Page 67 - Handbook of Adhesion Promoters

60 Substrates - Surface Condition and Treat-

Figure 4.7. Scheme of bubble collapse effects on the surface due to (i) symmetric collapse in liquid with forma-
tion of shock waves and liquid streaming; and (ii) asymmetric collapse with surface erosion. Insets show the
complexity of the ultrasonic treatment of surfaces involving processes at different hierarchy scales: for theoreti-
cal calculations (i) electronic state; (ii) atomic scale; (iii) pseudo-particles. [Adapted, by permission, from Skorb,
EV; Möhwald, H, Ultrasonic Sonochem., 29, 589-603, 2016.]

Depending on intensity, ultrasonication may cause formation of a rough metal inter-
face and trigger free radical polymerization of monomers in the interfacial region of the
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metal surface. Such formed polymer layer exhibits excellent adhesion to the bulk metal. 8
Synthesis, removal/cleaning of the surface from biofilms, polymers (hydrogels), and con-
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taminations are simultaneously possible. Ultrasonic treatment of metals and silicon can
be used for the development of active chemically-stabilized surface sponge-like struc-
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tures, recrystallization of the surfaces, formation of metal nanoalloys. Incorporation of
metal ions/nanoparticles into the bulk structure and formation of functional layers can also
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result from the ultrasonic treatment. Further details about the process can be found else-
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where.
The surface of TiNi shape memory alloy substrate cleaned by ultrasonic cleaning had
a considerable amount of adherent residue such as the diamond paste and the lapping oil,
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not removed by the ultrasonic cleaning. These contaminations caused the separation of
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the film from the substrate. Wiping the surface of alloy substrate with cotton gauze
soaked in organic solvent followed by ultrasonic cleaning was effective in the removal of
adherent residue and it improved the adhesion of the deposited pure titanium film and the
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alloy substrate.
4.2.2 MECHANICAL
Mechanical preparation of the adherent sample to improve adhesion includes grinding,
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sanding, sandblasting, and polishing. The grinding removes sharp edges and deep
grooves and it is conducted at low temperature to prevent structural changes of surface. 11
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In addition to machining (grinding), surface can be further polished by sanding. Sanding
papers have different grid sizes based on the inverted size of the particle (the lower the
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grid number the larger the particles on sandpaper). In the USA, grids are numbers from
24 to 1000 (average particle diameter from 1815 to 4 μm) and in Europe, paper designa-
tions are from P12 to P6000 (average particle diameter from 708 to 10.3 μm). The backing