Thermal characterization of titanium hydride in thermal oxidation process

Article abstract of DOI:10.1016/j.tca.2012.02.010

We investigated the thermal behavior of titanium hydride with different particle size at the different atmospheres using the thermal analysis techniques. The results demonstrated that the smaller particle has larger reactivity and showed less stable at hi

Full text of DOI:10.1016/j.tca.2012.02.010

Thermochimica Acta 542 (2012) 46–51
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Thermal characterization of titanium hydride in thermal oxidation process
Sneha Samala, Sunghwan Choa, Dong Wha Parkb, Hyungsun Kima,∗
a School of Materials Science and Engineering, INHA University, Incheon 402-751, Republic of Korea
b Department of Chemical Engineering, INHA University, Incheon 402-751, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 13 February 2012
We investigated the thermal behavior of titanium hydride with different particle size at the different
atmospheres using the thermal analysis techniques. The results demonstrated that the smaller particle
has larger reactivity and showed less stable at higher heating rates. Even in the thermal plasma with inert
atmosphere, titanium hydride was partially oxidized and an effective oxidation occurs in thermal plasma
reactor with oxygen as reactive gas. Milling process changed the stoichiometry of titanium hydride from
TiH2 to TiHy and the amount of hydrogen in titanium hydride affects its oxidation behavior.
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Titanium hydride
XPS
SEM
DTA-TG
Oxidation
1. Introduction
deeply investigated the effect of the amount of hydrogen in tita-
nium hydride [4].
Titanium hydride is a chemical compound of titanium and
hydrogen. The powder is grey to black in color with particle size
(d50: 3–50 ␮m). The true density of the powder is 3.8 g/cm3 [1].
This powder can be used as a high-purity hydrogen storage mate-
rial or as a foaming agent for the aluminum foam manufacturing
process. This material has various applications as a bonding mate-
rial (glass–metal and ceramic–metal) in wide areas from alloys to
inter-metallic compounds. Stable titanium hydride powder of high
purity can yield hydrogen at elevated temperatures in a reversible
reaction. Therefore, it is able to resist most chemical reagents, but
is attacked at elevated temperature by oxidizing agents and acids
[2].
Earlier there was disagreement among researchers about the
different dynamic schemes of titanium hydride (TiH2) thermal oxi-
dation [3–5]. According to Hartmann, finely dispersed titanium
hydride mixed with air ignites at 713 K [6]. But Anderson and Flesh-
man investigated the ignition temperature for fine TiH1.92 powder
and found it to be 873 K [7]. According to Antonova [8], the oxi-
dation of TiH1.54 starts at 773–823 K and the process is limited
by the diffusion of oxygen through the TiO2 film. The presence
of hydrogen from the hydride phase is not taken into account.
The chemical composition of the samples should exhibit a strong
influence in the oxidation dynamics. Even though titanium hydride
is extremely sensitive to the experimental atmosphere, especially
such atmospheric factors as oxygen, and heat, few studies have
In this study, the oxidation behavior of titanium hydride with
different particle sizes was investigated under air and inert atmo-
spheres using TG-DTA and thermal plasma reactor. A brief analysis
of titanium hydride was carried out in terms of physical, chem-
ical and thermal properties in thermal oxidation process. The
effect of milling on TiH2 particles has been studied. Both X-
ray diffraction and TG-DTA was used to analyze the structural
changes as well as to study the kinetics of transformation. The
effect of thermal plasma on the oxidation process has been ana-
lyzed in an argon atmosphere. The main purpose of this study
to investigate the reactivity of titanium hydride powders in air
and in an inert medium at high temperature. A detailed ther-
mal analysis of the dehydrogenation and the steps of oxide phase
formation towards titanium oxide has been carried out. The con-
version efficiency has been studied for titanium hydride to titanium
dioxide.
2. Materials and methods
The titanium hydride (TiH2) as starting material was purchased
from Sigma Aldrich (98% pure). Milling experiments were per-
formed with TiH2 powders (<50 ␮m) using a high energy ball mill
(Fritsch Pulverisette – S4) with zirconia vials and balls of 3 mm
diameter. Zirconia vial has an internal diameter of 33 mm and a
height of 20 mm with a capacity of 50 ml. Toluene was used as a
milling medium to carry out wet milling. This solvent acts as a pro-
cess control agent restricting the oxidation process through milling.
Milling was carried out with a rotational velocity of 300 rpm. A
sequence of 30 min milling with 30 min rest intervals to avoid too
high of a temperature rise. The powders were milled for up to 2 h
∗
Corresponding author. Tel.: +82 32 860 7545; fax: +82 32 862 5546.
E-mail address: kimhs@inha.ac.kr (H. Kim).
0040-6031/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2012.02.010

S. Samal et al. / Thermochimica Acta 542 (2012) 46–51
47
powder. XRD analysis was performed on the as received and milled
TiHy powders. Titanium hydride peaks were found in the form of
TiH2 as major peaks before milling; loss of hydrogen gas can be
observed after milling. TiH2 has its most intense peak at 2ꢀ ∼ 52.2◦
(Space group – I4/mmm) (JCPDS file no. 09-0371). TiH2 transforms
(111)
Raw (TiH2) powder
¯
into TiH1.924 (Space group – Fm3m/225), (JCPDS file no. 25-0982)
after 2 h milling.
Micron sized powders can be observed with irregular shapes in a
distorted orientation in the SEM image of the pure titanium hydride
powders is shown in Fig. 2(a). The sizes of the powders range over
more than two orders of magnitude from 0.5 to 50 ␮m. Average par-
ticle size is nearly equal to 35 ␮m. The powder size decreases with
respect to the milling time. It is observed that after 2 h of milling the
powder size decreases and cracking can be observed on the surface
area. Still, some original powders were left behind that retained
their size after milling.
(200)
(220)
(311)
(222)
Milled (TiH1.924) powder
The inset pictures in Fig. 2(b) show that cracking on the surface
occurs due to the milling. Titanium hydride powder was fractured
through the milling process and milled powders show typical mor-
phology having d50 ∼ 20 ␮m after the milling process. The SEM
image of the surface of a titanium hydride particles oxidized at
927 ◦C is shown in Fig. 2(c). This shows that the change in mor-
phology from the titanium hydride powder corresponds to the
formation of a continuous protective film on the surface. The pres-
ence of such a film is confirmed by the change of sample color in
the experiment. At temperature 927 ◦C the oxide phase represented
about 6% of the total weight change (not shown in figure, from
the EDS data). Oxide phases were not observed in the SEM image,
which is due to the oxygen dissolution in the titanium hydride.
Although the upper level of the powder does change its color, the as
received powder at the base of the alumina crucible in the TG-DTA
experiment retains the original color. So this confirms the partial
oxidation of titanium hydride in these experiments.
20
40
60
80
Degree (2θ)
Fig. 1. XRD spectrum of pure (98%) TiH2 powder and milled powder (2 h).
with a ball-to-powder weight ratio of 5:1, keeping the number of
balls constant at 25.
Theoretical analyses of the titanium hydride oxidation in an
argon plasma and with an argon plasma using oxygen gas were
carried out using the thermodynamic software FACTSAGE; exper-
iments were conducted in a thermal plasma reactor. The pressure
in the reactor was 750 Torr, with input power varying from 6 to
9 kW. Thermal analyses of the milled and the as received titanium
hydride were performed within a temperature range 21–927 ◦C
using a Rigaku, Thermoplus TG 8120 thermal analyzer. The rate
of heating was varied as 5, 10, 15, 20 and 25 ◦C/min in air medium.
The phase analysis was carried out for the as received and milled
powders using an X-ray diffractometer (DMAX 2500, Rigaku Co.).
Microstructural characterizations of the powders were carried
out using SEM (Model S-4200, Hitachi). The bonding character-
istic between the Ti and H was analyzed using the XPS (X-ray
Photoelectron Spectroscopy, K-Alpha and Thermo Scientific). The
stoichiometric amount of hydrogen in the titanium hydride powder
was determined by inductively coupled plasma atomic emission
spectroscopy (Thermo electron EA 1112).
TG-DTA analysis was carried out in air medium from 5 ◦C/min to
25 ◦C/min in steps of 5 ◦C and the results are presented in Fig. 3(a).
Dramatic physical changes occur in both the as received and the
milled powders after analysis. The powder changes from blackish-
brown to light yellow. The initial and final temperature of the as
received and milled powder decomposition also relate to the heat-
ing rate. Thermogravimetry loss weight curves for the as received
powder show that the weight loss increases with the increasing
heating rate shown in Fig. 3(b). During the process of thermal
decomposition for both the as received as well as the milled pow-
ders, loss of weight begins at 500 ◦C; this loss of weight ends when
the temperature is around 927 ◦C. According to Chen and Williams
[9] TGA reveals that weight loss of 1.72 wt.% occurred from 387 to
736 ◦C. This is quiet well in agreement with our result is shown
in Fig. 3(d). We found that the endothermic reaction correspond to
the temperature domain of the weight loss. This endothermic reac-
tion corresponds to the decomposition, which releases H2 gas from
3. Results and discussion
Fig. 1 displays the XRD patterns of the as received and the milled
TiH2 particles. The XRD pattern reveals the presence of pure, sharp
TiH2 peaks. Uniform background shifting can easily be observed.
The peak shape proves quite well the crystalline nature of the
Fig. 2. FE-SEM image of titanium hydride powders with: (a) as-received (d50: 35 ␮m), (b) milled powder (2 h) (d50: 20 ␮m), and (c) SEM image of the surface of a titanium
hydride particle oxidized at 927 ◦C.

48
S. Samal et al. / Thermochimica Acta 542 (2012) 46–51
Fig. 3. (a) DTA analyses of the titanium hydride powder with 35 ␮m particle size (TiH2, as received) with various heating rate from 5 ◦C/min, 10 ◦C/min, 15 ◦C/min, 20 ◦C/min
and 25 ◦C/min were carried out in air medium. (b) TG of the titanium hydride powder with 35 ␮m particle size (TiH2, as received) with various heating rate from 5 ◦C/min,
10 ◦C/min, 15 ◦C/min, 20 ◦C/min and 25 ◦C/min were carried out in air medium. (c) DTA thermal analyses of the milled titanium hydride powder 20 ␮m particle size varying
5
◦C/min, 10 ◦C/min, 15 ◦C/min, 20 ◦C/min and 25 ◦C/min ((d) TG as inset) was carried out in air medium. (d) TG of the milled titanium hydride powders 20 ␮m particle size
varying 5 ◦C/min, 10 ◦C/min, 15 ◦C/min, 20 ◦C/min and 25 ◦C/min were carried out in air medium.
the powder. As the process shifts towards the high temperature,
680
640
600
560
520
480
440
680
the milled powder shows a more intense peak that correlates to
the oxidation is shown in Fig. 3(c). This confirms that the reduced
particle size enhances the reactivity of oxidation.
640
600
560
520
480
440
Fig. 4 provides a graph showing the comparison of the heat-
ing rate with the onset temperature for the as received and the
milled powders. The reaction rate increases with respect to the
reduction in the particle size during milling. As a result, the onset
temperature is reduced dramatically in comparison to that of the as
received powders. Similarly, the DTA shows the reverse reactivity
in the cases of both the as received and the milled powders. The
onset temperature for the milled powder is higher in comparison
to that of the as received powder. As exothermic and endothermic
reactions play crucial roles in this analysis, the reaction process is
longer in the milled powder compared to that of the as received
powder. Oxidation is more effective in the case of the milled pow-
der because the residence time of the reactivity is longer and more
effective in the milled powder.
TG(as recieved)
DTA(milled)
TG(milled)
DTA(as recieved)
5
10
15
20
25
Heating rate ( )
0C/min
Fig. 4. Heating rate versus onset temperature of as received triangle (fill) for TG,
triangle (blank) for DTA, and milled: square (fill) for TG, square (blank) for DTA.
TG-DTA analyses showed notable differences in the lower tem-
perature, which are probably due to the surface area reduction
after milling, as can be seen in Fig. 3. There are peaks obtained

S. Samal et al. / Thermochimica Acta 542 (2012) 46–51
49
Fig. 5. XPS analysis of TiH2 samples: (a) the whole spectrum (b) Ti 2p scan (c) O 1s scan.
at 200–300 ◦C/min that remain constant. The intensity decreases
with the higher heating rate. DTA-curves of the samples show that
the most intensive oxidation process takes place in the tempera-
ture range corresponding to the higher hydrogen release from TiH2.
Table 1 provides a comparison study of the TG-DTA thermal analy-
sis from the as received and milled powders. This shows the partial
oxidation of titanium dioxide. The titanium hydride was subjected
to an elemental analysis test to determine the exact amount of
hydrogen content in the sample. The stoichiometric amount shows
that the hydrogen content is around 1.95 wt.% in the sample, as
calculated by using ICP-OES.
the peaks for Ti, O and C. Ti exhibits a peak Ti 2p3/2 at 464.5 eV. The
second major peak of Ti 2p1/2 is at 454.5 eV. The peak positions are
found to match with earlier reported data [10,11]. The O 1s spec-
tra presence at 532.7 eV can be attributed to TiOH or Ti–H2O. This
indicates the existence of different titanium–oxygen compounds
within the interface regions.
Fig. 6(a) and (b) provides a thermodynamical plot of TiH2 as a
function of temperature. This plot shows the equilibrium amounts
of moles of species formed with respect to temperature. The
chemical equilibrium compositions in the various systems were
calculated using a software program (FACTSAGE), which is based
on Gibb’s free energy minimization. The sample is inactive and
remains the same in an argon atmosphere. Plasma gases are also
taken into account in these thermodynamic calculations, but are
not shown in the plots due to their higher content. The graph shows
that at temperatures above 4800 K, which are found inside the
plasma jet, only the mono atomic H and Ti are stable. The possi-
ble reactions that may take place in this zone during the reaction
process are given in Table 2.
As for the X-ray photoelectron spectrum (XPS) of the TiH2 pow-
ders, Fig. 5(a) shows the full spectrum of the TiH2 powders; Fig. 5(b)
displays the spectrum for the Ti 2p level. The full pattern represents
Table 1
The comparison of thermal reaction for raw and milling powders at 20 ◦C/min heat-
ing rate.
Thermodynamic plots show the formation of solid Ti in the
argon atmosphere plasma. The efficiency of the oxidation process
depends on the temperature and treatment of the environment,
which quite well agrees with Gromov et al. [3]. This oxidation pro-
cess also depends on the flow rate of the reactive gases oxygen
Thermal reaction Raw powder Milled powder Reaction process
1st exothermic
2nd exothermic
1st endothermic
3rd exothermic
250
550
620
873
250
550
620
873
Formation of oxyhydride
Formation of hydroxides
The release of H2 gas
Formation of dioxide

50
S. Samal et al. / Thermochimica Acta 542 (2012) 46–51
r
TiO (TG-DTA)
2
r
a
r
r
r
r
a
r
a
a
TiO2(Thermal plasma)
20
40
Degree (2θ)
60
80
Fig. 7. XRD plot of oxidized product obtained from titanium hydride in thermal
plasma and TG-DTA method (r: rutile, a: anatase).
TiO2 and water vapor H2O (g) are found to remain stable at room
temperature. TiO2 can be collected from the inner wall of the reac-
tion tube. The product obtained after the thermal plasma treatment,
was found to be a mixture of anatase and rutile phases (with the
predominance of anatase for TiH2). Fig. 7 displays the XRD graphs of
the oxidized product obtained from titanium hydride after oxida-
tion. The oxidized product obtained from the TG-DTA clearly shows
that the rutile phases are more dominant in titanium dioxides. This
results in thin films on the sample surface and prevents further
oxidation, whereas the oxidized product obtained after thermal
plasma treatment with oxygen as reactive gas shows a mixture
of anatase and rutile phases and complete conversion of titanium
dioxide from titanium hydride.
Fig. 6. (a) Free energy minimization plot for the Ti–H plots in argon atmosphere. (b)
Free energy minimization plot for the Ti–H plots in argon + nitrogen atmosphere.
Complete conversion of titanium hydride to titanium oxide does
not take place. Mixtures of golden-green (TiyHOx) and golden-
yellow (TiO) with some brown color powder (TiH2−x) form [3].
When thermal plasma oxidation takes place in oxygen as reactive
gas the resulting product is titanium oxides. Therefore, the pro-
posed oxidation reaction in argon plasma with oxygen as reactive
gas is as follows
Table 2
The possible reactions occur during the reaction process in argon atmosphere.
Reaction process
Temperature range
Ti (s) + H2 (g) → TiH2 (s)
2Ti (l) → Ti (s)
<800 K
1300–2300 K
2300–3300 K
2300–3300 K
2H (g) → H2 (g)
Ti (g) → Ti (l)
TiHy → TiHy−x → TiO → Ti2O3 → Ti3O5 → TiO2.
(1)
It was found that the increase in the input power in the ther-
mal plasma resulted in an increase of the electron concentration.
Furthermore, an admixture of H2O vapors resulted in the quench
box inside the thermal plasma reactor. Indeed, hydrogen in TiHy is
known to exist in atomic form which is able to react with oxygen
and then to move into the lattice vacancies [17–19].
in the thermal plasma process. DTA-curves support the idea that
the most intensive oxidation process takes place in the tempera-
ture range of 21–927 ◦C, which correspond to the maximum of the
hydrogen release from the TiH2 [12–16]; shows that the thermal
plasma oxidation of the sample results in the formation of water
vapors in the high temperature zone. The hydrogen content in the
sample reacts with oxygen and comes out as water vapor. The pos-
sible sequential reactions, shown in Fig. 6(b), are summarized in
Table 3.
4. Conclusion
The physical and chemical properties of titanium hydride
show that this material is very sensitive to oxidizing agents.
Thermal analysis suggests that the oxidation mechanism of
titanium hydride depends on the oxidation method chosen
to make the process effective. The dynamics of the oxida-
tion of titanium hydride, TiHy is likely to follow the reaction
path TiHy → TiHy−x → TiO → Ti2O3 → Ti3O5 → TiO2. The oxidation
of TiH2 in argon plasma with oxygen as the reactive gas was
found to lead to mixtures of titanium oxides of different oxidation
degrees. The oxidation process is effective for the higher thermal
plasma input power. In these cases the presence of hydrogen in the
Table 3
The possible sequential reactions occur at argon atmosphere with reactive gas
oxygen.
Reaction process
Temperature
Ti3O5 (s) + H2 (g) → TiO2 (g) + H2O (g)
Ti2O3 (l) + 2OH (g) → Ti3O5 (s) + H2 (g)
2TiO (g) + O (g) → Ti2O3 (l)O (g) + H (g) → OH (g)
Ti (g) + O (g) → TiO (g)
Below 1300 K
2300–2800 K
2800–3800 K
3800–4300 K
4300–4800 K
Ti (l) → Ti (g)
O (l) → O (g)

S. Samal et al. / Thermochimica Acta 542 (2012) 46–51
51
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