Silicon carbide (SiC) ceramics have long been widely used in various advanced manufacturing fields due to their high hardness, high strength, small coefficient of thermal expansion, high thermal conductivity, good chemical stability, excellent thermal shock resistance and oxidation resistance. In addition to the above-mentioned characteristics of silicon carbide ceramics, porous silicon carbide ceramics, with their unique microscopic porous structure, have broad application prospects in fields such as metallurgy, chemical engineering, environmental protection and energy, greatly expanding the application scope of silicon carbide ceramics.
The special properties of porous silicon carbide ceramic mainly benefit from their unique porous structure, which includes porosity, pore size and distribution, and pore shape, etc. Therefore, it is necessary to regulate its porosity, pore size and distribution, as well as the shape of the pores through the preparation method to obtain the desired porous structure. Therefore, its preparation method has always been the focus of people’s research. This article mainly reviews the research progress in the preparation methods of porous silicon carbide ceramics at home and abroad in recent years.
1. Physical Method
The physical method refers to the fact that the voids in porous silicon carbide ceramics are caused by a series of physical phenomena during the preparation process, without the occurrence of chemical reactions or the generation of new substances. The main mechanism is to form a porous structure by relying on the voids left behind by the thermal contraction of solid substances, the evaporation of the liquid phase, and the direct sublimation of the solid phase. Common methods include particle stacking method, freeze-drying method, sol-gel method, etc. The 3D printing technology that has emerged in recent years can also be used to directly print and prepare porous structures.
1.1 Particle stacking method
The particle packing sintering method is the simplest way to prepare porous silicon carbide ceramics. The principle of this method is to utilize the sintering performance of ceramic particles themselves to form sintering necks between different SiC particles, thereby enabling the particle accumulation to form porous ceramics. To lower the sintering temperature, a certain amount of binder with a lower melting point is usually added to form a connection between different SiC particles. Since all the pores in the particle packing sintering method are transformed from the packing gaps between SiC particles, the porosity and pore size of the finished porous ceramics can be controlled by changing the powder size, the type and addition amount of the binder, and the sintering parameters.
The preparation of porous silicon carbide ceramics by the particle stacking method does not require the addition of additional pore-forming agents. The process is simple and relatively easy to control. However, the porosity of porous ceramics prepared by this method is generally low. The shape, pore size and porosity of the pores are mainly determined by the shape, particle size and distribution of the raw material particles, as well as the degree of sintering.
1.2 Freeze-drying Method
Freeze-drying is a method that involves uniformly mixing ceramic aggregates with water or organic solvents in the presence of an appropriate amount of dispersants or binders to form a slurry. Then, the well-mixed slurry is poured into a mold and rapidly frozen at low temperatures, allowing the liquid phase matrix to quickly solidify into a solid. Subsequently, the solidified solid phase is sublimated and removed through pressure reduction or vacuum drying treatment. The method of obtaining a green body with directionally arranged pore structures left inside the slurry and finally sintering it to produce porous silicon carbide ceramics.
1.3 3D Printing Method
The 3D printing method for preparing porous silicon carbide ceramics is a new type of preparation process that has developed in recent years. This process relies on a three-dimensional data model designed with the aid of computer assistance. Through the printing head, the binder is sprayed to stack the raw material powder layer by layer into a three-dimensional network structure. The combination of 3D printing and reaction sintering processes can achieve mold-free manufacturing and near-net-size forming of complex-shaped ceramics.
The 3D printing method for preparing porous silicon carbide ceramics features a simple forming process, high preparation and processing efficiency, and no need for molds. It can not only be used to prepare porous silicon carbide ceramics with complex shapes, uniform microstructures and good pore connectivity, but also the porosity and pore size of the porous ceramics are controllable and adjustable. However, this method is still in the exploratory research stage at present, and the process parameters still need to be further optimized. In addition, this method is difficult to prepare high-strength porous silicon carbide ceramics in one step. It requires the assistance of other processes to produce the desired products, which incurs relatively high costs.
1.4 Foaming
The foaming molding method involves adding gas or substances that can generate gas through subsequent processing to the ceramic green body or precursor, and then sintering it to obtain porous silicon carbide ceramics. Unlike other preparation methods, the foaming method is an effective process for preparing closed-cell ceramics.
2. Chemical Method
The chemical method refers to the fact that the porous structure in porous silicon carbide ceramics is formed by the decomposition or reaction of inorganic salts or added organic substances, leaving vacancies in the original positions. Common chemical methods for preparing porous silicon carbide ceramics include the pore-forming agent addition method, organic foam impregnation method, and biological template method, etc.
2.1 Organic Foam Impregnation
The organic foam impregnation method involves using organic foam as a template, evenly coating the prepared ceramic slurry on the template or immersing the template in the slurry to expel air, ensuring the slurry adheres evenly to the organic foam template. Then, through drying and high-temperature sintering, the organic template is removed, thereby obtaining porous ceramics.
The most significant drawback of this method is that it is unable to produce small-pore closed porosity products. The shape is restricted and the performance of the preform is greatly affected by the raw materials. The density and strength of the prepared porous ceramic materials are also difficult to control.
2.2 The Method of Adding Pore-forming Agents
The preparation of porous silicon carbide ceramics by adding pore-forming agents involves adding pore-forming agents to silicon carbide powder or precursors, and then removing the pore-forming agents through subsequent processes. As a result, the positions originally occupied by the pore-forming agents form pores, and then heating and sintering are carried out to form porous ceramics. Therefore, changing the type and dosage of pore-forming agents can conveniently control the porosity, pore morphology, pore size and distribution of the finished porous ceramics. The types of pore-forming agents are very extensive, including natural or synthetic organic polymers, liquids, salts, ceramics or other powders, etc. The removal processes of different pore-forming agents vary. Organic polymer pore-forming agents are usually removed by heating and decomposition, liquid pore-forming agents can be removed through crystallization and sublimation, salts can be removed by water filtration, and ceramic powders can be removed by appropriate solution filtration.
2.3 Biological Template Method
The microscopic pore structure in biomaterials is significantly different from that in synthetic materials. Due to its unique structure, the preparation of porous ceramic materials with similar structures using organisms as templates has received widespread attention [10]. The biological template method and the organic foam impregnation method share similarities. The organic foam impregnation method uses artificial sponge as the template, while the biological template method uses natural organisms as the template.
The biological template method for preparing porous silicon carbide ceramics has the advantages of simple process and low cost. It can produce ceramics with complex shapes and can replicate the structure of natural biological materials to the greatest extent. However, the biological template is prone to cracking during the high-temperature carbonization process, which has a significant impact on the mechanical properties of porous silicon carbide ceramics. Moreover, the pore structure of the prepared porous silicon carbide ceramics mainly depends on the microstructure of the biological template itself, and its designability is poor. In addition, this method also has some disadvantages, such as relatively low conversion efficiency of SiC, easy shedding of the SiC reaction layer, and a long preparation cycle.
Post time: Jul-22-2025