A method for heat treating a lead-free piezoelectric ceramic coating using a plasma torch

Abstract

This invention discloses a method for heat treatment of lead-free piezoelectric ceramic coatings using a plasma torch. The method includes steps such as preparing coating raw materials, preparing the substrate, thermal spraying, plasma torch heat treatment, and performance testing. This invention utilizes the efficient heat conduction heating technology and equipment of the plasma torch, which can greatly improve the heat transfer rate of the substrate, thereby accelerating the heat treatment time and improving the coating production efficiency.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric ceramic coating technology, and in particular to a method for heat-treating lead-free piezoelectric ceramic coatings using a plasma torch. Background Technology

[0002] Piezoelectric devices have been extensively studied for their applications in sensors, transducers, and capacitors. In recent years, researchers have sought to integrate sensors and transducers into smart structures, directly promoting the fabrication and research of piezoelectric materials. Simultaneously, the preparation of piezoelectric coatings has gradually become a popular research area. Because lead-containing piezoelectric ceramics contain lead, which is harmful to the human body, current research on piezoelectric ceramic coatings primarily focuses on lead-free piezoelectric ceramic coatings.

[0003] Traditional methods for preparing piezoelectric coatings, such as screen printing, physical vapor deposition (PVD), chemical solution deposition (CSD), and aerosol deposition (AD), cannot meet the practical requirements of open-air engineering operations, complex substrate shapes, large scale, and high productivity. Thermal spraying technology effectively avoids these shortcomings and has gradually become a mature coating preparation technology, widely used in the preparation of piezoelectric ceramic coatings (Sampath S, Schulz U, Jarligo MO, et al. Processing science of advanced thermal-barrier systems[J]. MRS bulletin,2012, 37(10): 903-910).

[0004] Ctibor P,eta prepared BT lead-free piezoelectric ceramic coatings on carbon steel substrates using thermal spraying technology. The dielectric properties of the BT lead-free piezoelectric ceramic coatings after in-furnace heat treatment were studied. Compared with those before heat treatment, both the dielectric constant and dielectric loss were greatly improved. (Ctibor P, Sedlacek J, Pala Z. Structure and properties of plasmasprayed BaTiO3 coatings after thermal posttreatment[J]. CeramicsInternational, 2015, 41(6): 7453-7460). However, the high temperature (1150℃) of traditional in-furnace heat treatment limits the application of coatings on metal substrates. The main reason is that metal substrates are easily and rapidly oxidized at high temperatures, which damages the substrate. Due to the long heat transfer time of in-furnace heat treatment on metal substrates, the required heat treatment cycle is relatively long, reducing production efficiency. Due to the large size of some engineering structures and parts, traditional in-furnace heat treatment is simply not feasible.

[0005] Scaling up the production of piezoelectric ceramic coatings requires on-site heat treatment. Plasma torch heat treatment of piezoelectric ceramic coatings effectively avoids these drawbacks. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a method for heat treatment of lead-free piezoelectric ceramic coatings using a plasma torch.

[0007] To achieve the above objectives, the technical solution provided by this invention is: a method for heat-treating lead-free piezoelectric ceramic coatings using a plasma torch, the method comprising the following steps:

[0008] 1) Weigh Bi2O3, Na2CO3, BaCO3, Li2CO3, Nb2O5, and TiO2 in a molar ratio of 1:1:0.255:0.434:0.434:4.255 for the synthesis of BNBTLN;

[0009] 2) The chemical obtained in step 1) is placed in a ball mill jar for a first ball milling, drying, sieving, pressing, and pre-calcining; then it is ball milled a second time, dried, and sieved to obtain powder.

[0010] 3) Prepare 316L stainless steel and prepare a TBC thermal barrier coating on the surface of 316L stainless steel to obtain a 316L-TBC substrate.

[0011] 4) Apply a layer of Pd / Ag bottom electrode to the surface of the 316L-TBC substrate;

[0012] 5) The BNBTLN coating material is deposited on a 316L-TBC substrate to obtain a BNBTLN coating.

[0013] 6) Perform plasma torch heat treatment on the BNBTLN coating obtained in step 5) and test its performance.

[0014] Preferably, in step 1), Na2CO3, BaCO3, and Li2CO3 are dried at 120°C for 24 hours before weighing.

[0015] Preferably, in step 2), the ball milling time is 24 hours, the rotation speed is 200 r / min, the ball milling beads are ZrO2, and the ball milling medium is anhydrous ethanol.

[0016] Preferably, in step 4), the Pd / Ag bottom electrode is brushed onto the surface of the 316L-TBC substrate using screen printing.

[0017] Preferably, in step 5), the BNBTLN coating material is deposited on the 316L-TBC substrate using argon plasma under a plasma power of 18KW via thermal spraying.

[0018] Preferably, in step 6), the BNBTLN coating is subjected to scanning heat treatment at a plasma torch temperature of 950°C, and the distance between the plasma torch and the BNBTLN coating is 120 mm.

[0019] Beneficial effects of this invention:

[0020] 1. This invention utilizes the heating technology and equipment of plasma torch for efficient heat conduction, which can greatly improve the heat transfer rate of the substrate, thereby accelerating the heat treatment time and improving the coating production efficiency.

[0021] 2. This invention utilizes plasma heating, which can improve heat transfer rate, to greatly shorten heating time, i.e., shorten heat treatment time, and can minimize oxidation of the metal substrate, thus preventing substrate damage.

[0022] 3. To address this issue, the present invention utilizes plasma torch technology, which allows operation in an open-air environment, thus effectively avoiding the drawback of some engineering structures and parts being too large to be placed inside the furnace for heat treatment. Attached Figure Description

[0023] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0024] Figure 1 These are the XRD diffraction patterns of the coating before and after heat treatment of the present invention;

[0025] Figure 2 These are comparison images of the surface morphology of the coating before and after heat treatment of the present invention;

[0026] Figure 3 These are test images of the piezoelectric properties of the coating before and after heat treatment of the present invention;

[0027] Figure 4 These are test diagrams of the dielectric properties of the coating before and after heat treatment of the present invention;

[0028] Figure 5 These are test images of the ferroelectric properties of the coating before and after heat treatment according to the present invention. Detailed Implementation

[0029] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Reference Figures 1-5 A preferred embodiment of the present invention provides a method for heat-treating a lead-free piezoelectric ceramic coating using a plasma torch, the method comprising the following steps:

[0031] 1) Weigh Bi2O3, Na2CO3, BaCO3, Li2CO3, Nb2O5, and TiO2 in a molar ratio of 1:1:0.255:0.434:0.434:4.255 for the synthesis of BNBTLN;

[0032] The purity of Bi2O3 is 99.99%, Na2CO3 is 99.5%, BaCO3 is 99.95%, Li2CO3 is 99.998%, Nb2O5 is 99.9%, and TiO2 is 99.90%.

[0033] According to [0.94(Bi 0.5 Na 0.5 TiO3-0.06BaTiO3] 0.98 -(LiNbO3) 0.02 Stoichiometry involves weighing all raw materials.

[0034] 2) The chemical obtained in step 1) is placed in a ball mill jar for a first ball milling, drying, sieving, pressing, and pre-calcining; then it is ball milled a second time, dried, and sieved to obtain powder.

[0035] After weighing, the obtained raw materials were mixed with alcohol in a ball mill jar and ball-milled for 24 hours using a planetary ball mill. The mixture was then dried and sintered in a furnace at 850°C for 2 hours, followed by sintering at 1000°C for another 5 hours. The resulting agglomerates were sieved through a screen to the desired particle size for use as coating raw materials.

[0036] 3) Prepare 316L stainless steel and prepare a TBC thermal barrier coating on the surface of 316L stainless steel to obtain a 316L-TBC substrate.

[0037] 4) Apply a bottom electrode layer to the surface of the 316L-TBC substrate;

[0038] 5) The BNBTLN coating material is deposited on a 316L-TBC substrate to obtain a BNBTLN coating.

[0039] 6) Perform plasma torch heat treatment on the BNBTLN coating obtained in step 5) and test its performance.

[0040] The principle of plasma torch heat treatment is to subject the workpiece to a vacuum heat treatment involving gas discharge. During gas discharge, ions from the selected gas strike the surface of the workpiece and penetrate into the surface layer, thus altering the chemical composition of the surface layer.

[0041] To improve the crystallinity of the perovskite phase and enhance the coating performance, the BNBTLN coating was heat-treated using a plasma torch method.

[0042] The performance test in step 6) is as follows:

[0043] X-ray diffraction (XRD) was used to test the crystal structure of the coatings before and after heat treatment. The surface morphology of the coatings before and after heat treatment was observed under field emission scanning electron microscopy (FESEM). The dielectric properties of the coatings before and after heat treatment were tested using an impedance analyzer. The ferroelectric properties of the coatings before and after heat treatment were studied using a ferroelectric analyzer at a frequency of 10 Hz. The piezoelectric properties of the heat-treated coatings were tested using a laser scanning vibrometer after polarization at 100°C with a DC electric field of 20 kV / cm for 10 min.

[0044] As a preferred embodiment of the present invention, it may also have the following additional technical features:

[0045] In this embodiment, before weighing in step 1), Na2CO3, BaCO3, and Li2CO3 are dried at 120°C for 24 hours. Since carbonate powders easily absorb moisture from the air, weighing errors are avoided.

[0046] In this embodiment, the ball milling time in step 2) is 24 hours, the rotation speed is 200 r / min, the ball milling beads are ZrO2, and the ball milling medium is anhydrous ethanol.

[0047] In this embodiment, in step 4), the Pd / Ag bottom electrode is brushed onto the surface of the 316L-TBC substrate using screen printing.

[0048] In this embodiment, in step 5), the BNBTLN coating material is deposited on the 316L-TBC substrate using argon plasma under a plasma power of 18KW via thermal spraying.

[0049] In this embodiment, step 6) involves performing a scanning heat treatment on the BNBTLN coating at a temperature of 950°C using a plasma torch, with the distance between the plasma torch and the BNBTLN coating being 120 mm.

[0050] This invention utilizes the highly efficient heat conduction technology and equipment of a plasma torch, which significantly improves the heat transfer rate of the substrate, thereby accelerating heat treatment time and increasing coating production efficiency. Furthermore, the plasma heating technology enhances heat transfer speed, greatly shortening heating time and thus heat treatment time, minimizing the risk of metal substrate oxidation and damage. Addressing this issue, the invention employs plasma torch technology that can be operated in open-air environments, effectively overcoming the limitation of some engineering structures and parts being too large to be placed in a furnace for heat treatment.

[0051] Specifically:

[0052] (1) such as Figure 1 As shown, X-ray diffraction was used to test the piezoelectric coatings before and after plasma torch heat treatment. All BNBTLN coatings deposited on the 316L-TBC substrate exhibited a perovskite phase, with slight additional diffraction peaks due to the amorphous state within the coating. After plasma torch heat treatment, all BNBTLN coatings displayed a single-phase perovskite structure. Compared to the coatings before heat treatment, the amorphous diffraction peaks disappeared, while the intensity of the crystalline diffraction peaks significantly increased. This indicates that plasma torch heat treatment effectively improved the crystallinity of the crystal.

[0053] (2) The surface morphology of the coating was observed using FESEM. Before heat treatment, a mixture of large spherical and small cubic particles was observed on the surface of the sprayed BNBTLN coating. The spherical feature was caused by the rapid solidification of the molten powder during the coating deposition process. After plasma torch heat treatment, the number of cubic particles increased, and their size was significantly larger than that of the coating before heat treatment, while the spherical feature gradually disappeared. This indicates that plasma torch heat treatment improves the crystallinity of the perovskite structure. Figure 2 As shown.

[0054] (3) The piezoelectric properties of the obtained coating were tested using a laser scanning vibrometer. The effective piezoelectric constant of the BNBTLN coating was measured to be d33 = 40 pm / v. Figure 3 As shown.

[0055] (4) Figure 4 and Figure 5 The figures show the test results for the dielectric and ferroelectric properties of the coating. Heat treatment significantly improved the dielectric constant of the BNBTLN coating, while the dielectric loss remained almost the same as before heat treatment. Figure 4 As shown; after heat treatment, the remanent polarization of the BNBTLN coating was significantly improved, and the PE curve was "higher" and "fatter" than before heat treatment, indicating that its ferroelectric properties were enhanced, such as... Figure 5 As shown.

[0056] (5) The specific electrical properties of the coating before and after plasma torch heat treatment are shown in Table 1.

[0057] Table 1. Comparison of electrical properties before and after plasma torch heat treatment

[0058] Specific Implementation Example 1:

[0060] A BNBTLN coating was synthesized using Bi₂O₃, Na₂CO₃, BaCO₃, Li₂CO₃, Nb₂O₅, and TiO₂ as raw materials. The above chemicals were weighed and placed in a ball mill jar for ball milling. The milling was performed using a planetary ball mill for 24 hours at a speed of 200 r / min.

[0061] The grinding beads and grinding media are ZrO2 and anhydrous ethanol, respectively. After ball milling, the mixture is dried, sieved, pressed into a column, pre-calcined, and sieved again to obtain the coating raw material we need.

[0062] The BNBTLN coating obtained by spraying the raw material onto a 316L-TBC substrate using thermal spraying technology was not subjected to plasma torch heat treatment. The results are as follows:

[0063] (1) Although the XRD diffraction pattern shows a perovskite phase, other slight diffraction peaks are caused by the amorphous state in the coating.

[0064] (2) The surface morphology of the coating was observed by FESEM. Before heat treatment, a mixture of large spherical and small cubic particles was observed on the surface of the sprayed BNBTLN coating. There were more spherical particles, indicating that the crystallinity of the perovskite structure was not very high.

[0065] (3) The piezoelectric properties of the obtained coating were tested using a laser scanning vibrometer, and the effective piezoelectric constant of the BNBTLN coating was measured to be d33 = 9pm / v.

[0066] (4) The dielectric properties of the coating were tested using an impedance analyzer, and its dielectric constant was found to be 538 and its dielectric loss was 0.024.

[0067] (5) The ferroelectric properties of the coating were studied using a ferroelectric analyzer, and its remanent polarization intensity was measured to be Pr = 8 μC / cm. 2 The PE curve is relatively "short" and "thin". Specific Implementation Example 2:

[0069] BNBTLN coatings were synthesized using Bi₂O₃, Na₂CO₃, BaCO₃, Li₂CO₃, Nb₂O₅, and TiO₂ as raw materials. The above chemicals were weighed and placed in a ball mill jar for ball milling. The milling was performed for 24 hours using a planetary ball mill at 200 rpm. The milling beads and milling media were ZrO₂ and anhydrous ethanol, respectively. After milling, the mixture was dried, sieved, pressed into a column, pre-calcined, and sieved again to obtain the desired coating raw material.

[0070] The raw material was sprayed onto a 316L-TBC substrate using thermal spraying technology, and the resulting BNBTLN coating was then subjected to plasma torch heat treatment. The results are as follows:

[0071] (1) All BNBTLN coatings exhibit a single-phase perovskite structure. The amorphous diffraction peaks disappear, while the intensity of the crystalline diffraction peaks is significantly enhanced, indicating a high degree of crystallinity.

[0072] (2) There are more cubic particles, and the spherical characteristics gradually disappear. The perovskite structure has a high degree of crystallinity.

[0073] (3) The piezoelectric properties of the obtained coating were tested using a laser scanning vibrometer, and the effective piezoelectric constant of the BNBTLN coating was measured to be d33 = 40 pm / v.

[0074] (4) The dielectric properties of the coating were tested using an impedance analyzer, and its dielectric constant was found to be 648 and its dielectric loss was 0.038.

[0075] (5) The ferroelectric properties of the coating were studied using a ferroelectric analyzer, and its remanent polarization intensity was measured to be Pr = 16 μC / cm. 2 The PE curve is too "high" and too "wide".

[0076] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0077] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means is within the protection scope of the present invention.

Claims

1. A method for heat-treating lead-free piezoelectric ceramic coatings using a plasma torch, characterized in that: The method includes the following steps: 1) Weigh Bi₂O₃ (99.99%), Na₂CO₃ (99.5%), BaCO₃ (99.95%), Li₂CO₃ (99.998%), Nb₂O₅ (99.9%), and TiO₂ (99.90%) with a purity of 1:1:0.255:0.434:0.434:4.255 in a molar ratio of 1:1:0.255:0.434:4.255, for the synthesis of [0.94(Bi 0.5 Na 0.5 TiO3-0.06BaTiO3] 0.98 -(LiNbO3) 0.02 (Abbreviated as BNBTLN); 2) The chemical obtained in step 1) is placed in a ball mill jar for a first ball milling, drying, sieving, pressing, and pre-calcining; then it is ball milled a second time, dried, and sieved to obtain BNBTLN coated powder. 3) Prepare 316L stainless steel and prepare a TBC thermal barrier coating on the surface of 316L stainless steel to obtain a 316L-TBC substrate. 4) A layer of Pd / Ag bottom electrode is brushed onto the surface of the 316L-TBC substrate using screen printing; 5) The BNBTLN coating material was deposited on the 316L-TBC substrate by argon plasma under a plasma power of 18KW using a thermal spraying method to obtain the BNBTLN coating. 6) Perform plasma torch scanning heat treatment on the BNBTLN coating obtained in step 5) at a temperature of 950℃, with the distance between the plasma torch and the BNBTLN coating being 120mm.

2. The method for heat-treating lead-free piezoelectric ceramic coatings using a plasma torch according to claim 1, characterized in that: Before weighing, Na2CO3, BaCO3, and Li2CO3 were dried at 120℃ for 24 hours.

3. The method for heat-treating lead-free piezoelectric ceramic coatings using a plasma torch according to claim 1, characterized in that: The ball milling process involves a milling time of 24 hours, a rotation speed of 200 r / min, ZrO2 balls, and anhydrous ethanol as the milling medium.

Images