Wet powder spraying

Schindler, J., Meyer-Olbersleben, F., Kirbach, B., (1998), Fabrication of FGM-foils for joining application by wet powder spraying , presented at 5th International Symposium on Functionally Graded Materials, Dresden, October 1998. 

These first experiments were based on symmetric cells with an electrode diameter of 10 mm, so-called button cells. The electrolyte was of the yttria-stabihzed zirconia (YSZ) type, 8YSZ based on 8mol% yttria-stabilized zirconia, with a thickness between 130 and 150 pm. On both sides, the electrode was applied by screen-printing or wet powder spraying (WPS) with a thickness of 50 pm, and the porosity was about 30%. A schematic view of a cross-section of the cell geometry is depicted in Figure 9.2. Various types of cathodes were screened by potentiodynamic current-potential measurements. Comparison of the electrochemical behavior in relation to material composition was based on the measured current density at an overpotential t] of—0.1 V. 

In Figure 17.14c, the contact situation on the cathode side between the interconnect channel and the cathode is highlighted. The contact layer applied by wet powder spraying covers all channel areas (bottom, top, and flanks) and on the top side it looks fairly homogeneous and flat, ensuring good cathodic contact (the gap is due to sample preparation). 

Oishi N, Yrxj Y (2010) Evaluation of metal supported ceria based solid oxide fuel cell fabricated by wet powder spray and sintering. J Electrochem Srx 157(1) B125-B129... 

Wet Powder Spraying Bilayer cathodes consisting of cathode and cathode current collector layer can be manufactured by wet powder spraying (WPS). The cathode contact layer is also applied on the metallic interconnects by spraying. Limitations of the technology are the overspray (the amount of suspension which is sprayed past the object to be coated) and the formation of a suspension mist which needs to be extracted by suction. The overspray can be recycled, though. 

Screen printing is expected to replace wet powder spraying in cathode production in the long run. The same procedure can also be applied for electrolyte production. The development target is multilayer printing, i.e., all layers will be printed on top of an anode substrate to form the SOFC cell. This would result in a reduction of sintering steps and therefore in considerable effort and cost reduction. 

The third characteristic process is wet powder spraying, by which the contact layer (between cathode and interconnector) is applied on the cathode. 

Zhou W, Shi H, Ran R, Cai R, Shao Z, Jin W (2008) Fabrication of an anode-supported yttria-stabilized zirconia thin film for solid-oxide fuel cells via wet powder spraying. J Power Sources 184(l) 229-237... 

Wet powder spraying Low Multi-layer deposition technique thin films of a few microns can be produced flexibility of size and shape of samples to be coated scalable High temperature needed for densification of electrolyte several deposition steps required to achieve sufficient thickness overspray... 

Processing 17Cr) Wet powder Wet powder Spraying cathode [42]... 

Wettable powders are prepared by blending the toxicant in high concentration, usually from 15 ndash 95%, with a dust carrier such as attapulgite which wets and suspends properly in water. One to two percent of a surface-active agent usually is added to improve the wetting and suspensibiUty of the powder. Sprays of wettable powders are used widely in agriculture because of their relative safety to plants. 

The Washburn test requires some specialized testing equipment to perform, and an alternate test is the drop penetration time test which is more directly related to the wetting of spray drops into a granulating powder (Hapgood et al., 2003). A drop of known volume is gently placed onto a small powder bed with porosity Sf, and the time taken for the drop to completely sink into the powder bed is measured. The drop penetration time, tp, is given by ... 

Catalyst carriers are often manufactured in a two-step process. In the first step, the solid material, e.g., silica or alumina, is precipitated from a solution and filtered. Then the wet powder is brought into the desired shape, as grains or pellets of a certain size, e.g., by spray drying, pressing or extrusion. The resulting particles are then dried and sintered at elevated temperatures. The more active catalytic material may be formed by co-precipitation. At elevated temperatures oxides are usually formed, that may be reduced to obtain a pure metal. Sometimes oxides or sulfides are the active species. 

Classically, aerosols are particles or droplets that range from about 0.15 to 5 p.m ia size and are suspended or dispersed ia a gaseous medium such as air. However, the term aerosol, as used ia this discussion, identifies a large number of products which are pressure-dispensed as a Hquid or semisohd stream, a mist, a fairly dry to wet spray, a powder, or even a foam. This definition of aerosol focuses on the container and the method of dispensiag, rather than on the form of the product. 

Aerosol dry shampoos fill an important market for those unable to tolerate wet hair, such as the sick and infirm. These products are based on oil absorbing powders which include talc, starch, and/or clay. They can be sprayed onto hair and then bmshed off after absorbing soils from the hair. 

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