Corrosion Science and Metal Finishing Flashcards

Vocabulary flashcards created from lecture notes covering key terms, concepts, and processes in corrosion science and metal finishing.

Corrosion

Any process of destruction (or deterioration) and consequent loss of a solid metallic material through an unwanted chemical or electrochemical attack by its environment, starting at its surface.

Dry Corrosion

Direct chemical corrosion involving the attack on metals by dry gases, mainly through chemical reactions such as air or oxygen reacting with the metal surface to form an oxide layer.

Wet Corrosion

Electrochemical corrosion involving reactions in an aqueous medium, where the conducting metal surface undergoes electrochemical reactions with moisture and atmospheric oxygen.

Differential Metal Corrosion

Also called galvanic corrosion, a type of corrosion occurring when two dissimilar metals are in contact in a corrosive conducting medium, causing the more active metal (with lower electrode potential) to act as the anode and corrode.

Galvanic Series

An arrangement of metals and alloys in increasing order of their corrosion resistance determined experimentally in a specific environment, such as seawater.

Differential Aeration Corrosion

Corrosion arising from an uneven supply of air on a metal surface, forming an oxygen concentration cell where the poorly oxygenated region acts as the anode and undergoes corrosion.

Waterline Corrosion

A form of differential aeration corrosion occurring in partially submerged steel structures (such as ships and water tanks), where the metal below the water line is poorly oxygenated, acts as an anode, and corrodes.

Pitting Corrosion

A localized form of differential aeration corrosion initiated by surface deposits (such as sand, dust, or water drops) or protective film breakdown, producing accelerated localized corrosion under the deposit.

Critical Humidity

The relative humidity threshold above which the atmospheric corrosion rate of a metal increases sharply.

Anodizing

An inorganic chemical conversion process for non-ferrous metals (such as Al, Zn, and Mg) where the base metal is made the anode in an acid bath under direct current to form a protective surface oxide layer.

Galvanizing

A protection process of coating an iron or steel surface with zinc metal via hot dipping at $425\text{--}430\text{ }^\text{o}\text{C}$ to prevent atmospheric corrosion.

Tinning

A process of coating a base metal with a continuous non-toxic layer of tin via hot dipping, widely used for manufacturing food containers and cooking utensils.

Cathodic Protection

A corrosion prevention strategy where an entire metallic structure is converted completely into a cathodic area, eliminating anodic sites to prevent corrosion.

Sacrificial Anode Method

A cathodic protection method where a metallic structure is electrically connected to a more active metal (e.g., Mg, Zn, Al) that corrodes preferentially to preserve the parent structure.

Impressed Current Method

A cathodic protection method where an external D.C. power supply applies current to a protected structure (connected to the negative terminal) and an inert graphite anode (positive terminal) to suppress corrosion.

Corrosion Penetration Rate (CPR)

The speed at which a metal deteriorates in a specific environment due to chemical reaction, or the amount of corrosion thickness loss per year, calculated as $\text{CPR} = \frac{KW}{ATD}$.

Metal Finishing

Surface treatment processes carried out to modify metal surface properties by depositing a layer of another metal or polymer, or by forming an oxide film.

Electroplating

The deposition of a metal layer onto a substrate surface by electrolysis in an electrolytic bath containing salt solution of the plating metal, with the substrate acting as the cathode.

Brighteners

Organic additives added to electroplating baths to produce fine-grained, shiny deposits by promoting plating parallel to the substrate surface.

Levellers

Organic additives (such as sodium allyl sulphonate) in plating baths that adsorb at rapid deposition sites to produce a deposit of uniform thickness.

Wetting Agents

Additives (such as sodium lauryl sulphate) added to plating baths to release hydrogen gas bubbles from the cathode surface and prevent hydrogen embrittlement.

Throwing Power

The capability of a plating bath to produce an even and uniform deposit over the entire surface of an object regardless of its geometric shape or complex recesses.

Electroless Plating

The controlled deposition of a continuous metallic film from its salt solution onto a catalytically active surface via an autocatalytic redox reaction using a chemical reducing agent without electrical energy.

Subtractive Technique in PCB Manufacture

A technique for producing double-sided printed circuit boards where copper-clad plastic boards are protected along circuit patterns, etched away elsewhere, and connected via drilled electroless copper through-holes.