Elaborate on Several Preparation Process Methods of Aluminum Nitride Industrial Ceramics

Aluminum nitride ceramics are relatively unpopular industrial ceramic materials, but their advantages can still be exerted in many places. Kezhong Ceramic Factory has certain methods for processing and preparing aluminum nitride ceramics. Below, we will introduce them to you.

1、 Common AlN body forming methods

The preparation of aluminum nitride ceramic body from aluminum nitride powder requires the use of forming technology to prepare the powder into a body, followed by sintering work, and finally completing the final ceramic processing to make silicon nitride ceramic sheets, ceramic tubes, etc., which are sold to a large number of customers. The main forming processes of aluminum nitride include dry pressing, isostatic pressing, tape casting, and injection molding.

1. Dry pressing forming

The picture shows a dry compression molding machine. Dry compression molding (axial compression molding) is a process of adding AlN powder, which has been pre treated with surfactants, to a metal mold and slowly applying pressure to make it a dense green body. The essence is to use external pressure and the interaction force between AlN powder particles to maintain a certain shape and density of the green body, which is conducive to ceramic sintering, can reduce the sintering temperature, and improve the density of the ceramic. Due to the easy hydrolysis of AlN powder, the commonly used water polyvinyl alcohol (PVA) in dry pressing cannot be used for the compaction of AlN powder, and paraffin and organic solvents can be used instead.

Advantages: The dry compression molding method is easy to operate, with fewer process steps and high efficiency.

Disadvantage: Unable to suppress complex geometric shapes of the billet; It is necessary to strictly control the pressure, as either too high or too low is not conducive to obtaining high-density AlN ceramic sintered parts.

2. Isostatic pressing forming

Isostatic pressing is an improved method of the traditional dry pressing method. AlN powder is placed in a high-pressure container, and the powder is placed in a molding mold made of elastic materials by using the characteristics of the non compressibility of the liquid and the pressure transmission of the liquid. The pressed powder is evenly pressed from different directions, and the liquid is used to pressurize the mold to form the green body.

Advantages: The compactness of green body is high, the density distribution is uniform, and it can be shaped in near net size;

Disadvantages: The expensive molding equipment and the presence of demolding problems limit its application in large-scale industrial production.

3. Casting forming

Tape casting is a very important process for forming ceramic substrates. Mix AlN powder and composite adhesive (composed of dispersant, solvent, binder, and plasticizer) evenly to obtain AlN casting slurry. The slurry after degassing and other processes is poured into the hopper, and after passing through the scraper edge, a thin layer with uniform thickness and smooth surface attached to the smooth belt is formed. After drying, a green body with good toughness is prepared; After the discharge and sintering, AlN substrate material is obtained.

Advantages: Simple equipment, continuous operation, high productivity, and high degree of automation;

Disadvantages: The requirements are relatively strict, and the slurry is very sensitive to changes in process parameters. The surface of the formed billet is rough and not fully bonded, with low strength. During the drying process, it is prone to blistering, cracking, bending deformation, and other phenomena; Simultaneously, casting can only be used for the production of sheet materials.

4. Injection molding

AlN ceramic injection molding is a method of powder injection molding applied to ceramic powder molding, which is based on plastic injection molding technology and has been developed through technological improvements. The basic process is to first add a binder to AlN powder and mix it evenly to form a viscoplastic feed. Under heating, the feed is injected into the mold cavity using an injection molding machine for condensation molding. After heating to remove the binder, it can be used for sintering, as shown in Figure 3. The rheological properties of the feed are an important factor affecting the quality of injection molded products. Usually, we hope that the viscosity of the feed is low, which requires good compatibility between the raw material powder and the binder, and even mixing.

Advantages: high density, uniform density distribution, can be used for complex shape green body forming, and the forming precision is high, without post machining;

Disadvantages: It is prone to defects such as underinjection, flash, fusion marks, and air pockets that affect the sintering of AlN ceramics. The prepared body requires high-temperature sintering to obtain AlN ceramics with high density and excellent performance, which are widely used in various fields. AlN, as a high melting point and strong covalent bond compound, has small atomic self diffusion coefficient and is difficult to sinter dense parts. It is necessary to select appropriate sintering methods and strictly control the sintering conditions to produce AlN ceramics with high density and required excellent properties.

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