Structure properties relationship in silicon oxycarbide glasses obtained by spark plasma sintering

Combined pyrolysis-ammonolysis treatment to retain C during nitridation of SiBOCN ceramics

“…3). As occurred in the TA system, the samples in TAP present increased mesopore volume in the samples heat treated under N 2 /NH 3 and NH 3 . Some authors have been reported the synthesis of stable microporous oxycarbonitride ceramics through ammonolysis of a polycarbosilane polymer where the micropores seem to be formed at the intermediate steps of the heat treatment by the creation of more robust units composed by SiNSi and SiCSi bonds rather than siloxane counterparts.…”

“…18) The density of the materials from the TA system increases during the pyrolysis treatment showing its maximum at 1073 K. In the ammonolysis treatment, the measured density of the samples is slightly higher than in the pyrolyzed ones reaching the value of 2.2 in the materials containing 10% APS. Similarly, the combined treatment lead to the more densified materials with density values comprised between 2.1 and 2.3 g/cm 3 . In the TAP system, the density also increases with the amount of £-APS and acquires values comprised between 2.0 and 2.4 g/cm 3 either in the pyrolyzed and ammonolyzed materials but remain constant to 2.1 g/cm 3 in the combined heat treatment independently on the amount of £-APS used during the synthesis.…”

“…Similarly, the combined treatment lead to the more densified materials with density values comprised between 2.1 and 2.3 g/cm 3 . In the TAP system, the density also increases with the amount of £-APS and acquires values comprised between 2.0 and 2.4 g/cm 3 either in the pyrolyzed and ammonolyzed materials but remain constant to 2.1 g/cm 3 in the combined heat treatment independently on the amount of £-APS used during the synthesis. This behavior does not contradict the observed bond density increase in the spectroscopic characterization, as it will be described later.…”

“…Helium picnometry was used to determine the real density of the obtained materials by using a Quantachrome Corp Monosorb multipicnometer in samples reduced to powder in an agate mortar and sieved below 50¯m. At least 5 measurements were carried out in each sample and the average value was obtained with a typical error of « 0.05 g/cm 3 . Real density measurements were carried out in powdered samples, nevertheless both nitrogen adsorption and mercury intrusion porosimetry were carried out in crushed ones.…”

“…14) Nevertheless, thermolysis of preceramic polymers under a NH 3 atmosphere leads to the elimination of most of the carbon through chemical transformation of SiH, SiCH 3 and SiCH=CH 2 bonds to imidonitride groups at temperatures probably below 750 K. 13), 15) During ammonolysis, the reaction of NH 3 with the carbon functionalities in the low temperature regime of the polymer-toceramic conversion 16) gives as a result a significant decrease of the carbon content in the final ceramic. The formation of BC 3 and BCN environments are less likely to occur.…”