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Gorzaloon wrote: " 'These tiles are super hi tech ceramics of some kind?'

Not really..they were even selling off spec ones for industrial use in the late 80's-90's. We had some at work. They were just a glorified zirconia fiberglass-like refractory wool molded and fired into lightweight "Fire Bricks"."

Zirconium, nor its impure oxide Zirconia are not used in the manufacture of the Shuttle tiles, according to NASA.

Instead the High-Temperature Reusuable Surface Insulation Tiles (HRSI) are made of nearly pure silica.

High-Temperature Reusable Surface Insulation Tiles

"The HRSI tiles are made of a low-density, high-purity silica 99.8-percent amorphous fiber (fibers derived from common sand, 1 to 2 mils thick) insulation that is made rigid by ceramic bonding. Because 90 percent of the tile is void and the remaining 10 percent is material, the tile weighs approximately 9 pounds per cubic foot. A slurry containing fibers mixed with water is frame-cast to form soft, porous blocks to which a collodial silica binder solution is added. When it is sintered, a rigid block is produced that is cut into quarters and then machined to the precise dimensions required for individual tiles.

HRSI tiles vary in thickness from 1 inch to 5 inches. The variable thickness is determined by the heat load encountered during entry. Generally, the HRSI tiles are thicker at the forward areas of the orbiter and thinner toward the aft end. Except for closeout areas, the HRSI tiles are nominally 6- by 6-inch squares. The HRSI tiles vary in sizes and shapes in the closeout areas on the orbiter. The HRSI tiles withstand on-orbit cold soak conditions, repeated heating and cooling thermal shock and extreme acoustic environments (165 decibels) at launch..."

NASA: High-Temperature Reusable Surface Insulation Tiles

The space shuttle engine contains a copper-silver-zirconium alloy:

"The space shuttle engine, for example, uses a copper-silver-zirconium alloy..."

Structural Materials in Aerospace Systems