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 ɣ N (S-phase).
Plywood panels are produced with polymeric adhesives derived from petroleum that can be hazardous to health and the environment, since they are made from non-renewable sources and contain organic solvents in their composition, which can cause diseases such as cancer. Polyurethane adhesives derived from castor oil-based are an alternative to those materials, because it is biodegradable and non-hazardous. The aim of this work was to evaluate the mechanical properties of plywood panels made with polyurethane adhesive derived from castor oil-based. Panels were produced with five sheets of Pinus caribaea bahamensis wood and three different adhesives: urea-formaldehyde, phenol formaldehyde, and polyurethane with a glue spread line of 180 g/m 2 for phenolic adhesives, and 120, 140, 160, 180 g/m 2 for polyurethane. The panels were evaluated in terms of specific mass, shear strength before and after immersion on boiling and cold water, in cycle and without immersion, and bending strength parallel and perpendicular to the fibers orientation. Results were statistically analyzed. The plywood panels produced with polyurethane adhesive derived from castor oil have superior shear strength and bending strength similar than those produced with the others tested adhesives, and the weight of 120 g/m 2 is the most suitable for bonding.
ObstractThe 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.
Influência da intensidade de corrente elétrica do tratamento térmico de indução eletromagnética nas propriedades mecânicas do aço ABNT 1045Influence of the electric current intensity of the electromagnetic induction heat treatment on the mechanical properties of ABNT 1045 steel
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