Calcium magnesium aluminate-calcium hexaluminate porous ceramic and preparation method thereof

Abstract

The invention particularly relates to calcium magnesium aluminate-calcium hexaluminate porous ceramic and a preparation method thereof. According to the technical scheme, the preparation method comprises the following steps: taking calcium aluminate cement, boehmite and light calcined magnesia as raw materials, adding the raw materials and cellulose into water, and mechanically stirring to obtain slurry; pouring the slurry on a heating plate, and drying to obtain a film-shaped green body; and laminating the film-shaped green body to obtain a ceramic green body, heating the ceramic green body to 1400-1600 DEG C at a rate of 2-5 DEG C / min, and carrying out heat preservation to obtain the calcium magnesium aluminate-calcium hexaluminate porous ceramic. The preparation method has the characteristics of simple and easy process, easy process control, low cost, high efficiency and environmental friendliness, and the prepared calcium magnesium aluminate-calcium hexaluminate porous ceramic is high in porosity, low in heat conductivity coefficient and excellent in mechanical property, and is widely applied to the fields of sewage treatment, air purification and heat insulation.

Description

Technical Field

[0001] This invention belongs to the field of porous ceramics technology. Specifically, it relates to a calcium magnesium aluminate-calcium hexaaluminate porous ceramic and its preparation method. Background Technology

[0002] Calcium hexaaluminate (CaO·6Al₂O₃, CA₆) is the compound with the highest melting point in the Al₂O₃-CaO binary system, reaching 1875°C, and has a coefficient of thermal expansion of 8.0 × 10⁻⁶. -6 At / °C, the theoretical density is 3.79 g / cm³. 3 Calcium hexaaluminate (CA6) exhibits low solubility in iron-containing slag, high stability in alkaline and reducing atmospheres (CO, H2), and low wettability to molten metal and slag. Due to its chemical stability, low coefficient of thermal expansion, and low thermal conductivity, CA6 porous ceramics are widely used in high-temperature kilns, metallurgical refractory materials, and aerospace insulation materials. However, CA6 porous ceramics suffer from insufficient high-temperature stability; above 1500℃, CA6 is prone to grain coarsening, leading to volume shrinkage and decreased thermal insulation performance. While high porosity reduces thermal conductivity, it significantly sacrifices compressive strength, creating a contradiction between mechanical properties and thermal conductivity.

[0003] The main methods for preparing porous ceramics of calcium hexaaluminate include the pore-forming agent method, the foaming method, and the gel casting method. The pore-forming agent method uses organic matter, which pollutes the environment when burned off, and the pore distribution is uneven; although the foaming method has uniform pore size, residual organic matter can easily contaminate the product; the gel casting method can control the pore structure, but the process is complex and costly.

[0004] Based on this, those skilled in the art have conducted research on improving the preparation process and enhancing the performance of porous calcium hexaaluminate ceramics. For example: The patented technology, "A Method for Preparing Porous Ceramics of Calcium Hexaaluminate" (CN109503197 B), involves mixing ρ-Al2O3 and calcium carbonate with deionized water, mechanically stirring, ultrasonically vibrating, molding, curing, drying in a constant temperature drying oven, demolding, and sintering in a high-temperature furnace under air atmosphere. Although this method produces porous ceramics of calcium hexaaluminate, it is not only complex and time-consuming, but also results in ρ-Al2O3 having a large specific surface area, high slurry viscosity, poor fluidity, and difficulty in molding. Furthermore, the decomposition of calcium carbonate releases a large amount of carbon dioxide, which is environmentally unfriendly.

[0005] The patented technology of "a uniformly structured porous calcium hexaaluminate ceramic" (CN 1116217219 A) involves wet ball milling of CaCO3 powder and boehmite AlOOH powder in ZrO2 ball milling media and ethanol solution, followed by drying, sieving, and machine pressing, and then calcining at high temperature to obtain porous calcium hexaaluminate ceramic. However, the process is complex and the cost of wet ball milling in ethanol media is high, making it unsuitable for large-scale applications.

[0006] The patented technology, "Porous ceramics of calcium hexaaluminate-spinel with ilmenite slag as the main material and its preparation method" (CN 113087517 B), uses activated alumina, natural magnesite, and ilmenite slag as raw materials and polyethylene glycol as a binder. The raw materials are first granulated, and then the ceramic powder is machine-pressed and fired to produce porous ceramics of calcium hexaaluminate-spinel. However, polyethylene glycol is widely used in various pharmaceutical preparations, resulting in high costs. The raw materials contain a certain amount of silica, which easily produces a silicate glass phase, reducing the mechanical properties of the material. Machine pressing results in low porosity and high thermal conductivity of the porous ceramics.

[0007] The patented technology, "A Calcium Zirconate-Calcium Hexaaluminate Composite Porous Ceramics and its Preparation Method" (CN 110407574 A), involves synthesizing calcium zirconate from calcium carbonate and zirconium oxide, and CA6 from alumina and calcium carbonate. The pre-synthesized powders are obtained through ball milling and sieving. Using the pre-synthesized calcium zirconate powder and CA6 powder as raw materials, and calcium aluminate cement as a binder, the mixture is formed through plastic extrusion or granulation and dry pressing, and finally fired to obtain the composite porous ceramics. However, this technology is not only complex and cumbersome, but also energy-intensive, costly, and produces products with low porosity. Furthermore, the thermal conductivity of calcium zirconate is higher than that of CA6, which is not conducive to reducing the thermal conductivity of the calcium hexaaluminate porous ceramics.

[0008] Calcium magnesium aluminate (CMA) materials are ternary compounds (CaO-MgO-Al2O3) formed by the solid solution reaction of CA6 and MgAl2O4 at high temperatures. They have attracted attention from those skilled in the art due to their numerous advantages. The patented technology, "An Industrial Preparation Method of CMA Material Based on MgO-Controlled Raw Material Crystal Morphology" (CN 110407574 A), uses alumina, calcium hydroxide, calcium carbonate, and magnesium oxide as raw materials. The slurry obtained by wet ball milling is dried, crushed, and sieved to obtain powder. The powder is then pressed into a green body, dried, sintered in air, and cooled to obtain a porous CMA material with a thermal insulation layer. However, this method suffers from high raw material costs, complex preparation processes, and low porosity. Summary of the Invention

[0009] The present invention aims to overcome the defects of the prior art and provides a method for preparing porous magnesium aluminate-calcium hexaaluminate ceramics that is simple, easy to control, low in cost, low in energy consumption, and environmentally friendly. The porous magnesium aluminate-calcium hexaaluminate ceramics prepared by this method have low thermal conductivity, high porosity, and excellent mechanical properties.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Using 10-30 wt% calcium aluminate cement, 60-80 wt% boehmite, and 5-10 wt% lightly calcined magnesium oxide as raw materials, and according to the raw material:cellulose:water mass ratio of 100:5-20:230-1900, the raw materials and cellulose are added to water and mechanically stirred to obtain a slurry; the slurry is then poured onto a heating plate and dried to obtain a thin film green body; the thin film green bodies are then stacked to obtain a ceramic green body, which is heated to 1400-1600℃ at a rate of 2-5℃ / min and held at that temperature to obtain calcium magnesium aluminate-calcium hexaaluminate porous ceramic.

[0011] The calcium aluminate cement has an Al2O3 content ≥70wt% and a CaO content ≥28wt%; the particle size of the calcium aluminate cement is ≤74μm.

[0012] The boehmite has an AlOOH content ≥98wt% and a particle size ≤10μm.

[0013] The MgO content of the lightly calcined magnesium oxide is ≥98wt%; the particle size of the lightly calcined magnesium oxide is ≤74μm.

[0014] The cellulose is one of cotton cellulose, lignocellulose, bamboo cellulose, and bacterial cellulose.

[0015] The mechanical stirring speed is 600~800, and the mechanical stirring time is 6~24 hours.

[0016] The temperature of the heating plate is 40~80℃.

[0017] The drying time is 1 to 3 hours.

[0018] The heat preservation time is 2 to 6 hours.

[0019] By adopting the above technical solution, the present invention has the following beneficial effects and outstanding features compared with the prior art: 1. This invention directly mixes raw materials and additive cellulose in an aqueous medium, then dries and fires them to produce porous magnesium aluminate-calcium hexaaluminate ceramics. This technology is simple, easy to control, and has high production efficiency. The calcium aluminate cement and lightly calcined magnesium oxide in the raw materials react with water to generate sheet-like hydrated calcium aluminate and magnesium hydroxide hydration products. The additive cellulose is a biodegradable natural nanostructured polymer material, exhibiting a ribbon-like shape with lengths ranging from hundreds of nanometers to micrometers. The fibers interweave to form a fine network structure, effectively dispersing and supporting the raw material powder, and gradually solidifying into shape. The magnesium hydroxide hydration products are uniformly dispersed within the cellulose network to form a stable structure. During drying, the cellulose shrinks to form network channels, facilitating rapid moisture removal from the ceramic green body, preventing sample cracking, and improving mechanical properties.

[0020] 2. The calcium aluminate cement and the hydration products of lightly calcined magnesium oxide, namely hydrated calcium aluminate and magnesium hydroxide, as well as the raw material boehmite, in the raw materials of this invention all have a two-dimensional platy or plate-like crystal morphology. The two-dimensional structures overlap with each other, which improves the strength of the ceramic green body while giving it a high porosity. In addition, the hydration products, raw materials, and additives undergo in-situ decomposition reactions during firing, releasing water vapor without releasing harmful or greenhouse gases, making it environmentally friendly. At the same time, the in-situ decomposition forms a porous structure with small and uniform pore size, which reduces the thermal conductivity of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic.

[0021] 3. This invention employs in-situ reaction technology to prepare porous ceramics of calcium magnesium aluminate and calcium hexaaluminate. The hydration products and boehmite decompose to generate active oxides, exhibiting high reactivity. This reduces the formation and sintering temperatures of calcium magnesium aluminate and calcium hexaaluminate, saving energy and lowering costs. Both the prepared calcium magnesium aluminate and calcium hexaaluminate exhibit two-dimensional lamellar morphology. The two lamellar materials overlap to form an effective bond, acting as a second-phase pinning mechanism, preventing grain coarsening and volume shrinkage at high temperatures. The overlapping of the two lamellar materials constitutes a porous structure with high porosity, small pore size, and uniform distribution. The more complex crystal structure of calcium magnesium aluminate results in a lower thermal conductivity than calcium hexaaluminate, ultimately yielding porous ceramics of calcium magnesium aluminate and calcium hexaaluminate with low thermal conductivity.

[0022] 4. The method of this invention is convenient, low-cost, and highly economical, suitable for large-scale industrial production. The prepared calcium magnesium aluminate-calcium hexaaluminate porous ceramic has high porosity, uniform pore size distribution, high strength, and excellent thermal insulation performance. It can be made into ceramic membranes, ceramic blocks, and complex-shaped objects for application in wastewater treatment, air purification, and thermal insulation, and has broad application prospects.

[0023] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared by this invention were tested and found to have a porosity of 70-90% and a bulk density of 0.82-1.68 g / cm³. 3 The compressive strength at room temperature is 30~160MPa; the thermal conductivity is 0.05~0.32W / (m·K).

[0024] This invention features simple and easy-to-implement process, easy process control, low cost, high efficiency and environmental friendliness. The prepared calcium magnesium aluminate-calcium hexaaluminate porous ceramic has high porosity, low thermal conductivity and excellent mechanical properties, and is widely used in sewage treatment, air purification and heat insulation. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of a calcium magnesium aluminate-calcium hexaaluminate porous ceramic prepared according to the present invention. Figure 2 for Figure 1The image shows a SEM image of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic. Figure 3 The XRD pattern of another porous ceramic, calcium magnesium aluminate-calcium hexaaluminate, prepared according to the present invention. Figure 4 for Figure 3 The image shows a SEM image of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic. Figure 5 The XRD pattern of another porous ceramic of calcium magnesium aluminate-calcium hexaaluminate prepared according to the present invention is shown. Figure 6 This is a SEM image of another porous ceramic, calcium magnesium aluminate-calcium hexaaluminate, prepared according to the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of protection thereof.

[0027] A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this specific embodiment is as follows: Using 10-30 wt% calcium aluminate cement, 60-80 wt% boehmite, and 5-10 wt% lightly calcined magnesium oxide as raw materials, and according to the raw material:cellulose:water mass ratio of 100:5-20:230-1900, the raw materials and cellulose are added to water and mechanically stirred to obtain a slurry; the slurry is then poured onto a heating plate and dried to obtain a thin film green body; the thin film green bodies are then stacked to obtain a ceramic green body, which is heated to 1400-1600℃ at a rate of 2-5℃ / min and held at that temperature to obtain calcium magnesium aluminate-calcium hexaaluminate porous ceramic.

[0028] The calcium aluminate cement has an Al2O3 content of ≥70wt% and a CaO content of ≥28wt%.

[0029] The boehmite has an AlOOH content of ≥98wt%.

[0030] The MgO content of the lightly calcined magnesium oxide is ≥98wt%.

[0031] The cellulose is one of cotton cellulose, lignocellulose, bamboo cellulose, and bacterial cellulose.

[0032] The mechanical stirring speed is 600~800, and the mechanical stirring time is 6~24 hours.

[0033] The temperature of the heating plate is 40~80℃.

[0034] The drying time is 1 to 3 hours.

[0035] The heat preservation time is 2 to 6 hours.

[0036] In this specific implementation: The particle size of the calcium aluminate cement is ≤74μm; The boehmite has a particle size ≤10μm; The particle size of the lightly calcined magnesium oxide is ≤74μm.

[0037] The details will not be repeated in the examples.

[0038] Example 1 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 10 wt% calcium aluminate cement, 80 wt% boehmite, and 10 wt% lightly calcined magnesium oxide as raw materials, the raw materials and cellulose were added to water at a mass ratio of 100:20:230, and mechanically stirred to obtain a slurry. The slurry was then poured onto a heating plate and dried to obtain a thin-film green body. The thin-film green bodies were then stacked to obtain a ceramic green body. The ceramic green body was heated to 1580°C at a rate of 2°C / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0039] The calcium aluminate cement has an Al2O3 content of 70.1 wt% and a CaO content of 28.9 wt%.

[0040] The boehmite has an AlOOH content of 98.2 wt%.

[0041] The MgO content of the lightly calcined magnesium oxide is 98.1 wt%.

[0042] The cellulose is cotton cellulose.

[0043] The mechanical stirring speed is 600 rpm, and the mechanical stirring time is 6 hours.

[0044] The temperature of the heating plate is 40°C.

[0045] The drying time is 2 hours.

[0046] The insulation time is 6 hours.

[0047] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 70% and a bulk density of 1.68 g / cm³. 3 The room temperature compressive strength is 160 MPa; the thermal conductivity is 0.32 W / (m·K).

[0048] Figure 1 The image shows the XRD pattern of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic prepared in Example 1. Figure 1It can be seen that the phase exhibits obvious characteristic diffraction peaks of calcium hexaaluminate (CA6) and calcium magnesium aluminate (CMA), indicating that the raw materials reacted fully and CA6 and CMA were generated in situ. The resulting product has high purity and is free of impurities.

[0049] Figure 2 for Figure 1 The SEM image shown is of calcium magnesium aluminate-calcium hexaaluminate porous ceramic. Figure 2 It can be seen that both CA6 and CMA exhibit a two-dimensional sheet-like morphology, with the sheet-like structures overlapping to form pores. The pore size is less than 10 μm and the pores are evenly distributed.

[0050] Example 2 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 20 wt% calcium aluminate cement, 71 wt% boehmite, and 9 wt% lightly calcined magnesium oxide as raw materials, the raw materials and cellulose were added to water at a mass ratio of 100:10:567, and mechanically stirred to obtain a slurry. The slurry was then poured onto a heating plate and dried to obtain a thin-film green body. The thin-film green bodies were then stacked to obtain a ceramic green body. The ceramic green body was heated to 1500℃ at a rate of 3℃ / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0051] The calcium aluminate cement has an Al2O3 content of 73.5 wt% and a CaO content of 28.7 wt%.

[0052] The boehmite has an AlOOH content of 98.7 wt%.

[0053] The MgO content of the lightly calcined magnesium oxide is 99.1 wt%.

[0054] The cellulose is bamboo cellulose.

[0055] The mechanical stirring speed is 750 rpm, and the mechanical stirring time is 12 hours.

[0056] The temperature of the heating plate is 55°C.

[0057] The drying time is 2.5 hours.

[0058] The heat preservation time is 3 hours.

[0059] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 78% and a bulk density of 1.42 g / cm³. 3 The compressive strength at room temperature is 119 MPa; the thermal conductivity is 0.25 W / (m·K).

[0060] Figure 3 The image shows the XRD pattern of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic prepared in Example 2. Figure 3 It can be seen that the phase exhibits obvious characteristic diffraction peaks of calcium hexaaluminate (CA6) and calcium magnesium aluminate (CMA), indicating that the raw materials reacted fully and CA6 and CMA were generated in situ. The resulting product has high purity and is free of impurities.

[0061] Figure 4 for Figure 3 The SEM image shown is of calcium magnesium aluminate-calcium hexaaluminate porous ceramic. Figure 4 It can be seen that both CA6 and CMA exhibit a two-dimensional sheet-like morphology with two phases interleaved and overlapping to form pores with a pore size of less than 10 μm and uniform distribution.

[0062] Example 3 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 18 wt% calcium aluminate cement, 75 wt% boehmite, and 7 wt% lightly calcined magnesium oxide as raw materials, the raw materials and cellulose were added to water at a mass ratio of 100:8:400, and mechanically stirred to obtain a slurry. The slurry was then poured onto a heating plate and dried to obtain a thin-film green body. The thin-film green bodies were then stacked to obtain a ceramic green body. The ceramic green body was heated to 1550°C at a rate of 5°C / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0063] The calcium aluminate cement has an Al2O3 content of 70.3 wt% and a CaO content of 29.1 wt%.

[0064] The boehmite has an AlOOH content of 98.3 wt%.

[0065] The MgO content of the lightly calcined magnesium oxide is 99.4 wt%.

[0066] The cellulose is cotton cellulose.

[0067] The mechanical stirring speed is 800 rpm, and the mechanical stirring time is 16 hours.

[0068] The temperature of the heating plate is 50°C.

[0069] The drying time is 3 hours.

[0070] The heat preservation time is 2 hours.

[0071] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 83% and a bulk density of 1.28 g / cm³. 3The compressive strength at room temperature is 75 MPa; the thermal conductivity is 0.18 W / (m·K).

[0072] Figure 5 The image shows the XRD pattern of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic prepared in Example 3. Figure 5 It can be seen that the phase exhibits obvious characteristic diffraction peaks of calcium hexaaluminate (CA6) and calcium magnesium aluminate (CMA), indicating that the raw materials reacted fully and CA6 and CMA were generated in situ. The resulting product has high purity and is free of impurities.

[0073] Example 4 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 30 wt% calcium aluminate cement, 60 wt% boehmite, and 10 wt% lightly calcined magnesium oxide as raw materials, the raw materials and cellulose were added to water at a mass ratio of 100:5:1900, and mechanically stirred to obtain a slurry. The slurry was then poured onto a heating plate and dried to obtain a thin-film green body. The thin-film green bodies were then stacked to obtain a ceramic green body. The ceramic green body was heated to 1600℃ at a rate of 4℃ / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0074] The calcium aluminate cement has an Al2O3 content of 70.9 wt% and a CaO content of 28.3 wt%.

[0075] The boehmite has an AlOOH content of 98.9 wt%.

[0076] The MgO content of the lightly calcined magnesium oxide is 98.7 wt%.

[0077] The cellulose is bacterial cellulose.

[0078] The mechanical stirring speed is 650 rpm, and the mechanical stirring time is 24 hours.

[0079] The temperature of the heating plate is 70°C.

[0080] The drying time is 1 hour.

[0081] The insulation time is 5 hours.

[0082] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 80% and a bulk density of 1.21 g / cm³. 3 The room temperature compressive strength is 86 MPa; the thermal conductivity is 0.21 W / (m·K).

[0083] Example 5 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 25 wt% calcium aluminate cement, 67 wt% boehmite, and 8 wt% lightly calcined magnesia as raw materials, and according to the raw material:cellulose:water mass ratio of 100:13:900, the raw materials and cellulose are added to water and mechanically stirred to obtain a slurry. The slurry is then poured onto a heating plate and dried to obtain a thin-film green body. The thin-film green bodies are then stacked to obtain a ceramic green body. The ceramic green body is heated to 1450℃ at a rate of 2.5℃ / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0084] The calcium aluminate cement has an Al2O3 content of 71.1 wt% and a CaO content of 28.1 wt%.

[0085] The boehmite has an AlOOH content of 98.1 wt%.

[0086] The MgO content of the lightly calcined magnesium oxide is 99.3 wt%.

[0087] The cellulose is lignocellulose.

[0088] The mechanical stirring speed is 700 rpm, and the mechanical stirring time is 20 hours.

[0089] The temperature of the heating plate is 60°C.

[0090] The drying time is 1.5 hours.

[0091] The heat preservation time is 4 hours.

[0092] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 88% and a bulk density of 1.06 g / cm³. 3 The room temperature compressive strength is 52 MPa; the thermal conductivity is 0.12 W / (m·K).

[0093] Figure 6 This is a SEM image of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic prepared in Example 5. Figure 6 It can be seen that both CA6 and CMA exhibit a two-dimensional lamellar morphology with a grain size of approximately 8 μm. The two phases are interspersed, and the lamellar structures overlap to form pores, resulting in high porosity and uniform pore size distribution.

[0094] Example 6 A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate and its preparation method. The preparation method described in this embodiment is as follows: Using 17wt% calcium aluminate cement, 78wt% boehmite, and 50wt% lightly calcined magnesia as raw materials, and according to the raw material:cellulose:water mass ratio of 100:15:257, the raw materials and cellulose are added to water and mechanically stirred to obtain a slurry. The slurry is then poured onto a heating plate and dried to obtain a thin film green body. The thin film green bodies are then stacked to obtain a ceramic green body. The ceramic green body is heated to 1400℃ at a rate of 3.5℃ / min and held at that temperature to obtain a porous ceramic of calcium magnesium aluminate-calcium hexaaluminate.

[0095] The calcium aluminate cement has an Al2O3 content of 70.4 wt% and a CaO content of 29.1 wt%.

[0096] The boehmite has an AlOOH content of 98.5 wt%.

[0097] The MgO content of the lightly calcined magnesium oxide is 98.6 wt%.

[0098] The cellulose is bamboo cellulose.

[0099] The mechanical stirring speed is 780, and the mechanical stirring time is 8 hours.

[0100] The temperature of the heating plate is 80°C.

[0101] The drying time is 3 hours.

[0102] The insulation time is 6 hours.

[0103] The porous ceramics of calcium magnesium aluminate-calcium hexaaluminate prepared in this embodiment were tested and found to have a porosity of 90% and a bulk density of 0.82 g / cm³. 3 The room temperature compressive strength is 30 MPa; the thermal conductivity is 0.05 W / (m·K).

[0104] Compared with existing technical solutions, this specific implementation method has the following beneficial effects and outstanding features: 1. This specific embodiment directly mixes the raw materials and additive cellulose in an aqueous medium, then dries and fires them to obtain porous magnesium aluminate-calcium hexaaluminate ceramics. This technology is simple, easy to control, and has high production efficiency. The calcium aluminate cement and lightly calcined magnesium oxide in the raw materials react with water to generate sheet-like hydrated calcium aluminate and magnesium hydroxide hydration products. The additive cellulose is a biodegradable natural nanostructured polymer material, exhibiting a ribbon-like shape with lengths ranging from hundreds of nanometers to micrometers. The fibers interweave to form a fine network structure, effectively dispersing and supporting the raw material powder, and gradually solidifying into shape. The magnesium hydroxide hydration products are uniformly dispersed within the cellulose network to form a stable structure. During drying, the cellulose shrinks to form network channels, facilitating rapid moisture removal from the ceramic green body, preventing cracking, and improving mechanical properties.

[0105] 2. In this specific embodiment, the calcium aluminate cement and the hydration products of lightly calcined magnesium oxide, namely hydrated calcium aluminate and magnesium hydroxide, as well as the raw material boehmite, all have two-dimensional platy or plate-like crystal morphologies. The two-dimensional structures overlap with each other, which improves the strength of the ceramic green body while giving it a high porosity. In addition, the hydration products, raw materials, and additives undergo in-situ decomposition reactions during firing, releasing water vapor without releasing harmful or greenhouse gases, making it environmentally friendly. At the same time, the in-situ decomposition forms a porous structure with small and uniform pore size, reducing the thermal conductivity of the calcium magnesium aluminate-calcium hexaaluminate porous ceramic.

[0106] 3. This specific embodiment uses in-situ reaction technology to prepare porous ceramics of calcium magnesium aluminate-calcium hexaaluminate. The hydration products and boehmite decompose to generate active oxides, which have high reactivity. This can reduce the formation temperature and sintering temperature of calcium magnesium aluminate and calcium hexaaluminate, saving energy and reducing costs. The prepared calcium magnesium aluminate and calcium hexaaluminate both exhibit two-dimensional plate-like morphology. The two plate-like materials overlap to form an effective bond and act as a second phase pinning, avoiding grain coarsening at high temperatures, which would lead to volume shrinkage. The two plate-like materials overlap to form a porous structure with high porosity, small pore size and uniform distribution. The crystal structure of calcium magnesium aluminate is more complex and has a lower thermal conductivity than calcium hexaaluminate. Finally, porous ceramics of calcium magnesium aluminate-calcium hexaaluminate with low thermal conductivity are obtained.

[0107] 4. This specific implementation method is convenient, low-cost, and highly economical, suitable for large-scale industrial production. The prepared calcium magnesium aluminate-calcium hexaaluminate porous ceramic has high porosity, uniform pore size distribution, high strength, and excellent thermal insulation performance. It can be made into ceramic membranes, ceramic blocks, and complex-shaped objects for application in wastewater treatment, air purification, and thermal insulation, and has broad application prospects.

[0108] The porous magnesium aluminate-calcium hexaaluminate prepared according to this specific embodiment was tested and found to have a porosity of 70-90% and a bulk density of 0.82-1.68 g / cm³.3 The compressive strength at room temperature is 30~160MPa; the thermal conductivity is 0.05~0.32W / (m·K).

[0109] This specific implementation method features simple and easy-to-implement process, easy process control, low cost, high efficiency and environmental friendliness. The prepared calcium magnesium aluminate-calcium hexaaluminate porous ceramic has high porosity, low thermal conductivity and excellent mechanical properties, and is widely used in sewage treatment, air purification and heat insulation.

Claims

1. A method for preparing porous ceramics of calcium magnesium aluminate-calcium hexaaluminate, characterized in that... The preparation method is as follows: using 10-30 wt% calcium aluminate cement, 60-80 wt% boehmite, and 5-10 wt% lightly calcined magnesium oxide as raw materials, the raw materials and cellulose are added to water at a mass ratio of 100:5-20:230-1900, and mechanically stirred to obtain a slurry; the slurry is then poured onto a heating plate and dried to obtain a thin film green body; the thin film green bodies are then stacked to obtain a ceramic green body, which is heated to 1400-1600℃ at a rate of 2-5℃ / min and held at that temperature to obtain calcium magnesium aluminate-calcium hexaaluminate porous ceramic.

2. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The calcium aluminate cement has an Al2O3 content ≥70wt% and a CaO content ≥28wt%; the particle size of the calcium aluminate cement is ≤74μm.

3. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The boehmite has an AlOOH content ≥98wt% and a particle size ≤10μm.

4. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The MgO content of the lightly calcined magnesium oxide is ≥98wt%; the particle size of the lightly calcined magnesium oxide is ≤74μm.

5. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The cellulose is one of cotton cellulose, lignocellulose, bamboo cellulose, and bacterial cellulose.

6. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The mechanical stirring speed is 600~800, and the mechanical stirring time is 6~24 hours.

7. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The temperature of the heating plate is 40~80℃.

8. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The drying time is 1 to 3 hours.

9. The method for preparing porous magnesium aluminate-calcium hexaaluminate according to claim 1, characterized in that, The heat preservation time is 2 to 6 hours.

10. A porous ceramic of calcium magnesium aluminate-calcium hexaaluminate, characterized in that... The calcium magnesium aluminate-calcium hexaaluminate porous ceramic is prepared by the method described in any one of claims 1 to 9.

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