Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 10, pp. 1858−1861.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
A.M. Borshchevskii, L.P. Baturova, E.P. Elizarova, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 10, pp. 1706−1709.
AND CORROSION PROTECTION OF METALS
Corrosion Behavior of Ti–Nb Alloys in Sulfuric Acid
A. M. Borshchevskii, L. P. Baturova, and E. P. Elizarova
St. Petersburg State Polytechnic University, St. Petersburg, Russia
Received July 20, 2009
Abstract—Specific features of the corrosion behavior of Ti–Nb alloys in a 40% H
solution were studied.
It is known that the chemical stability and a number
of other properties of binary alloys having the form of
solid solutions change under the action of a corrosive
medium discretely at compositions that are multiples
of n/8 atomic fractions (n = 1, 2–7) of the more stable
component. These alloy compositions are named
chemical stability boundaries [1, 2]. According to the
existing concepts, the chemical stability boundaries are
associated with enrichment of the alloy surface with
a more stable component in interaction with a corrosive
medium [3, 4].
A quantitative characteristic of dissolution of
homogeneous alloys is the coefﬁ cient of the selective
dissolution of a component, Z
, which is deﬁ ned as the
ratio between the contents of components in the solution
and alloy. In the case of a uniform dissolution of the
= 1 and the ratio of the partial dissolution rates
of the components is proportional to the ratio between the
contents of the components in the alloy. If the dissolution
rates of the components of the alloy markedly differ, then,
a mutual inﬂ uence of the components can be observed at
certain compositions for a number of systems , and the
dissolution rate of a component can be determined by that
of another component and may substantially differ from
its dissolution rate in the individual state. In selective
dissolution of alloys [7–9], a predominant transfer of
atoms of the unstable component into solution results in
that atoms of the more stable component accumulate on
the surface. In the course of dissolution of the alloy, there
may occur back deposition of the stable component from
solution, accompanied by formation of its own phase on
The aim of our study was to examine speciﬁ c features
of the corrosion behavior of Ti–Nb alloys forming
a continuous series of solid solutions  under the
conditions in which the individual dissolution rates of
the alloy components signiﬁ cantly differ.
The alloys were produced from titanium of VT-1
brand and NB-0 niobium. The content of Ti and Nb in the
alloys under study was varied as multiples of 5 ± 0.1 at %
(see table). A total of 19 alloys and pure Ti and Nb were
tested. According to , TiNb intermetallides can be
formed in alloys containing 47–87 at % Nb. The presence
of intermetallides can affect the corrosion behavior of
the alloys. Therefore, we studied the microstructure
of metallographic sections of alloys containing 40 and
70 at % Nb (at 1000× magniﬁ cation). It was found that
both the alloys have the same structure of a solid solution.
The absence of intermetallides in this system was also
reported in [12, 13].
The corrosion resistance of Ti and Nb is determined
by the stability of passive ﬁ lms in corrosive media .
Sulfuric acid with an increased concentration decomposes
the protective ﬁ lm of titanium dioxide, and thereby causes
its dissolution, whereas niobium is stable in acid media.
We chose as a corrosive medium in the study a 40 wt %
solution of H
because preliminary experiments
demonstrated a noticeable difference in the corrosion
behavior of pure metals in this medium: Ti dissolves
at a high rate and Nb is almost resistant. The corrosion
rate was determined in the study from the loss of mass
in g-at m
and g m
The results of our corrosion tests are listed in the table.
It can be seen that the dissolution rates of titanium and
niobium in a 40 wt % solution of H
are 1.25 and