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Corrosion is a chemical process that occurs on metals and other materials. There are various causes for corrosion, such as humidity and chemicals. Yet one of the most overlooked cause of corrosion is non-ideal pH levels. When the pH of the environment is outside the range of 6 to 8, the risk of corrosion increases. In this article, we will explore the effects of acidic-alkaline conditions on corrosion.
pH Scale
Better understanding of acidic-alkaline conditions comes from the study of pH scale. pH stands for potential hydrogen. As the name suggests, pH scales measures the amount of hydrogen and how active the hydrogen is. pH scale starts from 1 and ends at 14. The value of 7, the middle point of the scale is considered neutral. A neutral environment is not acidic, nor alkaline. The lower half of the scale (1-7) is acidic, while the upper part (7-14) is alkaline. A value between 0-1 pH is the highest range for acids while, between pH 13-14 is the highest for alkalis. For this article’s purpose, all we need to know is sub 7 pH is acidic and above 7 pH is alkali.
Acidic Corrosion
Acidic corrosion occurs when metals are exposed to an acidic environment. In an acidic environment, the concentration of hydrogen ions is high. High concentration of active hydrogen causes the metal to corrode.
The corrosion process involves the reaction of the metal with the acid. Like any reaction with acids, this results in the formation of metal salts and hydrogen gas. The rate of corrosion in an acidic environment is dependent on various factors. Concentration of the acid, the temperature, and the type of metal are some of the factors which are in effect.
The most common types of acidic corrosion is rusting. Rusting is the chemical reaction between a metal and oxygen. The resulting rust is a hydrated metal oxide. Metal oxides can weaken the metal and causes disintegration.
To prevent acidic corrosion, many strategies can be employed. One common method is to use coatings or paints. Paints and coatings provide a barrier between the metal and the acidic environment. Another option is to use an anode, which is a metal that is more reactive than the metal being protected. The more reactive anode corrodes instead of the metal desired to be protected.
Alkaline Corrosion
Corrosion at above 7 pH is called alkaline corrosion. An alkaline environment, is characterized by a high concentration of hydroxide ions. The corrosion process involves the reaction of the metal with the alkaline solution. These reactions result in the formation of metal hydroxides and hydrogen gas.
Alkaline corrosion can be particularly damaging to aluminum and magnesium alloys. The corrosion process can cause pitting, which can weaken the metal and cause it to fail.
To prevent alkaline corrosion, it is important to control the pH of the environment. Acidic solutions can be used to neutralize the alkaline nature of the environment. Also, the use of coating and paints are effective at alkaline protection as well.
Summary
Corrosion can occur under acidic or alkaline conditions. Acidic corrosion can result in rusting, while alkaline corrosion can cause pitting. To prevent corrosion, it is important to control the pH of the environment and to use protective coatings or sacrificial anodes. Understanding the effects of acidic and alkaline corrosion, is key to prevent damage on assets.
