Comparison of surface treatment methods for promoting the adhesion of glass on titanium

A glass allowing the wetting of titanium has previously been developed. Two surface treatments promoting glass adhesion on titanium are compared: preo xidation and phosphatation combined with preoxidation. After preoxidation a t 700 degrees C, a 1 mu m-thick TiO2 layer covers titanium. The phosphated titanium substrates are oxidized at 600 degrees C to obtain a 20 mu m-thick oxifluoride layer. After firing, glass adhesion is obtained with both surf ace treatments, but a "critical time of firing" appears with preoxidized ti tanium. WDS analysis suggests that diffusion of TiO2 into the glass is resp onsible for adhesion on preoxidized titanium, while a complex oxifluoride l ayer allows redox phenomena in the case of phosphated titanium. Pull-off te sts have measured a maximum strength from 1.5 to 3 MPa whatever the surface treatment. Measurement of transverse crack densities in the vitreous coati ngs gives a higher value for phosphated than for preoxidized titanium. This confirms that better adhesion is obtained after phosphatation treatment. ( C) 1998 Kluwer Academic Publishers.