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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 versus load plot for experiment Cd-1 and related height/fricion images. a) The friction vs. load plot shows that at low loads the calcite contact possess a slightly higher friction than that calculated for a single layer of calcian otavite, but at higher loads, the friction force is larger on the calcian otavite film. b) Height/friction image corresponding to a load of 14 nN. White lines on the height image represent the original calcite steps prior to the start of the calcian otavite film growth. c) Height/friction images corresponding to a load of 40 nN. d) Height/friction images corresponding to a load of 72 nN.
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Figure 3: Friction versus load plot for experiment Cd-1 and related height/fricion images. a) The friction vs. load plot shows that at low loads the calcite contact possess a slightly higher friction than that calculated for a single layer of calcian otavite, but at higher loads, the friction force is larger on the calcian otavite film. b) Height/friction image corresponding to a load of 14 nN. White lines on the height image represent the original calcite steps prior to the start of the calcian otavite film growth. c) Height/friction images corresponding to a load of 40 nN. d) Height/friction images corresponding to a load of 72 nN.

Mentions: As evidenced by the theoretical continuum mechanics models previously discussed, the friction characteristics of a tip-film contact can be dominated by different parameters at different load regimes (Fig. 2). To assess these parameters, a series of friction measurements as a function of load where carried out on calcite and Cd-rich films in experiments Cd.1 and Cd.11. Results from experiment Cd.1 are shown in Fig. 3. Fig. 3a shows the friction vs. load measurements for both the calcite and Cd-rich film. At low load (<40 nN) the friction for the calcite contact is higher than that of the Cd-rich film. Although small, the differences in friction are real as can be seen in Fig. 3b which shows the height and friction signals recorded at a load of 15 nN. At medium loads (≈40 nN) the measured friction for both contacts is approximately the same (Fig. 3c). At higher loads the friction contrast reverses and is the Cd-rich film contact the one displaying the higher friction. The recorded differences are again small, but significant (Fig. 3d). Results from experiment Cd.11 corroborate the differences in the load-dependent friction for the two contacts. In comparison, Hay et al. [29] only reported that the Cd-rich layers had a higher lateral force signal than the calcite substrate.


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 versus load plot for experiment Cd-1 and related height/fricion images. a) The friction vs. load plot shows that at low loads the calcite contact possess a slightly higher friction than that calculated for a single layer of calcian otavite, but at higher loads, the friction force is larger on the calcian otavite film. b) Height/friction image corresponding to a load of 14 nN. White lines on the height image represent the original calcite steps prior to the start of the calcian otavite film growth. c) Height/friction images corresponding to a load of 40 nN. d) Height/friction images corresponding to a load of 72 nN.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Friction versus load plot for experiment Cd-1 and related height/fricion images. a) The friction vs. load plot shows that at low loads the calcite contact possess a slightly higher friction than that calculated for a single layer of calcian otavite, but at higher loads, the friction force is larger on the calcian otavite film. b) Height/friction image corresponding to a load of 14 nN. White lines on the height image represent the original calcite steps prior to the start of the calcian otavite film growth. c) Height/friction images corresponding to a load of 40 nN. d) Height/friction images corresponding to a load of 72 nN.
Mentions: As evidenced by the theoretical continuum mechanics models previously discussed, the friction characteristics of a tip-film contact can be dominated by different parameters at different load regimes (Fig. 2). To assess these parameters, a series of friction measurements as a function of load where carried out on calcite and Cd-rich films in experiments Cd.1 and Cd.11. Results from experiment Cd.1 are shown in Fig. 3. Fig. 3a shows the friction vs. load measurements for both the calcite and Cd-rich film. At low load (<40 nN) the friction for the calcite contact is higher than that of the Cd-rich film. Although small, the differences in friction are real as can be seen in Fig. 3b which shows the height and friction signals recorded at a load of 15 nN. At medium loads (≈40 nN) the measured friction for both contacts is approximately the same (Fig. 3c). At higher loads the friction contrast reverses and is the Cd-rich film contact the one displaying the higher friction. The recorded differences are again small, but significant (Fig. 3d). Results from experiment Cd.11 corroborate the differences in the load-dependent friction for the two contacts. In comparison, Hay et al. [29] only reported that the Cd-rich layers had a higher lateral force signal than the calcite substrate.

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