Navegando por Autor "Costa, Maria Carolina Burgos Costa do"
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Artigo Influence of amine groups in the chemical structure of photochromic dyes on the rheological and mechanical properties of poly(methyl methacrylate) (PMMA)(Elsevier, 2017-07) Ito, Edson Noriyuki; Rego, José Kaio Max Alves do; Nascimento, José Heriberto Oliveira do; Agrawal, Pankaj; Melo, Tomas Jeferson Alves; Costa, Maria Carolina Burgos Costa doPolymer modification has been used as a means to improve the adhesion/bonding of compounds and/or particles to polymer chains, but this goal is not always achieved. Some compounds contain naturally reactive groups which, in contact with the polymer, can modify its properties. This work focused on the rheological (torque and parallel plates rheometry) and mechanical (tensile and impact) characterization of PMMA containing the DV31, DBL3 and DB79 aminic dyes and the DR73 inert dye. The rheological results indicated that the final torque (torque rheometry) varied in response to increasing dye concentrations, and that the various dyes under study exhibited distinct behaviors (parallel plates rheometry). The mechanical tests revealed that, overall, the effect of the dyes on the properties of PMMA was negligible, except for DV31, that led to the decrease in the impact strength, possibly due to the bond between chains or segments of chains of the polymer. The presence, amount and type of amine in the dyes gave rise to significant rheological changes in PMMA because of the reactivity between the amine and the ether group of PMMAArtigo Optimization of the process of obtaining RE2 O3 from xenotime using statistical design(Cerâmica, 2018) Costa, Maria Carolina Burgos Costa do; Gomes, Yara Feliciano; Ribeiro, S.; Motta, Fabiana Villela daThe study of the production of the mixed rare earth oxide (RE2O3) from xenotime via hydrometallurgy was performed to evaluate the significance of the effects of three factors including the melting temperature (A), the ratio of NaOH/xenotime (B), and time (C) for the first stage of alkaline fusion by using full 23 factorial design. Also, seven factors were studied including liquid/solid ratio (LS), inert (I1), excess HNO3 (EA), temperature (TL), inert (I2), time (HL), and inert (I3) for the second and third steps, which were the oxalic acid leaching and precipitation, using Plackett-Burman design (PBD). Optimizing factors for significance were performed using plots of interactions, analysis of variance (ANOVA), Pareto charts, surface charts, analysis of Student’s t-test and F test. A regression model was suggested and satisfactorily adjusted for the experimental data of the process of alkaline fusion, revealing an elevated coefficient of determination (R2 =0.92) to a Fcalculated value well above the Ftabulated value, at a 95% confidence level. The RE2 O3 was characterized by chemical analysis, X-ray diffraction, scanning electron microscopy, and specific surface area. This process resulted in a material with identical physical and chemical properties to the isolated compounds of rare earths and can be used as an alternative sintering additive in advanced ceramics, and indicated that the cost of final production of RE2O3 can be lower compared to commercial Y2O3