1070-4272/02/7512-1972 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 12, 2002, pp. 1972!1978. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 12, 2002,
Original Russian Text Copyright + 2002 by Lukiyanchuk, Rudnev, Tyrina, Panin, Gordienko.
AND CORROSION PROTECTION OF METALS
Anodic-Spark Layers Formed on Aluminum Alloy
in Tungstate-Borate Electrolytes
I. V. Lukiyanchuk, V. S. Rudnev, L. M. Tyrina, E. S. Panin, and P. S. Gordienko
Institute of Chemistry, Far-Eastern Division, Russian Academy of Sciences, Vladivostok, Russia
Received August 22, 2002
Abstract-The effect of sodium tungstate concentration in 0.4 M H
on the sparking voltage, thickness,
and the phase and elemental composition of coatings formed on AMtsM aluminum alloy (~98% Al) by an-
odic-spark oxidation in a galvanostatic mode (
) was studied.
The method of anodic-spark oxidation is com-
monly used to obtain coatings of various functional
purposes: corrosion-resistant, heat-resistant, wear-re-
sistant, etc. It was shown in [1, 2] that there exists
a relationship between the formation of vanadium-
phosphorus heteropolyoxo anions (HPA) in an aqueous
solution and joint proportional incorporation of phos-
phorus and vanadium compounds into coatings formed
on rectifying metals. The role of HPA consists in that
it delivers necessary elements to the anode surface,
which are then involved in high-temperature reactions
at the anode. It is suggested that thermolysis of com-
plexes contained in the deposit formed on the anode
occurs in regions adjacent to electric breakdown chan-
nels, with only compounds and glass phases insoluble
in the given electrolyte remaining in the coating.
The number of presently known HPA is enormous:
more than 65 elements can play the role of central
elements in these anions [3, 4]. It is important to es-
tablish the relationship between the presence of HPA
in an electrolyte and the composition of anodic-spark
coatings formed on metals being treated in order to
solve the problem of directed synthesis of coatings.
Tungstate-borate electrolytes are of interest because
borotungstate HPA are formed in them at pH < 8,
with the HPA hydrolyzed to borate and monotungstate
anions at higher pH values .
The aim of the present study was to analyze the spe-
cific features of formation and composition of coatings
formed on aluminum alloy in tungstate-borate elec-
trolytes, including cases with pH higher and lower than
this boundary value. It is noteworthy that the effect
of the pH of borate, and the concentration of tung-
state, electrolytes on the composition of anodic-spark
coatings on aluminum alloy was studied preliminarily
in [6, 7].
The electrolytes were prepared from distilled water
and the following reagents: Na
] . 10H
O of analytically pure
, and CH
COOH of chemically pure grade.
Potassium boroundetungstate K
was synthesized by a procedure described in .
Ammonium paratungstate was dissolved at 70oC.
The electrolyte containing tungstic and boric acids
and sodium tungstate was boiled for 1 h with stirr-
ing. All the other electrolytes were prepared by pour-
ing solutions together at room temperature. The elec-
trochemical cell employed and the pretreatment of
aluminum samples have been described previously
. Oxide layers were formed on 40 0 10 0 1mm
AMtsM alloy samples in the galvanostatic mode at
current densities of 3 A dm
in 10, 30, and 60 min.
In the course of anodic-spark oxidation, the electrolyte
temperature did not exceed 20oC. After treatment,
samples with coatings were thoroughly washed with
tap and distilled water and dried in air at room tem-
The sparking voltage was evaluated from the ap-
pearance of the first visually observable sparks on
the anode surface or by analysis of the forming curves
U = f (t) (from the onset of deviation from linearity of
the time dependence of the voltage across the elec-
trodes). As a measure of electrolyte development, Q
) was taken the quantity of electricity passed