Process for the forming of acid-resistant ceramic articles

Abstract

The application discloses a forming process of acid-resistant ceramic products, and aims to solve the problem of poor acid resistance of ceramics caused by microstructure defects and grain boundary impurities in the prior art. The steps of the process comprise the following: firstly, the surface of main raw material particles containing alumina and silicon dioxide is chemically modified, and a nanoscale metal oxide coating layer with high chemical inertness is generated in situ on the surface of the particles. Then, the modified powder is prepared into a high-uniform-density ceramic green body by using a gradient pulse pressure forming method, so as to eliminate internal defects. In the sintering step, a controllable atmosphere multi-stage treatment is adopted: firstly, high-temperature purification is carried out in a weak reducing atmosphere, so that the inherent alkali metal oxide impurities in the raw material are removed in the form of gas phase; and then, the inert atmosphere is switched to complete the final densification sintering. The acid-resistant ceramic product prepared by the process has the characteristics of high density and enhanced acid corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic material manufacturing technology, specifically relating to a molding and processing technology for acid-resistant ceramic products. Background Technology

[0002] The performance of traditional acid-resistant ceramics mainly relies on the inherent chemical inertness of their raw materials (such as quartz, feldspar, and clay) and the dense physical structure formed after firing. However, existing technologies generally suffer from the following problems, limiting further improvements in product performance and their application in more demanding environments:

[0003] On the one hand, traditional mixing and molding processes, such as dry pressing or extrusion molding, cannot completely avoid the generation of micron-sized pores, interfacial delamination, or stress concentration within the preform. These physical defects will still partially remain after sintering, becoming initial channels for acidic media penetration and corrosion, which greatly reduces the long-term service reliability of the product.

[0004] On the other hand, industrial raw materials commonly contain impurities such as alkali metal oxides (e.g., Na₂O, K₂O). During high-temperature sintering, these impurities, due to their low melting points, migrate and accumulate towards the grain boundary regions, forming an amorphous glassy phase. This glassy phase has far lower chemical stability than the main crystalline phase (e.g., mullite, corundum), making it the weakest link in the entire ceramic structure. In acidic environments, the acid preferentially corrodes these fragile grain boundaries, leading to grain detachment and ultimately causing macroscopic failure of the material.

[0005] To address these issues, some advanced technologies have attempted to use high-purity synthetic raw materials to avoid impurities, or employ sintering techniques such as hot pressing and hot isostatic pressing to reduce physical defects. However, these methods all suffer from drawbacks such as huge equipment investment, complex process control, and high energy consumption, leading to a sharp increase in product costs and making them difficult to promote and apply in most industrial scenarios. Therefore, a new molding and processing technology for acid-resistant ceramic products is needed to solve these problems. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide a novel forming and processing technology for producing high-performance acid-resistant ceramics by systematically and synergistically designing the particle surface, green body structure, and sintering atmosphere during the ceramic preparation process based on fundamental physical and chemical principles, thereby fundamentally eliminating corrosion channels and chemical weak points.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a molding and processing technology for acid-resistant ceramic products, comprising the following steps:

[0008] a) Surface modification: The ceramic main raw material particles containing alumina and silicon dioxide are subjected to surface chemical modification treatment to generate a nanoscale metal oxide coating layer in situ on the surface of the main raw material particles, which is used to improve the chemical inertness of the monomer particles.

[0009] b) Molding: The composite powder that has undergone surface modification in step a) is subjected to gradient pressure molding to obtain a ceramic green body with high uniform density, which is used to reduce sintering defects in the final product.

[0010] c) Sintering: The ceramic green body is placed in a controlled atmosphere for multi-stage sintering, which includes:

[0011] c1) Purification stage: Within the first preset temperature range, a weak reducing atmosphere is introduced for in-situ purification treatment so that the inherent alkali metal oxide impurities in the main raw material are volatilized and removed.

[0012] c2) Densification stage: In a second preset temperature range higher than the first preset temperature range, the furnace atmosphere is switched to an inert atmosphere for densification sintering to complete the final forming of the ceramic.

[0013] Furthermore, the surface chemical modification treatment in step a) employs the sol-gel method, and the metal oxide coating layer is selected from zirconium oxide, titanium oxide, or a combination thereof.

[0014] Furthermore, the thickness of the metal oxide coating layer is 5 to 50 nanometers.

[0015] Furthermore, the gradient pressure molding in step b) specifically includes three consecutive stages: low-pressure pre-compression, high-frequency pulse vibration compression, and high-pressure final compression of the composite powder.

[0016] Furthermore, the vibration frequency during the high-frequency pulse vibration pressurization stage is 10Hz to 50Hz.

[0017] Furthermore, the weakly reducing atmosphere in step c1) is a mixture of nitrogen and hydrogen.

[0018] Furthermore, the volume percentage of hydrogen in the weakly reducing atmosphere is 2% to 10%.

[0019] Furthermore, the first preset temperature range in step c1) is 600℃ to 1200℃, and the second preset temperature range in step c2) is 1200℃ to 1500℃.

[0020] Furthermore, during the densification stage in the second preset temperature range, the heat preservation time is 2 to 4 hours.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] This invention constructs a dual-protection structure from particles to grain boundaries by forming a chemically inert coating layer on the surface of raw material particles and purifying grain boundaries during sintering. This structure effectively hinders the physical penetration of acidic media along pores and the chemical erosion along grain boundaries, thereby improving the overall acid resistance of the product.

[0023] The process combination of this invention, particularly gradient pressure forming and in-situ purification sintering, systematically reduces microscopic defects in the final product. Gradient pressure forming reduces the original porosity of the green body, while atmosphere purification avoids the formation of unstable glassy phases at grain boundaries, ultimately resulting in a dense ceramic body with low porosity and pure grain boundaries.

[0024] The controlled atmosphere sintering process employed in this invention can actively remove alkali metal oxide impurities that are harmful to acid resistance from the green body during the sintering process. This characteristic allows for the production of high-purity ceramic products that previously required high-purity raw materials using conventional industrial-grade raw materials, while maintaining performance and controlling costs. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process flow for the preparation method of acid-resistant ceramics of the present invention;

[0026] Figure 2 This is a comparative schematic diagram showing the difference between the raw material particles before and after the surface coating treatment of the present invention;

[0027] Figure 3 This is a schematic diagram of the controlled atmosphere sintering process of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, specific embodiments of the invention will be described in detail below with reference to the accompanying drawings. It should be noted that these specific embodiments are merely illustrative of the invention and are not intended to limit it. Those skilled in the art, after reading this specification, can make modifications to these embodiments without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this invention.

[0029] This embodiment provides a molding and processing technology for high-performance acid-resistant ceramic products, the steps of which are as follows:

[0030] First, prepare ceramic raw material powder with a purity higher than 99.9%, including an average particle size (D50) of 3 μm and a specific surface area of ​​4.5 m². 2 80 parts by weight of α-alumina (α-Al₂O₃) powder with an average particle size of 1 μm and a specific surface area of ​​8.2 m² / g. 220 parts by weight of fused silica (SiO2) powder were prepared. Both powders were placed in a large-capacity beaker with 500 ml of anhydrous ethanol. Ethanol was chosen as the dispersion medium due to its good powder wettability and moderate evaporation rate. The suspension was dispersed for 30 minutes using a high-power ultrasonic probe emitting 20 kHz ultrasound to ensure complete dissolution of agglomerates between raw material particles, forming a uniform and stable suspension. Subsequently, 2 parts by weight of analytical grade zirconium chloride (ZrOCl2·8H2O) were weighed as a precursor and dissolved in 50 ml of anhydrous ethanol. Under mechanical stirring at 600 rpm, the zirconium chloride solution was slowly added dropwise to the ceramic powder suspension at a rate of approximately 2 mL / min. After the addition was complete, 2 mol / L ammonia solution was added dropwise to precisely adjust the pH of the system to 8-9. This process was carried out continuously for 2 hours in a constant-temperature magnetically stirred water bath at 50°C to complete the surface modification.

[0031] The above steps utilize the sol-gel reaction mechanism to hydrolyze and condense the zirconium chloride precursor on the particle surface, ultimately generating a uniform nanoscale hydrated zirconium oxide gel coating layer in situ. After the reaction is complete, the mixture is filtered and repeatedly washed with a large amount of deionized water until no chloride ion precipitate is detected by silver nitrate solution to ensure the removal of residual ions. Finally, it is dried in a forced-air oven at 110°C for 12 hours to obtain the surface-coated composite powder. It is understood that those skilled in the art can use similar methods with titanium source precursors such as titanium tetrachloride or tetrabutyl titanate to achieve similar titanium dioxide (TiO2) coating layers, following the same principles and achieving the same effect.

[0032] Next, to improve the molding performance and green strength of the powder, the dried composite powder was mixed and granulated with a 3% (w / w) polyvinyl alcohol (PVA) aqueous solution in a spray granulation tower to obtain spherical granulated powder with good flowability and a particle size of 80-100 μm. 100 g of this granulated powder was then filled into a high-precision cylindrical mold with an inner diameter of 50 mm, made of quenched H13 die steel, and subjected to gradient pressure molding. This process involves three stages:

[0033] First stage: Apply an initial static pressure of 15 MPa and maintain it for 30 seconds for pre-compression to expel most of the air between the powder particles;

[0034] The second stage: While maintaining a static pressure of 15MPa, a pulse dynamic pressure with a frequency of 30Hz is applied to the mold for 45 seconds. The energy introduced by this pulse vibration can effectively promote particle crushing and rearrangement, thereby improving the filling uniformity and density of the blank.

[0035] In the third stage, the pulsed pressure is immediately removed, and the pressure is quickly increased to the final forming pressure of 120 MPa, which is then held for 60 seconds to complete the final pressing. After forming, the pressure is slowly released, and the green body is carefully ejected from the mold. Compared with the traditional single-pressurization process, the ceramic green body obtained through this three-stage forming process has a more uniform internal stress distribution, a significantly reduced number of micro-defects, and sufficient transfer strength.

[0036] Then, the formed ceramic green body is placed in a tubular atmosphere sintering furnace using molybdenum disilicide (MoSi2) heating elements for crucial controlled atmosphere sintering. The sintering procedure is as follows:

[0037] First, in a flowing air atmosphere, the temperature was increased from room temperature to 600°C at a slow rate of 2°C / min, and held at 400°C for 2 hours. This stage was intended to gently and completely remove the PVA binder introduced during the granulation process. Then, the atmosphere was switched to a mixture of nitrogen and hydrogen (5% hydrogen by volume) at a flow rate of 200 SCCM (standard mL / min), and under this weakly reducing atmosphere, the temperature was further increased to 1100°C at a rate of 3°C / min.

[0038] In this purification stage, hydrogen reacts with alkali metal oxides to generate volatiles, thereby achieving in-situ purification of the material. Specifically, at high temperatures, hydrogen can reduce inherent alkali metal oxides (such as Na₂O) to elemental sodium (Na). Given that the boiling point of sodium (883°C) is much lower than the process temperature, it immediately volatilizes in gaseous form and is carried out of the furnace by the flowing carrier gas. This step eliminates harmful components that would form a fragile glassy phase at grain boundaries. Once the temperature reaches 1100°C, the furnace atmosphere is immediately switched to high-purity argon at a flow rate of 200 SCCM, and under this inert atmosphere, the temperature is increased to a peak temperature of 1480°C at a rate of 2°C / min and held at this temperature for 3 hours. Those skilled in the art will understand that this holding time can be adjusted within the range of 2 to 4 hours to achieve the best densification effect, depending on the size and thickness of the product. During this densification stage, the purified particle interfaces undergo diffusion and recrystallization, forming a pure and dense ceramic body. After the heat preservation is completed, the temperature is controlled by a program at a rate of 5℃ / min to avoid thermal stress caused by excessively rapid cooling, which could lead to cracking of the product.

[0039] Through the complete process described above, a high-performance acid-resistant ceramic product was finally obtained. The acid-resistant ceramic product prepared by the above process is characterized by high density and enhanced acid corrosion resistance. Its high density is attributed to gradient pressure molding and an effective sintering process, while its excellent acid corrosion resistance stems from the dual protection mechanism of particle coating and grain boundary purification constructed in this invention. These structural improvements enable the product prepared by this invention to be suitable for applications requiring stringent acid corrosion resistance, such as linings of chemical pickling tanks, components of hydrometallurgical reactors, or pipelines for transporting high-purity chemicals, thus achieving long-term stable use of the acid-resistant ceramic product in harsh acid corrosion environments.

[0040] To further verify the beneficial effects of the present invention, comparative samples and the present invention sample were prepared in this embodiment, and their key performance was compared and tested.

[0041] 1. Sample preparation

[0042] Comparative Example 1: The same α-alumina and fused silica raw materials and proportions as in Example 1 were used. However, no surface modification treatment was performed; the two powders were directly mechanically dry-mixed until homogeneous. The same granulation process as in Example 1 was used. During molding, instead of gradient pressure, a single pressure of 120 MPa was applied and held for 60 seconds. During sintering, instead of a controlled atmosphere, the temperature was raised to 1480°C at a rate of 5°C / min in a conventional air-atmosphere muffle furnace, held for 3 hours, and then cooled with the furnace.

[0043] Example 1 of the present invention: The preparation was carried out entirely according to the process steps described in Example 1.

[0044] 2. Performance Testing

[0045] Density test: The Archimedes displacement method was used to test the bulk density of the sample and calculate its relative density with respect to the theoretical density.

[0046] Acid corrosion resistance test: The sample was cut into 10mm×10mm×5mm blocks, accurately weighed, and then completely immersed in boiling 98% concentrated sulfuric acid for 48 hours. After removal, it was washed with deionized water, dried, and accurately weighed again to calculate the corrosion weight loss rate.

[0047] 3. Experimental Results and Analysis

[0048] Table 1 Performance Test Results

[0049]

[0050] The experimental results in the table above clearly show that:

[0051] First, regarding density, the relative density of Example 1 of this invention (99.5%) is significantly higher than that of Comparative Example 1 (96.2%). This directly proves that the gradient pulse pressure molding process used in this invention can more effectively eliminate voids between powder particles and obtain a more uniform and dense green body compared to the traditional single-pressurization process, thus laying the foundation for sintering a high-density final product.

[0052] Secondly, in terms of the core acid corrosion resistance performance, Example 1 of the present invention has a significant advantage. Its corrosion weight loss rate (0.4%) is less than one-tenth of that of Comparative Example 1 (5.1%), which strongly demonstrates the effectiveness of the dual protection mechanism constructed by the present invention.

[0053] In summary, this invention effectively solves the problems of insufficient density, grain boundary impurity enrichment, and unstable acid resistance in traditional acid-resistant ceramics by constructing a nano-oxide coating layer on the surface of ceramic raw material particles and combining it with gradient pressure molding and controlled atmosphere sintering. Experimental results clearly show that the embodiments of this invention are significantly superior to the comparative samples in terms of relative density and acid corrosion resistance, which well confirms the effectiveness of the dual protection strategy of "particle coating + grain boundary purification". Therefore, this invention can be widely applied in chemical equipment, metallurgical equipment, and high-purity chemical delivery systems, where strict acid resistance requirements are present, thereby achieving long-term stable use of ceramic products in harsh acid etching environments.

[0054] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A molding and processing technology for acid-resistant ceramic products, characterized in that, Includes the following steps: a) Surface modification: The ceramic main raw material particles containing alumina and silicon dioxide are subjected to surface chemical modification treatment to generate a nanoscale metal oxide coating layer in situ on the surface of the main raw material particles, which is used to improve the chemical inertness of the monomer particles. b) Molding: The composite powder that has undergone surface modification in step a) is subjected to gradient pressure molding to obtain a ceramic green body with high uniform density, which is used to reduce sintering defects in the final product. c) Sintering: The ceramic green body is placed in a controlled atmosphere for multi-stage sintering, which includes: c1) Purification stage: Within the first preset temperature range, a weak reducing atmosphere is introduced for in-situ purification treatment so that the inherent alkali metal oxide impurities in the main raw material are volatilized and removed. c2) Densification stage: In a second preset temperature range higher than the first preset temperature range, the furnace atmosphere is switched to an inert atmosphere for densification sintering to complete the final forming of the ceramic. The surface chemical modification treatment in step a) adopts the sol-gel method, and the metal oxide coating layer is selected from zirconium oxide, titanium oxide or a combination thereof; The gradient pressure molding in step b) specifically includes three consecutive stages: low-pressure pre-compression, high-frequency pulse vibration compression, and high-pressure final compression of the composite powder. The weak reducing atmosphere in step c1) is a mixture of nitrogen and hydrogen.

2. The molding process according to claim 1, characterized in that, The thickness of the metal oxide coating is 5 to 50 nanometers.

3. The molding process according to claim 1, characterized in that, The vibration frequency during the high-frequency pulse vibration pressurization stage is 10Hz to 50Hz.

4. The molding process according to claim 1, characterized in that, The volume percentage of hydrogen in the weakly reducing atmosphere is 2% to 10%.

5. The molding process according to claim 1, characterized in that, The first preset temperature range in step c1) is 600℃ to 1200℃, and the second preset temperature range in step c2) is 1200℃ to 1500℃.

6. The molding process according to claim 5, characterized in that, During the densification stage in the second preset temperature range, the heat preservation time is 2 to 4 hours.

7. An acid-resistant ceramic product prepared by the molding process according to any one of claims 1 to 6.

Images