Influence of Microstructures on Polarization Resistance and Hydrogen-Induced Cracking of a Micro-Alloyed Steel Submitted to Different Cooling Rates

The effect of different microstructures on the polarization resistance (Rp) and the hydrogen-induced cracking (HIC) of a micro-alloyed steel austenitized and submitted to different cooling rates was studied. Samples 19.1 x 6 x 2 mm, containing the whole thickness of the plate were extracted from a 20 mm plate and heat treated on a quenching dilatometer, were submitted to Rp and HIC corrosion tests. Both Rp and HIC tests followed as close as possible ASTM G59 and NACE standard TM0284-2003, in this case, modified only with regard to the size of the samples. Steel samples transformed from austenite by a slow cooling (cooling rate of 0.5 degrees C.s(-1)) showed higher susceptibility to hydrogen-induced cracking, with large cracks in the middle of the sample propagating along segregation bands, corresponding to the centerline of the plate thickness. For cooling rates of 10 degrees C.s(-1), only small cracks were found in the matrix and micro cracks nucleated at non-metallic inclusions. For higher cooling rates (40 degrees C.s(-1)) very few small cracks were detected, linked to non-metallic inclusions. This result suggests that structures formed by polygonal structures and segregation bands (were cutectoid microconstituents predominate) have higher susceptibility to HIC. Structures predominantly formed by acicular ferrite make it difficult to propagate the cracks among non-oriented and interlaced acicular ferrite crystals. Smaller segregation bands containing eutectoid products also help inhibit cracking and crack propagation; segregation bands can function as pipelines for hydrogen diffusion and offer a path of stress concentration for the propagation of cracks, frequently associated to non-metallic inclusions. Polarization resistance essays performed on the steel in theas received condition, prior to any heat treatment, showed larger differences between the regions of the plate, with a considerably lower Rp in the centerline. The austenitization heat treatments followed by cooling rates of 0.5 e 10 degrees C.s(-1) made more uniform the corrosion resistance along the thickness of the plate. The effects of heat treatments on the corrosion resistance are probably related to the microconstituent formed, allied to the chemical homogenization of the impurities concentrated on the centerline of the plate.

Compared performance of penetrometers and effect of soil water content on penetration resistance measurements

Modern agriculture techniques have a great impact on crops and soil quality, especially by the increased machinery traffic and weight. Several devices have been developed for determining soil properties in the field, aimed at managing compacted areas. Penetrometry is a widely used technique; however, there are several types of penetrometers, which have different action modes that can affect the soil resistance measurement. The objective of this study was to compare the functionality of two penetrometry methods (manual and automated mode) in the field identification of compacted, highly mechanized sugarcane areas, considering the influence of soil water volumetric content (θ) on soil penetration resistance (PR). Three sugarcane fields on a Rhodic Eutrudrox were chosen, under a sequence of harvest systems: one manual harvest (1ManH), one mechanized harvest (1MH) and three mechanized harvests (3MH). The different degrees of mechanization were associated to cumulative compaction processes. An electronic penetrometer was used on PR measurements, so that the rod was introduced into the soil by hand (Manual) and by an electromechanical motor (Auto). The θ was measured in the field with a soil moisture sensor. Results showed an effect of θ on PR measurements and that regression models must be used to correct data before comparing harvesting systems. The rod introduction modes resulted in different mean PR values, where the "Manual" overestimated PR compared to the "Auto" mode at low θ.

Spectral induced polarization: Laboratory measurements on sandy quartz samples of varied pore characteristics

Understanding the influence of pore space characteristics on the hydraulic conductivity and spectral induced polarization (SIP) response is critical for establishing relationships between the electrical and hydrological properties of surficial sedimentary deposits. Here, we present the results of laboratory SIP measurements on saturated quartz samples with granulometric characteristics ranging from fine sand to fine gravel. We alter the pore characteristics using three principal methods: (i) variation of the grain sizes, (ii) changing the degree of compaction, and (iii) changing the level of sorting. We then examine how these changes affect both the SIP response and the hydraulic conductivity. In general, the results indicate a clear connection between the applied changes in pore characteristics and the SIP response. In particular, we observe a systematic correlation between the hydraulic conductivity and the relaxation time of the Cole-Cole model describing the observed SIP effect for the whole range of considered grain sizes.

Results of rolling resistance measurements on twelve radial passenger car tires.

National Highway Traffic Safety Administration, Office of Research and Development, Washington, D.C.

Thermal resistance measurements on power transistors /

Mode of access: Internet.

Erosion-corrosion of mild steel in hot caustic. Part I: NaOH solution

A novel apparatus, high-pressure/high-temperature nickel flow loop, was constructed to study the effect of the flow on the rate of erosion-corrosion of mild steel in hot caustic. It has been successfully used to measure the corrosion rate of 1020 steel in 2.75 M NaOH solution at a temperature of 160 degrees C and velocities of 0.32 and 2.5 m/s. In situ electrochemical methods were used to measure the corrosion rate such as the potentiodynamic sweep, the polarization resistance method, and electrochemical impedance spectroscopy (EIS). Also used were the weight-loss method and scanning electron microscopy (SEM). Eight electrodes/coupons were used to monitor the metal loss rate, four were placed at the low velocity section, while the other four were placed in the high velocity section. The first three coupons in each section were placed within the disturbed flow region, while the fourth was placed in a fully developed flow region. The corrosion rate of the coupons in the high velocity section was generally higher than that of the coupons in the low velocity section. One coupon in the disturbed flow region had a significantly higher corrosion rate than the others. (c) 2005 Elsevier Ltd. All rights reserved.

Simultaneous optical signal-to-noise ratio and differential group delay monitoring based on degree of polarization measurements in optical communications systems

We present a simultaneous optical signal-to-noise ratio (OSNR) and differential group delay (DGD) monitoring method based on degree of polarization (DOP) measurements in optical communications systems. For the first time in the literature (to our best knowledge), the proposed scheme is demonstrated to be able to independently and simultaneously extract OSNR and DGD values from the DOP measurements. This is possible because the OSNR is related to maximum DOP, while DGD is related to the ratio between the maximum and minimum values of DOP. We experimentally measured OSNR and DGD in the ranges from 10 to 30 dB and 0 to 90 ps for a 10 Gb/s non-return-to-zero signal. A theoretical analysis of DOP accuracy needed to measure low values of DGD and high OSNRs is carried out, showing that current polarimeter technology is capable of yielding an OSNR measurement within 1 dB accuracy, for OSNR values up to 34 dB, while DGD error is limited to 1.5% for DGD values above 10 ps. For the first time to our knowledge, the technique was demonstrated to accurately measure first-order polarization mode dispersion (PMD) in the presence of a high value of second-order PMD (as high as 2071 ps(2)). (C) 2012 Optical Society of America

Influence of chloride ion concentration and temperature on the electrochemical properties of passive films formed on a superduplex stainless steel

Polarization measurements were conducted to monitor the corrosion behavior of superduplex stainless steel ASTM A995M-Gr.SA/EN 10283-Mat#1.4469(GX2CrNiMo26-7-4) when exposed to a) an electrolyte containing 22,700 parts per million (ppm) of chloride ions at seven different temperatures and b) an electrolyte at 25 GC and different chloride ion concentrations (5800, 22,700, 58,000 and 80,000 ppm of Cl(-)). The polarization curves indicate that the passive films formed are only slightly affected by NaCl concentration, but the pitting potential decreases drastically increasing the temperature, in particular >60 degrees C. The image analysis of the microstructure after potentiodynamic polarization showed that the pitting number and size vary in function of the temperature of the tested medium. Nyquist diagrams were determined by electrochemical impedance spectroscopy to characterize the resistance of the passive layer. According to Nyquist plots, the arc polarization resistance decreases increasing the temperature due to a catalytic degradation of the oxide passive films. (C) 2009 Elsevier Inc. All rights reserved.

Ureasilicate hybrid coatings for corrosion protection of galvanized steel in chloride-contaminated simulated concrete pore solution

Organic-inorganic hybrid (OIH) sol-gel coatings based on ureasilicates (U(X)) have promising properties for use as eco-friendly coatings on hot dip galvanized steel (HDGS) and may be considered potential substitutes for pre-treatment systems containing Cr(VI). These OIH coatings reduce corrosion activity during the initial stages of contact of the HDGS samples with highly alkaline environments (cementitious media) and allow the mitigation of harmful effects of an initial excessive reaction between cement pastes and the zinc layer. However, the behavior of HDGS coated with U(X) in the presence of chloride ions has never been reported. In this paper, the performance of HDGS coated with five different U(X) coatings was assessed by electrochemical measurements in chloride-contaminated simulated concrete pore solution (SCPS). U(X) sol-gel coatings were produced and deposited on HDGS by a dip coating method. The coatings performance was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curves measurements, macrocell current density and polarization resistance in contact with chloride-contaminated SCPS. The SEM/EDS analyses of the coatings before and after the tests were also performed. The results showed that the HDGS samples coated with the OIH coatings exhibited enhanced corrosion resistance to chloride ions when compared to uncoated galvanized steel.

In vivo electrochemical corrosion study of a CoCrMo biomedical alloy in human synovial fluids.

The present study was initiated with the aim to assess the in vivo electrochemical corrosion behaviour of CoCrMo biomedical alloys in human synovial fluids in an attempt to identify possible patient or pathology specific effects. For this, electrochemical measurements (open circuit potential OCP, polarization resistance Rp, potentiodynamic polarization curves, electrochemical impedance spectroscopy EIS) were carried out on fluids extracted from patients with different articular pathologies and prosthesis revisions. Those electrochemical measurements could be carried out with outstanding precision and signal stability. The results show that the corrosion behaviour of CoCrMo alloy in synovial fluids not only depends on material reactivity but also on the specific reactions of synovial fluid components, most likely involving reactive oxygen species. In some patients the latter were found to determine the whole cathodic and anodic electrochemical response. Depending on patients, corrosion rates varied significantly between 50 and 750mgdm(-2)year(-1).

Effects of fermentation products of pro- and prebiotics on trans-epithelial electrical resistance in an in vitro model of the colon

Evidence from in vivo and in vitro studies suggests that the consumption of pro- and prebiotics may inhibit colon carcinogenesis; however, the mechanisms involved have, thus far, proved elusive. There are some indications from animal studies that the effects are being exerted during the promotion stage of carcinogenesis. One feature of the promotion stage of colorectal cancer is the disruption of tight junctions, leading to a loss of integrity across the intestinal barrier. We have used the Caco-2 human adenocarcinoma cell line as a model for the intestinal epithelia. Trans-epithelial electrical resistance measurements indicate Caco-2 monolayer integrity, and we recorded changes to this integrity following exposure to the fermentation products of selected probiotics and prebiotics, in the form of nondigestible oligosaccharides (NDOs). Our results indicate that NDOs themselves exert varying, but generally minor, effects upon the strength of the tight junctions, whereas the fermentation products of probiotics and NDOs tend to raise tight junction integrity above that of the controls. This effect was bacterial species and oligosaccharide specific. Bifidobacterium Bb 12 was particularly effective, as were the fermentation products of Raftiline and Raftilose. We further investigated the ability of Raftilose fermentations to protect against the negative effects of deoxycholic acid (DCA) upon tight junction integrity. We found protection to be species dependent and dependent upon the presence of the fermentation products in the media at the same time as or after exposure to the DCA. Results suggest that the Raftilose fermentation products may prevent disruption of the intestinal epithelial barrier function during damage by tumor promoters.

Estudos de Durabilidade Frente ao Ataque Ácido de Compósitos Portland-Polímero para Cimentação de Poços de Petróleo

Portland-polymers composites are promising candidates to be used as cementing material in Northeastern oil wells of Brazil containing heavy oils submitted to steam injection. In this way, it is necessary to evaluate its degradation in the commonly acidizind agents. In addition, to identify how aggressive are the different hostile environments it is an important contribution on the decision of the acidic systems to be used in. It was investigated the performance of the Portland-polymer composites using powdered polyurethane, aqueous polyurethane, rubber tire residues and a biopolymer, those were reinforced with polished carbon steel SAE 1045 to make the electrochemical measurements. HCl 15,0 %, HCl 6,0 % + HF 1,5 % (soft mud acid), HCl 12,0 % + HF 3,0 % (regular mud acid) and HAc 10 % + HF 1,5 % were used as degrading environment and electrolytes. The more aggressive acid solution to the plain Portland hardened cement paste was the regular mud acid, that showed loss of weight around 23.0 %, followed by the soft mud acid, the showed 11.0 %, 15.0 % HCl with 7,0 % and, at last the 10.0 % HAc plus HF 1.5 % with just 1.0 %. The powdered polyurethane-composite and the aqueous polyurethane one showed larger durability, with reduction around 87.0 % on the loss of weight in regular mud acid. The acid attack is superficial and it occurs as an action layer, where the degraded layer is responsible for the decrease on the kinetic of the degrading process. This behavior can be seen mainly on the Portland- aqueous polyurethane composite, because the degraded layer is impregnated with chemically modified polymer. The fact of the acid attack does not have influence on the compressive strength or fratography of the samples, in a general way, confirms that theory. The mechanism of the efficiency of the Portland-polymers composites subjected to acid attack is due to decreased porosity and permeability related with the plain Portland paste, minor quantity of Ca+2, element preferentially leached to the acidic solution, wave effect and to substitute part of the degrading bulk for the polymeric one. The electrolyte HAc 10 % + HF 1,5 % was the least aggressive one to the external corrosion of the casing, showing open circuit potentials around +250 mV compared to -130 mV to the simulated pore solution to the first 24 hours immersion. This behavior has been performed for two months at least. Similar corrosion rates were showed between both of the electrolytes, around 0.01 μA.cm-2. Total impedance values, insipient arcs and big polarization resistance capacitive arcs on the Nyquist plots, indicating passivity process, confirm its efficiency. In this way, Portlandpolymers composites are possible solutions to be succeed applied to oilwell cementing concomitant submitted to steam injection and acidizing operation and the HAc 10,0 % + HF 1,5 % is the less aggressive solution to the external corrosion of the casing

Avaliação de inibidores verdes microemulsionados na inibição à corrosão do aço carbono AISI 1020

In general, among the corrosion inhibitors surfactants are the most commonly used compounds, because they are significantly effective by forming protective films on anodic and cathodic areas. In this study, microemulsions containing he biodegradable saponified coconut oil as surfactant (SME-OCS) was used as green corrosion inhibitors. With this purpose, methanolic extracts of Ixora coccinea Linn (IC) and a polar fraction rich in alkaloids (FA) obtained from Croton cajucara Benth solubilized in the SME-OCS system were examined in the presence of AISI 1020 carbon steel, in saline solution (NaCl 3,5 %). The efficiency of corrosion inhibition of IC and FA were evaluated in the following microemulsions: SME-OCS-IC and SME-OCS-FA. The microemulsion system SME-OCS in the presence and absence of IC and FA was assessed by measurements of weight loss and the electrochemical method of polarization resistance, with variation in the concentration of IC and FA (50 - 400 ppm), showing significant results of corrosion inhibition (83,6 % SME-OCS; 92,2 % SME-OCS-FA; and 95,3 % SME-OCS-IC)

Utilização de matérias primas vegetais para aplicabilidade como inibidores de corrosão

In the search for products that act as corrosion inhibitors and do not cause environmental, impact the use of plant extracts as corrosion inhibitors is becoming a promising alternative. In this work the efficiency of polar extracts (ethanol extracts) obtained from the plants Anacardium occidentale Linn (AO) and Phyllantus amarus Schum. & Thonn (PA) as corrosion inhibitors were evaluated in different concentrations. For that AO and PA extracts were solubilized in the microemulsion systems (SME) containing saponified coconut oil as surfactant (SME -OCS and SME-OCS-1) in saline (NaCl 3,5 %) solution, which was also used as electrolyte. Both SME-OCS and SME-OCS-1 were characterized by surface tension and viscosity methods showing a Newtonian fluid behavior. The SME-OCS and SME-OCS-1 systems satisfactorily solubilized the polar extracts AO and PA with measurements carried out by ultraviolet spectroscopy. The measurements of corrosion inhibition efficiencies were performed by the electrochemical linear polarization resistance (LPR) technique as well as weight loss, on the surface of AISI 1020 carbon steel. The maximum corrosion inhibition efficiencies were determined by extrapolation of Tafel plots, showing the following values: 95,6 % for the system SME-OCS-AO, 98,9 % for the system SME-OCS-AO-1 and 93,4 % for the system SME-OCS-PA

Desgaste corrosivo-cavitativo-erosivo de um aço-carbono em meio aquoso com frações de sal (NaCl), CO2 e particulados sólidos (SiO2)

A batch of eighty-four coupons of low carbon steel were investigated at laboratory conditions under a corrosive, cavitative-corrosive (CO2) and corrosive-erosive (SiO2 + CO2) in an aqueous salt solution and two levels of temperature. The following measurements were made on Vickers (HV0,05, HV0,10, HV0,20) Microhardness tests at three levels of subsurface layer. A turbulent flow collided on the cylindrical sample, with and without mechanical stirring and gas bubbling, with and without fluid contamination by solid particles of SiO2, at two temperatures. Surface Roughness and Waviness, under two conditions "as received, after machining" and "after worn out", as well as gravimetric and electrochemical parameter were measured on the two opposite generatrices of each cylindrical sample, on the flow upstream (0°) and downstream (180°) by Profilometry, Mass Variation and Linear Polarization Resistance (LPR). The results of the Microhardness and Surface Texture of all coupons were subjected to statistical comparison, using the software Statgraphics® Centurion XVI, 95% statistical certainty, and significant differences were observed in some arrays of measurements. The corrosive wear rate measured by LPR and mass variation shown to be sensitive to the presence of bubbles and hydrodynamic fluctuations inside the cell, considering the temperature and contamination of corrosive fluid by solid particles. The main results of visual inspection relative to some topologies of the surface damages involving different mechanisms that were seen to give explanation for some fluctuations in wear rates of the steel experimentally investigated