## 3 Results and Discussion  
An infrared camera was employed to take photographs of the samples with 75 mL of water in the precursor solution during combustion, and they are presented below in Figure 1. The photographs were taken at approximately the same time for the not-pretreated (a) and pretreated (b) samples at 70 \({}^{\circ}\)C.  
Figure 1: _Cont._  
It can be observed from Figure 1 that there were well-developed and clearly distinguished dendrites when the pretreatment was applied on the precursor solution. On the other hand, in the not-pretreated sample there were no developed structures, indicating a different mechanism during SCS that resulted in a different composition and microstructure of the obtained nanopowders. The other three water quantities were also investigated, and the results were the same as those presented (75 mL of water). At saturated nickel nitrate concentrations, dendrite growth in water can be explained from the perspective of a diffusion-limited aggregation process. The dendritic structure was due to the formation of hydrates while still in solution in combination with extensive gas emissions during SCS. These results were attributed to several controlling factors: the nickel nitrate crystal structure, the nature of diffusion through water as a solvent, the formation of nickel and nickel oxide, and the formation of strong bonds in glycine-nickel nitrate tetrahydrate (C\({}_{2}\)H\({}_{13}\)N\({}_{3}\)NiO\({}_{12}\)) during the reaction of glycine with nickel nitrate. It appeared that when these dendrites existed (with pretreatment) the reaction took place at a lower velocity as it was yielded through their complicated structure, and thus there was less time available for the oxidation of nickel. In previous studies, there were several examples of dendrite formation during combustion synthesis. [PERSON] et al. [19] studied the relationship between the combustion reaction mechanism induced by the exothermicity of the cobalt nitrate-glycine solution-combustion reactions and the morphological details of the nanocrystalline Co\({}_{3}\)O\({}_{4}\) with a multi-branching tree-like form of the powders. They suggested that the high enthalpy of combustion, the rapid sintering, and formation of the grain boundaries typical for the strong bonding among cobalt-oxide nanocrystallites and short-string particles that occurred led to the formation of dendritic agglomerates [19]. Furthermore, the sol-gel combustion method was employed by [PERSON] et al. [20] to synthesize modified salts based on the combustion of a sol or gel of Mg(NO\({}_{3}\))\({}_{2}\) and citric acid or urea in NaNO\({}_{3}\)-KNO\({}_{3}\). These results showed that MgO nanoparticles possess a dendritic structure with a length of tens to hundreds of nanometers and notably by increasing fuel, the dendritic structure grew beyond the nanometer size [20]. Finally, Ce\({}_{0.8}\)Sm\({}_{0.2}\)O\({}_{2\times}\) powders were derived by SCS using Ce(NO\({}_{3}\))\({}_{3}\)-6H\({}_{2}\)O and Sm(NO\({}_{3}\))\({}_{3}\)-6H\({}_{2}\)O as metal precursors and using different combustion fuel mixtures: (1) citric acid with ammonia, (2) cellulose and citric acid with a 2:1 molar ratio, and (3) sucrose. The reducer-oxidizer mixtures were stirred at 80 \({}^{\circ}\)C until a pale gel was formed. By further increasing the temperature, a white dendritic powder was formed for all combustion reactions [9]. Figure 2 demonstrates the patterns obtained from the XRD analysis for the examined nanopowders. Figure 1: Photographs of the (**a**) not-pretreated and (**b**) pretreated samples during combustion, taken using an IR camera at 70 \({}^{\circ}\)C.  
The XRD analysis revealed the major impact of the precursor solution's pretreatment. The two resulting phases, Ni and NiO, appeared to exist in various ratios in the final product. Figure 3 presents the semi-quantitative analysis of these two phases as a function of the preparation conditions.