There is only a small part of the land on the Earth, and most of the area is the ocean. Therefore, the marine climate is a climate that has a great impact on human life and material products.
The main corrosion component of the marine atmosphere is the salt fog formed by chlorides. These salt sprays are formed by the crushing of waves. Under the influence of wind, the oceanic atmosphere carries salt fog, spreads in all directions, and eventually sinks to the ground or exposed to outdoor material products, causing corrosion to materials or products. . Salt spray corrosion is the most common and destructive type of corrosion in atmospheric corrosion. Especially for metal materials, salt spray forms a conductive salt film on the surface. Due to the effect of the water film, metal materials are generated one by one. The tiny primary battery makes the metal material quickly rust and turns into a pile of useless waste. The metal plating parts will lose gloss to the surface plating under the effect of salt spray. In addition, the saline air in the mainland also contains a certain amount of salt mist. How does the salinity of saline or salty areas in the ocean or land become salt fog into the air? There are two arguments: seawater stirring theory and dust flying theory.
The theory of seawater agitation holds that due to the rising tide phenomenon caused by the gravity of the moon, seawater produces a lot of foam, and the wind brings these small droplets containing sodium chloride into the air. These small droplets undergo a series of complicated processes such as cracking, evaporation, and mixing. They enter the atmosphere in the form of salt mist, and then move to all directions through air convection and wind forces.
Another dusty theory is that the salt in the inland areas will be crushed into fine particles due to the influence of the natural climate such as high temperature, dryness, and rain. It is also the effect of the wind. The salt particles are rolled up into the air and small. The particles are suspended in the air and mixed with the water in the air. Under certain environmental conditions, salt mists form. Metals have a tendency to lose their original properties by generating compounds in nature. It is estimated that the world's annual corrosion of steel accounts for about 1/4 of annual production, which not only causes economic losses, but more importantly, it loses the original application function of the metal. This situation is particularly prominent in electronic devices and electrical products. Corrosion of metal materials, according to statistics, is mostly caused by salt spray corrosion.
There are numerous examples of salt mist-affecting product damage. After a certain military electrical insulator used in Hainan Province was absorbed by salt fog, the insulation resistance decreased drastically, and after a long time of cleaning and drying, it could not be used normally. Printed circuit boards used on the coast of the Panama Canal failed within 5 months due to a decrease in insulation. A seaplane power contactor is accompanied by salt crystals to increase resistance and circuit failure. The effect of salt spray on the performance of the product is so great. Therefore, how to improve the product's resistance to salt spray corrosion has received increasing attention. The salt spray test is another test method for environmental tests. It mainly uses the simulated salt spray environmental conditions created by salt spray test equipment to evaluate the corrosion resistance of products or metal materials, and provides test basis for improving product quality. The salt spray test was first proposed by JACapp at the 17th annual meeting of the American Society of Materials Testing (ASTM) in 1914. At that time, the aim was to obtain test conditions similar to that of the coastal atmosphere in order to study the reliability of the use of certain metal protective layers. It is to test the sample in a salt spray, which is the earliest application of the salt spray test. Since 1919, the United States National Bureau of Standards began to promote and apply. ASTM was listed as a provisional standard from 1939 to 1961 and has been revised several times. From 1962 as an official standard.
Since the 1950s, China has cooperated with the Eastern European countries such as the former Soviet Union to carry out salt spray testing. At that time, the trials were mainly military products and some important industrial products. Due to the fact that China’s industry was just starting up, the salt spray test work was slow. By the 1970s, with the development of the commodity economy, international trade has been increasing. As a test technology for evaluating the corrosion resistance of products, the salt spray test has obtained a lot of applications and developments.
The salt spray test is an artificially simulated salt spray environment test. Compared with the exposure test under atmospheric conditions, it has significant advantages: the corrosion environment can be controlled, the environment is reproducible, the test time is significantly shortened, and a large amount of manpower is saved. , financial and material resources. Its development and promotion are very fast. It has been developed from the initial pure neutral salt spray test to various forms such as acetate spray test, copper salt accelerated acetate spray test and alternating salt spray test. China has already adopted the salt spray test as a national standard and has carried out detailed stipulations. For example, the GB 2423.17 and GB 2423.18 standards promulgated by the People's Republic of China are specific standards for salt spray tests on electric and electronic products; GB 6458, GB 6459, and GB 6460 are salt spray test standards for metal coatings; GB 5938, GB 5939, The GB 5940 standard is a salt spray test standard that is specifically designed to evaluate the electroplating of light industrial products. The GB 1771 standard is mainly applied to the salt spray test standard for paint layers. With the advancement of science and technology, the application of salt spray test is more and more extensive, and the technology will be more improved than before.