Multiple metals doped polymer-derived SiOC ceramics for 3D printing

Multiple metals doped polymer-derived SiOC ceramics with octet truss structure were prepared by employing a photosensitive methyl-silsesquioxane as preceramic polymer through sol-gel method and Digital Light Processing 3D printing. The physical and chemical properties of the preceramic polymers and printed octet truss structure SiOC ceramics were investigated. Results show that the organosilicon preceramic polymers have outstanding photocuring properties and could transform into amorphous SiOC ceramics at 800–1200?°C. It is illustrated that the excellent mechanical properties of SiOC ceramics with octet truss structure (after 3D printing and pyrolysis) are attributed to the metal elements pinning in the amorphous matrix on the atomic level. Doping other metal elements such as Fe, Ni, Co, Pt, etc, is thought to bring promising properties for the lattice structure SiOC ceramics and potentially further expand its applications in the future.     

Ultrahigh figure-of-merit for hydrogen generation from sodium borohydride using ternary metal catalysts

We report further increase in the figure-of-merit (FOM) for hydrogen generation from NaBH₄ than reported in an earlier paper [1], where a sub-nanometer layer of metal catalysts are deposited on carbon nanotube paper (CNT paper) that has been functionalized with polymer-derived silicon carbonitride (SiCN) ceramic film. Ternary, Ru-Pd-Pt, instead of the binary Pd-Pt catalyst used earlier, together with a thinner CNT paper is shown to increase the figure-of-merit by up to a factor of six, putting is above any other known catalyst for hydrogen generation from NaBH₄. The catalysts are prepared by first impregnating the functionalized CNT-paper with solutions of the metal salts, followed by reduction in a sodium borohydride solution. The reaction mechanism and the catalyst efficiency are described in terms of an electric charge transfer, whereby the negative charge on the BH₄⁻ ion is exchanged with hydrogen via the electronically conducting SiCN/CNT substrate [1].     

Polymer-derived Biosilicate-C composite foams: Phase development and photothermal effect

Glass-ceramic matrix composites for bone-tissue regeneration were produced in the form of highly porous foams utilizing the ‘polymer-derived ceramics’ (PDCs) approach. More precisely, two different commercial silicone polymers (a poly-methyl-siloxane, MK, and a polymethyl-phenyl-silsesquioxane, H44), reacting with suitable Na₂O, CaO, and P₂O₅ yielding fillers were considered. The reaction was designed to yield products resembling Biosilicate® glass-ceramic i.e. Na₂CaSi₂O₆ embedded in a silico-phosphate glass matrix. Subsequently, the samples were heat treated either in the air or in the N₂ atmosphere, implying improvements in the mechanical properties and providing extra functionality. The pyrolysis in an inert atmosphere led to composites comprising a carbon phase, which promoted the absorption of infrared radiation. Such functionality makes the obtained composites promising in the perspective of disinfection of bone-tissue implants and photothermal therapy.     

Hierarchically structured polymer-derived ceramic fibers by electrospinning and catalyst-assisted pyrolysis

Hierarchically structured polymer-derived ceramic fibers were successfully produced by electrospinning a commercially available preceramic polymer to which a cobalt-based catalyst precursor was added, followed by pyrolysis in nitrogen at temperatures ranging from 1250 to 1400 °C. The nanowires formed via the vapor–liquid–solid (VLS) mechanism, involving the reaction of SiO and CO gases, generated from the decomposition of the polymer-derived-ceramic at high temperature, with the heating atmosphere assisted by the presence of nano-sized CoSi droplets. The main crystalline phase for the nanowires was Si₃N₄ below 1350 °C, and Si₂N₂O at 1400 °C, and the amount of nanowires increased with increasing heating temperature. Hierarchically structured fiber mats possessed a higher specific surface area (14.45 m²/g) than that of a sample produced without the cobalt catalyst (4.37 m²/g).