Additive-free low temperature sintering of amorphous Si B C powders derived from boron-modified polycarbosilanes: Toward the design of SiC with tunable mechanical, electrical and thermal properties

Abstract

Additive-free SiC ceramics are prepared from polymer-derived powders with Si, C and B elements homo-geneously distributed on the atomic level by rapid hot-pressing at 1750 °C and 1800 °C under argon and a load of 50 MPa. As-sintered samples display a Vickers hardness in the range of 9.6 ± 0.5 GPa-17.3 ± 1.9 GPa and an elastic modulus varying from 137 ± 3.4 GPa to 239 ± 6 GPa, both depending on the sample phase composition, crystallinity and porosity. Accordingly, the electrical conductivity changes from 340 to 3900 S/m whereas the thermal conductivity varies from 17.7 to 45.1 W/m K as a function of these characteristics. Thus, we demon-strated that a polycarbosilane containing 0.7 wt.% of boron could produce boron-doped SiC powders that de-monstrate tailored sinterability at temperatures as low as 1750 °C to form nearly dense SiC ceramics with adjusted hardness, Young's modulus, electrical and thermal conductivities.

Polymer-Derived Si-Based Ceramics: Recent Developments and Perspectives

“…Among them, thermal conductivity is the most concerned thermal parameter, and we mainly focus on thermal conductivity herein. The thermal conductivity of ceramic materials with strong covalent bonds is controlled by phonon transmission [43], and the materials' microstructure (impurities, crystallinity, grain boundaries, microcracks, micropores, etc.) has a great influence on phonon scattering [41], which in turn affects the thermal properties of materials.…”

“…When the BNNTs content exceeds the percolation threshold (36 vol%) [41], a percolation network is formed, leading to a jump in thermal conductivity. Bernard et al [43] prepared amorphous Si-B-C powder from B-modified polycarbosilane and adjusted its thermal properties. They found that the porosity of the sintered sample decreased significantly with the increase of the B content, which in turn increased the thermal conductivity of the sample.…”

“…The recent research progress and trends of PDCs are to functionalize them through various methods (such as additive doping [30,31,[41][42][43][44][45]) and to combine PDCs with 3D printing [4,10,[13][14][15]29,46] to explore new techniques to fabricate PDCs. By functionalizing PDCs, they have excellent mechanical, thermal, electrical, and dielectric properties.…”

“…Wilhelm's group [18] fabricated PDCs-SiOC with high specific surface area (~400 m 2 •g −1 ) by freeze casting and loading with Ni nanoparticles, and it displayed good catalytic activity; in the CO 2 methanation reaction, the maximum conversion rate was 0.49, and the maximum methane selectivity was 0.74. In addition, by functionalizing polymer-derived Si-based ceramics, it can also significantly improve its mechanical [5,15,43,47,61], thermal [41,43,[62][63][64], and electrical properties [6,14,26,40,43], which could be widely used in the preparation of conductive ceramics, sensors, membranes, coatings, and components for usage under harsh environments.…”

Fabrication of (SiC-AlN)/ZrB2 Composite with Nano-Micron Hybrid Microstructure via PCS-Derived Ceramics Route

“…PDCs are mainly composed of a network by free carbon and Si-rich nanodomains inside [ 9 ], while grains of PDCs are usually nanosized. This unique microstructure renders excellent physical and chemical properties in PDCs [ 10 , 11 ], such as thermal [ 12 , 13 , 14 , 15 ], electrical [ 16 , 17 , 18 ], electrochemical energy storage [ 19 , 20 ], and electromagnetic properties [ 21 , 22 , 23 , 24 , 25 ]. Nevertheless, during the pyrolysis of the ceramic precursors, a large amount of small molecule gas would be released, and the green body would shrink, with the formation of pores and cracks.…”