Beginners Guide to Corrosion - National Physical （初学者指南腐蚀国家物理）.pdf

Beginners Guide to Corrosion This document has been prepared by Bill Nimmo and Gareth Hinds of NPL’s Corrosion Group from various source material. It is intended to give an introduction to corrosion and its control in non-technical terms. More technical information is available on other areas of the NPL NCS website. Bill Nimmo and Gareth Hinds NPL February 2003 Beginners Guide to Corrosion February 2003 Page 1 of 10 CORROSION – BASICS What follows is a simple explanation of how corrosion occurs, what the different types are how problems can be solved. It is intended to be used by the non-expert to gain an initial appreciation of the subject before exploring further. 1 HOW DOES IT HAPPEN? 1.1 WHAT WE ALL KNOW We have all seen corrosion and know that the process produces a new and less desirable material from the original metal and can result in a loss of function of the component or system. The corrosion product we see most commonly is the rust which forms on the surface of steel and somehow Steel → Rust 1.2 TWO REACTIONS For this to happen the major component of steel, iron (Fe) at the surface of a component undergoes a number of simple changes. Firstly, Fe → Fen+ + n electrons the iron atom can lose some electrons and become a positively charged ion. This allows it to bond to other groups of atoms that are negatively charged. We know that wet steel rusts to give a variant of iron oxide so the other half of the reaction must involve water (H O) and