Solid corrosion products protective effect

Electrolytic corrosion occurs in regions I and IV with the formation of soluble iron ions. Solid corrosion products which can have a protective effect are formed in region II. This is the region of surface film passivity. Certain corrosive sub-... 

The protection mechanism is similar to that of metallic zinc coatings zinc is less noble than steel and protects the substrate by forming a galvanic corrosion cell, in which zinc is the anode. This mechanism is particularly active in presence of defects in the coating that provide an electrolyte path to the substrate surface. In addition, the atmospheric corrosion of zinc yields voluminous solid corrosion products (oxides, carbonates, etc.) that are capable of blocking pores or small defects in the coating, thereby reinforcing its barrier effect. 

Solid WI are used as triboengineering structural or lubricating materials. Plastics filled with solid lubricants are included in this class of materials since they lower the heat-induced strain in frictional joints through a reduction of the corrosion activity of the products of tribochemical reactions. Fusible metals and alloys of frictional parts may also ensure a protective effect... 

The corrosion products formed are the composition of the metal or alloy and the contaminants present in the atmosphere. For example, carbon steel does not have the ability to form its own protective coating except in a dry, clean atmosphere. Under these conditions, a thick oxide film will form that prevents further oxidation. Initiation of corrosion is the result of the presence of solid particles on the surface. This settled airborne dust promotes corrosion by absorbing SO2 and water vapor from the air. Even greater corrosive effects result when particles of hygroscopic salts, such as chlorides or sulfates, settle on the surface and form a corrosive electrolyte. 

Besides pure chemical corrosion, solid products of corrosion in the system will give rise to erosive corrosion, in which the particles moving with the fluid will impact onto the surfaces and can remove protective surface layers. Such corrosion effects are most pronounced in regions of high fluid-stream velocity. 

The purpose of chemical protective clothing is to protect the wearer against the effect of toxic or corrosive/caustic products which could enter the body (inhalation, skin absorption) or cause tissue damage upon contact with the skin. These products could be in vapor, liquid, or solid form. One type of material is not compatible with every type of chemical. While it may provide excellent resistance against one chemical, the same material may provide very poor or no protection against another chentical. The levels of protection under OSHA standards are as follows ... 

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