Mechanical-chemical destruction

O-rings are commonly found on mechanical vacuum pumps, rotary valves, and O-ring joints. O-rings are used to separate environments. If an O-ring is attacked by the chemicals from one or both of these separated environments and fails, it will lose its protective sealing capabilities. Similarly, if an O-ring is left in a chemically destructive environment, it may become dysfunctional without ever having been used. 

One of the most potent and physiologically irreversible mechanisms of antibiotic resistance is via chemical destruction of the antibiotic warhead or scaffold. This destruction can occur through several mechanisms, but hydrolytic approaches predominate (Fig. 4). Resistance to the highly important fS-lactam antibiotics by fi-lactamases is the archetype of this class. The fS-lactams include the natural product penicifhn and cephalos... 

Weatherability is defined as the retention of the general mechanical, chemical, electrical, and other physical properties when exposed outdoors for extended time periods. Good weatherability is important to the selection of materials for outdoor use. Sunlight, oxygen, moisture, and pollutants like acid gases can be destructive to plastic materials. The nature of attacks is by photodegradation, oxidative, and chemi-... 

Joint degeneration is the end-stage of a process of destruction of the articular cartilage, which results in severe pain, loss of motion, and occasionally, an angular deformity of the extremity [Buckwalter et al., 1993], Unlike bone, cartilage has a very limited capacity for repair [Salter, 1989]. Therefore, when exposed to a severe mechanical, chemical, or metabolic injury, the damage is permanent and often progressive. 

The isolation of these polymers from the biomass proceeds through the destruction of the cell membrane mechanically, chemically or eznymatically [42, 83], followed by the dissolution of the polyma- in a suitable solvent, for example chloroform, methylene chloride, 1,2-dichloro ethane or pyridine. The remnants of the cell walls are removed by filtration and/or centrifugation. Extraction, using mixed solvents, for example wate/organic solvent, is the last step applied for the final purification. 

Under the conditions of hydrodynamic solicitation of concentrated solutions, in order to explain the polymer concentration effect on the chain splitting mechanism, Y. Minoura and co-workers stated from two hypotheses, namely 1) the interaction between the polymer coil and solvent molecules and 2) the interaction of coil-ing-uncoiling type are essential for mechano-degradation [1045 -1049]. If the last one acts, the increase of concentration must favour the chains splitting, after an exponential law. This behaviou was not experimentally proved. K. Arai shown that the mechano-chemical destruction is not caused by the coiling-uncoiling interac-... 

Aspects of the sono-chemical degradation mechanism After the establish of the ultrasound waves physical and chemical components, the mechanisms of sono-chemical destruction have dominantly been interpreted on this basis. Thus, in the cavitation bubble collapse moment, N.Sata and H. Okuyama defined four types of possible reactions, namely 1) collision of the polymer - polymer molecules, occurring by a bimolecular reaction 2) collision of the polymer-solvent molecules, which proceeds by a pseudo-monomolecular reaction 3) intramolecular collision that occurs by a monomolecular reaction and 4) tearing resulting from the entanglement points that gives a monomolecular reaction. The authors accepted that the active centres of this type of reaction are free radicals and that about 30% from the efficiency of this process is assured by the subsequent reactions of the formed macroradicals with the polymer chains [1130, 1139]. 

At low concentration, the temperature influence is more marked. It strongly decreases as the concentration increases, reaching a maximum level. It joins the previously suggested idea of a phenomenon of saturation of the corrosive diffusion. This saturation could explain the observed limitation of the diffusion speed. This limitation also depends on the gradual creation of decomposition products of chemical species during the mechanism of destruction of tissue by the corrosive agent. 

Hair removers are designed to remove hair from the skin surface without cutting in order to avoid undesirable stubble. Cosmetic products have been developed for chemical destruction of hair, that is, depilation, and for facilitating mechanical hair removal, that is, epilation. 

Explosion is burning that takes place sonically, hence, a shock front is produced. The damage mechanisms are physical destruction from the shock wave, collateral damage from falling structures, and human bums. Suffocation and poisoning are not usually associated with an explosion because of its short duration. A chemical explosives such as nitroglycerine, trinitrotoluene, dynamite, and others were discussed in Section 7.2.6. 

Our immediate and instinctive reaction to an impact or explosion leaves a mental image of utter chaos and destruction. There may be a fascination with the power of such events, but our limited time resolution and limited pressure-sensing abilities cannot provide direct information on the underlying orderly mechanical, physical, and chemical processes. As with other phenomena not subject to direct examination by our human senses, the scientific descriptions of shock and explosion phenomena rest upon a collection of images of the processes which are derived from a range of experiences. The three principal sources of these images in shock science—experiment, theory, and numerical simulation—are indicated in the cartoon of Fig. 3.1. 

All bought-in items of plant, especially those supplied without adequate materials certification, should be subject to random inspection. Portable instruments are available for many types of non-destructive examination, chemical analysis and mechanical testing of fabricated items of plant. 

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