1. Transient Hotwire Measurement of
Diamondoid Thermal Conductivity
Esteban Pacheco • Matthew Powell-Palm
Transient Hotwire Raw Data
Iterations of
Experimental Setup
Thermal Conductivity Results
DeltaT[K]
Time [s]
Abstract
Materials of ultralow thermal conductivity have considerable potential as thermal insulators in micro and nanoscale electromechanical systems and as thermoelectric generators. We have developed a
method of experimentally determining the thermal conductivities of powdered crystalline substances at high pressures and low temperatures using a transient hotwire technique. We have successfully
determined the thermal conductivity of the diamondoid adamantane with this method and refined a novel experiemtnal procedure. We have attained good agreement with published values and will
test other diamdoids in the coming future.
λ =
q
4π
dΔT
dln(t)
Motivation Transient Hotwire
Adamantane is the most structurally simple
member the diamondoids. It undergoes a
high-entropy phase change at 208.7 K which
results in an increase in density from 1.08 to 1.18
g/cm3 and a transition from a plastic face
centered cubic to a normal tetratgonal
crystalline structure. It has a notably low room
temperature thermal conductivity of 0.21 W/m-K.
Having validatated our experimental method
with adamantane, we plan next to develop
polycrystalline diamondoid alloys, taking
advantage of unique phonon mismatches to
create substances of ultralow thermal
conductivity.
Theory
Derived from the Heat Conduction
Equation in a Radial Coordinate System
assuming infinite wire length.
Experimental Method
1. Compress powdered adamantane to 80,000 psi, forming single crystal.
2. Drill a tunnel through crystal.
3. Thread platinum wire probe through tunnel.
4. Recompress crystal with 8,000 psi, collapsing tunnel around wire.
5. Cool entire apparatus in cryostat, taking transient hotwire measurements.
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Adamantane Thermal Conductivity
Temperature (K)
ThermalConductivity(W/m−K)
Powell−Palm/Pacheco 2015
Powell−Palm/Pacheco 2015
Powell−Palm/Pacheco 2015
Wigren 2011
Cahill−Pohl Lower Limit
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