Biomaterials are effective alternatives for tissue substitution, including the bone tissue, since they do not pose risks of transmission of diseases or immune rejection. Nowadays, there is an interest in new materials capable of being associated with other substances which favor bone formation, especially natural biopolymers, in particular chitosan, which may present a potential for repairing bone defects and forms films that adhere to metal surfaces. Titanium, despite being a material greatly employed in implants because of its excellent physical properties, does not present bioactive characteristics, making it necessary to use methods of surface modification to enhance its biological response, favoring bone formation. This work aims at studying commercially pure titanium (cp-Ti) coating with chitosan using the biomimetic method and the evaluation of the effects of process variables as substrate surface conditions. Subsequently, the incorporation of AgNO3 was studied and its effects on corrosion resistance were evaluated. To evaluate the coating process, several tests were conducted, such as scanning electron microscopy, X-ray diffraction and infrared spectroscopy. From the results obtained, the efficacy of the chitosan film in inhibiting the corrosion of the metals is concluded, which was the target of this study, thus justifying its use for osseointegration and in several implants.
A hybrid magnetron sputtering process (dcMS/HiPIMS) was developed to manufacture nanostructured CrN/Cr1-xAlxN multilayers, motivated by improving the low-emission efficiency when applied on gas-nitrided diesel piston rings of a next-generation of combustion engines. In order to improve the mechanical, tribological, and corrosion behavior of the multilayers, the hybrid dcMS/HiPIMS process was designed by selecting the optimal sputtering procedure applied to AISI 440 base steel. The effect of substrate bias and carousel rotational speed on the phase composition, crystallographic texture, residual stresses, surface roughness, coating periodicity and densification, instrumented hardness, elastic modulus, as well as wear and corrosion resistance was determined. The results have demonstrated that hybrid magnetron sputtering produces multilayers with a superlattice structure, which outperforms commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation. Also, multilayer periodicities in the range of 5 to 10 nm yield the best tribological performance under bench tests for the piston ring/cylinder liner system.
The development of alternatives for wear protection in surface engineering can be responsible for a significant decrease in energy waste as a large amount of the energy produced in the world is lost due to tribological contact. Dynamic Glancing Angle Deposition has been recently evaluated as a route to produce coatings with improved wear performance. In this technique, the substrate oscillates along with a determined range in front of the sputtering target during the growth of the film. In this study, five oscillatory ranges (0, ±5°, ±10°, ±15°, ±20°) were probed to manufacture nanostructured Cr-Al-N coatings using direct current magnetron sputtering, and their impact was investigated on the grain morphology, phase formation, chemical composition, and performance of the coatings. FEG-SEM revealed the formation of multilayer-like architecture across the grains of the coatings. The deposition rate and hardness improved, and a more than 2-fold decrease in the material loss was observed in a comparison between the stationary-deposited conventional coating and the sample produced under ±10° oscillatory range. This indicated the potential use of this technique in future surface engineering applications.
The mechanical and wear behavior of CrN/CrAlN multilayers were improved by tailoring the experimental conditions of a hybrid magnetron sputtering process based on a high-power impulse (HiPIMS) and two direct current magnetron sputtering (dcMS) power supplies. To this end, the influence of the base layer and of the combination of Cr and CrAl targets, which were switched to the dcMS and HiPIMS power supplies in different configurations, were investigated with respect to the growth of ceramic CrN/CrAlN multilayers onto commercial gas-nitrided diesel piston rings. The microstructure, grain morphology, and mechanical properties were evaluated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and instrumented nanoindentation. Bench wear tests simulating the operation of a combustion engine were conducted against a gray cast iron cylinder liner under reciprocating conditions using 0W20 oil as a lubricating agent enriched with Al2O3 particles. The results revealed a significant increase in hardness, resistance to plastic strain, and wear resistance when two CrAl targets were switched to a HiPIMS and a dcMS power supply, and a Cr target was powered by another dcMS power supply. The compressive coating stresses were slightly reduced due to the soft Cr base layer that enabled stress relief within the multilayer. The proposed concept of hybrid magnetron sputtering outperformed the commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation.
Austenitic stainless steels processed by rolling are widespread in technological applications, since they have excellent mechanical and corrosion properties. This study investigated the effect of the cooling rate, microstructure and properties of 316L austenitic stainless steel under cold rolled conditions and by rapid solidification. The microstructure of the cold rolling processing steel was composed of austenite and a low percentage of delta ferrite. For the rapid solidification condition, the microstructure evolved from columnar and acicular dendrites to equiaxed dendrites with decreasing cooling rates, without the presence of delta ferrite due to the high cooling rate. Furthermore, thermal analyses in both routes revealed that oxidation kinetics was slower after rapid solidification in synthetic air. The microhardness in the cold rolling condition was lower than in the rapid solidification condition since the microstructure under the solidification condition is more refined. The sample in the rapid solidification condition region RS1 presented the highest corrosion resistance considering the pit potential. The passivation current density in the cold rolled condition was 5.72x10 -5 A/cm 2 , while under the rapid solidification condition, regions RS1 and RS2 were 2.24x10 -5 A/cm 2 and 3.72x10 -6 A/cm 2 , respectively, and region RS3, did not present a passivation region in a broad range of potentials.
Mining processes produce a massive amount of waste which, if not treated properly, can cause significant environmental and social impacts. Recently, some studies have focused on the use of mining waste as an alternative raw material. This work developed new sustainable ceramic formulations based on bentonite mining waste (BMW) for applications in porcelain stoneware. The BMW was incorporated into the ceramic masses in different percentages (0, 2.5, 5, 10, 15, 20, 25, and 40 wt.%), in partial replacement to feldspar and total to quartz. X-ray diffraction (XRD), differential thermal calorimetry (DTA), and thermogravimetry analysis (TGA) techniques were used to characterize bentonite waste. Samples (50 mm × 20 mm × 5 mm) were obtained by uniaxial pressing. Such samples were dried and sintered at 1150, 1200, and 1250 °C. The physical–mechanical properties (apparent porosity, water absorption, linear shrinkage, apparent density, and flexural strength) were evaluated for sintered samples. The phases formed after sintering treatments were characterized by XDR and scanning electron microscopy (SEM). The BMW presented a mineralogical composition suitable for use as ceramic raw material. In summary, our results presented that the new sustainable ceramic formulations sintered at 1250 °C have the potential for use in stoneware and porcelain stoneware.
Resumo: Este trabalho inventariou as emissões veiculares geradas no translado da comunidade universitária do centro da cidade para o campus de Poços de Caldas da UNIFAL-MG. Os resultados foram agrupados por segmento de usuários do transporte e categorias de veículos o que possibilitou estabelecer diretrizes para a mitigação e neutralização das emissões geradas. Utilizou-se dos registros de controle de acesso ao campus e de métodos estatísticos com aplicação de questionário especificamente elaborado para caracterização deste traslado. Estimou-se a carga poluidora gerada diariamente pelo transporte através de fatores de emissão obtidos por levantamento bibliográfico. O inventário contemplou as emissões de poluentes veiculares geradas nas categorias de transporte por ônibus, vans e veículos de passeio e pelos segmentos da comunidade universitária, alunos, professores e técnicos. Como resultados obteve-se diversos indicadores ambientais do Tipo PER (Pressão-Estado-Resposta) que podem contribuir na conscientização da comunidade universitária e subsidiar políticas e programas institucionais que visem melhor desempenho ambiental no transporte universitário. Palavras-chave:Qualidade do ar, Poluição do ar, Emissões veiculares.
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