No abstract

Zirconium nitride (ZrN) is a transition metal nitride of great interest due to its excellent physical and chemical properties. This study aims to synthesize ZrN fine powders by a facile and low‐cost urea route that avoids the use of any solvent. ZrCl4 and urea mixtures were heat‐treated at up to 1600˚C in nitrogen gas. The products were characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and thermogravimetric analysis. The effects of different processing parameters such as metal to urea molar ratio, heat treatment temperature, and dwelling time on the product phase and stoichiometry were studied to understand the synthesis method. In addition, synthesized ZrN powder was consolidated into near fully dense single‐phase bulk ceramic with a homemade flash sintering setup. A constant DC electrical field of ∼80 V/cm and pressure of ∼14 MPa at room temperature triggered flash sintering without pre‐heating, and the entire process finished in 200 s. The composition, microstructure, density, hardness, and oxidation properties of the sintered pellet were also characterized.

PrNi0.5Co0.5O3-δ (PNC) cathode material demonstrates total electrical conductivity on the order of ~300 S/cm at 400-600oC in air, and the conductivity shows a slight increase as temperature increases with an activation energy (from ln(σT) vs 1/T plot) of 10.9 kJ/mol. The introduction of water vapor (H2O) leads to a small (~0.16%) increase in total resistivity, which is reversible upon water removal and explained, tentatively, by the defect reaction of H2O + 2Oo x + 2h• = 2(OH)O • + 0.5O2. The thermal expansion coefficient (TEC) of PNC is measured to be 17.6×10-6/K by dilatometry and 18.43×10-6/K by in situ XRD up to 800oC. On the other hand, despite bulk chemical stability for both PNC and BZCYYb4411 powders against low percentage H2O and CO2, a PNC cathode symmetrical cell over proton conducting BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolyte shows degradation (or increase) in interfacial resistance upon introduction of 3% moisture or 5% CO2 into simulated air at temperature in the range of 650 to 450oC. In comparison, oxygen ion conducting symmetrical cells with PNC cathode and Ce0.9Gd0.1O2-δ (GDC) electrolyte show no change upon H2O and CO2 introduction. The observed sensitivity of the PNC cathode proton conducting symmetrical cell to H2O and CO2 is attributed to the preferred adsorption of H2O and CO2 molecules onto the BZCYYb4411 proton conducting electrolyte surface than on the PNC cathode, and such an explanation is supported by temperature programmed desorption (TPD) measurements for H2O and CO2 on both PNC and BZCYYb4411 powders.