An atomic force microscopy and molecular simulations study of the inhibition of barite growth by phosphonates

• Published in: Surface science 2004, Vol.553 (1), p.61-74
• Main Authors: Pina, C.M, Putnis, C.V, Becker, U, Biswas, S, Carroll, E.C, Bosbach, D, Putnis, A
• Format: Article
• Language: English
• Subjects: Adsorption isotherms; Atomic force microscopy; Computer simulations; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Crystallization; Exact sciences and technology; Growth; Physics
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2004.01.022

The effect of five phosphonic acids (hydroxyethylene diphosphonic acid, HEDP; nitro trimethyl phosphonic acid, NTMP; methylene diphosphonic acid, MDP; amino methylene phosphonic acid, AMP; and sodium phosphonobutane tricarboxylic acid, PBTC) on the growth of the barite(0 0 1) face has been investigated using atomic force microscopy (AFM). Experimental data have been obtained by in situ measurements of the velocities of barite monomolecular steps growing from solutions with different concentrations of each phosphonic acid. Adsorption isotherms, constructed by plotting individual monomolecular step rates versus inhibitor concentrations, indicate a Langmuir adsorption mechanism in the range of concentrations from 0.5 to 10 μmol/l. Both affinity constants calculated from adsorption isotherms and measurements of growth rates of barite monomolecular steps as a function of inhibitor concentration allowed us to give the following ranking of inhibitor effectiveness: PBTC > NTMP > MDP > HEDP ≫ AMP. Molecular simulations of the interaction of the phosphonic acids with barite(0 0 1) surfaces indicate that only kink sites along monomolecular steps can be considered as possible inhibition sites. This is in agreement with the AFM observations and measurements.