Nitinol - A Memory Metal

Problem In 1965 some scientists produced a very special nickel-titanium alloy which can remember its programmed form. They called this kind of alloy memory metal and the special compound Nitinol , because it was discovered in the Nickel-Titanium Naval Ordonnance Laboratory. The memory metals are often used in engines, motors and other pieces of equipment, for which it is important to have a certain form at a certain temperature, e.g. for closing a valve. The conversion temperature of the Nitinol composition NqTq is approximately 50°C. Samples of such memory metals, like nitinol wires, can be obtained from Educational Innovations (teachersource.com). 

Material Beaker samples of memory wire, memory metal pre-shaped springs. 

Procedure and Observation Bend a wire into any shape and hold it in the flame of a match or candle the wire spontaneously regains its shape (demonstrate it by using an overhead projector). Dip the wire which is re-formed into hot water and observe. Either press together or stretch out springs and place into hot water (overhead projector) once again the original form returns. 

Tip A nitinol wire can be reprogrammed to different shapes the new wire form has to be stabilized between two steel plates and heated red hot with a burner for several minutes. If an oven is available, the steel plates with the fixed wires can also be heated for 10 min at approximately 500°C. This new form always reemerges whenever the wire is reshaped at room temperature and then heated until the transformation temperature is exceeded. 

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