Thermal oxidation curing polycarbosilane fibers by alternating air and vacuum process

Abstract

<p>Polycarbosilane (PCS) fibers were cured by a process of alternating air and vacuum atmosphere periodically at thermal oxidation temperature.</p>

Advances in the Synthesis of Preceramic Polymers for the Formation of Silicon-Based and Ultrahigh-Temperature Non-Oxide Ceramics

“…Depending on the respective polymer, melt spinning can take place between 220 and 350 °C, in an inert atmosphere, and then spun fibers are either cured in air at >150 °C or under inert conditions by electron-beam (E-beam) radiation. , Air curing, while being advantageous in not requiring expensive E-beam curing equipment, does present drawbacks. , There are two important implications of air curing polycarbosilane fibers: (1) oxygen incorporation into the green fiber structure results in the evolution of oxygen-containing species like CO, CO 2 , or SiO 2 during subsequent high-temperature treatment, and (2) the pyrolyzed composition is not that of a pure amorphous SiC but primarily silicon oxycarbide (SiC x O y ) and excess carbon. , During a thermal air cure (thermal oxidation), oxygen incorporation primarily occurs at the Si–H in the polycarbosilane backbone; the Si–H bonds are partially replaced by Si–OH and eventually cross-link with neighboring molecules to form Si–O–Si bonds, as shown in Figure . The susceptibility of Si–H to oxygen increases with increasing temperature; thus, high cure temperatures are often employed for polycarbosilanes …”

Impact of Metals on (Star)Dust Chemistry: A Laboratory Astrophysics Approach

“…After 2 h at 200 • C, the massif exhibits three components and its integrated intensity has increased indicating that the Si-O-Si network rearranges itself. This evolution continues with the temperature increase up to 500 • C at which the spectrum exhibits features closer to those of silica but with strong mixing between the Si-O-Si and Si-C-Si vibrations, resulting in a peak at 1,000 cm −1 and a well-defined band due to the symmetric Si-O-Si stretching vibration at 810 cm −1 (Kirk, 1988;Innocenzi et al, 2003;Li et al, 2020). Besides, the Si-O-Ag shoulder at 965 cm −1 becomes an integral contribution to the massif.…”

“…The intense band at 1,030 cm −1 can be assigned to Si-O-Si asymmetric stretching mode in a silicon suboxide environment with a contribution of the Si-CH x(x≤2) -Si wagging mode, most probably positioned at around 1,020 cm −1 . The band in the 800 cm −1 range is likely a mix of the Si-O-Si symmetric stretching vibration at 810 cm −1 with contribution of the symmetric stretching vibration of Si-C usually appearing at 840 cm −1 , as well as several other bands between 700 and 900 cm −1 associated with Si-C and Si-O bonds of the organosilicon structure (Smith, 1960;Benítez et al, 2000;Raynaud et al, 2005;Despax and Raynaud, 2007;Li et al, 2020). Amongst the minor features, methyl CH stretching modes can also be observed at 2,960 and 2,904 cm −1 , together with the typical symmetric bending mode of Si-CH 3 at 1,260 cm −1 , which is related to the decomposition of HMDSO in the plasma.…”

Impact of metals on (star)dust chemistry: a laboratory astrophysics approach

“…After two hours at 200 • C, the massif exhibits three components and its integrated intensity has increased indicating that the Si-O-Si network rearranges itself. This evolution continues with the temperature increase up to 500 • C at which the spectrum exhibits features closer to those of silica but with strong mixing between the Si-O-Si and Si-C-Si vibrations, resulting in a peak at 1000 cm −1 and a well defined band due to the symmetric Si-O-Si stretching vibration at 810 cm −1 (Kirk, 1988;Innocenzi et al, 2003;Li et al, 2020). Besides, the Si-O-Ag shoulder at 965 cm −1 becomes an integral contribution to the massif.…”

“…The intense band at 1030 cm −1 can be assigned to Si-O-Si asymmetric stretching mode in a silicon suboxide environment with a contribution of the Si-CH x(x≤2) -Si wagging mode, most probably positioned at around 1020 cm −1 . The band in the 800 cm −1 range is likely a mix of the Si-O-Si symmetric stretching vibration at 810 cm −1 with contribution of the symmetric stretching vibration of Si-C usually appearing at 840 cm −1 , as well as several other bands between 700 and 900 cm −1 associated with Si-C and Si-O bonds of the organosilicon structure (Smith, 1960;Benítez et al, 2000;Raynaud et al, 2005;Despax and Raynaud, 2007;Li et al, 2020). Amongst the minor features, methyl CH stretching modes can also be observed at 2960 cm −1 and 2904 cm −1 , together with the typical symmetric bending mode of Si-CH 3 at 1260 cm −1 , which is related to the decomposition of HMDSO in the plasma.…”