Abstract
Thermal dehydration of dicalcium aluminate hydrate, C 2AH 8, has been investigated by simultaneous differential thermal and thermo gravimetric analysis (DTA/TGA), powder X-ray diffraction (XRD), temperature-dependent infrared spectroscopy (FT-IR), and BET method of surface area measurement. The temperature-dependent infrared measurements were studied by two-dimensional infrared (2D-IR) correlation spectroscopy. The structure of aluminum-oxide polyhedron, characterized by 27Al solid state NMR spectrum method and FT-IR, shows tetrahedron and octahedron as the main forms of aluminum-oxide polyhedrons in C 2AH 8 sample. From the results obtained a variety of structural transformations observed are explained as a consequence of the removal of loosely held interlayer water molecules at lower temperatures, followed by grafting process of the interlayer [Al(OH) 4] − anion. Structural model of a grafting process of the interlayer [Al(OH) 4] − tetrahedron onto hydroxylated octahedrons of [Ca 2Al(OH) 6] + layers has been proposed in order to explain observed loss of one water molecule, shrinkage of interlayer spacing and qualitative changes of FT-IR spectra. At higher temperatures the dehydroxylation of the lattice and decomposition of the interlayer species occurs, yielding amorphous material that crystallizes into C 3A and C 12A 7 at 885 °C. Those findings provide improvement in the interpretation of thermo-analytical results of calcium aluminate cements (CAC) hydration products, and better understanding of CAC conversion process.
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