Characterization of yellow and red inorganic pigments from Mg_(0.5)Cu_(1.5)VxP_(2−x)O_7 (0 ≤ x ≤ 2) solid solutions

摘要

The structural characterization of Mg_(0.5)Cu_(1.5)VxP_2−xO_7 (0.0 ≤ x ≤ 2.0) compositions was performed and the colour parameters of these materials measured. Solid solutions in the α-Cu_2P_2O_7, β-Cu_2P_2O_7 and β-Cu_2V_2O_7 structures were obtained by incorporation of V(Ⅴ) in the α-Cu_2P_2O_7 and β-Cu_2P_2O_7 structures and P(Ⅴ) in the β-Cu_2V_2O_7 structure. Solid solutions with the α-Cu_2P_2O_7 structure are obtained at 500-600 ℃ when the vanadium:phosphorus ratio is lower than 2/3 (x ≤ 1.2). At 600 ℃, these materials have a bright yellow colour. In these compositions, the transition to the β-Cu_2P_2O_7 structure occurs at 800 ℃. This transition modifies the colour but it keeps the yellow colouration for compositions. At 1000 ℃, the Cu3P2O8 phase coexists with the β-Cu_2P_2O_7 phase and the yellow colouration is lost. Solid solutions with the β-Cu_2V_2O_7 structure are obtained at 600-800 ℃ when the amount of vanadium is high (x ≥ 1.5). The increase in the amount of vanadium in Mg_(0.5)Cu_(1.5)VxP_2−xO_7 (0.0 < x ≤ 2.0) compositions changes the colour of the materials from yellow to red at 600 ℃ (the Mg_(0.5)Cu_(1.5)P_2O_7 composition, x = 0.0, is pale green). The colour of the materials darkens with increasing temperature and compositions with x > 1.5 melted at 1000 ℃.