3. Results and discussion
3.1. Explosive properties
The test results obtained for solid cyanamide and cyanamide,
50% solution in water, are summarized in Table 1. The investigated
test samples are not able to propagate a detonation or a deflagration
and the explosive power is insignificant according to the criteria
as defined [6]. Under defined confinement where high heating
rates are used the effects are low or medium. This is not a surprise
if the effect of heat to cyanamide is considered. Cyanamide
is able to dimerize and polymerize, respectively. At temperatures
below approx. 150 ◦C the “polymerization” stops at the dimer level
(dicyandiamide) (Fig. 2). At higher temperatures (starting at about
180 ◦C) the “polymerization” of cyanamide and dicyandiamide may
progress further to the trimer melamine (Fig. 3). Above 300 ◦C
melamine produces the 1,3,5-triazines melam, melem and melon
(Fig. 4) which have only recently been structurally characterized
[10].
Thus the observed effects in the heating under defined confinement
tests E.1 and E.3 are explainable by the “polymerization”
particularly because only a continuing rise of an adiabatic self-heating produces steam (in case of aqueous cyanamide solution)
and gaseous ammonia, which may build up pressure. According
to the UN Recommendations [4] self-reactive substances are
thermally unstable substances liable to undergo a strongly exothermic
decomposition even without participation of oxygen (air).
Such substances normally have heats of decomposition, as measured
with differential scanning calorimetry (DSC), equal or higher
than 300 J/g. Also cyanamide shows an exothermal heat (DSC) of
about 1360 J/g but this is owing to the dimerization/trimerization.
Cyanamide as well as aqueous solutions of it therefore should not
be assigned to the group of self-reactive substances according to
the transport regulations.