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Wengler, John (ed.) / Wisconsin engineer
Volume 87, No. 3 (February, 1983)

Christopherson, Penny J.
A walk on the dean's side,   pp. 10-[13]

Page [13]

on the left in Figure 1) loses elec-
tons by successive steps, going
from Cr +' to Cr +. t)ecomposition
of the resulting chromous (Iichro-
mate comI)lex takes place by acid
hydrolysis to form a chromnlous-
oxybisulfate complex:
    +                11
      cr-0)   1()0US-W()
     The positive end of this con-
plex is adsorbed onto the cathode
surface. Electrons are transferred
from the cathode to the adlsorbed
chromium ion, forming metallic
chromium  and regenerating the
(HS,())- ion. Thus, I)r. Hoare's
mechanism explains how sulfuric
acid, in the form
ion, participates
of the bisulfate
in the platingy
It HAS long been known that
   chromium   cannot be platedl
from a solution when initially pres-
ent as Cr+;3 because of the forma-
tion of the stable aquo complex,
[Cr(H20)),; +±1. Yet chromium caon be
plate(l when initially present as
Cr +Ei even though it must pass
through the Cr + :state before being
deposited. I)r. Hoare's mechanism
handles this paratlox by explaining
that the chromium ion being
deposited (on the left in Figdure 1) is
protected by the rest of the complex
as it passes through the Cr+:1 state,
so that the stable aquo complex
cannot form.
     The diffusion of the elec-
troactive complex apparently con-
trols the rate of the process, so that
shortening the diffusion path
increases the speed of chromium
deposition. A high rate of relative
motion between the electrolyte and
the cathode will shorten the path.
This caln be accomplished by rapid
flow or by agitation of the elec-
     I)r. Hoare found that the rate
of chromium deposition increased
with electrolyte flow until the proc-
ess was no longer dliffusion-con-
trolled. He also found that the use
of dilute electrolyte significantly
increased plating efficiency.
     "This project is an excellent
example," says I)r. Hoare, "of how
basic research and engineering
principles can be combined to
develop a new, successful process.
Now, we'd like to take on the chal-
lenge of plating successfully from
Cr +'i, which would be an even more
efficient way to provide corrosion
and wear resistance.
   General Motors
I)r. James Hoare
is a Research
Fellow at the
General Motors
Research LIab-
oratories. He is a member of the
Electrochemistry I)epartment.
     I)r. Hoare served as an elec-
tronics technician in the U.S. Navv
luring the Second World War. In
1949, he received his P'h.I). in phys-
ical chemistry from the Catholic
University of America. After an
assistant professorship at Trinitv
College in Washington, I).C., he
joined the US Naval Research Lab-
oratory as a phvsical chemist. fHe
became a staff member at (General
Motors in 1960.
     I)r. Hoare's sustaining inter-
est has been in electrochemical
kinetics and the mechanisms of
electrode processes. He is best
known to the scientific commuility
for his basic studies of hydrogen
and oxygen electrode mechanismus.
His book, The Electrochemilstrv of
Oxygen, publishedl in 19(68, is Con-
sidered a work of primary imnpor-
tance to the field. In addition to his
work on chromium plating, he is
responsible for the fundamental
research that helped make elec-
trochemical machining a precision

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