Study of Hydration Inhibitors on Aluminum Oxide Using Tunneling Spectroscopy and Molecular Electrostatic Potential Calculations

Abstract

Inelastic electron tunneling and ab initio molecular electrostatic potential calculations have been used to investigate the bonding of several phosphonate based hydration inhibitors adsorbed on aluminum oxide. Results are reported for phosphoric acid (PA), methylphosphonic acid (MPA), hydroxylmethylphosphonic acid (HMP), and nitrotrismethylphosphonic acid (NTMP). Tunneling spectra were taken for PA, HMP, and NTMP and the observed frequencies compared to values obtained from FTIR, IR, and Raman spectra of similar compounds. Upward shifts in the P=O and P‐O‐(H) stretch frequencies indicated that the phosphonates bond to the aluminum oxide surface through the phosphonate group. Ab initio quantum mechanical molecular electrostatic potentials (QMEP's) were calculated for PA, MPA, and HMP. Analysis of these results provided a means to understand on a molecular level the known variations in effectiveness for each of the inhibitors investigated.