Background
At present, the surface pretreatment before the coating of steel products is still dominated by the traditional phosphating process, although the phosphating process can improve the corrosion resistance of a metal substrate and the bonding force of a subsequent coating, phosphating solution contains harmful heavy metals, and a large amount of precipitates and harmful gases are generated in the phosphating process, so that serious environmental pollution is caused due to the discharge of waste water, and the development of an environment-friendly process is urgent. The newly developed metal surface treatment technology is mainly silane treatment technology. Although the silane film has good adhesion to the coating, the silanization process still has the following problems: (1) the silane solution has relatively short storage time and is easy to generate polycondensation and lose efficacy; (2) the silane treatment technology has relatively high requirements on the surface of a metal matrix and the cleanness of silane tank liquor; (3) the silane species has selectivity to the coating, is not easy to be widely applied, and has higher use cost than phosphating. The zirconium treatment can form an inorganic ceramic membrane on the surface of steel, and the zirconium technology has the advantages of energy conservation, environmental protection, stable bath solution, low cost and the like, and the process is simple, thus becoming a hotspot of research in recent years. The research in foreign countries mainly focuses on the film forming mechanism of the magnesium-aluminum alloy titanium-zirconium conversion film, the influence of components of the titanium-zirconium conversion film and conversion solution and process conditions on the corrosion resistance of the conversion film, and the like, and the research on the steel and iron member zirconium process is rarely reported in China. The Wangbanghong and Wangli take fluozirconate and cupric nitrate as solution to prepare nano-ceramic film on the surface of cold-rolled steel sheet. However, the treatment liquid of the process contains the limited discharge heavy metal ions, and the metal surface needs to be cleaned by deionized water before film formation, so that the treatment cost is increased, and the process is not beneficial to the popularization of the technology. In view of the above, it is necessary to design a method for preparing a zirconium forming film solution for steel surface.
Disclosure of Invention
The invention aims to provide a preparation method of a zirconium film forming liquid for the surface of steel, which has the advantages of energy conservation, environmental protection, stable bath solution, low cost and the like, and the process is simple.
In order to realize the aim, the invention provides a preparation method of a steel surface zirconium film-forming solution, which comprises the following steps:
firstly, weighing zirconium nitrate, manganese nitrate and epoxy silicate, putting the zirconium nitrate, the manganese nitrate and the epoxy silicate into a container for mixing, then adding 45% of fluozirconic acid for stirring and mixing to obtain a solution, regulating the pH value of the solution to be 2.0-4.0 by using triethanolamine, then adding tap water for stirring uniformly, and standing to obtain a film-forming solution.
Preferably, the concentration of the zirconium nitrate is 1.0-3.5g/L, the concentration of the fluorozirconic acid is 4.0-10ml/L, the concentration of the manganese nitrate is 1.0-5.0g/L, and the concentration of the epoxy silicate is 1.0 g/L.
Preferably, the steel test piece with the same specification is soaked in 5% of degreasing agent working solution for 6-7min, washed by tap water, then soaked in the film forming solution to form a film for 7.5min, after the film forming is finished, the test piece is taken out, washed by tap water, and dried at room temperature for 4 hours for later use.
Preferably, 50g of LS-206 alkaline degreasing agent is weighed and dissolved in 1000ml of tap water to prepare 50g/L of degreasing agent working solution.
Preferably, the concentration of zirconium nitrate is 2.5g/L, the concentration of fluorozirconic acid is 5.5ml/L, the concentration of manganese nitrate is 2.0g/L, and the concentration of epoxysilicate is 1.0 g/L.
Therefore, the preparation method of the zirconium film forming liquid for the steel surface has the advantages of energy conservation, environmental protection, stable bath solution, low cost and the like, and is simple in process.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Detailed Description
The invention provides a preparation method of a zirconium film forming liquid for a steel surface, which comprises the following steps:
firstly, weighing zirconium nitrate, manganese nitrate and epoxy silicate, putting the zirconium nitrate, the manganese nitrate and the epoxy silicate into a container for mixing, then adding 45% of fluorozirconic acid for stirring and mixing to obtain a solution, regulating the pH value of the solution to be 2.0-4.0 by using triethanolamine, then adding tap water for uniformly stirring and standing to obtain a film forming solution, wherein the concentration of the zirconium nitrate is 1.0-3.5g/L, the concentration of the fluorozirconic acid is 4.0-10ml/L, the concentration of the manganese nitrate is 1.0-5.0g/L, and the concentration of the epoxy silicate is 1.0 g/L.
Further, soaking the steel test piece with the same specification in 5% of degreasing agent working solution for 6-7min, washing with tap water, then soaking the steel test piece into the film forming solution to form a film for 7.5min, taking out the test piece after the film forming is finished, washing with tap water, and airing at room temperature for 4 hours for later use.
Further, 50g of LS-206 alkaline degreasing agent is weighed and dissolved in 1000ml of tap water to prepare 50g/L of degreasing agent working solution.
Further, the concentration of zirconium nitrate is 2.5g/L, the concentration of fluorozirconic acid is 5.5ml/L, the concentration of manganese nitrate is 2.0g/L, and the concentration of epoxy silicate is 1.0 g/L.
The reaction mechanism is as follows: cutting into 6cm × 2cm steel sheet is treated with oil removing agent working solution and then is used as working electrode, the working electrode is placed in an electrolytic bath with 200mL of film forming solution, a saturated calomel electrode is used as a reference electrode, the change of open circuit potential along with time under the optimal film forming condition is measured by using a CHI660C electrochemical workstation, the potential value is recorded every 0.1s, and the continuous scanning is carried out for 800s according to the change of the open circuit potential along with the time in the film forming process
The chemical composition of the zirconium film shown in the graph (FIG. 1) and Table 1 indicates that the film formation mechanism is as follows: as shown in FIG. 1
As can be seen from the graph, the film forming process is divided into three sections.
The first region potential sharply shifts negative, which means that H is performed first+Promoting the activation of the iron surface by the corrosive electrochemical anode dissolution reaction of the matrix, wherein the reaction formula is as follows:
Me+2H2ZrF6→Me(HZrF6)2+H2↑ (1)
the potential of the second segment is shifted from 120s, due to anodic dissolution reaction at the metal-solution interface [ H+]Reducing and starting to form a film under the condition of reaching the fluorozirconate precipitation, wherein the reaction formula is as follows:
Me(HZrF6)2+nH2O→MeZrF6·nH2O↓+H2ZrF6(Me is Fe or Mn) (2)
The potential of the third section tends to be stable, which indicates that the surface of the steel matrix is covered by the composite membrane, the anode is completely blocked, and the electrochemical dissolution reaction of the formed membrane and the membrane reaches dynamic balance.
TABLE 1 EDS energy Spectrum element content
Example 1
Firstly, adding 7mL/L fluorozirconic acid, 3.0g/L zirconium nitrate and 1.0g/L epoxy silicate, wherein the adding amount of manganese nitrate is respectively 1.0g/L, 2.0g/L, 3.0g/L, 4.0g/L and 5.0g/L to prepare 200mL of film forming liquid, regulating the pH value to 3.0 by triethanolamine, then soaking steel test pieces with the same specification in 5% degreasing agent working solution for 6-7min, washing by tap water, then respectively soaking the steel test pieces in the film forming liquid to form a film for 7.5min, after the film forming is finished, taking out the test pieces, washing by tap water, airing at room temperature for 4 hours for later use, and testing. It can be seen from FIG. 2 that when the manganese nitrate concentration is less than 2.0g/L, the corrosion resistance of the conversion coating is relatively weak, and as the concentration increases, the corrosion resistance increases slightly. This is because manganese ions are the main film-forming substance, and the following reaction occurs:
Mn2++2H2ZrF6+nH2O→MnZrF6·nH2O↓+H2ZrF6+2H+
from the above equation, it is understood that the increase in the content of metal manganese ions increases the deposition amount of the film, but when the concentration of manganese nitrate is higher than 2.0g/L, the corrosion resistance of the zirconium film decreases with the increase in the content of manganese nitrate, because brown precipitates in the deposition solution increase with the increase in the concentration of manganese ions, and the stability of the deposition solution deteriorates.
As can be seen from FIG. 3, when the concentration of manganese nitrate is less than 2.0g/L, the fatigue of the deposition solution increases with the increase in the concentration of manganese nitrate because manganese metal participates in the film-forming reaction to promote the formation of a film; when the concentration of the manganese nitrate is higher than 2.0g/L, the fatigue of the film-forming solution is reduced along with the increase of the concentration of the manganese nitrate, because excessive addition of metal manganese ions can cause precipitation in the film-forming process and the film-forming solution becomes turbid, the system stability is influenced, and the fatigue of the film-forming solution is reduced.
Example 2
Firstly, adding 2.0g/L manganese nitrate, 3.0g/L zirconium nitrate and 1.0g/L epoxy silicate, wherein the adding amount of fluozirconic acid is respectively 4.0g/L, 5.5g/L, 7.0g/L, 8.5g/L and 10.0g/L to prepare 1000mL of film-forming liquid, regulating the pH value to be 2.5 by triethanolamine, then soaking steel test pieces with the same specification in 5% degreasing agent working solution for 6-7min, washing by tap water, then respectively soaking the steel test pieces in the film-forming liquid for film formation for 7.5min, and after the film formation is finished, respectively soaking the steel test pieces in the film-forming liquid for film formation for 7.5minAnd taking out the test piece, washing the test piece by using tap water, and airing the test piece for 4 hours at room temperature for later use. It can be seen from FIG. 4 that Me (HZrF) is formed when the concentration of fluorozirconic acid is too low6)2The film forming substances are few and are not beneficial to the reaction of (2), so that the formed zirconium film is too thin, and the corrosion resistance of the formed zirconium film is poor or the zirconium film cannot be formed basically; however, when the amount is too large, the film forming reaction is too fast, and the formed zirconium film is loose and weak and is removed as soon as it is wiped off, so that the corrosion resistance time is remarkably shortened when the concentration is too large.
As shown in FIG. 6, when the concentration of fluorozirconic acid is higher than 4mL/L and lower than 5.5mL/L, the fatigue of the deposition solution increases as the concentration of fluorozirconic acid increases because fluorozirconic acid is an important substance for film formation, and an increase in the concentration of fluorozirconic acid promotes the film-forming substance MnZrF6·nH2Because of the generation of O, the number of iron sheets to be treated increases when the content of fluorozirconic acid is large; when the concentration of the fluorozirconic acid is higher than 5.5mL/L, the fatigue of the film-forming solution is reduced along with the increase of the concentration of the fluorozirconic acid, because the concentration of the fluorozirconic acid is too high to consume other film-forming substances, and finally the other film-forming substances are too low to form a uniform zirconium film or even fail to form the film, and the formed zirconium film is loose due to thickness and corrosion resistance of the zirconium film is reduced, so that the fatigue of the film-forming solution is reduced.
Example 3
Firstly, adding 5.5mL/L fluorozirconic acid, 2.0g/L manganese nitrate and 1.0g/L epoxy silicate, wherein the adding amount of zirconium nitrate is respectively 1.0g/L, 2.0g/L, 2.5g/L, 3.0g/L and 3.5g/L to prepare 200mL of film-forming liquid, regulating the pH value to 2.5 by triethanolamine, then soaking steel test pieces with the same specification in 5% degreasing agent working solution for 6-7min, washing by tap water, then respectively soaking in the film-forming liquid for 7.5min, after the film-forming is finished, taking out the test pieces, washing by tap water, airing at room temperature for 4 hours for later use, and testing. As can be seen from fig. 6, when the concentration of zirconium nitrate is low, the etching time is short because the concentration of zirconium nitrate is too low to reach the concentration required for film formation, so that the formed zirconium film is thin and even a dense and uniform zirconium film cannot be formed; however, when the amount is too large, the corrosion resistance time of the zirconium film decreases as it increases, and it is excessive Zr4+The formed hydroxide is attached to the surface of the zirconium film, so that the film is loose, the corrosion resistance is reduced, and meanwhile, when the concentration of the added zirconium nitrate is higher, the adding amount of the fluorozirconic acid and the zirconium nitrate cannot reach the mutual solution ratio, so that the solution is unstable, and a compact and uniform zirconium film cannot be formed.
As can be seen from FIG. 7, when the concentration of zirconium nitrate is less than 2.5g/L, the fatigue of the deposition solution is low because zirconium nitrate is the main film-forming substance, but the zirconium film is thin because of its low concentration; the fatigue of the film-forming solution is enhanced with the increase of the concentration of the zirconium nitrate, and is optimal at 2.5 g/L; when the concentration is increased again, because the film is formed, the film forming process is finished, and the excessive zirconium nitrate is deposited on the surface of the film, so that the zirconium film is loosened, and the fatigue is reduced.
Therefore, the preparation method of the zirconium film forming liquid for the steel surface has the advantages of energy conservation, environmental protection, stable bath solution, low cost and the like, and is simple in process.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the invention without departing from the spirit and scope of the invention.