1070-4272/05/7811-1840C2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 11, 2005, pp. 1840!1843. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 11,
2005, pp. 1872!1874.
Original Russian Text Copyright + 2005 by Malyshev, Duda, Shevchenko.
AND CORROSION PROTECTION OF METALS
Effect of High-Temperature Electrochemical Deposition
C Coatings on the Corrosion and Electrochemical
Behavior of Titanium
V. V. Malyshev, T. I. Duda, and V. M. Shevchenko
Kiev Polytechnic Institute, National Technical University of Ukraine, Kiev, Ukraine
Received May 12, 2002; in final form, May 2005
Abstract-The possibility of increasing the corrosion resistance of titanium by electroplating molybdenum
carbide coatings from the melts was studied.
Molybdenum and molybdenum carbide are widely
used as components of corrosion-resistant steels and
alloys and of coatings for surface modification. There-
fore, the corrosion and electrochemical behavior of
molybdenum and molybdenum carbide in aggressive
media attracts growing researchers’ attention. Various
methods are used for surface modification of titanium.
For example, the deposition of platinum-group metals
increases the corrosion resistance of titanium in hot
solutions of acids by several orders of magnitude
[1, 2]. However, noble metals are expensive, which
makes application of this protection method limited.
Alloying titanium with molybdenum shows promise
[1, 3, 4]. At the same time, the level of alloying en-
suring high corrosion resistance should be no less than
20325%. This level is successfully attained when,
for example, the method of diffusion saturation from
solid mixtures with the oxide activator in a vacuum or
under argon at 110031200oC is used for surface alloy-
ing of titanium samples with molybdenum . The
method of the high-temperature electrochemical syn-
thesis (HTES) from ionic melts allows the tempera-
ture of alloying of titanium with molybdenum, tung-
sten, and their carbides to be decreased to 8003900oC
and alloying time to be shortened considerably. In this
case, the corrosion resistance of St.3 and St.45 steels
in sodium chloride solutions and in hot concentrated
and dilute solutions of hydrochloric, sulfuric, and
phosphoric acids considerably increases.
In this study we examined the electrochemical and
corrosion behavior of titanium, onto which molybde-
num carbide coating was deposited by HTES, in a sul-
furic acid solution. Because Mo
C is in short supply
and is brittle at room temperature, it has not found
wide application in industry as structural material
[1, 8]. At the same time, it is an important alloying
component for coating deposition.
Molybdenum carbide was plated onto VT 130 tita-
nium by the HTES method from the melts of com-
position (mol %): 85 Na
, 5 MoO
, and 10
at 8003900oC and a cathodic current density
of 0.0430.12 A cm
in air. The maximum thickness
of the coatings was 50 mm.
An important condition for the successful coating
deposition is that the corrosion potential of titanium
should be more positive than that of carbide (31.60 to
31.90 V vs. the reference electrode (O
in the alloy studied). Therefore, we measured
the stationary potentials of titanium in a Na
5 mol % MoO
melt containing different amounts of
and estimated whether molybdenum carbide
coatings with good adhesion to the substrate can be
deposited. The stationary potentials were not es-
tablished for a long time and varied jumpwise. Ap-
parently, this is associated with dissolution of oxygen-
containing phases in the surface layer of the electrode.
After measuring the potentials, we studied the com-
position of surface layers formed on titanium and con-
firmed the presence of oxide phases weakly adherent
to the surface. The X-ray phase analysis of the surface
layers revealed Ti, TiO, and TiO
To form coatings strongly adherent to the support,
it was necessary to remove the oxide phases of titani-
um. Therefore, prior to the molybdenum carbide
deposition, titanium was nickel-plated in aqueous
solutions or subjected to surface nitriding at 6003
700oC. The stationary potential of nickel at 900oCin
the range of the Li
concentrations 5310 mol %
was 0.8931.07 V, the value considerably more posi-
tive than the deposition potential of carbide.