|Monthly Tech-Tip |
A 'phase' of a mineral is a physically different molecular or crystal structure induced by a set of conditions (i.e. temperature, pressure). Phases of silica, for example, are chemically the same but have different physical properties. If significant differences are imposed a phase will have its own name (i.e. diamond, graphite are phases of carbon). If differences are not significant an alteration of the same mineral name is used (i.e. alpha quartz, beta quartz). It is important to realize that a phase exists as a recognition of a physical change, not a chemical one. These changes are measurable by instruments that measure physical properties (e.g. a microscope or dilatometer). Cristobalite is a good example, it is a phase of silica and yet has very different properties (e.g. thermal expansion, crystal shape) than quartz, however they are chemically the same. The former can be created by submitting quartz to a high temperature and holding it there.
Catalysts encourage chemical reaction thus they would not be associated with phase changes. However the term 'catalyst' is sometimes used to refer to conditional changes that effect phase changes.
Raw ceramic materials are minerals or mixtures of minerals. By taking the characteristics of these into account technicians can rationalize the application of glaze chemistry.