Evaporative surface decomposition

According to detailed XRD analyses, the two catalyst preparation procedures under study formed solid solutions. The application of sol-gel method led to improved selectivity to olefins in the reaction of propane ODH, compared to the simple procedure of evaporation and decomposition. However, the propane conversion on the sol-gel catalysts was lower at the same experimental conditions, while the catalysts surface area was higher. Moreover, the sol-gel samples presented higher basicity as shown by C02 TPD. It could be explained by a better incorporation of Nd into the AEO lattice, creating cationic vacancies for attaining electroneutrality and thus rendering the nearby oxide anions coordinatively unsaturated and more basic. 

Factors that influence the burning rate of fuel packages include (1) the net heat flux received at the surface, q", and (2) the evaporative or decomposition relationships for the fuel. We can represent each as... 

Spent acid is sprayed into a decomposition furnace in the form of 500-1000 pm droplets (Dafft and White, 2002). The droplets present a large acid surface to the hot combustion gas, promoting rapid evaporation and decomposition. The droplets are most commonly produced by forcing the acid into the furnace through fine nozzles (Rohm and Haas, 2003 Bete, 2005). Spinning cup atomizers are also used. 

Definition The vaporization coefficient, is usually defined as the ratio of the actual flow of gaseous decomposition product J to the flow Jmax coming from an effusion cell, in which, it is assumed, decomposition products are in an ideal equilibrium with the reactant. For many substances, as found from comparative Knudsen-Langmuir TG measurements, -C 1, i.e., their free-surface decomposition proceeds much more slowly than would be expected from effusion observations. It is a common practice to explain this discrepancy by a multistage character of the evaporation process, by surface relief peculiarities or by impurities and defects (imperfections) in the reactant lattice. 

For bodies of big wall thickness the initial creation of open porosity is critical [Cal 90]. During heat treatment the evaporation and decomposition of the polymers generate gas inside the body. If the pores are not open or there are not enough paths to channel the gas to the surface of the exttu-date, pressure will build up inside the body and cracks will be created dur-... 

Finally, it is to be expected that the evaporation coefficient of a very stable compound, such as alumina, which has a large heat of sublimation resulting from the decomposition into the elements, will be low. Since the heat of evaporation must be drawn from the surface, in die case of a substance widr a low thermal conductivity such as an oxide, the resultant cooling of the surface may lead to a temperature gradient in and immediately below the surface. This will lower die evaporation rate compared to that which is calculated from the apparent, bulk, temperature of the evaporating sample as observed by optical pyromeuy, and thus lead to an apparently low free surface vaporization coefficient. This is probably die case in the evaporation of alumina in a vacuum. 

Vacuum Deposition-also vapor deposition or gas plating the deposition of metal coatings by means of precipitation (sometimes in vacuum) of metal vapor onto a treated surface. The vapor may be produced by thermal decomposition, cathode sputtering or evaporation of the molten metal in air or an inert gas. 

An aqueous solution of aluminium formate was being evaporated over a low flame. When the surface crust was disturbed, an explosion occurred. This seems likely to have been due to thermal decomposition of the solid, liberation of carbon monoxide and ignition of the latter admixed with air. 

In chemical vapor deposition (CVD or MOCVD), a film of the desired material is prepared by evaporation of volatile precursor molecules which then decompose to give a film deposited on the substrate. The ordering in the film as it grows is dictated by the surface ordering of the substrate, hence the deposition is epitaxial . The necessary decomposition of the precursor molecules can take place either on the surface of the substrate or in the gas phase close to it. 

Alkaline earth oxides (AEO = MgO, CaO, and SrO) doped with 5 mol% Nd203 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO2-TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd3+. Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed. 

Saito with a fine wire thermocouple embedded at the surface [3]. The scatter in the results are most likely due to the decomposition variables and the accuracy of this difficult measurement. (Note that the surface temperature here is being measured with a thermocouple bead of finite size and having properties dissimilar to wood.) Likewise the properties k. p and c cannot be expected to be equal to values found in the literature for generic common materials since temperature variations in the least will make them change. We expect k and c to increase with temperature, and c to effectively increase due to decomposition, phase change and the evaporation of absorbed water. While we are not modeling all of these effects, we can still use the effective properties of Tig, k, p and c to explain the ignition behavior. For example,... 

---