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Metal Glossary


This occurs in tubular products when the centres of the circles that describe the outside diameter and the bore do not coincide. It manifests itself as a variation in wall thickness around the tube.

Related terms: Concentricity

Electrochemical Corrosion

Corrosion, or metal dissolution, caused by the reaction M ? M+ + e- at the anode.

Electrochemical Protection

The prevention of corrosion in an electrolyte by manipulation of the electrode potential of steel.

Electrode Potential

The potential difference in a solution between the test electrode and a reference electrode, e.g. a saturated calomel electrode.

Electrode Reaction

A chemical half or partial reaction that occurs at an electrode surface. It is called a half or partial reaction as only either the oxidation or the reduction part of the overall cell reaction occurs at any one electrode.


There are two electrodes in an electrochemical or corrosion cell, the anode and cathode. They are the electron conductors, through which electrons can enter and leave an electrolyte permitting reactions such as dissolution at the anode and deposition at the cathode to occur.


An electrically conducting medium, such as a salt solution or a molten salt through which an electric current is transported by ions.

Electrolytic Polishing

An electrochemical method of imparting brilliance to the surface of a metal. The work-piece is made the anode and by careful selection of electrolyte and processing parameters a thin, uniform, surface layer is removed. It may be regarded as the opposite of electro plating.


A pure chemical substance that consists of just one type of atom as defined by its atomic number (the number of protons in its nucleus). Elements combine to make compounds, e.g. Copper Sulphate which contains Copper, Sulphur and Oxygen. An Alloy, e.g. Brass, is a solid solution of two or more elements.


The process in which a preheated billet is constrained within a strong container in a press and then pushed by a ram through a shaped die. The product, or extrusion, has the shape of the die along its whole length. Although some simple shapes are extruded in Stainless Steel, this process is most commonly used for Aluminium.