MORPHOLOGY CONTROL OF LEAD CARBOXYLATE POWDERS VIA ANIONIC SUBSTITUTIONAL EFFECTS

Lead carboxylate salts were precipitated from solutions containing 0-9 5 vol% ethyl alcohol in water, 0.005 M lead acetate, and 0.015 M dieth yl oxalate at room temperature. Transmission electron microscopy analy sis performed on samples prepared with 70-95 vol% ethyl alcohol and ag ed 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, elonga ted lathlike crystals (<3 mu m), the 85 vol% sample displayed low crys talline order 0.1-mu m spheres, and the 95 vol% system formed aggregat ed 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 pha se obtained in all systems after long aging times (t > 16 h), the form ation of the low crystalline order lead carbonate hydroxide could be m aintained 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. Th e excess carbon was attributed to the presence of oxalate ion in the p recipitate as shown by Fourier transform infrared (FTIR) spectroscopy. This substitutional incorporation of oxalate ion into the lead carbon ate hydroxide structure resulted in a decrease in the crystalline orde r of the precipitate due to lattice strain effects. Decreases in cryst alline order were reflected by the uniform morphology exhibited for th e 85 vol% system and were observed to enhance coating interactions bet ween polystyrene latex (sulfate and carboxylate surface groups) and ox alate-modified lead carbonate hydroxide.