Composition Zr Research Articles

Effect of CNTs-Assisted Ball Milling on Morphology and Oxidation Behavior of Zr Powders

Morphology evolution and oxidation behavior of Zr powders milled with and without CNTs for different time were compared. XRD and SEM were used to determine the phase composition and morphology of obtained Zr and Zr/CNTs powders. Thermogravity (TG) analysis was applied to evaluate the thermal oxidation behavior of Zr and Zr/CNTs. Results show that the phase composition of Zr after milling is not influenced by adding CNTs, but the morphology and oxidation behavior of Zr are influenced. In case of milling without CNTs, particle size of Zr continues to reduce from more than 10 μm to about 2∼3 μm when milling time increases from 1 h to 3 h. In case of CNTs-assisted milling, the particle size reduction of Zr is not obvious until milling time is prolonged to 3 h. This is because those CNTs adhered on the surface of Zr or CNTs-induced agglomerations among Zr prohibit the mechanical impact and fracturing effects of milling balls on Zr particles. Compared with direct milling of Zr, when the obtained Zr has similar particle size, adding CNTs lowers the onset oxidation temperature and peak exothermic temperature of Zr powders by 11∼37 °C, depending on milling time. This is ascribed to the high heat conductivity of CNTs which favors heat transfer between Zr particles. At the same time, oxidative mass gain of Zr/CNTs is slightly lower than that of the corresponding pure Zr when milling time is less than 2 h and then this trend reverses. The initial decrease in mass gain of Zr in Zr/CNTs mixtures under shorter milling time is related to two factors: one is CNTs-induced agglomerations of Zr, which prohibits the contact of Zr with oxygen and thus decreases the degree of oxidation, and the other is the delayed particle size reduction of Zr in Zr/CNTs mixtures. The subsequent reversal in mass gain for pure Zr and Zr/CNTs is due to the positive effect of particle size reduction of Zr in Zr/CNTs on its thermal oxidation just began, while the spontaneous oxidation-induced negative effect for well-refined pure Zr has become very obvious.

Breakdown Characteristics of TiN/HfxZr1-xO2/Al2O3/Ge Gate Stacks

Ge has been considered as an alternative channel material in place of Si because of its higher electron and hole mobility. Since direct deposition of high-k material on Ge leads to degradation of interface quality ultrathin Al2O3 is used as a passivation layer prior to high-k layer deposition. In addition, ZrO2/Al2O3 bilayer as gate dielectric on Ge is becoming popular since ZrO2 showed lower leakage current than HfO2 (1, 2). To further scale the effective oxide thickness (EOT) on Ge higher-k dielectric materials like Hf1-xZrxO2, with different Hf to Zr compositions has been explored. Furthermore, the recent introduction of post-deposition slot plane antenna plasma oxidation (SPAO) of the dielectric seems to enhance the interface as well as gate stack quality (3). In this work, we investigate the Time Dependent Dielectric Breakdown (TDDB) characteristics of the impact of TiN/HfxZr1-xO2/Al2O3/Ge gate stacks by changing the Zr content. Slot-plane antenna plasma oxidation (SPAO) was performed on these devices after the ALD deposition of the high-k layers. It was observed that the equivalent oxide thickness (EOT) decreases with Zr addition in HfO2 with up to 75% of Zr incorporation. With 100% Zr incorporation EOT increased significantly. This is possibly due to the formation of low-k interfacial GeO2 at the interface for 100% Zr whereas for other samples have comparatively thinner GeOx interfacial layers (3). Weibull plots shows that charge to breakdown (Q BD) increased with increase the Zr percentage. However, the breakdown acceleration factor decreased with Zr percentage up to 75% and increased rapidly for 100% Zr content. It is reported earlier (3) that GeO2 has the worst resistance to stress in terms of device stability compared to GeOx. Therefore, formation of thick GeO2 degrades the device with 100% Zr rapidly as compared to lower percentage of Zr. The authors would like to acknowledge K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, and G. J. Leusink of TEL Technology Center, Albany, NY for their help in device preparation.

Environmental impact of disposal of coal mining wastes on soils and plants in Rostov Oblast, Russia

Underground coal mining in Southern European Russia leads to soil cover destruction in areas directly occupied by spoil tips and rock dumps located nearby. Coal producing areas in Rostov Oblast were selected for a detailed consideration. Soil samples were taken from the uppermost horizons: a layer of 0–10cm of spoil tips and surrounding areas, as well as from 1.5m depth vertical soil profiles. The soil samples were analysed for mineral composition, particle-size distribution and gross contents of Cu, Zn, Pb, Ag, Sn, Mo, Ba, Co, Ni, Mn, Ti, V, Cr, Ga, P, Li, Sr, Y, Yb, Nb, Sc and Zr, using emission spectral analysis. The plant species of mining influenced areas were described. The process of Technosol formation at the waste sites was considered separately. Soils have not yet formed as a result of a self-restoration on the spoil tips aged more than 50years and burnt-out decades ago. A vegetation cover, which emerged during this time range, practically does not support the progress of any considerable soil-forming process. The ponds formed by the flooding of burning spoil tips, do not give the possibility for the formation of soils and hardly contribute to plant growth. The surface layers of spoil tips at all stages of their development are different from the surrounding steppe soils in geochemical characteristics and mineralogical composition. The atmospheric and water inflow of material from spoil tips changes (in the cases studied - worsens) a state of steppe soils within a radius of 1 km, and leads to the increase of heavy metal content in these soils.

Improved thermoelectric performance of n-type half-Heusler MCo1-xNixSb (M = Hf, Zr)

The MCoSb-based (M = Hf, Zr) half-Heusler compounds were recognized as a promising p-type thermoelectric (TE) material for more than 2 decades although the base compound is intrinsically n-type. Here we investigate the TE properties of Ni-substituted n-type MCoSb. The anomalous changes of carrier concentration and lattice thermal conductivity with higher amount of Ni indicate the presence of atomic disorder. Peak power factor of ∼33 μW cm−1 K−2 and peak ZT of 0.6 are obtained in ZrCo0.9Ni0.1Sb. Further substitute Zr by Hf suppresses the lattice thermal conductivity and yields a peak ZT exceeding 1 in the composition Zr0.5Hf0.5Co0.9Ni0.1Sb at 1073 K. Thus the MCoSb compounds possess promising TE properties by both n- and p-type doping, which is unique among the half-Heusler based TE materials.

Injection casting of U–Zr and U–Zr–RE fuel slugs and their characterization

ABSTRACTU–Zr fuel slugs containing rare-earth elements can be difficult to cast because of the high reactivity of rare-earth elements. In this study, U–Zr and U–Zr–RE (RE: a rare-earth alloy comprising 53% Nd, 25% Ce, 16% Pr, and 6% La by weight) fuel slugs were prepared by injection casting, and their characteristics were evaluated. The as-cast fuel slugs were fabricated to the full length of the mold, and they showed no thin sections or cracks. Compared to the theoretical density, the measured density of the U–Zr and U–Zr–RE fuel slug was lower and higher, respectively. Chemical analysis revealed that the Zr and RE compositions in the U–10Zr and U–10Zr–3RE fuel slugs matched the target composition within 1.0 wt%. However, the RE composition in the U–10Zr–7RE fuel slug differed from the target composition by over 4 wt%. The melting crucible was further deteriorated and the casting yield was lower for the casting of a high rare-earth bearing fuel slug.

ZrO2-NdO1.5 system: Investigations of phase relation and thermophysical properties

Exploring the structural and thermophysical behaviour of Nd-Substituted ZrO2 is vital in context of matrices for minor actinide transmutation. Hence, phase relations have been studied in this system using high temperature sintered samples prepared by gel combustion route. Phase characterization of Zr1−xNdxO2−x/2 (0.0≤x≤1.0) series was carried out using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). With increasing NdO1.5 content, the system evolved in the sequence of (a) monoclinic zirconia (b) mixture of monoclinic+cubic stabilized zirconia, (c) cubic stabilized zirconia (d) mixture of stabilized zirconia+pyrochlore (e) pyrochlore (f) mixture of pyrochlore+hexagonal Nd2O3 and (g) pure hexagonal Nd2O3. Lattice and bulk thermal expansion of few selected compositions were characterized by high temperature XRD (298–1273K) and dilatometry (323–1673K). Average coefficient of thermal expansion decreased with increasing NdO1.5 fraction in Zr1−xNdxO2−x/2 series (x=0.2, 0.3, 0.4, 0.5) solid solutions, which has been attributed to increasing order in cation sub-lattice resulting in overall increase in lattice stability. Thermal conductivity has been reported for a representative composition Zr0.8Nd0.2O1.90.

Synthesis characterization and hydrogenation behaviour of as quenched Ti41.5+XZr41.5-XNi17 (x=0, 3.5, 11.5 and 13.5) nano quasicrystalline ribbons

The present study describes the synthesis characterization and hydrogen storage behavior of Ti41.5+XZr41.5-XNi17 (x=0, 3.5, 11.5 and 13.5) nano quasicrystalline ribbons synthesized through rapid solidification technique. The nano quasicrystalline ribbons of alloys have been synthesized at Cu-wheel speed of 45 m/sec. The investigation also describes the effect of different compositions of Ti and Zr on the structure, microstructure and their correlation with hydrogen storage characteristics of as quenched nano quasicrystalline ribbons. It has been found that the hydrogen storage capacity of these ribbons increases with increasing the content of Ti in i-phase ribbons.

Phase formation and stability in TiO x and ZrO x thin films: Extremely sub-stoichiometric functional oxides for electrical and TCO applications

Abstract Most functional materials are thermodynamic equilibrium phases representing minima in the thermodynamic phase space. However, it is expected that many metastable phases with highly interesting properties also exist. Here, we report on a systematic approach to prepare thin-films of such non-equilibrium phases based on the gas phase deposition methods sputtering and pulsed laser deposition (PLD). Our synthetic strategy is to deposit a “precursor phase” which is amorphous or already a crystalline non-equilibrium phase. Subsequent heat treatment leads to the nucleation of crystalline phases which again may be metastable or stable compounds. In the present paper we focus on the binary systems Ti–O and Zr–O, both systems being widely applied and technologically relevant. Highly oxygen-deficient titanium oxide (TiO1.6) and zirconium oxide (ZrO) films prepared by pulsed laser deposition at room temperature are optically absorbing and possess electronic conductivities in the range of 10 S/cm. Both materials are metastable in respect to both composition and structure. For TiO1.6 we find an amorphous matrix with embedded grains of cubic titanium monoxide (γ-TiO) directly after deposition. Upon annealing nanocrystalline grains of metallic Ti are formed in the amorphous matrix due to an internal solid-state disproportionation whereas the electrical conductivity of the films increases and comes close to metal-like conductivity (1000 S/cm) at about 450 °C. Congruently, room temperature deposited ZrO films with an average composition of Zr:O= 1:1 contain small ZrO nanocrystals within an amorphous matrix. Heat treatment again leads to an internal disproportionation reaction whereas small crystals of Zr2O and ZrO2 precipitate at temperatures as low as 75 °C. Increasing the temperature then results in the crystallization of metastable tetragonal ZrO2 at about 400 °C. Sputter deposition allows a subtler control of the oxygen partial pressure. Slightly non-stoichiometric TiO2−x films form a degenerate semiconductor with room temperature conductivities as high as 170 S/cm. Moreover, controlling both, the doping level and the vacancy concentration of these films allows to control the phase formation and the transition temperature between the rutile and anatase TiO2 polymorphs. Niobium doping of sputter deposited TiO2 can lead to films with very high electrical conductivities while maintaining a high optical transmittance demonstrating the potential of the material as an alternative transparent conducting oxide (TCO) with extraordinary properties.

High-pressure behavior of A2B2O7 pyrochlore (A=Eu, Dy; B=Ti, Zr)

In situ high-pressure X-ray diffraction and Raman spectroscopy were used to determine the influence of composition on the high-pressure behavior of A2B2O7 pyrochlore (A = Eu, Dy; B = Ti, Zr) up to ∼50 GPa. Based on X-ray diffraction results, all compositions transformed to the high-pressure cotunnite structure. The B-site cation species had a larger effect on the transition pressure than the A-site cation species, with the onset of the phase transformation occurring at ∼41 GPa for B = Ti and ∼16 GPa B = Zr. However, the A-site cation affected the kinetics of the phase transformation, with the transformation for compositions with the smaller ionic radii, i.e., A = Dy, proceeding faster than those with a larger ionic radii, i.e., A = Eu. These results were consistent with previous work in which the radius-ratio of the A- and B-site cations determined the energetics of disordering, and compositions with more similarly sized A- and B-site cations had a lower defect formation energy. Raman spectra revealed differences in the degree of short-range order of the different compositions. Due to the large phase fraction of cotunnite at high pressure for B = Zr compositions, Raman modes for cotunnite could be observed, with more modes recorded for A = Eu than A = Dy. These additional modes are attributed to increased short-to-medium range ordering in the initially pyrochlore structured Eu2Zr2O7 as compared with the initially defect-fluorite structured Dy2Zr2O7.

Femtosecond laser induced nanostructuring of zirconium in liquid confined environment

The surface, structural, and mechanical properties of zirconium after irradiation with Ti: sapphire laser (800 nm, 30 fs, 1 kHz) have been investigated. The zirconium targets were exposed for a varying number of laser pulses ranging from 500 to 2000 at a fixed fluence of 3.6 J/cm2 corresponding to an intensity of 1.2×1014 W/cm2 in ambient environments of de-ionized water and propanol. A scanning electron microscope (SEM) was employed to investigate the surface morphology of the irradiated zirconium. The SEM analysis shows the formation of various kinds of features including nanoscale laser induced periodic surface structures (LIPSS), sponge like surface structure, flakes, conical structures, droplets, pores, and cavities. The energy dispersive x-ray spectroscopy (EDS) analysis exhibits the variation in chemical composition along with an enhanced diffusion of oxygen under both ambient conditions. The crystal structure and phase analyses of the exposed targets were explored by x-ray diffraction (XRD) and Raman spectroscopy techniques, respectively. The XRD analysis confirms the presence of various phases of zirconium hydride and zirconia after ablation in both de-ionized water and propanol. However, excessive hydrides are formed in the case of propanol. The Raman analysis supports the EDS and XRD results. It also reveals the presence of oxides (zirconia) after irradiation in both de-ionized water and propanol environments. The chemical reactivity of zirconium was significantly improved in the presence of liquids which were accountable for the growth of novel phases and modification in the chemical composition of the irradiated Zr. A nanohardness tester was employed to measure the nanohardness of the laser treated targets. The initial increase and then decrease in nanohardness was observed with an increase in the number of laser pulses in the de-ionized water environment. In the case of propanol, a continuous decrease in hardness was observed.

Precipitation of (Zr, Hf)C in FeCrAlYHfZr alloys during electroslag remelting process

Three-dimensional morphology of (Zr, Hf)C in FeCrAlYHfZr alloys during electroslag remelting (ESR) was revealed by the method of non-aqueous solution electrolysis. Two types of (Zr, Hf)C carbides in FeCrAlYHfZr alloys were detected: isolated cubic carbides of (Zr, Hf)C were precipitated in intragranular and dendritic ones were precipitated in the grain boundary. In alloys with sufficient [C], there was a linear relationship between the (mole pct Zr)/(mole pct Hf) in carbides and [mole pct Zr]/[mole pct Hf] in alloys with the slope close to unity, while HfC was easier to be formed than ZrC in alloys with insufficient [C]. Extensive calculations were carried out to predict the composition of (Zr, Hf)C in FeCrAlYHfZr alloys with various concentrations of [Zr], [Hf] and [C].

Phase Stability and Mechanical Properties of Ti-Cr-Sn-Zr Alloys Containing a Large Amount of Zr

The Young’s modulus of Ti-Cr-Sn-Zr alloy varies with the composition of Cr, Sn and Zr, in which the elements act as β stabilizers. Some Ti-Cr-Sn-Zr alloys show very low Young’s modulus under 50GPa. The amount of Zr in alloys with very low Young's modulus increases with the decrease of Cr. We investigated the Young’s modulus and deformation behavior of Ti-xCr-Sn-Zr (x=0~1mass%) alloys containing a large amount of Zr. The quenched microstructure of Ti-Cr-Sn-Zr alloys changes from martensitic structure to β single-phase structure if the amounts of β stabilized elements are increased. The Ti-Cr-Sn-Zr alloys with compositions close to the transitional composition of microstructure from martensite to β phase show minimum Young’s modulus. The clear microstructural transition disappears and the minimum Young’s modulus increases if the amount of Cr becomes too small. In Ti-Cr-Sn-Zr alloys containing a large amount of Zr, Young’s modulus depends on β phase that is intermingled with martensite.

Poisoning effect of oxygen on hydrogenation performance of a Zr-V-Ni Laves phase alloy

Zr-based Laves phase alloys have been considered as suitable getter materials for hydrogen isotopes recovery, storage and delivery and received considerable attention during past decades. This work focuses on hydrogenation performance of a pseudo-binary Zr-V-Ni Laves phase alloy with the composition of Zr(V0.95Ni0.05)2 after pre-exposure in different contents of O2. It is found that introduced pure oxygen can be rapidly absorbed by the fully activated Zr(V0.95Ni0.05)2 alloy within 40 s. All of the experimental samples pre-exposed in oxygen consist dominant C15 type ZrV2 Laves phase and minor Zr3V3O oxides. With the further increase the oxygen pressure to 4.0 kPa in specimen chamber, Bragg peaks of Zr2V, V-rich BCC solid solution phase and ZrO2 phase, including baddeleyite (α-ZrO2) with monoclinic structure and a small amount of tazheranite (γ-ZrO2) with cubic structure are observed in addition to the dominant ZrV2 and minor Zr3V3O phases. Meanwhile, it can be seen that the lattice parameter of cubic C15 type ZrV2 calculated from Rietveld refinement increases from 7.402 to 7.432 Å with the increase of O2 content and the corresponding unit cell volume increases 0.86 vol.% as the O2 pressure from 1.0 to 4.0 kPa, which indicates more oxygen atoms have been dissolved into the lattice of ZrV2. All of the oxygen poisoned Zr(V0.95Ni0.05)2 alloys can absorb hydrogen and the capacity decreases from 3.39 to 2.22 H A−1 with the increase of oxygen pressure from 1.0 to 4.0 kPa, comparing with the maximum hydrogen storage capacity (4.34 H A−1) of the fully activated fresh alloy. The existence of oxygen is found to decrease both capacity and kinetics of Zr(V0.95Ni0.05)2 by forming passivation layer oxides which block the dissociation of H2 molecule on the surface.

Synthesis, Structure and Electrochemical Properties of Garnet-like Lithium Conductor Li7-X-3yAl y La3Zr2-X Ta x O12

Fast lithium-ion conductors are key materials for the development of next generation energy storage devices such as all-solid-state lithium secondary batteries and rechargeable lithium-air batterie[1,2]. Among the fast lithium-ion conductors reported, garnet-like Li7La3Zr2O12 (LLZ) and its derivatives are one of the most promising materials because of their excellent chemical and electrochemical stability with lithium metal[2,3]. The substitution of Ta5+ in LLZ results in the highest ionic conductivities among the garnet-like compounds[3,4]. However, the contamination of Al3+ from Al2O3 crucible occurs during the synthesis. The difficulty in the determination of the Li+ and Al3+contents has impeded understanding of the conduction properties of these compounds. Therefore, we have investigated the phase relation in the Li7-x-3y Al y La3Zr2-x Ta x O12 system. We began by investigation of the phase relations in the pseudo-binary Li5La3Ta2O12–Li7La3Zr2O12 system, and then extended the investigation to the Al-doped system. Al-free Li7-x La3Zr2-x Ta x O12 pellets were fired in a magnesia crucible to avoid contamination with Al. To prevent the formation of the low-temperature cubic phase, which is easily formed by the Li+/H+exchange reaction with moisture in air below 400 °C, the samples obtained were annealed in an inert atmosphere prior to measurements. The structure and conduction properties of these compounds were then investigated using neutron diffraction, and AC impedance and nuclear magnetic resonance (NMR) spectroscopies. The relationship between the structure and ionic conductivity is discussed based on the results obtained. Polycrystalline Li7-x-3y Al y La3Zr2-x Ta x O12 (x = 0–2.0, y = 0–0.14) was synthesized by solid-state reaction. Phase identification was conducted using XRD (Rigaku RINT 2500 and Bulker D8) with Cu Kα radiation. Diffraction data were collected at each 0.02° step width in the 2θ range from 10 to 80°. Neutron diffraction data were corrected using time-of-flight (TOF) diffractometers: iMATERIA (BL20). Structural parameters were refined using the Rietveld refinement programs Z-Rietveld and Topas Ver. 4 for neutron diffraction and XRD data, respectively. The Li, La, Zr, Ta, Mg and Al compositions were analyzed using inductivity coupled plasma-optical emission spectroscopy (ICP-OES; Agilent Technologies ICP-OES 710). The ionic conductivity was measured by the AC impedance method using a frequency response analyzer (Solartron 1260) in the frequency range of 0.1 Hz to 1 MHz and in the temperature range from -20 to 100 °C in an inert gas atmosphere. Lithium diffusion in the bulk was determined from pulsed-gradient spin-echo (PGSE) NMR measurements. The tetragonal phase formed at x = 0–0.375 and the cubic phase appeared with x = 0.4–2.0 in the Li7-x La3Zr2-x Ta x O12 system. In the Al-doped system of Li7-x-3y Al y La3Zr2-x Ta x O12, the tetragonal phase was formed at x + 3y < 0.4. The border between the tetragonal and the cubic phases exists at Li6.6-z/2Al z /2La3Zr1.6+z Ta0.4-z O12. The tetragonal/cubic structure change corresponds to the order/disorder of lithium ions and is dependent on the cation content at the lithium sites. The ionic conductivity of the cubic compounds has a positive tendency with respect to the lithium content, whereas that of the tetragonal compounds is opposite. A high total ionic conductivity exceeding 5.0 × 10-4 S cm-1 at 25 °C was observed for Al-doped Li6.6-z/2Al z /2La3Zr1.6+z Ta0.4-z O12. The highest total conductivity of 1.03 × 10-3 S cm-1 at 25 °C with an activation energy of 0.35 eV was obtained at z = 0.275. Nuclear magnetic resonance spectroscopy revealed that Al3+ substitution decreases the diffusion of lithium ions in the structure. The high total conductivity of Al-doped Li6.6-z/2Al z /2La3Zr1.6+z Ta0.4-z O12may be due to the enhancement of lithium diffusion at the grain boundaries. This work was partly supported by the Japan Science and Technology Agency (JST) under the project “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA Spring)”. [1] K.H. Kim, Y. Iriyama, K. Yamamoto, S. Kumazaki, T. Asaka, K. Tanabe, C.A.J Fisher, T. Hirayama, R. Murugan and Z. Ogumi, J. Power Sources, 2011, 196, 764. [2] K. Ishiguro, H. Nemori, S. Sumahiro, Y. Nakata, R. Sudo, M. Matsui, Y. Takeda, O. Yamamoto and N. Imanishi, J. Electrochem. Soc., 161(5)(2014) A668. [3] R. Murugan, V. Thangadurai and W. Weppner, Angew. Chem. Int. Ed., 46(2007) 7778. [4] Y. Wang and W. Lai, Electrochem. Solid-State lett., 15 (2012) A68.

High-temperature laser coatings of the ZrB2–MoSi2 system on graphite

Coatings of the ZrB2–MoSi2 system on graphite (≤ 50 μm thick and 14–15 GPa in hardness) have been produced by pulse laser melting in air of two-layer powder coating with sublayers based on ZrB2 with additions of ZrSi2 and SiC. Different coating structures: eutectics of the ZrSiO4–SiO2 system based on zircon or a structure of micron-thick fibers of composition Zr(Mo)B2 are formed depending on the sublayer composition, which controls the coating heat conductivity and accordingly, the crystallization rate of the bath of melt. The prospects of this line of investigations are the improvement of a laser technology of the deposition of high-temperature coating using continuous wave lasers.

Group 4 complexes of salicylbenzoxazole ligands as effective catalysts for the ring-opening polymerization of lactides, epoxides and copolymerization of ε-caprolactone with L-lactide

A series of salicylbenzoxazole pro-ligand 2-(5-X-benzoxazol-2-yl)-6-R1-4-R2-phenol, L1H-L4H were subjected to reaction with titanium, zirconium and hafnium alkoxides. The substituents (R1, R2, X) present in the pro-ligand back bone are (H, H, H) for L1H; (H, H, Cl) for L2H; (Br, Br, H) for L3H; and (Cl, Cl, H) for L4H. The mononuclear Ti complexes, 1a-4a of [M(L)2(OiPr)2] formulation were prepared by combining the pro-ligands L1H-L4H with Ti(OiPr)4 in dry toluene. However, with the addition of H2O (0.5 M equiv.), the controlled hydrolysis of Ti complex 4a in a mixed solvent of THF/toluene produced oxo-bridged dinuclear Ti complex 5a having [M(μ-O)(L)2(OiPr)]2 formulation in good yield (≥75%) using L4H as the pro-ligand. The composition of the mononuclear Zr and Hf complexes of L1H-L4H are found to be quite similar to that of the Ti complexes. Additionally, mononuclear Zr complexes 1b-4b and Hf complexes 1c-4c were prepared. The oxo-bridged dinuclear Zr and Hf complexes 5b and 5c were isolated from the controlled hydrolysis reactions of mononuclear Zr and Hf complexes 4b and 4c. All these complexes were well characterized and crystal structure of six of the fifteen complexes were determined. These complexes were used as initiators for the ring-opening polymerization (ROP) of rac-LA, copolymerization of L-LA with ε-CL and homopolymerization of rac-epoxides. In particular, the dinuclear Zr complex (5b) was found to exhibit extremely high activity in these polymerization studies. Iso-enriched polymers were observed upon using the Zr and Hf complexes of the pro-ligands L3H or L4H as the initiator. DFT studies have been carried out on the ROP of lactides initiated by the Ti, Zr and Hf complexes 1a, 1b and 1c. The results indicated that the activation barrier to reach the transition state using Zr complexes is lower and hence facile as compared to the Ti and Hf complexes.

Thermal desorption behaviors of helium in Zr-Co films prepared by sputtering deposition method

The amorphous ZrCo films on Mo substrates with different 4He content were prepared through direct current (DC) magnetron sputtering deposition method. The atomic compositions of Zr, Co and He in Zr-Co films were measured using Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA), respectively. The helium desorption behaviors in the films were investigated. Microstructural changes during THDS measurement were analyzed with grazing incidence X-ray diffraction (GIXRD). It was found that ZrCo2 phase, an important disproportionation product in ZrCo hydriding-dehydriding process, was formed during the THDS experiment in a rising temperature range of 300 K–1323 K. The helium desorption signals can be evidently divided into three main zones and represent different trapping states. Synchronous desorption of hydrogen and helium was observed.

Development of Zr[sbnd]Fe[sbnd]V alloys for hybrid hydrogen storage system

The combination of unstable hydrogen storage materials with a high pressure tank provides a potential solution to on-board hydrogen storage system for fuel cell vehicles. However, none of the available solid-state materials can fulfill all the requirements. In this work, ZrFeV-based alloys were systematically investigated for the possible use in such kind of hybrid storage devices.Among these alloys studied here, the composition (Zr0.7Ti0.3)1.04Fe1.8V0.2 shows the best overall properties with a reversible hydrogen capacity of 1.51 wt%, and a hydrogen desorption pressure of 11.2 atm at 0 °C. Besides, this alloy also shows excellent stability without obvious capacity loss even after 200 hydrogen absorption/desorption cycles. Calculated results show that the gravimetric density of the hybrid storage system combining a 35 MPa high pressure tank with (Zr0.7Ti0.3)1.04Fe1.8V0.2 alloy is 1.95 wt% when the volumetric density reaches 40 kg/m3.

Structure-modulated ionic transport behavior in zirconia–dysprosia mixed oxides

In the present study, we report a systematic study on Zr1−xDyxO2−x/2 system exploring the effect of structure on ion-transport. All the compositions were synthesized by combustion route followed by high-temperature sintering and thoroughly characterized by X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and AC impedance studies. These studies revealed a phase relation wherein Zr0.9Dy0.1O1.95 exhibited coexistence of a monoclinic and cubic phase. The Dy3+ content greater than 10 mol% led to complete stabilization of cubic zirconia solid solutions. The structural evolution has also been monitored with Raman spectroscopy wherein very weak pyrochlore-type ordering in compositions with x ≥ 0.4 could be observed even when XRD showed a fluorite-type structure. The effect of structure-induced conductivity control was revealed by AC impedance analysis which bestowed a high ionic conductivity, 0.0048 Scm−1 at 700 K, on the nominal composition Zr0.8Dy0.2O1.90. This has been attributed to a very high disorder prevailing in this system due to the substitution of Zr4+ by Dy3+. It was revealed that the ionic conductivity behavior was driven by high pre-exponential factor which led to substantially high ionic conductivity for Zr0.8Dy0.2O1.90 despite almost equal activation energies observed for all the nominal compositions studied. Such high ionic conductivity for a zirconia-based system makes it a potential candidate for electrolyte for intermediate-temperature solid oxide fuel cell, as they are inherently stabler than ceria-based electrolytes.

Effect of torsion conditions under high pressure on the structure and strengthening of the Zr–1% Nb alloy

The effect of temperature and degree of deformation upon severe plastic deformation by torsion under a high pressure on the structure, phase composition, and microhardness of the industrial zirconium Zr–1% Nb alloy (E110) has been studied. The high-pressure torsion (HPT) (with N = 10 revolutions) of the Zr–1% Nb alloy at room temperature results in the formation of grain–subgrain nanosize structure with an average size of structural elements of 65 nm, increase in the microhardness by 2.3–2.8 times (to 358 MPa), and α-Zr → β-Zr and α-Zr → ω-Zr phase transformations. The increase in the HPT temperature to 200°C does not lead to a decrease in the microhardness of alloy owing to the increase in the fraction of ω-Zr phase, though the average size of structural elements increases to 125 nm. The increase in the temperature to 400°C during HPT with N = 10 revolutions leads to the grain growth in the α-Zr grain structure (~90%) to 160 nm and a decrease in the microhardness to 253–276 HV.