material. Examinations may be conducted on the surface of the refractory, internally
to evaluate the normal structure, or across interfaces between materials or
material and service environments to evaluate changes that occur. Naturally, it
is essential to define the nature of the information that is being sought in order
that the most effective approach can be taken. Generally, polished metallographic
sections are made from refractory samples although geological thin sections may
be appropriate.
Polished sections provide greatly improved spatial resolution but
reduced mineralogical information over thin sections. Selective etching techniques
are employed to enhance features such as grain boundaries and increase
contrast between phases and sometimes in phase identification.