Mechanical bonds

Octahedral substitution reactions (e.g. those involving cobalt(III) complexes) may proceed by both Sf l or 8 2 reactions. In the S l case a slow dissociative mechanism (bond breaking) may take place. Reaction with the substituting... 

In sintering, the green compact is placed on a wide-mesh belt and slowly moves through a controlled atmosphere furnace (Fig. 3). The parts are heated to below the melting point of the base metal, held at the sintering temperature, and cooled. Basically a solid-state process, sintering transforms mechanical bonds, ie, contact points, between the powder particles in the compact into metallurgical bonds which provide the primary functional properties of the part. 

Sintering. Basically a soHd-state process, sintering transforms compacted mechanical bonds between the powder particle into metallurgical bonds (23,34—38). 

Lamination. la lamination a film is prepared by caleaderiag or extmsioa (see Laminated materials, plastic). It is thea adhered to a textile at a laminator by either an adhesive or sufficient heat which partially melts the film to obtain a mechanical bond. There are a variety of adhesives available for lamination, including solvent systems, water-base latex systems, and various forms of hot melt adhesives (qv). 

Integral (or extruded). An aluminum outer tube from which fins have been formed by extrusion, mechanically bonded to an inner tube or liner. 

Mechanically bonded tubes may be obtained by mechanically stressing the fin material and/or the tube material to hold the two elements in pressure contact with one another. So called tension wound fins are formed by winding the fin material under tension in a helical manner along the length of the tube. 

Individual fins may be preformed and inserted over the tube, after which the mechanical bond may be obtained by either shrink fitting the fins onto the tube or by expanding the tube radially outward to make pressure contact with the fin material. The means to expand the tube may be hydraulic by pressurizing the tube beyond its yield point or it may be of a mechanical nature, in which an oversized ball or rod is pushed through the length of the tube, forcing the tube material outward against the fin. 

Adhesion, mechanical Bonding between two surfaces caused by interlocking action of molecules. 

Reinforcing fibers can be modified by physical and chemical methods. Physical methods, such as stretching [22], calandering [23,24], thermotreatment [25], and the production of hybrid yarns [26,27] do not change the chemical composition of the fibers. Physical treatments change structural and surface properties of the fiber and thereby influence the mechanical bondings in the matrix. 

Figure 10-10E. A cutaway section of plate-type fins showing the continuous surface contact of the mechanically bonded tube and fins. (Used by permission The Trane Co., La Crosse, Wis.)...

Aluminium cast onto steel or cast iron is used to produce integral aluminium/steel drums and bimetallic pistons. Aluminium clad onto other metals by mechanical bonding is used in heat-exchanger systems subject to multiple atmospheres or environments. The clad products are also used for cooking utensils and functional press work. 

Above this size, the flow of air over the condenser surface will be by forced convection, i.e. fans. The high thermal resistance of the boundary layer on the air side of the heat exchanger leads to the use, in all but the very smallest condensers, of an extended surface. This takes the form of plate fins mechanically bonded onto the refrigerant tubes in most commercial patterns. The ratio of outside to inside surface will be between 5 1 and 10 1. 

Spray 0.1 ohm per square foot hard, dense coating. mechanical bonding to plastic special applications equipment required requires special applicator safety procedures for dust and fumes warps thermoplastics not suitable for thin-walled designs not field repairable. 

For Sn2 reactions, no such simple correlations are found. In this mechanism bond breaking is about as important as bond making in the ratedetermining step, and substituents have an effect on both processes, often in... 

Also, from the dendrimer point of view, the introduction of mechanical bonds to dendrimers has an enormous potential to alter the properties of dendrimers in a controlled way. For example, in the synthesis of a Type II rotaxane dendrimers, the wheel components are introduced to the terminal groups of the dendrimers. This can improve the solubility of dendrimer in organic and/or aqueous media due to the formation of complexes soluble in such solvents. 

In particular, rotaxane dendrimers capable of reversible binding of ring and rod components, such as Type II, pseudorotaxane-terminated dendrimers, can be reversibly controlled by external stimuli, such as the solvent composition, temperature, and pH, to change their structure and properties. This has profound implications in diverse applications, for instance in the controlled drug release. A trapped guest molecule within a closed dendrimeric host system can be unleashed in a controlled manner by manipulating these external factors. In the type III-B rotaxane dendrimers, external stimuli can result in perturbations of the interlocked mechanical bonds. This behavior can be gainfully exploited to construct controlled molecular machines. 

Murphy et al. [34,45] have parameterized and extensively tested a QM/MM approach utilizing the frozen orbital method at the HF/6-31G and B3LYP/6-31G levels for amino acid side chains. They parameterized the van der Waals parameters of the QM atoms and molecular mechanical bond, angle and torsion angle parameters (Eq. 3, Hqm/mm (bonded int.)) acting across the covalent QM/MM boundary. High-level QM calculations were used as a reference in the parameterization and the molecular mechanical calculations were performed with the OPLS-AA force... 

Figure 8. Diagram showing that complexes with partial mechanical bonding (P) character, i.e., pseudorotaxanes and hemicarceplexes, are represented by the intersection set [AA n I] of the set of (wholly) mechanically-bound molecules (AA) and the set of isolated molecules (I) - in other words, the fuzzy region in between these two sets. Thus, the complexes in set P are endowed simultaneously with characteristics associated with species belonging to both AA and I. The numbers 1 and 0 have been assigned arbitrarily to the species that belong either entirely or not at all to the sets AA and I.

R. Jager, F. Vogtle, A New Synthetic Strategy towards Molecules with Mechanical Bonds Nonionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes , Angew. Chem Int. Ed. Engl. 1997,36,930-944. 

Mechanical bonding, 16 176 Mechanical carryover, 23 220 Mechanical cleaning, of flax fiber,... 

In general, both physical and weak chemical bonds are responsible for mucoadhesion. Physical/mechanical bond formation can be explained as the entanglement of the adhesive polymer and the extended mucin chains. When this diffusion is mutual, it leads to maximum bioadhesive strength. 

The dimer belongs to the rare group of compounds which are piezochromic. Rubbing in a mortar produces a red color due to mechanical bond-breaking and dissociation into the red-colored monomer. The -quinol structure of the 2,4,6-triphenylphenoxyl dimer has been confirmed by infrared studies of i 0-labeled material and by X-ray analysis of 3-bromo derivative. ... 

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