Method for the one-step preparation of a functional barium titanate coating

Abstract

This invention discloses a one-step method for preparing a barium titanate functional coating. The steps are as follows: 1. Barium hydroxide octahydrate is added as a barium source to excess glacial acetic acid and heated in a constant-temperature water bath. After stirring until the solution is clear and transparent, the solution is allowed to cool to room temperature to obtain solution A, with a pH of 5.0-6.8; 2. Tetrabutyl titanate is added as a titanium source to anhydrous ethanol and stirred until homogeneous to obtain solution B; 3. Under stirring at room temperature, solution B is added dropwise to solution A; after the addition of solution B is complete, stirring and aging are continued to obtain a barium titanate precursor solution; 4. A metal material is used as a substrate and pretreated to obtain a pretreated substrate; 5. The barium titanate precursor solution obtained in step 3 is sprayed onto the pretreated substrate using a solution plasma spraying process to prepare a barium titanate functional coating. This method is simple, yields a coating with uniform composition, good hardness, and certain density and dielectric properties.

Description

Technical Field

[0001] This invention relates to the technical field of coating preparation, specifically a one-step method for preparing barium titanate functional coatings. Background Technology

[0002] The rapid development of electronic information technology has led to the continuous expansion and deepening of research on functional dielectric materials. Barium titanate, as a functional electrolyte material, has attracted attention due to its high dielectric and ferroelectric properties, as well as its lead-free and environmentally friendly nature, and is widely used in aerospace, communication technology, and multilayer ceramic capacitors. The main methods for preparing barium titanate coatings include sol-gel method, magnetron sputtering, chemical vapor deposition, micro-arc oxidation, and plasma spraying. With the continuous development of thermal spraying technology, the deposition, development, and research of BaTiO3 coatings through plasma spraying has become an inevitable trend in recent years.

[0003] Plasma spraying is a technique that uses the ionization of inert gases such as argon, nitrogen, and hydrogen to create a high-temperature plasma arc. This arc melts the coating material and accelerates it to impact the substrate, resulting in a dense coating. Plasma spraying technologies include atmospheric plasma spraying (APS), high-velocity plasma spraying (HVOF), and solution precursor plasma spraying (SPPS). Compared to atmospheric plasma spraying (APS) and high-velocity plasma spraying (HVOF), solution precursor plasma spraying (SPPS) has less stringent requirements on powder particle size and requires relatively simpler equipment.

[0004] However, solution precursor plasma spraying (SPPS) technology is rarely used in existing technologies to prepare barium titanate functional coatings. This is mainly because traditional precursor solutions for preparing barium titanate do not precisely control the hydrolysis rate of the titanium source and the dissociation rate of the barium source, resulting in a lack of stable coordination structure between the titanium and barium sources. Furthermore, the use of incompatible titanium, barium, and solvent sources can lead to a situation where "the titanium source hydrolyzes first to form a precipitate, and the barium source coordinates later," resulting in component segregation in the system and further weakening the dielectric and mechanical properties of the material. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a one-step method for preparing barium titanate functional coatings. The prepared barium titanate functional coatings not only have uniform composition, but also have good bonding strength, good hardness, and certain density and dielectric properties.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A one-step method for preparing barium titanate functional coatings includes the following steps:

[0008] Step 1: Add barium hydroxide octahydrate as a barium source to excess glacial acetic acid and heat in a constant temperature water bath. Stir until the solution is clear and transparent, and then let it cool to room temperature to obtain solution A; the pH of solution A is 5.0-6.8.

[0009] Step 2: Add tetrabutyl titanate as a titanium source to anhydrous ethanol and stir until homogeneous to obtain solution B;

[0010] Step 3: While stirring at room temperature, add solution B dropwise to solution A; after solution B has been added, continue stirring, mixing and aging to obtain the barium titanate precursor solution.

[0011] Step 4: Use the metal material as the substrate and pretreat the substrate to obtain the pretreated substrate;

[0012] Step 5: The barium titanate precursor solution obtained in Step 3 is sprayed onto the pretreated substrate obtained in Step 4 using a solution plasma spraying process, thus preparing the barium titanate functional coating.

[0013] This invention uses barium hydroxide octahydrate as the barium source and glacial acetic acid as both reactant and solvent. The reaction is carried out under water bath heating to obtain solution A with a pH of 5.0-6.8, avoiding excessive water content. An ethanol solution of tetrabutyl titanate is then added dropwise to solution A. Simultaneously, the amounts of each raw material are precisely controlled to obtain a barium titanate precursor solution with a specific concentration and viscosity. These techniques collectively control the hydrolysis rate of the titanium source, ensuring a precise match between the barium ion release kinetics and the titanium source hydrolysis rate. This avoids the situation where the titanium source hydrolyzes first to form a precipitate, followed by barium source coordination, which can lead to component segregation in the system. By controlling the decomposition kinetics of the precursor solution and combining it with a suitable spraying process for solution plasma spraying, the phase composition of the coating is controlled, and grain growth is effectively suppressed. Ultimately, a nanoscale barium titanate functional coating with uniform composition, good hardness, good bonding strength, and certain density and dielectric properties can be obtained.

[0014] In particular, by optimizing the excess ratio of glacial acetic acid, glacial acetic acid can act as both a solvent and a reactant (ensuring complete reaction of the barium source to form stable barium acetate, avoiding the formation of impurity phases such as BaCO3, and improving product purity), thereby controlling the Ba... 2+ The dissociation rate is reduced, and the titanium source bonds to the titanium phase in a coordinated manner to form a hydrolytic complex, thus suppressing the risk of direct hydrolysis of the titanium source to form a precipitate; moreover, excess glacial acetic acid can maintain the weak acidity of the system (pH 5.0-6.8), ensuring that the addition of the titanium source avoids the formation of a precipitate due to an alkaline environment or H+. + Excessive dosage causes the reaction to run out of control; causing Ba 2+ The dissociation rate matches the hydrolysis rate of tetrabutyl titanate, achieving molecular-level co-condensation of titanium barium ions, thus ensuring that the final product's barium-to-titanium ratio is always maintained within the ideal range of 1:1.

[0015] In the one-step method for preparing barium titanate functional coatings described above, the molar ratio of glacial acetic acid to barium hydroxide octahydrate in step one is (2.02~2.10):1. This invention uses glacial acetic acid, ensuring that solution A generated from the reaction of glacial acetic acid and barium hydroxide octahydrate contains less water. This avoids the violent hydrolysis of tetrabutyl titanate upon contact with water, preventing uncontrolled reaction rates and the precipitation of the titanium source before it comes into contact with barium ions. Furthermore, a slight excess of glacial acetic acid provides a weakly acidic environment (pH 5.0-6.8), inhibiting the violent hydrolysis of tetrabutyl titanate. If too little glacial acetic acid is used, a small amount may evaporate with heating in the reaction bath, leading to incomplete reaction of the barium source; if too much glacial acetic acid is used, a large excess of H+ will result in… + It will react with tetrabutyl titanate's -(OC4H9) - The reaction promotes the violent hydrolysis of the titanium source to generate Ti(OH)4, but fails to generate the -Ba-O-Ti- coordination network structure.

[0016] In the one-step method for preparing barium titanate functional coatings described above, in step one, the barium source is barium hydroxide octahydrate. Barium hydroxide octahydrate can undergo an acid-base neutralization reaction with glacial acetic acid to generate a high-purity barium acetate solution, which serves as the barium source solution. This allows the titanium source solution to immediately complex with barium ions upon addition to the barium source solution, preventing excessive aggregation of hydrolysis intermediates to form Ti(OH)4. Furthermore, the stoichiometric ratio of barium hydroxide octahydrate to tetrabutyl titanate as the titanium source is easily controlled, resulting in a product with lower impurity content and higher uniformity compared to other barium sources. Simultaneously, the use of unstable barium hydroxide is avoided, as it readily reacts with carbon dioxide in the air to form barium carbonate, leading to reduced reagent purity and affecting reaction accuracy.

[0017] Furthermore, in step two, dissolving tetrabutyl titanate in anhydrous ethanol reduces the concentration of tetrabutyl titanate, which can effectively slow down the hydrolysis rate of tetrabutyl titanate and make the hydrolysis of tetrabutyl titanate controllable.

[0018] In the one-step method for preparing barium titanate functional coatings described above, step one involves a constant-temperature water bath heating temperature of 50-60℃ and a heating and stirring time of 40-60 minutes. This accelerates the reaction by increasing the thermal motion of the dissociated ions. 50-60℃ represents the equilibrium range for this reaction, considering both reaction kinetics and reactant volatilization, ensuring complete reaction of barium hydroxide octahydrate and shortening the equilibrium time. Excessively high temperatures (>60℃) lead to excessive volatilization of glacial acetic acid, while excessively low temperatures (<50℃) result in incomplete reaction of barium hydroxide octahydrate and a slow reaction rate. A stirring rate of 30-40 rpm ensures sufficient contact between barium hydroxide octahydrate and glacial acetic acid, promoting a uniform and thorough reaction. Insufficient or no stirring will result in incomplete reaction, leaving barium hydroxide residue in the system, which can lead to uncontrolled hydrolysis of the titanium source solution upon subsequent addition.

[0019] In the above one-step method for preparing barium titanate functional coatings, in step one, the concentration of barium in solution A is 3.25-3.8 mol / L.

[0020] In the one-step method for preparing barium titanate functional coatings described above, in step two, the molar ratio of titanium in the titanium source to barium in the barium source is 1:1. Titanium sources can be broadly categorized into titanium alkoxides and inorganic titanium sources. When inorganic salts are used as titanium sources (such as TiCl4 and TiOSO4), Ti is the dominant element in the system. 4+ The presence of a free state leads to a high hydrolysis rate, preventing it from reacting with Ba. 2+ Achieving kinetic matching can result in a barium titanate precursor solution that is layered or even contains flocculent precipitates, or exhibits a short-term increase in viscosity, failing to meet the maximum viscosity requirements for plasma spraying. Therefore, this application selects titanium alkoxides as the titanium source. Among them, tetrabutyl titanate shows the best performance, possessing high reactivity, good solubility, and a controllable hydrolysis rate. Although tetrabutyl titanate is sensitive to water, a homogeneous barium titanate precursor solution can be obtained by keeping the environment dry.

[0021] In the above one-step method for preparing barium titanate functional coatings, in step two, the stirring time is 10-20 min; and the concentration of titanium in solution B is 0.74-0.86 mol / L.

[0022] In the one-step method for preparing barium titanate functional coatings described above, in step three, solution B is added dropwise over 30-60 minutes with rapid stirring at a rate of 50-60 rpm. The purpose of rapid stirring is to allow the titanium source to diffuse instantaneously, eliminating local concentration gradients and ensuring the matching of reaction kinetics between barium and titanium ions. If the stirring speed is too slow, the titanium source will not diffuse in time, resulting in high local concentrations and hydrolysis of the titanium source, producing a white flocculent precipitate. If the stirring speed is too fast, it will destroy the solvation layer between the titanium source and ethanol, thus accelerating the hydrolysis of the titanium source, which is counterproductive. During the aging process, low-speed stirring at a rate of 30-40 rpm is used. Aging is to allow the Ba in the system to... 2+ The titanium hydrolysis intermediates in the system gradually grow through a condensation reaction, forming particle clusters. These small particle clusters then gradually connect with each other, eventually forming a three-dimensional network structure. If the aging process is too fast, it will destroy the already formed three-dimensional network structure; if it is too slow, it will lead to insufficient ion contact and incomplete reaction.

[0023] In the one-step method for preparing barium titanate functional coatings described above, the viscosity of the barium titanate precursor solution in step three is 0.5-10 mPa. An appropriate viscosity ensures that the spraying solution does not clog the spray gun during the spraying process. The preferred viscosity of the barium titanate precursor solution is 5-7 mPa. If the viscosity is too low, the ion concentration in the precursor solution will be too low, affecting the deposition efficiency of the coating; if the viscosity is too high, it will clog the spray gun, making coating preparation impossible. The concentrations of barium and titanium in the barium titanate precursor solution are both 0.6-0.7 mol / L. While ensuring the viscosity meets the requirements of plasma spraying, the concentrations of barium and titanium in the precursor solution should be increased as much as possible to improve subsequent deposition efficiency and further ensure coating quality.

[0024] In the above one-step method for preparing barium titanate functional coatings, in step four, the substrate is pure titanium, titanium alloy, stainless steel, or carbon steel. The substrate pretreatment method is as follows: after cleaning and drying the substrate, it is surface-blasted with 24-220 mesh white corundum, followed by ultrasonic cleaning with anhydrous ethanol, and then drying. The substrate blasting treatment increases the surface roughness of the substrate, which can ensure that the coating has ideal bonding strength on the substrate without affecting the surface structure of the coating. In this application, the substrate is preferably a titanium substrate, possibly because of the good matching of the thermal expansion coefficients between titanium and barium titanate, which reduces interfacial stress; at the same time, titanium forms a uniform TiO2 layer at high temperatures, which firmly bonds with the titanium substrate and provides a good bonding interface for the barium titanate functional coating, reducing interfacial defects and jointly promoting coating crystallization and performance.

[0025] The method for preparing barium titanate functional coatings in one step described above is characterized in that, in step five, the conditions for the solution plasma spraying process are as follows: spraying distance 50-100 mm; spraying power 50-100 kW; total gas flow rate 100-400 slpm; liquid delivery rate 10-40 mL / min; atomizing gas flow rate 10-20 L / h; substrate preheating temperature 120-300℃; and spray gun movement speed 400-700 mm / s.

[0026] If the spraying power is too high, the coating will over-melt, damaging the surface morphology and performance. If the spraying power is too low, there will be more unmelted and semi-melted particles in the coating, reducing the coating density, resulting in low coating bonding strength and decreased mechanical properties. If the spraying distance is too large, the molten particles will cool and decelerate before reaching the substrate surface. When the molten particles impact the substrate, the spreading coefficient will decrease, increasing porosity and unmelted particles, reducing density and bonding strength. If the spraying distance is too small, the particles will not melt sufficiently, and the impact deformation of the particles upon reaching the substrate surface will be insufficient. Furthermore, when the spraying distance is too close, the local heat flux will be too large, causing the substrate / deposited layer to heat up rapidly, easily leading to oxidation and phase transformation. It will also result in uneven coating thickness and structure. If the total gas flow rate is too low, the flame temperature will be low, and the precursor solution particles will not melt completely. When impacting the substrate, the particles will not spread completely, resulting in high coating porosity and decreased bonding strength. If the total gas flow rate is too high, the flame temperature will be high, causing the particles to over-melt and even decompose to form impurity phases. High flame temperature can also lead to substrate deformation and coating cracking. If the liquid feed rate is too high, the flame temperature will decrease, leading to incomplete pyrolysis of the precursor. A high feed rate will also produce large droplets, which can cause splashing, high porosity, increased roughness, and decreased interlayer adhesion. Conversely, a low feed rate will result in lower deposition efficiency, thinner coatings, and increased costs. Excessive atomizing gas flow rate can lead to excessively fine droplets, over-evaporation, and spray instability; insufficient flow rate results in excessively large droplets, insufficient heating, surface roughness, and increased defects. Conversely, a low preheating temperature leads to rapid solidification, insufficient spreading, increased internal stress and porosity defects, and poor interlayer adhesion; a high preheating temperature causes rapid solvent evaporation, increased porosity and thermal stress, substrate oxidation / deformation, and microstructure deterioration. Furthermore, excessive spray gun movement speed leads to insufficient heat / material throughput, weak adhesion, high porosity, and uneven thickness; insufficient speed leads to overheating, roughening, bubbling and cracking, material buildup, and oxidation. This application improves the efficiency of barium titanate preparation by adjusting the spraying process to prevent the generation of impurity phases. Under the spraying conditions of this application, the barium titanate precursor solution is sprayed, resulting in a coating with ideal chemical composition and microstructure.

[0027] The technical solution of the present invention achieves the following beneficial technical effects:

[0028] This invention uses barium hydroxide octahydrate as the barium source and glacial acetic acid as both reactant and solvent. The reaction is carried out under water bath heating to obtain solution A with a pH of 5.0-6.8, avoiding excessive water content in solution A. An ethanol solution of tetrabutyl titanate is then added dropwise to solution A. Simultaneously, the amounts of each raw material are precisely controlled to obtain a barium titanate precursor solution with a specific concentration and viscosity. These techniques collectively control the hydrolysis rate of the titanium source, ensuring a precise match between the barium ion release kinetics and the titanium source hydrolysis rate. This avoids the situation where the titanium source hydrolyzes first to form a precipitate, followed by barium source coordination, leading to component segregation in the system. By controlling the decomposition kinetics of the precursor solution and combining it with a suitable spraying process for solution plasma spraying, the phase composition of the coating is controlled, and grain growth is effectively suppressed. Ultimately, a nanoscale barium titanate functional coating with uniform composition, good hardness, good bonding strength, and certain density and dielectric properties can be obtained. Specifically:

[0029] (1) Barium hydroxide octahydrate can undergo an acid-base neutralization reaction with glacial acetic acid, ensuring that the barium source reacts completely to form stable barium acetate, avoiding the formation of impurity phases such as BaCO3, and improving product purity; acetate ions (CH3COO⁻) and titanium ions (Ti 4+ A stable complex is formed; this coordination reduces the reactivity of titanium and creates steric hindrance, significantly slowing down the hydrolysis rate of the titanium source. Under the condition that titanium is stabilized and slowly released by acetate ions, the Ba... 2+ The dissociation rate allows Ba²⁺ in the solution to fully contact the titanium species and rapidly undergo co-condensation, forming Ba-O-Ti bonds through oxygen bridges. This ensures that the release rate of barium ions from barium acetate matches the hydrolysis rate of tetrabutyl titanate, with hydrolysis and barium coordination proceeding synergistically. This prevents the titanium hydrolysis intermediate from undergoing a self-condensation reaction due to its inability to condense with barium ions; moreover, the acetate ions in the system can also inhibit the self-condensation of the titanium hydrolysis intermediate.

[0030] (2) Excess glacial acetic acid can maintain the weak acidity of the system (pH 5.0-6.8), ensuring that the addition of the titanium source avoids the formation of an alkaline environment or H+. + Excessive amounts can cause the reaction to run out of control (if the barium source reaction is incomplete, OH- may be present). - Under alkaline conditions, OH - Attack Ti 4+ The formation of Ti(OH)4 precipitate makes Ti 4+ Unable to connect with Ba 2+ Coordination; if H + Excessive amounts will react with the -(OC4H9) group of tetrabutyl titanate. - The reaction promotes the violent hydrolysis of the titanium source to form Ti(OH)4, preventing the formation of the -Ba-O-Ti-coordination network structure; further, Ba... 2+The dissociation rate matches the hydrolysis rate of tetrabutyl titanate, achieving molecular-level co-condensation of titanium barium ions, thus ensuring that the final product's barium-to-titanium ratio is always maintained within the ideal range of 1:1.

[0031] (3) By adding the titanium source solution dropwise to the barium source solution in a specific order, the hydrolysis rate of the titanium source is controlled. After the titanium source solution is added, it diffuses rapidly in the system under the action of rapid stirring, keeping the titanium source solution at a low concentration. Under the action of glacial acetic acid, the barium ions can quickly combine with tetrabutyl titanate to form a bimetallic complex, avoiding the formation of precipitation and ensuring that the titanium hydrolysis intermediate reacts completely with the barium ions. This avoids the occurrence of explosive hydrolysis of the system and the inability of the barium ions to complex with the titanium source when the entire titanium source solution is added to the barium source solution.

[0032] (4) This invention simplifies the process of traditional barium titanate preparation methods, significantly shortens the barium titanate preparation cycle, has high coating preparation efficiency, low energy consumption, and forms a dense and uniform coating structure. The prepared coating grains can reach the nanoscale, and the hardness of the barium titanate coating obtained by spraying is 570-1200 HV. 0.025 The thickness ranges from 20-110 μm, the porosity from 1-15%, the relative permittivity from 50-400, and the corresponding dielectric loss from 0.01-1. This method solves the problems of complex processes, high costs, and easy introduction of impurities during the preparation of barium titanate using traditional sol-gel methods, making it easier to achieve large-scale mass production. Attached Figure Description

[0033] Figure 1 Flowchart for preparing barium titanate coating by plasma spraying of the spraying liquid and solution of the present invention;

[0034] Figure 2 The images show the SEM and EDS spectra of the barium titanate coating prepared in Example 1 of this invention.

[0035] Figure 3 The image shows the XRD pattern of the barium titanate coating prepared in Example 1 of this invention.

[0036] Figure 4 This is a diagram showing the bonding strength of the barium titanate coating prepared in Example 1 of the present invention;

[0037] Figure 5 This is a hardness distribution diagram of the barium titanate coating prepared in Example 1 of the present invention;

[0038] Figure 6 This is the hysteresis loop diagram corresponding to the maximum electric field intensity of the barium titanate coating prepared in Example 1 of the present invention;

[0039] Figure 7 The dielectric spectrum of the barium titanate coating prepared in Example 1 of this invention;

[0040] Figure 8 The surface potential (KPFM) diagram of the barium titanate coating prepared in Example 1 of this invention;

[0041] Figure 9 The images show the SEM and EDS spectra of the barium titanate coating prepared in Example 2 of this invention.

[0042] Figure 10 The image shows the XRD pattern of the barium titanate coating prepared in Example 2 of this invention.

[0043] Figure 11 This is a bonding strength diagram of the barium titanate coating prepared in Example 2 of the present invention;

[0044] Figure 12 This is a hardness distribution diagram of the barium titanate coating prepared in Example 2 of the present invention;

[0045] Figure 13 This is the hysteresis loop diagram corresponding to the maximum electric field strength of the barium titanate coating prepared in Example 2 of the present invention;

[0046] Figure 14 The dielectric spectrum of the barium titanate coating prepared in Example 2 of this invention;

[0047] Figure 15 The surface potential (KPFM) diagram of the barium titanate coating prepared in Example 2 of this invention;

[0048] Figure 16 SEM image and EDS spectrum of the barium titanate coating prepared in Example 3 of this invention;

[0049] Figure 17 XRD pattern of the barium titanate coating prepared in Example 3 of this invention;

[0050] Figure 18 Bond strength diagram of the barium titanate coating prepared in Example 3 of this invention;

[0051] Figure 19 Hardness distribution diagram of the barium titanate coating prepared in Example 3 of this invention;

[0052] Figure 20 Hysteresis loop diagram of the barium titanate coating prepared in Example 3 of this invention under the maximum electric field intensity;

[0053] Figure 21 Dielectric spectrum of the barium titanate coating prepared in Example 3 of this invention;

[0054] Figure 22 Surface potential (KPFM) diagram of the barium titanate coating prepared in Example 3 of this invention;

[0055] Figure 23SEM image of the barium titanate coating prepared in the comparative example of this invention;

[0056] Figure 24 XRD pattern of the barium titanate coating prepared in the comparative example of this invention;

[0057] Figure 25 The bonding strength diagram of the barium titanate coating prepared in the comparative example of this invention;

[0058] Figure 26 Hardness distribution diagram of the barium titanate coating prepared in the comparative example of this invention;

[0059] Figure 27 Hysteresis loop diagram of the barium titanate coating prepared in the comparative example of this invention under the maximum electric field intensity;

[0060] Figure 28 The dielectric spectrum of the barium titanate coating prepared in the comparative example of this invention. Detailed Implementation

[0061] Example 1

[0062] This embodiment describes a one-step method for preparing barium titanate functional coatings, comprising the following steps:

[0063] Step (1): Add 386.276g of barium hydroxide octahydrate to 143.78mL of glacial acetic acid, stir for 1h in a 60℃ water bath at a stirring rate of 30-40rpm, and then cool to room temperature to obtain solution A (i.e., barium source solution). The pH of solution A is 6.0.

[0064] Step (2): Dissolve 418.442 mL of tetrabutyl titanate in 1000 mL of anhydrous ethanol and stir until homogeneous at a stirring speed of 30-40 rpm to obtain solution B (i.e., titanium source solution).

[0065] Step (3): Under rapid stirring at room temperature (stirring speed of 50-60 rpm), add solution B dropwise to solution A to ensure complete reaction, and complete the addition in 30-60 min; after solution B has been added, continue stirring and aging (stirring speed of 30-40 rpm, stirring and mixing time of 30-60 min), and the aging is completed to obtain barium titanate precursor solution.

[0066] Step (4): Use a titanium sheet as the substrate. The titanium sheet is 10*10*2mm in size. The titanium sheet is sandblasted with 24-220 mesh white corundum. After sandblasting, it is ultrasonically cleaned with anhydrous ethanol and dried to obtain the pretreated substrate.

[0067] Step (5): The barium titanate precursor solution is sprayed onto the pretreated substrate by solution plasma spraying process to prepare the barium titanate functional coating. The specific process parameters during spraying are: spraying power 70kW; spraying distance 80mm; liquid delivery rate 24mL / min; atomizing gas flow rate 12L / h; substrate preheating temperature 150℃; spray gun moving speed 500mm / s; number of spraying passes: 20 passes.

[0068] The barium titanate functional coating prepared in this embodiment has an average thickness of 101.11 μm and a porosity of 11.14%.

[0069] The electron microscopy and EDS spectra of the barium titanate functional coating prepared in this embodiment are shown in the figure. Figure 2 XRD pattern can be found Figure 3 The XRD and PDF peak positions of the BaTiO3 coating with titanium sheet as substrate are basically consistent. Due to cell distortion, the (200) peak splits into two peaks (200) and (002) near 45°. The diffraction peak at 45° in the figure shows asymmetric broadening, indicating that both cubic and tetragonal barium titanate phases exist in the coating. However, the extreme cold during plasma spraying and the presence of the amorphous phase make the peak splitting indistinct. Figure 2 and Figure 3 As can be seen from the example, a barium titanate functional coating was successfully prepared by solution plasma spraying. The coating has penetrating longitudinal cracks and pores.

[0070] observe Figure 4 Scratch tests were conducted on the barium titanate functional coating with titanium sheet as the substrate. The acoustic signal reached its maximum value when the scratch force was applied to 47.95 N, indicating that the coating has good bonding strength.

[0071] observe Figure 5 The Weibull distribution of the barium titanate functional coating with titanium sheet as the substrate can be obtained from the hardness test. It can be observed that the average hardness of the coating is 1174.5 HV. 0.025 The higher the hardness value, the stronger the coating's resistance to wear and the more effectively it can resist scratches.

[0072] The hysteresis loop of the coating under the maximum electric field strength that it can withstand was obtained by testing at a fixed frequency of 20Hz. Figure 6 ,observe Figure 6 It can be seen that the barium titanate functional coating based on titanium sheet exhibits a maximum polarization of 4.72 and a remanent polarization of 0.66 under a maximum electric field strength of 300 kV / cm. The ferroelectric domains of the coating are fully and stably oriented, demonstrating excellent ferroelectric properties.

[0073] observe Figure 7It can be seen that the dielectric constant and dielectric loss of the barium titanate coating with titanium sheet as substrate exhibit a single decreasing trend with increasing frequency. The dielectric constant decreases from 292.2 at a low frequency of 100 Hz to 10. 6 At 152.6 Hz, the dielectric loss decreased from 0.52 at 100 Hz to 10 at higher frequencies. 6 0.09 at Hz, from Figure 7 It can be seen that the dielectric response of the coating is dominated by the same polarization mechanism. Observation Figure 8 The surface potential (KPFM) is relatively uniform, with the highest surface potential reaching 831.9 mV and the lowest being 747.2 mV.

[0074] Example 2

[0075] This embodiment describes a one-step method for preparing barium titanate functional coatings, comprising the following steps:

[0076] Step (1): Add 386.276g of barium hydroxide octahydrate to 143.78mL of glacial acetic acid, stir for 1h in a 60℃ water bath at a stirring rate of 30-40rpm, and then cool to room temperature to obtain solution A. The pH of solution A is 6.0.

[0077] Step (2): Dissolve 418.442 mL of tetrabutyl titanate in 1000 mL of anhydrous ethanol and stir until homogeneous at a stirring speed of 30-40 rpm to obtain solution B.

[0078] Step (3): Under rapid stirring at room temperature (stirring speed of 50-60 rpm), add solution B dropwise to solution A to ensure complete reaction, and complete the addition in 30-60 minutes; after the addition of solution B is complete, continue stirring and aging at a stirring speed of 30-40 rpm for 30-60 minutes. After aging, the barium titanate precursor solution is obtained.

[0079] Step (4): Use a round stainless steel as the substrate. The stainless steel substrate has a size of Φ26mm*3mm. Use 24-220 mesh white corundum to perform surface sandblasting on the stainless steel substrate. After sandblasting, use anhydrous ethanol for ultrasonic cleaning and drying to obtain the pretreated substrate.

[0080] Step (5): The barium titanate precursor solution is sprayed onto the pretreated substrate by solution plasma spraying process to prepare the barium titanate ceramic coating. The specific process parameters during spraying are: spraying power between 70kW; spraying distance 90mm; liquid delivery rate 20mL / min; atomizing gas flow rate 10L / h; substrate preheating temperature 170℃; spray gun moving speed 500mm / s; and 10 spray passes.

[0081] The barium titanate functional coating prepared in this embodiment has an average thickness of 29.66 μm and a porosity of 1.95%.

[0082] The electron microscope and EDS spectra of the barium titanate functional coating prepared in this embodiment are shown in the figure. Figure 9 XRD pattern can be found Figure 10 The XRD and PDF peak positions of the BaTiO3 coating with stainless steel as the substrate are basically consistent. The diffraction peak at 45° in the figure shows an asymmetric broadening characteristic, indicating the simultaneous presence of cubic and tetragonal barium titanate phases in the coating. A significant baseline broadening is observed between 20-30°, indicating the presence of an amorphous phase in the coating. Due to the extreme cooling during plasma spraying and the presence of the amorphous phase, the peak separation is not obvious. Figure 9 as well as Figure 10 As can be seen from the example, a barium titanate functional coating was successfully prepared by solution plasma spraying. The coating has fewer longitudinal cracks and more pores.

[0083] observe Figure 11 Scratch tests can be performed on barium titanate functional coatings with stainless steel as the base material. The acoustic signal reaches its maximum value when the scratch force is applied to 28.30 N.

[0084] observe Figure 12 The Weibull distribution of the barium titanate functional coating with stainless steel as the substrate can be obtained by hardness testing. Observation shows that the average hardness is 571.8 HV. 0.025 .

[0085] The hysteresis loop of the barium titanate functional coating under the maximum electric field strength that it can withstand was obtained by testing at a fixed frequency of 20 Hz. Figure 13 ,observe Figure 13 It can be seen that the barium titanate functional coating based on titanium sheet has a maximum polarization intensity of 0.28 and a residual polarization intensity of 0.037 under a maximum electric field strength of 168 Kv / cm.

[0086] observe Figure 14 It can be observed that the dielectric constant and dielectric loss of the barium titanate functional coating with stainless steel as the substrate gradually decrease with increasing frequency at low frequencies, and increase slightly at high frequencies. The dielectric constant decreases from 59.7 at 100Hz to 47.6, and increases from 47.6 to 48.1 at high frequencies. The dielectric loss decreases from 0.15 at 100Hz to 0.025, and increases from 0.025 to 0.05 at high frequencies. Figure 14 It can be seen that the dielectric response of the coating is dominated by the same polarization mechanism. Observation Figure 15 The surface potential (KPFM) is unevenly distributed. As shown in the figure, the surface potential can reach a maximum of 257.5 mV and a minimum of 93.1 mV.

[0087] Example 3

[0088] This embodiment describes a one-step method for preparing barium titanate functional coatings, comprising the following steps:

[0089] Step (1): Place 386.276g of barium hydroxide octahydrate in 143.78mL of glacial acetic acid, stir for 1h in a 60℃ water bath at a stirring rate of 30-40rpm, and then cool to room temperature to obtain solution A. The pH of solution A is 6.0.

[0090] Step (2): Dissolve 418.442 mL of tetrabutyl titanate in 1000 mL of anhydrous ethanol and stir until homogeneous at a stirring speed of 30-40 rpm to obtain solution B;

[0091] Step (3): Under rapid stirring at room temperature (stirring speed of 50-60 rpm), add solution B dropwise to solution A and stir rapidly to ensure complete reaction. The addition should be completed within 30-60 minutes. After the addition of solution B is complete, continue stirring and aging at a stirring speed of 30-40 rpm for 30-60 minutes. The aging process is complete to obtain the barium titanate precursor solution.

[0092] Step (4): Use Ti6Al4V alloy as the substrate. The size of Ti6Al4V alloy is 10*10*2mm. The Ti6Al4V alloy substrate is sandblasted with 24-220 mesh white corundum. After sandblasting, it is ultrasonically cleaned with anhydrous ethanol and dried to obtain the pretreated substrate.

[0093] Step (5): The barium titanate precursor solution is sprayed onto the pretreated substrate by solution plasma spraying process to prepare the barium titanate functional coating. The specific process parameters during spraying are: spraying power 70kW; spraying distance 80mm; liquid delivery rate 30mL / min; atomizing gas flow rate 12L / h; substrate preheating temperature 150℃; spray gun moving speed 500mm / s; number of spraying passes: 10 passes.

[0094] The barium titanate functional coating prepared in this embodiment has an average thickness of 21.94 μm and a porosity of 13.68%.

[0095] The electron microscope and EDS spectra of the barium titanate functional coating prepared in this embodiment are shown in the figure. Figure 16 XRD pattern can be found Figure 17The XRD and PDF peak positions of the BaTiO3 coating based on TC4 titanium alloy are basically consistent, but there is a small impurity peak near 40°, which has low intensity and has little impact on the overall structure. The diffraction peak at 45° shows signs of peak splitting and asymmetric broadening. A slight peak splitting trend and tailing phenomenon are observed at the high-angle side (approximately 45.5°), indicating the simultaneous presence of cubic and tetragonal barium titanate phases in the coating. Figure 16 as well as Figure 17 As can be seen from the example, a barium titanate functional coating was successfully prepared by solution plasma spraying. The coating has penetrating longitudinal cracks, accompanied by a small number of transverse cracks and few pores.

[0096] observe Figure 18 Scratch tests were conducted on barium titanate functional coatings based on Ti6Al4V alloy. The acoustic signal reached its maximum value when the scratch force was applied to 43.25 N.

[0097] observe Figure 19 Hardness tests were conducted on the barium titanate functional coating based on Ti6Al4V alloy, and the average hardness of the coating was 936.79 HV. 0.025 .

[0098] The hysteresis loop of the barium titanate functional coating under the maximum electric field strength that it can withstand was obtained by testing at a fixed frequency of 20 Hz. Figure 20 ,observe Figure 20 It can be seen that the barium titanate functional coating based on Ti6Al4V alloy has a maximum polarization intensity of 0.76 and a residual polarization intensity of 0.11 under a maximum electric field strength of 227 Kv / cm.

[0099] observe Figure 21 The dielectric constant of the barium titanate functional coating based on Ti6Al4V alloy shows a single decreasing trend with increasing frequency, while the dielectric loss shows a single increasing trend with increasing frequency. The dielectric constant decreases from 256.1 at a low frequency of 100Hz to 10. 6 At 152.8 Hz, the dielectric loss increases from 0.02 at 100 Hz to 10 at higher frequencies. 6 0.82 at Hz, from Figure 21 It can be concluded that the barium titanate functional coating is dominated by different polarization mechanisms. Observation Figure 22 The surface potential (KPFM) is unevenly distributed. As shown in the figure, the surface potential can reach a maximum of 368.8 mV and a minimum of 263.5 mV.

[0100] As can be seen from the above embodiments, the BaTiO3 coating prepared using this application has a controllable coating structure. By combining different plasma spraying processes, ideal BaTiO3 coatings can be prepared. The differences in performance among the above embodiments are mainly due to the different coefficients of thermal expansion of the substrate and the coating, as well as the different plasma spraying processes. That is, by adjusting different substrates and process parameters during spraying, barium titanate functional coatings with different morphologies and properties can be obtained. The embodiments show that the comprehensive electrical and mechanical properties of the barium titanate functional coating on the titanium substrate are superior to those of the barium titanate functional coatings obtained on the other two substrates. This may be because the good chemical compatibility and matching coefficients of thermal expansion between titanium and barium titanate reduce interfacial stress. Simultaneously, titanium forms a uniform TiO2 layer at high temperatures, which firmly bonds with the titanium substrate while providing a good bonding interface for the barium titanate functional coating, reducing interfacial defects and jointly promoting coating crystallization and performance.

[0101] Comparative Example

[0102] The difference between this comparative example and Example 1 is that 386.276g of barium hydroxide octahydrate was added to 140mL of glacial acetic acid, while the rest of the steps were the same as in Example 1.

[0103] The barium titanate functional coating prepared in this comparative example has an average thickness of 110.68 μm and a porosity of 13.51%.

[0104] The electron microscope image of the barium titanate functional coating prepared in this comparative example is shown below. Figure 23 XRD pattern can be found Figure 24 The XRD and PDF peak positions of the BaTiO3 coating with titanium sheet as the substrate are basically consistent. Due to cell distortion, the tetragonal barium titanate peak (200) splits into two peaks (200) and (002) near 45°. The diffraction peak at 45° in the figure shows asymmetric broadening, indicating that both cubic and tetragonal barium titanate phases exist in the coating. However, the extreme cold during plasma spraying and the presence of amorphous phases make the peak splitting indistinct. There are small impurity peaks near 40°, but their intensity is not high and has little impact on the overall structure. The overall peak intensity in the XRD figure is not high, which may be due to the low crystallinity. Figure 23 It can be seen that the barium titanate functional coating prepared in this comparative example has large longitudinal cracks, high porosity, poor melting effect, and the upper part shows coating peeling and separation.

[0105] observe Figure 25 The scratch test results of the barium titanate functional coating prepared in this comparative example can be obtained. When the scratch force is applied to 3.15N, the acoustic signal of the coating reaches the maximum value, and when the force is applied to 11.4N, the acoustic signal of the coating reaches the second critical value.

[0106] observe Figure 26The hardness of the barium titanate functional coating prepared in this comparative example can be obtained by testing. The average hardness of the coating is 467.1 HV0.025.

[0107] The hysteresis loop of the barium titanate functional coating prepared in this comparative example under the maximum electric field strength was obtained by testing at a fixed frequency of 20 Hz. Figure 27 ,observe Figure 27 It can be seen that the barium titanate functional coating prepared in this comparative example has a maximum polarization intensity of 2.76 and a residual polarization intensity of 0.96 under a maximum electric field strength of 245 Kv / cm. The hysteresis loop area in the figure is relatively large, which is due to the large number of defects in the coating.

[0108] observe Figure 28 It can be observed that the dielectric constant of the barium titanate functional coating prepared in this comparative example exhibits a single decreasing trend with increasing frequency, while the dielectric loss exhibits a single increasing trend with increasing frequency. The dielectric constant decreases from 113.1 at a low frequency of 100 Hz to 10. 6 At Hz, the dielectric loss increases from 0.035 at 100Hz to 67.9 at higher frequencies. 6 0.13 at Hz, from Figure 28 It can be concluded that the barium titanate functional coating is dominated by different polarization mechanisms. The dielectric constant and dielectric loss values ​​in the figure are unstable at low frequencies. This is because the electric field distribution is uneven due to the large number of cracks in the coating.

[0109] By comparing the coating structure and performance of the barium titanate functional coatings prepared in Example 1 and the comparative examples, it can be found that when the molar ratio of glacial acetic acid to barium hydroxide octahydrate is 2:1 (i.e., glacial acetic acid is not excessive), due to the slight volatilization of glacial acetic acid during heating, the barium hydroxide octahydrate in the system cannot be completely neutralized with glacial acetic acid, resulting in a weakly alkaline system. Tetrabutyl titanate hydrolyzes faster in a weakly alkaline environment, easily forming titanium oxide precipitates. This leads to uneven mixing of the titanium and barium sources, causing unstable liquid delivery during spraying, resulting in low coating density, numerous cracks and pores, ultimately leading to a decrease in coating hardness and adhesion, and overall performance lower than that of the embodiments of the present invention. Furthermore, when anhydrous barium hydroxide in step 1 of Example 1 is replaced with barium hydroxide in other comparative experiments, the purity of the reagent decreases due to the easy reaction of barium hydroxide with carbon dioxide in the air to form barium carbonate, which also affects the coating quality.

[0110] In summary, this invention uses barium hydroxide octahydrate as the barium source and excess glacial acetic acid as both reactant and solvent to obtain a solution A with a pH of 5.0-6.8. An ethanol solution of tetrabutyl titanate is then added dropwise to this solution. Simultaneously, the precise control of the amounts of each raw material, along with the stepwise and sequential mixing of these specific components, controls the hydrolysis rate of the titanium source. This ensures a precise match between the barium ion release kinetics and the titanium source hydrolysis rate, avoiding the situation where the titanium source hydrolyzes first to form a precipitate, followed by barium source coordination, which leads to component segregation in the system. This process prepares a high-performance barium titanate precursor solution, enabling the preparation of a barium titanate functional coating on a metal substrate surface in a single step using solution plasma spraying technology.

[0111] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. Process for the preparation of a functional coating of barium titanate in one step, characterized in that, Includes the following steps: Step 1: Add barium hydroxide octahydrate as a barium source to excess glacial acetic acid and heat in a constant temperature water bath. Stir until the solution is clear and transparent, and then let it cool to room temperature to obtain solution A. The pH of solution A is 5.0-6.

8. The molar ratio of glacial acetic acid to barium hydroxide octahydrate is (2.02~2.10):

1. The constant temperature water bath temperature is 50-60℃, and the heating and stirring time is 40-60 minutes. Step 2: Add tetrabutyl titanate as a titanium source to anhydrous ethanol and stir until homogeneous to obtain solution B; Step 3: While stirring at room temperature, add solution B dropwise to solution A; After solution B is completely added, continue stirring and aging to obtain a barium titanate precursor solution. Solution B is added dropwise over 30-60 minutes, with rapid stirring at a rate of 50-60 rpm during the addition process. During aging, the stirring is slow at a rate of 30-40 rpm. The viscosity of the barium titanate precursor solution is 0.5-10 MPa. Step 4: Use the metal material as the substrate and pretreat the substrate to obtain the pretreated substrate; Step 5: The barium titanate precursor solution obtained in Step 3 is sprayed onto the pretreated substrate obtained in Step 4 using a solution plasma spraying process, thus preparing the barium titanate functional coating.

2. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step one, the concentration of barium in solution A is 3.25-3.8 mol / L.

3. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step two, the molar ratio of titanium in the titanium source to barium in the barium source is 1:

1.

4. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step two, the stirring time is 10-20 min; the concentration of titanium in solution B is 0.74-0.86 mol / L.

5. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step three, the concentrations of barium and titanium in the barium titanate precursor solution are both 0.6-0.7 mol / L.

6. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step four, the substrate is pure titanium, titanium alloy, stainless steel or carbon steel; the pretreatment method of the substrate is as follows: after cleaning and drying the substrate, it is sandblasted with 24-220 mesh white corundum, ultrasonically cleaned with anhydrous ethanol after sandblasting, and then dried.

7. The method for preparing barium titanate functional coatings in one step according to claim 1, characterized in that, In step five, the conditions for the solution plasma spraying process are as follows: spraying distance 50-100mm; spraying power 50-100kW; total gas flow rate 100-400slpm; liquid delivery rate 10-40mL / min; atomizing gas flow rate 10-20L / h; substrate preheating temperature 120-300℃; and spray gun movement speed 400-700mm / s.

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