Liquid phase sintering and microstructure–property relationships of silicon carbide ceramics with oxynitride additives

SiC, from Amorphous to Nanosized Materials, the Exemple of SiC Fibres Issued of Polymer Precursors

“…The infusible PCS was prepared by pressure pyrolysis of polydimethylsilane and the fibres formed by the dry spinning of concentrated PCS-based polymer solutions which were then pyrolysed in an inert atmosphere at 1000 to 1200°C. The room temperature ultimate tensile strength ranges between 2.5 and 3.5 GPa as a function of the fibre grade with Young's modulus ranging between ~200 and 400 GPa, very close to the best properties achieved for bulk ceramics, films or crystals : ~430 GPa (Biswas et al, 2001;Dirras et al, 2004;Chung & Han, 2008). The axial room temperature thermal conductivity ranges between ~2-3 (oxygen rich, amorphous SiC) up to 50-60 W/mK for crystalline nearly stoichiometric SiC (Simon & Bunsell, 1984).…”

Densification of silicon carbide using oxy-nitride additives for space-based telescope mirror applications

“…2 In the case of the system containing AlN + Y 2 O 3 , sintering is achieved by the formation of a transient liquid phase between AlN and Y 2 O 3 followed by a solution reprecipitation mechanism. 5,6 The densification was significant (99.6%) for the additive system with a total sintering additive content of 3.95 vol.%. We believe it is the first time that such a high From the mechanical and thermal properties summarized in Table 2, it can be observed that the material possesses the required properties for the mirror applications.…”

“…Microstructural features were observed in a scanning electron microscope (SEM) by viewing the samples that were polished and etched using a boiling solution of K 3 Fe(CN) 6 + KOH + H 2 O. SiC sintered to the highest density was tested for hardness and flexural strength in three point bending. Additionally, thermal conductivity, coefficient of thermal expansion, and elastic modulus were measured for this blank by the laser flash method, using a dilatometer and by pulse echo method, respectively.…”

“…AlN, which forms a solid solution with SiC, is used as a sintering aid but a processing temperature of over 2050 o C is required for full densification. 2 Various researchers have successfully demonstrated the feasibility of processing SiC to near theoretical density through liquid phase sintering at temperatures 5,6 However, most of them used sintering additives of 10 vol.% or more to achieve good densification. The use of a large quantity of sintering additives often compromises the fundamental properties of SiC, such as its thermal conductivity and creep resistance.…”

Effect of additive composition on mechanical properties of pressureless sintered silicon carbide ceramics sintered with alumina, aluminum nitride and yttria

“…(5) Biswas et al [21] investigated the relationships between microstructures and mechanical properties of gas-pressure sintered SiC ceramics with various AlN/Y 2 O 3 ratios. The fracture toughness of the SiC ceramics was dependent on the post annealing time after sintering, i.e., microstructure, and on sintering additive composition.…”