The effect of WC-17Co thermal spray coating by HVOF and hard chromium electroplating on the fatigue life and abrasive wear resistance of AISI 4340 high strength steel

One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC- 17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.

Effects of surface treatments on the fatigue strength of AISI 4340 aeronautical steel

Internal residual stresses significantly influence the fatigue strength of coated materials. It is well known that chromium plating is the most used electrodeposited coating for important industrial applications. However, pressure to identify alternatives or to improve the chromium electroplating process have increased in recent years, related to the reduction in fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride free hard chromium electroplating there called accelerated) is an improvement to the conventional process. One environmentally safer and cleaner alternative to hard chromium plating is tungsten carbide thermal spray coating applied by the High Velocity Oxy-Fuel (HVOF) process. To increase the fatigue strength of chromium plated materials, coating thickness and microcracks density are important parameters to be controlled. Techniques as compressive residual stresses induced by shot peening and multilayers, are also used. The aim of this study was to analyse the effects on AISI 4340 steel, in the rotating bending fatigue behaviour, of the: tungsten carbide thermal spray coating applied by HP/HVOF process; chemical nickel underplate, and shot peening process applied before coating deposition, in comparison to hard chromium electroplatings. Rotating bending fatigue test results indicate better performance for the conventional hard chromium plating in relation to the accelerated hard chromium electroplating. Tungsten carbide thermal spray coating and accelerated hard chromium plate over nickel resulted in higher fatigue strength when compared to samples conventional or accelerated hard chromium plated. Shot peening showed to be an excellent alternative to increase fatigue strength of AISI 4340 steel hard chromium electroplated. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Síntese, caracterização e aplicação de MCM-41 funcionalizado com diisopropilamina no processo de adsorção do dióxido de carbono

Emissions of CO2 in the atmosphere have increased successively by various mechanisms caused by human action, especially as fossil fuel combustion and industrial chemical processes. This leads to the increase in average temperature in the atmosphere, which we call global warming. The search for new technologies to minimize environmental impacts arising from this phenomenon has been investigated. The capture of CO2 is one of the alternatives that can help reduce emis ions of greenhouse gases. The CO2 can be captured through the process of selective adsorption using adsorbents for this purpose. Were synthesized by hydrothermal method, materials of the type MCM-41 and Al-MCM-41 in the molar ratio Si / Al equal to 50. The synthesis of gels were prepared from a source of silicon, sodium, water and aluminum in the case of Al-MCM-41. The period of synthesis of the materials was 5 days in autoclave at 100°C. After that time materials were filtered, washed and dried in greenhouse at 100 º C for 4 hours and then calcined at 450 º C. Then the calcined material was functionalized with the Di-isopropylamine (DIPA) by the method of wet impregnation. We used 0.5 g of material mesopores to 3.5 mL of DIPA. The materials were functionalized in a closed container for 24 hours, and after this period were dried at brackground temperature for 2 hours. Were subsequently subjected to heat treatment at 250°C for 1 hour. These materials were used for the adsorption of CO2 and were characterized by XRD, FT-IR, BET / BJH, SEM, EDX and TG / DTG. Tests of adsorption of CO2 was carried out under the following conditions: 100 mg of adsorbent, temperature of 75°C under flow of 100 mL/min of CO2 for 2 hours. The desorption of CO2 was carried out by thermogravimetry from ambient temperature to 900ºC under flow of 25 mL min of He and a ratio of 10ºC/min. The difratogramas X-ray for the synthesized samples showed the characteristic peaks of MCM-41, showing that the structure of it was obtained. For samples functionalized there was a decrease of the intensities of these peaks, with a consequent reduction in the structural ordering of the material. However, the structure was preserved mesopores. The adsorption tests showed that the functionalized MCM-41 is presented as a material promising adsorbent, for CO2 capture, with a loss of mass on the desorption CO2 of 7,52%, while that in Al-MCM- 41 functionalized showed no such loss

Electrochemical behavior of thermally sprayed stainless steel coatings in 3.4% NaCl solution

Four types of stainless steel coatings prepared by a high velocity oxy-fuel spraying system (HVOF) were studied. Differences among coated steels were related to the spraying parameters, which influenced the behavior of the samples against the corrosion. The electrochemical behavior of the stainless steel coatings was strongly influenced by porosity, the presence of micro- and macro-cracks, and also of un-melted particles. Once the electrolyte reached the steel substrate via these defects, the galvanic pair formed between the coating and substrate-accelerated corrosion, leading to the depletion of the coating. (C) 2004 Elsevier Ltd. All rights reserved.

Electrochemical behaviour of thermally sprayed Cr3C2-NiCr coatings in 0.5 M H2SO4 media

The electrochemical behaviour of coated Cr3C2-NiCr steel in aerated 0.5 M H2SO4 solution was studied by means of electrochemical a.c. and d.c. measurements. A complete structural characterization of the coated steel before and after electrochemical tests was also carried out to access the corrosion mechanism of coated steel, electrolyte penetration through the coating, and to confirm the results obtained using electrochemical techniques. Two types of Cr3C2-NiCr coatings produced by a high velocity oxy-fuel spraying system (HVOF) were studied. Differences between coated steels are related to the spraying parameters reflecting their behaviour against corrosion phenomena. The electrochemical behaviour of the coated steel was strongly influenced by porosity and the presence of microcracks in the coating. Once the electrolyte reaches the steel substrate, it corrodes in a galvanic manner resulting in coating detachment from the steel.

Coating residual stress effects on fatigue performance of 7050-T7451 aluminum alloy

The tendency of the aircraft industry is to enhance customer value by improving performance and reducing environmental impact. In view of availability, aluminum alloys have a historically tendency to faster insertion due to their lower manufacturing and operated production infrastructure. In landing gear components, wear and corrosion control of many components is accomplished by surface treatments of chrome electroplating on steel or anodizing of aluminum. One of the most interesting environmentally safer and cleaner alternatives for the replacement of hard chrome plating or anodizing is tungsten carbide thermal spray coating, applied by the high velocity oxy fuel (HVOF) process. However, it was observed that residual stresses originating from these coatings reduce the fatigue strength of a component.An effective process as shot peening treatment, considered to improve the fatigue strength, pushes the crack sources beneath the surface in most of medium and high cycle cases, due to the compressive residual stress field induced. The objective of this research is to evaluate a tungsten carbide cobalt (WC-Co) coating applied by the high velocity oxy fuel (HVOF) process, used to replace anodizing. Anodic films were grown on 7050-T7451 aluminum alloy by sulfuric acid anodizing, chromic acid anodizing and hard anodizing. The influence on axial fatigue strength of anodic films grown on the aluminum alloy surface is to degrade the stress-life performance of the base material. Three groups of specimens were prepared and tested in axial fatigue to obtain S-N curves: base material, base material coated by HVOF and base material shot peened and coated.Experimental results revealed increase in the fatigue strength of Al 7050-T7451 alloy associated with the WC 17% Co coating. on the other hand, a reduction in fatigue life occurred in the shot peened and coated condition. Scanning electron microscopy technique and optical microscopy were used to observe crack origin sites, thickness and coating/substrate adhesion. (c) 2007 Elsevier B.V. All rights reserved.

Corrosion behaviour of thermal sprayed nitinol coatings

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effects of tungsten carbide thermal spray coating by HP/HVOF and hard chromium electroplating on AISI 4340 high strength steel

In cases of decorative and functional applications, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. However, pressure to identify alternatives or to improve conventional chromium electroplating mechanical characteristics has increased in recent years, related to the reduction in the fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride-free hard chromium electroplating is an improvement to the conventional process, considering chemical and physical final properties. One of the most interesting, environmentally safer and cleaner alternatives for the replacement of hard chrome plating is tungsten carbide thermal spray coating, applied by the high velocity oxy-fuel (HVOF) process. The aim of this study was to analyse the effects of the tungsten carbide thermal spray coating applied by the HP/HVOF process and of the high efficiency and fluoride-free hard chromium electroplating (in the present paper called 'accelerated'), in comparison to the conventional hard chromium electroplating on the AISI 4340 high strength steel behaviour in fatigue, corrosion, and abrasive wear tests. The results showed that the coatings were damaging to the AISI 4340 steel behaviour when submitted to fatigue testing, with the tungsten carbide thermal spray coatings showing the better performance. Experimental data from abrasive wear tests were conclusive, indicating better results from the WC coating. Regarding corrosion by salt spray test, both coatings were completely corroded after 72 h exposure. Scanning electron microscopy technique (SEM) and optical microscopy were used to observe crack origin sites, thickness and adhesion in all the coatings and microcrack density in hard chromium electroplatings, to aid in the results analysis. © 2001 Elsevier Science B.V. All rights reserved.

Influence of thermal treatments in the corrosion behaviour of HVOF Cr 3C2-NiCr coatings

Thermal spray coatings as Cr3C2-NiCr obtained by high velocity oxy-fuel spraying (HVOF) are mainly applied due to their behaviour against aggressive erosive-abrasive and corrosive atmospheres and their thermal stability at high temperatures [1]. In order to increase the corrosion protection that it offers to the substrate trying to close the interconnected pores, it is possible to apply a thermal treatment with the gun during the spraying of the coating. This treatment could be applied in different ways. One of these ways consists of spraying only a few layers of coating followed by thermal treatment and finally the spray of the rest of layers. This thermal treatment on spraying is studied related to the corrosion properties of the system. The study comprises the electrochemical characterisation of the system by open circuit potential (OC), polarisation resistance (Rp), cyclic voltammetry (CV) and impedance spectroscopy measurements (EIS). Optical and scanning electron microscopy characterisation (OM and SEM) of the top and cross-section of the system has been used in order to justify the electrochemical results.

Greenhouse gas emission associated with sugar production in southern Brazil

Background: Since sugarcane areas have increased rapidly in Brazil, the contribution of the sugarcane production, and, especially, of the sugarcane harvest system to the greenhouse gas emissions of the country is an issue of national concern. Here we analyze some data characterizing various activities of two sugarcane mills during the harvest period of 2006-2007 and quantify the carbon footprint of sugar production.Results: According to our calculations, 241 kg of carbon dioxide equivalent were released to the atmosphere per a ton of sugar produced (2406 kg of carbon dioxide equivalent per a hectare of the cropped area, and 26.5 kg of carbon dioxide equivalent per a ton of sugarcane processed). The major part of the total emission (44%) resulted from residues burning; about 20% resulted from the use of synthetic fertilizers, and about 18% from fossil fuel combustion.Conclusions: The results of this study suggest that the most important reduction in greenhouse gas emissions from sugarcane areas could be achieved by switching to a green harvest system, that is, to harvesting without burning. © 2010 de Figueiredo et al; licensee BioMed Central Ltd.

Subsolagem em profundidade variada com base no mapeamento de áreas de manejo específico

Pós-graduação em Agronomia (Produção Vegetal) - FCAV

Avaliação do cádmio (Cd), chumbo (Pb), níquel (Ni) e zinco (Zn) em solos e plantas às margens de uma rodovia de tráfego intenso de veículos

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Petroleum contamination impact on macrobenthic communities under the influence of an oil refinery: Integrating chemical and biological multivariate data

Petroleum contamination impact on macrobenthic communities in the northeast portion of Todos os Santos Bay was assessed combining in multivariate analyses, chemical parameters such as aliphatic and polycyclic aromatic hydrocarbon indices and concentration ratios with benthic ecological parameters. Sediment samples were taken in August 2000 with a 0.05 m(2) van Veen grab at 28 sampling locations. The predominance of n-alkanes with more than 24 carbons, together with CPI values close to one, and the fact that most of the stations showed UCM/resolved aliphatic hydrocarbons ratios (UCM:R) higher than two, indicated a high degree of anthropogenic contribution, the presence of terrestrial plant detritus, petroleum products and evidence of chronic oil pollution. The indices used to determine the origin of PAH indicated the occurrence of a petrogenic contribution. A pyrolytic contribution constituted mainly by fossil fuel combustion derived PAH was also observed. The results of the stepwise multiple regression analysis performed with chemical data and benthic ecological descriptors demonstrated that not only total PAH concentrations but also specific concentration ratios or indices such as >= C24:< C24, An/178 and Fl/Fl + Py, are determining the structure of benthic communities within the study area. According to the BIO-ENV results petroleum related variables seemed to have a main influence on macrofauna community structure. The PCA ordination performed with the chemical data resulted in the formation of three groups of stations. The decrease in macrofauna density, number of species and diversity from groups III to I seemed to be related to the occurrence of high aliphatic hydrocarbon and PAH concentrations associated with fine sediments. Our results showed that macrobenthic communities in the northeast portion of Todos os Santos Bay are subjected to the impact of chronic oil pollution as was reflected by the reduction in the number of species and diversity. These results emphasise the importance to combine in multivariate approaches not only total hydrocarbon concentrations but also indices, isomer pair ratios and specific compound concentrations with biological data to improve the assessment of anthropogenic impact on marine ecosystems. (c) 2008 Elsevier Ltd. All rights reserved.

Urban air pollution: a representative survey of PM2.5 mass concentrations in six Brazilian cities

In urban areas of Brazil, vehicle emissions are the principal source of fine particulate matter (PM2.5). The World Health Organization air quality guidelines state that the annual mean concentration of PM2.5 should be below 10 mu g m(-3). In a collaboration of Brazilian institutions, coordinated by the University of Sao Paulo School of Medicine and conducted from June 2007 to August 2008, PM2.5 mass was monitored at sites with high traffic volumes in six Brazilian state capitals. We employed gravimetry to determine PM2.5 mass concentrations, reflectance to quantify black carbon concentrations, X-ray fluorescence to characterize elemental composition, and ion chromatography to determine the composition and concentrations of anions and cations. Mean PM2.5 concentrations and proportions of black carbon (BC) in the cities of Sao Paulo, Rio de Janeiro, Belo Horizonte, Curitiba, Recife, and Porto Alegre were 28.1 +/- 13.6 mu g m(-3) (38% BC), 17.2 +/- 11.2 mu g m(-3) (20% BC), 14.7 +/- 7.7 mu g m(-3) (31% BC), 14.4 +/- 9.5 mu g m(-3) (30% BC), 7.3 +/- 3.1 mu g m(-3) (26% BC), and 13.4 +/- 9.9 mu g m(-3) (26% BC), respectively. Sulfur and minerals (Al, Si, Ca, and Fe), derived from fuel combustion and soil resuspension, respectively, were the principal elements of the PM2.5 mass. We discuss the long-term health effects for each metropolitan region in terms of excess mortality risk, which translates to greater health care expenditures. This information could prove useful to decision makers at local environmental agencies.

Water-soluble organic compounds in air particulate matter analyzed by HPLC-DAD-MS and HPLC-MS/MS: abundance, sources and transformation of carboxylic acids, nitrophenols and nitrated proteins

Wasserlösliche organische Verbindungen (WSOCs) sind Hauptbestandteile atmosphärischer Aerosole, die bis zu ~ 50% und mehr der organischen Aerosolfraktion ausmachen. Sie können die optischen Eigenschaften sowie die Hygroskopizität von Aerosolpartikeln und damit deren Auswirkungen auf das Klima beeinflussen. Darüber hinaus können sie zur Toxizität und Allergenität atmosphärischer Aerosole beitragen.In dieser Studie wurde Hochleistungsflüssigchromatographie gekoppelt mit optischen Diodenarraydetektion und Massenspektrometrie (HPLC-DAD-MS und HPLC-MS/MS) angewandt, um WSOCs zu analysieren, die für verschiedene Aerosolquellen und -prozesse charakteristisch sind. Niedermolekulare Carbonsäuren und Nitrophenole wurden als Indikatoren für die Verbrennung fossiler Brennstoffe und die Entstehung sowie Alterung sekundärer organischer Aerosole (SOA) aus biogenen Vorläufern untersucht. Protein-Makromoleküle wurden mit Blick auf den Einfluss von Luftverschmutzung und Nitrierungsreaktionen auf die Allergenität primärer biologischer Aerosolpartikel – wie Pollen und Pilzsporen – untersucht.rnFilterproben von Grob- und Feinstaubwurden über ein Jahr hinweg gesammelt und auf folgende WSOCs untersucht: die Pinen-Oxidationsprodukte Pinsäure, Pinonsäure und 3-Methyl-1,2,3-Butantricarbonsäure (3-MBTCA) sowie eine Vielzahl anderer Dicarbonsäuren und Nitrophenole. Saisonale Schwankungen und andere charakteristische Merkmale werden mit Blick auf Aerosolquellen und -senken im Vergleich zu Daten anderen Studien und Regionen diskutiert. Die Verhätlnisse von Adipinsäure und Phthalsäure zu Azelainsäure deuten darauf hin, dass die untersuchten Aerosolproben hauptsächlich durch biogene Quellen beeinflusst werden. Eine ausgeprägte Arrhenius-artige Korrelation wurde zwischen der 3-MBTCA-¬Konzentration und der inversen Temperatur beobachtet (R2 = 0.79, Ea = 126±10 kJ mol-1, Temperaturbereich 275–300 K). Modellrechnungen zeigen, dass die Temperaturabhängigkeit auf eine Steigerung der photochemischen Produktionsraten von 3-MBTCA durch erhöhte OH-Radikal-Konzentrationen bei erhöhten Temperaturen zurückgeführt werden kann. Im Vergleich zur chemischen Reaktionskinetik scheint der Einfluss von Gas-Partikel-Partitionierungseffekten nur eine untergeordnete Rolle zu spielen. Die Ergebnisse zeigen, dass die OH-initiierte Oxidation von Pinosäure der geschwindigkeitsbestimmende Schritt der Bildung von 3-MBTCA ist. 3-MBTCA erscheint somit als Indikator für die chemische Alterung von biogener sekundärer organischer Aerosole (SOA) durch OH-Radikale geeignet. Eine Arrhenius-artige Temperaturabhängigkeit wurde auch für Pinäure beobachtet und kann durch die Temperaturabhängigkeit der biogenen Pinen-Emissionen als geschwindigkeitsbestimmender Schritt der Pinsäure-Bildung erklärt werden (R2 = 0.60, Ea = 84±9 kJ mol-1).rn rnFür die Untersuchung von Proteinnitrierungreaktionen wurde nitrierte Protein¬standards durch Flüssigphasenreaktion von Rinderserumalbumin (BSA) und Ovalbumin (OVA) mit Tetranitromethan (TNM) synthetisiert.Proteinnitrierung erfolgt vorrangig an den Resten der aromatischen Aminosäure Tyrosin auf, und mittels UV-Vis-Photometrie wurde der Proteinnnitrierungsgrad (ND) bestimmt. Dieser ist definiert als Verhältnis der mittleren Anzahl von Nitrotyrosinresten zur Tyrosinrest-Gesamtzahl in den Proteinmolekülen. BSA und OVA zeigten verschiedene Relationen zwischen ND und TNM/Tyrosin-Verhältnis im Reaktionsgemisch, was vermutlich auf Unterschiede in den Löslichkeiten und den molekularen Strukturen der beiden Proteine zurück zu führen ist.rnDie Nitrierung von BSA und OVA durch Exposition mit einem Gasgemisch aus Stickstoffdioxid (NO2) und Ozon (O3) wurde mit einer neu entwickelten HPLC-DAD-¬Analysemethode untersucht. Diese einfache und robuste Methode erlaubt die Bestimmung des ND ohne Hydrolyse oder Verdau der untersuchten Proteine und ernöglicht somit eine effiziente Untersuchung der Kinetik von Protein¬nitrierungs-Reaktionen. Für eine detaillierte Produktstudien wurden die nitrierten Proteine enzymatisch verdaut, und die erhaltenen Oligopeptide wurden mittels HPLC-MS/MS und Datenbankabgleich mit hoher Sequenzübereinstimmung analysiert. Die Nitrierungsgrade individueller Nitrotyrosin-Reste (NDY) korrelierten gut mit dem Gesamt-Proteinnitrierungsgrad (ND), und unterschiedliche Verhältnisse von NDY zu ND geben Aufschluss über die Regioselektivität der Reaktion. Die Nitrierungmuster von BSA und OVA nach Beahndlung mit TNM deuten darauf hin, dass die Nachbarschaft eines negativ geladenen Aminosäurerestes die Tyrosinnitrierung fördert. Die Behandlung von BSA durch NO2 und O3 führte zu anderend Nitrierungemustern als die Behandlung mit TNM, was darauf hindeutet, dass die Regioselektivität der Nitrierung vom Nitrierungsmittel abhängt. Es zeigt sich jedoch, dass Tyrosinreste in Loop-Strukturen bevorzugt und unabhängig vom Reagens nitriert werden.Die Methoden und Ergebnisse dieser Studie bilden eine Grundlage für weitere, detaillierte Untersuchungen der Reaktionskinetik sowie der Produkte und Mechanismen von Proteinnitrierungreaktionen. Sie sollen helfen, die Zusammenhänge zwischen verkehrsbedingten Luftschadstoffen wie Stickoxiden und Ozon und der Allergenität von Luftstaub aufzuklären.rn