Mechanical bonding process

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). 

Nonwoven bonding processes iatedock webs or layers of fibers, filaments, or yams by mechanical, chemical, or thermal means. The extent of bonding is a significant factor ia determining fabric strength, dexibiUty, porosity, density, loft, and thickness. Bonding is normally a sequential operation performed ia tandem with web formation, but it is also carried out as a separate and distinct operation. 

Some of the restrictions on the use of aluminum are caused by manufacturing and fabrication problems and by its low mechanical strength. However, aluminum is widely used and is competitive with Type 316 stainless steel in many instances. The explosion-bonding process has made the aluminum cladding of steel practical, and... 

The solvent-borne NR adhesives show an important mechanical component in the bonding process, and therefore bulk mechanical and rheological properties (addition of fillers is quite effective) are important. In fact, these adhesives are mainly suitable when at least one of the surfaces to be joined is water-porous (paper, concrete, leather, textiles). 

These observations were the basis for the proposal that polymers, like ionic crystals, exhibit shock-induced polarization due to mechanically induced defects which are forced into polar configurations with the large acceleration forces within the loading portion of the shock pulse. Such a process was termed a mechanically induced, bond-scission model [79G01] and is somewhat supported by independent observations of the propensity of polymers to be damaged by more conventional mechanical deformation processes. As in the ionic crystals, the mechanically induced, bond-scission model is an example of a catastrophic shock compression model. 

In the absence of solvation mechanisms, the process of homolytic bond scission in organic compounds requires much less energy than heterolytic bond scission... 

Catalysis, specific acid, 163 Catalytic triad, 171,173 Cavity radius, of solute, 48-49 Charge-relay mechanism, see Serine proteases, charge-relay mechanism Charging processes, in solutions, 82, 83 Chemical bonding, 1,14 Chemical bonds, see also Valence bond model... 

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... 

In impure metals, dislocation motion ocures in a stick-slip mode. Between impurities (or other point defects) slip occurs, that is, fast motion limited only by viscous drag. At impurities, which are usually bound internally and to the surrounding matrix by covalent bonds, dislocations get stuck. At low temperatures, they can only become freed by a quantum mechanical tunneling process driven by stress. Thus this part of the process is mechanically, not thermally, driven. The description of the tunneling rate has the form of Equation (4.3). Overall, the motion has two parts the viscous part and the tunneling part. 

The one-electron s, p, and d orbitals frequently used to explain observed stereochemistries are a convenient but arbitrary means of decomposing the electron density into spherical harmonics. They represent nothing more than a suitable basis set for a quantum mechanical calculation. When assigned solely on the basis of the observed geometry, they convey no very profound information about the bonding processes at work. It is much simpler and more informative to say that an atom is tetrahedrally coordinated than to say that it is sp hybridized, just as it is easier to say that it forms three equatorial or two axial bonds than to say it is sp or sp hybridized, respectively. Only in the case of the electronically distorted ions discussed in Chapter 8 does an orbital description provide a meaningful rationale for the observed stereochemistry. 

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