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Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale.

Cubillas P, Higgins SR - Geochem. Trans. (2009)

Bottom Line: Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique.Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms.In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Wright State University, 3640 Col, Glenn Hwy, Dayton, Ohio 45435, USA. pablo.cubillas-gonzales@manchester.ac.uk

ABSTRACT
Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

No MeSH data available.


Related in: MedlinePlus

Theoretical friction vs load curves for two different materials in contact with an AFM tip. a) Contact 1 has a higher surface adhesion than contact 2 (γ1 > γ2) but the same shear strength. b) Shear strength of contact 1 is higher than that of contact 2. c) Shear strength of contact 1 is lower than contact 2; adhesion of contact 1 is higher than contact 2.
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Figure 2: Theoretical friction vs load curves for two different materials in contact with an AFM tip. a) Contact 1 has a higher surface adhesion than contact 2 (γ1 > γ2) but the same shear strength. b) Shear strength of contact 1 is higher than that of contact 2. c) Shear strength of contact 1 is lower than contact 2; adhesion of contact 1 is higher than contact 2.

Mentions: By combining equations 1, 2 and 4 it is possible to model the load dependence of friction for a contact between an AFM tip and a surface. Fig. 2 shows different theoretical friction vs load curves for two different tip-sample contacts highlighting the effect of the contact shear strength (τ) and adhesion energy (γ). Fig. 2a shows the theoretical friction vs load curves for two substrates with different adhesion energies but the same contact shear strength. This difference does not affect the overall slope of the curves. In Fig. 2b the shear strength of contact 1 is higher than that of contact 2 but the adhesion energies are the same. This translates into a different slope for each curve. In fig. 2c both the contact shear strength and the adhesion energies are different for the two materials. In this case both curves will intersect each other at a certain point.


Friction characteristics of Cd-rich carbonate films on calcite surfaces: implications for compositional differentiation at the nanometer scale.

Cubillas P, Higgins SR - Geochem. Trans. (2009)

Theoretical friction vs load curves for two different materials in contact with an AFM tip. a) Contact 1 has a higher surface adhesion than contact 2 (γ1 > γ2) but the same shear strength. b) Shear strength of contact 1 is higher than that of contact 2. c) Shear strength of contact 1 is lower than contact 2; adhesion of contact 1 is higher than contact 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2719640&req=5

Figure 2: Theoretical friction vs load curves for two different materials in contact with an AFM tip. a) Contact 1 has a higher surface adhesion than contact 2 (γ1 > γ2) but the same shear strength. b) Shear strength of contact 1 is higher than that of contact 2. c) Shear strength of contact 1 is lower than contact 2; adhesion of contact 1 is higher than contact 2.
Mentions: By combining equations 1, 2 and 4 it is possible to model the load dependence of friction for a contact between an AFM tip and a surface. Fig. 2 shows different theoretical friction vs load curves for two different tip-sample contacts highlighting the effect of the contact shear strength (τ) and adhesion energy (γ). Fig. 2a shows the theoretical friction vs load curves for two substrates with different adhesion energies but the same contact shear strength. This difference does not affect the overall slope of the curves. In Fig. 2b the shear strength of contact 1 is higher than that of contact 2 but the adhesion energies are the same. This translates into a different slope for each curve. In fig. 2c both the contact shear strength and the adhesion energies are different for the two materials. In this case both curves will intersect each other at a certain point.

Bottom Line: Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique.Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms.In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, Wright State University, 3640 Col, Glenn Hwy, Dayton, Ohio 45435, USA. pablo.cubillas-gonzales@manchester.ac.uk

ABSTRACT
Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0-40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

No MeSH data available.


Related in: MedlinePlus