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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

Representative cross-section of an experiment where growth and friction contrast between layers had been observed. Fi indicates the friction computed for each layer stacking and Vi its advancement speed.
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Figure 9: Representative cross-section of an experiment where growth and friction contrast between layers had been observed. Fi indicates the friction computed for each layer stacking and Vi its advancement speed.

Mentions: Fig. 9 shows a "representative" cross section of a calcite surface following multilayer growth at moderate supersaturation levels (SI = 2–3) on experiments performed with both Ca-rich and Ca-free solutions. Friction of each "stack" was denoted as Fi, and Vi refers to its advancement speed. In principle two different scenarios can be envisioned to explain the friction variations between a single and double layer of SS: 1) There is no variation in the composition of the different layers (i.e., an atomically sharp interface) and friction changes between one layer and a double layer reflect only a difference in the mechanical properties due to strain in the overgrowths. 2) There is a variation in the chemistry of the growing layers, which will lead to differing chemical and mechanical properties (the latter possibly strain-related) and thus to a variation in friction.


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)

Representative cross-section of an experiment where growth and friction contrast between layers had been observed. Fi indicates the friction computed for each layer stacking and Vi its advancement speed.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Representative cross-section of an experiment where growth and friction contrast between layers had been observed. Fi indicates the friction computed for each layer stacking and Vi its advancement speed.
Mentions: Fig. 9 shows a "representative" cross section of a calcite surface following multilayer growth at moderate supersaturation levels (SI = 2–3) on experiments performed with both Ca-rich and Ca-free solutions. Friction of each "stack" was denoted as Fi, and Vi refers to its advancement speed. In principle two different scenarios can be envisioned to explain the friction variations between a single and double layer of SS: 1) There is no variation in the composition of the different layers (i.e., an atomically sharp interface) and friction changes between one layer and a double layer reflect only a difference in the mechanical properties due to strain in the overgrowths. 2) There is a variation in the chemistry of the growing layers, which will lead to differing chemical and mechanical properties (the latter possibly strain-related) and thus to a variation in friction.

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