A method for preparing a high-transparency, wear-resistant magnesium fluoride coating

Abstract

This invention discloses a method for preparing a high-transmittance, wear-resistant magnesium fluoride (MgF2) coating. By optimizing the polymer dosage, nanoporous magnesium fluoride (MgF2) powder was prepared using the sol-gel method and phase separation method. This powder was then used to prepare a coating on a polyvinyl chloride (PVC) substrate. The resulting magnesium fluoride (MgF2) coating, confirmed by a BET (Body-Earth Expansion Test) and scanning electron microscopy (SEM), exhibits a three-dimensional structure with pore sizes around 16 nm, containing 0.028‰ polyethylene oxide (PEO). The layer achieves a visible light transmittance of 93% and a Vickers hardness of 2889.1 kg / mm². 2 The friction coefficient in the wear test was 0.15.

Description

[Technical Field]

[0001] This invention relates to the field of porous material preparation technology, specifically to a method for preparing a highly transparent and wear-resistant magnesium fluoride coating. [Background Technology]

[0002] Magnesium fluoride (MgF2) is a tetragonal rutile crystal with superior optical properties, widely used as a coating material. MgF2 possesses excellent properties such as low refractive index (n = 1.38), a wide transparency band (120 nm-8000 nm), and a large band gap (Eg = 11 eV). MgF2 is an ionic compound formed by the electrostatic attraction of many ions with different charges. Therefore, it is very hard and difficult to compress at room temperature and pressure. Furthermore, MgF2 has advantages such as high mechanical strength, good thermal stability, and a high laser damage threshold, which helps prevent wear and damage from external materials, extending its service life and performance. Therefore, MgF2 coatings have numerous applications in the preparation of optical coatings.

[0003] Sol-gel technology primarily utilizes inorganic substances or metal alkoxides as precursors. Raw materials are uniformly mixed in a liquid phase, and through hydrolysis and condensation reactions, a stable, transparent sol system is formed in solution. The slow polymerization of colloidal particles creates a gel with a three-dimensional network structure, which is then further processed to obtain the desired material. The basic process of the sol-gel method includes five steps: precursor hydrolysis and condensation, gelation, aging, drying, and heat treatment.

[0004] Ostwald ripening is a phenomenon observed in sol-gel systems, where small particles in the solute migrate towards larger particles. First discovered by Friedrich Wilhelm Ostwald in 1986, who also provided an explanation for this phenomenon. Because thermodynamic systems continuously release energy, and larger particles possess lower energy, atoms on the surface of smaller particles detach from the particle surface according to the Kelvin equation and dissolve in the solvent. When this occurs in large quantities, the increased number of free atoms in the solvent leads to aggregation and migration towards the surface of larger particles. In sol-gel phase separation, the mesopores and micropores in the material framework are formed due to the Ostwald ripening mechanism. In the later stages of solution aging in hierarchical continuous bulk materials, the protruding parts of the already formed cross-linked network partially dissolve. The dissolved sol particles aggregate in the recessed areas and precipitate out. This mechanism allows micropores to rearrange, forming mesopores and micropores.

[0005] Nakanishi's group first reported the phenomenon of phase separation accompanying sol-gel in siloxane systems, and initially established theoretical criteria for preparing co-continuous porous bulk materials with phase separation accompanying sol-gel. They subsequently prepared porous bulk materials such as SiO2, TiO2, and ZrO2. The principle of this technology can be briefly described as follows: In the sol-gel process of a mixed system containing alkoxides and water-soluble organic polymers, the inorganic sol or polymeric monomers polymerize to form a gel, while the organic polymer induces spinolysis or metastable decomposition (SD), resulting in phase separation. By freezing or fixing the phase separation process through sol-gel conversion, the structure and morphology of the phase separation region at that time can be obtained, and finally, a porous bulk material can be obtained. [Summary of the Invention]

[0006] This invention addresses the shortcomings of existing magnesium fluoride coatings in terms of high transparency, wear resistance, and mechanical strength. It provides a method for preparing a high-transparency, wear-resistant magnesium fluoride coating, specifically a porous magnesium fluoride coating preparation method. This method is simple, time-efficient, low-cost, and environmentally friendly.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing a high-transparency, wear-resistant magnesium fluoride coating includes the following steps:

[0009] 1) Dissolve 25-30g of polyethylene oxide (PEO) (molecular weight 200,000) in a mixture of 900ml anhydrous ethanol and 100ml deionized water as a solvent. Dissolve 25-30g of MgCl2·6H2O in 300ml of H2O. Mix the dissolved PEO solution thoroughly with the H2O solution and heat to 80℃. Quickly mix 30ml of HF with the MgCl2·6H2O mixture at 80℃. Then add 1ml of nitric acid as a catalyst and maintain the temperature at 80℃ for 1 hour. After precipitation, stir again to disperse the precipitate. Age the dispersion at 75℃ for at least 3 hours. Finally, dry the sample in an oven at 60℃ to obtain porous MgF2.

[0010] 2) Clean the transparent PVC substrate until no dirt remains. Then, ultrasonically clean the PVC substrate sequentially with acetone, ethanol, and H2O for 30 minutes each. After cleaning, place the PVC substrate in a drying oven to dry. Add 1L of isopropanol, 5-7g of porous MgF2 powder, and 3g of surfactant (C) to a beaker. 18 H 29NaO3 and 2g of film-forming agent are uniformly dispersed in a solution. The film-forming agent is obtained by mixing polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) in a 1:3 mass ratio. The dried PVC substrate is placed on a spin coater, and an appropriate amount of solution is dropped onto the center of the PVC substrate using a pipette. The speed of the instrument is adjusted to obtain a coating with a thickness of 100-200nm. The spin-coated PVC substrate is removed and baked at 60℃ in a dryer. After naturally cooling to room temperature, a porous magnesium fluoride coating is obtained. The porous magnesium fluoride coating is detected by an automatic surface area and porosity analyzer (BET) and a scanning electron microscope (SEM). The coating containing 0.028‰ PEO has a three-dimensional structure with a pore size of 16nm. The porous magnesium fluoride coating has a light transmittance of 93% in the visible light region and a Vickers hardness of 2889.1kg / mm². 2 .

[0011] In this invention:

[0012] Step 2) describes adjusting the rotation speed of the instrument to 300 revolutions per minute.

[0013] The surfactant mentioned in step 2) is selected from C 18 H 29 NaO3.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The method for preparing a high-transmittance, wear-resistant magnesium fluoride coating according to the present invention, compared with other coatings currently available, the porous magnesium fluoride coating has the advantages of high transmittance, wear resistance, and high mechanical strength. The porous magnesium fluoride coating, as detected by an automated surface area and porosity analyzer (BET) and scanning electron microscope (SEM), shows that the layer containing 0.028‰ PEO has a three-dimensional structure with a pore size of 16 nm. The porous magnesium fluoride coating achieves a transmittance of 93% in the visible light region and a Vickers hardness value of 2889.1 kg / mm². 2 .

[0016] 2. The preparation method of the high-transparency and wear-resistant magnesium fluoride coating of the present invention has a relatively simple preparation process, a short preparation cycle, and does not use, leave residues or emit toxic solvents during the preparation process. It has low manufacturing cost and is green and environmentally friendly. [Attached Image Description]

[0017] Figure 1 These are microscopic morphology images and dry gel color state images of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1 of the present invention.

[0018] Figure 2 The nitrogen adsorption-desorption curve and BJH pore size distribution diagram of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1 of this invention are shown.

[0019] Figure 3 This is an XRD diffraction pattern of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1 of the present invention;

[0020] Figure 4 This is a hardness analysis diagram of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 2 of the present invention;

[0021] Figure 5 This is a comparison chart of the friction coefficient and mass and volume loss before and after wear of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 2 of the present invention.

Detailed Implementation Methods

[0022] The specific embodiments of the present invention will be further described below with reference to examples.

[0023] Example 1:

[0024] A method for preparing a high-transparency, wear-resistant magnesium fluoride coating involves using a sol-gel phase separation method to prepare porous powder with a continuous phase pore structure. The specific method is as follows:

[0025] 1) Preparation of magnesium fluoride gel: First, mix 50g of PEO solution with different molar amounts (0mol‰-0.029mol‰) of MgCl2·6H2O at 80℃, then add 30ml of HF and react rapidly with the mixture at 80℃ for 4h.

[0026] 2) Preparation of porous magnesium fluoride powder: The above porous magnesium fluoride gel was dried in an oven at 60°C to obtain porous MgF2 product;

[0027] 3) Preparation method of porous MgF2 coating: Porous magnesium fluoride powder prepared with different molar amounts is mixed with solvent, surfactant and film-forming agent to form a sol, and the coating is prepared by using a spin coater.

[0028] Figure 1 These are microscopic morphology images and dry gel color state images of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1.

[0029] Figure 2 The nitrogen adsorption-desorption curve and BJH pore size distribution diagram of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1 are shown.

[0030] Figure 3 This is an XRD diffraction pattern of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 1.

[0031] result:

[0032] Preparation of magnesium fluoride gel: 50g of MgCl2·6H2O and different molar amounts (0mol‰-0.029mol‰) of PEO solution were thoroughly mixed at 80℃. 30ml of HF was added and reacted rapidly with the mixture at 80℃ for 4h. The microstructure and color of the porous magnesium fluoride dry gels with different molar amounts (0mol‰-0.029mol‰) are shown in the figures. Figure 1 As shown, where:

[0033] Figure 1 a is a scanning electron microscope image of PEO magnesium fluoride dry gel with 0 mol‰ added;

[0034] Figure 1 b is a scanning electron microscope image of PEO magnesium fluoride dry gel with 0.002 mol‰ added;

[0035] Figure 1 c is a scanning electron microscope image of PEO magnesium fluoride dry gel with 0.008 mol‰ added;

[0036] Figure 1 Image d is a scanning electron microscope image of a dry gel containing 0.2 mol‰ PEO magnesium fluoride;

[0037] Figure 1 e is a scanning electron microscope image of PEO magnesium fluoride dry gel with 0.028 mol‰ added;

[0038] Figure 1 f is a scanning electron microscope image of PEO magnesium fluoride dry gel with 0.029 mol‰ added;

[0039] from Figure 1 As can be seen, with the increase of PEO content, the pore structure of magnesium fluoride dry gel increases. When the PEO content reaches 0.029 mol‰, the gel structure tends to be loose and the strength decreases significantly. Therefore, the content of added PEO should not be lower than 0.028 mol‰.

[0040] Figure 1 g, 1h, and 1i are photographs of PEO magnesium fluoride dry gels with added 0 mol‰, 0.008 mol‰, and 0.028 mol‰, respectively. As can be seen from the images, the magnesium fluoride dry gel has a blocky structure, is white and semi-transparent, and has a certain strength.

[0041] Nitrogen adsorption-desorption curves and BJH pore size distribution diagrams of PEO porous magnesium fluoride dry gels with different molar amounts (0 mol‰-0.029 mol‰) are shown in the figure. Figure 2 As shown, from Figure 2Figure a shows that magnesium fluoride dry gel powders with different contents of PEO (0.008-0.028 mol‰) exhibit typical adsorption-desorption curves of mesoporous materials, showing an adsorption-desorption hysteresis phenomenon. The pore size range, as shown in Figure b, is below 50 nm.

[0042] XRD diffraction patterns of PEO porous magnesium fluoride dry gels with different molar amounts (0 mol‰-0.029 mol‰) at different temperatures (60℃ and 500℃) are shown in the figure. Figure 3 As shown, from Figure 3 It can be seen that the magnesium fluoride dry gel exhibits the characteristic diffraction peaks of magnesium fluoride crystals after heat treatment at 500℃.

[0043] Example 2:

[0044] A method for preparing a high-transparency, wear-resistant magnesium fluoride coating includes the following steps:

[0045] Preparation of porous magnesium fluoride coating: A certain amount of solvent, different molar amounts (0 mol‰-0.029 mol‰) of PEO porous MgF2 powder, and surfactant (C) were added to a beaker. 18 H 29 The solution contains NaO3 and film-forming agents (PVDF and NMP), which are then uniformly dispersed in the solution. An appropriate amount of solution is dropped onto the center of the PVC substrate using a pipette, and the speed of the instrument is adjusted to obtain a coating of suitable thickness.

[0046] Figure 4 This is a hardness analysis diagram of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 2 of this invention;

[0047] Figure 5 This is a comparison chart of the friction coefficient and mass and volume loss before and after wear of a high-transparency, wear-resistant magnesium fluoride coating product obtained in Example 2.

[0048] result:

[0049] Microstructure images of porous magnesium fluoride coatings prepared by spin coating and a comparison of transmittance of PEO porous MgF2 coatings with different molar amounts (0 mol‰-0.029 mol‰) are shown in the figure. Figure 4 As shown:

[0050] from Figure 4 (a) The scanning electron microscope image of the magnesium fluoride coating shows that the magnesium fluoride coating is about 5 micrometers thick and has a porous surface.

[0051] Figure 4(b) shows the transmittance curves of magnesium fluoride coatings with different PEO contents. It can be seen that as the PEO content increases from 0 to 0.028 mol‰, the average transmittance of the coating gradually increases (from 92.67% to 93.9%). This indicates that the porous magnesium fluoride prepared by adding PEO has a good effect on improving the transmittance of the coating.

[0052] The hardness comparison chart of PEO magnesium fluoride coatings with contents of 0-0.028 mol‰ is shown below. Figure 5 As shown in the figure, the hardness of the PVC substrate (sample T) is 2684.4, which is 2995.0 kg / mm². 2 The hardness of the magnesium fluoride coating without added PEO (PEO content 0.028 mol‰) decreased to 2603.3 kg / mm. 2 As the PEO content increased to 0.028 mol‰, the hardness of the magnesium fluoride coating increased to 2889.1 kg / mm². 2 If the coating thickness is doubled, the coating hardness further increases to 2995.0 kg / mm². 2 It is evident that the addition of PEO increases the hardness of the magnesium fluoride coating.

[0053] The results show that:

[0054] As can be seen from the comparison of Examples 1-2 and the above figures, the magnesium fluoride coating prepared without PEO has lower hardness.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, any improvements and changes made without departing from the inventive concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a high-transparency, wear-resistant magnesium fluoride coating, characterized in that: Includes the following steps: 1) Dissolve 25-30g of polyethylene oxide in a mixture of 900mL anhydrous ethanol and 100mL deionized water as a solvent. Dissolve 25-30g of MgCl2·6H2O in 300mL of H2O. Mix the dissolved PEO solution thoroughly with the H2O solution and heat to 80℃. Quickly mix 30mL of HF with the MgCl2·6H2O mixture at 80℃. Then add 1mL of nitric acid as a catalyst and maintain the temperature at 80℃ for 1 hour. After precipitation, stir again to disperse the precipitate. Age the dispersion at 75℃ for at least 3 hours. Finally, dry the sample in an oven at 60℃ to obtain porous MgF2. 2) Clean the transparent PVC substrate until no dirt remains. Then, ultrasonically clean the PVC substrate sequentially with acetone, ethanol, and H2O for 30 minutes each. After cleaning, place the PVC substrate in a drying oven to dry. Add 1L of isopropanol, 5-7g of porous MgF2 powder, 3g of surfactant, and 2g of film-forming agent to a beaker and disperse them evenly in the solution. The surfactant is selected from C... 18 H 29 The film-forming agent, NaO3, is obtained by mixing polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (N-Methylpyrrolidone) in a 1:3 mass ratio. After drying, the PVC substrate is placed on a spin coater, and an appropriate amount of solution is dropped onto the center of the PVC substrate using a pipette. The spin coater is adjusted to 300 rpm to obtain a coating with a thickness of 100-200 nm. The spin-coated PVC substrate is then removed and baked at 60°C in a dryer. After natural cooling to room temperature, a porous magnesium fluoride coating is obtained. The porous magnesium fluoride coating, detected by an automatic surface area and porosity analyzer and a scanning electron microscope, shows that the coating containing 0.028‰ PEO exhibits a three-dimensional structure with a pore size of 16 nm. The porous magnesium fluoride coating achieves a light transmittance of 93% in the visible light region and a Vickers hardness of 2889.1 kg / mm². 2 .

Images