Holistic model for atmospheric corrosion Part 5 – Factors controlling deposition of salt aerosol on candles, plates and buildings

The paper describes a number of studies relating to the retention of marine salts on atmospheric corrosion test plates and the cleaning of such salts in field exposures. Data from three separate field studies are presented. In each study, instrumented zinc plates were openly exposed to the atmosphere. Plates were exposed in tropical, subtropical and temperate regions of Australia in severe marine, marine, urban and inland exposure conditions. Plates were washed at various times during exposure and, in some cases, they were ultrasonically cleaned after exposure. Ion chromatographic analysis was undertaken to determine the ion contents of the wash-off and ultrasonic cleaning solutions, and thus the salts present on the exposed plates. Sites and plates were also instrumented with rain gauges, salt candles, relative humidity sensors, surface temperature sensors and surface wetness sensors. Changes in the relative humidity at which the surfaces became wet were determined and used as a guide to infer the presence of salts on the surfaces. The effect of rainfall on the presence of salt was then determined. The factors controlling salt retention on surfaces are discussed, including the possibility that the ability of a surface to retain salt changes with time, and that sources of chloride other than crystalline salt may exist. The relevance of the study to atmospheric corrosion is discussed.

Section: Resultsmentioning

confidence: 99%

Field studies of surface cleaning and salt retention on openly exposed metal plates

Cole¹,

Ganther²,

Lau³

2006

“…The present paper focuses on the initial reaction of a wet aerosol with a metal surface and how the impact conditions determine the morphology of salt deposits. Previous papers [1][2][3][4][5] have developed a methodology for predicting airborne salt aerosol content and surface aerosol flux based on a knowledge of salinity sources and transport processes, and the rate of deposition of this marine aerosol onto salt candles, surfaces and buildings. However, to develop an accurate understanding of how deposited pollutants react with the surface, it is necessary to have an understanding of the form of such deposits.…”

Section: Introductionmentioning

confidence: 99%

Holistic model for atmospheric corrosion Part 6 – From wet aerosol to salt deposit

Cole

Lau²,

Paterson³

2004

Self Cite

This paper is the sixth paper outlining a holistic model of atmospheric corrosion. Previous papers outline how airborne salinity could be estimated at any given location and how the deposition onto a surface could be modelled. This paper investigates the initial reactions of raindrops or deposited marine aerosols on metal surfaces (zinc, galvanised steel, aluminium and gold). It combines short term field exposures with a series of controlled laboratory experiments. Surface changes to the metal upon field exposure are characterised by the nature and distribution of corrosion nodules, oxide films and retained salts. Eleven distinct forms of surface change are observed. The conditions promoting each pattern of surface changes were estimated by comparison with laboratory tests with a variety of deposition modes. Laboratory tests included deposition of saline droplets in three size ranges. A strategy to use the results in a holistic model of corrosion is proposed.CEST/2132

“…As shown inTable 1, chloride concentration measured in the Province of Western Coast (Red Sea) is generally high.Frasan, Hakal and Wajah shows the highest salinity values: 740, 704 and 608 mg m 22 d 21 Cl 2 respectively, which belong to categories S 3 (the rest belong to S 2 ). These results show that atmospheric salinity depends on the wind pattern at each specific site 10,[29][30][31][32][33][34][35][36]. The main part of anthropogenic SO 2 pollution is caused by combustion of fossil fuels and algae decomposition.…”

mentioning

confidence: 99%

Studies of galvanised steel atmospheric corrosion in Saudi Arabia

Syed

2011

This paper summarises the results obtained for galvanised steel specimens exposed in Saudi Arabia region for four years at four pure marine and five mixed marine (SO 2 polluted) sites. The atmospheres at these sites were characterised climatologically and in terms of their pollution level so that their corrosivity could be expressed in accordance with ISO standards. Chemical characterisation of the galvanised steel corrosion product layers was performed using X-ray diffraction. The main phases determined were zincite (ZnO), simonkolleite [Zn 5 (OH) 8 Cl 2 .H 2 O], smithsonite (ZnCO 3 ), magnetite (Fe 3 O 4 ), gordaite [NaZn 4 (SO 4 )Cl(OH) 6 Cl.6(H 2 O)], hematite (Fe 2 O 3 ), zinkosite (ZnSO 4 ), zinc chloride (ZnCl 2 ), zinc hydroxide sulphate hydrate [(Zn(OH) 2 ) 3 (ZnSO 4 )(H 2 O) 3 ] and zinc sulphate hydroxide hydrate [ZnSO 4 (OH) 2 .5H 2 O] was found on the specimens. The results obeyed well with the empirical kinetics equation of the form C5Kt n ,where K and C are the corrosion losses in mg cm 22 after 1 and 't' years of the exposure respectively, and 'n' is constant. Based on 'n' values, the corrosion mechanism of galvanised steel is predicted. The results obtained show that the corrosion rate of galvanised steel is a function of both the chloride, SO 2 pollution level and the humidity. Corrosion rate of galvanised steel specimens have been obtained by loss of weight after each year of exposure. Experimental Specimen preparationGalvanised steel specimens with 99?63% (0?22%Mn, 0?1%S, 0?12%P, 0?04%C and 0?01%Si) purity were used in this experiment. Before exposure, the surface of the