Pressureless sintering of boron carbide

B4C powder compacts were sintered using a graphite dilatometer in flowing He under constant heating rates. Densification started at 1800degreesC. The rate of densification increased rapidly in the range 1870degrees-2010degreesC, which was attributed to direct B4C-B4C contact between particles permitted via volatilization of B2O3 particle coatings. Limited particle coarsening, attributed to the presence or evolution of the oxide coatings, occurred in the range 1870degrees-1950degreesC. In the temperature range 2010degrees-2140degreesC, densification continued at a slower rate while particles simultaneously coarsened by evaporation-condensation of B4C. Above 2140degreesC, rapid densification ensued, which was interpreted to be the result of the formation of a eutectic grain boundary liquid, or activated sintering facilitated by nonstoichiometric volatilization of B4C, leaving carbon behind. Rapid heating through temperature ranges in which coarsening occurred fostered increased densities. Carbon doping (3 wt%) in the form of phenolic resin resulted in more dense sintered compacts. Carbon reacted with B2O3 to form B4C and CO gas, thereby extracting the B2O3 coatings, permitting sintering to start at similar to1350degreesC.