Alkali-corrosion-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery material

Abstract

The invention relates to the technical field of crucibles, in particular to an alkali-corrosion-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, which comprises a silicon carbide ceramic matrix made of silicon carbide composite ceramic, an in-situ binding layer is formed on the surface of a matrix through a sol-gel method and is subjected to medium-high temperature heat treatment, and the layer is a rare earth modified composite oxide protective layer. According to the invention, the rare earth modified composite oxide protective layer is synergistically modified by introducing rare earth elements such as yttrium and lanthanum, so that the intrinsic stability and penetration resistance of the protective layer in a high-temperature molten alkali environment are remarkably improved; and meanwhile, a silicon dioxide transition layer is generated on the surface of the substrate in situ through a unique pre-oxidation process, so that the protective layer and the silicon carbide substrate are tightly combined through firm chemical bonding, and the critical load is obviously higher than that of a traditional spraying coating, so that the structure is endowed with thermal shock resistance, and is not easy to crack or peel off in a violent rapid cooling and rapid heating cycle.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crucibles, in particular to a high-temperature melting alkali-resistant high-thermal-conductivity crucible for sodium / lithium / potassium battery materials. BACKGROUND

[0002] With the rapid development of sodium ion, lithium ion and potassium ion batteries, higher requirements are put forward for the synthesis and preparation of key positive electrode materials (such as layered oxides, polyanion compounds, etc.) thereof; the high-temperature solid-phase melting method is the core process for preparing these materials, which is usually carried out at a high temperature of more than 1000 DEG C using a strong alkaline medium for melting; such extreme working conditions pose a severe challenge to the comprehensive performance of the melting container: the container not only needs to have excellent high-temperature structural strength and high thermal conductivity to ensure the uniformity and efficiency of the reaction, but also must have excellent alkali metal molten salt corrosion resistance to ensure the purity of the material, prolong the service life of the crucible and avoid the introduction of impurities.

[0003] Silicon carbide ceramics are considered as ideal matrix materials for the above-mentioned applications due to their high melting point, high thermal conductivity and good mechanical strength; however, in a high-temperature molten alkali environment, traditional silicon carbide ceramics will still be significantly corroded, resulting in structural damage and performance degradation, which is difficult to meet the needs of long-period and high-purity battery material melting; in order to improve the corrosion resistance of the silicon carbide crucible, the prior art usually adopts surface coating for protection, such as applying an oxide layer on the surface by thermal spraying or physical vapor deposition; however, most of these coatings only form a physical or simple mechanical bond with the silicon carbide matrix, and the interface bonding force is weak; in the thermal cycle process of high-temperature melting, microcracks are easily generated at the interface, and even the coating is peeled off, thereby failing to effectively block the penetration of the molten alkali medium, resulting in failure of protection; in view of this, we propose a high-temperature melting alkali-resistant high-thermal-conductivity crucible for sodium / lithium / potassium battery materials. SUMMARY

[0004] The present application aims to provide a high-temperature melting alkali-resistant high-thermal-conductivity crucible for sodium / lithium / potassium battery materials to solve the problems of the prior art that most of these coatings only form a physical or simple mechanical bond with the silicon carbide matrix, and the interface bonding force is weak; in the thermal cycle process of high-temperature melting, microcracks are easily generated at the interface, and even the coating is peeled off, thereby failing to effectively block the penetration of the molten alkali medium, resulting in failure of protection.

[0005] The present application provides a high-temperature melting alkali-resistant high-thermal-conductivity crucible for sodium / lithium / potassium battery materials, which comprises a ceramic matrix prepared from silicon carbide composite ceramics; An in-situ bonding layer is formed on the surface of the ceramic matrix by a sol-gel method and subjected to a medium-high temperature heat treatment, and the layer is a rare earth modified composite oxide protective layer.

[0006] Preferably, the thickness of the rare earth modified composite oxide protective layer is 1-10 μm.

[0007] Preferably, the preparation process of the alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials is as follows: S1.1, the surface of the ceramic substrate is cleaned and dried in a drying oven at 120°C; then pre-oxidation treatment is performed to obtain a pretreated substrate; S1.2, rare earth salts, tetraethyl orthosilicate and aluminum isopropoxide are mixed and dissolved in anhydrous ethanol at a mass ratio of 1:10, a complexing agent is added to control the pH value to 3-6, and a film-forming aid is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, and the thickness of the wet film formed by single coating is 0.5-5.0 μm after drying; S1.4, the coated substrate is heat treated at 150-400°C for 1-3h under nitrogen; This stage aims to fully decompose the nitrate precursors (such as yttrium nitrate and lanthanum nitrate) in the composite sol into corresponding oxides, and remove organic solvents and film-forming aids; the exhaust port of the heat treatment equipment is connected to an alkali liquor absorption device to treat the generated nitrogen oxide gas.

[0008] Subsequently, high-temperature heat treatment is performed under nitrogen to obtain an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0009] Preferably, in S1.1, the cleaning treatment is plasma cleaning, the cleaning power is 200-600W, and the treatment time is 2-10min.

[0010] Preferably, in S1.1, the pre-oxidation treatment is to preheat the dried substrate in air at 800-950°C for 10-60min to generate a 0.1-1.0 μm thick silicon dioxide transition layer on the surface in situ.

[0011] Preferably, in S1.2, the rare earth salt is composed of yttrium nitrate and lanthanum nitrate, and the molar ratio of yttrium to lanthanum is 1:0.2-1.0.

[0012] Preferably, in S1.2, the molar ratio of rare earth salt, tetraethyl orthosilicate and aluminum isopropoxide is 0.05-0.30:1:0.5-2.0.

[0013] Preferably, in S1.2, the complexing agent is acetylacetone, and the addition amount is 0.5-1.5 times the total molar amount of isopropyl aluminum and rare earth salt; The film-forming aid is polyethylene glycol, and the addition amount is 0.1-2.0% of the total mass of the composite sol.

[0014] As preferred, in S1.3, the spraying atomization pressure is 0.2-0.5 MPa, and the spraying gun moving speed is 10-30 cm / s.

[0015] As preferred, in S1.4, the high-temperature heat treatment adopts two-stage holding: first holding at 800-900℃ for 0.5-1 h; then raising to 1000-1200℃ for 1-2 h.

[0016] Compared with the prior art, the present application has the following advantages: In the alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, the rare earth modified composite oxide protective layer is modified by introducing yttrium, lanthanum and other rare earth elements, which significantly improves the intrinsic stability and anti-permeation ability of the protective layer in a high-temperature molten alkali environment; yttrium ions mainly promote the densification of the coating and the formation of stable nanocrystalline phase, while lanthanum ions effectively fill the grain boundaries and pin the micro-cracks, and the two work together to make the mass loss rate per unit area of the protective layer extremely low in the severe alkali corrosion test; at the same time, the unique pre-oxidation process generates a silica transition layer in situ on the surface of the substrate, which tightly bonds the protective layer and the silicon carbide substrate through strong chemical bonding, and the critical load is significantly higher than that of traditional sprayed coatings, thereby giving the structure thermal shock resistance and preventing it from cracking or peeling off in severe quenching and heating cycles. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0018] The present application provides an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, which comprises a ceramic substrate made of silicon carbide composite ceramic. An in-situ bonding layer formed on the surface of the ceramic substrate by sol-gel method and subjected to high-temperature heat treatment is a rare earth modified composite oxide protective layer.

[0019] The main components of the ceramic substrate made of silicon carbide composite ceramic include: 70-95% silicon carbide, 4-25% silicon carbide fiber, and 1-5% aluminum oxide. The ceramic substrate is prepared by reaction sintering method, with an average particle size of 3-5 μm, a sintering temperature of 1800-2000℃, a density of ≥98%, and a surface roughness Ra<0.1 μm after mechanical polishing.

[0020] Tetraethyl orthosilicate (CAS No. 78-10-4, purity 99.5%) was purchased from Jinan Hui Fengda Chemical Co., Ltd.

[0021] Aluminum isopropoxide (CAS No. 555-31-7, purity 99.9%), yttrium nitrate (CAS No. 13494-98-9, purity 99.9%), lanthanum nitrate (CAS No. 10277-43-7, purity 99.9%) were purchased from Shanghai Melin Biochemical Technology Co., Ltd.

[0022] Acetylacetone (CAS No. 123-54-6, purity 99%) was purchased from Shandong Jinyueyuan New Material Co., Ltd.

[0023] Example 1: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, Plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 200 W, the time is 10 min, and drying is performed in a drying box at 120°C; Subsequently, the cleaned and dried substrate is preheated at 800°C in air for 30 min to form a 0.1 μm-thick silica transition layer in situ on the surface, obtaining a pretreated substrate; S1.2, Rare earth salt (composed of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate, and aluminum isopropoxide are mixed (molar ratio of 0.18:1:1.2), dissolved in anhydrous ethanol at a mass ratio of 1:10, acetylacetone is added (the amount of addition is 0.5 times the total molar amount of aluminum isopropoxide and rare earth salt), the pH value is controlled at 3, and polyethylene glycol is added (0.1% of the total mass of the composite sol) to form a composite sol; S1.3, The composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.2 MPa, and the moving speed of the spray gun is 10 cm / s, so that the wet film formed by single coating has a thickness of 0.5 μm after drying, and the total thickness is 1 μm; S1.4, The coated substrate is heat treated at 150°C under nitrogen for 3h; Subsequently, high-temperature heat treatment is performed under nitrogen, first at 800°C for 0.5h, then at 1000°C for 1h, obtaining an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0024] Example 2: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, Plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 200 W, the time is 10 min, and drying is performed in a drying box at 120°C; Subsequently, the cleaned and dried substrate is pre-heated at 800°C for 30 minutes in air to form a 0.1 μm-thick silica transition layer on the surface in situ, obtaining a pretreated substrate; S1.2, a rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.2), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol at a mass ratio of 1:10, acetylacetone is added (the addition amount is 0.5 times the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 3, and polyethylene glycol (0.1% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.2 MPa, the moving speed of the spray gun is 10 cm / s, the thickness of the wet film formed by single coating is 0.5 μm after drying, and the total thickness is 1 μm; S1.4, the coated substrate is heat treated at 150°C for 3h under nitrogen; Subsequently, high-temperature heat treatment is carried out under nitrogen, first at 800°C for 0.5h, then at 1000°C for 1h, obtaining an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0025] Embodiment 3: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, the surface of the ceramic substrate is subjected to plasma cleaning treatment, the power is 200W, the time is 10min, and drying is carried out in a drying box at 120°C; Subsequently, the cleaned and dried substrate is pre-heated at 800°C for 30 minutes in air to form a 0.1 μm-thick silica transition layer on the surface in situ, obtaining a pretreated substrate; S1.2, a rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:1.0), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol at a mass ratio of 1:10, acetylacetone is added (the addition amount is 0.5 times the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 3, and polyethylene glycol (0.1% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.2 MPa, the moving speed of the spray gun is 10 cm / s, the thickness of the wet film formed by single coating is 0.5 μm after drying, and the total thickness is 1 μm; S1.4, the coated substrate is heat treated at 150°C for 3h under nitrogen; Subsequently, high-temperature heat treatment is carried out under nitrogen, first at 800 DEG C for 0.5 h, and then at 1000 DEG C for 1 h, to obtain the alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0026] Example 4: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 200 W, the time is 10 min, and drying is performed at 120 DEG C in a drying box; Subsequently, the cleaned and dried substrate is preheated at 800 DEG C in air for 30 min, so that a 0.1-μm-thick silicon dioxide transition layer is generated in situ on the surface, to obtain a pretreated substrate; S1.2, rare earth salts (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate, and aluminum isopropoxide are mixed (the molar ratio is 0.05:1:0.5), dissolved in anhydrous ethanol at a mass ratio of 1:10, acetylacetone is added (the addition amount is 0.5 times the total molar amount of aluminum isopropoxide and rare earth salts), the pH value is controlled at 3, and polyethylene glycol is added (0.1% of the total mass of the composite sol) to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomization pressure of spraying is 0.2 MPa, the moving speed of the spray gun is 10 cm / s, so that the wet film formed by single coating has a thickness of 0.5 μm after drying, and the total thickness is 1 μm; S1.4, the coated substrate is heat treated at 150 DEG C under nitrogen for 3 h; Subsequently, high-temperature heat treatment is carried out under nitrogen, first at 800 DEG C for 0.5 h, and then at 1000 DEG C for 1 h, to obtain the alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0027] Example 5: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 200 W, the time is 10 min, and drying is performed at 120 DEG C in a drying box; Subsequently, the cleaned and dried substrate is preheated at 800 DEG C in air for 30 min, so that a 0.1-μm-thick silicon dioxide transition layer is generated in situ on the surface, to obtain a pretreated substrate; S1.2, the rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (the molar ratio is 0.30:1:2.0), dissolved in anhydrous ethanol with a mass ratio of 1:10, the pH value is controlled at 3 by adding acetylacetone (the addition amount is 0.5 times of the total molar amount of aluminum isopropoxide and rare earth salt), and polyethylene glycol (0.1% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomization pressure of spraying is 0.2 MPa, the moving speed of the spray gun is 10 cm / s, the thickness of the wet film formed by single coating is 0.5 μm after drying, and the total thickness is 1 μm; S1.4, the coated substrate is heat treated at 150°C for 3h under nitrogen; Then high temperature heat treatment is carried out under nitrogen, first at 800°C for 0.5h, then at 1000°C for 1h, to obtain an alkali corrosion resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials.

[0028] For all examples and comparative examples, the alkali corrosion resistance is determined by the following method: the prepared coated crucible or coated test piece is washed and dried, the initial mass (M1) is accurately weighed by an analytical balance, sufficient anhydrous NaOH or KOH is filled into the crucible, and placed in a muffle furnace, under air atmosphere, at 500-600°C for 24-100 hours (accelerated life test); after natural cooling, the residual alkali block is carefully poured out, the crucible is repeatedly boiled in boiling water until the washing liquid is neutral detected by pH test paper, to completely remove the corrosion products and residual alkali; after the crucible is completely dried, the final mass (M2) is weighed; the mass loss rate per unit inner surface area is calculated as (M1-M2) / S (unit: mg / cm²).

[0029] The bonding strength (adhesion) of the coating and the substrate is determined by using a scratch tester, a standard diamond indenter (such as Rockwell C type) is used to scratch the surface of the coating at a constant or increasing load, while the indenter moves at a constant speed, the critical load is determined by the sudden change of acoustic emission signal and the peeling of the coating; the first critical load usually corresponds to the appearance of microcracks in the coating; the second critical load corresponds to the large-scale peeling of the coating from the substrate; the critical load (Lc2) when the coating completely fails is recorded, in Newton (N); the higher the Lc2 value, the stronger the bonding strength.

[0030] The cross-sectional porosity is determined by polishing the cross-section of the coated test piece to prepare a metallographic sample, obtaining a backscattered electron image, and using analysis software to perform threshold segmentation and binary processing to distinguish pores from solid materials; the software automatically calculates the percentage of pore area to the total analysis area, i.e. the surface porosity is obtained.

[0031] Table 1 Performance data of rare earth modified composite oxide protective layer

[0032] As can be seen from Table 1, the mass loss rate of Example 1 is the lowest (0.45 mg / cm 2 ), and the bonding strength is the highest (42.5 N), which indicates that at this ratio, the densification effect of Y 3+ and the grain boundary blocking effect of La 3+ reach a balance, forming the most dense, most firmly bonded and most corrosion-resistant protective layer.

[0033] Example 2 (low La) has a significant decrease in corrosion resistance and an increase in porosity, which confirms that the key role of La 3+ in filling defects and blocking permeation channels is insufficient.

[0034] Example 3 (high La) has a significant decrease in bonding strength, and excessive La 3+ introduces a larger lattice stress, resulting in an increase in coating brittleness and a higher risk of failure in scratch testing.

[0035] Comparing Examples 1, 4 and 5, Example 4 (low rare earth salt, low Al) has the worst corrosion resistance and the highest porosity, because the lack of rare earth salt elements and network formers results in a loose protective layer structure that cannot effectively block alkali corrosion.

[0036] Example 5 (high rare earth salt, high Al) has the lowest bonding strength, and excessive rare earth and aluminum can result in too many brittle phases (such as rare earth-rich phases or corundum phases), and the mismatch of the thermal expansion coefficient with the substrate increases, thereby reducing the adhesion.

[0037] Example 6: A preparation process for an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 400 W, the time is 10 min, and drying is performed in a drying box at 120°C; Then the cleaned and dried substrate is preheated at 850°C in air for 40 min to generate a 0.6 μm thick silica transition layer in situ on the surface, obtaining a pretreated substrate; S1.2, the rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol with a mass ratio of 1:10, acetylacetone is added (the addition amount is 1.0 times of the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 6, and polyethylene glycol (1.5% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomization pressure of spraying is 0.4 MPa, the moving speed of the spray gun is 20 cm / s, the thickness of the wet film formed by single coating is 3.0 μm after drying, and the total thickness is 6 μm; S1.4, the coated substrate is heat treated at 300℃ under nitrogen for 3h; Then high temperature heat treatment is carried out under nitrogen, first at 850℃ for 1h, then raised to 1100℃ for 2h, to obtain an alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials.

[0038] Example 7: a preparation process of an alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, the surface of the ceramic substrate is treated by plasma cleaning, the power is 400W, the time is 10min, and the drying is carried out in a drying box at 120℃; Then the cleaned and dried substrate is preheated at 850℃ in air for 40min, so that a transition layer of silicon dioxide with a thickness of 0.1 μm is generated in situ on the surface, to obtain a pretreated substrate; S1.2, the rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol with a mass ratio of 1:10, acetylacetone is added (the addition amount is 1.0 times of the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 6, and polyethylene glycol (1.5% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomization pressure of spraying is 0.4 MPa, the moving speed of the spray gun is 20 cm / s, the thickness of the wet film formed by single coating is 3.0 μm after drying, and the total thickness is 6 μm; S1.4, the coated substrate is heat treated at 300℃ under nitrogen for 3h; Then high temperature heat treatment is carried out under nitrogen, first at 850℃ for 1h, then raised to 1100℃ for 2h, to obtain an alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials.

[0039] Example 8: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 400W, the time is 10min, and drying is performed at 120°C in a drying box; Then the cleaned and dried substrate is preheated at 850°C in air for 40min, so that a 1.0μm-thick silica transition layer is generated in situ on the surface, obtaining a pretreated substrate; S1.2, rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol according to mass ratio 1:10, acetylacetone is added (the addition amount is 1.0 times of the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 6, and polyethylene glycol (1.5% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.4MPa, the moving speed of the spray gun is 20cm / s, so that the wet film formed by single coating has a thickness of 3.0μm after drying, and the total thickness is 6μm; S1.4, the coated substrate is heat treated at 300°C for 3h under nitrogen; Then high-temperature heat treatment is carried out under nitrogen, first at 850°C for 1h, then at 1100°C for 2h, obtaining an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials.

[0040] Example 9: A preparation process of an alkali-resistant high-thermal-conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, plasma cleaning treatment is performed on the surface of the ceramic substrate, the power is 400W, the time is 10min, and drying is performed at 120°C in a drying box; Then the cleaned and dried substrate is preheated at 850°C in air for 40min, so that a 0.6μm-thick silica transition layer is generated in situ on the surface, obtaining a pretreated substrate; S1.2, rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol according to mass ratio 1:10, acetylacetone is added (the addition amount is 1.0 times of the total molar amount of isopropyl alcohol and rare earth salt), the pH value is controlled at 6, and polyethylene glycol (1.5% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.4 MPa, the moving speed of the spray gun is 20 cm / s, the thickness of the wet film formed by single coating is 3.0 μm after drying, and the total thickness is 6 μm; S1.4, the coated substrate is heat treated at 300°C under nitrogen for 3h; Then high temperature heat treatment is carried out under nitrogen, first at 850°C for 1h, then raised to 1000°C for 2h, to obtain the alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials.

[0041] Example 10: a preparation process of an alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials, comprising the following steps: S1.1, the surface of the ceramic substrate is treated by plasma cleaning, the power is 400 W, the time is 10 min, and drying is carried out in a drying box at 120°C; Then the cleaned and dried substrate is preheated at 850°C in air for 40 min to form a 0.6 μm thick silica transition layer on the surface in situ, to obtain a pretreated substrate; S1.2, the rare earth salt (consisting of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.6), tetraethyl orthosilicate and aluminum isopropoxide are mixed (molar ratio is 0.18:1:1.2), dissolved in anhydrous ethanol according to the mass ratio of 1:10, the pH value is controlled at 6 by adding acetylacetone (the addition amount is 1.0 times of the total molar amount of aluminum isopropoxide and rare earth salt), and polyethylene glycol (1.5% of the total mass of the composite sol) is added to form a composite sol; S1.3, the composite sol is coated on the surface of the pretreated substrate by spraying, the atomizing pressure of spraying is 0.4 MPa, the moving speed of the spray gun is 20 cm / s, the thickness of the wet film formed by single coating is 3.0 μm after drying, and the total thickness is 6 μm; S1.4, the coated substrate is heat treated at 300°C under nitrogen for 3h; Then high temperature heat treatment is carried out under nitrogen, first at 850°C for 1h, then raised to 1200°C for 2h, to obtain the alkali-resistant high thermal conductivity crucible for high temperature smelting of sodium / lithium / potassium battery materials.

[0042] Determination of thermal shock stability: the crucible sample is washed and dried, the surface is observed to ensure that there is no initial crack; the sample is placed in a muffle furnace preheated to 1000°C, and kept for 15 minutes; the sample is quickly taken out with a crucible tongs and immediately immersed in room temperature deionized water for 5 minutes; the sample is taken out, dried, and the coating surface and edge are carefully checked for cracks, peeling or peeling; record the first visible damage (such as edge peeling >1mm2 ) the number of thermal cycles experienced.

[0043] Table 2 Performance data of high-thermal-conductivity crucible resistant to caustic attack

[0044] Comparative Example 6-8, the bonding strength and thermal shock stability of Example 7 decreased significantly, which was due to the fact that the too thin (0.1 μm) and discontinuous SiO2 transition layer could not form an effective stress buffer layer between the protective layer and the SiC substrate, resulting in insufficient interfacial bonding force.

[0045] The thermal expansion mismatch between the too thick (1.0 μm) SiO2 layer and the SiC substrate in Example 8 was more significant, and a higher residual tensile stress was generated during the cooling process after heat treatment, thereby triggering a network of microcracks; these microcracks became a fast channel for molten caustic penetration, and at the same time significantly reduced the thermal shock resistance of the coating.

[0046] Comparative Examples 6, 9, and 10, Example 6 (temperature 1100℃) was the most optimal process point in terms of performance, and this temperature was sufficient to ensure that the protective layer was fully densified and completely reacted with the transition layer in situ to form a strong composite structure.

[0047] Example 9 (temperature 1000℃) had the worst corrosion resistance, and the insufficient temperature resulted in an incomplete sintering densification process of the protective layer, with more open pores remaining inside, which could not effectively block the corrosion of the molten caustic.

[0048] Example 10 (temperature 1200℃) had a significant decrease in bonding strength and thermal shock stability, and the excessively high temperature led to excessive oxidation of the SiC substrate surface, which destroyed the original interface structure; the grains in the protective layer became coarse, which reduced the toughness; and the difference in the thermal expansion coefficient with the substrate was greater, which generated a higher residual stress during cooling, making the coating more prone to peeling in thermal shock.

[0049] After the above determination, Example 6 was selected as the optimal example; Comparative Example 1: Compared with Example 6, the difference is that no rare earth modified composite oxide protective layer is added.

[0050] Comparative Example 2: Compared with Example 6, the difference is that only yttrium nitrate is used as the rare earth source.

[0051] Comparative Example 3: Compared with Example 6, the difference is that no rare earth salt is added to the rare earth modified composite oxide protective layer, and only tetraethyl orthosilicate and aluminum isopropoxide are used.

[0052] Comparative Example 4: Compared with Example 6, the difference is that no pre-oxidation treatment is performed on the cleaned substrate.

[0053] Table 3 Performance data of high-thermal-conductivity crucible resistant to alkali corrosion

[0054] The mass loss rate of Comparative Example 1 is as high as 12.50 mg / cm 2 , while that of Example 6 is only 0.48 mg / cm 2 .

[0055] This directly proves the necessity of the protective layer. The SiC substrate without protection is corroded in high-temperature molten alkali and cannot meet the use requirements at all.

[0056] The performance of Comparative Example 2 is significantly lower than that of Example 6, especially the corrosion resistance and the bonding strength; single Y 3+ can promote densification, but lacks the grain boundary filling and crack pinning effect of La 3+ , resulting in a decrease in the penetration resistance and toughness of the protective layer, and the comprehensive performance cannot reach the optimum.

[0057] Comparative Example 3 has very poor corrosion resistance (2.85 mg / cm 2 ). Without rare earth modification, the stability, densification and alkali corrosion resistance of the pure aluminum-silicon oxide coating at high temperature are seriously insufficient; the rare earth elements fundamentally improve the protective ability of the coating by forming stable nanocrystalline phases (such as YAG) and reinforced glass phases.

[0058] The bonding strength (28.4 N) and thermal shock stability (12 times) of Comparative Example 4 show a cliff-like drop; this proves that the pre-oxidation generated SiO2 transition layer is the key to realizing strong interface chemical bonding. Without this bridge, it is easy to crack and peel off under thermal stress, resulting in protection failure.

[0059] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A crucible with alkali resistance and high thermal conductivity for high-temperature smelting of sodium / lithium / potassium battery materials, characterized in that, Including ceramic matrices made of silicon carbide composite ceramics; An in-situ bonding layer is formed on the surface of a ceramic substrate by a sol-gel method and subjected to medium- and high-temperature heat treatment. This layer is a rare earth modified composite oxide protective layer.

2. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 1, characterized in that, The thickness of the rare earth modified composite oxide protective layer is 1-10 μm.

3. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 1, characterized in that, The preparation process of the alkali-resistant and high thermal conductivity crucible used for high-temperature melting of sodium / lithium / potassium battery materials is as follows: S1.1 The surface of the ceramic substrate is cleaned and dried in a drying oven at 120°C; then a pre-oxidation treatment is performed to obtain the pretreated substrate. S1.

2. Mix rare earth salts, tetraethyl orthosilicate and aluminum isopropoxide, dissolve in anhydrous ethanol at a mass ratio of 1:10, add a complexing agent to control the pH value at 3-6, and add a film-forming aid to form a composite sol. S1.3 The composite sol is applied to the pretreated substrate surface by spraying, so that the thickness of the wet film formed by a single coating is 0.5-5.0μm after drying; S1.

4. The coated substrate is heat-treated under nitrogen at 150-400℃ for 1-3 hours. Subsequently, high-temperature heat treatment under nitrogen was carried out to obtain an alkali-resistant and high thermal conductivity crucible for high-temperature melting of sodium / lithium / potassium battery materials.

4. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In S1.1, the cleaning process is plasma cleaning, with a cleaning power of 200-600W and a processing time of 2-10 minutes.

5. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In step S1.1, the pre-oxidation treatment involves preheating the cleaned and dried substrate in air at 800-950°C for 10-60 minutes to generate a silicon dioxide transition layer with a thickness of 0.1-1.0 μm on its surface in situ.

6. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In S1.2, the rare earth salt is composed of yttrium nitrate and lanthanum nitrate, wherein the molar ratio of yttrium to lanthanum is 1:0.2-1.

0.

7. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In step S1.2, the molar ratio of rare earth salt, tetraethyl orthosilicate, and aluminum isopropoxide is 0.05-0.30:1:0.5-2.

0.

8. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In step S1.2, the complexing agent is acetylacetone, and its addition amount is 0.5-1.5 times the total molar amount of aluminum isopropoxide and rare earth salt. The film-forming aid is polyethylene glycol, and its addition amount is 0.1-2.0% of the total mass of the composite sol.

9. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In step S1.3, the atomization pressure of the spraying is 0.2-0.5 MPa, and the spray gun moving speed is 10-30 cm / s.

10. The alkali-resistant and high thermal conductivity crucible for high-temperature smelting of sodium / lithium / potassium battery materials according to claim 3, characterized in that, In S1.4, the high-temperature heat treatment adopts a two-stage heat preservation method: first, heat preservation at 800-900℃ for 0.5-1h; then heat preservation at 1000-1200℃ for 1-2h.

Images