Flash deposition

Service corrosion effects Undercoats, flash deposits produced by strike baths, and immersion deposits are potential sources of weakness. If their structure is faulty it affects the subsequent layers built on the faulty foundation. The greater the number of stages, the higher the probability of faults. 

Little attention has been devoted to the study of carbon layers prepared by the simplest deposition technique - flash evaporation. By flash evaporation carbon layers of different thickness can be produced for routine SEM and TEM electron microscopy. In general, there is a need for these layers to be fine grain, even coating, with uniform and controllable layer thickness. Flash deposition is distinguished from other techniques (e.g. vacuum evaporation, ion beam) by short deposition time and low total power input. The thickness of flash prepared carbon layer should be controlled, but at present none of the conventional methods in general use allows precise and reproducible deposition and layer thickness... 

Electrokinetic analysis results of flash deposited carbon layers on PTFE are presented in Fig. 5 [41]. It is clear, that after carbon deposition decreases zeta potential obtained by... 

Acid Neutral Alkaline Hard gold Soft gold Color gilding (flash deposition) Gold alloy Electroformed gold... 

Decorative gold flash baths can be formulated for any gold shade, for the achievanent of the desired color designation according to the international standard [68], by addition of so-called metallic brighteners as the cyanide complex of the relevant metal. A variety of different shades and colors can be produced by alloying with metals such as silver, copper, nickel, tin, or zinc. Table 11.5 reports some example formulations of color gold baths for flash deposition. 

Alkaline cyanide electrolytes have been in use for years in color gold flash deposition, but they are currently being increasingly substituted by weakly acidic baths. Weakly acidic baths are also largely used for the electrodeposition of thick gold alloy deposits in a range of... 

Decorative, either flash color gold or thick coatings Decorative flash deposition Thick deposits for decorative-functional applications... 

Carbon disulphide should never be used if any alternative solvent is available, as it has a dangerously low flash-point, and its vapours form exceedingly explosive mixtures with air. Ether as a solvent for recrystallisation is much safer than carbon disulphide, but again should be avoided whenever possible, partly on account of the danger of fires, and partly because the filtered solution tends to creep up the walls of the containing vessel and there deposit solid matter by complete evaporation instead of preferential crystallisation. 

The second indication is a faint smoke-like cloudiness in the zone of the tube which is being heated by the Bunsen this is readily visible as the interior of the tube is normally quite clear and bright. This is a later stage of development of the flash-back than the rise of pressure, already mentioned, and should be counteracted by moving the Bunsen immediately to the point of the combustion tube where heating was commenced. In either case the Bunsen should then be moved slowly forwards as before. A flash-back is attended by the deposition of carbon particles, carried back by the explosion wave, on the cold walls of the tube. Care should be taken that these are completely burnt off as the Bunsen is slowly moved forward again. 

Tetrahydronaphthalene [119-64-2] (Tetralin) is a water-white Hquid that is insoluble in water, slightly soluble in methyl alcohol, and completely soluble in other monohydric alcohols, ethyl ether, and most other organic solvents. It is a powerhil solvent for oils, resins, waxes, mbber, asphalt, and aromatic hydrocarbons, eg, naphthalene and anthracene. Its high flash point and low vapor pressure make it usehil in the manufacture of paints, lacquers, and varnishes for cleaning printing ink from rollers and type in the manufacture of shoe creams and floor waxes as a solvent in the textile industry and for the removal of naphthalene deposits in gas-distribution systems (25). The commercial product typically has a tetrahydronaphthalene content of >97 wt%, with some decahydronaphthalene and naphthalene as the principal impurities. 

There is some beneficiation of talc by froth flotation (qv), practiced especially on ultramafic-type deposits. In this process (Fig. 2), talc is milled to its hberation size (—100 mesh (ca 0.15 mm)) using ball mills or ring-type roUer mills and then slurried at 10—30% in water. Flotation is done in conventional multistage float cells using methyl amyl alcohol as a frother. Typically two to four stages are required to upgrade the ore from 50—70% talc to 90—98%. The product is filtered and then flash-dried and milled to a final product. 

Seawater Distillation. The principal thermal processes used to recover drinking water from seawater include multistage flash distillation, multi-effect distillation, and vapor compression distillation. In these processes, seawater is heated, and the relatively pure distillate is collected. Scale deposits, usually calcium carbonate, magnesium hydroxide, or calcium sulfate, lessen efficiency of these units. Dispersants such as poly(maleic acid) (39,40) inhibit scale formation, or at least modify it to form an easily removed powder, thus maintaining cleaner, more efficient heat-transfer surfaces. 

Process Control. Some hot nickel and flash electroless copper solutions are plated to the point of exhaustion and then discarded. Most baths are formulated to give bath fives of >6 turnovers of the bath constituents some reach steady-state buildup of the by-products and can be used indefinitely. AU. regenerable solutions should be filtered to remove particulates that can cause deposit roughness and bath instability. 

Highest heat-transfer coefficients are obtained in FC evaporators when the liquid is aUowed to boil in the tubes, as in the type shown in Fig. 11-122 7. The heating element projects into the vapor head, and the hquid level is maintained near and usuaUy slightly below the top tube sheet. This type of FC evaporator is not well suited to salting solutions because boiling in the tubes increases the chances of salt deposit on the waUs and the sudden flashing at the tube exits promotes excessive nucleation and production of fine ciystals. Consequently, this type of evaporator is seldom used except when there are headroom hmitations or when the hquid forms neither salt nor scale. 

Feed Slurry Temperature Temperature can be both an aid and a limitation. As temperature of the feed slurry is increased, the viscosity of the hquid phase is decreased, causing an increase in filtration rate and a decrease in cake moisture content. The limit to the benefits of increased temperature occurs when the vapor pressure of the hquid phase starts to materially reduce the allowable vacuum. If the hquid phase is permitted to flash within the filter internals, various undesired resiilts may ensue disruption in cake formation adjacent to the medium, scale deposit on the filter internals, a sharp rise in pressure drop within the filter drainage passages due to increased vapor flow, or decreased vacuum pump capacity. In most cases, the vacuum system should be designed so that the liquid phase does not boil. 

Water wash. This method is used to remove deposits. Distilled water is sprayed into the air inlet at a speeified rate and engine speed. This speed is normally at a redueed rpm so that the water will not flash into steam in the eompressor and therefore beeome ineffeetive on the latter stages or diffuser. 

Before desalters came into common use, crude pipe stills were frequently equipped with flash drums to minimize salt deposition on hot surfaces. In the flash drum system, the crude is heated to about 300 F. under enough pressure to suppress vaporization. The pressure is released as the crude enters the flash drum and all of the water (along with a small amount of crude) is flashed off, leaving the salt as a... 

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