Pretreatment method, surface

Electrode Pretreatment. There is ample evidence that the rate of electron transfer at a solid electrode is sensitive to the surface state and previous history of the electrode. An electrode surface that is not clean usually will manifest itself in a voltage-sweep experiment to give a decrease in the peak current and a shift in the peak potential. Various pretreatment methods have been employed to clean or activate the surface of electrodes the process is intended to produce an enhancement of the reversibility of the reaction (i.e., produce a greater rate of electron transfer).97 This activation or cleaning process may function in two ways by removing adsorbed materials that inhibit electron transfer and by altering the microstructure of the electrode surface. 

XANES. - Au(CH3)2(acac)/MgO X-ray absorption, near edge spectroscopy (XANES) was used to determine the oxidation state of MgO-supported Au particles. These samples were prepared by decorating the surface of MgO with a Au(III) complex Au(CH3)2(acac). The samples were then analyzed for Au oxidation state as a function of the pretreatment gas (He or H2) and pretreatment method. With increasing temperature of treatment, in either He or H2, the Au was reduced from the cation to the metal. In the absence of H2, it was speculated... 

The geometric surface area is only a basic parameter for the corrosion rate expression in normalized unit g/m2 within normalized test duration. An actual surface area is mentioned [2], but not defined in standards [1, 2] therefore we use the geometric surface and try to evaluate influence of various factors that increase the real surface area. The corrosion rate depends on such surface parameters as surface roughness and its anisotropy, evenness of material composition on the surface, pretreatment of surface, storage of samples before the corrosion test, and so on. Inasmuch as these parameters have no proper units for quantitative estimation expression, it was impossible to evaluate their contribution to the combined uncertainty of the tested surface area. The nominal value of surface roughness in the standard method is indicated as i a=1.3 0.4 pm, but in our case 7 a=0.67 0.01 mm, with an anisotropy Rai=0.60 pm (along the plate) and i aj=0.74 pm (across the plate). 

Pretreatment methods such as flaming, corona treatment, or ND plasma treatment are not useful, or even disadvantageous, with cyanacrylate adhesives due to the formation of acidic cleavage products or components on the surface. 

Grinding, brushing or sanding (with the exception of the above-mentioned Saco method) do not cause chemical modifications of the material s surface. A clean surface results with a characteristic structure corresponding to the composition of the material, as shown in Figure 7.6. Therefore, physical and chemical pretreatment methods are aimed at the chemical modification of the surfaces. Thus, on the one hand it is possible to further enhance the adhesive forces for extremely high demands on bonded joints, and on the other hand, to make poorly bondable material (e.g., plastics) bondable at all. Since physical methods are mainly used in bonding of plastics, they are described in Section 9.2.4. 

The group of chemical surface pretreatment methods also includes pickling. Here, thinned acids are applied, which remove layers on the metal surfaces via chemical reactions resulting in metallically clean surfaces. The respective application regulations apply, too. 

For the application of the explained surface pretreatment methods and their effects, the structure of surface layers typical for metal materials will be described below (Figure 7.7). 

Finally, an important difference between mechanical and chemical surface pretreatment methods should be pointed. Concerning their effects, the former are only limited to the adhesive surface area, that is, they are not able to protect the neighboring areas of the adhesive surface against possible stress from the ambience. 

In contrast to this, mechanical surface pretreatment methods, as described in Section 7.1, are universally applicable. With the process steps... 

Owing to the deformability of plastics - in particular of thermoplastics - mechanical pretreatment methods are applicable only to a very limited extent. So for example, if jet pressure is too high the blasting abrasive can be shot into the surface. For polyethylene and polypropylene for instance, the SACO-mefhod described in Section 7.1.2.1 has proven its worth. It develops a surface suitable for the formation of adhesive forces by means of chemically modified blasting abrasives (silication). 

This test method is preferably used for the comparative evaluation of adhesives and surface pretreatment methods, since it enables the indication of the differences in the adhesive and cohesive behavior of the adhesive layers with high sensitivity. Pressure-sensitive adhesives (adhesive tapes, adhesive labels) are also tested according to this principle. 

Flame treatment Surface pretreatment method, especially for plastics, by means of an acetylene, propane or butane flame burning in excess oxygen. Results in improved surface wettability by the adhesive due to the chemical entrapment of oxygen atoms in the polymer surface. 

Diamond nucleation rates on non-diamond substrates vary from 10 to 10 cm h, depending on synthesis conditions, substrate materials and surface pretreatment methods (polishing, etching, seeding, or annealing). 

In an effort to enhance diamond nucleation and to control film morphology, extensive work on the nucleation and early growth stages has been performed. As a result, technology problems associated with the nucleation of polycrystalline diamond films have been adequately addressed. A number of nucleation enhancement methods have been developed that enable the control of nucleation density over several orders of magnitude. Nucleation density has been increased from < 10 cm on untreated substrates up to 10 cm on scratched or biased substrates. The effects of surface conditions on nucleation processes have been investigated to provide the guideline for the selection of optimum surface pretreatment methods. In this chapter, substrate materials, surface pretreatment methods and their influences on diamond nucleation are discussed. 

SURFACE PRETREATMENT METHODS AND NUCLEATION ENHANCEMENT MECHANISMS... 

Diamond nucleation on non-diamond surfaces without pretreatment is usually too slow to obtain continuous films within a reasonable time. A variety of surfece pretreatment methods have been developed to enhance diamond nucleation rate and density on various substrates, including ... 

Another alternative surface pretreatment method, which can enhance diamond nucleation and avert surface damage, is covering or coating substrate surfaces with overlayers. The overlayers may involve graphite fibers, clusters, or films, thin films of met-... 

Surface nucleation rates and densities of diamond on non-diamond substrates vary fi-om 10 to 10 cm h and from 10 to 10 cm, respectively, depending on substrate materials, surface pretreatment methods, and synthesis conditions. The possible maximum nucleation density of diamond would be 10 cm . ... 

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