Beschreibung:
<jats:sec><jats:label /><jats:p>A major challenge in the processing of compact polymer derived ceramics is the removal of pores. Even after field‐assisted sintering (FAST) under pressure, a certain level of porosity remains within samples and parts. In order to reduce the porosity, a novel route is developed making use of the addition of trimethyl borate to a polysilsesquioxane‐type preceramic polymer system; trimethyl borate is a molecular boron oxide precursor. It is found that boron‐oxide free samples show a high compression rate during field‐assisted sintering between 1400 and 1600 °C, boron oxide and boron oxide/alumina containing samples show this effect already between 1350 and 1500 °C. In a tentative reaction mechanism, this effect is assigned to the formation of a borosilicate glass by chemical reactions of boron oxide with the silica component of the polysiloxane‐derived ceramic; this glassy phase assists the densification process by viscous flow. The porosity in boron oxide‐containing samples is found to be between 0.3% and 1.4% while boron oxide‐free samples show a total porosity of ≈38% after processing under identical conditions.</jats:p></jats:sec>