陳蕙雅思教材 - 雅思閱讀精選 (Nitinol)

Nitinol

Nitinol is one of themost extraordinary metals to be discovered this

century: A simple alloyof nickel and       titanium, nitinol hassome perplexing

properties. A metal witha memory, it can be made to remember any shape

into     which it is fashioned, returning to thatshape whenever it is heated.

For example, a piece ofnitinol wire bent to form a circle that is then

heated and quenched willremember this shape. It may then  be bent or

crumpled, but  on reheating, will  violently untwist, reformingits

original shape.         This remarkable ability is calledShape  Memory Effect

(SME); other  alloys, such as brasses,  are known  to possess it to a  

limited  extent. No one fully understands SME, andnitinol remains

particularly perplexing,for,  whenever it         performs this peculiar feat, it

appears to be breakingthe laws of thermodynamics by springing back into

shape with greater forcethan was used to deform it in the first place.

But  not only is nitinol capable  of remembering, it  also has  the  

ability to"learn". If the heating-cooling-crumpling-reheating process is

carried out sufficientlyoften, and the metal is always crumpled in              

exactly the same way, thenitinol will not only remember its original

shape, but gradually itlearns to remember         its crumpledform as well, and

will begin to return tothe same crumpled shape every time it is cooled.

Eventually, the metalwill crumple and uncrumple, totally unaided, in

response to changes intemperature and without any sign       ofmetal fatigue.

Engineers have producedprototype engines that are driven by the force of

nitinol springing fromone shape to         another as italternately encounters

hot and cold water. Theenergy from these remarkable engines  is,

however,  not                   entirely  free: heat  energy  is required  to  produce  

the temperaturedifferences needed to run the engine. But the optimum

temperatures at which themetal reacts can be controlled by altering the

proportions of nickel totitanium; some alloys will even perform at room

temperature. Thenecessary temperature range between the warm and the

cold    can be as little as twelve degreescentigrade.

鎳鈦合金鎳鈦諾是這個世紀所發現的最不尋常的金屬之一，作為鎳和鈦的簡單的一種合 金，鎳鈦諾具有一些令人驚歎的特徵。  

這是一種有記憶力的金屬，人們可以使它記住它被 塑成的任何形狀，並在加熱後恢復這一形狀。  比如，一節鎳鈦諾線圈在加熱冷卻後會記住 圓圈這形狀。  

隨後它可能被彎折成其它形狀，但一旦再次加熱，就會迅速地自動恢復成最 初的圓圈狀。  這種不尋常的能力被稱為形狀記憶效果(SME)。  

其它一些合金如黃銅在一定

程度上也具有這種特性。  目前人們對  SME  這一特性尚缺乏透徹的認識，而鎳鈦諾尤其使

人驚奇，因為每當它展現這一驚人的功能時，似乎都違背了熱力學原理。  因為它在恢復原 有形狀時所釋放的力比人們使它變形所施加的力大得多。

鎳鈦諾不僅有記憶力，還能"學習

"。 如果加熱-冷卻-彎曲-再加熱這一過程重複一定次數，且每次冷卻後它都被絲毫不差地彎

成同一形狀，它不僅可以記住最初的形狀，還能逐漸記住它被彎成的形狀，並開始在每次冷 卻時恢復這一形狀。  

最終，它會自動地隨溫度變化而彎曲和恢復這些形狀，並且沒有任何 疲勞跡象。  工程師們已製造出一些發動機樣機，利用鎳鈦合金在交替遇熱水和冷水時迅速

改變形狀所產生的力做推動力。  然而這些神奇的發動機工作時並非完全不耗能，因為必須 有熱能來製造溫差才能使機器運轉。  

但人們可以通過改變合金中鎳鈦的比例來控制使它反 應的最佳溫度。  有的鎳鈦合金甚至能在室溫下做出反應，冷暖之間的最小溫差只有 12℃。