Addition of poisons

Environment Reduce kinetics of cathodic reaction Lower potential of metal Cathodic inhibition Reduce a , reduce O2 concentration or concentration of oxidising species lower temperature, velocity agitation Cathodically protect by sacrificial anodes or impressed current sacrificially protect by coatings, e.g. Zn, Al or Cd on steel Formation of calcareous scales in waters due to increase in pH additions of poisons (As, Bi, Sb) and organic inhibitors to acids... 

Colloidal platinum still further resembles organic ferments in its action upon hydrogen peroxide in that its activity is reduced or partially paralysed by the addition of poisons such as hydrogen cyanide, hydrogen sulphide, or mercuric chloride. After a time, however, the metal may recover from these. 

FIGURE 77 Impact resistance of films as a function of the polymer melt index. The addition of poisons to the reactor affects LCB levels in the polymer. In contrast to 02, CO diminishes elasticity, which in turn results in less orientation in the blown film, and therefore improved impact and tear resistance. (Cr/silica-titania catalyst, activated at 650 °C, polymer density of 0.938 g mL, film thickness 25 pm). 

The case of the 1-ln. copper webs (Table II) shows less effect than the previous case but does, however, further illustrate that the initial addition of poison, whether it be copper or cadmium, is much more effective than larger quantities added subsequently. 

The function of fhe zone control system is to maintain a specified amount of reactivity in the reactor, this amount being determined by the deviation from the specified reactor power set point. If the zone control system is imable to provide the necessary correction, the program in the reactor regulating system draws on other reactivity control devices. Positive reactivity can be added by withdrawal of absorbers. Negative reactivity can be induced by insertion of mechanical control absorbers or by automatic addition of poison to the moderator. 

The cytochromes of beef heart have sharp absorption bands in the reduced state by adjusting the concentration of cell particles, samples can be prepared for spectroscopic examination which show bands at 605 mju, 564 mju, 550 m/x, 520 mju, 445 m/<, 430 mu, and 415 m/i. These bands represent peaks in the absorption spectra of at least three different pigments. The component with bands at 605 m/t and 445 m/i is called cytochrome a the bands at 564 m i, 520 mu, and 430 mj are attributed to csrtochrome b cytochrome c is responsible for absorption at 550 nut, 520 m/t, and 415 m/t. The bands at the longest wavelength (605, 564, and 550 m/t) are the a bands of each cytochrome (a, b, and c). The 520 band is the band of cytochromes b and c. The bands at the lower wavelengths are called Soret bands or y bands. The association of the various bands with individual compounds was made by noting the appearances and disappearances on changing from aerobic to anaerobic condition and back, and on the addition of poisons to the preparation. 

When refrigeration of samples is not possible, addition of poisoning chemicals is another option. The intention of this procedure is to poison those species which are responsible for consumption of nutrients. Of the various agents investigated, only three have found widespread application acidification (mostly with sulphuric acid), chloroform and mercury(/7) chloride. For a thorough review see Kirkwood (1992). 

The reactor protection system comprises two independent fast acting shutdown systems. Shutdown system-1 (SDS-1) is based on mechanical shut-off rods with boron carbide based absorbers in forty lattice positions, providing a total negative reactivity worth of 75 mk with all rods inserted, and a worth of 47 mk with two maximum worth rods not available, shutdown system-2 (SDS-2) is based on a liquid poison injection into the moderator. In addition, a pressurized addition of poison, passively driven by steam pressure, takes place in the event of over pressure in the MHT system. 

State the mechanism of cathodic inhibition by addition of poisons of Group VA elements. 

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