​Wettability of sapphire crystals

Wettability of sapphire crystals

The efficacy of sapphire used in chemical engineering and medical implants (among other factors) is defined by the wettability of its surface when it comes in contact with liquid substances. Wettability is one of the "bioactive" factors of the implant surface. According to the surface For the purpose, both maximum and minimum wettability are required. At the same time, there is little literature on wetting of sapphire. In the literature [98] dealing with the contact wetting angle, the surface free energy of sapphire is determined to be 52.95 erg /cm2, but the corresponding crystallographic plane is not indicated. In the mineralogical literature, wettability features of 92-80º are most common; these data are also not linked to crystallographic features. This is why the range of wetting angles is so wide . Sapphire is anisotropic; so the surface free energy is very different for each crystallographic plane [99].

The wettability is quantitatively characterized by the wetting angle Q0 formed on the solid surface along the contact surface. This value, according to Foxe's formula, is related to the surface energy of the material and is determined by the three-phase interface in contact with the wetting line ( s-l, s-g, l-g) surface free energy (SFE):

cosQ = (σs-g-σs-l)/σl-g (2.11)

The number of free bonds per unit area can be thought of as an approximate measure of this energy.

The surface free energy in a real crystal is determined by the number, type and distribution of structural defects. To unify these parameters, the crystal was grown at a rate of 10 mm/h and vacuum annealed at 1,950 °C. Then a 18 mm diameter and 10 mm thick sheet was cut from the crystal. Disc; orientation error is less than 1º. The surface of the sample is polished to Rz=0.05μm, wiped with alcohol-moistened cotton, wiped with water-moistened cloth and dried in air. The wetting angle Q0 of the remaining water droplets is measured using an optical microscope , the crystallographic planes (0001);{1010};{112 0};{1012} and the (0001) plane doped with 0.1%Cr and the {112 0} plane doped with 0.05%Ti were studied. Wettability. The surface is wetted with distilled water, glycerol and isobaric solution (0.9%NaCl) in air atmosphere at 25℃. The wetting angle measurement error is 0.5-1.3%.

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