Zr Intermetallic Compounds Research Articles

Hydrogen storage properties of Zr 1-xTi xCo intermetallic compound

The intermetallic compound Zr 1-xTi xCo was prepared and its suitability for hydrogen storage was investigated. The alloys obtained by magnetic levitation melting with the composition of Zr 1-xTi xCo (x =0, 0.1, 0.2 and 0.3, at. %) show single cubic phase by X-ray diffraction. A single sloping plateau was observed on each isothermal, and pressure-composition-temperature (PCT) measurement results show that the equilibrium hydrogen desorption pressure of Zr 1-xTi xCo alloy increases with increasing Ti content. The desorption temperatures for supplying 100 kPa hydrogen are about 665, 642, 621 and 614 K for ZrCo, Zr 0.9 Ti 0.1Co, Zr 0.8Ti 0.2Co and Zr 0.7Ti0.3Co alloy, respectively. Repeated hydrogen absorption and desorption cycles do not generate separated ZrCo, TiCo and ZrH 2 phases, indicating that alloys have good thermal and hydrogen stabilization.

Microstructure and characterization of phases in TIG welded joints of Zircaloy-4 and stainless steel 304L

Tungsten inert gas (TIG) welded joints between Zircaloy-4 and stainless steel 304L have been studied by scanning electron microscope (SEM) having energy dispersive system (EDS) as an attachment. Intermetallic compound Zr(Cr, Fe)2 and Zr2Fe–Zr2Ni eutectic phase have been observed in the molten zone. The surface area occupied by intermetallic compound Zr(Cr, Fe)2 is about twice compared to Zr2Fe–Zr2Ni eutectic phase. The shape of the intermetallic compound is rod like. The phases were also identified by using X-ray diffraction (XRD) technique. EDS and XRD results are quite in agreement.

Crystal Structure of the New Intermetallic Compounds Zr2‐xLix+ySi1‐y (x = 0.17, y = 0.12) and Its Relation with the Disilicide ZrSi2.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Absorption kinetics and dynamics of gaseous impurities in helium and hydrogen by intermetallic compounds

Absorption kinetics and dynamics of various gaseous impurities in helium and hydrogen by intermetallic compounds Zr 0.8Ti 0.2Mn 2 and ZrCrFe were studied in the range of impurity concentration 10 −6–10 −2 vol.%, the temperature range 570–1170 K and at 0.3–3.3 MPa of gas pressure. Kinetic equation of the first order chemical reaction was used for evaluation of the sorption rate constants. The dependencies of the rate constant of methane and nitrogen sorption on the amount of the impurity absorbed were obtained for various temperatures of the getter and gas pressures. Length of mass transfer zone and dynamic sorption capacity were measured for dynamics of different impurities absorption from a multi-component gas mixture. The effect of various gas–solid reactions on dynamics of the impurities absorption has been observed.

Hardness and microstructural studies of electron beam welded joints of Zircaloy-4 and stainless steel

Electron beam welded joints between Zircaloy-4 and stainless steel 304L are investigated due to their importance in the nuclear industry. The molten and heat affected zones (HAZs) are found to be free of defects. Diffusion of Fe, Cr and Ni is observed in Zircaloy-4 near the molten zone and of Zr and Sn in the stainless steel. A rod-shaped intermetallic compound Zr(Cr,Fe) 2 and eutectic phases ZrCr 2–liquid (Zr,Fe) and Zr 2Fe–Zr 2Ni are present in the molten zone. The hardness of the molten zone, containing Zr(Cr,Fe) 2, is much higher than the rest of the molten zone and the HAZs.

Effect of electron irradiation on the phase stability of Fe–9Zr–3B alloy

Effect of electron irradiation on the structural and phase stability of amorphous phase and crystallites in Fe–9Zr–3B alloy was examined. Amorphous ribbons were produced by a single-roller-melt-spinning method. Some specimens were annealed at 873 and 1073 K to obtain α-Fe and the duplex structure composed of α-Fe phase and Fe–Zr intermetallic compounds, respectively. Electron irradiation on the amorphous and crystalline specimens were performed at dose rates of 1.7×10 24 and 7.5×10 23 m −2 s −1. The electron irradiation accelerated crystallization from the amorphous phase, while the α-Fe and the intermetallic compounds remained stable in annealed specimens. During electron irradiation, cubic-Fe 2Zr crystallized from the amorphous phase prior to α-Fe precipitates in melt-spun specimens without annealing, while the α-Fe precipitation advanced during annealing

Single crystal growth of incongruent intermetallic compound ZrCo 2Si 2 using W crucibles

Single crystals of incongruently melting intermetallic compound Zr(Co 0.85Fe 0.15) 2Si 2 with the tetragonal ThCr 2Si 2 structure were grown from the liquid with composition of Zr 5(Co 0.775Fe 0.225) 16Si 16 by the Bridgman method using W crucibles. Application of the microscopic techniques to the arc-melted as-cast specimens turned out to be a useful tool for qualitative determination of the phase diagram.

The Consolidation Behavior of L12 Phase Al3Zr & (Al+12.5at%)3Zr Powders with Nanocrystalline Structure During Spark Plasma Sintering

AbstractThe spark plasma sintering (SPS) of L12 phase Al3Zr and (Al+12.5at.%Cu)3Zr powders with a nanocrystalline microstructure has been studied to produce bulk intermetallic compounds which maintain metastable structures such as L12 structure and nanocrystalline microstructure. The powders were prepared by 10 h planetary ball milling (PBM). Full-density L12 (Al+12.5at.%Cu)3 Zr intermetallic compounds were obtained by SPS for 0 min. at 600°C. The smallest grain size was obtained in the specimen prepared at 600°C for 0 min., which was 20-30 nm as confirmed by TEM observation. Accordingly, the highest micro-hardness, 989.5 HV, was obtained in the specimen and this value was three times higher than those of the specimens with micro grain sizes. Full density Al3Zr intermetallics were prepared by SPS at 700°C for 0 min.. However, their crystal structure was D023 and micro-hardness was 778.1 HV. By using SPS, the sintering time can be reduced within 10 min.

Surface and electrochemical characterization of Ni–Zr intermetallic compounds

In this paper the Ni–Zr system has been considered with the aim of investigating the role of composition and structure of an early–late transition metals system on the electrocatalytic activity, for the hydrogen evolution reaction. As a matter of fact, pure Ni and Zr show low activity, while their intermetallic compounds generate a higher catalytic efficiency. Five alloys, with increasing Ni content starting from Ni 33Zr 67 up to Ni 75Zr 25, have been prepared and characterized. The alloy of composition (Ni 0.55Mn 0.30V 0.10Co 0.05) 2.1Zr has also been considered, in order to investigate the catalytic efficiency related to a Laves structure. The thickness and composition of the surface oxides have been investigated and their effect on reducing the catalytic efficiency of the as-prepared alloys has been discussed. The activity of the samples submitted to a surface activation treatment with hydrofluoric acid, that removes the oxide layer and allows to evidence the properties of the compounds, has been observed to increase significantly. The trend of the electrocatalytic efficiency with the composition of the alloys is discussed considering a synergetic effect between Ni and Zr. The Laves phase appears slightly more active than the binary intermetallic compound.

The α-Zr phase field in the Zr-Sn-O system

Tin and oxygen contents stabilize the hexagonal (hcp) phase at temperatures where the cubic (bcc) should be the stable structure of zirconium. The transition temperature T[sup hcp[leftrightarrow]bcc] which is 863 C (1136 K) for pure zirconium can be raised to 982 C (1255 K) or 2130 C (2403 K) with convenient Sn or O additions. The univariant phase equilibrium in the ternary system Zr-Sn-O involving the hcp solid solution [alpha]Zr, the intermetallic compound Zr[sub 5]Sn[sub 3] and the oxide [alpha]ZrO[sub 2] was previously studied. A review of the accessible works regarding this ternary system was presented in that paper. The aim of the present work is to outline more accurately the boundaries of the [alpha]Zr field on isothermal sections at 1050 C and 1300 C supported by experimental composition determinations.

Amorphization of Zr 3Fe under electron irradiation

The intermetallic compound Zr 3Fe has been made amorphous by 0.9 MeV electron irradiation. By performing this irradiation in situ, it was possible to conduct a systematic study of the influence of temperature, dose rate, electron energy and specimen orientation on the amorphization process. The critical temperature and the critical dose for amorphization were determined, and shown to depend on dose rate. By varying the electron energy, we determined the displacement energies for the Zr and Fe atoms in Zr 3Fe, and showed that, at low electron energy, the amorphization rate is dependent on specimen orientation. We analyze these results in terms of a model based on amorphization occurring at a damage level where the modified free energy of the irradiated crystal exceeds the free energy of the amorphous phase. This model is shown to predict the amorphization kinetics, i.e. the critical temperature and critical dose for amorphization. We also compare amorphization induced by electron and ion irradiation.

Study on the precipitates in Zircaloy-4 by Mössbauer spectroscopy

Mössbauer spectroscopy of 57 Fe was used to study the content and structure of precipitates in different thermal-treated Zircaloy-4 specimens. The spectra of Zircaloy-4 have two sets of peaks. One of them can be ascribed to precipitates of intermetallic compound Zr(Cr,Fe) 2. The structure of the specimen is changed by thermal treatment. The area of the Mössbauer peak is also changed. Content of Zr(Cr,Fe) 2 in a water quenched sample is the same as that in an as-received (50% cold worked) sample. The content of alloying element-iron in matrix between precipitates is not an important factor which has an influence on corrosion resistance of Zircaloy-4.

Iron-bearing precipitates in Zircaloys: a Mössbauer spectroscopy study

Mössbauer spectroscopy of 57Fe was used to study the chemical form and distribution of iron in Zircaloy-2 and Zircaloy-4. The spectra of Zircaloy-4 consist of two overlapping quadrupole-split doublets, which can be ascribed to precipitates of the pseudobinary Laves-phase intermetallic compound Zr(Cr,Fe) 2, which has a hexagonal MgZn 2 (C14) type structure and cubic MgCu 2 (C15) type structure. In Zircaloy-2, a large fraction of iron was also found in the form of Zr 2(Fe,Ni) precipitates, having a tetragonal Al 2Cu (C16) type structure. Characteristic room-temperature values of Mössbauer spectral parameters were determined for the three types of intermetallic precipitates. At liquid helium temperature, both alloys exhibit a poorly resolved magnetic hyperfine splitting, attributed to the low-temperature ferromagnetism of cubic Zr(Cr,Fe) 2 Laves-phase particles. This effect is more pronounced in Zircaloy-4 than in Zircaloy-2. The possibility of determining volume fractions of different phases from their relative spectral areas is discussed.

ジルカロイ-4の耐食性に及ぼす析出金属間化合物の酸化挙動の影響

The role of precipitates in the corrosion of Zircaloy-4(Zr-1.5 mass%Sn-0.22%Fe-0.11%Cr) has been studied by high resolution transmission electron microscopy/energy dispersive X-ray spectroscopy (HRTEM/EDS) with electron microbeam and field emission scanning electron microscopy (FE-SEM/EDS). In Zircaloy-4, the solubility of Fe and Cr is low, and Fe and Cr precipitate as an intermetallic compound Zr(Fe, Cr)2. The size of the precipitate changed with temperature in the intermediate annealing process. The size of precipitates in the specimen annealed at 780°C are significantly larger than that in the specimen annealed at 630°C. The corrosion rate in pressurized steam at 400°C was higher in Zircaloy-4 with finer Ze(Fe, Cr)2 particles precipitated by the intermediate annealing at 630°C.The observation of the corroded layers by HRTEM/EDS showed that the surfaces of precipitates oxidized together with the matrix and decomposed to dissolve into ZrO2 during the corrosion. As the precipitates oxidize, the atomic ratio of Fe/Cr in the precipitates changes from 2 in the metal to 0.5 in the oxide. This phenomenon suggests that Fe component predominantly diffused into the matrix.The cations of Fe and Cr generated by oxidation and diffused into the matrix ZrO2, were thought to replace Zr4+ sites. The higher corrosion rate in Zircaloy-4 with finer precipitates was attributed to larger amounts of Fe and Cr cations that are made available during the early stage of corrosion.

Aromatization of ethane over Pt,Ga/HZSM-5 catalyst and the effect of intermetallic hydrogen acceptor on the reaction

The effect of the hydride-forming intermetallic compound Zr 2Fe on the aromatization of ethane over Pt,Ga/HZSM-5 catalyst has been studied under different reaction conditions (temperature, GHSV, ethane dilution with Ar). In the presence of intermetallic hydrogen acceptor aromatics yield from ethane at 500°C was 6-fold higher and reached 61 wt.-% as a result of releasing hydrogen elimination, selectivity to aromatics being 78%. The fused-ring aromatics formation appeared to be more sensitive to hydrogen removal than BTX formation. The yield of BTX may be improved by ethane dilution with inert gas.

Hydrogenation of Zr 6FeAl 2 and crystal structure of Zr 6FeAl 2D 10

The intermetallic compound Zr 6FeAl 2 was hydrogenated (deuterated) at room temperature and investigated by X-ray and neutron powder diffraction. The hydride (deuteride) crystallizes with hexagonal symmetry (space group P 62c; deuteride: a = 8.1354(4) A ̊ , c = 7.0940(6) A ̊ , V = 406.62(5) A ̊ 3, Z = 2 , refined composition Zr 6FeAl 2D 9.82(3)). Its metal atom substructure derives from an ordered Fe 2P type host structure (space group P 62m ) by small atomic displacements that lead to a doubling of the c axis. Deuterium occupies two types of tetrahedral [Zr 4], one type of tetrahedral [Zr 3Fe] and one type of trigonal bipyramidal [Zr 3Fe 2] interstices, thus avoiding the neighbourhood of aluminium. The metal-deuterium bond distances are in the range Zr-D = 2.03–2.22 Å and Fe-D = 1.73–1.77 Å, while the shortest Al-D distance is 2.90 Å. The hydrogen sorption properties of Zr 6FeAl 2 are intermediate to those of Zr 2Fe and Zr 2Al.

Role of hydride phases in the catalytic activity of Zr 2Ni for the dehydrogenation of methanol

The intermetallic compound Zr 2Ni showed high catalytic activity for methanol dehydrogenation in the temperature region of 375–500 K when it was subjected to a series of pretreatments under HF, NaOH and hydrogen. The reaction followed a two-step process, one of them being responsible for the initial higher catalytic activity. The pretreatments were found to generate secondary phases, such as fluorides and hydrides and also nickel clusters at the catalyst surface, the presence of which was found to be vital for the observed catalytic activity. The bulk of the intermetallic compound was, however, converted into a single-phase hydride after the above mentioned pretreatments. The removal of stored hydrogen and the oxidation of nickel sites during the reaction led to the progressive loss of catalyst activity. It is proposed that the secondary hydride phases act as support to the catalytically active nickel clusters, thus helping in better metal dispersion.

Effect of hydrogen absorption on structure, superconductivity, magnetic susceptibility and heat capacity of Zr 2Rh

The superconducting intermetallic compound Zr 2Rh (CuAl 2-type C16 tetragonal structure with T c ≈ 11 K) can be hydrided at room temperature and about 1 atm hydrogen pressure to give a composition Zr 2RhH x ( x = 4.25 ± 0.25) without a change in crystal structure. This is the first report on the stabilization of a hydride phase with an appreciable hydrogen content. Results of X-ray diffraction, electrical resistivity, magnetic susceptibility and heat capacity are reported on the hydride phase and compared with those of the parent compound. It is found that: (i) Zr 2RhH 4.25 exhibits metallic behaviour similar to Zr 2Rh; however, no superconducting transition is seen down to 1.8 K; (ii) the hydride is Pauli paramagnetic, but its susceptibility is reduced to almost one-half of the value of the parent compound; (iii) the Debye temperature of the hydride is almost twice that of Zr 2Rh, indicating stronger bonding despite the increased interatomic separation; (iv) the electronic specific heat coefficient is reduced by almost an order of magnitude on hydriding. Approximate estimates of the density of states at the Fermi level and the electron-phonon coupling constant have been obtained for the intermetallic compound and the hydride.

New hydride formation of MoSi 2-type intermetallic compounds at hydrogen pressures up to 2000 atm

The interaction of the MoSi 2-type intermetallic compounds Zr 2Pd, Hf 2Pd and Hf 2Cu with hydrogen at pressures up to 2000 atm has been investigated. Absorption and desorption isotherms were measured at 293 K. For each system the formation of two hydride phases was established: tetragonal A 2BH ∼3 and orthorhombic A 2BH 5.5–6. The volume expansions for these phases were 8%–10% and 21%–25% respectively. The thermal desorption of hydrogen from these phases was also studied.

Hydrogen absorption characteristics of the Zr -xHo xCo 2 system in the pressure range 0–40 bar

Hydrogen absorption pressure-composition isotherms were determined for the intermetallic compounds Zr 1-xHo xCo 2 ( x=0.4, 0.6 and 0.8) belonging to the C-15-type Laves phase structure in the temperature range 50–200 °C at pressures up to 40 bar. The maximum hydrogen concentration (number of hydrogen atoms per formula unit) increases from 0.1 to 3.8 as the holmium concentration ( x) is increased from 0 to 1. The ratio of the number density of hydrogen atoms in the alloy to the density of liquid hydrogen lies in the range 0.1–1.24. The absorption of hydrogen is accompanied by a maximum of 19% expansion in the unit cell volume of the host without any change in the C-15-type Laves phase structure. For higher values of x the materials are highly distorted when the hydrogen concentration exceeds about 3.0 and tend towards the amorphous state. The relative partial molar enthalpy (Δ H H) and entropy (Δ S H) of hydrogen absorption in these materials are found to lie in the range 7–43 kJ (mol H) −1 and 10–115 J K −1 (mol H) −1 respectively. The hydrogen absorption kinetics recorded at different temperatures for all the compositions indicate that the kinetics are fast for lower x values.