environmental effects

Corrosion

It is the gradual destruction of material, usually metals, by chemical reaction with its environment. Simply corrosion is nothing but electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting( called the formation of iron oxides,) is a suitable and familiar example of electrochemical corrosion. This type of destruction typically forms an oxide(s) or salt(s) of the original metal. Corrosion not only occur in metals but in also materials such as ceramics or polymers. Corrosion in any material degrades the useful properties of that material and the structures affecting strength, appearance, and permeability to gasses and liquids. Apart, Corrosion phenomenon is less visible and are less predictable. The two types of corrosion are

Galvanic Corrosion

Galvanic corrosion is a phenomenon that occurs when two different metals are made to have physical or electrical contact and are immersed in a common electrolyte, or when the same metal is kept to an electrolyte with variable concentrations. In a galvanic corrosion, the more active metal ( called the anode) corrodes at an accelerated rate and the more noble metal ( called the cathode) corrodes at a retarded rate. However when immersed separately, each metal corrodes at its own specific rate.

Several factors such as types of metal r the relative size of the anode, and operating conditions (salinity, temperature, moisture, etc.) affect galvanic corrosion. The value of the surface area ratio of the cathode and anode ultimately affects the corrosion rates of the materials. Galvanic corrosion has advantages as well, and it is often utilized in sacrificial anodes.

Stress Corrosion

Stress-corrosion cracking is defined as cracking caused by the simultaneous presence of tensile stress as well as a specific corrosive medium. Many investigators have categorized all the cracking failures formed in corrosive mediums as stress-corrosion cracking This includes failures due to hydrogen embrittlement.

During such corrosion, the alloy or metal is virtually unattacked over most of its surface, while fine cracks develop through it. This cracking has serious consequences as it can occur at stresses within the range of specific design stress. The two classic cases of stress-corrosion cracking are "caustic embrittlement" of steel, and another the "season cracking" of brass.

Protection against Corrosion

Following are usually applied corrosion protection process.

1. Coatings Applied

Painting and the application of enamel are the most widely used anti-corrosion treatments. Corrosion prevention by coating occurs by providing a barrier of corrosion-resistive material between the corrosive environment and the victimized material. Painted coatings are relative, cheap, easy to apply and have fast drying rates although unsuitable temperature and moisture content may cause dry time to be different.

2. Reactive Coatings

If the environment is controlled (especially in re-circulating systems), corrosion inhibitors like reactive coatings can often be added to it. These form an electrically insulating or chemically impermeable coating on outward or exposed metal surfaces, to suppress any unwanted electrochemical reactions.

3. Anodization

This climbing descender is anodized with a yellow finish. Aluminum alloys usually undergo a surface treatment. Electrochemical conditions in the electrolytic bath are carefully tuned so that uniform pores within several nanometers wide be visible in the metal's oxide film. Anodizing is very resilient to corrosion and weathering, so it is widely used for building facades and other areas that the planes that will come into regular contact with the elements.

4. Bio-film Coatings

A new form of protection has been developed by applying certain species of bacterial films layer to the surface of metals in highly corrosive environments.

5. Controlled Permeability Formwork

(CPF) is actually a method of stopping the corrosion by naturally enhancing the durability of the cover during concrete placement. It has been used extensively in environments to fight against the effects of chlorides, carbonation(addition of carbon) ,frost and abrasion.

6. Cathodic Protection

It is known as a technique to prevent the corrosion of a metal by making the exposed surface, the cathodic part of an electrochemical cell.

7. Sacrificial Anode Protection

The more electropositive metal is placed on the surface of metal to be protected. The electropositive metal corrodes away preventing corrosion of required metal.

8. Anodic Protection

This process is based to impresses anodic current on the surface to be protected (opposite to the cathodic protection). It is suitable for metals that exhibit passive behavior (e.g., stainless steel) and suitable passive current over a variable range of potentials. It is used in extremely corrosive environments, e.g., solutions of sulfuric acid