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GRE阅读题目解析:晶体结构

2017-05-15 09:10:00来源：新东方在线整理

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　　查看全部：GRE阅读答案解析(汇总)

　　GRE阅读题目解析:晶体结构

　　P6

　　When a molten metal or metallic alloy is cooled to a solid, a crystalline structure is formed that depends on the particular alloy composition. In contrast, molten nonmetallic glass-forming materials, when cooled, do not assume a crystalline structure, but instead retain a structure somewhat like that of the liquid--an amorphous structure. At room temperature, the natural long-term tendency for both types of materials is to assume the crystalline structure. The difference between the two is in the kinetics or rate of formation of the crystalline structure, which is controlled by factors such as the nature of the chemical bonding and the ease with which atoms move relative to each other. Thus, in metals, the kinetics favors rapid formation of a crystal line structure, whereas in nonmetallic glasses the rate of formation is so slow that almost any cooling rate is sufficient to result in an amorphous structure.

　　11. The author implies that the rate at which the molten materials discussed in the passage are cooled is a determinant of the

　　(A) chemical composition of the resulting solids

　　(B) strength of the chemical bonds that are formed

　　(C) kinetics of the materials' crystalline structure

　　(D) structure the materials assume

　　(E) stability of the materials' crystalline structure

　　12. It can be inferred from the passage that, theoretically, molten nonmetallic glasses assume a crystalline structure rather than an amorphous structure only if they are cooled

　　(A) very evenly, regardless of the rate

　　(B) rapidly, followed by gentle heating

　　(C) extremely slowly

　　(D) to room temperature

　　(E) to extremely low temperatures

　　13. Select the sentence in which the author illustrates the causes of the rate of formation of the crystalline structure.

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