Aluminum hydroxide gel characterization within a calcium aluminate cement paste by combined Pair Distribution Function and Rietveld analyses

There are many commercially important multiphase materials which contain amorphous phases, such as cement pastes, porcelains, glass-ceramics or pharmaceutical compounds. However, the analysis of amorphous phase(s) within cement matrices that contain high amounts of crystalline phase(s) is a challenge. Here, we report measurements of total scattering data quantitatively analyzed by Pair Distribution Function (PDF) minimization and Rietveld methodology to determine phase compositions including both amorphous and nanocrystalline phase contents in cement-related samples. Furthermore, laboratory techniques were used to complement the sample characterization. In addition to five reference materials, the main phase of calcium aluminate cements, CaAl2O4 hydrated at 50 °C to yield crystalline hydrogarnet, Ca3Al2(OH)12, (43 wt%) and nanocrystalline aluminum hydroxide gel, Al(OH)3·0.1H2O (50 wt%) was also investigated. The PDF analyses revealed that the hydroxide gel has a gibbsite local structure with an average particle size close to 5 nm. PDF and Rietveld quantitative phase analysis results fully agree.