Concentration films

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

X-ray diffraction showed the gray (low-water-concentration) films to have the pattern of SnS, while compositional analysis showed them to be Sn deficient by typically 10%. Crystals were large (micron-sized or larger). The other films tended to be mixtures of approximate compositions Sn2Ss and SnS2, with a nee-dle-like morphology (typically 1 p.m long by 0.1 p.m wide). 

Quantitative studies performed by Bulgarian and Dutch scientists [e.g. 14,95,159,160] in the period of 1962 - 1964 proved that two different equilibrium states of black films exist which are realised under certain conditions, i.e. capillary pressure, electrolyte and surfactant concentration, film radius, etc. Studies with macroscopic film [e.g. 308] under a variety of conditions confirmed that fact. 

If we allow the process of dissolution to continue without setting up any artificial currents to aid diffusion this concentrated film in direct contact with the solid is going to become thicker and thicker and the speed of dissolution is going to become slower and slower as the thickness increases. This is not due to the effect of mass action alone but also because it takes a definite period of time for the dissolved particles to... 

In summary, at comparable concentrations, films containing Irgafos 126 are superior electret materials compared to films containing Irgafos P-EPQ. This result is in agreement with the fact that Irgafos 126 is a more efficient antioxidant than Irgafos P-EPQ [70],... 

Fig. VIII-7. The thickness of primary Fig. VIII-8. Film lifetime, tf, as a function (curve /) and Newtonian (curve 2) black of surfactant concentration films as a function of electrolyte concentration...

Figure 5-17. Dependencies of T1O2 thin film deposition rates on water vapor concentration. Films grown at atmospheric pressure using Ti(Oi-Pr)4 as the precursor source (Data from [127]).

As the shaft turns at a speed of about 60 r.p.m., a film of feed water is picked up by the disk (5) and passes approximately 1/8 inch from the condenser plates. Water vapor transfers by diffusion through the air from the hot feed water film on the disk surface to the colder condenser surface. The residual water film on the disk is cooled by the evaporation and its salinity is increased. The disk surface then returns to the reservoir, where the cool concentrated film is washed off and the film is renewed with hot feed water. 

Figure 16.20. Conductivity change of a poly(pyrrolephenylsulphonate) film treated with aqueous NaOH solutions of various concentrations. Film thickness is 90 micron A, treated with 50% NaOH B, treated with 2% NaOH and C, treated with 10% NaOH. Adapted from Polymer 11, 899 (1986), with permission of Elsevier Science Ltd., Kidlington.

Rhodamine 6G-impregnated Nafion films were prepared by first casting a thin film of Nafion on microscope cover slips from the Naflon solution as purchased. After the solvent had completely evaporated, the films were dipped in aqueous Rhodamine 6G (1 mM) for about 10 minutes to make a "concentrated" film. For more dilute... 

So, to better understand the rhodamine 6G-Nafion film dynamics, lifetimes of the "dilute" and "concentrated" films were measured. Using the fiber optic, the "dilute" film was found to have a single emitting component of 3.8 0.18 ns which corresponds well to free rhodamine 6G in solution (3.7 ns). However, the "concentrated" film results were always best described by more complex decay process. 

In another experiment, a variation of this method was used to prepare an interpenetrating network of polypolypyrrole and poly(vinylacetate) [66]. Pyrrole monomer was added to stirred solutions of poly(vinylacetate) and FeCla in different concentrations. Films were cast from these solutions before pyrrole polymerization was complete and washed to remove excess oxidant. A 5% percolation threshold was observed, with a plateau conductivity of 10 S cm. Polypyrrole forms a network by spinodal decomposition and poly(vinylacetate)... 

Fig. 7. Ageing behavior with regard to the electrical conductivity of poly(pyrrolephenylsulfonate) film exposed to NaOH solutions of different concentration. Film thickness, 90 /xm ageing temperature, 140°C time of exposure, 240 min. Reprinted with permission from H. Munstedt, Polymer 27, 899 (1986). Copyright 1986, Elsevier Science Ltd., Oxford.

In the range in which zirconium shows corrosion resistance in H2SO4, a passive film is formed on zirconium that is predominantly cubic zirconium oxide (Zr02) with only traces of the monoclinic phase. ° Zirconium corrodes in highly concentrated H2SO4 (e.g., 80%) because loose films are formed that prove to be zirconium disulfate tetrahydrate [Zr(S04)2-4H20]. Also, at the higher acid concentrations, films that flake off are formed and are probably partly zirconium hydrides. ... 

Polymer Monomer purity IV (dLg- Polymerization concentration Film (wt % of the final polymer) formation process ... 

For mass transfer the effective film (i.e., concentration film) thickness is 8c, in meters, and the chemical flux is regulated by molecular diffusion. Being highly turbulent, the fluid beyond is rapidly mixed and providing no resistance to mass transfer. 

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