Electrophoretic deposition molding method for advanced ceramics

1. Process principle of electrophoretic deposition molding

The basic principle of electrophoretic deposition is that due to the charged particles dispersed in the suspension, they must undergo directional movement under the action of an electric field. According to the DLVO theory, an increase in electrolyte concentration can induce the aggregation of colloidal systems. Under the action of an external electric field, the concentration of electrolyte near the electrode can increase, which is equivalent to reducing the potential near the electrode, causing particles to flocculate on the surface of the sample as the electrode. Electrodeposition generally cannot directly create a solid bond between the coating and the substrate, and subsequent heat treatment is usually required after deposition to enhance the adhesion between the coating and the substrate.

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2. The process and application of electrophoretic deposition molding

(1) The process of electrophoretic deposition molding

The electrophoretic deposition process includes the preparation of a stable suspension, the interactions between particles in the suspension, the directional motion of particles under an electric field, and the deposition process on the electrode.

① Preparation of stable suspension

The preparation of a stable suspension containing raw powder is a prerequisite for electrophoretic deposition. The suspension and stability principles of electrophoretic deposition slurry are the same as those of injection molding slurry and in-situ solidification molding slurry.

② Electrophoretic deposition process

The reason why solid particles in the suspension deposit on the electrode is mainly due to the increase in electrolyte concentration near the electrode, which leads to particle flocculation. As a result, the potential near the electrode decreases. Charged solid particles undergo an electrochemical Redox on the electrode surface, becoming electrically neutral, thus depositing on the electrode and resting. The rate of electrodeposition is crucial for controlling the deposition thickness. Hamaker proposed that the quality of electrophoretic sediment is directly proportional to the concentration of the suspension, deposition time, deposition electrode surface area, and deposition electric field intensity.

(2) Application of electrophoretic deposition molding

Electrophoretic deposition molding technology can be used to prepare layered composites, bioceramics, fiber/whisker reinforced Ceramic matrix composite, functional ceramics and other new materials, and has a very broad application prospect. Compared with single structure ceramic materials, the strength and toughness of layered composite ceramic materials are significantly improved. In layered composite ceramic materials, the thinner the thickness of each layer, the better its mechanical properties.

3. Characteristics of electrophoretic deposition molding

(1) The range of materials used is very wide, and can be applied to almost all material aspects, such as the deposition of non-metallic, metallic, semiconductor and other materials.

(2) Easy to control the composition of sedimentary layers, especially convenient for mixed sedimentary layers.

(3) The deposition rate is extremely high, and the electrophoresis of a 0.025mm deposition layer takes only 10 seconds.

(4) The thickness of the sedimentary layer is easy to accurately control.

(5) The thickness of the sedimentary layer is very uniform, which can deposit complex shaped parts.

(6) The deposition layer is dense, with few pores and firm bonding, and its density and bonding force can be controlled from the process.

4. Main defects in electrophoretic deposition molding

Although electrophoretic deposition molding is simple, flexible, reliable, and can be applied to the preparation of many materials, there are still many drawbacks to electrophoretic deposition molding technology.

(1) The sedimentary layer is mostly particle accumulation and requires supplementary treatment such as compaction, annealing, sintering, etc., which is limited by the performance of the matrix material.

(2) The media used are mostly organic materials, some of which have high costs and complex preparation processes.

(3) The working voltage is high.

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