| 1. |
- Bergström, L, et al.
(författare)
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Estimation of Hamaker constants of ceramic materials from optical data using Lifshitz theory
- 1996
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Ingår i: Journal of The American Ceramic Society. - 0002-7820 .- 1551-2916. ; 79, s. 339-348
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Tidskriftsartikel (refereegranskat)abstract
- The Hamaker constants of 8 different ceramic materials, 6H-SiC, tetragonal, partially stabilized-ZrO2 (3% Y2O3), b-Si3N4, a-Al2O3, Y2O3, sapphire (single crystal a-Al2O3), MgO, MgAl2O4, and fused silica, across air, water, and n-dodecane at room temperature and across silica at 2000 K have been calculated from optical data using Lifshitz theory. Spectroscopic ellipsometry was used to measure the photon energy dependence of the refractive index, n, and the extinction coefficient, k, in the visible and near-UV range on several important ceramic materials. This relatively simple, nondestructive technique has proved to yield reliable optical data on sintered, polycrystalline materials like Si3N4, SiC, ZrO2 and Al2O3. For the other materials, Y2O3, sapphire, MgO, MgAl2O4 and fused silica, optical data from the literature were used to calculate the Hamaker constants. The calculated Hamaker constants were estimated to be accurate within ± 10%.
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| 2. |
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| 3. |
- Bogdanovic, G., et al.
(författare)
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Tip friction - torsional spring constant determination
- 2000
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 19:4, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- A non-destructive technique is presented for verifying torsional spring constants used in lateral force microscopy. Various calibrations of the microscope are required and these are detailed. The technique produces reasonable values which tend to be larger than those predicted from considerations of the cantilever dimensions. The differences are discussed in terms of length corrections and particularly the uncertainty in the thickness of the cantilevers, which has an enormous effect on the values obtained through a priori calculations. Methods for inferring the thickness are discussed. Further, artefacts in conventional force measurements related to the experiments performed here are discussed.
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| 4. |
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| 5. |
- Laarz, E, et al.
(författare)
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Silicon nitride colloidal probe measurements: Interparticle forces and the role of surface-segment interactions in poly(acrylic acid) adsorption from aqueous solution
- 2001
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Ingår i: Journal of The American Ceramic Society. - 0002-7820 .- 1551-2916. ; 84, s. 1675-1682
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Tidskriftsartikel (refereegranskat)abstract
- Direct measurements of forces between silicon nitride surfaces in the presence or poly(acrylic acid) (PAA) are presented. The force-distance curves were obtained at pH > pH(iep) with an atomic force microscopy (AFM) colloidal-probe technique using a novel spherical silicon nitride probe attached to the AFM cantilever. We found that PAA adsorbs onto the negatively charged silicon nitride surface, which results in an increased repulsive surface potential. The steric contribution to the interparticle repulsion is small and the layer conformation remains flat even at high surface potentials or high ionic strength. The general features of the stabilization of ceramic powders with PAA are discussed; we suggest that PAA adsorbs onto silicon nitride by sequential adsorption of neighboring segments ("zipping"), which results in a flat conformation. In contrast, the long-range steric force found in the ZrO2/PAA system at pH > pH(iep) arises because the stretched equilibrium bulk conformation of the highly charged polymer is preserved via the formation of strong, irreversible surface-segment bonds on adsorption.
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| 6. |
- Meurk, A, et al.
(författare)
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Direct measurement of repulsive and attractive van der Waals forces between inorganic materials
- 1997
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 13, s. 3896-3899
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Tidskriftsartikel (refereegranskat)abstract
- The repulsive and attractive interactions between silicon nitride and silica across diiodomethane and 1-bromonaphtalene were measured using an atomic force microscope (AFM). By combining measuremnets of asymmetric (silicon nitride versus silica) and symmetric (silicon nitride versus silicon nitride) material combinations in these solvents, a thorough analysis of the nature of the observed force curves was enabled. The sign, magnitude and separation distance scaling of the interactions could be well described with a van der Waals interaction between a flat surface and a sphere using calculated Hamaker constants from Lifshitz theory.
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| 7. |
- Meurk, A
(författare)
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Microscopic stick-slip in friction force microscopy
- 2000
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Ingår i: Tribology letters. - 1023-8883 .- 1573-2711. ; 8, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- Friction force measurements were performed on 2-hydroxy stearic acid (2-HSA) and 12-hydroxy stearic acid (12-HSA) coated silica surfaces in air using an atomic force microscope. The 2-HSA displayed viscoelastic behaviour with a yield point as the static–dynamic friction transition. Steady sliding motion was replaced by microscopic stick–slip at lower velocities and higher loads. Stick–slip motion was successfully described and fitted to a phenomenological model ascribed to interfacial material melting and freezing in periodic cycles. The stick–slip periodicity is of the same order as the contact diameter. The 12-HSA did not experience a yield point and exhibited steady sliding over the entire load and velocity regime. We attribute these observations to the difference in molecular configuration, shear strength and adsorption density of the stearic acid layers.
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| 8. |
- Meurk, A, et al.
(författare)
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Silicon nitride granule friction measurements with an atomic force microscope: effect of humidity and binder concentration
- 2001
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Ingår i: Powder Technology. - 0032-5910 .- 1873-328X. ; 119, s. 241-249
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Tidskriftsartikel (refereegranskat)abstract
- This study introduces the atomic force microscope (AFM) for direct measurement of internal and external friction in ceramic powder pressing. The experiments were performed between two single granules and a granule and a hard metal substrate as a function of granule binder concentration, relative humidity and sliding velocity. Granule-substrate measurements proved the friction coefficient to decrease with increasing humidity within a specific binder concentration, the effect being more pronounced for low concentrations. The friction coefficient also decreased with increasing binder concentration. Evaluation of the adhesion force showed a steady increase with both humidity and binder concentration. A substantial difference, almost an order of magnitude, was seen for the highest binder concentration at low and high humidities. We attribute these findings to the hygroscopic nature of the binder, poly(ethylene glycol) (PEG). Softening of the PEG at increasing humidities lowers the friction coefficient but increases the adhesion force. The results are consistent with flowability measurements and pressing performance.
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| 9. |
- Zhmud, BV, et al.
(författare)
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Application of charge regulation model for evaluation of surface ionization parameters from atomic force microscopy (AFM) data
- 2000
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 164, s. 3-7
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Tidskriftsartikel (refereegranskat)abstract
- The present state of affairs with calculation of electrostatic interaction between two charge regulated surfaces is briefly reviewed, placing a special emphasis on assumptions and limitations of underlying physical models. An application of the charge regulation model for evaluation of surface ionization parameters from the interaction force profile measured with an atomic force microscope in a symmetric silica¯silica system is demonstrated. The site density and the dissociation equilibrium constant of surface silanols are determined. As can be judged from the results obtained, surface silanols are considerably more acidic than it was considered before.
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| 10. |
- Zhmud, BV, et al.
(författare)
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Evaluation of surface ionization parameters from AFM data
- 1998
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 207, s. 332-343
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Tidskriftsartikel (refereegranskat)abstract
- A new application of atomic force microscopy (AFM) for evaluation of surface ionization parameters on the basis of a charge regulation model is demonstrated. Interactions between symmetrical silicon nitride and silica surfaces have been measured in aqueous electrolytic solutions at different pH and separations from a few Debye lengths down to zero. The obtained experimental data are reported and interpreted on a quantitative level in the framework of Derjaguin's approximation; the computational procedure used for this purpose is outlined. Surface charge density, surface potential, and species concentrations are calculated as functions of pH and separation, unveiling the limits of applicability of classical constant-charge and constant-potential approximations. The integrity of the results on the charge properties of interacting surfaces is discussed in reference to electrokinetic and titration data; potential problems caused by the existence of non-DLVO forces and surface irregularities being highlighted.
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