Hobbies And Interests
Martensite
Nickel titanium at cooler temperatures -- below -4°F -- is known as martensite, and its molecules have a rhomboid crystal structure, meaning that its shape has six sides and each side has four edges, but it's not a cube because the angles and sides are not symmetrical. On one side of the molecule, the angles measure 98.8° and 81.2°, and its edges measure 0.46 nanometers (nm) and 0.30 nm. The edges of adjacent faces measure 0.30 nm and 0.41 nm.
Austenite Start Temperature
As nickel titanium is heated above a certain temperature, it begins to transition from martensite into austenite. This temperature ranges from -4°F to 140°F, depending on the amount of nickel in the compound. Specifically, the complex molecular structure of martensite begins to shift into a simpler cubic structure. The distance between the atoms along the edges of the cubic structure is 0.3 nm. The angles at any given corner of the cube measure 90°.
Properties
One of nickel titanium's more unusual properties is its "shape memory." In austenite form, the alloy is fairly rigid and has a particular shape. When it changes to martensite after exposure to lowered temperatures, nickel titanium becomes more elastic and flexible. However, if the alloy is heated again and reverts to austenite, the alloy will take on the shape it had before cooling, regardless of what shape it had as martensite. This phenomenon of "remembering" its former shape is called "shape memory."
Applications
A variety of industries use nickel titanium. In dentistry, nickel titanium is a vital component in certain types of braces. In sports, the alloy is used as a golf club insert. The communications industry uses nickel titanium in the retractable antennas of certain cell phones. In women's fashion, the alloy is used to make the underwire in bras.