Magnesium oxide multiphase aggregate with multilayer core-shell structure, preparation method and application

Abstract

The invention discloses a magnesium oxide multiphase aggregate with a multilayer core-shell structure as well as a preparation method and application of the magnesium oxide multiphase aggregate. The aggregate comprises a porous magnesium oxide core, a spinel shell layer and a RE2O3 shell layer, the spinel shell layer is formed in situ, and the RE2O3 shell layer covers the spinel shell layer in a continuous manner. The preparation method is simple in process and low in cost, and the prepared product has the characteristics of excellent thermal shock resistance and erosion resistance and low high-temperature vacuum volatilization rate, and is suitable for being used as a lining raw material of a refractory material for smelting high-quality steel and high-temperature alloy.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature refractory material preparation, and in particular to a multi-layer core-shell structured magnesium oxide composite aggregate and a preparation method thereof. Background Art

[0002] Magnesia-based basic refractories have extremely high melting points, excellent corrosion resistance, and the ability to absorb certain inclusions in the melt. Therefore, their products are widely used in the melt pool area of high-temperature melts. However, traditional magnesia raw materials (such as periclase) contain high impurities and are easily hydrated. Furthermore, periclase has a high thermal expansion coefficient, resulting in poor thermal shock resistance in the resulting products. Therefore, in the field, periclase is generally used after forming a composite phase based on it.

[0003] For example, prior art CN118545982A discloses a method for preparing fused magnesium lanthanum / cerium sand refractory raw materials. This method uses light-burned magnesium oxide powder, lanthanum oxide powder, and cerium oxide powder as raw materials, and produces the fused magnesium lanthanum / cerium sand refractory raw materials through mixing, pelletizing, and electric melting. This refractory raw material requires ultra-high-temperature electric melting, which is costly and time-consuming. Furthermore, it is difficult for magnesium oxide to form a tight bond with lanthanum oxide / cerium oxide, posing a risk of cracking during use.

[0004] For example, prior art CN119080514A discloses a lightweight periclase-spinel aggregate and its preparation method. This method uses light-burned magnesium oxide fine powder, aluminum hydroxide fine powder, nickel oxide fine powder, and polyvinyl alcohol as raw materials, and produces the lightweight periclase-spinel aggregate through stirring, mechanical pressing, drying, sintering, crushing, and screening. However, this method has difficulty controlling the decomposition of MgO at high temperatures to produce Mg and O gases, which is not conducive to improving the corrosion resistance of the product.

[0005] Finally, prior art CN108821750A discloses a sintered magnesia with a micro-nano composite pore structure and a method for preparing the same. This method uses magnesium-containing raw material powder and a soluble magnesium salt as raw materials, and produces the sintered magnesia with a micro-nano composite pore structure through mechanical pressing, drying, and high-temperature sintering. However, the product has an excessively high apparent porosity, making it susceptible to flaking and impurities due to insufficient strength in actual service environments. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art and aims to provide a magnesium oxide refractory raw material with simple preparation process, low cost, high thermal shock resistance, high corrosion resistance and ultra-low high temperature vacuum volatility.

[0007] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a multi-layer core-shell structured magnesium oxide composite aggregate, comprising: a porous magnesium oxide core; a spinel shell layer, wherein the spinel shell layer is formed in situ; and a RE2O3 shell layer, wherein the RE2O3 shell layer continuously covers the spinel shell layer.

[0008] Furthermore, RE in the RE2O3 is one or more of Y, La and Ce, and the thickness of the RE2O3 shell is 24-32 μm.

[0009] Furthermore, the bulk density of the aggregate is 3.11-3.45 g / cm 3 ; and / or, the apparent porosity of the aggregate is 10.52-11.25%.

[0010] In a second aspect, the present invention provides a method for preparing a multi-layer core-shell structured magnesium oxide composite aggregate, the method comprising the following steps: Step 1: preparing green ball I, using a first powder containing Mg as a matrix, mixing with a binder, and then forming a ball to obtain green ball I; Step 2: preparing green ball II, mixing the green ball I with a second powder, and attaching the second powder to the green ball I to obtain green ball II, wherein the second powder contains Al and RE elements; Step 3: Drying: Drying the green ball II; Step 4: sintering, sintering the dried green ball II to obtain a multi-layer core-shell structured magnesium oxide composite aggregate, wherein the aggregate includes an in-situ formed spinel shell layer.

[0011] Furthermore, the first powder is salt lake light-burned magnesium; and / or the binder is nano-magnesium hydroxide aqueous solvent; and / or the second powder is a mixed powder containing Al(OH)3 powder and RE2O3 powder.

[0012] Furthermore, the content of each material in the preparation method is expressed as follows in weight percentage: 46-68 parts by weight of salt lake light-burned magnesia, wherein the MgO content is greater than 99.9wt%, the particle size D 0.5 <0.74μm; 13-25 parts by weight of nano magnesium hydroxide aqueous solvent, wherein the Mg(OH)2 content is >99.8wt%, the concentration is 500ppm-4000ppm; 30-48 parts by weight of Al(OH)3 powder, wherein the Mg(OH)2 content is >99.9wt%, the particle size D 0.5 <0.74μm; 2-4 parts by weight of RE2O3 powder, wherein the RE2O3 content is >99.9wt%, particle size D 0.5 <5μm.

[0013] Furthermore, the preparation method of the nano-magnesium hydroxide aqueous solvent is to add the aluminum hydroxide into the pure water at a mass ratio of nano-magnesium hydroxide to pure water of 1-8:1999, and stir until the mixture is uniform.

[0014] Furthermore, the sintering process adopts a step-by-step heat preservation method, first heating to 750-900°C and keeping it for 1-2 hours, then heating to 1500-1550°C and keeping it for 2-4 hours, and finally heating to 1780-1900°C and keeping it for 3-6 hours.

[0015] In a third aspect, the present invention further provides a use of an aggregate, wherein the aggregate can be used to prepare masonry materials for furnaces, such as castables, refractory bricks, and the like.

[0016] In a fourth aspect, the present invention further provides an application of an aggregate, which can be used for steel casting or high-temperature alloy vacuum melting.

[0017] Due to the adoption of the above technical solution, the present invention has the following positive effects compared with the prior art: First, the present invention achieves significant lightweighting while also improving the material's thermal shock resistance. The invention pioneered the concept of heat-insulated sintering at 750-900°C, allowing nano-magnesium hydroxide to decompose in situ to produce micro-nano closed pores. Furthermore, the "salt mother phase" structure left behind by the nano-magnesium hydroxide raw material ensures that these pores are not completely eliminated during the medium-temperature sintering process, thereby forming a porous magnesium oxide core structure. These micro-nano closed pores effectively alleviate thermal stress, inhibiting the formation and propagation of internal cracks, thereby improving the thermal shock resistance of magnesium oxide refractory materials while also reducing their bulk density.

[0018] Secondly, the present invention significantly improves the material's service performance. After the first stage of sintering, the temperature is raised to the second stage (1500°C-1550°C) and maintained for 2-4 hours. The highly active Al(OH)3 adhering to the outer layer begins to decompose into Al2O3. Leveraging the different diffusion rates between the MgO-Al2O3-RE2O3 phases at high temperatures and the insolubility of the intermediate phase products in the MgO-RE2O3 system, a solid-phase reaction produces a dense and uniform intermediate MgAl2O4 layer. RE2O3 is distributed throughout the outermost layer of the aggregate, forming a continuous, dense rare earth oxide shell. Within this multi-layered core-shell structure, the rare earth oxides exhibit excellent resistance to slag and alloy corrosion. Combined with the porous MgO core structure, they suppress the thermal expansion of the magnesia below high temperatures, improving the thermal shock resistance of the product. The in-situ formed spinel layer and dense RE2O3 shell not only ensure aggregate strength, but also reduce the intracrystalline volatility and slag erosion and penetration distance under high-temperature vacuum conditions.

[0019] Third, the preparation method of the present invention is simple and efficient. The present invention can obtain a "porous magnesium oxide core + continuous dense spinel shell + continuous dense RE2O3 shell" structure (P magnesium oxide @ D spinel @ D RE2O3 core-shell structure, i.e. MgO@MgAl2O4@RE2O3) through a one-step sintering process. The apparent porosity of the aggregate is 10.52-11.25%; the bulk density is 3.11-3.45 g / cm 3 Under the conditions of 1700°C and 10Pa, the temperature and pressure were maintained for 1 hour, and the high-temperature vacuum volatility was 1.0-1.4%. After three water coolings at 1100-20°C, the sphere integrity was 96-100%. The integrity of the spheres before and after water cooling was used to characterize the thermal shock resistance of the raw material. The slag erosion depth of the sample was 95-108μm, the continuous rare earth oxide shell thickness was 24-32μm, and the continuous spinel shell thickness was 160-210μm. Compared with existing technologies, the performance is significantly improved.

[0020] In summary, the present invention has the characteristics of simple process and low cost. The prepared multi-layer core-shell structure lightweight spherical refractory aggregate has low high-temperature vacuum volatility, excellent thermal shock resistance and excellent hydration resistance. It is suitable for the vacuum melting process of high-temperature alloys or the vacuum secondary refining process of clean steel. It is expected to be used in the melting process of high-quality steel and high-temperature alloys, and solve the problems of thermal shock resistance and high vacuum volatility of existing magnesium oxide raw materials that pollute molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the microstructure of the multi-layer core-shell structure MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate in Example 1.

[0022] Figure 2 This is the CT structure of the multi-layer core-shell structure MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate in Example 3. DETAILED DESCRIPTION

[0023] In order to further understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments, which does not limit the scope of protection of the present invention.

[0024] Example 1: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight magnesium oxide composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 48 parts by weight of salt lake light-burned magnesium are added to 13 parts by weight of a nano-magnesium hydroxide aqueous solution as a binder, wherein the concentration of the nano-magnesium hydroxide aqueous solution is 3000 ppm; and a forced mixer ball-forming method is used to prepare high-strength green balls I. The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: adding the nano magnesium hydroxide to pure water at a mass ratio of nano magnesium hydroxide to pure water of 6:1999, and stirring and mixing the mixture evenly.

[0025] Step 2: Add 48 parts by weight of Al(OH)3 powder and 4 parts by weight of Y2O3 powder (i.e., RE is Y in this case) to a ball mill and mill for 1 hour to obtain a uniformly mixed second powder. Add the green ball I prepared in Step 1 and the second powder to a disc ballizer, allowing the second powder to adhere to the green ball I, to produce green ball II. Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 900°C and keep it for 1 hour, then heat it to 1500°C and keep it for 2 hours, and finally heat it to 1780°C and keep it for 6 hours. Cool it naturally in the furnace to obtain a lightweight spherical refractory aggregate with a multi-layer core-shell structure of MgO@MgAl2O4@RE2O3.

[0026] After testing, the yttrium oxide continuous shell layer thickness of the MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate with a multi-layer core-shell structure described in this embodiment is 28 μm, and the spinel shell layer is continuous and has a thickness of 210 μm.

[0027] Example 2: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight magnesium oxide composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 53 parts by weight of salt lake light-burned magnesium is used as a base, 23 parts by weight of a nano-magnesium hydroxide aqueous solution is added as a binder, wherein the concentration of the nano-magnesium hydroxide aqueous solution is 500 ppm; and a forced mixer ball-forming method is used to prepare high-strength green balls I. The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: adding the nano magnesium hydroxide to pure water at a mass ratio of nano magnesium hydroxide to pure water of 1:1999, and stirring and mixing the mixture evenly.

[0028] Step 2: Add 44 parts by weight of Al(OH)3 powder and 3 parts by weight of Ce2O3 powder (i.e., RE is Ce in this case) to a ball mill and mill for 2 hours to obtain a uniformly mixed second powder. Add the green ball I prepared in Step 1 and the second powder to a disc ball making machine, so that the second powder adheres to the green ball I, to produce green ball II. Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 850°C and keep it for 2 hours, then heat it to 1530°C and keep it for 3 hours, and finally heat it to 1900°C and keep it for 3 hours. Cool it naturally in the furnace to obtain a lightweight spherical refractory aggregate with a multi-layer core-shell structure of MgO@MgAl2O4@RE2O3.

[0029] After testing, the cerium oxide continuous shell layer thickness of the MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate with a multi-layer core-shell structure described in this embodiment is 32 μm, and the spinel shell layer is continuous and has a thickness of 160 μm.

[0030] Example 3: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight magnesium oxide composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 60 parts by weight of salt lake light-burned magnesium is used as a base, 25 parts by weight of a nano-magnesium hydroxide aqueous solution is added as a binder, wherein the concentration of the nano-magnesium hydroxide aqueous solution is 1000 ppm; and a forced mixer ball-forming method is used to prepare high-strength green balls I; The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: adding the nano magnesium hydroxide to pure water at a mass ratio of nano magnesium hydroxide to pure water of 2:1999, and stirring and mixing the mixture evenly.

[0031] Step 2: Add 37 parts by weight of Al(OH)3 powder and 3 parts by weight of La2O3 powder (i.e., RE is La in this case) to a ball mill and mill for 2 hours to obtain a uniformly mixed second powder. Add the green ball I prepared in Step 1 and the second powder to a disc ballizer, allowing the second powder to adhere to the green ball I, to produce green ball II. Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 750°C and keep it for 2 hours, then heat it to 1550°C and keep it for 4 hours, and finally heat it to 1800°C and keep it for 4 hours. Cool it naturally in the furnace to obtain a lightweight spherical refractory aggregate with a multi-layer core-shell structure of MgO@MgAl2O4@RE2O3.

[0032] After testing, the lanthanum oxide continuous shell layer thickness of the MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate with a multi-layer core-shell structure described in this embodiment is 30 μm, and the spinel shell layer is continuous and has a thickness of 192 μm.

[0033] Example 4: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight magnesium oxide composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 68 parts by weight of salt lake light-burned magnesium are added to 20 parts by weight of a nano-magnesium hydroxide aqueous solution as a binder, wherein the concentration of the nano-magnesium hydroxide aqueous solution is 4000 ppm; and a forced mixer ball-forming method is used to prepare high-strength green balls I. The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: adding the nano magnesium hydroxide into pure water at a mass ratio of nano magnesium hydroxide to pure water of 8:1999, and stirring and mixing the mixture evenly.

[0034] Step 2: Add 30 parts by weight of Al(OH)3 powder and 2 parts by weight of La2O3 powder (i.e., RE is La in this case) to a ball mill and mill for 3 hours to obtain a uniformly mixed second powder. Add the green ball I prepared in Step 1 and the second powder to a disc ball making machine, so that the second powder adheres to the green ball I, to produce green ball II. Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 800°C and keep it for 1.5 hours, then heat it to 1520°C and keep it for 3 hours, and finally heat it to 1850°C and keep it for 5 hours. Cool it naturally in the furnace to obtain a lightweight spherical refractory aggregate with a multi-layer core-shell structure of MgO@MgAl2O4@RE2O3.

[0035] After testing, the lanthanum oxide continuous shell layer thickness of the MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate with a multi-layer core-shell structure described in this embodiment is 24 μm, and the spinel shell layer is continuous and has a thickness of 188 μm.

[0036] Example 5: This embodiment provides a method for preparing a multi-layer core-shell structure lightweight magnesium oxide composite aggregate by one-step sintering, which specifically includes the following steps: Step 1: 55 parts by weight of salt lake light-burned magnesium is used as a base, 18 parts by weight of a nano-magnesium hydroxide aqueous solution is added as a binder, wherein the concentration of the nano-magnesium hydroxide aqueous solution is 2000 ppm; and a forced mixer ball-forming method is used to prepare high-strength green balls I; The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: adding the nano magnesium hydroxide to pure water at a mass ratio of nano magnesium hydroxide to pure water of 4:1999, and stirring and mixing the mixture evenly.

[0037] Step 2: Add 43 parts by weight of Al(OH)3 powder and 2 parts by weight of Ce2O3 powder (i.e., RE is Ce in this case) to a ball mill and mill for 1 hour to obtain a uniformly mixed second powder. Add the green ball I prepared in Step 1 and the second powder to a disc ball making machine, so that the second powder adheres to the green ball I, to produce green ball II. Step 3, drying the green ball II; Step 4: Add the dried green ball II into a sintering furnace, heat it to 860°C and keep it for 1 hour, then heat it to 1540°C and keep it for 3 hours, and finally heat it to 1830°C and keep it for 4 hours. Cool it naturally in the furnace to obtain a lightweight spherical refractory aggregate with a multi-layer core-shell structure MgO@MgAl2O4@RE2O3.

[0038] After testing, the cerium oxide continuous shell layer thickness of the MgO@MgAl2O4@RE2O3 lightweight spherical refractory aggregate with a multi-layer core-shell structure described in this embodiment is 31 μm, and the spinel shell layer is continuous and has a thickness of 200 μm.

[0039] Example 6: In order to test the performance of the aggregates prepared in Examples 1-5 above and the aggregates prepared by the prior art (it should be noted that in order to make the results comparable, the testing of various performance indicators adopts unified conditions, for example, the high-temperature vacuum volatility is measured at a temperature of 1700°C and a pressure of 10Pa, and the heat and pressure are maintained for 1 hour; the sphere integrity percentage is measured after three times of water cooling at 1100-20°C, and the sphere integrity percentage before and after water cooling is used to characterize the thermal shock resistance of the raw material), the results are shown in the following table:

[0040] It can be seen from the above table that the key performance of the aggregate designed in this application is better than that of the existing technology when used in high temperature environment.

[0041] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A multi-layer core-shell structure magnesium oxide composite aggregate, characterized in that: The aggregate includes: porous magnesium oxide core; a spinel shell layer, the spinel shell layer being formed in situ; and, A RE2O3 shell layer covers the spinel shell layer in a continuous manner.

2. The multi-layer core-shell structure lightweight magnesium oxide composite aggregate according to claim 1, characterized in that: RE in the RE2O3 is one or more of Y, La and Ce, and the thickness of the RE2O3 shell is 24-32 μm; and / or, The thickness of the spinel shell is 160-210 μm.

3. A multi-layer core-shell structure lightweight magnesium oxide composite aggregate according to claim 1 or 2, characterized in that: The bulk density of the aggregate is 3.11~3.45g / cm 3 and / or, The apparent porosity of the aggregate is 10.52-11.25%.

4. A method for preparing a multi-layer core-shell structured magnesium oxide composite aggregate, characterized in that: The method comprises the following steps: Step 1: preparing green ball I, using a first powder containing Mg as a matrix, mixing with a binder, and then forming a ball to obtain green ball I; Step 2: preparing green ball II, mixing the green ball I with a second powder, and attaching the second powder to the green ball I to obtain green ball II, wherein the second powder contains Al and RE elements; Step 3: Drying: Drying the green ball II; Step 4: sintering, sintering the dried green ball II to obtain a multi-layer core-shell structured magnesium oxide composite aggregate, wherein the aggregate includes an in-situ formed spinel shell layer.

5. The preparation method according to claim 4, characterized in that The first powder is salt lake light-burned magnesia; and / or, The binder is a nano magnesium hydroxide aqueous solvent; and / or, The second powder is a mixed powder containing Al(OH)3 powder and RE2O3 powder.

6. The preparation method according to claim 5, characterized in that The content of each material in the preparation method is expressed as follows in weight percentage: 46-68 parts by weight of salt lake light-burned magnesia, wherein the MgO content is greater than 99.9wt% and the particle size is D 0.5 <0.74μm; 13-25 parts by weight of nano magnesium hydroxide aqueous solution, wherein the Mg(OH)2 content is greater than 99.8wt% and the concentration is 500ppm-4000ppm; 30-48 parts by weight of Al(OH)3 powder, wherein the Mg(OH)2 content is greater than 99.9wt% and the particle size is D 0.5 <0.74μm; 2-4 parts by weight of RE2O3 powder, wherein the RE2O3 content is greater than 99.9wt% and the particle size is D 0.5 <5μm.

7. The preparation method according to claim 5 or 6, characterized in that: The preparation method of the nano magnesium hydroxide aqueous solvent is as follows: according to the mass ratio of nano magnesium hydroxide to pure water being 1-8:1999, the aluminum hydroxide is added to the pure water, and the mixture is stirred until uniformly mixed.

8. The preparation method according to any one of claims 4 to 6, characterized in that The sintering process adopts a step-by-step heat preservation method, first heating to 750-900°C and keeping warm for 1-2 hours, then heating to 1500-1550°C and keeping warm for 2-4 hours, and finally heating to 1780-1900°C and keeping warm for 3-6 hours.

9. Use of the aggregate according to claims 1-3 or the aggregate prepared by the method according to claims 4-8, characterized in that: The aggregate is used for preparing castables and bricks.

10. Use of the aggregate according to claims 1-3 or the aggregate prepared by the method according to claims 4-8, characterized in that: The aggregate is used for steel casting or high-temperature alloy vacuum melting.

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