Strength Increase of Alumina Foams by a Sodium Aluminosilicate Glass Coating with Subsequent Na⁺ ? K⁺ Ion Exchange (Gorilla Glass Coating)

Reticulated alumina ceramic foams manufactured by the Schwartzwalder technique are coated with a sodium aluminosilicate glass using an aqueous precursor containing alumina particles and sodium silicate. After a heat treatment, a well-adhering glass layer with a thickness between 10 and 120 mu m is obtained. Besides the strut surface, the glass phase also penetrates the hollow strut cavities as well as strut cracks. The total porosity of the glass-coated foams is between 88% and 90%, and the open cellular structure is not negatively affected by the glass coating. The compressive strength increases by a factor of two under consideration of the decrease in total porosity; a compressive strength in the order of magnitude of 2 MPa is feasible. An ion exchange of Na(+ )by K+ into the glass coating layer (chemical strengthening) is successfully demonstrated, but does not result in an additional improvement of the compressive strength.