**2.6.1 Solution combustion method**

Combustion synthesis is an effective, low-cost method for production of various useful materials. Today, it has become a very popular approach for preparation of nanomaterials.

Solution combustion synthesis (SCS) is a versatile, simple and rapid process, which allows effective synthesis of variety of nanosize materials. This process involves a self-sustained reaction in homogeneous solution of different oxidizers (e.g., metal nitrates) and fuels (e.g., urea, glycine, hydrazides). Depending on the type of the precursors, as well as on conditions used for the process organization, the SCS may occur as either volume or layer-by-layer propagating combustion modes. This process not only yields nanosize oxide materials but

freeze-dryer will carry out its function: to provoke the sublimation of the solvent. For that, the frozen solution undergoes an important vacuum created by a pump, allowing the solvent to sublimate and being the latter frozen once again into a big drum at a very low

After one/two day(s) the dried solution – called now *precursor* – is disconnected from the freeze-dryer and treated at certain temperature in order to allow the reaction between the different reagents which are mixed in extremely fine and close way. This method allows much lower both dwelling times and heating temperatures, at the time that makes easier the

One method often employed is to melt the reagents together and then later anneal the solidified melt. If volatile reagents are involved these are usually put in an ampoule that is evacuated (the reagent mixture is kept cold – by keeping the bottom of the ampoule in liquid nitrogen, e.g.) and then sealed. The sealed ampoule is then put in an oven/furnace

Pechini method is a widely used method consisting of the mix of metal nitrate solution of the starting materials with a stoichiometric amount of citric acid. The resulting solution is stirred on a hot plate and the temperature stabilized at about 90ºC, at which point ethylene glycol is added at a mass ratio of 40:60 with respect to citric acid. The temperature is maintained constant up to the resin formation, which polymerizes at about 300ºC. The

This method, as a soft-chemistry one, leads to homogeneous and low crystalline products at relatively low temperatures, but they usually require expensive initial compounds and/or

Some relative new methods are worth being mentioned, like the solution combustion

Combustion synthesis is an effective, low-cost method for production of various useful materials. Today, it has become a very popular approach for preparation of

Solution combustion synthesis (SCS) is a versatile, simple and rapid process, which allows effective synthesis of variety of nanosize materials. This process involves a self-sustained reaction in homogeneous solution of different oxidizers (e.g., metal nitrates) and fuels (e.g., urea, glycine, hydrazides). Depending on the type of the precursors, as well as on conditions used for the process organization, the SCS may occur as either volume or layer-by-layer propagating combustion modes. This process not only yields nanosize oxide materials but

precursor powders are heated for several hours at various temperatures.

method, the sonochemical method, and the microwave assisted synthesis.

temperature inside the device.

and given a certain heat treatment.

complicated synthesis procedures.

**2.6.1 Solution combustion method** 

way to get pure phases.

**2.4 Melt method** 

**2.5 Pechini method** 

**2.6 Other methods** 

nanomaterials.

also allows uniform (homogeneous) doping of trace amounts of rare-earth impurity ions in a single step.

### **2.6.2 Microwave assisted method**

Microwave heating allows a rapid heating rate, however, the final yield decreases compared with the conventional methods. It leads to the synthesis of materials by consumption of less energy.
