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This study deals with the anodisation of titanium grade 2 in 0.5-M sulphuric acid using a pulsed signal in a unipolar regime. The electrical parameters investigated are voltage, frequency and duty cycle. The use of duty cycles with a high percentage of anodic polarisation (90%), combined with high frequencies (1000 Hz) and the higher voltage tested (220 V), favoured the establishment of a plasma regime involving strong dielectric discharges, allowing the growth of thicker oxides but with rough architecture. The corrosion resistance of the formed film has been characterised by potentiodynamic tests in 0.5-M NaBr for localised corrosion resistance and by immersion tests in 10% v/v sulphuric acid solution for a uniform corrosion assessment. Current–time curves, visual observations and electron microscope analysis (scanning electron microscopy, energy-dispersive X-ray spectroscopy) were the tools selected to provide a correlation between technological parameters and oxide growth mechanism. For localised and uniform corrosion, anodisation at 220 V with a high level of anodic polarisation (90%) and frequency (1000 Hz) was verified to be particularly advantageous. 相似文献
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A. Cigada B. Mazza P. Pedeferri G. Salvago D. Sinigaglia G. Zanini 《Corrosion Science》1982,22(6):559-578
Stress corrosion cracking (SCC) of AISI 304L and AISI 316L stainless steels, cold-worked under various conditions (i.e. at different degrees of deformation obtained by drawing and rolling at room temperature and at liquid nitrogen temperature) has been carried out in H2O containing 1000 ppm Cl? at 250°C and in a boiling MgCl2 solution. The effect of heat treatments at 400 and 900°C on the SCC of previously cold-worked steels has also been studied. Particular attention was directed towards heat treatment at 400°C. In steels deformed at room temperature, it increases the SCC resistance. By contrast, for steels deformed at liquid nitrogen temperature, heat treatment at 400°C reduces the SCC resistance if carried out for short periods of time (1–6 h). Hardness measurements, structural analyses via X-rays, scanning and transmission electron microscopy (SEM and TEM), as well as modified Strauss tests, seem to prove that reduced stress corrosion resistance is not to be related to the chromium-rich carbides precipitation which could have been accelerated by the presence of α′-martensite. Instead, they tend to suggest that perhaps this phenomenon is connected to an increase in the level of internal micro-stresses which are generated by a reciprocal re-ordering of the α′ and γ structural phases. 相似文献
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Andrea Brenna Silvia Beretta Riccardo Uglietti Luciano Lazzari MariaPia Pedeferri Marco Ormellese 《腐蚀工程科学与技术》2017,52(4):253-260
The criterion used to verify the cathodic protection condition of a structure is based on structure-to-electrolyte potential measurement, which can include an ohmic drop contribution. Among the available techniques, the use of potential probes with internal reference electrode and of corrosion coupons with a so-called soil-access tube represents the most appropriate way to measure the IR-free potential, eliminating the ohmic drop contribution. An alternative is represented by on-off technique if equalising, galvanic or stray currents are not present. Laboratory tests have been carried out in soil-simulating solution on cathodically protected carbon steel in order to evaluate the effectiveness of off-potential for the assessment of cathodic protection. Instant-off potential is not reliable in overprotection condition; moreover, the accuracy of the measurement is strongly influenced by the presence of external current as galvanic or equalising currents. The effect of low-pass filter in the data acquisition system on the potential reading is discussed. 相似文献
5.
Prevention of steel corrosion in concrete exposed to seawater with submerged sacrificial anodes 总被引:2,自引:0,他引:2
Luca Bertolini Matteo GastaldiMariaPia Pedeferri Elena Redaelli 《Corrosion Science》2002,44(7):1497-1513
This paper presents the results of a study of the effectiveness of submerged sacrificial anodes in preventing the onset of pitting corrosion in the emerged part of marine piles. Experimental tests were carried out on reinforced concrete columns with steel embedded both in chloride free concrete and chloride contaminated concrete in order to compare the effects of sacrificial anodes on passive steel and on corroding steel. Results have shown, at least under the present testing conditions, that sacrificial anodes may be more effective in preventing corrosion initiation (i.e. in providing cathodic prevention) than in controlling ongoing pitting corrosion (i.e. in guaranteeing cathodic protection). Monitoring criteria for this type of prevention are also discussed. 相似文献
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A potentiostatic scratching technique has been used to study the breakdown potentials of stainless steel 304, Incoloy, Inconel 600, Monel 400 and Hastelloy C in chloride solution at pH 8 as a function of chloride activity, temperature and metal cold work. For the first four alloys break-down occurs through pitting. For Hastelloy C there is no pitting process, and breakdown occurs by a transpassive reaction, probably involving oxidation of Mo and Cr in the film to soluble anions. 相似文献
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Walter Navarrini Tommaso Brivio Dmitrij Capobianco Maria Vittoria Diamanti Mariapia Pedeferri Luca Magagnin Giuseppe Resnati 《Journal of Coatings Technology and Research》2011,8(2):153-160
In this study amorphous fluorinated coatings applied to anodized titanium surface have been investigated. A copolymer between
tetrafluoroethylene and perfluoro-4-trifluoromethoxy-1,3-dioxole (AD60) and two perfluoropolyether containing ammonium phosphate
(F10) or triethoxysilane (S10) functionalities have been tested. To estimate the color alteration of the anodized titanium
surfaces due to the application of the coatings, spectrophotometric analyses have been made. Water and n-dodecane contact angles as well as apparent surface energy have been evaluated. Ellipsometry and atomic force microscopy
data have been used to measure the thickness of the fluorinated coatings. A tailored mechanical preliminary test has also
been explored to evaluate the adhesion of the coatings on the anodized titanium surface. The resistance to surface soiling
with castor oil was also preliminarily investigated. The fluorinated coating tested on anodized titanium showed a low apparent
surface energy and high chromatic aspect conservation, this is particularly evident for the titanium anodized coated with
triethoxysilane functionalities fluoropolymers S10. 相似文献
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The paper discusses the peculiarities of cathodic protection applied to steel in carbonated concrete, which are strictly connected to the production of alkalinity at the steel surface. Results of a research on the application of cathodic protection to specimens with steel bars in carbonated concrete are discussed. A thin layer of concrete was realkalized within a period of 4–5 months by applying a current density of 10 mA/m2 and steel could repassivate even in the presence of small contents of chlorides. A lower current density of 5 mA/m2 could only maintain steel passive when the concrete in the vicinity of the steel had been previously realkalized through the application of a start‐up current density of 70 mA/m2 for one month. Protection mechanisms are investigated and design of cathodic protection of steel in carbonated concrete is outlined. The possibility of obtaining protection on deeper rebars is also considered. 相似文献
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Targets of this work have been: testing of duplex stainless steel in field (into a geothermal well) and in laboratory NACE environment in presence of crevices and sharp defects; development of testing based on fracture mechanics and comparsion with traditional testing approach. The following types of specimens have been used: smooth specimens for tensile tests at constant load with artificial crevices, U-bend specimens and 1/2″ WOL-modified fracture mechanics specimens. The results are only in partial accordance with available literature data and suggest to be very careful in extending laboratory results to real conditions, where, for instance, crevices and sharp defects always exist. 相似文献
10.
B. Mazza P. Pedeferri D. Sinigaglia A. Cigada G. Fumagalli G. Re 《Corrosion Science》1979,19(7):907-921
This paper describes the results of a study concerning the electrochemical and corrosion behaviour of AISI Types 304L and 316L stainless steels, cold worked under various conditions, in 1M H2SO4 and in 0.1M HCl de-aerated solutions. Anisotropic behaviour of specimen surfaces with different orientations to the direction of deformation has been observed. Stress corrosion cracking of the deformed steels can occur at room temperature in the 0.1M HCl solution both in the active and transition regions of the polarization curves. 相似文献