Minor Phases and Impurities

Many impurities can be detected at the 1-10 ng/g level in simple systems. However, the limit of quantitative determination in practical 

Emission spectroscopy is the most generally applicable of the survey methods although there are limitations on its sensitivity. It is widely used for characterization of solids, powders, liquids, and gases and has the capability of detecting up to 70 elements by direct current arc excitation. Determination of nonmetallic elements is also possible with emission spectroscopy, but this requires special techniques that are infrequently used. 

Spark-source mass spectrometry can detect all elements, with sensitivities often as good as 1 ng/g. Residual gases in the vacuum system restrict detection limits for carbon, oxygen, and nitrogen to 

X-ray spectroscopy can also be employed for survey analysis of impurities and has the advantage of being nondestructive. Lower limits of detection are rarely better than 10-100 ppm, unless preconcentration is used, and the elements of the first period cannot be detected at low concentrations. 

Electrical measurements are useful for determining the total content of electrically active impurities in conductors and semiconductors. The shape of the freezing curve gives considerable information on total impurities in a material with a suitable melting point. Special techniques must be used for most metals that melt at high temperatures or for materials that decompose on melting. 

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