Vapor decomposition

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

Vapor decomposition (14,15) iavolves dryiag, decomposiag, and vaporising a spray of salt precursor solution ia a plasma, and subsequentiy nucleating and growing ceramic particles ia the vapor. Silicon carbide [12504-67-5] SiC, powder is produced by this method. 

Tetravalent silicon is the only structural feature in all silicon sources in nature, e.g. the silicates and silica even elemental silicon exhibits tetravalency. Tetravalent silicon is considered to be an ana-logon to its group 14 homologue carbon and in fact there are a lot of similarities in the chemistry of both elements. Furthermore, silicon is tetravalent in all industrially used compounds, e.g. silanes, polymers, ceramics, and fumed silica. Also the reactions of subvalent and / or low coordinated silicon compounds normally lead back to tetravalent silicon species. It is therefore not surprising that more than 90% of the relevant literature deals with tetravalent silicon. The following examples illustrate why "ordinary" tetravalent silicon is still an attractive field for research activities Simple and small tetravalent silicon compounds - sometimes very difficult to synthesize - are used by theoreticians and preparative chemists as model compounds for a deeper insight into structural features and the study of the reactivity influenced by different substituents on the silicon center. As an example for industrial applications, the chemical vapor decomposition (CVD) of appropriate silicon precursors to produce thin ceramic coatings on various substrates may be mentioned. 

For our experiments, a carbon fiber cloth (Figure 3 a) was prepared by carbonization of viscose under neutral atmosphere for 15 minutes, successively at 400, 700 and 1000°C. The carbon cloth was coated with pyrolytic carbon, using chemical vapor decomposition of propylene (2.5 ml/mn) diluted in nitrogen (100 ml/mn) during 10 minutes at 900°C. The resulting composite carbon material exhibits a very low irreversible capacity and 1.5 times the reversible capacity of graphite9 11. 

Generation of Smoke, Toxic and Corrosive Fire Products. Smoke, toxic and corrosive products are generated in fires as a result of vaporization, decomposition and combustion of materials in the presence or absence of air. 

Table 2 Char yield, vaporization/decomposition temperatures (7, /7d), limiting oxygen index (LOI) and UL 94 ratings for polymers...

Solvent degreasing Vapors perchloroethylene, trichlorethylene, vapor decomposition (e.g., phosgene)... 

Nasibulin AG, Richard 0, Kauppinen El, Brown DP, Jokiniemi JK, Altman IS (2002) Nanoparticle synthesis by copper (II) acetylacetonate vapor decomposition in the presence of oxygen. Aerosol Sci Technol 36 899-911... 

The vaporization/decomposition of Rb2S04 has been studied by mass spectrometry and the torsion-effusion method.23 Molecular vaporization accounts for 75% of the total, with the decomposition... 

Umeno T, Fukuda K, Wang H, Dimov N, Iwao T, Yoshio M. Novel anode material for lithium-ion batteries Carbon-coated silicon prepared by thermal vapor decomposition. Chem Lett 2001 30 1186-1187. 

In the case of carbon nanotubes (CNTs), numerous syntheses methods have been developed during the last years, for example, the discharge between two graphite electrodes, laser ablation, hydrocarbon decomposition, and catalytic chemical vapor decomposition (CCVD) however, the most applied methods are arc discharge, laser ablation, and CVD [177-179]. 

We have previously shown that solid particle formation from TTIP in supercritical alcohol occurs at lower temperature than for pure vapor decomposition [1]. This allows us to assume that the first step in Ti02 formation from titanium alkoxide under our experimental conditions is alcohol dehydration followed by hydrolysis reactions. 

Energy is provided to this endothermic reaction by the conduction, convection, and radiation from the furnace walls. This type of decomposition can also be caused on a hot substrate to produce a ceramic film. This process is called chemical vapor decomposition (CVD). 

Klitenick, M.A., Frederickson, C.J., Manton, W.I. Acid-vapor decomposition for determination of zinc in brain tissue by isotope dilution mass spectrometry. Anal. Chem. 55,921-923... 

The characterization of relatively complex polymers is usually carried out by means of coupled techniques because sometimes a single technique is not enough to elucidate their structures. Pyrolysis of polymers is an old technique used many years ago to identify materials by their vaporized decomposition products. The coupling of this simple method with a powerful identification technique, such as infrared (IR) spectroscopy or, often, mass spectrometry (MS), has demonstrated its utility for the analysis of polymeric materials and, mainly, for the characterization of their degradation products. 

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. ... 

Early reports of the formation of carbon nanotube (CNT) arrays in templates are given in [51]. Aligned CNT with a diameter of about few nm with sufficient graphitic character were made by chemical vapor decomposition (CVD) using propylene gas. The CNTs were made with Fe and Co catalysts or without catalysts. The... 

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