Plasma spray processing

Despite the progress outlined in this chapter, much work remains to be done in the metal surface preparation arena. For example, there is still no ideal surface preparation method that does for steel what anodization processes do for aluminum and titanium. The plasma spray process looks encouraging but because it is slow for large areas and requires rather expensive robot controlled plasma spray equipment, its use will probably be limited to some rather special applications. For more general use, the sol-gel process has potential if future studies confirm recently reported results. 

White BD, Kesler O, and Rose L. Air plasma spray processing and electrochemical characterization of SOFC composite cathodes. J. Power Sources 2008 178 334—343. 

Kesler O, Plasma spray processing of planar solid oxide fuel cells. Mat. Sci. Forum 2007 539-543 1385-1390. 

The substrate material was TC4(Ti-6Al-4V), and the sprayed powders were 8wt%Y203 partially stabilized Zr02 and Ni-4.5Co-20Cr-4Al-lY alloy, the Zr02/NiCoCrAlY graded coating was fabricated by air plasma spraying process . ... 

Final goal, however, is the preparation of compositionally graded materials made of Mg2(Si,Ge,Sn) crystals. The preparation of the powders by mechanical alloying and their properties after hot pressing is topic of the third section. The high reactivity of the Mg is the main difficulty which has to be overcome. For the preparrational route the problems have been solved. The next step will be the transfer to the plasma spray process. 

Another Ni-based solid oxide fuel cell (SOFC) electrode was developed on which a YSZ (yttria-stabilized zirconia) cermet and Lanthanum chromite were deposited by a slurry coating method. It was also suggested that a plasma spraying process can be used for the cermet deposition on the electrodes. The following reactions are expected to take place in a fuel cell employing a natural gas source, where internal reforming takes place on the Ni-YSZ electrode ... 

Jaworski, R., Pawlowski, L., Roudet, F., Kozerski, S., and La Maguer, A. (2008b) Influence of suspension plasma spraying process parameters on Ti02 coating microstructure. J. Therm. Spray Technol.,... 

Pasandideh-Fard, M. and Mostaghimi, J. (1995) On the spreading and solidification of molten particles in a plasma spray process effect of thermal contact resistance. Plasma Chem. Plasma Process., 16 (1), S83-S98. 

It can be assumed that coatings formed from lower crystallinity particles exhibit low residual stress because feedstock also has inherent porosity that would tend to relieve process-induced stresses. A comparison of the high velocity oxy-fuel and plasma spray processes has revealed that the residual stress is lower in the former process (Knowles et al. 1996). Heat treatment at temperatures of 800°C can minimize these process-induced stresses (Brown et al. 1994). Despite the large influence of thickness on coating strength, no difference in bone apposition has been found for 50 pm and 100 pm coatings. 

A schematic of the DC-arc plasma spray is shown in Fig. 8-1. Plasma spray processes can be broken down into three major categories ... 

Thermal Plasma Spray. Analyzing equation (8-1), determine the effect of the exponential factor n on the uniformity of velocity, enthalpy, and temperature distributions. Calculate the relative radius corresponding to a decrease of the parameters twice with respect to those at the torch axis. How does thermal plasma uniformity affect the quality and characteristics of the thermal plasma spray process ... 

Dussoubs, B. (1998), 3D Modeling of die Plasma Spray Process, Ph.D. Thesis, University of Limoge, France. 

At DLR in Stuttgart, Germany, a concept in which all cell layers are produced by means of plasma spraying processes was developed in the mid-1990s. The cells are based on a metal substrate which promises to be more resistant to oxidation than the nickel-based anode substrate. Even though the power densities were increased in the last few years, they are still considerably below the values achieved for the anode substrates [18, 19]. 

Figure 1.13 (a) Schematic diagram of the plasma spray process and (b) experimental setup of the electrostatic spray deposition technique. 

Chen, D., Jordan, E., Cell, M., Wei, M., 2008. Apatite formation on alkahne-treated dense Ti02 coatings deposited using the solution precursor plasma spray process. Acta Biomater. 4, 553-559. http //dx.doi.Org/10.1016/j.actbio.2007.ll.008. 

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