To sinter Ca₂Mn₃O₈ powder using Spark Plasma Sintering (SPS) at 873 K (600°C), the most suitable die and punch material is graphite, specifically high-density types like Poco EDM-3 or Toyo TTK. Graphite is electrically conductive (essential for SPS), thermally stable, and compatible with the moderate sintering temperature you're using.

To prevent reactions between the oxide powder and graphite, apply a hexagonal boron nitride (h-BN) coating inside the die and on the punch surfaces. Use a vacuum or inert gas atmosphere (argon or nitrogen) to avoid oxidation of the graphite tooling.

At 873 K, graphite tooling is safe, effective, and widely used for oxide ceramics like Ca₂Mn₃O₈.

Check for details operational principle of this equipment: Thermal Technology LLC (USA) Model: SPS 10-3 or SPS 25-10