MICROSTRUCTURAL AND MICROCHEMICAL CHARACTERIZATION OF A CALCIUM ALUMINATE-POLYMER COMPOSITE (MDF CEMENT)

The microstructure of a macrodefect-free (MDF) cement has been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and high-resolution electron microscopy (HREM). The microchemistry of ultramicrotomed samples has been studied by energy dispersive spectrometry (EDS) and parallel electron energy loss spectrometry (PEELS). MDF cement consists of CaAl2O4 and CaAl4O7 grains randomly distributed in a polymer matrix. The ceramic/polymer interface contains an amorphous interphase inside of which are distributed very fine crystallites of the metastable hydration product Ca2Al2O5.8H2O. PEELS analyses of the interphase revealed the presence of carbon, indicating that Ca2Al2O5.8H2O was most likely stabilized by the intercalation of polymeric chains into its basal interlayers. The polymer phase preferably cross-links with Al. In situ environmental cell electron microscopy showed that moisture uptake of MDF cements occurred by polymer swelling and interphase dissolution. The role of the interfacial interphase in dry and wet mechanical properties is discussed.