Morphology Control of Lead Carboxylate Powders via Anionic Substitutional Effects

Abstract

Lead carboxylate salts were precipitated from solutions containing 0-95 vol% ethyl alcohol in water, 0.005 M lead acetate, and 0.015 M diethyl oxalate at room temperature. Transmission electron microscopy analysis performed on samples prepared with 70-95 vol% ethyl alcohol and aged for 35 min revealed that the initial precipitate consisted of lead carbonate hydroxide particles of differing morphologies and degrees of crystallinity. The 70 vol% system displayed well-crystallized, elongated lathlike crystals (<3 μm), the 85 vol% sample displayed low crystalline order 0.1-μm spheres, and the 95 vol% system formed aggregated networks of interconnected low crystalline order particles. In the absence of diethyl oxalate, the 85 vol% sample formed platey particles composed of plumbonacrite. While lead oxalate was the equilibrium phase obtained in all systems after long aging times ( t > 16 h), the formation of the low crystalline order lead carbonate hydroxide could be maintained by adding ammonium hydroxide. Thermal gravimetric analysis (TGA) coupled with carbon, hydrogen, and nitrogen combustion analysis (CHN) revealed that excess carbon was present in the 85 vol% sample. The excess carbon was attributed to the presence of oxalate ion in the precipitate as shown by Fourier transform infrared (FTIR) spectroscopy. This substitutional incorporation of oxalate ion into the lead carbonate hydroxide structure resulted in a decrease in the crystalline order of the precipitate due to lattice strain effects. Decreases in crystalline order were reflected by the uniform morphology exhibited for the 85 vol% system and were observed to enhance coating interactions between polystyrene latex (sulfate and carboxylate surface groups) and oxalate-modified lead carbonate hydroxide.