Environment-friendly refractory brick for RH vacuum furnace lining and preparation method

Abstract

The invention relates to an environment-friendly refractory brick for an RH (Ruhrstahl Heraeus) vacuum furnace lining. The environment-friendly refractory brick comprises the following raw materials in percentage by weight: 45-70% of fused magnesia, 12-25% of monoclinic zirconium oxide, 3-15% of magnesium aluminate spinel micro powder and 0.05-0.1% of aluminum powder, the raw materials comprise, by weight, 3%-9% of magnesium hydroxide gel, 6%-17% of aluminum hydroxide gel, 0.35%-4.5% of a complexing magnesium-aluminum cementing agent, 0.2%-3.5% of phenolic vinyl ester, 0.52%-3.1% of polyvinyl alcohol, 0.02%-0.5% of brucite fibers and 0.02%-0.12% of boric acid; the preparation method comprises the following steps: preparing the premix; preparing a granular premix; carrying out dry mixing and stirring on the micro-powder premix, the particle premix, magnesium hydroxide gel, aluminum hydroxide gel, a complexing magnesium-aluminum cementing agent, phenolic vinyl ester, polyvinyl alcohol and boric acid; adding water to prepare a molded mixture; baking after pressure forming; and reserving. The corrosion resistance of the lining can be improved by not less than 12%, the medium permeability resistance can be improved by not less than 11%, the compressive strength is not less than 85 MPa and the volume density is not less than 3.0 g / cm < 3 > at normal temperature when the brick is not fired, and the production cost is correspondingly reduced.

Description

Technical Field

[0001] The present invention relates to a refractory material and a preparation method thereof, and more particularly to an environment-friendly refractory brick for the lining of an RH vacuum furnace and a preparation method thereof. Background Art

[0002] The RH vacuum refining technology is a simple, economical and effective secondary refining technology. Its functions have developed to include degassing and purification, oxygen blowing and decarburization, slag making for desulfurization and dephosphorization, and alloying. The refining treatment time has also increased significantly. Correspondingly, the requirements for refractory materials used in RH refining furnaces are getting higher and higher.

[0003] Under the conditions of vacuum and high temperature, the RH vacuum furnace is intermittently subjected to the splashing and scouring of molten steel, accompanied by the erosion of refining slag and temperature fluctuations. For the lining materials, especially the dipping tube, circulation tube and lower trough parts, in addition to scouring and erosion, there are also structural spalling and thermal shock spalling, which have a great impact on the service life of refractory materials. Traditional refractory materials for the lining of RH vacuum furnaces mainly use magnesia-chrome products. In the use environment of high temperature, alkaline and oxidizing atmosphere, due to their containing Cr2O3 and lacking environmental friendliness, they are gradually being replaced. For example, after retrieval:

[0004] The literature with the Chinese patent application number CN202311126806.0 discloses "A Refractory Material for the Lining of an RH Vacuum Furnace and a Preparation Method Thereof". It includes a lining matrix formed by a three-dimensional woven preform and a filler filled in the three-dimensional woven preform, and a molybdenum disilicide-silicon nitride coating doped with titanium dioxide and potassium hexatitanate whiskers on the surface of the lining matrix; the carbon-aluminum oxide fiber is obtained by successively subjecting polyacrylonitrile fiber, pitch fiber and aluminum silicate fiber with a mass ratio of 1:1:3 to stabilization treatment, carbonization treatment and graphitization treatment; the molybdenum disilicide-silicon nitride coating includes the following raw materials: molybdenum disilicide powder, silicon nitride powder, titanium dioxide powder, potassium hexatitanate whiskers, high-hydrogen-content silicone oil, divinylbenzene, chloroplatinic acid. The refractory material for the lining of the vacuum furnace prepared in this literature has not very strong thermal shock stability and spalling resistance, and adopts a multi-layer composite structure, which is relatively complex for large-scale production and has a relatively high cost, being not conducive to popularization and application.

[0005] The literature with the Chinese patent application number CN202310585028.5 discloses "A Composite Refractory for RH Refining Furnace and Its Preparation Method", which includes the following raw material components: 50 - 85wt% corundum, 5 - 20wt% chromium-aluminum alloy powder, 10 - 30wt% magnesia, and additionally 2 - 5wt% binder. After mixing the above raw materials with the binder evenly, they are pressed into shape and dried to obtain an AlCr-MgO-Al2O3 composite green body, which is fired in an air atmosphere at 1200°C - 1700°C to prepare an Al2O3 composite refractory with in-situ composite reinforcement of MgAl2O4, MgCr2O4, and MgAlON, that is, a MgAl2O4-MgCr2O4-MgAlON-Al2O3 composite refractory. Although this literature improves the erosion resistance and medium penetration resistance of the material to a certain extent, it still contains a small amount of Cr, which is polluting to the environment.

[0006] In order to develop chromium-free refractories for refining furnaces, reduce the energy consumption in the production process of refractories, improve the service life of refractories, and enhance the level of green manufacturing of steel, each steel mill has continuously tried to fire magnesia-zircon, magnesia-spinel, magnesia-spinel-titanium, and magnesia-spinel-zircon bricks and unburned magnesia-aluminum spinel bricks, etc., and has made great progress. Currently, the service life of the lower trough of the domestic RH vacuum furnace is about 400 heats. However, to further improve the service life of the refractory lining of the RH vacuum furnace and reduce costs is still a difficult problem in the industry.

[0007] Currently, in this technical field, it is very important to develop a new type of environmentally friendly refractory lining for RH vacuum furnaces with impact resistance, spalling resistance, erosion resistance, and thermal shock resistance. Summary of the Invention

[0008] The present invention aims to overcome the deficiencies in the prior art, such as environmental pollution caused by chromium content, poor erosion resistance and thermal shock resistance of the refractory lining of the RH vacuum furnace, and easy spalling. It provides an environmentally friendly refractory brick for the lining of the RH vacuum furnace and its preparation method, which can increase the erosion resistance of the lining by no less than 12%, increase the medium penetration resistance by no less than 11%, have a compressive strength ≥ 85 MPa at normal temperature without firing the brick, and a bulk density of not less than 3.0 g / cm 3 , and the production cost is correspondingly reduced.

[0009] Measures to achieve the above object:

[0010] An environment-friendly refractory brick for the lining of an RH vacuum furnace, the raw material composition and mass percentage content thereof are as follows: fused magnesia: 45-70%, monoclinic zirconia: 12-25%, magnesium aluminate spinel fine powder: 3-15%, aluminum powder: 0.05-0.1%; magnesium hydroxide gel: 3-9%, aluminum hydroxide gel: 6-17%, complex magnesium-aluminum binder: 0.35-4.5%, phenolic vinyl ester: 0.2-3.5%, polyvinyl alcohol: 0.52-3.1%, antigorite fiber: 0.02-0.5%, boric acid: 0.02-0.12%.

[0011] It is characterized in that: the mass percentage content of zirconia in the monoclinic zirconia is not less than 98%.

[0012] The particle size grade and mass percentage content in the monoclinic zirconia are as follows: the particle size is 3 to >1 mm: 38-67%, the particle size is 1 to >0.088 mm: 10-25%, and the particle size is ≤0.088 mm: 16-35%.

[0013] It is characterized in that: the mass percentage content of alumina in the magnesium aluminate spinel fine powder is not less than 75%, and the particle size is

[0014] It is characterized in that: the particle size of the aluminum powder is ≤0.074 mm.

[0015] It is characterized in that: the mass percentage content of Mg(OH)2 in the magnesium hydroxide gel is not less than 65%.

[0016] It is characterized in that: in the aluminum hydroxide gel, the mass percentage content of Al(OH)3 is not less than 78%.

[0017] It is characterized in that: the mass percentage content of the aluminum-magnesium complex in the complex magnesium-aluminum binder is not less than 90%.

[0018] A method for preparing an environment-friendly refractory brick for the lining of an RH vacuum furnace, the steps thereof are as follows:

[0019] 1) Mix the magnesium aluminate spinel fine powder and aluminum powder weighed according to the mass ratio into a premix, and after mixing for 8-15 minutes, a uniform fine powder premix is obtained;

[0020] 2) Add the fused magnesia, monoclinic zirconia, and antigorite fiber weighed according to the mass ratio to the mixture and stir, and after stirring for 5-25 minutes, a uniform granular premix is obtained;

[0021] 3) Put the fine powder premix and the granular premix into a mixer, and at the same time add the magnesium hydroxide gel, aluminum hydroxide gel, complex magnesium-aluminum binder, phenolic vinyl ester, polyvinyl alcohol, and boric acid according to the set amount for dry mixing and stirring, and the stirring time is 10-30 minutes;

[0022] 4) Add water accounting for 3 - 8% of the total mass percentage of the dry mixture prepared in step 3) to obtain a formed mixture.

[0023] 5) Subject the formed mixture prepared in step 4) to pressure forming and then baking, controlling the baking temperature at 110 - 245 °C and the baking time at 10 - 13 h.

[0024] 6) Keep in reserve.

[0025] Functions and mechanisms of each component and main processes in the present invention

[0026] The reason for adding 45 - 70% of fused magnesia in the present invention is that fused magnesia has characteristics such as high melting point, high refractoriness, good thermal stability, and corrosion resistance, and can withstand high-temperature environments, resist the erosion of slag, molten steel, etc., and extend the service life of the kiln. However, when the addition amount is less than 45%, the high-temperature type and corrosion resistance of the prepared refractory brick cannot be guaranteed; when the addition amount is higher than 70%, the composition is single and the thermal shock stability cannot be ensured.

[0027] The reason for adding 12 - 25% of monoclinic zirconia in the present invention is that monoclinic zirconia will react with alumina in the raw materials to form zircon spinel at high temperatures, thus effectively improving the corrosion resistance of the lining material. However, when the addition amount is less than 12%, the corrosion resistance cannot be guaranteed; when the addition amount is higher than 25%, the strength and high-temperature resistance cannot be guaranteed. The reason for adding a small amount of aluminum hydroxide gel and magnesium hydroxide gel in the present invention is that they can not only act as binders, in-situ react to form magnesium aluminate spinel whiskers at high temperatures, improve the pore structure, reduce the pore diameter, improve the corrosion resistance and anti-media penetration performance of the material, but also improve the thermal shock stability and corrosion resistance of the inner lining refractory material.

[0028] The reason for adding polyvinyl alcohol and phenolic vinyl ester in the present invention is that they can form a porous carbon skeleton after decomposition to guide the directional growth of whiskers. However, when the addition amount is less than the set value, too little porous skeleton is generated and the whisker formation cannot be fully guided; when the addition amount is higher than the set value, the molecular weight of the organic polymer is too large and the denseness and strength of the material cannot be guaranteed at high temperatures.

[0029] The reason for adding a small amount of complex magnesium-aluminum binder in the present invention is that the complex magnesium-aluminum binder contains both organic groups and inorganic structures, has both the flexibility of organic materials and the high-temperature resistance of inorganic materials, and helps to improve the high-temperature resistance and spalling resistance of the refractory material as a binder. However, when the addition amount is less than the set value, the binding effect of the binder cannot be achieved; when the addition amount is higher than the set value, too much binder decomposes at high temperatures, which affects the strength of the refractory brick.

[0030] The reason for adding antigorite fibers to the present invention is that at high temperatures, they can improve the toughness and high-temperature strength of the material. However, when the addition amount is lower than the set value, it is not conducive to improving the toughness of the material and affects the thermal shock stability of the refractory brick; when the addition amount is higher than the set value, it affects the high-temperature strength of the refractory brick.

[0031] Compared with the prior art, the present invention can increase the erosion resistance of the inner lining by no less than 12%, increase the medium penetration resistance by no less than 11%, the compressive strength at normal temperature without firing the brick is ≥85 MPa, and the bulk density is not less than 3.0 g / cm 3 and the production cost is correspondingly reduced. Detailed implementation method

[0032] The present invention will be described in detail below:

[0033] Example 1

[0034] An environmentally friendly refractory brick for the inner lining of an RH vacuum furnace, the raw material composition and mass percentage content are: fused magnesia: 65%, monoclinic zirconia: 15%, magnesia-alumina spinel fine powder: 6%, aluminum powder: 0.11%; magnesium hydroxide gel: 4%, aluminum hydroxide gel: 7%, complex magnesium-aluminum binder: 0.5%, phenolic vinyl ester: 0.4%, polyvinyl alcohol: 1.30%, antigorite fiber: 0.6%, boric acid: 0.09%;

[0035] The mass percentage content of MgO in the fused magnesia is 98%; the particle size grade and mass percentage content in the fused magnesia are: 60% with a particle size of 5 to 3 mm, 17% with a particle size less than 3 to ≥1 mm, and 23% with a particle size <1 mm;

[0036] The mass percentage content of zirconia in the monoclinic zirconia is 98.2%; the particle size grade and mass percentage content in the monoclinic zirconia are: 43% with a particle size of 3 to >1 mm, 22% with a particle size of 1 to >0.088 mm, and 35% with a particle size ≤0.088 mm;

[0037] The mass percentage content of alumina in the magnesia-alumina spinel fine powder is 76%, and the particle size is

[0038] The particle size of the aluminum powder is ≤0.074 mm;

[0039] The mass percentage content of Mg(OH)2 in the magnesium hydroxide gel is 65.6%;

[0040] In the aluminum hydroxide gel, the mass percentage content of Al(OH)3 is 79%;

[0041] The mass percentage content of the aluminum-magnesium complex in the complex magnesium-aluminum binder is 91.5%;

[0042] Preparation method:

[0043] 1) Weigh the magnesia-alumina spinel fine powder and aluminum powder according to the mass ratio: 6%, 0.11%, and mix them into a premix. After 15 minutes of mixing, a uniform fine powder premix is obtained;

[0044] 2) Weigh the fused magnesia: 65%, monoclinic zirconia: 15%, and brucite fiber 0.6% according to the mass ratio, add them to the mixture and stir. After 16 minutes of stirring, a uniform granular premix is obtained;

[0045] 3) Put the fine powder premix and the granular premix in a mixer, and at the same time add magnesium hydroxide gel: 4%, aluminum hydroxide gel: 7%, complex magnesium-aluminum binder: 0.5%, phenolic vinyl ester: 0.4%, polyvinyl alcohol: 1.30%, boric acid: 0.09% according to the set amount for dry mixing and stirring. The stirring time is 22 minutes;

[0046] 4) Add water according to 5.8% of the total mass percentage of the dry mix in step 3) to obtain a molding mix;

[0047] 5) Press the molding mix obtained in step 4) under a pressure of 800t, then bake it. The baking temperature is 146°C and the baking time is 12h;

[0048] 6) Keep it for standby.

[0049] After testing, the unfired brick in this example has a compressive strength of 110 MPa at room temperature, a bulk density of 3.36 g / cm 3 , the erosion resistance is increased by 19.4%, and the resistance to medium penetration is increased by 17.2%.

[0050] Example 2

[0051] An environment-friendly refractory brick for the lining of an RH vacuum furnace, the raw material composition and mass percentage content thereof are: fused magnesia: 68%, monoclinic zirconia: 13%, magnesia-alumina spinel fine powder: 5%, aluminum powder: 0.07%; magnesium hydroxide gel: 4.5%, aluminum hydroxide gel: 6.5%, complex magnesium-aluminum binder: 0.51%, phenolic vinyl ester: 1.4%, polyvinyl alcohol: 0.8%, brucite fiber: 0.12%, boric acid: 0.10%;

[0052] The mass percentage content of MgO in the fused magnesia is 98.3%; the particle size grade and mass percentage content in the fused magnesia are: those with a particle size of 5 to 3 mm: 58%, those with a particle size less than 3 to ≥1 mm: 16%, those with a particle size <1 mm: 26%;

[0053] The mass percentage content of zirconia in the monoclinic zirconia is 98.4%; the particle size grade and mass percentage content in the monoclinic zirconia are as follows: for particle size from 3 to >1 mm: 48%, for particle size from 1 to >0.088 mm: 24%, and for particle size ≤0.088 mm: 28%;

[0054] The mass percentage content of alumina in the magnesium aluminate spinel fine powder is 83%, and the particle size is in

[0055] The particle size of the aluminum powder is ≤0.074 mm;

[0056] The mass percentage content of Mg(OH)₂ in the magnesium hydroxide gel is 66.8%;

[0057] In the aluminum hydroxide gel, the mass percentage content of Al(OH)₃ is 83%;

[0058] The mass percentage content of the aluminum-magnesium complex in the complex magnesium-aluminum binder is 93.5%;

[0059] Preparation method:

[0060] 1) Mix the magnesium aluminate spinel fine powder weighed according to the mass ratio: 5% and the aluminum powder: 0.07% to form a premix. After mixing for 10 min, a uniform fine powder premix is obtained;

[0061] 2) Add the fused magnesia weighed according to the mass ratio: 68%, the monoclinic zirconia: 13%, and the antigorite fiber 0.12% to the mixture and stir. After stirring for 18 min, a uniform particle premix is obtained;

[0062] 3) Add the fine powder premix and the particle premix to a mixer, and simultaneously add the magnesium hydroxide gel: 4.5%, the aluminum hydroxide gel: 6.5%, the complex magnesium-aluminum binder: 0.51%, the phenolic vinyl ester: 1.4%, the polyvinyl alcohol: 0.8%, and the boric acid: 0.10% according to the set amounts for dry mixing and stirring. The stirring time is 25 min;

[0063] 4) Add water according to 5.3% of the total mass percentage of the dry mix in step 3) to obtain a molding mix;

[0064] 5) Press the molding mix obtained in step 4) under a pressure of 800 t, then bake it. The baking temperature is 115 °C and the baking time is 13 h;

[0065] 6) Set aside for later use.

[0066] After testing, the unfired brick in this example has a compressive strength of 101 MPa at room temperature, a bulk density of 3.29 g / cm 3 , the erosion resistance is improved by 18.9%, and the resistance to medium penetration is improved by 17.8%.

[0067] Example 3

[0068] An environmentally friendly refractory brick for the lining of an RH vacuum furnace, the raw material composition and mass percentage content thereof are: fused magnesia: 60%, monoclinic zirconia: 12%, magnesia-alumina spinel fine powder: 4%, aluminum powder: 0.1%; magnesium hydroxide gel: 5%, aluminum hydroxide gel: 8%, complex magnesium-aluminum binder: 4%, phenolic vinyl ester: 3.45%, polyvinyl alcohol: 3%, antigorite fiber: 0.4%, boric acid: 0.05%;

[0069] The mass percentage content of MgO in the fused magnesia is 97%; the particle size grade and mass percentage content in the fused magnesia are: those with a particle size of 5 to 3 mm: 64%, those with a particle size less than 3 to ≥1 mm: 16%, those with a particle size <1 mm: 20%;

[0070] The mass percentage content of zirconia in the monoclinic zirconia is 98.1%; the particle size grade and mass percentage content in the monoclinic zirconia are: those with a particle size of 3 to >1 mm: 41%, those with a particle size of 1 to >0.088 mm: 23%, those with a particle size ≤0.088 mm: 36%;

[0071] The mass percentage content of alumina in the magnesia-alumina spinel fine powder is 78%, and the particle size is

[0072] The particle size of the aluminum powder ≤0.074 mm;

[0073] The mass percentage content of Mg(OH)₂ in the magnesium hydroxide gel is 68.6%;

[0074] In the aluminum hydroxide gel, the mass percentage content of Al(OH)₃ is 83%;

[0075] The mass percentage content of the aluminum-magnesium complex in the complex magnesium-aluminum binder is 90.8%;

[0076] Preparation method:

[0077] 1) Mix the magnesia-alumina spinel fine powder: 4% and aluminum powder: 0.1% weighed according to the mass ratio to form a premix, and after 8 minutes of mixing, a uniform fine powder premix is obtained;

[0078] 2) Add the fused magnesia: 60%, monoclinic zirconia: 12%, and antigorite fiber 0.4% weighed according to the mass ratio and mix and stir. After 23 minutes of stirring, a uniform particle premix is obtained;

[0079] 3) Put the fine powder premix and the particle premix in a mixer, and at the same time add the magnesium hydroxide gel: 5%, aluminum hydroxide gel: 8%, complex magnesium-aluminum binder: 4%, phenolic vinyl ester:

[0080] 3.45%, polyvinyl alcohol: 3%, boric acid: 0.05% are dry-mixed and stirred for 13 minutes.

[0081] 4) Add water according to 3.4% of the total mass percentage of the dry mixture in step 3) to obtain a molding mixture.

[0082] 5) Press the molding mixture obtained in step 4) under a pressure of 800 t and then bake it. The baking temperature is 205 °C and the baking time is 11 h.

[0083] 6) Keep it in reserve.

[0084] After testing, the unburned bricks in this example have a compressive strength of 90 MPa at room temperature and a bulk density of 3.12 g / cm 3 , the erosion resistance is improved by 16.4%, and the resistance to medium penetration is improved by 12.7%.

[0085] Example 4

[0086] An environmentally friendly refractory brick for the lining of an RH vacuum furnace, the raw material composition and mass percentage content are: fused magnesia: 46%, monoclinic zirconia: 24%, magnesia-alumina spinel fine powder: 13%, aluminum powder: 0.06%; magnesium hydroxide gel: 8%, aluminum hydroxide gel: 6%, complex magnesium-aluminum binder: 0.76%, phenolic vinyl ester: 0.61%, polyvinyl alcohol: 1.5%, antigorite fiber: 0.04%, boric acid: 0.03%.

[0087] The mass percentage content of MgO in the fused magnesia is 99.2%; the particle size grade and mass percentage content in the fused magnesia are: 56% with a particle size of 5 to 3 mm, 19% with a particle size less than 3 to ≥1 mm, and 25% with a particle size <1 mm.

[0088] The mass percentage content of zirconia in the monoclinic zirconia is 97.2%; the particle size grade and mass percentage content in the monoclinic zirconia are: 46% with a particle size of 3 to >1 mm, 23% with a particle size of 1 to >0.088 mm, and 31% with a particle size ≤0.088 mm.

[0089] The mass percentage content of alumina in the magnesia-alumina spinel fine powder is 76%, and the particle size is

[0090] The particle size of the aluminum powder is ≤0.074 mm.

[0091] The mass percentage content of Mg(OH)2 in the magnesium hydroxide gel is 67.3%.

[0092] In the aluminum hydroxide gel, the mass percentage content of Al(OH)3 is 82.4%.

[0093] The mass percentage of the aluminum-magnesium complex in the complex magnesium-aluminum binder is 93.6%.

[0094] Preparation method:

[0095] 1) Weigh magnesium-aluminum spinel micropowder: 13% and aluminum powder: 0.06% according to the mass ratio and mix them into a premix. After 13 minutes of mixing, a uniform micropowder premix is obtained.

[0096] 2) Add fused magnesia: 46%, monoclinic zirconia: 24%, and brucite fiber 0.04% weighed according to the mass ratio and mix and stir. After 9 minutes of stirring, a uniform granular premix is obtained.

[0097] 3) Put the micropowder premix and the granular premix into a mixer and simultaneously add magnesium hydroxide gel: 8%, aluminum hydroxide gel: 6%, complex magnesium-aluminum binder: 0.76%, phenolic vinyl ester: 0.61%, polyvinyl alcohol: 1.5%, and boric acid: 0.03% according to the set amount for dry mixing and stirring. The stirring time is 28 minutes.

[0098] 4) Add water according to 5.8% of the total mass percentage of the dry mix in step 3) to obtain a molding mix.

[0099] 5) Press the molding mix obtained in step 4) under a pressure of 800 t to form and then bake it. The baking temperature is 240 °C and the baking time is 10 h.

[0100] 6) Set aside.

[0101] After testing, the unfired brick in this example has a compressive strength of 86 MPa at room temperature, a bulk density of 3.01 g / cm 3 , the erosion resistance is improved by 15.2%, and the resistance to medium penetration is improved by 11.3%.

[0102] This specific embodiment is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. An environment-friendly refractory brick for the lining of an RH vacuum furnace, the raw material composition and mass percentage content of which are as follows: fused magnesia: 45-70%, monoclinic zirconia: 12-25%, magnesia-alumina spinel fine powder: 3-15%, aluminum powder: 0.05-0.1%; magnesium hydroxide gel: 3-9%, aluminum hydroxide gel: 6-17%, complex magnesia-alumina binder: 0.35-4.5%, phenolic vinyl ester: 0.2-3.5%, polyvinyl alcohol: 0.52-3.1%, antigorite fiber: 0.02-0.5%, boric acid: 0.02-0.12%.

2. The environmentally friendly refractory brick for the lining of an RH vacuum furnace according to claim 1, wherein: The mass percentage content of MgO in the fused magnesia is not less than 97%; The particle size grade and mass percentage content in the fused magnesia are as follows: those with a particle size of 5 to 3 mm: 40-65%, those with a particle size less than 3 to ≥1 mm: 5-22%, those with a particle size <1 mm: 18-35%.

3. The environmentally friendly refractory brick for the lining of an RH vacuum furnace according to claim 1, characterized in that: The mass percentage content of zirconia in the monoclinic zirconia is not less than 98%; Those with a particle size of 3 to >1 mm: 38-67%, those with a particle size of 1 to >0.088 mm: 10-25%, those with a particle size ≤0.088 mm: 16-35%.

4. The environmentally friendly refractory brick for the lining of an RH vacuum furnace according to claim 1, characterized in that: The mass percentage of alumina in the magnesia-alumina spinel fine powder is not less than 75%, and the particle size is in 5. The environmentally friendly refractory brick for the inner lining of an RH vacuum furnace according to claim 1, characterized in that: The particle size of the aluminum powder is ≤0.074 mm.

6. The environmentally friendly refractory brick for the inner lining of an RH vacuum furnace according to claim 1, characterized in that: The mass percentage content of Mg(OH)₂ in the magnesium hydroxide gel is not less than 65%.

7. The environmentally friendly refractory brick for the inner lining of an RH vacuum furnace according to claim 1, characterized in that: In the aluminum hydroxide gel, the mass percentage content of Al(OH)₃ is not less than 78%.

8. The environmentally friendly refractory brick for the inner lining of an RH vacuum furnace according to claim 1, characterized in that: The mass percentage content of the aluminum-magnesium complex in the complex magnesia-alumina binder is not less than 90%.

9. A method for preparing an environment-friendly refractory brick for the lining of an RH vacuum furnace as described in claim 1, the steps of which are as follows: 1) Mix the magnesia-alumina spinel fine powder and aluminum powder weighed according to the mass ratio into a premix, and after mixing for 8-15 minutes, a uniform fine powder premix is obtained; 2) Add the fused magnesia, monoclinic zirconia, and antigorite fiber weighed according to the mass ratio to the mixture and stir. After stirring for 5-25 minutes, a uniform particle premix is obtained; 3) Put the fine powder premix and the particle premix into a mixer, and at the same time add magnesium hydroxide gel, aluminum hydroxide gel, complex magnesia-alumina binder, phenolic vinyl ester, polyvinyl alcohol, and boric acid according to the set amount for dry mixing and stirring, and the stirring time is 10-30 minutes; 4) Add water according to 3-8% of the total mass percentage of the dry mix prepared in step 3) to obtain a molding mix; 5) Subject the molding mix prepared in step 4) to pressure molding and then baking, control the baking temperature at 110- 245 °C, and the baking time is 10-13 hours; 6) Reserve for use.