Preparation method of coarse-grained ceramic tile based on multi-stage pressure field and rheology regulation

Abstract

The application belongs to the technical field of advanced ceramic manufacturing, and relates to a preparation method of coarse-grained ceramic tile based on a multistage pressure field and rheology regulation, and the specific steps of the preparation method are as follows: a cross-scale particle grading system containing millimeter-level coarse particles and micron-level fine particles is constructed according to a Dinger-Funk equation, a distribution coefficient qq is 0.20-0.25, wherein the maximum particle diameter of the coarse particles is 2.0 mm-4.0 mm, and the particle diameter of the fine particles is less than or equal to 10 microns; a slurry with three rheological characteristics of 'high static yield stress, shear thinning and moderate thixotropy' is prepared; a porous polyurethane mold with a median pore diameter of 15 microns-25 microns is adopted, a two-stage pressure grouting process of 'low-pressure filling-high-pressure dewatering' is implemented, gradient drying and high-temperature sintering are carried out, and ceramic combination of the matrix and the coarse particles is realized. The application fundamentally solves the segregation problem of coarse particles in a complex-shaped green body.

Description

Technical Field

[0001] This invention belongs to the field of advanced ceramic manufacturing technology, specifically relating to a method for preparing coarse-grained corundum-mullite ceramic tiles for linings of high-temperature industrial equipment (including but not limited to gas turbine combustion chambers), and in particular a pressure slurry casting method that achieves three-dimensional uniform distribution of millimeter-sized coarse particles in a complex-shaped green body through the synergistic control of multi-level pressure fields and slurry rheology. Background Technology

[0002] Lining materials for high-temperature equipment such as gas turbine combustion chambers need to be used for a long time in environments with high temperatures exceeding 1500°C, severe thermal shock, and high-speed airflow erosion. In order to balance thermal shock resistance, high-temperature strength, and wear resistance, millimeter-sized coarse particles (≥2 mm) must be introduced into the material system to form a "coarse particle-matrix" two-phase structure.

[0003] Currently, the forming of coarse-grained refractory materials mainly relies on the following technical approaches, but all of them have insurmountable technical defects: 1. Traditional refractory castable molding (vibration casting, self-flowing casting) can accommodate millimeter-sized coarse particles, and the particle size distribution design is mature; however, its inherent defects are: coarse particles are prone to gravity settling and flow segregation during vibration or self-flowing, resulting in uneven composition and structure in the upper and lower parts of the green body; the molding process cannot apply external pressure to drive densification to eliminate internal large pores.

[0004] 2. Traditional pressure injection molding can produce high-density preforms, which are suitable for complex shapes and high-precision parts; however, its inherent defects are that it is limited to fine-particle systems (d ≤ 100 μm) and cannot accommodate millimeter-sized coarse particles. The reasons include coarse particle settling, mold clogging, and insufficient demolding strength.

[0005] 3. Existing improved technologies (such as CN103732560A) disclose die-casting slurry for gas turbine heat shields, which contains millimeter-sized coarse particles and xanthan gum additives, and adopts a die-casting process. Its technical limitations are as follows: although the technology attempts to introduce coarse particles, it does not solve the problem of segregation of coarse particles during the molding process; it adopts a single pressure injection mode, which cannot simultaneously achieve the two contradictory goals of "anti-segregation" and "high density"; it does not establish a matching mechanism for the mold-particle interface, which poses a risk of fine particles clogging the mold; and the uniformity of the billet after molding still depends on the stability of the particle size distribution itself, lacking active control methods.

[0006] In summary, there is currently no molding method that can actively prevent the segregation of millimeter-level coarse particles, achieve high densification, and ensure uniform particle distribution in complex shapes. Summary of the Invention

[0007] This invention aims to provide a method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control. This method solves three major technical problems, namely coarse particle segregation, insufficient densification, and mold blockage, through the synergistic effect of three core mechanisms: "triple rheological feature construction", "two-stage pressure field control" and "mold-particle interface matching", thereby achieving a three-dimensional uniform distribution of millimeter-level coarse particles in a complex-shaped green body.

[0008] This invention does not simply combine "castable gradation" with "pressure grouting," but rather establishes a new molding paradigm in the gaps of existing technology through the following three systematic innovations:

[0009] The technical solution adopted in this invention is as follows: A method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control, the specific steps of which are as follows: Step 1: Cross-scale design of particle size distribution: Coarse particles, i.e., aggregate: Select tabular corundum, fused white corundum, or fused mullite, with a critical particle size d. max =2.0~4.0 mm; Fine particles serve as the matrix: Activated alumina micro powder (<10 µm) and mullite fine powder are selected; Gradation model: The Dinger-Funk equation was used for full-scale particle packing design, with a distribution coefficient q = 0.20~0.25; This allows fine particles to fully fill the gaps between coarse particles, reducing water demand and providing sufficient interparticle contact points in the slurry. Particle size range: coarse particles dmax=2.0~4.0 mm, fine particles ≤10 μm; Grading equation: The mass fraction of each particle size component is calculated according to the Dinger-Funk equation, and the distribution coefficient q = 0.20~0.25; In other words, the specific amount added is determined by both the q value and the particle size range, and the value varies depending on the ratio of different raw materials. The Dinger-Funk equation is: CPFT / 100 = (Dq - Dsq) / (DLq - Dsq), where: CPFT: Cumulative percentage of particles smaller than a certain particle size D D: Particle size DL: Maximum particle size in the system Ds represents the smallest particle size in the system. q: Particle size distribution coefficient.

[0010] Step 2: Construction of the three-fold rheological characteristics of the slurry: Preparation process: Dry powder involves high-speed premixing of aggregates and matrix → slow addition of aqueous solution containing additives → high-speed dispersion → vacuum degassing to obtain slurry; The additives are xanthan gum or inorganic thixotropic agents, dispersants, and temporary binders; the amount of xanthan gum or inorganic thixotropic agents added is 0.01% to 0.02% of the total mass of the slurry; the dispersant is a polycarboxylate, and the amount added is 0.01% to 0.02% of the total mass of the slurry; the amount of temporary binder added is 0.5% to 1.5% of the total mass of the slurry.

[0011] The xanthan gum described herein serves as both a thickener and a thixotropic agent, belonging to the category of thixotropic agents. The pseudoplasticity of xanthan gum achieves a synergistic effect of high viscosity at rest (locking in coarse particles) and low viscosity under shear (ensuring filling), thereby achieving the target slurry characteristics of yield stress (>10 Pa). Xanthan gum has a dual function: to meet the fluidity requirements of the slurry during casting, a dispersant is introduced, and the dispersant's ability to thin the slurry under shear is synergistic with the low viscosity under shear of xanthan gum.

[0012] The slurry must possess the following three rheological characteristics, none of which can be omitted:

[0013] Rheological monitoring: A falling ball viscometer is used to monitor dynamic viscosity and thixotropy to ensure that the slurry simultaneously meets the three requirements of "static anti-settling, smooth flow, and demolding". Step 3: Mold-Particle Interface Matching Mechanism Mold material: porous polyurethane (PU), median pore diameter d 50 =15~25μm.

[0014] Ternary matching relationship: (1)d 50,mold >d fine particle : To prevent fine particles from clogging the mold pores; d 50,mold This refers to the median diameter of the pores in a multi-hole mold, d fine particle This refers to the median particle size of the fine powder in the raw material; (2)d 50,mold ≪d coarse particle Preventing coarse particle leakage; coarse particle refers to the particle size of coarse aggregate particles that play a skeletal role in the material; (3) The mold is wetted with water before use to maintain a stable filtration interface; The establishment of the ternary matching relationship is to simultaneously solve the problems of fine particle clogging of the mold pores, coarse particle leakage or embedding, and unstable filtration interface. The core lies in: d fine particle < d50,mold ≪ d coarse particle.

[0015] The left inequality (dfine < d50,mold) allows some fine particles to enter the pores on the surface layer of the mold, forming an (arch effect) to construct a stable initial filter cake layer instead of complete clogging. The right inequality (d50,mold ≪ dcoarsed50) ensures that coarse particles are completely retained inside the filter cake and cannot contact the mold surface, preventing leakage or embedding. In short, the core goal is: let what should pass through pass through (water, a small amount of fine particles), and what should not pass through not pass through (coarse particles), while maintaining the long-term stable operation of the filtration interface.

[0016] In the initial stage of filtration, the filter cake layer is formed. When the slurry is injected into the mold, the pressure drives the liquid phase (water) to drain through the mold pores. At this time: fine particles (≤10 μm) enter the surface layer of the pores partially because their size is slightly smaller than the mold pore diameter (15 - 25 μm). The particles form an "arch" or "bridging" structure at the pore entrance, blocking subsequent particles from penetrating deeper. This thin layer composed of fine particles is the initial filter cake layer.

[0017] In the middle and late stages of filtration, the filter cake layer thickens. After the initial filter cake layer is formed, its effective pore diameter is much smaller than the original mold pore diameter (due to the smaller gaps between particle accumulations). Subsequent fine particles and a small amount of medium particles are retained outside the filter cake layer, and the filter cake gradually thickens. Coarse particles (2 - 4 mm) are always blocked on the outermost side of the filter cake layer and do not contact the mold surface; the water passes continuously through the filter cake layer and the mold pores, achieving solid-liquid separation.

[0018] The advantage of this design that is not "completely impermeable" is that if the mold pore diameter is smaller than all particles (including fine particles), the opposite problems will occur. That is, the initial filtration resistance is extremely high, and dehydration cannot start; fine particles cannot enter the surface layer of the mold at all and cannot form a stable filter cake anchorage; The water in the slurry cannot be drained, and the molding fails.

[0019] Before use, the mold is wetted with water to pre-fill the air in the mold pores, reducing initial filtration resistance and ensuring smooth water drainage during the initial grouting stage. During grouting, the grout is first slowly filled at a low pressure of 0.05–0.15 MPa to maintain a plunger flow state. This low pressure prevents coarse particles from rotating and segregating, while fine particles initially accumulate on the mold surface (intermediate pore size 15–25 μm) to form a uniform initial filter cake layer. This filter cake layer effectively traps subsequent coarse particles (preventing them from contacting the mold surface) without clogging the mold pores. Subsequently, the pressure is increased to 1.5–4.0 MPa for high-pressure dehydration, forcing water to quickly pass through the filter cake layer and the mold, achieving high-density molding of the green body with an apparent porosity controlled at 18%–23%. After molding, 0.2–0.5 MPa is introduced. MPa of compressed air is used for back-blowing demolding, which utilizes the air cushion effect to form a uniform air film at the interface between the blank and the mold, greatly reducing demolding resistance and avoiding blank cracking or coarse particle peeling caused by mechanical ejection, thereby ensuring the integrity and surface quality of complex-shaped ceramic tiles.

[0020] Step 4: Multi-level pressure field control: The "two-stage pressure field" is adopted to address the two contradictory goals of coarse particle segregation and densification. In the low-pressure filling stage, the high yield stress and plunger flow characteristics of the grout are used to fill the coarse particles in a "whole-body pushing" manner, avoiding the rotation and segregation of coarse particles caused by the flow velocity gradient in traditional pressure grouting. In the high-pressure dewatering stage, the limitation of traditional castables being unable to apply external pressure is overcome, and high densification is achieved. "Integral displacement" filling refers to a process where, under low pressure, the slurry flows with almost equal velocity across its cross-section, propelling the entire slurry forward like a rigid plunger, with no relative motion within. In contrast, ordinary fluids flow with zero velocity at the pipe wall and maximum velocity at the center, forming a parabolic velocity distribution. In this flow pattern, significant velocity gradients exist between fluid elements at different radial positions, causing suspended coarse particles (2–4 mm) to rotate, tumble, and migrate relative to each other, ultimately leading to particle segregation. When the slurry requires high yield stress (>10 Pa), the shear stress under low pressure is insufficient to disrupt its internal gel network. The slurry does not undergo interlaminar shearing but instead slides as a whole. During flow, the velocity is approximately equal across almost all areas of the cross-section, propelling the entire slurry forward like a rigid "plunger" or "piston." Coarse particles are "locked" in the slurry by the gel network and move with the slurry as a whole, avoiding the rotation, tumbling, and segregation of coarse particles caused by velocity gradients in traditional flows, thus ensuring uniform distribution of coarse particles in complex-shaped ceramic tiles.

[0021] The pressure range of the low-pressure filling stage is 0.05 to 0.15 MPa, and the time is 3 to 5 minutes, in order to maintain the plunger flow state and prevent coarse particles from rotating and segregating.

[0022] The high-pressure dehydration stage has a pressure range of 1.5 to 4.0 MPa and a time of 20 to 40 minutes, which is used to force the water out and form a high-density filter cake.

[0023] Step 5: Drying and Sintering Gradient drying: 40°C / 24h → 80°C / 6h → 120°C / 24h, utilizing the water retention and strength of the temporary binder to prevent cracking of the coarse particle interface caused by rapid moisture evaporation; High-temperature sintering: 1550°C~1750°C, to achieve the bonding of the matrix and coarse ceramic particles.

[0024] The present invention proposes a method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control. Using the above technical solution, the method has the following beneficial effects:

[0025] In conclusion, This invention introduces for the first time an active anti-segregation mechanism of "high yield stress locking + low pressure plunger flow filling" in a pressure grouting system, which fundamentally solves the problem of coarse particle segregation in complex shaped billets.

[0026] This invention decouples the pressure field into two stages: "low-pressure filling" and "high-pressure dehydration," optimizes them separately, and achieves synergy between the two.

[0027] This invention establishes a ternary matching relationship of "mold aperture > fine particle size and < coarse particle size", ensuring the long-term stable operation of the filter interface.

[0028] This invention combines optimized castable formulation and improved fine-particle pressure grouting, overcoming their respective limitations. In particular, it introduces a synergistic control mechanism of "two-stage pressure field" and "three rheological characteristics," which requires cross-disciplinary technical insights and systematic experimental verification. It is by no means an obvious and simple combination.

[0029] The molding method of this invention application can simultaneously achieve the following three objectives: The coarse particle content is ≥30 vol.%, the apparent porosity is ≤23%, and the particles are uniformly distributed in three dimensions in complex shapes. Detailed Implementation

[0030] The present invention will be described in detail with reference to specific embodiments: Example 1: Ingredients: The maximum particle size is 3 mm. The tabular corundum is coarse, and the matrix is ​​finely composed of sintered alumina powder and mullite powder. The proportions are calculated according to the Dinger-Funk equation (q=0.25q=0.25). Pulping: Add 0.03% Dolapix CE64 dispersant, 1.0% temporary binder, and 0.015% xanthan gum, add water and stir. The solid content is about 85-90 wt%. The static yield stress was measured to be 12 Pa, and the dynamic viscosity decreased to 8 Pa·s under shear.

[0031] Grouting: Use a PU mold with a pore size of 20 μm, first fill at 0.05 MPa for 3 minutes, then increase the pressure to 2.0 MPa and hold for 30 minutes.

[0032] Results: Demolding was successful, and the green body showed no cracks. After sintering at 1650°C, the ceramic tile exhibited a uniform distribution of coarse particles and no sedimentation layer. The apparent porosity was 22%, and the flexural strength at room temperature was 16 MPa.

[0033] Comparative Example 1 (Traditional Vibration Casting) Vibration molding was used with the same formula. Results: The bottom of the sample was enriched with coarse particles, while the top was enriched with fine powder, resulting in uneven density and macroscopic cracks after sintering.

[0034] Comparative Example 2 (Single pressure grouting, without rheological control) The same formula was used, but without the addition of xanthan gum and temporary binder, and grouting was performed directly at a pressure of 1.0 MPa. Result: During the filling process, coarse particles settled significantly, fine particles clogged the mold surface, and the green body had insufficient strength after demolding and cracked during drying.

[0035] Comparative Example 3 (Comparison with Formulation CN103732560A) The formulation described in Example 1 of CN103732560A (multi-peak particle size distribution + 0.05% xanthan gum) was used for molding using a single pressure injection molding process. Results: Although the slurry had basic stability, the molded green body still exhibited localized segregation of coarse particles, and the demolding success rate was low.

Claims

1. A method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control, characterized in that: The specific steps of the preparation method are as follows: Step 1: Construct a cross-scale particle gradation system containing millimeter-scale coarse particles and micrometer-scale fine particles based on the Dinger-Funk equation, with a distribution coefficient qq of 0.20 to 0.25, wherein the maximum particle size of coarse particles is 2.0 mm to 4.0 mm, and the particle size of fine particles is ≤10 μm; Step 2: Construction of the three-fold rheological characteristics of the slurry: A slurry with triple rheological characteristics of "high static yield stress, shear thinning, and moderate thixotropy" was prepared, with a static yield stress ≥10 Pa and a dynamic viscosity that can be reduced to below 10 Pa·s under shear. Step 3: Mold-particle interface matching mechanism and multi-level pressure field control; A porous polyurethane mold with a median pore size of 15 μm to 25 μm was used to implement a two-stage pressure grouting process of "low-pressure filling - high-pressure dehydration". The two-stage pressure grouting process addresses the two contradictory goals of coarse particle segregation and densification. The pressure in the low-pressure filling stage is 0.05 MPa to 0.15 MPa to maintain a plunger flow state to prevent coarse particle segregation; the pressure in the high-pressure dehydration stage is 1.5 MPa to 4.0 MPa. Step 4: Drying and Sintering Gradient drying: Utilizing the water retention and strength of the temporary binder to prevent cracking of the coarse particle interface caused by rapid moisture evaporation; High-temperature sintering: 1550°C~1750°C, to achieve the bonding of the matrix and coarse ceramic particles.

2. The method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to claim 1, characterized in that: The coarse particles, i.e., the aggregate, are selected from tabular corundum, fused white corundum, or fused mullite; the fine particles, i.e., the matrix, are selected from activated alumina micro powder or mullite fine powder.

3. The method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to claim 1, characterized in that: The slurry preparation process in step two is as follows: dry powder is prepared by high-speed premixing of aggregates and matrix → slow addition of aqueous solution containing additives → high-speed dispersion → vacuum degassing to obtain slurry; the slurry achieves the rheological characteristics through the synergistic effect of dispersant, temporary binder and thickener. The additives are xanthan gum or inorganic thixotropic agents, dispersants, and temporary binders; the thickener is xanthan gum or inorganic thixotropic agents, added at 0.01% to 0.02% of the total mass of the slurry; the dispersant is a polycarboxylate, added at 0.01% to 0.02% of the total mass of the slurry raw materials; and the temporary binder is added at 0.5% to 1.5% of the total mass of the slurry.

4. The method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to claim 1, characterized in that: The low-pressure filling stage lasts for 3 to 5 minutes to maintain the plunger flow state and prevent coarse particles from rotating and segregating. The high-pressure dehydration stage lasts for 20 to 40 minutes to force water out and form a high-density filter cake.

5. The method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to claim 1, characterized in that: In step three, the center aperture of the mold is larger than the particle size of the fine particles in the slurry, but smaller than the particle size of the coarse particles.

6. The method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to claim 1, characterized in that: In step four, gradient drying uses three temperature stages: 40°C, 80°C, and 120°C, with each stage held for 6 to 24 hours.

7. The coarse-grained ceramic tile prepared by the method for preparing coarse-grained ceramic tiles based on multi-level pressure field and rheological control according to any one of claims 1 to 5, characterized in that, Its apparent porosity is 18% to 23%, and its microstructure has a uniform distribution of millimeter-sized coarse particles without sedimentation or stratification.

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