Detection of autocatalytic decomposition behavior of energetic materials using APTAC

Article abstract of DOI:10.1007/s10973-005-6982-3

Characterization of autocatalytic decomposition reactions is important for the safe handling and storage of energetic materials. Isothermal differential scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition of energetic materials. However, isothermal DSC tests are time consuming and the choice of experimental temperature is crucial. This paper shows that an automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient screening tool for the identification of autocatalytic decomposition behavior of energetic materials. Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine family. High concentrations of HAN are used as liquid propellants, and low concentrations of HAN are used primarily in the nuclear industry for decontamination of equipment. Because of its instability and autocatalytic decomposition behavior, HAN has been involved in several incidents. This paper presents calorimetric measurements for the thermal decomposition of 24 mass% HAN/water. APTAC heat-wait-search and heat-soak-search modes are used to characterize the thermal decomposition of HAN. By comparing the kinetic analysis for the two modes, it is concluded that HAN shows strong autocatalytic decomposition behavior. The most likely decomposition pathway of HAN is proposed to explain the observed autocatalytic behavior.

Full text of DOI:10.1007/s10973-005-6982-3

Journal of Thermal Analysis and Calorimetry, Vol. 83 (2006) 1, 125–130
DETECTION OF AUTOCATALYTIC DECOMPOSITION BEHAVIOR OF
ENERGETIC MATERIALS USING APTAC
*
C. Wei, W. J. Rogers and M. S. Mannan
Mary Kay O’Connor Process Safety Center, Department of Chemical Engineering, Texas A&M University, College Station
TX 77843-3574, USA
Characterization of autocatalytic decomposition reactions is important for the safe handling and storage of energetic materials. Iso-
thermal differential scanning calorimetry (DSC) has been widely used to detect autocatalytic decomposition of energetic materials.
However, isothermal DSC tests are time consuming and the choice of experimental temperature is crucial. This paper shows that an
automatic pressure tracking calorimeter (APTAC) can be a reliable and efficient screening tool for the identification of autocatalytic
decomposition behavior of energetic materials.
Hydroxylamine nitrate (HAN) is an important member of the hydroxylamine family. High concentrations of HAN are used as
liquid propellants, and low concentrations of HAN are used primarily in the nuclear industry for decontamination of equipment. Be-
cause of its instability and autocatalytic decomposition behavior, HAN has been involved in several incidents.
This paper presents calorimetric measurements for the thermal decomposition of 24 mass% HAN/water. APTAC
heat–wait–search and heat–soak–search modes are used to characterize the thermal decomposition of HAN. By comparing the ki-
netic analysis for the two modes, it is concluded that HAN shows strong autocatalytic decomposition behavior. The most likely de-
composition pathway of HAN is proposed to explain the observed autocatalytic behavior.
Keywords: APTAC, autocatalytic reactions, energetic materials, hydroxylamine nitrate
Introduction
studied the autocatalytic decomposition phenomenon
and kinetic models using isothermal DSC data. A
screening method based on dynamic DSC measurement
was developed to identify autocatalytic decomposition
by Bou-Diab and Fierz [4]. According to this method,
the decomposition is autocatalytic if the apparent activa-
tion energy calculated by a first order kinetic model is
higher than 220 kJ mol–1. Under adiabatic conditions,
Hydroxylamine nitrate (NH2OH·HNO3) is commer-
cially available in clear and colorless water solutions,
and it has been used primarily as a reductant in nuclear
material processing and for decontamination of equip-
ment. The U.S. Army has also explored the use of high
concentrations of HAN as an oxidizer in a liquid propel-
lant mixture. Due to its chemical properties, HAN has
been involved in many incidents. On 14 May, 1997, an
explosion occurred in the Chemical Preparation Room
of the Plutonium Reclamation Facility at Hanford’s Plu-
tonium Finishing Plant. Thereafter, the U.S. Department
of Energy investigated the incident and prepared a tech-
nical report on HAN/nitric acid mixture properties [1].
This report describes the autocatalytic decomposition
behavior of HAN/nitric acid mixture and the effects of
metal ions on the thermal decomposition in which the
onset temperature of the autocatalytic reaction decreases
with the increase of nitric acid to HAN ratio. In this pa-
per, the autocatalytic decomposition of HAN without
nitric acid is analyzed.
th
the temperature vs. time curves for n order reactions
th
and autocatalytic reactions are different. For n order re-
actions, the temperature increase starts immediately af-
ter the onset temperature, while for autocatalytic reac-
tions, the temperature increase is relatively small during
the induction period and then suddenly grows rapidly.
This paper presents the study of autocatalytic decompo-
sition
using
APTAC
heat–wait–search
and
heat–soak–search modes. The objective of this study is
to explore the potential of adiabatic calorimeters to iden-
tify autocatalytic decomposition of energetic materials.
Experimental
An autocatalytic reaction is a chemical reaction in
which a product (or a reaction intermediate) acts as a
catalyst [2], and the observed reaction rate is found to
increase with time. This property poses a challenge for
the prolonged storage of chemicals that can undergo
autocatalytic decomposition. Chervin and Bodman [3]
Sample
Hydroxylamine nitrate (24 mass% in water solution,
Aldrich catalog number 438235) was used without
further purification and analysis.
*
Author for correspondence: mannan@tamu.edu
1388–6150/$20.00
© 2006 Akadémiai Kiadó, Budapest
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands

WEI et al.
Automatic pressure tracking adiabatic calorimeter
(APTAC)
of the shutdown criteria was met. If no exotherm was
detected, the apparatus heated the sample to the next
search temperature and the steps repeated until one of
the shutdown criteria was met. The onset temperature
is defined as the temperature when an exotherm is de-
tected and it is usually the lowest temperature at which
the sample self-heat rate surpasses the preset threshold
(0.05°C min–1) in the ‘search’ or ‘adiabatic’ mode.
The APTAC heat–soak–search mode was also
used: the sample was heated to a certain soak tempera-
ture and held adiabatically. Every sixty minutes or if the
sample temperature rose 1°C above the soak tempera-
ture, the self-heating rate would be polled and compared
with a pre-defined sensitivity threshold. If the self-heat-
ing rate exceeded the threshold, a runaway reaction was
detected and the sample was kept adiabatically. If the
self-heating rate was less than the threshold, the sample
would be cooled back to the soak temperature. The steps
continued for a defined period. If it failed to detect
self-heat at the end of soak period, the system would
proceed with a standard heat–wait–search mode. The
HSS method is generally used to test the effectiveness of
inhibitors added to the reactants. In this study, the HSS
method was employed to study the effect of auto-
catalysis on the decomposition of the reactive system.
The autocatalysis would be generated during the soak
period and thus allowed the reactants to eventually run-
away in an adiabatic system when its concentration
reached a certain level. Appropriate soak time and tem-
perature should be chosen based on the knowledge of
the reactive system.
Adiabatic calorimetry has proven to be an extremely
useful tool to assess thermal hazards of reactive chemi-
cals. It can minimize heat losses by maintaining the tem-
perature of the sample surroundings as close as possible
to the temperature of the sample. The APTAC calorime-
ter can be operated in a variety of test modes, such as
heat–wait–search, heat ramps, and isothermal aging
with temperatures up to 500°C and pressures ranging
from vacuum to 13.8 MPa. It can track exotherms at
heat generation rates from 0.04 to 400°C min–1. It can
produce low thermal inertia data, because it utilizes the
DIERS pressure compensating technique in which the
pressure outside the sample cell is controlled to match
the pressure inside the sample cell. For the present work,
HAN measurements were conducted in glass sample
cells of nominal 100 cm3, which can provide a neutral
environment for the reactions, and also in titanium and
stainless steel sample cells of nominal 130 and 50 cm3,
respectively, to test the effect of metals on the thermal
decomposition. Teflon coated thermocouples were used
to prevent the contact of hydroxylamine solution with
thermal transmitter metals.
APTAC cannot directly measure heat of reaction,
but the system of sample and sample cell was kept
nearly adiabatic during runaway reaction. Therefore,
part of the reaction heat was adsorbed by the sample
cell, and the remainder was used to increase the temper-
ature of the sample and vaporize volatile materials. The
fact that sample heat capacity changes with temperature,
composition, and phase changes makes it even more dif-
ficult to estimate the heat of the reaction from the exper-
imental data. The liquid heat capacity of hydroxylamine
nitrate is missing in the literature. Because water was the
solvent and a major product in this experiment, the heat
capacity of liquid water (4.18 J g–1 °C–1) was used to es-
timate the thermal inertia (φ=(MsCs+MbCb)/MsCs, where
M is the mass, C is the heat capacity and subscripts b
and s refer to the sample bomb and the sample, respec-
tively). A detailed description of the APTAC can be
found in the reference [5].
A summary of APTAC test setup conditions is
presented in Table 1. For the sample cell, the maxi-
mum allowable pressure imbalance is 1034 kPa. Due
to the extremely rapid exothermic reactivity of hydro-
xylamine nitrate solution, it is difficult for the APTAC
to track pressure rise fast enough, and the pressure im-
balance was above 690 kPa even when small samples
(about 4 g) were used in these tests. Stirring was not
necessary because only small amounts of sample were
used. To prevent undesired contaminations, the tubing
lines between the sample cell and transducers and also
the tubing leading to the on/off valve that closes the
sample cell during tests were flushed with acetone fol-
lowing every experiment. The tubing was dried by
flushing with compressed nitrogen.
Methods
The APTAC heat–wait–search mode was used: the
sample was heated at 2°C min–1 to a starting tempera-
ture, and the temperature was allowed to stabilize for
25 min, following which the APTAC searched for
exothermic behavior. During the search period of
25 min, the temperature of the containment vessel gas
was adjusted to match that of the sample. If the
self-heat rate of the sample was greater than a preset
threshold (0.05°C min–1), the apparatus tracked the
reaction adiabatically until the reaction ended or one
Results and discussion
Heat–wait–search (HWS) result
The HWS mode was employed to determine the over-
all decomposition behavior of hydroxylamine nitrate,
such as onset temperature (T0), maximum temperature
(Tmax), maximum pressure (Pmax), self-heating rate at
126
J. Therm. Anal. Cal., 83, 2006

AUTOCATALYTIC DECOMPOSITION BEHAVIOR OF ENERGETIC MATERIALS
Table 1 Summary of the APTAC experimental setup conditions
Thermocouple
Heat mode
Teflon coated
H–W–S/H–S–S
Start temperature/°C
Limit temperature/°C
Temperature increment/°C
Cool down temperature/°C
Exotherm threshold/°C
Heat rate/°C min–1
Stirring
50/150
180
10
Minimum pressure/kPa
Over pressure/kPa
Lower band/kPa
Upper band/kPa
138
7
–69
69
50
0.05
2
Exotherm limit/°C
Soak time/min
300
1440
NO
NO
NO
Venting
Injection
Shut down criteria
Temperature level/°C
Heat rate/°C min–1
Pressure imbalance/kPa
300
400
Pressure level/kPa
8274
Pressure rate/kPa min–1
13790
1034
Table 2 APTAC HWS results of the thermal decomposition of hydroxylamine nitrate
HAN
4.2 g
T0/
°C
Tmax
°C
/
Pmax
/
dT/dt0/
dT/dtmax
/
dP/dtmax
/
Non-condensable/ Phi factor, ΔHrxn
/
kPa
°C min–1 °C min–1 kPa min–1
kPa 50°C
φ
kJ mol–1
Glass cell 171.3±0.2 196.1±0.7 2041±34 0.07±0.01 416±20 1200±386
283±7
179±14
379±7
3.3
2.0
3.6
–138±4
–96±13
–180±8
Ti cell
150.1±3.1 178.5±0.9 1338±21 0.06±0.01 279±50
193±48
SS cell
139.2±3.2 168.9±1.7 1565±62 0.06±0 179±53 2027±372
the onset temperature (dT/dt0), maximum self-heating
rate (dT/dtmax), heat of reaction (ΔHrxn), and non-con-
densable product pressure at 50°C. The experimental
results using glass, titanium, and stainless steel sample
cells are presented in Table 2 and Figs 1 and 2. The ef-
fect of sample cell material on onset temperatures
shows that a glass cell can provide a neutral environ-
ment, and metals such as titanium and stainless steel
can catalyze the decomposition of hydroxylamine ni-
trate. Compared with glass, titanium initiates the de-
composition at a lower temperature, but less heat is
evolved from the reaction, while stainless steel can
cause 30% more heat release from the decomposition.
The decomposition curve of hydroxylamine ni-
trate is compared with that of 50 mass% hydro-
xylamine/water in Fig. 3. Hydroxylamine nitrate de-
composition starts at 170°C and the temperature in-
creases slowly until 180°C at which point suddenly
the temperature increases very rapidly to the maxi-
mum temperature of 196°C. The temperature curve of
hydroxylamine nitrate appears to be two stages: a
slow initiation stage followed by a fast explosion
stage. These two stages form a sharp corner as empha-
sized by the circle in Fig. 3. On the contrary, for the
decomposition of hydroxylamine, the temperature in-
crease starts immediately after the onset temperature
and smoothly curves up to the maximum temperature.
Previous studies showed that hydroxylamine decom-
position was a 1st order reaction with apparent activa-
tion energy of 121 kJ mol–1 [6]. From comparison of
the decomposition temperature curves, it can be con-
cluded that hydroxylamine nitrate decomposition is an
autocatalytic reaction. Initially the decomposition
shows only little heat release and therefore the temper-
ature increase is slow. After an induction period, the
concentration of the autocatalyst reaches a threshold
level and the reaction rate becomes very rapid.
Fig. 1 Temperature vs. time profiles for HAN decomposition in
1 – glass, 2 – titanium and 3 – stainless steel sample cells
Fig. 2 Pressure vs. time profiles for HAN decomposition: in
1 – glass, 2 – titanium and 3 – stainless steel sample cells
J. Therm. Anal. Cal., 83, 2006
127

WEI et al.
Fig. 4 HSS experimental results of hydroxylamine nitrate in a
glass sample cell; 1 – temperature, 2 – pressure
Fig. 3 Comparison of decomposition curve of hydroxylamine
nitrate with hydroxylamine; 1 – HA, 2 – HAN
Heat–soak–search (HSS) result
In order to test the aging effect on the thermal decom-
position of hydroxylamine nitrate, the HSS method
was employed. The experimental results using glass, ti-
tanium, and stainless steel sample cells are presented in
Table 3 and Figs 4–6. The soak temperatures were cho-
sen as 20 degree lower than onset temperatures of the
HWS results, and the soak period was 24 h. During the
soak and search periods, although temperature is al-
most constant, the pressure increase is detected be-
cause the decomposition is undergoing with a low
self-heat rate. In the titanium cell, a fast explosion oc-
curred at the end of soak period of 24 h. In the glass
and stainless steel cells, significant self-heat rates were
not detected during the soak period, so the apparatus
proceeded with the HWS mode. The detected onset
temperatures are lower than the ones of the HWS mode
alone. Besides the onset temperatures, the maximum
self-heat rates and maximum pressure rates were also
lower in Table 3 than the ones in Table 2. During the
soak and search periods, the initiation reaction starts
and autocatalyst is generated. If the self-heat rate is not
sufficient, the temperature will be cooled down to the
soak temperature. Therefore, some heat loss occurred
during the soak period, and the estimated heats of reac-
tion were reduced significantly in the HSS mode.
Fig. 5 HSS experimental results of hydroxylamine nitrate in a
titanium sample cell; 1 – temperature, 2 – pressure
Fig. 6 HSS experimental results of hydroxylamine nitrate in a
stainless steel sample cell; 1 – temperature, 2 – pressure
cause a significant amount of autocatalyst is accumu-
lated during the soaking period of 24 h.
Kinetic analysis
In this study, assuming that the decomposition follows
th
an n order reaction, the activation energies of the ther-
mal decomposition of hydroxylamine nitrate were cal-
culated from a pseudo zero-order rate constant, k*, us-
ing the method developed by Townsend and Tou [7].
The Arrhenius parameters can be estimated from the
straight lines fitting to lnk* vs. 1000/T curves. The
plots of lnk* vs. 1000/T with a reaction order of 0.1 are
given in Fig. 8. The self-heat rate of hydroxylamine ni-
trate decomposition increases very rapidly with tem-
perature, therefore the straight lines in Fig. 8 have
The self-heat rates of the HWS and HSS modes
are compared in Fig. 7. The peaks correspond to the
fast explosion, and the corresponding self-heat rate
points seem like straight lines because the reaction is
very fast. The temperature corresponding to the maxi-
mum self-heat rate is 15 degree lower in the HSS
mode than that in the HWS mode. The fast explosion
can occur at a significantly lower temperature be-
Table 3 APTAC HSS results of the thermal decomposition of hydroxylamine nitrate
Non-
ΔHrxn
/
Soak T/
T0/
°C
Tmax
°C
/
Pmax
/
dT/dt0/
dT/dtmax
/
dP/dtmax
/
Phi
HAN
4.2g
condensable
kPa (50°C)
kJ mol–1
°C
kPa
°C min–1 °C min–1 kPa min–1
factor, φ
Glass cell
Ti cell
150
150
120
165.4±5.3 183.9±4.7 1606±124 0.07±0.03 344±18 765±214
283±7
165±7
365±7
3.3
2.0
3.6
–172±7
–42±13
–75±17
131.2±1.1 143.2±4.7 710±83 0.05±0.02 128±51
127.3±2.1 140.2±4.8 945±76 0.07±0.02 139±39
83±28
41±14
SS cell
128
J. Therm. Anal. Cal., 83, 2006

AUTOCATALYTIC DECOMPOSITION BEHAVIOR OF ENERGETIC MATERIALS
th
autocatalytic reaction and an n order reaction using
activation energies, more experimental data sets are
necessary.
Autocatalytic decomposition mechanism
Thermal decomposition products of hydroxylamine
nitrate were analyzed to be nitric acid, water, and gas
products (83% nitrous oxide, 17% nitrogen), and two
overall Eqs (1), (2) of equal importance were pro-
posed [9]. The decomposition pathway was also stud-
ied by a few groups [9, 10]. Based on information
from the literature and quantum mechanical calcula-
tions using Gaussian 03 [11], a detailed decomposi-
tion mechanism is represented by a digraph in Fig. 9.
Hydroxylamine nitrate is in equilibrium with nitric
acid and hydroxylamine. The dissociated hydroxy-
lamine reacts with nitric acid, producing nitrous acid,
nitroxyl (HNO), and water most likely via an interme-
diate N-hydroxyl hydroxylamine (H3NO2). The inter-
mediate nitrous acid is scavenged by hydroxylamine
also via the intermediate H3NO2, producing nitroxyl
and water. Nitroxyl can be either dimerized into ni-
trous oxide or scavenged by nitric acid to form nitrous
acid, an important intermediate that causes the auto-
catalytic decomposition of hydroxylamine nitrate. A
small amount of nitrogen is most likely due to interac-
tion between nitroxyl and hydroxylamine.
Fig. 7 Comparison of 1 – HWS and 2 – HSS experimental re-
sults of hydroxylamine nitrate in a glass cell
Fig. 8 Comparison of 1 – HWS and 2 – HSS kinetic analysis
of hydroxylamine nitrate decomposition in a glass cell
3HONH+ NO– ⇒N2O+N2+2HNO3+5H2O (1)
3
3
4HONH+ NO– ⇒3N2O+2HNO3+7H2O
(2)
3
3
Conclusions
Fig. 9 Detailed mechanism of hydroxylamine nitrate de-
composition. Species – final products; spe-
The thermal decomposition of 24 mass% hydroxy-
lamine nitrate/water was analyzed using the APTAC.
From heat–wait–search and heat–soak–search modes
experimental results, the decomposition shows strong
autocatalytic behavior. Adiabatic calorimeter is also a
promising technique to detect autocatalytic reaction.
The temperature curve of autocatalytic reaction
shows two stages: a slow initiation stage and a fast ex-
plosion stage. The explosion stage occurs very sud-
denly and quickly. By comparing HWS and HSS ex-
perimental results, the explosion stage can start at a
much lower temperature after a certain aging period.
From the kinetic analysis results, the apparent activa-
tion energy of an autocatalytic decomposition will be
cies – autocatalyst; HAN – hydroxylamine nitrate;
HA – hydroxylamine; — – dominant steps,
---
– less dominant steps
steep slopes and correspondingly very high values of
activation energies. The two straight lines obtained
from the HWS and HSS experimental results are al-
most parallel, and corresponding activation energies
are about the same value of 585 kJ mol–1. At low tem-
peratures, the rate constants of the HSS mode are
higher than those of the HWS mode because auto-
catalyst has accumulated during the HSS mode.
Compared with other members of the hydroxy-
lamine family [8], hydroxylamine nitrate has a large
activation energy. Therefore, a very high activation en-
th
very large if an n order kinetic model is used to fit
the adiabatic calorimetric data.
A plausible decomposition mechanism for hydroxy-
lamine nitrate was proposed. Nitrous acid was found to
be the intermediate that caused the autocatalytic behavior.
In order to temper the autocatalytic reaction, the concen-
th
ergy obtained by fitting n order rate constant can be
an information cue of autocatalytic behavior. How-
ever, in order to determine a boundary between an
J. Therm. Anal. Cal., 83, 2006
129

WEI et al.
NH2O2⇒NO+H2O
NH2O+NO⇒2HNO
HNO2+NH2OH H3NO2+HNO
–102.8
86.5
tration of nitrous acid should be limited. Since nitrous
acid was proposed to be generated from nitric acid, inad-
vertent addition of nitric acid to HAN may cause poten-
tial explosions. One way to control the concentration of
nitrous acid was to use hydrazine (N2H2) [1], because it
reacts faster with nitrous acid than HAN. However,
hydrazine possesses hazardous properties and has poten-
tial for explosive formations. To handle HAN safely, low
concentrations of HAN may be used, and contamination
needs to must be avoided.
138.7
–351.9
18.0
2HNO N2O+H2O
HNO+NH2OH 2NH2O
2NH2O N2+2H2O
–487.0
References
1 Technical Report on Hydroxylamine Nitrate, in US De-
partment of Energy, February 1998.
2 Compendium of Chemical Terminology, Ed. A. Wilkinson,
Vol. 2nd Edition, 1997, Blackwell Scientific Publications:
Oxford.
Acknowledgements
This research was supported by the Mary Kay O’Connor Pro-
cess Safety Center at Texas A&M University. We would like
to thank the Supercomputing Facility at Texas A&M Univer-
sity for computer time and the Laboratory for Molecular Sim-
ulation (LMS) at Texas A&M University for software and
support. A discussion with Dr. Marc E. Levin from Shell
Global Solutions was very helpful.
3 S. Chervin and G. T. Bodman, Thermochim. Acta,
392–393 (2002) 371.
4 L. Bou-Diab and H. Fierz, J. Hazard. Mater., 93 (2002) 137.
5 S. Chippett, P. Ralbovsky and R. Granville, The APTAC:
a high pressure, low thermal inertia, adiabatic calorimeter,
in International Symposium on Runaway Reactions, Pres-
sure Relief Design, and Effluent Handling, 1998, New Or-
leans: American Institute of Chemical Engineers.
6 L. O. Cisneros, W. J. Rogers and M. S. Mannan,
J. Hazard. Mater., 95 (2002) 13.
List of abbreviations
7 D. I. Townsend and J. C. Tou, Thermochim. Acta,
37 (1980) 1.
T0
Onset temperature at which exothermic
decomposition is first detected /°C
8 L. O. Cisneros, W. J. Rogers and M. S. Mannan,
Thermochim. Acta, 414 (2004) 177.
Tmax
Pmax
Max. temperature due to decomposition /°C
9 J. C. Oxley and K. R. Brower, Proceedings of SPIE-The In-
ternational Society for Optical Engineering, 872 (1988) 63.
10 J. W. Schoppelrei and T. B. Brill, J. Phys. Chem. A,
101 (1997) 8593.
Max. pressure generated due to decomposition /kPa
dT/dt0 Self-heating rate at onset temperature /°C min–1
dT/dtmax Max. self-heating rate /°C min–1
ΔHrxn
Heat of reaction /kJ mol–1
11 Gaussian 03, Revision B.04, M. J. Frisch, G. W. Trucks,
H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman,
J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant,
J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox,
H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala,
K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain,
O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and
J. A. Pople, Gaussian, Inc., Pittsburgh PA, 2003.
Appendix
The likely reaction pathways are listed below. The enthalpy of
each molecule was calculated using Gaussian 03 at the
B3LYP/cc-PVDZ level of theory. The heats of reaction were
calculated as ΔHrxn=ΣΔHproducts–ΣΔHreactants. The thermody-
namically favored pathways are listed in bold.
Reaction schemes
ΔHrxn/kJ mol–1
74.0
NH2OH·HNO3 NH2OH+HNO3
NH2OH+HNO3 H3NO2+HNO2
H3NO2 H2O+HNO
10.0
–13.0
NH2OH+HNO3⇒N2H2O3+H2O
NH2OH+HNO3⇒HNO2+HNO
NH2OH+HNO3⇒NH2O+H2NO3
43.9
–46.8
148.4
NH2O+H2NO3⇒HNO+HNO2+H2O –151.3
HNO+HNO3 HNO2+HNO2
NH2OH+HNO3⇒NH2O+NO2+H2O
NH2O+NO2⇒HNO2+HNO
HNO2+NH2OH⇒NH2O2+NH2O
NH2O2+NH2O⇒2HNO+H2O
–128.7
28.8
–31.7
142.1
–16.3
DOI: 10.1007/s10973-005-6982-3
130
J. Therm. Anal. Cal., 83, 2006