# Preliminary Investigation of Geopolymer Foams as Coating Materials
## 3 Results and Discussion  
In the first stage, the geopolymerization process consisted of dissolving the base materials, breaking the bonds between silicon and oxygen and between aluminum and oxygen, and then starting the polycondensation process, after which a three-dimensional structure was created. The most important components of the materials susceptible to the geopolymerization process were the presence of silicon and aluminum. Table 4 shows the oxide composition of the fly ash used. This material mostly contains SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\). The analysis of the oxide composition showed that this material also contains oxides of iron, potassium, calcium, manganese, and titanium. Titanium in geopolymeric materials affects plasticity but is most often considered an impurity. Other scientific studies revealed the nucleating activity of the crystallization process in the geopolymerization process [36; 37; 38; 39]. Base materials were also tested using a particle size analyzer, and the results are presented in Table 5 and Figure 1. The mean size of fly ash was equal to around 17 \(\upmu\)m, while river sand was found to be larger, and its mean particle size was approximately 730 \(\upmu\)m.  
The first stage of the research was the selection of the spray gun nozzle. As part of the selection process of the appropriate nozzle, a nozzle with a diameter of 4 \(\times\) 10\({}^{-3}\) m to \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Oxide** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **K\({}_{2}\)O** & **CaO** & **MgO** & **TiO\({}_{2}\)** & **Na\({}_{2}\)O** & **P\({}_{2}\)O\({}_{5}\)** & **SO\({}_{2}\)** \\ \hline Fly ash & 49.69\% & 24.84\% & 7.20\% & 3.59\% & 3.77\% & 1.52\% & 1.13\% & 1.88\% & 0.33\% & 0.96\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Oxide composition of fly ash. Figure 1: Analysis of particle size of based materials: (a) fly ash and (b) river sand. \begin{table}
\begin{tabular}{c c c} \hline \hline
**D-Values** & **Fly Ash** & **River Sand** \\ \hline D\({}_{10}\) (\(\upmu\)m) & 2.208 & 400.776 \\ D\({}_{50}\) (\(\upmu\)m) & 12.268 & 647.689 \\ D\({}_{90}\) (\(\upmu\)m) & 36.175 & 1036.757 \\ Mean size (\(\upmu\)m) & 16.975 & 730.226 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The particle size of based materials. \(8\times 10^{-3}\) m was tested, using the medium working range of the gun pressure (0.51-0.65 MPa). The material was spread from a distance of 0.25 m. The first results when using a nozzle with a diameter of \(8\times 10^{-3}\) m provided satisfactory results. However, the sprayed layer was too thick, and the sprayed material ran off the pad, resulting in an uneven and irregular surface (Figure 2c). The use of a nozzle with a diameter of \(6\times 10^{-3}\) m contributed to better results than a nozzle with a larger diameter. The spraying process was correct. A reduction in the nozzle diameter limited the material spread, resulting in a more uniform and even layer of the geopolymer material. The final effect had much better quality than the material sprayed with the \(8\times 10^{-3}\) m nozzle (Figure 2b). The last sample of the tested nozzle diameters was the one with a diameter of \(4\times 10^{-3}\) m. The spray test showed that this diameter was too small for the consistency of the geopolymeric mass, creating a back pressure that resulted in the supply system being blocked, thus restricting the flow (Figure 2a). Based on the conducted research, the nozzles with a diameter of \(6\times 10^{-3}\) m were selected for further investigation. After selecting the optimal diameter of the spray nozzle, we proceeded to obtain the optimal working pressure of the spray. Table 6 shows the results of spraying the geopolymer layers. As shown in Table 3, and with the help of a pressure gauge, the pressure ranges at which it was possible to operate the spray gun were determined.