Temperature effects on the 27Al NMR spectra of polymeric aluminum hydrolysis species

• Published in: Journal of magnetic resonance (1969) 1989-08, Vol.84 (1), p.121-133
• Main Authors: Fitzgerald, John J, Johnson, Loren E, Frye, James S
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Infrared spectra; Molecular properties and interactions with photons; Molecular spectra; Physics
• ISSN: 0022-2364; 1557-8968
• DOI: 10.1016/0022-2364(89)90010-3

27Al NMR studies at 39.10 MHz of highly hydrolyzed, concentrated aluminum chlorohydrate (ACH) solutions ( n = [ OH]/[ Al] = 2.50 , “Al 2 (OH) 5Cl”) from 2.5 to 0.2 M Al in various supporting electrolytes at room temperature (RT) and 82°C are reported. The complex 27Al NMR resonance features for ACH solutions, attributed to two unique polymeric species of unknown structure, are dependent upon concentration, temperature, and the nature and concentration of the supporting electrolyte anion. Major differences are observed in the 27Al NMR of fresh and “aged” 1.0 M ACH solutions obtained at RT, at 82°C, and at RT following temperature elevation to 82°C. These latter NMR spectra exhibit dramatic and irreversible resonance changes in comparison with RT NMR data obtained for fresh ACH solutions prior to elevation to 82°C. These 27Al NMR results, together with gel filtration chromatography data, provide evidence for the irreversible depolymerization of large molecular weight polycationic species to intermediate sized molecular weight polymeric species following dilution, aging, or temperature elevation. This depolymerization reaction is concentration, temperature, and anion dependent and provides a clearer understanding of the kinetic processes occurring for the polymeric aluminum species in ACH solutions.