USE OF OXIDE CERAMIC AS A FUNCTIONAL PROTECTIVE BARRIER
N. M. Chigrinova
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp.4–8,November, 2001.
Features of the process of formation of ceramic coatings using the method of anode microscopic-arc oxidation
(AMAO) are discussed and results of a study of the effect due to electrolyte composition and AMAO
electrophysical parameters on the growth kinetics and structure of ceramic layers are given.
High-technology oxide ceramic materials exhibit, as a
rule, a unique set of performance characteristics such as heat
endurance, high temperature and mechanical strength, hard-
ness, and resistance to chemical corrosion.
These materials as well as films and coatings fabricated
from them are capable of performing as shields, or protective
barriers, in engineering assemblies and components designed
for operation under different conditions.
Protective coatings based on oxide ceramics can be pre-
pared using electrochemical methods, for example, anode
oxidation. Conventionally, this technology can be classified
into four groups  involving thick-layer, spark, microsco
pic-arc, and arc techniques.
The operating voltage as a function of time for these
techniques (the so-called “formation curves”) is shown sche
matically in Fig. 1.
Stage I in all the curves corresponds to the formation of a
thin anode film; the theory of this process has been deve
loped by Verwey and Mott . In a film-forming process, the
ion current (I
) as a function of the field strength (E ) under
fixed initial and finite conditions is described as
= A exp BE, (1)
where A and B are empirical constants. Using Faraday’s law
relating the current I
to the growth rate of the anode oxide
film (dh/dt), one can write :
= NVv exp
W W qaE
where N is the number of ions transferred through a unit
cross-sectional area normal to the direction of ion current,
V is the average volume of oxide film formed per ion trans
ferred, n is the frequency of ion oscillation in the initial state
(» 1012 Hz), W
is the ion barrier height in the initial state,
is a contribution to the effective energy of activation by
which account is taken of the fact that ions persist in a com-
plex “dynamic” state (both initial and intermediate) rather
than in a “static” state and that the ions are correlated in their
movement, at least, on a local scale, q is the ionic charge, a is
the barrier’s full width at half-maximum, k is the dielectric
constant, T is the temperature, and E is the field strength.
Stage II in curves 2 and 3 is a sparking stage. In curve 2,
three stages with different voltage rates are distinguished.
Refractories and Industrial Ceramics Vol. 42, Nos. 11 – 12, 2001
1083-4877/01/1112-0381$25.00 © 2001 Plenum Publishing Corporation
Research Institute for Powder Metallurgy, Minsk, Belarus.
I II III IV
Fig. 1. Formation curves characteristic of various anode oxidation
techniques: 1 — thick layer; 2 — spark; 3 — microscopic arc; 4 —
is the sparking voltage, U
is the microscopic discharge
voltage, and U
is the arc discharge voltage.