Parallel chains

Conveyors may be of parallel-chain, mat, slat, woven wire-mesh belt, or cast-alloy type. Automatic tensioning devices are used to maintain belt tension during heating and cooung. The product may rest directly on the conveyor or on special supports built into it. RoUer-conveyors are used for large pieces. Flame curtains are provided for sealing the ends and for protection of special treating atmospheres. 

SC2CI3 and its Br analogue are of unknown structure, as are reported La2X3 phases, though Y2CI3 and Y2Br3 have been shown to consist of parallel chains of Ye octahedra, the chains being linked by Cl atoms ... 

SC7CI10 is composed of a double chain of Scfi octahedra sharing edges, and a parallel chain of ScCle octahedra ... 

SC7C1,0 Double chains of edge-sharing metal octahedra with M Xg-type environment with parallel chains of edge-sharing MCl octahedra... 

The softening behaviour of a thermoplastic material depends to a large extent on the flexibility of the chain and the ability to crystallise. Significant cross-linking of a reasonably stiff-chained polymer will lead to material that is unlikely to soften below its decomposition temperature. Intermediate to the linear and cross-linked polymers are various ladder polymers in which the polymer molecule consists of a pair of more-or-less parallel chains bridged in a manner analogous to the rungs of a ladder. 

Fig. 18.—Antiparallel packing arrangement of 2-fold poly(ManA) (15) helices, (a) Stereo view of two unit cells roughly normal to the hoplane. The helix at the center (filled bonds) is antiparallel to the two in the back (open bonds). Intrachain hydrogen bonds stabilize each helix. Association of helices through direct hydrogen bonds involve the carboxylate groups for parallel chains, but involve the axial hydroxyl groups for antiparallel chains, (b) A view of the unit-cell contents down the t-axis highlights the interactions between the helices.

A layer of tetrahedra can be considered as being built up by linking parallel chains. That this is not a mere formalism is shown by the existence of intermediate stages. Two linked silicate chains result in a ribbon of the composition [Si4Of ] it has two kinds of tetrahedra, one kind being joined via three and the other kind via two vertices, [SiO Oj SiOj/jOj ]3 Silicates of this type are termed amphiboles. They are fibrous and also used to be used as asbestos. 

We note here that all the information presently available on high molecular weight polymer crystal structures is compatible with the bundle model. While very nearly all crystalline polymer polymorphs involve all-parallel chain arrangements, even the only known exception, namely y-iPP [104,105], where chains oriented at 80° to each other coexist, is characterized by bilayers of parallel chains with opposite orientation. This structure is thus easily compatible with crystallization mechanisms involving deposition of bundles of 5-10 antiparallel stems on the growing crystal surface. Also the preferred growth... 

Fig. 1. The basic arrangements of /f-strands in hydrogen-bonded /f-sheets (A) parallel chains, (B) antiparallel chains. Green spheres of different sizes denote side chain groups...

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