Fumed silica combustion process

These processes are very rapid and allow the preparation of inorganic supports in one step. This technique allows large-scale manufacturing of supports such as titania, fumed silica, and aluminas. Sometimes the properties of the material differ from the conventional preparation routes and make this approach unique. Multicomponent systems can be also prepared, either by multimetallic solutions or by using a two-nozzle system fed with monometallic solutions [22]. The as-prepared powder can be directly deposited onto substrates, and the process is termed combustion chemical vapor deposition [23]. 

The authors proposed a mechanism that accounts for the reduction in flammability properties, which depends on physical processes in the condensed phase rather than chemical reactions. Three factors are critical in determining the silica behavior during the combustion process the density and surface area of the additive, the melt viscosity of the polymer. The interplay between these factors can determine whether the silica will accumulate near the surface or sink through the polymer melt. Fumed silica and silica gel provide examples for the first case where the silica particles accumulated on the surface and formed an insulating layer that provide protection to the underlying polymer. This is in contrast to the other case where the fused silica particles sank through the polymer melt. 

A process called flame combustion synthesis is widely used to manufacture catalysts containing carbon black, fumed silica, or titania [277-279]. 

An interesting approach in making mullite powders has been via combustion synthesis [36], An aqueous heterogeneous redox mixture containing aluminum nitrate, silica fume (soot), and urea in the appropriate mole ratio is mixed together. When rapidly heated to 500°C, the mixture boils, foams, and can be ignited with a flame. The process yields weakly crystalline mullite powder in less than 5 min. Fully crystalline mullite can be obtained by incorporating an extra amount of oxidizer, such as ammonium perchlorate in the solution. 

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