DETERMINATION OF HYDROGEN IN HYDROGENATED TITANIUM  AND ZIRCONIUM DIBORIDES USING AN ASD FieldSpec 3 FR  SPECTRORADIOMETER 

Abstract

The results of spectrometry with an ASD FieldSpec 3 FR spectroradiometer at wavelengths ranging from 350 to 2500 nm for hydrogenated amorphous and crystalline titanium and zirconium diborides are presented. The results were used to determine changes in the spectral characteristics of hydrogen in bulk and film TiB₂ and ZrB₂. The spectrometry was performed with the contact method using a Unit Contact Probe. The bulk test samples and spraying targets were prepared by the powder metallurgy method. X-ray diffraction identified that the samples had crystalline structure. Thin films of titanium and zirconium diborides were produced by magnetron sputtering of TiB₂ and ZrB₂ targets in an argon atmosphere. The structure of the films was studied using an EMP-100 electron diffractometer employing the transmission method at a residual pressure of ~7 · 10^–3 Pa. The electron diffraction patterns showed a strong 'halo' at the center, being indicative of amorphous structure of the films, promoting hydrogen transfer process. The samples were hydrogenated from the gas phase at a hydrogen pressure of 0.1 MPa and a temperature of 870 K. A critical analysis of published methods for the quantitative determination of hydrogen in high-temperature borides was provided. The spectrometry method is advantageous in that it is fast, precise, nondestructive, and surface-sensitive, and the entire spectrum is displayed in real time. The intensities of the Brackett B_β and Balmer H_β hydrogen lines for crystalline and amorphous TiB₂ were compared, and the absorption of hydrogen by the crystalline sample was found to be 4.1 times higher than that by the amorphous one. In polycrystalline TiB₂, lines with a halfwidth of 200–300 nm were observed at 500 and 750 nm, which was explained by the subbarrier tunneling of hydrogen atoms between neighboring interstitials, ranging, in particular, for many lattice parameters. The absorbed hydrogen amount in the amorphous film was 1.4 times higher than on the starting film. Magnetron sputtering of ceramic targets was known to lead to the introduction of impurities several tens of nanometers in size (short-range crystalline ordering) into the film, to which the hydrogen penetration process was sensitive. The presence of hydrogen atoms resulted in spectral bell-like curves, partially overlapping each other. By analogy with metal amorphous alloys, the shape of these curves could be explained by quasi-interstices. In the amorphous titanium diboride, a bell-like Balmer H_β curve was observed, confirming short-range crystalline ordering. Correlation between the hydrogen absorption and the lattice energy and bonding energy of Me–B atoms was established. When hydrogen was absorbed by crystalline titanium and zirconium diborides, TiB₂ was found to absorb higher amounts of hydrogen because of lower lattice energy and Ti–B atomic bond energy. As the spectroradiometer method is prompt and informative, we can recommended it for the identification of hydrogenated amorphous and crystalline ceramic materials.