Pure ZrN Research Articles

One-step formation of ZrON thin film on surface of carbon fine particles for membrane electrode assembly

Zirconium nitride and oxynitride films were deposited on alumina or carbon particles by reactive sputtering using a magnetron sputtering apparatus with a Zr hollow cylindrical target and a vibrating equipment with heating capability. The vibrating equipment developed in this study was effective if the particles are spherical and highly monodisperse. Uniform film deposition was achieved over the entire surface of highly monodisperse spherical alumina particles using the vibrating equipment during deposition. Pure ZrN crystalline layers was deposited under Ar and N2 gas flows with heating on XC-72 carbon powder particles removed adsorbed oxygen. Energy dispersive x-ray spectroscopy mapping analysis for deposited XC-72 carbon particles showed ubiquitous film deposition on agglomerated particles regardless of vibration during sputtering. Uniform film deposition with vibrating equipment was achieved on the entire surface of CGB-10 particles with more spherical and monodisperse than XC-72 but precipitated crystalline phase depended on unintentional oxygen chemisorbed on the particles. Addition and increase in flow rate of oxygen to the sputtering gas resulted in the formation of desired crystalline phase, Zr2ON2, Zr7O8N4, and monoclinic ZrO2, precipitated in the film using CGB-10 particles with chemisorbed oxygen removed. Current density for oxygen reduction reaction measured for MEA made from CGB-10 particles with ZrON-based crystals deposited was larger than that for thin film deposited on a carbon plate substrate.

Simultaneous enhancement of hardness, lubrication and corrosion resistance of solid solution Zr-Y-N film

Transition-metal nitrides (TMNs) can be widely applied as protective coatings for precision parts, and improving their key performance characteristics is essential to make them more robust and durable in harsh environments. High-performance TMNs require establishing the structure-property relationship, and structural modulation is an effective procedure for optimizing their properties. Herein, high hard Zr-Y-N solid solution structure film with trace of solute Y atom fabricated by reactive magnetron sputtering and demonstrated excellent lubricating behavior under the condition of based oil, as well as superior corrosion resistance in a 3.5 wt% NaCl solution. It should be noted that the solid solution Zr-Y-N film is 40.1 % harder than pure ZrN film due to solid solution strengthening, resulting in a hardness of 29.0 GPa. During the sliding process of tribological behavior, the synergistic effect of in-situ formation Y2O3 and ZrO2 lubricating phase on the Zr-Y-N worn surface would significantly reduce the friction coefficient to 0.019. Additionally, based on the results obtained from the impedance spectrum and polarization curve, solute Y can enhance the corrosion resistance of ZrN by its compact solid solution structure, resulting in a corrosion current of S1 (1.71 E−05 A/cm2) that is much lower than that of ZrN (1.05 E−04 A/cm2), which is an important factor in optimizing the comprehensive performance of ZrN films. The novel strategy would be to open a window for more significantly improving the hardness of TMNs-based film by incorporating solute Y atoms, thereby further improving lubricating behavior and corrosion resistance.

Effect of hafnium contaminant present in zirconium targets on sputter deposited ZrN thin films

Zirconium nitride thin films deposited by reactive magnetron sputtering recurrently present small amounts of hafnium (~1 at.%) in their composition derived from an inherent impurity existing in Zr targets. Hf presence in ZrN coatings is neglected by most of the researchers despite its known potential to modify properties of thin films. In this work, pure ZrN (0.9 at.% Hf contaminant) and ZrHfN thin films with intentional hafnium addition of 1.8, 3.7 and 5.5 at.% were deposited by reactive magnetron sputtering and characterized by RBS, GAXRD, SEM, nanohardness and high temperature oxidation tests. Based on the results, it is suggested that inherent hafnium presence in zirconium targets contributes for the good hardness values and oxidation resistance at 773 K registered for ZrN thin films.

Structural, electronic and magnetic properties of small bimetallic zirconium–palladium clusters: Ab initio study

Structural, electronic and magnetic properties of small bimetallic zirconium–palladium clusters, ZrnPdm (n+m⩽5), have been investigated using density functional theory with considering generalized gradient approximation and PBE functional. We have determined the ground state conformations of the bimetallic zirconium–palladium clusters by substitution of Zr and Pd atoms in the optimized lowest energy structures of pure zirconium and palladium clusters. Results reveal that binding energies of the pure Zrn clusters are significantly higher than Pdn clusters with the same number of atoms. Also it is found that binding energy of the Zrn and Pdn clusters increase with growth of the number of consisting atoms in the clusters. Results indicate that, for both Zrn and Pdn clusters the binding energy of planar forms is lower than three-dimensional structures. We have also found that the binding energy of the Pdn clusters increase with substituting one or more Zr atoms in these clusters. We have also studied the HOMO–LUMO energy gap and magnetic moment of the pure and combined Zr and Pd clusters. The energy gap analysis of the pure and combined Pd and Zr clusters show that in generally the HOMO–LUMO gap of the bimetallic ZrnPdm clusters increase in comparison with their corresponding pure clusters with the same number of atoms. According to the spin polarization DFT calculations all of the ZrnPdm (n+m⩽5) have net magnetic moments as instance the Zr2, Pd2 and ZrPd clusters show a total magnetic moment value of 2μB. Some more discussions around charge population and density of states of considered clusters as well as their structural properties have been discussed in the context.

Synthesis of ZrN Nanopowder via Soft Urea Pathway

High pure ZrN nanopowder was synthesized from Z-U or ZO-U precusors by using ZrCl4 and ZrOCl2·8H2O as zirconium source, urea as solid N source. The preceramic precursors characterized by FT-IR were prepared via coordination between zirconium ions and urea molecules. Both precursors were further pyrolyzed at rela- tively low temperatures to yield ZrN. XRD and SEM techniques were used to examine the microstructures of the ce- ramic powders, while TG-DTA was used to study the pyrolysis process. It appears that the crystal water has strong ef- fect on the coordination chemistry of Zr ions, resulting in obvious differences in molecular structures of two precursors. Such structural differences have strong effects on purity and morphologies of the as-prepared ZrN nanopowder. Ap- parently, the Z-U precursor from ZrCl4 is more liable to acquire high pure ZrN nanopowder.

Sintering and characterization of (Pu,Zr)N

Nitride fuel, with the composition of (Pu0.4Zr0.6)N, is fabricated for studying the sinterability of nitride fuel as a function of oxygen concentration in the material. Oxygen concentration of up to 0.6wt% evidently enhances the densification of the material. Increasing the sintering temperature from 1923 to 1973K improves the sintered pellet densities by up to 3.8%TD. In addition, the measured thermophysical and electrical properties of (Pu0.4Zr0.6)N reveal that the values are close to those of PuN. Elevated oxygen concentration in the material decreases its thermal conductivity. Oxygen concentration of 0.34wt% in (Pu,Zr)N is a consequence of the fabrication process, considering the relatively pure ZrN (0.03wt% O) and PuN (0.08wt% O) powders initially fabricated.

Effect of N and Zr content on structure, electronic structure and properties of ZrBCN materials: An ab-initio study

Atomic structure, electronic structure and properties of ZrBCN materials were studied using ab-initio calculations. We focus on the effect of N and Zr content and compare our results with the characteristics of samples prepared by reactive magnetron sputtering. We find that the materials are characterized by a mixture of covalent and metallic bonding. The metallic-to-covalent ratio is primarily controlled by the N content, and well correlated with measured electrical resistivity. ZrN bonds have the highest preference to form out of all bonds in the ZrBCN system. Hard nanostructure forms at high Zr and low N content, containing (i) pure ZrN and (ii) (theoretically predicted and experimentally observed) solid solution close to ZrB0.50N0.50. The results allow one to tailor ZrBCN compositions which can combine different functional properties, such as high thermal stability, high hardness and electrical conductivity.

Densification and mechanical properties of hot-pressed ZrN ceramics doped with Zr or Ti

Abstract The densification of hot-pressed ZrN ceramics doped with Zr or Ti have been investigated at 1500–1700 °C. It is shown that either Zr or Ti additive can facilitate the densification process. ZrN with 20 mol% Zr or Ti (named ZNZ and ZNT) sintered at 1700 °C can achieve above 98% relative densities whereas densification temperature up to 2000 °C is necessary for pure ZrN. The densification improvements are attributed to solid solution of Zr or Ti into ZrN to form non-stoichiometric ZrN1−x or (Zr, Ti)N1−x. The microstructures and mechanical properties of ZNZ and ZNT samples have been examined. Large grain size and flat fracture surface existed in ZNT sample sintered at 1700 °C, which lead to poor toughness as low as 2.3 MPa m1/2. On the contrary, the fracture toughness of ZNZ sample sintered at 1700 °C was up to 5.9 MPa m1/2, attributed to fine and uniform grain size distribution.

Effects of the Ta content on the microstructure and electrical property of reactively sputtered Ta xZr 1−xN thin films

The Ta xZr 1−xN films were prepared by reactive magnetron sputtering and the concentration of zirconium and tantalum was regulated by controlling the power to the sputtering guns. The effects of the Ta content on the microstructure, composition and electrical properties of Ta xZr 1−xN films were investigated by x-ray diffraction, field-emission electron probe micro-analyzer, atomic force microscopy, x-ray photoelectron spectroscopy, four point probe and Hall-effect measurements. Results indicated that the Ta xZr 1−xN films with different Ta contents were crystallized in NaCl-type structure. However, the lattice constant of Ta xZr 1−xN films decreased with the increase of the Ta content due to the smaller ionic radius of Ta 5+ comparing with that of Zr 4+. The decreasing lattice constant of Ta xZr 1−xN films with the Ta content evidenced the successful substitution of Zr with Ta. The electrical resistivity of Ta xZr 1−xN films showed a minimum value of 78 μΩ cm at Ta content of 3.5 at.% and then increased with the increase of Ta content. Hall measurements indicated that the electrical conduction of films was essentially due to electrons (n-type). And the increase of carrier density and mobility at a Ta content of 3.5 at.%, caused by the extra d valence electron of Ta and the less electron scattering of grain boundaries, was responsible for the further decreasing of resistivity from pure ZrN x films.

Reactive magnetron cosputtering of hard and conductive ternary nitride thin films: Ti–Zr–N and Ti–Ta–N

Ternary transition metal nitride thin films, with thickness up to 300 nm, were deposited by dc reactive magnetron cosputtering in Ar–N2 plasma discharges at 300 °C on Si substrates. Two systems were comparatively studied, Ti–Zr–N and Ti–Ta–N, as representative of isostructural and nonisostructural prototypes, with the aim of characterizing their structural, mechanical, and electrical properties. While phase-separated TiN–ZrN and TiN–TaN are the bulk equilibrium states, Ti1−xZrxN and Ti1−yTayN solid solutions with the Na–Cl (B1-type) structure could be stabilized in a large compositional range (up to x=1 and y=0.75, respectively). Substituting Ti atoms by either Zr or Ta atoms led to significant changes in film texture, microstructure, grain size, and surface morphology, as evidenced by x-ray diffraction, x-ray reflectivity, and scanning electron and atomic force microscopies. The ternary Ti1−yTayN films exhibited superior mechanical properties to Ti1−xZrxN films as well as binary compounds, with hardness as high as 42 GPa for y=0.69. All films were metallic, the lowest electrical resistivity ρ∼65 μΩ cm being obtained for pure ZrN, while for Ti1−yTayN films a minimum was observed at y∼0.3. The evolution of the different film properties is discussed based on microstructrural investigations.

Superconductivity in (Zr1−xTax)Nz (0.1 ≦ x ≦ 0.9)

Dc magnetic susceptibility measurements between 1.8 and 15K have been carried out on nine samples in (Zr1−xTax)Nz (x=0.1–0.9) to study the superconducting phase transitions in this N-containing system. It is found that the superconducting transition temperature Tc increases with Ta concentration up to x=0.6, then decreases. A Tc,onset peak value of 13.4K occurs in the sample with nominal composition (Zr0.4Ta0.6)N0.39. The improvement, with respect to pure ZrN (Tc=10.7K), on the superconducting critical temperature Tc is about 25% by optimal doping with Ta.

Synthesis and formation mechanism of cubic ZrN nanopowders by mechanochemical reaction of ZrCl 4 and Li 3N

A mixture of tetrachloride (ZrCl 4) and lithium nitride (Li 3N) powders was milled in a high-energy ball mill under Ar ambient. Mechanochemical reaction of ZrCl 4 and Li 3N occurred during the milling process and produced LiCl and ZrN with rocksalt structure. It was found by in situ measurement of surface temperature of the vial in milling process that the reaction began as milling time reached about 7 min and finished in a few of seconds, accompanied by release of a great deal of heat. This result implies that the reaction is a self-propagating one, and that ZrN powders can be fabricated by milling in very short time. By chemical separation of the products, high pure ZrN powders with nanometer scale were obtained. The present work provides a technique for synthesis of high pure ZrN nanopowders with short time, large mass and low cost. The thermodynamic and kinetic mechanisms of formation of the ZrN are discussed in detail.

Thermophysical characterization of ZrN and (Zr,Pu)N

Nitride compounds are currently considered as possible fuels for advanced nuclear reactors. Among the relevant properties to be investigated, thermophysical quantities such as heat capacity and thermal diffusivity/conductivity are key to ensure safe operation of the fuel in the reactor. Both physical and chemical phenomenological experimental activities are included in this effort. The experimental procedures were optimized to limit oxidation of materials in presence of even small quantities of oxygen and moisture, especially during the measurements at high temperature. Heat capacity and thermal diffusivity/conductivity were measured for ZrN and (Zr,Pu)N compounds. A consistent set of results was obtained from low- and high-temperature C p measurements for both materials. The excess C p of solution was estimated. Increasing trends with temperature were observed for the thermal diffusivity and conductivity of both materials in the temperature range considered, confirming the metallic behavior of this class of materials. The presence of Pu causes an almost constant decrease of the thermal conductivity compared to the pure ZrN matrix.

Effect of germanium addition on the properties of reactively sputtered ZrN films

For the first time, Zr–Ge–N films were deposited on silicon and steel substrates by sputtering a Zr–Ge composite target in reactive Ar– N2 mixture. The films were characterised by electron probe microanalysis, X-ray diffraction, micro-Raman spectroscopy and depth-sensing indentation. The effects of the Ge content and substrate bias voltage on the films’ structure, internal stress, hardness and oxidation resistance were investigated. Substrate bias strongly influenced the chemical composition of the films being observed by means of a steep decrease in the Ge content for negative bias voltages higher than � 80 V. In these cases, a significant hardness improvement was registered. For � 100 V biased films, in the Ge concentrations range tested in this study, only ZrN grains were evidenced by X-ray diffraction. The film compressive stresses increased with the germanium concentration. An unexpected effect of the Ge content on the films’ hardness was observed. In spite of the increase in the compressive stresses of the films with increasing Ge content, the hardness monotonously dropped from 38 GPa for pure ZrN down to 21.5 GPa for 4.6 at.% Ge. Addition of Ge into ZrN-based coatings induced an improvement of the oxidation resistance and it favoured the tetragonal form of zirconia in oxidised Zr–Ge–N coatings. D 2005 Elsevier B.V. All rights reserved.

Influence of sputtering conditions on microstructure and mechanical properties of Zr–Si–N films prepared by radio-frequency-reactive sputtering

ZrN and ZrSiN films were prepared in an rf-sputtering apparatus which has a pair of targets facing each other (referred to as the facing target-type rf sputtering). In order to investigate the influence of substrate temperature on the structure and mechanical properties of Zr–Si–N films, the substrate temperature during the deposition was changed from 373 K to 673 K. Only one phase with a cubic B1 NaCl structure, typical for ZrN, can be clearly identified in all Zr–Si–N films in this study. Increasing substrate temperature can improve crystalline quality in all Zr–Si–N films in this study. Grain sizes of all Zr–Si–N thin films, despite the Si content, increase linearly with increasing substrate temperature. However, the grain growth speed with increasing substrate temperature in a pure ZrN thin film is much faster than that in Zr–Si–N thin films, because Si atom occupation of interstitial sites tends to lock diffusion paths and thus stabilize the structure. The hardness of Zr–Si–N films with low Si content, such as 3 at. % Si, decreases after the substrate temperature increases above 600 K because the internal stress drops. In the high Si content Zr–Si–N films, the hardness improved by increasing substrate temperature due to the increased strength in the grain boundaries.

Factors Affecting the Formation Rate of ZrN by the Carbothermal Nitridation Method

Factors affecting the formation rate of zirconium nitride by the carbothermal nitridation method were studied. Use of finer particle-sized zirconia powder showed the higher formation rate of zirconium nitride. A single-phase of zirconium nitride with cubic symmetry was obtained by firing graphite and zirconia (0.35μm) mixed compact with a molar ratio C/ZrO2=4 at 1400°C for 12h in flowing nitrogen gas. The formation process of zirconium nitride was in competition with partial nitridation of zirconia, occurring in the non-transformable tetragonal zirconia phase. It was not possible to obtain stoichiometric and pure ZrN by carbothermal nitridation method. The presence of ZrN seed crystals restrained the formation of zirconium nitride.

Thermodynamic Analysis and Synthesis of Zirconium Nitride by Thermal Nitridation of Sol-Gel Zirconium Oxide

Thermodynamic calculations were performed using the SOLGASMIX-PV computer program to predict the possibility of converting zirconia to zirconium nitride by thermal nitridation in the presence of methane and ammonia. Conversion diagrams were constructed for the ZrO[sub 2]-NH[sub 3]-CH[sub 4] system over a range of reaction conditions such as temperature, total system pressure, and reagent concentrations. Formation of pure ZrN phase was predicted in the range 1800-2000 K and total system pressures of 0.1-1.0 atm. It is shown experimentally, in the present work, that zirconium nitride can indeed by synthesized by thermal nitridation of zirconia using ammonia and methane at a reaction temperature much lower than that predicted by thermodynamic considerations alone. In addition, no deposition of carbon was observed at the lower temperatures employed during synthesis. Low pressure together with the introduction of excess hydrogen favors the conversion of zirconia to zirconium nitride as well as decrease the reaction temperature for conversion to take place. 28 refs., 13 figs., 2 tabs.