Find Out More
Dana Keeps Zinc Plating
While National Plating has
created a new line using
automated barrels, Dana has
automated its entire zinc
plating line through the use
of some interesting
To find out more on
how centrifuges can be
used in wastewater
treatment, check ou the PF
Online article, "Centrifuge
Plumbing fixtures and fittings
have been attractively finished
using a trivalent chromium
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By Nabil Zaki
Despite the simplicity of their formula- tions, chromium plating baths are more complicated to
operate than most plating baths, and they require rigorous controls.
In plating from hexavalent chromium baths, sulfate and fluoride ions act as catalysts.
Temperature, current density and bath composition affect the film characteristics and current
efficiency. These parameters are therefore carefully controlled in order to obtain specific deposit
properties and plating rates.
Thicknesses of deposits vary from 0.25-0.5 micron, or more for hard chromium plating.
Bath Composition. Chromic acid and sulfate are the necessary ingredients. Chromic-to-sulfate
ratios range from 75:1 to 250:1. The composition depends primarily on whether the bath is
co-catalyzed, for example, with fluorides, fluosilicates or fluoborates, and on the application
(decorative or hard chromium).
Cr+6 is the source of chromium deposited from these baths. Chromic acid, Cr03, is the main
component in solution makeup. Cr+6 is reduced to Cr+3, which in turn is reduced to unstable
Cr+2 and further to Cr0.
Some Cr+3 is normally found in operating baths, and indeed in the absence of Cr+3, little or no
deposit is obtained. The introduction of small amounts of reducing agents to a new solution
helps in bath startup.
An amount of Cr+3 exceeding 2-3% of the chromic acid content, however, reduces cathode