Silicon coatings, diffusion

Ji and Kumar [107] presented an invention in which, after treatment with PTFE, the cathode diffusion layers are coated with a silicon solution in order to enhance the hydrophobic properties of the DFs. This silicon does not have to be coated over the whole surface of the DL, but could be coated in just certain areas, depending on the design of the cell, the location of fhe cell wifhin a stack, and the desired hydrophobic properties. It was demonstrated how a DL with the silicon coating improved the performance of a single fuel cell when operating at high relative humilities [107]. 

Another example is the silicidizing of tantalum, basically an oxidation— reduction reaction. The packing is sodium fluoride and silicon. After deposition, the coating diffuses continuously into the substrate, according to the following reactions ... 

FIGURE 2.10 An array of commercially available and commonly used plastic plates for both sitting and hanging drop vapor diffusion crystallization. Also in the picture is a box of silicone coated cover slips for hanging drops. Courtesy of Hampton Research. 

M.A. Harper and R.A. Rapp, Codeposition of Chromium and Silicon in Diffusion Coatings for Iron-Base Alloys Using Pack Cementation, Surface Modification Technologies TV, T.S. Sudarshan, D.G. Bhat, and M. Jeandin, Ed., TMS, 1991, p 415... 

Silicon diffusion (Ihrigising) is not commonly applied to steels, but is increasingly used to protect the refractory metals - (disilicide coatings). 

Up to 550°C, aluminium coatings may be used in the as applied condition, and the hot-dipped aluminium-silicon alloy may be used up to at least 680°C, but for service at higher temperatures additional diffusion treatment is recommended for all except Calorised coatings. 

Up to 750°C, the performance of all aluminium diffusion coatings is considered to be very good, but above this temperature the results appear to be dependent on the coating thickness, diffusion treatment and the specific service environment. Sprayed aluminium coatings can be used up to 900°C after diffusion treatment. Hot-dipped coatings also benefit from additional diffusion treatment, and omission of silicon from the coating alloy improves performance at the elevated temperatures. 

Rebenne, H. E., and Bhat, D. G., Effect of Diffusion Interface on Adhesion and Machining Performance of TiN-Coated Silicon-Nitride Cutting Tools, Proc. ThirdInt. Conf. on Surface Modification Technologies, Neuchatel, Switzerland (Aug., 1989)... 

The wafers are processed into solar cells, the majority of which have a diode structure, as sketched in Figure 11.4, characterized by a thin, diffused, doped emitter, screen-printed front and back contacts and a front-surface antireflective coating. Prior to the effective cell manufacturing step, a chemical treatment of the silicon wafers removes... 

At pressures below ca. 0.05 atm. it was not possible to photograph the propellant strand through the bell jar window because white fumes evolved during the burning and coated the window (recall the discussion about combustion inefficiency at very low pressure). The problem was alleviated by washing a thin film of oil (silicone diffusion pump fluid) down the inside of the window. 

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