Conversion layers

However, the method will not enhance the external quantum yield of the LED, moreover, proper optical coupling between the layers has to be achieved in order not to decrease the QY loo much [61. One of the obvious problems is the principal requirement of having the ITO-covered glass substrate between the color converter and the cmitLer layer. This can also lead to color bleeding, an effect where the emitter layer excites not only the conversion layer, it is supposed to address but also neighboring ones. 

The open circuit potential data for the B210/NVP system mirrors the behavior of the rust ratings over the temperature range examined. A plausible explanation of the change of the open circuit potential is as follows. As temperature is increased, the composition of the various oxides and hydroxides which make up the zinc phosphate conversion layer and the base iron oxide layer undergo changes. 

Thin film transistor (TFT) arrays are produced inexpensively and in large numbers for use in modern computer monitors and televisions. This readout system can be combined with amorphous hydrated silicon or amorphous selenium which is deposited over the large surface of the TFT array and acts as the X-ray conversion layer. Having established themselves firmly as an X-ray detector for medical imaging already, they have until now failed to make an impact on the field of crystallography, their high noise level being the main drawback. It can be surmised with some confidence that this type of detector will become standard equipment in the near future. 

The SiC coating was composed of two layers a thin SiC conversion layer (several pm) and a thick CVD coating layer. The conversion layer was formed by chemical reaction of gas phase Si with carbon in the substrate. The gaseous Si was provided by thermal decomposition of bubled SiCl, in which carrier gas was H,. The aim of the conversion layer is to make bonding strength of the coating higher. The CVD layer was thermally deposited at three kinds of temperatures, 1800, 1600 and 1200"C, named hereafter CVD-18, -16 and -12, respectively. 

The results for CVD-16 represent the effect of conversion layer. It is obvious from these results that within the present experimental condition longer conversion time is preferable and comparison with other data should be done on the base of the conversion time 3hrs. 

An epitaxial SiC conversion layer may form during the carburization of single-crystal Si substrates and the SiC layer facilitates the deposition of ordered diamond films.The in situ carburization provides an economical alternative to obtaining epitaxial diamond films on single-crystal SiC. 

Many factors contribute to the corrosion resistance of a modern painted steel or aluminum product including the nature of organic coating, the metal substrate and/or metal coating, and the conversion layer. It is impossible to speak of the corrosion resistance afforded by the conversion layer without reference to the total product. In this section, we will briefly describe some phenomena unique to the conversion layer, which do contribute to the corrosion resistance. A detailed description of corrosion mechanisms under paint is given in Chapter 5.4. 

Conversion Coatings Conversion layers have been described in detail in chapter 5.3. In this section, the effects of the pretreatment on the kinetics of the coating delamination are discussed with focus on the electrochemical principles. 

For conversion layers the substrate metal provides ions, which become part of the protective coating after the electrochemical... 

Conversion layers lead to an increased adhesion strength of organic coatings on metals xmder dry and wet conditions. In addition, the kinetics of ion and electron transfer processes at the metal-polymer interface are slowed down. In case of iron and zinc, especially the oxygen reduction rate, which strongly influences the delamination kinetics of the coating, is reduced. 

Galvanized steel For galvanized steel, the most prominent conversion layers are phosphate layers for automotive and chromate layers for cod-coating applications [4,185]. 

The corrosion-protection metal layers, deposited on a substrate as described in the previous sections, are often subjected to some posttreatment. The following describes the most widely used procedures the formation of an additional organic film, or the formation of a conversion layer. 

Chemical Methods. Chemical methods include pickling, which can be used to remove scale and metal oxides. Sulfuric acid and hydrochloric acid are usually used to treat steel and zinc, while nitric acid, nitric acid-hydrofluoric acid, or sulfuric acid-hydrofluoric acid are used for aluminum. Although pickling in phosphoric acid is somewhat slower, it has the advantage that a thin conversion layer of the substrate phosphates is produced, which provides temporary corrosion protection... 

Conversion layers generally consist of inorganic compounds formed on the metal surface. They are used to increase the corrosion resistance and to improve the paint adhesion of the metal surface. 

The surface weight of conversion layers is 0.05-5 g/m. With higher surface weights the flexibility of the layers decreases, which has an adverse effect on the flexural adhesion of the organic coating. 

For the yellow chromating of aluminum, solutions containing chromium(VI) compounds as well as simple or complex fluorides and activators are used to accelerate layer formation. The pH value is 1.5-2.5 at total bath concentrations of 5-20 g/L. The conversion layers consist of oxides or hydrated oxides of trivalent and hexava-lent chromium and aluminum. The color of the layer may range from colorless through yellowish iridescent to yellowish brown, corresponding to an increase in the surface weight from 0.1 to 3 g/m. ... 

Aqueous, chromium-free acidic solutions have also been developed for aluminum materials that may contain complex fluorides of titanium and zirconium, phosphate, and special organic compounds. These solutions are applied by spraying or dipping (up to 60 °C) and produce thin, almost colorless conversion layers with a surface weight < 0.1 g/m. ... 

The primary components of the GLAST pair conversion telescope are the solid state (silicon strip) tracker and the segmented Csl calorimeter. The tracker has 12 conversion layers (0.5 radiation lengths) plus a front veto... 

With the use of the electrochemical impedance spectroscopy the bilayer alkyd coatings based on the lacquer PF-170 superimposed on the duralumin alloy D 6T was investigated. Such alloy has a much wide application in aircraft constmction, transport, in building industry, etc. Typical protection scheme of the constructions in a case of such alloy application consists in the formation of the conversion layer on the surface of the metal. For example, at the expense of the oxidation, priming and upper vamish-and-paint layer. 

These equations assume equilibrium adsorption exists at the passive film interface. Island-type adsorption instead of the uniform adsorption assumed in these equations has also been suggested. The standard coating based on chromate conversion layers is used to protect high-strength A1 alloys. The primer may contain chromate pigments that enhance protection. The chromium protection mechanism is described by Edeleanu and Evans [89]. 

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