Surface analysis of porcelain fused to metal systems

Summary 

Objective

The effect of four different, commonly performed, metal–ceramic alloy, surface preparation stages, were investigated to observe surface compositional changes.

Methods

Two metal–ceramic alloys were examined (Pd/Ag alloy and a Ni/Cr alloy). Discs 12mm diameter and 2mm thick were produced using the lost wax casting process. Prior to casting alloy ingots were examined using X-ray fluorescence spectrometry (XRF) to determine bulk composition. The four preparation stages were (1) devesting and Al₂O₃ blasted; (2) ground smooth and Al₂O₃ blasted; (3) oxidation firing; (4) firing cycle for opaque porcelain application. X-ray photoelectron spectroscopy (XPS) surface analysis was performed after each surface preparation stage to determine changes in surface composition. SEM with EDS was also used to identify surface composition.

Results

XRF and manufacturers compositional analysis of the alloys showed similar findings for the major elements. XPS analysis showed that at preparation stages 3 and 4 evidence of elemental migration to the surface (In with Pd/Ag alloy and Cr and Mn with Ni/Cr alloy). Alumina was also seen on the alloy surfaces, with SEM/EDS confirming Al₂O₃ particles embedded in the surface of the alloys.

Significance

Surface composition is very different from the batch composition. Surface preparation stage 3 is essential in bringing to the alloy surface elements which could be directly involved in the metal–ceramic bond. Elements and their oxides, in various forms, cover the surface of the alloys. Al₂O₃ particles can remain embedded in the alloy surface during porcelain application.

Keywords: Metal–ceramic alloys, X-ray photoelectron spectroscopy, Surface analysis, Oxide layer