Optimizing Additive Ratios in Alkaline Zincate Electrodeposition
125
Finally, the leveler inhibits deposition at high points on a rough deposit and promotes
deposition at the low points. Common carriers are polyvinyl alcohol (PVA) [10, 11],
polyaliphatic amines, aliphatic polyamines, and heterocyclic amines. Brighteners
(booster) tend to be aromatic aldehydes [12]. Vanillin is a common leveler [13]. The
correct combination of the plating additives is critical to producing smooth, bright
deposits [10, 13].
A common method to evaluate a plating bath’s ability to produce a bright and
shiny appearance is Hull cell testing [9]. The Hull cell is trapezoidal in shape with
the cathode angled away from the anode. The changing distance between the anode
and cathode produces a uniform current distribution. This allows the Hull cell to
produce an electrodeposit over a range of current densities in one experiment. The
resulting plate can be examined to determine if the desired appearance is produced
within the current density range exhibited in the plating operation [9].
Experimental
Hull Cell Testing
A standard 267 mL Lucite Hull cell from Kocour was utilized. The anode was a
low-carbon steel mesh with dimensions of 8.6 × 0.6 cm. The cathode was a zinc
coated stainless steel plate with the zinc removed prior to plating. The zinc coating
was removed by immersing the plate in a 50% v/v HCl solution for ~15 s until no
gassing was detected. The de-zinced plate was rinsed with de-ionized (D.I.) water
prior to placing in the Hull cell.
Synthetic plating solutions were prepared using a commercially available zinc
“pre-mix” solution (Technilloy ZN NI 7222). The “pre-mix” solution contained 162–
170 g/L Zn and 500 g/L NaOH as determined by titration. The “pre-mix” was diluted
using reagent grade NaOH and/or D.I. water to achieve zinc concentrations ranging
from 30 to 40 g/L Zn at a NaOH concentration of 210 g/L. Additives were introduced into the electrolyte 20 min prior to each experiment. Three commercially
available additives were investigated—a carrier (Eldiem Carrier), a booster (Eldiem
Booster), and a leveler (Bright Enhancer 2x). They were examined individually and
in combination.
2.0 amps of direct current were supplied from a 20 V Extech, Model #382275
power supply for 5 mins to plate zinc in the Hull cell. No external agitation was used.
The plating was performed at elevated temperature. The solution was preheated to
44 °C and then transfer to the Hull cell. The plating test was started immediately
without heating. The temperature decreased by approximately 1 °C during the fiveminute experiment.
Following the experiment, the zinc-plated cathode was removed from the Hull
cell and rinsed with D.I. water. To simulate the actually plating line, the coated part
125
Finally, the leveler inhibits deposition at high points on a rough deposit and promotes
deposition at the low points. Common carriers are polyvinyl alcohol (PVA) [10, 11],
polyaliphatic amines, aliphatic polyamines, and heterocyclic amines. Brighteners
(booster) tend to be aromatic aldehydes [12]. Vanillin is a common leveler [13]. The
correct combination of the plating additives is critical to producing smooth, bright
deposits [10, 13].
A common method to evaluate a plating bath’s ability to produce a bright and
shiny appearance is Hull cell testing [9]. The Hull cell is trapezoidal in shape with
the cathode angled away from the anode. The changing distance between the anode
and cathode produces a uniform current distribution. This allows the Hull cell to
produce an electrodeposit over a range of current densities in one experiment. The
resulting plate can be examined to determine if the desired appearance is produced
within the current density range exhibited in the plating operation [9].
Experimental
Hull Cell Testing
A standard 267 mL Lucite Hull cell from Kocour was utilized. The anode was a
low-carbon steel mesh with dimensions of 8.6 × 0.6 cm. The cathode was a zinc
coated stainless steel plate with the zinc removed prior to plating. The zinc coating
was removed by immersing the plate in a 50% v/v HCl solution for ~15 s until no
gassing was detected. The de-zinced plate was rinsed with de-ionized (D.I.) water
prior to placing in the Hull cell.
Synthetic plating solutions were prepared using a commercially available zinc
“pre-mix” solution (Technilloy ZN NI 7222). The “pre-mix” solution contained 162–
170 g/L Zn and 500 g/L NaOH as determined by titration. The “pre-mix” was diluted
using reagent grade NaOH and/or D.I. water to achieve zinc concentrations ranging
from 30 to 40 g/L Zn at a NaOH concentration of 210 g/L. Additives were introduced into the electrolyte 20 min prior to each experiment. Three commercially
available additives were investigated—a carrier (Eldiem Carrier), a booster (Eldiem
Booster), and a leveler (Bright Enhancer 2x). They were examined individually and
in combination.
2.0 amps of direct current were supplied from a 20 V Extech, Model #382275
power supply for 5 mins to plate zinc in the Hull cell. No external agitation was used.
The plating was performed at elevated temperature. The solution was preheated to
44 °C and then transfer to the Hull cell. The plating test was started immediately
without heating. The temperature decreased by approximately 1 °C during the fiveminute experiment.
Following the experiment, the zinc-plated cathode was removed from the Hull
cell and rinsed with D.I. water. To simulate the actually plating line, the coated part