Metal oxide vaporization-decomposition

Reaction of metal oxide vapor with gasified carbon (under vacuum) Sonochemical decomposition of metal carbonyl... 

The auxiliary electrolyte is generally an alkali metal or an alkaline earth metal halide or a mixture of these. Such halides have high decomposition potentials, relatively low vapor pressures at the operating bath temperatures, good electrolytic conductivities, and high solubilities for metal salts, or in other words, for the functional component of the electrolyte that acts as the source of the metal in the electrolytic process. Between the alkali metal halides and the alkaline earth metal halides, the former are preferred because the latter are difficult to obtain in a pure anhydrous state. In situations where a metal oxide is used as the functional electrolyte, fluorides are preferable as auxiliary electrolytes because they have high solubilities for oxide compounds. The physical properties of some of the salts used as electrolytes are given in Table 6.17. 

What is unique about metal particles burning in oxygen is that the flame temperature developed is a specific known value—the vaporization-dissociation or volatilization temperature of the metal oxide product. This temperature could be referred to as a boiling point. This interesting observation is attributable to the physical fact that the heat of vaporization-dissociation or decomposition of the metal oxide formed is greater than the heat available to raise the condensed state of the oxide above its boiling point. That is, if <2r is the heat of reaction of the metal at the reference temperature 298 K and (H° - H gi) is the... 

Ozone decomposes readily to oxygen in the presence of a catalyst, such as manganese dioxide or other metal oxides. It also decomposes in the presence of chlorine or bromiae vapor. Such decomposition also occurs slowly noncat-... 

Explosibility. Liquid ethylene oxide is stable to detonating agents, but the vapor will undergo explosive decomposition. Pure ethylene oxide vapor will decompose partially however, a slight dilution with air or a small increase in initial pressure provides an ideal condition for complete decomposition. Copper or other acetylide-forming metals such as silver, magpesium, and alloys of such metals should not be used to handle or store ethylene oxide because of the danger of the possible presence of acetylene. Acetylides detonate readily and will initiate explosive decomposition of ethylene oxide vapor. In the presence of certain catalysts, liquid ethylene oxide forms a poly-condensate. 

Gas Phase. The decomposition of gaseous ozone is sensitive not only to homogeneous catalysis by light, trace organic matter, nitrogen oxides, mercury vapor, and peroxides, but also to heterogeneous catalysis by metals and metal oxides. 

Rather than produce an atomic vapor by evaporation from a solid surface, an aerosol may be generated from an aqueous salt solution by an atomization procedure. The aerosol can then be evaporated so that the salt condenses into a particle. This is known as the spray-pyrolysis technique. The flame decomposition method is a modification of this technique, in which the aerosol is introduced into a high-temperature flame (1200-3000 K). The precursor is vaporized and oxidized to form metal-oxide particles. 

This chapter is intended to cover major aspects of the deposition of metals and metal oxides and the growth of nanosized materials from metal enolate precursors. Included are most types of materials which have been deposited by gas-phase processes, such as chemical vapor deposition (CVD) and atomic layer deposition(ALD), or liquid-phase processes, such as spin-coating, electrochemical deposition and sol-gel techniques. Mononuclear main group, transition metal and rare earth metal complexes with diverse /3-diketonate or /3-ketoiminate ligands were used mainly as metal enolate precursors. The controlled decomposition of these compounds lead to a high variety of metal and metal oxide materials such as dense or porous thin films and nanoparticles. Based on special properties (reactivity, transparency, conductivity, magnetism etc.) a large number of applications are mentioned and discussed. Where appropriate, similarities and difference in file decomposition mechanism that are common for certain precursors will be pointed out. 

Vapor decomposition is a powder preparation technique useful in a few cases when a vapor phase precursor exists (often an organometallic compound) which can be decomposed to the desired composition . The vapor decomposition usually takes place at elevated temperatures. Single component oxide powders of high purity can be prepared by vapor decomposition of metal alkoxides for example, Zr02 is prepared by pyrolyzing zirconium tetra-t-butoxide. ... 

Ethylene oxide vapor is extremely flammable at concentrations ranging from 3% to 100% and subject to explosive decomposition. Although liquid ethylene oxide is relatively stable, contact with acids, bases, or heat, particularly in the presence of metal chlorides and oxides, can lead to a violent polymerization. 

Thermal dissociation in the solid phase takes place if the decomposition point of the product is signihcantly lower than its vaporization point. In the opposite case, thermal dissociation takes place in the gas phase. Halides usually have a significantly lower dissociation temperature than the corresponding oxides that is, dissociation in solid phase is barely possible. The extremely high electron density in a graphite tube at temperatures above 1200°C can lead to a reduction of stable metal oxides of, for instance, iron, chromium, and manganese in solid or liquid phase. This reduction is typically observed at temperatures of around 500°C lower than the dissociation point of the oxides. The last reaction is the dissociation of carbides in the gas phase ... 

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