# X-ray Diffraction Study of Metallized Polyethylene for Creating Heat Storage Systems
## 3 Results and Discussion
Thus, the result of the stage of polyethylene granules activation is the amorphization of the material, as indicated by a decrease in intensity and broadening of the peaks, as well as the calculated crystallite sizes (Table 3). The shift in the position of the peaks is insignificant, which may be due to the absence of changes in the structure of the crystal lattice. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **Degree of Crystallinity** & **Position** & **Height** & **Width** & \
\begin{tabular}{c} **Size** \\ **L** \\ \end{tabular} &
\begin{tabular}{c} **Distance** \\ **d** \\ \end{tabular} \\ \hline \multirow{4}{*}{Metallized PE granules} & \multirow{4}{*}{0.388} & 21.4 & 191.2 & 1.2 & 73.0 & 4.2 \\ \cline{3-6}  & & 23.7 & 60.1 & 1.2 & 73.7 & 3.8 \\ \cline{3-6}  & & 19.7 * & 53.0 & 8.9 & - & - \\ \hline \multirow{4}{*}{Plate made of metallized PE granules} & \multirow{4}{*}{0.501} & 21.1 & 386.4 & 0.5 & 187.5 & 4.2 \\ \cline{3-6}  & & 23.5 & 128.0 & 0.6 & 151.3 & 3.8 \\ \cline{3-6}  & & 20.1 * & 54.0 & 5.3 & - & - \\ \hline \hline \end{tabular}  
*—amorphous phase.  
\end{table} 
Table 3: Results of calculations of the parameters of crystalline peaks and the amorphous phase of polyethylene. Figure 5: Diffraction pattern of metallized polyethylene granules and the plate pressed from them that underwent one heating and cooling cycle. The increase in the degree of crystallinity of the plates, in comparison with the (initial and metallized) polyethylene granules from which they are obtained, can be explained by their slower cooling, which results in the possibility of obtaining a larger number of crystallization centers and a slower crystal growth rate. Granular polymers are produced industrially by rapid cooling. In order to determine the influence of cyclic stability of the developed heat-accumulating material, X-ray diffraction analysis was performed every 100 cycles of heating and cooling. To avoid the possible influence of peaks of the crystalline phase of copper on the calculation of the degree of polyethylene crystallinity, the diffraction curve was limited to the range from 14\({}^{\circ}\) to 28\({}^{\circ}\). Figure 6 shows the graphical results of the analysis of the diffraction pattern of the heat-accumulating material after 100 heating and cooling cycles. The analysis of the results in Table 4 makes it possible to state that the degree of crystallinity of the heat-accumulating material naturally decreases with an increase in the number of heating and cooling cycles. The height of crystalline peaks and the crystallite size also decrease. The peak positions do not shift significantly depending on the number of heating and cooling cycles, which indicates the unchanged crystal structure of the material. The most intense decrease in the degree of crystallinity is observed in the range of 100-400 heating and cooling cycles. The general decrease in the degree of crystallinity is about 2.5 times and is quite significant. The experimental conditions included heating the material to a temperature of about 270 \({}^{\circ}\)C, which is approximately 150 \({}^{\circ}\)C higher than the melting point of polyethylene. Considering the low thermal stability of organic polymers, heating to high temperatures will lead to thermal destruction of macromolecules, their possible recombination, and cross-linking. The formation of a new structure characterized by defects will complicate the close packing of macromolecules, which will cause a decrease in the degree of crystallinity. Such a decrease in the crystallinity of polyethylene will naturally affect the efficiency change of the heat-accumulating material usage. To estimate the amount of heat that could be accumulated in the material, it is necessary to calculate the content of the amorphous and crystalline polymer phases. Figure 6: Diffraction pattern of heat-accumulating material after 100 heating and cooling cycles: 1—experimental curve, 2—crystalline peaks, 3—amorphous phase.