Development prospect of coating pretreatment proce

2022-08-04
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Zirconia Technology: the development prospect of coating pretreatment process by Richard Moore, chemical engineer and Bruce Dunham, innovation director of Dubois chemicals in charleneville, Ohio, USA this article introduces the readers to zirconia technology, which is a process that utilizes transition metal pretreatment, low-temperature cleaning technology and water purification effect optimization technology. Its advantages also include: zirconia technology can reduce the demand of metal finishers for heat energy; Reduce the large amount of phosphate precipitation caused by operation. Remove phosphate to maintain and improve product quality. More importantly, this article shows people the specific experimental work in cooperation with users, the technical detection in the field and the best results achieved in cooperation with end users. At the same time, this article will further show people how to treat harmful substances in sewage, how to reduce the use consumption of purified water, and how to help metal finishing companies save a lot of time and money

as water is a precious resource, green environmental protection has gradually become a competitive, profitable and legal production requirement. A senior manufacturer recently said, "There is no doubt that the standards for waste liquid treatment are changing. Some chemical enterprises close to the community are discharging a large amount of industrial waste liquid. If possible, this issue should be reconsidered.

due to the increasingly stringent restrictions on environmental protection and the intensification of global competition, manufacturers and equipment manufacturers are forced to change their traditional production processes. A good example is the European Union. The European Union has twice the population density of the United States, but has more Less fresh water resources. As a necessary resource for living, the EU has initiated stricter water use regulations. As early as the beginning of 2007, the European Parliament adopted an amendment to the previous regulations on the use of phosphate, with the goal of completely eradicating the use of phosphate within three years. This approach has led to a major change in the field of coating pretreatment, which generally adopts the traditional iron and zinc phosphate treatment

as a result, people began to study phosphate free chemistry, which is a very challenging field of metal coating preparation. These efforts have been very successful. At the same time, the basic raw materials of these chemicals come from transition metals including zirconium, titanium and vanadium (Figure 6). These elements exhibit chemical properties similar to those of chromium, but there is no need to worry about their toxicity. Like any other new technology, it has its drawbacks. The most important thing is to put forward higher requirements for water quality, accurate cleaning and rust treatment

however, the latest development of science and technology has solved these problems. People have found effective substitutes for phosphates through a large number of pretreatment operations, thus developing new chemicals. These chemicals, known as zirconia, can not only meet or promote the ease of use, enhance the adhesion of coatings and the corrosion prevention of common phosphate based chemicals, but also obtain other benefits such as less use of chemical raw materials and low-temperature operation

history of phosphate pretreatment chemistry

historians trace it back to the second industrial revolution in. During this period, the development of chemical industry, petroleum, electric power and steel industry led to a new phenomenon: the mass production of consumer goods. Therefore, people put forward higher requirements to protect these steel products from corrosion

William Alexander Ross, the British inventor, first started the research on phosphate coating and obtained a patent in 1869. Tomas watts coslett, also an inventor from Britain, first proposed the iron phosphate coating method by dissolving iron sheets in phosphoric acid in 1906. Coslett subsequently patented his invention in the United Kingdom and the United States

by 1912, inventor Frank Rupert Granville Richards further invented manganese phosphate based on the iron phosphate process invented by coslett. He obtained a patent in 1913. In the following two decades, the manufacturing process of manganese phosphate has been improved. Although this process provides sufficient corrosion resistance and coating adhesion, manganese needs to be used. Manganese is very expensive. With the outbreak of World War II, the demand for manganese in the United States has become very difficult

in the 1930s, employees of the American chemical coating company invented the zinc phosphate process. Compared with manganese phosphate, this process has a higher energy utilization rate and became the main war material of the United States during World War II. In the second half of the 20th century, the chemical processes of iron phosphate and zinc phosphate were further improved mainly through the addition of various paint accelerators (organic and inorganic) and other additives such as cleaning components (surfactants or solvents), but the basic process and chemical principles remained unchanged

comparison between iron phosphate and zinc phosphate

although manganese phosphate is still used in limited cases, the coating pretreatment chemicals used today are mainly composed of iron phosphate or zinc phosphate. Their purpose is the same, that is, to produce a coating that can improve the adhesion and corrosion resistance of the coating

although they have the same purpose, they have their own advantages and disadvantages, which makes their products different. Knowing their corresponding advantages and disadvantages is convenient for manufacturers to decide which production process is more appropriate. General knowledge also provides manufacturers with a better understanding of the technical problems of zirconia replacing iron or zinc. Iron phosphate is made of a non crystalline steel substrate coating. Zirconia is made into gray, gold, blue and purple coatings for selection (Fig. 1). Generally, it is lighter, easier to control, more flexible, firm and economical than the coating generated by zinc

iron phosphate processing can be carried out separately or in multiple steps, and cleaning and phosphate treatment are also at the same stage. This operation process can be completed after spraying, soaking, scrubbing, steaming and other processes. In general, iron phosphate coatings provide greater physical adhesion and corrosion resistance (Figure 2)

on the other hand, the crystalline coating formed by zinc phosphate is usually gray from the surface (Fig. 3). The formation and size of these crystals can be manually controlled by various additives or operating parameters. Compared with iron phosphate, zinc phosphate solvent produces a large amount of coating, high operating costs and is more difficult to maintain

zinc phosphate processing needs to be divided into multiple steps and cleaned and adjusted before the zinc phosphate stage. Zinc phosphate can be sprayed or soaked during processing. Zinc phosphate provides better physical adhesion and corrosion resistance

selection of phosphate

although there has been a successful record in the last century, people are still seriously studying the application of phosphate because it is harmful to water resources. In short, phosphate causes eutrophication, and the increase of chemical nutrients in water leads to the continuous growth of plants. The growth and final decay of plants will reduce the oxygen content in the water and cause a large number of fish deaths due to hypoxia (Fig. 4)

both the local sewage treatment area and the environmental protection agency have strengthened the strict restrictions on the discharge of industrial waste liquid, or in some cases, completely prohibit the discharge of phosphate. These restrictions will only become more and more strict in the future. If you are lucky enough not to face these restrictions now, you may often deal with them in the next decade

people are increasingly worried about the use of phosphate. In response, chemical suppliers began to introduce phosphate free pretreatment technology to the market. These chemical principles include polymer technology, acid substitutes, solvents, undercoats and metal based coatings. Among these phosphate substitutes, silane technology is the most popular

silane molecules have a variety of properties. The monopole of this molecular group has affinity for the coating, and the other pole can directly store the data with the metal surface to the host collector for endogenous reaction. In the pretreatment process, they "connect" the coating with the metal surface. Although people have achieved success in some specific cases, silane has its disadvantages compared with phosphate. First, silane molecules react with coatings only in a few specific resins. This means that if the manufacturer applies this technology in the production of coating line, there are limitations. The target of 7-8% silane in the solution pool is also more difficult to control and monitor than iron phosphate. At the same time, compared with the color of phosphate coating, silane looks clear, and it is basically impossible to judge whether the silane coating is available from one side. Finally, silane treated parts are more susceptible to spark erosion. At the same time, silane solution is more prone to deterioration than phosphate solution, and its service life is shorter than phosphate solution

due to these limitations, silane cannot completely and effectively replace iron phosphate and zinc phosphate in most pretreatment systems. Therefore, chemical plants continue to study other phosphate substitutes. Throughout the pretreatment industry, the latest development is the chemical manufacturing industry based on fluorescent zirconium. The coating on the workpiece surface is lighter and thinner

the road to zirconia

fluoro based acids (such as fluorozirconate and fluorotitanate) have been used in metal processing for decades. Fluorinated acid is often used in aluminum treatment. However, it is not easy to realize from simple aluminum treatment to phosphate coating treatment of preparatory parts (including cold and hot rolled steel, aluminum, galvanized steel and other soft metals). The earliest attempt to use fluorinated acid was to replace iron phosphate, but it produced a more unstable solution than iron phosphate, making parts more susceptible to rust and corrosion

people continue to work hard for the application formula of fluorozirconate, which makes the European nanotechnology enter the American market. Nanotechnology can surpass the corrosion resistance of iron phosphate, and in some cases can match the corrosion resistance of zinc phosphate. However, the formation of the earliest nanotechnology also has defects. First of all, chemical raw materials are easy to be corroded by low carbon steel liquid. Users need to improve their cleaning equipment before production. At the same time, the parts are easy to be corrupted by the covering after treatment. Therefore, the development of effective phosphate substitutes to prevent corrosion is still in progress. This achievement can be found in the latest zirconia production technology published by Dubois chemicals. Like other phosphate substitutes, zirconia is based on fluorinated acid, which contains a unique mixture of additives and catalysts to help the parts finish the coating faster and more tightly. In this way, the processed coating can avoid corrosion of components and reduce the generation of sediment

establish and use zirconia tank

in order to properly show how zirconia acts as a substitute for phosphate in pretreatment, it is very useful to observe how zirconia tank works. In fact, the use of zirconia tank is very similar to that of iron phosphate tank. It can be used in the existing cleaning equipment of iron phosphate without changing the physical properties of the cleaning equipment. The concentration of zirconia commonly used is 1% - 5%, which is very similar to the parameters of iron phosphate, and in some cases, the concentration can be as low as 0.5%

also very similar to the parameters of ferric phosphate, the pH of zirconia solution is maintained at 4.0 to 5.0 (Fig. 7). The pH of the solution will be changed by ordinary alkaline substances, such as potassium, sodium or ammonium hydroxide. If the pH is too low, the coating will not deposit on the surface and will rust. If the pH is too high, it will lead to poor coating forming effect and instability (Fig. 8). Oxidation at 115 ° f

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