A barium titanate-based ptc ceramic material and a method for producing the same
By coating the surface of barium titanate-based PTC ceramics with MnO2-doped barium borosilicate glass-phase precursors and combining it with a segmented sintering process, the contradiction between grain boundary oxidation and densification is resolved, achieving a balance in performance, improving the step-up resistance ratio and resistance stability, and making it suitable for self-temperature-controlled heating elements and overcurrent protection devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YIDU BOTONG ELECTRONIC CO LTD
- Filing Date
- 2026-03-23
- Publication Date
- 2026-06-09
AI Technical Summary
In the preparation of barium titanate-based PTC ceramics, it is difficult to optimize the sufficiency of grain boundary oxidation and the final degree of densification in a coordinated manner, resulting in poor room temperature resistivity and resistance ratio performance.
A modified barium titanate powder was coated with a MnO2-doped barium borosilicate glass phase precursor. The oxidation was promoted at medium and low temperatures and the pores were filled at high temperatures through a segmented sintering process. Combined with a boric acid-polyvinyl alcohol dynamic soft gel network to protect the integrity of the coating layer, the porosity and interfacial reaction were synergistically optimized.
It significantly improves the step-up resistance ratio, resistance stability and mechanical reliability of PTC ceramics, and achieves a performance balance between room temperature conductivity and thermal switching characteristics, making it suitable for self-temperature controlled heating elements and overcurrent protection devices.
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Abstract
Description
Technical Field
[0001] This application relates to the field of ceramic materials, and in particular to a barium titanate-based PTC ceramic material and its preparation method. Background Technology
[0002] Positive temperature coefficient (PTC) thermistor ceramics are a class of functional materials whose resistivity increases by orders of magnitude with increasing temperature near the Curie temperature. Barium titanate (BaTiO3)-based PTC ceramics, with their advantages of adjustable Curie temperature, high chemical stability, and moderate cost, have been widely used in self-regulating heating elements, overcurrent protection devices, temperature sensing, and automotive electronics. The realization of high-performance barium titanate-based PTC ceramics relies on the precise coordination of microstructures: on the one hand, the ceramic matrix must be composed of highly n-type semiconducting grains with high density to ensure low and stable resistivity and good mechanical properties at room temperature; on the other hand, a high and uniform barrier layer must be formed at the grain boundaries, which is the core mechanism for generating a significant PTC effect (i.e., high resistance-to-weight ratio). The construction of this barrier layer depends on the oxidation behavior of the grain boundary regions during sintering, i.e., through oxygen vacancy recombination and oxygen ion adsorption, forming an oxygen-rich insulating layer at the grain boundaries, thereby effectively hindering electron migration across grain boundaries.
[0003] In traditional manufacturing processes, the sufficiency of grain boundary oxidation is highly dependent on the diffusion efficiency of oxygen in the green body. To promote deep oxygen penetration into the grain boundaries, a moderate level of interconnected porosity needs to be maintained during the low-to-medium temperature sintering stage (not exceeding 1000℃) to construct effective gas transport channels. However, this requirement is fundamentally contradictory to the goal of ultimately obtaining a highly dense ceramic matrix. Specifically, if a higher porosity is deliberately maintained or the densification process is delayed to enhance oxidation, it will be difficult to completely eliminate residual pores during the high-temperature sintering stage, resulting in excessively high room temperature resistivity, poor conductivity uniformity, and decreased mechanical strength. Conversely, if the formation of particle sintering necks and pore closure are accelerated to pursue high density (e.g., by increasing the heating rate or adding strong sintering aids), it is easy to cause premature pore closure, severely hindering oxygen diffusion to the grain boundaries, resulting in insufficient grain boundary oxidation and insufficient barrier height, ultimately manifesting as a significant decrease in the up-resistance ratio and weakened PTC switching characteristics. Summary of the Invention
[0004] This application provides a barium titanate-based PTC ceramic material and its preparation method, aiming to solve the technical problem of difficulty in synergistically optimizing the sufficiency of grain boundary oxidation and the final densification degree in the preparation of high-performance barium titanate-based PTC ceramics, and to achieve a performance balance between room temperature resistivity and resistance ratio.
[0005] In a first aspect, this application provides a barium titanate-based PTC ceramic material, which is made of modified barium titanate and donor dopant in a mass ratio of 100:0.05 to 0.2. The modified barium titanate includes barium titanate and a MnO2-doped barium borosilicate glass phase precursor coated on the surface of barium titanate. The sintering method of the PTC ceramic material is as follows: the ceramic blank is placed in a reducing atmosphere and heated to 600 to 700°C for debinding; then it is placed in an oxygen-containing atmosphere and heated to 750 to 850°C for catalytic oxidation; and then sintered in an oxygen-containing atmosphere at 1200 to 1350°C.
[0006] In any of the above technical solutions, the molar ratio of BaO, B2O3, and SiO2 in the MnO2-doped barium borosilicate glass precursor is 1:(1.5-2.5):(5-7); and the mass fraction of MnO2 in the MnO2-doped barium borosilicate glass precursor is 5%-8%.
[0007] In any of the above technical solutions, the reducing atmosphere is selected from H2 / N2 mixture or CO / N2 mixture.
[0008] In any of the above technical solutions, the oxygen concentration of the oxygen-containing atmosphere is ≤5%.
[0009] In any of the above technical solutions, the heating rate of the debinding stage is 1-3℃ / min, and the holding time is 2-3h; the heating rate of the catalytic oxidation stage is 3-5℃ / min, and the holding time is 1-2h; the heating rate of the sintering stage is 5-10℃ / min, and the holding time is 2-4h.
[0010] In any of the above technical solutions, the D50 particle size of the barium titanate is 0.8 to 1.2 μm.
[0011] In any of the above technical solutions, the method for preparing the modified barium titanate is as follows:
[0012] Tetraethyl orthosilicate, trimethyl borate, barium nitrate, and chelating agent were added sequentially to anhydrous ethanol and stirred until homogeneous to obtain a precursor solution. Deionized water was added dropwise to the solution, and the pH was adjusted to 8-9 with ammonia. The solution was stirred to hydrolyze the precursor. Manganese nitrate solution was added and stirred until homogeneous to obtain a composite sol.
[0013] The composite sol is uniformly sprayed onto the surface of barium titanate particles by spray coating, the coated powder is dried, and then heat-treated at 400-500℃ to obtain the final product.
[0014] In any of the above technical solutions, the chelating agent is preferably citric acid.
[0015] In any of the above technical solutions, the hydrolysis time is preferably 1 to 2 hours.
[0016] In the spray coating process, the amount of composite sol accounts for 2.5 to 4.0 wt% of the total mass of composite sol and barium titanate.
[0017] The modified barium titanate used in this application achieves synergistic optimization of porosity and interfacial reactions throughout the sintering process by coating the surface with a MnO2-doped barium borosilicate glass precursor. Specifically, during the binder removal stage at 600–700°C, binder removal and reduction sintering help generate oxygen vacancies within the ceramic body, promoting the subsequent formation of oxygen-containing grain boundary layers and reducing room temperature resistivity. Furthermore, under a reducing atmosphere, MnO2 is partially converted to Mn2O3, and Mn... 3+ As an acceptor dopant, it is uniformly distributed at the grain boundaries, providing active sites for subsequent catalytic oxidation. During the catalytic oxidation stage at 750–850℃, the high silicon content keeps the glassy precursor in a high-viscosity softened state rather than a melted state. Together with the interconnecting pores of the uniformly dispersed manganese oxide, it forms a physical isolation layer between particles, effectively inhibiting the premature formation of sintering necks in barium titanate particles, maintaining a high porosity, and providing a continuous channel for oxygen to diffuse into the depth of the grain boundaries. Meanwhile, Mn... 3 It possesses excellent redox catalytic activity, efficiently adsorbing and activating gaseous oxygen molecules, promoting their dissociation into active oxygen species, accelerating the recombination reaction of oxygen vacancies at grain boundaries, and driving the formation of oxygen-containing grain boundary layers, which is beneficial for building grain boundary barriers. After entering the sintering stage at 1200–1350℃, the glassy precursor fully melts into a low-viscosity melt, efficiently filling residual micropores under capillary action, significantly increasing density, effectively improving mechanical strength and reducing room temperature resistivity; the molten glassy precursor also acts as a highly active ion channel, promoting the addition of external donor dopants (such as Nb). 5+ Mn diffuses uniformly into the crystal lattice, ensuring uniform semiconductivity of the grains. Simultaneously, Mn... 3+ Partially dissolved at high temperature at grain boundaries (replacing Ti) 4+ The location of the manganese oxide, together with the formed oxygen-containing grain boundary layer, constructs a high and uniform double grain boundary barrier, improving the lift-to-drag ratio. In the catalytic oxidation and sintering process, the valence state change of manganese oxide leads to a functional transformation, which, in conjunction with the phase transformation of the glassy precursor, effectively resolves the contradiction between the need for high porosity in oxidation and the need for closed pores in compaction.
[0018] It should be noted that the high SiO2 content in the barium borosilicate glass precursor coating layer keeps the glass precursor in a high-viscosity softened state (non-molten) during the catalytic oxidation stage at 750–850℃, effectively inhibiting premature sintering of barium titanate particles and maintaining interconnected pores. B2O3 not only enhances the glass-phase structure against Nb... 5+ Mn 3+Plasma's dissolving power accelerates its diffusion; it also weakens the SiO2 network strength, enabling the glass phase precursor to possess sufficient fluidity at 1200–1350℃, promoting pore filling and densification. BaO, on the one hand, enhances the chemical compatibility (both containing Ba) between the glass phase precursor and the BaTiO3 matrix, improving interfacial wetting, promoting uniform coating and pore filling, which is beneficial for Nb. 5+ On the one hand, it facilitates the migration of donor ions in the glass phase; on the other hand, it provides an alkaline environment, which is conducive to the migration of Mn. 3+ It remains stable during the catalytic oxidation stage.
[0019] It is worth noting that in traditional preparation processes, the raw material powders (BaO, B2O3, SiO2) of the barium borosilicate glass phase precursor are usually added separately to barium titanate, blended, and then pressed and sintered. However, this method results in the random dispersion of the glass phase precursor powders, which are prone to agglomeration or segregation. This leads to an excess (insulation) or absence of glass phase at local grain boundaries, making it difficult to form an isolation film and achieve the porosity control effect mentioned above during sintering. That is, maintaining interconnected porosity in the medium and low temperature stages to ensure sufficient oxidation of grain boundaries, and efficiently filling pores to improve density in the high temperature stage. In addition, the MnO2 powder is separated from the glass phase precursor and barium titanate, and tends to agglomerate inside the glass phase precursor during sintering, far from the grain boundaries, and cannot effectively exert its catalytic oxidation effect.
[0020] In any of the above technical solutions, the donor dopant is selected from one or more of niobium pentoxide, antimony pentoxide, and lanthanum oxide.
[0021] Preferably, the PTC ceramic material has a resistance ratio ≥3.0×10⁴ and a room temperature resistivity <100Ω·cm; suitable for applications in temperature sensors and other fields.
[0022] In any of the above technical solutions, the raw materials for preparing the PTC ceramic material include: a premix of barium titanate and donor dopant, a polyvinyl alcohol solution of 6-8 wt% of the premix, and a dispersant of 0.5-2 wt% of the premix.
[0023] In any of the above technical solutions, the raw materials for preparation include boric acid, and the amount of boric acid used is 1.5 to 2.5% of the dry weight of the polyvinyl alcohol solution.
[0024] Secondly, this application provides a method for preparing a barium titanate-based PTC ceramic material, comprising the following steps:
[0025] The premix of modified barium titanate and donor dopant, polyvinyl alcohol solution, dispersant, and boric acid are mixed and granulated to obtain granulated material; the granulated material is then pressed into ceramic green body under a pressure of 150-200 MPa.
[0026] The ceramic blank is heated to 600-700℃ to remove the binder; then heated to 750-850℃ and held for catalytic oxidation; then heated to 1200-1350℃ for sintering to obtain the final product.
[0027] In any of the above technical solutions, the concentration of the polyvinyl alcohol solution is 4-8 wt%.
[0028] In any of the above technical solutions, the dispersant is selected from one or more of ammonium polyacrylate, ammonium citrate, or triethanolamine.
[0029] In the granulation process, boric acid and polyvinyl alcohol, under weakly alkaline conditions or mechanical shear heat, form a dynamic three-dimensional soft gel network in situ with BO coordination bonds as nodes. This network provides a certain buffering effect under high pressure of 150–200 MPa. The reversible fracture of the coordination bonds absorbs impact energy, effectively dispersing stress and preventing microcracks or peeling of the MnO2-doped barium borosilicate glass phase precursor coating on the modified barium titanate surface due to localized stress concentration. The integrity of this coating layer has a significant impact on the performance of PTC ceramics. If the coating layer is damaged, the particle isolation and catalytic oxidation functions will be weakened during sintering, leading to disordered pore closure, insufficient grain boundary oxidation, and uneven barrier height. This directly causes a decrease in the up-resistivity ratio and an abnormal increase in room temperature resistivity, weakening the PTC switching characteristics and long-term stability. Thanks to the shear-thinning properties of the coordination network, this soft gel ensures the integrity of the coating layer while having minimal impact on the flowability of the granulated material, ensuring a uniform and dense green body structure.
[0030] It should be noted that the soft gel network formed by the coordination of boric acid and polyvinyl alcohol does not affect the decomposition and volatilization of the adhesive during the high-temperature sintering process, and the adhesive can be discharged normally.
[0031] In summary, this application has the following beneficial effects:
[0032] This application achieves porosity control during sintering through the synergistic combination of MnO2-doped barium borosilicate glass precursor coating and segmented sintering processes. During the medium- and low-temperature stages, interconnected pores are maintained to ensure sufficient grain boundary oxidation, while the high-temperature stage efficiently fills pores to increase density. Simultaneously, a double grain boundary barrier is constructed, enhancing the uniform diffusion of donor elements. A boric acid-polyvinyl alcohol dynamic soft gel buffer system is used to protect the integrity of the coating layer structure, thereby achieving a performance balance between the room-temperature conductivity and thermistor switching characteristics of PTC ceramics. This significantly improves its resistance ratio, resistance stability, and mechanical reliability, providing key material support for high-performance self-regulating temperature devices and overcurrent protection components. Detailed Implementation
[0033] Preparation Example
[0034] Preparation Example 1: Modified barium titanate was prepared by the following method:
[0035] 125.0 g (0.6 mol) of tetraethyl orthosilicate, 41.6 g (0.4 mol) of trimethyl borate, 26.1 g (0.1 mol) of barium nitrate, and 25.0 g of citric acid were sequentially added to 2.0 L of anhydrous ethanol. The mixture was stirred at 300 rpm for 30 min at 30 °C to obtain a clear precursor solution. While stirring continuously, 150 mL of deionized water was added dropwise at a rate of 20 mL / min, and the pH of the system was adjusted to 9 with 5% ammonia solution. Stirring continued for 1.5 h to allow the precursor to fully hydrolyze and condense. Subsequently, 80 mL of an aqueous solution of 12.0 g (0.048 mol) of manganese nitrate (tetrahydrate) was added, and the mixture was stirred for 1 h to obtain a composite sol. The molar ratio of each raw material, based on the final oxides formed, was approximately 1:2:6 for BaO, B₂O₃, and SiO₂; the mass fraction of MnO₂ was approximately 6.0%.
[0036] Using a centrifugal spray drying device, 100g of the above composite sol was uniformly sprayed onto the surface of barium titanate powder (approximately 3.1kg) with a D50 of 1.0μm under conditions of inlet air temperature of 200℃ and outlet air temperature of 90℃. The coated powder was dried at 80℃ for 2h, and then placed in a muffle furnace. Under a static air atmosphere, the temperature was increased to 450℃ at 2℃ / min and held for 2h to complete the decomposition of organic matter and the pre-sintering of the MnO2-doped barium borosilicate glass phase precursor. After natural cooling, the modified barium titanate powder was obtained.
[0037] Preparation Example 2: Modified barium titanate was prepared by the following method:
[0038] 142.0 g (0.68 mol) of tetraethyl orthosilicate, 33.3 g (0.32 mol) of trimethyl borate, 26.1 g (0.1 mol) of barium nitrate, and 22.0 g of citric acid were sequentially added to 1.6 L of anhydrous ethanol. The mixture was stirred at 300 rpm for 30 min at 30 °C to obtain a clear precursor solution. While stirring continuously, 130 mL of deionized water was added dropwise at a rate of 15 mL / min, and the pH of the system was adjusted to 8 with 5% ammonia solution. Stirring continued for 2 h to allow the precursor to fully hydrolyze and condense. Subsequently, 80 mL of an aqueous solution of 12.1 g (0.048 mol) of manganese nitrate (tetrahydrate) was added, and the mixture was stirred for 1 h to obtain a composite sol. The molar ratio of each raw material, based on the final oxides formed, was approximately 1:1.6:6.8 for BaO, B₂O₃, and SiO₂; the mass fraction of MnO₂ was approximately 5.8%.
[0039] Using a centrifugal spray drying device, 100g of the above composite sol was uniformly sprayed onto the surface of barium titanate powder (approximately 3.7kg) with a D50 of 1.2μm under conditions of inlet air temperature of 195℃ and outlet air temperature of 85℃. The coated powder was dried at 80℃ for 2h, and then placed in a muffle furnace. Under a static air atmosphere, the temperature was increased to 480℃ at 2℃ / min and held for 2.5h to complete the decomposition of organic matter and the pre-sintering of the MnO2-doped barium borosilicate glass phase precursor. After natural cooling, the modified barium titanate powder was obtained.
[0040] Preparation Example 3: Modified barium titanate was prepared by the following method:
[0041] 108.3 g (0.52 mol) of tetraethyl orthosilicate, 50 g (0.48 mol) of trimethyl borate, 26.1 g (0.1 mol) of barium nitrate, and 28.0 g of citric acid were sequentially added to 2.0 L of anhydrous ethanol. The mixture was stirred at 35 °C and 400 rpm for 25 min to obtain a clear precursor solution. While stirring continuously, 160 mL of deionized water was added dropwise at a rate of 25 mL / min, and the pH of the system was adjusted to 9 with 5% ammonia solution. Stirring continued for 1.0 h to allow the precursor to fully hydrolyze and condense. Subsequently, 110 mL of an aqueous solution of 18.2 g (0.073 mol) of manganese nitrate (tetrahydrate) was added, and the mixture was stirred for 1 h to obtain a composite sol. The molar ratio of each raw material, based on the final oxides formed, was approximately 1:2.4:5.2 for BaO, B₂O₃, and SiO₂; the mass fraction of MnO₂ was approximately 6.5%.
[0042] Using a centrifugal spray drying device, 100g of the above composite sol was uniformly sprayed onto the surface of barium titanate powder (approximately 2.5kg) with a D50 of 0.8μm under conditions of inlet air temperature of 200℃ and outlet air temperature of 90℃. The coated powder was dried at 90℃ for 1.5h, and then placed in a muffle furnace. Under a static air atmosphere, the temperature was increased to 500℃ at 3℃ / min and held for 1.5h to complete the decomposition of organic matter and the pre-sintering of the MnO2-doped barium borosilicate glass phase precursor. After natural cooling, the modified barium titanate powder was obtained.
[0043] Preparation Example 4, modified barium titanate, differs from Preparation Example 1 in that manganese nitrate (tetrahydrate) was not added during the preparation of the composite sol.
[0044] Example
[0045] Example 1: A barium titanate-based PTC ceramic material was prepared by the following steps:
[0046] Take 1000g of modified barium titanate powder, 1.25g of niobium pentoxide, and 13g of ammonium polyacrylate dispersant (lnb-1750, Wuhan Lanabai) prepared in Preparation Example 1, and dry mix them in a three-dimensional mixer for 40min until homogeneous; dissolve 4.2g of polyvinyl alcohol (Kuraray PVA-117, Japan) in 65.8g of deionized water to prepare a 6.0wt% aqueous solution, add 0.084g of analytical grade boric acid (2.0% of the dry weight of PVA), and stir until completely dissolved; spray the above boric acid-containing PVA solution into the premix, and stir in a planetary mixer. The material was wet-mixed at 300 rpm for 25 min in a pellet mill and passed through an 80-mesh stainless steel sieve to obtain a granulated material with good flowability. The granulated material was placed in an isostatic pressing mold and pressed into Φ20mm×2.0mm round blanks at 180MPa pressure for 30s. The blanks were placed in a tube sintering furnace, and a reducing mixed gas (CO:N2=1:4, total flow rate 200mL / min) was first introduced, and the temperature was raised to 675℃ at 2.0℃ / min and held for 3h to remove the binder. Then the atmosphere was switched, and a low-oxygen mixed gas (O2:N2=3:97, oxygen concentration 3.0 vol%, total flow rate 200mL / min) was introduced, and the temperature was raised to 800℃ at 4.0℃ / min and held for 1.5h for catalytic oxidation. Finally, the temperature was raised to 1300℃ at 8.0℃ / min and held for sintering for 3.0h. The furnace was then cooled to room temperature to obtain the PTC ceramic element.
[0047] Example 2: A barium titanate-based PTC ceramic material was prepared by the following steps:
[0048] Take 1000g of modified barium titanate powder, 0.55g of niobium pentoxide, and 6g of ammonium polyacrylate dispersant (lnb-1750, Wuhan Lanabai) prepared in Preparation Example 2, and dry mix them in a three-dimensional mixer for 30 minutes until uniform; dissolve 2.4g of polyvinyl alcohol (Kuraray PVA-117 from Japan) in 57.6g of deionized water to prepare a 4.0wt% aqueous solution, add 0.036g of analytical grade boric acid (1.5% of the dry weight of PVA), and stir until completely dissolved; spray the above boric acid-containing PVA solution into the premix and granulate it in a planetary mixer. The mixture was wet-mixed at 300 rpm for 20 min and passed through a 100-mesh stainless steel sieve to obtain a granulated material with good flowability. The granulated material was placed in an isostatic pressing mold and pressed into Φ20mm×2.0mm round blanks at 150MPa pressure for 30s. The blanks were placed in a tube sintering furnace, and a reducing mixed gas (CO:N2=1:4, total flow rate 200mL / min) was first introduced, and the temperature was raised to 610℃ at 1.5℃ / min and held for 3.0h to remove the binder. Then the atmosphere was switched, and a low oxygen mixed gas (O2:N2=4:96, oxygen concentration 4.0 vol%, total flow rate 200mL / min) was introduced, and the temperature was raised to 750℃ at 3.0℃ / min and held for 2.0h for catalytic oxidation. Finally, the temperature was raised to 1220℃ at 5.0℃ / min and held for sintering for 4.0h. The furnace was then cooled to room temperature to obtain the PTC ceramic element.
[0049] Example 3: A barium titanate-based PTC ceramic material was prepared by the following steps:
[0050] Take 1000g of modified barium titanate powder, 2.0g of niobium pentoxide, and 20g of ammonium polyacrylate dispersant (lnb-1750, Wuhan Lanabai) prepared in Preparation Example 3, and dry mix them in a three-dimensional mixer for 40min until uniform; dissolve 5.6g of polyvinyl alcohol (Kuraray PVA-117 from Japan) in 64.4g of deionized water to prepare an 8.0wt% aqueous solution, add 0.14g of analytical grade boric acid (2.5% of the dry weight of PVA), and stir until completely dissolved; spray the above boric acid-containing PVA solution into the premix and granulate it in a planetary mixer. The mixture was wet-mixed at 300 rpm for 30 min and passed through an 80-mesh stainless steel sieve to obtain a granulated material with good flowability. The granulated material was placed in an isostatic pressing mold and pressed into Φ20mm×2.0mm round blanks at 200MPa pressure for 30s. The blanks were placed in a tube sintering furnace, and a reducing mixed gas (CO:N2=1:4, total flow rate 200mL / min) was first introduced, and the temperature was raised to 695℃ at 3.0℃ / min and held for 2.0h to remove the binder. Then the atmosphere was switched, and a low-oxygen mixed gas (O2:N2=5:95, oxygen concentration 5.0 vol%, total flow rate 200mL / min) was introduced, and the temperature was raised to 850℃ at 5.0℃ / min and held for 1.2h for catalytic oxidation. Finally, the temperature was raised to 1350℃ at 10.0℃ / min and held for sintering for 2.0h. The furnace was then cooled to room temperature to obtain the PTC ceramic element.
[0051] Example 4: A barium titanate-based PTC ceramic material, which differs from Example 1 in that the amount of boric acid used is 0.126g (3.0% of the dry weight of PVA).
[0052] Example 5: A barium titanate-based PTC ceramic material, which differs from Example 1 in that the amount of boric acid used is 0.042g (1.0% of the dry weight of PVA).
[0053] Example 6: A barium titanate-based PTC ceramic material, which differs from Example 1 in that boric acid is not added.
[0054] Comparative Example
[0055] Comparative Example 1, a barium titanate-based PTC ceramic material, differs from Example 1 in that the green body sintering process does not include a catalytic oxidation stage, as detailed below:
[0056] The green blank was placed in a tube sintering furnace. First, a reducing mixed gas (CO:N2=1:4, total flow rate 200mL / min) was introduced, and the temperature was raised to 675℃ at 2.0℃ / min and held for 3 hours to remove the binder. Then, the atmosphere was switched, and a low oxygen mixed gas (O2:N2=3:97, oxygen concentration 3.0 vol%, total flow rate 200 mL / min) was introduced. The temperature was raised to 1300℃ at 8.0℃ / min and held for 3.0 hours. The furnace was then cooled to room temperature to obtain the PTC ceramic element.
[0057] Comparative Example 2, a barium titanate-based PTC ceramic material, differs from Example 1 in that the modified barium titanate prepared in Example 1 is replaced with an equal amount of modified barium titanate prepared in Example 4.
[0058] Comparative Example 3, a barium titanate-based PTC ceramic material, differs from Example 1 in that each component of the MnO2-doped barium borosilicate glass precursor is independently added to barium titanate for ceramic preparation. The specific operation is as follows:
[0059] Weigh out 998.7g of uncoated ordinary barium titanate powder (D50=1.0μm), 0.28g of barium oxide (passed through a 325-mesh sieve), 0.26g of boron trioxide (passed through a 325-mesh sieve), 0.66g of silicon dioxide (D50 approximately 30-40nm), 0.08g of manganese dioxide (D50=0.8μm), and 1.25g of niobium pentoxide. Place them in a three-dimensional mixer and dry mix for 40 minutes until homogeneous. Dissolve 4.2g of polyvinyl alcohol (Kuraray PVA-117 from Japan) in 65.8g of deionized water to prepare a 6.0wt% aqueous solution. Add 0.084g of analytical grade boric acid (2.0% of the dry weight of PVA) and stir until completely dissolved. Complete dissolution; the above-mentioned boric acid-containing PVA solution was sprayed into the premix, wet-mixed at 300 rpm for 25 min in a planetary mixer granulator, and passed through an 80-mesh stainless steel sieve to obtain a granulated material with good flowability; the granulated material was placed in an isostatic pressing mold and pressed into Φ20mm×2.0mm round blanks at 180MPa pressure for 30s; the blanks were placed in a tube sintering furnace, and a reducing mixed gas (CO:N2=1:4, total flow rate 200mL / min) was first introduced, and the temperature was raised to 675℃ at 2.0℃ / min and held for 3h to remove the binder; then the atmosphere was switched, and a low-oxygen mixed gas (O2:N2=3:97, oxygen concentration 3.0) was introduced. (vol%, total flow rate 200 mL / min), catalytic oxidation was carried out by heating to 800℃ at 4.0℃ / min and holding for 1.5h; finally, the temperature was increased to 1300℃ at 8.0℃ / min and sintered for 3.0h, and then cooled to room temperature in the furnace to obtain PTC ceramic elements.
[0060] Comparative Example 4 is a barium titanate-based PTC ceramic material, which differs from Example 1 in that an equal amount of unmodified barium titanate (D50=1.0μm) is used to replace the modified barium titanate prepared in Preparation Example 1.
[0061] Performance testing
[0062] Experiment 1: Room Temperature Resistivity Measurement
[0063] Sample preparation: The PTC ceramic discs prepared in the examples and comparative examples were ultrasonically cleaned and dried on both sides. Ohmic contact silver electrode paste was uniformly coated on both sides of the ceramic disc using screen printing, with a coating thickness of approximately 10-15 μm. The coated ceramic discs were placed in a muffle furnace and heated to 550±10℃ at a rate of 3-5℃ / min in air atmosphere, held at that temperature for 20-30 minutes for sintering, and then cooled in the furnace.
[0064] Test Method: The test was conducted according to the method specified in GB / T 41606-2022 "Barium Titanate-Based High Dielectric Strength and Low Resistivity Thermistors". A digital source meter was used in conjunction with a four-wire test fixture, and the test was performed in a constant temperature environment of 25±1℃. The sample was placed in the fixture, ensuring good contact between the four probes and the silver electrode. An appropriate DC current was applied, so that the voltage drop across the sample was within the range of 10mV-100mV. Based on the sample's geometry (thickness and electrode area), the voltage was calculated using the formula ρ=(V / I). Calculate the room temperature resistivity (ρRT) using (A / t), where A is the electrode area and t is the sample thickness. Measure each sample at least three times at different locations and take the average value.
[0065] Experiment 2: Measurement of PTC effect intensity (lift-to-drag ratio)
[0066] Sample preparation: Same as Experiment 1.
[0067] Test Method: The method specified in GB / T 41606-2022 "Barium Titanate-Based High Dielectric Strength and Low Resistivity Thermistors" was followed. Using an impedance analyzer equipped with a high-temperature probe station or temperature-controlled furnace, the sample was placed in a temperature-controlled device and heated from room temperature (25℃) to 250℃ at a constant rate (2±0.5℃ / min). During the heating process, the resistance value of the sample was collected every 1-5℃. The sampling points were increased in the temperature range where the resistance changed rapidly (near the Curie temperature).
[0068] Data processing: Plot the resistance-temperature (RT) curve; determine the room temperature resistance R from the curve. 25 and maximum resistance R max Calculate the lift-to-drag ratio R max / R 25 .
[0069] Table 1. Performance Test Results
[0070]
[0071] Experimental data analysis:
[0072] Compared to Example 1, Example 4 showed a deterioration in room temperature resistivity and resistance-to-weight ratio. This may be because excessive boric acid led to over-crosslinking of the PVA gel network, weakening its shear-thinning properties, reducing the fluidity of the granulated material, and generating a micro-density gradient during green body pressing. This, in turn, damaged the pore connectivity during the catalytic oxidation stage and resulted in uneven densification during the high-temperature stage, thus doubly weakening the construction of grain boundary barriers and the continuity of the conductive network.
[0073] In Example 5, the room temperature resistivity increased significantly, and the resistance-to-weight ratio decreased. This was because the coordination bond density was insufficient, which could not effectively dissipate the compressive stress, and the MnO2-doped barium borosilicate glass phase precursor peeled off locally. The damaged areas lost their particle isolation function during the catalytic oxidation stage, and some pores closed prematurely, hindering oxygen diffusion and resulting in insufficient grain boundary oxidation. At the same time, the glass phase was unevenly filled locally during the high-temperature stage, leading to a highly dispersed barrier height and increased bulk resistivity.
[0074] The overall performance degradation in Example 6 indicates that the lack of boric acid and the absence of a BO coordination buffer network lead to localized stress concentration during pressing, which can easily damage or even break and peel off the glass phase precursor coating. During sintering, Mn cannot be effectively enriched at the grain boundaries, resulting in a sharp drop in catalytic oxidation efficiency, failure of the pore control mechanism, and deterioration of the grain boundary barrier height and uniformity, which directly manifests as a decrease in the rise-to-resistance ratio and resistance stability.
[0075] Compared to Example 1, Comparative Example 1 showed a significant decrease in resistivity and good room temperature resistivity. This indicates that the catalytic oxidation stage at 700–850 °C plays an irreplaceable role in the construction of grain boundary barriers. The reason is that skipping this stage closes the oxygen diffusion channels in the early stage of heating, resulting in insufficient recombination of oxygen vacancies at grain boundaries and the inability to form a high-barrier oxygen-containing layer. Although high-temperature sintering achieves densification, the reduced barrier density weakens the PTC effect.
[0076] Comparative Example 2 showed a significant decrease in drag ratio. This indicates that MnO2 doping plays a crucial role in catalytic activity and barrier construction. The reason for this is that the absence of Mn... 3+ At the catalytic center, the activation and dissociation efficiency of gaseous oxygen molecules decreases, and grain boundary oxidation is insufficient; simultaneously, Mn 3+ The acceptor element cannot dissolve in the double barrier of the grain boundary and relies only on the physical oxygen layer. The barrier height and thermal stability are insufficient, which directly leads to a decrease in the rise-to-drag ratio.
[0077] Compared to Example 1, Comparative Example 3 showed an increase in room temperature resistance and a significant decrease in average resistance-to-weight ratio. This indicates that powder blending cannot achieve the interface control effect of the coating layer. The reason is that the glassy precursor and MnO2 powder are randomly distributed, easily agglomerating and segregating during sintering, making it impossible to form a continuous isolation film on the particle surface; the interconnected pores are significantly reduced during the catalytic oxidation stage, and Mn elements have difficulty migrating directionally to the grain boundaries, resulting in localized barrier deficiencies or excessive thickness, manifested as a decrease in resistance-to-weight ratio, large performance fluctuations, and poor reliability. Furthermore, the barium titanate surface lacks a molten glassy phase as a highly active ion channel, and the donor dopant (Nb)... 5+ The ability and uniformity of diffusion into the lattice decrease, and the semiconductivity of the grains is insufficient, which manifests as an increase in room temperature resistance.
[0078] Compared to Example 1, Comparative Example 4 showed an increase in room temperature resistivity and a decrease in the rise-resistivity ratio. This is because, without a glassy precursor for isolation, the particles rapidly form sintering necks to close pores at low temperatures, hindering oxygen diffusion and resulting in insufficient grain boundary oxidation. Simultaneously, the lack of a high-temperature molten glassy phase to fill micropores and promote donor diffusion leads to high bulk resistivity, uneven semiconductivity of grains, and weak grain boundary barriers. This demonstrates the necessity of the MnO2-doped barium borosilicate glassy precursor coating layer in this application for achieving dynamic porosity control.
[0079] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.
Claims
1. A PTC ceramic material based on barium titanate, characterized in that, The material is made from modified barium titanate and donor dopant in a mass ratio of 100:0.05 to 0.
2. The modified barium titanate includes barium titanate and a MnO2-doped barium borosilicate glass phase precursor coated on the surface of barium titanate. The sintering method of the PTC ceramic material is as follows: the ceramic blank is placed in a reducing atmosphere and heated to 600 to 700°C for debinding; then it is placed in an oxygen-containing atmosphere and heated to 750 to 850°C for catalytic oxidation; and then sintered in an oxygen-containing atmosphere at 1200 to 1350°C.
2. The PTC ceramic material based on barium titanate according to claim 1, characterized in that, In the MnO2-doped barium borosilicate glass precursor, the molar ratio of BaO, B2O3, and SiO2 is 1:(1.5-2.5):(5-7).
3. The PTC ceramic material based on barium titanate according to claim 1, characterized in that, The mass fraction of MnO2 in the MnO2-doped barium borosilicate glass precursor is 5% to 8%.
4. The PTC ceramic material based on barium titanate according to claim 1, characterized in that, The heating rate of the debinding stage is 1-3℃ / min, and the holding time is 2-3h; the heating rate of the catalytic oxidation stage is 3-5℃ / min, and the holding time is 1-2h; the heating rate of the sintering stage is 5-10℃ / min, and the holding time is 2-4h.
5. The barium titanate-based PTC ceramic material according to any one of claims 1 to 4, characterized in that, The method for preparing the modified barium titanate is as follows: Tetraethyl orthosilicate, trimethyl borate, barium nitrate, and chelating agent were added sequentially to anhydrous ethanol and stirred until homogeneous to obtain a precursor solution. Deionized water was added dropwise to the solution, and the pH was adjusted to 8-9 with ammonia. The solution was stirred to hydrolyze the precursor. Manganese nitrate solution was added and stirred until homogeneous to obtain a composite sol. The composite sol is uniformly sprayed onto the surface of barium titanate particles by spray coating, the coated powder is dried, and then heat-treated at 400-500℃ to obtain the final product.
6. The barium titanate-based PTC ceramic material according to claim 5, characterized in that, In the spray coating process, the amount of composite sol accounts for 2.5 to 4.0 wt% of the total mass of composite sol and barium titanate.
7. The PTC ceramic material based on barium titanate according to claim 1, characterized in that, The donor dopant is selected from one or more of niobium pentoxide, antimony pentoxide, and lanthanum oxide.
8. The PTC ceramic material based on barium titanate according to claim 1, characterized in that, The raw materials for preparing the PTC ceramic material include: a premix of modified barium titanate and donor dopant, a polyvinyl alcohol solution of 6-8 wt% of the premix, and a dispersant of 0.5-2 wt% of the premix.
9. The PTC ceramic material based on barium titanate according to claim 8, characterized in that, The raw materials used in the preparation include boric acid, and the amount of boric acid used is 1.5 to 2.5% of the dry weight of the polyvinyl alcohol solution.
10. The method for preparing the barium titanate-based PTC ceramic material according to any one of claims 1 to 9, characterized in that, include: The granulated material is obtained by mixing and granulating a premix of modified barium titanate and donor dopant, polyvinyl alcohol solution, dispersant, and boric acid. The granulated material is pressed into ceramic blanks under a pressure of 150-200 MPa. The ceramic blank is heated to 600-700℃ to remove the binder; then heated to 750-850℃ and held for catalytic oxidation; then heated to 1200-1350℃ for sintering to obtain the final product.