ORNL developed #gelcasting for “technical” #ceramics #materials (including #silicon-nitride) in the 1980s and 1990s, and this is a #popsci overview; apparently Mark Janney, Stephen Nunn, Claudia Walls, and Ogbemi Omatete are recognized as the inventors. Apparently the advantage over slipcasting is that shrinkage is uniform and the green casting is strong enough to be machinable. Initial experiments used methylcellulose, which gels when heated with water, as the gelifying binder, but “multifunctional acrylate” polymers (??) were the binder that made gelcasting practical, followed by water-based #acrylamide, then less-toxic methacrylamide.
on 02015-08-15the #TCE range of different common #materials; e.g. fused silica is 0.55ppm/°, invar is 1.3, #silicon-nitride is 3.2, titanium is 9.5, copper is 16.7, polymers are 50–200, and silicone is 30–300.
on 02015-08-14This “micro” “MEMS” gas #turbine runs at 500krpm on, obviously, an #air-bearing (they achieved a record speed of 1.2Mrpm), with a 20mm rotor (in a total 100mm×110mm casing) producing 1kW. The turbine itself is die-sink-EDM-machined conductive ceramic (composite #silicon-nitride and titanium nitride) to withstand the 1200 K gas; supposedly 20% overall efficiency with the 74.5%-efficient recuperator. This seems like overkill on the efficiency front for mobile-power uses (cellphones, laptops, drones), where the big issue is that batteries have an #energy-density of about 500kJ/kg, while hydrocarbons are at almost 50MJ/kg, so any efficiency over about 1% would be a victory condition for microturbines over batteries.
on 02015-08-14