Ultra-low thermal conductivities of hot-pressed attapulgite and its potential as thermal insulation material

In the past, there have been very few reports on thermal properties of attapulgite which is a widely used clay mineral. In this work, we report on extremely low thermal conductivities in attapulgite samples synthesized by hot-pressing. Attapulgite powder was hot-pressed at different temperatures into bulk samples, and a systematic study was conducted on the microstructures and thermal properties. Differential scanning calorimetry analysis shows that hot-pressing induces a rapid dehydration of the attapulgite powders. X-ray diffraction data and scanning/transmission electron microscopy reveal that the hot-pressed attapulgite features high porosity and complex microstructures, including an amorphous phase. As a result, the hot-pressed attapulgite exhibits thermal conductivity less than 2.5 W m−1 K−1 up to 600 °C. For one sample with porosity of 45.7%, the thermal conductivity is as low as 0.34 W m−1 K−1 at 50 °C. This suggests the potential of hot-pressed attapulgite as a candidate for thermal barrier materials.