制反应管内的气体压力、冷却气体的流速、熔球的温度等因素可以对粉体的尺寸分布进行控制。通常情况下反应管内气流量增大，颗粒的平均尺寸减小；金属熔球的温度升高，颗粒平均尺寸增大。理论模拟的结果表明，金属微粉的流速增大，颗粒的平均粒径减小，与实验结果趋势一致。制备出的纳米粉体的粒径分布符合对数正态分布，纳米铜粉中存在很多单晶颗粒。
对于纳米块体材料的制备和性能进行了初步的研究。通过模压成形的纳米金属铝和铜的块体的密度只有普通体材料密度的75％左右，表明得到的未经烧结的纳米铝块体内部可能还存在很多孔隙或很多疏松的组织。对纳米铝块体材料的退火实验表明，模压成形的铝块体材料的退火温度(300℃)比常规的铝材(400℃)要低，退火保温时间应在30分钟以上。在300℃下保温120分钟的退火中铝的晶粒从45nm长大到了62nm，晶粒长大明显。所测定的纳米铝块体材料的电阻温度系数是普通多晶铝块体材料的50多倍。在我们测定的纳米金属铝材料中，电阻率随温度的升高而增大、随晶粒度尺寸增大而减小。晶粒尺寸为44nm和50nm的1#和2#样品的电阻率分别在25K和45K附近开始随温度的升高快速增大，在曲线上出现拐点。普通纯铝样品的电阻率在75K附近开始随温度升高开始快快速增加。普通铝样品的室温(300K)电阻率与低温(1.9K)的比值为45，而纳米块体铝材料的室温低温电阻率比值为2左右，前者为后者的近20倍。
There are mainly three parts in this paper. The first is the calculation of Al clusters in 2 to 7 atoms, the second is the simulation of preparation with flow-levitation method in theory, and the third is the preliminary study of the preparation and property of metal nanomaterials.
In the need of adulterating target materials with metal clusters as tracing materials, we calculated the cluster behavior of Al materials in theory. The preliminary study was carried out in no more than 7 atoms, considering the much time in calculation and limitation of theory model Gaussian98 program, the B3LYP method and the 6-311+G* basis function were used in the calculation. The structure and energy level of the Al clusters include 2 atoms to to 7atoms was calculated with ab initio method. Discrete energy levels were found in the clusters, which is different from the energy level distribution of bulk materials. The clusters have planar structures with less than 5 atoms and three-dimensional geometric structures with more than 6 atoms. The number of the nearest atoms in the Al clusters increases with the increase of the clusters, and the number runs to 12, which is the number of the nearest atoms in bulk Al materials. The magic number did not appear in the Al clusters as in the alkali metals clusters' ba
sed on our calculation. This research based the calculation of multi-element-system clusters in the near future.
The size of the nanoparticles prepared with the flow-levitation method can be controlled by controling the gas pressure in the action tube, the velocity of cooling gas flow and the temperature in the melt metal globule. Generally the average size of the particles decreases with the increase of the flow in the tube, and it increases with the rise of the temperature of the melt metal globule. The results of theory simulation are close to that of experiments. The size distribution of the particles is in agreement with the lognormal distribution. Single-crystallized particles were found in the copper nanoparticles we prepared.
We preliminarily studied the preparation and the property of nano-bulk Al. The density of the Al bulk nanomaterials is only 75 percent of mat of normal ordinary coarse crystallized counterparts, which means there are a lot of holes or loosen structure in the nano-bulk Al. The nano-bulk Al should be kept more man 30 minutes at temperature no more than 300℃ to annealed which is much lower than that of ordinary Aluminum materials. The coefficient of resistance to temperature of the nano-bulk Al is more than 50 times that of ordinary Al materials. The resistance of the nano-bulk Al increases with the increase of the temperature and decrease with the increase of the grain size. The resistance of sample l#(44nm) and
sample 2#(50nm) rises rapidly from 25k and 45k respectively, and an inflexion appears at the temperature in the resistance-temperature curves. The same inflexion appears at 75K in the resistance-temperature curves. The ration of the resistance at 300K to that at 1.9k of ordinary Al is about 2, however, the same ratio of the nano-metal Al is about 45, which is about 20 times that of ordinary Al's.
由于靶材料掺入金属团簇示踪材料的需要，我们对铝材料的团簇行为进行了理论计算，考虑到计算量和理论模型的缺陷，初步研究是在7个原子以内进行的。计算方法是采用Gaussia98程序的B3LYP的方法和全电子的基函数6-311+G*，对Al2—Al7小团簇的结构和能级进行了ab initio计算。我们计算的结果表明：Al_2～Al_7的铝团簇中能级分布具有一些分立的能级，不同于普通块体材料的能级分布。原子数少于5个原子时，铝团簇具有稳定的平面结构，而铝团簇从六个原子的开始具有了三维空间立体结构。在2～7个原子构成的铝团簇中，Al团簇的平均配位数随着团簇中原子个数的增加而增加，随原子个数的增加而趋近于体相的12个。就我们计算的结果来言，Al_2～Al_7的铝团簇中没有出现象碱金属那样的幻数结构。这一研究为我们今后开展多元素体系的团簇计算奠定了基础。
自悬浮定向流方法制备纳米铝粉和铜粉的过程中，通过控制反应管内的气体压力、冷却气体的流速、熔球的温度等因素可以对粉体的尺寸分布进行控制。通常情况下反应管内气流量增大，颗粒的平均尺寸减小；金属熔球的温度升高，颗粒平均尺寸增大。理论模拟的结果表明，金属微粉的流速增大，颗粒的平均粒径减小，与实验结果趋势一致。制备出的纳米粉体的粒径分布符合对数正态分布，纳米铜粉中存在很多单晶颗粒。
对于纳米块体材料的制备和性能进行了初步的研究。通过模压成形的纳米金属铝和铜的块体的密度只有普通体材料密度的75％左右，表明得到的未经烧结的纳米铝块体内部可能还存在很多孔隙或很多疏松的组织。对纳米铝块体材料的退火实验表明，模压成形的铝块体材料的退火温度(300℃)比常规的铝材(400℃)要低，退火保温时间应在30分钟以上。在300℃下保温120分钟的退火中铝的晶粒从45nm长大到了62nm，晶粒长大明显。所测定的纳米铝块体材料的电阻温度系数是普通多晶铝块体材料的50多倍。在我们测定的纳米金属铝材料中，电阻率随温度的升高而增大、随晶粒度尺寸增大而减小。晶粒尺寸为44nm和50nm的1#和2#样品的电阻率分别在25K和45K附近开始随温度的升高快速增大，在曲线上出现拐点。普通纯铝样品的电阻率在75K附近开始随温度升高开始快快速增加。普通铝样品的室温(300K)电阻率与低温(1.9K)的比值为45，而纳米块体铝材料的室温低温电阻率比值为2左右，前者为后者的近20倍。
There are mainly three parts in this paper. The first is the calculation of Al clusters in 2 to 7 atoms, the second is the simulation of preparation with flow-levitation method in theory, and the third is the preliminary study of the preparation and property of metal nanomaterials.
In the need of adulterating target materials with metal clusters as tracing materials, we calculated the cluster behavior of Al materials in theory. The preliminary study was carried out in no more than 7 atoms, considering the much time in calculation and limitation of theory model Gaussian98 program, the B3LYP method and the 6-311+G* basis function were used in the calculation. The structure and energy level of the Al clusters include 2 atoms to to 7atoms was calculated with ab initio method. Discrete energy levels were found in the clusters, which is different from the energy level distribution of bulk materials. The clusters have planar structures with less than 5 atoms and three-dimensional geometric structures with more than 6 atoms. The number of the nearest atoms in the Al clusters increases with the increase of the clusters, and the number runs to 12, which is the number of the nearest atoms in bulk Al materials. The magic number did not appear in the Al clusters as in the alkali metals clusters' ba
sed on our calculation. This research based the calculation of multi-element-system clusters in the near future.
The size of the nanoparticles prepared with the flow-levitation method can be controlled by controling the gas pressure in the action tube, the velocity of cooling gas flow and the temperature in the melt metal globule. Generally the average size of the particles decreases with the increase of the flow in the tube, and it increases with the rise of the temperature of the melt metal globule. The results of theory simulation are close to that of experiments. The size distribution of the particles is in agreement with the lognormal distribution. Single-crystallized particles were found in the copper nanoparticles we prepared.
We preliminarily studied the preparation and the property of nano-bulk Al. The density of the Al bulk nanomaterials is only 75 percent of mat of normal ordinary coarse crystallized counterparts, which means there are a lot of holes or loosen structure in the nano-bulk Al. The nano-bulk Al should be kept more man 30 minutes at temperature no more than 300℃ to annealed which is much lower than that of ordinary Aluminum materials. The coefficient of resistance to temperature of the nano-bulk Al is more than 50 times that of ordinary Al materials. The resistance of the nano-bulk Al increases with the increase of the temperature and decrease with the increase of the grain size. The resistance of sample l#(44nm) and
sample 2#(50nm) rises rapidly from 25k and 45k respectively, and an inflexion appears at the temperature in the resistance-temperature curves. The same inflexion appears at 75K in the resistance-temperature curves. The ration of the resistance at 300K to that at 1.9k of ordinary Al is about 2, however, the same ratio of the nano-metal Al is about 45, which is about 20 times that of ordinary Al's.
引文
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4．苏品书，超微粒子材料技术[M]，复汉出版社(1989)．
5. Du Y W, J. Appl. Phys., 63, 4100 (1988).
6．都有为、徐明详、吴坚等，物理学报[J]，41(1)，149(1992)．
7. Mo C M, Yuan Z, Zhang L D, et al., Nanostructured Mater., 2, 113(1993).
8. Tabagi H, Ogawa H, Appl. Phys. Lett., 56(24), 2379(1990).
9. Wu W, Herrman J M, Pichat P, Carat., 3, 73(1989).
10. Frank S N, Bard A J., J. Phys. Chem., 81, 1484(1997).
11. Wang K Y, Shen T D, Ouan M X et al. J Mater Sci. Lett, 1993, 18: 29.
12．候碧辉，易俗等。金属学报[J]，1997，33(4)：427-431．
13. Yinmin Wang, Mingwei Chen, Fenghua Zhou & En Ma. High tensile ductility in nanostructured metal. Nature, 419, 912-915(2002).
14. Gleiter H, Progress in Mater. Sci., 33, 223(1989).
15. Yoshizawa Y et al. J Appl Phys, 1988, 6: 6044.
16. Shull R D, Mcmichael R D, Ritter T J. Nanostructured Materials, 1993, 2: 205.
17. Trudean M Let al. Nanostructured Materials, 1992, 1(6): 457
18．王广厚、韩民，物理学进展[J]，10(3)，248(1990)．
19. Hahn H, Averback R S, J. Appl. Phys., 87(2), 113(1990).
20. Erb U. Nanostructured Materials, 1995, 6: 533
21. Gleiter H V. Trans Japan Inst Metal suppl, 1986, 27: 43.
22. Hughes R O, Smith S D, Pande C S, et al. Scrip Metall, 1986, 20: 93.
23. Berkowitz A E, Walter J L. J Mater Res, 1987, 2: 277.
24. Koch C C. Nanostructured Mater, 1993, 2: 109.
25．梅本富，吴炳尧．材料科学与工程[J]，1992，10(4)：1．
26. Kawamura Y, et al. Mater Sci Eng, 1998, 98: 449.
27. Noh T H, et al. J Magn Mater, 1992, 128: 129.
28. Gorria P, et al. J Appl Phys, 1993, 73(10): 6600.
29．刘佐权等．金属学报[J]，1996，32(8)：862．
30. Akishisa Inone, Akira Murakami, Tao Zhang, et al. Mater Trans, JIM 1997, 38:189.
31. Akishisa Inoue, Hisat Koshiba, Tao Zhang, et al. Mater Trans, JIM, 1997, 38: 577.
32. Akishisa Inoue, Zhang T, Zhang W, Takeuchi A. Mater Trans, JIM, 1996, 37: 99.
33. Peker A, Johnson W L, Appl phys Lett, 1993, 63: 2342.
34. Akishisa Inoue, Takahiro Aoki, Hisamichi Kimura, Mater Trans, JIM, 1997, 38:175.
35．何国，陈国良，材料科学与工艺[J]，1998，6：105
36. LU K, WEI W D, WANG J T. The mechanism of crystalline Ni_(88)P_(12) [J]. Scripta Metal Mater, 1990(24): 2319-2321.
37. XU B S, TAANAKA S I. Formation and bonding of platinum nanoparticles controlled by high energy beam irradiation [J]. Nanostructured materials, 2000(12): 915-918.
38．李冬剑，丁炳哲，胡壮麒等，科学通报[J]，1994，19：1749．
39. Yao B, Ding g Z, Sui G L, et al. J Mater Res, 1996, 11: 912.
40. Valiev R Z, Korasilnikov N A, et al. Mater Sci Eng 1991, A137: 35.
41. Valley R Z, Krasilnikov N A, Tzenev N K. Mater Sci Eng, 1991, A137: 35.
42. AdduIov R Z, VaIiev R Z, Krasilnikov N A, Mater. Sci. Lett., 1990, 9: 1445.
43. Valiev R Z, Koznikov A V, Mulyukov R R, Mater. Sci. Eng., 1993, A168: 141.
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