| dc.description.abstract | The investigations described in this thesis have been
aimed at contributing to the understanding of the thermal
decomposition characteristics of some of the substituted
ammonium and phosphonium perchlorates. The importance of
such a study arises from the extensive applicabilities of
the high?energy compounds of nitrogen and phosphorus in
propellants, pyrotechnics and/or explosives for various civil
and military purposes. Ammonium perchlorate is the oxidizer
of choice in solid rocket propellants and mainly because of
this reason, its thermal decomposition studies have been
carried out in detail. The study of the thermal properties
of the substituted ammonium perchlorates, some of which have
been tried as auxiliary oxidizers, has, however, not been
paid due attention and hence methyl?substituted ammonium
perchlorates were chosen for thermal studies carried out
in the present investigation. Ammonium perchlorate, NH?ClO?,
is relatively stable at ordinary conditions whereas its
immediate analogue phosphonium perchlorate, PH?ClO? (nitrogen
and phosphorus being in the same group of the periodic table
of elements) is extremely unstable and explodes violently
in the dry state. Substituted phosphonium perchlorates
are, however, stable at ordinary conditions. The thermal
decomposition studies of none of these phosphonium
perchlorates have been reported so far. It was, therefore,
interesting to synthesise and study the thermal behaviour
of some of these compounds and compare their thermal
properties with those of the corresponding substituted
ammonium perchlorates.
The work presented in this thesis is divided into seven
chapters. Chapter 1 is an introduction to the present
work. This incorporates an account of the importance and
properties of perchlorates in general, the various aspects
of thermal decomposition and explosion of solids and liquids/
melts and the decomposition characteristics of a few typical
non?metallic oxy?salts. In addition, the scope of the
present investigation is outlined.
Chapter 2 deals with the various experimental techniques
and analytical methods employed in the present study. The
chief techniques are differential thermal analysis (DTA),
thermogravimetric analysis (TGA), mass spectrometry and
explosion delay measurements. The methods of chemical
analysis and spectroscopic techniques such as nuclear
magnetic resonance (NMR) and infrared (IR) spectroscopy
which have been used for characterizing the compounds
prepared during the present investigation are briefly outlined.
Chapter 3 describes the studies on the thermal
decomposition and explosion sensitiveness of mono?, di? and
tri?methylammonium perchlorates. A new feature in the DTA
trace of monomethylammonium perchlorate, viz., another
exotherm beyond the one due to the decomposition of the
compound, has been observed. This has been attributed to the
decomposition of ammonium perchlorate formed as a decomposition
product of monomethylammonium perchlorate. The
possible reactions that can lead to the formation of
ammonium perchlorate as a result of the decomposition of
monomethylammonium perchlorate have been discussed. In
addition, the relative thermal stability of mono?, di? and
tri?methylammonium perchlorates has been studied by various
techniques. Decomposition temperatures as observed from
DTA and TGA, the values of activation energy for decomposition
and explosion and the results of the mass?spectrometric
analysis of the gaseous decomposition products have been
discussed in terms of the relative thermal stability of
these compounds. The observations have been explained
essentially in terms of decomposition via a dissociation
step. An attempt has been made to correlate thermal
decomposition with explosion.
The study of the thermal behaviour of tetramethylammonium
and phosphonium perchlorates is presented in
Chapter 4. A decomposition process via a primary
dissociation step, involving a methyl?group transfer from
the cation to the anion, has been proposed. Evidence for
such a proposition comes from the results of some decomposition
experiments at low pressures and by mass?spectrometric
analysis of the gaseous decomposition products. Results
of the investigations on the kinetics of thermal decomposition
of these compounds are also included in this chapter.
Chapter 5 is devoted to a comparative study of the
thermal decomposition characteristics of tetramethylammonium
and ?phosphonium perchlorates, nitrates and picrates. This
study sheds light on the decomposition mechanism of these
quaternary onium salts. The explosion sensitiveness of
these compounds is also presented in this chapter. The
relative thermal stability of the tetramethylammonium
and phosphonium compounds is in the order, perchlorate >
nitrate > picrate. The ammonium compounds are found to be
more stable than the corresponding phosphonium compounds.
The observations have been explained in terms of a dissociation
step involving a methyl?group transfer in the
decomposition of these compounds.
Chapter 6 is concerned with the thermal characterization
of some triphenyl?substituted phosphonium perchlorates where
the fourth substituent is –H, –CH?, –n?C?H? or –NH? group.
The relative thermal stabilities of the alkyl?substituted
triphenylphosphonium perchlorates have been determined by
DTA, TGA and explosion delay measurements. The results of
the residual analysis of the decomposition products and
other data presented in this chapter support the primary
step of decomposition proposed in Chapter 4.
From the point of view of the use of ammonium
perchlorate (AP) as an oxidizer in solid rocket propellants,
it may be of interest to see if some of these substituted
onium compounds studied during the present investigation,
when doped into or mixed with AP crystals, modify its
thermal decomposition characteristics. The effects on the
thermal behaviour of AP using tetramethylammonium and
?phosphonium perchlorates as additives are dealt with in
Chapter 7. It is seen that the thermal characteristics
of AP when co?crystallised or mixed with these compounds
are considerably modified. | |
