Numerous experimental techniques may be used to establish the boundaries within a phase diagram. In the following paragraphs a number of simple but effective methods, which may be used as the basis of a student laboratory programme are discussed. Other techniques involve the use of sophisticated equipment and are used mainly by research workers. An alternative name for phase diagrams is equilibrium diagrams and the attainment of equilibrium is an important part of many of the practical methods. When a dynamic method is used, as for example in the thermal analysis of a steel to determine thermal arrest points, the results obtained will not be true equilibrium transformation temperatures. Arrest points noted during heating will lie above the equilibrium values and those noted during cooling will be lower than equilibrium values. If the rates of heating and cooling in the test were both similar and fairly slow the mean of the heating and cooling values will approximate to the true equilibrium values.
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