Study On The Effect Of The Electrical Parameter Of Micro-arc Oxide Treatment On The Bond Strength Of Titanium To Porcelain

Titanium receives considerable amount of interests as a ceramic fused metal. But the bonding strength of titanium-porcelain system is still lower than that of conventional Ni-Cr/porcelain system, primarily because of the strong reactivity of Ti to non-metallic elements, such as oxygen, hydrogen, and nitrogen at high temperatures. Micro-arc oxidation is a recently developed surface treatment technology. To improve the bond strength of titanium-porcelain system, a protective ceramic film was created via micro-arc oxidation on titanium before porcelain fused on it. Electrolyte has strong influences on the structure and property of ceramic coatings created by micro-arc oxidation.Objectives: This study was made to evaluate the influence of electrical parameters including electrolyte and concentration at micro-arc oxide treatment on the bond strength of titanium to porcelain.Methods: Experiment1: NaB₄O₇,NaH₂PO₄,Na₂SiO₃ and KF were selected to be studied in this part. CP titanium specimens in the size of 25mm×3mm×0.5mm were treated with micro-arc oxidation(MAO) in this 4 solution respectively. Then the ceramic coating was observed by scanning electron microscope(SEM).After the porcelain was fused, the effect of the electrolyte on bonding strength of tatinium/porcelain were determine via a three-point-flexure-test according to ISO9693.The electrolytes used in the group which had the highest bonding strangth value were selected for experiment2. CP titaniunm specimens in the size of 25mm×3mm×0.5mm were treated with micro-arc oxidation(MAO) in solution of three different concentration respectively. After an ultra-low-fusing porcelain were applied, a three-point-flexure-test was employed to evaluate the bond strength of titaniunm to porcelain. The surface of the specimens was observed by SEM and EDS , as well as the interface between titanium and porcelain.In order to reduce the thickness and improve the quality of the film created in high concentration solutions, a lower voltage was applied in MAO treatment, and the effect on bonding strength was identified by three-point-flexure-test and SEM.Results: The bond strength values between porcelain and titanium treated with MAO in Na₂SiO₃ and KF solution was significantly higher then the control group's and other two group's. SEM indicated there was a crack in the ceramic coating created in NaH₂PO₄ and NaB₄O₇, implying the weakness of the coating. The bonding strength of this two group was lower then that of Na₂SiO₃ group and KF group.The bond strength of ceramic and titanium treated in solutions with deferent electrolyte concentration were compared in experiment2. Group 20g/L had the highest bond strength values in both Na₂SiO₃ and KF solutions according to the three-point-flexure-test. SEM /EDS suggested that a porous thin layer of oxide which contains Si or F element was created by MAO in Na₂SiO₃ or KF solutions. Higher concentration of Na₂SiO₃ (KF) lead to more Si (F) element in oxide, but a lower in bond strength values paradoxically. Increasing in electrolyte concentration lead to larger current in MAO procedure ,which brought faster film grown and thicker coating during the same time. SEM photograph of the interface area of ceramic and titanium indicated that there were tiny cracks between oxide film and the Ti substrata in group 30g/L and 40g/L, while group 20g/L had no defect.Bonding strength value of group Na₂SiO₃ 20g/L treated with 300V and group 40g/L treated with 260V has no statistical significance,and group KF 20g/L treated with 300V and group 40g/L treated with 220V has no statistical significance according to the three-point-flexure-test. SEM photograph indicated that the coating created in 40g/L Na₂SiO₃ solutions with 260V and 40g/L KF solutions with 220V was compacted and well bonded to the substrata.Conclusions: MAO treating can improve bonding strength between titanium and ceramic. Na₂SiO₃ and KF are better than NaB₄O₇ or NaH₂PO₄ as electrolyte used for titanium MAO. Higher concentration of Na₂SiO₃ (KF) lead to lower bonding strength value under a consistent voltage of 300V. But 40g/L Na₂SiO₃,in pairs of 260V,or 40g/L KF in pairs of 220V, brought excellent bonding between titanium and ceramic.