Papers by Author: Claudinei dos Santos

Abstract: The objective of this work is to recycle the printed circuit boards of electronic equipment discarded and mix them with polypropylene (PP) to produce a new composite. Six types of mix of discarded printed circuit boards were analyzed: new boards with and without copper, used boards without components and with and without copper, used boards without components and without copper, used boards with copper track, used boards with copper track and burned and used boards with components. Boards were disintegrated and employed as reinforcement with polypropylene matrix (5% m/m). Specimens were produced for flexural and impact tests. Results showed that specimen’s properties depend on the mix composition. In all of the cases, pure PP properties were enhanced when it was replaced by 5% of waste materials discard.

Abstract: In the work, mechanical properties of palm fibers/low density polyethylene (LDPE) composites were studied. These fibers were mixed with the polymeric matrix (LDPE) in a thermokinetic mixer, in which fibers were responsible for 5 to 20 wt% in the composition. After the mixture, composites were dried, ground in mill and placed in an injector camera according to ASTM D-638 and ASTM D-790 specifications. Specimens were tested in tensile, impact, flexural and Shore A hardness mode. Results showed the addition fibers in polymeric matrix presented increase mechanical properties when compared to pure polymer

Abstract: In this study, the effect of ball/powder ratios for grinding particles of a dental alloy consisting of 66%Co-28%Cr-6%Mo was investigated. Metal powders were obtained from SPEX mill, with tungsten carbide balls, setting the milling time to 60 minutes, 50% of volume of grinding vessel filled with powder and argon inert atmosphere. The ball/powder ratio was varied between 4:1, 6:1, 8:1, 10:1.The powders were characterized by XRD indicating Co as only crystalline phase present, which indicates that Cr and Mo enter into solid solution with the matrix Co. Measurement of crystallite size conducted using the Scherrer equation indicate the crystallite size about 10 to 6nm, due to the increase of the ball/powder ratio of 4:1 to 10:1. The morphology of the milled powders were analyzed by scanning electron microscopy (SEM) and indicate that the agglomerates created by the grinding process must have average sizes varying between 100μm and 200μm with the modification of the ball/powder.

Abstract: In this work, different commercial Co-Cr-Mo powders were used in selective laser sintering. Commercial powders with particle size distribution between 5 and 50μm were sintered by laser sintering, and characterized. The samples were characterized by X-ray diffraction, indicating Co as the only crystalline phase. Relative density was measured by Archimedes method showing values between 90 and 96% of TD, depending on the powder used. Scanning electron microscopy performed on the cross section of the sintered samples, indicates that the microstructural features are similar, but the surface finish of the samples differ significantly due to the morphology and size distribution of the starting powders used.

Abstract: This paper presents the microstructural characterization of particle systems used in equipment for selective laser sintering. Three distinct commercial metal powders, with chemical composition based on Co-Cr-alloy, were characterized by X-ray diffraction, scanning electron microscopy and particle size distribution. The powders showed regular spherical particles with varying sizes and crystalline phase of Co-solid solution. Different powders present particle size among 55nm and 245 nm. This behavior affects the sinterability of samples submitted to the selective laser sintering.

Abstract: In this work, compacting powders of different ZrO₂(Y₂O₃) are investigated relating the particle size, compaction pressure, and use of binders. Powders of ZrO₂ stabilized with 3mol % Y₂O₃ with an average particle size of 0.15 to 0.7μm presence of both bonding and 0.15μm without addition of binder, were uniaxially compacted with pressures of 30 to 115MPa. Green density between 40% and 50% were obtained. The results indicate that powders sized less densification above 1400°C, while the larger sizes only after reaching full densification above 1500°C. Crystallographic characterization indicates that the powders have a percentage of monoclinic phases in the range of 15% to 26%, but only after sintering tetragonal phase is identified.

Abstract: The yttria stabilized zirconia, ZrO₂ (Y₂O₃) has been widely used in dental prosthesis manufactured by CAD/CAM technique. This material is developed in the form of pre-sintered blocks, which are machined by extracting various customized prosthesis and generating a loss of about 30% of material. ZrO₂(Y₂O₃) is notably a toughening for other ceramics, and has a high cost, so reusing discards these applications less noble, is strategically interesting. In this work the proposal is to recover discharges of ZrO₂ (Y₂O₃) arising from prosthetic laboratories, reprocess them in order to reduce the particles size and subsequently sintering, demonstrating the potential use in applications less noble in dentistry. Discharges Residual of ZrO₂-(Y₂O₃) were fragmented and then sieved to particle size separation. Powders of smaller than 63 μm were uniaxially pressed at different pressures. The compacts were characterized by the relative density showing green density of the order of 40%. After characterization, compacts were sintered at 1550°C-2h. The sintered material was characterized as its relative density and crystalline phases.

Abstract: The crystallization process of lithium disilicate glass-ceramic with SiO₂ from rice husk silica replacing the high-purity SiO₂ starting powder has been investigated in this work. Glasses were developed at the stoichiometric composition of 66%.molSiO₂:33%.molLiO₂ using commercial SiO₂ and the one obtained by thermochemical treatment of rice husk. The influence of rice husk-SiO₂ on crystallization process to different granulometry, microstructure and kinetic behavior was determined and discussed. Investigations were carried out by means of differential thermal analysis (DTA), X-ray fluorescence (XRF), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Amorphous and transparent glasses were obtained after melting. The lithium disilicate glass-ceramic crystallization peaks (Tp) are between 550 to 660°C to different granulometry (<63μm, 63μm < x < 250μm and 1mm < x < 2mm) and DTA heat rates (5; 10; 15; and 20°C/min) in both glasses from different silica sources, and the formed phase was Li₂Si₂O₅ as the crystalline phase after DTA thermal analysis as XRD confirmation. Improve in mechanical properties were estimated by morphological analysis of the microstructure modification in increasing the heat treatments temperature by SEM. The increase of glass substitution for crystalline phase was also observed with SEM images to both glass-ceramics from different silica sources.

Abstract: ZrO₂ ceramics are one of the most important materials used in dental prostheses production, due to their excellent mechanical resistance and chemical inertness in the mouth environment. Nevertheless, the combination of low pHs and fluoride presence is able to reduce the chemical stability of these ceramics. In this work, the resistance of commercial blocks of micrometric and nanometric sized Y₂O₃-stabilized ZrO₂ ceramics (ProtMat Materiais Avançados® and Ivoclar®) was evaluated in Fusayama artificial saliva of different pHs with (and without) the presence of fluoride ions. The study was based on the analysis of the amount of Zr⁴⁺ and Y³⁺ ions dissolved in the artificial saliva after different exposure times using ICP OES technique. The XRD technique was also employed to investigate the phase transformations occurring during the degradation process in artificial saliva. The micrometric sized ZrO₂ ceramics presented higher resistance in the artificial saliva than nanometric sized structures.

Abstract: Studies has been reported a significant incidence of chipping of the feldspathic porcelain veneer in zirconia-based restorations. The purpose of this study was to compare the three-point flexural strength (MPa), Weibull parameters, Vickers hardness (VHN) and Vickers indentation fracture toughness (MPa/mm^1/2) in feldspatic porcelains for metal and for zirconia frameworks. Bar specimens were made with the porcelains e.MaxCeram (EM) and VitaVM9 (V9) for zirconia core, and Duceragold (DG) and VitaVMK95 (VK) for metal core (n= 15). Kruskal-Wallis and Dun test were used for statistical analysis. There was no significant difference (p=0.31) among the porcelains in the flexural strength (Median= 73.2; 74.6; 74.5; 74.4). Weibull calculation presented highest reliability for VK (10.8) followed by EM (7.1), V9 (5.7) and DG (5.6). Vickers hardness test showed that EM (536.3), V9 (579.9) and VK (522.1) had no difference and DG (489.6) had the lowest value (p.001). The highest fracture toughness was to VK (1.77), DG (1.58) had an intermediate value while V9 (1.33) and EM (1.18) had the lowest values (p.001). Despite of the suitable flexural strength, reliability and high hardness, the porcelains used to zirconia-based fixed dental prostheses showed lower fracture toughness values.