Surface chemistry of fatty acid adsorption at apatite and other surfaces studied using Fourier transform infrared spectroscopy.

摘要

Carboxylate surfactant adsorption at apatite {dollar}rm lbrack Casb{lcub}10{rcub}(POsb4)sb6 Fsb2rbrack{dollar} and fluorite {dollar}rm lbrack CaFsb2rbrack{dollar} surfaces has been studied by ex-situ and in-situ FTIR internal reflection spectroscopy (FTIR/IRS) in this thesis research. Oleate adsorption isotherms at a fluorapatite surface have been determined at different pH values and temperatures using a fluorapatite single crystal as a reactive internal reflection element (IRE). The results were compared with previous results determined by the solution depletion method and with the results for fluorite and calcite systems. Significant discrepancies were found and discussed in details. In addition, the hydrophobicity of the surface after oleate adsorption has been studied.; It has been established, through previous spectroscopic studies, that for alkaline pH long alkyl chain carboxylic acids chemisorb at calcium-bearing semisoluble salt mineral surfaces at surface coverages of less than monolayer coverage and that this chemisorbed carboxylate is characterized by a singlet IR absorption peak at 1550 cm{dollar}sp{lcub}-1{rcub}{dollar}. Above monolayer coverage the calcium dicarboxylate salt precipitates at the surface. The surface precipitated calcium dicarboxylate salt is distinguished from the chemisorbed carboxylate by a doublet IR absorption peak at 1575 and 1540 cm{dollar}sp{lcub}-1{rcub}{dollar}.; It was found in this study that the characteristic band for the adsorbed carboxylate at a fluorite surface was not surface coverage dependent. Detailed spectroscopic studies of Langmuir-Blodgett monolayers of stearic acid and/or calcium distearate transferred at various surfaces reveal that whenever the carboxylate group has enough spatial freedom to form the thermodynamically stable 7-fold coordination structure, the doublet is observed characteristic of a mixed coordination state (unidentate and bidentate). If the spatial freedom is restricted, such as is the case for a monolayer of adsorbed carboxylate, then the singlet is observed characteristic of bridging coordination.; Wetting of quartz {dollar}rmlbrack SiOsb2rbrack{dollar} and francolite (a cryptocrystalline carbonate fluorapatite) by water and oil in the absence and presence of fatty acid was studied by a high speed video technique. The results from this experimental work clearly show the preferential transfer of oil to the francolite surface and help to explain flotation technology that has been developed by industry.; Finally, polygonal IRE geometry, with which more reflections can be obtained, was developed for FTIR/IRS studies and its application was demonstrated.