Page 462 - Handbook of Thermal Analysis of Construction Materials

Section 5.0 - Zinc Oxychloride Cement 437

5.0 ZINC OXYCHLORIDE CEMENT

The reaction of zinc oxide with zinc chloride in water gives an
extremely hard zinc oxychloride cement product which is not attacked by
acids or boiling water. [23] The main hydrated products are two zinc
oxychloride hydrates, 4ZnO•ZnCl •5H O and ZnO•ZnCl •2H O. The former
2 2 2 2
product is very stable and insoluble, but is associated with very poor
workability while the latter is not stable in water and can cause excessive
solubility and leaching. Zinc oxychloride would, therefore, not appear to
have sufficiently reliable properties to justify practical application. TG and
DTG curves for the 4:1:5 and 1:1:2 phases are plotted in Fig. 27. The 1:1:2
phase undergoes a two-step dissociation beginning at about 230°C. The
weight loss corresponding to half the constituent water occurred above the
melting point of anhydrous ZnCl , i.e., 275°C. Weight loss ceased at a level
2
slightly above that corresponding to a complete loss of ZnCl and H O. The
2
2
4:1:5 phase dissociates at 160°C to the 1:1:2 phase and ZnO, and at higher
temperatures undergoes the same dissociation as the 1:1:2 sample.

Figure 27. TG and DTG curves for 4:1:5 and 1:1:2 phases in zinc oxychloride cements. [23]