Refractory compounds plasma

Minimizing Spectral Interferences The most important spectral interference is a continuous source of background emission from the flame or plasma and emission bands from molecular species. This background emission is particularly severe for flames in which the temperature is insufficient to break down refractory compounds, such as oxides and hydroxides. Background corrections for flame emission are made by scanning over the emission line and drawing a baseline (Figure 10.51). Because the temperature of a plasma is... 

Yu. I. Krasnokutsky, V.G. Verecshak, Poluchenie tugoplavkikh soedinenii v plazme (Preparation of refractory compounds in plasma) Vischa Schola, Kiev, 1987 (in Russian). 

Reductive nitrosylation, transition metal nitrosyl complexes, 34 296-297 ReFejSj cluster, 38 41-43 self-assembly system, 38 41-42 Refining, of actinide metals, see Actinide, metals, purification Refractory compounds heat treatment of solids, 17 105-110 crystal growth, 17 105, 106 decomposition, 17 107,-110 spheroidization, 17 106, 107 preparation of, using radio-frequency plasma, 17 99-102... 

The plasma chemical method is relatively often used now for preparing many nanopowders for production of refractory compounds (nitrides, oxides, carboni-trides, and their compositions) [6]. The process of preparing aluminum nitride nanopowder by this technique is based on evaporation of aluminum in high temperature nitrogen flow, following chemical interaction, and subsequent condensation of reaction product. It means that this process could be considered as a kind of combustion synthesis. 

Y. I. Rrasnokutsky, B. G. Vereschak, Production of Refractory Compounds in Plasma, Vyscha Shkola, Kiev, 1987. 

The high plasma temperature ensures complete atomization of the sample (even in the case of refractory compounds) and also prevents the formation of di- or polyatomic species. Therefore, most matrix effects common for flame and electrothermal atomization techniques are eliminated in ICP-AES. 

In chemical vapor deposition (CVD) reactive vapor precursors react to produce solid materials in the gas phase or at the solid-gas interface on the substrate surface at appropriate temperatures. Typical precursors used in the CVD process are metal hydrides, metal chlorides, and metal organic compounds. In the case that the precursor species are metal organic compounds, the process is called metal-organic chemical vapor deposition (MOCVD). The precursor molecules are introduced into a reactor sometimes with a carrier gas and decompose by means of heat, irradiation of UV light, or electrical plasma formed in the gas. Thermal CVD is the most commonly used method. This technique has an advantage that refractory materials can be vapour-deposited at relatively low temperatures,... 

Hydrogen reduction of chlorides in thermal plasma can be apphed not only to produce powder of individual metals but also to produce different intermetalhc compounds. The composition of the generated crystals copies the composition of the chloride mixture in the gas phase. This effect permits the production of the intermetallic compounds with the required composition. Refractory intermetallic compounds based on niobium and vanadium were synthesized from their chlorides (conversion close to 100%) in a hydrogen plasma jet generated by RF-ICP discharge (Bashkirov Medvedev, 1968). The reaction products were crystallized on a substrate sustained at a temperature of about 1000°C. The plasma-metallurgical technology is proven to be effective in the synthesis of vanadium-Hsilicon... 

Table 8-4. General Chemieal Characteristics of Plasma Etching of Refractory Metals and Some Other Compounds...

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