Unfired magnesia spinel brick and manufacturing method thereof

Abstract

To provide an unfired magnesia spinel brick that has excellent thermal spalling resistance and volume stability and exhibits high hot strength, which contributes to the reduction of carbon dioxide emissions, and a manufacturing method thereof.SOLUTION: The manufacturing method for the unfired magnesia spinel brick is characterized by comprising: a first step of adding 1 to 2 mass% of an aqueous solution of sodium aluminate, expressed in terms of outer percentage, to 100% of a refractory raw material containing magnesia and spinel as main components and 1 to 2 mass% of basic aluminum lactate, and kneading the mixture to obtain a molded body of any shape; and a second step of drying the molded body obtained in the first step.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention mainly relates to a method for manufacturing a refractory that can be used as an inner lining of a furnace for firing cement, lime, etc.

Background Art

[0002] Magnesia spinel bricks are excellent in heat spalling resistance and volume stability and are mainly used in rotary kilns for firing cement and lime.

[0003] For example, in Patent Document 1 (Japanese Patent Laid-Open No. 08-026816), the problem is "to provide a magnesia spinel refractory suitable for the inner lining bricks of a rotary kiln for firing cement raw materials, lime raw materials, etc.", and "a magnesia spinel refractory characterized by having 15 to 30% of spinel clinker containing 3 to 10% of ZrO2 and 50 to 80% of high-purity electrofused magnesia clinker or seawater magnesia clinker with a large crystal diameter" has been proposed.

[0004] In the magnesia spinel refractory described in Patent Document 1, in order to be stably used even under high-temperature operation, an electrofused magnesia clinker with a MgO content of 98% and a large crystal diameter of 50 μm or more is used, and a spinel clinker containing 3 to 10% of ZrO2 is used to provide a sintering promotion effect and increase the thermal shock strength.

[0005] In addition, in the durable magnesia-spinel cement and the refractory for lime calcination kiln described in Patent Document 2 (Japanese Patent Application Laid-Open No. 07-061857), "to provide magnesia-spinel bricks that improve wear resistance without inhibiting the excellent spalling resistance of magnesia-spinel bricks." As an issue, "in a magnesia-spinel refractory formed by blending a magnesia clinker and an MgO—Al2O3-based spinel clinker, as the magnesia clinker, a sintered magnesia clinker having a bulk specific gravity in the range of 3.20 to 3.37 is used at 20% by weight or more. High-durability cement and magnesia-spinel fired bricks for lime calcination kilns." has been proposed.

[0006] In the durable magnesia-spinel cement and the magnesia-spinel fired bricks for lime calcination kiln described in the above Patent Document 2, by simply using a magnesia clinker having a predetermined bulk specific gravity, it is possible to increase the hot strength in order to improve the wear resistance without sacrificing other physical properties.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the magnesia-spinel refractories described in the above Patent Document 1, the durable magnesia-spinel cement described in the above Patent Document 2, and the refractories for lime calcination kilns are all fired refractories manufactured through a firing process, and a large amount of carbon dioxide is inevitably emitted in the manufacturing process.

[0009] On the other hand, from the perspective of carbon neutrality and global warming suppression in recent years, unfired refractories that do not require a firing process are excellent. However, the fact is that there is no high-strength unfired magnesia spinel brick that is excellent in heat-resistant spalling property and volume stability.

[0010] In view of the above problems in the prior art, an object of the present invention is to provide an unfired magnesia spinel brick that contributes to the reduction of carbon dioxide emissions, is excellent in heat-resistant spalling property and volume stability, and exhibits high hot strength, and a method for manufacturing the same.

Means for Solving the Problems

[0011] As a result of intensive research on unfired magnesia spinel bricks and their manufacturing methods in order to achieve the above object, the present inventors have found that it is extremely effective to contain basic aluminum lactate in refractory raw materials and add an aqueous sodium aluminate solution during kneading, and have reached the present invention.

[0012] That is, the present invention A first step of obtaining a molded body of any shape after kneading by adding 1 to 2% by mass of an aqueous sodium aluminate solution externally to 100% of a refractory raw material mainly composed of magnesia and spinel and containing 1 to 2% by mass of basic aluminum lactate; A second step of drying the molded body obtained in the first step, and A method for manufacturing an unfired magnesia spinel brick, characterized by comprising:

[0013] Conventionally, in unfired magnesia spinel bricks that do not undergo a firing process, those that exhibit high strength, excellent heat-resistant spalling property and volume stability, and high hot strength have not been found. On the other hand, in the unfired magnesia spinel brick of the present invention, by mixing an appropriate amount of basic aluminum lactate and an aqueous sodium aluminate solution, all of these properties can be imparted.

[0014] More specifically, by mixing an appropriate amount of basic aluminum lactate and sodium aluminate, gelation occurs and aluminum lactate is produced. Since aluminum lactate has a moisturizing effect, the drying of the refractory soil is suppressed, and a good molded body can be obtained (the first step).

[0015] Also, when the obtained molded body is dried at an appropriate temperature, lactates such as sodium lactate remain without decomposition, and a decrease in strength can be suppressed (the second step).

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

[0017] By adding an aqueous solution of sodium aluminate having an Al2O3 solid content concentration of 10 to 20% by mass in an amount of 1 to 2% by mass based on 100% of the refractory raw material containing basic aluminum lactate, lactates such as sodium lactate are decomposed and lactic acid evaporates during the heating process when used in an actual furnace, and highly active aluminum reacts with magnesia, and spinelization due to the reaction between aluminum and magnesia can proceed sufficiently and smoothly.

[0018] Furthermore, in the method for producing the unburned magnesia spinel brick of the present invention, it is preferable that the drying temperature in the second step is 200 to 320°C. By setting the drying temperature to 200°C or higher, the decomposition of sodium lactate and the decomposition of lactic acid can be suppressed while allowing the drying to proceed sufficiently and smoothly. By setting the drying temperature to 320°C or lower, a decrease in the strength of the unburned magnesia spinel brick can be suppressed, and an increase in carbon dioxide emissions related to the drying process can be suppressed.

[0019] Also, the present invention provides an unburned magnesia spinel brick containing 0.5 to 1.5% by mass of lactate ions, and having a flexural strength at 1200°C of 5 MPa or more.

[0020] ​ The unfired magnesia spinel brick of the present invention is obtained by the method for producing an unfired magnesia spinel brick of the present invention, mainly composed of magnesia and spinel, and containing 1 to 2% by mass of basic aluminum lactate. Based on 100% of the refractory raw material, 1 to 2% by mass of an aqueous sodium aluminate solution is added externally and kneaded, and then a first step of obtaining a molded body of any shape is carried out, and a second step of drying the molded body obtained in the first step is passed through, and it contains 0.5 to 1.5% by mass of lactate ions.

[0021] In addition, the unfired magnesia brick of the present invention has high hot strength, and the flexural strength at 1200 °C is 5 MPa or more. By the method for producing an unfired magnesia brick of the present invention, a dense molded body is obtained, and by drying the molded body at an appropriate temperature, lactates such as sodium lactate remain without decomposition. As a result, lactates such as sodium lactate decompose and lactic acid evaporates during the heating process up to 1200 °C, and highly active aluminum reacts with magnesia, and spinelization due to the reaction between aluminum and magnesia can proceed sufficiently and smoothly, so that high hot strength can be exhibited.

Effects of the Invention

[0022] According to the present invention, it is possible to provide a high-strength unfired magnesia spinel brick excellent in heat-resistant spalling property and volume stability, which contributes to the reduction of carbon dioxide emissions, and a method for producing the same.

Modes for Carrying Out the Invention

[0023] Hereinafter, typical embodiments of the unfired magnesia spinel brick of the present invention and a method for producing the same will be described in detail, but the present invention is not limited only to these.

[0024] 1. Method for producing unfired magnesia spinel brick The manufacturing method of the unfired magnesia spinel brick of the present invention mainly consists of magnesia and spinel, and based on 100% of the refractory raw material containing 1-2% by mass of basic aluminum lactate, 1-2% by mass of an aqueous sodium aluminate solution is externally added and kneaded, and then a first step of obtaining a molded body of any shape and a second step of drying the molded body obtained in the first step are included. Hereinafter, each step will be described in detail.

[0025] (1) First step The first step is a step of obtaining a molded body of any shape after adding and kneading 1-2% by mass of an aqueous sodium aluminate solution externally to 100% of the refractory raw material mainly composed of magnesia and spinel and containing 1-2% by mass of basic aluminum lactate.

[0026] (1-1) Main components As the refractory raw material serving as the main component, magnesia particles and spinel particles can be used. The mixing ratio of the magnesia particles and the spinel particles is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately adjusted according to the desired properties of the unfired magnesia spinel brick.

[0027] It is preferable to mix raw materials with different particle sizes for the magnesia particles and the spinel particles. By mixing and using raw materials with different particle sizes, good heat-resistant spalling resistance can be imparted to the unfired magnesia spinel brick.

[0028] The type of the magnesia raw material is not particularly limited as long as the effects of the present invention are not impaired. For example, conventionally known fused magnesia, seawater magnesia, natural magnesia, etc. can be used. Regarding the purity of the magnesia raw material, in order to avoid the reduction of corrosion resistance and the influence of over-sintering due to impurities, it is preferable to use a high-purity one with 95% by weight or more.

[0029] The types of spinel raw materials and the ratio of MgO to Al2O3 are not particularly limited as long as the effects of the present invention are not impaired. For example, conventionally known alumina-magnesia spinel (MgAl2O4) can be used. Also, for the spinel raw material, similar to the magnesia raw material, it is preferable to use a high-purity one of 95% by weight or more. The spinel raw material is not particularly limited, and fused spinel, calcined spinel, etc. can be used.

[0030] (1-2) Essential additive component (binder) As an essential additive component, 1 to 2% by mass of basic aluminum lactate is added. Further, based on 100% of the refractory raw material mainly composed of magnesia and spinel and containing 1 to 2% by mass of basic aluminum lactate, 1 to 2% by mass of an aqueous sodium aluminate solution is added externally.

[0031] The Al2O3 solid content concentration of the aqueous sodium aluminate solution is preferably 10 to 20% by mass, and more preferably 14 to 18% by mass. By adding externally 1 to 2% by mass of an aqueous sodium aluminate solution having an Al2O3 solid content concentration of 10 to 20% by mass to 100% of the refractory raw material containing 1 to 2% by mass of basic aluminum lactate, the spinelization due to the reaction between aluminum and magnesia can proceed sufficiently and smoothly.

[0032] (1-3) Optional additive components For example, as a molding aid, 1 to 3% by mass of sorbitol can be added externally based on 100% of the refractory raw material. Sorbitol is mainly composed of D-sorbitol, represented by HOCH2(CHOH)4CH2OH, is a powder that easily dissolves in water, and is generally used as a surfactant or a food additive. By adding sorbitol, the filling property of the kneaded clay, the lubricity between particles are improved, the change over time of the clay is reduced, and slacking is suppressed. Also, it has no toxicity, and a molded body with a high molding density can be obtained. Also, additives used as molding aids for fired spinel bricks such as bittern and magnesium sulfate can also be used.

[0033] In addition, as long as the effects of the present invention are not impaired, various optional components known in the art, such as alumina, zirconia, and iron oxide, may be added to the magnesia spinel brick.

[0034] (1-4) Kneading and forming The refractory raw materials as the main components, the essential additive components, and the optional additive components are kneaded and formed into an arbitrary shape. The methods of kneading and forming are not particularly limited, and various conventionally known methods used in the production of refractories can be applied.

[0035] Here, in the method for producing the unfired magnesia spinel brick of the present invention, by mixing an appropriate amount of sodium aluminate and basic aluminum lactate, gelation occurs and aluminum lactate is generated. Since aluminum lactate has a moisturizing effect, drying of the clay is suppressed and a good molded body can be obtained.

[0036] (2) Second step The second step is a step of drying the molded body obtained in the first step to obtain an unfired magnesia spinel brick.

[0037] When the molded body obtained in the first step is dried at an appropriate temperature, lactates such as sodium lactate remain without decomposition, and a decrease in strength can be suppressed.

[0038] The drying temperature is preferably 200 to 320°C. By setting the drying temperature to 200°C or higher, excess moisture can evaporate and dehydrate to increase the strength. Also, by setting the drying temperature to 320°C or lower, lactates such as sodium lactate remain without decomposition, a decrease in strength can be suppressed, and an increase in carbon dioxide emissions related to the drying process can be suppressed. The drying temperature is more preferably 250 to 300°C.

[0039] 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.

[0040] Incidentally, the method for manufacturing the unfired magnesia spinel brick of the present invention does not prevent firing the unfired magnesia spinel brick under appropriate conditions after drying.

[0041] 2. Unfired magnesia spinel brick The unfired magnesia spinel brick of the present invention is characterized by containing 0.5 to 1.5% by mass of lactate ions and having a flexural strength of 5 MPa or more at 1200°C.

[0042] The method for measuring the content of lactate ions in the unfired magnesia spinel brick is not particularly limited, and various conventionally known measurement methods can be used. For example, lactate ions can be quantified by thermogravimetric analysis. More specifically, using a differential thermal-thermogravimetric simultaneous analyzer, the unfired magnesia spinel brick is heated under an air flow, and the weight change at 350 to 400°C, which is the decomposition evaporation temperature of lactic acid derived from aluminum lactate and sodium lactate, may be measured.

[0043] Also, the method for measuring the flexural strength of the unfired magnesia spinel brick at 1200°C is not particularly limited, and various conventionally known measurement methods can be used. For example, using a hot bending test apparatus, a three-point bending test may be performed under an air atmosphere at 1200°C. The flexural strength of the unfired magnesia spinel brick at 1200°C is preferably 7 MPa or more, and more preferably 9 MPa or more.

[0044] Also, the unfired magnesia spinel brick of the present invention has sufficient strength even at room temperature and has a higher compressive strength than a fired magnesia spinel brick having an equivalent composition and not containing lactate ions.

[0045] Furthermore, the unfired magnesia spinel brick of the present invention has excellent corrosion resistance, hot spalling resistance, and resistance to tissue embrittlement. Specifically, it has corrosion resistance, hot spalling resistance, and resistance to tissue embrittlement comparable to those of a fired magnesia spinel brick having an equivalent composition and not containing lactate ions.

[0046] The representative embodiments of the present invention have been described above. However, the present invention is not limited to these only, and various design changes are possible, and all of these design changes are included in the technical scope of the present invention.

Example

[0047] ≪Example≫ The raw materials were adjusted at the ratios shown as Example 1 to Example 6 in Table 1, kneaded with a high-speed mixer, and formed by a hydraulic press in a shape of 230×230×85 mm. A batch dryer was used for drying, and it was held at 200 to 320 °C for 8 hours to obtain unfired magnesia spinel bricks which are the examples of the present invention. The values in Table 1 indicate mass %, and the addition amounts of the sodium aluminate aqueous solution, the sorbitol aqueous solution, and water are shown as external values with respect to the total amount of the magnesia clinker, the spinel clinker, and the basic aluminum lactate. Further, for the magnesia clinker and the spinel clinker, the particle size is shown, and for the sodium aluminate aqueous solution, the Al2O3 solid content concentration (mass %) is shown.

[0048] ≪Comparative Example≫ Unfired magnesia spinel bricks were obtained in the same manner as in the examples except that the raw materials were adjusted at the ratios shown as Comparative Example 1 to Comparative Example 8 in Table 1. Here, only for Comparative Example 1, a tunnel kiln type firing kiln was used and fired at a maximum temperature of 1750 ± 10 °C.

[0049]

Table 1

[0050] [Evaluation] For each of the unfired magnesia spinel bricks obtained as the examples and the comparative examples, the corrosion resistance, the compressive strength, the hot strength, the heat resistance spalling property, and the resistance to tissue embrittlement were evaluated. In addition, the content of lactate ions contained in each unfired magnesia brick was measured.

[0051] (1) Corrosion resistance The corrosion resistance was evaluated by a rotating drum erosion test. The test method is as follows. The test piece was lined inside the drum and carried out at 1750 ± 50 °C using an oxygen - propane burner. As the erosion material, a mixture of Portland cement and potassium sulfate mixed at a ratio of 5:1 was put in. After the test of holding for 6 hours while replacing the erosion material every hour, the sample was cut in a direction perpendicular to the working surface, and the wear amount was measured at 8 points to obtain the average wear amount. The average wear amount was expressed as an index with the erosion amount of Comparative Example 1 being 100. The obtained results are shown in Table 2. The smaller the index, the better the corrosion resistance. When the index is 105 or less, it is marked as 〇, when it is more than 105 and less than 110, it is marked as △, and when it is 110 or more, it is marked as ×.

[0052] (2) Compressive strength A 60 mm × 60 mm × 60 mm test piece was used to measure the compressive strength using an Amthaler - type strength measuring test device. The compressive strength was evaluated as an index with the fired magnesia spinel brick of Comparative Example 1, which is a fired product, being 100. The obtained results are shown in Table 2.

[0053] (3) Hot strength A 30 mm × 30 mm × 120 mm test piece was used to measure the hot strength using a hot bending test device. The results of three - point bending (span distance between supports 80 mm) in an air atmosphere at 1200 °C are shown as numerical values (MPa). The obtained results are shown in Table 2. The larger the numerical value, the higher the hot strength. When it is less than 5, it is marked as ×, when it is 5 or more and less than 7, it is marked as △, and when it is 7 or more, it is marked as 〇.

[0054] (4) Thermal spalling resistance The evaluation of thermal spalling resistance was carried out by the air - cooling method based on JIS R2657. The temperature condition was 1400 °C, and heating and cooling were carried out up to 10 times at most. When spalling occurred during the process, the number of operations at the time of spalling was recorded. When no spalling occurred until the end, the depth of the crack was measured. The depth of the crack was relatively compared, and when the crack was large, it was marked as "large", when it was medium, it was marked as "medium", and when it was small, it was marked as "small". The obtained results are shown in Table 2.

[0055] (5) Resistance to tissue embrittlement The specimen piece after the heat-resistant spalling property test was cut in a direction perpendicular to the working surface, and the surface state of the cut surface was confirmed. The depth of grain detachment from the heating surface was taken as the tissue embrittlement layer, and the tissue embrittlement resistance was evaluated. When the grain detachment range was 60 or less, it was marked as ○; when it was more than 60 and 80 or less, it was marked as △; when it was more than 80, it was marked as ×. The obtained results are shown in Table 2.

[0056] (6) Lactate ion content The lactate ions were quantified by thermogravimetric analysis. As the measuring apparatus for differential thermal-thermogravimetric simultaneous analysis, STA7300 manufactured by Hitachi High-Tech Science Corporation was used. The weighing of the sample (unfired magnesia spinel brick) was carried out on the balance beam of STA7300. Approximately 10 mg of the sample was placed in a platinum measuring container and set in the above measuring apparatus. Under an air flow of 200 ml / min, the temperature was raised from 20 to 1000 °C at a rate of 5 °C / min to obtain a DTG curve. Based on the weight loss peak at 350 - 400 °C due to the decomposition and evaporation of lactic acid derived from aluminum lactate and sodium lactate, the content of lactate ions contained in the unfired magnesia spinel brick was determined. The obtained results are shown in Table 2.

[0057]

Table 2

[0058] In the examples of the present invention, the content of lactate ions in all unfired magnesia spinel bricks is 0.5 - 1.5 mass%. Also, all unfired magnesia spinel bricks exhibit high hot strength, and the hot bending strength at 1200 °C is 5 MPa or more. On the other hand, in the comparative examples, there is no unfired magnesia spinel brick that contains 0.5 - 1.5 mass% of lactate ions and has a hot bending strength of 5 MPa or more at 1200 °C.

[0059] In addition, for the examples of the present invention, the evaluation of corrosion resistance and heat-resistant spalling resistance is ○ for all unfired magnesia spinel bricks. In Example 4 where a sorbitol aqueous solution was used instead of water, the embrittlement range increased slightly, but the evaluation of tissue embrittlement resistance is Δ or higher for all unfired magnesia spinel bricks in the examples. Also, the evaluation of hot bending strength is Δ or higher for all unfired magnesia spinel bricks in the examples. In particular, in Example 3, the evaluation of hot bending strength is ○, and good results are obtained in all evaluation items. As a result, it can be seen that the unfired magnesia spinel brick of Example 3 has characteristics equivalent to those of the fired magnesia spinel brick of Comparative Example 1.

[0060] On the other hand, in Comparative Example 2 where the addition amount of basic aluminum lactate is too small, the bonding phase does not exist sufficiently, so the hot bending strength is low, and the evaluations of heat-resistant spalling resistance and tissue embrittlement resistance are also ×. In Comparative Example 3 where the addition amount of basic aluminum lactate is too large, since a large amount of lactic acid that does not contribute to spinel bonding is contained, the evaluation of corrosion resistance is ×.

[0061] In Comparative Example 4 where the Al2O3 solid content concentration of the sodium aluminate aqueous solution is too low, the bonding phase does not exist sufficiently, so the hot bending strength is low. In Comparative Example 5 where the Al2O3 solid content concentration of the sodium aluminate aqueous solution is too high, drying during molding becomes faster and it is difficult to obtain the strength of the molded body, so the hot bending strength is low.

[0062] In Comparative Example 6 where the addition amount of the sodium aluminate aqueous solution is too large, as a result of an increase in the soda content, the evaluations of corrosion resistance and tissue embrittlement resistance are ×.

[0063] Also, in Comparative Example 7 where the drying temperature is too low and Comparative Example 8 where the drying temperature is too high, the compressive strength is low.

[0064] From the above results, it can be seen that in order to obtain a high-strength unfired magnesia spinel brick with excellent heat-resistant spalling properties and volume stability, it is important to add 1 to 2% by mass of an aqueous sodium aluminate solution externally to 100% of a refractory raw material mainly composed of magnesia and spinel and containing 1 to 2% by mass of basic aluminum lactate.

Claims

1. A first step of obtaining a molded body of any shape by adding 1 to 2% by mass of an aqueous sodium aluminate solution externally to 100% of a refractory raw material mainly composed of magnesia and spinel and containing 1 to 2% by mass of basic aluminum lactate, followed by kneading; A second step of drying the molded body obtained in the first step; characterized by having the above, A method for producing unfired magnesia spinel bricks.

2. The Al of the aqueous sodium aluminate solution ２ O ３ shall have a solid content concentration of 10 to 20% by mass, A method for producing unfired magnesia spinel bricks according to Claim 1, characterized by the above.

3. The temperature of the drying in the second step is set to 200 to 320°C; A method for producing unfired magnesia spinel bricks according to Claim 1 or 2, characterized by the above.

4. Containing 0.5 to 1.5% by mass of lactate ions, The flexural strength at 1200°C is 5 MPa or more; Unfired magnesia spinel bricks, characterized by the above.

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