Factors Influencing the Corrosion Rate Metal Objects

CORROSION, 2000

The formation of corrosion products during atmospheric corrosion on open and confined surfaces of electrogalvanized steel exposed to periodic wet/dry conditions was studied. The composition of the corrosion products was determined using Fourier transform infrared spectroscopy (FTIR) and extra information about the phases present was obtained by x-ray diffraction (XRD). Corrosion products that formed consisted mainly of different amounts of zinc oxide (ZnO), hydrozincite (Zn 5 [OH] 6 [CO 3 ] 2), and simonkolleite (Zn 5 [OH] 8 Cl 2 •H 2 O). These results were compared to results obtained previously for pure zinc. The wet/dry pattern of the exposure had a large influence on the composition of the corrosion products. Similar proportions of zinc oxide, simonkolleite, and hydrozincite formed on electrogalvanized steel as formed on zinc on open surfaces exposed for shorter drying times. When the drying time was longer, simonkolleite was the dominant compound on electrogalvanized steel and zinc. In contrast, zinc oxide was the dominant compound on confined surfaces of electrogalvanized steel exposed for shorter drying times, whereas similar proportions of zinc oxide, simonkolleite, and hydrozincite were formed on confined zinc surfaces. These results are explained as a result of differences in the corrosion rates and in the extent of localized corrosion as a result of different drying rates for the open and confined surfaces. Zinc oxide forms on electrogalvanized steel as a result of the formation of areas of bare iron caused by the high corrosion rate and high degree of localization. The areas of bare iron act as sites for an oxygen reduction reaction, creating high pH values in the confined space. Conditions that favor a high corrosion rate and high degree of localization of the corrosion, such as higher chloride ion concentrations and shorter drying times, result in the formation of zinc oxide on electrogalvanized steel. The degree of confinement influences more significantly the composition of the corrosion products. At intermediate crevice widths, at which the corrosion rates are highest, zinc oxide dominates the corrosion products.

Corrosion may be defined as the destruction or deterioration in properties of materials by interaction with their environments. It is a natural phenomenon. Engineers generally consider corrosion when dealing with metallic materials. However, the process affects all sorts of materials, for example, ceramics, plastics, rubber etc. Rusting of iron and steel is the most common example of corrosion. Swelling in plastics, hardening of rubber, deterioration of paint, and fluxing of the ceramic lining of a furnace are all incidences of corrosion in non metallic materials. Metallurgists may think of corrosion as reverse extractive metallurgy. Metals are extracted from their compounds occurring in nature through extractive metallurgy processes involving considerable expenditure of energy, natural resources, time, and man power. Corrosion works to convert the metal I back into the same compounds.

Two methods of combating corrosion which are widely used in New Zealand are cathodic protection and chemical inhibitors. Both methods depend on controlling the charge on the metal surface, and this can be monitored by measuring the potential of the metal. The conditions needed to stop corrosion can then be predicted from an electrochemical phase diagram. Cathodic protection is effected by forcing the potential to a negative region where the metal is completely stable. This can be done by using a sacrificial anode made from a more reactive metal, or using an external power supply to change the amount of charge on the metal surface. Cathodic protection is well suited to steel structures in marine or underground environments. There is a class of chemical inhibitors which work by removing electrons from the metal, thereby pushing the potential into a positive region where an oxide film spontaneously forms. This results in a stable, passive surface with a very low corrosion rate. Industries apply this technology in processes where the inhibitor can be conveniently added without causing environmental or health problems.

Progress in Organic Coatings, 2011

InTech eBooks, 2012

Corrosion of metals or alloys occurs due to chemical or electrochemical reactions with their environment, which often results in drastic deterioration in the properties of metals or materials comprising thereof. Corrosion takes place on a steel surface, due to the development of anodic and cathodic areas, through oxidation and reduction reactions, forming of oxides of metals alloys. There are several corrosion causing agents or "corrodents" such as soot, sulphate salts, chloride ions, temperature, salinity, pH, dissolved gases, humidity, bacteria, sand, gravels, stones, mechanical stresses and also several protection methods employed for corrosion resistance such as the application of alloys, composites, inhibitors, cathodic and anodic protection, protective linings and coatings (

Corrosion is the deterioration of materials by chemical interaction with their environment.

Journal of Thermal Analysis and Calorimetry, 2007

Jnl of Aust. Inst. Steel Construction, 1998

Inorganic zinc silicates coatings and hot dip galvanizing are widely used for corrosion protection of structural steel, where they provide long life protection in a variety of atmospheric environments. This paper looks at the features of both these coatings, comparing them and showing the situations where each can be used.

The destruction or deterioration of a metal and its properties through chemical or electrochemical action to the surrounding environment is defined as metal corrosion. Since humans began using metal, this phenomenon has been found. Consequently, people took action to prevent metal corrosion consciously. For example, Herodotus, an ancient Greek historian, and Plinius, an ancient Roman natural scientist, have used tin to prevent the corrosion of iron. In China, Sn-bronze has appeared as early as the Shang dynasty. The excavated swords of kings Wu and Yue, which were cast in Sn-bronze, are as good as new ones after having been buried under the earth for 2600 years.