​Mechanical properties of sapphire crystals

Mechanical properties of sapphire crystals

Density, measured by hydrostatic weighing, with an accuracy of 0.05%. The density of sapphire ranges from 3.97 to 3.99 g/cm3, and the density of dark ruby containing 2.97% Cr2O3 is 4.013 g/cm3 There is a linear relationship with the content of chromium. Some impurities, such as titanium, calcium, etc., reduce the density value. The calculated value of density is slightly larger than the experimental value, which is related to the existence of micropores, microcracks, etc. in the real crystal .

Hardness. The Mohs hardness is 9; the hardness measured according to the Chiway 15-point hardness scale is 12. The Knoop hardness measured parallel and perpendicular to the C axis is 1,900 and 2,200 kg/mm2. Knoop hardness value The range is 1,525 to 2,200kg/mm2. The microhardness values measured by microindentation of the surface are 19.40 GPa (parallel to the optical axis), 23.15 GPa (60º angle to the optical axis), and 22.0 GPa (parallel to the optical axis) The axis is vertical). The microhardness of α-Al218O is significantly higher (the bond of Al2-18O is shorter than that of Al2-16O).

The Friction coefficient was studied with a load perpendicular to the polished end face. The lower part of the friction pair rotates, while the upper part remains stationary. The sliding friction coefficient of this sapphire pair is determined by the direction (Fig. 2.52) [68] . For the friction with steel, this is determined by the pressure and the lubricant used (table 2.10). The wear resistance is (according to Mackensen) 0.12 mm.

The elastic constant of sapphire is measured at room temperature [69,70] and the temperature for determining flexibility is listed in Tables 2.48 and 2.49.

The measured ultimate strength values for different types of sapphire are listed in Table 2.57.

Tensile strength is 275-400 MPa (4-6 104 psi);

Bending strength is 450-895 MPa. According to other sources, the bending strength is 1.03 GPa (1.5•105 psi) parallel to the C axis and 758 MPa (1.1•105 psi) perpendicular to the C axis psi) (list of major sapphire manufacturers).

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