Wetting and Spreading

Notice in Table XVIII-1 a value for the self-diffusion of Ni on Ni(lll) measured using radioactive Ni. More gross processes can occur. Supported Ni crystallites (on alumina) may show spreading and wetting phenomena due to complex interactions with the substrate [146]. 

Surfactant An adjuvant which improves the emulsifying, dispersing, spreading, and wetting properties of a pesticide. 

Another important consideration in preparing mixed-oxide catalysts is the spontaneous monolayer dispersion of oxides and salts onto surfaces of support substrates on calcination. Both temperature and duration of calcination are important here, as discussed in the reviews by Xie and Tang [63] and by Knozinger and Taglauer [64]. If this dispersion step is inadequate or incomplete, the resulting oxide layer, and any reduced metal surface from it, will not be reproducible from the same catalyst system therefore, one can then have different catalysts prepared at different times and, of course, from one laboratory to another. Spreading and wetting phenomena in preparation of supported catalysts is discussed in Section A.2.2.1.3. 

When 02>ai, cos 0i is positive, i.e. 0i<9O° hence the liquid having the smaller surface tension against the solid will spread and wet the solid. 

Is it important to know y to such accuracy except for academic reasons Hardly. Theoretically determined values (chapter 2) differ from actual values by several mN m L In virtually every case in practice, changes of y" (as a function of time, temperature, solute concentration, etc.) rather than its absolute value are considered, or y is considered in combination with other surface and interfacial tensions (e.g. in spreading and wetting). Even if the absolute value is not exactly known, variations in it can usually be established with an accuracy that is satisfactory for the problem at hand. 

Trisiloxanes represent a unique subset within conventional silicone polyether copolymers. Their well-defined compact siloxane backbone affords distinctive application benefits (e.g., spreading and wetting). However, they tend to be more prone to hydrolysis. 

KEW MECHANTSMS OF SINTERING AND RlCDlSPERSION INDUCED BY SPREADING AND WETTING... 

M0O3 and the support Y-AI2O3 prior to any thermal treatment so as to facilitate spreading and wetting. 

Low energy ion scattering (LEIS) is the most surface-sensitive technique available today and is therefore exceptionally well suited for the study of spreading and wetting in... 

Transition Metal Salts and Oxides on Alumina. Transition metal salts, particularly chlorides and nitrates, are frequently used as starting materials for the preparation of supported transition metal oxides or supported precursors for supported metal catalysts. Also, many catalytic materials, particularly supported molybdenum and tungsten oxide and sulfide catalysts, contain transition metal ions, namely Co, Ni , and Fe " as promoters. Thus, it is interesting to study the spreading and wetting behavior of salts of these transition metals and of their oxides. This is of particular importance for promoted catalyst materials, since in practice the incorporation of the active phase and the promoter should be possible in one step for economic reasons. 

When a liquid is placed on a solid surface, either it will spread and wet that surface (Fig. 10.22fl) or it will bead up (Fig. 10.22ft). The degree of wetting and whether a system is wetting or nonwetting are quantified by the equilibrium contact angle 9 that forms between the liquid and the solid and is defined in Fig. Q.22a and ft. A simple balance of forces indicates that at equilibrium... 

The previously reviewed investigations of spreading and wetting make it possible to give a simple and fundamental explanation of the epilame treatment of Woog [27, 28]. Essentially the epilame is a modification of the substrate surface. A close-packed adsorbed monolayer of a higher fatty acid, such as stearic acid, has a value of 24 dynes per cm. Any oil or other liquid having a surface tension, yLv°> 20°C. 

Previously published J. Venzmer, S. P. Wilkowski, "Trisiloxane Surfactants — Mechanisms of Spreading and Wetting , Pesticide Formulations and Application Systems, 18, ASTM STP 1347, (Eds J. D. Nalewaja, G. R. Goss, R. S. Tann), American Society for Testing and Materials, 1998. 

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