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THERMAL PROPERTIES
standard. To determine the heat capacity of an explosive, one must establish a base
line that indicates the differential heat loss of the two aluminum sample containers
at the init:ial temperature. This is done by placing two empty sample containers in
the DSC sample holders and subjecting them to a linearly increasing temperature.
Next, a weighed sample of test explosive is placed in one container, both containers
are subjected to the linearly increasing temperature, and the heat flow rate is
recorded as a function of temperature. Then the procedure is repeated with a
weighed sample of synthetic sapphire.
The heat capacity at any temperature is calculated by using C, = C,,(m,) X
(h)/mh,, where C, = heat capacity of the explosive at temperature T, C,] = heat
capacity of the sapphire at temperature T, m = weight of the explosive sample, ml
= weight of the sapphire, h = baseline deflection of the explosive sample, and h, =
baseline deflection of the sapphire.
2.2 Thermal Conductivity. Two steady-state procedures have been used to
determine the thermal conductivity of explosives. The first is the guarded hot plate
(GHP) procedure that the American Society for Testing and Materials (ASTM)
uses and d.escribedto test insulating materials in ASTM Source C-177. The second
procedure involves a differential scanning calorimeter.’ The DSC sample is much
smaller and more suitable for testing high explosives than is the GHP sample.
The DSC method requires two identical right circular cylinders, one of the test
material and the other of a reference material. The thermal conductivity is deter-
mined, under steady-state conditions, from the heat flow and temperature drop
along the cylinder length. The following equations apply.
and
where
and
91
k:lAIAT
_ L1
‘kiiA2*T
92 =--
L2 '
q1 - q, = DSC output,
A = area of cylinder base,
L = cylinder length,
AT = temperature drop along the cylinder length,
kl = thermal conductivity of reference material,
k, = thermal conductivity of unknown.
Because AT, A, and L of both the reference and unknown are indentical, the ther-
mal conductivity of the unknown is given by
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