Environmental Engineering Reference
In-Depth Information
develops through rapid heating of the mixture, at relatively decreased temperature,
below 500
C.
Compared to other methods, combustion method has certain advantages, such
as: is a simple method, short reaction time, low energy consumption, and friendly
with the environment. Moreover, the end product is directly obtained as a result of
combustion, without further calcination, so that without supplementary energy
consumption.
Increased interest for this unconventional synthesis method is due to diverse
range of variables, through which the combustion processes can be conducted and
directed so that the reaction products can be fitted within large limits.
Factors influencing self-propagated combustion reaction are [
71
,
72
]:
• Nature of oxidant agent and combustion agent;
• Molar ratio between combustion agent/oxidant;
• Presence of additives with auxiliary roles;
• Initiation temperature and heating velocity;
• Volume of raw matter mixtures;
• Water amount (water) from raw matters;
• Pressure.
Mukasyan et al. [
73
] showed that maximum temperature reached during the
reaction and reaction duration are two main elements controlling the properties of
the resulting powder, mainly the amorphous or crystalline characteristics and size
of particles from the reaction product. The difference between particles size
obtained by using different combustion agents is explained by different combustion
gases amount which is released by different exothermal reactions, and different
temperature from the reactant system [
74
].
Li et al. [
75
] showed that for different metallic cations, organic combustion
agents with different functional groups have different complexion power. This will
influence both formation and morphology of the desired product.
McKittrick [
71
] and Jung [
76
] declare that utilization of larger amount of
combustion agent will result in increased combustion temperature developed dur-
ing the reaction.
Reduced size of particles is due to increased gases volume, which will induce
sample expansion, thus impairing development of particles synthesis and growing
in size. Considering this aspect, Ozuna et al. [
77
] formulated the hypothesis that
higher the pressure in raw matter is, higher will be the specific surface of the
resulting powder, because the oxidation process is strongly exothermal, and
the reaction time is very reduced (~1 s); pressure within the system increases
even more, and the resulting combustion gases disintegrate the structure of solid
material, thus contributing to significant reduction of particle size and spectacular
increase of specific surface.
