A review on fundamentals and applicationsof electrophoretic deposition (EPD)

Laxmidhar Besraa,*,Meilin Liub

Progress in Materials Science 52 (2007) 1–61

指導教授：王聖璋 演講者：黃俊嘉

2009/12/16

Outline

• Definition• Factors influencing

– the suspension– the process

• Role of polymer binders in EPD• Practical considerations• Water-based & Non-aqueous EPD• Results and discussion• Conclusion

Definition

Property Electroplating EPD

Moving species Ions Solid particles

Charge transfer on deposition

Ion None

Reduction conductance of

liquid medium High Low

Preferred liquid Water Organic

ω C E t‧ ‧

Factors influencing

(ω) the deposit yield

( ) the particle mass concentration in the suspension

( ) the permittivity of vacuum

( ) the relative permittivity of the solvent

( ) the zeta potential of the particles

( ) the viscosity of the solvent

Hamaker equation

( ) the applied potential

( ) the distance between the electrodes

( ) the deposition time

parameters related to the suspension

SEM images of YBCO film electrophoretically deposited on silver electrode from its suspension in acetone at 10 V for 180 s (film A: mean particle size = 3 μm; film B: mean particle size = 0.06 μm). The films were calcined at 945°C for 1 h and annealed at 500°C for 6 h.For crack formation smaller particle is better than larger particles because for larger particles the mobility of particles electrophoresis must be higher than that gravity

Particle size

Physical properties of solvents

Dielectric constant of liquid can affect the particle dissociative power,with too low a dielectric constant, deposition fails because of insufficient dissociative power, whilst with a high dielectric constant, the ionic concentration in the liquid must remain low .

EP Dielectric constantelectric field

1

low viscosity, high dielectric constant and low conductivity

(1) stabilization of the suspension by determining the intensity of repulsive interaction between particles

(2) determining the direction and migration velocity of particle during EPD

(3) determining the green density of the deposit

Zeta potential

high electrostatic repulsion can be avoid particle agglomeration ，If the particle charge is low, the particles would coagulate even for relative large inter-particle distances, leading to porous, sponge-like deposits. particle charge packing density

2.2

Parameters related to the process

Effect of deposition time

Relationship between deposit thickness and time of deposition for ZnO coatings on copper electrode at different applied potential

Current density versus deposition time for deposition of hydroxyapatite at different applied voltages: (a) 50 V; (b) 100 V; (c) 200 V

Applied voltage

Weight of deposited hydroxyapatite on Ti6Al4V substrate versus applied voltage for different deposition durations: (a) 30 s and (b) 120 s

Stability of current density of n-propanol for different applied voltages

the unstable current density influences the quality of deposition morphology.

particles move so fast that they cannot find enough time to sit in their best positions to form a close-packed structure.

A is constant-current and constant-suspension concentration

B is constant-current but decreasing suspension concentration

C is constant-voltage and constant-suspension concentration

D is constant-voltage but decreasing suspension concentration

• Role of polymer binders in EPD– obtain adherent deposits and prevent cracks

and the adsorbed polymer can provide steric stabilization of suspension of ceramic particles and reduce viscosity of the suspension.

• Practical considerations– how to avoid cracking in the ceramic coating

during drying and sintering– 10–15% linear shrinkage.– moderate control on drying– liquid phase sintering – SOFC

Water-based & Non-aqueous EPD

water organic

Applied voltage low higher

conductivity higher low

chemical stability bad good

density low higher

flammability no yes

toxicity no yes

cost low higher

乙基丙酮

丁酮 甲苯 + 乙醇

電位

electrical double layer

電位

吸附層 擴散層

表面應力

吸附面

德拜長度

DLVO theory

靜電斥力

凡德瓦力

最小總位能

次小總位能能障

Vt = VR+VA

穩定狀態

團聚狀態

沉降狀態

Results and discussion

• Deposit yield proportional particle mass concentration in the suspension 、 applied potential 、 deposition time.

• For crack formation smaller particle is better than larger particles

• low viscosity, high dielectric constant and low conductivity for suspension

• Zeta potential suspension would affect the stability of the direction and rate of electrophoretic particles, deposition density

• Film thickness is proportional to deposition time, applied voltage

• add polymer binders– obtain adherent deposits– prevent cracks – stabilization of suspension of ceramic particles – reduce viscosity of the suspension.

• moderate on drying may avoid the formation of drying cracks.

• the organic liquids has higher density ,good chemical stability,low conductivity

defect is higher voltages ,the cost, toxicity and flammability

Ethyl alcohol–acetylacetone 、 Methyl ethyl ketone (MEK) 、 Toluene-ethyl alcohol

Conclusion EPD 為近年來生產製造技術上，一種先進的製程， 其製程簡單、操作簡單和具有成本效益的沉積方法。 EPD 製程的重點在於要選擇對的溶劑 ( 低黏度、高

介電常數和低電導率 ) 、粉末的選擇小顆粒優於大顆粒、調整 pH 值來使 zeta 電位遠離等電位，膠體便可以穩定分散、添加適度的黏結劑可以提昇裂紋的產生、穩定懸浮液和降低懸浮液的黏度。

發展水性電泳沉積將有助於減少成本，也可以減少非水性電泳沉積對環境的破壞