Layer-rolled structure

An important question relating to the structure of nanotubes is Are nanotubes made of embedded closed tubes, like "Russian dolls," or are they composed of a single graphene layer which is spirally wound, like a roll of paper Ijima et al. [2] espouse the "Russian doll" model based on TEM work which shows that the same number of sheets appear on each side of the central channel. Dravid et al. [4], however, support a "paper roll" structural model for nanotubes. 

A GDL is also an important component of the AFC. For these fuel cells, the GDLs are usually made by a rolling procedure similar to that used in the paper industry. The activated carbon/PTFE mixture is rolled onto a current collector made of planar nickel mesh. By using GDL and a two-layer electrode structure, the Pt loading in the AFC can be reduced to 0.3 mg cm-2 [76],... 

The purpose of reeling is to wind up the continuously produced paper web on reel spools building up paper rolls of up to 4.5 m diameter. The paper rolls have to fit the requirements of any following process steps. These mainly concern the paper roll structure such as hardness and overall shape. As reehng is a discontinuous process economic aspects as regards broke due to roll change/tum-up are important as well. This concerns the so-called top broke at the outside of the finished parent roll and the bottom broke at the inner layers of the spool. 

Such an internally fluid structure can be achieved by rolling the smectic layers into concentric cylinders (so-called "jelly roll" structure) (see Figure 2.19). 

According to Lvov et at (2008) the reason why planar kaolinite rolls into a tube remains unclear. In the review article of Joussein et at (2005) some questions are pointed out. Dixon and Mckee (Dixon McKee, 1974) proposed the tubes are formed by layer rolling, caused by dimensional mismatch between the octahedral and tetrahedral layers and weak interaction bonds. In the hydrated halloysite, the rolling leaves a small space between the adjacent layers, although the dehydration does not change the structure. As reported by Bailey (1990) the dimensional mismatch between the octahedral and tetrahedral layers also occurs to kaolinite. However, the mismatch is corrected by rotation of alternate tetrahedral in opposite directions, while in halloysite the rotation is blocked by interlayer water molecules. 

Because of the low glass transition temperature it is not possible to make clear film, stable at room temperature, by quenching. Some improvement in clarity may be obtained by cold rolling as this tends to dispose the crystal structure into layers (see Chapter 6). 

For composite stiffeners, all shapes are builtup from individual layers of material. Of course, some stiffener shapes can be produced by roll forming or pultrusion, for example, and then fastened to panels. Or, the stiffened panel could be made in a single operation involving the placement, usually by hand, of individual laminae of various dimensions in positions such that a builtup structure results. Stiffeners can be fastened to panels by bonding, stitching, or mechanical fastening. 

The structure of millscale consists of three superimposed layers of iron oxides in progressively higher states of oxidation from the metal side outwards, viz. ferrous oxide (FeO) on the inside, magnetite (Fe304) in the middle and ferric oxide (Fe203) on the outside. The relative portions of the three oxides vary with the rolling temperatures. A typical millscale on 9.5 mm mild steel plate would be about 50/tm thick, and contain approximately 70% FeO, 20% Fej04 and 10% FejOj. 

The metallic catalyst support can be in form of chips, open-mesh and reinforced wire structures, and staggered layers of metal screens or saddles. In one design, screens woven from metallic wires 0.01 to 0.03 in. diam are placed in a deep stack. In another design, metal foils 0.004 in. thick are perforated and expanded to form a screen, which is then rolled into a cylinder. See Fig. 12. 

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