(i) Ceramic Forming Process Using Electrophoresis of Colloidal Particles

Example in direct shaping of ceramics by electrophoretic deposition using conductive polymer-coated non-conductive ceramic substrates. This technique can be utilized for fabricating various shape-controlled ceramics, such as dental crown.

J. Am. Ceram. Soc., 91[5], 1674-77 (2008)

Multicolor light emitting devises prepared by laminating yellow green and red SiAlON phosphors. The electrophoretic deposition process enables easy emission color tuning by controlling the thickness of each phosphor layer.

J. Ceram. Soc. Jpn.,[1], 1-4 (2010)

The state in which particles with diameters on the order of 10-7 to 10-9m are dispersed in a gas or liquid is called a colloidal system. Because colloidal particles are larger than solute molecules and ions and always have an electrical charge, they have distinctive features, including Brownian motion, Tyndall scattering, dialysis, electrophoresis, etc., and exhibit phenomena such as coagulation and salting out. Submicron to nano-sized ceramic particles dispersed in liquids such as water and non-aqueous solutions display precisely the same propert ies as colloidal particles. Thus, it is possible to obtain dense solidified compacts by promoting aggregation of charged dispersed ceramic particles by an appropriate method. This forming method is called the colloidal process and is used as a method of manufacturing ceramics with complex shapes.

We are engaged in research on processes which apply the phenomenon of electrophoresis of charged colloidal particles in liquids as a forming technique for ceramic films. When an electric field is applied to a suspension of ceramic particles, the particles in the space filled with the liquid are electrophoresed and deposited on the electrode surfaces. The particle layer deposited by this method has a density equal to or greater than that consolidated by cold isostatic pressing (CIP) at 200MPa, and densification is possible at lower temperatures. Fabrication of laminates with a controlled film thickness is also easy.

The electrophoretic deposition process is increasingly applied to fields where application had been difficult in the past. This is possible as a result of the development of techniques for the preparation of suspensions suitable for the electrophoretic deposition process, deposition of particles on nonconductive substrates, suppression of electrolysis of aqueous solutions by applying DC pulse current, among other advances. Recently, oriented ceramic films and oriented laminated composites, crystal orientation in which is controlled, have been fabricated successfully by combining a magnetic orientation technique using a high magnetic field and the electrophoretic deposition process.

We are engaged in research aimed at achieving high functions and diversity in various ceramic materials by manipulating colloidal particles in liquids under electrical and magnetic fields in order to control the microstructure of the formed compacts, including environment and energy-related materials such as anode-supported fuel cells, photoelectrodes for dye-sensitized solar cells, photocatalyst films, and thermoelectric modules, medical materials such as dental crown materials, and structural materials such as ceramic veneer materials, among others.