Influence of application method and sintering temperature on porosity and thermal conductivity of two commercial silicon carbide based castables

Information about thermal conductivity of refractory castables is
crucial in heat conducting structures. Two commercial castables
were studied to find out the effect of silicon carbide content (58-
67 %) and installation method on thermal conductivity. One cast-
able was designed to be installed by casting and the other one was
shotcrete castable. The shotcrete castable was casted and shot-
creted in to metal mold sized 200x200x50 mm. The other castable
was casted in laboratory conditions and on site. Porosities and
thermal conductivities were measured from samples after heat
treatment at 400, 600, 800 and 1000 ˚C. Thermal conductivities
were measured by transient plane source method, porosities were
measured by Archimedes’ method and microstructures were char-
acterized by scanning electron microscopy. Thermal conductivi-
ties varied from 6.8-16.3 W/mK and porosities 12.74-21.92 %.
Thermal conductivity of measured samples increased with SiC
content and higher heat treatment temperature as expected. Po-
rosities and thermal conductivities in castables casted in labora-
tory and on site varied only slightly. In shotcrete castable applied
by casting the porosity and thermal conductivity were higher than
in shotcreted sample. So the interconnection between low poros-
ity and high thermal conductivity was not as clear as expected.