Composite ceramic material used as lining of garbage incinerator and preparation method of composite ceramic material

Abstract

The invention discloses a composite ceramic material used as a lining of a garbage incinerator and a preparation method of the composite ceramic material, and belongs to the field of refractory materials, and the material is a hafnium boride-based strong interface bonded layered composite material containing silicon, boron, carbon and nitrogen. The material is prepared from hafnium boride, polyborosilazane, niobium silicide, tantalum silicide, silicon nitride, silicon carbide, silicon carbide fibers and other raw materials according to a certain proportion through the processes of mixing, drying, forming, curing, cracking, sintering and the like. The lining material of the garbage incinerator has the advantages that the density is high, and the anti-scouring and wear-resistant properties are excellent; the cracking and falling of the lining of the garbage incinerator caused by chemical erosion or mechanical failure can be avoided; various waste incineration environment occasions can be met; good thermal shock resistance is achieved, and damage of temperature change in the waste incineration process to a furnace body lining can be resisted; and no toxic or harmful gas or heavy metal is released in the using process, so that reliable safety and environmental friendliness are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of refractory materials, and particularly relates to a composite ceramic material used as the inner lining of a waste incinerator and a preparation method thereof. Technical Background

[0002] In today's society, the treatment of domestic waste is a headache, especially in large cities with dense populations. The accumulation of a large amount of waste brings problems such as the occupation of good farmland, air pollution, water pollution, fire hazards, and the spread of infectious diseases, so it needs to be treated in a timely manner. Common methods for treating waste are landfill treatment or incineration in an incinerator. Landfill treatment will pollute groundwater and emit odors, and there is less and less land available for landfill in many cities; waste incineration has the advantages of timely treatment, large treatment capacity, high degree of harmlessness, and recoverable heat, and has become the main method for treating waste in most countries. The waste incinerator is a key device in the waste incineration process, and its performance directly affects the efficiency of waste incineration and environmental protection indicators. The main function of the combustion chamber of the waste incinerator is to fully burn domestic waste at high temperatures and convert the waste into harmless gases and solid residues. The temperature in the combustion chamber of the domestic waste incinerator generally needs to be maintained at 850 - 1000 °C, and the main components in the combustion flue gas are carbon dioxide (CO2), water (H2O), nitrogen (N2), oxygen (O2), and harmful gases such as nitrogen oxides (NO x ), hydrogen chloride (HCl), sulfur oxides (SOx), heavy metals, organic chlorides, furans (poly-chlorinated dibenzo-furans, PCDFs), and incomplete combustion gases (such as CO), etc.

[0003] Therefore, the combustion chamber needs to have good heat insulation performance, oxidation resistance, chemical corrosion resistance, wear resistance, and thermal shock resistance, and the inner lining of the combustion chamber of the incinerator is the key material layer that directly contacts the solid, liquid, and gas phases during the waste incineration process. The refractory materials used in the combustion chamber of the waste incinerator need to have the following characteristics: (1) high temperature resistance and good heat insulation; (2) corrosion resistance and good volume stability; (3) earthquake resistance, wear resistance, and erosion resistance.

[0004] Common materials are refractory materials such as clay bricks, high-alumina bricks, and silicon carbide. Clay bricks belong to weakly acidic refractory products and can resist the erosion of acidic slag and acidic gases, but cannot be used in alkaline environments. High-alumina bricks contain chemical components of AL2O3 and Na2O. The two react to form an intermediate sodium aluminate at high temperatures, and the formation of the intermediate causes internal expansion cracks, making the refractory brick structure brittle. During the use of silicon carbide (SiC) refractory materials, a single SiO2 protective layer is formed on the surface, but SiO2 has multiple polymorphic transformations, resulting in more cracks and fractures in the single SiO2 protective layer. Each of these three materials has its own weaknesses, so it is very important to develop a lining material for the combustion chamber of a waste incinerator that can adapt to various high-temperature environments such as acidic, alkaline, oxidative, and corrosive salts and has excellent performance.

[0005] Hafnium boride (HfB2) is a grayish-black crystal with metallic luster and belongs to the hexagonal crystal system. The B-Hf ionic bond and B-B covalent bond between the boron (B) atomic plane and hafnium (Hf) atomic plane determine that HfB2 has a high melting point (melting point is 3315 °C), a low thermal expansion coefficient (6.88×10 -6 K -1 ) and excellent chemical stability (almost does not react with all chemical reagents except HF). In hafnium boride, a very strong covalent bond is formed between hafnium atoms and boron atoms, which makes the hardness of hafnium boride ceramics exceed 2500 Vickers hardness. Hafnium atoms are heavy metals in terms of relative mass, but they are not in the category of heavy metals in the sense of environmental pollution. Therefore, HfB2-based ceramics are very suitable as refractory lining materials for waste incinerators.

[0006] Heavy metal pollutants discharged with flue gas and fly ash during waste incineration cannot be decomposed by microorganisms, accumulate in organisms, and ultimately cause harm to the human body through the food chain. Research shows that the release behavior of different heavy metal elements is significantly affected by the atmosphere in the incinerator. Elements such as Cr, Cd, and Pd have low volatilization rates in an oxidizing atmosphere. Therefore, in actual incineration, to reduce the volatilization of toxic heavy metals such as Cr, Cd, and Pd, it is necessary to maintain an oxidizing atmosphere in the waste incinerator. The antioxidant performance of HfB2 with a high hafnium content is 10 times greater than that of zirconium boride, but its high-temperature antioxidant performance still needs to be further improved to enhance its service life and market competitiveness. Research results show that a dense film layer (composed of hafnium oxide (HfO2) and borosilicate glass) can be formed on the surface of HfB2-based refractory materials introduced with silicides, isolating external oxygen from entering the material interior and thus preventing further internal oxidation.

[0007] During the use of a waste incinerator, the gas volume and gas temperature inside the furnace fluctuate greatly. At the same time, the movement of waste at high temperatures causes great thermal shock to some parts of the incinerator (such as the furnace bottom, feeding port, and side walls, etc.). Therefore, the lining material is required to have excellent thermal shock resistance and thermal shock performance. The fracture toughness of a material is its ability to prevent crack propagation. The higher the fracture toughness, the stronger the ability to prevent crack propagation, and thus the better the thermal shock resistance and thermal shock performance. Therefore, the fundamental way to improve the thermal shock resistance and thermal shock resistance of HfB2 ceramics lies in improving their fracture toughness. The fracture toughness of single HfB2 ceramics is ≤ 3 MPam 1 / 2 After introducing particles, fibers, and whiskers, the fracture toughness of HfB2-based composites does not exceed 7 MPam 1 / 2 . Some achievements have been made by using second-phase toughening, but the toughening effect is limited and still cannot meet the needs of engineering applications. Therefore, new toughening methods must be found. Summary of the Invention

[0008] The purpose of the present invention is to overcome the defects of the existing lining materials of waste incinerators and provide a hafnium boride-based strongly interfacial bonded laminated composite ceramic material containing silicon boron carbon nitride and its preparation method. This lining material of the waste incinerator has functions such as volume stability, wear resistance to airflow erosion, and thermal shock resistance, and can meet various high-temperature environmental occasions of waste incineration.

[0009] The composite ceramic material is composed of substrate layers that do not contact the waste and bear residual compressive stress and substrate layers that bear residual tensile stress stacked alternately, and finally the substrate layer that contacts the waste and bears residual compressive stress is stacked. After all layers are stacked, the composite ceramic material is formed through pre-pressing, curing, pyrolysis, and sintering;

[0010] Among them, the preparation method of the substrate layer that bears residual tensile stress is: mixing hafnium boride powder and silicon carbide powder to obtain ball-milled material A, mixing ball-milled material A with absolute ethanol, using ZrO2 beads as the mixing medium and ball-milling for 6 - 8 h, then adding silicon carbide fibers and continuing to ball-mill for 3 - 4 hours. After the ball-milling is completed, it is dried under reduced pressure, and then mixed with polyboron carbon nitride silane and subjected to aging treatment, and pressed into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer that bears residual tensile stress;

[0011] Among them, the preparation method of the substrate layer that does not contact the waste and bears residual compressive stress is: mixing hafnium boride, silicon carbide, and niobium silicide powders to obtain ball-milled material B, mixing ball-milled material B with absolute ethanol, using ZrO2 beads as the mixing medium and ball-milling for 9 - 12 h. After the ball-milling is completed, it is dried under reduced pressure, and then mixed with polyboron carbon nitride silane and subjected to aging treatment, and pressed into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer that does not contact the waste and bears residual compressive stress;

[0012] Among them, the preparation method of the substrate layer that contacts the garbage and bears residual compressive stress is as follows: Mix hafnium boride, silicon carbide, tantalum silicide, niobium silicide and silicon nitride powders to obtain ball-milled material C. Mix ball-milled material C with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 9 - 12 h. After the ball-milling is completed, carry out reduced-pressure drying, and then mix with polyboron carbonitride silane and carry out aging treatment, and press into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer that contacts the garbage and bears residual compressive stress.

[0013] Among them, in the substrate layer that bears residual tensile stress: the volume percentage of hafnium boride is 70 - 75 vol%; the volume percentage of silicon carbide fiber is 13 - 15 vol%; the volume percentage of silicon carbide powder is 12 - 15 vol%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the volume of the powder solid phase;

[0014] In the substrate layer that does not contact the garbage and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of silicon carbide powder is 10% - 13%, the volume percentage of niobium silicide is 10 - 14%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the volume of the powder solid phase;

[0015] In the substrate layer that directly contacts the garbage and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of tantalum silicide is 3% - 5%, the volume percentage of niobium silicide is 3% - 5%, the volume percentage of silicon nitride is 3% - 4%, the volume percentage of silicon carbide is 11% - 13%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the volume of the powder solid phase.

[0016] Among them, the particle size of the hafnium boride powder does not exceed ≤13 μm and the purity is ≥99%; the diameter of the silicon carbide fiber is 8 - 12 μm and the length is 80 - 150 μm; the average particle size of the silicon carbide powder is ≤15 μm and the purity is ≥99%; the average particle size of the niobium silicide powder is ≤15 μm and the purity is ≥99%; the average particle size of the silicon nitride powder is ≤15 μm and the purity is ≥99%; the average particle size of the tantalum silicide powder is ≤15 μm and the purity is ≥99%; polyboron carbonitride silane is in 99% liquid form, with a molecular weight (Mn) of 700 - 900 and a viscosity of 10000 - 20000 cp.

[0017] Among them, in the preparation processes of the substrate layer that bears residual tensile stress, the substrate layer that does not contact the garbage and bears residual compressive stress, and the substrate layer that contacts the garbage and bears residual compressive stress, the volume ratio of the powder to absolute ethanol is 1:1 - 1.5, and the volume ratio of ZrO2 beads to the powder is 1:1.5 - 2.

[0018] Among them, the conditions for the reduced-pressure drying are to place it under a negative pressure of 400 - 600 mmHg and at a temperature of 55 - 65 °C;

[0019] Among them, the pressure of the preloading is 5-10 MPa, and the pressure holding time is 10-15 min;

[0020] Among them, the curing conditions are as follows: heating to 170 °C at a heating rate of 2-3 °C / min in a nitrogen atmosphere and holding for 2.5-3 h to complete the curing of polyboron carbonitride silane;

[0021] Among them, the pyrolysis is carried out under nitrogen protection, heating the temperature from 170 °C to 800 °C at a rate of 2-3 °C / min, keeping the pressure at 5-10 MPa, and completing the pyrolysis process of polyboron carbonitride silane;

[0022] Among them, the sintering is carried out after the pyrolysis process. The pressure is increased from 5-10 MPa to 20-25 MPa, the furnace body temperature is increased from 800 °C to 1750-1850 °C at a heating rate of 5 °C-15 °C / min, and the heat preservation sintering is carried out for 50-80 min. The vacuum degree in the furnace is kept ≤ 10 -2 Pa.

[0023] Among them, the number of the substrate layers that do not contact the garbage and bear residual compressive stress is the same as that of the substrate layers that bear residual tensile stress, which is 5-8 layers. The substrate layer that contacts the garbage and bears residual compressive stress is the surface layer.

[0024] The present invention also provides a preparation method of a composite ceramic material used as the inner lining of a waste incinerator, which is prepared according to the following steps:

[0025] The first step: mixing materials.

[0026] When mixing the powders used for the substrate layer bearing residual tensile stress, first, the hafnium boride powder and silicon carbide powder taken according to the designed ratio are used as the ball-milling materials. This material and absolute ethanol are put into the ball-milling tank of a vertical planetary ball mill according to a volume ratio of 1:1-1.5 for mixing. ZrO2 beads are selected as the mixing medium (the bead diameter is 2-10 mm, the proportion of the beads with a diameter of 8-10 mm is about 30%, the proportion of the beads with a diameter of 5-7 mm is 50%, the proportion of the beads with a diameter of 2-4 mm is 20%, and the volume of the grinding balls and the sample loaded accounts for 50% of the volume of the ball-milling tank). After ball-milling and mixing for 6-8 hours, the vertical planetary ball mill is paused and the ball-milling tank is opened. The silicon carbide fibers weighed according to the designed ratio are put into the tank, and the ball-milling and mixing are continued for 3-4 hours.

[0027] When mixing the powders for the substrate layer that bears residual compressive stress, first, take each powder according to the designed proportion (the powders that do not contact the substrate with garbage are: hafnium boride, silicon carbide, and niobium silicide; the powders that contact the substrate with garbage are: hafnium boride, silicon carbide, tantalum silicide, niobium silicide, and silicon nitride). Take this material as the ball-milling material and add it to a vertical planetary ball mill with absolute ethanol in a volume ratio of 1:(1 - 1.5) for mixing. Select ZrO2 beads for mixing (the bead particle size is 2 - 10 mm, the proportion of beads with a diameter of 8 - 10 mm is about 30%, the proportion of beads with a diameter of 5 - 7 mm is 50%, the proportion of beads with a diameter of 2 - 4 mm is 20%, and the volume of the grinding balls and the sample loaded accounts for 50% of the volume of the ball-milling tank), and mix for 9 - 12 hours.

[0028] Step 2: Drying.

[0029] Place the uniformly mixed slurry into a rotary evaporator. Use a vacuum pump to make the evaporation flask under a negative pressure of 400 - 600 mmHg. The evaporation flask rotates at 50 - 100 revolutions per minute (to form a thin film of the solvent and increase the evaporation area) and is simultaneously placed in a water bath for constant-temperature heating at 55°C - 65°C. The solution in the flask evaporates and dries in the negatively pressured and rotating flask.

[0030] Step 3: Preparation and forming.

[0031] Put the dried solid-phase powder material and polyboron carbonitride silane in a certain designed proportion into a blender and stir into a mud. Then let it age for 24 h, and use a tablet press to press it into a film with a film thickness of 0.5 - 0.8 mm. Cut the pressed films respectively, stack them alternately with one layer of compressive stress substrate and one layer of tensile stress substrate, and finally stack the compressive stress substrate layer that directly contacts the garbage (the components are: hafnium boride, silicon carbide, niobium silicide, silicon nitride, and polyboron carbonitride silane). The total number of substrate layers is 11 - 17 layers. Put the stacked substrates in accordance with the requirements into the corresponding graphite mold (the surface of the mold is pre-coated with an NB coating to reduce the friction during the subsequent pressing process), and place the mold on a press for pre-pressing (the pressure is 5 - 10 MPa, and the pressure is maintained for 10 - 15 min).

[0032] Step 4: Curing, pyrolysis, and sintering.

[0033] Place the pre-pressed graphite mold containing the material in a sintering furnace. First, heat it to 170°C at a heating rate of 2-3°C / min in a nitrogen atmosphere (50mL / min), and keep it warm for 2.5-3h to complete the curing of polyboron carbon nitride silane. During the curing process, the hydraulic press applies a pressure of 5-10MPa through the graphite mold. Then, under nitrogen protection (50mL / min), the temperature is raised from 170°C to 800°C at a rate of 2-3°C / min to complete the cracking process of polyboron carbon nitride silane. After the cracking process, the pressure is first raised from 5-10MPa to 20-25MPa, and then the furnace temperature is raised from 800°C to the required temperature at a heating rate of 5-15°C / min. The entire sintering is carried out in a furnace body at a temperature of 1750-1850°C, and the sintering is kept warm for 60min. The vacuum degree in the furnace is kept ≤10 during the entire sintering process. -2 Pa, nitrogen protective gas in the whole process, taken out after cooling down in the furnace.

[0034] Beneficial Effects

[0035] The layered structure design uses the residual stress field generated by the difference in thermal expansion coefficient as the main toughening method. The present invention is mainly aimed at the use of HfB2 ceramics as the lining of waste incinerators, and introduces the layered structure design into the HfB2-based material to improve its resistance to high-temperature complex airflow erosion and thermal shock. The presence of residual stress during thermal shock weakens the thermal stress field at the crack tip, and at the same time makes the layered ceramics show the characteristics of being insensitive to surface defects, and its high-temperature oxidation resistance will not be reduced. In addition, silicon boron carbon nitride (SiBCN) ceramics are introduced into this layered structure to improve its high-temperature oxidation resistance. This layered HfB2-based composite ceramic structure containing silicon boron carbon nitride (SiBCN) ceramics has hardly been reported in the field of waste incinerator linings.

[0036] By utilizing the difference in thermal expansion coefficients between the HfB2 matrix and the additive, residual thermal stress is introduced into the material during the sintering process. Residual tensile stress is generated in the substrate with a larger thermal expansion coefficient, while residual compressive stress is generated in the substrate with a smaller thermal expansion coefficient. In this layered HfB2-based composite material, the two substrate layers with different thermal expansion coefficients are alternately stacked, and the substrate that bears the residual compressive stress is the outermost layer.

[0037] Polyborosilazane is in liquid phase and is used as an adhesive when making HfB2 ceramic substrates. At the same time, this polyborosilazane is pyrolyzed at high temperature to obtain silicon boron carbon nitrogen (SiBCN) ceramics with excellent performance, which can be used as a sintering aid for the matrix HfB2 to achieve sintering densification and microstructure optimization of HfB2 ceramics. In 2020, Hao Wei of Shanghai Jiaotong University used precursor pyrolysis SiCN ceramics as HfC sintering aids in his doctoral thesis "Research on the Effect of Boron Silicon Compounds on the Toughening Mechanism and Anti-Oxidation / Ablation Behavior of Hafnium Carbide-based Ceramics" and achieved good results. SiBCN can withstand high temperatures of 2000°C, which is much better than the temperature resistance of other silicon-based ceramic materials, and can generate a dense borosilicate glass protective film in an oxidizing environment, so the oxidation resistance of HfB2 ceramics is greatly improved.

[0038] The layered hafnium boride-based waste incinerator lining material in the present invention includes two types of substrates that bear residual tensile stress and residual compressive stress. The tensile strength of HfB2 ceramic material is much smaller than the compressive strength, and the difference between the two is more than 10 times. Therefore, the tensile strength should be appropriately increased for substrates that bear residual tensile stress. At the same time, the corresponding use environment requirements such as the material's oxidation resistance, chemical corrosion resistance and good volume stability are enhanced. Taking the above factors into consideration, for substrates that bear residual tensile stress, some fiber or whisker-state silicides should be introduced to increase the tensile strength of the matrix (fiber and whisker morphology have the most obvious effect on the tensile strength of the material). On October 27, 2017, the World Health Organization's International Agency for Research on Cancer published a preliminary list of carcinogens for reference. Silicon carbide whiskers are on the list of Class 2A carcinogens, so safe and cost-effective silicon carbide fibers are selected.

[0039] The outermost substrate in direct contact with the garbage and a certain number of internal substrates are subject to residual compressive stress. The compressive strength of HfB2 ceramics is much greater than its tensile strength. Therefore, the compressive strength of the substrates subject to residual compressive stress does not need to be increased.

[0040] For HfB2 substrates that are subjected to residual compressive stress but are not in direct contact with the waste, the additive is a mixed powder of silicon carbide and niobium silicide to adjust the thermal expansion coefficient of the substrate.

[0041] Waste incineration produces a large amount of gas (such as Cl2, SO2, CO and alkali metal vapor, etc.), a large amount of dust and solid particles. Therefore, other additives should be introduced into the outermost substrate that is in direct contact with the waste and bears residual compressive stress to ensure that this outermost layer has reliable chemical corrosion resistance, excellent oxidation resistance, and outstanding anti-erosion and wear resistance. Therefore, the additive in the outermost HfB2 substrate is mainly a silicide mixture whose thermal expansion coefficient can be adjusted within a certain range. This silicide mixture contains tantalum silicide (the thermal expansion coefficient at room temperature is about 7.3×10 -6 K -1)、Niobium silicide (room temperature thermal expansion coefficient is about 7.1×10 - 6 K -1 )、Silicon carbide (room temperature thermal expansion coefficient is about 3.8×10 -6 K -1 )、Silicon nitride (room temperature thermal expansion coefficient is about 2.8×10 -6 K -1 ) etc.

[0042] The interface between each substrate layer is the medium for transmitting stress and strain. A reasonable interface bonding strength is an important factor to ensure the service life and safety of the entire lining material of the waste incinerator. Given the complex service environment and temperature of the incinerator lining, strong interface bonding helps the substrates to jointly withstand the complex load environment during use. Therefore, the HfB2-based laminated ceramics in the present invention use hot pressing sintering to achieve strong interface bonding between the substrates, and at the same time, it can also ensure that the material has high density and excellent erosion and abrasion resistance.

[0043] The lining material of the waste incinerator in the present invention is a hafnium boride-based strong interface bonding laminated composite ceramic containing silicon boron carbon nitrogen, which is prepared by a series of forming processes from raw materials such as hafnium boride, polyborosilazane, niobium silicide, tantalum silicide, silicon nitride, silicon carbide, and silicon carbide fibers in a certain proportion and then hot pressing sintering.

[0044] The advantages of the present invention are that it has high density and excellent erosion and abrasion resistance, and can resist the erosion of solid particle materials and hot gas flows; it can avoid the cracking and falling off of the lining of the waste incinerator caused by chemical erosion or mechanical failure; it has excellent chemical corrosion resistance and can meet various waste incineration environment occasions; it has good thermal shock resistance and can resist the damage of temperature changes during the waste incineration process to the furnace lining; no toxic and harmful gases and heavy metals are released during use, and it has reliable safety and environmental protection. This method has simple process and short production cycle, and is suitable for large-scale industrial production. Description of the Drawings

[0045] Figure 1 Cross-sectional view of the composite ceramic material prepared in Example 1. Detailed Embodiments

[0046] In the embodiments of the present invention, the particle size of hafnium boride powder does not exceed ≤13μm, and the purity is ≥99%; the diameter of SiC fibers is 8-12μm, and the length is 80-150μm; the average particle size of silicon carbide powder is ≤15μm, and the purity is ≥99%; the average particle size of niobium silicide powder is ≤15μm, and the purity is ≥99%; the average particle size of silicon nitride powder is ≤15μm, and the purity is ≥99%; the average particle size of tantalum silicide powder is ≤15μm, and the purity is ≥99%; polyboron carbon nitride silane is in liquid form with 99%, molecular weight (Mn) 700-900, and viscosity 10000-20000 cp.

[0047] The present invention will be described in detail below in conjunction with specific embodiments.

[0048] Embodiment 1

[0049] This embodiment provides a preparation method of a composite ceramic material used as the inner lining of a waste incinerator, which specifically includes the following steps.

[0050] The first step: Mixing

[0051] When the powders used for the substrate layer bearing residual tensile stress are mixed by volume percentage, first, 70% hafnium boride powder and 15% silicon carbide powder are used as the ball-milling materials. This material and absolute ethanol are put into the ball-milling tank of a vertical planetary ball mill at a volume ratio of 1:1.5 for mixing. ZrO2 beads are selected as the mixing medium, and the ratio of grinding beads to powders is 1:1.5. The bead diameter is 2 - 10 mm, the proportion of large beads is 30%, the proportion of medium-diameter beads is 50%, and the proportion of smaller-diameter beads is 20%. The volume of the grinding beads and the sample loaded accounts for 50% of the volume of the ball-milling tank. After ball-milling and mixing for 8 hours, the vertical planetary ball mill is paused and the ball-milling tank is opened, and 15% silicon carbide fibers are put into the tank, and then ball-milling and mixing continue for 4 hours.

[0052] When the powders used for the substrate layer bearing residual compressive stress are mixed by volume percentage, for the powders of the substrate not in contact with the waste, the powders are 73% hafnium boride, 13% silicon carbide, and 14% niobium silicide; for the powders of the substrate in contact with the waste, the powders are 73% hafnium boride, 13% silicon carbide, 5% tantalum silicide, 5% niobium silicide, and 4% silicon nitride. The powder materials are used as the ball-milling materials and are added to the vertical planetary ball mill with absolute ethanol at a volume ratio of 1:1.5 for mixing. ZrO2 beads are selected for mixing (the proportion of large beads is about 30%, the proportion of medium-diameter beads is 50%, the proportion of smaller-diameter beads is 20%, and the volume of the grinding beads and the sample loaded accounts for 50% of the volume of the ball-milling tank), and the mixing is carried out for 9 hours.

[0053] The second step: Drying

[0054] The uniformly mixed material slurry is placed in a rotary evaporator. Through a vacuum pump, the evaporation flask is under a negative pressure of 400 - 600 mmHg. The evaporation flask rotates at 100 revolutions per minute (to form a thin film of the solvent and increase the evaporation area) and is simultaneously placed in a water bath for constant-temperature heating at 65°C. The solution in the flask is evaporated and dried in the negative-pressure and rotating flask.

[0055] The third step: Preparation and shaping

[0056] The dried powder solid-phase material and polyboron carbonitride silane with an addition amount of 20% of the volume of the powder solid phase are put into a blender and stirred into a mud material, which is then aged for 24 h, and pressed into a film by a tablet press, with the film thickness being 0.5 mm. The pressed films are respectively cut, stacked alternately with one layer of compressive stress substrate and one layer of tensile stress substrate, and finally the compressive stress substrate layer in contact with the garbage directly is stacked. The total number of all substrate layers is 17 layers. The stacked substrates are loaded into the corresponding graphite mold as required (the surface of the mold is pre-coated with an NB coating to reduce the friction during the subsequent pressing process), and the mold is placed on a press for pre-pressing (pressure 10 MPa, pressure holding for 10 min).

[0057] Step 4: Curing, pyrolysis, and sintering

[0058] The graphite mold filled with the pre-pressed material is placed in a sintering furnace. First, it is heated to 170 °C at a heating rate of 3 °C / min in a nitrogen atmosphere (50 mL / min) and held for 3 h to complete the curing of polyboron carbonitride silane. During the curing process, a pressure of 10 MPa is applied by a hydraulic press through the graphite mold. Then, under nitrogen protection (50 mL / min), the temperature is raised from 170 °C to 800 °C at a rate of 3 °C / min to complete the pyrolysis process of polyboron carbonitride silane. After the pyrolysis process is completed, the pressure is first raised from 10 MPa to 25 MPa, and then the furnace body temperature is raised from 800 °C to the required temperature at a heating rate of 15 °C / min. The whole sintering is carried out in a furnace body at a temperature of 1850 °C and held for sintering for 60 min. The vacuum degree in the furnace is maintained at ≤10 -2 Pa during the whole process, and nitrogen is used as the protective gas. After cooling with the furnace, it is taken out.

[0059] Example 2

[0060] This example provides a preparation method of a composite ceramic material used as the inner lining of a waste incinerator, which specifically includes the following steps.

[0061] Step 1: Mixing materials

[0062] When the powder used for the residual tensile stress substrate layer is mixed by volume percentage, first, 75% hafnium boride powder and 12% silicon carbide powder are used as the ball-milling materials. This material and absolute ethanol are put into the ball-milling tank of a vertical planetary ball mill according to a volume ratio of 1:1 for mixing. ZrO2 beads are selected as the mixing medium, and the ratio of grinding balls to powder is 1:1.8. The bead diameter is 2 - 10 mm, the proportion of beads with a diameter of 8 - 10 mm is about 30%, the proportion of beads with a diameter of 5 - 7 mm is 50%, and the proportion of beads with a diameter of 2 - 4 mm is 20%. The volume occupied by the grinding balls and the sample loaded accounts for 50% of the volume of the ball-milling tank. After ball-milling and mixing for 6 hours, the vertical planetary ball mill is paused and the ball-milling tank is opened, and 13% silicon carbide fiber is put into the tank, and ball-milling and mixing continue for 3 hours.

[0063] When the powders for the substrate layer bearing residual compressive stress are mixed by volume percentage, for the powders that do not contact the substrate with waste, the powders are 80% hafnium boride, 10% silicon carbide, and 10% niobium silicide; for the powders that contact the substrate with waste, the powders are 80% hafnium boride, 11% silicon carbide, 3% tantalum silicide, 3% niobium silicide, and 3% silicon nitride. The powder materials are taken as ball-milling materials and added into a vertical planetary ball mill with absolute ethanol at a volume ratio of 1:1 for mixing. ZrO2 beads are selected for mixing (the large beads account for about 30%, the medium-diameter beads account for 50%, the small-diameter beads account for 20%, and the volume of the grinding balls and the sample loading accounts for 50% of the volume of the ball mill tank), and the mixing is carried out for 12 hours.

[0064] Step 2: Drying

[0065] The uniformly mixed slurry is placed into a rotary evaporator. The evaporation flask is made to be under a negative pressure of 400 - 600 mmHg through a vacuum pump. The evaporation flask rotates at 50 revolutions per minute (to form a thin film of the solvent and increase the evaporation area) and is simultaneously placed in a water bath for constant-temperature heating at 55°C. The solution in the flask is evaporated and dried in the rotating flask under negative pressure.

[0066] Step 3: Preparation and forming

[0067] The dried solid-phase powder materials and polyboron carbonitride silane with an addition amount of 15% of the volume of the solid-phase powder are put into a stirrer to be stirred into a mud material, and then it is aged for 18 h. It is pressed into a film by a tablet press, and the film thickness is 0.8 mm. The pressed films are respectively cut. They are alternately laminated with one layer of compressive stress substrate and one layer of tensile stress substrate, and finally the compressive stress substrate layer in contact with the waste directly is stacked. The total number of all substrate layers is 11 layers. The stacked substrate multi-layers are loaded into the corresponding graphite mold as required (the surface of the mold is pre-coated with an NB coating to reduce the friction during the subsequent pressing process). The mold is placed on a press for pre-pressing (pressure 5 MPa, holding pressure for 15 min).

[0068] Step 4: Curing, pyrolysis, and sintering

[0069] The pre-pressed graphite mold containing the material is placed in a sintering furnace. First, the temperature is raised to 170°C at a heating rate of 2°C / min in a nitrogen atmosphere (50mL / min), and the temperature is kept at this temperature for 2.5 hours to complete the curing of polyboron carbon nitride silane. During the curing process, the hydraulic press applies a pressure of 5MPa through the graphite mold. Then, under nitrogen protection (50mL / min), the temperature is raised from 170°C to 800°C at a rate of 2°C / min to complete the cracking process of polyboron carbon nitride silane. After the cracking process, the pressure is first raised from 5MPa to 20MPa, and then the furnace temperature is raised from 800°C to the required temperature at a heating rate of 5°C / min. The entire sintering is carried out in a furnace body at a temperature of 1750°C, and the temperature is kept at this temperature for 80 minutes. The vacuum degree in the furnace is kept ≤10 during the entire sintering process. -2 Pa, nitrogen protective gas in the whole process, taken out after cooling down in the furnace.

[0070] Example 3

[0071] This embodiment provides a method for preparing a composite ceramic material used as the lining of a waste incinerator, which specifically includes the following steps.

[0072] Step 1: Mixing

[0073] When the powders used for the substrate layer bearing the residual tensile stress are mixed by volume percentage, 72% of hafnium boride powder and 13.5% of silicon carbide powder are first used as ball milling materials, and this material and anhydrous ethanol are put into the ball milling tank of the vertical planetary ball mill at a volume ratio of 1:1.25 for mixing, ZrO2 balls are selected as the mixing medium, the ratio of grinding balls to powder is 1:2, the ball particle size is 2-10mm, the balls with a diameter of 8-10mm account for about 30%, the balls with a diameter of 5-7mm account for 50%, and the balls with a diameter of 2-4mm account for 20%, and the volume of grinding balls and sample filling accounts for 50% of the volume of the ball milling tank. After ball milling and mixing for 7 hours, the vertical planetary ball mill is paused, the ball milling tank is opened, 14.5% silicon carbide fiber is put into the tank, and the ball milling and mixing is continued for 3.5 hours.

[0074] When the powders used for the substrate layer bearing the residual compressive stress are mixed by volume percentage, the powders of the substrate not in contact with the garbage are 76% hafnium boride, 11.5% silicon carbide and 12.5% ​​niobium silicide; the powders of the substrate in contact with the garbage are 76% hafnium boride, 11.5% silicon carbide, 4.5% tantalum silicide, 4.5% niobium silicide and 3.5% silicon nitride. The powder materials are used as ball milling materials and are added into a vertical planetary ball mill with anhydrous ethanol in a volume ratio of 1:1.25. ZrO2 beads are used for mixing (large beads account for about 30%, medium diameter beads account for 50%, smaller diameter beads account for 20%, and the volume of grinding balls and sample filling accounts for 50% of the volume of the ball mill), and the mixing is carried out for 11 hours.

[0075] Step 2: Drying

[0076] Place the uniformly mixed material slurry into a rotary evaporator. Use a vacuum pump to make the evaporation flask under a negative pressure of 400 - 600 mmHg. The evaporation flask rotates at 75 revolutions per minute (to form a thin film of the solvent and increase the evaporation area) and is simultaneously placed in a water bath for constant-temperature heating at 60 °C. The solution in the flask evaporates and dries in the rotating flask under negative pressure.

[0077] The third step: Preparation of forming

[0078] Put the dried powder solid-phase material and 17% of polyboron carbonitride silane by volume of the powder solid phase into a blender and stir into a mud, then age for 36 h, and use a tablet press to press into a film with a film thickness of 0.7 mm. Cut the pressed films respectively, stack them alternately with one layer of compressive stress substrate and one layer of tensile stress substrate, and finally stack the compressive stress substrate layer (composition: hafnium boride, silicon carbide, niobium silicide, silicon nitride and polyboron carbonitride silane) in direct contact with the garbage. The total number of all substrate layers is 15 layers. Load the stacked substrates in accordance with the requirements into the corresponding graphite mold (the surface of the mold is pre-coated with NB coating to reduce the friction during the subsequent pressing process), and place the mold on a press for pre-pressing (pressure 7 MPa, holding pressure for 13 min).

[0079] The fourth step: Curing, pyrolysis, sintering

[0080] Place the graphite mold with the pre-pressed material into a sintering furnace. First, in a nitrogen atmosphere (50 mL / min), raise the temperature to 170 °C at a heating rate of 2.5 °C / min and hold for 2.7 h to complete the curing of polyboron carbonitride silane. During the curing process, the hydraulic press applies a pressure of 7.5 MPa through the graphite mold. Then, under nitrogen protection (50 mL / min), raise the temperature from 170 °C to 800 °C at a rate of 2.5 °C / min to complete the pyrolysis process of polyboron carbonitride silane. After the pyrolysis process ends, first raise the pressure from 7.5 MPa to 22.5 MPa, and then raise the furnace body temperature from 800 °C to the required temperature at a heating rate of 10 °C / min. The whole sintering is carried out in a furnace body at 1800 °C and held for sintering for 50 min. The vacuum degree in the furnace is maintained ≤ 10 -2 Pa during the whole process, and the nitrogen protection gas is used. Take it out after cooling with the furnace.

[0081] The test results of the hafnium boride-based strongly interfacial bonded laminated composite ceramic material containing silicon boron carbon nitrogen prepared in Examples 1 - 3 of the present invention for use as the inner lining of a waste incinerator are shown in the following table:

[0082]

[0083] The finally prepared hafnium boride-based strong interface bonding layered composite ceramic material containing silicon boron carbon nitride used as the inner lining of the waste incinerator has the following technical parameters: apparent porosity ≤ 10.8%, flexural strength ≥ 427 Mpa, fracture toughness ≥ 12.28 MPa·m 1 / 2 , it can withstand a thermal shock temperature ΔT of 695 °C; when the specimen is immersed in the molten salt for 120 minutes, the erosion thickness ≤ 15 μm; the spalling resistance ≤ 13.8%.

[0084] The present invention has been described in detail above. The above is only the preferred embodiment of the present invention, and it cannot limit the scope of implementation of the present invention. That is, all equal changes and modifications made according to the scope of this application should still fall within the scope covered by the present invention.

Claims

1. A composite ceramic material used as the inner lining of a waste incinerator, characterized in that: The composite ceramic material is formed by alternately laminating a substrate layer that does not contact the garbage and bears residual compressive stress and a substrate layer that bears residual tensile stress, and finally laminating a substrate layer that contacts the garbage and bears residual compressive stress. After the lamination of each layer is completed, it undergoes pre-pressing, curing, cracking, and sintering to form the composite ceramic material; Among them, the preparation method of the substrate layer bearing residual tensile stress is as follows: mix hafnium boride powder and silicon carbide powder to obtain ball-milled material A, mix ball-milled material A with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 6 - 8h, then add silicon carbide fibers and continue ball-milling for 3 - 4 hours. After the ball-milling is completed, carry out reduced-pressure drying, and then mix with polyboron carbonitride silane and carry out aging treatment, and press it into a film with a thickness of 0.5 - 0.8mm, which is the substrate layer bearing residual tensile stress; Among them, the preparation method of the substrate layer that does not contact the garbage and bears residual compressive stress is as follows: mix hafnium boride, silicon carbide, and niobium silicide powders to obtain ball-milled material B, mix ball-milled material B with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 9 - 12h. After the ball-milling is completed, carry out reduced-pressure drying, and then mix with polyboron carbonitride silane and carry out aging treatment, and press it into a film with a thickness of 0.5 - 0.8mm, which is the substrate layer that does not contact the garbage and bears residual compressive stress; Among them, the preparation method of the substrate layer that contacts the garbage and bears residual compressive stress is as follows: mix hafnium boride, silicon carbide, tantalum silicide, niobium silicide, and silicon nitride powders to obtain ball-milled material C, mix ball-milled material C with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 9 - 12h. After the ball-milling is completed, carry out reduced-pressure drying, and then mix with polyboron carbonitride silane and carry out aging treatment, and press it into a film with a thickness of 0.5 - 0.8mm, which is the substrate layer that contacts the garbage and bears residual compressive stress.

2. The composite ceramic material used as the inner lining of a waste incinerator according to claim 1, wherein: In the substrate layer bearing residual tensile stress: the volume percentage of hafnium boride is 70 - 75 vol%; the volume percentage of silicon carbide fibers is 13 - 15 vol%; the volume percentage of silicon carbide powder is 12 - 15 vol%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the solid phase volume of the powder; In the substrate layer that does not contact the garbage and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of silicon carbide powder is 10% - 13%, and the volume percentage of niobium silicide is 10 - 14%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the solid phase volume of the powder; In the substrate layer that directly contacts the garbage and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of tantalum silicide is 3% - 5%, the volume percentage of niobium silicide is 3% - 5%, the volume percentage of silicon nitride is 3% - 4%, and the volume percentage of silicon carbide is 11% - 13%; the liquid phase of polyboron carbonitride silane is 15% - 20% of the solid phase volume of the powder.

3. The composite ceramic material used as the inner lining of a waste incinerator according to claim 2, wherein: The particle size of the hafnium boride powder does not exceed ≤13 μm, and the purity is ≥99%; the diameter of the silicon carbide fiber is 8 - 12 μm, and the length is 80 - 150 μm; the average particle size of the silicon carbide powder is ≤15 μm, and the purity is ≥99%; the average particle size of the niobium silicide powder is ≤15 μm, and the purity is ≥99%; The average particle size of the silicon nitride powder is ≤15 μm, and the purity is ≥99%; the average particle size of the tantalum silicide powder is ≤15 μm, and the purity is ≥99%; polyboron carbonitride silane is in liquid form with 99%, molecular weight (Mn) 700 - 900, and viscosity 10000 - 20000 cp.

4. The composite ceramic material used as the inner lining of a waste incinerator according to claim 1, characterized in that: During the preparation of the substrate layer with residual tensile stress, the substrate layer with residual compressive stress not in contact with the garbage, and the substrate layer with residual compressive stress in contact with the garbage, the volume ratio of the powder to absolute ethanol is 1:1 - 1.5, and the volume ratio of ZrO2 beads to the powder is 1:1.5 - 2.

5. The composite ceramic material used as the inner lining of a waste incinerator according to claim 1, characterized in that: The conditions for reduced-pressure drying are to place it under a negative pressure of 400 - 600 mmHg and at a temperature of 55 - 65 °C; The pressure for pre-pressing is 5 - 10 MPa, and the pressure holding time is 10 - 15 min.

6. The composite ceramic material used as the inner lining of a waste incinerator according to claim 1, characterized in that: The conditions for curing are to raise the temperature to 170 °C at a heating rate of 2 - 3 °C / min in a nitrogen atmosphere and keep it warm for 2.5 - 3 h to complete the curing of polyboron carbonitride silane; The pyrolysis is to raise the temperature from 170 °C to 800 °C at a speed of 2 - 3 °C / min under nitrogen protection, keep the pressure at 5 - 10 MPa, and complete the pyrolysis process of polyboron carbonitride silane; The sintering process is as follows: after the cracking process is completed, the pressure is increased from 5 - 10 MPa to 20 - 25 MPa, the furnace body temperature is raised from 800 °C to 1750 - 1850 °C at a heating rate of 5 °C - 15 °C / min, and then sintered for 50 - 80 min while maintaining the vacuum degree in the furnace ≤ 10 -2 Pa.

7. The composite ceramic material used as the inner lining of a waste incinerator according to claim 1, characterized in that: The number of substrate layers with residual compressive stress not in contact with the garbage and the substrate layers with residual tensile stress is the same, which is 5 - 8 layers, and the substrate layer with residual compressive stress in contact with the garbage is the surface layer.

8. A preparation method of the composite ceramic material used as the inner lining of a waste incinerator according to claim 1, characterized in that, It includes the following steps: ① The preparation method of the substrate layer with residual tensile stress is as follows: Mix the hafnium boride powder and the silicon carbide powder to obtain the ball-milled material A, mix the ball-milled material A with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 6 - 8 h, then add the silicon carbide fiber and continue to ball-mill for 3 - 4 h. After the ball-milling is completed, carry out reduced-pressure drying, then add 10 - 20% by volume of polyboron carbonitride silane, and after mixing, carry out aging treatment for 18 - 36 h, and press it into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer with residual tensile stress; ② The preparation method of the substrate layer with residual compressive stress not in contact with the garbage is as follows: Mix the hafnium boride, silicon carbide, and niobium silicide powders to obtain the ball-milled material B, mix the ball-milled material B with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 9 - 12 h. After the ball-milling is completed, carry out reduced-pressure drying, then add 10 - 20% by volume of polyboron carbonitride silane, and after mixing, carry out aging treatment for 18 - 36 h, and press it into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer with residual compressive stress not in contact with the garbage; ③ The preparation method of the substrate layer that contacts the garbage and bears residual compressive stress is as follows: Mix hafnium boride, silicon carbide, tantalum silicide, niobium silicide and silicon nitride powders to obtain ball-milled material C. Mix ball-milled material C with absolute ethanol, select ZrO2 beads as the mixing medium and ball-mill for 9 - 12 h. After the ball-milling is completed, carry out reduced-pressure drying. Then add polyboron carbonitride silane with a volume fraction of 10 - 20%, and carry out aging treatment for 18 - 36 h after mixing. Press it into a film with a thickness of 0.5 - 0.8 mm, which is the substrate layer that contacts the garbage and bears residual compressive stress; ④ Cut the pressed films into the same size, stack them alternately with one layer of the substrate layer that does not contact the garbage and bears residual compressive stress and one layer of the substrate layer that bears residual tensile stress, and finally stack the substrate layer that contacts the garbage directly and bears compressive stress. The total number of all substrate layers is 11 - 17 layers. Load the stacked substrate multi-layers into a mold and pre-press them under a pressure of 5 - 10 MPa, and keep the pressure for 10 - 15 min; ⑤ Place the mold with the pre-pressed material in a sintering furnace. First, raise the temperature to 170 °C at a heating rate of 2 - 3 °C / min in a nitrogen atmosphere and keep it warm for 2.5 - 3 h to complete the curing of polyboron carbonitride silane. Apply a pressure of 5 - 10 MPa during the curing process; ⑥ Under nitrogen protection, raise the temperature from 170 °C to 800 °C at a speed of 2 - 3 °C / min to complete the pyrolysis process of polyboron carbonitride silane; ⑦After the cracking process is completed, increase the pressure from 5 to 10 MPa to 20 to 25 MPa, and increase the furnace body temperature from 800 °C to 1750 to 1850 °C at a heating rate of 5 °C to 15 °C / min, and keep it for heat preservation and sintering for 50 to 80 min. Keep the vacuum degree in the furnace ≤ 10 - 2 Pa during the whole sintering process.

9. The preparation method of the composite ceramic material used as the inner lining of a waste incinerator according to claim 8, characterized in that: In the substrate layer that bears residual tensile stress: the volume percentage of hafnium boride is 70 - 75 vol%; the volume percentage of silicon carbide fiber is 13 - 15 vol%; the volume percentage of silicon carbide powder is 12 - 15 vol%; the polyboron carbonitride silane liquid phase is 15% - 20% of the volume of the powder solid phase; In the substrate layer that does not contact the garbage and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of silicon carbide powder is 10% - 13%, the volume percentage of niobium silicide is 10 - 14%; the polyboron carbonitride silane liquid phase is 15% - 20% of the volume of the powder solid phase; In the substrate layer that contacts the garbage directly and bears residual compressive stress: the volume percentage of hafnium boride is 73 - 80 vol%; the volume percentage of tantalum silicide is 3% - 5%, the volume percentage of niobium silicide is 3% - 5%, the volume percentage of silicon nitride is 3% - 4%, the volume percentage of silicon carbide is 11% - 13%; the polyboron carbonitride silane liquid phase is 15% - 20% of the volume of the powder solid phase.

10. The preparation method of the composite ceramic material used as the inner lining of a waste incinerator according to claim 8, characterized in that: During the preparation processes of the substrate layer that bears residual tensile stress, the substrate layer that does not contact the garbage and bears residual compressive stress, and the substrate layer that contacts the garbage and bears residual compressive stress, the volume ratio of the powder to absolute ethanol is 1:1 - 1.5, and the volume ratio of ZrO2 beads to the powder is 1:1.5 - 2.

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