Hydroxyapatite and Other Biomedical Coatings by Electrophoretic Deposition - Biological and Biomedical Coatings: Processing and Characterization - page 83

TABLE 3.1
Comparison between Electrophoretic and Electrolytic Deposition Processes

Parameter ElectrophoreticDeposition ElectrolyticDeposition

System Suspension Solution

Moving species Particles Ions or complexes

Electrode reactions None Electrogeneration of OH - and

neutralization of cationic species

System electrical conductivity Low High

Deposited material Ceramics or metal Metal

Deposition rate 10 0 -10 3 µm/min 10 -3 -10 0 µm/min

Deposit thickness 10 0 -10 3 µm 10 -3 -10 1 µm

Deposit composition control By powder stoichiometry By solution composition

Source: Heavens, S.N., Advanced Ceramic Processing and Technology , William Andrews Publishing/Noyes, Park

Ridge, NJ, 1990; Besra, L., Liu. M., Prog. Mater. Sci ., 52 , 1, 1-61, 2007. With permission.

There are two basic components of electrophoretic deposition: electrophoresis and deposi-
tion [22]. That is, the process includes movement of charged particles in a suspension toward
an electrode under the influence of an electric field followed by deposition on the electrode.
Calcination or firing generally follows in order to (1) convert the weak initial physical bond
to a stronger chemical bond, (2) pyrolyze any binder (if used), and (3) densify the deposit. A
schematic of the process of cathodic electrophoretic deposition is shown in Figure 3.2.
In addition to the fabrication of coatings, electrophoretic deposition can be used to pro-
duce the following [20,22,24]:

• Die-formed monolithic shapes
• Free-standing monolithic shapes
• Laminates
• Infiltrated porous bodies
• Infiltrated woven fiber preforms

In the fabrication of coatings, electrophoretic deposition offers a number of advantages
over other methods of fabrication:

• Even (matched) profile over irregular surfaces
• Highly precise and reproducible coating thicknesses
• High deposition rates
• Operation in air
• Simplicity of materials and process
• Low cost of infrastructure and operation
• Capacity to produce patterned coatings (using a mask)
• Capacity to produce composite coatings (as above)
• Capacity to operate continuously

For these reasons, electrophoretic deposition is of considerable interest from the technical
and commercial perspectives.