Influence of palygorskite on in-situ thermal behaviours of clay mixtures and properties of fired bricks

Clay mixtures have been added with a palygorskite containing clay at 0 wt% to 50 wt% for brick button firing. Through an effective integration of in-situ temperature controllable XRD, thermogravimetric and dilatometric analyses, the real-time thermal behaviours of clay mixtures were studied. Also, the physical, mechanical and thermal performance of obtained fired brick buttons were investigated. The addition of palygorskite containing clay has increased the content of amorphous phases in fired brick buttons, while quartz, cristobalite, mullite and hematite were suppressed. Cordierite, spinel and magnetite are new minerals developed in obtained brick buttons. From 25 to 1150 °C, the brick green bodies underwent five mass loss steps and six dilatometric/contractions. The fibrous morphology of palygorskite no longer existed after 1150 °C firing. Instead, larger-sized acicular cordierite particles are developed. Adding palygorskite has resulted in lower porosity, higher drying shrinkage, firing shrinkage and compressive strength in fired buttons due to reinforced liquid-phase sintering. The effect of palygorskite on vitrification tended to be non-linear and non-uniform. In addition, the colours of brick buttons changed from "light camel" to "black olive" with palygorskite content. Since cracks were developed on the brick buttons added with 40 wt% and 50 wt% palygorskite containing clay, the optimum addition dosage was set at 30 wt%. The obtained compressive strength and thermal diffusivity (25 °C) at this addition amount are 153.8 MPa (24.5% higher than the control sample) and 0.788 mm²/s, respectively.