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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

Friction measurements as a function of time for calcite, Ot-1 and Ot-2 layers for experiment Cd.6. Error bars correspond to the calculated standard deviation of the friction.
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Figure 5: Friction measurements as a function of time for calcite, Ot-1 and Ot-2 layers for experiment Cd.6. Error bars correspond to the calculated standard deviation of the friction.

Mentions: Fig. 5 shows the measured friction as a function of time for the layer of calcite, Ot-1 and Ot-2 from the Cd.6 experiment. This figure reveals that at a load of 25 nN, Ot-1 forms a contact with the AFM tip with a friction force 20% higher than that of the contact with calcite, whereas Ot-2 shows an increase of 80% with respect to the original calcite surface. This is in contrast to the values reported in Fig. 3 where at a load of 25 nN the Cd-rich layer has a higher friction than calcite. Since the experiments where performed with different cantilevers this inconsistency is probably due to a difference in the tip radius. Additionally, the relative differences in friction between calcite, Ot-1 and Ot-2 varied for different experiments performed in Ca-free solutions, even when supersaturation and load conditions were similar, raising additional questions on the effect of other experimental parameters as discussed in the Methods section.


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)

Friction measurements as a function of time for calcite, Ot-1 and Ot-2 layers for experiment Cd.6. Error bars correspond to the calculated standard deviation of the friction.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Friction measurements as a function of time for calcite, Ot-1 and Ot-2 layers for experiment Cd.6. Error bars correspond to the calculated standard deviation of the friction.
Mentions: Fig. 5 shows the measured friction as a function of time for the layer of calcite, Ot-1 and Ot-2 from the Cd.6 experiment. This figure reveals that at a load of 25 nN, Ot-1 forms a contact with the AFM tip with a friction force 20% higher than that of the contact with calcite, whereas Ot-2 shows an increase of 80% with respect to the original calcite surface. This is in contrast to the values reported in Fig. 3 where at a load of 25 nN the Cd-rich layer has a higher friction than calcite. Since the experiments where performed with different cantilevers this inconsistency is probably due to a difference in the tip radius. Additionally, the relative differences in friction between calcite, Ot-1 and Ot-2 varied for different experiments performed in Ca-free solutions, even when supersaturation and load conditions were similar, raising additional questions on the effect of other experimental parameters as discussed in the Methods section.

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