## 1 Introduction  
Magnesium oxychloride cement (MOC), also known as Sorel cement, was discovered by French engineer [PERSON] in 1867 [1]. Since then, it has often been compared to Portland cement (PC), which was discovered just a few years earlier. It is formed using a mixture of magnesium oxide with an aqueous solution of magnesium chloride in a certain ratio. The ratios in the system MgO-MgCl\({}_{2}\)-H\({}_{2}\)Oare significant for each phase of MOC: Phase 2 (2 Mg(OH)\({}_{2}\).MgCl\({}_{2}\)-4H\({}_{2}\)O, MOC 2-1-4) and Phase 9 (9 Mg(OH)\({}_{2}\).MgCl\({}_{2}\).5H\({}_{2}\)O, MOC 9-1-5), which are stable at elevated temperatures (\(\sim\)100 \({}^{\circ}\)C); and Phase 3 (3 Mg(OH)\({}_{2}\).MgCl\({}_{2}\).8H\({}_{2}\)O, MOC 3-1-8) and Phase 5 (5 Mg(OH)\({}_{2}\).MgCl\({}_{2}\).8H\({}_{2}\)O, MOC 5-1-8), which are stable at ambient temperature until they react with CO\({}_{2}\) or H\({}_{2}\)O. [2; 3; 4] The crystal structures of Phase 3 and 5 formed by double and triple ribbons of edges shared MgO\({}_{6}\) octahedra with water molecules and chloride anions in the interstitial region are shown in Figure 1. The drawings were produced by VESTA Software [5]. MOC phases and MOC-based composites have been intensively studied in recent years. Synthesis, structure, and the thermal stability of magnesium oxychlorides in particular were studied in detail [6; 7]. MOC is a non-hydraulic versatile binder with specific properties, which make it superior to PC. One of the most significant properties is its specific density, which is considerably lower and possesses materially high compressive and flexural strength. Other superior properties are its elevated fire resistance, resistance to abrasion, and low thermal conductivity. All of these properties develop in quite a short curing time, so the material is suitable for quick repairs. Further, MOC is not affected by oils, grease, or paint [8; 9; 10; 11], and it is less alkaline (pH-10) than PC, making it appropriate for use with glass fibers and preventing the aging process as well as with other fillers and aggregates such as tire rubber, synthetic resin, and wood particles [12]. The advantage of MOC also lies in the fact that it has a high bonding capacity with different types of fillers including secondary raw materials coming from industrial processes. The versatility and functional performance of MOC-based materials have spurred considerable research into product design, development, and characterization [13; 14; 15]. Properties of MOC cement-based materials make them applicable in many ways--primarily as a flooring material, but also in fire protective systems, grinding wheels, decoration, wall insulation, and others [16; 17]. At the same time, these materials have also some disadvantages, especially when they come into contact with water [18; 19]. MOC has a low water resistance due to magnesium chloride leaching, a corrosive compound that causes severe damage when it comes in contact with metals [20; 21; 22]. The rest of the material is then left in the form of hydrated brucite (Mg(OH)\({}_{2}\)) as the binding phase. This process can be prevented by improving the stability of MOC in humid conditions, which can be achieved naturally by letting the surface of Sorel cement react with CO\({}_{2}\) from the air. The reaction provides magnesium chlorocarbonates to the surface of the original material. Another method of improving MOC is to use a very small amount of additives such as phosphoric acid or soluble phosphates of alkali metals, alkaline earth metals, aluminum, ammonia, or iron. This step causes the formation of  
Figure 1: Crystal structures of Phase 3 (left) and Phase 5 (right). Mg atoms are located in the centers of distorted octahedra formed by oxygen atoms. Cl atoms—green; O atoms—blue. Green-blue spheres in the Phase 5 structures correspond to a mixed site occupied by chloride anions and water molecules (hydrogen atoms are not shown). insoluble phosphate complexes that enhance the waterproofness of Sorel cement [23; 24].