Aluminum nitride ceramics have many advantages, such as excellent insulation, thermal conductivity, high temperature resistance, corrosion resistance and matching with the thermal expansion coefficient of silicon. Forming technology is the key technology of ceramic preparation, which is one of the important links to improve product performance and reduce production cost.
With the rapid development of industrial technology, the traditional forming method has been difficult to meet the requirements of people in the performance and shape of ceramic materials. In recent years, the wet forming of ceramics has become the focus of research, because it has the advantages of simple process, high production efficiency, low cost and can prepare complex shape products, which is easy to be industrialized and popularized.
Wet forming includes casting, grouting, injection molding and injection molding.
1. Casting of AlN Ceramics
A slurry forming method in which the slurry flows evenly to or is coated on the support plate, or is evenly brushed on the support surface with a blade to form a slurry film, which is dried to form a uniform blank film of a certain thickness. The casting process includes slurry preparation, casting, drying and baseband separation.
Casting process flow chart
Solvents and dispersants
High solid content of the casting slurry is one of the key factors for the preparation of high performance AlN Ceramics by casting. Solvent and dispersant are the key to high solid content casting slurry. The solvent must meet the following conditions:
(1) It must be soluble with other additives, such as dispersant, binder and plasticizer, etc;
(2) The chemical property is stable and does not react with powder;
(3) It has good wettability to powder particles;
(4) Easy to volatilize and burn;
(5) It is safe, hygienic and has little environmental pollution.
Common organic solvents and physical properties of water
Binders and plasticizers
The main purpose of adding binder and plasticizer to the casting slurry is to improve the strength, toughness and ductility of the sheet. When the casting sheet is naturally dried at room temperature, the solvent is constantly volatilized, and the binder can cure itself into a three-dimensional network structure to prevent the particles in the sheet from settling, and give the sheet a certain strength. The introduction of plasticizer ensures the flexibility of the sheet and reduces the glass transition temperature of the binder at room temperature and lower temperature.
The technological features of tape casting are as follows:
Advantages: the equipment is not too complex, the process is stable, can be produced continuously, the efficiency is high, the degree of automation is high, the blank film performance is uniform and easy to control, suitable for manufacturing various ultra-thin ceramic devices, alumina ceramic substrate, etc.
Disadvantages: small bulk density and high shrinkage.
2. Injection molding of aluminum nitride ceramics
Ceramic injection molding (CIM) is a new technology for manufacturing ceramic parts with complex shapes, which has unique advantages in the preparation of complex small parts. With the continuous expansion of the scale of electronic ceramics industrialization in recent years, the attractive application prospect of CIM technology is worth looking forward to. The process mainly includes feed preparation, injection molding, degreasing and sintering.
Injection molding process flow chart
binder
The binder is the carrier of AlN ceramic powder, which determines the rheological and injection properties of the injection molding. A good binder can maintain the shape and reduce the deformation and degreasing defects.
Ceramic injection molding binder shall meet the following conditions:
(1) The viscosity of injection molding is moderate, and the viscosity can not fluctuate too much with the temperature, so as to reduce the defects;
(2) It has good wettability and adhesion to powder;
(3) It has high thermal conductivity and low thermal expansion coefficient.
(4) Generally, it is composed of multi-component organics, and single organic binder is difficult to meet the fluidity requirements.
Rubber discharging process
Because of the high content of organic matter in the body of injection molding, too fast discharging will cause the body to crack, blister, delamination and deformation. Therefore, how to quickly and efficiently discharge rubber becomes a major difficulty of injection molding. The process includes hot discharge and solvent discharge. At first, it mainly used hot rubber discharge to simply burn the organic matter. This way has high energy consumption and long time. In order to improve the efficiency of discharging, some scholars have explored the technology of solvent discharging. Due to the large proportion of paraffin in the binder, the solvent discharge is mainly to dissolve the paraffin in the green body, and other binders can still maintain the shape of the green body. The combination of solvent and thermal process can greatly shorten the time of discharging.
Injection molding process features:
(1) It can form all kinds of complex shapes in near net size, with little (or no) machining;
(2) The green density of the product is even, and the surface finish and strength are high;
(3) The sintered body of the formed product has excellent performance and good consistency;
(4) It is easy to realize mechanization and automatic production with high production efficiency.
3. Injection molding of AlN Ceramics
The basic principle of the process is to add organic monomers into the slurry with low viscosity and high solid content. Under the action of catalyst and initiator, the organic monomers in the slurry are crosslinked and polymerized to form a three-dimensional network structure, so that the slurry is solidified in situ, and then demoulded, dried, organics removed and sintered to obtain the required ceramic parts.
Injection molding process flow chart
Injection molding process features:
The green body has high strength, good overall uniformity, can be used for near net size forming, is suitable for preparing complex shape ceramic parts and industrial promotion, has no difficulty in discharging glue, and has low cost.
Tape casting and injection molding have certain advantages in the preparation of AlN Ceramics. With the development of science and technology and the importance of environmental pollution, gel casting and gelcasting will replace the two methods and become the main production methods of AlN Ceramics, thus promoting the popularization and application of AlN Ceramics.
(source of this paper: powder mesh)
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