Technical paper on phosphating of metal surface 1
Technical problems of phosphating treatment before coating on metal surface
Abstract: The phosphating process of zinc salt before metal surface coating was mainly studied, and the appropriate formula and technological conditions were determined through experiments. The experimental results show that compared with ordinary zinc phosphating process, this process has the characteristics of good corrosion resistance of phosphating film, low phosphating temperature, short phosphating time, good impact resistance and uniformity.
[Keywords:] metal; Phosphating treatment process; Phosphating film
Classification number of China Library: TG 174 Document ID: A DocumentNo.:1009-914x (2016)17-0063-02.
Phosphating treatment is to form a nonmetallic and non-conductive porous phosphating film on the metal surface (mainly steel and zinc) through chemical reaction. Phosphating process is widely used in industry, mainly used as the base material of paints and coatings.
At present, medium and high temperature phosphating has been widely studied and applied at home and abroad. However, it consumes a lot of energy, takes a long time to treat and has a large amount of sediment, which is not conducive to modern production. In order to improve the quality of phosphating solution and reduce the energy consumption cost, phosphating process has become a current research trend to develop in the direction of low temperature, less slag and high quality. In this paper, low temperature zinc-manganese phosphating was studied, and the best formula and process conditions were determined.
1 experimental part
1. 1 test drug
Zinc oxide, manganese carbonate, sodium carbonate, nitric acid (65%), phosphoric acid (85cA), sodium nitrite, nickel nitrate and copper sulfate (all analytically pure).
Development of 1.2 phosphating solution
ZnO, MnCO3 and NaCO3 were dissolved in water to make paste. Mix phosphoric acid and nitric acid together. Slowly mix the above two parts of liquid and stir until the reaction is complete. After the reaction, a colorless and transparent solution was obtained. Due to the exothermic reaction, special attention should be paid to safety in operation. After the reaction is completed, nickel nitrate is added and stirred until it is completely dissolved. Let stand for more than 1 h for later use. If the working fluid is prepared, phosphating is required.
1.3 determination of properties of phosphating film
1.3. 1 visual inspection
Visual inspection is the simplest and most effective means to evaluate the quality of phosphating film on site. General inspection items include: crystal granularity, uniformity, hue, luster, spots, pulverization, etc. This can be roughly judged.
1.3.2 microstructure microscopic method
Enlarge the phosphating film by 100 ~ 1000 times with an electron microscope, and observe the crystal shape, size and arrangement. The smaller the crystal size, the better it is to control it below tens of microns. The more uniform the arrangement, the smaller the porosity.
1.3.3 corrosion performance measurement method
The most commonly used method is copper sulfate drop test. At room temperature (15 ~ 25. C) Drop a drop of 3% copper sulfate solution on the surface of phosphatized parts that are not soaked in oil, and start the stopwatch at the same time. After 30 seconds, no rose color changes to qualified.
2 Results and discussion
2. 1 Function and influence of main components
2. 1. 1 zinc dihydrogen phosphate
When preparing phosphating solution, the dosage of manganese carbonate, sodium carbonate, nitric acid (65%), phosphoric acid (85%) and sodium nitrite are 12 g/L, 0/35g/L, 2 10g/L, respectively. When it reaches a certain amount, the corrosion resistance of phosphating film decreases with the increase of sodium dihydrogen phosphate, because zinc dihydrogen phosphate mainly plays a role in regulating the total acidity. When the content is too high, the film formation speed is fast, the film is rough and loose, the adhesion is poor, and there is floating ash on the surface. When the content is too low, the composition of the solution changes rapidly, it is difficult to adjust, the phosphating ability is weak, and even the film is thin and does not form a film, which leads to the decrease of corrosion resistance of the phosphating film. The optimum dosage of zinc oxide is determined by experiments to be 80-90g/L.
2. 1.2 oxidation promoter
Other reaction conditions are the same as 2. 1. 1, and zinc oxide is 85g/L. Generally, NO3-/NO2-, NO3-/ClO3-/NO2- are used for phosphating at normal temperature and low temperature. The oxidation accelerator system is good, and NO2- not only forms a film quickly, but also crystallizes the phosphating film finely. The determination is very convenient, so the management of bath liquid is simple and problems are not easy to occur. Organic nitro compound accelerator system, although it does not need to be replenished frequently, is due to the main accelerator ClO 2-; The determination of organic nitro compounds is complicated. In practical application, too much or too little accelerant will turn the bath into dark brown, which brings inconvenience to the determination of total acidity and free acidity. The main component of the accelerator in this experiment is NO3-/NO2- system. The accelerator system has good effect, fast film forming speed and fine crystallization. However, the dosage of accelerator must be controlled within the specified range, and too low content will make the surface of phosphating film uneven. If the content is too high, Fe+2 will accumulate too much, and the phosphating film is prone to yellow rust. The optimum dosage of nitric acid is130 ~140 g/L.
2. 1.3 Influence of nickel and manganese ions in phosphating solution
Other reaction conditions are the same as 2. 1. 1, and zinc oxide is 85 l. The experimental results are shown in figure 1 ~ 2 by adjusting the dosage of nickel nitrate and manganese carbonate.
Nickel is a bivalent metal with higher potential than zinc, which can participate in film formation, partially replace iron ions in phosphating film to form new crystallization active centers, promote film formation, refine grains, enhance film adhesion, reduce phosphating temperature and shorten phosphating time. The addition of nickel salt is too small, which has no effect and no adverse effects, but it will increase the cost of phosphating solution. Manganese ions can improve the hardness, corrosion resistance and adhesion of phosphating film, reduce the phosphating temperature, increase the reaction speed, reduce the film thickness, make the phosphating film darker and have metallic luster, and also reduce the amount of expensive metallic nickel. The experimental results show that the amount of nickel nitrate is 1O-20 g/L and the amount of manganese carbonate is l0-l5g/L. ..
2.2 The influence of phosphating process
2.2. 1 temperature effect
Other reaction conditions are the same as 2. 1. 1, and the reaction temperature is changed. The experimental results are shown in Figure 4.
If the temperature is raised properly, the point of low energy barrier can be activated to become crystal? Activity center? However, if the temperature is too high, a large amount of Fe+2 will be produced, which will lead to the unstable composition of phosphating solution, high consumption, dust on the surface of workpiece or failure to form a film, easy yellowing and poor corrosion resistance, so the phosphating time depends on the temperature. Controlling the phosphating temperature between 35-45℃ can not only ensure the proper phosphating speed and film quality, but also reduce the sediment. When the temperature is low, the phosphating speed slows down and the film layer is discontinuous.
2.2.2 The influence of acidity
It is more suitable to control the PH value of bath solution than to control the acidity ratio in phosphating process. Because no matter whether the phosphating solution is H3PO4 or phosphate, they all have multi-step dissociation equilibrium in the aqueous solution at the same time:
Since/= K2 (at 25℃, K2=0.0 13) is in the phosphating system, substituting Equations (2) and (3) into the expression of equilibrium constant K2 gives:
C total =5.7? 10-5( +7.6 ? 10-2 +4.8? 10- 10 +2. 1? 10-22 (4)
On the premise of meeting the K2 expression, the relationship between the PH value of phosphating solution and the total concentration of H3PO4 or phosphate in phosphating solution can be calculated by Formula (4), and the calculation results are shown in Table 4.
Effect of phosphating time
Other reaction conditions are the same as 2. 1. 1. Changing the reaction time, phosphating time is an important factor, which can save the cost, but the process is unstable and difficult to control, and the performance of phosphating film is unstable. Phosphating time is long and cost is high. The obtained phosphating film has poor quality, recrystallization of crystal surface, rough and thick film layer and poor adhesion. The phosphating time of this process should be controlled at about 3 min, and an ideal phosphating film can be formed.
3 Conclusion
Through a lot of repeated experiments on iron plate, the best technological formula is obtained: the dosage of zinc oxide is 80-90 g/L, manganese carbonate 10- 15 g/L, sodium carbonate 15-20 g/L, and nitric acid (65%)130-. The total acid/free acid is between 18-25. Compared with ordinary zinc phosphating process, the phosphating film has the advantages of good corrosion resistance, low phosphating temperature, short phosphating time, good corrosion resistance, good adhesion to the coating, good impact resistance and good uniformity, which improves the disadvantages of ordinary zinc phosphating process, such as more sediments, high energy consumption and durable phosphating solution.
The second paper on phosphating technology of metal surface
Preliminary study on sustainable development of phosphorus chemical industry
The sustainable development of phosphorus chemical industry includes three basic requirements: scientific utilization of resources, all-round development of the industry and effective protection of the environment. This paper analyzes the main problems such as low level of resource utilization, unreasonable industrial structure and serious environmental pollution, and puts forward some policy suggestions on actively promoting independent innovation, vigorously developing circular economy and strengthening industrial integration.
Keywords: basic requirements and policy suggestions for the sustainable development of phosphorus chemical industry
Phosphorus chemical industry is an industry based on phosphate rock resources, with phosphate fertilizer, phosphate and phosphide as its main products, and it is one of the important strategic industries in the national economy. The basic requirements of sustainable development of phosphorus chemical industry are analyzed, the main problems existing at present are studied, and relevant policy suggestions are put forward.
First, the basic requirements for the sustainable development of phosphorus chemical industry
Although there are still great differences in the understanding of sustainable development in academic circles, and different definitions have been made from the perspectives of economics, sociology, ecology and systematics, it is generally believed that sustainable development should be? Meet the needs of contemporary people without compromising the development of future generations' ability to meet needs? . In this sense, the sustainable development of phosphorus chemical industry at least includes the following three requirements.
1, scientific utilization of resources
Sustainable development emphasizes taking different protection measures for resources with different attributes. For non-renewable resources such as minerals, oil and natural gas, it is necessary to improve their utilization rate and replace them with renewable resources as much as possible to prolong their service life. Phosphorus ore is a typical non-renewable resource. Although China's proven reserves are relatively large, ranking second in the world, second only to Morocco, it is rich but not rich, and it is listed as one of the 20 minerals that cannot meet the needs of national economic development in 20 10 years by the Ministry of Land and Resources. In recent years, the annual production capacity of phosphorus chemical products in China is nearly 8.5 million tons, and the resource consumption ranks first in the world. China's phosphorus chemical products not only meet the needs of domestic production and life, but also export a large number of traditional primary phosphorus chemical products, which still belong to? Resource export type? Development model. On the contrary, many developed countries strictly protect and scientifically use their own phosphate rock resources, mainly for producing high-end products, and explicitly restrict exports. The sustainable development of phosphorus chemical industry should first make good use of phosphate rock, which is the premise and foundation of development.
2. Overall development of industry
Sustainable development must first emphasize development; Without development, sustainable development will become water without resources and trees without roots. As a complete industrial chain, phosphorus chemical industry has many links and forms, such as phosphate mining, processing, transportation, protection, research and development, export and so on. There are 27 provinces in China with phosphate rock distribution, but the overall distribution is relatively scattered, mainly concentrated in Yunnan, Guizhou, Sichuan, Hubei, Hunan and other five provinces with relatively rich resources, and the industrial concentration is low. At the same time, China's phosphorus chemical products are mainly primary products such as phosphate fertilizer, and there are few refined, special and chemical products; The stamina of industrial development is insufficient. There are many small and medium-sized enterprises, few large enterprises, insufficient capacity investment and insufficient technological innovation ability, whether it is phosphate mining or phosphorus chemical products. The sustainable development of phosphorus chemical industry inevitably requires us to always take development as a distinct theme, solve outstanding problems in current development with development vision, development ideas and development methods, promote the continuous improvement of the development ability and level of phosphorus chemical industry and promote the all-round development of the whole phosphorus chemical industry.
3. Effectively protect the environment
While encouraging economic growth, sustainable development emphasizes limiting the satisfaction of human needs, not exceeding the carrying capacity of resources and environment, focusing on improving quality, improving efficiency, saving energy, reducing waste, changing traditional production and consumption patterns, realizing the harmony between man and nature, and effectively protecting the environment on which human beings depend. At present, the phosphorus chemical industry in China is in a relatively backward situation, and the production of some phosphorus chemical products has brought great pollution to the environment. For example, yellow phosphorus is the parent product of thermal phosphorus chemical industry, which has long been considered as high energy consumption and high pollution? Sunset? In industry, some developed countries have stopped production or announced that they will no longer produce yellow phosphorus. Contrary to this trend, the yellow phosphorus production in China has increased greatly in recent years. The slag, ferrophosphorus and furnace gas produced in the production of yellow phosphorus have caused serious pollution to the environment. In addition to the production of yellow phosphorus, the production of other phosphorus chemical products, if not protected enough, will also cause different degrees of damage to the environment. Therefore, the sustainable development of phosphorus chemical industry in China must not only promote economic development, but also consider the carrying capacity of the environment as much as possible, so as to effectively meet the requirements of contemporary and future generations for environmental development.
Second, the main problems of sustainable development of phosphorus chemical industry
Under the background of economic globalization, phosphorus chemical industry is facing fierce competition on a global scale. Judging from the basic requirements of sustainable development, China's phosphorus chemical industry still faces many problems, mainly in the following three aspects.
1, the level of resource utilization is low.
Phosphate rock resources are very scarce, but the comprehensive utilization in China is generally inadequate and unreasonable. In China, 80% of phosphate rocks are sedimentary rocks, 70% are low-grade collophanite, and underground mining accounts for about 60% of the total. Even in Yunnan and Guizhou provinces where rich minerals are concentrated, there are a large number of poor minerals, which are rich in mineral impurities and difficult to mine. But on the contrary, most mines in China belong to small and medium-sized mines, especially small collective and individual mines. The production equipment is quite crude, the technical force is very weak, the management work is lagging behind, and there are widespread phenomena of indiscriminate mining and indiscriminate digging, easy mining and abandoning difficulties, and the limited resources are wasted. At the same time, even in high-quality phosphorus-rich areas, there are phosphorus-rich mines due to development concepts, production technology and other reasons. Superior ore and inferior use? 、? High quality and low use? A considerable number of high-quality minerals are used to produce low-concentration calcium magnesium phosphate and ordinary superphosphate, and the utilization level of resources is low, and some valuable elements are abandoned, which intensifies the consumption speed of high-quality resources.
2. The industrial structure is unreasonable.
After the development in recent years, China has formed a relatively complete industrial structure of phosphorus chemical industry. From the perspective of industrial production structure, China's phosphorus chemical enterprises still mainly produce primary phosphorus chemical enterprises such as yellow phosphorus, sodium tripolyphosphate and calcium hydrogen phosphate, while there are few enterprises that produce fine and special phosphorus chemical products and high value-added organophosphorus products. From the perspective of industrial regional layout, China's phosphorus chemical industry is mainly distributed in Yunnan, Guizhou, Hubei and other five provinces with concentrated phosphorus resources, but the information exchange between regions is not smooth enough. Industrial chain? It is not complete enough. It is not enough to pay attention to reducing unnecessary repeated investment and strengthening mutual cooperation. The resource advantages of these places have not been transformed into industrial advantages, which are not only far from the phosphorus chemical industry abroad, but also incompatible with the requirements of China's economic and social development. From the perspective of industrial growth mode, the economic growth of the whole phosphorus chemical industry still belongs to the traditional mode of high input, high consumption, low output and low efficiency. The mode of relying on scientific and technological innovation to promote economic growth has not yet been formed, and the industrial structure needs to be adjusted and upgraded urgently.
3. The environmental pollution is serious.
In phosphate mining, people will cut down forest vegetation, peel off topsoil or wash it with water, which will inevitably cause certain ecological damage and environmental deterioration. At the same time, phosphorus chemical industry is a typical industry with high energy consumption, high emission and high pollution. Three wastes? The emission intensity is much higher than the average level of other industries. The development of phosphorus chemical industry has brought a lot of environmental pollution. The most typical example is the disorderly discharge of waste from phosphorus chemical industry near Dianchi Lake in Yunnan Province, which leads to excessive phosphorus content in Dianchi Lake and excessive eutrophication of water body, which has attracted extensive attention from domestic and foreign media. This incident has made people fully aware of the pollution problem of phosphorus chemical products, and Jiangsu, Xiamen, Shenzhen, Kunming and other provinces and cities have explicitly banned the use of phosphorus-containing detergents. Generally speaking, the distribution of phosphate rock and the development area of phosphorus chemical industry in China are basically densely populated and economically active areas. Due to the limitation of mining and production technology, the contradiction between high emission and pollution of phosphorus chemical industry and limited living space and environmental capacity of human beings is very prominent.
Three. Policy Suggestions on Sustainable Development of Phosphorus Chemical Industry
The 11th Five-Year Development Guide of Phosphorus Chemical Industry in China proposes to rationally develop and utilize resources, optimize the layout of mining areas, strengthen independent innovation and technological progress, and promote the sustainable development of phosphorus chemical industry. In order to achieve this goal, this paper suggests starting from three aspects.
1, actively promote independent innovation
Promoting independent innovation is the basic premise of changing the mode of economic growth, the objective need of maintaining long-term stable and rapid economic development, and the important guarantee of building a resource-saving and environment-friendly society. From the technical point of view, the general trend of new technology development in phosphorus chemical industry in the world is: the combination of wet method and thermal method, with wet method as the main method. At the same time, in order to meet the needs of human society in many aspects, develop fine phosphorus chemical products and increase the added value of non-renewable resources. The low level of resource utilization, unreasonable industrial structure and serious environmental pollution in phosphorus chemical industry in China are closely related to poor mineral processing equipment, weak production technology and few high-tech applications. In order to promote the development of phosphorus chemical industry, we must first adhere to the road of independent innovation, increase the intensity of technological innovation, take strengthening the ability of independent innovation as the central link in adjusting the industrial structure and changing the development mode, learn from the latest international technological achievements such as comprehensive utilization technology of low-grade phosphate rock, wet-process phosphoric acid purification technology and green synthesis technology of fine phosphorus chemical industry, strengthen the pace of introducing, digesting, absorbing and innovating again, vigorously promote original innovation and integrated innovation, and strive to break through the key that affects and restricts the development of phosphorus chemical industry.
2. Vigorously develop circular economy.
Circular economy meets the requirements of Scientific Outlook on Development, and it is a paradigm of social production and reproduction with high efficiency and recycling of resources as the core and low consumption, low emission and high efficiency as the basic characteristics. It is necessary to overcome the problem of high resource consumption in phosphorus chemical industry. Three wastes? Serious emissions and other issues, resolutely get rid of? Pollution first and then treatment? The traditional development path should realize the transformation from the traditional economic growth mode to the sustainable economic growth mode, promote the recycling of phosphorus and phosphorus chemical wastes, the coupling cycle of phosphorus-coal-salt chemistry, the comprehensive utilization of phosphorus chemical, salt chemistry and coal chemical wastes, make full use of every element in phosphate rock resources, reduce the consumption of phosphate rock, and effectively reduce or even eliminate it? Waste? Emissions, maximize the use of scarce and precious natural resources, develop circular economy, reduce production costs and achieve sustainable development. In recent years, some large phosphorus chemical enterprises in China have begun to explore the development of circular economy. For example, Sanhuan Company of Yuntianhua Group insists on resource saving, comprehensive utilization and clean production. Reduce, reuse and recycle? Based on the principle of scientific and technological innovation and technological progress, we have taken the road of new industrialization and vigorously developed circular economy, and achieved remarkable results. While enterprises independently develop circular economy, our government should introduce corresponding policies and measures to encourage and support phosphorus chemical enterprises to take the road of circular economy development, and try their best to achieve maximum development benefits and real scientific development with the least consumption of resources.
3. Strengthen industrial integration.
In recent years, some provinces rich in phosphate rock resources have successively issued a series of local policies on resource protection and industrial development, such as Yunnan Province's Market Access Conditions for Phosphate Rock Resources Exploitation and Hubei Province's Notice on the Total Control Plan for Phosphate Rock Exploitation this year, which have effectively promoted the standardization and rapid development of the industry and formed a number of competitive large groups. However, these integration work is still limited to one province, and cross-regional and cross-industry integration has not yet appeared. This paper suggests that China should adhere to the principles of government guidance, market orientation and enterprise orientation, and further strengthen the integration of phosphorus chemical industry nationwide: from the government guidance, the relevant central departments should strengthen macro-control, introduce the access conditions of yellow phosphorus industry as soon as possible, establish strict supervision mechanism and policy coordination mechanism, and strengthen the self-discipline function of the industry; From the development mode, we should adapt to the mainstream of international chemical development, rationally allocate production factors, implement clean production and? Three wastes? Unified governance to realize industrial park, intensification and integration; From the industrial structure, properly control the production of yellow phosphorus, actively develop intermediate products such as phosphide, vigorously develop downstream products such as phosphorous acid, adhere to the combination of inorganic phosphorus chemical industry and organophosphorus chemical industry, change the single production mode, and constantly optimize the industrial structure; From the perspective of enterprise reorganization, through merger, holding and combination, we will strive to form a number of international, large-scale, refined and specialized enterprise groups, improve the overall technical level and market share, and promote and promote the sustainable development of phosphorus chemical industry.
In a word, China should seek development through independent innovation, circular economy and environmental protection, so as to realize the sustainable development of phosphorus chemical industry.
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