Foreign materials, deposition

One problem with heterogeneous catalysis is that the solid catalyst is easily poisoned. Foreign materials deposited on the catalytic surface during the reaction reduce or even destroy its effectiveness. A major reason for using unleaded gasoline is that lead metal poisons the Pt-Rh mixture in the catalytic converter. 

Fine-grained deposits are usually obtained from complex ion solutions, eg, cyanide, or using certain addition agents. These deposits are less pure, less dense, and exhibit higher electrical resistivities because of the presence of foreign material. 

Deposits stimulate tubercle formation. Hence, regions where foreign material accumulates are common tubercle breeding grounds. Stagnant, low-flow areas also promote tubercle growth. 

The ability of a detergent or detergent component to keep foreign material away from the solid material from which it has been removed to prevent re-deposition. See also Detergent. 

This case raises the possibility of silicone deposition from cutaneous manipulation with silicone-coated instruments over a relatively short duration of time. In addition, the case is remarkable in that the latency from exposure to the foreign material to the onset of lesions was relatively short (6-12 months). 

Once deposited on bone, plutonium is not released until the bone is physically destroyed. It may become buried under a new layer of mineral or may be taken up by special cells that digest foreign materials. As these cells die, the plutonium accumulates in immobilized deposits of hemosiderin, an insoluble iron storage protein that contains a large core of polymeric iron hydroxides and phosphates. These deposits are located close to the bone surfaces in the reticuloendothelial cells of the bone marrow10). 

For tray colnmns, liquid flow constrictions are normally found in the tray downcomers. Example causes are lack of adequate froth collapse time, excessive pressure drop for flow under the downcomer baffle, and foreign materials being left in the downcomer by construction people. For packed columns, clogged support plates, broken packings, or growth of fouling deposits can cause liquid flow restrictions. 

Soft contact lenses, and to a lesser extent hard contact lenses, can accumulate foreign materials on their surfaces and possibly within their polymer matrices. The deposits are composed primarily of substances present in the tear fluid (I). The deposits cloud the lens, cause the wearer discomfort, and may be responsible for a variety of inflammatory conditions including giant papillary conjunctivitis. Manifestations of this syndrome consist of increased mucus, mild itching, decreased lens tolerance, and the development of giant... 

Sauerbrey substituted the area mass density A mq of an additional quartz wafer by the area mass density mf of the deposited foreign material. He made the assumption that for small mass changes, the addition of foreign mass can be treated as an equivalent mass change of the quartz crystal itself. His relation for the frequency change of the loaded crystal is... 

---