Abstract in English:The effects of combustion thermal spraying parameters namely combustion pressure, feeding rate, and carrier gas on the wear resistance, friction coefficient, and Knoop hardness of poly (ethylene terephthalate) (PET) films were investigated. The PET coatings were characterized by measuring the wear coefficients by calowear-type testing, the friction coefficients by a pin-on-disk test, and Knoop hardness. The abrasive wear and friction coefficients of the coatings were compared with the values of a post consumer PET bottle chip reference sample. The structural characteristics of the coatings were investigated by X ray diffraction. Statistical analysis of the results allowed for the systematic characterization of the influence of the process variables mentioned above on the coating wear, friction, and microhardness values. Specifically, this study shows that the process parameters affect the wear coefficient and Knoop hardness significantly, but not the friction coefficient. The degree of crystallinity of the PET coatings varied from 20 to 26%.
Abstract in English:The purpose of this study was to evaluate the transmittance of seven different composite resins. Ten specimens were prepared (10 mm diameter, 2 mm thickness) for each experimental group, as follows: G1- Charisma® A2 (Heraeus-Kulzer); G2- FiltekTM Supreme A2E (3M/ESPE); G3- FiltekTM Supreme A2B (3M/ESPE); G4-FiltekTM Supreme YT (3M/ESPE); G5- Esthet-X® A2 (Dentsply); G6- Esthet-X® YE (Dentsply); G7- Durafill® A2 (Heraeus-Kulzer) and G8- FiltekTM Z-100 A2 (3M/ESPE). The transmittance mode was measured using a UV-visible spectrophotometer (Cary Instruments) at 400-760 nm. The specimens were evaluated at three different times: zero hour (initial), 24 hours and 10 days after immersion in artificial saliva. The differences in transmittance were determined by two-way analysis of variance (ANOVA) and Tukey's test. The various composite resins showed significant differences in the wavelength dependence of transmittance. The mean values of transmittance increased significantly, with wavelengths increasing from 400 to 760 nm. The performance of the experimental groups was similar in terms of immersion time, considering that at time zero and after 10 days, all the groups showed similar results, which were statistically higher than the values obtained after 24 hours of immersion. The FiltekTM Supreme YT composite resin presented the highest mean transmittance values along the wavelengths at the three measured times. Esthet-X® YE and Durafill® yielded similar mean transmittance values, which were higher than those of the other groups. This study shows that the transmittance values of composite resins are directly related with the type, size and amount of inorganic filler particles.
Abstract in English:The finite element method is used to compute and analyze the residual stresses particularly near the fiber/epoxy interface, and these stresses need to be taken into account. An axisymmetric model has been used for stress computation and analysis, in this work two cases are considered by using an epoxy matrix with respectively glass and carbon fibers with a different volume fiber. Numerical calculation results show that the stresses are important. The interface is affected by thermal stresses particularly in the free edge. The normal and shear stresses values have an influence on the behaviour of the composite during service.
Abstract in English:Glass ionomer cements are widely employed in dentistry due to their physical, biological and mainly anti-caries properties. Glass ionomers consist of an aluminosilicate glass matrix modified with other elements, and they contain large quantities of fluorine. In this study, we report on the preparation of calcium-fluoroaluminosilicate glasses by a nonhydrolytic sol-gel route as an alternative approach to obtaining alumina-silica matrices. The glass powders were prepared via the non-hydrolytic sol-gel method, by mixing AlCl3, SiCl4, CaF2, AlF3, NaF, and AlPO4. The powders were studied by thermal analysis (TG/DTA/DSC), photoluminescence (PL), nuclear magnetic resonance (NMR27Al-29Si), and X ray diffraction (XRD). TG/DTA/DSC analyses revealed a constant mass loss due to structural changes during the heating process, which was confirmed by NMR and PL. A stable aluminosilicate matrix with potential future application as a glass ionomer base was obtained.
Abstract in English:Silicon nitride based ceramics have been widely used as structural ceramics, due mainly to their thermo-mechanical properties such as high density, high thermal shock resistance, corrosion resistance and chemical stability. The aim of this study was to determine the influence of rare earth and aluminum oxide additions as sintering aids on densification, microstructure and mechanical properties of silicon nitride. Silicon nitride mixtures with 91 wt. (%) Si3N4 and 9% wt. (%) additives were prepared and sintered. The density, microstructure and mechanical properties of the sintered specimens of these mixtures were determined. In most specimens, scanning electron microscopic examination and X ray diffraction analysis revealed elongated grains of β-Si3N4 with aspect ratio of about 2.0 and dispersed in a glassy phase. The density of the sintered specimens was higher than 94% of the theoretical density (td) and specimens with La2O3 and Al2O3 additions exhibited the highest value. The results of this investigation indicate that the rare earth ion size influences densification of silicon nitride, but this correlation was not observed in specimens containing two different rare earth oxides. The hardness values varied in direct proportion to the density of the specimens and the fracture toughness values were influenced by the composition of the intergranular glassy phase.
Abstract in English:In the present work, non-isothermal crystallization data in the form of heat flow vs. temperature curves were generated using the Nakamura Model and its typical parameters reported in the literature for polypropylene. The values obtained for these curves were added to experimental baselines of a DSC to introduce typical noises in the calorimetric traces generated. The Master Curve Approach was applied by one of the authors to retrieve the non-isothermal crystallization rate constant for these simulated curves without information about the conditions used to generate these pseudo-experimental curves. Thus, the applicability of the Master Curve Approach was tested for data perfectly described by the Nakamura Model. With this procedure, the authors were able to check the sensitivity of the method to uncertainties in the determination of the induction time. The results showed good agreement between the pseudo-experimental curves and the curves simulated using the retrieved non-isothermal crystallization rate constant. However, this good agreement was only possible due to a compensation effect, because some of the parameters showed significant differences between the pseudo-experimental and retrieved values. Among these parameters are the pre-exponential factor of the non-isothermal crystallization rate constant, the temperature of the onset of the crystallization process, and the initial degree of crystallinity of the differential form of the Nakamura Model. These problems were not caused by the Master Curve Approach, but by inherent difficulties in the DSC analysis.
Abstract in English:The ever increasing accumulation of plastic waste in the environment has motivated research on polymers that degrade rapidly after being discarded as possible substitutes for conventional inert plastics. Biodegradable polymers can be an alternative, since they have non-toxic residual products and low environmental permanence. Poly (hydroxybutyrate) is a biodegradable polymer with a strong potential for industrial purposes, but its thermal instability and fragility limit its applications. Thus, an alternative to improve the processability and properties of poly (hydroxybutyrate) is to mix it with another polymer, not necessarily a biodegradable one. In this work, different mixtures of poly(hydroxybutyrate) or PHB and polypropylene or PP were extruded and injected. After processing, the blends were studied and their miscibility, mechanical properties and degradability in different soils were analyzed. The main results indicated that the PHB/PP blends had better mechanical properties than pure PHB, as well as improved immiscibility and higher degradation in alkaline soil. The poly-hydroxybutyrate/polypropylene blends showed a tendency for lower crystallinity and stiffness of the polymer matrix, proportional to the amount of polypropylene in the blends, rendering them less stiff and fragile. The degradation tests showed that both pure PHB and blends with 90% PHB and 10% PP were degraded, with loss of their mechanical properties and weight.
Abstract in English:Recent interest in polymer/organoclays nanocomposites systems is motivated by the possibility of achieving enhanced properties and added functionality at lower clay loading as compared to conventional micron size fillers. By adding montmorillonite clay to polyamide 6 increases the Young modulus, yield strength and also improves barrier properties. In this work, nanocomposites of polyamide 6 with montmorillonite clay were obtained. The clay was chemically modified with three different quaternary ammonium salts such as: Dodigen, Genamin and Cetremide. In this case, a dispersion of Na-MMT was stirred and a salt equivalent to 1:1 of cation exchange capacity (CEC) of Na-MMT was added to the dispersion. The montmorillonite clay (untreated and treated by ammonium salts) and nanocomposites were characterized by X ray diffractions. Also the nanocomposites were characterized by transmission electron microscopy and mechanical properties. The results indicated that all the quaternary ammonium salts were intercalated between the layers of clay, leading to an expansion of the interlayer spacing. The obtained nanocomposites showed better mechanical properties when compared to polyamide 6. The clay acted as reinforcing filler, increasing the rigidity of nanocomposites and decreasing its ductility.
Abstract in English:The aim of this study was to verify the influence of investment granulometry on the castability and surface roughness of Ni/Cr castings. Four investments were selected for casting according to decreasing order of granulometry: Heat Shock > Micro Fine 1700 > Gilvest HS > Castotal. Castability was verified by means of 40 specimens made with a polyester screen and determined from the number of segments completely filled by the cast alloy. To analyze the roughness, 40 disk-shaped wax patterns were made (15 x 3 mm), and after inclusion in the investments, they were cast and analyzed, before and after polishing (Mitutoyo SJ-201). The measurements were statistically analyzed (1-ANOVA - Tukey - p < 0.05) and it was verified that Heat Shock provided the worst castability with significant difference (p < 0.05) when compared with other investments. This material and Castotal presented similar roughness before and after polishing, with statistically significant difference (p < 0.05) between them and Gilvest and Micro Fine. It was concluded that investments with smaller granulometry provided castings that were more complete, but not smoother.
Abstract in English:Mechanical and tribological properties os AISI 304 and AISI 316 stainless steels submited to glow discharge ion nitriding are reported.The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ´-Fe4N and - Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.
Abstract in English:Polyamide 66 (PA66) nanofibers of different molecular weights were obtained by electrospinning of formic acid solutions. An ionic salt, NaCl, was also added to the solutions to increase the conductivity. PA66 concentrations between 15-17 wt.(%)/v and electrical fields between 2.0 and 2.5 kV/cm were the best conditions to produce the smallest nanofibers; however, the addition of NaCl increased the fibers average diameters.The characterization of the fibers was done by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide angle X rays diffraction (WAXD) and Fourier Transformed Infrared (FTIR). As the molecular weight decreased, the nanofibers average diameters also decreased; however, critical number average and weight average molecular weights were necessary for electrospinning. As the amounts of carboxyl terminal groups (CTG) increased, the nanofibers average diameters decreased; however, above CTG's critical values of 8.7 x 10-5 mol.g-1 no electrospinning was possible. The addition of ionic salt increased the electrical conductivity of the solutions and increased the nanofibers' average diameters. By DSC, residual solvent in all the electrospun mats was found; two melting endotherms, one between 248 and 258 °C and the other one between 258 and 267 °C, depending on the sample were also observed. These endotherms were attributed to the melting, re-crystallization and re-melting of the PA66 α-phase. The nanofibers had low % of crystallinity compared to a textile fiber. By WAXS and FTIR, confirmation of the presence of α-phase crystals, of small dimensions and highly imperfect and of a very small amount of β and γ-phases crystals in the nanofibers structure was obtained.
Abstract in English:Titanium in hosted by a clay matrix has important applications in a variety of catalysts. However, there is insufficient information about of textural and structural characteristics of the titanium in matrix clay at room temperature and after thermal treatment. In this study, titanium in host matrix clay was obtained by treating montmorillonite clay minerals with different OH-Ti solutions. The titanium-solutions containing partially hydrolyzed titanium were obtained using a TiCl4 solution with and without the addition of glycerol. The amount of Ti added to the solid was 20 mmol Ti per gram of clay. Thermal treatments were carried out at 500 and 1,000 °C in an air atmosphere. The solids were characterized by X ray diffraction, thermal analyses, infrared spectroscopy, N2 adsorption-desorption isotherms. The products presented different structural and textural characteristics and, after calcination at 1,000 °C, anatase and rutile in different proportions were present in the samples.
Abstract in English:The LZSA glass-ceramic system (Li2O-ZrO2-SiO2-Al2O 3) shows interesting properties, such as good chemical resistance, low thermal expansion, high abrasion resistance, and a low dielectric constant. However, in order to obtain a high performance material for specific applications, the sintering behavior must be better understood so that the porosity may be reduced and other properties improved. In this context, a sintering investigation for a specific LZSA glass-ceramic system composition was carried out. A 18.8Li2O-8.3ZrO2-64.2SiO2-8.7Al 2O3 glass was prepared by melting the solids, quenching the melt in water, and grinding the resulting solid in order to obtain a powder (3.68 μm average particle diameter). Subsequently, the glass powder was characterized (chemical analysis and determination of thermal properties) and the sintering behavior was investigated using optical non-contact dilatometry measurements. The results showed that the crystallization process strongly reduced the sintering in the temperature interval from 785 to 940 °C, and a maximum thermal shrinkage of 15.4% was obtained with operating conditions of 1020 °C and 180 minutes.
Abstract in English:Mineral extraction and processing industries have been cited as sources of environmental contamination and pollution. However, waste recycling represents an alternative recovery option, which is interesting from an environmental and economic standpoint. In this work, recycling of kaolin processing waste in the manufacture of mullite-based ceramics was investigated based on the statistical design of mixture experiments methodology. Ten formulations using kaolin processing waste, alumina and ball clay were used in the experiment design. Test specimens were fired and characterized to determine their water absorption and modulus of rupture. Regression models were calculated, relating the properties with the composition. The significance and validity of the models were confirmed through statistical analysis and verification experiments. The regression models were used to analyze the influence of waste content on the properties of the fired bodies. The results indicated that the statistical design of mixture experiments methodology can be successfully used to optimize formulations containing large amount of wastes.
Abstract in English:Elementary Al and Mo powder mixtures have been processed by high energy ball milling up to milling times of 100 hours. The shift of the pitting potential and the X ray analysis of green milled samples showed that part of the Mo has formed a supersaturated solid solution of Mo in Al. Elementary Mo powder, however, was still present after 100 hours of milling. Sintering led to the formation of the intermetallic Al12Mo phase.
Abstract in English:Microstructural evolution in three dimensions of nucleation and growth transformations is simulated by means of cellular automata (CA). In the simulation, nuclei are located in space according to a heterogeneous Poisson point processes. The simulation is compared with exact analytical solution recently obtained by Rios and Villa supposing that the intensity is a harmonic function of the spatial coordinate. The simulated data gives very good agreement with the analytical solution provided that the correct shape factor for the growing CA grains is used. This good agreement is auspicious because the analytical expressions were derived and thus are exact only if the shape of the growing regions is spherical.
Abstract in English:Nanocrystalline particles of magnesioferrite (MgFe2O4) were prepared by a sol-gel/combustion method using iron nitrate, Fe(NO3)3.9H2O, magnesium nitrate, Mg(NO3)2.6H2O, and citric acid, C6H8O7.H2 O, and annealed for 2 hours at 400, 500 and 600 °C. The average particle size, determined by X ray diffraction, was found to depend on the annealing temperature and varied from 〈D〉 = 8.1 to 〈D〉 = 17.8 nm. By measuring at several temperatures the relative intensity of the Mössbauer spectra due to superparamagnetic particles and to ferrimagnetic particles, we determined the size distribution of the nanoparticles in the samples. It was found to be a log-normal distribution with a most probable diameter that varied from Dm = 6.4 to 17.2 nm and a full width at half-height ΔD in the 5-6 nm range.
Abstract in English:The purpose of this study was to investigate the superficial rugosity of commercially pure titanium cast, under the action of different fluoride dental solutions and synthetic saliva. All specimens received the standard metallography procedure for titanium and were divided in groups: Group 1) synthetic saliva pH 7.0; Group 2) 1.23% APF gel pH 3.5;, Group 3) 2% NaF gel pH 6; Group 4) 0.05% NaF solution pH 4.0; and Group 5) 0.05% NaF solution pH 7.5. The specimens were exposed to these solutions for 16 minutes and immersed in synthetic saliva for 96 hours. The surfaces were analyzed in a roughness device and the results were statistically treated - Snededor 'F' and Bonferroni test. In addition, scanning electron microscopy was employed to observe the surface morphology after the test. The Group 2 was the only one which had a significant increase in the superficial roughness. Authors concluded that the fluoride solutions of dental use that have a high concentration of fluoride and low pH are harmful to the surface of cast titanium.
Abstract in English:Silk fibroin is a fibrous protein that has been extensively studied for application in the biomedical field, and has been used as a scaffold for bone tissue engineering. Biomaterials made of proteins are prone to physical and chemical degradation during storage; lyophilization, a drying method that consists of freezing and drying steps, is known to promote minimal changes in structure and biological activity of biomaterials. This study evaluates the effect of freezing methods on the properties of lyophilized porous silk fibroin membranes. The membranes were obtained from silk fibroin solution, frozen in liquid nitrogen or ultrafreezer, lyophilized, and then characterized by XRD, FTIR, TGA, DSC and SEM. Although the membranes presented similar physical, chemical and microstructural characteristics, quench freezing with liquid nitrogen, followed by lyophilization, promoted collapse of the membranes, while slow cooling performed by ultrafreezer preserved membrane integrity.
Abstract in English:Bioactive glass/polymer hybrids are promising materials for biomedical applications because they combine the bioactivity of these glasses with the flexibility of polymers. In this work it was evaluated the effect of increasing the PVA content of the on structural characteristics and mechanical properties of hybrid. The hybrids were prepared with 70 wt. (%) SiO2-30 wt. (%) CaO and PVA fractions of 20 to 60 wt. (%) by the sol-gel method. The structural and mechanical characterization was done by FTIR, SEM and compression tests. To reduce the acidic character of the hybrids due to the catalysts added, different neutralization solutions were tested. The calcium acetate alcoholic solution was the best neutralizing method, resulting in foams with final pH of about 7.0 and small sample contraction. The foams presented porosity of 60-85 wt. (%) and pore diameters of 100-500 μm with interconnected structure. An increase of PVA fraction in the hybrids improved their mechanical properties. The scaffolds produced provided a good environment for the adhesion and proliferation of osteoblasts.
Abstract in English:The objective of the present study was to evaluate the quality and intensity of the tissue response to two synthetic hydroxyapatites implanted in critical defects in the skulls of rats. Sixty animals were divided into three experimental groups: I (control), II (HA-1 = HA with 28% crystallinity) and III (HA-2 = HA with 70% crystallinity). They were sacrificed 1, 3, 6, and 9 months after implantation (n = 5 individuals per group/period). Histomorphometric analysis included i) counting of polymorphonuclear leucocytes, mast cells, macrophages and foreign body multinucleated giant cells stained with anti-lysozyme; ii) microvascular density stained with anti-Factor VIII and iii) degree of cell proliferation stained with anti-PCNA. There were no significant differences between the experimental groups in either the quality or quantity of cells in the inflammatory infiltrate, or the degree of angiogenesis and cell proliferation. We conclude that HA-1 and HA-2 are biocompatible and that the physico-chemical differences of these biomaterials did not affect cellular response.
Abstract in English:In this work, we propose natural rubber latex (NRL) membranes as a protein delivery system. For this purpose Bovine Serum Albumin (BSA) was incorporated into the latex solution for in vitro protein delivery experiments. Different polymerization temperatures were used, from -10 to 27 °C, in order to control the membrane morphology. These membranes were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), as well as the Lowry Method to measure the BSA release. SEM and AFM microscopy analysis showed that the number, size and distribution of pores in NRL membranes can be varied, as well as its overall morphology. We have found that the morphology of the membrane is the predominant factor for higher protein release, compared with pore size and number of pores. Results demonstrated that the best drug-delivery system was the membrane polymerized at RT (27 °C), which does release 66% of its BSA content for up to 18 days. Our results indicate that NRLb could be used in the future as an active membrane that could accelerate bone healing in GBR.