Unfired brick and method for producing the same

Abstract

To provide an unfired brick which contributes to the reduction of carbon dioxide emission and has excellent hot characteristics such as high temperature strength and thermal spalling resistance, and to provide a method for producing the unfired brick.SOLUTION: A first step of adding and kneading 1 to 2 mass% of a sodium aluminate aqueous solution to 100% of a refractory raw material containing magnesia or magnesia and spinel as main components and 1 to 2 mass% of basic aluminum lactate, and then obtaining a molded body having an arbitrary shape, and a second step of drying the molded body obtained in the first step to obtain a dried body, wherein a phosphate is added to the main component to which the sodium aluminate aqueous solution is added in the first step, A content of phosphorus (P) in the dried body is from 0.2 to 0.6% by mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a refractory material that can be used as a lining or the like for industrial furnaces such as those used in iron and steel making, non-ferrous metal smelting, lime making, cement making, and glass making. [Background technology]

[0002] Magnesia spinel bricks have excellent heat spalling resistance and volume stability, and are mainly used in rotary kilns that burn cement and lime. Magnesia spinel bricks are fired refractories that are manufactured through a firing process, but from the perspective of reducing carbon dioxide emissions, unfired refractories that do not undergo a firing process are superior.

[0003] For example, Patent Document 1 (JP Patent Publication No. 9-87007) proposes "a magnesia unfired brick characterized by containing 0.5 to 10% by weight of a metal powder containing aluminum, 0.5 to 3% by weight of a resin containing carbon converted to fixed carbon, and the remainder being a refractory material mainly composed of magnesia," with the objective of "generating spinel around magnesia particles and forming a structure in which the magnesia particles are bound by the secondarily generated spinel in order to improve slag penetration into magnesia bricks with excellent slag corrosion resistance."

[0004] In the magnesia unfired brick described in Patent Document 1, aluminum reacts with carbon in the resin at temperatures around 800°C to form aluminum carbide. As the temperature rises further, the aluminum carbide reacts with CO in the atmosphere inside the brick to form alumina and carbon. Alumina reacts with magnesia, the brick's raw material, to form spinel. This spinel is formed at temperatures around 1000°C. Therefore, when used as the lining of a molten metal vessel, the working surface will have a structure primarily composed of magnesia and secondary spinel. Because this secondary spinel is highly reactive, when it comes into contact with slag, components such as FeO and MnO in the slag are dissolved in the spinel, preventing its penetration into the brick's interior. Furthermore, CaO in the slag is trapped by the alumina before spinel formation as a CaO·Al2O3 compound, preventing its penetration into the brick's interior.

[0005] Furthermore, Patent Document 2 (JP 2000-272956 A) proposes an unfired alumina-magnesia brick with a composition of 94.7% by weight of Al2O3, 5.3% by weight of MgO, 80% by weight of electrofused alumina and 10% by weight of calcined alumina as alumina raw materials, 5% by weight of electrofused magnesia with a particle size of 3.36 to 1.0 mm, and 5% by weight of electrofused spinel with a particle size of 1.0 mm or less as magnesia raw materials, with the objective of providing an unfired refractory material that has good corrosion resistance and does not crack, peel, or open joints when used to line the ladle of a secondary refining furnace.

[0006] In the unfired alumina-magnesia brick described in Patent Document 2, it is said that the corrosion resistance, expansion amount, and compressive strength can be controlled by adjusting the magnesia content within an appropriate range, selecting magnesia and spinel as magnesia supply raw materials, and selecting their blending ratio and particle size. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-87007 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-272956 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the unfired magnesia brick described in Patent Document 1 and the unfired alumina-magnesia brick described in Patent Document 2 are primarily intended to improve corrosion resistance, and it is difficult to say that their hot properties, such as high-temperature strength, are sufficient.

[0009] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide an unfired brick which contributes to reducing carbon dioxide emissions and which has excellent hot properties such as high-temperature strength and heat spalling resistance, and a method for producing the same. [Means for solving the problem]

[0010] In order to achieve the above object, the present inventors have conducted extensive research into unburned bricks and methods for producing the same, and as a result have found that it is extremely effective to incorporate basic aluminum lactate into the refractory raw material, add an aqueous solution of sodium aluminate during kneading, and also add a phosphate, thereby arriving at the present invention.

[0011] That is, the present invention provides: a first step of adding 1 to 2 mass% of an aqueous solution of sodium aluminate to 100% of a refractory raw material containing magnesia or magnesia and spinel as a main component and containing 1 to 2 mass% of basic aluminum lactate, and kneading the mixture to obtain a molded body of any desired shape; a second step of drying the molded body obtained in the first step to obtain a dried body, In the first step, a phosphate is added to the main component to which the aqueous sodium aluminate solution has been added, so that the phosphorus (P) content of the dry product is 0.2 to 0.6 mass%; The present invention provides a method for producing unburned bricks, characterized by the above.

[0012] In the past, no unburned bricks that have not undergone a firing process have been found that exhibit high strength, excellent heat spalling resistance, and volume stability, as well as high hot strength. In contrast, the unburned bricks of the present invention can be imparted with all of these properties by mixing appropriate amounts of basic aluminum lactate, an aqueous sodium aluminate solution, and a phosphate.

[0013] More specifically, mixing appropriate amounts of basic aluminum lactate and sodium aluminate causes gelation, producing aluminum lactate. Aluminum lactate has a moisturizing effect, preventing the clay from drying out and allowing for the production of a good molded body (first step). Furthermore, the addition of phosphate forms rhenanite (CaNaPO4: melting point 1830°C) as a binding phase, which has a relatively high melting point. This gives the unfired bricks obtained in the second step high hot strength.

[0014] Here, by setting the phosphorus (P) content of the dried product after the second process to 0.2% by mass or more, the hot strength improvement effect due to the formation of renanit can be sufficiently obtained. On the other hand, by setting the phosphorus (P) content of the dried product after the second process to 0.6% by mass or less, the effect of adding phosphate on the gelation of basic aluminum lactate can be reduced. Furthermore, by setting the phosphorus (P) content to 0.6% by mass or less, the sodium content increased by adding phosphate increases, and the formation of low-melting-point substances can be suppressed.

[0015] In the unfired brick of the present invention, it is preferable to add at least one of sodium phosphate glass, monocalcium phosphate, potassium phosphate glass, and aluminum phosphate as the phosphate, which can reduce the effect of the addition of the phosphate on the gelation of basic aluminum lactate and more reliably obtain the effect of improving hot strength by forming rhenanite.

[0016] In the method for producing unburned bricks of the present invention, it is preferable that the Al2O3 solid content concentration of the aqueous sodium aluminate solution is 10 to 20 mass %.

[0017] By adding an aqueous sodium aluminate solution with an Al2O3 solids concentration of 10 to 20 mass % in an outer percentage of 1 to 2 mass % to 100% refractory raw material containing basic aluminum lactate, lactate salts such as sodium lactate decompose during the heating process when used in an actual furnace, lactic acid evaporates, and the highly active aluminum reacts with magnesia, allowing the reaction between aluminum and magnesia to form a spinel sufficiently and smoothly.

[0018] Furthermore, the drying temperature in the second step is preferably 200 to 300° C. By setting the drying temperature to 200° C. or higher, it is possible to prevent the decomposition of sodium lactate and lactic acid while allowing the drying to proceed sufficiently and smoothly, and by setting the drying temperature to 300° C. or lower, it is possible to prevent the strength of the unburned bricks from decreasing and to prevent an increase in carbon dioxide emissions associated with the drying step.

[0019] The present invention also provides The main component is magnesia or magnesia and spinel, The phosphorus (P) content is 0.2 to 0.6 mass%; Also provided is an unfired brick characterized by:

[0020] The unfired brick of the present invention is preferably obtained by the unfired brick manufacturing method of the present invention, and by setting the phosphorus (P) content to 0.2 to 0.6 mass%, the unfired brick has high strength, high-temperature strength, and excellent heat spalling resistance. The main components are magnesia or magnesia and spinel, and there are no particular restrictions on the ratio of magnesia to alumina as long as magnesia is contained.

[0021] In addition, it is preferable that rhenanite (CaNaPO4) is formed in the unburned brick of the present invention. Rhenanite, which has a high melting point, serves as a binder phase, thereby imparting excellent high-temperature strength and heat spalling resistance to the unburned brick.

[0022] The unburned brick of the present invention preferably has a bending strength of 10 MPa or more at 1200°C. Having a bending strength of 10 MPa or more at 1200°C, the brick can be suitably used as the lining of industrial furnaces in iron and steel manufacturing, non-ferrous metal smelting, lime manufacturing, cement manufacturing, glass manufacturing, etc.

[0023] The method for producing unfired bricks of the present invention produces dense green bodies, and drying the green bodies at an appropriate temperature leaves lactate salts such as sodium lactate undecomposed. As a result, during the heating process up to 1200°C, lactate salts such as sodium lactate decompose and lactic acid evaporates, allowing highly active aluminum to react with magnesia, allowing the reaction between aluminum and magnesia to form a spinel complex sufficiently and smoothly. In addition, the addition of phosphoric acid turns rhenanite, which has a high melting point, into a binder phase, allowing the unfired bricks to exhibit high hot strength.

[0024] Furthermore, the unburned brick of the present invention preferably has a compressive strength of 100 MPa or more. Having a high compressive strength at room temperature in addition to excellent hot strength can improve the reliability and durability of the unburned brick. [Effects of the Invention]

[0025] According to the present invention, it is possible to provide an unfired brick that contributes to reducing carbon dioxide emissions and has excellent hot properties such as high-temperature strength and heat spalling resistance, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0026] Representative embodiments of the unburned brick and the method for producing the same of the present invention will be described in detail below, but the present invention is not limited to these.

[0027] 1. Manufacturing method of unburned bricks The method for producing unfired bricks of the present invention comprises the following steps: a first step of adding 1 to 2 mass% of an aqueous solution of sodium aluminate to 100% of a refractory raw material containing magnesia or magnesia and spinel as the main component and 1 to 2 mass% of basic aluminum lactate, kneading the mixture, and then obtaining a molded body of any shape; and a second step of drying the molded body obtained in the first step to obtain a dried body, wherein in the first step, a phosphate is added to the main component containing the aqueous solution of sodium aluminate, so that the phosphorus (P) content of the dried body is 0.2 to 0.6 mass%. Each step will be described in detail below.

[0028] (1) First step The first step is a step for obtaining a molded body of any shape by adding 1 to 2 mass% of an aqueous sodium aluminate solution to 100% of a refractory raw material mainly composed of magnesia or magnesia and spinel and containing 1 to 2 mass% of basic aluminum lactate, and kneading the mixture.The greatest feature of the method for producing an unburned brick of the present invention is that in the first step, a phosphate is further added to the main component to which the aqueous sodium aluminate solution has been added.

[0029] (1-1) Main component The refractory raw material serving as the main component can be magnesia particles or magnesia particles and spinel particles. The mixing ratio of magnesia particles to spinel particles is not particularly limited as long as it does not impair the effects of the present invention, and may be appropriately adjusted depending on the desired properties of the unfired brick. Alternatively, magnesia particles may be used as the main component without using spinel particles.

[0030] It is preferable to mix raw materials of magnesia particles and spinel particles having different particle sizes, as this can impart good heat spalling resistance to the unfired brick.

[0031] The type of magnesia raw material is not particularly limited as long as it does not impair the effects of the present invention, but it is possible to use, for example, conventionally known electrofused magnesia, seawater magnesia, natural magnesia, etc. Furthermore, with regard to the purity of the magnesia raw material, it is preferable to use one with a high purity of 95% by weight or more in order to avoid a decrease in corrosion resistance due to impurities and the effects of over-sintering.

[0032] The type of spinel raw material and the ratio of MgO to Al2O3 are not particularly limited as long as they do not impair the effects of the present invention. For example, conventionally known alumina-magnesia spinel (MgAl2O4) or magnesia-magnesia spinel can be used. As with the magnesia raw material, it is preferable to use a spinel raw material with a high purity of 95% by weight or more. The spinel raw material is not particularly limited, and electrofused spinel, calcined spinel, etc. can be used.

[0033] (1-2) Essential additives (binders) As an essential additive, 1 to 2 mass% of basic aluminum lactate is added. In addition, 1 to 2 mass% of an aqueous solution of sodium aluminate is added to 100% of the refractory raw material, which is mainly composed of magnesia and spinel and contains 1 to 2 mass% of basic aluminum lactate.

[0034] The Al2O3 solid content concentration of the sodium aluminate aqueous solution is preferably 10 to 20 mass%, more preferably 14 to 18 mass%. By adding an aqueous sodium aluminate solution having an Al2O3 solid content concentration of 10 to 20 mass%, with an outer percentage of 1 to 2 mass%, to 100% of a refractory raw material containing 1 to 2 mass% basic aluminum lactate, the reaction between alumina and magnesia to form a spinel can be sufficiently and smoothly promoted.

[0035] Furthermore, in order to utilize rhenanite, which has a high melting point, as a binder phase, a phosphate is added to the main component to which the sodium aluminate aqueous solution has been added. The type of phosphate to be added is not particularly limited as long as it does not impair the effects of the present invention, but it is preferable to add at least one of sodium phosphate glass, monocalcium phosphate, potassium phosphate glass, and aluminum phosphate. Here, the amount of phosphate added may be adjusted so that the phosphorus (P) content in the final unburned brick is 0.2 to 0.6 mass%.

[0036] (1-3) Optional additives For example, 1 to 3 mass% of sorbitol can be added as a molding aid to 100% of the refractory raw material. Sorbitol, primarily composed of D-sorbitol and represented by the formula HOCH2(CHOH)4CH2OH, is a powder that readily dissolves in water and is generally used as a surfactant or food additive. Adding sorbitol improves the packing properties of the kneaded clay and the lubrication between particles, reduces changes in the clay over time, and inhibits slaking. It is also non-toxic and can produce compacts with high molding density. Additives used as molding aids for fired bricks, such as bittern and magnesium sulfate, can also be used.

[0037] In addition, various other conventionally known optional components such as alumina, zirconia and iron oxide used in magnesia bricks and magnesia-spinel bricks may be added as long as they do not impair the effects of the present invention.

[0038] (1-4) Mixing and molding The refractory raw material as the main component, the essential additive components, and the optional additive components are kneaded and formed into a desired shape. The kneading and forming methods are not particularly limited, and various conventional methods used in the production of refractories can be applied.

[0039] In the method for producing unburned bricks of the present invention, gelation occurs by mixing appropriate amounts of sodium aluminate and basic aluminum lactate, resulting in the production of aluminum lactate. Aluminum lactate has a moisturizing effect, which prevents the clay from drying out, making it possible to obtain a good molded body. Furthermore, adding a phosphate in an amount that results in a phosphorus (P) content of 0.2 to 0.6 mass% in the final unburned bricks does not inhibit gelation caused by mixing appropriate amounts of sodium aluminate and basic aluminum lactate.

[0040] (2) Second process The second step is a step for drying the molded body obtained in the first step to obtain an unfired brick.

[0041] If the molded body obtained in the first step is dried at an appropriate temperature, lactate salts such as sodium lactate remain without decomposition, and a decrease in strength can be suppressed.

[0042] The drying temperature is preferably 200 to 300°C. By setting the drying temperature to 200°C or higher, excess water is evaporated, resulting in dehydration and increased strength. Furthermore, by setting the drying temperature to 300°C or lower, lactate salts such as sodium lactate remain without decomposition, preventing a decrease in strength and preventing an increase in carbon dioxide emissions associated with the drying process.

[0043] The method for drying the molded body is not particularly limited, and various conventionally known methods used in the production of unfired refractories can be applied.

[0044] The method for producing unburned bricks of the present invention does not preclude the unburned bricks from being fired under appropriate conditions after drying.

[0045] 2. Unburned bricks The unburned brick of the present invention can be suitably obtained by the unburned brick manufacturing method of the present invention, and is characterized by containing magnesia or magnesia and spinel as main components and having a phosphorus (P) content of 0.2 to 0.6 mass %.

[0046] The method for measuring the phosphorus (P) content in the unburned brick is not particularly limited, and various conventionally known measuring methods can be used, such as fluorescent X-ray analysis, EPMA measurement, and SEM-EDS measurement.

[0047] Furthermore, it is preferable that rhenanite (CaNaPO4) is formed in the unburned brick of the present invention. Rhenanite, which has a high melting point, serves as a binder phase, thereby imparting excellent high-temperature strength and heat spalling resistance to the unburned brick. The method for confirming the formation of rhenanite is not particularly limited, and examples thereof include X-ray diffraction measurement and selected area electron diffraction in transmission electron microscope observation.

[0048] The unburned brick of the present invention preferably has a bending strength of 10 MPa or more at 1200°C. Having a bending strength of 10 MPa or more at 1200°C, the brick can be suitably used as the lining of industrial furnaces in iron and steel manufacturing, non-ferrous metal smelting, lime manufacturing, cement manufacturing, glass manufacturing, etc.

[0049] The method for measuring the bending strength of an unfired brick at 1200°C is not particularly limited, and various conventionally known measuring methods can be used. For example, a three-point bending test can be carried out using a hot bending tester in an air atmosphere at 1200°C. The bending strength of the unfired brick at 1200°C is preferably 10 MPa or more, and more preferably 11 MPa or more.

[0050] The unburned brick of the present invention preferably has a compressive strength of 100 MPa or more. Having a high compressive strength at room temperature in addition to excellent hot strength improves the reliability and durability of the unburned brick. The compressive strength is more preferably 110 MPa or more, and most preferably 120 MPa or more.

[0051] Furthermore, the unfired brick of the present invention has excellent corrosion resistance and structural embrittlement resistance. Specifically, compared with a brick having the same composition but not containing 0.2 to 0.6 mass % of phosphorus (P) (a brick in which rhenanite is not formed), the unfired brick of the present invention has corrosion resistance and structural embrittlement resistance equal to or greater than those, and further has extremely excellent hot strength and hot spalling resistance.

[0052] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. [Example]

[0053] Example The raw materials were prepared in the proportions shown in Table 1 as Examples 1 to 5, kneaded in a high-speed mixer, and molded into a 230 x 230 x 85 mm shape using a hydraulic press. A batch-type dryer was used for drying, and the bricks were kept at 200 to 320°C for 8 hours to obtain unburned bricks representing the examples of the present invention. The values ​​in Table 1 are shown in mass %, and the amounts of various phosphates, aqueous sodium aluminate solutions, aqueous sorbitol solutions, and water added are shown as outer multipliers relative to the total amount of magnesia clinker, spinel clinker, and basic aluminum lactate. The particle size of the magnesia clinker and spinel clinker and the Al2O3 solids concentration (mass %) of the aqueous sodium aluminate solution are also shown.

[0054] Comparative Example Unfired bricks were obtained in the same manner as in the Examples, except that the raw materials were adjusted to the proportions shown in Comparative Examples 1 to 6 in Table 1. Only Comparative Example 1 was fired in a tunnel kiln at a maximum temperature of 1750±10°C.

[0055] [Table 1]

[0056] [evaluation] The unfired bricks obtained as examples and comparative examples were evaluated for corrosion resistance, compressive strength, hot strength, heat spalling resistance, and microstructural embrittlement resistance. In addition, the phosphorus (P) content of each unfired brick was measured.

[0057] (1) Corrosion resistance Corrosion resistance was evaluated by a rotating drum corrosion test. The test method was as follows: Test specimens were lined inside a drum, and the test was conducted at 1750±50°C using an oxygen-propane burner. A 5:1 mixture of Portland cement and potassium sulfate was added as the corrosion material. After the test was held for 6 hours with the corrosion material replaced every hour, the specimen was cut perpendicular to the running surface, and the amount of wear was measured at 8 points to calculate the average amount of wear. The average amount of wear was expressed as an index, with the amount of wear in Comparative Example 1 being 100. The results are shown in Table 2. A smaller index indicates better corrosion resistance; an index of 105 or less was evaluated as ◯, an index of more than 105 but less than 115 was evaluated as △, and an index of 115 or more was evaluated as ×.

[0058] (2) Compressive strength The compressive strength of a 60mm x 60mm x 60mm specimen was measured using an Amsler strength testing device. The results are shown in Table 2. A rating of 0 indicates a value of 100MPa or more, △ indicates a value of 70MPa or more but less than 100MPa, and × indicates a value of less than 70MPa.

[0059] (3) Hot strength The hot strength of a 30mm x 30mm x 120mm test piece was measured using a hot bending tester. Three-point bending (support distance 80mm) was performed in an air atmosphere at 1200°C, and the results are shown in Table 2. A hot bending strength of 10MPa or more was evaluated as ◯, a hot bending strength of 5MPa or more but less than 10MPa as △, and a hot bending strength of less than 5MPa as ×.

[0060] (4) Heat spalling resistance Heat spalling resistance was evaluated using the air cooling method based on JIS R2657. The temperature condition was 1400°C, and heating and cooling was performed a maximum of 10 times. If the specimen spalled during the process, the number of operations at which it spalled was recorded, and if it did not spall until the end, the depth of the crack was measured. The depths of the cracks were compared relative to one another, with large cracks being rated "large," medium cracks being rated "medium," and small cracks being rated "small." Large cracks were rated "x," medium cracks being rated "△," and small cracks being rated "◯." The results are shown in Table 2.

[0061] (5) Resistance to structural embrittlement After the heat spalling resistance test, the test piece was cut perpendicular to the working surface and the surface condition of the cut surface was confirmed. The depth of grain shedding from the heated surface was taken as the embrittled layer and the resistance to embrittlement was evaluated. When the grain shedding range was 50 mm or less, it was marked as ◯, when it was between 50 mm and 60 mm, it was marked as △, and when it was over 60 mm, it was marked as ×. The results are shown in Table 2.

[0062] (6) Phosphorus (P) content The phosphorus (P) content was measured using X-ray fluorescence analysis. The measurement was performed using a ZSX Primus III+ manufactured by Rigaku Corporation. The results are shown in Table 2.

[0063] [Table 2]

[0064] In the examples of the present invention, all unburned bricks have a phosphorus (P) content of 0.2 to 0.6% by mass. Furthermore, all unburned bricks exhibit high hot strength, with a hot bending strength of 10 MPa or more at 1200°C. In contrast, in the comparative examples, there are no unburned bricks with a hot bending strength of 10 MPa or more at 1200°C, except for the unburned brick of Comparative Example 1, which is a fired material.

[0065] Furthermore, in the examples of the present invention, the heat spalling resistance of all unfired bricks was evaluated as ◯. In contrast, among the comparative examples, only the unfired brick of Comparative Example 1, which is a fired material, was evaluated as ◯. Even when phosphate (sodium phosphate glass) was added, the heat spalling resistance of Comparative Example 5, in which the (P) content of the unfired brick was 0.96 mass%, was evaluated as △, and the heat spalling resistance of Comparative Example 6, in which the (P) content was 1.92 mass%, was evaluated as ×. This is because the phosphorus content increases as the amount of sodium phosphate glass added increases, making it easier for low-melting-point substances to be formed.

[0066] Furthermore, in the examples of the present invention, all the unfired bricks were evaluated as "good" in terms of corrosion resistance, resistance to structural embrittlement and compressive strength. This shows that the unfired bricks of the present invention are not only excellent in hot properties such as high-temperature strength and heat spalling resistance, but also in corrosion resistance, resistance to structural embrittlement and compressive strength.

[0067] In contrast, in Comparative Example 2, in which alumina cement was added without adding phosphate, low-melting-point substances were more likely to be produced due to the high CaO content, and the hot bending strength and heat spalling resistance were reduced.

[0068] In Comparative Example 3, which uses a carbon bond with the addition of phenolic resin, the hot bending strength is reduced due to oxidation. In Comparative Example 4, which uses powdered sodium silicate, low-melting-point substances are easily formed due to SiO2 and Na2O, and the hot bending strength and heat spalling resistance are reduced.

[0069] From the above results, it is clear that in order to obtain unfired bricks with excellent hot properties such as high-temperature strength and heat spalling resistance, it is important to add 1 to 2 mass% of an aqueous solution of sodium aluminate in an outer percentage to 100% of a refractory raw material containing magnesia or magnesia and spinel as the main components and 1 to 2 mass% of basic aluminum lactate, and further to add a phosphate to adjust the phosphorus (P) content of the dry product to 0.2 to 0.6 mass%.

Claims

1. a first step of adding 1 to 2 mass% of an aqueous solution of sodium aluminate to 100% of a refractory raw material containing magnesia or magnesia and spinel as a main component and containing 1 to 2 mass% of basic aluminum lactate, and kneading the mixture to obtain a molded body of any desired shape; a second step of drying the molded body obtained in the first step to obtain a dried body, In the first step, a phosphate is added to the main component to which the sodium aluminate aqueous solution has been added, so that the phosphorus (P) content of the dry product is 0.2 to 0.6 mass%; A method for manufacturing unburned bricks, characterized by:

2. adding at least one of sodium phosphate glass, monocalcium phosphate, potassium phosphate glass, and aluminum phosphate as the phosphate; 2. The method for producing unburned bricks according to claim 1, wherein

3. The Al content of the sodium aluminate aqueous solution ２ O ３ The solid content concentration is 10 to 20% by mass.

3. The method for producing unburned bricks according to claim 1 or 2, characterized in that:

4. The main component is magnesia or magnesia and spinel, The phosphorus (P) content is 0.2 to 0.6 mass%; An unfired brick characterized by:

5. Renanit (CaNaPO ４ ) is formed, 5. The unfired brick according to claim 4,

6. The bending strength at 1200°C is 10 MPa or more; 6. The unburned brick according to claim 4 or 5,

7. The compressive strength is 100 MPa or more.

6. The unburned brick according to claim 4 or 5,

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