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Estructura de la materia
- 3. LIQUIDO VAPOR VAPOR LIQUIDO Energia + Energia SOLIDO LIQUIDO LIQUIDO Energia + Energia SOLIDO
- 15. Estructura Cristalina Estructura NO Cristalina Oro, amalgama, yeso, metal Ceramicas puras Porcelana Inlcusiones cristalinas: color, opacidad, CET, resistencia, radiopacidad, etc.
- 28. Fin de la presentación..
Notas del editor
- The total potential and kinetic energy associated with the random motions of the molecules of a material. An object that feels hot has more thermal energy inside it than when the object is cool.
- f. Fís. Magnitud termodinámica que mide la parte no utilizable de la energía contenida en un sistema. Fís. Medida del desorden de un sistema. Una masa de una sustancia con sus moléculas regularmente ordenadas, formando un cristal, tiene entropía, mucho menor que la misma sustancia en forma de gas con sus moléculas libres y en pleno desorden.
- Estructuras no cristalinas: tienen una estructura desordenada, con difusion mas rapida con mucho menor energia
- Adhesion es atraccion entre diferentes moleculas.
- Proyeccion que sirven de anclaje para la retencion
- The surface atoms of a solid tend to form bonds to other atoms in close proxirn-ity lo the surface and reduce the surface energy of the solid. This attraction across the interface between unlilte molecules is called adhesion. For example, molecules in the air may be attracted to the suuiaceand become adsol-becion the material sur- face. Silvel-,platin~~man,d gold adsorb oxygen readily. For gold, the honding forces are of the secondary type; but in the case of silver, the attraction may be controlled by chemical or primary bonding, and silver oxide may form. When primary bonding is involved, the adhesion is termed chemisorption, as com- pared with physical bonding by van der Waals forces. In chemisorption, a chemical bond is formed between the adhesive and the adherend. An example of this type of adhesion is an oxide film formed on the surface of a metal or a layer of solder bonded to a metallic substrate. Thus, van der Waals forces are weaker than primary bonding because they are intermolecular rather than intramolecular. The development of van der Waals forces invariably precedes chemisorption. As the distance between the adhesive and the adherend diminishes, primary bonding may become effective. However, chemisorption is limited to the monolayer of adhe- sive present on the adherend. 7'he surface energy and the adhesive qualities of a given solid can be reduced by any surface impurity, such as adsorbed gas, an oxide,or human st~cretionshe functional chemical groups available or the type, of crys-tal plane of a space lattice presenl at the s~~rfacT.ay afkct lhe surf'lce energy. In summary, thc grt.atc.1- the surface energy, the grr;rtrl- the capacity lor adhesion.
- importa~lceA Glrn of water only one molecule thick on the surface of the solid may lower the surface energy of the adherend and prevent any wetting by the adhesive Likewise, an oilyfilm on a metallic su~facemay also inhibit the contact of an adhesive The su~face energy of some substances is so low that few, if any, liquids wet their surfaces. Some organic substances, such as dental waxes, are of this type. Close pack- ing of the structural organic groups and the presence of halogens may prevent wet- ting. Teflon (polytetrafluoroethylene), a commercial synthetic resin, is often used when it is desirable to prevent the adhesion of films to a surface Metals, on the other hand, interact strongly with liquid adhesives because of their high surfaceenergy. In general, the comparatively low surface energies of organic and most inorganicliquids permit them to spread freely on solids of high surface energy. Formation of a strong adhesive joint requi~esgood wettingThe cleanliness of the surface is of particula~
- Representación (hecha por mi) de la accion de fuerzas mecanicas y cambios termicos sobre la union resina diente.
- absorcion Adsorcion Sorcion quimica