Novel silicon oxycarbide/spodumene glass-ceramic composites with tailored thermal expansion coefficient

Highly densified silicon oxycarbide (SiOC)/spodumene composites with low coefficient of thermal expansion (CTE) were obtained just selecting the spark plasma sintering temperature employed. For the first time we proposed the use of spodumene a cheap and natural available lithium aluminium silicate mineral as meltable/ active filler for SiOC-derived composites, due to its powerful fluxing properties and also its very low CTE. SiOC/ spodumene composites sintered at 1200 degrees C display a very low CTE (0.128 +/- 0.004-1.902 +/- 0.002 x 10-6 K-1) due to the alpha,beta-transformation of spodumene. At higher sintering temperatures the CTE increases to 3.288 +/- 0.004 x 10-6 and 4.516 +/- 0.006 x 10-6 K-1 (1300 and 1400 degrees C) due to the beta-SiC formation. In this range of temperature, spodumene promotes the phase separation of SiOC and subsequent crystallization of cristobalite and beta-SiC. The maximum values of hardness (11.5 +/- 0.5 GPa) and elastic modulus (91 +/- 4 MPa) are reached at 1300 degrees C, where the SiOC/composite displays a neat densification and the lowest roughness (1.61 +/- 0.01 nm).