宫东风25个考研英语阅读经典试题及答案(17)

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宫东风25个考研英语阅读经典试题及答案(17)


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  SAMPLE 17

  [物理学]

  The intensive work of materials scientists and solid-state physicists has given rise to a class of solids known as amorphous metallic alloys or glassy metals. There is a growing interest among theoretical and applied researchers alike in the structural properties of these materials.

  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 crystallines 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. For glassy metals to be formed, the molten metal must be cooled extremely rapidly so that crystallization is suppressed.

  The structure of glassy metals is thought to be similar to that of liquid metals. One of the first attempts to model the structure of a liquid was that by the late J. D. Bernal of the University of London, who packed hard spheres into a rubber vessel in such a way as to obtain the maximum possible density. The resulting dense, random-packed structure was the basis for many attempts to model the structure of glassy metals.

  Calculations of the density of alloys based on Bernal-type models of the alloys metal component agree fairly well with the experimentally determined values from measurements on alloys consisting of a noble metal together with a metalloid such as alloys of palladium and silicon or alloys consisting of iron phosphors, and carbon, although small discrepancies remained. One difference between real alloys and the hard spheres area in Bernal models is that the components of an alloy have different size, so that models based on two sizes of spheres are more appropriate for a binary alloy for example. The smaller metalloid atoms of the alloys might fit into holes in the dense random-packed structure of the larger metal atoms.

  One of the most promising properties of glassy metals is their high strength combined with high malleability. In usual materials, one finds an inverse relation between the two properties, whereas for many practical applications simultaneous presence of both properties is desirable. One residual obstacle to practical applications that is likely to be overcome is the fact that glassy metals will crystallize at relatively low temperatures when heated slightly.

  1. The author is primarily concerned with discussing

  [A] crystalline solids and their behavior at different temperatures.

  [B] molten materials and the kinetics of the formation of their crystalline structure.

  [C] glassy metals and their structural characteristics.

  [D] metallic alloys and problems in determining their density.

  2. The author’s attitude toward the prospects for the economic utilization of glassy metals is one of

  [A] disinterest.

  [B] impatience.

  [C] optimism.

  [D] apprehension.

  3. According to the text, which of the following determines the crystalline structure of a metallic alloy?

  [A] At what rate the molten alloy is cooled.

  [B] How rapid the rate of formation of the crystalline phase is.

  [C] How the different-sized atoms fit into a dense random-packed structure.

  [D] What the alloy consists of and in what ratios.

  4. Which of the following best describes the relationship between the structure of liquid metals and the structure of glassy metals, as it is presented in the text?

  [A] The latter is an illustrative example of the former.

  [B] The latter is a large-scale version of the former.

  [C] The former is a structural elaboration of the latter.

  [D] The former is a fair approximation of the latter.

  5. It can be inferred from the text 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] very slowly.

  [D] to room temperature.
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  [答案与考点解析]

  1. 【答案】C

  【考点解析】本题是一道中心主旨题。本文的中心主旨句是首段的第二句,该句中的“these materials”指的就是首段第一句中的“amorphous metallic alloys or glassy metals”。可见本题的正确答案应该是C。考生一定要知道:破解中心主旨题的关键在于抓住全文的中心主旨句。

  2. 【答案】C

  【考点解析】本题是一道审题定位题。根据题干中的“prospects”(前景)可将本题的答案信息迅速确定在尾段,因为尾段首句中的“promising”(有前途的)暗示本段讲某种事物的前景或未来。本题的确切答案信息来源在尾段的最后一句,该句中的“that is likely to be overcome”暗示本题的正确答案是C。考生在解题时一定要具备迅速地审题定位能力,还要具备理解原文深层含义的能力。

  3. 【答案】D

  【考点解析】这是一道细节推导题。根据题干中的“crystalline structure”可将本题的答案迅速确定在第二段的首句,该句中的“depends on”和题干中的“determines”相互呼应。通过仔细理解第二段的首句可推导出本题的正确选项是D。请考生注意原文中“composition”和选项中“consists of”的转换。考生在解题时一定要具备细节推导能力,不能只停留于文字的表面含义。

  4. 【答案】D

  【考点解析】这是一道细节推导题。根据题干中的“the structure of liquid metals and the structure of glassy metals”可将本题的答案信息来源迅速确定在第三段的首句。该句中的“similar”一词暗示选项D是正确答案。考生在解题时应重视对立对比关系。

  5. 【答案】C

  【考点解析】本题是一道总结归纳信息并进行引申推导题型。从本题题干中的“molten nonmetallic glasses”可断定本题的答案信息在本文第二段,因为该句中包含有题干中的核心词语“molten nonmetallic glasses”。我们需要归纳和总结本段的每一句话,尤其是第三、四句的内容,另外本段尾句的含义为推导(infer)出本题的正确选项C起到至关重要的作用。考生在破解此类题型时一定要注意首先归纳和总结原文中相应出题点的全面信息,更要注意逻辑推导的能力。

  [参考译文]

  材料科学家和固体物理学家的深入研究已促进了一种固体物质的出现,这类固体被称为非晶体金属合金,也就是玻璃金属。理论和应用研究者对这些材料的结构特性的兴趣正与日俱增。

  当一种熔化的金属和金属合金冷却成固体时,依赖于特定的合金成份将形成各种晶体结构。相比之下,熔化的非金属、玻璃类材料在冷却后将不会形成晶体结构,而是保留一点类似于液体的非晶体结构,在室温条件下,两类材料的自然的长期倾向都形成了晶体结构。它们之间的不同在于动态性,即形成晶体结构的速度。这种动态性受下述两种因素控制:化学结合的性质和分子之间相互运动的自由程度。由此,对金属而言,动态历程有利于晶体结构的快速形成;而对非金属来说,这种形成速度非常慢,以至于任何自然冷却速度都足以形成一种非晶体结构。要想形成玻璃金属,熔化的金属必须以极快的速度冷却,以抑制晶体的形成。

  人们认为玻璃金属的结构与液态金属的结构类似。创建这种液体结构模型的第一次尝试是已故的伦敦大学的J. D.鲍纳尔进行的,他将坚硬的球体尽可能多地填塞进一个橡胶容器中,以便得到一种最大可能的密度。这个密度结果以及随机填塞结构以后便成为试图建立玻璃金属结构模型的基础。

  基于鲍纳尔模型,由合成金属的成份组成对合金密度的计算结果与实验测得的结果相当地吻合,当然一些细微的差异仍然存在。实验结果是通过测量由一种重金属和类金属组成的合金得到的,如钯和硅的合金,或铁磷和碳组成的合金。实际的合金和鲍纳尔模型所用的球体之间的差别在于合金的成份有不同的体积大小,因此,基于两种大小的球体的模型更适合于两类物质的合金。合金中非金属的小原子可能填进由大原子随机填塞形成的紧密结构中。

  玻璃金属最有前景的一个特征是高强度与高延伸性的结合。在常见的晶体材料中,这两种特性一般是成反比的,但人们渴望它们同时存在。在实际用途中可能还有一个问题急待解决,即当玻璃金属在相对的低温下慢慢加热时,它会逐渐变为晶体结构。

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