發(fā)布時間：2019-01-12 10:03

【摘要】：近年來,納米材料的應用越來越廣泛,特別是對貴金屬納米材料的研究更是納米材料領域的研究熱點之一。本文采用分子動力學方法和嵌入原子勢,對不同尺寸銀納米晶在高溫弛豫下的能量和微觀結構演變進行了模擬研究。首先,對于沿相互垂直{110}、{211}和{111}面切割形成的近正方體截面銀納米晶,體系溫度、體系尺寸均對原子的能量分布有影響:同種體系原子平均勢能隨溫度的升高而增加,而在相同溫度下的不同體系原子能量分布密度比較相近,但是體系尺寸越小,原子平均能量越高,原子勢能在高能區(qū)所占的比例越多,能量越分散。通過模擬還發(fā)現(xiàn),體系在升溫過程中,原子平均能量隨溫度的升高出現(xiàn)線性增加,當溫度到達某一溫度(熔點)時體系會出現(xiàn)能量的突變,這個突變點大小與體系尺寸有關,尺寸越小,突變溫度越低。然后,體系能量的改變使原子的排列發(fā)生改變,銀納米晶隨著溫度的上升,從規(guī)則的立方體結構開始,先從角再到邊再到面出現(xiàn)原子遷移重組,最后銀納米晶演變?yōu)榍蛐�。銀納米晶的熔化演變過程表明:納米晶的高溫熔化可分三個階段,即很短時間的表面預熔,較長時間的表面原子無序和重排,迅速的全面熔化。最先出現(xiàn)原子遷移重組的是八個頂角,其次是十二條棱邊,最后是六個面,這種遷移重組使得納米晶的比表面減小,體系的能量減小。另外,銀納米晶在熔化過程中出現(xiàn)明顯的各向異性行為:)211(面熱穩(wěn)定性最低,最先熔化,其次是(110)面,熱穩(wěn)定性最高的是?111?面,最后熔化。研究結果還表明:不同晶面最層和次外層的穩(wěn)定壽命相差不大且時間極短,第三層及以內的穩(wěn)定壽命較長且依次少量增加。但對于不同晶面,第三層及以內的穩(wěn)定壽命差異較大,最短的是)211(面,最長的是?111?面,(110)面介于兩者之間。
[Abstract]:In recent years, the application of nanomaterials has become more and more extensive, especially the research of noble metal nanomaterials is one of the research hotspots in the field of nanomaterials. In this paper, the energy and microstructure evolution of silver nanocrystals with different sizes under high temperature relaxation have been simulated by molecular dynamics method and intercalated atomic potential. First, the temperature of the silver nanocrystals with near-square cross-section, which are cut along the faces of {110}, {211} and {111}, is calculated. The size of the system has an effect on the energy distribution of atoms: the average potential energy of the same system increases with the increase of temperature, but the energy distribution density of different systems at the same temperature is similar, but the smaller the system size is, The higher the average atomic energy is, the more the potential energy in the high energy region is, and the more dispersed the energy is. It is also found by simulation that the average atomic energy increases linearly with the increase of temperature during the heating process. When the temperature reaches a certain temperature (melting point), there will be a sudden change of energy in the system, which is related to the size of the system. The smaller the size, the lower the mutation temperature. Then, the change of energy of the system changes the arrangement of atoms. With the increase of temperature, the silver nanocrystals begin with the regular cube structure, and the atoms migrate and recombine from angle to edge to surface, finally silver nanocrystals become spherical. The melting evolution of silver nanocrystals shows that the melting of nanocrystals at high temperature can be divided into three stages: surface premelting for a very short time, disordered and rearranged surface atoms for a long time, and rapid total melting. The atom migration recombination occurs first in eight vertices, then in 12 edges, and finally in six surfaces. This migration recombination reduces the specific surface of nanocrystals and reduces the energy of the system. In addition, the anisotropic behavior of silver nanocrystals in the melting process is obvious:) 211 (surface thermal stability is the lowest, first melting, followed by (110) surface, the highest thermal stability is? 111? Face, finally melt. The results also show that the stable life of the most layer and the subouter layer of the different crystal planes is not different and the time is very short, and the stable life of the third layer and the inner layer is longer and slightly increased in turn. But for different crystal planes, the stability life of the third layer and the inner layer varies greatly, the shortest one is 211 (face, the longest is? 111? The (110) plane is between the two.
【學位授予單位】：江西理工大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB383.1;O614.122

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本文編號：2407654