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RISS 인기검색어
- 검색키워드
- 저자 : Leandro Jos da Silva (검색결과 2 건)
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Corrosion resistance assessment of nickel-titanium endodontic files with and without heat treatment
Costa Tatiana Dias,Silva Elison da Fonseca e,Caetano Paula Liparini,Campos Marcio José da Silva,Resende Leandro Marques,Machado André Guimarães,do Carmo Antônio Márcio Resende 대한치과보존학회 2021 Restorative Dentistry & Endodontics Vol.46 No.1
Objectives: The aim of this study was to evaluate the corrosion resistance of heat-treated (Reciproc and WaveOne) and non-heat-treated (ProTaper and Mtwo) superelastic nickel-titanium endodontic files when immersed in a 5.25% sodium hypochlorite solution. Materials and Methods: Anodic polarization curves were obtained with potential sweeps that began at the open circuit potential or corrosion potential (Ecorr). The pitting potential (Epit) was identified on the anodic polarization curve as the potential at which a sudden increase in current was observed. The micromorphology of the 28 tested files was analyzed before and after the electrochemical assay using scanning electron microscope (SEM). The data were analyzed using 1-way analysis of variance with the post hoc Bonferroni test (for Ecorr) and the Student t-test for independent samples (for Epit). Results: The mean Ecorr values were 0.506 V for ProTaper, 0.348 V for Mtwo, 0.542 V for Reciproc, and 0.321 V for WaveOne files. Only WaveOne and Protaper files exhibited pitting corrosion, with Epit values of 0.879 V and 0.904 V, respectively. On the SEM images of the ProTaper and WaveOne files, cavities suggestive of pitting corrosion were detected. Conclusions: Signs of corrosion were observed in both heat-treated and non-heat-treated files. Of the evaluated files, WaveOne (a heat-treated file) and ProTaper (a non-heat-treated file) exhibited the lowest corrosion resistance.
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Cementitious Porous Material Applied to Precision Aerostatics Bearings
Leandro Jos da Silva,Tulio Hallak Panzera,Luciano Machado Gomes Viera,Christopher Rhys Bowen,Jaime Gilberto Duduch,Juan Carlos Campos Rubio 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2
The use of porous materials as restrictor in aerostatic bearings provides many advantages over conventional restrictors, such as small variation of temperature, high damping, high operational speeds, limited wear and capacity to support radial, axial, and combined loads, being considered important features for precision machines and instruments. This work evaluates the load carrying capacity for different air gaps and pressures of thrust porous bearing made with cementitious composites. The cementitious composites consisted of Portland cement and monomodal silica particles (44 μm) were fabricated via uniaxial cold-pressing (10 MPa). The load capacity was determined for different air pressures, such as 3, 4, 5 and 6 bar. The air gap was measured using pneumatic transducers. A pneumatic instability was observed when the air pressure level increased from 3 to 6 bar. A similar loading capacity, for bearing gaps between 7 and 30 μm, was achieved in comparison to hot-pressed porous alumina found in the literature. In addition, the cementitious porous bearing provided a superior loading capacity for gaps higher than 10 μm when compared to graphite porous bearing found in the literature. The results revealed the cementitious composites are promising materials for porous restrictor in aerostatic thrust bearings.
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