Absorption, discharge, and internal partitioning behavior of hydrogen in the tantalum and tantalum oxide system investigated by in situ oxidation SIMS and ab initio calculations

Abstract

Hydrogen behavior in tantalum and tantalum oxide thin films was examined using the in situ oxidation secondary ion mass spectrometry (in situ oxidation SIMS) method previously developed by the authors. Oxidation of Ta films by the introduction of O2 into the sputter deposition chamber immediately after film growth was found to reduce the amount of H absorbed in the Ta films by 2.7 times for samples exposed to lab air at ambient temperature; the difference increased to 4.8 times for samples exposed to air at 300 °C. From these results, it is apparent that Ta absorbs H from H2 or through reaction with H2O in air and that an oxide film “cap” largely stymies H absorption. To investigate the redistribution of hydrogen during oxidation of Ta, sputtered Ta films were implanted with deuterium, and some were subsequently anodized. In situ oxidation SIMS analysis of Ta2O5/Ta bilayer films created by anodization of deuterium (D)-implanted Ta films revealed no deuterium in the upper Ta2O5 portion; however, the total amount of deuterium detected in the underlying Ta layer of the anodized samples was close to the total amount of deuterium measured in the Ta layer of a nonanodized, D-implanted Ta film. These results indicate that during anodization, D is concentrated in the residual metal region as it is excluded from the growing oxide film. Ab initio calculations of H interstitial defects in Ta and Ta2O5 revealed that the heat of formation, ΔH, for H interstitial defects in Ta is 1.31 eV lower than that of Ta2O5; this result is consistent with the observed H blocking property of oxide films and the observed redistribution of D from oxide to metal during anodization.

Towards a direct measurement of the 17O(p, γ)18F 65 keV resonance strength at LUNA

“…order to monitor the BIB, 300 C were collected on target made as Ta 17 2 O 5 targets but using Ultra Pure Water (UPW), with natural (0.04%) 17 O abundance. Tantalum is, indeed, a natural absorber of H and D [16] and the p+D (Q = 5493 keV) reaction produces a single γ-ray very close in energy to the 17 O(p, γ) 18 F 65 keV resonance γ-ray, see Fig. 3.…”

Advances in radiative capture studies at LUNA with a segmented BGO detector

“…res. = 65 keV resonance, a well-known problem of tantalum is its ability to store hydrogen and deuterium [42]. With the modest energy resolution of the BGO detector, the signature of a single γ-ray produced by the 2 H(p, γ) 3 He reaction (Q = 5493 keV) cannot be resolved from the signal of 17 O(p, γ) 18 F (Q = 5607 keV).…”

Initial study on thermal stability of cold spray tantalum coating irradiated with deuterium for fusion applications

“…Tantalum (Ta) is a widely used material in chemistry, medical applications, electronics, aerospace and nuclear industry [9] because of its high melting temperature, excellent room-temperature ductility [10] and outstanding corrosion resistance [5,11]. Ta, similar to titanium (Ti), exhibits exothermic hydrogen absorption which results in a much higher hydrogen isotopes (HIs) inventory compared to other refractory metals such as tungsten (W) and molybdenum (Mo) [12][13][14]. In addition, the low sputtering rate of Ta by HIs (see figure 1), as well as the high radiation damage resistance of Ta to neutrons and gamma radiation [15], makes it a promising candidate material for the HIs retaining first-wall interface of laboratory fusion devices such as WHAM.…”

“…However, it has been shown that Ta subjected to a high dose of HIs and subsequent thermal cycling may result in structural modifications due to a possible formation of various hydride states of Ta [20 -22]. Moreover, oxidation of Ta surface may reduce HIs absorption [13,23] affecting the desired functionality of the coatings as the retaining first-wall material of Plasma-Facing Components (PFCs). Thus, it is important to systematically investigate the evolution of surface and bulk morphology, chemical composition, mechanical properties and retention mechanisms in the cold spray coatings subjected to high hydrogen fluxes and thermal cycling at elevated temperatures matching the expectations for PFCs in fusion devices.…”