Long-service-life Si3N4 combined SiC refractory material for garbage incinerator and preparation method of long-service-life Si3N4 combined SiC refractory material

Abstract

The invention discloses a long-life Si3N4 combined SiC refractory material for a garbage incinerator and a preparation method, and relates to the technical field of garbage incineration. The material comprises SiC fine powder of SiC particles, Si powder, Y2O3 micro powder, MgO micro powder, a binding agent and boride micro powder. In the invention, a proper amount of boride micro powder is introduced as an additive (TiB2 or AlB2) for the first time to prepare the long-life Si3N4 combined SiC refractory material for the garbage incinerator, firstly, the boride micro powder is not easy to agglomerate, high in activity, small in addition amount and low in cost; secondly, boride is superior to Si3N4, SiC reacts with water vapor to generate B2O3 and an oxide, the oxide can continue to play a role in regulating quartz crystallization after part of B2O3 is volatilized, and the stability is good; thirdly, boride is beneficial to promoting nitridation of Si powder to generate Si3N4 whiskers based on a gas-gas mechanism, and has dual effects of reducing apparent porosity and delaying crystallization of high-temperature water vapor oxidation film quartz; the method has practical application value for prolonging the service life of the SiC refractory material and improving the economic benefit of a waste incineration power plant.

Description

Technical Field

[0001] The invention relates to the technical field of waste incineration, and in particular to a long-life Si3N4 combined SiC refractory material for a waste incinerator and a preparation method thereof. Background Art

[0002] Using waste incinerators to generate electricity is an effective way to reduce, harmlessly treat and recycle domestic waste. The key parts of the waste incinerator, such as the first channel water-cooled wall and water-cooled inclined roof, require refractory materials with excellent slag corrosion resistance, thermal shock stability and thermal conductivity. Therefore, Si3N4 combined with SiC refractory materials has become one of the preferred materials;

[0003] However, due to the high water content of garbage, Si3N4 and SiC are easily oxidized with water vapor to generate quartz and Si(OH)4 gas under long-term high temperature. Therefore, the Si3N4 combined with SiC refractory material has weak resistance to high-temperature water vapor oxidation, resulting in volume expansion and loose structure, which not only affects the service life of the refractory material, but also greatly increases the shutdown and renovation cost of the garbage incinerator, affecting the economic benefits.

[0004] At present, there are three main measures to improve the high temperature steam oxidation resistance of Si3N4 combined SiC refractory materials;

[0005] One is to reduce the apparent porosity of the refractory material itself and hinder the diffusion of water vapor into the material. This is achieved by adding metal elements and metal oxides to catalyze the nitridation of Si powder. However, the additives are nano-scale, easy to agglomerate, and have poor uniform dispersion and activity.

[0006] Second, it delays the crystallization of the quartz phase of the high-temperature water vapor oxidation film. Studies have shown that adding 0.4% BC significantly improves the material's oxidation resistance. This is because BC has a high activity and reacts with water vapor before Si3N4 and SiC to generate B2O3, ensuring the stable existence of the glass phase protective film. However, the operating temperature of the garbage incinerator is 800-1200℃, and some B2O3 is volatile and has low stability.

[0007] The third is to introduce a bonding phase with excellent resistance to high-temperature steam oxidation to partially replace Si3N4, such as CA6, AlN and Yb2Si2O7. CA6 remains chemically stable in high-temperature steam, AlN can form a dense alumina layer, and Yb2Si2O7 is a high-temperature bonding phase. However, these bonding phases are currently expensive, which limits their industrial applications.

[0008] Publication No. CN1837149A discloses a refractory castable for a waste incinerator. By adding a composite organic admixture, a waste incinerator lining material with high strength, anti-oxidation properties, resistance to erosion by waste melt, and good thermal stability is obtained. This invention solves the performance problem of refractory castables caused by the water-cement ratio and is not suitable for block sintering materials.

[0009] Publication No. CN114292118A discloses a long-life castable for a waste incinerator and its preparation method. By adding artificial pre-synthesized inorganic material leucite to the waste incinerator castable, and utilizing the characteristics of leucite being stable in a high-temperature alkali-corrosion environment, the prepared waste incinerator castable has the characteristics of long service life, high high-temperature strength, good thermal shock stability, and strong resistance to alkaline ash erosion, thereby extending the service life of the waste incinerator and generating huge economic benefits. The main purpose of the above invention is to improve the resistance to alkaline ash erosion, not the resistance to high-temperature water vapor oxidation;

[0010] Publication number CN117756523A discloses a method for preparing an anti-oxidation refractory coating for the surface of silicon carbide products, wherein the materials are ball-milled and mixed evenly to obtain a refractory slurry, which is evenly coated on the SiC product, naturally dried, and dried at 110°C. After high-temperature treatment, a refractory coating for the surface of SiC products with high bonding strength and stable performance is obtained. Compared with coatings in the prior art, the coating prepared by the present invention has the characteristics of high bonding strength, high temperature resistance, and good thermal shock resistance. The coating can be used continuously on the surface of silicon carbide products for about two months. Multiple coatings are required for long-term use, which increases the number of shutdowns and maintenance of thermal equipment and reduces operating efficiency.

[0011] In view of the above problems, the inventors proposed a long-life Si3N4 combined with SiC refractory material for waste incinerators and a preparation method thereof to solve the above problems. Summary of the invention

[0012] In order to solve the problems of poor activity, low stability or high cost in the prior art, the object of the present invention is to provide a long-life Si3N4 combined SiC refractory material for a waste incinerator and a preparation method thereof.

[0013] In order to solve the above technical problems, the present invention adopts the following technical solution: a long-life Si3N4 combined with SiC refractory material for a waste incinerator, wherein the refractory material is made of the following components:

[0014] SiC particles

[0015] SiC fine powder

[0016] Si powder

[0017] Y2O3 powder

[0018] MgO powder

[0019] Binder

[0020] Boride powder

[0021] The purity of the SiC particles is ≥97%, and the particle sizes are 5-3mm, 3-1mm and 1-0mm;

[0022] The purity of the SiC fine powder is ≥97% and the particle size is 200 mesh;

[0023] The purity of the Si powder is ≥99.9% and the particle size is 325 mesh;

[0024] The purity of the Y2O3 micro powder is ≥99.9% and the particle size is 325 mesh;

[0025] The purity of the MgO micropowder is ≥98%, and the particle size is 325 meshes.

[0026] Preferably, the binder is any one of a polyvinyl alcohol solution and sulfite pulp waste liquid, the concentration of the polyvinyl alcohol solution is 5%, and the volume density of the sulfite pulp waste liquid is 1.15-1.25 g / cm 3 ;

[0027] The boride micropowder is any one of TiB2 and AlB2, the purity of the TiB2 micropowder is ≥99.5%, and the particle size is 10-5μm, and the purity of the AlB2 micropowder is ≥99.5%, and the particle size is 10-5μm.

[0028] The present invention also provides a method for preparing a long-life Si3N4 combined SiC refractory material for a waste incinerator, comprising the following steps:

[0029] S1. Mixing

[0030] According to the weight percentage, select the proportion of 60-70% SiC particles, 10-15% SiC fine powder, and 10-20% Si powder, add 7-10% binder, 1-3% Y2O3 powder, 1-3% MgO powder, and 0-1% boride powder, add all SiC particles and half of SiC fine powder, Si powder, Y2O3 powder, MgO powder, and boride powder in a blender, add half of the binder and stir for 3-5 minutes, then add the other half of SiC fine powder, Si powder, Y2O3 powder, MgO powder, and the other half of the binder and stir for 3-5 minutes, mix evenly, and trap the material for 12 hours for standby use;

[0031] S2, Forming

[0032] The blocks are semi-dry molded into blocks of specified size on a friction brick press or hydraulic press, with a molding pressure of 200 MPa and pressure maintained for 1 minute;

[0033] S3. Drying

[0034] The formed block specimens were dried in a drying kiln at 110°C for 12-36h;

[0035] S4, Sintering

[0036] Si3N4 combined with SiC refractory material was prepared by reaction sintering in a nitriding furnace, with flowing high-purity nitrogen protection and a staged insulation method. The heating system was as follows: heating to 1250°C at a rate of 3°C / min and keeping for 2h, then heating to 1350°C at a rate of 1°C / min and keeping for 2h, and finally heating to 1400°C at a rate of 1°C / min and keeping for 6-10h, and then naturally cooling.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. In the present invention, it is proposed for the first time to introduce an appropriate amount of boride powder as an additive (TiB2 or AlB2) to prepare a long-life Si3N4 combined with SiC refractory material for a waste incinerator. First, the boride powder is not easy to agglomerate and has high activity, and the added amount is small and the cost is low; secondly, the boride is superior to Si3N4 and SiC in reacting with water vapor to generate B2O3 and oxides. The oxide can continue to play a role in regulating quartz crystallization after part of B2O3 volatilizes, and has good stability; thirdly, the boride helps to promote the nitridation of Si powder to generate Si3N4 whiskers based on the gas-gas mechanism, and has the dual effects of reducing the apparent porosity and delaying the crystallization of quartz of high-temperature water vapor oxidation film;

[0039] 2. The present invention specifically solves the problem of weak oxidation resistance of Si3N4 combined with SiC refractory materials used in waste incinerators, which has practical application value for extending the life of SiC refractory materials and improving the economic benefits of waste incineration power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 The present invention is a process flow chart for preparing a long-life Si3N4 combined SiC refractory material for a waste incinerator.

[0042] Figure 2 XRD patterns of Si3N4 combined with SiC refractory materials with different TiB2 addition amounts in the present invention.

[0043] Figure 3 These are microstructural photographs of Si3N4 combined with SiC refractory materials with different TiB2 addition amounts of the present invention.

[0044] Figure 4The XRD patterns of the refractory materials after high-temperature steam oxidation at different TiB2 addition amounts of the present invention.

[0045] Figure 5 This is the microstructure of the refractory material after high-temperature steam oxidation at different TiB2 addition amounts of the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Embodiment 1: Figure 1-5 As shown, the present invention provides a preparation method of a long-life Si3N4 combined SiC refractory material for a garbage incinerator. According to the weight percentage, 70% SiC particles, 10% SiC fine powder, and 20% Si powder are selected, and 2% Y2O3 micropowder and 2% MgO micropowder are added. First, all SiC particles and half of the powder (SiC fine powder, Si powder, Y2O3 micropowder and MgO micropowder) are added to a mixer, and 8% sulfite pulp waste liquid is added and stirred for 3-5 minutes, and then the other half of the powder and 8% sulfite are added. The acid pulp waste liquid is stirred for 3-5 minutes, mixed evenly, and then trapped for 12 hours for standby use, and then semi-dry molded into blocks on a hydraulic press with a molding pressure of 200MPa and a pressure holding time of 1 minute. After drying at 110℃ in a drying kiln for 12 hours, it is sent to a nitriding furnace for reaction sintering under the protection of flowing high-purity nitrogen. The heating system is: heating to 1250℃ at a rate of 3℃ / min and keeping it for 2 hours, then heating to 1350℃ at a rate of 1℃ / min and keeping it for 2 hours, and finally heating to 1400℃ at a rate of 1℃ / min and keeping it for 6-10 hours, and then cooling naturally;

[0048] Example 2: According to the weight percentage, 70% SiC particles, 10% SiC fine powder, 20% Si powder were selected, and 2% Y2O3 powder, 2% MgO powder and 0.4% TiB2 powder were added. First, all SiC particles and half of the powder (SiC fine powder, Si powder, Y2O3 powder, MgO powder and TiB2 powder) were added to the mixer, and 8% sulfite pulp waste liquid binder was added and stirred for 3-5 minutes, and then the other half of the powder and 8% sulfite pulp waste liquid were added and stirred. 3-5min, mix evenly and trap the material for 12h, then semi-dry form it into blocks on a hydraulic press, with a forming pressure of 200MPa, and hold the pressure for 1min. Dry it in a drying kiln at 110℃ for 12h, then send it into a nitriding furnace, and react and sinter under the protection of flowing high-purity nitrogen. The heating system is: heat up to 1250℃ at a rate of 3℃ / min and hold it for 2h, then heat up to 1350℃ at a rate of 1℃ / min and hold it for 2h, and finally heat up to 1400℃ at a rate of 1℃ / min and hold it for 6-10h, and cool it naturally.

[0049] Example 3: According to the weight percentage, 70% SiC particles, 10% SiC fine powder, 20% Si powder were selected, and 2% Y2O3 powder, 2% MgO powder and 0.6% TiB2 powder were added. First, all SiC particles and half of the powder (SiC fine powder, Si powder, Y2O3 powder, MgO powder and TiB2 powder) were added to the mixer, and 8% sulfite pulp waste liquid was added and stirred for 3-5 minutes, and then the other half of the powder and 8% sulfite pulp waste liquid were added and stirred for 3-5 minutes. 5min, after mixing evenly, the material is trapped for 12h for standby use, and then semi-dry molded into blocks on a hydraulic press, with a molding pressure of 200MPa, and the pressure is maintained for 1min. After drying at 110℃ in a drying kiln for 12h, it is sent to a nitriding furnace for reaction sintering under the protection of flowing high-purity nitrogen. The heating system is: heating to 1250℃ at a rate of 3℃ / min and keeping it for 2h, then heating to 1350℃ at a rate of 1℃ / min and keeping it for 2h, and finally heating to 1400℃ at a rate of 1℃ / min and keeping it for 6-10h, and cooling naturally;

[0050] Example 4: According to the weight percentage, 70% SiC particles, 10% SiC fine powder, 20% Si powder were selected, and 2% Y2O3 powder, 2% MgO powder and 0.6% AlB2 powder were added. First, all SiC particles and half of the powder (SiC fine powder, Si powder, Y2O3 powder, MgO powder and AlB2 powder) were added to the mixer, and 8% sulfite pulp waste liquid was added and stirred for 3-5 minutes, and then the other half of the powder and 8% sulfite pulp waste liquid were added and stirred for 3-5 minutes. 5min, after mixing evenly, the material is trapped for 12h for standby use, and then semi-dry molded into blocks on a hydraulic press, with a molding pressure of 200MPa, and the pressure is maintained for 1min. After drying at 110℃ in a drying kiln for 12h, it is sent to a nitriding furnace for reaction sintering under the protection of flowing high-purity nitrogen. The heating system is: heating to 1250℃ at a rate of 3℃ / min and keeping it for 2h, then heating to 1350℃ at a rate of 1℃ / min and keeping it for 2h, and finally heating to 1400℃ at a rate of 1℃ / min and keeping it for 6-10h, and cooling naturally;

[0051] The performance test data of Examples 1, 2, 3 and 4 are shown in Table 1;

[0052]

[0053]

[0054] Table 1

[0055] Compared with the bulk density, apparent porosity, mechanical properties (compressive strength, room temperature flexural strength, high temperature flexural strength), and high temperature steam oxidation resistance (volume expansion rate, mass increase rate) of the first embodiment of the original technical solution, the second, third, and fourth embodiments of the present invention all perform excellently;

[0056] Reduce the apparent porosity of refractory materials and improve the resistance to high temperature steam oxidation:

[0057] Taking the technical effect of TiB2 additive as an example, Figure 2 and Figure 3 The XRD patterns and microstructure photos of refractory materials with different TiB2 addition amounts are shown. TiB2 can react with O2 before Si powder, reducing the oxygen partial pressure in the system. Figure 2 As the amount of TiB2 added increases, the silicon oxynitride phase decreases, which confirms this point. The decrease in oxygen partial pressure increases the SiO partial pressure in the system, promoting the generation of a large number of Si3N4 whiskers based on the gas-solid reaction mechanism of SiO gas and nitrogen, forming a three-dimensional network structure to fill the internal pores. Figure 3 ( Figure 3In the figure, the addition amounts of (a), (b), (c), (d), (e) and (f) are 0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0% respectively. This dense structure helps to slow down the mass transfer and diffusion of water vapor into the interior of the material under high-temperature water vapor environment and improve the high-temperature hydration resistance. However, the addition of excessive TiB2 will cause abnormal growth of Si3N4 grains or generate a large amount of glass phase. The optimal addition amount is 0.4-0.6%;

[0058] Adjust quartz crystallization to alleviate volume expansion and improve resistance to high temperature steam oxidation:

[0059] Taking the technical effect of TiB2 additive as an example, in a high-temperature steam environment, TiB2 is superior to Si3N4 and SiC in reacting with steam to generate B2O3 and TiO2. Figure 4 and Figure 5 These are the XRD patterns and microstructure photos of the refractory materials with different TiB2 additions after 1000℃ high temperature steam oxidation for 300h. Figure 4 It can be seen that the addition of TiB2 helps to reduce the proportion of α-quartz in the crystallization product and promotes the precipitation of SiO2 in the form of β-quartz, thereby reducing volume expansion and controlling structural damage. Figure 5 visible( Figure 5 In the figure, the addition amounts of (a), (b), (c), (d), (e) and (f) are 0, 0.2%, 0.4%, 0.6%, 0.8% and 1.0% respectively. The addition of TiB2 can reduce the viscosity of the glass phase of the oxide film and increase the spreading area of ​​the protective film. Both of the above points are beneficial to improving the resistance to high temperature steam oxidation;

[0060] Improve the comprehensive performance of refractory materials and extend their service life:

[0061] Appropriate addition of boride additives can optimize the pore structure, increase the mechanical properties at room and high temperatures, and improve the resistance to high-temperature water vapor oxidation while ensuring excellent slag corrosion resistance, thermal shock stability and thermal conductivity, thereby improving the overall performance and obtaining a long-life Si3N4 combined with SiC refractory material.

[0062] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A long-life Si3N4 combined SiC refractory material for a waste incinerator, characterized in that: The refractory material is made of the following ingredients: SiC particles SiC fine powder Si powder Y2O3 powder MgO powder Binder Boride powder The purity of the SiC particles is ≥97%, and the particle sizes are 5-3mm, 3-1mm and 1-0mm; The purity of the SiC fine powder is ≥97% and the particle size is 200 mesh; The purity of the Si powder is ≥99.9% and the particle size is 325 mesh; The purity of the Y2O3 micro powder is ≥99.9% and the particle size is 325 mesh; The purity of the MgO micropowder is ≥98%, and the particle size is 325 meshes.

2. A long-life Si3N4 combined SiC refractory material for a waste incinerator as claimed in claim 1, characterized in that: The binder is any one of a polyvinyl alcohol solution and a sulfite pulp waste liquid, the concentration of the polyvinyl alcohol solution is 5%, and the volume density of the sulfite pulp waste liquid is 1.15-1.25 g / cm 3 ; The boride micropowder is any one of TiB2 and AlB2, the purity of the TiB2 micropowder is ≥99.5%, and the particle size is 10-5μm, and the purity of the AlB2 micropowder is ≥99.5%, and the particle size is 10-5μm.

3. A method for preparing a long-life Si3N4 combined SiC refractory material for a waste incinerator as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Mixing According to the weight percentage, select the proportion of 60-70% SiC particles, 10-15% SiC fine powder, and 10-20% Si powder, add 7-10% binder, 1-3% Y2O3 powder, 1-3% MgO powder, and 0-1% boride powder, add all SiC particles and half of SiC fine powder, Si powder, Y2O3 powder, MgO powder, and boride powder in a blender, add half of the binder and stir for 3-5 minutes, then add the other half of SiC fine powder, Si powder, Y2O3 powder, MgO powder, and the other half of the binder and stir for 3-5 minutes, mix evenly, and trap the material for 12 hours for standby use; S2, Forming Semi-dry forming into blocks of specified size on a friction brick press or hydraulic press, with a forming pressure of 200 MPa and pressure holding for 1 minute; S3. Drying The formed block specimens were dried in a drying kiln at 110°C for 12-36h; S4, Sintering Si3N4 combined with SiC refractory material was prepared by reaction sintering in a nitriding furnace, with flowing high-purity nitrogen protection and a staged insulation method. The heating system was as follows: heating to 1250°C at a rate of 3°C / min and keeping for 2h, then heating to 1350°C at a rate of 1°C / min and keeping for 2h, and finally heating to 1400°C at a rate of 1°C / min and keeping for 6-10h, and then naturally cooling.

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