Thermal Properties of SiOC Glasses and Glass Ceramics at Elevated Temperatures

Abstract

In the present study, the effect of the chemical and phase composition on the thermal properties of silicon oxide carbides (SiOC) has been investigated. Dense monolithic SiOC materials with various carbon contents were prepared and characterized with respect to their thermal expansion, as well as thermal conductivity. SiOC glass has been shown to exhibit low thermal expansion (e.g., ca. 3.2 × 10−6 K−1 for a SiOC sample free of segregated carbon) and thermal conductivity (ca. 1.5 W/(m∙K)). Furthermore, it has been observed that the phase separation, which typically occurs in SiOC exposed to temperatures beyond 1000–1200 °C, leads to a decrease of the thermal expansion (i.e., to 1.83 × 10−6 K−1 for the sample above); whereas the thermal conductivity increases upon phase separation (i.e., to ca. 1.7 W/(m∙K) for the sample mentioned above). Upon adjusting the amount of segregated carbon content in SiOC, its thermal expansion can be tuned; thus, SiOC glass ceramics with carbon contents larger than 10–15 vol % exhibit similar coefficients of thermal expansion to that of the SiOC glass. Increasing the carbon and SiC content in the studied SiOC glass ceramics leads to an increase in their thermal conductivity: SiOC with relatively large carbon and silicon carbides (SiC) volume fractions (i.e., 12–15 and 20–30 vol %, respectively) were shown to possess thermal conductivities in the range from 1.8 to 2.7 W/(m∙K).

Phase evolution of SiOC‐based ceramic nanocomposites derived from a polymethylsiloxane modified by Hf‐ and Ti‐alkoxides

“…Similar to SiCN/HfO 2 , ceramic nanocomposites based on SiOC/HfO 2 are expected to be potential candidate materials, which can be applied as thermal/environmental barrier coatings aimed at high temperatures (1300°C‐1600°C) under oxidative and corrosive conditions . The improved oxidation resistance of SiOC/HfO 2 ceramic nanocomposites is ascribed to the formation of HfSiO 4 (hafnon) at elevated temperatures…”

“…Similar to SiCN/HfO 2 , ceramic nanocomposites based on SiOC/HfO 2 are expected to be potential candidate materials, which can be applied as thermal/environmental barrier coatings aimed at high temperatures (1300°C-1600°C) under oxidative and corrosive conditions. 15,21,22 The improved oxidation resistance of SiOC/HfO 2 ceramic nanocomposites is ascribed to the formation of HfSiO 4 (hafnon) at elevated temperatures. 23 To systematically advance the promising high-temperature-resistant SiOC/HfO 2 nanocomposites, we here report on the influence of derivatives of Hf-alkoxides used for chemical modification of the preceramic polymethylsilsesquioxane (PMS) on the phase evolution after ceramization and subsequent oxidation in air up to 1500°C.…”

Influence of free carbon on the Young's modulus and hardness of polymer‐derived silicon oxycarbide glasses

“…Contrary to the oxynitrides, which are formed by a homogeneous amorphous network and are generally obtained from melting, SiOCs are produced through a pyrolysis process and have a more complex nanostructure consisting of a disordered SiOC network and a free carbon phase . The disordered network is built‐up by mixed Si units sharing bonds simultaneously with O and C atoms and can be described by the formula: SiC x O 2(1− x ) , 0 ≤ x ≤ 1 in which “ x ” is the amount of substituted C. Accordingly, the composition of the SiOC glasses is usually reported as: SiC x O 2(1− x ) + y C free . A sketch of the SiOC nanostructure is shown in Figure .…”

Effect of composition and high-temperature annealing on the local deformation behavior of silicon oxycarbides

“…The synthesis procedure of the investigated SiOC glass and glass-ceramics is described in detail in Refs. [18] and [21]. Different polymeric precursors were used to realize a series of SiOC materials with various amounts of segregated carbon.…”

“…The resulting monolithic xerogels were pyrolyzed in an alumina tube furnace for 3 h at 1100 °C in argon atmosphere (heating rate of 25 °C/h). Details on the preparation of C1-SiOC-1100 are reported in [21].…”