Polymer-derived mullite–SiC-based nanocomposites

Influence of nano-aluminum filler on the microstructure of SiOC ceramics

“…Crystalline silicon as well as ␥-Al 2 O 3 can be detected in the samples heat-treated up to 1300 • C. The ␥-Al 2 O 3 -to-␣-Al 2 O 3 phase transformation usually takes place at around 1100 • C but in the presence of amorphous SiO 2 the transition temperature can rise up to 1300 • C. 23,39 Although it is expected that the ␦-andAl 2 O 3 transition phases are also present in the ceramic matrix, their X-ray reflexes were not found in the XRD patterns. The reflexes of ␣-Al 2 O 3 phase are detected starting with 1200 • C, and at 1300 • C mullite starts to form.…”

“…The cross-linking process occurs over a wide temperature range and strings together three mass loss steps (from 95 to 250 • C, DTG peak at 145 • C; from 250 to 500 • C, DTG peak at 349 • C, from 500 to 590 • C, DTG peak at 531 • C). In these temperature ranges the masses m/z = 15, 27 and 29 refer to ethyl fragments, as well as to the main mass fragments of acetaldehyde, corresponding to a decomposition of the included solvent acetone 23 (Fig. 1b).…”

“…Zirconium acetylacetonate (C 20 H 28 O 8 Zr, Sigma-Aldrich, USA, referred to as catalyst) was used as a cross-linking agent. 23 Aluminum (50-80 nm particle size, H.C. Starck, Germany) was used as a filler. The mixture AlMK (11 vol.% aluminum + 89 vol.% MK polymer) was prepared in a planetary ball mill, sieved (100 m), cross-linked during warm pressing (180 • C, 25 MPa, 30 min) using a hydraulic press (warm press type 123, H. Collin) and subsequently pyrolyzed for 3 h under flowing argon atmosphere at temperatures of 1100, 1200, and 1300 • C. Further annealing treatments (argon atmosphere, 1400 • C and 1500 • C for 3 h) were performed on bulks pyrolyzed at 1300 • C in argon atmosphere to analyze the crystallization behavior.…”

Pressureless synthesis of fully dense and crack-free SiOC bulk ceramics via photo-crosslinking and pyrolysis of a polysiloxane

“…To avoid these problems, the use of passive or active filler particles was proposed in order to act against shrinkage and mass loss and thus allow the production of crack-free monoliths with low residual porosities. 5,6 By combining passive and active fillers, near net shape production of PDC-based parts is possible since zero shrinkage can be achieved. 7 Hence, filler-free PDC-based parts can only be produced either by having high porosity 8 or by keeping the parts very thin.…”

Multifunctional advanced ceramics from preceramic polymers and nano-sized active fillers

“…In our experiments, we never fired the precursor composite material in Ar atmosphere, because we were aiming at producing fully oxide or oxynitride phases; however when heating in inert (Ar or He) atmosphere is performed, nanocomposites containing SiC and the desired oxide phase can be obtained. 55 It should also be observed that, because of the features discussed above, when processing a preceramic polymer component containing nano-sized fillers, there is a strong tendency to form equilibrium, that is crystalline, phases and therefore this approach is less suited to the production of glasses. However, if the processing temperature is sufficiently low, in the presence of multiple fillers (e.g.…”