Synthesis of Large Platelets of Egyptian Blue via Pseudomorphosis after NaRUB-18

Abstract

A colored platy substrate with appreciable aspect ratio can improve the hiding power while extending the color range of pearlescent pigments. One of the oldest synthetic pigments, Egyptian blue, possesses a layered structure and a platy morphology, making it a promising colored substrate for pearlescent pigments, which derives its blue color from CuII. Unfortunately, existing synthesis routes are either not technically benign or lack the natural platy morphology. Here, we introduce a new synthesis route starting with large, square-shaped platelets of a synthetic layered sodium silicate (NaRUB-18). As evidenced by Rietveld refinement and scanning electron microscopy, NaRUB-18 can be converted with conservation of this attractive morphology (pseudomorphosis) into Egyptian blue.