The phase diagram for the binary system K 2CrO 4CaCrO 4

The phase diagram for the binary system K ₂CrO ₄CaCrO ₄ has been determined for CaCrO ₄ concentrations up to 60 mole%, using the techniques of differential thermal analysis, X-ray diffraction, and drop calorimetry. Essential features of the phase diagram are: the solid-solid phase transition for pure K ₂CrO ₄ at 670°C, β-K ₂CrO ₄ ⇄ α-K ₂CrO ₄; a eutectoid reaction at 14 mole% CaCrO ₄ and 548°C, β-K ₂CrO ₄ ⇄ α-K ₂CrO ₄ + K ₂CrO ₄ · CaCrO ₄; a peritectoid event at 50 mole% CaCrO ₄ and 640°C, β-K ₂CrO ₄ + CaCrO ₄ ⇄ K ₂CrO ₄ · CaCrO ₄; and a eutectic reaction at 51 mole% CaCrO ₄ and 678°C, L ⇄ β-K ₂CrO ₄ + CaCrO ₄. X-ray diffraction studies lead to the determination of the unit cell dimensions for the K ₂CrO ₄ · CaCrO ₄ double salt, a C-centered monoclinic form with a₀ = 7.615(6) Å, b₀ = 22.797(15) Å, c₀ = 9.777(9) Å, β = 115.45(5)°.