A light-weight periclase-zirconite aggregate with core-shell structure and a preparation method thereof

Abstract

The application relates to a light periclase-zirconite aggregate with a core-shell structure and a preparation method thereof.The technical scheme is as follows: 84.0-96.0 wt% of magnesium hydroxide powder and 4.0-16.0 wt% of zirconite powder are used as raw materials, 2.0-5.0 wt% of aluminum hydroxide powder and 2.5-5.0 wt% of polyvinyl alcohol of the raw materials are additionally added, stirring is carried out, forming is carried out, drying is carried out, then the temperature is kept at 800-1100 DEG C for 1-3 hours, then the temperature is kept at 1400-1600 DEG C for 1-4 hours, cooling is carried out, crushing is carried out, screening is carried out, and packaging is carried out, so that the light periclase-zirconite aggregate with a core-shell structure is prepared.The light periclase-zirconite aggregate with a core-shell structure prepared by the application has the characteristics of high closed-pore porosity, small pore size, high strength, low thermal conductivity, excellent thermal shock resistance and excellent corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the technical field of lightweight periclase aggregates. Specifically, it relates to a core-shell structured lightweight periclase-zircon aggregate and its preparation method. Background Technology

[0002] Magnesia, with its high melting point (approximately 2800℃) and excellent resistance to alkaline slag, is a widely used refractory material in the linings of steelmaking converters, electric furnaces, ladles, and other metallurgical furnaces. Current methods for producing dense magnesia involve grinding lightly calcined magnesia into pellets and then calcining them at high temperatures, ensuring high density and excellent performance. However, dense magnesia has a high thermal conductivity, leading to significant heat dissipation from the furnace lining, which is detrimental to energy conservation and emission reduction in high-temperature industries. Therefore, low thermal conductivity has become the main development direction for magnesia in the future.

[0003] The patented technology "A sintered magnesia with a micro-nano composite pore structure and its preparation method" (CN108821750A) uses magnesium oxide micro powder and soluble magnesium solution as raw materials to prepare lightweight magnesia with a micro-nano composite pore structure. However, the porous lightweight magnesia has a high apparent porosity and a low closed porosity, which makes it difficult for its strength and corrosion resistance to meet the requirements of use.

[0004] The patented technology "Lightweight periclase-magnesia-olivine refractory material and its preparation method" (CN107445632A) uses magnesite, silica powder and silica sol as raw materials to prepare lightweight magnesia bonded with olivine. The main drawback of this technology is that the natural magnesite has a high impurity content, and a liquid phase will form at high temperature, which promotes the merging and growth of pores, thereby increasing the pore size and thermal conductivity of the magnesia and reducing the erosion resistance of the magnesia.

[0005] The patented technology, "A Lightweight Periacritic-Magnesium Aluminum Spinel Ramming Material and Its Preparation Method" (CN107285807B), utilizes magnesite and Al-containing... 3+ Porous periclase-magnesium aluminum spinel aggregate was prepared using solution as raw material. However, due to the excessive spinel content and excessive reaction expansion, the pores in this aggregate were large open pores, which significantly deteriorated the erosion resistance of the aggregate. Summary of the Invention

[0006] The present invention aims to overcome the defects of the prior art and provides a lightweight periclase-zircon aggregate with core-shell structure, characterized by high closed porosity, small pore size, high strength, low thermal conductivity, and excellent thermal shock resistance and erosion resistance, as well as its preparation method.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] Using 84.0–96.0 wt% magnesium hydroxide fine powder and 4.0–16.0 wt% zircon fine powder as raw materials, 2.0–5.0 wt% aluminum hydroxide fine powder and 2.5–5.0 wt% polyvinyl alcohol are added to the raw materials, stirred evenly, shaped, and dried; then kept at 800–1100℃ for 1–3 hours, and then kept at 1400–1600℃ for 1–4 hours, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate.

[0009] The magnesium hydroxide fine powder has a Mg(OH)2 content > 99 wt% and a particle size of 300–800 μm.

[0010] The zircon fine powder has a ZrSiO4 content > 98 wt% and a particle size < 20 μm.

[0011] The aluminum hydroxide fine powder has an Al(OH)3 content > 98 wt% and a particle size < 10 μm.

[0012] The pH value of the polyvinyl alcohol is 5 to 8.

[0013] The molding method is machine pressing, and the pressure of machine pressing is 5-15 MPa.

[0014] The drying temperature is 80–110°C, and the drying time is 8–12 hours.

[0015] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0016] The core-shell structured lightweight periclase-zircon aggregate prepared by this invention uses magnesium hydroxide with a particle size of 300-800 μm as raw material. This magnesium hydroxide can decompose in situ at 800-1100℃ to form aggregates containing numerous micro- and nano-pores and MgO microcrystals. Simultaneously, the Al2O3 formed from the decomposition of fine aluminum hydroxide powder has a small particle size and high activity, allowing it to diffuse into the aggregates and react with the MgO microcrystals to form the MgAl2O4 phase. The volume expansion accompanying in-situ spinelization hinders the merging, growth, and expulsion of pores within the aggregates, resulting in a core-shell structured lightweight periclase-zircon aggregate with small pore size and low thermal conductivity.

[0017] The zircon powder added in this invention reacts with MgO upon further temperature increase, forming a dense shell composed of Mg2SiO4 and ZrO2 around the agglomerate core. This seals the numerous micropores within the MgO agglomerates, ensuring the aggregate possesses a high porosity. The Mg2SiO4 and ZrO2 phases formed in this invention strengthen the bonding between agglomerates. Simultaneously, the ZrO2 phase and the microporous agglomerate core can absorb some thermal stress and promote crack deflection, endowing the lightweight periclase-zircon aggregate with a core-shell structure with high strength and excellent thermal shock resistance. Furthermore, the core-shell structure formed in this invention has a very high density, and the formed Mg2SiO4 and ZrO2 phases can react with the infiltrated slag, generating high-melting-point CaZrO3 and a high-viscosity liquid phase between the agglomerates. This effectively prevents further penetration and erosion by the slag, significantly improving the erosion resistance of the manufactured product.

[0018] The lightweight periclase-zircon aggregate with a core-shell structure prepared by this invention was tested and found to have the following characteristics: apparent porosity of 2.0–5.0%; closed porosity of 12.5–17.5%; average pore size of 0.15–0.30 μm; flexural strength of 125–165 MPa; thermal conductivity of 2.5–6.0 W / (m·K) at 500℃; and thermal shock resistance with a residual strength retention rate of 60–75% after one water cooling at 900℃.

[0019] Therefore, the core-shell structured lightweight periclase-zircon aggregate prepared by this invention has the characteristics of high closed porosity, small pore size, high strength, low thermal conductivity, excellent thermal shock resistance and excellent erosion resistance. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the scope of protection thereof:

[0021] A core-shell structured lightweight periclase-zircon aggregate and its preparation method. The preparation method described in this specific embodiment is as follows:

[0022] Using 84.0–96.0 wt% magnesium hydroxide fine powder and 4.0–16.0 wt% zircon fine powder as raw materials, 2.0–5.0 wt% aluminum hydroxide fine powder and 2.5–5.0 wt% polyvinyl alcohol are added to the raw materials, stirred evenly, shaped, and dried; then kept at 800–1100℃ for 1–3 hours, and then kept at 1400–1600℃ for 1–4 hours, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate.

[0023] The pH value of the polyvinyl alcohol is 5 to 8.

[0024] The pressure of the machine pressing is 5-15 MPa.

[0025] The drying temperature is 80–110°C, and the drying time is 8–12 hours.

[0026] The Mg(OH)2 content of the magnesium hydroxide fine powder is >99 wt%.

[0027] The zircon fine powder has a ZrSiO4 content > 98 wt%.

[0028] The aluminum hydroxide fine powder has an Al(OH)3 content > 98 wt%.

[0029] In this specific implementation:

[0030] The molding method is machine pressing;

[0031] The particle size of the magnesium hydroxide fine powder is 300-800 μm;

[0032] The particle size of the zircon fine powder is <20μm;

[0033] The particle size of the aluminum hydroxide fine powder is <10μm.

[0034] The details will not be repeated in the examples.

[0035] Example 1

[0036] A lightweight periclase-zircon aggregate with a core-shell structure and its preparation method. The preparation method described in this embodiment is as follows:

[0037] Using 84.0 wt% magnesium hydroxide fine powder and 16.0 wt% zircon fine powder as raw materials, and adding 2.0 wt% aluminum hydroxide fine powder and 2.5 wt% polyvinyl alcohol to the raw materials, the mixture is stirred evenly, shaped, and dried; then it is kept at 800℃ for 1 hour, and then kept at 1400℃ for 1 hour, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate.

[0038] The magnesium hydroxide fine powder has a Mg(OH)2 content of 99.1 wt%.

[0039] The zircon fine powder has a ZrSiO4 content of 98.1 wt%.

[0040] The aluminum hydroxide fine powder has an Al(OH)3 content of 98.1 wt%.

[0041] The pH value of the polyvinyl alcohol is 5.

[0042] The pressure of the machine pressing is 5 MPa.

[0043] The drying temperature is 80℃, and the drying time is 8 hours.

[0044] The lightweight periclase-zircon aggregate with a core-shell structure prepared in this embodiment was tested and found to have the following characteristics: apparent porosity of 5.0%; closed porosity of 17.5%; average pore size of 0.30 μm; flexural strength of 125 MPa; thermal conductivity of 2.5 W / (m·K) at 500℃; and thermal shock resistance with a residual strength retention rate of 60% after one water cooling at 900℃.

[0045] Example 2

[0046] A lightweight periclase-zircon aggregate with a core-shell structure and its preparation method. The preparation method described in this embodiment is as follows:

[0047] Using 96.0 wt% magnesium hydroxide fine powder and 4.00 wt% zircon fine powder as raw materials, and adding 5.0 wt% aluminum hydroxide fine powder and 5.0 wt% polyvinyl alcohol to the raw materials, the mixture is stirred evenly, shaped, and dried; then it is kept at 1100℃ for 3 hours, and then kept at 1600℃ for 4 hours, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate.

[0048] The magnesium hydroxide fine powder has a Mg(OH)2 content of 99.2 wt%.

[0049] The zircon fine powder has a ZrSiO4 content of 98.3 wt%.

[0050] The aluminum hydroxide fine powder has an Al(OH)3 content of 98.3 wt%.

[0051] The pH value of the polyvinyl alcohol is 8.

[0052] The pressure of the machine pressing is 15 MPa.

[0053] The drying temperature is 110°C, and the drying time is 12 hours.

[0054] The lightweight periclase-zircon aggregate with a core-shell structure prepared in this embodiment was tested and found to have the following characteristics: apparent porosity of 2.0%; closed porosity of 12.5%; average pore size of 0.15 μm; flexural strength of 165 MPa; thermal conductivity of 6.0 W / (m·K) at 500℃; and thermal shock resistance with a residual strength retention rate of 75% after one water cooling at 900℃.

[0055] Example 3

[0056] A lightweight periclase-zircon aggregate with a core-shell structure and its preparation method. The preparation method described in this embodiment is as follows:

[0057] Using 90.0 wt% magnesium hydroxide fine powder and 10.00 wt% zircon fine powder as raw materials, 4.0 wt% aluminum hydroxide fine powder and 3.5 wt% polyvinyl alcohol are added to the raw materials. The mixture is stirred evenly, shaped, and dried. Then, it is kept at 1000℃ for 2 hours and then at 1500℃ for 2 hours. After cooling, crushing, screening, and packaging, a core-shell structured lightweight periclase-zircon aggregate is obtained.

[0058] The magnesium hydroxide fine powder has a Mg(OH)2 content of 99.4 wt%.

[0059] The zircon fine powder has a ZrSiO4 content of 98.5 wt%.

[0060] The aluminum hydroxide fine powder has an Al(OH)3 content of 98.5 wt%.

[0061] The pH value of the polyvinyl alcohol is 6.

[0062] The pressure of the machine pressing is 8 MPa.

[0063] The drying temperature is 90°C, and the drying time is 9 hours.

[0064] The lightweight periclase-zircon aggregate with a core-shell structure prepared in this embodiment was tested and found to have the following characteristics: apparent porosity of 3.5%; closed porosity of 14.5%; average pore size of 0.25 μm; flexural strength of 145 MPa; thermal conductivity of 3.5 W / (m·K) at 500℃; and thermal shock resistance with a residual strength retention rate of 68% after one water cooling at 900℃.

[0065] Example 4

[0066] A lightweight periclase-zircon aggregate with a core-shell structure and its preparation method. The preparation method described in this embodiment is as follows:

[0067] Using 94.0 wt% magnesium hydroxide fine powder and 6.00 wt% zircon fine powder as raw materials, and adding 3.5 wt% aluminum hydroxide fine powder and 4.0 wt% polyvinyl alcohol to the raw materials, the mixture is stirred evenly, shaped, and dried; then it is kept at 900℃ for 3 hours, and then kept at 1500℃ for 3 hours, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate.

[0068] The magnesium hydroxide fine powder has a Mg(OH)2 content of 99.5 wt%.

[0069] The zircon fine powder has a ZrSiO4 content of 98.6 wt%.

[0070] The aluminum hydroxide fine powder has an Al(OH)3 content of 98.6 wt%.

[0071] The pH value of the polyvinyl alcohol is 7.

[0072] The pressure of the machine pressing is 12 MPa.

[0073] The drying temperature is 100℃, and the drying time is 10 hours.

[0074] The lightweight periclase-zircon aggregate with a core-shell structure prepared in this embodiment was tested and found to have the following characteristics: apparent porosity of 4.5%; closed porosity of 15.5%; average pore size of 0.20 μm; flexural strength of 135 MPa; thermal conductivity of 3.0 W / (m·K) at 500℃; and thermal shock resistance with a residual strength retention rate of 72% after one water cooling at 900℃.

[0075] This specific implementation method has the following advantages compared with the prior art:

[0076] The core-shell structured lightweight periclase-zircon aggregate prepared in this specific embodiment uses magnesium hydroxide with a particle size of 300-800 μm as raw material. This magnesium hydroxide can decompose in situ at 800-1100℃ to form aggregates containing numerous micro- and nano-pores and MgO microcrystals. Simultaneously, the Al2O3 formed from the decomposition of fine aluminum hydroxide powder has a small particle size and high activity, allowing it to diffuse into the aggregates and react with the MgO microcrystals to form the MgAl2O4 phase. The volume expansion accompanying in-situ spinelization hinders the merging, growth, and expulsion of pores within the aggregates, resulting in a core-shell structured lightweight periclase-zircon aggregate with small pore size and low thermal conductivity.

[0077] In this specific embodiment, the added zircon powder reacts with MgO as the temperature rises further, forming a dense shell composed of Mg2SiO4 and ZrO2 around the agglomerate core. This seals the numerous micropores within the MgO agglomerates, ensuring the aggregate has a high porosity. The Mg2SiO4 and ZrO2 phases formed in this embodiment strengthen the bonding between agglomerates. Simultaneously, the ZrO2 phase and the microporous agglomerate core absorb some thermal stress and promote crack deflection, endowing the lightweight periclase-zircon aggregate with a core-shell structure with high strength and excellent thermal shock resistance. Furthermore, the core-shell structure formed in this embodiment has a very high density, and the formed Mg2SiO4 and ZrO2 phases can react with the infiltrated slag, generating high-melting-point CaZrO3 and a high-viscosity liquid phase between the agglomerates. This effectively prevents further penetration and erosion by the slag, significantly improving the erosion resistance of the manufactured product.

[0078] The lightweight periclase-zircon aggregate with a core-shell structure prepared according to this specific embodiment was tested and found to have the following characteristics: apparent porosity of 2.0–5.0%; closed porosity of 12.5–17.5%; average pore size of 0.15–0.30 μm; flexural strength of 125–165 MPa; thermal conductivity of 2.5–6.0 W / (m·K) at 500 °C; and thermal shock resistance with a residual strength retention rate of 60–75% after one water-cooling at 900 °C.

[0079] Therefore, the core-shell structured lightweight periclase-zircon aggregate prepared in this specific embodiment has the characteristics of high closed porosity, small pore size, high strength, low thermal conductivity, excellent thermal shock resistance and excellent erosion resistance.

Claims

1. A method for preparing a light-weight periclase-zircon core-shell aggregate, characterized in that: Using 84.0~96.0wt% magnesium hydroxide fine powder and 4.0~16.0wt% zircon fine powder as raw materials, 2.0~5.0wt% aluminum hydroxide fine powder and 2.5~5.0wt% polyvinyl alcohol are added to the raw materials, stirred evenly, shaped, and dried; then kept at 800~1100℃ for 1~3 hours, and then kept at 1400~1600℃ for 1~4 hours, cooled, crushed, screened, and packaged to obtain a core-shell structured lightweight periclase-zircon aggregate; The magnesium hydroxide fine powder has a Mg(OH)2 content > 99 wt% and a particle size of 300~800 μm; The zircon fine powder has a ZrSiO4 content > 98 wt% and a particle size < 20 μm; The aluminum hydroxide fine powder has an Al(OH)3 content > 98 wt% and a particle size < 10 μm.

2. The process for the preparation of core-shell structured lightweight magnesia-zircon lightweight aggregate according to claim 1, characterized in that The pH value of the polyvinyl alcohol is 5-8.

3. The process for the preparation of core-shell structured lightweight magnesia-zirconite aggregates according to claim 1, characterized in that The molding method is machine pressing, and the pressure of machine pressing is 5~15MPa.

4. The process for the preparation of core-shell structured lightweight magnesia-zirconite aggregates according to claim 1, characterized in that The drying temperature is 80~110℃, and the drying time is 8~12 hours.

5. A core-shell structured lightweight periclase-zircon aggregate, characterized in that... The core-shell structured lightweight periclase-zircon aggregate is the core-shell structured lightweight periclase-zircon aggregate prepared by the preparation method according to any one of claims 1 to 4.