Schematic illustration of a cell assembly. (a) Longitudinal section of the cell assembly: (1) steel ring, (2), (3) graphite heater resistance, (4) Pt electrode (a, b, c, and d in (b)), (5) sample, (6), (7) MgO insulation material, (8) pyrophyllite. (b) Cross section of the cell assembly: (9) Al₂O₃ tube insulation material, (10) chromel-alumel type thermocouple (e, f, g, and h). Figure adapted with permission from Ref. [25].