Backing layer

Figure Bl.24.5. Backscattering spectrum of a thin Ni film (950 A) with near monolayers ( 30 x 10 at cm of An on the front and back surfaces of the Ni film. The signals from the front and back layers of An are shown and are separated in energy from each other by nearly the same energy width as the Ni signal.

Manual stencils are made by knife-cutting special film stencil materials. These consist of two plastic layers. The image to be printed is cut through one layer, and this part of the stencil is placed in contact with the underside of the screen. A solvent, which is insoluble in the ink but attaches the cut stencil to the screen, is appHed and then the backing layer is removed. Manual stencils can also be produced by drawing directly on the screens using special materials. 

MEAs used in this study were prepared in the following procedure [5]. The diffusion backing layers for anode and cathode were a Teflon-treated (20 wt. %) carbon paper (Toray 090, E-Tek) of 0.29 mm thickness. A thin diffusion layer was formed on top of the backing layer by spreading Vulcan XC-72 (85 wt. %) with PTFE (15 wt. %) for both anode and cathode. After the diffusion layers were sintered at a temperature of 360 C for 15 min., the catalyst layer was then formed with Pl/Ru (4 mg/cm ) and Nafion (1 mg/cm ) for anode and with Pt (4 mg/cm ) and Nafion (1 mg/cm ) for cathode. The prepared electrodes were placed either side of a pretreated Nafion 115 membrane and the assembly was hot-pressed at 85 kg/cm for 3 min. at 135 C. 

Figure 63 Scanning electron micrographs of the failure surface of the white backing layer of the bad packaging sample. Four layers were clearly visible in the SEM images. They are labeled as follows (1) outer clear polyester layer, (2) middle opaque polyethylene layer,... 

Figure 4.1 shows a schematic of a typical polymer electrolyte membrane fuel cell (PEMFC). A typical membrane electrode assembly (MEA) consists of a proton exchange membrane that is in contact with a cathode catalyst layer (CL) on one side and an anode CL on the other side they are sandwiched together between two diffusion layers (DLs). These layers are usually treated (coated) with a hydrophobic agent such as polytetrafluoroethylene (PTFE) in order to improve the water removal within the DL and the fuel cell. It is also common to have a catalyst-backing layer or microporous layer (MPL) between the CL and DL. Usually, bipolar plates with flow field (FF) channels are located on each side of the MFA in order to transport reactants to the... 

For example, if fhe DL is used on the side of fhe cell where fhe fuel or oxidant is in gas phase, then this part can be referred to as gas diffusion layer (GDL). When bofh fhe CL and the DL are mentioned as one component, then the name "diffusion electrode" is commonly used. Because the DL is of a porous nature, it has also been called "diffusion medium" (DM) or "porous transporf layer" (PTL). Sometimes the DL is also referred to as fhe component formed by an MPL and a backing layer. The MPL has also been called the "water management layer" (WML) because one of its main purposes is to improve the water removal inside the fuel cell. In this chapter, we will refer to these components as MPL and DL because these names are widely used in the fuel cell indusfry. 

In electrochemical systems, metal meshes have been widely used as the backing layers for catalyst layers (or electrodes) [26-29] and as separators [30]. In fuel cells where an aqueous electrolyte is employed, metal screens or sheets have been used as the diffusion layers with catalyst layers coated on them [31]. In direct liquid fuel cells, such as the direct methanol fuel cell (DMFC), there has been research with metal meshes as DLs in order to replace the typical CFPs and CCs because they are considered unsuitable for the transport and release of carbon dioxide gas from the anode side of the cell [32]. 

A layer of carbon black and PTFE is usually deposited on top of one of the DL surfaces (forming a diffusion double layer) as shown in Figure 4.18. This catalyst backing layer or MPL forms smaller pores than the DL (20-200 nm... 

J. M. Song, H. Uchida, and M. Watanabe. Effect of wet-proofing treatment of carbon backing layer in gas diffusion electrodes on the PEFC performance. Electrochemistry 73 (2005) 189-193. 

C. Xu, T. S. Zhao, and Q. Ye. Effect of anode backing layer on the cell performance of a direct methanol fuel cell. Electrochimica Acta 51 (2006) 5524—5531. 

J. T. Gostick, M. W. Fowler, M. D. Pritzker, M. A. loannidis, and L. M. Behra. In-plane and through-plane gas permeability of carbon fiber electrode backing layers. Journal of Power Sources 162 (2006) 228-238. 

DMFC modeling thus aims to provide a useful tool for the basic understanding of transport and electrochemical phenomena in DMFC and for the optimization of cell design and operating conditions. This modeling is challenging in that it entails the two-phase treatment for both anode and cathode and that both the exact role of the surface treatment in backing layers and the physical processes which control liquid-phase transport are unknown. 

Divisek et al. presented a similar two-phase, two-dimensional model of DMFC. Two-phase flow and capillary effects in backing layers were considered using a quantitatively different but qualitatively similar function of capillary pressure vs liquid saturation. In practice, this capillary pressure function must be experimentally obtained for realistic DMFC backing materials in a methanol solution. Note that methanol in the anode solution significantly alters the interfacial tension characteristics. In addition, Divisek et al. developed detailed, multistep reaction models for both ORR and methanol oxidation as well as used the Stefan—Maxwell formulation for gas diffusion. Murgia et al. described a one-dimensional, two-phase, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymer membrane for a liquid-feed DMFC. 

Figure 39. Images of bubble dynamics in the DMFC anode with carbon paper backing layer for 2 M MeOH feed and nonhumidified air at 100 mA/cm and 85...

When diffracted X-ray beams fall on a photographic film at different angles, as the different layer lines in a cylindrical-film rotation photograph do, it is necessary to correct for the absorption of X-rays in different thicknesses of film. (Since double-coated films are normally used, the effect on the back layer depends on the absorption in the film.) This was first considered by Cox and Shaw (1930) Whittaker (1953) gives a formula which is more accurate and deals with greater obliquity and a thicker film Grenville-Wells (1955) gives the corrections when the multiple film method is used. 

Timing layer Acid layer Estar support Backing layer... 

Transducer crystals are normally cut to a resonant frequency, the duckness being one-half die acoustic wavelength. A bond between die crystal transducer and the specimen matches the acoustic impedance, and carries the acoustic power into the latter. Backing layers may be fixed to the rear surface of the transducer. These layers are selected to reflect power forward into the crystal and specimen in some applications. On the odier hand, they may be selected to absorb power so as not to complicate signals received in material testing applications. 

Bioadhesive tablets can be made by the compression of polymers or can consist of a matrix base or bilayers, with an impermeable backing layer covering the layer with the drug and the mucoadhesion polymer. Examples of these systems are discussed below. 

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