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

Abstract

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 ⁰C display a very low CTE (0.128±0.004–1.902±0.002 × 10−6 K−1) due to the α,β-transformation of spodumene. At higher sintering temperatures the CTE increases to 3.288±0.004 × 10−6 and 4.516±0.006 × 10−6 K−1 (1300 and 1400 ⁰C) due to the β-SiC formation. In this range of temperature, spodumene promotes the phase separation of SiOC and subsequent crystallization of cristobalite and β-SiC. The maximum values of hardness (11.5 ± 0.5 GPa) and elastic modulus (91±4 MPa) are reached at 1300 ⁰C, where the SiOC/composite displays a neat densification and the lowest roughness (1.61±0.01 nm).