Synergizing in-grown Ni3N/Ni heterostructured core and ultrathin Ni3N surface shell enables self-adaptive surface reconfiguration and efficient oxygen evolution reaction

Gaseous nitriding of Ni-4 wt pct Ti alloy plates led to the development of double expanded austenite (γ
 N1 and γ
 N2) at the surface of the nitride plates. Grazing-incidence X-ray diffraction analysis demonstrated that the component γ
 N1 is located close to the surface and the component γ
 N2 is located at a certain depth below the specimen surface, in correspondence with a layered character of the nitrided zone beneath the surface as revealed by optical microscopy. Electron probe microanalysis, atom probe tomography, and Laue microdiffraction analysis did not reveal a significant difference in nitrogen content of the γ
 N1 and γ
 N2 sublayers. By X-ray diffraction stress analysis it was shown that the only significant differences of the two expanded austenite layers is a pronounced difference in compressive stress parallel to the surface: the γ
 N1 layer is subjected to a huge compressive stress, as large as a few GPa, whereas a relatively modest stress prevails in the γ
 N2 layer.

The Nature and Origin of “Double Expanded Austenite” in Ni-Based Ni-Ti Alloys Developing Upon Low Temperature Gaseous Nitriding

В последние несколько лет водород стал основным источником энергии; однако его хранение и транспортировка на дальние расстояния остаются ключевыми проблемами для его широкого использования. Аммиак рассматривается как потенциальная среда для переноса и хранения водорода. Так, аммиак обладает большей энергоемкостью, чем водород, его легче транспортировать и он позволяет использовать альтернативное топливо, не содержащее CO2, которое можно использовать в различных системах производства электроэнергии. В этом отношении технология твердооксидных топливных элементов (ТОТЭ) считается одной их перспективных с точки зрения прямого преобразования аммиака в электричество с высокой эффективностью. Поскольку ТОТЭ работают при высоких температурах (>600°С), они не требуют дополнительной энергии для внешнего риформинга и крекинга аммиака. В этой статье мы критически рассматриваем основные достижения, прогресс и перспективы ТОТЭ, работающих на аммиачном топливе.

Progress and prospects in direct ammonia solid oxide fuel cells: A review

Ni3N was prepared by gaseous nitriding of nickel substrates using gas mixtures of high nitrogen activities, composed of NH3 and H2 at 1 atm and at temperatures between 175 °C and 550 °C. At least above 300 °C closed Ni3N layers developed, which possess distinct compressive macrostrain parallel to the surface. The observed hkl-anisotropy of the macrostrain could be ascribed to the elastic anisotropy as indicated by the single-crystal elastic constants of Ni3N obtained from firstprinciples calculations performed in this work. The macrostress originates from the thermal misfit between layer and substrate, developing upon cooling. The extent of macrostress is reduced by partial misfit accommodation by plastic deformation as well as by porosity.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291412000404

Ni3N compound layers produced by gaseous nitriding of nickel substrates; layer growth, macrostresses and intrinsic elastic anisotropy

The N uptake of thin Ni foils was monitored by use of nitriding experiments performed in NH3-H2 gas atmospheres as function of the atmosphere’s composition between 673 K and 873 K (400 °C and 600 °C). With increasing nitriding potential $$ r_{\text{N}} = {{p_{{{\text{NH}}_{3} }} } \mathord{\left/ {\vphantom {{p_{{{\text{NH}}_{3} }} } {p_{{{\text{H}}_{2} }}^{3/2} }}} \right. \kern-0pt} {p_{{{\text{H}}_{2} }}^{3/2} }} $$
 (with $$ p_{{{\text{NH}}_{3} }} $$
 and $$ p_{{{\text{H}}_{2} }}^{{}} $$
 being the partial pressures of the ammonia and hydrogen in the nitriding atmosphere at the Ni specimen’s surface) first an increasing uptake of N by the terminal Ni[N] solid solution was observed up to about 1 at. pct N. Upon surpassing a threshold nitriding potential, the Ni3N compound was formed. A thermodynamic interpretation of the observed data is only possible by taking into account the (small) degree of decomposition of the NH3 at the surface of the specimens, to arrive at the effective values of r
 N genuinely acting at the surface of the specimen. The data obtained were used to determine model descriptions for (i) the Gibbs energy of dissolution of N into Ni[N] (at infinite dilution), which was modeled as an ideal interstitial solid solution, and (ii) the Gibbs energy of formation of Ni3N (in equilibrium with Ni[N]). The thermodynamic model descriptions of Ni[N] and Ni3N, associated with these Gibbs energies, were used to calculate the Ni-rich part of the phase diagram Ni-N. A comparison of the values of the Gibbs energy of dissolution of N in various 3d-metal based terminal solid solutions reveals a considerable decrease of the stability of such solutions with increasing atomic number.

/pdf/experimental-investigation-and-thermodynamic-modeling-of-the-211vwofepd.pdf

Experimental Investigation and Thermodynamic Modeling of the Ni-Rich Part of the Ni-N Phase Diagram

Gaseous nitriding of cobalt and nickel in NH3/H2 atmospheres at 400-550°C can lead to formation of e-Fe3N1+x-type Co3N1+x/Ni3N compound layers, as shown by X-ray dif- fractometry and optical microscopy. X-ray stress measurements reveal compressive stresses in Ni3N compound layers. GDOES measurements demonstrate that upon nitriding also sig- nificant amounts of N (in the order of 1-5 at.%) are incorporated in the substrate underneath the compound layer (if present), thereby building Co-N and Ni-N solid solutions. For the fcc- Ni-N solid solution penetration-depth dependent X-ray stress measurements show that the uptake of N is accompanied by an expansion of the cubic stress-free lattice parameter a0.

X-ray diffraction investigations on gas nitrided nickel and cobalt

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Ni3N compound layers produced by gaseous nitriding of nickel substrates; layer growth, macrostresses and intrinsic elastic anisotropy

Ni3N compound layers produced by gaseous nitriding of nickel substrates; layer growth, macrostresses and intrinsic elastic anisotropy

X-ray diffraction investigations on gas nitrided nickel and cobalt