Aluminum segregation

Examine the copper-aluminum phase diagram and predict whether cgb /c o is larger for copper segregating to grain boundaries in aluminum or aluminum segregating to grain boundaries in copper. 

Modification of the top electrode may also be achieved. This was done by adding a small amount of surfactant, such as an ether phosphate or an ether sulfate, to the spin-coal solution of the luminescent polymer [89[. The lipophobic ether chains segregate at the surface of the (predominantly) hydrocarbon polymer, becoming available for complexation with the aluminum cathode which is deposited on top. Thus, the dipole in the surfactant points away from the electrode and lowers its work function to improve the injection of electrons. 

FIG. 37 10-iJLm X 10-jj.m SPFM images showing the phase separation between the hydrated aluminum sulfate and the excess unreacted sulfuric acid as the humidity is lowered. The aluminum sulfate salt precipitates, forming a solid lentillike deposit. At the lowest RH (32%), segregated acid droplets are surrounded by flat ( 20 A-thick) pancakes of liquid. (From Ref. 85.)... 

Theoretical calculations [43] based on first principles molecular dynamics discussed in Sect. 3.2.6 have suggested that Mg Al LDHs are most stable for n = 3 (i.e. x = 0.25) and indeed many minerals, including hydrotalcite itself, have this stoichiometry [4]. It has been reported that the synthesis of LDHs (with benzoate or terephthalate anions in the interlayers) from solutions containing Mg/Al = 2, leads to LDHs having the same composition when the synthesis is carried out at moderate temperatures but LDHs with Mg/Al = 3 (plus AlOOH) when the reaction is carried out under hydrothermal conditions [44]. It was proposed that the latter ratio represents the thermodynamically most favorable product. A similar observation has been reported [45] for solutions with Ni VPe = 2, where hydrothermal preparation led to segregation of an LDH with Ni VPe = 3 and Ni Fe 204. An attempt to synthesize a Co sAl LDH resulted in partial oxidation of the Co and formation of a Co o.yCo o.s LDH with complete migration of Al " from the layers to generate interlayer aluminum oxy-species [46]. 

The recovery of aluminum metal is divided into two steps, i. e., the production of pure alumina (Bayer Process) and its molten salt electrolysis. Raw aluminum obtained by reduction electrolysis already has a high purity (99.5-99.7%). Refining methods for raw aluminum to obtain higher purities include the segregation process (99.94-99.99% Al) and three-layer electrolysis (99.99-99.998% Al) [142, 236]. Besides these, processes are available whereby the aluminum is anodically dissolved in an organic electrolyte and then cathodically deposited [37, 118, 217, 221]. The dissolution as well as the deposition process contribute to the electrolytic refining of aluminum. 

A method for coating microchannel walls with layers as thick as 25 pm was developed by Stefanescu et al. [181]. The microreactor was built from FeCrAl (Aluchrom ). The metal surface was first chemically treated in several steps and afterward annealed at 1200 °C for 1 h to trigger the segregation of aluminum and the formation of an alumina layer on the metallic surface. An alumina washcoat was subsequently deposited from a slurry onto the microstructure and characterized by various physical methods. The authors varied the properties such as viscosity, particle size, and pH of the slurry. Acrylic acid, a component used as dispersant and binder, was found to be particularly important for the adhesion of the alumina layer. 

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