Bassett force

As pointed out in Section 1.1a rhombic-based pyramidal diamond (Knoop test) is also used in the microindentation study of polymers (Balta Calleja Bassett, 1977). Again, the microhardness value is here derived from the force applied divided by the projected area of the impression (see eq. (1.3)). 

The Vickers microhardness test gives a smaller indentation for a given force than the Knoop test and is less sensitive to material anisotropy. The Knoop test is easier to use because the impression is longer for a given load and usually only one measurement per test is required. The microhardness measurement with the Knoop diamond is quite sensitive to material anisotropy because of the twofold symmetry of indentation. Nevertheless, the Vickers diamond, as we shall show below, also detects anisotropy conveniently (Balta Calleja Bassett, 1977 Balta Calleja et al, 1980a). 

The method of direct visual observation can be used in conjunction with in-situ Raman spectra. X-ray absorption fine structure (XAFS) and X-ray diffraction measurements (Zotov and Keppler, 2000 Fulton et al., 2000 Schmidt and Rickers, 2003 Bassett etal., 2000 Mayanovic etal., 2003) to study salt solubility, metal ion hydration, complexation and oxidation state in aqueous solution in a wide range of temperatures and pressures, and with the hydrothermal scanning force microscopy technique (Higgins etal., 1998) for observation of the advance or retreat of atomic layers (steps) on a crystal surface during the processes of dissolution or crystal growth. 

Figure 3. Cross-section drawing of the Bassett cell showing the hemi-cylinder hardened rocker supports for anvil alignment and the very simple force generating mechanism of a driving nut pushing against a movable piston in a guiding cylinder [8].

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