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The Forming Method of Boron Carbide Ceramics 


Boron carbide has a history of nearly 170 years of development, and its atomic structure has been widely studied in recent years. Its main crystal structure is a 12 atom icosahedron and a three atom chain connected to the icosahedron. This structure is also known as a hexagonal structure, where carbon atoms and boron atoms can replace each other, resulting in boron carbide having many isomers.

The unique crystal structure of boron carbide determines its many excellent properties. Boron carbide has extremely high hardness (second only to diamond and cubic boron nitride), and its hardness does not change significantly under high temperature conditions; Boron carbide has a low density and a high melting and boiling point; Excellent thermal shock resistance and good thermal stability; Boron carbide is insoluble in water and does not react with acids or bases at room temperature; Meanwhile, boron carbide has extremely strong neutron absorption ability, with a high neutron capture cross-section and a wide capture energy spectrum.

The Forming Method of Boron Carbide Ceramics 

Dry pressing molding

Dry pressing is a commonly used molding method for preparing boron carbide ceramic bodies. Mix the powder with a small amount of adhesive to form pellets, put them into the mold, and apply pressure on the press. The powder particles get close to each other in the mold and tightly combine under the action of internal friction, forming a green body with a certain shape. According to the size of the sample thickness, it can be divided into single compression and two-way compression. When the sample thickness is small (<3mm), one-way compression is mostly used, and when the thickness is large, two-way compression can be used.

Gel casting

The gel casting process is to mix the ceramic powder with the aqueous solution of organic monomer, cross-linking agent and dispersant to prepare a suspension with high solid content and low viscosity, and then add initiator and catalyst to inject the suspension into the non porous mold. Under certain temperature conditions, the organic monomer is induced to polymerize to form a three-dimensional network gel structure, which results in the slurry being solidified in situ to form a ceramic green. This method can meet the requirements of near net size molding. The key of gel casting process is to prepare B4C-Al slurry with high solid content and good fluidity. For boron carbide aluminum composite ceramics, the effect of dispersant and solid content on slurry viscosity should be considered when gel casting process is adopted.

Gel casting has many advantages over traditional molding methods. Due to the sufficient filling of flowing liquid slurry in the mold, this process can prepare complex shaped components with high strength and good plasticity of the green body, which can be machined into more precise components. In addition, the mold does not require high requirements, and the sintered components have high purity, making this method have broad prospects. In addition, this method has a wide range of applications and can prepare single or composite materials. However, the cost of the monomers used in this process is generally relatively high, and it does not have a competitive advantage in preparing products with simple shapes and low added value.

Isostatic pressing forming

Isostatic pressing is a method of placing a boron carbide sample under pressure in a container, utilizing the property of liquid to evenly transmit pressure, and uniformly pressurizing the sample from all directions to obtain a dense green body.

Compared to steel mold pressing, this forming method has more advantages. One is the ability to suppress complex shapes such as concave and hollow shapes; Secondly, during pressing, the relative displacement between the boron carbide powder and the elastic mold is very small, so the friction loss is also small and the density distribution of the pressed blank is uniform; The third is that the billet has high strength, making it easy to process and transport. Due to the use of rubber and plastic as mold materials, the cost is relatively low. In addition, cold isostatic pressing can significantly increase the density of the sintered block, change the pore size distribution, reduce small pores, and increase the average pore size to homogenize the structure, which is very helpful for subsequent sintering.