WO2022033192A1

WO2022033192A1 - Method for preparing metal surface chemical conversion film

Info

Publication number: WO2022033192A1
Application number: PCT/CN2021/102114
Authority: WO
Inventors: 仝晓强
Original assignee: 中国民航大学
Priority date: 2020-08-10
Filing date: 2021-06-24
Publication date: 2022-02-17
Also published as: CN113186527A

Abstract

Disclosed is a more economical and environmentally-friendly method for preparing a metal surface chemical conversion film, belonging to the technical field of metal anticorrosive coatings. In the present invention, an aluminum alloy is mainly used as a matrix to prepare a zeolite membrane by means of a solid-phase method and a steam-assisted method. In the preparation process of the solid-phase method, a seed crystal is coated onto the metal surface by means of an electrostatic spraying technology to finally realize the successful preparation of the zeolite membrane in raw material dry powder. In the preparation process of the steam-assisted method, a dry gel is also coated onto the metal surface by means of an electrostatic spraying technology to finally realize the conversion of the zeolite membrane in steam. The solid-phase method and the steam-assisted method involved in the present invention can effectively avoid the problems of solution validity period and waste liquid treatment involved in the traditional preparation method of a chemical conversion film such as dipping and spraying. In the present invention, an electrostatic spraying technology is used for coating a solid raw material onto the metal surface for reaction, such that the film-forming efficiency is high, and the film layer is denser. The popularization of the present invention has good social, environmental and economical benefits.

Description

A kind of preparation method of metal surface chemical conversion film

technical field

The invention belongs to the technical field of preparation of protective or functional coatings such as corrosion resistance, decoration and wear resistance of metal surfaces, and in particular relates to a coating preparation method.

Background technique

The corrosion protection of metals and alloys has always been a topic of concern to the industry. The preparation of chemical conversion coatings on metal surfaces is an important means of corrosion protection for metals and alloys. From the most commonly used chromate conversion film in the past, to the widely used phosphate film, to the newly developed silanized film, zirconium salt, stannate, molybdate, cobaltate and organic phytic acid, mono There are many types of anti-corrosion conversion coatings, such as chromium-free and phosphorus-free films such as nitric acid and zeolite conversion coatings. Various conversion coatings based on the reaction of metal substrates and chemical reagents have their own characteristics.

At present, the preparation methods of chemical conversion coatings are mainly based on dipping and spraying. This method has the following disadvantages: First, not all materials are suitable for chemical conversion in solution (such as: metals or alloys that are sensitive to aqueous solutions, and structural Secondly, during the formation of the chemical conversion film, the metal is easily dissolved in the immersion liquid and the spray liquid, resulting in "potion" pollution, which will greatly shorten the validity period of the potion and increase the preparation cost; The process in which the solution is the main reaction medium has the difficult problem of waste liquid treatment. In recent years, some patents have also mentioned the use of steam-assisted methods to realize and promote the formation of chemical conversion coatings, but there is still no basic process of chemical dipping or spraying. For example, in patent CN 101849031 B, it is mentioned that the final composite film is obtained by immersing in a phosphating solution and then treating it in steam containing ammonium dihydrogen phosphate; CN 201010565125 mentions that the use of steam containing phosphoric acid is used to perform surface treatment on metals and finally A phosphating film is obtained on the steel surface; CN 108165968A mentions that the alloy is pretreated with water vapor containing sodium hydroxide to solve the problem of uneven coating caused by the phenomenon of "liquid flow".

Metal-based zeolite conversion film is a new type of environmentally friendly anti-corrosion film, and its anti-corrosion performance has been confirmed by many papers and patents (Electrochem.Solid ST.2001,4,B23-26; CN103818089 A; CN201610021241). Zeolite membrane is an environmentally friendly and high-performance corrosion-resistant coating, and its conventional preparation method is hydrothermal method. The implementation of this method requires the reaction raw material solution to be carried out in a high temperature and high pressure reaction kettle. On the one hand, the cost is high, the safety is poor, and the film forming stability is poor; secondly, the size of the product is limited by the space of the reaction kettle. All these restrict the wide application of anti-corrosion zeolite membranes. The vapor phase method proposed by Xu Wenyang and Dong Jinxiang of Taiyuan University of Technology in 1992 and the solid phase synthesis method proposed by Xiao Fengshou et al. of Zhejiang University in recent years pointed out the direction for the development of low-cost pollution-free zeolite membrane preparation routes (CN1051334A, CN201210118788). At present, the reports on the preparation of anti-corrosion zeolite membranes by steam-assisted method or solid-phase method at home and abroad mainly include two categories: one is to first coat seed crystals and then use solid-phase method to prepare anti-corrosion zeolite membranes in dry powder raw materials (Lu Xiaofei). , Zhejiang University Doctoral Dissertation, 2019, 132-145); the other is to first coat the metal surface with zeolite gel by dip coating technology, and then prepare the zeolite membrane in steam (Thin Solid Films. 2013, 529, 327-332) . The disadvantage of these methods is that the seed coating process of the former is cumbersome, and it needs to be immersed in a polymer solvent to increase the effective coating area of the seed; It is unstable, and the gel layer on the metal surface obtained by the dip coating method is prone to cracks, and it is very easy to cause macroscopic cracks in the final zeolite membrane, which are not conducive to the industrial scale-up of the preparation process.

Electrostatic spraying is a method of using the principle of corona discharge to charge tiny particles of paint and adsorb them on the surface of conductive workpieces. At present, it has been widely used in various coating processes. The coating obtained by electrostatic spraying is uniform and dense, which is suitable for the coating of workpieces of various shapes and can fully meet the needs of the industry. In view of the current situation of metal-based chemical conversion coating preparation, this patent intends to introduce the very mature electrostatic spraying technology in the industry into the solid-phase method and the steam-assisted crystallization method. Develop more environmentally friendly and economical electrostatic spraying-steam-assisted crystallization technology and electrostatic spraying-solid phase crystallization technology to realize the preparation of zeolite membranes and even phosphating membranes and other chemical conversion membranes. Finally, the disadvantages of various conversion film preparation technologies mentioned above are effectively overcome.

SUMMARY OF THE INVENTION

The purpose of the present invention is to take the preparation of metal surface zeolite membrane as a typical example, and to propose a more economical and environmentally friendly preparation technology of chemical conversion membrane that can be promoted. Compared with the widely used dipping and spraying technology, the vapor phase/solid phase preparation method proposed in the present invention can obtain the metal anti-corrosion coating without contacting the substrate with the solution and without generating waste liquid, thereby being more environmentally friendly and economical. .

Specifically, in terms of metal-based zeolite conversion membranes, compared with the currently reported method for preparing a zeolite membrane in a solid phase after using polyethyleneimine (Polyethyleimine, PEI) to "graft" the surface of an aluminum alloy to prepare a seed layer, the present invention uses The electrostatic spraying method realizes the coating of the crystal seed on the metal, the process is simpler and the efficiency is higher; compared with the currently reported method of first dipping and then preparing the zeolite membrane in steam, the electrostatic spraying method is used in the present invention to replace the dipping method. The coating method can effectively avoid the cracks that occur when the gel layer is prepared by the dip coating method, thereby increasing the compactness of the final zeolite membrane.

The specific technical scheme of the present invention can be divided into two parts: solid-phase method and steam-assisted method, and the details are as follows: (electrostatic spraying-solid-phase method):

Step 1: Alloy or Metal Pretreatment

Immerse the selected alloy substrate in a beaker containing petroleum ether or cetyl trimethyl ammonium bromide, and sonicate for 5 to 10 minutes in an ultrasonic cleaner for degreasing. This process can also be replaced by steam degreasing. . After cleaning with deionized water, the aluminum alloy is soaked in 30 _% H2O2 for _30-60 minutes, or treated in steam for 5-10 minutes. Rinse with deionized water after taking it out, and finally put it in an oven at 60°C and dry it for 1 to 2 hours.

Step 2: Preparation of raw dry powder

In the preparation process of dry powder, the molar ratio reported in the literature (Lu Xiaofei, Zhejiang University doctoral dissertation, 2019, 132-145) was used to weigh the raw materials: sodium silicate nonahydrate: 0.58 tetrapropylammonium bromide: 1.19 silicon dioxide: 1.82 Ammonium chloride. The above raw materials are thoroughly mixed and milled to obtain dry powder.

Step 3: Preparation of Seed Crystals

The purchased seed crystals were ball-milled to obtain seed crystal powder. Seeds for this step can also be prepared using a reported formulation (Journal of American Chemical Society. 2000, 122, 3530).

Step 4: Coating Seeds

Put the metal substrate after step 1 into the spray booth, and use the seed crystal prepared in step 3 for electrostatic spraying. The spraying voltage is 50-70KV and the current is 80μA.

Step 5: Preparation of Zeolite Membrane by Solid Phase Method

Put the seeded substrate obtained in step 4 into an airtight container, and at the same time add the dry powder prepared in step 2 and bury the substrate, and keep the temperature at 170° C. for 15-24 hours.

The above-mentioned purchased seed crystal has a silicon-alumina ratio of 100, which is a sodium-type MFI zeolite.

The above-mentioned seed crystal spray thickness is about 20 microns.

(Electrostatic spraying-steam-assisted method):

Step 1: Alloy or Metal Pretreatment

Immerse the selected alloy substrate in a beaker containing petroleum ether or cetyl trimethyl ammonium bromide, and sonicate in an ultrasonic cleaner for 5 to 10 minutes for degreasing. This process can also be carried out using steam degreasing. alternative. After cleaning with deionized water, the aluminum alloy was soaked in 30 _% H2O2 for _30-60 minutes, or treated in steam for 5-10 minutes. Rinse with deionized water after taking it out, and finally put it in an oven at 60°C and dry it for 1 to 2 hours.

Step 2: Preparation of Xerogel Powder

A certain amount of white carbon black, tetrapropylammonium bromide, sodium hydroxide and distilled water are mixed and stirred evenly. Keep the molar ratio as: 0.25 tetrapropylammonium bromide: silicon dioxide: 0.1 sodium hydroxide: 28 water. After aging for 2 hours, water was evaporated to dryness to obtain a xerogel, and the obtained xerogel was ball-milled to finally obtain a xerogel powder.

Step 3: Apply the Xerogel Layer

Put the metal substrate after step 1 into the spray booth, and use the dry gel powder prepared in step 3 for electrostatic spraying with a spraying voltage of 50-70 kV and a current of 80 μA.

Step 4: Preparation of Zeolite Membrane by Steam-Assisted Method

Finally, the metal sprayed with dry gel powder was put into steam at 180°C for 24 hours, and the zeolite membrane was obtained after cleaning.

The above-mentioned dry gel powder coating thickness is in the range of 50-800 μm.

The above-mentioned metals or alloys can be extended from aluminum alloys and magnesium alloys to other types of metals.

The above-mentioned steam source can be obtained by using vaporized water in a closed reactor or by using a steam generator.

The corresponding solid-phase method or steam-assisted method in the preparation process of the above-mentioned zeolite conversion membrane can be fully extended to the production process of various chemical conversion membranes such as phosphating and zirconium salting, and only needs to modify the specific formula.

The formulation of the above-mentioned zeolite membrane preparation can be fine-tuned according to specific needs.

Description of drawings

Figures 1 and 2 show the XRD patterns of the zeolite coatings obtained in Examples 1 and 2.

Figures 3 and 4 show the SEM pictures of the zeolite coatings obtained in Example 1 and Example 2

detailed description

In the following examples, aluminum alloys with specifications of 40mm×20mm×1mm are used, and the aluminum alloy model is 1060, and the reactors are all stainless steel reaction kettles lined with 150ml polytetrafluoroethylene.

Example 1

(1) At room temperature, the aluminum sheet was soaked in a solution of cetyltrimethylammonium bromide (surfactant) with a mass fraction of 0.05% for 5 minutes to remove the oil and dirt on the surface of the aluminum sheet. After washing with ionized water, it was soaked in a 30% H ₂ O ₂ solution for 50 minutes, and the aluminum sheet was taken out and washed with deionized water, placed in an oven at 60°C, and dried for 2 hours.

(2) Dissolve 10.6 g of tetrapropyl ammonium bromide and 3.2 g of sodium hydroxide in 290 ml of water, add 132 ml of 40% silica sol, stir evenly, air dry, and finally in a ball mill at 600 rpm The speed ball milled for 2 hours and set aside.

(3) The aluminum alloy sheet is connected to the positive electrode, the spray gun is the cathode, the air pressure is adjusted to 0.2-0.4 MPa, and the dry gel powder after ball milling is used as the spray coating for spraying, and the spray thickness is about 200 μm.

(4) put the aluminum sheet after spraying into the reaction kettle, inject 5 ml of water at the bottom of the reaction kettle and separate it from the metal sheet, put the lid and seal on the reaction kettle and place it in a constant temperature oven with a preset temperature of 170 ° C to crystallize 20 Hour. After crystallization, the aluminum sheet was taken out, washed with deionized water, and air-dried.

Example 2

(2) Weigh 10.0 grams of sodium MFI seed crystal powder with a silicon-to-aluminum ratio of 100, add it to the ball milling jar of a planetary ball mill, and then ball-mill at 400 rpm for 1 hour. Take out for use.

(3) 28.4 grams of sodium silicate nonahydrate, 7.1 grams of white carbon black, 15.4 grams of tetrapropylammonium bromide and 9.8 grams of ammonium chloride were weighed and mixed, and were milled in a ball mill for 0.5 hours and then taken out for use.

(4) The aluminum alloy sheet is connected to the positive electrode, the spray gun is the cathode, the air pressure is adjusted to 0.2-0.4MPa, and the seed powder after ball milling is used as the spray coating for spraying, and the spray thickness is about 20 μm.

(5) Put the aluminum alloy sheet coated with crystal seeds into the reaction kettle, pour the dry powder prepared in step 3 into the buried aluminum sheet, and react at 180° C. for 20 hours. After crystallization, the aluminum sheet was taken out, washed with deionized water, and air-dried.

Claims

The electrostatic spraying-solid phase method in the method includes the following steps: (1) metal pretreatment, (2) preparing dry powder of raw materials required for the solid phase method, (3) preparing MFI seeds, (4) coating the seeds, (5) Preparation of MFI zeolite coating by solid phase method.
The electrostatic spraying-steam-assisted method in the method includes the following steps: (1) metal pretreatment, (2) preparing xerogel powder (3) coating xerogel powder, (4) preparing MFI zeolite by steam-assisted method coating.
The process according to claim 1 and claim 2 is characterized in that electrostatic spraying is combined with solid-phase method or electrostatic spraying and steam-assisted method are combined, and the seed crystal or xerogel layer is coated by electrostatic spraying to avoid solution immersion or Disadvantages of spraying to prepare chemical conversion coatings.
The electrostatic spraying technology mentioned in claim 3 is characterized in that the coating used for spraying is not a traditional coating coating, but a raw material powder used for the next solid phase or vapor phase reaction.
The electrostatic spraying technology mentioned in claim 3, characterized in that the powder coating is obtained by ball milling.
The seed crystal or xerogel powder according to claim 1 and claim 2, characterized in that the particle size is below 100 μm.
The raw material dry powder mentioned in the right 1 is characterized in that the raw material used and the molar proportioning range are as follows: sodium silicate nonahydrate: (0.3～0.8) tetrapropyl ammonium bromide: (0.8～1.3) silicon dioxide: (1.4～2.2) Ammonium chloride.
As the dry gel powder mentioned in the right 2, it is characterized in that the raw material used and the molar proportioning range are as follows: (0.2～0.5) tetrapropylammonium bromide: silicon dioxide: (0.05～0.3) sodium hydroxide: ( 10～10000) water.
As mentioned in the right 1 and the right 2, the crystallization temperature and the crystallization time range are as follows:

Time: 15～48 hours; Temperature: Time: 170～190℃.