# X-ray Diffraction Study of Metallized Polyethylene for Creating Heat Storage Systems
## 2 Materials and Methods  
Listen PL-10 (Unipetrol) granulated polyethylene was used in the research. The granules of the initial polyethylene were metallized using a developed technology, which included the activation of the surface of the granules as a result of their processing in a ball mill with finely dispersed zinc [32]. Such processing allows obtaining a catalytically active surface of the granules, which is used in the next stage of chemical metallization. The process of activating polyethylene granules was carried out in a laboratory mill with a volume of 4 L with ceramic cylindrical grinding bodies, at a rotation speed of 125 rpm. The following components were loaded into the mill: polymer--300 g, finely dispersed zinc--30 g, and grinding bodies--1.5 kg; the duration of processing was 1 h. The presence of zinc particles on the surface of the polyethylene granules ensures the start of the copper ion reduction in a stabilized electroless copper plating solution. The further reduction of copper ions by formaldehyde is an autocatalytic process and occurs on the formed copper surface. This ensures the formation of a copper coating on the surface of the polyethylene granule, the thickness of which can be adjusted by the parameters of the metallization process (concentration of the components of electroless copper plating solution, duration of metallization, the number of repeated metallizations) [33; 34; 35]. The composition of the electroless copper plating solution is as follows (mmol/L): CuSO\({}_{4}\):5H\({}_{2}\)O--60, EDTA-Na\({}_{2}\) (C\({}_{10}\)H\({}_{4}\)N\({}_{2}\)Na\({}_{2}\)O\({}_{8}\):2H\({}_{2}\)O)--67, NaOH--375, stabilized formalin--365. The necessary content of copper on polyethylene granules was provided by repeated metallization. Obtaining images of coppered polyethylene granules was carried out using a Vision Lynx EV0504 microscope (Vision Engineering Ltd., Woking, UK). SEM images and energy dispersive studies of the surface of copper granules were performed applying a Zeiss EVO-40 XVP microscope (ZEISS, Jena, Germany). The obtained copper-coated polyethylene granules were used as a heat-accumulating material, in which the presence of copper having a high thermal conductivity will provide better heat supply and removal in the bulk material. Another advantage of using copper-coated granules is obtaining a material in which copper is evenly distributed throughout the entire bulk of the material. Moreover, no additional processing procedures (mixing) are required for such uniform distribution of copper in the bulk of the heat-accumulating material. The formation of the heat-accumulating material structure will occur during the first melting of the material, accompanied by the destruction of the metal shell and the formation of individual copper particles of different sizes. Due to the high viscosity of polymer melts and the absence of convective flows of the substance, sedimentation of copper particles will occur very slowly. This will ensure the formation of the structure with a large number of thermally conductive copper particles, which are separated by the polymer material. For the research, heat-accumulating material was used in the form of a square plate 2 mm thick with a lateral length of 10 mm, obtained by preliminary hot pressing of metallized polyethylene granules (copper content--10 wt.%). In order to study the effect of the cyclical use of the heat-accumulating material on the crystal structure of the heat-accumulating material, an experiment was developed that involved heating and cooling of the heat-accumulating material. The material was heated on a solid metal plate heated to 280 \({}^{\circ}\)C, followed by the air convection cooling.