Temperature-stable ceramic material for voltage transformer and preparation method of temperature-stable ceramic material

Abstract

The invention provides a temperature-stable ceramic material for a voltage transformer and a preparation method thereof, the chemical formula of the temperature-stable ceramic material for the voltage transformer is [(1-a-b). BaTiO3 + a.NaNbO3 + b.Bi (Me0. 5Ti0. 5) O3] + x.glass, 0.2 < = a < = 0.3, 0.2 < = b < = 0.3, Me is a metal element, the glass is ZnO-B2O3-SiO2 glass powder, x is the mass ratio of [(1-a-b). BaTiO3 + a.NaNbO3 + b.Bi (Me0. 5Ti0. 5) O3], and 0.5 wt% < = x < = 1 wt%. BaTiO3 and Bi (Me0. 5Ti0. 5) O3 in a specific proportion are introduced into barium titanate, so that the Curie temperature peak of ferroelectric is effectively moved, the change of the dielectric constant is smoother, the material has the advantages of large dielectric constant and small temperature change coefficient, and the room-temperature dielectric constant can be greater than 490; and meanwhile, due to the introduction of ZnO-B2O3-SiO2 glass powder, the densification process of the material at a relatively low sintering temperature is promoted, so that the sintering temperature of the system is relatively low, and loss reduction is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of electrical equipment, and in particular relates to a temperature-stable ceramic material for a voltage transformer and a preparation method thereof. Background Art

[0002] With the advancement of the construction of smart grids, there are more and more measuring sensors for physical signals of the power grid, such as voltage and current, and they need to meet higher precision requirements. For example, voltage and current sensors and power-taking devices are often integrated in primary and secondary fusion equipment, among which accurate measurement of voltage signals is of great significance. Electronic voltage transformer is a new type of voltage measurement device that converts high voltage signals such as phase sequence voltage and zero-sequence neutral point voltage signals into lower voltage signals, and further transmits them to the subsequent signal detection and processing system. Electronic voltage transformers can be roughly divided into resistive voltage division, capacitive voltage division, and resistance-capacitance voltage division according to their voltage division principles. Among them, capacitive voltage division has the advantages of high reliability and has broad application prospects.

[0003] Capacitive electronic voltage transformer adopts the form of capacitor series voltage division, which includes one or more high-voltage side capacitors with relatively small capacity and higher voltage resistance, and one or more low-voltage side capacitors with large capacity and lower voltage resistance, which are proportional to the tested high-voltage signal. It can be seen that capacitors are key components of electronic voltage transformers, which affect the accuracy and stability of electronic voltage transformers. Commonly used capacitors can be divided into ceramic capacitors and polymer film capacitors according to the type of material. Ceramic capacitors, as inorganic dielectrics, have advantages in long-term operation.

[0004] According to the calculation formula of capacitance:

[0005]

[0006] Where C is capacitance, ε is dielectric constant, S is electrode area, and d is dielectric thickness. Under the premise of meeting a certain capacitance, the larger the dielectric constant ε, the smaller the volume of the ceramic capacitor; in addition, the ambient temperature of the electronic voltage transformer will change during operation, and the power system generally considers the temperature stability of the equipment in the range of -40℃ to +70℃. Therefore, the ceramic capacitance C, that is, the dielectric constant ε, should also have a low temperature change rate within this temperature range (generally based on 20℃). However, the existing ceramic materials used in electronic voltage transformers have the disadvantages of small dielectric constant and high temperature change rate, which cannot meet the use requirements of the power system.

[0007] In addition, the sintering temperature of ceramic materials used in current electronic voltage transformers is relatively high, generally above 1300°C, resulting in high energy consumption. High temperature easily causes element volatilization and uneven reaction. At the same time, the current government's restrictions on harmful elements are becoming increasingly stringent, and existing high dielectric constant materials generally contain lead elements, which do not meet environmental protection requirements.

[0008] Therefore, the development of electronic voltage transformers requires solving the problems of low dielectric constant and high temperature change rate of ceramic dielectric materials. At the same time, problems such as high ceramic sintering temperature and lead content are not conducive to the manufacture and promotion of electronic voltage transformers. Summary of the invention

[0009] The purpose of the present invention is to provide a temperature-stable ceramic material for a voltage transformer for a smart grid with a high dielectric constant, a low temperature change rate, a low sintering temperature and no lead, in order to solve the problems that the ceramic dielectric material used in the current electronic voltage transformer has a low dielectric constant, a high temperature change rate, a high sintering temperature and contains lead, and a preparation method thereof. The purpose of the present invention is achieved by adopting the following technical solutions:

[0010] A temperature-stable ceramic material for a voltage transformer, wherein the chemical formula of the ceramic material is [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3]+x·glass, wherein 0.2≤a≤0.3, 0.2≤b≤0.3, Me is a metal element, the glass is ZnO-B2O3-SiO2 glass powder, and x is relative [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3], 0.5wt%≤x≤1wt%.

[0011] Preferably, the metal element Me is one of Zn and Mg.

[0012] Preferably, the mass ratio of the components of the ZnO-B2O3-SiO2 glass powder is 60-70:20-30:5-15.

[0013] Preferably, the (1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )The components of O3 are introduced by BaCO3, Bi2O3, MeO, Na2CO3, Nb2O5 and TiO2.

[0014] Based on the same inventive concept, the present invention also provides a method for preparing the temperature-stable ceramic material for a voltage transformer, comprising the following steps:

[0015] According to [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3]+x·glass, weighing raw materials BaCO3, Bi2O3, MeO, Na2CO3, Nb2O5, TiO2 according to the stoichiometric ratio, and mixing them uniformly by ball milling to obtain a ball-milled mixture;

[0016] The ball-milled mixture is dried, calcined at 800-900° C. for 6 hours, crushed, and ZnO-B2O3-SiO2 glass powder is added to perform secondary ball milling to obtain pre-sintered powder;

[0017] The pre-burned powder is dried, granulated, and pressed into a shape according to the requirements of the electronic voltage transformer on capacitance, size, and shape to obtain an embryonic body;

[0018] The embryo body is placed in a muffle furnace and heated to 600°C at a rate of 1-3°C / min, kept warm for 2-10 hours for debinding, and then heated to 1000-1050°C, kept warm for 2-4 hours for sintering, cooled to room temperature, and silver electrodes are fired to obtain the temperature-stable ceramic material for the voltage transformer.

[0019] Preferably, Bi2O3 is in excess of 0.5% according to the stoichiometric ratio.

[0020] Preferably, the ball milling process and the secondary ball milling process use a planetary ball mill, the ball milling medium is anhydrous ethanol or deionized water, the rotation speed is 300-400 r / min, and the ball milling time is 12-24 h.

[0021] Preferably, in step S2, the granulation process uses a polyvinyl alcohol solution with a mass fraction of 4.5% to 5.5% as a binder.

[0022] Preferably, in step S3, the pressing process may adopt one of single-sided pressing, double-sided pressing or cold isostatic pressing, and the shape of the embryo body may be one of cylindrical, disc-shaped or long strip-shaped.

[0023] Preferably, the voltage transformer may be provided with lead wires, bolt electrodes, or encapsulated using temperature-stable ceramic materials according to specific design requirements of the electronic voltage transformer.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The temperature-stable ceramic material for voltage transformer of the present invention has the chemical formula [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5)O3]+x·glass, wherein 0.2≤a≤0.3, 0.2≤b≤0.3, Me is a metal element, the glass is ZnO-B2O3-SiO2 glass powder, and x is relative [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3], 0.5wt%≤x≤1wt%. The temperature-stable ceramic material for voltage transformer for smart grid of the present invention is obtained by introducing a specific ratio of BaTiO3 and Bi(Me 0.5 Ti 0.5 )O3, a solid phase reaction occurs, which not only effectively moves the Curie temperature peak of the ferroelectric, but also makes the change of the dielectric constant more gentle, ensuring that the dielectric constant remains stable within the range of -40 degrees to +70 degrees required by the power grid, and has the advantages of a large dielectric constant and a small temperature variation coefficient. The room temperature dielectric constant can be greater than 490; at the same time, ZnO-B2O3-SiO2 glass powder has a lower melting point. Its introduction promotes the densification process of the material at a lower sintering temperature, helps to form a more uniform microstructure, improves the contact between grains, promotes crystal growth, and makes the solid phase reaction more efficient, so that the system has a lower sintering temperature and a dense grain structure, which is conducive to reducing losses. The lower sintering temperature is conducive to reducing energy consumption, while suppressing the volatilization of volatile elements such as Bi and Na at high temperatures, which is also beneficial for the subsequent production of multilayer ceramic capacitors, because it means that metal slurries with lower melting points can be used.

[0026] 2. The method for preparing the temperature-stable ceramic material for the voltage transformer for the smart grid of the present invention is simple to operate and easy to implement, and has a lower sintering temperature, which is beneficial to reducing energy consumption. Bi2O3 is 0.5% excessive in the stoichiometric ratio, which can compensate for the volatilization of the Bi element at high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figures 1 to 7 This is a SEM image of the temperature-stable ceramic material for voltage transformer according to embodiments 1 to 7 of the present invention;

[0028] Figures 8 to 14 The dielectric constant variation curve of the temperature-stable ceramic material for voltage transformer according to embodiments 1 to 7 of the present invention;

[0029] Fig.15 This is a SEM image of the ceramic material described in Comparative Example 1 of the present invention;

[0030] Fig.16 This is a curve showing the change of dielectric constant of the ceramic material described in Comparative Example 1 of the present invention with temperature. DETAILED DESCRIPTION

[0031] Example 1

[0032] This embodiment provides a temperature-stable ceramic material for a voltage transformer, wherein the chemical formula of the material is [0.6BaTiO3+0.2NaNbO3+0.2Bi(Me 0.5 Ti 0.5 )O3]+0.5wt% glass, the raw materials for preparation are BaCO3, Bi2O3, MeO, Na2CO3, Nb2O5, TiO2, wherein the purity of each raw material is greater than 99.5%, and the glass is ZnO-B2O3-SiO2 glass.

[0033] Preparation method:

[0034] S1. Weigh the above raw materials according to the stoichiometric ratio, wherein Bi2O3 is 0.5% in excess according to the stoichiometric ratio, and use anhydrous ethanol as the ball milling medium, and use a planetary ball mill for 24h at a speed of 300r / min to obtain a mixture after ball milling;

[0035] S2. The ball-milled mixture was dried at 100°C, the ball-milling medium was removed, and the mixture was calcined at 850°C for 6h. The calcined material was crushed, 0.5wt% of ZnO-B2O3-SiO2 glass was added, and then anhydrous ethanol was used as the ball-milling medium and the mixture was ball-milled in a planetary ball mill for 24h at a speed of 300r / min to obtain a pre-calcined powder;

[0036] S3. The pre-calcined powder was dried at 90 ° C, granulated with a 5% polyvinyl alcohol solution as a binder, and then pressed into a disc shape using a single-sided pressurization form to obtain an embryo;

[0037] S4. Place the embryo body in a muffle furnace, heat it to 600°C at a rate of 3°C / min, keep it warm for 2 hours to debind, continue to heat it to 1050°C for sintering, keep it warm for 2 hours, cool it to room temperature, grind and polish it, and burn silver electrodes to obtain the temperature-stable ceramic material for the voltage transformer for the smart grid.

[0038] Embodiment 2-7

[0039] The raw material ratio and preparation method of the temperature-stable ceramic material for voltage transformer provided in Examples 2 to 7 are substantially the same as those in Example 1, and the differences are shown in Table 1.

[0040] Table 1 Raw material ratio and preparation conditions

[0041]

[0042]

[0043] Comparative Example 1

[0044] This comparative example provides a ceramic material, whose chemical composition and preparation method are basically the same as those of Example 1, except that: a=0.4; b=0.4.

[0045] Comparative Example 2

[0046] This comparative example provides a ceramic material, whose chemical composition and preparation method are basically the same as those of Example 1, except that: x = 0. It cannot be sintered into porcelain.

[0047] Comparative Example 3

[0048] This comparative example provides a ceramic material, whose chemical composition and preparation method are basically the same as those of Example 6, except that: x = 0. It cannot be sintered into porcelain.

[0049] Test Case

[0050] Since Comparative Examples 2 and 3 did not form ceramics, the ceramic materials obtained in Examples 1 to 7 and Comparative Example 1 were taken, and their microscopic morphologies were observed under a scanning electron microscope (SEM) to obtain their SEM images; their dielectric constants at different temperatures were tested to obtain their dielectric constant variation curves with temperature; and their change rates at -40°C and 70°C relative to room temperature (20°C) and room temperature losses were calculated.

[0051] Test results: The SEM images of Examples 1 to 7 are as follows: Figures 1 to 7 As shown, the dielectric constant changes with temperature. Figures 8 to 14 As shown; the SEM picture of Comparative Example 1 is as shown Fig.15 The dielectric constant changes with temperature as shown in Fig.16 The change rate of its relative dielectric constant relative to room temperature (20°C) and the room temperature loss are shown in Table 2.

[0052] Table 2 Test results

[0053]

[0054] According to the above test results, it can be seen that the ceramic materials of Examples 1 to 7 are more compact and uniform in microstructure, better in dielectric constant, lower in room temperature loss, less than 4% in temperature change rate, and greater than 490 in room temperature dielectric constant, especially under the raw material ratio and preparation conditions of Example 1, the room temperature dielectric constant can reach more than 680, while the temperature change rate of the comparative example is as high as 15%, indicating that the ceramic material obtained by the raw material ratio and preparation method of the present invention can obtain a compact structure and good electrical properties at a lower sintering temperature, which is conducive to the development of electronic voltage transformers. Comparative Example 2 cannot be sintered into porcelain at 1050°C and Comparative Example 3 cannot be sintered into porcelain at 1000°C, indicating that the ZnO-B2O3-SiO2 glass powder is necessary for sintering into porcelain. In the raw material ratio of Comparative Example 1, the values ​​of a and b are 0.4, and the performance of the obtained ceramic material is not ideal, indicating that it is necessary to adopt the raw material ratio described in this application.

[0055] Although the present invention has been disclosed as above by the embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A temperature-stable ceramic material for a voltage transformer, characterized in that: The chemical formula of the ceramic material is [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3]+x·glass, wherein 0.2≤a≤0.3, 0.2≤b≤0.3, Me is a metal element, the glass is ZnO-B2O3-SiO2 glass powder, and x is relative [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3], 0.5wt%≤x≤1wt%.

2. The temperature-stable ceramic material for voltage transformer according to claim 1, characterized in that: The metal element Me is one of Zn and Mg.

3. The temperature-stable ceramic material for voltage transformer according to claim 1, characterized in that: The mass ratio of the components of the ZnO-B2O3-SiO2 glass powder is 60-70:20-30:5-15.

4. The temperature-stable ceramic material for voltage transformer according to claim 1, characterized in that: The (1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )The components of O3 are introduced by BaCO3, Bi2O3, MeO, Na2CO3, Nb2O5 and TiO2.

5. A method for preparing the temperature-stable ceramic material for voltage transformer according to any one of claims 1 to 4, characterized in that: The steps include: According to [(1-ab)·BaTiO3+a·NaNbO3+b·Bi(Me 0.5 Ti 0.5 )O3]+x·glass, weighing raw materials BaCO3, Bi2O3, MeO, Na2CO3, Nb2O5, TiO2 according to the stoichiometric ratio, and mixing them uniformly by ball milling to obtain a ball-milled mixture; The ball-milled mixture is dried, calcined at 800-900° C. for 6 hours, crushed, and ZnO-B2O3-SiO2 glass powder is added to perform secondary ball milling to obtain pre-sintered powder; The pre-burned powder is dried, granulated, and pressed into a shape according to the requirements of the electronic voltage transformer on capacitance, size, and shape to obtain an embryonic body; The embryo body is placed in a muffle furnace and heated to 600°C at a rate of 1-3°C / min, kept warm for 2-10 hours for debinding, and then heated to 1000-1050°C, kept warm for 2-4 hours for sintering, cooled to room temperature, and silver electrodes are fired to obtain the temperature-stable ceramic material for the voltage transformer.

6. The preparation method according to claim 5, characterized in that: The Bi2O3 is in excess of 0.5% to 1% according to the stoichiometric ratio.

7. The preparation method according to claim 5, characterized in that: The ball milling process and the secondary ball milling process adopt a planetary ball mill, the ball milling medium is anhydrous ethanol or deionized water, the rotation speed is 300-400 r / min, and the ball milling time is 12-24 hours.

8. The preparation method according to claim 5, characterized in that: The granulation process uses a polyvinyl alcohol solution with a mass fraction of 4.5-5.5% as a binder.

9. The preparation method according to claim 5, characterized in that: The pressing molding adopts one of single-sided pressing, double-sided pressing or cold isostatic pressing; the shape of the embryo body is one of cylindrical, disc-shaped or long strip.

10. The preparation method according to claim 5, characterized in that: According to the specific design requirements of the electronic voltage transformer, the voltage transformer can be provided with lead wires, bolt electrodes, or encapsulated using temperature-stable ceramic materials.

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