- Abstract Fully dense boron carbide specimens were fabricated by the spark plasma sintering (SPS) technology in the absence of any sintering additives. Densification starts at 1500° C and the highest densification rate is reached at about 1900° C. The microstructure of the ceramic sintered at 2200° C, with heating rates in the 50–400° C/min range, displays abnormal grain growth, while for a 600° C/min heating rate a homogeneous distribution of finely equiaxed grains with 4.05±1.62 μm average size was obtained. TEM analysis revealed the presence of W-based amorphous and of crystalline boron-rich B 50 N 2 secondary phases at triple-junctions. No grain-boundary films were detected by HRTEM. The formation of a transient liquid alumino-silicate phase stands apparently behind the early stage of densification.