Selected Definitions Corrosion: It is defined as the process of decomposition or destruction of metallic material in presence of environmen through chemical reactions. Galvanic corrosion: This occur when current flow from anode to cathode. The anode represent more active metal whil cathode represent less active metal. Intergranular Cladding:
corrosion:
This is a chemical or electrochemical attack on the grain boundaries of a metal.
It is the bonding of dissimilar metals.
Passivating potential: It is the potential develop at critical point. Passivating current:
The flow of current decrease to minimum value above the passivating potential.
12.1 INTRODUCTION A large number of equipments are used for manufacturing of drugs. When the solution which is corrosive in nature comes in contact with the equipment, it can destroy the performance and fabrication of the equipment. Therefore, great care should be adopt during selection of material for construction of equipment. Corrosion is defmed as the process of decomposition or destruction of metallic material in presence of environment through chemical reactions. Corrosion is a natural process. Corrosion may be dry or wet type. Dry corrosion occurs in the absence of an aqueous environment, usually in the presence of gases and vapors, mainly at high temperatures. Wet corrosion is due to attack of aqueous media.
Table 12.1: Difference between Dry and wet corrosion Dry corrosion Corrosion occurs in the absence of moisture.
Wet corrosion Corrosion occurs in presence of conducting medium It is a rapid process It depends on the size of the anodic part of metal. Corrosion occurs at anode but rust is deposited at cathode.
The process is slow. The process of corrosion is uniform. Corrosion products are produced at the site of corrosion
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