rate of 1 u00b0 c min the heat treated thin plate was carbonized by elevating the temperature in an inert gas current from room temperature to 1 000 u00b0 c at a rate of 10 u00b0 c min immediately the carbonized thin plate was allowed to cool to room temperature to obtain a thin carbon plate of 180 u03bcm in thickness the properties of the thin carbon plate obtained are shown in the table given later 50 g of methylenediphenyl diisocyanate mdi was reacted in the presence of 0 13 g of a carbodiimidization catalyst 1 phenyl 3 methylphosphorene oxide in 880 ml of tetrahydrofuran at 68 u00b0 c for 12 hours to obtain a polycarbodiimide solution the solution was developed on a glass plate and a dry method was applied to obtain a polycarbodiimide thin plate of 200 u03bcm in thickness the thin plate was subjected to a heat treatment by elevating the temperature from 150 u00b0 c to 250 u00b0 c at a rate of 1 u00b0 c min and keeping the plate at 250 u00b0 c for 3 hours the heat treated thin plate was heated from room temperature to 1 000 u00b0 c at a rate of 10 u00b0 c min in an inert gas current and then immediately allowed to cool to obtain a thin carbon plate of 180 u03bcm in thickness the properties of the thin carbon plate obtained are shown in the table given later the polycarbodiimide thin plate obtained in example 1 was heated from 150 u00b0 c to 350 u00b0 c at a rate of 2 u00b0 c min and then carbonized in the same manner as in example 1 to obtain a thin carbon plate.