Zr Powders Research Articles

粉体押出成形によるＭｇ‐Ｚｒ合金の創製と機械的特性

In order to improve the mechanical properties of functional Mg alloys, the forming process was investigated using Mg powder mixed with Zr powder. Fine and coarse Mg and Zr powders were used and Zr content was varied from 1 mass% to 20 mass%. Milling time was 7.2 ks and the mixed powders were pressed at a temperature of 573 K and then extruded at an extrusion ratio of 30 at the same temperature. The mechanical properties of the hot-extruded alloys were examined and the effects of powder size and Zr content were discussed. In the hot-extruded Mg-Zr alloys using fine Mg and Zr powders, Zr particles were dispersed uniformly within its microstructure. It was found that the mechanical properties such as Vickers hardness, Young's modulus, bending strength and internal friction increased significantly with increasing Zr content, compared with the hot-extruded Mg material and the hot-extruded Mg-Zr alloys using coarse Mg and Zr powders. Furthermore, such mechanical properties of the hot-extruded Mg-Zr alloys using fine Mg and Zr powders were improved considerably compared with AZ31 wrought alloy, AZ91 casting alloy and the damping casting alloys such as MCM and K1A. Therefore, it was confirmed that the hot-extruded Mg-Zr alloys fabricated in this study has a potential as a structural and functional Mg alloy.

Study on the thermal degradation of CeO2-ZrO2 solid solution by XAFS and XRD

A homogeneous CeO2-ZrO2 solid solution has an ordered cation arrangement and exhibits the highest oxygen storage/release capacity (OSC) among several types of CeO2-ZrO2 with the same composition (Ce/Zr = 1). The crystal structure of this CeO2-ZrO2 solid solution is usually termed the “κ-CeZrO4 phase”. Its OSC performance degrades upon high-temperature treatment under an oxidative atmosphere. Using Ce K- and Zr K-edges XAFS and powder XRD, this research investigated the structural change along with the thermal degradation of κ-CeZrO4. The fresh sample was aged at 973 K, 1273 K and 1473 K under an oxidative atmosphere. Their OSC performances were characterized at 773 K by a thermo-gravimetric method. The OSC performance deteriorated in the order: the fresh sample ≈ 973 K > 1273 K > 1473 K-aged samples. We also found that, if the temperature went beyond 1273K, the Ce/Zr ordered arrangement would collapse, and the local structure around Ce and Zr ions would also be changed remarkably. These results indicated that the OSC was strongly dependent on the atomic structure.

Radiographic Characterization of Thermal Spray Jets Produced by Electrothermal Explosion of Ceramic Powders

Thermal spray jets composed of Zr–B–O molten particles produced by the electrothermal explosion of a mixed powder of Zr and B2O3 were quantitatively characterized of their velocity, volumetric mass density, and mass velocity by flash radiography, to investigate a unique characteristic of a coating formed by using such jets, i.e., the mixing of a substrate material with a coating. Yttria-stabilized zirconia balls were used as tracers of jet flow. Mass velocity, i.e., mass flow rate per unit cross section of the flow, in a cylindrical space in front of the virtual position of a substrate was calculated using the velocity of the tracers and the volumetric mass density of the jet. The maximum mass velocity in the present spraying was two orders of magnitude larger than that in conventional plasma spraying. Thus, the very high mass velocity probably contributes to the appearance of the unique characteristic.

Preparation and characterization of composite membranes composed of zirconium tricarboxybutylphosphonate and polybenzimidazole for intermediate temperature operation

Zirconium tricarboxybutylphosphonate, Zr(O 3PC(CH 2) 3(COOH) 3) 2, was synthesized by slowly decomposing zirconium fluoro-complexes in the presence of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) to prepare inorganic/organic composite membranes based on polybenzimidazole (PBI). Composite membranes composed of zirconium tricarboxybutylphosphonate (Zr(PBTC)) particles embedded in PBI were formed by evaporating the solvent from a suspension of Zr(PBTC) particles in a PBI solution. Composite membranes with 50 wt.% Zr(PBTC) exhibited uniform distribution of the particles throughout the thickness, as ascertained by scanning electron microscopy. The conductivities measured for compacted Zr(PBTC) powder and PBI-based membranes with 50 wt.% Zr(PBTC) were 6.74 × 10 −2 and 3.82 × 10 −3 S cm −1, respectively, at 200 °C for P H 2O / P s=1. Functionalization of the PBI with phosphoric acid groups obtained by treatment with phosphoric acid and with sulfonic acid groups obtained by post-sulfonation thermal treatment with sulfuric acid improved the proton conductivity of 50 wt.% Zr(PBTC) membranes to 5.24 × 10 −3 and 8.14 × 10 −3 S cm −1 under the same measurement conditions. Zr(PBTC)/PBI membranes thus have great potential as proton exchange membrane fuel cells (PEMFCs).

Experimental technique for studying high-temperature phases in reactive molten metal based systems

Containerless, microgravity experiments for studying equilibria in molten metal–gas systems have been designed and conducted onboard of a NASA KC-135 aircraft flying parabolic trajectories. An experimental apparatus enabling one to acoustically levitate, laser heat, and splat quench 1–3 mm metal and ceramic samples has been developed and equipped with computer-based controller and optical diagnostics. Normal-gravity testing determined the levitator operation parameters providing stable and adjustable sample positioning. A methodology for optimizing the levitator performance using direct observation of levitated samples was developed and found to be more useful than traditional pressure mapping of the acoustic field. In microgravity experiments, spherical specimens prepared of pressed, premixed powders of ZrO2, ZrN, and Zr, were acoustically levitated inside an argon-filled chamber at one atmosphere and heated by a CO2 laser up to 2800 K. Using a uniaxial acoustic levitator in microgravity, the location of the laser-heated samples could be maintained for about 1 s, so that local sample melting was achieved. Oscillations of the levitating samples in horizontal direction became pronounced in microgravity. These oscillations increased during the sample heating and eventually resulted in moving the sample out of the stable position and away from the laser beam.

Consolidation behavior of L12 phase (Al + 12.5 at.% Cu)3Zr powder with nanocrystalline structure during CIP and subsequent sintering

The mechanically alloyed (Al + 12.5 at.% Cu) 3 Zr powders were consolidated by cold isostatic pressing (CIP) and subsequent sintering. Effects of CIP pressure and sintering temperature on the stability of metastable L1 2 phase and nanocrystalline structure were investigated. Before sintering, the powders were CIPed at 138, 207, 276, and 414 MPa. The relative densities of the CIP compacts were not greatly affected by the CIP pressure. However, the L1 2 phase of the specimen CIPed at pressures greater than 276 MPa was partially transformed into D0 23 . The optimum consolidation conditions for maintaining L1 2 phase and nanocrystalline microstructure were determined to be CIP at 207 MPa and sintering at 800 °C for 1 h for which the grain size was 34.2 nm and the relative density was 93.8%. Full density specimens could be prepared by sintering above 900 °C, however, these specimens consisted of L1 2 and D0 23 phases. The grain sizes of all the specimens were confirmed by TEM and XRD, and were found to be less than 40 nm. This is one of the smallest grain sizes ever reported in trialuminide intermetallic compounds.

粉体押出成形によるマグネシウム合金の機械的特性の改善

In order to improve the strength of the functional MCM (Mg-Cu-Mn) casting alloy that has been developed as one of damping Mg alloys, the powder extrusion process was applied and the effect of Zr addition was studied using MCM alloy powder mixed with Zr powder. For the powder hot-extruded alloys produced, microstructure characterization was performed using optical microscope and the mechanical properties such as Vickers hardness and bending strength were evaluated. Young's modulus and internal friction were also measured with the free resonance frequency technique. It was found that grain size increased with increasing extrusion temperature and grain size refinement was recognized to occur around Zr particles dispersed in the matrix. Vickers hardness was nearly similar to, or slightly lower than, that of the conventional casting alloys such as AZ91 and AM60, while bending strength and Young's modulus were improved remarkably compared with those casting alloys. The internal friction was the same as that of the conventional damping alloys. Based on the above experimental results, it was concluded that the high performance of the functional MCM alloy could be achieved with the powder extrusion process.

Proton conductivity of zirconium tricarboxybutylphosphonate/PBI nanocomposite membrane

The preparation process and proton transport properties of zirconium tricarboxybutylphosphonate Zr(O3PC(CH2)3(COOH)3)2 (Zr(PBTC))/polybenzimidazole (PBI) composite membranes have been investigated with a view to developing a novel electrolyte for direct methanol fuel cells. A compacted Zr(PBTC) powder sample and a Zr(PBTC)/PBI composite membrane with 50 wt.% Zr(PBTC) content show conductivities of 6.74 × 10–2 S cm–1 and 3.82 × 10–3 S cm–1 at 200 °C under a fully humid condition, respectively. Post-sulfonation thermal treatment, which has a great effect on the ligand structure of PBI, gives a marked increase in the conductivity of the membrane by a factor of 2 in the same condition. This effect is mainly attributed to the proton transport via sulfonic acid groups bonded to the PBI unit.

Amorphization of Ni60Nb20Zr20 by mechanical alloying

Abstract Elemental Ni, Nb and Zr powder mixtures with composition Ni 60 Nb 20 Zr 20 were mechanically alloyed in a ball mill. The evolution of structure of the powders was investigated with a combination of X-ray diffractometry and differential scanning calorimetry and was compared with corresponding melt spun samples. Mechanical alloying of Ni 60 Nb 20 Zr 20 alloy involves two consecutive amorphization reactions. Mechanical alloying first leads to the amorphization reaction between Ni and Zr layers with a strong thermodynamic driving force as well as fast kinetics for Ni–Zr amorphization compared with Ni–Nb amorphization. On further milling the kinetic requirements for a Ni–Nb amorphization reaction is fulfilled and consequently a Ni–Nb amorphous phase forms. The resulting two amorphous phases homogenize at longer milling times.

Preparation and thermal stability of mechanically alloyed amorphous Ni–Zr–Ti–Si composites

Abstract The feasibility of preparing amorphous Ni57Zr20Ti20Si3 composite powders by mechanical alloying of pure Ni, Zr, Ti, Si, and ceramic powder mixture after 5 h milling was investigated. The as-milled powders were examined by X-ray diffraction, scanning electron microscopy, and differential thermal analysis. Amorphous Ni57Zr20Ti20Si3 composite powders were prepared successfully at the end of milling for all the compositions studied. The thermal stability of the amorphous matrix is not significantly affected by the presence of the ceramic particles. It is suggested a partial dissolution of the atoms constituting the ceramic species in the amorphous phase can result change of matrix composition and lead to the variation of the glass transition and crystallization behaviors.

Local structure of deuterated Ti-Zr alloy

The Ti–Zr alloy system is isomorphous over the total concentration range. A neutron zero-scattering alloy can be obtained at the composition Ti0.676Zr0.324 because of negative and positive coherent neutron scattering amplitudes of Ti and Zr respectively. A (Ti0.676Zr0.324)D0.31 amorphous alloy was synthesized by mechanical alloying (MA) under a deuterium-gas atmosphere of 0.08 MPa. In contrast, it is found that the MA of Ti and Zr powders under a deuterium-gas atmosphere of 2.0 MPa forms a nano-crystalline (Ti0.676Zr0.324)D1.54 alloy, which is composed of TiH2 and ZrH2 crystalline compounds.

Computer Simulation Approach to the Chemical Mechanisms of Self-Propagating High-Temperature Reactions: Effect of Phase Transitions on the Thermite Reaction between O2 Gas and Zr Powders

The Zr + O2 → ZrO2 self-propagating high-temperature synthesis (SHS) has been investigated by computer simulation with a model accounting for two concurrent oxidation mechanisms (solid-state diffusion and gas-phase transport of oxygen) and for melting of reagent and product, under the external conditions defined by two process parameters: amount of zirconia added as diluent in the starting mixture (dilution degree) and partial pressure of oxygen reagent. The results are compared with those of a closely similar model that does not account for the phase transitions. Allowance for phase transitions shows many marked effects on the dynamic behavior of the SHS (which propagates in a steady mode under a wider range of dilution degrees) and on the macrokinetic parameters (space and time profiles of temperature and advancement degree of oxidation and time evolutions of wave speed and combustion temperature). These effects can be used for assessing the mechanism of an SHS from real experiments.

Formation of Cu–Zr–Ni amorphous powders with significant supercooled liquid region by mechanical alloying technique

The amorphous Cu–Ni–Zr alloys were successfully synthesized by mechanical alloying mixtures of pure crystalline Cu, Ni and Zr powders with SPEX high-energy ball mill. These ranges are similar to those for amorphous alloys produced by melt-spinning techniques. The structure and thermal stability of these alloys were analyzed by X-ray diffraction and differential scanning calorimeter. Several amorphous alloy samples were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T g and T x, i.e. Δ T x (= T g− T x), is 34 K for Cu 10Zr 60Ni 30, 48 K for Cu 20Zr 60Ni 20, 78 K for Cu 40Zr 55Ni 5, 81 K for Cu 50Zr 35Ni 15, 61 K for Cu 50Zr 40Ni 10 and 64 K for Cu 50Zr 45Ni 5.

Kinetics of solid state reaction between zirconium and copper(I) chloride

The kinetics of the reaction between Zr and CuCl powders have been studied under vacuum by means of thermogravimetry in the range from 250 to 330°C. The reactivity of the Zr–CuCl system is significantly affected by the mixing operation, the ratio of Zr and CuCl in the mixture and the thickness of the ZrO2 film on the Zr particles. It is established that the kinetics of reaction was governed by a nucleation and growth mechanism with an apparent activation energy of 93±3 kJ mol−1 and for these low reaction temperatures only Cu and Cu5Zr were identified.

Dynamic behaviour and chemical mechanism in the self-propagating high-temperature reaction between Zr powders and oxygen gas

The self-propagating high-temperature reaction between zirconium powders and oxygen gas has been investigated by computer simulated experiments using a one-dimensional model which accounts for (a) solid state diffusion in the oxide layer growing at the surface of each reacting zirconium grain and (b) the gaseous flux of oxygen molecules towards the reacting grain. Two process parameters—dilution with additional zirconia, and oxygen pressure in the reaction environment—have been considered. The results show that the reaction can propagate under steady conditions with constant wave velocity and maximum temperature or under various unsteady conditions. The main process parameter controlling the dynamic behaviour is the dilution degree, with oxygen pressure playing a minor role. Diffusion through the product layer and pressure flux can both be found as the rate determining step under steady propagation conditions, while unsteady propagation is always under diffusion control. Lowering oxygen pressure has a stabilizing effect on unsteady propagation.

The carbothermal reduction synthesis of Zr(C,O) nanoparticles from binary carbonaceous-zirconia aerogel

The most widely used process for ZrC production is carbothermal reduction of zirconium dioxide (ZrO2) in the presence of carbon (C). Since the traditional process uses a physical mixture of solid reactants as precursor, leading to the interruption of intimate contact between ZrO2 and C, the reduction reaction rate is extremely slow and a complete reaction is practically impossible by this method. In recent years the sol-gel method has been regarded as a suitable method for the preparation of ultrafine ceramic materials [1, 2]. The binary sol-gel process reported by H. Preiss et al. [3, 4] has been used in the preparation of silicon carbides and Zr(C,O,N) solid solutions. Compared to the conventional methods in which zirconia is mixed and milled with carbon powders, the binary sol-gel approach allows that the reactants are mixed at the colloidal level. The primary advantage provided by use of binary sol-gel precursors is the intimate contact between reactants. In this paper, we present the preparation of binary carbonaceous-zirconia aerogel by sol-gel supercritical fluid drying method. We have also focused our interest on the BET surface area, crystallization and morphology of nanometric Zr(C,O) powders with loose agglomeration obtained by carbothermal reduction under argon. ZrOCl2 · 8H2O was dissolved in distilled water to obtain a stock solution of 0.2 M concentration. To improve the agglomeration of final powders [5], 200 ml of absolute ethanol were added into the 200 ml of 0.2 M aqueous ZrOCl2 solution, and then the pH of the mixture was also adjusted to pH = 8 by a dilute ammonia solution under stirring for 2 h to form a colorless sol. The sol was washed by centrifugation using distilled water in order to remove Cl− ion, and then washed with ethanol repeatedly to remove water to obtain zirconia alcosol. The zirconia alcosol was mixed with carbonaceous alcosol under stirring for 24 h to form binary carbonaceous-zirconia alcosol. In this study, a higher C : ZrO2 than the stoichiometric ratio (3 : 1) was desirable to separate ZrO2 particles with carbon and prevent the fast growth of ZrO2 particles during heat-treatment. The binary alcosol was dried under supercritical conditions to prepare binary aerogel. The preparation method of carbonaceous alcosol has been described in detail in Ref. [6]. The carbothermal reduction experiments were conducted in a graphite crucible using a high-temperature alumina tube furnace in flowing argon of 2 L/min. The time of keeping at desired temperature was 1 h. The carbothermal reduction products of binary aerogel at various temperatures under argon atmosphere for 1 h also show loose appearance structure. The XRD spectra recorded for the binary carbonaceouszirconia aerogel and its annealed powders are shown in Fig. 1. It shows that the binary aerogel powders are completely amorphous with featureless spectrum. At 1300 ◦C, the spectrum (Fig. 1b) already presents many small peaks which can be attributed to ZrO2 and trace of Zr(C,O) phase. Distinct peaks can be observed at 2θ = 30.1◦, 35.3◦, 50.2◦ and 59.3◦ for the cubic ZrO2, and at 2θ = 28.1◦ for monoclinic ZrO2. In addition, the peaks appear at 2θ = 33.2◦ and 38.4◦, which clearly indicates the formation of cubic Zr(C,O)

Mechanically induced gas–solid reaction for the synthesis of nanocrystalline ZrN powders and their subsequent consolidations

Equiatomic nanocrystalline ZrN powders with an average grain size of less than 8 nm in diameter have been fabricated by high energy ball-milling elemental powders of Zr under nitrogen gas-flow at room temperature. The ductile powders of Zr tend to agglomerate during the first stage of the reactive ball milling (RBM; <11 ks) to form powder particles with larger diameters. The powders are then intensively disintegrated into smaller particles during the second stage of milling (11–43 ks). These disintegrated particles that have fresh or new surfaces begin to react with the milling atmosphere (nitrogen) during this stage of milling to form a cubic phase of ZrN powder coexisting with unreacted hcp-Zr powder. Towards the end of milling (86–173 ks), a single phase of nanocrystalline ZrN (NaCl-structure) is obtained. The powders of this end-product have spherical like morphology with average particle size of about 0.4 μm in diameter. Cold and hot pressing techniques were employed to consolidate the powders at the several stages of the RBM. The as-milled and as-consolidated powders were characterized as a function of the RBM time by means of X-ray diffraction, transmission electron microscopy, scanning electron microscopy, optical metallography and chemical analyses. The results have shown that the consolidated ZrN compact of the end product (173 ks of RBM) still maintains its unique nanocrystalline characteristics with an average grain size of less than 80 nm. Density measurements of these consolidated samples of the end-products (86–173 ks of the RBM) show that they are essentially fully dense (above 99% of the theoretical density for ZrN). The dependences of the hardness on the grain size and the consolidation temperatures were investigated.

The effect of ternary addition on the formation and the thermal stability of L1 2 Al 3Zr alloy with nanocrystalline structure by mechanical alloying

We have tried to produce nanocrystalline L1 1 Al+25 at.% Zr+12.5 at.% M (M=Cu, Ni, Mn) alloys by planetary ball milling of elemental powders. Systematic studies on ternary addition on the formation and the thermal stability of metastable L1 2 phase are also given in this study. L1 2 Al 3Zr alloy was effectively prepared by mechanical alloying of elemental powders of Al and Zr for 3 h. In the case of ternary addition the L1 2 phase was formed after 6-h milling for Cu and 3-h milling for Ni. In Mn addition, the L1 2 phase was formed after 3 h and transformed into an amorphous phase after 6 h. The as-milled L1 2 Al 3Zr and L1 2 Al 5Zr 2Cu alloy powder had nanocrystalline structures with grain sizes less than 10 nm. L1 2 Al 3Zr alloy transformed into stable D0 23 phase at 625°C. L1 2 phase has been stabilized significantly by ternary addition up to over 900°C for Cu and 850°C for Ni, respectively. Amorphous Mn added to Al 3Zr alloy crystallized to L1 2 phase at 770°C and the crystallized L1 2 phase was stable up to over 900°C. The nanocrystalline structure was maintained after 20-min heat treatment at 900°C.

Coercivity in mechanically milled Pr–Co–Zr powders with TbCu7 structure

The structural, microstructural, and magnetic properties of the PrCo7−xZrx (x=0, 0.2, 0.3, and 0.4) powders produced by mechanical milling have been studied with the aim of developing fine microstructure and high coercivity in these powders. X-ray diffraction, transmission electron microscope, and magnetic measurements show that a single phase with TbCu7-type structure and with high anisotropy of up to 100 kOe is obtained in as-cast PrCo6.7Zr0.3 alloy. Magnetic hardening is developed in the mechanically milled powders. An optimum coercivity of 5.3 kOe has been obtained in PrCo6.7Zr0.3 powders milled for 2 h and annealed at 800 °C for 1 min, which shows a uniform microstructure of the 1:7 phase with an average grain size of about 10–15 nm. The observed magnetic hardening is believed to arise from the high anisotropy field of the Pr(Co, Zr)7 phase and the uniform nanoscale microstructure developed by mechanical milling and subsequent annealing.

アモルファス・ナノ結晶制御と高機能材料 メカニカルアロイングによるＡｌ‐Ｎｉ‐Ｚｒ三元系における非晶質相の生成

The formation of amorphous phase, which are invented by Al, Ni and Zr powder, were investigated. Oscillatory ball mill was used to carry out MA (mechanical alloying) in this investigation. DMA (Double Mechanical Alloying) method was also taken, where binary amorphous phases were firstly formed by MA, and the third element powder was added to those amorphous phases, and milled by MA again. The results of DMA were compared with the results of normal MA. For MA of Al-Zr mixed powder, amorphous phases were formed for 72ks in the case of Al-40-50 mol%Zr, while Ni-Zr amorphous phases were obtained at the same milling time for Ni-35-60 mol%Zr. Ternary Al-Ni-Zr amorphous phases were successively obtained by 72 ks of DMA for 30-40 mol%Al and MAed amorphous Ni-35-60 mol%Zr mixed powders. From these results, it was shown that the DMA method was more effective and prepare a wide range ternary amorphous phase than conventional MA method. Furthermore it was confirmed that the hardness of Al-Ni-Zr amorphous alloys decreased with increasing Ni/Zr and Al/(Ni-Zr) ratios, resulted in stable amorphous phases up to higher temperature.