Scanning electron microscopy, X-ray diffraction and thermal analysis study of the TiH2 foaming agent

• Published in: Materials characterization 2012-10, Vol.72, p.87-93
• Main Authors: Mandrino, Djordje, Paulin, Irena, Škapin, Srečo D.
• Format: Article
• Language: English
• Subjects: Aluminium foams; Cross-disciplinary physics: materials science; rheology; Dehydrogenation; DSC; DSL; Exact sciences and technology; Foaming agent; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; SEM; Solidification; TiH2; Titanium hydride; XRD
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2012.07.005

The decomposition of commercially available TiH2 was investigated while performing different thermal treatments. TiH2 powder, which is widely used as a foaming agent, was heat treated at 450°C for various times, from 15min to 120min. Scanning electron microscopy (SEM) images of the surfaces at different magnifications were obtained and interpreted. A Bragg–Brentano X-ray diffractometer was used to measure the X-ray diffraction (XRD) spectra on all five samples. A close examination of the diffraction spectra showed that for an as-received sample and samples undergoing the longest thermal treatment (1 and 2h) these spectra can be explained as deriving from cubic TiH1.924, while for the other two samples they can be explained as deriving from tetragonal TiH1.924. A constant-unit-cell-volume phase transition between the cubic and tetragonal phases in TiH2−y-type compounds had been described in the literature. The unit-cell parameters obtained from measured spectra confirm that within the measurement uncertainty the unit-cell volume is indeed constant in all five samples. Thermo-gravimetry (TG) and differential thermal analysis (DTA) measurements were performed on all the samples, showing that the intensity of the dehydrogenation depends on the previous treatment of the TiH2. After the thermal analysis XRD of the samples was performed again and the material was found to exhibit a Ti-like unit cell, but slightly enlarged due to the unreleased hydrogen. ► TiH2 samples were cubic or tetragonal TiH1.924 ► Onset of the hydrogen release temperature increases with the pre-treatment time. ► Thermal dehydrogenation for the as-prepared TiH2 is a three-step process. ► After thermal analysis 2 residual hydrogen TiHx phases, close to αTi, appeared.