A metallurgical study of the contamination zone at the surface of dental Ti castings, due to the phosphate-bonded investment material: the protection efficacy of a ceramic coating

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Commercial pure (cp) titanium exhibits remarkable advantages compared to conventional dental alloys, mostly in the fields of biocompatibility and corrosion resistance. Today there exist very optimistic perspectives for the use of titanium as an ideal alternative for the conventional dental alloys. However, titanium casting procedure shows some serious difficulties related mainly with its high melting point and its great chemical reactivity at high temperatures. As a result, an extensive contamination is observed in Ti castings when SiO2-based investment materials are used (phosphate-bonded or silica-bonded). In the present work, a detailed metallurgical study of the contamination zone of Ti castings due to Si, P and O, was performed. The new phases which formed, were investigated and analyzed using mainly light and scanning electron microscopy, as well as energy dispersion spectrometry. These phases were found to be: α-Ti, β-Ti and a Ti-Si compound. An attempt was done to prevent the contamination of cast Ti by using a wax pattern coating technique. The protection efficacy of a ZrO2 coating was proven. Ti castings without contamination were obtained in this way.

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