Particle coating interactions in the synthesis of uniform ceramic oxide powders

Particle coating interactions between a basic lead carbonate hydroxide (Pb{dollar}sb3{dollar}(CO{dollar}sb3)sb2{dollar}(OH){dollar}sb2{dollar}) and inorganic core particles were studied to determine the role of oxalate (C{dollar}sb2{dollar}O{dollar}sb4sp={dollar}) anionic substitution and surface complexation in the enhancement of coating interactions. C{dollar}sb2{dollar}O{dollar}sb4sp={dollar} was found to substitute for CO{dollar}sb3sp={dollar} during the formation of Pb{dollar}sb3{dollar}(CO{dollar}sb3)sb2{dollar}(OH){dollar}sb2{dollar} as shown by TGA, selected area electron diffraction, and FTIR. The low crystalline order oxalate modified Pb{dollar}sb3{dollar}(CO{dollar}sb3)sb2{dollar}(OH){dollar}sb2{dollar} (LCH) exhibited a greater affinity for polystyrene and silica surfaces than the unmodified Pb{dollar}sb3{dollar}(CO{dollar}sb3)sb2{dollar}(OH){dollar}sb2{dollar}.; The LCH phase was used to coat uniform silica core particles in amounts ranging from 1 to 50 wt%. The coated particle samples were characterized according to energy dispersive spectroscopy, electrophoretic mobility, density, and particle size distribution analysis (TEM, dynamic light scattering (DLS), centrifugal sedimentation, and BET specific surface area) techniques. Observation of the coated particles indicated that 50 wt% LCH was required to totally encapsulate the silica core particles; lower LCH loadings appeared as clusters on the silica surface. The most useful data was obtained from the density, specific surface area, and particle size analyses. The experimentally measured density values for and composite core/shell particles displayed good agreement with theoretical calculations. Discrepancies in particle size analysis results obtained by TEM and DLS for coated particles were adequately treated by the application of derived correction factors based on the polydispersity index (Thomas, 1987) and the density difference between coated and uncoated particles.; The adsorption of lead on goethite ({dollar}alpha{dollar}-FeOOH) and oxalate equilibrated goethite was measured to gauge whether oxalate surface complexation played a role in the surface nucleation of the coating phase. While the adsorption of lead on untreated goethite gave indication of the formation of a surface precipitate at sorption densities in excess of 170 {dollar}mu{dollar}mol/g (1300 {dollar}mu{dollar}mol/g maximum adsorption density at added (Pb{dollar}sp{lcub}2+{rcub}{dollar}) 4.8 x 10{dollar}sp{lcub}-3{rcub}){dollar} the adsorption of lead on oxalate equilibrated goethite was less than one-half (613 {dollar}mu{dollar}mol Pb{dollar}sp{lcub}2+{rcub}/{dollar}g) of the maximum amount of lead adsorbed under identical conditions by the untreated goethite. TEM was used to show that LCH coating formation occurred via a heterocoagulation mechanism involving 5-10 nm LCH clusters. These results indicated that the role of oxalate in the coating process was limited to influencing the crystalline order of the LCH phase.