Titanium particles deposited by electrophoretic deposition
3 EPD of Ti particles requires the usage of charging agent to provide additional
surface charge for the stabilization and electrophoretic mobility of suspension particles and also for their deposition process [1, 4, 8]. Most importantly, these charging agents
also act as binders to increase bonding between the deposited particles and bonding with the substrate [1, 4, 8]. The commonly used charging agents for the EPD of metallic
particles were aluminium chloride AlCl
3
[5, 9], poly diallyldimethylammonium chloride PDADMAC [10, 11] and polyethyleneimine PEI [12, 13]. Although the
effect of these charging agents had been extensively conducted by these studies, a direct comparison of the effect of these charging agents on the EPD of Ti particles has never
been reported. Furthermore, there is a lack of discussion on the role of these charging agents on the mechanism of electrophoretic deposition, particularly on the noncolloidal
coarse particles. The objective of the present work was to compare and investigate the effect of
aluminium III chloride AlCl
3
, polyethyleneimine PEI, poly diallyldi- methylammonium chloride PDADMAC] on the EPD of coarse Ti particles in
absolute ethanol medium. The effect of the charging agent on the bonding strength EPD will be deduced based on the following criteria: i planar surface microstructure
of the Ti deposit, ii deposit yield, and iii electrophoretic mobility of the Ti particles.
2.0 EXPERIMENTAL PROCEDURE
2.1 Preparation of Suspension
The as-received Ti particles 99.7 wt, SE-Jong Materials Co. Ltd., South Korea used for the current study was platy, subangular, and of medium sphericity.
Their particle size range was ~1-50 μm, with a median size d
50
of ~17 μm. Suspension was prepared by adding 0.1 g of Ti powder to 20 mL of absolute ethanol
4 99.7 wt, CSR Ltd., Australia to give a solids loading of 5 mg.mL
-1
. After magnetically stirred gently for 1 min, small amount of a selected charging agent 0.1-0.7
wt from Ti particles weight basis was added and followed by magnetic stirring for 30 min at the same stirring speed. The temperature of the suspension was maintained at
~25 C throughout the preparation process.
Table 1: Details of charging agents used for EPD of Ti particles all the chemicals are reagent grade and were supplied by Sigma-Aldrich Co., Australia
Charging Agent Average
Molecular Weight amu
True Density g.cm
-3
Concentration prior to
Addition into Suspension
Medium Symbol
Aluminium III Chloride
NA 2.44
0.375 M in water
AlCl
3
Polyethyleneimine 10,000-
25,000 1.03
10
-2
M in absolute
ethanol PEI-10K
Polyethyleneimine solution
60,000- 750,000
1.04 50 wv in
water PEI-60K
Polyethyleneimine solution
600,000- 1,000,000
1.04 50 wv in
water PEI-600K
Polydiallyldimethyl ammonium chloride
solution 100,000-
200,000 1.04
20 wt in water
PDADMAC- 100K
Polydiallyldimethyl ammonium chloride
solution 400,000-
500,000 1.04
20 wt in water
PDADMAC- 400K
NA: Not applicable For the suspension using PEIs as the charging agents, small amount of acid was
added as the protonating agent of the amine functional groups in the PEI polymers [16]. List of Ti particles suspensions prepared using different cationic charging agents are
shown in Table 1. Further description of the Ti particles and ethanol used in the current work had been stated in the previous work [15].
Titanium particles deposited by electrophoretic deposition
5 2.2
EPD Process The circuit in the EPD set-up consisted of mutually parallel electrodes at a fixed
separation, connected by alligator clips to a d.c. programmable power supply EC2000P, E-C Apparatus Corp., USA. The cathode working electrode or substrate
consisted of SAE 1006-grade low-carbon steel, the anode counter-electrode consisted of 304 grade stainless steel. Both the electrodes have submerged dimensions of 10 mm
H 10 mm W 1.5 mm T and were supplied by BlueScope Steel Ltd., Australia. The
low-carbon steel substrates were hand-polished to P320-grit 46.2 m particle size SiC
paper, ultrasonically cleaned in absolute ethanol, and air-dried for 30 minutes before deposition. Each suspension was magnetically stirred for ~1 min following lowering of
the electrodes into the suspension. After this, the voltage was applied. Each sample was removed from the suspension slowly at constant pulling rate of 0.2 mm.s
-1
immediately after EPD ended.
2.3 Characterizations
Measurements were undertaken in terms of determination of the EPD yield weight gaintotal submerged surface area as a function of addition level of charging
agent. The weight gain was determined after EPD for each cathode by air drying for ~30 min and weighing 0.00001 g precision, BT25S, Sartorius AG, Germany. All of
these deposit yield data are the averages of five individual measurements with standard error of approximately ±0.0001 gcm
2
. The particle and deposit morphologies as well as the general appearance of the deposits were assessed by scanning electron
microscopy SEM, 15 kV accelerating voltage, secondary electron emission mode, S3400N, Hitachi High-Technologies Corporation, Japan. The electrophoretic mobility
6 and electrical conductivity were determined using a phase-analysis light-scattering zeta
potential analyser ZetaPALS; sole setting of ~10 V.cm
-1
electric field bias change with 2 Hz frequency sinusoidal wave, 0.005-
30 μm size range, scattering light source [678 nm wavelength], Brookhaven Instruments Co., USA. All of these electrophoretic
mobility data are the averages of ten individual measurements with standard error of approximately ±0.1
m.cmV.s.
3.0 RESULTS AND DISCUSSION
