Reactive deposition compounds formed

In direction evaporation, the evaporant is the refractory compound itself, whereas in reactive or activated reactive evaporation (ARE), a metal or a low valency metal compound is evaporated in the presence of a partial pressure of a reactive gas to form a compound deposit, eg, Ti is evaporated in the presence of N2 to form TiN, or Si or SiO is evaporated in the presence of O2 to form Si02. 

Many chemical component-s present in such aerosols are relatively stable they can be measured long after (days, week.s, or more) the aero.sol has been collected on a filter or impactor plate, for example. Short-lived reactive and/or volatile species such as peroxides and aldehydes are not usually determined. This may make it difficult to evaluate the health and ecological effects of aerosols because chemically reactive chemical species tend to be the most active biochemically. The chemical components present in the particles collected on a filter or impactor plate may react with each other when they are in close proximity. Particle deposits in filters or on surfaces may also react with molecular components of the gases flowing over them. Chemical reactions between the gas and aerosol may not affect mea.surement.s of metallic elements but may modify chemical speciation (compound form) on the collector surface. All of these factors must be taken into account in selecting sampling and measurement methods for aerosol chemical properties. 

With all reactive depositions, it is a prior condition to have an adequate supply of reactants which can undergo collisions and react following the chemical reaction to form the desired compound film. There have been numerous theoretical treatments and reviews of reactive evaporation [390-397] of reactive sputtering [398-415] and to a smaller extent of reactive ion plating [416-422]. 

Because of their chemical reactivity, the Group lA elements never occur as free metals in nature. They do occur extensively in silicate minerals, which weather to form soluble compounds of the elements (particularly of sodium and potassium). These soluble compounds eventually find their way to landlocked lakes and oceans, where they concentrate. Enormons nnderground beds of sodium and potassium compounds formed when lakes and seas became isolated by geologic events the wate eventually evaporated, leaving solid deposits of alkali metal compounds. Commercially, sodium and potassium compounds are conunon, and both sodium and lithium metals arc available in quantity. 

Reactive deposition is the formation of a film of a compound either by co-deposition and reaction of the constituents, or by the reaction of a deposited species with the ambient gaseous or vapor environment. Reaction with a gaseous ambient is the most common technique. In the case of reactions with a gas or vapor if the reacting species form a volatile compound, etching results. If the product of the reacting species is non-volatile, a... 

Reaction probability (reactive deposition) The probabiUty that a reactive gas species impinging on a surface will react with the surface to form a compound. The probability depends on the reactivity of the species, residence time on the surface, surface coverage, surface mobility, reaction-enhancing processes such as concurrent electron or ion bombardment, etc. 

Reactive deposition (film formation) A film deposition process in which the deposited species reacts with an ambient gas, an adsorbed species, or a co-deposited species to form a compound material. See also Quasi-reactive deposition. 

The high reactivity of the 5-position in 1.3-selenazoles toward electrophilic substitution was also observed on azocoupling. By reacting molar quantities of an aqueous solution of a diazonium salt with an ethanolic solution of a 2-arylamino selenazole. for example, the corresponding 2-arylamino-5 azoselenazoles are formed in a smooth reaction (100). They deposit from the deeply colored solution and form intenselv red-colored compounds after their recrystallization from a suitable solvent (Scheme 36l. 

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