Metal corrosion and protection

When the metal and the surrounding medium contact, due to the damage caused by the chemical and electrochemical effects between called the corrosion of metals. From the thermodynamics point of view, in addition to a few precious metals ( Such as au, pt) Have all sorts of metal, into the trend of the ion, is the metal corrosion is spontaneous widespread phenomenon. After corrosion, in shape, colour and lustre and mechanical performance will be changed, equipment damage, pipe leaks, product contamination, caused the combustion or explosion and other malignant accident and the serious waste of resources and energy, a huge loss to national economy. It is estimated that the world's developed countries each year the economic loss caused by metal corrosion of its gross national product (GNP) 3. 5% ~ 4. 2%, more than a year of various natural disasters ( Fire, wind and earthquake, etc. ) The sum of losses. Some even estimated scrap and the loss of metal corrosion around the world each year is about 100 million tons! Study corrosion mechanism, therefore, to take protective measures for the economic development has a very significant metal anticorrosion method are many, mainly to improve the nature of metal, separates the protected metal and corrosive medium, or for metal surface treatment, improve the environment of corrosion and electrochemical protection. ( 1) To improve the nature of metal according to the different USES to select different corrosion resistant alloy material composition, or adding alloying elements in the metal, to improve its corrosion resistance, can prevent or slow down the corrosion of metal. Nickel is made of stainless steel in steel, for example, can enhance anti-corrosion ability. ( 2) Form a protective layer on the metal surface covered all kinds of protective layer, separates the protected metal and corrosive medium, is an effective method of preventing metal corrosion. In general use in industrial protective non-metallic metal protective layer and protective layer two categories. They are using chemical method, physical method and electrochemical method. 1) metal phosphating of iron and steel products to oil, rust removal, soak in the specific composition of phosphate solution, can be in the metal surface to form a layer of phosphate film does not dissolve in water, this process is called phosphating. Phosphating film show dark gray to dark gray, generally for 5 microns ~ 20 microns thickness, in the atmosphere has good corrosion resistance. Membrane is micro pore structure, adsorption ability of paint and so on, such as used as a paint bottom, corrosion resistance can be further improved. (2) the oxidation treatment of the metal iron and steel products will be added to the mixed solution of naoh and nano2, heat treatment, the surface can form a layer thickness is about 0. 5μm～1. 5 microns blue oxide film ( Main ingredients of fe3o4) To achieve the purpose of steel corrosion, this process is called bluing, hereinafter referred to as blue. This kind of oxide film has great flexibility and lubricity, does not affect the accuracy of parts. Parts of the precision instruments and optical instruments, spring steel, bluing commonly used stalloy, fine wire, etc. (3) non-metallic coating with non-metal materials such as paint, plastic, enamel, mineral oils and other protective layer is formed on the coating on metal surface, called a non-metallic coating, also can achieve the purpose of corrosion protection. For example, boat, car, water