Low-expansion ceramic fiber board and preparation method thereof

Abstract

According to the low-expansion ceramic fiber board and the preparation method thereof, high-purity aluminum silicate fibers and refined cordierite powder are compounded, and the nanoscale permeation effect of ammonia type silica sol is combined, so that the fibers and the powder form a three-dimensional network bonding structure, and the thermal expansion coefficient is reduced; the wettability of the combination of the fibers and the powder is remarkably improved by a pre-dispersion process of the cationic starch, and the block mass rate is reduced; the vacuum-assisted compression molding and the gradient calcining process are synergistic, so that the density uniformity of the product is improved, and high-temperature cracking is avoided.

Description

Technical Field

[0001] The invention relates to a low-expansion ceramic fiberboard and a preparation method thereof. Background Art

[0002] At present, ceramic fiberboard is widely used in the lining of high-temperature industrial kilns. It is usually prepared with aluminum silicate fiber as the main material, which is formed with a binder and then calcined.

[0003] In traditional processes, fiberboard has the following problems: the interface bonding strength between aluminum silicate fiber and binder is insufficient, resulting in low fiberboard strength; the thermal expansion coefficient of fiber and matrix material is greatly different during calcination, which easily produces microcracks. The thermal expansion coefficient at 30-1000℃ is generally higher than 5×10⁻ 6 / ℃; the slag shot content is too high, usually ≥5%, which affects the fiber dispersion and causes uneven board density; existing processes mostly use direct dry mixing, which makes the fibers and powders easily agglomerated and requires high-content binders (such as phosphates) for plasticization, but it is easy to decompose and cause structural degradation at high temperatures. In addition, cordierite powder is mostly added directly using micron-level premixes without optimizing the raw material particle size and powder preparation process. The sintering activity between the powders is insufficient, making it difficult to form stable chemical bonds with the fibers. In the molding process, the mold pressure is insufficient, usually ≤50MPa, resulting in a low degree of densification of the board, which is prone to deformation or cracking during the subsequent baking and calcination processes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low-expansion ceramic fiberboard.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a low-expansion ceramic fiber board, characterized in that it is made of the following raw materials in weight percentage: 10%-70% aluminum silicate fiber; 10%-85% cordierite powder, with a particle size of 2-4 μm; 10%-25% ammoniacal silica sol; and cationic starch, with an addition amount of 5%-30% of the total weight of the above aluminum silicate fiber, cordierite powder and ammoniacal silica sol.

[0006] Preferably, the aluminum silicate fiber has a shot content of ≤2% and a sedimentation volume of ≤5 ml / g.

[0007] Preferably, the aluminum silicate fiber has a shot content of 0.5%-1.5% and a sedimentation volume of 3-4.5 ml / g.

[0008] Preferably, the cordierite powder is obtained by ball milling cordierite ore, the ball milling speed is ≥300 r / min, the ball milling time is ≥8 hours, and the grinding medium is alumina balls.

[0009] Preferably, the cationic starch is added in an amount of 10%-25% of the total weight, and is pre-dispersed separately in the mixing system at a speed of ≥350 r / min for more than 30 minutes.

[0010] Another technical problem to be solved by the present invention is to provide a method for preparing a low-expansion ceramic fiberboard.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a low-expansion ceramic fiber board as described in any one of the above embodiments, comprising the following steps: step 1, ball milling the cordierite raw material at ≥300r / min for ≥8 hours to obtain 2-4μm cordierite powder; step 2, mixing the cordierite powder with ammonia silica sol at 150r / min for ≥10 minutes, adding aluminum silicate fiber and stirring at a speed of ≥500r / min for ≥30 minutes; step 3, pre-dispersing cationic starch separately at ≥350r / min for ≥30 minutes, then adding the mixture generated in step 2, and continuing to stir for ≥5 minutes; step 4, pressing the mixture at 60-100MPa and holding the pressure for ≥5 minutes; step 5, drying at 300-350℃ for 36-72 hours; step 6, programmed temperature calcination: raising the temperature to 800℃ within 3 hours, then raising the temperature to 1300℃ in ≥4 hours, and holding the temperature for ≥4 hours.

[0012] Preferably, the material temperature is controlled at 40-60° C. during stirring in step 2, and a double-layered ribbon stirrer is used.

[0013] Preferably, in step 6, calcination is performed in a nitrogen atmosphere at 800-1300° C., with a heating rate of 2-3° C. / min.

[0014] Preferably, vacuum-assisted molding is used during pressing in step 4, and the vacuum degree is ≤-0.08 MPa.

[0015] The scope of the present invention is not limited to technical solutions formed by a specific combination of the above-mentioned technical features, but also includes other technical solutions formed by any combination of the above-mentioned technical features or their equivalents. For example, technical solutions formed by replacing the above-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0016] Due to the application of the above-mentioned technical solution, the present invention has the following advantages over the existing technology: the present invention provides a low-expansion ceramic fiberboard and a preparation method thereof. By compounding high-purity aluminum silicate fibers with refined cordierite powder and combining it with the nano-scale penetration effect of ammonia-type silica sol, the fibers and powder form a three-dimensional network bonding structure, reducing the thermal expansion coefficient. The pre-dispersion process of cationic starch significantly improves the wettability of the fiber-powder combination and reduces the agglomeration rate. The vacuum-assisted pressing and gradient calcination process work synergistically to improve the uniformity of the product density and avoid high-temperature cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Attachment Figure 1 The figure is a schematic diagram of the process for preparing low expansion ceramic fiberboard. DETAILED DESCRIPTION

[0018] A low-expansion ceramic fiberboard is made from the following raw materials: aluminum silicate fiber (10%-70%): slag shot content ≤2%, sedimentation volume ≤5 ml / g, preferably slag shot content 0.5%-1.5% and sedimentation volume 3-4.5 ml / g; cordierite powder (10%-85%): particle size 2-4 μm, prepared by alumina ball milling of cordierite ore, ball milling speed ≥300 r / min and time ≥8 hours, speed ≥300 r / min to ensure sufficient crushing of the powder and prevent coarse particles from affecting sintering activity; ammonia-type silica sol (10%-25%); cationic starch: added in an amount of 5%-30% by weight of the total raw materials, preferably 10%-25%, and stirred at ≥350 r / min for ≥30 minutes during pre-dispersion.

[0019] like Figure 1 As shown in FIG, the preparation method of the low expansion ceramic fiberboard is specifically as follows: cordierite powder preparation: the cordierite ore is ball-milled at ≥300r / min for ≥8h to obtain 2-4μm powder; initial mixing: the cordierite powder and ammonia silica sol are stirred at 150r / min for ≥10min; fiber dispersion: aluminum silicate fiber is added and stirred at a high speed of ≥500r / min for ≥30min, preferably using a double-layer spiral ribbon stirrer and controlling the temperature at 40-60°C; starch premixing: cationic starch is separately mixed at ≥350r / min for ≥10min. / min pre-dispersion for ≥30min, then add to the mixing system and continue stirring for ≥5min; molding: the mixture is pressed at 60-100MPa for ≥5min, preferably with vacuum assistance, and the vacuum degree is ≤-0.08MPa; drying: drying at 300-350℃ for 36-72h; calcination: heating to 800℃ for 3h, then heating to 1300℃ for ≥4h and keeping warm for ≥4h, and nitrogen is used to protect the environment in the 800-1300℃ stage (heating rate 2-3℃ / min).

[0020] Ball milling time ≥8h can ensure that the median particle size of cordierite powder is ≤4μm and the specific surface area is ≥5m² / g, thereby improving sintering activity; vacuum-assisted pressing ≤-0.08MPa can reduce the porosity of the material to below 15% and the thermal expansion coefficient by 10%-15%; nitrogen-protected calcination inhibits fiber surface oxidation and significantly improves the flexural strength at 1300℃ to ≥8MPa.

[0021] By compounding high-purity aluminum silicate fiber with refined cordierite powder and combining it with the nano-scale penetration of ammonia-type silica sol, a three-dimensional network bonding structure is formed between the fiber and the powder, and the thermal expansion coefficient is reduced to (2-5)×10⁻ 6 / ℃; the pre-dispersion process of cationic starch significantly improves the wettability of the fiber-powder interface and reduces the agglomeration rate by ≥40%; the vacuum-assisted pressing and gradient calcination process work synergistically to improve the product density uniformity by more than 20% and avoid high-temperature cracking.

[0022] Example 1: Raw material preparation: aluminum silicate fiber: 25 kg (50%), slag ball content 1.2%, sedimentation volume 4 ml / g; cordierite powder: 20 kg (40%), particle size 2-4 μm (D50 = 3.2 μm); ammonia silica sol: 3 kg (6%); cationic starch: 2 kg (4%), calculated based on the total weight of aluminum silicate fiber, cordierite powder and ammonia silica sol.

[0023] Preparation process: Preparation of cordierite powder: Place cordierite ore in a ball mill, add alumina balls as grinding media, set the speed to 350r / min, and ball mill for 10 hours to obtain cordierite powder with D50=3.2μm; Primary mixing: Add 20kg of cordierite powder and 3kg of ammonia silica sol into a blender and stir at 150r / min for 12 minutes; Fiber dispersion: Add 25kg of aluminum silicate fiber, switch to a double-layer spiral ribbon blender, stir at 550r / min for 35 minutes, and control the material temperature at 45°C; Starch premixing: 2kg of cationic starch is premixed separately at 400r / min Disperse for 35 minutes, then add the mixed system and continue stirring for 8 minutes; pressing molding: fill the mixture into the mold, maintain the pressure at 80MPa for 6 minutes, and use vacuum assistance (vacuum degree -0.09MPa); drying: place the formed fiberboard in the drying equipment and dry it at a constant temperature of 320℃ for 48 hours; calcination: adopt programmed temperature rising calcination: first stage: heat to 800℃ within 3 hours; second stage: heat to 1300℃ within 4.5 hours and keep warm for 5 hours; 800-1300℃ stage: introduce nitrogen protection (flow rate 5L / min), and the heating rate is 2.5℃ / min.

[0024] Test results: Thermal expansion coefficient (×10⁻ 6 / ℃): 3.8; Powder loss rate (%): 5.2; Flexural strength at room temperature (MPa): 10.2; Density (kg / m³): ≥900; Water absorption rate: 10.23%; Loss on ignition (%): 1.54%; Flatness (mm): ≤0.13 In this embodiment, a three-dimensional network structure is formed by combining 50% aluminum silicate fiber and 40% cordierite powder with the nano-scale penetration of ammonia-type silica sol, which reduces the thermal expansion coefficient from 30 to 1000°C to 3.8×10⁻. 6 / ℃, significantly better than the thermal expansion coefficient which is usually ≥5×10⁻ 6 / ℃ traditional fiberboard, through 1300℃ calcination and nitrogen protection process to promote the chemical bonding of cordierite powder and aluminum silicate fiber, so that the flexural strength of the fiberboard can reach 10.2MPa, the refractory temperature is 1450℃, suitable for high-temperature kiln lining, this embodiment also adopts vacuum assisted pressing to reduce the porosity to below 15%, thereby avoiding baking cracking; the double-layer spiral ribbon is stirred at a speed of 550r / min to ensure that the fibers are evenly dispersed without lumps.

[0025] This embodiment is suitable for industrial scenarios that are cost-sensitive and require stable performance.

[0026] Example 2: Based on Example 1, the amount of cationic starch added was adjusted to 10% (5 kg) of the total raw materials, and the pre-dispersion process was optimized: the starch was pre-dispersed at 450 r / min for 40 minutes, and then mixed with the main ingredients for 10 minutes.

[0027] Test results: Thermal expansion coefficient: 3.5×10⁻ 6 / ℃; powder loss rate: 4.0%; flexural strength at room temperature: 11.6MPa; density: ≥930kg / m³; water absorption rate: 9.86%; loss on ignition: 1.42%; flatness: ≤0.18mm.

[0028] In this embodiment, the starch pre-dispersion time is extended to 40 minutes to fully wrap the fiber surface, thereby improving the interfacial bonding between the fiber and powder and increasing the flexural strength to 11.6 MPa. At the same time, the plasticizing effect of starch optimizes particle filling, reducing the porosity from 15% to 12%, further reducing the local stress caused by uneven heat conduction, and is suitable for high-fiber content formulas to solve the problem of poor mixing uniformity at high fiber ratios.

[0029] This embodiment is suitable for working conditions that need to withstand mechanical shock or thermal shock.

[0030] Example 3: Based on Example 1, the nitrogen flow rate and heating rate in the calcination stage were adjusted: 800-1300°C stage: the nitrogen flow rate was increased to 8 L / min, and the heating rate was 3°C / min.

[0031] Test results: Thermal expansion coefficient: 3.6×10⁻ 6 / ℃; powder loss rate: 2.1%; flexural strength at room temperature: 10.3MPa; density: ≥950kg / m³; water absorption rate: 9.65%; loss on ignition: 1.63%; flatness: ≤0.16mm.

[0032] This embodiment uses high-flow nitrogen to inhibit oxidation of the fiber surface. After calcination, a dense layer is formed on the surface of the board, and the powder loss rate is reduced from 5.2% to 2.1%, thereby extending the service life. The heating rate is accelerated, and the grain coarsening time is shortened at a heating rate of 3°C / min. The cordierite grain size distribution is more uniform, that is, the SEM shows a particle size deviation of ≤10%. At the same time, the increase in the heating rate can shorten the total calcination time by about 1 hour, thereby reducing energy consumption while ensuring performance.

[0033] This embodiment is applicable to dust-sensitive fields, such as kilns in the electronics industry.

[0034] The present invention significantly reduces the thermal expansion coefficient and improves the mechanical properties by optimizing the raw material ratio, starch premixing and calcination process, and is suitable for harsh environments such as high-temperature kiln linings.

[0035] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A low expansion ceramic fiberboard, characterized by: Made from the following raw materials in percentage by weight: Aluminum silicate fiber 10%-70%; Cordierite powder 10%-85%, particle size 2-4μm; Ammonia type silica sol 10%-25%; Cationic starch is added in an amount of 5%-30% of the total weight of the aluminum silicate fiber, cordierite powder and ammonia silica sol.

2. The low expansion ceramic fiberboard according to claim 1, characterized in that: The aluminum silicate fiber has a slag ball content of ≤2% and a sedimentation volume of ≤5 ml / g.

3. The low expansion ceramic fiberboard according to claim 2, characterized in that: The aluminum silicate fiber has a slag shot content of 0.5%-1.5% and a sedimentation volume of 3-4.5 ml / g.

4. The low expansion ceramic fiberboard according to claim 1, characterized in that: The cordierite powder is obtained by ball milling cordierite ore, the ball milling speed is ≥300r / min, the ball milling time is ≥8 hours, and the grinding medium is alumina balls.

5. The low expansion ceramic fiberboard according to claim 1, characterized in that: The cationic starch is added in an amount of 10%-25% of the total weight, and is pre-dispersed separately in the mixing system at a speed of ≥350 r / min for more than 30 minutes.

6. A method for preparing the low-expansion ceramic fiberboard according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: ball milling the cordierite raw material at ≥300 r / min for ≥8 hours to obtain 2-4 μm cordierite powder; Step 2: mixing cordierite powder and ammonia silica sol at 150 r / min for ≥10 minutes, adding aluminum silicate fiber and stirring at a speed of ≥500 r / min for ≥30 minutes; Step 3: Pre-disperse the cationic starch at ≥350 r / min for ≥30 minutes, then add the mixture generated in step 2 and continue stirring for ≥5 minutes; Step 4: Press the mixture into shape at 60-100 MPa and maintain the pressure for ≥5 minutes; Step 5, drying at 300-350°C for 36-72 hours; Step 6, programmed temperature calcination: raise the temperature to 800°C within 3 hours, then raise the temperature to 1300°C in ≥4 hours, and keep the temperature for ≥4 hours.

7. The preparation method according to claim 6, characterized in that: During stirring in step 2, the material temperature is controlled at 40-60° C., and a double-layer spiral ribbon stirrer is used.

8. The preparation method according to claim 6, characterized in that: In step 6, calcination is performed in a nitrogen atmosphere at 800-1300° C., with a heating rate of 2-3° C. / min.

9. The preparation method according to claim 6, characterized in that: During the pressing in step 4, vacuum assisted molding is adopted, and the vacuum degree is ≤-0.08MPa.

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