The datasheet give a thermal conductivity of 15 BTU-in/hour.F.Ft^2
Converting that value to SI units gives 2.16 W/mK (Using the engineering toolbox converter)
However different sources are giving a value of about 35 W/mk at room temperature for Al2O3
That's a large difference !
Any clue ?
The Cotronics data sheet shows 1.2 W/mK for pure alumina
35 W/mK sounds rather high. That would be equivalent to the thermal conductivity of Pb.