Suggested Chemistry of Zinc Oxychloride Cements

Abstract

Solutions of ZnCl 2 were prepared from ZnCl 2 · n H 2 O and by reaction of zinc metal with HCl. Specific gravities and pH values were determined as a function of composition. A ternary phase, 4ZnO·ZnCl 2 ·5H 2 O, was precipitated when the ZnCl 2 solutions were diluted to a pH of 5.48 ± 0.05. Mixtures of ZnO with ZnCl, and HCI solutions were equilibrated in sealed containers and analyzed by X‐ray diffraction. The resulting phase diagram shows 2 ternary phases, 4ZnO·ZnCl 2 ·5H 2 O (4·1·5) and ZnO·ZnCl 2 ·2H 2 O (1.1.2), both of which are soluble to the extent of < 1 wt% in ZnCl 2 solutions. Thermogravimetric data indicate that the 1.1.2 phase loses half the constituent H 2 O at ∼230°C and the remainder, with ZnCl 2 , at higher temperatures. The 4.1.5 phase dissociates to ZnO and 1.1.2 at ∼160°C. The system ZnCl 2 ‐H 2 O is not binary, but is a section through the ternary system ZnO‐HCl‐H 2 O, with the solubility curve of the 4.1.5 phase intersecting the ZnCl 2 ‐H 2 O section in dilute solutions.