A cement-free magnesia castable and a method of using the same

Abstract

This invention relates to the field of refractory materials technology, and more particularly to a cementless magnesia castable and its application method. The castable consists of aggregate, matrix material, and a water-reducing agent; the aggregate is 60-80 parts of magnesia particles; the matrix material is: fine magnesia powder, active α-Al₂O₃ micro powder, sintered corundum powder, silica micro powder, and aluminum-based metal microcapsules. The application method of the cementless magnesia castable is as follows: the water-reducing agent and matrix material are mixed evenly to obtain a premixed matrix material; the aggregate and premixed matrix material are stirred evenly, water is added and wet-mixed to obtain a slurry; the evenly mixed slurry is poured into a mold, vibrated to form the slurry, and then cured. This cementless magnesia castable exhibits certain initial strength, excellent high-temperature performance, excellent resistance to slag erosion and thermal shock, and a long service life, making it widely applicable in tundishes and ladles.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a cement-free magnesia castable and its application method. Background Technology

[0002] Magnesia castables, primarily made from magnesia sand, possess advantages such as high refractoriness, high load softening temperature, good resistance to alkaline slag erosion, excellent compatibility with molten steel, and low oxygenation and pollution to the molten steel, meeting the requirements for clean steel smelting. In modern industrial production, the quality and performance requirements for magnesia castables are increasingly stringent. The binder used in magnesia castables, to a certain extent, determines the quality, microstructure, and high-temperature performance of the castable. Currently, the binder system is developing towards "purification" and "stabilization." "Purification" refers to minimizing the introduction of impurities into the binder, as impurities are generally detrimental to high-temperature performance. "Stabilization" aims to minimize the damage to the material structure caused by the volatilization or decomposition of the binder.

[0003] Magnesia refractory castables initially used calcium aluminate cement binder. This type of cement-bound castable achieved sufficiently high early strength and excellent workability at low ambient temperatures. The main minerals in the cement are calcium monoaluminate (CA) and calcium dialuminate (CA2), and it generally also contains a very small amount of calcium dodecacalcium heptaaluminate (C). 12 A7). After the castable is mixed with water, the calcium aluminate minerals CA, CA2, and C in the cement... 12 A7 reacts with water, and the intertwined growth of hydration products causes the castable to gradually solidify and harden. Although cement has high early strength and excellent workability, its use also brings some disadvantages: on the one hand, the loss of bound water during heating destroys the structure of the castable, leading to spalling or even cracking; on the other hand, the CaO introduced by cement easily reacts with SiO2, MgO, Al2O3, and other substances in the castable or the environment to form low-melting-point compounds, thereby reducing high-temperature mechanical properties and slag resistance. This limits the service temperature and lifespan of cement-bonded castables.

[0004] Magnesium oxychloride cement is used as the binder for magnesia-based castables. Magnesium oxychloride cement is a gel material formed by the ternary components MgO-MgCl2-H2O, possessing advantages such as rapid setting, high strength, good elasticity, and convenient molding. The high-temperature decomposition product of magnesium oxychloride cement is active MgO. Using it as a binder for magnesia-based refractory castables offers advantages such as not introducing harmful substances, high load softening temperature, good slag resistance, and low cost. However, a drawback is that the flexural strength of the castable significantly decreases after heat treatment at 1100℃. This is mainly due to the dehydration and decomposition reaction of the magnesium oxychloride cement gel during heating, transforming it into MgO, thus destroying the cementitious structure and greatly weakening the performance of the castable.

[0005] Polyphosphates (mainly sodium polyphosphate) are used as binders in monolithic refractories, with sodium tripolyphosphate and sodium hexametaphosphate being common binders for magnesia castables. Sodium tripolyphosphate dissolves in water to form sodium monohydrogen phosphate and sodium dihydrogen phosphate. These two compounds react with MgO to form sodium magnesium phosphate, thus creating a binding effect. When used as a binder for magnesia castables, the castables harden quickly, exhibit high strength, and possess good thermal shock resistance. Sodium tripolyphosphate undergoes polymerization upon heating, which enhances material strength, without causing a loosening of the green body structure due to phase transformation. Therefore, materials bound with it maintain high strength from room temperature to intermediate temperatures. However, the hot strength of the castable decreases after a liquid phase appears at high temperatures.

[0006] When sodium hexametaphosphate is used as a binder, it hydrolyzes in water to form sodium dihydrogen phosphate (NaH2PO4). NaH2PO4 reacts with alkaline earth metal oxides such as magnesia to form castables at room temperature, forming Mg(H2PO4)2. After drying, Mg(H2PO4)2 quickly forms MgHPO4, which has high binding properties and allows the castable to harden rapidly. Mg(H2PO4)2 and MgHPO4 condense at approximately 500℃ to form magnesium polyphosphate [Mg(PO3)2]. n and [Mg2(P2O7)] n This further improves the strength of the bond, maintaining a fairly high strength over a considerable temperature range before the liquid phase appears (before 800℃). However, after the liquid phase appears at high temperatures, the hot strength of the castable decreases.

[0007] Currently, magnesia-based castables mainly use SiO2 micro powder binder, utilizing the reaction of MgO and SiO2 micro powder with water to form MgO-SiO2-H2O gel to generate bonding strength. This bonding system has the following characteristics: (a) SiO2 micro powder particles are small, have a large specific surface area, and are spherical, which improves the fluidity and density of the castable; (b) It does not introduce impurities such as CaO and Na2O. As the temperature increases, MgO and SiO2 can react to form the high-melting-point phase forsterite (M2S), improving the high-temperature performance of the material; (c) The gel contains less bound water, allowing for slow dehydration over a wide temperature range during heating, resulting in low weight loss. Therefore, the castable has good anti-cracking properties and is beneficial for rapid baking. Due to its good performance, high cost-effectiveness, and relatively stable performance, the MgO-SiO2-H2O bonding system is used in a series of precast components such as small and medium-sized ladle castables, tundish slag retaining walls, and impact plates. However, excessive silicon dioxide can cause the material to produce too much liquid phase (magnesium silicate) at high temperatures, which seriously affects its performance at high temperatures and also significantly "oxygenates" the molten steel.

[0008] For example:

[0009] (1) Chinese patent application number CN201510298745.5, "Calcium aluminate cement-bonded alumina-magnesia castable and its preparation method", uses calcium aluminate cement as a binder and titanium dioxide / calcium carbonate / magnesia oxide micro powder as a composite additive. Titanium dioxide promotes sintering, and magnesium oxide reacts with corundum to form spinel. The properties of calcium carbonate being converted into highly active calcium oxide at high temperature greatly improve the strength of the alumina-magnesia castable. However, due to the large amount of cement added, the cement contains a small amount of CaO. CaO reacts with Al2O3 and SiO2 in the castable at high temperature to form low-melting-point substances, which will seriously reduce the performance of the castable at high temperatures.

[0010] (2) Chinese patent application number CN201110251826.1, entitled "An Amide Binder for Cement-Free Castables," describes an amide binder containing acrylamide, N-N'-methylenebisacrylamide, ammonium persulfate, tetramethylethylenediamine, or a tetramethylethylenediamine complex. This binder is added to the castable by dissolving it in water, effectively solving the problem of surface pulverization and significantly improving the flexural and compressive strength of the castable. However, the amide binder releases harmful gases (NO3) during use.

[0011] (3) Chinese patent application number CN201210216100.9, entitled "An Alumina-Magnesium Refractory Castable and Its Preparation Method", uses a mixture of hydrated alumina micro powder and pure aluminate cement as a bonding system. During high-temperature use, magnesium aluminum spinel will be generated in situ inside the castable, and microcracks will be generated inside the castable, which can buffer the thermal stress generated during rapid cooling and heating, and has strong thermal shock resistance. However, the amount of pure aluminate cement added is large, and more liquid phase will be generated at high temperatures, resulting in poor high-temperature performance of the material.

[0012] (4) Chinese patent application number CN200710052468.5, entitled "An aluminum-magnesium lightweight cementless castable and its preparation method", produces porous ceramics as aggregate, mainly using magnesium oxide and silica micro powder as binders. This binder can form a good chain-like network with water, making the matrix more compact and avoiding the disadvantages of using calcium aluminate cement as a binder, such as the inability to use the material at high temperatures, easy structural spalling, and poor slag resistance. However, excessive SiO2 in the system can cause the material to produce too much liquid phase at high temperatures, which seriously affects its performance at high temperatures, limits the service temperature of aluminum-magnesium materials, and brings significant "oxygenation" to the molten steel.

[0013] (5) Chinese patent application number CN201210134262.8, "A silica sol-bonded magnesium intermediate ladle preform and its manufacturing method," uses silica sol as a binder. The SiO2 particles in the silica sol are evenly distributed in the preform, forming a dense and uniform structure with extremely strong resistance to steel slag erosion and molten steel scouring. However, it still has the problems of long curing time and low strength after baking. Summary of the Invention

[0014] The purpose of this invention is to address the aforementioned shortcomings of existing technologies by providing a cement-free magnesium-based castable and its application method. This castable exhibits certain initial strength, excellent high-temperature performance, superior resistance to slag erosion and thermal shock, and a long service life, making it widely applicable in tundishes and ladles.

[0015] The present invention provides a cementless magnesium castable, wherein the castable is composed of aggregate, matrix material and water-reducing agent;

[0016] The aggregate is 60-80 parts of magnesium sand particles;

[0017] The substrate is:

[0018]

[0019] The method for preparing the aluminum-based metal microcapsules is as follows:

[0020] S1. Aluminum powder or aluminum-based alloy powder is placed in a metal compound solution for reduction reaction. After stirring for a period of time, metal nanoparticles are deposited on the surface of aluminum powder or aluminum-based alloy powder. Magnesium salt is added to the solution and stirred for 30 minutes. After filtration and drying, microcapsule precursor is obtained.

[0021] S2. The microcapsule precursor is heat-treated in air at 150°C to 500°C and then naturally cooled to obtain aluminum-based metal microcapsules.

[0022] Furthermore, the aluminum powder or aluminum-based alloy powder has a particle size ≤74μm, and the aluminum-based alloy powder contains Si and Fe, with the Si content being less than 40wt%.

[0023] Furthermore, in step S1 of the method for preparing aluminum-based metal microcapsules, a reduction reaction is carried out at 40–60°C and stirred for 30–60 min.

[0024] Furthermore, in step S1 of the method for preparing aluminum-based metal microcapsules, the metal compound solution is an iron chloride solution or a nickel chloride solution, and the metal nanoparticles are nano-Fe or nano-Ni particles.

[0025] Furthermore, in step S1 of the method for preparing aluminum-based metal microcapsules, the magnesium salt is one of magnesium nitrate, magnesium oxalate, and magnesium carbonate.

[0026] Furthermore, the magnesia particles include:

[0027] 18-25 parts of magnesia particles with a diameter of less than 5 mm and greater than or equal to 3 mm.

[0028] 24-30 parts of magnesia particles with a diameter of less than 3 mm and greater than or equal to 1 mm.

[0029] 18-25 parts of magnesia particles with a diameter of less than 1 mm and greater than 0.1 mm;

[0030] The MgO content of the fine magnesia powder is ≥96wt%, the particle size of the fine magnesia powder is ≤40μm, and the fine magnesia powder is one of fused magnesia and sintered magnesia.

[0031] Furthermore, the water-reducing agent content is 0.1-0.4% of the sum of aggregate and matrix material, and the water-reducing agent is one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, and sodium silicate.

[0032] A method for using the above-mentioned cementless magnesium castable involves mixing 0.1-0.4% of a water-reducing agent and matrix material (total of aggregate and matrix material) to obtain a premixed matrix material; stirring the aggregate and the premixed matrix material evenly, adding 3-4% of water (total of aggregate and matrix material), and stirring for 1-3 minutes to obtain a slurry; pouring the slurry into a mold, vibrating to form the slurry, and curing for 1-3 days.

[0033] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0034] 1. The aluminum-based metal microcapsules added to the cement-free magnesium castable of this invention have good sphericity, which can improve the fluidity of the castable, reduce the amount of water added, and make the castable structure more compact.

[0035] 2. The aluminum-based metal microcapsules added to the cementless magnesia castable of this invention contain boehmite, metal nanoparticles (Fe or Ni), and nano-MgO on their surface. Nano-MgO has a large specific surface area and high activity; when mixed with water, it forms a network structure and exhibits setting properties, improving the early strength of the cementless castable. Furthermore, it does not form low-melting-point phases at high temperatures, thus improving the refractoriness and high-temperature performance of the magnesia castable. The metal nanoparticles can act as catalysts to promote the formation of magnesium aluminum spinel whiskers / fibers.

[0036] 3. The aluminum-based metal microcapsules added to the cement-free magnesium castable of the present invention rupture at temperatures above 600°C, exposing the aluminum metal, which combines with oxygen in situ to form nano-Al2O3 and Al2O3 whiskers, resulting in micro-expansion that fills the pores and improves the density of the material.

[0037] 4. The cement-free magnesia castable of this invention involves the in-situ reaction of magnesium oxide in magnesia particles, fine magnesia powder, and aluminum-based metal microcapsules with nano-Al2O3 at high temperature to generate magnesium aluminum spinel whiskers / fibers, which significantly improves the strength of the castable. Furthermore, the micro-expansion generated by the in-situ reaction to generate magnesium aluminum spinel whiskers / fibers helps to fill pores, reduce pore size, prevent slag penetration, and improve the erosion resistance and permeability of the castable. Attached Figure Description

[0038] Figure 1 The microstructure of the cementless magnesium castable of the present invention after calcination at 1500℃ for 3 hours is shown. Detailed Implementation

[0039] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0040] Example 1

[0041] A cement-free magnesium castable is composed of aggregates, matrix materials and water-reducing agents.

[0042] The aggregate is:

[0043] 18 parts of magnesia particles with a particle size of less than 5 mm and greater than or equal to 3 mm;

[0044] 30 parts of magnesia particles with a particle size of less than 3 mm and greater than or equal to 1 mm;

[0045] Eighteen portions of magnesia particles with a diameter of less than 1 mm and greater than 0.1 mm.

[0046] The substrate is:

[0047]

[0048]

[0049] The method for preparing the aluminum-based metal microcapsules is as follows:

[0050] S1. Place aluminum powder or aluminum-based alloy powder in a metal compound solution and carry out a reduction reaction at 60°C. After stirring for 60 min, metal nanoparticles are deposited on the surface of the aluminum powder or aluminum-based alloy powder. Continue to add magnesium nitrate to the solution, stir for 30 min, filter and dry to obtain the microcapsule precursor.

[0051] S2. The microcapsule precursor is heat-treated in air at 300°C and then naturally cooled to obtain aluminum-based metal microcapsules.

[0052] The method of using the cement-free magnesium castable is as follows: Mix the aggregate and matrix material with 0.4% water-reducing agent to obtain a premixed matrix material; use a cement mortar mixer to mix the aggregate and premixed matrix material evenly, add 3% water (the sum of the aggregate and matrix material) for wet mixing, and mix for 1-3 minutes to obtain a slurry; pour the evenly mixed slurry into a mold, vibrate to form, and cure for 1-3 days.

[0053] The cement-free magnesium castable prepared in Example 1 of this invention, after heat treatment at 1100℃ for 3 hours, was tested and found to have the following characteristics: flexural strength at room temperature of 15 MPa, compressive strength at room temperature of 80 MPa, apparent porosity of 14%, and bulk density of 2.99 g / cm³. 3 After heat treatment at 1500℃ for 3 hours, the following results were obtained: flexural strength at room temperature 20 MPa, compressive strength at room temperature 160 MPa, apparent porosity 12%, and bulk density 3.10 g / cm³. 3 .

[0054] The process parameters for Examples 1-4 are shown in Tables 1 and 2:

[0055] Table 1

[0056]

[0057] Table 2

[0058]

[0059] The performance results of cement-free magnesium castables in Examples 1-4 are shown in Table 3:

[0060] Table 3

[0061]

[0062] Figure 1 This is the microstructure of the cement-free magnesium castable of the present invention after calcination at 1500℃ for 3 hours. From... Figure 1 It can be seen that after calcination at 1500℃ for 3 hours, a large number of magnesium aluminum spinel whiskers / fibers are generated in the matrix. These whiskers / fibers intertwine to form a network structure, which has the effect of strengthening and toughening.

[0063] For any points not covered above, existing technologies shall apply.

[0064] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A cement-free magnesium castable, characterized in that, The castable is composed of aggregate, matrix material and water-reducing agent; The aggregate is 60-80 parts of magnesium sand particles; The substrate is: 10-20 parts of fine magnesia powder 2-6 parts of active α-Al2O3 micro powder 5-10 parts of sintered corundum fine powder 0.1~0.5 parts of silica powder, 2-8 parts of aluminum-based metal microcapsules; The method for preparing the aluminum-based metal microcapsules is as follows: S1. Aluminum powder or aluminum-based alloy powder is placed in a metal compound solution for reduction reaction. After stirring for a period of time, metal nanoparticles are deposited on the surface of aluminum powder or aluminum-based alloy powder. Magnesium salt is added to the solution and stirred for 30 minutes. After filtration and drying, microcapsule precursor is obtained. The metal compound solution is ferric chloride solution or nickel chloride solution, and the metal nanoparticles are nano-Fe or nano-Ni particles. S2. The microcapsule precursor is heat-treated in air at 150°C to 500°C and then naturally cooled to obtain aluminum-based metal microcapsules.

2. The cement-free magnesium castable as described in claim 1, characterized in that, The aluminum powder or aluminum-based alloy powder has a particle size ≤74μm, and the aluminum-based alloy powder contains Si and Fe, with the Si content being less than 40wt%.

3. The cement-free magnesium castable as described in claim 1, characterized in that, In step S1 of the method for preparing aluminum-based metal microcapsules, a reduction reaction is carried out at 40~60℃ and stirred for 30~60 min.

4. The cement-free magnesium castable as described in claim 1, characterized in that, In step S1 of the method for preparing aluminum-based metal microcapsules, the magnesium salt is one of magnesium nitrate, magnesium oxalate, and magnesium carbonate.

5. The cement-free magnesium castable as described in claim 1, characterized in that, The magnesium sand particles include: 18-25 parts of magnesia particles with a diameter of less than 5 mm and greater than or equal to 3 mm. 24-30 parts of magnesia particles with a diameter of less than 3 mm and greater than or equal to 1 mm. 18-25 parts of magnesia particles with a diameter of less than 1 mm and greater than 0.1 mm; The MgO content of the fine magnesia powder is ≥96wt%, the particle size of the fine magnesia powder is ≤40μm, and the fine magnesia powder is one of fused magnesia and sintered magnesia.

6. The cement-free magnesium castable as described in claim 1, characterized in that, The water-reducing agent content is 0.1-0.4% of the sum of aggregate and matrix material, and the water-reducing agent is one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate and sodium silicate.

7. A method of using the cement-free magnesium castable as described in any one of claims 1-6, characterized in that: Mix the aggregate and matrix material with 0.1-0.4% water-reducing agent to obtain a premixed matrix material; stir the aggregate and the premixed matrix material evenly, add 3-4% water (total of aggregate and matrix material), stir for 1-3 minutes to obtain a slurry; pour the slurry into a mold, vibrate to form, and cure for 1-3 days.

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