Cesar Aguzzoli

Physicochemical, structural, and mechanical properties of Si3N4 films annealed in O2

The physicochemical, structural, and mechanical properties of silicon nitride films deposited by radio frequency reactive magnetron sputtering were investigated before and after thermal annealing in O182. As-deposited films were essentially amorphous, stoichiometric, and free from contaminants for a wide range of deposition parameters, with hardness figures ranging from 16.5–22 GPa, depending mainly on the deposition temperature. After O182 annealing at 1000 °C, films hardness converged to 21 GPa, independently of the deposition temperature, which is explained based on the crystallization of the films at this annealing temperature. Moreover, oxygen is incorporated only in 7.5 nm of the Si3N4, forming silicon oxynitride at the top surface of the film, indicating a good oxidation resistance at high temperature. Finally, the elastic strain to failure (H3/E2), which mimics the wear resistance of the film, doubles after the 1000 °C annealing. These observations show the great potential of silicon nitride as a ...

Bias influence on titanium interlayer for titanium nitride films

This work investigates the deposition of TiN thin films by cathodic arc evaporation on stainless steel AISI 304 substrate for decorative applications. The applied voltage bias on the substrate during the Ti interlayer deposition was varied, and several properties were determined. The chemical profile, crystalline structure and microstructural properties were analysed by glow discharge optical emission spectroscopy, glancing angle X-ray diffraction and SEM techniques respectively. In addition, nanoindentation and sliding tests were performed in order to evaluate the hardness and scratch resistance of TiN thin films. The results showed that the applied voltage bias during the Ti interlayer deposition step could modify some properties of the TiN thin films. Indeed, lower oxygen contents and higher critical loads to start a plastic deformation (scratch resistance) of the TiN thin films are achieved at higher applied voltage biases during the Ti interlayer deposition. A higher scratch resistance is capable of imparting a long term durability of metallic pieces for decorative applications.

Influence of the chemical surface structure on the nanoscale friction in plasma nitrided and post-oxidized ferrous alloy

Friction is a ubiquitous phenomenon in everyday activities spanning from vehicles where efficient brakes are mandatory up to mechanical devices where its minimum effects are pursued for energy efficiency issues. Recently, theoretical models succeed correlating the friction behavior with energy transference via phonons between sliding surfaces. Therefore, considering that the energy losses by friction are prompted through phonons, the chemical surface structure between sliding surfaces is very important to determine the friction phenomenon. In this work, we address the issue of friction between a conical diamond tip sliding on different functionalized flat steel surfaces by focusing the influence of the chemical bonds in the outermost layers on the sliding resistance. This geometry allows probing the coupling of the sharp tip with terminator species on the top and underneath material surface at in-depth friction measurements from 20 to 200 nm. Experimentally, the friction coefficient decreases when nitrogen atoms are substituted for oxygen in the iron network. This effect is interpreted as due to energy losses through phonons whilst lower vibrational frequency excitation modes imply lower friction coefficients and a more accurate adjustment is obtained when a theoretical model with longitudinal adsorbate vibration is used.

Thermally-driven H interaction with HfO2 films deposited on Ge(100) and Si(100)

In the present work, we investigated the thermally-driven H incorporation in HfO2 films deposited on Si and Ge substrates. Two regimes for deuterium (D) uptake were identified, attributed to D bonded near the HfO2/substrate interface region (at 300 °C) and through the whole HfO2 layer (400–600 °C). Films deposited on Si presented higher D amounts for all investigated temperatures, as well as, a higher resistance for D desorption. Moreover, HfO2 films underwent structural changes during annealings, influencing D incorporation. The semiconductor substrate plays a key role in this process.

Pretreatment effect of the pure titanium surface on hybrid coating adhesion based on tetraethoxysilane and methyltriethoxysilane

Hybrid coatings based on silicon alkoxide precursors are one of the options for coating metal surface biomaterials such as pure titanium (Ti). However, the nature and the metal surface preparation, before the coating application, are of fundamental importance for perfecting the coating/surface adhesion. In this study, three different pretreatments were used for the Ti surface: Kroll, Piranha and NaOH. After the pretreatment, the coating was applied by the dip-coating process, using the sol–gel method from the silicon alkoxide precursors, tetraethoxysilane and methyltriethoxysilane. The results of thermogravimetric analysis showed that the tested coatings had excellent thermal stability. The pretreatment with NaOH solution increased the surface roughness of the Ti, thus modifying its surface energy and increasing its wettability. Field emission scanning electron microscopy showed a homogeneous coating with good adhesion of the hybrid coating to the Ti surface, and higher layer thickness on the surface treated with NaOH. In addition, its electrochemical performance was better than the surfaces pretreated with acids.Graphical Abstract

Implantação de Íons de Nitrogênio em PMMA Através de uma Fonte Kaufman

A modificacao de superficies e uma tecnica que a engenharia tem feito uso ha muito tempo, para melhoria de propriedades em materiais. O poli metil-metacrilato (PMMA), por ser um material de constante uso em aplicacoes biomedicas, exige que sua superficie apresente caracteristicas favoraveis a adesao celular e compatibilidade com tecidos. Os polimeros, de uma maneira geral, quando submetidos a tratamentos em plasma, tendem a formar grupos funcionais que alteram propriedades opticas, quimicas, fisicas e de biocompatibilidade. Em funcao disso, este trabalho propos realizar a funcionalizacao de substratos de PMMA atraves da fonte de ions Kaufman. Amostras de PMMA foram submetidas ao feixe de ions de nitrogenio gerado pela fonte Kaufman, em diversas condicoes. A caracterizacao foi feita pelas tecnicas de GD-OES, FTIR e EDS. Ficou comprovado, atraves do perfil de concentracao de nitrogenio obtido por GD-OES, que a quantidade de nitrogenio na superficie aumenta gradativamente com o tempo de implantacao e a potencia. Outro indicio foi a analise em FTIR, que mostrou presenca de aminas nas faixas entre 1654-655 cm-1 e 3300-3700 cm-1. A analise em EDS, porem, comprovou tambem a presenca de ferro e cromo, agentes citotoxicos, que precisam ser eliminados para a continuidade dos trabalhos. http://dx.doi.org/10.18226/23185279.v5iss1p31

Influence of Surface Microstructure and Chemical Composition on the Corrosion Resistance of Plain Steel Modified by Plasma-Assisted Diffusion

The influence of surface microstructure and chemical composition on the corrosion behavior of AISI 1045 (UNS G10450) plain steel modified by plasma-assisted diffusion of nitrogen and oxygen was investigated. A detailed surface characterization was performed before and after cyclic potentiodynamic polarization and salt spray tests, using scanning electron microscopy at low and high resolutions, energy-dispersive x-ray spectroscopy, x-ray diffraction, and glow discharge optical emission spectroscopy. The corrosion resistance as determined by cyclic potentiodynamic polarization was found to depend more strongly on the morphology and composition of the outermost oxynitride layer than on its thickness. For post-oxidation times below and above 90 min, the oxynitride layer presented defects that can act as pathways for corrosive species. The degradation of the corrosion resistance for longer processing times is through cracking of granules, which were previously formed at shorter times owing to the hydrogen accu...

Development of adhesive compositions using powder coating residues

The industry of powder coatings, for base polyester/epoxy, produces about 300 kg.day−1 of residue in a production of 6,000 kg.day−1 (5% residue). Powder coatings with equal or lower to 10 μm of granulometer are considerate residues. The use of these residues in the formulation of adhesives is studied in the present work. Portions of residue with 0.1 a 0.5 g.mL−1 were tested with 7 solvents and 5 kinds of elastomers. Two solvents compatible with the residue and three elastomers, so, three mixtures were obtained: A, B and C; then, 15 g of a petroleum derivated was additioned. The mass of mixtures was homogenized in a mechanic stirrer for 15 minutes. The preliminary tests have demonstrated that the adhesives A, B and C had effective adherence in carpet on cement slab and HDF® (High Density Fiber). The formulations of A, B and C show superior to other 8 tested specially in: fast drying, migration of adhesive upon the surface (carpet) and adherence to the slab. According to the rules ASTM D2094 and D2095 the results of tension test are compared to commercial adhesives, resulting that adhesive C had an efficiency similar to a commercial adhesive for the same utilization.