Suppression of free Si formation during liquid phase sintering of polysiloxane-derived, porous silicon carbide ceramics

Abstract

Porous silicon carbide ceramics were prepared from a polysiloxane, carbon black, SiC filler, sacrificial templates (co-polymer microbeads) and Al2O3-Y2O3 additives by a carbothermal reduction and subsequent sintering process. The effect of the sintering temperature on the microstructural development and structural characteristics of the porous ceramics was examined by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The polysiloxane-derived silicon carbide (PDSC) specimens showed a more homogeneous pore distribution than the powder-processed ones. Both the PDSC and powder-processed specimens contained only β -SiC when sintered at 1700°C. On the other hand, the PDSC specimens sintered at 2000°C revealed the formation of free Si clusters, detected by XRD and Raman spectroscopy, whereas the powderprocessed ones showed only the SiC phases. The formation of such Si clusters was effectively suppressed by adding an excess of carbon during the synthetic process. Raman spectroscopy revealed the existence of carbon layers in the 1700°C-sintered specimens, which were hardly detectable in the 2000°C-sintered ones.

Processing and properties of macroporous silicon carbide ceramics: A review

“…Polymer precursors and artificial templates have also been used for producing porous SiC ceramics via sacrificial template method. Kim and his colleagues [45,[119][120][121][122][123][125][126][127][128] developed a new processing method for fabricating macroporous SiC ceramics from carbon-filled polysiloxane by carbothermal reduction and subsequent sintering process. The strategy adopted for making porous SiC ceramics involves the following: (i) fabricating a formed body from a mixture of polysiloxane, carbon source such as phenol resin or carbon black, SiC powder as an optional inert filler, sacrificial templates, and sintering additives; (ii) pyrolysis of polymeric materials; (iii) synthesizing SiC by carbothermal reduction; and (iv) sintering the materials.…”

Processing of polysiloxane-derived porous ceramics: a review

“…The high-temperature strength reduction caused by the formation of free Si in the high-temperature reaction between SiC and sintering additives (Al 2 O 3 ) could be effectively suppressed by the addition of excess carbon [103]. In another work, the expandable microspheres were in situ foamed during extrusion at 130…”

“…The carbothermal reduction and subsequent sintering of SiOC foams, templated from hollow microspheres or polymer microbeads, resulted in open-cell SiC ceramics possessing a compressive strength of 240-290 MPa and a flexural strength of 60-100 MPa at 40% porosity [103,105]. The proper composition of starting mixture of SiC powder and polysiloxane-derived SiC resulted in a flexural strength of 57 MPa at 50% porosity [18].…”

SiC Nanowire Sponges as Electropressure Sensors

“…15 As one of the simplest and most cost-effective approaches, in situ carbothermal reduction has been an effective technique for SiC nanomaterials synthesis. 16 On the basis of the low-cost silicon oxide (SiO 2 , SiO, or SiOC), various forms of porous carbon template (graphene foam (GF) 17,18 and carbonized dough 13 ) were used to create porous SiC via carbonization. 12 The resultant structures strongly depend on the initial C/SiO 2 matrix and interaction between reagents.…”