The heat capacity of titanium di-and tetrachloride over the temperature range 7-314 K

Article abstract of DOI:10.1134/S0036024406100189

The temperature dependences of the heat capacities of titanium di-and tetrachloride were studied by vacuum adiabatic calorimetry. The parameters of fusion (T _tr, Δ_tr H, and Δ_tr S) were determined for TiCl₄. The

Full text of DOI:10.1134/S0036024406100189

ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 10, pp. 1656–1660. © Pleiades Publishing, Inc., 2006.
Original Russian Text © G.A. Berezovskii, E.M. Snigireva, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 10, pp. 1863–1867.
CHEMICAL THERMODYNAMICS
AND THERMOCHEMISTRY
The Heat Capacity of Titanium Di- and Tetrachloride
over the Temperature Range 7–314 K
G. A. Berezovskiia and E. M. Snigirevab
a Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
e-mail: berez@che.nsk.su
b Moscow Physicotechnical Institute, Institutskii proezd 9, Dolgoprudnyi, Moscow oblast, 141700 Russia
e-mail: snigireva–helen@mail.ru
Received October 31, 2005
Abstract—The temperature dependences of the heat capacities of titanium di- and tetrachloride were studied
by vacuum adiabatic calorimetry. The parameters of fusion (Ttr, ∆trH, and ∆trS) were determined for TiCl4. The
thermodynamic functions of the substances were calculated over the temperature range 10–300 K. The results
obtained were compared with literature data.
DOI: 10.1134/S0036024406100189
The thermodynamic characteristics of titanium was synthesized following the procedure described
chlorides, which have been widely used in technologi- in [7] from titanium metal shavings obtained from
cal processes, are contained in data banks and hand- titanium refined by the iodine process and titanium tet-
books [1, 2]. However, no experimental data on low- rachloride. According to the chemical analysis data, the
compositions of the samples were TiCl4.00
temperature heat capacities had been reported for the
Ti–Cl system up to 1990. In this system, three stable
chlorides, namely, TiCl2, TiCl3, and TiCl4, exist. The
heat capacity of TiCl3 was measured from 53 to 296 K
only [3], and the thermodynamic characteristics of tita-
nium chlorides at 298.15 K are given in [1, 2] with a
reference to a private communication. Numerous refer-
ences to works in which the temperature and enthalpy
of fusion of TiCl4 were measured are given in [1]. In
database [2], the heat capacities of titanium chlorides at
100 and 200 K and, for TiCl4, also at the melting point
(249.046 K) are given. We, however, know of no origi-
nal works in which the heat capacity of TiCl4 in the
crystalline state was measured. Note that, in [4], thermo-
dynamic calculations were performed using the titanium
chloride parameters from [2]. Work [4] contains abun-
dant bibliography on the thermodynamic properties of
the Ti–Cl system. In 1990, we published the results
obtained in measurements of the heat capacities of two
0.02
and TiCl2.00 0.02. Titanium was determined gravi-
metrically in the form of TiO2, and chlorine, potenti-
ometrically by titration with a solution of silver
nitrate. The diffractogram of the TiCl2.00 sample on
the whole corresponded to the literature data on tita-
nium dichloride [8]. The samples were hygroscopic
and easily oxidizable and were therefore handled in
a dry box in the atmosphere of a dry purified
inert gas.
The isobaric heat capacity Cp of titanium chlorides
was measured in an adiabatic vacuum calorimeter
with pulsed heating [5]. A nickel calorimetric ampule
was used to work with chemically active compounds.
The temperature of the ampule was measured by a
TSPN-4 (R0 = 50 Ω) platinum resistance thermometer
and calculated by the SST-68 standard table. Tests
with a reference compound (benzoic acid) gave close
agreement with the standard values. The TiCl4 and
TiCl2 sample weights were 5.385 and 4.302 g, respec-
tively.
titanium chlorides, TiCl2.07
and TiCl2.98 0.02, from
0.05
5 to 315 K [5, 6]. That work was part of complex
studies of the Ti–Cl system. Here, we present the
experimental data on two more samples, titanium tet-
rachloride and titanium dichloride with a composi-
tion closer to stoichiometry than that of the sample
studied in [6]. We found that the TiCl2.07 0.05 sample
contained a substantial amount of titanium trichlo-
ride as an impurity.
The heat capacity of titanium tetrachloride was
measured over the temperature range 6.93–314 K
(Table 1). Below the melting point Tm, the Cp(T) depen-
dence was a smooth curve without anomalies (figure).
The mean deviation of the experimental heat capacity
values from the smoothed Cp(T) curve was 1.5% below
20 K and 0.1% from 30 K to Tm. The heat capacity of
the liquid phase from 249 to 300 K was constant to
within 0.2%. The actually measured value CS (heat
Titanium tetrachloride of os. ch. (special purity)
grade was additionally distilled. Titanium dichloride
1656

THE HEAT CAPACITY OF TITANIUM DI- AND TETRACHLORIDE
1657
Table 1. Experimental heat capacities (Cp, J/(mol K)) of titanium tetrachloride, M = 189.712 g/mol
T, K
Cp
T, K
Cp
T, K
Cp
T, K
Cp
Series 1
Series 3
Series 4
13.14
14.14
15.36
16.83
18.32
19.68
21.19
23.29
25.86
28.46
31.17
34.03
36.94
43.43
47.47
52.23
56.96
62.45
68.08
73.47
78.98
8.032
9.826
12.00
14.53
17.12
19.44
21.97
25.42
29.46
33.22
36.96
40.78
44.44
51.71
56.02
60.37
64.60
68.54
71.37
74.23
76.96
301.91
305.74
309.88
313.99
148.9
149.2
149.2
149.2
79.93
83.43
77.24
78.97
80.75
82.37
83.97
85.82
87.40
88.84
90.12
91.36
92.87
93.99
95.39
96.73
98.15
99.65
101.22
102.9
104.4
106.0
107.6
109.1
241.12
242.92
245.52
249.05
253.35
258.02
278.26
285.80
149.5
148.8
149.2
148.4
148.9
149.6
149.1
149.6
87.57
91.51
Series 2
95.74
182.33
187.44
192.48
197.46
202.38
207.25
212.08
216.86
221.59
226.27
231.15
236.22
240.83
244.94
110.2
111.6
112.7
114.1
115.2
116.6
117.8
119.0
120.2
121.4
122.8
124.1
128.3
135.4
100.26
104.61
108.81
112.99
117.22
121.43
125.53
129.79
134.20
139.22
144.83
150.32
155.70
160.97
166.52
172.59
178.56
Series 5
259.42
264.25
268.86
273.83
278.76
148.9
148.5
148.4
148.5
148.5
Series 6
6.93
7.41
1.374
1.602
2.194
3.131
3.989
5.057
6.473
8.29
9.26
10.16
11.10
12.14
capacity at saturated vapor pressure) was assumed to was 0.085 mol %. The entropy of fusion was deter-
mined as ∆fusH/Tm. The characteristics of fusion of
equal Cp, because the difference between these values
close to the melting point was less than 0.1% and could
therefore be ignored. Note that the first three points in
series 4 (Table 1, points from 241.1 to 245.5 K) corre-
sponded to the heat capacity of the supercooled liquid
phase. Three experiments were performed to determine
the enthalpy of fusion ∆fusH. The second and third
experiments were conducted with interrupting heating
in certain time intervals following the procedure
described in [9]. This procedure allows the melting
TiCl4 are summarized in Table 2.
Cp, J/(mol K)
140
100
°
points of absolutely pure compounds (Tm ) and sam-
ples under study (Tm) and the amount of impurities in
the samples to be determined. The results of the sec-
ond and third experiments were Tm = 248.85 and
60
1
2
°
248.88 K and Tm = 248.88 and 248.93 K, respec-
20
tively. The amount of impurities N in the sample cal-
culated by the equation
0
100
200
300 T, K
Heat capacities of (1) TiCl and (2) TiCl over the temper-
4
2
2
°
°
N = [∆mH(Tm – Tm)/R(Tm ) ] × 100%,
ature range 7–314 K.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 10 2006

1658
BEREZOVSKII, SNIGIREVA
Table 2. Characteristics of phase transitions in TiCl4 and TiCl3
[6], however, show that the Cp(T) curve is smooth over
this temperature interval too. Note that several points
deviate from the smoothed Cp(T) curve by no more than
1% close to 220 and 250 K. Clearly, this is explained by
the presence of titanium trichloride and tetrachloride
impurities. A comparison of the excess enthalpies of
these impurity anomalies with the enthalpies of transi-
tions in TiCl3 and TiCl4 led us to conclude that these
impurities were present in exceedingly small amounts,
less than 0.01% each. They could not substantially
influence the enthalpies and entropies of TiCl2 at 298 K.
It is, however, of interest that heat capacity measure-
ments are a very sensitive method for detecting small
impurities. Of course, if the impurities are substances
with phase transitions.
according to our data and [1, 5]
∆trH°,
∆trS°,
Compound
Ttr, K
J/mol
J/(mol K)
Fusion
248.91 0.02 9960 40 40.03 0.16
TiCl4
TiCl4 [1] 249.05 0.01 9970 40
Polymorphic transition
40.00
TiCl3 [5]
TiCl3 [1]
219.5 0.2
220.1 0.1
1790 10 8.150 0.005
1480 10 6.74
The smoothed Cp(T) dependences obtained for
TiCl4 and TiCl2 were used to calculate the Φ°(T), S°(T),
and H°(T)–H°(0) thermodynamic functions at several
selected temperatures (Tables 4 and 5). The extrapola-
tion of the heat capacities to 0 K was performed on the
assumption that the Cp(T) dependences below 8 K were
proportional to T3. The accuracy of the thermodynamic
The heat capacity of titanium dichloride was mea-
sured from 8.4 to 313 K (Table 3). The mean deviation
of the experimental heat capacities from the smoothed
Cp(T) curve was 1.0% below 20 K and ~0.1% from
20 to 270 K. No anomalies were observed over the
whole temperature range. No experimental values were
obtained between 270 and 300 K. The data on TiCl2.07 functions was estimated from the spread of experimen-
Table 3. Experimental heat capacities (Cp, J/(mol K)) of titanium dichloride, M = 118.79 g/mol
T, K
Cp
T, K
Cp
T, K
Cp
T, K
Cp
Series 1
217.06
218.25
218.97
219.68
220.40
221.22
222.41
224.31
62.69
62.91
62.41
63.16
63.38
64.06
63.83
63.94
Series 5
Series 7
300.57
303.59
306.72
310.00
313.07
70.08
69.57
70.30
71.00
70.79
111.26
115.57
119.74
124.27
128.68
133.45
139.06
147.13
157.53
167.56
177.25
186.68
195.86
40.79
42.42
43.82
45.40
46.62
48.21
49.58
51.41
53.68
55.60
57.43
59.01
60.20
8.39
9.40
0.1361
0.2913
0.3182
0.4270
0.5570
0.6952
0.9416
1.185
1.188
1.389
1.581
1.902
2.267
2.696
3.344
4.154
5.001
5.909
6.889
10.45
11.54
12.53
13.58
14.68
15.80
16.87
17.96
19.13
20.60
22.27
24.03
26.40
29.11
31.63
34.06
36.52
Series 2
79.81
81.64
83.41
85.14
86.81
88.45
90.04
94.82
100.21
102.96
27.84
28.53
29.42
30.29
31.00
31.82
32.38
34.45
36.70
37.68
Series 4
227.88
232.05
236.20
240.20
244.17
248.26
252.52
256.75
260.74
264.70
268.62
63.98
64.40
64.80
65.16
65.53
66.09
66.71
66.90
67.04
67.34
67.47
Series 6
45.04
48.62
52.33
57.41
63.26
68.79
10.44
12.27
14.03
16.62
19.70
22.34
Series 3
205.80
210.00
214.16
61.56
61.96
62.40
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 10 2006

THE HEAT CAPACITY OF TITANIUM DI- AND TETRACHLORIDE
1659
°
°
Table 4. Main thermodynamic functions of TiCl4 (Cp (T), Table 5. Main thermodynamic functions of TiCl2 (Cp (T),
Φ°(T), and S°(T), J/(mol K); H°(T) – H°(0), J/mol)
Φ°(T), and S°(T), J/(mol K); H°(T) – H°(0), J/mol)
°
°
T, K
Cp (T)
Φ°(T)
S°(T)
H°(T) – H°(0)
T, K
Cp (T)
Φ°(T)
S°(T)
H°(T) – H°(0)
10
15
20
25
30
35
40
45
50
60
70
80
90
3.816
11.17
19.88
28.04
35.40
42.04
48.06
53.51
58.41
66.54
72.61
77.47
81.77
85.66
92.37
98.36
104.1
109.6
114.7
119.8
125.0
0.394
1.164
2.466
4.231
6.337
8.683
11.19
13.81
16.50
21.98
27.48
32.90
38.19
43.34
53.16
62.37
71.05
79.24
87.01
94.42
101.5
104.5
104.5
110.0
119.4
128.2
1.443
4.270
8.680
14.01
19.78
25.75
31.76
37.74
43.64
55.04
65.78
75.80
85.17
93.99
110.2
124.9
138.4
151.0
162.8
174.0
184.6
189.2
229.2
235.7
246.7
257.0
10.49
46.59
124.3
244.4
403.3
597.2
822.7
1077
10
15
20
25
30
35
40
45
50
60
70
80
90
0.278
1.004
1.763
2.953
4.447
6.272
8.283
10.47
12.89
17.97
22.99
27.85
32.41
36.57
43.93
49.80
54.18
57.87
60.77
63.32
65.25
67.03
68.32
69.77
0.037
0.099
0.209
0.363
0.564
0.814
1.113
1.461
1.856
2.778
3.864
5.088
6.425
7.855
10.92
14.14
17.45
20.78
24.08
27.34
30.53
33.65
36.70
39.66
0.128
0.353
0.735
1.251
1.917
2.735
3.703
4.803
6.030
8.825
11.98
15.36
18.91
22.55
29.88
37.12
44.06
50.66
56.92
62.83
68.42
73.72
78.74
83.50
0.908
3.799
10.53
22.20
40.57
67.24
103.6
150.4
208.7
362.8
567.8
822.2
1124
1357
1984
2681
3432
4228
100
5066
120
140
160
180
200
220
240
6848
100
1469
8756
120
140
160
180
200
220
240
260
280
300
2276
10780
12920
15160
17510
19950
21070
31030
32680
35650
38620
3216
4258
5379
6567
7808
248.91 127.4
248.91 148.7
9094
10420
11770
13150
260
280
300
148.7
148.7
148.7
298.15 69.63 0.15 39.40 0.10 83.07 0.16 13020 20
298.15 148.7 0.3 127.4 0.3 256.0 0.5 38350 80
Table 6. Heat capacity and thermodynamic functions of titanium chlorides at 298.15 K (according to our data and [1, 2, 6])
°
Compound
Cp (T), J/(mol K)
S°(T), J/(mol K)
H°(T) – H°(0), kJ/mol
Φ°(T), J/(mol K)
TiCl4
148.7 0.3
145.2 0.2
98.60 0.10
97.15 0.30
69.63 0.12
69.83 0.40
71.13 0.11
256.0 0.3
252.4 0.4
135.0 0.2
139.7 1.2
83.07 0.16
87.4 4.0
38.35 0.04
37.49 0.60
20.81 0.03
20.92 0.08
13.02 0.02
13.30 0.08
13.42 0.03
127.4 0.2
126.6
TiCl4 [1, 2]
TiCl3 [6]
TiCl3 [1, 2]
TiCl2
65.2 0.2
69.5
39.4 0.1
42.8
TiCl2 [1, 2]
TiCl2.07 [6]
85.98 0.26
40.97 0.15
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 10 2006

1660
BEREZOVSKII, SNIGIREVA
tal values over the whole temperature range of mea-
surements. All the thermodynamic parameters at
298.15 K known for titanium chlorides are listed in
Table 6. The discrepancies between our and the litera-
ture data are evidence that experimental heat capacity
measurements like those performed in this work are
necessary. At the same time, our and literature [1] data
on the parameters of fusion of TiCl4 are in close agree-
ment (Table 2). This can be explained by repeated mea-
surements of the temperature and enthalpy of fusion of
titanium tetrachloride. For completeness, Tables 2 and
6 also contain the thermodynamic data on TiCl3
obtained by us in [5, 6]. In the present work, we used
pure samples and a verified procedure for measure-
ments. This allows us to claim the absence of substan-
tial systematic errors in the thermodynamic character-
istics of titanium chlorides obtained.
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