CN113372813B

CN113372813B - Preparation method of montmorillonite/sol-gel composite coating

Info

Publication number: CN113372813B
Application number: CN202110536558.1A
Authority: CN
Inventors: 张俊喜; 刘煊煊; 高燕; 王启伟; 杜卓玲
Original assignee: Shanghai Electric Power University
Current assignee: Shanghai Electric Power University
Priority date: 2021-05-17
Filing date: 2021-05-17
Publication date: 2022-08-23
Anticipated expiration: 2041-05-17
Also published as: CN113372813A

Abstract

The invention relates to a preparation method of a montmorillonite/sol-gel composite coating, which comprises the following steps: (1) chemically modifying montmorillonite by adopting CC, CTAB or APTES to obtain modified montmorillonite; (2) uniformly mixing GPTMS, tetraethoxysilane, deionized water and absolute ethyl alcohol, adding glacial acetic acid serving as a catalyst, and fully hydrolyzing to obtain organic-inorganic hybrid silica sol; (3) dispersing modified montmorillonite in absolute ethyl alcohol to obtain a dispersion liquid, dropwise adding the dispersion liquid into organic-inorganic hybrid silica sol, and aging to obtain a montmorillonite/sol-gel composite system; (4) and putting the coating object into a montmorillonite/sol-gel composite system, heating in a water bath, taking out and drying to prepare the montmorillonite/sol-gel composite coating on the coating object. The invention can solve the problem of poor compatibility of montmorillonite and an organic-inorganic hybrid silica sol system, and the prepared composite coating can form more durable protection on the magnesium alloy substrate.

Description

Preparation method of montmorillonite/sol-gel composite coating

Technical Field

The invention belongs to the technical field of metal surface anticorrosive coatings, and relates to a preparation method of a montmorillonite/sol-gel composite coating.

Background

The silica sol-gel coating can form silica sol by hydrolyzing and condensing a silane precursor under certain conditions, and then dehydrate and polymerize the silane precursor on the metal surface by changing the conditions to form a film, and belongs to a hybrid high-molecular polymer coating. The preparation method has the advantages of mild and controllable reaction conditions, uniform components, easy doping, good bonding force with a metal substrate and the like, so that the preparation method is widely concerned by researchers in the field. However, the sol-gel coating is often modified because the film is easily cracked due to volume shrinkage caused by solvent volatilization in the film forming process, the difference between the thermal expansion coefficients of the metal substrate and the coating, and the like, and a thick complete film is difficult to form, so that sufficient protection cannot be provided for the substrate.

Montmorillonite is a valuable polymer coating reinforcing nano material due to the unique properties of high specific surface area, high heat conductivity, high mechanical property and the like. In addition, the two-dimensional montmorillonite nanosheets have a good barrier effect on oxygen, water and various aggressive ions. Thus, the addition of such nanofillers to polymer coatings enables effective protection of metal substrates. However, montmorillonite nanoplatelets have low compatibility with most non-polar solvents and polymers, and thus montmorillonite needs to be modified to better perform its function as a filler.

The preparation of high performance polymer/montmorillonite composites (PLS) by adding montmorillonite (or other layered silicate) to a polymer matrix often requires solving two key problems: firstly, how to make the distribution of montmorillonite in polymer present a highly random peeling state; secondly, how to establish a strong bonding (or connection) between the polymer matrix and the nano-montmorillonite layer. The intercalation method is an effective method for stripping two-dimensional materials, and the proper intercalation agent is selected to effectively strip layered materials and also can be used as a 'chemical anchor' between a polymer matrix and two-dimensional fillers. The nano montmorillonite sheet layer treated by the intercalating agent with the two characteristics is dispersed in the silica sol-gel coating, so that Cl can be effectively prolonged ^- Diffusion channels for plasma aggressive ions; on the other hand, due to the nano-size effect, defects caused by internal stress during volume shrinkage can be effectively reduced, thereby improving the corrosion resistance of the coating. More importantly, the two-dimensional montmorillonite nano-plate can be used as a template to guide the assembly process of silica sol particles to a certain extent, thereby obtaining a coating with a more compact structure and better protection performance.

In the prior art, the research on the aspect of constructing the strong bonding between the filler and the matrix in the preparation process of the composite coating is not much. Therefore, aiming at the problems of the silica sol-gel coating and the montmorillonite, the preparation method of the montmorillonite/sol-gel composite coating is provided to solve the problems in the prior art.

Disclosure of Invention

The invention aims to provide a preparation method of a montmorillonite/sol-gel composite coating, which aims to improve the protection effect on coating objects such as magnesium alloy and the like and form more durable protection and the like.

The purpose of the invention can be realized by the following technical scheme:

a preparation method of a montmorillonite/sol-gel composite coating comprises the following steps:

(1) chemically modifying montmorillonite with Choline Chloride (CC), Cetyl Trimethyl Ammonium Bromide (CTAB) or 3-aminopropyl triethoxysilane (APTES) to obtain modified montmorillonite;

(2) uniformly mixing 3-glycidyl ether oxypropyltrimethoxysilane (GPTMS), Tetraethoxysilane (TEOS), deionized water and absolute ethyl alcohol (EtOH), adding glacial acetic acid (HAc) as a catalyst, and fully hydrolyzing to obtain organic-inorganic hybrid silica sol;

(3) dispersing modified montmorillonite in absolute ethyl alcohol to obtain a dispersion liquid, dropwise adding the dispersion liquid into organic-inorganic hybrid silica sol, and aging to obtain a montmorillonite/sol-gel composite system;

(4) and putting the coating object into a montmorillonite/sol-gel composite system, heating in a water bath, taking out and drying to prepare the montmorillonite/sol-gel composite coating on the coating object.

Further, in the step (1), the total cation exchange amount of the montmorillonite used is 110mmol/100 g.

Further, in the step (1), the modification process of the montmorillonite by using choline chloride and hexadecyl trimethyl ammonium bromide specifically comprises the following steps:

(A) adding water into montmorillonite to prepare slurry, performing ball milling treatment, adding water for dilution, and treating in a shearing machine to obtain a mixed solution;

(B) and (3) placing the mixed solution in a water-bath heating and stirring system, adding choline chloride or hexadecyl trimethyl ammonium bromide which is twice of the total amount of montmorillonite cation exchange, heating in a water bath, washing and drying the obtained reaction product to obtain modified montmorillonite, and marking the modified montmorillonite as CC-MMT or CTA-MMT respectively.

In addition, in the modification process herein, about 300ml of deionized water was added per 10g of montmorillonite to prepare a dispersion.

Furthermore, in the step (A), the rotation speed of the ball milling treatment is 200-300rpm for 4-8h, and the rotation speed of the treatment in the shearing machine is 4000-6000rpm for 1-3 h.

Furthermore, in the step (B), the temperature of the water bath heating is 60-90 ℃ and the time is 8-10 h.

Further, in the step (1), the process of modifying montmorillonite by using 3-aminopropyltriethoxysilane specifically comprises:

and dispersing montmorillonite in cyclohexane, dropwise adding 3-aminopropyltriethoxysilane accounting for the total cation exchange amount of the montmorillonite while stirring, and stirring at room temperature to react to obtain modified montmorillonite, which is marked as AP-MMT.

Further, in the step (2), the molar ratio of the 3-glycidoxypropyltrimethoxysilane to the tetraethoxysilane to the absolute ethyl alcohol to the deionized water is x (4-x) to 40:16, wherein x is more than 0 and less than 4. Here, the amount of glacial acetic acid added may be small, for example 8.86g GPTMS may correspond to one drop of HAc. Preferably, 8.86g of GPTMS, 2.6g of TEOS and 23g of EtOH are added dropwise with 1 drop of HAc, mixed thoroughly by magnetic stirring at room temperature for 10min, and 3.6 g of deionized water (molar ratio GPTMS: TEOS: EtOH: H) are added dropwise with stirring ₂ O is 3:1:40:16), sealing with a preservative film, pre-hydrolyzing at room temperature for 30min, and then continuously stirring at 50 ℃ for 3h to obtain pure hybrid silica sol (namely organic-inorganic hybrid silica sol).

Further, in the step (2), the process of sufficient hydrolysis specifically comprises: pre-hydrolyzing at room temperature for 20-40min, and stirring at 40-60 deg.C for hydrolysis for 2-4 hr.

Further, in the step (3), the adding amount of the modified montmorillonite meets the following requirements: the mass ratio of the modified montmorillonite in the composite coating which is finally solidified into a film is 0.5-20%.

Further, in the step (3), the aging process conditions specifically include: stirring was continued at room temperature for 24 h.

Further, in the step (4), the coating object is magnesium alloy, and pretreatment such as polishing and cleaning can be performed before coating.

Further, in the step (4), the temperature of the water bath heating is 40-60 ℃, optionally 50 ℃, and the time is 0.5-2h, optionally 1 h.

Further, in the step (4), the temperature used in the drying process is 90-150 ℃, optionally 120 ℃, and the time is 1-3 hours, optionally 2 hours.

According to the invention, CC and CTAB belong to quaternary ammonium salts, and can be completely ionized in water to generate quaternary ammonium-based particles and halide ions, wherein the positively charged quaternary ammonium-based ions can easily replace sodium ions among montmorillonite layers and are combined with negatively charged montmorillonite layers, so that the montmorillonite layers are modified to obtain modified montmorillonite with different properties, for example, the CC is used for modifying the montmorillonite to introduce alcoholic hydroxyl groups with certain activity among the montmorillonite layers, and the CTAB is used for modifying the montmorillonite to introduce long-chain alkyl among the montmorillonite layers; APTES is a silane coupling agent, which can be grafted to montmorillonite through dealcoholization reaction with silicon hydroxyl at the edge of the montmorillonite layer, so as to introduce active amino into the montmorillonite layer.

Precursors GPTMS and TEOS used in the preparation process of the silica sol can perform hydrolysis reaction under the acid catalysis condition, generate condensation to a certain degree, and form silica sol particles after aging. GPTMS is used as an organic component in the precursor, so that the surface of the prepared silica sol particle is provided with related groups such as an epoxy group and the like which can react with the prepared modified montmorillonite, and meanwhile, the conditions such as cracking and the like generated in the film forming process of pure inorganic components can be avoided, and the formation of a complete film layer is facilitated; TEOS as an inorganic component in the precursor can effectively enhance the stability of the subsequent film. The temperature and time affect the thickness of the film formed during the process of inserting the metal to be coated into the coating liquid water bath for heating. The temperature used in the subsequent drying process has great influence on the quality of the film layer, and when the temperature is lower, the drying time is longer; when the temperature is too high, the film layer may crack due to the difference between the thermal expansion coefficients of the film layer and the metal substrate.

Meanwhile, since the bonding between the sol-gel coating and the substrate mainly depends on the Si-O-Me bonding relationship (Me is a metal substrate), the composite coating of the present invention can be applied to metals including but not limited to magnesium alloys, such as aluminum, iron, etc., according to the related documents and related experiments.

Compared with the prior art, the preparation method is simple and feasible, the required equipment is simple, and the prepared composite coating has more durable protective capability compared with a pure sol-gel coating.

Drawings

FIG. 1 is a schematic diagram of the action mechanism of CC-MMT on the coating in example 1;

FIG. 2 is a plot of the polarization of different samples from example 1;

FIG. 3 is the surface topography of various coated samples of example 1 after 7 days of immersion;

FIG. 4 is a plot of polarization for different samples from example 2;

FIG. 5 is a diagram showing the evolution of the electrochemical impedance spectrum and a related equivalent circuit for analysis in example 2, wherein the evolution of the electrochemical impedance spectrum is within 15 days after different samples are soaked;

FIG. 6 is the surface topography of the various coated samples of example 2 after 15 days of immersion;

FIG. 7 shows the dispersion stability of the sol system in comparative example 1, in which unmodified and CC-modified montmorillonites were added, respectively.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

In the following examples, montmorillonite (sodium-based, cation exchange amount 110mmol/100g) was purchased from Hubei Sanding science and technology Co., Ltd, CC (AR), CTAB (AR) and absolute ethyl alcohol (CP) were purchased from Shanghai pharmaceutical group chemical Co., Ltd, APTES (98%) was purchased from Shanghai Tatan chemical Co., Ltd, GPTMS (97%) and TEOS (99%) were purchased from Shanghai Mielin Biotechnology Co., Ltd.

Otherwise, unless otherwise specified, all the conventional commercial raw materials or conventional processing techniques are used in the art.

Example 1

(1) Carrying out intercalation modification on montmorillonite: the CC and CTAB modification method comprises the following steps: adding 100ml of deionized water into 10g of original montmorillonite to prepare slurry, and treating for 6 hours in a ball mill at 250 rpm; adding water to dilute to a certain degree, and treating for 2 hours at 5000rpm in a shearing machine; and (3) placing the mixed solution in a water bath heating and stirring system, adding an intercalating agent (CC or CTAB) which is twice of the total amount of montmorillonite cation exchange, and treating for 8 hours at 80 ℃. And repeatedly centrifuging and washing to remove redundant intercalators and impurity ions, dispersing a finally washed sample into a small amount of absolute ethyl alcohol, drying at 60 ℃, and grinding for later use to obtain modified montmorillonite which is respectively marked as CC-MMT and CTA-MMT.

(2) 8.86g GPTMS, 2.6g TEOS and 23g EtOH are taken, 1 drop HAc is dripped, the mixture is fully mixed by magnetic stirring for 10min at room temperature, and 3.6 g deionized water (the molar ratio is GPTMS: TEOS: EtOH: H) is dripped while stirring ₂ O is 3:1:40:16), sealing by using a preservative film, carrying out prehydrolysis for 30min at room temperature, then setting the temperature to 50 ℃, and continuously stirring for 3h to obtain pure silica sol.

(3) 45mg of CC-MMT and CTA-MMT are respectively taken and respectively dispersed in 5ml of absolute ethyl alcohol by ultrasonic treatment for 10 min.

(4) Dropwise adding the anhydrous ethanol dispersion liquid of montmorillonite into the pure silica sol, stirring for 5h, then carrying out ultrasonic treatment on the whole sol gel system for 1h, and then continuously stirring the mixed liquid for 24 h. And then vertically immersing the magnesium alloy sample into the coating liquid, heating the magnesium alloy sample in a water bath for 1h at the temperature of 50 ℃, and taking out the magnesium alloy sample. After the sample was allowed to stand at room temperature for 12 hours, it was placed in a forced air dryer and treated at 120 ℃ for 2 hours for further use.

As shown in fig. 1, CC-MMT has three roles in the coating: firstly, the nano-scale filler can be used for filling defects generated in the forming process of the sol-gel coating; secondly, the diffusion path of the aggressive medium can be greatly prolonged; finally, strong bonding can be formed between the coating and the sol-gel coating, so that aggressive media are difficult to diffuse through a filler/coating interface, and the coating structure is more compact and stable.

Table 1 shows the polarization curve fitting parameters for different samples in example 1, from left to right for the different samples bare magnesium alloy, pure sol-gel treated samples, CC-MMT added sol-gel treated samples, CTA added sol-gel treated samples.

TABLE 1

As shown in fig. 2 in combination with the fitting parameters of table 1, the corrosion resistance of the coating sample prepared according to the above example 1 and the AZ31B bare magnesium alloy is, from low to high, in order: bare magnesium alloy (-1.4993V,1.4421x 10) ^-5 A·cm ^-2 )<Pure sol-gel coatings (-1.5398V,3.3484x 10) ^-7 A·cm ^-2 )<CTA-MMT/sol-gel composite coating (-1.5062V,9.0643x 10) ^-8 A·cm ^-2 )<CC-MMT/Sol-gel doped coating (-1.4609V,4.3982x 10) ^-8 A·cm ^-2 ) The coating thickness was about 7.5. mu.m. Meanwhile, the protection of the metal substrate was reduced to a very low level after soaking the pure sol-gel coating samples for 3 days, while the CC-MMT/sol-gel coating and CTA-MMT/sol-gel coating samples were soaked for 7 days and 5 days, respectively, before being reduced to the level of the pure sol-gel coating samples.

As shown in fig. 3, after soaking for 7 days, the pure hybrid sol-gel coating without the modified montmorillonite presents a full cracking/peeling appearance, the sol-gel coating with the CC-MMT only has a few electrolyte permeation traces, and the sol-gel coating with the CTA-MMT has a certain degree of cracking.

Example 2

(1) Carrying out graft modification on montmorillonite: 1g of original montmorillonite is dispersed in 50ml of cyclohexane, APTES which is twice of the total amount of montmorillonite cation exchange is added into the mixture while stirring, the mixture is stirred for 5 hours at room temperature to fully perform grafting reaction, and the obtained modified montmorillonite is marked as AP-MMT.

(2) A pure sol was prepared in the same manner as in step (2) of example 1.

(3) An absolute ethanol dispersion of AP-MMT was prepared in the same manner as in step (3) of example 1.

(4) The AP-MMT dispersion is dispersed into pure silica sol in the same step (4) as in example 1, and after stirring is continued for 24h, the temperature is adjusted to 50 ℃ to evaporate a part of the solvent so as to increase the viscosity of the system. And then vertically immersing the magnesium alloy sample into the coating liquid, heating the magnesium alloy sample in a water bath for 1h at the temperature of 50 ℃, and taking out the magnesium alloy sample. The sample is placed at room temperature for 12h and then treated in a forced air drier at 120 ℃ for 2h for further use.

As shown in fig. 4, the corrosion resistance of the coating sample prepared according to the above example and the AZ31B bare magnesium alloy is, from weak to strong, as follows: bare magnesium alloy (-1.4993V,1.4421x 10) ^-5 A·cm ^-2 )<Pure sol-gel coating (-1.496V,1.03X10 ^-7 A·cm ^-2 )<AP-MMT/sol-gel composite coating (-1.482V,6.77x 10) ^-8 A·cm ^-2 ). The coating thickness was about 20 μm.

Table 2 shows the polarization curve fitting parameters for the different samples of example 2, wherein PSG represents the pure sol-gel coating sample, APSG represents the coating sample prepared by adding AP-MMT coating solution, and tables 3 and 4 are the same.

TABLE 2

Table 3 and table 4 show the parameters for electrochemical impedance spectroscopy fitting within 15 days of soaking the different samples in example 2.

TABLE 3

TABLE 4

As shown in fig. 5, when analyzing the electrochemical impedance spectrum of the coating sample prepared in the above example after soaking for 15 days, it can be seen that the equivalent circuit of fig. 5(e) can be used for analyzing the impedance spectrum of the hybrid sol-gel coating sample with AP-MMT added within 15 days of soaking, while the equivalent circuit of fig. 5(f) is used for matching the pure hybrid sol-gel coating without montmorillonite added for 7 days and 15 days of soaking, which shows that the coating structure changes with the increase of soaking time.

As shown in fig. 6, the surface layer of the pure hybrid sol-gel coating (i.e., fig. 6a) was cracked more severely after soaking the coating sample prepared in example 2 above for 15 days, while the hybrid sol-gel coating with AP-MMT added (i.e., fig. 6b) was cracked only a little.

Of the several coatings prepared in example 1, CC-MMT has a good interfacial force with the sol-gel coating and thus a more durable protection than CTA-MMT/sol-gel coating.

In example 2, AP-MMT can also form stronger interface acting force with the sol-gel coating, and compared with a pure sol-gel coating, the AP-MMT has a denser structure, so that the failure damage form in the soaking stage is changed.

Comparative example 1:

compared with the example 1, the method is mostly the same, except that the modification of the montmorillonite is omitted, namely the original montmorillonite is added into the pure silica sol. FIG. 7 shows the dispersion stability of the silica sol system after adding unmodified montmorillonite (a) and CC modified montmorillonite (b) to the silica sol system, dispersing uniformly and standing for 24 h. It can be seen from the figure that most of montmorillonite is settled after the unmodified montmorillonite is dispersed into the silica sol and stands for 24 hours, while the CC modified montmorillonite is not obviously settled, and obviously, the occurrence of a large amount of settlement is not beneficial to the subsequent preparation of a coating with uniform components. Through modifying montmorillonite (including CC and APTES), a group which has certain reaction activity and good compatibility with an organic-inorganic hybrid silica sol system is introduced into a montmorillonite layer, and the dispersion stability of the montmorillonite in the silica sol system can be enhanced, so that a composite coating with excellent performance is prepared.

Example 3:

compared with the example 1, most of the method is the same, except that the hydrolysis process in the step (2) is as follows: prehydrolysis was carried out for 20min at room temperature, followed by hydrolysis with stirring at 60 ℃ for 2 h.

Example 4:

compared with the example 1, the method is mostly the same, except that the hydrolysis process in the step (2) is specifically as follows: prehydrolysis was carried out for 40min at room temperature, followed by hydrolysis with stirring at 40 ℃ for 4 h.

Example 5:

compared with the embodiment 1, the method is mostly the same, except that in the step (4), the temperature of water bath heating is 40 ℃, and the time is 0.5 h; the temperature used in the drying process is 90 ℃ and the time is 3 h.

Example 6:

compared with the embodiment 1, the method is mostly the same, except that in the step (4), the temperature of water bath heating is 60 ℃, and the time is 2 hours; the temperature used in the drying process is 150 ℃ and the time is 1 h.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.

Claims

1. The preparation method of the montmorillonite/sol-gel composite coating is characterized by comprising the following steps:

(1) chemically modifying montmorillonite with 3-aminopropyl triethoxysilane to obtain modified montmorillonite;

(2) uniformly mixing 3-glycidyl ether oxypropyltrimethoxysilane, tetraethoxysilane, deionized water and absolute ethyl alcohol, adding glacial acetic acid serving as a catalyst, and fully hydrolyzing to obtain organic-inorganic hybrid silica sol;

(4) placing the coating object in a montmorillonite/sol-gel composite system, heating in a water bath, taking out and drying to prepare a montmorillonite/sol-gel composite coating on the coating object;

in the step (1), the process of modifying the montmorillonite by using the 3-aminopropyltriethoxysilane is specifically as follows:

dispersing montmorillonite in cyclohexane, adding dropwise 3-aminopropyl triethoxysilane in the total amount of montmorillonite cation exchange while stirring, and stirring at room temperature to react to obtain modified montmorillonite, which is marked as AP-MMT;

in the step (2), the molar ratio of the 3-glycidoxypropyltrimethoxysilane to the tetraethoxysilane to the absolute ethyl alcohol to the deionized water is x (4-x) to 40:16, wherein x is more than 0 and less than 4.

2. The method for preparing the montmorillonite/sol-gel composite coating according to claim 1, wherein in the step (2), the process of sufficient hydrolysis is specifically as follows: pre-hydrolyzing at room temperature for 20-40min, and stirring at 40-60 deg.C for hydrolysis for 2-4 hr.

3. The preparation method of the montmorillonite/sol-gel composite coating according to claim 1, wherein in the step (3), the adding amount of the modified montmorillonite satisfies the following requirements: the mass ratio of the modified montmorillonite in the composite coating which is finally solidified into a film is 0.5-20%.

4. The method for preparing the montmorillonite/sol-gel composite coating according to claim 1, wherein in the step (3), the aging process conditions are as follows: stirring was continued at room temperature for 24 h.

5. The method for preparing montmorillonite/sol-gel composite coating according to claim 1, wherein in step (4), the coating object is magnesium alloy.

6. The method for preparing the montmorillonite/sol-gel composite coating according to claim 1, wherein in the step (4), the water bath heating temperature is 40-60 ℃, and the time is 0.5-2 h;

the temperature used in the drying process is 90-150 ℃ and the time is 1-3 h.