Carbonization behaviour of pitch in the presence of inert material

The influence of silica gel (< 45 μm) as an inert additive on the carbonization reactions of A240 pitch was investigated by optical microscopy, measurements of transferable hydrogen, high-temperature e.s.r. and high-temperature ¹H n.m.r. Additions of silica gel have the effect of reducing the size of the optical texture of mesophase which appears in the early stages of carbonization. The higher the concentration of silica gel, the smaller is the amount of transferable hydrogen. The spin concentration of pitch increases with increasing silica gel content. Measured values of ΔH _{1 2}, using high-temperature ¹H n.m.r., suggest that the molecular motions in the pitch become restricted on addition of silica gel. The effect of silica gel on the physical properties and chemical reactivity of carbonizing pitch is discussed.