_Applied_  
_sciences_  
_Article_  
**Synthesis, Structure, and Thermal Stability of Magnesium Oxochloride 5 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O**  
**[PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 1, [PERSON] 2, [PERSON] 2, [PERSON] 2 and [PERSON] 1,*\({}^{\text{\textregistered}}\)**  
1 Department of Inorganic Chemistry, Faculty of Chemical Technology, University of Chemistry and Technology, Technicka 5, 166 28 Prague 6, Czech Republic; [EMAIL_ADDRESS] (A.J.); [PERSON]SS] (M.L.); [EMAIL_ADDRESS] (A.-M.L.); [EMAIL_ADDRESS] (F.A.); [EMAIL_ADDRESS] (D.S.)  
2 Department of Materials Engineering and Chemistry, Faculty of Civil Engineering, Czech Technical University in Prague, Thakurova 7, 166 29 Prague 6, Czech Republic; [EMAIL_ADDRESS] (M.P.); [EMAIL_ADDRESS] (M.Z.); [EMAIL_ADDRESS] (Z.P)  
* Correspondence: [EMAIL_ADDRESS]; Tel.: +42-022-044-2002  
Received: 29 January 2020; Accepted: 25 February 2020; Published: 2 March 2020  
**Featured Application: The results obtained in the paper can find use in the design of low-energy building composites. The formation of Phase 5 of magnesium oxochloride cement (MOC 5-1-8 phase) can be beneficially used in repair works, where fast hardening is of particular importance for the functionality of the protected and repaired layers. The fast precipitation of MOC 5-1-8 phase can also be beneficially used in prefabrication, where it can allow possible unmolding after short time period, which makes the production process of prefabricated elements more effective. Therefore, MOC can be used as the only binder of advanced types of building materials with specific application potentials. Moreover, the lower CO2 path of MOC compared to the production of Portland cement gives evidence for the environmental benefits of building materials based on MOC.**  
Today, low-energy and low-carbon footprint alternatives to Portland cement are searched because of huge CO\({}_{2}\) emissions coming from Portland clinker calcination. Because of some superior properties of magnesium oxchloride cement (MOC) and the lower carbon footprint of its production, MOC became an intensively studied material with high application potential for the design and development of construction products. In this contribution, magnesium oxchloride with stoichiometry 5 Mg(OH)\({}_{2}\)-MgCl\({}_{2}\)-8H\({}_{2}\)O (Phase 5) was prepared and characterized. The kinetics of formation and the phase composition of the material were determined using X-ray diffraction and consequent Rietveld analysis. The morphology was studied by scanning electron microscopy, and the chemical composition was determined by both energy-dispersive spectroscopy and X-ray fluorescence. Moreover, the simultaneous thermal analysis in combination with mass spectroscopy and Fourier-transform infrared spectroscopy was employed to study the thermal stability. Using mass spectroscopy, we were able to clarify the mechanism of water and hydrochloric acid release, which was not previously reported. The observed structural and chemical changes induced by exposure of studied samples to elevated temperatures were linked with the measured residual macro and micro parameters, such as bulk density, specific density, porosity, water absorption, compressive strength, and pore size distribution. The Phase 5 revealed a needle-like crystalline morphology which formed rapidly and was almost completed after 96 h, resulting in relatively high material strength. The four-day compressive strength of magnesium oxchloride cement was similar to the 28-day compressive strength of Portland cement. The thermal stability of Phase 5 was low as the observed disruptive thermal processes were completed at temperatures lower than 470 \({}^{\circ}\)C.  
**Keywords: magnesium oxychloride cement; non-hydraulic binder; MOC phases; kinetics of formation; thermal stability** +
Footnote †: journal: Journal of Chemical Physics