ABSTRACT This work aimed to analyze the influence of treatment pressure on the interaction between stearic acid and an Argon-Oxygen plasma. The fixed variables were the applied RF plasma power (50 W), treatment time (30 min), and treatment starting temperature (273 K). The pressure was varied as follows: 0.2, 0.6, and 1.0 Torr. For all treatment conditions, the etching of the samples was observed, as evidenced by the mass loss of the specimens and by following the gaseous by-products of reactions employing a mass spectrometer coupled to the reaction chamber. Optical emission spectroscopy followed the emission lines of oxygen active species. Functionalization of the specimens was also observed, as shown by the results obtained by Fourier-transform infrared spectroscopy (FTIR) and through XRD analysis. A liquid phase was formed for samples treated at 0.6 and 1.0 Torr, which favored the functionalization process and broadened the band present in the region from 1750 to 1700 cm–1, resulting in amorphous phases. An increase in the intensity of the characteristic peaks of esters was also observed. It can be concluded that the higher pressure favors the formation of a liquid phase and reaction kinetics, resulting in higher functionalization and lower etching.

Abstract ISO 5832-1 stainless steel specimens were plasma nitrided at different nitrogen potentials. The main goal was to obtain the S-phase with different nitrogen concentrations and free of chromium-based precipitates. The control of nitrogen potential was made by pulsing the gas at predetermined times: 10/10, 05/15, 02/18, and 01/19, where the numbers represent the time in minutes that the nitrogen flow was kept on/off, respectively. For all pulsing conditions, the nitriding was carried out at 450 °C for 2 hours. After nitriding, specimens were characterized by means of optical (OM) and electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microhardness. Results show that the nitrided layer thickness decreases with decreasing times of nitrogen pulse, and that lower times of nitrogen flow lead to lower precipitation of chromium nitrides. It can be thus concluded that the use of intermittent nitrogen flow is an alternative to control the nitrided layer in terms of thickness, hardness, and the amount of nitrogen present in phase ɣN (S-phase).

Abstract The use of araucaria pine nut shell in polymer composites may increase the pine nut value and help protec araucaria (Araucaria angustifolia) itself, which is an endangered species. The aim of this work is to study the influence of the size of pine nut shell fiber on the mechanical properties of composites made of this shell and polyurethane derived from castor oil. Composites with different polyurethane contents were manufactured with dried untreated pine nut shell sieved through 30 and 50 mesh sieves (0.6 and 0.3 mm, respectively). Composites were shaped by mechanical mixing of the components followed by hot pressing. Properties such as density, water absorption, and flexural strength were measured. Specimens were also characterized by SEM, FTIR, and TGA. The flexural strength of PU/0.3mm pine nut shell composites with 30% PU (wt%) was 57.7 MPa, and their water absorption was 7.37% after 24 hours of immersion.

Specimens of ISO 5832-1stainless steel were submitted to low temperature plasma nitriding treatment and Solution Heat Treatment after Plasma Nitriding (SHTPN) process aiming to obtain a S-phase, chromium precipitates-free, surface layer. The following techniques were used for analysis: scanning electron microscopy (SEM), optical microscopy (OM), microhardness, X-ray diffraction (XRD) and wavelength dispersive spectroscopy (WDS) microanalysis. Corrosion resistance was evaluated by means of potentiodynamic anodic polarization and open-circuit measurements of corrosion potential. Results indicated that the S-phase layer with N concentrations of about 0.9 wt% and 2 µm thick was formed during low temperature plasma nitriding, while layers with concentratios of about 0.45 wt% of N and up to 200 µm thick resulted from the SHTPN process. Results proved the increase in localized corrosion resistance caused by nitrogen in solid solution for both processes, as well as the deleterious effect caused by the precipitation of chromium nitride.