Abstract:In this paper, the electrochemical corrosion resistance of near-nano and nanostructured WC-Co cemented carbides was investigated. WC powders with an average grain size d BET in the range from 95 nm to 150 nm and with an addition of vanadium carbide (VC) and chromium carbide Cr 3 C 2 as grain growth inhibitors were used as starting powders. The mixtures with 6 wt. % and 9 wt. % Co were consolidated by two different processes; sintering in hydrogen atmosphere and the sinter-HIP process. WC-Co samples were researched by direct current and alternating current techniques in the solution of 3.5% NaCl at room temperature. Corrosion parameters such as corrosion potential (E corr ), corrosion current density (j corr ) and polarization resistance (R p ) were determined by electrochemical techniques. From the conducted research, it was found that the consolidation processes and microstructural characteristics-grain growth inhibitors, grain size of the starting WC powders and η-phase-influenced the electrochemical corrosion resistance. η-phase enhanced the formation of a passive layer on the samples' surfaces, thereby reducing the tendency of the sample dissolution and increasing the stability of oxides forming therewith a passive layer on the sample surface.
BackgroundAn increasing demand for esthetic restorations has resulted in an increased use of all-ceramic restorations, such as zirconium. However, one of the challenges the orthodontist must be willing to face is how to increase bond strength between the brackets and various ceramic restorations.Bond strength can beaffected bybracket type, by the material that bracketsaremade of, and their base surface design or retention mode.Aim: of this study was to perform a comparative analysis of the shear bond strength (SBS) of metallic and ceramic orthodontic brackets bonded to all-zirconium ceramic surfaces used for prosthetic restorations, and also to evaluate the fracture mode of these two types of orthodontic brackets.Material and methodsTwenty samples/semi-crowns of all-zirconium ceramic, on which orthodontic brackets were bonded, 10 metallic and 10 ceramic polycrystalline brackets, were prepared for this research. SBS has been testedby Universal Testing Machine, with a load applied using a knife edged rod moving at a fixed rate of 1 mm/min, until failure occurred. The force required to debond the brackets was recorded in Newton, then SBS was calculated to MPa. In addition, the samples were analyzed using a digital camera magnifier to determine Adhesive Remnant Index (ARI). Statistical data were processed using t-test, and the level of significance was set at α = 0.05.ResultsHigher shear bond strength values were observed in metallic brackets bonded to zirconium crowns compared tothoseof ceramic brackets, with a significant difference. During the test, two of the ceramic brackets were partially or totally damaged.ConclusionMetallic brackets, compared to ceramic polycrystalline brackets, seemed tocreate stronger adhesion with all-zirconium surfaces due to their better retention mode. Also, ceramic brackets showed higher fragility during debonding.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.