Formation Of Zirconium Nitride Research Articles

Oxidation of Zircaloy-4 in steam-nitrogen mixtures at 600–1200 °C

High-temperature oxidation of zirconium alloys in steam-nitrogen atmospheres may be relevant during various nuclear accident scenarios. Therefore, isothermal oxidation tests with Zircaloy-4 in steam-nitrogen mixtures have been performed at 600, 800, 1000, and 1200 °C using thermogravimetry. The gas compositions were varied between 0 and 100 vol% nitrogen including 0.1 and 90 vol%. The strong effect of nitrogen on the oxidation kinetics of zirconium alloys was confirmed in these tests in mixed steam-nitrogen atmospheres. Even very low concentrations of nitrogen (starting from less than 1 vol%) strongly increase reaction kinetics. Nitrogen reduces transition time from protective to non-protective oxide scale (breakaway). The formation of zirconium nitride, ZrN, and its re-oxidation is the main reason for the highly porous oxide scales after transition. The results of this study have shown the safety relevant role of nitrogen during severe accidents and, more generally, suggest the need of using well controlled gas atmospheres for experiments on oxidation of zirconium alloys.

Air oxidation of Zircaloy-4, M5® and ZIRLO™ cladding alloys at high temperatures

The paper presents the results of isothermal and transient oxidation experiments of the advanced cladding alloys M5® and ZIRLO™ in comparison to Zircaloy-4 in air at temperatures from 973 to 1853 K. Generally, oxidation in air leads to a strong degradation of the cladding material. The main mechanism of this process is the formation of zirconium nitride and its re-oxidation. From the point of view of safety, the barrier effect of the fuel cladding is lost much earlier than during accident transients with a steam atmosphere only. Comparison of the three alloys investigated reveals a qualitatively similar, but quantitatively varying oxidation behavior in air. The mainly parabolic oxidation kinetics, where applicable, is comparable for the three alloys. Strong differences of up to 500% in oxidation rates were observed after transition to linear kinetics at temperatures below 1300 K. The paper presents kinetic rate constants as well as critical times and oxide scale thicknesses at the point of transition from parabolic to linear kinetics.

In Situ Synthesis of ZrN(ZrO2)/Si2N2O Composite Materials from Zircon by Carbothermal Reduction-Nitridation Process

ZrN(ZrO2)/Si2N2O composite materials were synthesized by in-situ carbothermal reduction-nitridation process, with zircon and carbon black as raw materials. The influences of heating temperature and carbon content on synthesis process were investigated, the phase composition and microstructure of the synthesized materials were characterized by X-ray diffraction and scanning electronic microscope. It was found that the decomposition of ZrSiO4 as well as the formation of ZrN and Si2N2O could be promoted by increasing heating temperature and carbon content. ZrN(ZrO2)/Si2N2O composite materials could be synthesized at 1480°C for 6h by heating the sample with ZrSiO4/C mass ratio of 100/40. The ZrN and Si2N2O in the synthesized materials existed in particle shape with an average grain size of about 1–2μm. Introduction Recently, an important research trend of refractories is to develop non-oxides materials such as nitrides, carbides, borides and silicides as well as their composites [1,2]. Among them, zirconium nitride (ZrN) and Silicon oxynitride (Si2N2O) display many outstanding properties, such as high melting points, hardness and strength, excellent corrosion and oxidation resistance [3-5]. zirconium oxide (ZrO2) also exhibits high toughness and strength, excellent corrosion and thermal shock resistance[6]. It is believed that combining ZrN, ZrO2 and Si2N2O into composite materials might yield excellent high temperature combination properties. In the present work, ZrN(ZrO2)/Si2N2O composite materials were synthesized by in-situ carbothermal reduction-nitridation process, with zircon and carbon black as raw materials. The influences of heating temperature and carbon content on synthesis process of the materials were investigated. The carbothermal reduction-nitridation reaction process was also discussed.

Evolution of the phase-structure state during annealing of Fe-ZrN films grown by magnetron sputtering

The evolution of the phase-structure state of Fe-ZrN films grown by RF magnetron sputtering and annealed at T = 200–650°C has been studied by transmission electron microscopy, high-resolution electron microscopy, and X-ray diffraction analysis. It has been found that the initial state of the film contains 1- to 5-nm crystallites of α-Fe-based solid solution supersaturated with nitrogen. The number of such crystallites increases, the concentration of nitrogen in them decreases and 2- to 10-nm nanocrystallites of ZrN and Fe2N nitride phases appear after annealing. The formation of zirconium nitride at the first stage (200–500°C) is associated with a decrease in the degree of supersaturation of the α-Fe lattice with nitrogen. At a higher annealing temperature (650°C), a decrease in the nitrogen concentration in the lattices of both the bcc Fe and zirconium nitride phase leads to the formation of iron nitride crystallites.

Prototypical experiments relating to air oxidation of Zircaloy-4 at high temperatures

The mechanism of the reaction between Zircaloy-4 and air at temperatures from 800 to 1500 °C was studied. Air attack under prototypical conditions with air ingress during a hypothetic severe nuclear reactor accident was investigated. Oxidation in air and in air and nitrogen-containing atmospheres leads to a major degradation of the cladding material. The main mechanism is the formation of zirconium nitride and its re-oxidation. Pre-oxidation in steam prevents air attack as long as the oxide scale is intact. Under steam/oxygen starvation conditions, the oxide scale is reduced and significant external nitride formation takes place. When modeling air ingress in severe accident computer codes, parabolic correlations for oxidation in air may be applied only for high temperatures (>1400 °C) and for pre-oxidized cladding (⩾1100 °C). Under all other conditions, faster, rather linear reaction kinetics should be applied.

Interaction of Failed Fuel Rods Under Air Ingress Conditions

In the late phase of a severe reactor accident, the molten corium interacts with the vessel wall, and it can lead to the failure of the lower head. Through the failed bottom wall, part of the corium can flow into the cavity, and air can enter the primary circuit. The residual fuel in the core periphery will be further oxidized in air atmosphere. The degradation process will accelerate, and new chemical species will be formed, which can have an impact on the release of radioactive materials.Two experiments were carried out with electrically heated nine-rod pressurized water reactor-type bundles in the CODEX (COre Degradation EXperiment) facility to provide experimental data on the behavior of real fuel bundles under air oxidation conditions. The main objective of the tests was the investigation of oxidation phenomena, and some other important aspects (e.g., enhanced fission product release) were not addressed.The CODEX air ingress tests indicated the acceleration of oxidation phenomena and core degradation processes during the late phase of the vessel melt through accident, when air can have access to the residual fuel bundles in the reactor core. The degradation process was accompanied with zirconium-nitride formation and release of uranium-rich aerosols.

Nitriding of Zirconia by Irradiation with NdrYAG Laser Beam

ABSTRACTThe surface of partially stabilized zirconia ceramics was irradiated by a Nd:YAG laser in various atmospheres. Zirconia strongly absorbed YAG's laser beam and changed its chemistry and microstructure. The change of color of zirconia into gold was due to the formation of zirconium nitride (ZrN) observed on the irradiated surface in air, nitrogen or ammonia, which was confirmed by X-ray diffraction and secondary ion mass spectroscopy. The observed ZrN phase was 10-20 um in thickness at the irradiated area by the direct beam. The adhesion between formed ZrN and YSZ substrate was very weak.

Surface interactions of fluorozirconate glass with low energy implanted Ar, N and O ions

Abstract A fluorozirconate glass was implanted with 15keV Ar, N and O ions. The implanted samples were characterized with optical spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and water corrosion tests. The surface of Ar-ion implanted glass was depleted in fluorine and enriched with metallic zirconium precipitate. It was electrically conductive and susceptible to water corrosion. The N-ion implantation induced metallic zirconium and zirconium nitride formation as well as F depletion. The N-ion implanted surface was also conductive but strong against water corrosion. The oxyfluoride surface layer formed by O-ion implantation showed little influence on optical and electrical properties of the glass, and was highly durable against water corrosion. The significant dependence of the surface properties on implanted species is discussed with consideration of both physical andchemical features of incident ions.

A thermodynamic analysis of the formation of zirconium nitride from zirconium tetrachloride

On the basis of a thermodynamic calculation of the heterogeneous system zirconium-nitrogen-hydrogen-chlorine the feasibility is demonstrated of obtaining zirconium nitride in the condensed state, with a virtually complete transformation of the metal into the nitride and a comparatively low expenditure of energy (about 80,000 kJ/kg), at temperatures of 2000–2400°K, a pressure of 1 bar, and a 50-fold dilution of the stoichiometric composition to a Zr∶N∶Cl∶H ratio of 1∶50∶4∶200. Use of ammonia instead of nitrogen at the same ratio of the elements increases the amount of energy expended to 106,000 kJ/kg.

Formation of Zirconium Nitride by Means of Nitrogen Plasma Jet

Formation of Zirconium Nitride by Means of Nitrogen Plasma Jet