SAMPLE 17

　　[物理學]

　　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.

　　[答案與考點解析]

　　1. 【答案】C

　　【考點解析】本題是一道中心主旨題。本文的中心主旨句是首段的第二句，該句中的“these materials”指的就是首段第一句中的“amorphous metallic alloys or glassy metals”。可見本題的正確答案應該是C。考生一定要知道：破解中心主旨題的關鍵在于抓住全文的中心主旨句。

　　2. 【答案】C

　　【考點解析】本題是一道審題定位題。根據題干中的“prospects”(前景)可將本題的答案信息迅速確定在尾段，因為尾段首句中的“promising”(有前途的)暗示本段講某種事物的前景或未來。本題的確切答案信息來源在尾段的最后一句，該句中的“that is likely to be overcome”暗示本題的正確答案是C。考生在解題時一定要具備迅速地審題定位能力，還要具備理解原文深層含義的能力。

　　3. 【答案】D

　　【考點解析】這是一道細節推導題。根據題干中的“crystalline structure”可將本題的答案迅速確定在第二段的首句，該句中的“depends on”和題干中的“determines”相互呼應。通過仔細理解第二段的首句可推導出本題的正確選項是D。請考生注意原文中“composition”和選項中“consists of”的轉換。考生在解題時一定要具備細節推導能力，不能只停留于文字的表面含義。

　　4. 【答案】D

　　【考點解析】這是一道細節推導題。根據題干中的“the structure of liquid metals and the structure of glassy metals”可將本題的答案信息來源迅速確定在第三段的首句。該句中的“similar”一詞暗示選項D是正確答案。考生在解題時應重視對立對比關系。

　　5. 【答案】C

　　【考點解析】本題是一道總結歸納信息并進行引申推導題型。從本題題干中的“molten nonmetallic glasses”可斷定本題的答案信息在本文第二段，因為該句中包含有題干中的核心詞語“molten nonmetallic glasses”。我們需要歸納和總結本段的每一句話，尤其是第三、四句的內容，另外本段尾句的含義為推導(infer)出本題的正確選項C起到至關重要的作用。考生在破解此類題型時一定要注意首先歸納和總結原文中相應出題點的全面信息，更要注意邏輯推導的能力。

　　[參考譯文]

　　材料科學家和固體物理學家的深入研究已促進了一種固體物質的出現，這類固體被稱為非晶體金屬合金，也就是玻璃金屬。理論和應用研究者對這些材料的結構特性的興趣正與日俱增。

　　當一種熔化的金屬和金屬合金冷卻成固體時，依賴于特定的合金成份將形成各種晶體結構。相比之下，熔化的非金屬、玻璃類材料在冷卻后將不會形成晶體結構，而是保留一點類似于液體的非晶體結構，在室溫條件下，兩類材料的自然的長期傾向都形成了晶體結構。它們之間的不同在于動態性，即形成晶體結構的速度。這種動態性受下述兩種因素控制：化學結合的性質和分子之間相互運動的自由程度。由此，對金屬而言，動態歷程有利于晶體結構的快速形成;而對非金屬來說，這種形成速度非常慢，以至于任何自然冷卻速度都足以形成一種非晶體結構。要想形成玻璃金屬，熔化的金屬必須以極快的速度冷卻，以抑制晶體的形成。

　　人們認為玻璃金屬的結構與液態金屬的結構類似。創建這種液體結構模型的第一次嘗試是已故的倫敦大學的J. D.鮑納爾進行的，他將堅硬的球體盡可能多地填塞進一個橡膠容器中，以便得到一種最大可能的密度。這個密度結果以及隨機填塞結構以后便成為試圖建立玻璃金屬結構模型的基礎。

　　基于鮑納爾模型，由合成金屬的成份組成對合金密度的計算結果與實驗測得的結果相當地吻合，當然一些細微的差異仍然存在。實驗結果是通過測量由一種重金屬和類金屬組成的合金得到的，如鈀和硅的合金，或鐵磷和碳組成的合金。實際的合金和鮑納爾模型所用的球體之間的差別在于合金的成份有不同的體積大小，因此，基于兩種大小的球體的模型更適合于兩類物質的合金。合金中非金屬的小原子可能填進由大原子隨機填塞形成的緊密結構中。

　　玻璃金屬最有前景的一個特征是高強度與高延伸性的結合。在常見的晶體材料中，這兩種特性一般是成反比的，但人們渴望它們同時存在。在實際用途中可能還有一個問題急待解決，即當玻璃金屬在相對的低溫下慢慢加熱時，它會逐漸變為晶體結構。