Non-fired brick and method for producing same

Abstract

Provided are: a non-fired brick that contributes to reducing carbon dioxide emissions and has excellent hot properties such as high-temperature strength and thermal spalling resistance; and a method for producing the non-fired brick. The method for producing a non-fired brick according to the present invention is characterized by comprising: a first step for additionally adding 1 to 2 mass% an aqueous solution of sodium aluminate to 100% of a refractory raw material that contains magnesia or magnesia and spinel as main components and 1 to 2 mass% basic aluminum lactate, kneading the mixture, and then obtaining a molded body of any desired shape; and a second step for drying the molded body obtained in the first step to obtain a dried body, wherein, in the first step, phosphate is added to the main components to which the aqueous solution of sodium aluminate has been added, and phosphorus (P) content of the dried body is adjusted to 0.2 to 0.6 mass%.

Description

Unburned bricks and their manufacturing method

[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.

[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 (Japanese Patent Laid-Open Publication No. 9-87007) proposes "an unfired magnesia 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 "producing spinel around magnesia particles and forming a structure in which the magnesia particles are bound by the secondarily produced 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, and as the temperature rises further, the CO in the atmosphere inside the brick reacts with aluminum carbide to form alumina and carbon. Alumina reacts with magnesia, the brick material, to form spinel, and 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 mainly composed of magnesia and secondary generated spinel. This secondary generated spinel is highly reactive, so when it comes into contact with slag, components such as FeO and MnO in the slag are solid-dissolved in the spinel, preventing it from penetrating deep into the brick. Furthermore, the CaO component in the slag is converted into CaO.Al by the alumina before the spinel is formed. ２ O ３ It is said that the substances are captured as compounds and prevented from penetrating into the brick.

[0005] In addition, Patent Document 2 (JP 2000-272956 A) aims to provide an unfired refractory that has good corrosion resistance and does not develop cracks, peeling, or gaps when used for lining the ladle of a secondary refining furnace, and ２ O ３ 94.7% by weight of SiO2, 5.3% by weight of MgO, 80% by weight of fused alumina and 10% by weight of calcined alumina as alumina raw materials, 5% by weight of fused magnesia having a particle size of 3.36 to 1.0 mm and 5% by weight of fused spinel having a particle size of 1.0 mm or less as magnesia raw materials."

[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 setting the amount of magnesia within an appropriate range, selecting magnesia and spinel as magnesia supply raw materials, and selecting the blending ratio and particle size of these.

[0007] Japanese Patent Laid-Open No. 9-87007 Japanese Patent Laid-Open No. 2000-272956

[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.

[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 method for producing an unburned brick, comprising: a first step of adding 1 to 2 mass% of an aqueous sodium aluminate solution 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, kneading the mixture, and then obtaining a molded body of a desired 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 to which the aqueous sodium aluminate solution has been added, so that the phosphorus (P) content of the dried body is 0.2 to 0.6 mass%.

[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 an appropriate amount of basic aluminum lactate and sodium aluminate causes gelation and produces aluminum lactate. Since aluminum lactate has a moisturizing effect, it prevents the clay from drying out, allowing for the production of a good molded body (first step). Furthermore, by adding a phosphate, rhenanite (CaNaPO ), which has a relatively high melting point, can be used as a binder phase. ４ The resulting unfired brick obtained in the second step has 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 the addition of 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, the Al content of the sodium aluminate aqueous solution is ２ O ３ The solid content is preferably 10 to 20% by mass.

[0017] 100% of the refractory raw material containing basic aluminum lactate is 1 to 2 mass% of Al in outer percentage. ２ O ３ By adding an aqueous sodium aluminate solution having a solid content of 10 to 20% by mass, lactate salts such as sodium lactate are decomposed during the heating process when the material is used in an actual furnace, causing lactic acid to evaporate, and the highly active aluminum reacts with magnesia, allowing the reaction between aluminum and magnesia to form a spinel, which can proceed 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 an unburned brick characterized by comprising magnesia or magnesia and spinel as a main component, and having a phosphorus (P) content of 0.2 to 0.6 mass %.

[0020] The unfired brick of the present invention is preferably obtained by the manufacturing method of the unfired brick of the present invention, and by adjusting 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, in the unfired brick of the present invention, rhenanite (CaNaPO ４ The rhenanite, which has a high melting point, serves as a binder phase, thereby imparting excellent high-temperature strength and heat spalling resistance to the unfired 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, and the like.

[0023] The method for producing unfired bricks of the present invention produces dense molded bodies, and drying the molded bodies at an appropriate temperature leaves lactate salts such as sodium lactate undecomposed. As a result, during heating 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.

[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.

[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 manufacturing method of unburned bricks of the present invention comprises the following steps: a first step of adding 1 to 2 mass % of an aqueous sodium aluminate solution to 100% of a refractory raw material containing magnesia or magnesia and spinel as the main component and containing 1 to 2 mass % of basic aluminum lactate, kneading the mixture, and then obtaining a molded body of any desired 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, 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 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 containing magnesia or magnesia and spinel as the main component and containing 1 to 2 mass % of basic aluminum lactate, kneading the mixture, and then forming a molded body of any shape. The greatest feature of the method for producing an unfired 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 Magnesia particles or magnesia particles and spinel particles can be used as the refractory raw material that is the main component. The mixing ratio of magnesia particles and 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. Furthermore, 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] Types of spinel raw materials and MgO and Al ２ O ３ The ratio is not particularly limited as long as it does not impair the effects of the present invention. For example, a conventionally known alumina-magnesia spinel (MgAl ２ O ４ ) 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, fired spinel, etc. can be used.

[0033] (1-2) Essential Additive Component (Binder) 1 to 2 mass % of basic aluminum lactate is added as an essential additive component. In addition, 1 to 2 mass % of an aqueous solution of sodium aluminate is added in an outer percentage to 100% of the refractory raw material containing magnesia and spinel as main components and containing 1 to 2 mass % of basic aluminum lactate.

[0034] Al in sodium aluminate solution ２ O ３ The solid content is preferably 10 to 20% by mass, more preferably 14 to 18% by mass. ２ O ３ By adding an aqueous solution of sodium aluminate with a solid content of 10 to 20% by mass, the reaction between alumina and magnesia to form a spinel can proceed sufficiently and smoothly.

[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. 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% by mass of sorbitol can be added as a molding aid to 100% of the fire-resistant raw material. Sorbitol is mainly composed of D-sorbitol, and HOCH ２ (CHOH) ４ CH ２ It is represented by the formula OH and is a powder that dissolves easily in water. It is generally used as a surfactant and food additive. The addition of sorbitol improves the packing properties of the kneaded clay and the lubrication between particles, reduces changes in the clay over time, and suppresses 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) Kneading and Forming 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 conventionally known 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 and allows for the production of a good molded product. 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 Step The second step is a step for drying the molded body obtained in the first step to obtain unfired bricks.

[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 Brick 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 comprising 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] The unfired brick of the present invention contains renanit (CaNaPO ４ It is preferable that rhenanite, which has a high melting point, forms a binder phase, thereby imparting excellent high-temperature strength and heat spalling resistance to the unfired brick. There is no particular limitation on the method for confirming the formation of rhenanite, but for example, X-ray diffraction measurement or selected area electron diffraction in transmission electron microscope observation can be used.

[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, and the like.

[0049] The method for measuring the bending strength of an unburned 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 unburned 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) (i.e., no rhenanite is 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.

[0053] Examples Raw materials were prepared in the proportions shown in Table 1 as Examples 1 to 7, kneaded in a high-speed mixer, and molded into a shape of 230 x 230 x 85 mm 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 that are examples of the present invention. The values ​​in Table 1 are shown in mass%, and the amounts of various phosphates, aqueous sodium aluminate solution, aqueous sorbitol solution, 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 Al content of the aqueous sodium aluminate solution are shown. ２ O ３ The solid content concentration (mass %) is shown.

[0054] Comparative Examples 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]

[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, which 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 rated as ◯, an index of more than 105 but less than 115 was rated as △, and an index of 115 or more was rated as ×.

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

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

[0060] (4) Heat Spalling Resistance Heat spalling resistance was evaluated by the air cooling method based on JIS R2657. The temperature condition was 1400°C, and heating and cooling were performed a maximum of 10 times. If the specimen peeled off during the process, the number of operations at the time of the peeling was recorded, and if the specimen did not peel off until the end, the depth of the crack was measured. The depths of the cracks were compared relative to each other, and a large crack was rated as "large," a medium crack as "medium," and a small crack as "small." Furthermore, a large crack was rated as "x," a medium crack as "△," and a small crack as "◯." 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 heating surface was taken as the embrittled layer, and the resistance to structural embrittlement was evaluated. When the grain shedding range was 50 mm or less, it was marked as ◯, when it was more than 50 mm and less than 60 mm, it was marked as △, and when it was more than 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 fluorescent X-ray analysis. For the measurement, a ZSX Primus III+ manufactured by Rigaku Corporation was used. The results are shown in Table 2.

[0063]

[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 the 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 low due to oxidation. In Comparative Example 4, which uses powdered sodium silicate, SiO ２ , Na ２ The O content makes it easier for low-melting-point substances to form, resulting in a decrease in hot bending strength and heat spalling resistance.

[0069] From the above results, it is clear that in order to obtain unfired bricks excellent in 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 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 so that the phosphorus (P) content of the dried product is 0.2 to 0.6 mass %.

Claims

1. A method for producing unfired bricks, comprising: 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, phosphate is added to the main component to which the aqueous solution of sodium aluminate has been added, so that the phosphorus (P) content of the dried body is 0.2 to 0.6 mass%.

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

3. The Al content of the sodium aluminate aqueous solution ２ O ３ 3. The method for producing unburned bricks according to claim 1, wherein the solid content is 10 to 20% by mass.

4. An unfired brick characterized by having magnesia or magnesia and spinel as its main components and a phosphorus (P) content of 0.2 to 0.6 mass%.

5. Renanit (CaNaPO ４ 5. The unburned brick according to claim 4, wherein the unburned brick is formed of a granular material.

6. An unfired brick according to claim 4 or 5, characterized in that the bending strength at 1200°C is 10 MPa or more.

7. The unfired brick according to claim 4 or 5, characterized in that it has a compressive strength of 100 MPa or more.

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