Lid brick of electrofused zirconia corundum brick furnace and its preparation method

Abstract

The present invention belongs to the technical field of refractory materials, and particularly relates to a cover brick for an electrofused zirconium corundum brick furnace and a preparation method thereof. Based on the total mass fraction of 100 parts of high-purity dense tabular corundum powder, alumina granulated powder and high-purity calcium aluminate cement, it is composed of the following raw materials in parts by weight: corundum powder with a particle size of 10 mm < particle size ≤ 20 mm, 10 - 20 parts, corundum powder with a particle size of 6 mm < particle size ≤ 10 mm, 10 - 20 parts, corundum powder with a particle size of 3 mm < particle size ≤ 6 mm, 5 - 15 parts, corundum powder with a particle size of 1 mm < particle size ≤ 3 mm, 10 - 26 parts, corundum powder with a particle size of 0.1 mm < particle size ≤ 1 mm, 16 - 28 parts, corundum powder with a particle size of 2000 mesh < particle size ≤ 325 mesh, 5 - 10 parts; alumina granulated powder, 5 - 15 parts; high-purity calcium aluminate cement, 3 - 10 parts; water reducing agent, 1 part. The present invention has good alkali erosion resistance, high strength, good heat shock resistance, long service life, large spalling size and little pollution to the product.

Description

Technical Field

[0001] The invention belongs to the technical field of refractory materials, and particularly relates to a furnace cover brick of an electric fused zirconium corundum brick furnace and a preparation method thereof. Background Art

[0002] Fused zirconium corundum bricks (AZS fused-cast bricks) are mainly used for high-temperature and erosion-resistant kiln refractory materials such as glass industry pool kilns, glass electric kilns, slides in the steel industry, and kilns in the sodium silicate industry. They are a type of fused-cast refractory material. The electric arc furnace is one of the key equipment for the production of AZS fused-cast bricks. The lining of the electric arc furnace is mainly composed of the furnace bottom, furnace wall, and furnace cover. When using an electric arc furnace for melting and casting, the casting temperature is ≥1800℃. The molten AZS material is corrosive, and the lining material must be resistant to high temperature and chemical erosion. The requirements for the electric arc furnace cover are to have excellent load softening temperature, thermal shock stability, alkali steam erosion resistance, certain spalling resistance, and long service life. In addition, the furnace cover will peel off as the use time increases. In order to prevent contamination of the entire furnace AZS material, the peeling material is preferably in block form rather than powder form, so as to promptly detect and isolate the contaminated AZS liquid.

[0003] China's invention patent application publication number CN111807849A proposes a long-life, corrosion-resistant and spalling-resistant electric arc furnace cover and its preparation method. The electric arc furnace cover uses high-alumina bauxite and plate-shaped corundum as aggregates, and a powder composed of magnesium-aluminum spinel powder, nano-alumina micropowder and plate-shaped corundum powder. The electric arc furnace cover provided by this patent has good thermal vibration resistance and spalling resistance. Its main raw material is high-temperature sintered plate-shaped corundum, which has high purity and a refractoriness of 2000 degrees; the fused spinel powder has excellent thermal shock resistance, and the material chemical properties are close to the properties of electric arc furnace slag. However, this invention is mainly designed for electric furnace steelmaking, aiming to increase the service life of the steelmaking furnace. The fused spinel powder used to improve thermal shock resistance is an impurity for molten ASZ and is not suitable for AZS furnace covers.

[0004] The Chinese invention patent application publication number CN103121850A proposes a cement-free corundum preform and its production method. In steelmaking production, the comprehensive performance of the cement-free corundum preform is better than that of the low-cement corundum preform, which avoids the influence of CaO on the purity of steel. The patent's cement-free corundum preform has an apparent porosity of 10%-15%, which is low. When used as an ASZ furnace cover, it is not conducive to the discharge of moisture from the furnace cover in a high temperature environment, and it is easy to cause the furnace cover to crack and burst.

[0005] At present, most of the patent documents related to the electric arc furnace cover are water-cooled furnace covers used in metallurgy, etc., which are not suitable for ASZ brick furnaces. When the corundum prefabricated parts without cement bonding are used as the ASZ furnace cover, the furnace cover is easy to crack at high temperatures; although adding metal fibers can prevent the furnace cover from cracking at high temperatures, the AZS bricks will be mixed with impurities after the furnace cover peels off, affecting the quality; the corundum prefabricated parts with added elemental silicon solve the difficult problems of poor high-temperature mechanical properties and thermal shock stability of ordinary corundum prefabricated parts, but the alkali steam corrosion resistance cannot meet the requirements of the ASZ brick electric furnace cover.

[0006] In summary, the technical difficulties of traditional AZS furnace cover bricks are as follows:

[0007] 1. In order to improve the thermal shock resistance of the product and extend its service life, raw materials such as spinel powder, brown corundum, bauxite, etc. are mostly used. When used to make AZS furnace cover bricks, impurities will be introduced to pollute the product and affect the quality of AZS bricks;

[0008] 2. When the use temperature of AZS furnace cover brick exceeds 1800℃, due to its low porosity, it will burst when the temperature rises rapidly during use. In order to prevent the brick from bursting, explosion-proof fibers are added. During use, alkali steam will penetrate into the interior of the brick through the channel created by the explosion-proof fibers, and the product has poor resistance to alkali steam erosion;

[0009] 3. The aggregate particle size of the unsintered furnace cover bricks currently on the market is basically below 10mm, with poor thermal shock stability and short service life. Summary of the invention

[0010] In order to solve the above technical problems, the present invention provides a furnace cover brick for an electric fused zirconium corundum brick furnace, which has high bulk density, good alkali corrosion resistance, high strength, good thermal shock resistance, long service life, and the peeling material is block-shaped, large in size, easy to identify, and has little pollution to the product. The present invention also provides a preparation method thereof.

[0011] The furnace cover brick of the fused zirconium corundum brick furnace of the present invention is composed of the following raw materials in parts by weight, based on 100 parts by weight of the total parts by weight of high-purity dense plate-shaped corundum powder, alumina granulated powder and high-purity calcium aluminate cement:

[0012] High-purity dense plate-like corundum powder:

[0013] 10-20 parts of corundum powder with a particle size of 10mm<≤20mm,

[0014] 6mm<particle size≤10mm corundum powder, 10-20 parts,

[0015] 3mm<particle size≤6mm corundum powder, 5-15 parts,

[0016] Corundum powder with a particle size of 1mm<≤3mm, 10-26 parts,

[0017] Corundum powder with a particle size of 0.1 mm < particle size ≤ 1 mm, 16 - 28 parts,

[0018] Corundum powder with a particle size of 2000 mesh < particle size ≤ 325 mesh, 5 - 10 parts;

[0019] Aluminum oxide granulating powder, 5 - 15 parts;

[0020] High - purity calcium aluminate cement, 3 - 10 parts;

[0021] Water - reducing agent, 1 part.

[0022] Preferably, the chemical composition of the high - purity dense tabular corundum powder: Al2O3 > 99.4 wt.%, Fe2O3 < 0.05 wt.%, SiO2 < 0.1 wt.%, Na2O < 0.4 wt.%.

[0023] Preferably, the crystal form of aluminum oxide in the aluminum oxide granulating powder is α - Al2O3, and the chemical composition: Al2O3 > 98.5 wt.%, Fe2O3 < 0.05 wt.%, SiO2 < 0.3 wt.%, Na2O < 0.3 wt.%.

[0024] Preferably, the aluminum oxide granulating powder is prepared as follows:

[0025] After grinding aluminum oxide powder with a particle size of 2000 mesh < particle size ≤ 325 mesh using a ball mill, add an aqueous solution of PVA (polyvinyl alcohol) with a solid content of 6 wt.%, and grind at low speed until D50 ≤ 5 μm, then use spray drying for spray granulation; the mass of the PVA aqueous solution is 3% of the mass of the aluminum oxide powder.

[0026] Preferably, the chemical composition of the high - purity calcium aluminate cement is 75 wt.% < Al2O3 < 85 wt.%, 15 wt.% < CaO < 25 wt.%.

[0027] Preferably, the water - reducing agent is a combination of HDA - 1 and HDA - 1W.

[0028] The preparation method of the furnace cover brick of the electro - fused zircon corundum brick furnace described in the present invention includes the following steps:

[0029] S1 Green body production: After uniformly stirring the high - purity dense tabular corundum powder, aluminum oxide granulating powder, high - purity calcium aluminate cement, and water - reducing agent, add water and stir until it becomes a fluid mud; pour the mud into a mold, vibrate it for molding, promote air exhaust, and then stand for curing to obtain a green brick;

[0030] S2 Natural curing: The green brick after demolding is naturally cured for 24 - 48 h to harden and obtain a green body;

[0031] S3 Drying and Sintering: Place the green body in a drying oven for drying, and then place the dried green body in a kiln for sintering.

[0032] Preferably, the drying temperature is 100 - 120 °C, and the drying time > 48 h; the sintering temperature is 1280 - 1580 °C, and the heat preservation time ≥ 20 h.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The present invention does not use raw materials such as magnesium oxide, titanium dioxide, slag, elemental silicon, and metal fibers. There are few alkali metal oxides and little glass phase in the product. When sintering or used in an environment of > 1800 °C, there is little liquid phase generated by the glass phase in the product. At the same time, the viscosity of the liquid phase changes little with the increase of temperature, which can improve the high-temperature performance, such as thermal shock stability.

[0035] 2. The present invention uses high-purity dense tabular corundum powder as the aggregate. The high-purity dense tabular corundum powder has a high density, high strength, and strong resistance to thermal stress. To a certain extent, it can withstand high-temperature fracture and reduce the generation of thermal shock cracks. When used as an aggregate, it is beneficial to improve the thermal shock stability of the product; use corundum powder with a particle size of 10 mm < particle size ≤ 20 mm to increase the grain size of the aggregate to 10 - 20 mm, so as to expand the original crack length in the refractory material, reduce the degree of thermal shock crack propagation, reduce thermal shock damage, thereby improving the thermal shock stability, reducing the spalling amount of the AZS furnace cover, and extending the service life of the furnace cover.

[0036] 3. The present invention adopts a 6-level particle size grading to make the closest packing between particles. After high-temperature firing, the bulk density and compressive strength of the product are improved, which is beneficial to resisting the thermal stress caused by repeated heating and cooling during the use of the furnace cover brick; the porosity is reduced, which is beneficial to resisting the penetration of alkali steam, thereby improving the alkali resistance.

[0037] 4. The present invention uses alumina granulating powder and high-purity dense tabular corundum fine powder as the matrix, which reduces the glass phase content in the matrix and helps to improve the erosion resistance. The alumina granulating powder has a uniform particle size, which is beneficial to improving the fluidity of the mud, solving the problem of corner defects caused by using raw materials with a large particle size of 10 - 20 mm when molding the mud containing large particle size particles with a mold. At the same time, it can fill the gaps between granular materials, improve the density of the product, reduce the porosity, thereby improving the matrix strength and making it beneficial for the spalling material to become a block; PVA is introduced as a binder and lubricant during the granulation of the alumina granulating powder. PVA is an organic substance and volatilizes during sintering, providing a channel for the removal of water vapor during the sintering process, preventing the product from cracking due to too high saturated water vapor pressure during the sintering process and use process, and extending the service life; the present invention does not introduce other impurities, leaving no residue during sintering or use, reducing the generation of glass phase, improving the high-temperature performance, and being beneficial to the improvement of alkali resistance.

[0038] 5. The present invention is sintered at a temperature above 1280°C. After high-temperature firing, the product has high strength, and the thermal shock resistance is >30 times when water-cooled at 1100°C. Compared with the prior art, the service life of the furnace cover can be increased by 30%.

[0039] 6. It was unexpectedly found during the use of the furnace cover brick of the present invention that when spalling began in the later stage of use, the spalled matter was bricks. Compared with the granular spalling of the prior art, the pollution to the product was greatly reduced. The corundum impurity ratio of the AZS product decreased from 5% to less than 1%, and significant economic benefits have been achieved.

[0040] 7. The formula of the furnace cover brick of the electrofused zircon corundum brick furnace of the present invention is simple to form, and the types of raw materials required are few, which is conducive to production operation and large-scale production. Detailed Embodiments

[0041] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0042] In actual operation, a temperature control fluctuation difference of 2°C is allowed. All raw materials used in the embodiments are commercially available unless otherwise specified.

[0043] The chemical compositions of some raw materials in the examples and comparative examples are shown in Table 1 below.

[0044] Table 1 Chemical Composition Table of High-Purity Dense Tabular Corundum Powder Raw Materials

[0045]

[0046] The alumina granulated powder is prepared as follows:

[0047] The alumina powder with a particle size of 2000 mesh and ≤325 mesh is ground using a ball mill, and then an aqueous PVA solution with a solid content of 6 wt.% is added and ground until D50≤5 μm, and then spray granulation is carried out using the spray drying method; the mass of the aqueous PVA solution is 3% of the mass of the alumina powder.

[0048] Example 1

[0049] The preparation method of the furnace cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0050] S1 Green body production: By weight, 85 parts of high-purity dense tabular corundum powder, 12 parts of alumina granulated powder, 3 parts of high-purity calcium aluminate cement, 0.5 part of water reducer HDA-1, and 0.5 part of water reducer HDA-1W are stirred for 3 min, and then water with a mass fraction of 4.3% of the above-mentioned materials is added and stirred for 5 min until a fluid mud is formed; the mud is poured into a mold and vibrated for 3 min to form, and after promoting gas exhaust, it is left to cure to obtain a green brick;

[0051] S2 Natural curing: The green bricks after demolding are naturally cured for 24 h to harden and obtain the green body;

[0052] S3 Drying and sintering: The green body is placed in a drying oven for drying at a drying temperature of 100 °C for 50 h, and the dried green body is placed in a shuttle kiln for sintering at a sintering temperature of 1380 °C for 32 h.

[0053] Example 2

[0054] The preparation method of the furnace cover brick of the electrofused zirconium corundum brick furnace described above includes the following steps:

[0055] S1 Green body production: By weight, 80 parts of high-purity dense tabular corundum powder, 15 parts of alumina granulating powder, 5 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W are stirred for 3 min, and then 4.1% mass fraction of water of the above-mentioned materials is added and stirred for 5 min until it becomes a fluid mud; The mud is poured into the mold and vibrated for 3 min to form, and after promoting exhaust, it is left standing for curing to obtain green bricks;

[0056] S2 Natural curing: The green bricks after demolding are naturally cured for 48 h to harden and obtain the green body;

[0057] S3 Drying and sintering: The green body is placed in a drying oven for drying at a drying temperature of 100 °C for 50 h, and the dried green body is placed in a shuttle kiln for sintering at a sintering temperature of 1480 °C for 24 h.

[0058] Example 3

[0059] The preparation method of the furnace cover brick of the electrofused zirconium corundum brick furnace described above includes the following steps:

[0060] S1 Green body production: By weight, 85 parts of high-purity dense tabular corundum powder, 11 parts of alumina granulating powder, 4 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W are stirred for 3 min, and then 4.2% mass fraction of water of the above-mentioned materials is added and stirred for 5 min until it becomes a fluid mud; The mud is poured into the mold and vibrated for 3 min to form, and after promoting exhaust, it is left standing for curing to obtain green bricks;

[0061] S2 Natural curing: The green bricks after demolding are naturally cured for 36 h to harden and obtain the green body;

[0062] S3 Drying and sintering: The green body is placed in a drying oven for drying at a drying temperature of 100 °C for 54 h, and the dried green body is placed in a shuttle kiln for sintering at a sintering temperature of 1580 °C for 20 h.

[0063] Example 4

[0064] The preparation method of the cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0065] S1 Blank production: By weight, mix 84 parts of high-purity dense tabular corundum powder, 13 parts of alumina granulating powder, 3 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W and stir for 3 minutes. Then add water with a mass fraction of 4.2% of the above-mentioned materials and stir for 5 minutes until it becomes a fluid mud. Pour the mud into a mold and vibrate for 3 minutes to form. After promoting exhaust, let it stand for curing to obtain a blank brick;

[0066] S2 Natural curing: The blank brick after demolding is naturally cured for 24 hours to harden and obtain a blank body;

[0067] S3 Drying and sintering: Put the blank body into a drying oven for drying at a drying temperature of 120°C for 54 hours. Put the dried blank body into a shuttle kiln for sintering at a sintering temperature of 1580°C for 20 hours.

[0068] Example 5

[0069] The preparation method of the cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0070] S1 Blank production: By weight, mix 75 parts of high-purity dense tabular corundum powder, 15 parts of alumina granulating powder, 10 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W and stir for 3 minutes. Then add water with a mass fraction of 4.1% of the above-mentioned materials and stir for 5 minutes until it becomes a fluid mud. Pour the mud into a mold and vibrate for 3 minutes to form. After promoting exhaust, let it stand for curing to obtain a blank brick;

[0071] S2 Natural curing: The blank brick after demolding is naturally cured for 48 hours to harden and obtain a blank body;

[0072] S3 Drying and sintering: Put the blank body into a drying oven for drying at a drying temperature of 100°C for 54 hours. Put the dried blank body into a shuttle kiln for sintering at a sintering temperature of 1550°C for 24 hours.

[0073] Example 6

[0074] The preparation method of the cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0075] S1 Green body production: By weight, mix 90 parts of high-purity dense tabular corundum powder, 6 parts of alumina granulating powder, 4 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W for 3 minutes, then add water with a mass fraction of 4.2% of the above-mentioned materials and stir for 5 minutes until a fluid mud is obtained; pour the mud into a mold and vibrate for 3 minutes to form, promote exhaust, and then statically cure to obtain a green brick;

[0076] S2 Natural curing: The green brick after demolding is naturally cured for 24 hours to harden and obtain a green body;

[0077] S3 Drying and sintering: Put the green body into a drying oven and dry at a drying temperature of 100°C for 54 hours, then put the dried green body into a shuttle kiln for sintering at a sintering temperature of 1450°C for 24 hours.

[0078] Example 7

[0079] The preparation method of the furnace cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0080] S1 Green body production: By weight, mix 85 parts of high-purity dense tabular corundum powder, 12 parts of alumina granulating powder, 3 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W for 3 minutes, then add water with a mass fraction of 4.2% of the above-mentioned materials and stir for 5 minutes until a fluid mud is obtained; pour the mud into a mold and vibrate for 3 minutes to form, promote exhaust, and then statically cure to obtain a green brick;

[0081] S2 Natural curing: The green brick after demolding is naturally cured for 48 hours to harden and obtain a green body;

[0082] S3 Drying and sintering: Put the green body into a drying oven and dry at a drying temperature of 100°C for 54 hours, then put the dried green body into a shuttle kiln for sintering at a sintering temperature of 1400°C for 30 hours.

[0083] Example 8

[0084] The preparation method of the furnace cover brick of the electrofused zircon corundum brick furnace includes the following steps:

[0085] S1 Green body production: By weight, mix 90 parts of high-purity dense tabular corundum powder, 5 parts of alumina granulating powder, 5 parts of high-purity calcium aluminate cement, 0.5 part of water reducing agent HDA-1, and 0.5 part of water reducing agent HDA-1W for 3 minutes, then add water with a mass fraction of 4.2% of the above-mentioned materials and stir for 5 minutes until a fluid mud is obtained; pour the mud into a mold and vibrate for 3 minutes to form, promote exhaust, and then statically cure to obtain a green brick;

[0086] S2 Natural curing: The green bricks after demolding are naturally cured for 48 h to harden, obtaining the green body;

[0087] S3 Drying and sintering: The green body is placed in a drying oven for drying at a drying temperature of 100 °C for 60 h, and the dried green body is placed in a shuttle kiln for sintering at a sintering temperature of 1300 °C for 24 h.

[0088] In Examples 1-8, the proportions of the raw materials are shown in Table 2 below.

[0089] Table 2 Raw material proportion table in Examples 1-8

[0090]

[0091] Comparative Example 1

[0092] The difference between this Comparative Example 1 and Example 1 is only that high-purity dense tabular corundum powder II with the same mass is used to replace high-purity dense tabular corundum powder I, that is, high-purity dense tabular corundum powder I is not used in Comparative Example 1, and the dosage of high-purity dense tabular corundum powder II is 20 parts by mass.

[0093] Comparative Example 2

[0094] The difference between this Comparative Example 2 and Example 1 is only that bimodal α-Al2O3 fine powder (Shandong Hengjia High-Purity Aluminum Industry Technology Co., Ltd., chemical composition Al2O3 > 98.5 wt.%, Fe2O3 < 0.05 wt.%, SiO2 < 0.3 wt.%, Na2O < 0.3 wt.%) is used to replace the alumina granulating powder in equal amount.

[0095] Comparative Example 3

[0096] The difference between this Comparative Example 3 and Example 1 is only that fused AZS is used to replace high-purity dense tabular corundum powder. Specifically, fused AZS I, fused AZS II, fused AZS III, fused AZS IV, fused AZS V, and fused AZS VI are used to replace high-purity dense tabular corundum powder I, high-purity dense tabular corundum powder II, high-purity dense tabular corundum powder III, high-purity dense tabular corundum powder IV, high-purity dense tabular corundum powder V, and high-purity dense tabular corundum powder VI in equal amount respectively.

[0097] The chemical composition of the fused AZS is shown in Table 3.

[0098] Table 3 Chemical composition table of fused AZS in Comparative Example 3

[0099]

[0100] Comparative Example 4

[0101] The difference between Comparative Example 4 and Example 1 is only that the total amount of high-purity dense tabular corundum powder is the same as that in Example 1, but the specific gradation is different from that in Example 1, specifically:

[0102] High-purity dense tabular corundum powder Ⅰ, 31 parts by mass;

[0103] High-purity dense tabular corundum powder Ⅱ, 10 parts by mass;

[0104] High-purity dense tabular corundum powder Ⅲ, 5 parts by mass;

[0105] High-purity dense tabular corundum powder Ⅳ, 16 parts by mass;

[0106] High-purity dense tabular corundum powder Ⅴ, 18 parts by mass;

[0107] High-purity dense tabular corundum powder Ⅵ, 5 parts by mass.

[0108] Comparative Example 5

[0109] The difference between Comparative Example 5 and Example 1 is only that high-purity dense tabular corundum powder Ⅰ is used to replace high-purity dense tabular corundum powders Ⅱ-Ⅵ in equal amounts, that is, only high-purity dense tabular corundum powder Ⅰ is used for high-purity dense tabular corundum powder.

[0110] Performance test

[0111] The physical property test results of the fused zirconia corundum furnace roof bricks prepared in Examples 1-8 and Comparative Examples 1-5 are shown in Table 4 in detail. Among them, the apparent porosity and bulk density are tested according to "GB / T 2997-2015 Test methods for bulk density, apparent porosity and true porosity of dense shaped refractory products"; the cold crushing strength is tested according to "GB / T 5072-2023 Test method for cold crushing strength of refractories at normal temperature"; the alkali resistance test is tested according to "JC / T 808-1996 Test method for alkali resistance of aluminosilicate refractory castables"; the thermal shock resistance is tested according to "YB / T 376.1-1995 Test method for thermal shock resistance of refractory products", and the dry mass of the specimen after the thermal shock test is divided by the dry mass of the specimen before the test, which is called the mass loss rate.

[0112] Table 4 Physical property test results of the fused zirconia corundum furnace roof bricks in Examples 1-8 and Comparative Examples 1-5

[0113]

[0114] As can be seen from Table 4, in Examples 1-8, by adjusting the addition amount of high-purity dense tabular corundum powder and the amount of alumina granulating powder within the scope defined in the present invention, the bulk density ≥ 3.10 g / cm 3, the apparent porosity ≤ 14.8%, the compressive strength ≥ 78.2 MPa; the alkali resistance ≥ grade 2, the number of times of 50% breakage rate in the water-cooled thermal shock test at 1100 °C ≥ 30 times, and the exfoliated particles are all massive blocks > 30 mm. The prepared furnace cover bricks have a high bulk density, good alkali erosion resistance, high strength, good heat shock resistance, a long service life, the exfoliated materials are massive, large in size, easy to identify, and cause little pollution to the products.

[0115] The bulk density of Example 1 is 3.15 g / cm 3 , the apparent porosity is 14.8%, the compressive strength is 96.6 MPa, the alkali resistance is grade 1, the number of times of 50% breakage rate in the water-cooled thermal shock test at 1100 °C is 32 times, and at the same time, the exfoliated particles are all massive blocks > 30 mm. The bulk density of Comparative Example 1 is 2.88 g / cm 3 , the apparent porosity is 22.7%, the compressive strength is 37.8 MPa, the alkali resistance is grade 3, the number of times of 50% breakage rate in the water-cooled thermal shock test at 1100 °C is 14 times, and the exfoliated material is debris of 1 - 10 mm. Compared with Comparative Example 1, Example 1 has an increased bulk density, a decreased apparent porosity, an increased compressive strength, and the alkali resistance is increased to grade 1, and the exfoliated particles are block materials > 30 mm. It can be seen that using high-purity dense tabular corundum powder Ⅰ with 10 mm < particle size ≤ 20 mm is beneficial to improving the alkali resistance and changing the exfoliation particle size.

[0116] The bulk density of Comparative Example 2 is 3.04 g / cm 3 , the apparent porosity is 21.3%, the compressive strength is 67.5 MPa, the alkali resistance is grade 3, the number of times of 50% breakage rate in the water-cooled thermal shock test at 1100 °C is 18 times, and the exfoliated material is debris of 1 - 10 mm. Compared with Comparative Example 2, Example 1 has an increased bulk density, a decreased apparent porosity, an increased compressive strength, and the alkali resistance is increased to grade 1. It can be seen that using the alumina granulating powder of the present invention is beneficial to both the alkali resistance and the thermal shock temperature stability. The alumina granulating powder is spherical with uniform particle size, which can improve the fluidity of the mud, reduce the porosity of the product, and increase the bulk density; the PVA added to the alumina granulating powder is an organic substance, which can provide a channel for the exclusion of combined water in the green brick after volatilization at > 1000 °C and provide a channel for the exclusion of water vapor in the use environment of > 1800 °C, and can prevent the furnace cover bricks from cracking. Except for PVA, the alumina granulating powder does not add additives containing alkali metals, inorganic salts, etc. When used in combination with high-purity dense tabular corundum powder Ⅵ, it does not increase the glass phase in the matrix, improves the matrix strength, is beneficial to improving the acid resistance, forms exfoliated materials > 30 mm, and improves high-temperature properties such as thermal shock stability.

[0117] The bulk density of Comparative Example 3 is 3.07 g / cm 3, the apparent porosity is 17.5%, the compressive strength is 42.9 MPa, the alkali resistance is grade 3, the number of times of 50% damage rate in the water-cooled thermal shock test at 1100 °C is less than 30 times, and at the same time, the exfoliated particles are all debris. Compared with Comparative Example 3, the bulk density of Example 1 is increased, the apparent porosity is decreased, the compressive strength is increased, the alkali resistance is increased to grade 1, and the exfoliated particles are lump materials with a size greater than 30 mm. It was unexpectedly found that the use of all corundum-based raw materials is beneficial to the formation of lump materials with a size greater than 30 mm for the exfoliated materials. Both the aggregate and the matrix material are homogeneous bodies, and the shrinkage is consistent during sintering, which is beneficial to the change of the exfoliated materials from debris with a size of 1-10 mm to lump materials with a size greater than 30 mm.

[0118] The bulk density of Comparative Example 4 is 3.09 g / cm 3 , the apparent porosity is 16.5%, the compressive strength is 43.5 MPa, the alkali resistance is grade 3, the number of times of 50% damage rate in the water-cooled thermal shock test at 1100 °C is 29 times, and the exfoliated materials are debris with a size of 1-10 mm. Compared with Comparative Example 4, the bulk density of Example 1 is increased, the apparent porosity is decreased, the compressive strength is increased, and the alkali resistance is increased to grade 1. In Comparative Example 4, the dosage of high-purity dense tabular corundum powder Ⅰ with a particle size of 10 mm < particle size ≤ 20 mm exceeds the range, which is not conducive to achieving the closest packing. The powder cannot fully wrap the granular material, reducing the density during sintering, and has no effect on increasing the bulk density, reducing the porosity, increasing the acid and alkali resistance, and increasing the thermal shock stability of the product.

[0119] The bulk density of Comparative Example 5 is 2.83 g / cm 3 , the apparent porosity is 25.2%, the compressive strength is 38.4 MPa, the alkali resistance is grade 3, the number of times of 50% damage rate in the water-cooled thermal shock test at 1100 °C is 14 times, and the exfoliated materials are debris with a size of 1-20 mm. Compared with Comparative Example 5, the bulk density, compressive strength, thermal shock stability, and acid and alkali resistance of Example 1 are all increased. In Comparative Example 5, when the high-purity dense tabular corundum powder is a bulk material, the grading is unreasonable and the closest packing of the particles is not achieved. The bonding degree between the particles and the matrix part is reduced, and during use, it is more susceptible to medium erosion, resulting in exfoliated materials being debris with a size of 1-20 mm.

Claims

1. The cover brick of an electrofused zirconia corundum brick furnace, characterized in that, Based on the total mass fraction of high-purity dense tabular corundum powder, alumina granulating powder and high-purity calcium aluminate cement being 100 parts, it is composed of the following raw materials in parts by weight: High-purity dense tabular corundum powder: Corundum powder with particle size 10mm < particle size ≤ 20mm, 10 - 20 parts, Corundum powder with particle size 6mm < particle size ≤ 10mm, 10 - 20 parts, Corundum powder with particle size 3mm < particle size ≤ 6mm, 5 - 15 parts, Corundum powder with particle size 1mm < particle size ≤ 3mm, 10 - 26 parts, Corundum powder with particle size 0.1mm < particle size ≤ 1mm, 16 - 28 parts, Corundum powder with particle size 2000 mesh < particle size ≤ 325 mesh, 5 - 10 parts; Alumina granulating powder, 5 - 15 parts; High-purity calcium aluminate cement, 3 - 10 parts; Water reducing agent, 1 part.

2. The cover brick of the electrofused zirconia corundum brick furnace according to claim 1, characterized in that, Chemical composition of high-purity dense tabular corundum powder: Al2O3 > 99.4wt.%, Fe2O3 < 0.05wt.%, SiO2 < 0.1wt.%, Na2O < 0.4wt.%.

3. The cover brick of the electrofused zirconia corundum brick furnace according to claim 1, characterized in that, The crystal form of alumina in the alumina granulating powder is α - Al2O3, and the chemical composition: Al2O3 > 98.5wt.%, Fe2O3 < 0.05wt.%, SiO2 < 0.3wt.%, Na2O < 0.3wt.%.

4. The cover brick of the electrofused zirconia corundum brick furnace according to claim 1, characterized in that, The alumina granulating powder is prepared by the following method: After grinding alumina powder with particle size 2000 mesh < particle size ≤ 325 mesh using a ball mill, add a PVA aqueous solution with a solid content of 6wt.%, grind until D50 ≤ 5μm, and then perform spray granulation using the spray drying method; the mass of the PVA aqueous solution is 3% of the mass of the alumina powder.

5. The cover brick of the electrofused zirconia corundum brick furnace according to claim 1, characterized in that, Chemical composition of high-purity calcium aluminate cement: 75wt.% < Al2O3 < 85wt.%, 25wt.% < CaO < 15wt.%.

6. The cover brick of the electrofused zirconia corundum brick furnace according to claim 1, characterized in that, The water reducing agent is a combination of HDA - 1 and HDA - 1W.

7. A method for preparing a furnace cover brick of an electrofused zirconia corundum brick furnace according to any one of claims 1-6, characterized in that, It includes the following steps: S1 Green body production: After uniformly stirring high-purity dense tabular corundum powder, alumina granulating powder, high-purity calcium aluminate cement, and water reducing agent, add water and stir until it becomes a fluid mud; pour the mud into a mold and vibrate it to form, promote air exhaust, and then statically cure to obtain a green brick; S2 Natural curing: The green brick after demolding is naturally cured for 24 - 48h to harden, obtaining a green body; S3 Drying and sintering: Put the green body into a drying oven for drying, and put the dried green body into a kiln for sintering.

8. The preparation method of the cover brick of the electrofused zirconia corundum brick furnace according to claim 7, characterized in that, The drying temperature is 100 - 120°C, and the drying time > 48h; the sintering temperature is 1280 - 1580°C, and the heat preservation time ≥ 20h.

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