An investigation into the crystal structure of some diarylide yellow pigments using x-ray powder diffraction

Synthesis of the diarylide yellow pigments CI Pigments Yellow 12, 13, 14 and 63 using traditional aqueous procedures initially gives the pigments in a relatively amorphous form which becomes crystalline when heat-treated. The crystalline form which develops has been shown to be the same as that which has been characterised by single crystal analysis on the basis of a comparison between the calculated and experimental x-ray powder diffraction profiles. Differential scanning calorimetry (DSC) investigation of the weakly-crystalline pigment samples demonstrates an exothermic crystallisation process.