[Changes in microstructure of ceramic alloys after heat and electrochemical acid treatment]

The technique of electrochemical etching was developed by Dr. Tegart for application in both research and industry in 1959. There is considerable evidence showing that in conjunction with chemical bonding, surface roughness of etched casting restorations can apparently improve the mechanical adherence between the porcelain and the metal. It is obvious that surface roughness produced by sandblasting or electrochemical etching of the metal substrate not only provides mechanical interlocking but also increases the surface area for porcelain attachment. It was observed in this study that a properly heat-treated surface was significantly rougher than a surface without appropriate treatment after electrochemical acid etching. The roughness of base metals also treated with 0.5N nitric acid appeared greater obvious than those treated with 10% sulfuric acid. The etching pattern can be evaluated by selective removal of the alloy phases present between the dendritic arms in the base metal alloy. The technique of electrochemical acid etching is limited to alloys that solidify with a multiphasic structure- that is, a base metal alloy. And there are no known noble alloys suitable for this technique in this experiment. Electrolytic etching is most conveniently evaluated under a light microscope at about 30-80 magnifications to inspect surface relief and etching patterns. It remains to be determined by further research what is the exact cause of the increased roughness and how it improves the metal for ceramic mechanical bonding.