Number Of Primary Centers Research Articles

Investigation into the dependence of time characteristics of ignition and combustion of iron nanopowders on air on the duration of passivation after synthesis

A method of estimating the extent of passivation of iron nanopowders based on color high-speed filming is suggested. It is established that the number of primary centers of combustion and the time of their emergence depend on the passivation time: the more the passivation time is, the lower the number of primary centers of combustion is. This allows using the dependence for estimating both the extent of passivation and the minimum time of complete passivation. A method for calculating the time of complete passivation for the sample of arbitrary thickness is suggested.

Effect of dehydration on porous structure of monolithic aerogels based on fibrous aluminum oxyhydroxide

Aluminum oxide monolithic aerogels (PMAOs) with specific surfaces of up to 400 m2/g and densities of up to 0.004 g/cm3 were obtained by the direct oxidation of metallic aluminum by water vapors. Studies of the obtained aerogels using the methods of scanning and transmission electron microscopy showed that a freshly prepared aerogel represents the amorphous structure from alumina fibrous with a diameter of about 5 nm. Parameters of a porous aerogel structure were determined from the isotherms of adsorption of nitrogen vapors at 77 K. It is shown that the specific surface area decreases by 50% upon the dehydration of aerogel by temperature pretreatment at 900°C until the phase transition temperature is reached. At the same time, heat treatment at temperatures above 1200°C results in a phase transition at which significant contraction of structure occurs and the specific surface area decreases to 20 m2/g. The number of primary adsorption centers was obtained from comparative plots of water vapor adsorption. It was found that preliminary dehydration only slightly affects the number of primary centers of water adsorption.