SPECTROCHIMICA
ACTA
PART B
Spectrochimica Acta Part B 50 (1995) 1459-1468
ELSEVIER
Mechanism of thermal decomposition of hydrated copper
nitrate in vacuo
Boris V. L'vov* and Alexander V. Novichikhin
Department of Analytical Chemistry, St. Petersburg Technical University, St. Petersburg 195251,
Russia
Received 14 June 1995; accepted 26 June 1995
Abstract
The general scheme of three-stage thermal decomposition of Cu(NO3)2.3H20 to CuO has been refined
based on evolved-gas-analysis data with a quadrupole mass analyzer (Jackson et al., Spectrochim. Acta
Part B, 50 (1995) 1423). Quantitative evaluation of the composition of the gaseous products shows that
the first stage involves primarily deaquation, and the second stage, primarily denitration of the original
hydrated nitrate. The basic nitrate formed in the second stage most probably has the formula
Cu(NO3)2.3Cu(OH)2. It has been established that the molecular oxygen observed in the third stage of
decomposition is produced by catalytic decomposition of NO2 on the surface of CuO. The presence of
Cu-containing ions in all stages of the process is consistent with the gasification mechanism of thermal decomposition.
Keywords: Copper nitrate decomposition; Evolved gas analysis; Gasification mechanism; Nitrous dioxide
catalytic decomposition
1. I n t r o d u c t i o n
This work represents a logical continuation of the series of previous publications [1-3]
dealing with a study of thermal decomposition of the metal nitrates by evolved gas analysis
(EGA) of the decomposition products with a quadrupole mass analyzer (QMA). We may recall
that Ref. [1] describes the techniques used and general results obtained in an investigation of
thermal decomposition of the nitrates of Ag, Cd, Cu and Pb, while Refs. [2] and [3] contain
an interpretation of the results in terms of two radically different (gasification and condensation)
mechanisms. In contrast to the anhydrous nitrates of Ag, Cd, and Pb, copper nitrate can exist
in several hydrated forms and proceeds, accordingly, through several stages of thermal
decomposition. Therefore, in order to facilitate the discussion, we restricted ourselves in
Ref. [2] to analyzing thermal decomposition of the anhydrous nitrates of Ag, Cd and Pb, while
reserving a separate publication for the hydrated copper nitrate.
Investigation of thermal decomposition of the hydrated copper nitrate by classical differential
thermal analysis (DTA) has been the subject of a large number of publications [4-9]. Thermal
* Corresponding author.
0584-8547/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0584-8547(95)01402-0
1460
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
decomposition was achieved both in air at atmospheric pressure [4-8] and in vacuo [9]. In the
latter case, the DTA was complemented by EGA with a magnetic mass spectrometer [9]. Wang
et al. ]10] later used EGA with QMA to study atomization of the copper nitrate in a graphite
furnace in vacuo. Their study unexpectedly revealed the appearance at 400 K of the Cu ÷ and
CuO ÷ ions, together with ions of masses 126 and 142, which were assigned [10] to the Cu2
and CueO molecules, respectively.
Despite common features observed in the above studies 14-9], their interpretation is markedly different. In particular, the first of the three endothermic peaks in the DTA traces observed
at about 400 K was assigned to the melting of Cu(NO3)2.3H20 or to its dissolution in the water
of crystallization [4-8], or to the thermal decomposition of Cu(NO3)2.5/2H20 to the basic
nitrate 3Cu(NO3)2.Cu(OH)2 [9]. The last peak observed in the 540-580 K region is assigned
to the thermal decomposition to CuO of the basic nitrate of the types Cu(NO3)2.2Cu(OH)2 [5]
or Cu(NO3)e.3Cu(OH)2 [6,7]. In contrast to all other authors, Keeley and Maynor [1 I] deny
the formation of any intermediates in the thermal decomposition of Cu(NO3)2.3H2 O to CuO.
The purpose of this work is to use the experimental data [1] and the theoretical concepts
following from the gasification mechanism of thermal decomposition [2] as a basis for understanding the appearance in the gas phase of Cu-containing molecules, and for refining the
general scheme of thermal decomposition of hydrated copper nitrate.
2. Results and discussion
2.1. Qualitative analysis of results
Figs. 1 and 2 present signal traces due to gaseous particles released from 12 p,g of Cu as
its hydrated nitrate salt, when heated on a graphite platform at a rate of 1 K s-~. The difference
between these two experiments is that in the first case the 12 Ixl volume of the salt solution
was dried in air at 340 K in 2 ixl portions for about 15 min, while in the second, it was maintained additionally in vacuo for 20 h at 300 K. This difference resulted in a change of the peak
positions and, what is most essential, in the disappearance in the second case of the additional
peak at 430 K. Its appearance in the first of our experiments (Fig. 1) could be due to melting
of Cu(NO3)2.3H20. The melting point of this nitrate is 387 K [9] to 391 K [7]. Melting of the
dry nitrate residue brings about a reduction of sample surface and, as a consequence, a
reduction in the flux of evaporating molecules. If the melting occurs concurrently with signal
growth, it manifests itself in the appearance of a second peak. The maximum of the first peak
in Fig. 1 lies at 405 K. The deviation by 15 K from the melting point in the vicinity of 400 K
is associated, as noted before [2[, with the temperature difference between the low conductivity
nitrate and the graphite platform. In the second experiment, the melting falls on the dropping
part of the OH + and NO~ peaks and reveals itself only in their slight inflections. Thus the first
two peaks in Fig. 1 (at 405 and 430 K) derive, most probably, from the same process.
Table 1 compares typical peaks in the DTA and EGA traces observed in Refs. [4,6,7,9] and
in our study. Despite the strong differences in experimental conditions, there is an overall
similarity in the position of the peaks. Just as with the nitrates of other elements (Ag, Cd and
Pb) [2], the release of volatile components (H20, NO2 and O2) in thermal decomposition of
the copper nitrate is accompanied by the appearance of the ionic species of the metal and its
compounds, namely, Cu ÷, CuO ÷, CuNO~ and Cu(NO3) ~ .
The intense sublimation of anhydrous Cu(NO3)2 in vacuo was observed by Addison and
Hathaway [12] in the late 1950s. The saturated vapor pressure of Cu(NO3) 2 w a s found to vary
from 42 Pa at 430 K to 470 Pa at 496 K. Above 499 K the stability of C u ( N O 3 ) 2 drops dramatically. In this connection, the presence of fairly large amounts of gaseous Cu(NO3)2 molecules
in all stages of the thermal decomposition below 500 K is in no way surprising.
The other Cu-containing ions (Cu ÷, CuO ÷ and CuNO~) are produced primarily by ionization
of C u ( N O 3 ) 2 molecules by the 70 eV electrons. This is supported by the peaks of all Cucontaining ions and NO~ peaks being similar, with the exception of the last peak, where the
C u ( N O 3 ) 2 molecules become unstable, and the CuO molecules form by the direct decompo-
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1461
105095(I-
(a)
A
o,
j/NO 2
850.
7511
651)
02
550
4511
35025015(I511-50
300
325
3;0
375
41;0
415
4~1
475
5(;0
5½5
5;0
5+5
60[I
Temperature, K
120-
(b)
Cu
95
7O
. CuO
.Cu(NO3)2
/CuNO3
20-
30t)
325
351}
375
41){)
425
4511
475
Temperature. K
Mass spectral signals for 12 i~g Cu as its hydrated nitrate salt heated on the graphite platform: (a) volatile and
non-volatile species.
F i g . 1.
(b)
sition of the basic nitrate Cu(NO3)2.3Cu(OH)2. Note that, as seen in Figs. 1 and 2, the CuO +
peak turns out to be substantially larger than the Cu(NO3)~ peak.
A qualitative analysis of the traces in Figs. 1 and 2 also reveals an essential difference in
signal trace pattern for the NO~ and OH + ions; namely, the strongest peaks due to NO~ and
Cu-containing ions near 460 K are accompanied by a fairly weak OH + peak.
Of particular interest is the appearance of a strong oxygen peak in the last stage of the
process (at 530 K) associated with the formation of CuO. It is remarkable, first of all, in that
the O~ peak clearly lags behind the peaks due to the OH + and NO~ ions (Figs. 1 and 2). This
suggests that it is of a different origin than the OH + and NO~ peaks. No less strange is the
earlier observation [1,2] of the appearance of oxygen in the course of decomposition of the
Cd and Pb nitrates when copper nitrate is added to the samples, and the absence of the O~
peak when the same nitrates are decomposed without Cu(NO3)2 present. An analysis of these
features has led us to the assumption that the 02 appears in the catalytic decomposition of
NO2 in the presence of CuO by the reaction
2NO2--*2NO + 02
(1)
that is thermodynamically favorable at 500 K.
This hypothesis accounts for many features of this phenomenon: (i) the delay of the O~
peak with respect to the NO~ and OH + peaks (Figs. 1 and 2), until CuO, acting as a catalyst
for process (1), has accumulated on the platform surface in sufficient amount; (ii) the appearance of the 02 peak in the thermal decomposition of the Cd and Pb nitrates in the presence
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1462
'iii
1
s.,o_]
(a)olJ
/~N02
~
[
650-
"7,
250150-
300
325
350"
375
4(~)
425
4S
475
'~l)O
525
~(
5hO
.........
525
550
575
600
575
601)
Temperature. K
120-
9~-
(b)
ItCu
70-
.1 CuO
45-
2(I-
_
300
i
ri
,
i
325
350
375
,RR)
:
~
425
i
4;0
475
Temperature. K
Fig. 2. The same as in Fig. 1. The dry sample was maintained additionally for 20 h in vacuo at 300 K.
Table 1
Peaks on the DTA and EGA curves for the decomposition of Cu(NO3)2.3H20
Authors
Method
Peak temperature/K
I
I1
III
5 g 100 mesh sample, 15 K min -~
425
490
583
2 g powder sample, 4 K min -]
180 mg finely powdered sample,
15 K min -]
10 mg single crystal, 1 K min ]
389
409
472
473
536/549
583
367/430
458
EGA (vac)
10 mg single crystal, 1 K min -z
370
456
EGA (vac)
EGA (vac)
46 t~g sample, 60 K min -~
46 p,g sample, maintained 20 h in
vacuo at 300 K, 60 K min -~
405/430
388
478
440
Not
observed
Not
observed
520/533
528
Gordon and Campbell DTA (air)
(1955) [4]
Sirina et al. (1970) [6] DTA (air)
(/hose and Kanungo
DTA (air)
(1981) [7]
Taylor et al. (1986) [9] DTA (vac)
This work
Experimental conditions
(sample, heating rate)
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1463
of copper nitrate [1,2] which decomposes to CuO before the nitrates of Cd and Pb; (iii) the
absence of the O~ peak if the Cu nitrate and the Cd and Pb nitrates on the platform are spatially
separated; (iv) the change in the ratio of the NO~ and NO + signals toward a relative growth
of the latter (this point will be considered in more detail below).
2.2. Quantitative analysis of results
2.2.1. Procedure for calculation of gaseous-product composition
To make the interpretation of the above observations more reliable and to reveal characteristic features of the thermal decomposition process, consider the results of the measurements
from the quantitative standpoint. We shall invoke the same procedure for transforming the
intensities li, or integrated intensities Qi, to fractions ni, of the corresponding particles, as the
one used before [2], taking into account the isotopic composition oq of the detected particles,
the ionization cross section cri, and a correction coefficient Bi, allowing for the partial decomposition of detected molecules in the course of their ionization by electrons
n~ -
ai
(2)
o/-i ~i o'i
In doing this, we shall, just as before [2], neglect the differences in the quadrupole transmission
coefficient %, and electron detector gain for ions differing in mass. This neglect was borne
out by the comparison of the results calculated by the two schemes, with and without taking
into account the "q coefficient, for a number of decomposition processes with a reliably predicted ratio of light and heavy gaseous particles [2]. This comparison has supported the validity
of the simplified scheme that disregards the ~i coefficient.
Table 2 lists the values of the a and cr parameters for the relevant particles, taken from the
literature [13-16]. The values of the ~ parameters for the Oz, NO2, and H20 molecules were
calculated based on intensity ratios of the ions produced in the ionization of the molecules by
70 eV electrons [17]
/ Ion + = 4.6
(3)
/NO+ / INO~= 2.6
(4)
Io~ / Io+ = 4.6
(5)
IH20+
/
Table 2
Parameters used in calculations of gaseous composition
Particle
a [13]
cr × 10~6/
cm 2
Ref.
63Cu
63CUO
0.692
0.692
0.308
0.308
1
1
1
1
1
1
1
1
3.80
5.26
9.63
15.45
1.33
2.79
2.89
2.91
4.37
1.46
2.92
2.13
[14]
[15]
[15]
[ 15]
[16]
[15]
[16]
[15]
[15]
[15]
[16]
[15]
65CUNO3
65Cu(NO3)2
H2
H20
N2
NO
NO2
O
02
OH
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1464
The calculation of 8 was done by taking into account the difference in the ionization cross
sections of the particles being compared, with the use of the obvious relation
na la O"b
-- =
nb
--
(6)
Ib O'a
The value of 8a was derived from the formula
8a -
na
-
1+
nb
=
1 + ~lb
O"a
(7)
na + nb
The intensity ratios (3)-(5) and the ~r parameters presented in Table 2 yield 802 = 0.82, 8OH
= 0.22 and 8NO2 = 0.20. The calculation of 8o2 took into account the two-fold difference in
oxygen content between the 02 and O particles.
2.2.2. Simulation of the 03 peak
Our quantitative analysis of the assumed process of catalytic decomposition of NO2 to NO
and 02 was based on one of the experiments with a tantalum platform (Fig. 3). Regrettably, the
NO + signal in the graphite-platform experiments presented in Figs. 1 and 2 was not measured.
We base the simulation of the O3 peak on the fact that the total signal intensity /No+ is
determined partially by the NO molecules produced in the ionizer in the dissociation of NO2,
and partially by those entering the ionizer as a result of catalytic decomposition of NO2 on
the platform surface. The intensity of the NO + signal governed by ionization of NO2 molecules
should be 2.6 INO~ (see Eq. 4)). The remainder of the signal/No ÷ - 2.6 Iso~, is due to the NO
molecules entering the ionizer from the platform surface. The ionization cross sections of the
NO and 02 molecules being equal, this contribution should be twice the lo3 signal, i.e.
Io~ ~
lNo+ -- 2.6 1NO~
2
(8)
The O~ peak calculated from this expression (see Fig. 3) is in agreement both in magnitude
and position with the experimentally observed O~ peak, thus supporting the hypothesis of NO2
decomposition to NO and 02. The slight difference between the O~- peak tails is due to a drift
of the NO + signal baseline.
2.2.3. Composition of gasified components
We turn now to calculating the composition of the gas phase in the course of thermal
decomposition of the hydrated copper nitrate. We are going to use the results of the two
3~(I(I
25O0
2OO0
o)
t/O~
~
1500~
/,
II ~
475
I
500
"
l
\
~25
l
~
02 calc
550
l
57g
Temperature. K
Fig. 3. Comparison of O~ peak observed in the stage of Cu(NO3)2.3Cu(OH)2 decomposition with the simulated peak
(dotted line) using Eq. (8). A tantalum platform was used, The temperature scale was reduced to that of the
graphite platform.
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1465
experiments displayed in Figs. 1 and 2. To reveal the mechanism involved in individual stages
of the process, we divided the temperature interval studied into several parts corresponding to
the assumed stages. The boundaries between the stages were set at the signal minima in Figs. 1
and 2.
To convert the integrated signal intensities to the relative amounts of particles corresponding
to these signals, we used the scheme given in Section 2.2.1. The results of these calculations
are listed in Tables 3 and 4. The last columns of Tables 3 and 4 contain the total amounts of
nitrogen £N, and of copper ~Cu, released in the individual stages of the process, together
with their ratio, ZCu/ZN. When summing up the nitrogen-containing particles in the last stage,
we took into account the partial decomposition of NO2 to NO and ½02 by adding twice the
amount of 02 to the sum of these particles. Thus we have in this case
~ N = n(NO2) + 2n(O2) + n(CuNO3) + 2n(Cu(NO3)2)
(9)
An analysis of the data listed in Tables 3 and 4 permits the following conclusions.
(i) The ratio of the total amount of released water to that of evolved nitrogen (~N) is 1.24
in the first experiment and 1.62 in the second, yielding an average of 1.4 + 0.2. The theoretical
ratio of these components in Cu(NO3)2-3H20 is 1.5. In view of the measurement errors and
our inadequate knowledge of the ~ parameters, the agreement appears to be fairly good. This
agreement supports once more the validity of calculation scheme which neglects the difference
in the -r parameters for ions with different masses when working on the QMA employed in
this and previous publications [1-3]. The inclusion of differences between the "r parameters
would raise this ratio from 1.4 to 2.2.
(ii) In the last stage of the process (at 530 K) involving thermal decomposition of the basic
copper nitrate to CuO, i.e. determined by the reaction
Cu(NO3)~.3Cu(OH)2 ---* 4CuO + 2NO2 + 3H20 + 0.5 02
(10)
there should evolve a quarter of the initial amount of NO2 and H20 present in the starting
salt, namely, 2NO2 and 3H20 molecules out of 8 and 12 of these molecules, respectively,
contained in four Cu(NO3)2.3H20 molecules. However, as follows from the data presented in
Tables 3 and 4, about one half of the total amount of NO2 and H20 is released at this stage.
This suggests that one or both preliminary thermal decomposition stages are far from being
completed. Superposition of thermal decomposition processes involving several compounds
precludes calculation of the kinetic parameters (activation energies and decomposition appearance temperature) as was done earlier [2] in the case of the anhydrous nitrates of Ag, Cd and
Pb. Apart from this, the required thermodynamic functions for a number of the reaction components are unavailable.
(iii) The ratio of the total amount of gasified copper ECu, to that of nitrogen ]£N, is about
3% in both experiments, which corresponds to 6% gasified copper with respect to the nitrate.
This value correlates with the estimate of copper losses in Ref. [3], and also with the results
of thermogravimetric studies [9], where the copper losses amounted to the same 6% and a
layer of CuO was observed on the walls of the vacuum vessel. The yield of Cu-containing
particles in the stage of basic nitrate decomposition is 10-20 times lower than that in the first
two stages. We explain this, on the one hand, by a low thermal stability of Cu(NO3) 2 molecules
above 500 K and, on the other, by the formation of a CuO shell around decomposed particles
of Cu(NO3)2.3Cu(OH) 2 which prevents other Cu-containing molecules (CuO and Cu20)
entering the gas phase.
(iv) The appearance of water below 100°C in the absence of any other particles is apparently
due to residual drying of the samples. When the sample drying time is increased (Table 4),
the amount of water evolved in this stage drops by nearly one order of magnitude.
(v) The relative fraction of NO2 decomposing to NO and 02 in the last stage of the process
is 0.43 + 0.2. This is in agreement with the hypothesis of the catalytic decomposition of NO2,
because only half of the NO2 molecules produced in a sample decomposition strike the CuOcovered surface of sample particles and platform.
(vi) Despite the apparent similarity between the positions of the first DTA peak (obtained
in air) and the first EGA peak (produced in vacuo), the relevant processes are different. In the
1466
B.V. L'vov, A.V. N o v i c h i k h i n / S p e c t r o c h i m i c a Acta Part B 50 (1995) 1 4 5 9 - 1 4 6 8
Z
Z
~q
Z
©
Z
Z
©
z
©
©
~Z
r~
©
Z
Z
Z
Z
Ca.
o
e-
+=
¢q
e0
:2
0
t~
¢q
I"~
t¢)
t¢~
.=,
0
Z
Z
Y..~.
r~
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
1467
first case, the endothermic peak is seen to appear at an almost constant mass [6,7], while in
the second, it is accompanied by losses of up to 30--50% water and 15-20% nitrogen (Tables
3 and 4). Similar losses were also observed to occur by Taylor et al. [9].
(vii) Because the ratio n('ZN)ln(EH20) in the last thermal decomposition stage is about 0.6
(Tables 3 and 4), it is difficult to agree with the conclusion of Taylor et al. [9] that in the
preliminary stage of the process a basic nitrate of the type 3Cu(NO3)z-Cu(OH)2 is formed,
where this ratio is six. On the contrary, the universally accepted formula of the basic nitrate,
Cu(NO3)2.3Cu(OH)2, is in good agreement with the ratio found here.
3. Conclusions
Thermal decomposition of C u ( N O 3 ) 2 " 3 H 2 0 in vacuo proceeds in three stages, their rate
maxima lying at about 400, 460 and 530 K. Regrettably, incomplete decomposition and partial
sublimation of Cu(NO3): do not permit a quantitative description of the stoichiometry of the
first two stages of the process and of the formula of the intermediate produced in the first
stage. Nevertheless, the results obtained give us grounds to maintain that stage I involves
mainly deaquation, and stage II mainly denitration of Cu(NO3)z.3H20. The basic nitrate formed
in the second stage of thermal decomposition is most probably Cu(NO3)2.3Cu(OH)>
The results of this study are in agreement with the gasification mechanism of thermal
decomposition and previous studies [2]. The gaseous molecules (Cu(NO3)2, H20, C u ( O H ) 2 and
CuO) colliding with the surface of adjacent reagent particles recombine to form more thermally
stable products, the low hydrated nitrate, basic nitrate or oxide. The layer of these products
thus formed inhibits gasification of the reagent and results in its incomplete decomposition.
If observed at low temperatures, the Cu +, CuO + and CuNO~ ions are produced in the dissociation of volatile Cu(NO3)2 molecules in the QMA ionizer. At high temperatures, CuO
molecules originate partly from direct thermal decomposition of the basic nitrate.
The molecular oxygen detected in the course of decomposition of Cu(NO3)2.3Cu(OH)2 is
produced in the catalytic decomposition of NO2 on the surface of CuO by the reaction
2NO2 ---, 2NO + O2. The chemical form of the oxygen directly evolved in stages II and IlI
in the process of sample decomposition remains unclear. This problem requires additional
measurements of other possible oxygen-containing particles, such as O, N205, or HNO3.
We note in conclusion that the results obtained in this investigation provide a basis for
interpretation of some features in the copper atomization process in graphite furnaces used in
atomic absorption spectrometry, in particular, of the difference in the so-called "release order"
observed in the atomization of Au and Cu [10,18]. The reason for copper being distributed in
the form of particles of the same size, irrespective of original sample mass, i.e. of the firstorder release, could be the three-stage decomposition and, accordingly, triple redistribution of
the original sample (hydrated copper nitrate) over the surface, in contrast to the one-stage
decomposition of the gold nitrate. Other metals forming hydrated nitrates (Co, Ni, Cr, etc.)
should reveal the same feature.
Acknowledgments
This research was supported in part by the USA National Science Foundation through grant
No. CHE9020591. The authors thank Professor James Holcombe for the opportunity of collaboration in this project and the possibility for one of the authors (A.V.N.) to work in his laboratory at the University of Texas at Austin, TX, during 4 months. The authors also thank Dr.
Leonid Polzik for comments on the draft of this manuscript.
References
[1] J. Jackson, A.V. Novichikhin, R.W. Fonseca and J.A. Holcombe, Spectromchim. Acta Part B, 50 (1995) 1423.
[2] B.V. L'vov and A.V. Novichikhin, Spectrochim. Acta Part B, 50 (1995) 1427.
1468
[3]
[4]
[5[
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
B.V. L'vov, A.V. Novichikhin/Spectrochimica Acta Part B 50 (1995) 1459-1468
J. Jackson, R.W. Fonseca and J.A, Holcombe, Spectrochim. Acta Part B, 50 (1995) 1449.
S. Gordon and C. Campbell, Anal. Chem., 27 (1955) 1102.
P.N. Palei, I.G. Sentyurin and I.S. Sklyareno, Zh. Anal. Khim., 12 (1957) 318.
A.M. Sirina, I.I. Kalinichenko and A.I. Purtov, Russian J, Inorg. Chem., 15 (9) (1970) 1258.
J. Ghose and A. Kanungo, J. Therm. Anal., 20 (1981) 459.
J. Mu and D.D. Perlmutter, Thermochim. Acta, 56 (1982) 253.
T.J. Taylor, D. Dollimore and G.A. Gamlen, Thermochim. Acta, 103 (1986) 333.
P. Wang, V. Majidi and J.A. Holcombe, Anal. Chem., 61 (1989) 2652.
W.M. Keeley and H.W. Maynor, J. Chem. Eng. Data, 8 (1963) 297.
C.C. Addison and B.J. Hathaway, J. Am. Chem. Soc., 80 (1958) 3099.
Quantities, Units and Symbols in Physical Chemistry, Blackwell Scientific, Oxford, 1988.
J.B. Mann, in Proc. Int. Conf. on Mass Spectroscopy, Kyoto University Press, Tokyo, 1970, p. 814.
J.W. Otvos and D.P. Stevenson, J. Am. Chem. Soc., 78 (1956) 546.
E. Bmer and C.D. Bartky, J. Chem. Phys., (1965) 2466.
F.W. McLafferty and D.B. Stauffer, The Wiley/NBS Registry of Mass Spectral Data, Vol. 1, Wiley, New York,
1988, p. 3.
[18] J. McNally and J.A. Holcombe, Anal. Chem., 59 (1987) 1105.