DEMAT - Departamento de Engenharia de Materiais

URI Permanente desta comunidadehttps://repositorio.ufrn.br/handle/1/130

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Dilatometric behavior and microstructure of sintered Fe–NbC and Fe–TaC composites
(Springer, 2006-12-16) Martinelli, Antonio Eduardo; Paulo, Domingos Sávio de Araújo; Nascimento, Rubens Maribondo do; Távora, Michele Portela; Gomes, Uílame Umbelino; Alves Júnior, Clodomiro
Fe-reinforced composites were manufactured by the addition of 10–20 wt.% NbC or TaC particles aiming at improved mechanical and wear behavior. Two varieties of Fe powders from Hoeganaes Corp. were used, Ancorsteel 1000B and 45P. Composites produced using the former variety included a small amount of Fe3P to induce liquid-phase sintering whereas 45P powder was pre-alloyed with P by the manufacturer. The hardness of the matrix was adjusted adding carbon to the composite mixture. The powders were milled for different times and annealed prior to pressing. A dilatometric study was carried out under hydrogen to establish optimum sintering profiles. Relative densities up to 97% TD were achieved. Both microstructure and density of the sintered pellets were evaluated in order to establish correlations involving composition, processing parameters and microstructure of the composite
Effect of workpiece geometry on the uniformity of nitrided layers
(Elsevier, 2001-05-01) Alves Júnior, Clodomiro; Silva, Eronildes Felisberto da; Martinelli, Antonio Eduardo
The growth behavior of plasma-nitrided layers on workpieces with complex geometry was systematically investigated. AISI 316 stainless steel pellets with different heights were nitrided under a mixture of N2–80% H2 at different temperatures (673, 773 and 843 K) and pressures (100 and 500 Pa). Significant differences in thickness and hardness of the resulting nitrided layers were observed as a function of nitriding parameters. The thickness of nitrided layers increased with sample height, excepted those nitrided at 843 K. The diameter of eroded rings, commonly observed on nitrided samples, varied with coupon height. Changes in both layer thickness and eroded ring diameter are presently addressed based on the thermal balance and charge density that take place near the edges of the samples
Electrochemical behavior of steel-FeNbC composites used in the production of oxygen
(ABM, ABC, ABPol, 2005-04) Silva, Ariadne de Souza; Martinelli, Antonio Eduardo; Scatena júnior, Hélio; Silva, Jorge Herbert Echude; Alves Júnior, Clodomiro; Távora, Michele Portela
The electrocatalytic properties of steel-FeNbC composites were evaluated after potentiostatic ageing with the purpose of establishing the potential use of such materials as electrodes for the industrial production of oxygen. The effect of processing parameters, involved in the production of the composites by powder metallurgy, such as milling conditions and compaction pressure, on the performance of the electrodes was also studied. The electrodes were characterized according to their electrical resistance in NaOH 1M solution, considering that the purpose of the application requires this value to be ~ 0.5 W.cm2. This parameter was evaluated from repetitive electrochemical measurements carried out from 0.7 V to 1.5 V (vs. Ag/AgCl) by electrode anodization. Changes in the electrochemical behavior of the electrodes, especially concerning the O2 evolution in alkaline medium, were studied as a function of the applied potential. The results revealed that the electrocatalytic activity of the electrodes increased upon ageing, probably as a consequence of the growth of oxide layers and/or increase in the conductivity of the material, resulting in current gain and corresponding decrease in the polarization resistance to 0.75 W cm2
Growth of nitrided layers on Fe–Cr alloys
(Elsevier, 2000-02-29) Alves Júnior, Clodomiro; Rodrigues, José de Anchieta; Martinelli, Antonio Eduardo
Chromium is an important alloying element present in numerous commercial steels. A systematic study on the nitriding behavior of Fe–Cr alloys is helpful in predicting the properties of nitrided Cr-alloyed steels. Aspects such as microstructural evolution, growth kinetics, and mechanical properties should be particularly emphasized. Fe–Cr alloys containing 5, 10, and 20 wt.% Cr have been arc melted and subsequently plasma nitrided under a N2–80% H2 atmosphere. The microstructure of the resulting nitrided layers was characterized and the microhardness profiles evaluated. Thicker layers developed on low chromium alloys. Differences in hardness profiles were also observed as a function of chromium contents. Nitriding Fe–5% Cr alloys resulted in two discrete fronts, refereed to as the diffusion front and the transformation front. Transformed regions sustained a decrease in hardness from 1000 down to 600 HV, associated with the conversion of homogeneously dispersed fine precipitates into coarser needle like particles immersed in the ferritic matrix. Similar behavior was not observed for the other alloys, where both fronts developed simultaneously
Low-temperature synthesis of single-phase crystalline LaNiO3 perovskite via Pechini method
(Elsevier, 2002-03) Fernandes, Joana D. G.; Melo, Dulce Maria de Araújo; Zinner, Léa Barbieri; Salustiano, Clayton de Matos; Silva, Z. R.; Martinelli, Antonio Eduardo; Nasar, Marinalva Cerqueira; Alves Júnior, Clodomiro; Silva, Elson Longo da; Bernardi, Maria Inês Basso
LaNiO3 powders were prepared from polymeric precursors. The material was calcinated either under flowing oxygen or in air at temperatures ranging from 300 to 800 °C. The formation of new phases upon calcination was investigated using X-ray diffraction, thermal gravimetric analysis, Fourier-transform infrared spectroscopy and CHN analysis. The results revealed the formation of a single-phase powder having the perovskite structure at temperatures as low as 600 °C. The atmosphere did not significantly affect the final product
Manufacturing of highly porous titanium by metal injection molding in combination with plasma treatment
(Elsevier, 2017-01) Daudt, Natália de Freitas; Bram, Martin; Barbosa, Ana Paula Cysne; Laptev, Alexander M.; Alves Júnior, Clodomiro
Highly-porous titanium was produced by metal injection molding (MIM) of feedstock containing potassium chloride particles as a space holder. Macroporosity was generated by dissolving the potassium chloride particles in water. Challenges for MIM of highly-porous parts include shape retention during debinding and sintering and achieving open surface porosity. This study demonstrates that plasma treatment can remedy both these effects for highly-porous titanium. Plasma treatment of unsintered MIM samples enables attaining porosities of up to 64% in combination with good dimensional accuracy. The effect of plasma treatment on the uptake of interstitial impurities, dimensional accuracy, sintered microstructure and porosity, as well as the interaction of the plasma with partially-debinded MIM samples, was investigated. Highly-porous titanium produced by MIM and plasma treatment is attractive for biomedical implants due to its low impurity content, good dimensional accuracy and shape stability in combination with enhanced open porosity, the latter contributing to bone ingrowth and implant fixation
Novel antibacterial silver coating on PET fabric assisted with hollow-cathode glow discharge
(Wiley, 2020-07-30) Nascimento, Rubens Maribondo do; Naeem, Muhammad; Felipe, M. B. M. C.; Medeiros, Silvia Regina Batistuzzo de; Costa, Thércio Henrique de Carvalho; Libório, Maxwell Santana; Alves Júnior, Clodomiro; Nascimento, Igor Oliveira; Sousa, R. R. M.; Feitor, Michelle Cequeira
The silver-coated fabrics are of much importance because of their outstanding antibacterial features and are useable in several medical and hygienic applications. The silver deposition on fabrics by conventional techniques is not feasible because of their high processing cost, long processing duration, complex equipment, and multiple steps processing (nanoparticle synthesis and subsequent deposition on fabrics). In this novel study, the antibacterial silver coating is deposited by using a hollow cathode discharge (HCD) capable of generating high-density plasma, and thus it exhibits high-efficiency processing. The silver is deposited on woven and non-woven PET fabrics for various treatment times (10-60 minutes), and their antibacterial performance against E. coli and S. aureus bacterial is tested. The XRD results verified the deposition of silver with (111) preferred orientation, while SEM analysis depicted the uniform/ homogeneous deposition of silver particles. The interfacial free energy of adhesion depicts that after the silver deposition on both fabrics, the surface is actively unfavorable for bacterial adhesion. The antibacterial test revealed that the silver-coated woven and non-woven PET fabrics exhibit exceptional antibacterial activity against E. coli and S. aureus bacteria. As the HCD technique is relatively cost-effective, no need for specific sputtering targets, eco-friendly, and require single-step processing for silver deposition. Thus the results are expected to be of remarkable importance to prepare silver-coated antibacterial fabrics useable in hospitals and other appropriate applications
Production of hydrogen from methane using pulsed plasma and simultaneous storage in titanium sheet
(Elsevier, 2006-01) Silva, C. F. da; Ishikawa, Tomaz; Santos, Sydney Ferreira; Alves Júnior, Clodomiro; Martinelli, Antonio Eduardo
High-frequency pulsed plasma (HFPP) was applied to produce hydrogen by reforming natural gas. The process is based on the molecular dissociation of the gas into different ionized species, such as H+ and H+2 . The plasma was generated applying a pulsed voltage in an atmosphere of methane. The efficiency of the system was optimized by adjusting the frequency of the pulsed plasma aiming at maximum selectivity to hydrogen. The reforming of natural gas was accompanied by the simultaneous storage of hydrogen in a hollow cathode set-up made of titanium. Hydrogen contents higher than 900 ppm (in weight%) were stored in the Ti cathode. The efficiency of the method was compatible to industrial applications. Pyrolitic carbon condensed on the lower walls of the reactor but did not interfere with the kinetics of hydrogen absorption. In fact, the carbon produced in such manner could be considered a byproduct of the process and can be used as natural gas adsorbent once adequately activated
Surface modification of Ti implants by plasma oxidation in hollow cathode discharge
(Elsevier, 2006-01-24) Silva, M. A. M.; Martinelli, Antonio Eduardo; Alves Júnior, Clodomiro; Nascimento, Rubens Maribondo do; Távora, Michele Portela; Vilar, Carlos da Silva
As a result of superior biocompatibility and mechanical adequacy, titanium has been widely used in the manufacture of dental implants. On the downside, relatively long periods are normally required to fully integration of the bone into the implant. Surface modification techniques have the potential to shorten the osseointegration time of implants significantly contributing to patient comfort. In this work, plasma discharge in oxidizing atmospheres was used to modify the surface of Ti implants by the production of rough surfaces that consists of a mixture of Ti-oxides. The results showed that considerable improvement on surface roughness and mechanical stability of the oxidized layers could be achieved by confining the effect of the plasma discharge by shielding the cathodic region of the reactor. Processing parameters including temperature, time and pressure were optimized and applied to commercially available Ti implants. Improved wetting was obtained, which is potentially associated to shorter osseointegration periods
The effect of pulse width on the microstructure of d.c.-plasma-nitrided layers
(Elsevier, 1999-12-15) Alves Júnior, Clodomiro; Rodrigues, José de Anchieta; Martinelli, Antonio Eduardo
Modern ion nitriding equipment are powered by pulsed sources in order to prevent arcing and overheating. In industrial applications, the pulse frequency is usually adjusted to set the working temperature. However, frequency variations may drastically affect the plasma species population, and consequently, the microstructure of the final nitrided layer. In this study, AISI-409 steel was nitrided in a mixture of 20% N2–80% H2 using a d.c power source. The depth and microstructure of the nitrided layer were assessed as a function of the time that the voltage was off, toff, in the range of 1–4 ms during a 10 ms pulse cycle. The results suggested that both the microstructure and mechanical behavior of the nitrided layer were affected by toff. Long toff values imply a deleterious effect on the mechanical properties of the nitrided layers

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