999 resultados para Corrosion monitoring
Resumo:
Since the discovery of multiple bioactivities for agarobiose oligomers, a quantitative method has been in great need to monitor the agarobiose oligomers. This report demonstrates that agarobiose oligomers can be separated with high resolution in HPLC after introducing a-naphthylamine into compounds. Agarobiose oligomers ranged from biose to decaose were isolated by Sephadex column. HPLC analysis indicated that each oliomer could be quantified with good linearity and a low detection limit of 0.1-4 mug/ml. The chromatographic profiles of agaro-oligosaccharides with different hydrolysis modes (hydrochloride, citric acid, solid acid, and hydroxyl radical degradation) showed that agarobiose could be obtained more than 57.8% using solid acid mediated hydrolysis, while hydrochloride acid could degrade agar into a series of agaro-oligosaccharides from biose to decaose. The yield of oligosaccharides was low if hydrolyzed by citric acid. The Fenton degradation can increase the speed of hydrolysis, but the product was complex. (C) 2004 Elsevier B.V. All rights reserved.
Resumo:
A newly synthesized benzoic-triazole derivative 3,5-dimethylbenzoic acid [1,2,4]triazol-l-ylmethyl ester (DBT) was investigated as a corrosion inhibitor of mild steel in 1 M HCl solution using weight loss measurements, potentiodynamic polarization, SEM, and EIS methods. The results revealed that DBT was an excellent inhibitor, and the inhibition efficiencies obtained from weight loss and electrochemical experiments were in good agreement. Using the potentiodynamic polarization technique, the inhibitor was proved to have a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the metal surface. The number of water molecules (X) replaced by a molecule of organic adsorbate was determined from the Flory-Huggins, Dhar-Flory-Huggins, and Bockris-Swinkels substitutional adsorption isotherms applied to the data obtained from the gravimetric experiments performed on a mild steel specimen in 1 M HCl solution at 298 K.
Resumo:
Research on corrosion of steel structures in various marine environments is essential to assure the safety of structures and can effectively prolong their service life. In order to provide data for anticorrosion design of oil exploitation structures in the Bohai Bay, the corrosion behaviour and properties of steel in beach soil, using typical steel samples (Q235A carbon steel and API 5Lx52 pipeline steel) buried 0.5, 1.0 and 1.5 m deep under typical beach soils in Tanggu, Yangjiaogou, Xingcheng, Yingkou and Chengdao for 1-2 years were studied. The carbon steel and pipeline steel were both corroded severely in the beach soil, with the form of corrosion being mainly uniform with some localised attack (pitting corrosion). The corrosion rate of the carbon steel was up to 0.16 mm/year with a maximum penetration depth of 0.76 mm and that of the pipeline steel was up to 0.14 mm/year, with a maximum penetration depth of 0.53 mm. Compared with carbon steel, the pipeline steel generally had better corrosion resistance in most test beach soils. The corrosion rates and the maximum corrosion depths of carbon steel and pipeline steel were in the order: Tanggu>Xingcheng>Chengdao>Yingkou>Yangjiaogou with corrosion altering with depth of burial. The corrosion of steel in the beach soil involves a mixed mechanism with different degrees of soil aeration and microbial activity present. It is concluded that long term in situ plate laying experiments must be carried out to obtain data on steel corrosion in this beach soil environment so that the effective protection measures can be implemented.
Resumo:
Four research methods, such as weight loss test, electrochemical techniques, adsorption isotherm, and quantum chemical calculation, were employed in this paper to study the inhibition efficiency (IE) and inhibition mechanism of three 2H-pyrazole-triazole derivatives, BHOT, FHOT, and CHOT in 1 M HCl solution for mild steel. Using the electrochemical technique, three inhibitors were proved to show a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the steel surface. The adsorption models of three compounds were established at different temperatures according to their adsorption isotherms. The results of the quantum chemical calculation method indicated that the adsorption sites of 2H-pyrazole-triazole derivatives were strongly centralized on benzene ring, triazole ring, or other substituents. All the results showed that the three derivatives were excellent inhibitors in I M HCl solution for mild steel.
Resumo:
The inhibitory effect of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and 2,4,6-tri(2-pyridyl)-s-triazine (TPT) molecules on the corrosion of mild steel in 1 mol/L HCl and microcosmic inhibitory mechanism were investigated by X-ray photoelectron spectroscopy and ellipsometry. XPS results showed that C Is and N Is peaks of TTC, C Is and N Is peaks of TPT and their integral areas were obtained, which suggested the layer of the inhibitors (TTC or TPT) should have effectively protected the mild steel surface from the corrosion; and the depression from the inhibitors for the corrosion of mild steel surface was studied using ellipsometry combined with potentiodynamic polarization and the phasic difference was gained, which displayed the inhibitory coverage of the inhibitors formed.
Resumo:
A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods (BEMs) coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT (show strain rate test) in seawater.
Resumo:
The oxo-triazole derivative (DTP) was synthesized and its inhibiting action on the corrosion of mild steel in sulphuric acid was investigated by means of weight loss, potentiodynamic polarization, EIS and SEM. The results revealed that DTP was an excellent inhibitor and the inhibition efficiencies obtained from weight loss experiment and electrochemical experiment were in good agreement. Potentiodynamic polarization studies clearly revealed that DTP acted essentially as the mixed-type inhibitor. Thermodynamic and kinetic parameters were obtained from weight loss of the different experimental temperatures, which suggested that at different temperatures (298-333 K) the adsorption of DTP on metal surface obeyed Langmuir adsorption isotherm model. (C) 2009 Elsevier Ltd. All rights reserved.
Resumo:
An impedimetric immunosensor was fabricated for rapid and non-labeled detection of sulfate-reducing bacteria, Desulforibrio caledoiensis (SRB) by immobilizing lectin-Concanavalin A using an agglutination assay. The immobilization of lectin was conducted using amine coupling on the surface of a gold (Au) electrode assembled with 11-Mercaptounclecanoic acid. Electrochemical impedance spectroscopy (EIS) was used to verify the stepwise assembly of the sensor system. The work conditions of the impedimetric immunosensor, such as pH of the buffer solutions and the incubation time of lectin, were optimized. Faradic impedance spectra for charge transfer for the redox probe Fe(CN)(6)(3-/4-) were measured to determine SRB concentrations. The diameter of the Nyquist diagram that is equal to the charge-transfer resistance (RI) increased with increasing SRB concentration. A linear relationship between R-ct and SRB concentration was obtained in SRB concentration range of 1.8 to 1.8 x 10(7) cfu/ml. The variation of the SRB population during the growth process was also monitored using the impedimetric immunosensor. This approach has great potential for simple, low-cost. and time-saving monitoring of microbial populations. (C) 2009 Elsevier B.V. All rights reserved.
Resumo:
Corrosion inhibition by some new triazole derivatives on mild steel in 1 M hydrochloric acid solutions has been investigated by weight loss test, electrochemical measurement, scanning electronic microscope analysis and quantum chemical calculations. The results indicate that these compounds act as mixed-type inhibitors retarding the anodic and cathodic corrosion reactions and do not change the mechanism of either hydrogen evolution reaction or mild steel dissolution. The studied compounds following the Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The effect of molecular structure on the inhibition efficiency has been investigated by ab initio quantum chemical calculations. The electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (LUMO-HOMO), dipole moment and molecular orbital densities were calculated. (C) 2009 Published by Elsevier B.V.
Resumo:
Susceptibility to stress corrosion cracking of X56 steel and its relationship with hydrogen permeation behaviour in atmospheric environment containing H2S was investigated by hydrogen permeation tests at a slow strain rate. The results show that: the fracture strain decreases with the decrease of strain rate under the same experimental conditions; the fracture strain also decreases with the increase of H2S concentration under the same strain rate, and the increased concentration of H2S has no significant effect on the hydrogen permeation in the first wet, etc. dry cycle, however has lead to increased hydrogen permeation in the later cycles. The SEM images of the fractured surfaces show clear evidences of enhanced stress corrosion cracking susceptibility by H2S.
Resumo:
Along with the development of marine industries, especially marine petroleum exploitation, more and more pipelines are buried in the marine sediment. It is necessary and useful to know the corrosion environment and corrosiveness of marine sediment. In this paper, field corrosion environmental factors were investigated in Liaodong Bay marine sediment containing sulfate-reducing bacteria (SRB) and corrosion rate of steel in the partly sediment specimens were determined by the transplanting burying method. Based on the data, the fuzzy clustering analysis (FCA) was applied to evaluate and predict the corrosiveness of marine sediment. On that basis, the influence factors of corrosion damage were discussed.
Resumo:
Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na2SO3 which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer. (c) 2005 Elsevier Ltd. All rights reserved.
Resumo:
Seabed sediment (SBS) is a special soil that is covered by seawater. With the developments in marine oil exploitation and engineering, more and more steel structures have been buried in SBS. SBS corrosion has now become a serious problem in marine environment and an important issue in corrosion science. In this paper, approach in the field of SBS corrosion is reviewed. Electrochemical and microbial corrosion factors, corrosion mechanism, measurement of metal corrosion rate, corrosion evaluation and prediction of corrosion are also discussed here.
Resumo:
The inhibition effect of metal-free phthalocyanine (H2Pc), copper phthalocyanine (CuPc) and copper phthalocyanine tetrasulfuric tetrasodium salt (CuPc center dot S(4)center dot Na-4) on mild steel in I mol/l HCl in the concentration range of 1.0 X 10(-5) to 1.0 X 10(-3) mol/l was investigated by electrochemical test, scanning electron microscope with energy dispersive spectrometer (SEM/EDS) and quantum chemical method. The potentiodynamic polarization curves of mild steel in hydrochloric acid containing these compounds showed both cathodic and anodic processes of steel corrosion were suppressed, and the Nyquist plots of impedance expressed mainly as a capacitive loop with different compounds and concentrations. For all these phthalocyanines, the inhibition efficiency increased with the increase in inhibitor concentration, while the inhibition efficiencies for these three phthalocyanines with the same concentration decreased in the order Of CuPc center dot S(4)center dot Na-4 > CuPc > H2Pc according to the electrochemical measurement results. The SEM/EDS analysis indicated that there are more lightly corroded and oxidative steel surface for the specimens after immersion in acid solution containing 1.0 x 10(-3) mol/l phthalocyanines than that in blank. The quantum chemical calculation results showed that the inhibition efficiency of these phthalocyanines increased with decrease in molecule's LUMO energy, which was different from the micro-cyclic compounds. (c) 2005 Elsevier B.V. All rights reserved.
Resumo:
The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea-mud region. The sulfate reducing bacteria (SRB) in the sea-mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea-mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea-mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea-mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea-mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.