Diffusion surface treatments

Permeant movement is a physical process that has both a thermodynamic and a kinetic component. For polymers without special surface treatments, the thermodynamic contribution is ia the solution step. The permeant partitions between the environment and the polymer according to thermodynamic rules of solution. The kinetic contribution is ia the diffusion. The net rate of movement is dependent on the speed of permeant movement and the availabiHty of new vacancies ia the polymer. 

To produce wear-resistant or hardened surfaces, thin layers of borides can be prepared on metal surfaces by reaction and diffusion (see Metal SURFACE treatments). Boride powders can be formed iato monolithic shapes by cold pressing and sintering, or by hot pressiag. 

In developing criteria for the ranking of adhesive formulations or adherend surface treatments or primers, it is necessary to distinguish between two different situations. In one case (contact adhesion), a true interface is believed to exist across which intermolecular forces are engaged, while in the other, an interphase is formed by diffusive interpenetration or interdigitation between the adhesive and the adherend (diffusion interphase adhesion). Even in the case of contact adhesion, more often than not, an mi vphase of macroscopic thickness forms on... 

The diffusion of electrons plays a major role in the surface treatment of polymers in a gas plasma apparatus. The adhesion of PE tapes increases to a maximum by this treatment at 0.20 to 0.30 A for 20 to 30 s [40]. IR absorption at 1600-1750 cm increases 1.5-fold on discharge treatment owing to the formation of polar >C==0 and —COOH groups, which increase tape adhesion. 

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

The diffusion length of photogenerated charge carriers is one of the important parameters governing the efficiency of a solar cell. In conventional cells, this is an intrinsic property of the semiconductor and its purity [34]. However, in DSSCs, the diffusion length is a function of the rate of reaction (4) and, thus, varies with different redox couples, surface treatments, and so forth. When the oxidation of R [reaction (2)] is chemically irreversible, the diffusion length of electrons is effectively infinite, whereas with kinetically fast, reversible redox couples (see Section VI), it approaches zero with unpassivated interfaces. 

Sm2Fei7Nx powders are produced commercially since 1999 by the reduction and diffusion process [136]. The currently mass-produced powder has a BHimx of 290 kJ/m3 with /ioMt = 1.35 T and fi(iHc = 1.1 T. Milling and surface treatment have been optimized to improve the squareness of the demagnetization curve and resistance to corrosion [137]. 

As with metallic substrates, primers may be used to protect treated nonmetallic substrates. After surface treatment, a high-energy substrate has an active surface that will readily adsorb atmospheric contamination. The primer protects the treated surface until the time when the adhesive or sealant is applied. Primers are especially useful in this way for the protection of polymeric parts that are treated by flame or corona discharge. Primers also find benefit on polymeric substrates in that their solvents will soften the surface, and some of the primer resin will diffuse into the bulk of the substrate, thereby increasing the adhesive strength by molecular diffusion. 

Cavitation and the resulting surface-hardening effects of ultrasound due to the reduction in the thickness of the diffusion layer, has been utilized to improve performance in the finishing of machined components and other surface treatment techniques such as electro-polishing and pickling. 

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