Abstract :
Under certain conditions of conductivity
and at constant current, electrophoretic deposition
(EPD) of alumina powder from an acidic suspension is
accompanied by an anomalous voltage rise across the
deposited particulate layer. This voltage rise, which is
much greater than can be accounted for by the
blocking of the electrode by non-conducting particles,
is the signal of the formation of a very uniform, dense
alumina deposition layer. To determine the conditions
necessary to induce this effect and discover its origins,
a series of systematic EPD trials with increasing
quantities of HCL is comprehensively examined. It is
shown that both of these effects can be accounted for
by the formation of an ion depleted conduction layer in
the solvent at the deposition electrode, which is
marked by extremely high voltage gradients. The
resulting electrophoretic force on particles in this layer
is several orders of magnitude higher than the force on
particles in the rest of the system and consolidates the
particles to form the observed densely compacted
layer. This high voltage gradient layer also results in a
significant self-leveling effect for deposition thickness.
A complete description of the various types of deposition
observed in this series of trials is then given in
which EPD is treated as a series of three steps:
accumulation, deposition, and consolidation. This
description identifies the origin of several effects seen
during EPD and is intended to help the reader identify
the conditions necessary to induce ion depletion
enhanced, automatic leveling electrophoretic deposition.
