U.S. Pat.No. USP4298405 198 1 proposes a phosphating process, which can form an iron-based phosphating film with good quality and moderate film weight on steel surface at normal temperature (10 ~ 38℃). Phosphating can be carried out by immersion method or liquid spraying method. An example of the formula is as follows.
Formula l
Composition (mass fraction) Composition (mass fraction)
Ammonium dihydrogen phosphate 82 nonionic surfactant lO
Potassium nitrite (accelerator) 8
Formula 2
Composition (mass fraction) Composition (mass fraction)
Potassium dihydrogen phosphate 72 sodium nitrate 8
Sodium nitrite nonionic surfactant l0
The United States patent (USP400376 1) also proposed a two-step iron-based phosphating process, and the phosphate content in the second step was increased by about 50% ~ 100% compared with that in the first step. The pH value of phosphating solution is 4.3 ~ 6.5, and 0.05 ~ 1.09/L short-chain alkylamine (C2 ~ 4) and 0.0 1 ~ 1.5g/L nonionic surfactant wetting agent are added. The formula and process of phosphating solution are as follows:
Assembly parts
Primary sodium phosphate 9g/L diethylamine 0.4g/L.
Hydroxylamine sulfate 0.4g/l octanoic acid 0.2g/l
Nonionic wetting agent 0.6g/l
Process conditions:
The temperature was 65℃ for 3min.
Injection pressure 1.5 kg/cm2
The main component of iron-based thin film phosphating solution (or alkali metal) is phosphate, usually sodium, potassium and ammonium salts of phosphoric acid, pyrophosphate and polyphosphoric acid. Accelerators, surfactants and additives are also needed. The choice of accelerator is particularly important, which directly affects the speed of phosphating process, the quality, corrosion resistance and temperature of phosphating film. According to the characteristics of iron-based phosphating process, Wang Dunjia and others chose nitrate, chlorate, molybdate and organic nitro compounds as accelerators, and after repeated experiments, the compound accelerator formula was obtained. An iron-based phosphating solution was developed with this composite accelerator, and its typical formula is as follows.
Composition (mass fraction) Composition (mass fraction)
Nail2P04 16 surfactant 1.6
Na2HP04 8 Composite Additive 3.4
Compound accelerator 5.6 water 65.42
Wang Desong and others have developed a light iron-based phosphating solution containing composite accelerator and suitable surfactant, and its formula is as follows. Among them, the dosage of composite accelerator affects the phosphating effect, and the phosphating effect is poor when the dosage is small; Too much dosage will not only passivate the metal surface, which is not conducive to phosphating reaction, but also produce more phosphating precipitates, which will make the phosphating sample seriously dusty. The application effects of alkyl alcohol amide, fatty alcohol polyoxyethylene ether (AEO) and sodium dodecyl sulfonate in phosphating solution were studied. The results show that the corrosion resistance of phosphating film can be improved by adding a small amount of surfactant, and the effect of alkyl alcohol amide is better than that of fatty alcohol polyoxyethylene ether and sodium dodecyl sulfonate. The dosage of alkyl alcohol amide should be 0.1~ 0.29/L. When it is too low, the effect is not obvious, and when it is too high, the alkyl alcohol amide is easy to precipitate.
Assembly parts
20g/L of sodium phosphate and 2-5g/L of composite accelerator.
85% phosphoric acid 12g/L surfactant 0. 1 ~ 0.39/L
Sodium nitrate 10 ~ 15g/l
(2) Zinc-based phosphating is a kind of phosphating system that has been studied more in recent years, especially zinc-calcium phosphating solution has the advantages of fast deposition speed, thin coating and low price. Zinc phosphating is mainly used to coat the bottom layer. There are many formulas of zinc phosphating solution at home and abroad, and its main components are basically the same. The basic components are zinc ions, phosphates, oxidants, accelerators, etc.
Nonionic surfactant is an organic additive widely used in zinc phosphating solution. The addition of some nonionic surfactants can not only wet the workpiece surface and overcome the poor degreasing, but also reduce the film weight, prolong the life of phosphating tank and improve the performance of phosphating film. T.S.Nsankara et al. studied sorbitol monostearate, Madiha Shoeib et al. studied tall oil fatty acid ethoxy compound (TOFA) and oleyl alcohol ethoxy compound (OA). It is found that adding nonionic surfactant into phosphating solution can significantly reduce the film weight and matrix dissolution, because nonionic surfactant is adsorbed on the surface of the test plate.
T.S.N.T.S.N. Sankara narayanan and M. Subaiyan studied the function of organic amine in phosphating and the properties of phosphating film. They use clean fatty amines, such as dodecylamine, tetradecylamine, hexadecylamine and octadecylamine. However, in acidic medium, the coexistence of amines, especially primary amines, with HN02 is problematic, because nitrosamine compounds with carcinogenic effects are easily generated. Adding phosphating solution to clean amine does not affect pH value, total acidity, free acidity and acid ratio, and the concentration is10 ~125mg/L. At low concentration, the weight of phosphating film decreases greatly, and with the increase of concentration, the film weight rises. Although these amines can reduce the weight of the membrane, they can improve the quality and protection of the membrane in some ways. In this series of amines (C 12 ~ C 18), the membrane weight increases with the increase of alkyl chains in amine molecules. Because in acidic medium (pH 2.7 1), amine exists in the form of spreading cation (RNH3+). This cation is adsorbed on the template, which increases the hydrogen potential, not only reduces the surface area of the membrane (cathode surface), but also reduces the dissolution of metal. Comparing the weight of phosphating film obtained from phosphating solution containing this series of amine additives, it can be seen that the phosphating solution containing dodecylamine is the lightest and the phosphating solution containing octadecylamine is the heaviest. Because dodecylamine has the smallest depolarization performance, its existence prevents the maximum charge transfer in the process of metal dissolution. The concentration of various amine additives has the same effect on the membrane weight. At first, it rises to the maximum with the increase of concentration, and then decreases with the increase of concentration. This trend can be explained by the surface activity of amines. At low concentration, these amines exist in the form of cationic monomers, which are adsorbed on the interface of steel magnetized liquid by electrostatic force, and the film formation is inhibited due to the barrier effect of this adsorption. When the concentration of amine increases to a certain value, the membrane weight increases, which may be due to the association of micellization. However, when the amine concentration continues to increase beyond a certain value (each additive is different), the increase of membrane weight decreases, which is due to the polymerization of amine molecules into micelles. Due to adsorption, a large number of micelles exist on the surface of steel, resulting in a larger area coverage, thus reducing the weight of the membrane.
In addition, the addition of clean amine can also reduce the water absorption of the membrane, which may be due to the hydrophobicity of hydrophobic amine chain. The decreasing order of water absorption is from dodecylamine to octadecylamine, which clearly shows that more monomers are adsorbed in the presence of dodecylamine. Although the weight of the membrane is reduced, it gives higher hydrophobicity.
Guo Liangsheng developed a zinc phosphating solution (SL-6A) at room temperature. Adding a small amount of 0P emulsifier into phosphating solution can accelerate the phosphating process and improve the phosphating effect. The formula of SL-6A phosphating solution is as follows.
Assembly parts
Potassium dihydrogen phosphate 57.87g/L copper nitrate 0 0. 10/0g/L.
Nan 02 0.60 g/L OP emulsifier 0. 1.25ml/L
Sodium fluoride 3.50g/L water balance
Zeng et al. reported zinc-manganese series color film phosphating solution and zinc-calcium series gray film phosphating solution using composite accelerators. Accelerator A is made of EDTA, nitrogen-containing organic matter, ferrous sulfate, copper nitrate and water according to a certain proportion and process; Accelerator 8 is prepared from sodium oxalate, sodium dodecyl sulfonate, saturant T and water according to a certain proportion and process. The best formula of phosphating solution is as follows.
① Formula of phosphating solution for zinc-manganese series color film
Composition (mass fraction) Composition (mass fraction)
Phosphoric acid (85%) 1.60 potassium sodium tartrate 0.05
Nitric acid (99%) 1.20 accelerator A0.50
Zinc oxide (99%) 0.50 accelerator B0.30
Manganese oxide (9596) 0.30 and water 95.55.
② The best formula of zinc-calcium ash film phosphating solution.
Composition (mass fraction) Composition (mass fraction)
Phosphoric acid (85%) 1.20 sodium pyrophosphate (98%) 0.20
Zinc nitrate (95%) 0.50 accelerator A0.50
Calcium dihydrogen phosphate (95%) 0.30 accelerator B0.80
Tartaric acid (99%) 0. 10 water 96.20
HEDP(98%) 0.20
Wherein the accelerator A is made of potassium chlorate, sodium tungstate, sodium carbonate and water according to a certain proportion and process; Accelerator B is prepared from diethanolamine, TX- 10 nonionic surfactant, colloidal titanium and water according to a certain proportion and process.
Liang et al. have developed a multifunctional phosphating solution for zinc basement membrane at room temperature, which is dark gray in color and can remove oil, rust and phosphating in one step. The results of copper sulfate drop test, immersion test and electrochemical test show that the phosphating film has good corrosion resistance. The multifunctional phosphating solution can be phosphatized at room temperature, and the phosphating method can be applied, which solves the problem that some large workpieces cannot be soaked in the tank for phosphating. The best phosphating solution formula is as follows.
Composition (mass fraction) Composition (mass fraction)
Zinc oxide 4.8 sodium tartrate 0.24
Phosphoric acid (85%) 20.3b additive 1.68
Accelerator 5.3 water 67.3
Sodium dodecyl sulfonate 0. 14 pH 1. 12
Thiourea 0.24
Wang Desong of Hebei University of Science and Technology and others studied the effects of three surfactants, alkyl alcohol amide, fatty alcohol polyoxyethylene ether (AEO), sodium dodecyl sulfate and a cationic polymer, on the phosphating effect of zinc-based phosphating solution at room temperature. It is found that when the dosage of cationic polymer is fixed at 0.03 g/L, adding a proper amount of surfactant to the phosphating solution can obviously improve the phosphating effect. Because the stability of alkyl alcohol amide in acidic environment is poor, it will precipitate when the dosage is 0. 1g/L, so it is not suitable for use in this zinc phosphating solution. The effect of fatty alcohol polyoxyethylene ether on phosphating solution is obviously better than that of sodium dodecyl sulfonate, and the phosphating effect of phosphating solution is further improved with the increase of the dosage of fatty alcohol polyoxyethylene ether. The application research of cationic polymer shows that the phosphating effect is better when the dosage of cationic polymer is 0.03 g/L (the surfactant used is fatty alcohol polyoxyethylene ether, the dosage is 0.2 g/L). The formula of zinc phosphating solution is as follows.
Assembly parts
Zinc dihydrogen phosphate 30g/L composite accelerator 2 ~ 5g/L.
85% phosphoric acid 1 0g/l nickel nitrate1g/l
Sodium phosphate 5g/L surfactant 0. 1-0.3g/L
Citric acid 5g/L cationic polymer 0.0 1 ~ 0.05g/L
3 ~ 5g/l sodium nitrate
A small amount of nonionic surfactant 0P- 10 was added to the AC- 1 room temperature zinc phosphating solution developed by Sun Qingchi of Petroleum University, which was mainly used for wetting and infiltration, dispersion and solubilization, and improving surface cleanliness. Hydrophilic and hydrophobic groups in OP- 10 molecules are aligned and adsorbed on the solution/metal interface, forming a thin molecular film, thus reducing the surface tension of the substrate and making the H+ on the metal surface evenly distributed. Once H+ is reduced to H2, it can easily escape from the metal surface, thus avoiding the retention of H2 and accelerating phosphating. In addition, 0P- 10 can also reduce the porosity and water absorption of the film, promote the formation of a hard and dense phosphating film on the metal surface, and obviously improve the uniformity and water resistance of the film. AC- 1 phosphating solution has good stability, less sediment, uniform, dense and smooth film, strong corrosion resistance and no ash hanging. The service life is about 1.6 times that of ordinary phosphating solution. The basic formula of phosphating solution is as follows.
Composition (mass fraction) Composition (mass fraction)
0.2-0.8 of phosphoric acid and 0.1-0.2 of organic matter.
Sodium dihydrogen phosphate 1.5 ~ 3.0 organic B0.1~ o.2.
Sodium tungstate 0.20p- 10 0.02
Zinc nitrate 1.o ~ 3.5 tap water balance
Sodium nitrite 0.02-0. 10
(3) Phosphating of lead salt In l970, John W.F put forward the phosphating process of lead salt. The phosphating solution consists of nitric acid, phosphoric acid, lead oxide, sodium chloride and isooctyl phenyl polyoxyethylene. The preparation method of phosphating solution is as follows: 2 19 parts of industrial nitric acid (70%) and 26.4 parts of industrial phosphoric acid (85%) are added to 640 parts of water, and 80.4 parts of lead oxide is added to the above mixed solution with constant stirring. After the lead oxide is completely dissolved, add 1.5 parts of sodium chloride and 1 part of isooctyl phenyl polyethoxy. The phosphating bath solution was prepared by diluting the above solution with 1425 parts of water. The total acid value is 1 10. The phosphating solution can be used for phosphating steel products, galvanized steel products and lead products. The obtained phosphating film is uniform, weldable, can improve the cold drawing performance of metals, has good corrosion resistance, and is an excellent organic coating bottom layer.
Adding surfactant into phosphating solution can improve the film-forming effect of phosphating solution. In addition, it also plays a dispersing role and helps to keep the components in solution. The most effective surfactants are ethylene oxide polycondensates, especially those containing 3-25 ethoxy groups (one CH2- one CH2O), such as polyoxyethylene esters of oleic acid and polyoxyethylene ethers of alkyl phenols. Isooctyl phenyl polyoxyethylene in lead salt phosphating solution is a nonionic surfactant.