CaO-SiO-AlO-BO-FeO-NaO / KO composite dielectric ceramic material for high-frequency plasma capacitor vacuum cavity and preparation method of CaO-SiO-AlO-BO-FeO-NaO / KO composite dielectric ceramic material

Abstract

The invention belongs to the technical field of high-frequency plasma and dielectric materials, and particularly relates to a CaO-SiO2-Al2O3-B2O3-Fe2O3-Na2O / K2O composite dielectric ceramic material for a high-frequency plasma capacitor vacuum cavity and a preparation method of the CaO-SiO2-Al2O3-B2O3-Fe2O3-Na2O / K2O composite dielectric ceramic material. The material is prepared from CaO, SiO2, Al2O3, B2O3, Fe2O3, Na2O and K2O in proportion, and a compact glass ceramic matrix is formed by liquid phase sintering at 820-900 DEG C; the dielectric constant epsilon of the material under the condition of 1MHz is 20-35, the dielectric loss tan delta is less than 1 * 10 <-3 >, and the material contains 0.5-1.0 wt% of organic phase to improve toughness and thermal stability. The material provided by the invention has excellent air tightness, thermal shock resistance and high-frequency stability, can maintain high Q-value resonance characteristics in a range of 1-100MHz, is suitable for high-frequency plasma capacitor vacuum cavities, vacuum dielectric structural members and high-frequency energy storage and transmission systems, and is used as an insulating medium and a structural support material.

Description

Technical Field

[0001] This invention relates to the field of high-frequency plasma and dielectric composite materials, and particularly to a CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O composite dielectric ceramic material for high-frequency plasma capacitive vacuum cavities and its preparation method. This material is suitable for use as an insulating medium and structural support material in high-frequency resonant discharge systems, vacuum dielectric structural components, and capacitive energy storage and transmission devices. Background Technology

[0002] Current high-frequency discharge devices mostly use single alumina (Al2O3) or quartz (SiO2) as the dielectric liner. Although these materials have high insulation and chemical stability, they still suffer from problems such as dielectric breakdown, thermal cracking, and low Q-value loss under high-frequency and high-voltage conditions. For example, Michizono et al. (2009) pointed out in Applied Surface Science that the high-frequency window of alumina is one of the main causes of klystron failure due to multiple electrons and surface discharge [Michizono et al., Appl. Surf. Sci. 255 (2009) 8599–8603]; Di Marco et al. (2016) reported in Ceramics International that the dielectric loss of high-purity alumina in the GHz band varies significantly with grain size and density [DiMarco et al., Ceram. Int. 42 (2016) 10859–10865]; while Woode and Armstrong (1994) measured the loss tangent of alumina at 9 GHz to be approximately 4.3 × 10⁻⁶. -5 This shows that its low-loss characteristics are highly dependent on purity and sintering process [Electronics Letters 30 (1994) 1850–1851].

[0003] Furthermore, the significant difference in thermal expansion coefficients between traditional dielectric materials and metal electrodes can easily lead to stress concentration under thermal cycling or high-power resonance conditions, resulting in vacuum cavity sealing failure or partial discharge. Donald et al. (2011) pointed out in a review in the Journal of Materials Science that if the expansion coefficients of glass-ceramic-metal sealing structures are mismatched, residual tensile stress at the interface will be generated, leading to crack propagation [J.Mater.Sci.46(2011)1975–2000].

[0004] On the other hand, plasma resonant systems require the dielectric layer to maintain a high dielectric constant, low dielectric loss, and good thermomechanical stability to achieve high-Q resonance and stable energy coupling in the 1MHz–100MHz frequency band. Currently commonly used commercial LTCC materials (such as DuPont) TM GreenTape TM 951 has a dielectric constant of approximately 7.8 and a loss tangent of approximately 6 × 10⁻⁶. -3 [See publicly available product datasheets] This makes it difficult to meet the requirements of high-Q resonant cavities for low-loss dielectrics in the 1MHz–100MHz frequency band. In recent years, studies by Wang et al. (2021) and Ceramics–Silikáty (2022) have shown that CaO–Al2O3–SiO2–B2O3 (CASB) glass-ceramic-Al2O3 composites can achieve ε-values ​​using the LTCC process. r ≈10–12, tanδ<10 -4 It exhibits good performance and thermal stability [Wang et al., Ceram.Int.47(2021); Ceram.Silikáty 66(2022)310–324].

[0005] In summary, existing single dielectric materials generally suffer from problems such as high dielectric loss, thermal expansion mismatch, poor thermal shock resistance, and easy breakdown in high-frequency discharge and resonance applications, making it difficult to meet the requirements of high-frequency resonant systems for low-loss and high-stability dielectrics.

[0006] Therefore, the market urgently needs a composite dielectric ceramic material system that combines high dielectric constant, low dielectric loss, good thermo-mechanical matching and high airtightness to be suitable for high-frequency plasma capacitor vacuum cavities and related high-frequency energy conversion devices. Summary of the Invention

[0007] This invention belongs to the field of high-frequency plasma dielectric materials technology, specifically relating to a CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O composite dielectric ceramic material for high-frequency plasma capacitor vacuum cavities and its preparation method.

[0008] This material, through the combination of multi-component oxide system design and liquid phase sintering process, can maintain low dielectric loss, high Q value and excellent airtightness under high frequency conditions of 1MHz–100MHz. It is suitable as an insulating medium and structural support material in high frequency plasma capacitor cavities, vacuum dielectric structural components and high frequency energy storage and dissipation systems.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] This invention provides a high-frequency plasma capacitor vacuum cavity material based on a CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O composite dielectric system and its preparation method, as detailed below:

[0011] (1) Material composition

[0012] The composite medium ceramic material is composed of CaO, SiO2, Al2O3, B2O3, Fe2O3, Na2O and K2O, with each component prepared in a mass ratio of (18–24):(45–52):(8–12):(6–9):(2–5):(1–3), and is sintered in the liquid phase at 820–900℃ to form a dense glass-ceramic matrix.

[0013] The density of the obtained material is greater than 2.6 g / cm³. 3 The dielectric constant ε is 20–35 under 1MHz conditions, and the dielectric loss tanδ is less than 1×10⁻⁶. -3 The coefficient of thermal expansion is (6–9)×10 -6 K -1 It has thermal expansion characteristics similar to those of commonly used metal electrodes, thus ensuring the thermo-mechanical matching stability of the sealing structure.

[0014] (2) Organic phase regulation

[0015] The material contains 0.5–1.0 wt% organic phase residue (selected from epoxy resin, phenolic resin or their carbides), which forms a stress buffer microlayer during sintering to improve the toughness and thermal shock resistance of the medium and prevent cracks from forming during thermal cycling.

[0016] (3) Preparation method

[0017] The preparation method of this composite dielectric ceramic material includes the following steps:

[0018] (a) Weigh out the raw materials CaCO3, SiO2, Al2O3, H3BO3, Fe2O3 and Na2CO3 / K2CO3 according to the proportions;

[0019] (b) Ball milling in ethanol medium for 10–12 hours, drying and pre-calcining at 850°C for 2 hours to form a uniform precursor powder;

[0020] (c) Add 0.5–1.0 wt% organic binder, mix thoroughly, and then perform molding or isostatic pressing.

[0021] (d) Liquid phase sintering at 820–900℃ for 2–3 hours to form a dense glass-ceramic composite;

[0022] (e) High-frequency dielectric material with high airtightness is obtained after vacuum drying and surface encapsulation treatment.

[0023] The beneficial effects of this invention are:

[0024] The advantages provided by this invention are as follows:

[0025] 1) High dielectric properties and low loss

[0026] With a dielectric constant ε>30 and dielectric loss tanδ<1×10-3 at 1MHz, it can maintain a high Q value and stable resonance characteristics under high frequency discharge conditions.

[0027] 2) Excellent thermal stability and crack resistance

[0028] The CaO–SiO2–B2O3 eutectic phase structure significantly improves thermal shock resistance and structural integrity, preventing microcracks from forming in the cavity during frequent start-ups and shutdowns.

[0029] 3) High reliability of vacuum sealing

[0030] The material's coefficient of thermal expansion matches that of commonly used metal electrodes (Mo, W, Ni), and can maintain a coefficient of 10 for extended periods. -6 Pa-level vacuum sealing stability.

[0031] 4) Long lifespan and discharge uniformity

[0032] Fe2O3 micro-doping improves the thermal conductivity and electric field uniformity of materials, reduces the risk of partial discharge and dielectric breakdown, and extends the lifespan of plasma devices.

[0033] 5) Good process compatibility and low cost

[0034] Mass production can be achieved using conventional ceramic processing equipment (such as ball mills, presses, and electric furnaces), without the need for high-pressure or vacuum sintering equipment. The process is simple, highly repeatable, and suitable for industrialization. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides a method for preparing a CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O–organic composite medium material, the process steps of which are as follows:

[0038] (1) Raw material preparation

[0039] Weigh out CaCO3, SiO2, Al2O3, H3BO3, Fe2O3, Na2CO3 and K2CO3 as raw materials, and mix them according to the mass ratio of oxides CaO:SiO2:Al2O3:B2O3:Fe2O3:Na2O / K2O = 20:48:10:8:3:2.

[0040] (2) Wet ball milling and pre-reaction

[0041] Add the prepared powder to the ethanol medium, add zirconia balls at a ball-to-powder ratio of 5:1, add 0.5wt% dispersant, and ball mill for 12 hours.

[0042] After drying, the mixture is passed through a 200-mesh sieve and pre-reacted at 750–800℃ for 1–2 hours to fully decompose the carbonate and boric acid and generate the reaction precursor.

[0043] (3) Organic phase introduction and molding

[0044] Add 1.0–1.5 wt% organic binder (PVA or acrylic resin) and 0.3–0.5 wt% plasticizer to the pre-reacted powder, mix evenly, and then spray granulate.

[0045] It is formed by molding or casting, with a molding pressure of 100–200 MPa.

[0046] (4) Staged degreasing

[0047] The temperature is increased to 280–300℃ at 1℃ / min and held for 1–2 hours, then increased to 380–420℃ and held for 1–2 hours to remove most of the organic matter and retain 0.5–1.0 wt% of organic residual phase.

[0048] (5) Liquid phase sintering

[0049] Liquid phase sintering was carried out by heating to 850–890℃ at a rate of 2–3℃ / min in air and holding for 2–3 hours, followed by furnace cooling.

[0050] Based on composition design and physical model calculations, the theoretical bulk density of the resulting dielectric material can reach 2.6 g / cm³. 3 The theoretical dielectric constant ε (1MHz) is 20–35, and the theoretical dielectric loss tanδ (1MHz) is less than 1×10⁻⁶. -3 The coefficient of thermal expansion is (6–9)×10 -6 K -1 .

[0051] (6) Performance evaluation methods

[0052] The above parameters are theoretically calculated values ​​based on the effective medium theory (Maxwell–Garnett model) and known empirical data of the CaO–SiO2–Al2O3–B2O3 glass-ceramic system.

[0053] Subsequent performance verification can be performed by using an LCR meter to measure ε and tanδ, the Archimedes method to measure density, and thermomechanical analysis to measure the coefficient of thermal expansion.

[0054] Example 2

[0055] This embodiment provides another method for preparing CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O–organic composite media material. The main difference from Example 1 is that the glass powder is prepared by melting-quenching-pulverizing route.

[0056] (1) Raw material preparation and ball milling

[0057] The raw material composition and proportions are the same as in Example 1. The mixture was wet-milled for 12 hours and then dried.

[0058] (2) Melting-quenching to produce glass powder

[0059] The mixed powder is placed into an alumina crucible and melted at 1150–1220℃ for 0.5–1.5 hours. After being removed, it is water-quenched or roll-quenched into glass sheets.

[0060] The glass slide is broken and then ball-milled a second time to D. 50 The particle size is 1–3 μm, resulting in glass powder.

[0061] (3) Shaping and debinding-sintering

[0062] After adding 1.0–1.5 wt% organic binder and 0.3–0.5 wt% plasticizer, granulate or pulp, and degrease according to the degreasing procedure of Example 1 (dual platform of 280–300°C and 380–420°C).

[0063] Liquid-phase densification is completed by heating to 820–880℃ at a rate of 2–3℃ / min and holding for 2–3 hours.

[0064] (4) Theoretical performance parameters

[0065] Based on dielectric theory calculations and thermodynamic model extrapolations, the theoretical bulk density of the sample can reach 2.6 g / cm³. 3 The theoretical dielectric constant ε (1MHz) is 20–35, and the theoretical dielectric loss tanδ (1MHz) is less than 1×10⁻³, which is consistent with the theoretical results of Example 1.

[0066] Based on the two embodiments above, theoretical calculations and component design analysis confirm that:

[0067] The CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O–organic composite dielectric system can form high density, high dielectric constant, low dielectric loss and good thermo-mechanical matching characteristics under liquid phase sintering conditions of 820–900℃. It is suitable for use as an insulating and supporting material in high-frequency plasma capacitor vacuum cavities and related vacuum dielectric packaging structures.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A CaO–SiO2–Al2O3–B2O3–Fe2O3–Na2O / K2O composite dielectric ceramic material for high-frequency plasma capacitor vacuum cavities, Its features are, The material is prepared by mixing CaO, SiO2, Al2O3, B2O3, Fe2O3, Na2O and K2O in a mass ratio of (18–24):(45–52):(8–12):(6–9):(2–5):(1–3) and then sintering it in the liquid phase at 820–900℃ to form a glass-ceramic matrix. The material has a dielectric constant ε of 20–35, a dielectric loss tanδ of less than 1×10-3, and contains 0.5–1.0 wt% organic phase to improve toughness and thermal stability. This material is suitable for use as an insulating and structural medium in plasma capacitive vacuum cavities in the high-frequency range of 1MHz–100MHz.

2. The composite dielectric ceramic material according to claim 1, Its features are, The material has a density greater than 2.6 g / cm³. 3 The coefficient of thermal expansion is (6–9)×10 -6 K -1 .

3. The composite dielectric ceramic material according to claim 1, Its features are, The organic phase is selected from epoxy resin, phenolic resin or their carbonized residues, and forms a micro-stress buffer layer during sintering to improve crack resistance.

4. The composite dielectric ceramic material according to claim 1, Its features are, The thickness of the material can be adjusted to 1–10 mm according to the requirements of mechanical strength and electric resonant frequency.

5. The composite dielectric ceramic material according to claim 1, Its features are, The material can be made into different geometric shapes such as flat plates, cylinders or spheres, and used as the structural insulation layer of high-frequency plasma capacitor vacuum cavities.

6. A method for preparing the composite dielectric ceramic material according to any one of claims 1-5, Its features are, Includes the following steps: (1) Weigh out the raw materials CaCO3, SiO2, Al2O3, H3BO3, Fe2O3 and Na2CO3 / K2CO3 according to the proportion; (2) Ball milling in ethanol medium for 10–12 hours, drying and pre-calcining at 850°C for 2 hours to form primary powder; (3) Add 0.5–1.0 wt% organic binder, mix evenly, and then mold. (4) Sintering in the liquid phase at 820–900℃ for 2–3 hours yields a dense composite medium; (5) After vacuum drying and packaging, a composite dielectric ceramic material for high-frequency plasma capacitor vacuum cavity is obtained.

7. The method according to claim 6, Its features are, The ball milling media are zirconia balls with a solid-liquid ratio of 1:(1.0–1.5). Molding is carried out by compression molding or isostatic pressing.

8. The composite dielectric ceramic material and its preparation method according to any one of claims 1–7, Its features are, The chemical composition, raw material form, or process steps of the material system shall not change the main performance parameters of the material. —Including dielectric constant (20–35), dielectric loss (tanδ<1×10⁻⁶) -3 Density (≥2.6 g / cm³) 3 ) and coefficient of thermal expansion (6–9×10 -6 K -1 Under the premise that the present invention can be adjusted or replaced by functionally equivalent oxides or precursors, and the same technical effect as the present invention can still be achieved, all of which should be considered to fall within the protection scope of the present invention.