On melting of B4C boron carbide under pressure
  The pressure dependence of melting temperatures for boron carbide and B4C-carbon eutectic has been studied up to 8 GPa, and it was found that in both cases the melting curves exhibit negative slope (-13\pm6 K/GPa), that is indicative of higher density of the melt as compared to the solid phase. 
Vladimir A. Mukhanov, Petr S. Sokolov and Vladimir L. Solozhenko
cond-mat.mtrl-sci