Editing Corrosion (section)

===Rate of corrosion===
[[File:NdFeB corrosion.jpg|thumb|These [[neodymium magnet]]s corroded extremely rapidly after only five months of outside exposure]]
The formation of an oxide layer is described by the [[Deal–Grove model]], which is used to predict and control oxide layer formation in diverse situations. A simple test for measuring corrosion is the weight loss method.<ref>{{cite book |title=Fundamentals of corrosion – Mechanisms, Causes and Preventative Methods |first=Philip A. |last=Schweitzer |publisher=Taylor and Francis Group |year=2010 |isbn=978-1-4200-6770-5 |page=25 }}</ref> The method involves exposing a clean weighed piece of the metal or alloy to the corrosive environment for a specified time followed by cleaning to remove corrosion products and weighing the piece to determine the loss of weight. The rate of corrosion ({{Math|''R''}}) is calculated as

:<math>R = \frac{kW}{\rho At}</math>

where {{Math|''k''}} is a constant, {{Math|''W''}} is the weight loss of the metal in time {{Math|''t''}}, {{Math|''A''}} is the surface area of the metal exposed, and {{Math|''ρ''}} is the density of the metal (in g/cm<sup>3</sup>).

Other common expressions for the corrosion rate is penetration depth and change of mechanical properties.