Substrate surface preparation

In classical kinetic theory the activity of a catalyst is explained by the reduction in the energy barrier of the intermediate, formed on the surface of the catalyst. The rate constant of the formation of that complex is written as k = k0 cxp(-AG/RT). Photocatalysts can also be used in order to selectively promote one of many possible parallel reactions. One example of photocatalysis is the photochemical synthesis in which a semiconductor surface mediates the photoinduced electron transfer. The surface of the semiconductor is restored to the initial state, provided it resists decomposition. Nanoparticles have been successfully used as photocatalysts, and the selectivity of these reactions can be further influenced by the applied electrical potential. Absorption chemistry and the current flow play an important role as well. The kinetics of photocatalysis are dominated by the Langmuir-Hinshelwood adsorption curve [4], where the surface coverage PHY = KC/( 1 + PC) (K is the adsorption coefficient and C the initial reactant concentration). Diffusion and mass transfer to and from the photocatalyst are important and are influenced by the substrate surface preparation. 

In essence, the durability of metal/adhesive joints is governed primarily by the combination of substrate, surface preparation, environmental exposure and choice of adhesive. As stated earlier, the choice of the two-part nitrile rubber modified epoxy system (Hughes Chem - PPG) was a fixed variable, meeting the requirement of initial joint strength and cure cycle and was not, at this time, examined as a reason for joint failure. Durability, as influenced by substrate, surface preparation, and environmental exposure were examined in this study using results obtained from accelerated exposure of single lap shear adhesive joints. 

One of the factors that may be responsible for the sometimes disparate conclusions found in the literature regarding CPs for corrosion control is the wide variation in metal substrate surface preparation. There is very little consistency in the way substrate surfaces are prepared. At the very least, authors should completely describe their surface preparation protocol, including the time interval and conditions of storage (if any) between substrate preparation and coating application. In this section, we briefly review common approaches to substrate surface preparation. 

From a manufacturing point of view, adhesives require some critical processing steps, such as substrate surface preparation, controlled adhesive applications, and curing cycles. However, the elimination of mechanical... 

In this test, small spots of the adhesive are placed onto a substrate. Surface preparation, application procedures, and curing conditions are to be as similar as possible to those used in the quantitative test and/or the actual adhesively bonded Joint. The adhesive spots are allowed to cure according to the manufacturers specifications. To test adhesion, this ASTM standard practice recommends the use of a thin stainless steel spatula or similar probe as a prying lever to assess the relative difficulty of removing the adhesive from the substrate. If the results are acceptable, standard quantitative adhesive test procedures can be used to obtain quantitative measurement of the adhesive s performance. 

Table 5.2 Effect of Metal Substrate Surface Preparation in Adhesive Bonded Joints ...

Substrate surface preparation, which affects the nucleation, and interface formation in a desirable manner without introducing flaws into the surface. 

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