12 research outputs found
Application of automated electrical resistance sensors for measurement of corrosion rate of copper, bronze and iron in model indoor atmospheres containing short-chain volatile carboxylic acids
Évaluation normalisée de l’environnement du patrimoine
La méthode de mesurage de la corrosion du cuivre décrite ici a été utilisée pour évaluer les conditions de conservation des collections patrimoniales : les résultats d’études réalisées dans des conditions de conservation ou d’exposition permanentes ou temporaires montrent que cette méthode est un outil efficace qui permet non seulement de comparer les bâtiments, les vitrines, les réserves mais aussi de les classer en fonction de leur corrosivité
In situ monitoring of corrosion mechanisms and phosphate inhibitor surface deposition during corrosion of zinc–magnesium–aluminium (ZMA) alloys using novel time-lapse microscopy
In-situ time-lapse optical microscopy was used to examine the microstructural corrosion mechanisms in three zinc-magnesium-aluminium (ZMA) alloy coated steels immersed in 1% NaCl pH 7. Preferential corrosion of MgZn2 lamellae within the eutectic phases was observed in all the ZMA alloys followed by subsequent dissolution of Zn rich phases. The total extent and rate of corrosion, measured using time-lapse image analysis and scanning vibrating electrode technique (SVET) estimated mass loss, decreased as Mg and Al alloying additions were increased up to a level of 3 wt% Mg and 3.7 wt% Al. This was probably due to the increased presence of MgO and Al2O3 at the alloy surface retarding the kinetics of cathodic oxygen reduction. The addition of 1 x 10-2 mol/dm3 Na3PO4 to 1% NaCl pH 7 had a dramatic influence on the corrosion mechanism for a ZMA with passivation of anodic sites through phosphate precipitation observed using time-lapse. Intriguing rapid precipitation of filamentous phosphate was also observed and it is postulated that these filaments nucleate and grow due to super saturation effects. Polarisation experiments showed that the addition of 1 x 10-2 mol/dm3 Na3PO4 to the 1% NaCl electrolyte promoted an anodic shift of 50mV in open circuit potential for the ZMA alloy with a reduction in anodic current of 2.5 orders of magnitude suggesting that it was acting primarily as an anodic inhibitor supporting the inferences from the time-lapse investigations. These phosphate additions resulted in a 98% reduction in estimated mass loss as measured by SVET demonstrating the effectiveness of phosphate inhibitors for this alloy system
STANDARDIZED ASSESSMENT OF CULTURAL HERITAGE ENVIRONMENTS BY ELECTRICAL RESISTANCE MEASUREMENTS
International audienc
Vliv prestupu tepla na nerovnomerne formy koroze korozivzdornych oceli
Susceptibility of metals to corrosion attack under conditions of heat transfer is in most cases evaluated regarding the surface temperature of the metal only and the influence of the heat flux itself is disregarded. This thesis studies the effect of heat transfer on corrosion of stainless steel in water environments under non-boiling conditions, when the influence of the heat flux and the surface temperature is separated on principle. The theoretical part concerns possible factors affecting processes that influence the corrosion rate of metallic materials under conditions of heat transfer. Effect of heat temperature and heat flux on mass transfer, kinetics of surface reactions and environment composition are discussed here, as well as effects of temperature gradient in the metal and possibility of inhomogeneity formation in the system at present of heat flux. This part does not concern the localized forms of corrosion only, but it deals with the heat transfer influence on corrosion processes in general. All the available sources concerning exparimental studies of heat transfer influence on corrosion are summarized in the annex. Requirements on construction of basic types of experimental devices are considered as well. Corrosion tests were aimed at verifying the influence of heat transfer on initiation and propagation of intergranular and pitting corrosion and stress corrosion cracking of austenitic stainless steel under conditions close to real systems or well correlating with these. Three devices in four modifications were constructed. The samples were exposed at surface temperatures from 40 to 105 C and heat fluxes from -60 to 300 kWm-2, while the value of one of these variables was kept constant. With the exception of corrosion cracking, exposure and electrochemical tests were performed. Measurements of the heat transfer influence have revealed that the material resistance depends on the surface temperature as well as on the heat flux. Increasing the surface temperature had a negative effect in all cases and led to increase in susceptibility to the given type of corrosion attack. Effect of heat flux depended on its direction, intensity, corrosion system and surface temperature, and it differed as well in different stages of corrosion attack. The heat flux showed to be positive (suppressing corrosion) in case of propagation of the intergranular corrosion and initiation and repassivation of pitting corrosion. In the initiation stage of localized corrosion, heat flux affects most significantly the passive film resistance, namely in changing its quality (for example thickness), as well as it causes a change of the environment aggressivity (the aggressive ions activities, oxidizing power of the environment, flow velocity). In the propagation stage of localized attack, presence of the temperature gradient in the metal itself has the most significant influence, thanks to which the temperature inside pits or cracks differs from the temperature on the free surface. The mentioned factors are partially connected and their influence takes place at the same time, while they affect the metal resistance often in opposite ways. Higher reliability of operating the heat exchange devices made of stainless steels can be reached, regarding the localized corrosion, above all by decreasing the surface temperature from the medium side that may cause the attack, which can be possibly done by decreasing input as well as output medium temperature and increasing the heat flux by flow intensification. From the corrosion point of view it is suitable to construct the exchangers as parallel-flow ones and to prevent formation of deposits on the heat exchanging surfacesAvailable from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
Application of automated electrical resistance sensors for measurement of corrosion rate of copper, bronze and iron in model indoor atmospheres containing short-chain volatile carboxylic acids
Composition of corrosion products formed on Zn–Mg, Zn–Al and Zn–Al–Mg coatings in model atmospheric conditions
Real-time monitoring of indoor air corrosivity in cultural heritage institutions with metallic electrical resistance sensors
A system for continuous monitoring of atmospheric corrosivity has been developed. An electronic unit measures and records changes in the electrical resistance of a thin metal track applied on an insulating substrate. If the metal corrodes, the effective cross sectional area of the track decreases and the electrical resistance increases. Sensors made of silver, copper, iron/steel, zinc, lead, tin, aluminium, bronze, and brass at thicknesses from 50 nm to 250 m were tailored for environments with different corrosivities. The developed technology proved capable of providing high sensitivity, allowing for real-time corrosion monitoring even in low-corrosive indoor cultural heritage facilities. Laboratory tests showed good reproducibility with the standard deviation of parallel measurements at less than ±20% for metals which corrode uniformly in the tested environments. Several examples selected from a broad testing programme in partner museums, libraries, and other institut ions show successful applications of the logger system for characterization of air quality control in indoor locations, during transport and in temporary exhibitions; assessment of new buildings and storage facilities; and fundamental studies of optimal conservation and storage procedures. A first outline of a classification system for lead, which is particularly sensitive to the presence of carboxylic acids, is given. The technique has a large potential as an independent method for monitoring air quality in facilities displaying and storing valuable objects of cultural heritage