Pressureless Sintering of Boron Carbide

Abstract

B4C powder compacts were sintered using a graphite dilatometer in flowing He under constant heating rates. Densification started at 1800°C. The rate of densification increased rapidly in the range 1870°–2010°C, 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 1870°–1950°C. In the temperature range 2010°–2140°C, densification continued at a slower rate while particles simultaneously coarsened by evaporation–condensation of B4C. Above 2140°C, 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 ∼1350°C.

Tough and dense boron carbide obtained by high-pressure (300 MPa) and low-temperature (1600°C) spark plasma sintering

“…A temperature of 1800°C was indicated in ref. 5) to be the temperature where densification starts. Usually, practical sintering temperatures are above 2250°C.…”

Processing, Mechanical and Nuclear Characterization of Boron Carbide Ceramics Consolidated by Spark Plasma Sintering

“…B 4 C is evaluated as an ideal material for nuclear applications, especially as control rods in reactors and shielding material in neutron shielding systems, due to its high hardness; being the third hardest material after diamond and cubic boron nitride, high flexural strength, low density, high wear resistance, chemical stability and thermal neutron cross-section value properties [1,2].…”

“…In recent years, spark plasma sintering (SPS) technique has been used widely for manufacturing B 4 C and B 4 C containing ceramics because of its improvements on microstructural effects of said materials since it prevents grain coarsening [2]. With applying pulsed direct current, SPS enhances densification and the sintering process is completed at lower temperatures in shorter durations without grain growth compared to the traditional sintering techniques (pressureless sintering, hot pressing and hot isostatic pressing).…”

Spark Plasma Sintering of Boron Carbide Powder

“…This procedure helps to obtain B4C samples with a relative density higher than 95%. But the processing temperature still exceeds 2150 ∘ C [6].…”