1070-4272/04/7709-1397C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 9, 2004, pp. 1397!1403. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9,
2004, pp. 1409!1415.
Original Russian Text Copyright + 2004 by D’yachkov.
AND INDUSTRIAL INORGANIC CHEMISTRY
Features of Oxidation of Titanium Group Metals in Air
V. I. D’yachkov
St. Petersburg State University, St. Petersburg, Russia
Received July, 9, 2004
Abstract-The kinetics and mechanism of oxidation of titanium, zirconium, and hafnium in air at 9733
1473 K were studied in relation to the properties of the metals.
The kinetics and mechanism of oxidation of titani-
um, zirconium, and hafnium were extensively studied,
but the behavior of these metals actually was not
compared under identical conditions, except for cer-
tain data in . At the same time, such data are of
both practical and scientific interest, as they give
insight into the features of oxidation of these metals.
The purpose of this work was to reveal how the
properties of titanium, zirconium, and hafnium affect
the kinetic parameters, temperature dependence of rate
constants, and activation energy of the oxidation,
the diffusion mechanism of scaling, and properties
of the scale.
Experiments were carried out in air with control-
lable humidity at a pressure of 101.3 kPa in the range
97331473 K. The materials under study were high-
purity metals (99.93% Ti, 99.80% Zr, and 99.70% Hf)
melted in a fluidized bed in an electromagnetic field
in an atmosphere of purified argon . The technique
of the preparation of 1.0(1.5)01.00(0.230.5)-cm
samples with a grain size of about 50 mm and the
experimental procedures in use are described in .
Comparison shows that the parameters of the oxi-
dation of titanium, zirconium, and hafnium are essen-
tially different. In particular (Table 1), the rate of Ti
oxidation at 107331473 K is much lower than that of
Zr, but much higher (at T > 1073 K) than that of Hf.
Processing of the oxidation curves (Fig. 1) shows
that Evans equation (1)  and laws close to parabol-
ic, cubic, and sometimes linear (2)3(4) are obeyed:
q = K
t + C, (1)
t + C, (2)
t + C, (3)
q = K
t + C, (4)
where q is the weight of absorbed gases; t, time; C,
a constant; K
, and K
, rate constants of the oxida-
tion by linear, parabolic, and cubic laws, respectively.
In fact, laws (2)3(4) are not strictly fulfilled in the
case of the Zr and Hf oxidation, and the experimental
data can be formally described by expression (5) with
various n values.
= Kt + C. (5)
As follows from Table 2, the kinetics of Ti oxida-
tion (3 h) at 107331373 K almost fully follows Evans
equation (1) (Fig. 2), which suggests nonstationary
character of this process and, hence, comparable con-
trol of its rate by diffusion and by interphase reactions
[6, 7]. At T < 1073 K, the equation is obeyed only
at the beginning of the test, being then replaced by
another relationship with 2 < n < 3 in expression (5).
Above 1373 (1423) K, the Evans law is not obeyed
owing to a considerable influence of a strong over-
heating of the sample surface on the kinetics of the
oxidation in the initial period . With Hf (3 h), the
Evans law is obeyed only at 97331023 K and, as op-
posed to Ti, above 1423 K, whereas in the range
107331423 K it is obeyed only at the beginning of
the oxidation (Fig. 2), with the subsequent transition
to dependence (2), which is close to parabolic. With
Table 1. Weight gain Dq oxidation of Ti, Zr, and Hf in air
for 3 h
, at indicated temperature, K
³ 973 ³ 1073³ 1173³ 1273³ 1323³ 1373 ³ 1473
Ti ³ 0.40 ³ 1.5 ³ 7.9 ³ 21.5 ³ 34.4 ³ 31.7 ³ 35.7
Zr ³ 2.00 ³ 3.1 ³13.2 ³ 31.1 ³ 54.5 ³ 43.1 ³ 82.9
Hf ³ 0.40 ³ 1.5 ³ 2.2 ³ 9.3 ³ 8.0 ³ 10.3 ³ 19.2