High-hardness high-strength low-temperature sintered composite ceramic material and preparation method thereof
By combining modified manganese silicon slag and active silicon aluminum composite materials with a variety of industrial solid wastes and a specific sintering process, the problems of high energy consumption and insufficient performance of traditional ceramic materials have been solved. This has enabled the preparation of high-hardness and high-strength low-temperature sintered composite ceramic materials, thereby improving the performance and resource utilization efficiency of ceramic materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUJIAN DEHUA QUANFENG CERAMICS CO LTD
- Filing Date
- 2026-05-08
- Publication Date
- 2026-06-05
AI Technical Summary
In existing technologies, traditional ceramic materials rely on natural mineral raw materials such as kaolin, feldspar, and quartz, resulting in high energy consumption per unit product. Furthermore, the application of industrial solid waste in ceramics suffers from insufficient activity, large fluctuations in composition, and insufficient research on synergistic effects, leading to low product performance and difficulty in application in high-value-added fields.
A variety of industrial solid wastes, including modified manganese silicon slag, active silicon-aluminum composite material, and low-temperature composite flux, are used to modify the manganese silicon slag through a silanization-hypotriacetic acid covalent grafting-aluminum tripolyphosphate in-situ deposition method. Combined with a specific sintering process, a multiphase synergistic enhanced microstructure is formed, achieving low-temperature sintering densification.
This research has achieved high-hardness and high-strength low-temperature sintered composite ceramic materials, made resource-efficient use of various industrial solid wastes, improved the performance of ceramic materials, reduced production energy consumption, and solved the constraints of traditional ceramic materials in terms of resources and energy consumption.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of ceramic preparation technology, specifically relating to a high-hardness, high-strength, low-temperature sintering composite ceramic material and its preparation method. Background Technology
[0002] Ceramic materials are widely used in building decoration, sanitary ware, and daily consumer goods due to their good hardness, wear resistance, chemical stability, and decorative properties. However, the traditional ceramic industry has long relied on high-quality natural mineral raw materials such as kaolin, feldspar, and quartz, and the sintering temperature is generally above 1150℃, resulting in high energy consumption per unit of product. It faces increasingly prominent constraints in both raw material resource consumption and production energy consumption.
[0003] To address these challenges, utilizing industrial solid waste to replace natural mineral raw materials and adopting low-temperature rapid sintering technology have become a research hotspot and an important direction for industrial development in the ceramics field.
[0004] In terms of solid waste resource utilization, existing technologies have extensively explored the application of various industrial solid wastes in ceramics. For example, bulk solid wastes such as blast furnace slag, steel slag, fly ash, tailings, and waste glass are used extensively to produce low-value-added building ceramics such as ceramsite, permeable bricks, and plaza bricks because their chemical composition is similar to that of traditional ceramic raw materials. However, these applications generally suffer from the following technical bottlenecks: (1) Insufficient activity of solid waste and shallow utilization level; most studies only use solid waste as a simple filler or substitute material without deep activation and modification, resulting in low participation in the ceramic body, weak interface with the matrix, and difficulty in forming an effective reinforcing phase. The final product has low key performance indicators such as strength and hardness, which limits its application in high-value-added fields. (2) Large fluctuation in composition and difficulty in quality control; the source and batch differences of solid waste lead to large fluctuations in its chemical composition, especially the unstable content of impurities such as Fe2O3, MgO, and MnO, which easily causes problems such as product color difference, unstable firing regime, and poor product performance consistency. Existing technologies lack effective means for fine pretreatment and surface functionalization modification of solid waste. (3) Insufficient research on solid waste synergistic effects; existing research focuses on simple compounding of single or two types of solid waste, lacking systematic design for component complementarity and activity synergy among multiple solid wastes, and failing to fully explore the potential of multi-solid waste systems in low-temperature eutectic melting and in-situ self-generated reinforcing phases.
[0005] In terms of low-temperature sintering technology, existing technologies mainly reduce sintering temperature by introducing low-melting-point glass powder, borosilicates, composite fluxes, etc. For example, waste liquid crystal display (LCD) glass powder and borosilicate glass are used as fluxes because they contain components such as B2O3 and SrO with low melting points. However, relying solely on low-melting-point liquid phases to bond the green body often leads to the following problems: (1) Incomplete crystal phase development and limited mechanical properties; Excessive amorphous glass phases will inhibit the growth and development of reinforcing crystal phases such as mullite and anorthite in the green body. The resulting ceramic material structure is mainly composed of glass phase-bonded aggregate particles, which is essentially a glass ceramic. Its hardness, wear resistance, flexural strength and other mechanical properties are far inferior to melt self-crystallized ceramics reinforced by interwoven crystal phase networks such as whiskers and fibers. (2) Poor high-temperature performance; A large amount of low-viscosity glass phases leads to a significant decrease in the creep resistance of ceramic materials at high temperatures, which limits their application in certain environments requiring high-temperature resistance.
[0006] Therefore, there is an urgent need to develop a high-hardness, high-strength, low-temperature sintering composite ceramic material and its preparation method, so as to prepare a high-value-added composite ceramic material with excellent mechanical properties. Summary of the Invention
[0007] To address the shortcomings of existing technologies, the present invention aims to provide a high-hardness, high-strength, low-temperature sintered composite ceramic material and its preparation method.
[0008] To achieve the above objectives, the present invention provides the following technical solution: A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 35-45 parts of active silicon-aluminum composite material, 20-25 parts of modified manganese silicon slag, 10-15 parts of α-alumina micro powder, 12-18 parts of sodium feldspar, 8-12 parts of wollastonite, 10-15 parts of low-temperature composite flux, and 80-100 parts of water.
[0009] Preferably, a high-hardness, high-strength, low-temperature sintered composite ceramic material comprises the following raw materials by weight: 38-42 parts of active silicon-aluminum composite material, 20-25 parts of modified manganese silicon slag, 10-15 parts of α-alumina micro powder, 15-18 parts of sodium feldspar, 10-12 parts of wollastonite, 10-13 parts of low-temperature composite flux, and 85-95 parts of water.
[0010] Preferably, the modified manganese silicon slag is prepared as follows: Manganese silicon slag powder was added to an ethanol aqueous solution, followed by the addition of γ-aminopropyltriethoxysilane. The mixture was stirred and reacted. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. Triazine triacetic acid was added to deionized water, followed by the addition of EDC and NHS. The pH was adjusted to 5-6, and the mixture was stirred and activated at 25°C for 30-40 min. The pH of the system was then adjusted to 7-7.5, and the aminated manganese silicon slag was added. The mixture was subjected to a constant-temperature reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. The organomanganese silicon slag was added to an aluminum sulfate solution and stirred for 30-40 min. Then, sodium tripolyphosphate solution was added dropwise to carry out a hydrothermal reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag.
[0011] Preferably, the volume ratio of ethanol to water in the ethanol-water solution is 90-95:5-10, the mass ratio of manganese silicon slag to γ-aminopropyltriethoxysilane is 100:5-8, the stirring reaction temperature is 65-75℃, and the time is 3-4 hours; the mass ratio of hyponitrotriacetic acid, EDC, NHS, and aminated manganese silicon slag is 8-12:5-7:4-5:100, the isothermal reaction temperature is 35-40℃, and the time is 4-6 hours; the mass concentration of the aluminum sulfate solution is 3-5%, the mass concentration of the sodium tripolyphosphate is 2-3%, the mass ratio of the organomanganese silicon slag, aluminum sulfate solution, and sodium tripolyphosphate solution is 100:350-450:600-800, and the hydrothermal reaction temperature is 120-140℃, and the time is 2-3 hours.
[0012] Preferably, the preparation method of the active silicon-aluminum composite material is as follows: Waste refractory brick powder and phosphogypsum were mixed evenly and soaked in ammonium sulfate solution. After soaking, the mixture was ball-milled and then added to sodium humate solution. The mixture was heated and stirred. After stirring, the mixture was filtered, dried, and broken up to obtain active silicon-aluminum composite material.
[0013] Preferably, the mass ratio of the waste refractory brick powder to phosphogypsum is 60-70:30-40, the mass concentration of the ammonium sulfate solution is 8-12%, the soaking temperature is 60-70℃, and the soaking time is 2-3 hours; the ball milling speed is 400-500 r / min, and the time is 2-3 hours; the mass concentration of the sodium humate solution is 5-8%, and the heating reaction temperature is 60-70℃, and the time is 1-1.5 hours.
[0014] Preferably, the preparation method of the low-temperature composite flux is as follows: borosilicate waste glass powder, nano-bismuth oxide, and calcium fluoride are mixed, ball-milled in anhydrous ethanol, and dried to obtain the low-temperature composite flux.
[0015] In this invention, a ternary low-temperature composite flux system is constructed using borosilicate waste glass powder, bismuth oxide, and calcium fluoride. The borosilicate waste glass powder contains a high content of B2O3, which significantly reduces the viscosity of the glass phase, enabling the liquid phase to possess good wetting and pore-filling capabilities at lower temperatures. Bismuth oxide, with a melting point of approximately 820°C, is miscible with molten borosilicate glass, further widening the effective liquid phase temperature range and reducing the surface tension of the liquid phase, thus improving the wettability of the liquid phase to solid particles. Calcium fluoride acts as a mineralizing agent, providing F... - Ions lower the nucleation activation energy of hard mineral phases in the system, which is beneficial for promoting their crystallization under liquid-phase assistance; on the other hand, F - With Ca in the system 2+ The presence of phosphate ions provides the thermodynamic conditions for participating in the formation of calcium- and phosphorus-containing mineral phases. The synergistic effect of the three components lowers the liquid phase generation temperature of the system. At a lower sintering temperature, the liquid phase is sufficient and evenly distributed, ensuring good densification of the green body in this temperature range. At the same time, the liquid phase is mainly composed of solid waste borosilicate glass, reducing the amount of special low-temperature sintering aid used.
[0016] Preferably, the borosilicate waste glass powder, nano bismuth oxide, and calcium fluoride are mixed in a mass ratio of 70-75:15-20:10-15, and the ball milling speed is 400-500 r / min for 4-6 h.
[0017] This invention also protects a method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material as described above, comprising the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and obtain a slurry by wet ball milling. Then, obtain ceramic green body by slurry casting or pressing and drying. S2. The ceramic is fed into the kiln for sintering. After sintering, it is naturally cooled to room temperature with the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0018] Preferably, the wet ball milling time in step S1 is 4-6 hours; the pressing pressure is 25-35 MPa; the drying temperature is 100-120°C, and the green body moisture content is less than 1%; the sintering process in step S2 is as follows: heating to 350-450°C at 2-3°C / min and holding for 1-1.5 hours; then heating to 700-750°C at 4-6°C / min and holding for 1-1.5 hours; then heating to 950-1000°C at 3-5°C / min and holding for 2-3 hours.
[0019] In this invention, a three-stage sintering process is employed. The heating rate and holding time of each stage correspond to the temperatures of organic decomposition, liquid phase formation, and mineral phase development in the green body. The first stage is the binder removal stage, where slow heating and sufficient holding ensure that organic components such as sodium humate, γ-aminopropyltriethoxysilane segments, and hypozonyltriacetic acid coupling layer in the green body are completely oxidized and decomposed before liquid phase formation, preventing organic matter from being encapsulated by the subsequent liquid phase and forming closed pores. The second stage is the liquid phase initiation stage, where borosilicate waste glass softens to form an initial liquid phase, and CaF2 mineralizer begins to activate. Holding time in this stage allows the liquid phase to spread evenly between particles. The third stage is the densification and mineral phase recombination stage, where the liquid phase fully fills the residual pores to complete densification. The aluminum tripolyphosphate functional layer deposited in situ on the surface of the modified manganese silicon slag particles decomposes in this stage, releasing Al 3+ With PO4 3- Directional enrichment at the particle contact interface induces the crystallization of hard phosphate phases such as AlPO4; simultaneously, the active silica-alumina components, calcium components, manganese components and phosphate components in the system form a reinforced structure with multiple high-melting-point hard minerals interpenetrating each other under the assistance of the liquid phase; this sintering method avoids the deformation and porosity defects of the green body caused by rapid heating, and achieves ceramics with low water absorption and high density at a relatively low maximum sintering temperature.
[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The high-hardness, high-strength, low-temperature sintering composite ceramic material provided by the present invention uses modified manganese silicon slag derived from solid waste of manganese alloy smelting, active silicon aluminum composite material with waste refractory brick powder and phosphogypsum as the main raw materials, and low-temperature composite flux with borosilicate waste glass powder as the main raw material. Multiple industrial solid wastes are simultaneously utilized as resources, and the derivative components of each solid waste complement each other in the sintering process. Modified manganese silicon slag provides Mn, Si active components and aluminum tripolyphosphate interface activation layer; active silicon aluminum composite material provides highly active Al2O3-SiO2 sintering skeleton; low-temperature composite flux forms a sufficient liquid phase at 950–1000℃, filling the pores between particles, so that the system can be densified under conditions lower than the traditional ceramic sintering temperature. Multiple components interact with each other in the sintering process, which is conducive to the formation of multiple high-melting-point hard mineral phases in the matrix, thereby forming a multi-phase synergistic enhancement microstructure, so that the ceramic material can obtain high hardness and flexural strength at the same time, realizing the unity of solid waste reduction, resource utilization and ceramic performance improvement.
[0021] (2) The high-hardness, high-strength, low-temperature sintering composite ceramic material provided by this invention is prepared by modifying manganese silicon slag. The surface of the manganese silicon slag is modified by a three-step method of silanization-covalent grafting of hyponitrotriacetic acid-aluminum tripolyphosphate in situ deposition. First, the manganese silicon slag is reacted with γ-aminopropyltriethoxysilane to introduce active amino groups, which is beneficial to subsequent reactions. Then, hyponitrotriacetic acid is introduced as a grafting layer. The carboxyl groups in the hyponitrotriacetic acid molecules are activated by EDC / NHS and form amide bonds with the aminated manganese silicon slag. The iminodiacetic acid structure exposed after grafting coordinates with Al in a tridentate N, O manner. 3+ This forms a strong chelating anchor, fundamentally inhibiting the loss of aluminum source in the aqueous system; subsequently, through the in-situ deposition of aluminum tripolyphosphate, P3O 10 5- Al anchored to the surface of organomanganese silicon slag 3+ Heterogeneous nucleation reaction occurs preferentially, and a functional layer of aluminum tripolyphosphate is uniformly coated on the particle surface. This functional layer releases Al-P active components in situ during the high-temperature sintering stage, promoting the directional crystallization of hard mineral phases at the particle interface. Compared with the method of directly adding aluminum phosphate, the interface bonding is tighter, effectively improving the density and mechanical properties of the ceramic matrix.
[0022] (3) The high-hardness, high-strength, low-temperature sintering composite ceramic material provided by this invention is prepared by a multi-step process of ammonium sulfate solution activation-mechanical ball milling-sodium humate organic coating. Refractory brick powder and phosphogypsum are mixed and then soaked in ammonium sulfate solution. NH4 + With SO4 2- Synergistic activation of Ca in the silica-alumina phase and phosphogypsum of waste refractory bricks 2+ The process involves disrupting the dense aluminosilicate crystal structure to enhance reactivity; subsequent mechanical ball milling further refines the particle size, exposing numerous highly active fracture surfaces; finally, an aqueous solution of sodium humate is used to organically coat the powder surface. The carboxyl and phenolic hydroxyl groups in the sodium humate molecules coordinate and adsorb with the fresh fracture surfaces of the particles, forming an organic acid salt protective layer. On the one hand, this layer effectively prevents the highly active particles from becoming inactive and agglomerated during drying and storage through steric hindrance; on the other hand, this organic layer vaporizes during the sintering and debinding stage, forming local activation channels, reducing material transport resistance, and promoting rapid formation of low-temperature sintering. By modifying refractory brick powder and phosphogypsum through specific methods, compared with a single ball milling process, the sintering activity of silicon-aluminum raw materials can be more effectively improved, which is conducive to promoting the full development of silicon-aluminum hard mineral phases at lower sintering temperatures and improving the density and mechanical properties of the products. Detailed Implementation
[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0024] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.
[0025] In this invention, EDC is 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride; NHS is N-hydroxysuccinimide.
[0026] The chemical composition of the manganese silicon slag, by mass percentage, is: SiO2 35-45%, MnO 15-25%, Al2O3 8-15%, CaO 5-10%, MgO 2-6%, with the remainder being impurities; the waste refractory bricks are obtained from waste refractory bricks dismantled during major overhauls or partial repairs of industrial kilns (including but not limited to steelmaking converters, electric arc furnaces, ferroalloy submerged arc furnaces, non-ferrous metal smelting furnaces, cement rotary kilns, glass kilns, etc.), and are obtained as powder material after mechanical crushing and grinding, with the chemical composition by mass percentage: Al2O3 45-65%, SiO2 25-40%, with the remainder being impurities; the chemical composition of the borosilicate waste glass powder, by mass percentage, is: B2O3 8-15%, Al2O3 2-8%, Na2O+K2O 4-10%, with the remainder being impurities. Example 1
[0027] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of modified manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0028] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 7g of γ-aminopropyltriethoxysilane. The mixture was stirred at 70℃ for 3.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 10g of hypozinogenyltriacetic acid was added to 1L of deionized water, followed by the addition of 6g of EDC and 4.5g of... NHS was prepared, and the pH was adjusted to 5.5. The mixture was then stirred and activated at 25°C for 35 min. The pH of the system was adjusted to 7.5, and 100 g of aminated manganese silicon slag was added. The mixture was then reacted at 38°C for 5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100 g of organomanganese silicon slag was added to 400 g of 4% aluminum sulfate solution. After stirring for 35 min, 700 g of 2.5% sodium tripolyphosphate solution was added dropwise while stirring. After the addition was completed in 35 min, the mixture was hydrothermally reacted at 130°C for 2.5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Mix 650g of waste refractory brick powder and 350g of phosphogypsum evenly, add to 3L of 10% ammonium sulfate solution, soak at 65℃ for 2.5h, filter and dry after soaking, ball mill at 450r / min for 2.5h, filter and dry after ball milling, then add to 3L of 7% sodium humate solution, stir at 65℃ for 1.5h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The preparation method of the low-temperature composite flux is as follows: 730g borosilicate waste glass powder, 170g nano bismuth oxide and 130g calcium fluoride are mixed, 90g anhydrous ethanol is added, ball milling is performed for 5 hours, and then dried to obtain the low-temperature composite flux. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material. Example 2
[0029] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: The composition consists of 35 parts of active silicon-aluminum composite material, 20 parts of modified manganese silicon slag, 10 parts of α-alumina micro powder, 12 parts of sodium feldspar, 8 parts of wollastonite, 10 parts of low-temperature composite flux, and 80 parts of water.
[0030] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 90:10), followed by the addition of 5g of γ-aminopropyltriethoxysilane. The mixture was stirred at 65℃ for 4h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 8g of hypozinogenamic triacetic acid was added to 1L of deionized water, followed by the addition of 5g of EDC and 4g of NHS. The pH was adjusted to 5, and the mixture was stirred and activated at 25℃ for 30min. The pH was then adjusted to 7, and 100g of aminated manganese silicon slag was added. The mixture was reacted at 35℃ for 6h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100g of organomanganese silicon slag was added to 350g of 5% aluminum sulfate solution. After stirring for 30min, 600g of 3% sodium tripolyphosphate solution was added dropwise while stirring. After the addition was completed in 30min, the mixture was hydrothermally reacted at 120℃ for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Mix 600g of waste refractory brick powder and 400g of phosphogypsum evenly, add to 3L of 8% ammonium sulfate solution, soak at 60℃ for 3h, filter and dry after soaking, ball mill at 400r / min for 3h, filter and dry after ball milling, then add to 3L of 5% sodium humate solution, stir at 60℃ for 1h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The preparation method of the low-temperature composite flux is as follows: 700g of borosilicate waste glass powder, 150g of nano bismuth oxide, and 100g of calcium fluoride are mixed, 80g of anhydrous ethanol is added, the mixture is ball-milled for 6 hours, and then dried to obtain the low-temperature composite flux.
[0031] A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 4 hours to obtain a slurry. Press it into shape at 25 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 350℃ at 2℃ / min and held for 1.5h; then the temperature is increased to 700℃ at 4℃ / min and held for 1.5h; then the temperature is increased to 950℃ at 3℃ / min and held for 3h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material. Example 3
[0032] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 45 parts of active silicon-aluminum composite material, 25 parts of modified manganese silicon slag, 15 parts of α-alumina micro powder, 18 parts of sodium feldspar, 12 parts of wollastonite, 15 parts of low-temperature composite flux, and 100 parts of water.
[0033] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 8g of γ-aminopropyltriethoxysilane. The mixture was stirred at 75℃ for 3h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 12g of hypozinotriacetic acid was added to 1L of deionized water, followed by the addition of 7g of EDC and 5g of NHS. The pH was adjusted to 6, and the mixture was stirred and activated at 25℃ for 40min. The pH of the system was then adjusted to 7.5, and 100g of aminated manganese silicon slag was added. The mixture was kept at 40℃ for 4h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100g of organomanganese silicon slag was added to 450g of 3% aluminum sulfate solution. After stirring for 40min, 800g of 2% sodium tripolyphosphate solution was added dropwise while stirring. After the addition was completed in 40min, the mixture was hydrothermally reacted at 140℃ for 2h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: 700g of waste refractory brick powder and 300g of phosphogypsum were mixed evenly and added to 3L of 12% ammonium sulfate solution. The mixture was soaked at 70℃ for 2 hours. After soaking, the mixture was filtered and dried. The mixture was then ball-milled at 500r / min for 2 hours. After ball milling, the mixture was filtered and dried. Then, the mixture was added to 3L of 8% sodium humate solution and stirred at 70℃ for 1.5 hours. After stirring, the mixture was filtered, dried, and broken up to obtain active silicon-aluminum composite material. The preparation method of the low-temperature composite flux is as follows: 750g borosilicate waste glass powder, 200g nano bismuth oxide and 150g calcium fluoride are mixed, 100g anhydrous ethanol is added, ball milling is performed for 6 hours, and then dried to obtain the low-temperature composite flux.
[0034] A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 450℃ at 3℃ / min and held for 1 hour; then the temperature is increased to 750℃ at 6℃ / min and held for 1 hour; then the temperature is increased to 1000℃ at 5℃ / min and held for 2 hours. After sintering, the ceramic green body is naturally cooled to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material. Comparative Example 1
[0035] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0036] The preparation method of the active silicon-aluminum composite material is as follows: Mix 650g of waste refractory brick powder and 350g of phosphogypsum evenly, add to 3L of 10% ammonium sulfate solution, soak at 65℃ for 2.5h, filter and dry after soaking, ball mill at 450r / min for 2.5h, filter and dry after ball milling, then add to 3L of 7% sodium humate solution, stir at 65℃ for 1.5h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The preparation method of the low-temperature composite flux is as follows: 730g borosilicate waste glass powder, 170g nano bismuth oxide and 130g calcium fluoride are mixed, 90g anhydrous ethanol is added, ball milling is performed for 5 hours, and then dried to obtain the low-temperature composite flux. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh out manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0037] Compared with Example 1, the manganese silicon slag in this comparative example was not modified. Comparative Example 2
[0038] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of modified manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0039] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 7g of γ-aminopropyltriethoxysilane. The mixture was stirred at 70℃ for 3.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 100g of aminated manganese silicon slag was added to 400g of 4% aluminum sulfate solution. After stirring for 35min, 700g of 2.5% sodium tripolyphosphate solution was added dropwise while stirring. After the addition was completed in 35min, the mixture was hydrothermally reacted at 130℃ for 2.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Mix 650g of waste refractory brick powder and 350g of phosphogypsum evenly, add to 3L of 10% ammonium sulfate solution, soak at 65℃ for 2.5h, filter and dry after soaking, ball mill at 450r / min for 2.5h, filter and dry after ball milling, then add to 3L of 7% sodium humate solution, stir at 65℃ for 1.5h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The preparation method of the low-temperature composite flux is as follows: 730g borosilicate waste glass powder, 170g nano bismuth oxide and 130g calcium fluoride are mixed, 90g anhydrous ethanol is added, ball milling is performed for 5 hours, and then dried to obtain the low-temperature composite flux. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0040] Compared to Example 1, the modified manganese slag in this comparative example did not contain hyponitrotriacetic acid. Comparative Example 3
[0041] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of modified manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0042] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 7g of γ-aminopropyltriethoxysilane. The mixture was stirred at 70℃ for 3.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 10g of hypozinogenamic triacetic acid was added to 1L of deionized water, followed by the addition of 6g of EDC and 4.5g of NHS. The pH was adjusted to 5.5, and the mixture was stirred and activated at 25℃ for 35min. The pH of the system was then adjusted to 7.5, and 100g of aminated manganese silicon slag was added. The mixture was kept at 38℃ for 5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100g of organomanganese silicon slag was mixed evenly with 14g of aluminum tripolyphosphate to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Mix 650g of waste refractory brick powder and 350g of phosphogypsum evenly, add to 3L of 10% ammonium sulfate solution, soak at 65℃ for 2.5h, filter and dry after soaking, ball mill at 450r / min for 2.5h, filter and dry after ball milling, then add to 3L of 7% sodium humate solution, stir at 65℃ for 1.5h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The preparation method of the low-temperature composite flux is as follows: 730g borosilicate waste glass powder, 170g nano bismuth oxide and 130g calcium fluoride are mixed, 90g anhydrous ethanol is added, ball milling is performed for 5 hours, and then dried to obtain the low-temperature composite flux. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0043] Compared with Example 1, the modified manganese silicon slag in this comparative example was obtained by physical blending of organomanganese silicon slag and aluminum tripolyphosphate. Comparative Example 4
[0044] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of modified manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0045] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 7g of γ-aminopropyltriethoxysilane. The mixture was stirred at 70℃ for 3.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 10g of hypozinogenyltriacetic acid was added to 1L of deionized water, followed by the addition of 6g of EDC and 4.5g of... NHS was prepared, and the pH was adjusted to 5.5. The mixture was stirred and activated at 25°C for 35 min. The pH of the system was then adjusted to 7.5. 100 g of aminated manganese silicon slag was added, and the mixture was reacted at 38°C for 5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100 g of organomanganese silicon slag was added to 550 g of 4% aluminum sulfate solution and stirred for 35 min. 700 g of 2.5% sodium tripolyphosphate solution was added dropwise. After the addition was completed in 35 min, the mixture was hydrothermally reacted at 130°C for 2.5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: 650g of waste refractory brick powder and 350g of phosphogypsum were mixed evenly and ball-milled at 450r / min for 2.5h. After ball milling, active silicon-aluminum composite material was obtained. The preparation method of the low-temperature composite flux is as follows: 730g borosilicate waste glass powder, 170g nano bismuth oxide and 130g calcium fluoride are mixed, 90g anhydrous ethanol is added, ball milling is performed for 5 hours, and then dried to obtain the low-temperature composite flux. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0046] Compared with Example 1, the active silicon-aluminum composite material in this comparative example was only ball-milled, without ammonium sulfate soaking and sodium humate treatment. Comparative Example 5
[0047] A high-hardness, high-strength, low-temperature sintered composite ceramic material, comprising the following raw materials by weight: 10 parts of active silicon-aluminum composite material, 23 parts of modified manganese silicon slag, 13 parts of α-alumina micro powder, 15 parts of sodium feldspar, 10 parts of wollastonite, 13 parts of low-temperature composite flux, and 90 parts of water.
[0048] The method for preparing the modified manganese silicon slag is as follows: 100g of manganese silicon slag powder was added to 1L of ethanol-water solution (ethanol to water volume ratio of 95:5), followed by the addition of 7g of γ-aminopropyltriethoxysilane. The mixture was stirred at 70℃ for 3.5h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. 10g of hypozinogenyltriacetic acid was added to 1L of deionized water, followed by the addition of 6g of EDC and 4.5g of... NHS was prepared, and the pH was adjusted to 5.5. The mixture was stirred and activated at 25°C for 35 min. The pH of the system was then adjusted to 7.5. 100 g of aminated manganese silicon slag was added, and the mixture was reacted at 38°C for 5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. 100 g of organomanganese silicon slag was added to 550 g of 4% aluminum sulfate solution and stirred for 35 min. 700 g of 2.5% sodium tripolyphosphate solution was added dropwise. After the addition was completed in 35 min, the mixture was hydrothermally reacted at 130°C for 2.5 h. After the reaction was completed, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Mix 650g of waste refractory brick powder and 350g of phosphogypsum evenly, add to 3L of 10% ammonium sulfate solution, soak at 65℃ for 2.5h, filter and dry after soaking, ball mill at 450r / min for 2.5h, filter and dry after ball milling, then add to 3L of 7% sodium humate solution, stir at 65℃ for 1.5h, filter, dry and break up after stirring to obtain active silicon-aluminum composite material; The low-temperature composite flux is borosilicate waste glass powder; A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and wet ball mill for 5 hours to obtain a slurry. Press it into shape at 30 MPa and dry it at 110℃ until the moisture content of the green body is less than 1% to obtain a ceramic green body. S2. The ceramic green body is fed into the kiln for sintering. The sintering process is as follows: the temperature is increased to 400℃ at 2.5℃ / min and held for 1.5h; then the temperature is increased to 730℃ at 5℃ / min and held for 1.5h; then the temperature is increased to 980℃ at 4℃ / min and held for 2.5h. After sintering, the ceramic green body is allowed to cool naturally to room temperature in the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
[0049] Compared with Example 1, the low-temperature composite flux in this comparative example is borosilicate waste glass powder.
[0050] The high-hardness, high-strength, low-temperature sintered composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1-5 were subjected to performance tests. Fracture toughness was tested according to standard GB / T 23806-2009; flexural strength was tested according to standard GB / T6569-2006; Vickers hardness was measured using a micro Vickers hardness tester with a load of 10 N and a loading time of 10 s. The hardness value was the average of five measurements. Water absorption was tested by taking five ceramic product fragments, washing and drying them, and weighing them separately. The fragments were then separated and placed in distilled water and boiled for 3 hours, with the water level maintained at least 10 mm above the fragments. The fragments were then removed, and the water adhering to their surfaces was wiped off with a water-saturated cloth. The weight of each fragment was quickly measured, and the average water absorption rate of the five fragments was calculated to obtain the water absorption rate of the ceramic product. The test results are shown in Table 1 below.
[0051] Table 1
[0052] As can be seen from Table 1 above, the high-hardness, high-strength, low-temperature sintered composite ceramic material prepared by this invention has high hardness and good mechanical properties, and has good application prospects.
[0053] The above description is a further detailed explanation of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.
[0054] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A high-hardness, high-strength, low-temperature sintered composite ceramic material, characterized in that, By weight, it includes the following ingredients: 35-45 parts of active silicon-aluminum composite material, 20-25 parts of modified manganese silicon slag, 10-15 parts of α-alumina micro powder, 12-18 parts of sodium feldspar, 8-12 parts of wollastonite, 10-15 parts of low-temperature composite flux, and 80-100 parts of water. The modified manganese silicon slag is prepared as follows: Manganese silicon slag powder was added to an ethanol-water solution, followed by the addition of γ-aminopropyltriethoxysilane. The mixture was stirred and reacted. After the reaction was complete, the mixture was filtered, washed, and dried to obtain aminated manganese silicon slag. Triazine triacetic acid was added to deionized water, followed by the addition of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide. The pH was adjusted to 5-6, and the mixture was activated by stirring at 25°C for 30-40 minutes. The pH was then adjusted to 7-7.5, and the aminated manganese silicon slag was added. The mixture was reacted at a constant temperature. After the reaction was complete, the mixture was filtered, washed, and dried to obtain organomanganese silicon slag. The organomanganese silicon slag was added to an aluminum sulfate solution and stirred for 30-40 minutes. Sodium tripolyphosphate solution was then added dropwise to initiate a hydrothermal reaction. After the reaction was complete, the mixture was filtered, washed, and dried to obtain modified manganese silicon slag. The preparation method of the active silicon-aluminum composite material is as follows: Waste refractory brick powder and phosphogypsum were mixed evenly and soaked in ammonium sulfate solution. After soaking, the mixture was ball-milled and then added to sodium humate solution. The mixture was heated and stirred. After stirring, the mixture was filtered, dried, and broken up to obtain active silicon-aluminum composite material. The preparation method of the low-temperature composite flux is as follows: Borosilicate waste glass powder, nano-bismuth oxide, and calcium fluoride are mixed, ball-milled in anhydrous ethanol, and dried to obtain the low-temperature composite flux.
2. The high-hardness, high-strength, low-temperature sintered composite ceramic material according to claim 1, characterized in that, By weight, it includes the following ingredients: 38-42 parts of active silicon-aluminum composite material, 20-25 parts of modified manganese silicon slag, 10-15 parts of α-alumina micro powder, 15-18 parts of sodium feldspar, 10-12 parts of wollastonite, 10-13 parts of low-temperature composite flux, and 85-95 parts of water.
3. The high-hardness, high-strength, low-temperature sintered composite ceramic material according to claim 1, characterized in that, The volume ratio of ethanol to water in the ethanol-water solution is 90-95:5-10; the mass ratio of manganese silicon slag to γ-aminopropyltriethoxysilane is 100:5-8; the stirring reaction temperature is 65-75℃ and the time is 3-4h; the mass ratio of hypozinotriacetic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and aminated manganese silicon slag is 8-12:5-7:4-5:100; the isothermal reaction temperature is 35-40℃ and the time is 4-6h; the mass concentration of the aluminum sulfate solution is 3-5%; the mass concentration of the sodium tripolyphosphate is 2-3%; the mass ratio of the organomanganese silicon slag, aluminum sulfate solution, and sodium tripolyphosphate solution is 100:350-450:600-800; the hydrothermal reaction temperature is 120-140℃ and the time is 2-3h.
4. The high-hardness, high-strength, low-temperature sintered composite ceramic material according to claim 1, characterized in that, The mass ratio of waste refractory brick powder to phosphogypsum is 60-70:30-40; the mass concentration of the ammonium sulfate solution is 8-12%; the soaking temperature is 60-70℃ and the soaking time is 2-3 hours; the ball milling speed is 400-500 r / min and the time is 2-3 hours; the mass concentration of the sodium humate solution is 5-8%; and the heating reaction temperature is 60-70℃ and the heating time is 1-1.5 hours.
5. The high-hardness, high-strength, low-temperature sintered composite ceramic material according to claim 1, characterized in that, The borosilicate waste glass powder, nano bismuth oxide, and calcium fluoride are mixed in a mass ratio of 70-75:15-20:10-15. The ball milling speed is 400-500 r / min, and the time is 4-6 h.
6. A method for preparing a high-hardness, high-strength, low-temperature sintered composite ceramic material as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Weigh the modified manganese silicon slag, active silicon aluminum composite material, low-temperature composite flux, sodium feldspar, wollastonite, and α-alumina micro powder according to the formula, mix them evenly, add water, and obtain a slurry by wet ball milling. Then, obtain ceramic green body by slurry casting or pressing and drying. S2. The ceramic is fed into the kiln for sintering. After sintering, it is naturally cooled to room temperature with the kiln to obtain a high-hardness, high-strength, low-temperature sintered composite ceramic material.
7. The preparation method according to claim 6, characterized in that, The wet ball milling time in step S1 is 4-6 hours; the pressing pressure is 25-35 MPa; the drying temperature is 100-120℃, and the green body moisture content is less than 1%; the sintering process in step S2 is as follows: heat up to 350-450℃ at 2-3℃ / min and hold for 1-1.5 hours; then heat up to 700-750℃ at 4-6℃ / min and hold for 1-1.5 hours; then heat up to 950-1000℃ at 3-5℃ / min and hold for 2-3 hours.