Introduction

• chemical purity of components in the material studied.
• physical characteristics of samples
  (add a picture of a metal compound in powder form or add the picture in McCallister, p. 429, of a processing technique by which small powder particles of metal alloys are produced)
• time criterion. Experiments must be carried out until equilibrium is attained.
• constancy of composition. Compositions must remain constant during experiments.
• chemical composition and chemical analysis. The material studied is analyzed before the experiment (and sometimes after) to identify its composition.

With the criteria listed above in mind, phase equilibria relations are determined through many techniques, each falling under one of the following categories: (a paragraph will be written for each technique listed)

I. Static Methods. Static methods are those in which the temperature of the sample is held constant until equilibrium is attained.

• quenching methods
• static method in which phases in samples are mechanically separated at the equilibrium temperature
• methods involving the vapor phase
  (diagram of a gas-mixing apparatus, like the one on p. 120 of reference 2)

II. Dynamic Methods. Methods of phase equilibrium determination at other than ambient conditions.

• thermal methods of analysis. Two most common methods include thermal analysis where time vs. temperature curve shows thermal arrest at the phase change, and differential thermal analysis (DTA)
  (diagram of DTA instrument, p. 90 of reference 3)
• electrical conductivity measurements. At subsolidus temperatures, formation of a new phase will usually be evidenced by a change in slope in the conductivity vs. temperature curve.
• thermal gravimetric analysis
• dilatometric methods (picture of a dilatometer assembly, p. 135 of reference 2)

Once phase equilibrium relations are established, it is necessary to identify the phases present in the specimen. The primary methods of phase identification are:

• optical microscopy
• x-ray diffraction
• electron microscopy (SEM and TEM)

These methods account for over 95% of direct phase identification. Other techniques include: (a brief description will be given for each method)

• Mossbauer spectroscopy
• infrared spectroscopy

References

[1] Materials Science and Engineering: An Introduction. William D. Callister
[2] Phase Diagrams: Materials Science and Technology, Volume I. Edited by Allen M. Alper.
[3] Thermal Analysis - Techniques & Applications. Edited by E. L. Charsley and S. B. Warrington.