CN116813334B - Porous lead-free piezoelectric ceramic element, air-coupled porous lead-free ultrasonic transducer and preparation method thereof - Google Patents
Porous lead-free piezoelectric ceramic element, air-coupled porous lead-free ultrasonic transducer and preparation method thereof Download PDFInfo
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Abstract
本发明公开了多孔无铅压电陶瓷元件、空气耦合多孔无铅超声换能器及其制备方法，属于超声换能器技术领域。所述元件中孔隙均匀分布，孔隙率为55％‑75％，孔结构为Gyroid；其制备方法包括：无铅陶瓷粉经光固化3D打印成多孔压电陶瓷元件。本发明公开的空气耦合多孔无铅超声换能器包含多孔压电陶瓷元件。本发明提供的多孔无铅压电陶瓷元件，通过孔隙的设计，使得声阻抗降低到5.95MRayl，利于与空气实现声阻抗。本发明提供的空气耦合多孔无铅超声换能器，检测灵敏度达到‑27dB以下。
The present invention discloses a porous lead-free piezoelectric ceramic element, an air-coupled porous lead-free ultrasonic transducer and a preparation method thereof, and belongs to the technical field of ultrasonic transducers. The pores in the element are evenly distributed, the porosity is 55%-75%, and the pore structure is Gyroid; the preparation method thereof comprises: the lead-free ceramic powder is 3D-printed into a porous piezoelectric ceramic element by photocuring. The air-coupled porous lead-free ultrasonic transducer disclosed in the present invention comprises a porous piezoelectric ceramic element. The porous lead-free piezoelectric ceramic element provided by the present invention reduces the acoustic impedance to 5.95 MRayl through the design of the pores, which is conducive to the realization of acoustic impedance with air. The air-coupled porous lead-free ultrasonic transducer provided by the present invention has a detection sensitivity of less than 27 dB.
Description
Technical Field
The invention relates to the technical field of ultrasonic transducers, in particular to a porous lead-free piezoelectric ceramic element, an air coupling porous lead-free ultrasonic transducer and a preparation method thereof.
Background
The piezoelectric air-coupled ultrasonic transducer has the advantages of complete non-invasiveness and non-contact, and has wide application in the field of nondestructive detection (such as food, medical treatment, new energy sources and the like). The traditional piezoelectric air-coupled ultrasonic transducer consists of a piezoelectric element, a matching layer, a back lining, a shielding interface, a signal wire and a shell (part of the probe is also provided with a matching circuit). The piezoelectric element is used as a core element for realizing the mutual exchange of an electric signal and an ultrasonic signal, and is mostly prepared into a 1-3 composite piezoelectric element (1 represents one-dimensional communication of piezoelectric ceramics and 3 represents three-dimensional communication of resin), a ceramic sheet is cut into a ceramic column array, epoxy resin is poured into gaps of the array, and redundant resin is removed after the resin is solidified. The 1-3 composite piezoelectric element can effectively reduce the acoustic impedance of the piezoelectric ceramic, and is beneficial to realizing the acoustic impedance matching of the piezoelectric element and air. However, as the volume fraction of the ceramic in the air coupling ultrasonic transducer 1-3 composite piezoelectric element is higher, the acoustic impedance of the air coupling ultrasonic transducer still reaches 5-30 MRayl, so that only a small part of ultrasonic waves can be received from the air entering the piezoelectric element, and the sensitivity of the air coupling ultrasonic transducer is limited.
At present, the sensitivity of the piezoelectric air-coupled ultrasonic transducer (used for analysis of composite materials and metal flaw detection) with the working frequency of 200-500 kHz in the market is-30 to-40 dB (the test distance is 10 cm). Compared with the sensitivity of the underwater acoustic transducer which is-10 to-20 dB (the test distance is 50 cm), the method has a larger difference. Therefore, the air-coupled ultrasonic transducer is difficult to respond to small signals generated by partial material defects (defects deeper inside the material), and the use scene of the air-coupled ultrasonic transducer is limited.
Piezoelectric ceramics adopted by the traditional transducer are mostly PZT materials, and the materials contain lead, so that the environment is polluted, and the disposal cost after scrapping is increased.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a porous piezoelectric ceramic element, an air coupling porous lead-free ultrasonic transducer and a preparation method thereof. The element is prepared from lead-free ceramics as raw materials to eliminate environmental pollution and facilitate subsequent recovery treatment. And lead-free ceramics need to have good piezoelectric performance so that the transducer can better realize the conversion of electric energy and acoustic energy, and the performance of the transducer is improved. According to the invention, the porous piezoelectric element is prepared in a 3D printing (DLP) mode to realize the adjustable porosity of the piezoelectric element, and the acoustic impedance of the piezoelectric element is adjusted by adjusting the porosity, so that the difficulty in matching the piezoelectric element with the acoustic impedance of air is reduced, and the sensitivity of the transducer for receiving signals is improved.
The technical scheme of the invention is as follows:
The porous lead-free piezoelectric ceramic element has pores distributed homogeneously and porosity of 55-75% and pore structure Gyroid, and is prepared through photocuring 3D printing.
In a more preferable technical scheme, the pores are in various shapes such as spheres, diamonds and the like, and have better strength, high piezoelectricity and low acoustic impedance by combining pore distribution and pore structure.
In a more preferable technical scheme, the chemical formula of the lead-free ceramic powder is 0.51Ba (Zr 0.2Ti0.8)O3-0.49(Ba0.7Ca0.3)TiO3).
In a more preferable technical scheme, the 3D printing further comprises the steps of designing the pore size, the shape of the pores and the porosity by using Matlab plug-in units according to actual use requirements.
The preparation method of the porous lead-free piezoelectric ceramic element comprises the following steps:
s1, preparation of lead-free ceramic powder
Placing BaTiO 3,TiO2,CaCO3,ZrO2 powder into a ball milling tank according to a chemical formula of 0.51Ba (Zr 0.2Ti0.8)O3-0.49(Ba0.7Ca0.3)TiO3), pouring absolute ethyl alcohol into the ball milling tank to submerge the powder, placing the ball milling tank into a ball mill, ball milling the powder for 10-14 h at a rotating speed of 260r/min, drying the powder to obtain powder, placing the powder into a crucible to presintered in a muffle furnace, heating the powder to 1220-1250 ℃ at a heating rate of 4-5 ℃ during presintering, preserving the heat for 3-5 h, placing the presintered ceramic powder into the ball milling tank, adding absolute ethyl alcohol, ball milling the ceramic powder for 20-30 h at a rotating speed of 260r/min, drying the ball milling slurry for 12-14 h to obtain ceramic powder, and sieving the ceramic powder with a sieve of 60-100 meshes to obtain ceramic powder with small and uniform particle size required by 3D printing;
S2.3D printing porous leadless piezoelectric ceramic element
The ceramic powder prepared in the step S1 is made into printing slurry, the slurry is poured into DLP printing, a Matlab plug-in is used for designing a required void structure and void ratio, the printing is carried out layer by layer under illumination for 15S under the power of 10mW/cm 2, the printed printing piece is subjected to glue discharging, a tube furnace is selected for vacuum glue discharging, the temperature is increased to 200 ℃ at 0.2 ℃ per minute, the temperature is kept for 2 hours, the temperature is increased to 400 ℃ at 0.3 ℃ per minute, the temperature is kept for 3 hours, and the temperature of the printing piece subjected to glue discharging is increased to 1500 ℃ in a muffle furnace for 4 hours.
In a more preferable technical scheme, in step S2, the step of preparing the ceramic powder prepared in S1 into printing slurry specifically includes the following steps:
The ceramic powder prepared in the step S1 is weighed and poured into a ball mill tank, dispersant and surfactant with the mass of 1% of the ceramic powder are added, absolute ethyl alcohol and zirconia balls are added, the mixture is ground for 12 hours at the rotating speed of 300rpm, the mixture is placed into an oven for 10 hours after ball milling, absolute ethyl alcohol is fully removed, the mixture is ground by a mortar, and passes through a 200-mesh fine screen, finally ceramic fine powder with uniform particle size distribution and surface modification treatment is obtained, the modified ceramic fine powder with the corresponding mass is weighed according to the solid content requirement (volume fraction of 42% -49%) of the piezoelectric ceramic slurry, triton X-100 dispersant with the mass of 0.5% -2% of the mass of the piezoelectric ceramic powder is weighed, proper acrylate monomers (such as HEA, HDDA, TMPTA and the like) are selected according to the requirements of photocuring activity and viscosity of the piezoelectric ceramic slurry, the viscosity of 3D printing slurry is gradually increased along with the gradual increase of the acrylate monomer, the mass of 1% -3% of TPO photoinitiator is finally weighed, the silicon fine powder with the mass of 0.5% -0.6% of the total mass of the piezoelectric ceramic slurry is obtained, the ceramic slurry is subjected to uniform foam removal, the ultrasonic dispersion is carried out by the ultrasonic dispersion is carried out for 3 minutes, the high-low-speed vibration, the ceramic slurry is subjected to high-vibration, and the final vibration is carried out for 3 min, and the final vibration is carried out, and the slurry is subjected to high-vacuum ball milling and the high-grinding treatment, and the final slurry is obtained, and the slurry is subjected to high-vacuum and high-mixing and has high activity conditions.
An air-coupled porous lead-free ultrasonic transducer comprising the porous piezoelectric ceramic element described above.
The preparation method of the air-coupled porous lead-free ultrasonic transducer comprises the following steps:
S3, preparation of air coupling porous ultrasonic transducer
Mixing epoxy resin, a curing agent and hollow glass beads according to a mass ratio of 5:1:5-6, curing for 8-12 hours at 80 ℃ to obtain a matching layer, polishing the cured matching layer to 2mm, and bonding the matching layer to a porous piezoelectric ceramic element through a porous piezoelectric element connecting wire to obtain the air coupling porous transducer.
The air-coupled porous transducer provided by the invention directly uses air as a back lining, and has high sensitivity.
It should be noted that the epoxy resin and the curing agent described in the present invention are optional common combinations for those skilled in the art, and the e51 epoxy resin and the t31 curing agent are taken as examples in the embodiment of the present invention.
Compared with the prior art, the invention has the following beneficial effects:
According to the porous lead-free piezoelectric ceramic element provided by the invention, through the design of the pores, the acoustic impedance is reduced to 5.95MRayl, the acoustic impedance is favorably realized with air, and the energy of ultrasonic waves received in the air is increased.
The air coupling porous lead-free ultrasonic transducer provided by the invention has the detection sensitivity reaching below-27 dB, and is beneficial to the detection of small signal defects generated on a material part.
Drawings
FIG. 1 is a graph showing the piezoelectric constant test results of piezoelectric ceramics.
Fig. 2 is a plot of porosity versus piezoelectric constant.
Fig. 3 is a relationship of porosity to piezoelectric voltage coefficient.
Fig. 4 is a plot of porosity versus acoustic impedance.
Fig. 5 is a physical diagram of the prepared lead-free porous piezoelectric ceramic element (a) and the air-coupled porous lead-free ultrasonic transducer (b).
Fig. 6 is the results of the performance test of the air-coupled porous lead-free ultrasonic transducer of example 6.
Fig. 7 is the results of the performance test of the air-coupled porous lead-free ultrasonic transducer of comparative example 1.
Detailed Description
Examples 1 to 5
The porous lead-free ceramic element has the porosity of 55%, 60%, 65%, 70% and 75% in sequence, a pore structure of Gyroid and a diamond-shaped pore shape, and the preparation method comprises the following steps:
Step1, preparation of leadless ceramic powder
The step is to prepare the ceramic powder required by the preparation of the porous piezoelectric element for the subsequent photocuring 3D printing. The preparation method comprises the steps of weighing BaTiO 3,TiO2,CaCO3,ZrO2 according to a chemical formula of 0.51Ba (Zr 0.2Ti0.8)O3-0.49(Ba0.7Ca0.3)TiO3) (with good piezoelectric property and no toxicity and environmental friendliness), placing the prepared powder into a ball milling tank, pouring absolute ethyl alcohol to submerge the powder, placing the ball milling tank into a ball mill, ball milling for 12h at a rotating speed of 260r/min, pouring the slurry into a tray after ball milling for drying for 12h to obtain ceramic powder, placing the powder into a crucible for presintering in a muffle furnace, heating to 1230 ℃ at a heating rate of 4 ℃ for heat preservation for 5h during presintering, placing the presintering ceramic powder into the ball milling tank, adding absolute ethyl alcohol, ball milling for 24h at a rotating speed of 260r/min, drying the ball milling slurry for 12h to obtain ceramic powder, and sieving the ceramic powder with a 60-mesh sieve to obtain the ceramic powder with small and uniform particle size required by 3D printing.
To test the performance of the ceramic powder, the ceramic powder prepared in examples 1 to 5 was granulated using PVA, and dry-pressed to form a ceramic sheet of Φ10x0.5mm (pressure 80 to 100MPa, dwell time 30 to 60 s). Sintering in a muffle furnace, heating to 650 ℃ at a heating rate of 2.5 ℃ per minute, maintaining the temperature for 30min to remove PVA, and heating to 1500 ℃ from 650 ℃ per minute for 4h after the glue discharging is finished. The sintered ceramic sheet was coated with low temperature silver paste as an electrode (baked at 90 ℃). The ceramic plate was polarized at a voltage of 3kV/mm for 10min at normal temperature. The piezoelectric properties of the ceramic sheet were measured using a quasi-static d33 tester as shown in FIG. 2.
As can be seen from FIG. 2, the piezoelectric properties of the prepared lead-free ceramics are about 405pC/N, and the piezoelectric properties of the PZT-5 piezoelectric ceramics which are commercially available are about 420-480 pC/N, which are widely different.
Step 2 printing of the porous piezoelectric element
The step is divided into preparation of printing slurry, printing of the piezoelectric element with the porous structure and sintering of ceramics. The preparation of printing slurry, namely weighing self-made piezoelectric ceramic powder with certain mass, pouring the self-made piezoelectric ceramic powder into a ball milling tank, adding a dispersing agent and a surfactant, wherein the mass of the dispersing agent is 1% of that of the piezoelectric ceramic powder, adding absolute ethyl alcohol and zirconia balls, milling the mixture for 12 hours at a rotating speed of 300rpm, placing the mixture into a baking oven for 10 hours after ball milling, fully removing the absolute ethyl alcohol, milling the mixture by a mortar, and sieving the mixture by a 200-mesh sieve to finally obtain the piezoelectric ceramic powder with uniform particle size distribution and surface modification treatment. According to the solid content requirement of the piezoelectric ceramic slurry, the modified piezoelectric ceramic powder with the corresponding mass is weighed, and Triton X-100 dispersing agent with the mass of 0.5% -2% of the mass of the piezoelectric ceramic powder is weighed. According to the requirements of the photocuring activity and viscosity of the piezoelectric ceramic slurry, selecting a proper acrylic monomer, weighing a TPO photoinitiator with the mass of 1-3% of the mass of the monomer, and finally weighing a non-silicon defoamer accounting for 0.5% of the total mass of the piezoelectric ceramic slurry. Mixing all the above components by ultrasonic vibration for 30min, and placing into a ball milling tank. Ball milling is carried out for 3 hours at the rotating speed of 250rpm, and the obtained slurry is subjected to vacuum defoaming treatment, so that the piezoelectric ceramic slurry with low viscosity, high solid content, high photo-curing activity and uniform dispersion is finally obtained. 3D printing of porous ceramics, firstly, pouring slurry into DLP printing by using a void structure and a void ratio required by Matlab plug-in design, and printing layer by illumination for 15s under the power of 10mW/cm 2. And discharging the glue of the printed piece, namely heating the printed piece to 200 ℃ by adopting a tube furnace for vacuum glue discharging at 0.2 ℃ per min, preserving heat for 2 hours, heating the printed piece to 400 ℃ at 0.3 ℃ per min, and preserving heat for 3 hours. And heating the printing piece subjected to glue discharge in a muffle furnace at 5 ℃ per min for 1500 ℃ and preserving heat for 4 hours.
The sintered printing piece is coated with medium-temperature silver paste as an electrode (the temperature is raised to 500 ℃ per minute for 1 h). The print was polarized at normal temperature for 10min at a voltage of 3 kV/mm. Its piezoelectric constant was tested. As a result, as shown in fig. 3, the piezoelectric constant of the piezoelectric element remains substantially unchanged as the porosity increases. The piezoelectric constant d 33 was tested using a ZJ-3AN quasi-static d 33 tester.
The dielectric constants of the ceramics with different porosities are tested by using a digital bridge, the piezoelectric voltage constant g 33 of the ceramics with different porosities is obtained by calculation, the calculation formula is shown in the figure, and the result is shown in figure 4. As the piezoelectric ceramic porosity increases, the piezoelectric voltage constant g 33 rises. The high piezoelectric voltage is beneficial to improving the sensitivity of the ultrasonic transducer as a receiving probe.
Wherein ε r is the relative permittivity, ε is the sample permittivity, ε 0＝8.85x10-12 F/m is the permittivity of air.
The acoustic impedance is calculated from the following formula:
Z=ρc(4)
c=2fpt (5)
Where Z is acoustic impedance, c is sample acoustic velocity, ρ is sample density, f p is antiresonant frequency (measured by digital bridge), and t is sample thickness.
As shown in fig. 5, the acoustic impedance of the porous piezoelectric element gradually decreases as the porosity increases, which is advantageous to match with the acoustic impedance of air, increase the ultrasonic transmittance, and improve the ultrasonic energy transmission efficiency.
However, the strength of the ceramic was lowered and the piezoelectric performance was lowered due to the increase in the porosity of the ceramic, and in this experiment, a porous ceramic having a porosity of 70% was selected as the piezoelectric element (d 33: 327pC/N, acoustic impedance: 5.95 MRayl).
Example 6
A porous lead-free piezoelectric ceramic element in which the shape of the pores was spherical was obtained in the same manner as in example 1.
Example 7
An air-coupled porous ultrasonic transducer comprising the porous lead-free piezoelectric ceramic element prepared in example 5 was prepared as follows:
Step 3, preparation of air coupling porous ultrasonic transducer
And (3) preparing a matching layer, namely mixing the e51 epoxy resin with the t31 curing agent and the hollow glass beads according to a mass ratio of 5:1:6. Curing for 8h at 80 ℃ and polishing the cured matching layer to 2mm. And bonding the matching layer to the porous piezoelectric ceramic by connecting wires of the porous piezoelectric element, and selecting an air back to prepare the air coupling porous transducer.
As shown in FIG. 6, the sensitivity of the air coupling transducer tested at 10cm is-27 dB, compared with the sensitivity of the air coupling transducer at-30 to-40 dB in the market, the performance is greatly improved, small signals generated by partial defects of the material can be better detected, and the deep defects of the material are analyzed.
Comparative example 1
The piezoelectric ceramic support d 33 with the porosity of 40% is 372pC/N, g 33 is 43.87mV.m/N, acoustic impedance is 13MRayl, and the test result of the piezoelectric ceramic support d 33 is shown in FIG. 7:
the test result shows that the sensitivity is-46 dB, and the receiving sensitivity is poorer than that of porous piezoelectric ceramics with 70% porosity.
Comparative example 2
The piezoelectric ceramic bracket with the porosity of 80 percent has incomplete structure due to the damage caused by low strength in the printing sintering and thermal polarization processes due to the too high porosity, and is difficult to be used for preparing the air-coupled porous ultrasonic transducer.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (5)
1. The preparation method of the air coupling porous lead-free ultrasonic transducer is characterized in that,
The air coupling porous lead-free ultrasonic transducer comprises a porous lead-free piezoelectric ceramic element;
3D printing is carried out on the lead-free ceramic powder to obtain a porous lead-free piezoelectric ceramic element, wherein the pores in the porous lead-free piezoelectric ceramic element are uniformly distributed, the porosity is 55% -75%, and the pore structure is Gyroid;
Mixing epoxy resin, a curing agent and hollow glass beads according to a mass ratio of 5:1:5-6, curing for 8-12 hours at 80 ℃ to obtain a matching layer, polishing the cured matching layer to 2mm, bonding the matching layer to porous piezoelectric ceramics by using a porous lead-free piezoelectric element connecting wire to obtain an air coupling porous transducer;
The preparation method of the porous lead-free piezoelectric ceramic element comprises the following steps:
s1, preparation of lead-free ceramic powder
Placing BaTiO 3,TiO2,CaCO3,ZrO2 powder into a ball milling tank according to a chemical formula of 0.51Ba (Zr 0.2Ti0.8)O3-0.49(Ba0.7Ca0.3)TiO3), pouring absolute ethyl alcohol into the ball milling tank to submerge the powder, placing the ball milling tank into a ball mill, ball milling the powder for 10-14 h at a rotating speed of 260r/min, drying the powder to obtain powder, placing the powder into a crucible to presintered in a muffle furnace, heating the powder to 1220-1250 ℃ at a heating rate of 4-5 ℃ during presintering, preserving the heat for 3-5 h, placing the presintered ceramic powder into the ball milling tank, adding absolute ethyl alcohol, ball milling the ceramic powder for 20-30 h at a rotating speed of 260r/min, drying the ball milling slurry for 12-14 h to obtain ceramic powder, and sieving the ceramic powder with a sieve of 60-100 meshes to obtain ceramic powder with small and uniform particle size required by 3D printing;
S2.3D printing porous leadless piezoelectric ceramic element
Pouring the ceramic powder prepared in the step S1 into a DLP printer, using Matlab plug-in to design a required void structure and void ratio, illuminating for 15S to print layer by layer under the power of 10mW/cm 2, discharging glue from the printed printing part, heating the printing part to 200 ℃ by selecting a tubular furnace for vacuum glue discharging at 0.2 ℃ per min, preserving heat for 2h, heating to 400 ℃ at 0.3 ℃ per min, preserving heat for 3h, heating the printing part after glue discharging to 1500 ℃ in a muffle furnace at 5 ℃ per min, and preserving heat for 4h;
in step S2, the step of preparing the ceramic powder prepared in S1 into printing paste specifically includes the following steps:
The ceramic powder prepared in the step S1 is weighed and poured into a ball mill tank, dispersant and surfactant with the mass accounting for 1% of the mass of the ceramic powder are added, absolute ethyl alcohol and zirconia balls are added, the mixture is ground for 12 hours at the rotating speed of 300rpm, the mixture is placed into a baking oven for 10 hours after ball milling, absolute ethyl alcohol is fully removed, the mixture is ground by a mortar, and passes through a 200-mesh fine screen, finally ceramic fine powder with uniform particle size distribution and surface modification treatment is obtained, the modified ceramic fine powder and Triton X-100 dispersant with the mass accounting for 0.5% -2% of the mass of the piezoelectric ceramic powder are weighed, acrylate monomers and non-silicon defoamer with the mass accounting for 1% -3% of the mass of the monomers are weighed and mixed for 30-40 minutes by ultrasonic vibration, and the obtained slurry is put into a ball mill tank for 3-4 hours at the rotating speed of 250rpm, and finally piezoelectric ceramic printing slurry is obtained by vacuum defoaming treatment.
2. The method according to claim 1, wherein the lead-free ceramic powder has a chemical formula of 0.51Ba (Zr 0.2Ti0.8)O3-0.49(Ba0.7Ca0.3)TiO3.
3. The method of claim 1, wherein the 3D printing further comprises designing pore size, pore shape and porosity using Matlab inserts.
4. A method of manufacturing according to claim 3, wherein the shape of the hole comprises any one of spherical shape and diamond shape.
5. The method of claim 1, wherein the acrylic monomer comprises any one of HEA, HDDA, TMPTA.
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