Solid-liquid and vapor-liquid equilibria for the binary system isobutane diamantane were determined according to the synthetic method in the tempera
ture range (320-530) K and the pressure range (0.3-10) MPa. Also, the three
-phase curve solid diamantane-liquid-vapor was determined. The results show
that the slope of this curve demonstrates a discontinuity, which can be ex
plained by the existence of two solid modifications of diamantane. The two
branches of this equilibrium intersect at the S-1-S-2 equilibrium line of d
iamantane. The influence of the occurrence of two modifications of diamanta
ne on isobaric solid-liquid equilibria is less distinct.