| http://www.w3.org/ns/prov#value | - Non-limiting examples of matrix materials include one or more of : rare earth metals, metal oxides including titania, zirconia, magnesia, thoria, beryllia, quartz, silica or sols, and mixtures thereof; for example, silica-magnesia, silica-zirconia, silica-titania, silica-alumina and silica-alumina-thoria. [0040] In one embodiment, matrix materials are natural clays, such as those from the families
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