Porous mullite ceramic with spinel pore layer structure and method for producing same
By preparing porous mullite ceramics with a magnesium-aluminum spinel porous layer structure, the problem of poor resistance to alkali metal compound corrosion of mullite ceramics at high temperatures was solved, achieving high strength, low thermal conductivity and excellent resistance to alkali corrosion. The process is simple and low cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 陈伟雄
- Filing Date
- 2024-10-18
- Publication Date
- 2026-07-03
Smart Images
Figure CN119330744B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ceramic technology, and in particular to a porous mullite ceramic with a spinel pore layer structure and its preparation method. Background Technology
[0002] Porous ceramics, due to the numerous closed or interconnected pores in their internal structure, can increase the specific surface area and reduce the thermal conductivity, making them widely used in filtration, catalyst supports, and thermal insulation materials. Mullite porous ceramics, in particular, possess excellent high-temperature resistance, thermal shock stability, and mechanical strength, ensuring durability and reliability in practical applications. However, mullite exhibits poor resistance to alkali metal compounds (R, R₂O, ROH, etc., where R represents Li, Na, or K) at high temperatures. Alkalis or their salts typically diffuse into the material in liquid or gaseous states, reacting with the alkali and causing volume expansion, leading to corrosion of the working surface layer. The rate of alkali or salt corrosion is related to the number and size of pores in the mullite. Therefore, the high porosity and low thermal conductivity of porous mullite limit its practical applications.
[0003] As in (Li Guangqi, Chen Junhong, Jia Yuanping, et al. Damage Mechanism of Silicon Carbidemullite Bricks for Transition Zone of Cement Rotary Kilns[J]. China , In the article "s Reefractories, 2020, 29(4):35-39", it is mentioned that in the transition zone of the cement rotary kiln converter, alkaline vapor will enter the internal pores of silicon carbide-mullite bricks, forming a high-temperature liquid phase zone, dissolving Al2O3 and SiO2 in the bricks. The precipitated potassium feldspar, potassium chloride and other crystals destroy the original structure of the bricks, increase the difference in thermal expansion coefficients between the high-temperature dense end and the metamorphic layer, causing the bricks to crack and peel off.
[0004] Domestic and international scholars have conducted extensive research on the poor resistance of aluminosilicate materials, represented by mullite, to alkali metal compound corrosion. A common approach is to introduce alkaline refractory materials such as magnesia, magnesia spinel, dolomite, forsterite, and limestone into the material system. For example, in the paper (Wang Ruining. Preparation and Performance Study of Mullite-Spinel High-Temperature Materials [D]. Xi'an University of Architecture and Technology, 2005.), mullite and magnesia spinel were uniformly mixed and sintered, hoping to utilize the excellent corrosion resistance of magnesia spinel to improve the overall corrosion resistance of the composite material. It is worth noting that because the introduced spinel phase is in a free state, alkali metal compounds will still preferentially react with mullite, so although the alkali corrosion resistance of the material system is improved, it is not significantly enhanced. Summary of the Invention
[0005] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a porous mullite ceramic with a spinel pore layer structure exhibiting excellent resistance to alkali compound erosion, and a method for its preparation.
[0006] The present invention discloses a method for preparing porous mullite ceramics with a spinel pore layer structure, using lightweight spherical mullite micro powder, sintered corundum micro powder, silicon micro powder, and fused magnesia / starch (MgO@(C6H)). 10 Using O5)n) composite pore-forming agent as raw material, after adding binder and mixing, the mixture is encapsulated, machine-pressed, dried and calcined to obtain porous mullite ceramics with spinel pore layer structure.
[0007] Among them, the fused magnesia / starch (MgO@(C6H) 10 The preparation method of O5)n composite pore-forming agent is as follows: a mixed gel is prepared by using starch, fused magnesium abrasive and water, the mixed gel is dried and then ball-milled until the particle size is less than 0.074 mm to obtain the composite pore-forming agent;
[0008] The lightweight spherical mullite powder is obtained by crushing, drying, grinding, granulating, and calcining secondary bauxite at high temperature.
[0009] Furthermore, lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch (MgO@(C6H) 10 The mass ratio of O5)n) composite pore-forming agent is 40-60: 20-40: 6-10: 8-18.
[0010] Furthermore, aluminum dihydrogen phosphate solution is used as a binder, and the aluminum dihydrogen phosphate solution accounts for 8-10 wt% of the raw material.
[0011] Furthermore, the roasting is carried out at 1350-1450℃ for 3-4 hours.
[0012] Furthermore, the fused magnesia / starch (MgO@(C6H)10 The preparation process of the O5)n) composite pore-forming agent is as follows: starch, fused magnesia and water are mixed in a mass ratio of 1:(0.8~1.6):(2.5~4). The mixture is placed in a constant temperature magnetic stirring water bath and heated and stirred. When the temperature rises to 70~75℃, it is allowed to stand for 1~1.5h to obtain a mixed gel. The gel is cooled to room temperature and dried at 100~110℃ for 12~24h. The dried material is ball-milled until the particle size is less than 0.074mm to obtain the composite pore-forming agent.
[0013] Furthermore, the ball milling medium is corundum balls, and the ball-to-material ratio is 3:1 to 5:1.
[0014] Furthermore, the starch is any one of corn starch, sweet potato starch, or tapioca starch amylopectin.
[0015] Furthermore, the specific preparation method of the lightweight spherical mullite powder is as follows: secondary bauxite is crushed to 30-90mm, dried in a dryer, ground to 200-400 mesh, granulated by a granulator, and then calcined in a rotary kiln at a high temperature of 1400-1500℃ to obtain lightweight spherical mullite of various particle sizes.
[0016] Furthermore, the main chemical composition of the fused magnesia is: MgO content ≥ 95.03 wt%, Al2O3 content ≤ 0.18 wt%, SiO2 content ≤ 1.65 wt%; and the particle size of the fused magnesia is ≤ 0.074 mm.
[0017] Furthermore, the main chemical components of the lightweight spherical mullite micro powder are: Al2O3 content ≥ 62.29 wt%, SiO2 content ≥ 30.8 wt%, and MgO content ≤ 0.3 wt%.
[0018] Furthermore, the lightweight spherical mullite powder has a particle size ≤0.074mm, an apparent porosity of 29.1%, and a median pore size of 10.30μm.
[0019] Furthermore, the main chemical composition of the sintered corundum micro powder is: Al2O3 content ≥ 99.46wt%, SiO2 content ≤ 0.09wt%; and the particle size of the sintered corundum micro powder is ≤ 0.074mm.
[0020] The main chemical components of the silicon micro powder are: SiO2 content ≥ 96.11 wt%, Al2O3 content ≤ 0.51 wt%, MgO content ≤ 0.25 wt%; and the particle size of the silicon micro powder is ≤ 0.109 mm.
[0021] A porous mullite ceramic with a spinel pore layer structure prepared by the preparation method described above.
[0022] Compared with the prior art, the present invention has the following advantages:
[0023] 1. This invention utilizes the gelatinization and aging properties of amylopectin to prepare core-shell structured fused magnesia / starch (MgO@(C6H)2) 10 O5)n) composite pore-forming agent, during the pore-forming process, the shell layer (starch) will burn away to form pores, and the exposed core (fused magnesia) will react with the pore wall (mullite) to form a magnesium aluminum spinel pore layer structure (such as Figure 2 Porous mullite ceramics (as shown). By adjusting the magnesia / starch composite ratio in the composite pore-forming agent, the pore structure (thickness, size, and distribution of magnesium aluminum spinel pores, etc.) in the ceramic can be designed in a controllable manner.
[0024] 2. The lightweight spherical mullite micropowder used in this invention is a functionalized refractory raw material. The spherical geometry gives the micropowder good flowability, controllable particle size, and dense packing characteristics. The interior of the spherical micropowder contains a grid formed by cross-stacked columnar mullite, and the grid surface is covered with a certain amount of glass phase, resulting in numerous tiny closed pores within the micropowder. Compared to traditional raw materials such as bauxite, mullite, and alumina, porous mullite ceramics prepared using lightweight spherical mullite micropowder as the main raw material have the advantages of being lightweight, having low conductivity, and high strength.
[0025] 3. This invention utilizes fused magnesia / starch (MgO@(C6H) 10 The structure and chemical composition of the O5)n) composite pore-forming agent were studied. During the preparation of porous mullite ceramics using an organic combustion method, fused magnesia reacted with free alumina at high temperatures, forming pores with a magnesium-aluminate spinel pore layer structure (such as...). Figure 2 (As shown). Due to spinel's excellent resistance to alkali metal compound corrosion, the presence of a spinel shell structure can solve the problem that when a free spinel phase is directly introduced into mullite materials, the aluminum-silicon bonded phase will still preferentially react with alkali and cannot block alkali penetration.
[0026] 4. Due to the difference in thermal expansion coefficients between spinel and mullite, microcracks will form at the interface between the spinel pore layer and the mullite matrix in the porous ceramics prepared by this invention. By adjusting the amount of silicon powder added in the raw materials and utilizing the high glass phase of lightweight spherical mullite powder, the microcracks can be effectively sealed and controlled into a collection of closed pores. Compared with the multiphase ceramics prepared by the traditional mechanical mixing of spinel and mullite, this method reduces the problems caused by cracks, visible pores, and through pores, and improves the strength and alkali corrosion resistance of porous mullite.
[0027] The porous mullite ceramic with a spinel-like porous structure prepared by this invention has a bulk density of 1.01–2.09 g·cm³. -3The apparent porosity is 32.5–56.1%; the compressive strength is 58.5–91.1 MPa; the thermal conductivity is 0.21–0.47 W / (m·K); and the resistance to soda ash corrosion is 18.4–31.8% higher than that of porous mullite ceramics without spinel pores.
[0028] Therefore, the present invention has the characteristics of low preparation cost, simple process and controllable process; the prepared spinel porous mullite ceramic has low bulk density, low thermal conductivity, high compressive strength and excellent resistance to alkali metal compound corrosion. Attached Figure Description
[0029] Figure 1 SEM image of the porous mullite ceramic with spinel pore layer structure prepared in Example 1;
[0030] Figure 2 This is a schematic diagram of the porous mullite ceramic with a spinel pore layer structure prepared in Example 1. Detailed Implementation
[0031] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.
[0032] Fused magnesia / starch (MgO@(C6H) 10 Preparation of O5)n) composite pore-forming agent
[0033] The starch, fused magnesia, and water were mixed in a mass ratio of 1:(0.8-1.6):(2.5-4). The mixture was heated and stirred in a constant temperature magnetic stirring water bath. When the temperature reached 70-75℃, it was allowed to stand for 1 hour to allow the starch to gelatinize, resulting in a mixed gel of starch and fused magnesia. After the gel cooled and aged, it was dried at 100-110℃ for 12-24 hours. After drying, the material was ball-milled until the particle size was less than 0.074 mm to obtain the composite pore-forming agent.
[0034] The main chemical components of fused magnesia are: MgO content ≥ 95.03 wt%, Al2O3 content ≤ 0.18 wt%, SiO2 content ≤ 1.65 wt%; and particle size ≤ 0.074 mm.
[0035] The starch is any one of corn starch, sweet potato starch, or tapioca starch, or amylopectin.
[0036] Preparation of the lightweight spherical mullite micro powder
[0037] Secondary bauxite is crushed to 30-90mm, dried in a dryer, ground to 200-400 mesh, granulated by a granulator, and then calcined in a rotary kiln at 1400-1500℃ to produce clinker. After sieving, lightweight spherical mullite of various particle sizes is obtained.
[0038] The main chemical components of the lightweight spherical mullite powder are: Al2O3 content ≥62.29wt%, SiO2 content ≥30.8wt%, MgO content ≤0.3wt%; the particle size of the lightweight spherical mullite powder is ≤0.074mm, the apparent porosity is 29.1%, and the median pore size is 10.30μm.
[0039] Preparation of porous mullite ceramics with spinel porous layer structure
[0040] Using 40–60 wt% lightweight spherical mullite micro powder, 20–40 wt% sintered corundum micro powder, 6–10 wt% silica micro powder, and 8–18 wt% composite pore-forming agent as raw materials, and adding 8–10 wt% aluminum dihydrogen phosphate solution of the aforementioned raw materials as a binder, the mixture is mixed for 60–120 min, encapsulated and trapped for 12–24 h, machine-pressed at 80–120 MPa, dried at 90–110 °C for 12–24 h, and held at 1350–1450 °C for 3–4 h, a porous mullite ceramic with a spinel pore layer structure is obtained.
[0041] The main chemical components of sintered corundum micro powder are: Al2O3 content ≥ 99.46wt%, SiO2 content ≤ 0.09wt%; and particle size of sintered corundum micro powder ≤ 0.074mm.
[0042] The main chemical components of silicon micro powder are: SiO2 content ≥ 96.11 wt%, Al2O3 content ≤ 0.51 wt%, MgO content ≤ 0.25 wt%; and the particle size of silicon micro powder ≤ 0.109 mm.
[0043] Example 1
[0044] First, starch, fused magnesia and water were mixed in a mass ratio of 1:0.9:2.6. The mixture was heated and stirred in a constant temperature magnetic stirring water bath. When the temperature reached 70℃, it was left to stand for 1 hour to allow the starch to gelatinize and obtain a mixed gel. After the gel cooled and aged, it was dried at 100℃ for 12-15 hours. After drying, the material was ball-milled until the particle size was less than 0.074 mm to obtain the composite pore-forming agent.
[0045] Then, in a mass ratio of 40:20:6:8, lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch (MgO@(C6H) 10 Using O5)n) composite pore-forming agent as raw material, and adding 8wt% of aluminum dihydrogen phosphate solution as binder, the mixture is mixed for 60-90 min, encapsulated and trapped for 12-15 h, machine-pressed at 80-90 MPa, dried at 90-100℃ for 12-15 h, and kept at 1350-1400℃ for 3-3.5 h to obtain a porous mullite ceramic with a spinel pore layer structure.
[0046] The porous mullite ceramic with a spinel-layered structure prepared in this embodiment has a bulk density of 2.09 g·cm³. -3 The apparent porosity was 32.5%; the compressive strength was 58.5 MPa; the thermal conductivity was 0.47 W / (m·K); and the resistance to soda ash corrosion was 40.17%, which is 18.4% higher than that of the porous mullite ceramic without spinel pores prepared in Comparative Example 1.
[0047] Example 2
[0048] First, starch, fused magnesia and water are mixed in a mass ratio of 1:1.1:3.0. The mixture is heated and stirred in a constant temperature magnetic stirring water bath. When the temperature rises to 70℃, it is left to stand for 1 hour to allow the starch to gelatinize and obtain a mixed gel. After the gel cools and ages, it is dried at 100℃ for 15-18 hours. After drying, the material is ball-milled until the particle size is less than 0.074 mm to obtain a composite pore-forming agent.
[0049] Then, a mixture of lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch (MgO@(C6H)) in a mass ratio of 60:40:10:18 was prepared. 10 O5)n) composite pore-forming agent, plus 8-9 wt% aluminum dihydrogen phosphate solution as binder, are mixed for 60-90 min, encapsulated and trapped for 15-18 h, machine-pressed at 90-100 MPa, dried at 90-100℃ for 15-18 h, and kept at 1350-1400℃ for 3-3.5 h to obtain a porous mullite ceramic with a spinel pore layer structure.
[0050] The porous mullite ceramic with a spinel-like porous structure prepared in this embodiment was tested and found to have a bulk density of 1.65 g·cm³. -3 The apparent porosity was 40.75%; the compressive strength was 69.9 MPa; the thermal conductivity was 0.35 W / (m·K); and the resistance to soda ash corrosion was 38.81%, which is 22.5% higher than that of the porous mullite ceramic without spinel pores prepared in Comparative Example 1.
[0051] Example 3
[0052] A porous mullite ceramic with a spinel-like porous structure and its preparation method. The preparation method described in this embodiment is as follows:
[0053] First, starch, fused magnesia, and water were mixed in a mass ratio of 1:1.3:3.5. The mixture was heated and stirred in a constant temperature magnetic stirring water bath. When the temperature reached 75°C, it was allowed to stand for 1.5 hours to allow the starch to gelatinize and obtain a mixed gel. After the gel cooled and aged, it was dried at 110°C for 18–21 hours. After drying, the material was ball-milled until the particle size was less than 0.074 mm to obtain the composite pore-forming agent.
[0054] Then, in a mass ratio of 50:30:8:15, lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch (MgO@(C6H) 10 Using O5)n composite pore-forming agent as raw material, and adding 10wt% aluminum dihydrogen phosphate solution of the raw material as a binder, the mixture is mixed for 90-120 min, encapsulated and trapped for 18-21 h, machine-pressed at 100-110 MPa, dried at 100-110℃ for 18-21 h, and kept at 1400-1450℃ for 3.5-4 h to obtain a porous mullite ceramic with a spinel pore layer structure.
[0055] The porous mullite ceramic with a spinel-like porous structure prepared in this embodiment has a bulk density of 1.54 g·cm³. -3 The apparent porosity was 44.4%; the compressive strength was 75.6 MPa; the thermal conductivity was 0.31 W / (m·K); and the resistance to soda ash corrosion was 37.01%, which is 28.5% higher than that of the porous mullite ceramic without spinel pores prepared in Comparative Example 1.
[0056] Example 4
[0057] A porous mullite ceramic with a spinel-like porous structure and its preparation method. The preparation method described in this embodiment is as follows:
[0058] First, starch, fused magnesia, and water were mixed in a mass ratio of 1:1.5:3.8. The mixture was heated and stirred in a constant temperature magnetic stirring water bath. When the temperature reached 75°C, it was allowed to stand for 1.5 hours to allow the starch to gelatinize and obtain a mixed gel. After the gel cooled and aged, it was dried at 110°C for 21–24 hours. After drying, the material was ball-milled until the particle size was less than 0.074 mm to obtain the composite pore-forming agent.
[0059] Then, using a mass ratio of 55:25:10:18, lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch (MgO@(C6H) 10 O5)n composite pore-forming agent, plus 10wt% aluminum dihydrogen phosphate solution as binder, is mixed for 90-120 min, encapsulated and trapped for 21-24 h, machine-pressed at 110-120 MPa, dried at 100-110℃ for 21-24 h, and kept at 1400-1450℃ for 3.5-4 h to obtain a porous mullite ceramic with spinel pore layer structure.
[0060] The porous mullite ceramic with a spinel-like porous structure prepared in this embodiment has a bulk density of 1.01 g·cm³. -3The apparent porosity was 56.1%; the compressive strength was 91.1 MPa; the thermal conductivity was 0.21 W / (m·K); and the resistance to soda ash corrosion was 35.79%, which is 31.8% higher than that of the porous mullite ceramic without spinel pores prepared in Comparative Example 1.
[0061] Comparative Example 1
[0062] In addition to using starch as a pore-forming agent (non-electrofused magnesia / starch (MgO@(C6H)) 10 O5)n) composite pore-forming agent), all other aspects are the same as in Example 1.
[0063] The porous mullite ceramic prepared in Comparative Example 1 was tested and found to have a bulk density of 2.79 g·cm³. -3 The apparent porosity is 28.9%; the compressive strength is 57.3 MPa; the thermal conductivity is 0.44 W / (m·K); and the resistance to soda ash corrosion is 47.56%.
[0064] Table 1
[0065]
[0066] Figure 1 SEM images of the porous mullite ceramic with a spinel pore layer structure prepared in Example 1 are shown in Table 1, and EDS analysis is also presented. It can be seen that the inner surface layer of the "pores" in the ceramic is a magnesium aluminum spinel layer, and the ceramic matrix is a mullite phase. This indicates that the "pores" inside the porous mullite ceramic exhibit the characteristics of a spinel pore layer structure.
[0067] For any points not covered above, existing technologies shall apply.
[0068] 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 method for preparing porous mullite ceramics with a spinel porous layer structure, characterized in that: Using lightweight spherical mullite micro powder, sintered corundum micro powder, silicon micro powder, and fused magnesia / starch composite pore-forming agent as raw materials, after adding a binder and mixing, the mixture is encapsulated, pressed, dried, and calcined to obtain porous mullite ceramics with a spinel pore layer structure. The preparation method of the fused magnesia / starch composite pore-forming agent is as follows: a mixed gel is prepared by using starch, fused magnesia and water, the mixed gel is dried and then ball-milled until the particle size is less than 0.074 mm to obtain the composite pore-forming agent; The lightweight spherical mullite micro powder is obtained by crushing, drying, grinding, granulating, and calcining secondary bauxite at high temperature. The mass ratio of lightweight spherical mullite powder, sintered corundum powder, silica powder, and fused magnesia / starch composite pore-forming agent is 40-60:20-40:6-10:8-18.
2. The preparation method according to claim 1, characterized in that: Aluminum dihydrogen phosphate solution is used as a binder, and the aluminum dihydrogen phosphate solution is 8-10 wt% of the raw material.
3. The preparation method according to claim 1, characterized in that: The roasting process involves maintaining the temperature at 1350–1450℃ for 3–4 hours.
4. The preparation method according to claim 1, characterized in that: The preparation process of the fused magnesia / starch composite pore-forming agent is as follows: starch, fused magnesia and water are mixed in a mass ratio of 1:(0.8~1.6):(2.5~4). The mixture is placed in a constant temperature magnetic stirring water bath and heated and stirred. When the temperature rises to 70~75℃, it is allowed to stand for 1~1.5h to obtain a mixed gel. The gel is cooled to room temperature and dried at 100~110℃ for 12~24h. The dried material is ball-milled until the particle size is less than 0.074mm to obtain the composite pore-forming agent.
5. The preparation method according to claim 1, characterized in that: The specific preparation method of the lightweight spherical mullite powder is as follows: secondary bauxite is crushed to 30-90mm, dried in a dryer, ground to 200-400 mesh, granulated by a granulator, and then calcined in a rotary kiln at a high temperature of 1400-1500℃ to obtain lightweight spherical mullite of various particle sizes.
6. The preparation method according to claim 1, characterized in that: The main chemical composition of the fused magnesia is: MgO content ≥ 95.03 wt%, Al2O3 content ≤ 0.18 wt%, SiO2 content ≤ 1.65 wt%; the particle size of the fused magnesia is ≤ 0.074 mm. The main chemical components of the lightweight spherical mullite powder are: Al2O3 content ≥ 62.29 wt%, SiO2 content ≥ 30.8 wt%, and MgO content ≤ 0.3 wt%. The lightweight spherical mullite powder has a particle size ≤0.074mm, an apparent porosity of 29.1%, and a median pore size of 10.30μm.
7. The preparation method according to claim 1, characterized in that: The main chemical composition of the sintered corundum micro powder is: Al2O3 content ≥ 99.46wt%, SiO2 content ≤ 0.09wt%; the particle size of the sintered corundum micro powder is ≤ 0.074mm. The main chemical components of the silicon micro powder are: SiO2 content ≥ 96.11 wt%, Al2O3 content ≤ 0.51 wt%, MgO content ≤ 0.25 wt%; and the particle size of the silicon micro powder is ≤ 0.109 mm.
8. A porous mullite ceramic with a spinel pore layer structure prepared by the preparation method according to any one of claims 1-7.