The System PbO-Chromium Oxide in Air

Phase relations in the system PbO‐chromium oxide were determined in air at high temperatures and are considered in terms of the PbO‐Cr2O3−O2 ternary because of reactions with atmospheric oxygen. Although not necessarily binary at all temperatures, four established subsystems characterize the air equilibria and indicate oxidation‐reduction of chromium. The PbO‐PbCrO4 join contains the compounds Pb5CrO3 and Pb5CrO8 and consists of two portions, PbO‐Pb2CrO6 and Pb2CrO5−PbCrO4 The former is binary at all temperatures studied, while the latter exists only below 753° C because of the decomposition of PbCrO4 at 753°C to Pb2CrO5 and Cr2O3 with oxygen evolution. Similarly, the join PbCrO4−Cr2O3 exists only below 753°C yielding to Pb2CrO3−Cr2O3 equilibria above this temperature.