The effect of pressure to several hundred kilobars has been measured on samples of pyrolytic graphite of density 2.18 and 2.20. Measurements along the c axis show a relatively high resistance which decreases with increasing pressure and levels at high pressure, apparently due to strongly decreasing compressibility. Along the a axis the resistance is low, but increases at higher pressures apparently due to recrystallization.
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Samara et al. (1962) studied this question.
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