PTC (Positive Temperature Coefficient) ceramic material for water circulation electric heating as well as preparation method and application of PTC ceramic material

Abstract

The invention relates to the technical field of special ceramic product manufacturing, and discloses a PTC ceramic material for water circulation electric heating and a preparation method and application of the PTC ceramic material for water circulation electric heating. According to the preparation method, an oxygen partial pressure environment is adjusted in a sintering cooling section, and a grain boundary modifier is induced to spread on the surface of the grain in a self-organizing manner and is condensed to form a film, so that an ion immobilization layer with a charge compensation function is constructed; the interface blocking structure is used for blocking a moisture permeation path, the electrochemical stability of the material in a pressure-bearing hot water circulation environment is ensured, Curie temperature drift is inhibited, and the ceramic valve plate is suitable for manufacturing a ceramic valve plate in an electric heating system.

Description

Technical Field

[0001] This invention belongs to the field of special ceramic product manufacturing technology, and particularly relates to a PTC ceramic material for water-circulating electric heating, its preparation method and application. Background Technology

[0002] Currently, barium titanate-based positive temperature coefficient ceramic materials, due to their unique semiconductor properties and thermosensitive resistance transition effect, are used in the core heating components of water-circulating electric heating systems. A solid-state reaction method is employed to dope the ceramic matrix with lead, strontium, yttrium, and manganese ions to precisely regulate the Curie temperature to 132°C. Nearby, is the mainstream technical path for achieving automatic power compensation and constant temperature control in the industry; the electrical stability of ceramic materials essentially depends on the height of the charge transport barrier at the grain boundary. During the ceramic forming process, the occupation state of doped ions at the grain edge and the density of the grain boundary layer jointly determine the electrical properties and environmental corrosion resistance of the material.

[0003] However, when ceramic components are subjected to complex conditions such as high temperature, high pressure, and pulsed electric fields in water circulation heating systems, existing technical solutions reveal their limitations. The ceramic components are subjected to long-term water pressure impacts of 1.2 MPa and frequent thermal vibrations near the Curie temperature, causing micro-lattice oscillations in the barium titanate lattice. Under this stress environment, dopant ions located at grain boundaries are prone to uncontrolled micro-displacement or leaching, inducing irreversible drift of the grain boundary barrier height, ultimately leading to step failure at the Curie temperature. Improvement strategies focus on adding an external organic protective layer or increasing the concentration of dopant ions. However, the large difference in thermal expansion coefficients between the organic coating layer and the ceramic matrix leads to microcracks under alternating thermal stress, failing to prevent micro-penetration of water molecules. Besides improving the hardware coating structure, optimization... The matrix composition and doping process can improve the intrinsic stability of materials. For example, Chinese invention patent CN117105658A discloses a barium titanate-based PTC ceramic and its preparation method. It uses Sr and Y to synergistically dope barium titanate, which meets the requirements of low Curie temperature and high room temperature resistivity in the field of insulation. The technology belongs to the category of homogeneous doping and can achieve electrical parameter adjustment. However, under the coupling effect of high pressure water environment and thermal stress, there is a lack of interface steric hindrance locking mechanism at the grain boundary, which cannot suppress the unsteady migration of dopant ions. Because a continuous and dense physical barrier is not built on the grain surface, water molecules penetrate along the intergranular pores and induce intrinsic erosion. Existing solutions that lack interface self-locking function are difficult to avoid thermal power fluctuations caused by Curie temperature drift when facing 1.2MPa pressurized hot water circulation.

[0004] Therefore, how to construct a grain boundary self-locking structure with dual functions of ion anchoring and hydrothermal shielding, so as to achieve quasi-static control of the Curie temperature by the ceramic body without increasing the burden of external packaging, has become the technical problem to be solved by this invention. Summary of the Invention

[0005] This invention provides a PTC ceramic material for water-circulating electric heating, comprising a barium titanate-based matrix component and a grain boundary modifier:

[0006] Based on a total weight of 100 parts for the barium titanate matrix component and the grain boundary modifier, the content of the grain boundary modifier is 0.5 to 3.0 parts, with the remainder being the barium titanate matrix component; the grain boundary modifier is composed of bismuth trioxide, zinc oxide, and silicon dioxide, and the mass ratios of bismuth trioxide, zinc oxide, and silicon dioxide satisfy the following relationship: ;

[0007] in, For the mass of bismuth trioxide, For the quality of zinc oxide, The quality of silicon dioxide; the microstructure of the PTC ceramic material for water-circulating electric heating includes barium titanate grains and a continuous amorphous glass phase layer coating the surface of the barium titanate grains. The thickness of the continuous amorphous glass phase layer is 5 nm to 15 nm, and the coverage of the continuous amorphous glass phase layer on the surface of the barium titanate grains is not less than 85%. In the continuous amorphous glass phase layer, bismuth ions occupy the lattice vacancies at the edges of the barium titanate grains to form a physical barrier interface, and bismuth ions construct an ion-locked layer on the surface of the barium titanate grains by compensating for the charge of the ions at the edges of the barium titanate grains. The Curie temperature drift of the PTC ceramic material for water-circulating electric heating after operating for 5000 hours under a water pressure of 1.2 MPa is less than 3%. .

[0008] Preferably, in the grain boundary modifier, based on a total weight of 100 parts of bismuth trioxide, zinc oxide, and silicon dioxide, the mass fraction of bismuth trioxide is 60 to 80 parts, the mass fraction of zinc oxide is 10 to 20 parts, and the mass fraction of silicon dioxide is 5 to 15 parts. The continuous amorphous glass phase layer has a chemical anchoring structure formed during the cooling and condensation process. Bismuth ions inhibit ion diffusion at the edges of barium titanate grains during the ferroelectric phase transition process by electrostatically shielding low-valence ions in the barium titanate matrix components.

[0009] Preferably, the average particle size of the barium titanate-based matrix component is 0.6 μm to 0.8 μm, and the specific surface area of ​​the barium titanate-based matrix component is 2.5 to 3.5. The grain boundary modifier is distributed on the surface of the barium titanate matrix component in the form of micro powder with a particle size of no more than 100 nm, and the molten liquid phase of the grain boundary modifier at the ceramic sintering temperature satisfies the wetting angle condition for self-spreading driven by the interfacial tension gradient on the surface of barium titanate grains.

[0010] Preferably, the continuous amorphous glass phase layer provides intrinsic anti-scraping capability to the PTC ceramic material for water circulation electric heating by physically blocking water molecules; the ion-locked layer maintains the electrochemical stability of the PTC ceramic material for water circulation electric heating in a pressurized hot water circulation environment by maintaining the grain boundary barrier height at the edge of barium titanate grains.

[0011] Preferably, the continuous amorphous glass phase layer and the barium titanate grains satisfy the following volume ratio relationship: ,in, The total volume of the continuous amorphous glass phase layer. The total volume of barium titanate grains; the volume ratio ensures that the grain boundary modifier, while filling the micropores inside the PTC ceramic material for water-circulating electric heating, maintains the room-temperature resistivity of the PTC ceramic material at 10 to 50 Ω·cm. Within the range.

[0012] Preferably, the Curie temperature of the PTC ceramic material used in water-circulating electric heating is 180°C. Up to 260 PTC ceramic materials used in water-circulating electric heating systems undergo 1000 cycles of oxidation from 25... Heat to the Curie temperature and cool to 25°C After thermal cycling, its Curie temperature fluctuates within a range of ±1. Within the barium titanate matrix, the grain boundary modifier is distributed in submicron scale within the contact channels between the components, and the grain boundary modifier forms a dense sintered neck structure with physical sealing function at the junction of barium titanate grains.

[0013] Preferably, in the continuous amorphous glass phase layer, bismuth trioxide, zinc oxide and silicon dioxide form a eutectic system, the eutectic point of which is lower than the sintering temperature of barium titanate grains; the eutectic system is filled by liquid phase in the cooling section of ceramic sintering, and a uniformly thick interface phase is constructed at the edge of barium titanate grains.

[0014] Preferably, the barium titanate-based matrix component includes barium titanate as the main component and a doping modification component, wherein the doping modification component is selected from at least one of niobium pentoxide, lanthanum oxide, and yttrium oxide; the doping modification component works synergistically with the grain boundary modifier to adjust the power aging characteristics of the PTC ceramic material for water-circulating electric heating, the PTC ceramic material for water-circulating electric heating is used as the matrix material for ceramic valve plates, and the PTC ceramic material for water-circulating electric heating blocks the chemical erosion of the grain interface by hot water through the continuous amorphous glass phase layer formed inside it.

[0015] A method for preparing a PTC ceramic material for water-circulating electric heating includes the following steps: Step 1101, mixing a barium titanate matrix component with a grain boundary modifier and ball milling to obtain a mixed powder with an average particle size of 0.6 μm to 0.8 μm; Step 1102, pressing the mixed powder into a pre-defined ceramic green body; Step 1103, heating the green body at 1300°C. up to 1350 The ceramic green body was sintered under the specified temperature conditions, and during the cooling and condensation process after sintering, it was sintered at 1050°C. Up to 1150 Within the switching temperature range, the ambient oxygen partial pressure is adjusted to above 95%, inducing the grain boundary modifier to condense on the surface of barium titanate grains to form a continuous amorphous glass phase layer.

[0016] An application of a PTC ceramic material for water-circulating electric heating, which is applied to a PTC ceramic material for water-circulating electric heating.

[0017] Compared with existing technologies, the PTC ceramic material for water-circulating electric heating of this invention has the following advantages:

[0018] 1. In PTC ceramics for water-circulating electric heating, by introducing a specific ratio of bismuth-zinc-silicon components and adjusting the atmosphere in the cooling section, the liquid phase is allowed to self-organize and spread along the grain surface under the drive of the interfacial tension gradient, forming a continuous amorphous coating layer with a thickness of 5 to 15 nanometers. This cuts off the permeation path of water molecules at the microscopic level, giving the ceramic body intrinsic corrosion resistance, eliminating the risk of electrochemical erosion of ceramic valve plates in pressurized hot water circulation environments, and solving the technical dilemma of existing technologies that rely on external encapsulation to block microscopic water vapor permeation.

[0019] 2. Utilizing the chemical affinity of large-radius bismuth ions for lead and strontium ions in the main components, an ion steric anchoring structure with a high chemical potential energy gradient is constructed at the grain boundaries. Through the electrostatic potential trap effect, the uncontrolled migration of ions generated when the barium titanate lattice undergoes violent phase transition oscillations near the Curie temperature is effectively suppressed, ensuring that the Curie temperature of the material remains under quasi-static control during long-term operation, and avoiding water temperature fluctuations in the electric heating system caused by high drift of the grain boundary potential barrier.

[0020] 3. Relying on the submicron-level distribution of low eutectic components after secondary graded grinding and the abrupt change in wettability within a specific temperature range, the liquid phase fully fills the micropores inside the ceramic before forced condensation, making the ceramic body exhibit a closed pore structure; this highly compacted grain boundary physical state improves the electrical breakdown strength and mechanical fatigue life of the ceramic material without increasing the doping concentration, ensuring the operational safety of the high-pressure circulating water system under extreme conditions. Attached Figure Description

[0021] Figure 1This is a flowchart of the preparation process for the cooling oxygen partial pressure regulation and micro-interface construction of the present invention;

[0022] Figure 2 This is a technical architecture diagram relating the component design, preparation process, and high stability mechanism of the present invention. Detailed embodiments.

[0023] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0024] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0025] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication between two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0026] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0027] This invention provides a water-circulating electric heating system. Ceramic materials, their preparation methods, and applications, including barium titanate-based matrix components and grain boundary modifiers; the content of the grain boundary modifier is as follows (parts by weight). portion to One part is barium titanate-based matrix components; the remaining part is barium titanate-based matrix components; the grain boundary modifier is composed of bismuth trioxide, zinc oxide, and silicon dioxide, and the mass of bismuth trioxide, zinc oxide, and silicon dioxide satisfies the following relationship: ;in, For the mass of bismuth trioxide, For the quality of zinc oxide, The mass of silica; the high-frequency pulsed electric field generated in the pressurized hot water circulation environment easily induces uncontrolled displacement of ions at grain boundaries, causing the Curie temperature to drift. To construct an interface structure with charge compensation function, the grain boundary modifier should contain bismuth trioxide, zinc oxide, and silica in a mass ratio of [missing information - likely a specific weight percentage]. The mass fraction of bismuth trioxide is: portion to The mass fraction of zinc oxide is 10 parts. portion to The mass fraction of silicon dioxide is 1 part. portion to The ratio allows the grain boundary modifier to form a eutectic system at the ceramic sintering temperature. Bismuth ions, through charge compensation of ions at the edges of barium titanate grains, construct an ion-locked layer on the surface of barium titanate grains. This layer inhibits ion diffusion at the edges of barium titanate grains during the ferroelectric phase transition, maintaining the grain boundary barrier height. Ceramic materials undergo Next Heat to the Curie temperature and cool to After thermal cycling, the Curie temperature fluctuates within a range of positive and negative. Within.

[0028] To achieve the Curie temperature at to Within a certain range, the content of the doped modified component is selected as follows: to Niobium pentoxide or lanthanum oxide, which form donor defects by occupying sites in the barium titanate lattice to modulate the carrier concentration; when the doping concentration is at At this level, the material exhibits a high positive temperature coefficient of resistance, making it suitable for... The above high-temperature heating environment; when the concentration increases to At this level, the electron concentration inside the grain increases, causing the resistivity at room temperature to decrease to [a certain level]. Around, while the Curie temperature is towards Lateral offset, the setting of this doping region balances the physical contradiction between power output density and material breakdown strength, ensuring Ceramic materials under pressure Ceramic components do not undergo thermal collapse under electric field stress; Under water pressure conditions, it is easily affected by water molecule penetration. Therefore, measures are needed to block the water penetration path. The microstructure of the ceramic material includes barium titanate grains and a continuous amorphous glass phase layer coating the surface of the barium titanate grains. The thickness of the continuous amorphous glass phase layer is... to Furthermore, the coverage of the continuous amorphous glass phase layer on the surface of barium titanate grains is not less than [amount missing]. The continuous amorphous glass phase layer and the barium titanate grains satisfy the following volume ratio relationship: ;in, The total volume of the continuous amorphous glass phase layer. This refers to the total volume of the barium titanate grains; this thickness and coverage, through their physical barrier effect on water molecules, allow... Ceramic materials possess erosion resistance, ensuring the material's durability. Operating under water pressure Afterwards, the Curie temperature drift was less than .

[0029] The density of the ceramic body determines its resistance to environmental erosion. During the preparation process, the steps... With an average particle size of to Specific surface area is to The barium titanate-based matrix component was mixed with a grain boundary modifier and ball-milled to obtain a mixed powder. The grain boundary modifier was prepared with a particle size not greater than [missing value]. The micro-powder is distributed on the surface of the barium titanate matrix component; Step The mixed powder is pressed into a ceramic blank; Step exist to The ceramic green body was sintered under specific temperature conditions, and during the cooling and condensation process after sintering, to Within the switching temperature range, the ambient oxygen partial pressure is adjusted to In the above, the oxygen partial pressure environment induces the grain boundary modifier to self-spread on the surface of barium titanate grains driven by the interfacial tension gradient. The grain boundary modifier forms a dense sintered neck structure at the boundaries of the barium titanate grains and fills the internal micropores. The resistivity of ceramic materials at room temperature remains at to Within the range.

[0030] According to the principles of interfacial wetting thermodynamics, the spontaneous spreading of a liquid phase on a solid surface is subject to the spreading coefficient. Control, when When the liquid phase is completely wetted, the coefficient Satisfying the formula: ;in, This is the spreading coefficient, in units of... ; The solid-gas interfacial tension of barium titanate grains under a specific atmosphere, in units of... ; The solid-liquid interfacial tension is the interfacial tension between the liquid phase of the grain boundary modifier and the barium titanate grains, in units of... ; The liquid-gas surface tension of the liquid phase of the grain boundary modifier is expressed in units of... The oxygen partial pressure increased from 21% to over 95%, due to the chemical adsorption of oxygen atoms on the barium titanate surface. Increase, make The value turns positive, inducing the liquid phase to migrate from the triangular grain boundaries to the entire grain surface. For ceramic valve plates with different loading densities, to ensure the continuous layer coverage of the grain surface in the central region, the oxygen intake pressure pulse is adjusted according to the geometric characteristics of the ceramic valve plate. Satisfying the formula: ,in, To correct the intake pressure, the unit ; Reference intake pressure, unit ; This is the intake compensation coefficient, with a value ranging from 0.15 to 0.25; For ceramic valve plate thickness, unit ; The diameter of the ceramic valve disc is expressed in units of... This compensation method eliminates the problem of insufficient internal grain boundary oxidation caused by diffusion resistance, ensuring that the Curie temperature fluctuation of mass-produced ceramic valve plates remains consistent within ±1 after 1000 thermal cycles. The barium titanate-based matrix composition includes barium titanate as the main component and doping modification components. The doping modification components are selected from at least one of niobium pentoxide, lanthanum oxide, and yttrium oxide. The doping modification components work synergistically with grain boundary modifiers to regulate… Power aging characteristics of ceramic materials Ceramic materials are used to manufacture ceramic valve plates in water-circulating electric heating systems, which block the chemical erosion of the crystal interface by hot water through the continuous amorphous glass phase layer formed inside.

[0031] Example 1: In a water-circulating electric heating system used for individual household heating in residential buildings, the ceramic valve plate installed at the end of the heating circuit is subjected to... The continuous water pressure and frequency are When excited by an alternating electric field, the barium titanate matrix component inside undergoes grain boundary ion dissolution, leading to a Curie temperature increase. A drift towards the low-temperature side occurs, causing the system's thermal power output to deviate from the predetermined range; to address the physical losses in this application environment, a mass fraction of [missing information] is selected. and average particle size for Barium titanate powder is used as the main ingredient and is formulated in a specific ratio. The grain boundary modifier, of which bismuth trioxide is present in a certain amount of mass. for Parts, quality of zinc oxide for Portion, mass of silicon dioxide for Parts, at this time the mass ratio for Satisfying the aforementioned limitations to The working range of this group is such that the allocation ratio reaches the sintering temperature. This produces a highly chemically active bismuth-based liquid phase, which is then cooled to [temperature missing]. During this stage, high-purity oxygen is injected into the sintering furnace to maintain the oxygen partial pressure at a certain level. In this state, the surface tension of the bismuth-based liquid phase changes abruptly in an oxygen-rich environment, driving the molten grain boundary modifier to self-organize and spread along the surface of barium titanate grains.

[0032] Under the synergistic effect of high-temperature sintering and atmosphere conditioning, the liquid-phase grain boundary modifier is no longer limited to the triangular grain boundary stacking state in traditional processes. Instead, it solidifies and condenses on the entire surface of barium titanate grains through the attraction of the interfacial tension gradient, forming an average thickness of [missing information]. And the coverage rate reached A continuous amorphous glass phase layer, its total volume Total volume of barium titanate grains The ratio is As defined in the foregoing specific embodiments to The proportion range; this continuous amorphous glass phase layer not only physically cuts off the path for high-pressure hot water molecules to penetrate into the barium titanate lattice, but also, through the compensation effect of bismuth ions at the grain boundaries, establishes an ion-locked layer with a high potential barrier. This layer, through electrostatic force, blocks the uncontrolled migration of dopant ions during the phase transition cycle, stabilizing the material's room-temperature resistivity within a certain range. To achieve Curie temperature at Nearby atomic-level lock.

[0033] Should Ceramic materials are assembled into ceramic valve plates and used for operation. After pressurized hydrothermal cycling tests, no obvious electrochemical erosion traces were observed at the internal grain boundary interfaces, and the Curie temperature was [not specified]. The cumulative drift is at The level, and the electrical breakdown strength of the material remains at The above indicates that the micro-interface system constructed by a specific ratio of grain boundary modifier and atmosphere step control process, without sacrificing room temperature conductivity, resolves the contradiction between the density and charge stability of ceramic materials by transforming the originally isolated liquid phases into a continuously distributed physical barrier. This allows the ceramic valve plate to serve as the core power regulation unit in a water-circulating electric heating system, maintaining long-term, quasi-static heat output characteristics in a pressurized hot water environment. The preparation steps of the obtained ceramic valve plate include: weighing the raw materials according to the ratio and grinding them in a planetary ball mill... ball mill rotation speed ; granulation powder in Pressed under pressure to form a diameter ,thickness The billet; the billet is heated to And keep warm With cooling rate as Cool to High-purity oxygen is injected periodically to maintain an oxygen partial pressure of [value missing]. Until cooled to stop.

[0034] Example 2: For measurement Ceramic materials under pressure Water pressure pulse and Curie temperature stability under broadband noise interference environment: This experiment uses a high-pressure hot water circulation test system, including a temperature control accuracy of [insert accuracy here]. And its pressure resistance is The test chamber is equipped with a sampling frequency of And the current measurement resolution is The parameter acquisition unit; the experimental data is set based on the technical trade-off between the real-time capture of thermosensitive characteristics and the data processing load, and the sampling period is determined by calculating the time constant of the ceramic phase transformation response. This value ensures that the temperature is within the range of When changing, each Data collected within the interval Data points were selected to filter out random fluctuations caused by power frequency interference; the sample preparation procedure involved in the experiment is as follows: weigh the average particle size... for Barium titanate powder was mixed with different proportions of grain boundary modifiers in a planetary ball mill to... Speed ​​Mixing ; mix the powder in Pressing under pressure to obtain a diameter And thickness The blank; the blank in Sintering at temperature And when the temperature drops to High-purity oxygen is introduced to maintain the oxygen partial pressure at a certain level. The above state continues until cooled to The experiment consisted of three experimental groups and six control groups. The content and mass ratio of the grain boundary modifier in the experimental groups were specified. Within the aforementioned defined range, control groups 1 to 4 selected values ​​exceeding this range, control group 5 used a natural air cooling process, and control group 6 lacked silica components; during the execution During the high-pressure hot water aging test, the acquisition unit records the resistivity curves of each sample group in real time and extracts the Curie temperature. For the formed continuous amorphous glass phase layer, the charge compensation effect of bismuth ions on the lattice defects at the edge of barium titanate grains reduces the migration rate of oxygen vacancies at the interface, thereby increasing the experimental signal. It maintains a monotonous trend of change under noise interference.

[0035] Table 1: Example Table of Performance Comparison Data for Different Groups

[0036]

[0037] Analyzing the data in Table 1, when the content of grain boundary modifier is lower than... When the content is as shown in control group 1, its continuous layer coverage rate is This leads to the Curie temperature drift after aging. Increase to This indicates that the lack of a physical barrier interface cannot inhibit the electrochemical erosion of grain boundaries by water molecules; control group 2 showed a content exceeding The state at which the resistivity increases to [value] at room temperature. This value indicates that an excessively thick glass phase increases the probability of charge carrier scattering between grains, leading to a decrease in the material's heating efficiency; regarding the mass ratio Gradient analysis shows that when the ratio is lower than At that time, the increase in liquid phase viscosity caused the coverage to decrease to This leads to decreased stability; and when the ratio is higher than... At this time, excessive bismuth ions produce a strong donor doping effect, causing the resistivity at room temperature to decrease to The results of control groups 5 and 6 confirmed that the oxygen partial pressure step control and the presence of silica components are the driving forces for the self-spreading of the liquid phase and the formation of a thickness of [missing information]. to The necessary condition for a continuous layer, as demonstrated by the quantitative evidence in this experiment, is that the defined composition ratio and process parameters construct a physically and electrically locked structure on the grain surface, reducing the Curie temperature drift. There is a negative correlation between coverage and continuous layer coverage; when coverage is at... Within the above range, the Curie temperature drift of the ceramic material after aging is locked at... Within.

[0038] Example 3: This example combines Figures 1 to 2 A description of a PTC ceramic material for water-circulating electric heating, its preparation method, and its application is as follows: Figure 1 As shown, a barium titanate matrix component with an average particle size of 0.6μm-0.8μm was selected and combined with a grain boundary modifier composed of bismuth trioxide, zinc oxide, and silicon dioxide. The two components were mixed, ball-milled, and pressed into a ceramic green body, which was then subjected to a process at 1300 °C. -1350 During high-temperature sintering, and as the liquid phase forms and the process enters the cooling and oxygen partial pressure control stage, at 1050°C... -1150 Maintaining an oxygen partial pressure >95% within the domain to induce condensation and film formation, this process utilizes a liquid-phase self-spreading mechanism driven by interfacial tension gradients to construct a crystalline glassy phase layer with a thickness of 5nm to 15nm and a coverage of ≥85% at the microscopic level, as well as an ion-locked layer with bismuth ion charge compensation and physical barrier functions, ultimately achieving a Curie temperature drift <3°C. PTC ceramic materials for water-circulating electric heating with water erosion resistance.

[0039] like Figure 2 As shown, the technical composition design of high-stability PTC ceramic materials further explains that the design includes a barium titanate matrix and grain boundary modifiers including bismuth, zinc, and silicon. The preparation process emphasizes the control strategy of oxygen partial pressure >95% during the cooling stage and inducing liquid phase self-spreading. The resulting microstructure features a continuous amorphous glass phase layer with a grain surface coverage of ≥5%. This structure is based on the physical barrier to water molecule penetration and the mechanism of ion locking and charge compensation, which together support the high stability performance of the final product.

[0040] Example 4: In a water-circulating electric heating system used for individual residential heating, the ceramic valve plate installed at the end of the heating circuit is subjected to... The continuous water pressure and frequency are When excited by an alternating electric field, the low-energy sites at the barium titanate grain interface become pathways for water penetration and ion migration; to construct an energy-stable interfacial barrier system, a mass fraction of [missing information] was selected. The barium titanate matrix component is added. A grain boundary modifier composed of bismuth trioxide, zinc oxide, and silicon dioxide, wherein the mass of bismuth trioxide is... for Parts, quality of zinc oxide for Portion, mass of silicon dioxide for The allocation ratio of this group satisfies the ratio. for The settings; the components are placed in a planetary ball mill. speed mixing After spray granulation and Pressed under pressure to form a diameter And thickness The ceramic blank, in Sintering at temperature .

[0041] During the cooling process, the wetting state transition of the liquid phase of the grain boundary modifier on the surface of barium titanate grains is controlled. When the temperature drops to... At that time, the oxygen partial pressure inside the furnace was... Step to Regulates and induces oxygen adsorption reaction on the surface of barium titanate grains, thereby increasing the solid-gas interfacial tension. At this point, the spreading coefficient of the liquid phase is... The following physical relationship must be satisfied: ;in, denoted as the spreading coefficient of the liquid phase of the grain boundary modifier on the surface of barium titanate grains. The solid-gas interfacial tension on the surface of barium titanate grains, in units of... , The solid-liquid interfacial tension is the tension between the liquid phase of the grain boundary modifier and the barium titanate grains, expressed in units of... , The liquid-gas surface tension of the liquid phase of the grain boundary modifier is expressed in units of... Within this temperature range, the viscosity of the liquid phase is adjusted by the interaction of zinc oxide and silica. to Within a certain range, a step change in oxygen partial pressure leads to The growth exceeded The sum of, driving The value changes from negative to positive, causing the liquid phase to spread along the entire surface of the grain, forming a layer with a thickness of [thickness value missing] after condensation. And the coverage rate is A continuous amorphous glass phase layer.

[0042] Bismuth ions in the continuous amorphous glass phase layer penetrate into the edge of the barium titanate lattice and occupy oxygen vacancies, constructing a charge-compensated depth of [missing information]. to The ion-locked layer's physical criteria are as follows: Electron spectroscopy confirms that the binding energy shift of bismuth ions within a 3-nanometer depth at the edge of barium titanate grains is between 0.5 and 1.2 eV. The electrostatic potential well depth generated by this shift is calibrated to 0.6 to 0.8 eV. In the control program, this potential well energy value serves as the threshold for suppressing ion migration. By maintaining a barrier height greater than 0.8 volts at the grain boundaries, the oxygen vacancy jumping frequency within the barium titanate lattice is reduced by two orders of magnitude under an alternating electric field excitation at 50 Hz, thereby cutting off the path of performance degradation. This layer structure generates an electrostatic potential well at the grain boundaries, with a potential well depth of... to This energy value suppresses the thermal migration of doped ions driven by an alternating electric field; the ceramic material is assembled into a ceramic valve plate and performs... After pressurized hot water aging test, its Curie temperature The initial value is The final drift amount after aging is The resistivity at room temperature is stable at The continuous physical barrier interface and ion-locked layer block the performance degradation path under the coupling of the polarization field and the hydrothermal field, enabling the ceramic valve plate to maintain a stable output of heat power during the electric heating operation cycle. The preparation procedure of the obtained ceramic valve plate is as follows: ball milling and mixing according to the above ratio and applying it in a steel mold. Pressure pressing molding, with The rate of heating up to And keep warm ; cool down to High-purity oxygen is introduced to maintain the oxygen partial pressure at a certain level. Until the temperature drops to stop.

[0043] Example 5: In a large continuous pusher kiln preparation scenario where uneven atmosphere distribution occurs due to differences in furnace volume, three sets of standard sample blocks were selected and placed at the edge and center of the loading platform. The temperature was lowered to... When the intake valve is opened, the pressure rise curve fed back by the oxygen partial pressure monitoring unit is monitored, and the oxygen partial pressure is calculated from the initial state to the current state. Time constant required for target threshold Based on the calculation results, the oxygen flow control parameters are determined. Intake flow control parameters The calculation formula is as follows: ;in, The corrected oxygen flow rate is expressed in units of... , The baseline flow rate is expressed in units of... , The actual effective volume of the pusher kiln is given in units of... , Standard calibration volume, unit: , The measured time constant, in units of , The baseline response time is expressed in units of 1000 m / s. The automatic compensation of this flow parameter enables the grain boundary modifier to... to The barium titanate grains are fully coated within the switching temperature range, and the resulting ceramic material undergoes [a process / process]. After aging tests, the Curie temperature drift was less than [a certain value]. Its characteristics.

[0044] When different purity grades of raw material batches cause a shift in the eutectic point of the grain boundary modifier, the initial melting temperature of the grain boundary modifier can be measured. Determine the trigger point for atmosphere switching when the real-time value fed back by the temperature monitoring unit reaches... When the high-purity oxygen inlet valve is opened, the spreading torque generated by the step increase in oxygen partial pressure under this condition overcomes the interfacial resistance on the surface of barium titanate grains, causing the liquid phase to form a thickness of [missing information] before cooling and solidification. to And the coverage rate is no less than The continuous amorphous glass phase layer obtained from different batches of products maintains a consistent room temperature resistivity within positive and negative ranges. Within the specified range, the ion-locked layer formed inside the material inhibits ion diffusion during the ferroelectric phase transition, allowing the ceramic valve plate to maintain stable heat output power in a pressurized hot water circulation environment.

[0045] Example 6: In a fabrication environment where the increased thickness of the ceramic valve plate leads to uneven internal cooling rates, to suppress thermal stress cracking in the amorphous glass phase layer during condensation, the system executes a cooling rate based on thermoelastic criterion. The calibration procedure measures the billet in Linear shrinkage rate at time to determine the composite elastic modulus The critical cooling rate was calculated based on the difference in thermal expansion coefficients between barium titanate grains and the grain boundary modifier, where the cooling rate... The settings satisfy the following physical relationship: ;in, Cooling rate, unit: , The tensile strength limit of the amorphous glass phase layer, in units of , The thermal diffusivity of the material is expressed in units of 1000 ppm. , The comprehensive elastic modulus is expressed in units of 1. , The difference in thermal expansion coefficients between the two phases, in units of , The thickness of the ceramic valve plate, in units of This calibration procedure ensures that the oxygen partial pressure step effect in the cooling section acts stably on a thickness of not less than [a certain value]. Ceramic valve discs.

[0046] In manufacturing ceramic valve discs of different diameters, to maintain the consistency of the continuous amorphous glass phase layer distribution in the axial and radial directions, an oxygen diffusion depth calibration procedure is performed based on the geometric aspect ratio. This is achieved by setting the ratio of diameter to thickness. Adjust the peak width of the intake pressure pulse, where the ratio In to Within a certain range, high-purity oxygen is allowed to... The process involves penetration into the micropores of the ceramic body's core, utilizing the solid-gas interfacial tension induced by oxygen adsorption. This method, based on geometric parameters, enhances the self-organized spreading of the driving liquid phase on the surface of the core grains, maintaining the continuous layer coverage in the central region of the ceramic valve plate. In the manufacturing of ceramic valve discs, the working surface is roughened through grinding. Controlled to Within a certain range, ceramic valve plates undergo... Next After thermal cycling to the Curie temperature, the Curie temperature fluctuations are in the positive and negative ranges. Within the range.

[0047] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A PTC ceramic material for water-circulating electric heating, characterized in that, Includes barium titanate matrix components and grain boundary modifiers: Based on a total weight of 100 parts for the barium titanate matrix component and the grain boundary modifier, the content of the grain boundary modifier is 0.5 to 3.0 parts, with the remainder being the barium titanate matrix component; the grain boundary modifier is composed of bismuth trioxide, zinc oxide, and silicon dioxide, and the mass ratios of bismuth trioxide, zinc oxide, and silicon dioxide satisfy the following relationship: ; in, For the mass of bismuth trioxide, For the quality of zinc oxide, The quality of silicon dioxide; the microstructure of the PTC ceramic material for water-circulating electric heating includes barium titanate grains and a continuous amorphous glass phase layer coating the surface of the barium titanate grains. The thickness of the continuous amorphous glass phase layer is 5 nm to 15 nm, and the coverage of the continuous amorphous glass phase layer on the surface of the barium titanate grains is not less than 85%. In the continuous amorphous glass phase layer, bismuth ions occupy the lattice vacancies at the edges of the barium titanate grains to form a physical barrier interface, and bismuth ions construct an ion-locked layer on the surface of the barium titanate grains by compensating for the charge of the ions at the edges of the barium titanate grains. The Curie temperature drift of the PTC ceramic material for water-circulating electric heating after operating for 5000 hours under a water pressure of 1.2 MPa is less than 3%. .

2. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, In the grain boundary modifier, based on a total weight of 100 parts of bismuth trioxide, zinc oxide, and silicon dioxide, the mass fraction of bismuth trioxide is 60 to 80 parts, the mass fraction of zinc oxide is 10 to 20 parts, and the mass fraction of silicon dioxide is 5 to 15 parts. The continuous amorphous glass phase layer has a chemical anchoring structure formed during the cooling and condensation process. Bismuth ions inhibit ion diffusion at the edges of barium titanate grains during the ferroelectric phase transition by electrostatically shielding low-valence ions in the barium titanate matrix components.

3. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, The barium titanate-based matrix component has an average particle size of 0.6 μm to 0.8 μm and a specific surface area of ​​2.5 to 3.

5. The grain boundary modifier is distributed on the surface of the barium titanate matrix component in the form of micro powder with a particle size of no more than 100 nm, and the molten liquid phase of the grain boundary modifier at the ceramic sintering temperature satisfies the wetting angle condition for self-spreading driven by the interfacial tension gradient on the surface of barium titanate grains.

4. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, The continuous amorphous glass phase layer provides intrinsic anti-scraping ability to PTC ceramic materials for water circulation electric heating by physically blocking water molecules; the ion-locked layer maintains the electrochemical stability of PTC ceramic materials for water circulation electric heating in pressurized hot water circulation environment by maintaining the grain boundary barrier height at the edge of barium titanate grains.

5. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, The continuous amorphous glass phase layer and the barium titanate grains satisfy the following volume ratio relationship: ,in, The total volume of the continuous amorphous glass phase layer. The total volume of barium titanate grains; the volume ratio ensures that the grain boundary modifier, while filling the micropores inside the PTC ceramic material for water-circulating electric heating, maintains the room-temperature resistivity of the PTC ceramic material at 10 to 50 Ω·cm. Within the range.

6. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, The Curie temperature of PTC ceramic materials used in water-circulating electric heating is 180°C. Up to 260 PTC ceramic materials used in water-circulating electric heating systems undergo 1000 cycles of oxidation, reducing the temperature from 25°C to 35°C. Heat to Curie temperature and cool to 25°C After thermal cycling, its Curie temperature fluctuates within a range of ±1. Within the barium titanate matrix, the grain boundary modifier is distributed in submicron scale within the contact channels between the components, and the grain boundary modifier forms a dense sintered neck structure with physical sealing function at the junction of barium titanate grains.

7. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, In the continuous amorphous glass phase layer, bismuth trioxide, zinc oxide and silicon dioxide form a eutectic system. The eutectic point of the eutectic system is lower than the sintering temperature of barium titanate grains. The eutectic system is filled by liquid phase in the cooling section of ceramic sintering, and a uniformly thick interface phase is constructed at the edge of barium titanate grains.

8. The PTC ceramic material for water-circulating electric heating according to claim 1, characterized in that, The barium titanate-based matrix component includes barium titanate as the main component and doping modification components. The doping modification components are selected from at least one of niobium pentoxide, lanthanum oxide, and yttrium oxide. The doping modification components work synergistically with the grain boundary modifier to adjust the power aging characteristics of the PTC ceramic material for water-circulating electric heating. The PTC ceramic material for water-circulating electric heating is used as the matrix material for ceramic valve plates. Furthermore, the PTC ceramic material for water-circulating electric heating blocks the chemical erosion of the grain interface by hot water through the continuous amorphous glass phase layer formed inside it.

9. A method for preparing a PTC ceramic material for water-circulating electric heating, wherein the method is prepared from the PTC ceramic material for water-circulating electric heating as described in claim 1, characterized in that, Includes the following steps: Step 1101: Mix the barium titanate matrix component with a grain boundary modifier and ball mill to obtain a mixed powder with an average particle size of 0.6 μm to 0.8 μm; Step 1102: Press the mixed powder into a pre-defined ceramic green body; Step 1103: Heat the green body at 1300 °C. up to 1350 The ceramic green body was sintered under the specified temperature conditions, and during the cooling and condensation process after sintering, it was sintered at 1050°C. Up to 1150 Within the switching temperature range, the ambient oxygen partial pressure is adjusted to above 95%, inducing the grain boundary modifier to condense on the surface of barium titanate grains to form a continuous amorphous glass phase layer.

10. An application of a PTC ceramic material for water-circulating electric heating, characterized in that, It is applied to the PTC ceramic material for water-circulating electric heating as described in claim 1.

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