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The optimization of sintering behaviour of iron chalcogenides superconducting materials is mandatory to enhance their critical current density, in order to pursuit their application in the production of superconducting wires. In this context it has been investigated here the effect of oxygen contamination on the material densification, considering the issues related to industrial oxygen-free isolated production lines. Our results show that the densification process is negatively affected by oxygen contamination. However, despite the difference in density, all sintered samples are characterized by similar structural and morphological features, and show comparable electrical and magnetic properties, with low critical current densities (Jc3 A/cm2). These results suggest that densification is not the key limiting factor in these conditions, and that grain boundary or misorientation factors may play a greater role in limiting the performance of sintered iron chalcogenides superconductors.

In this paper, the effect of post synthesis annealing treatments on a Fe(Se,Te) polycrystalline material is evaluated and discussed. The samples have been obtained via melting route. The material has been subjected to a high-temperature annealing treatment, carried out for 45 h at 680 °C. The role of the cooling step was investigated comparing samples obtained after a controlled cooling or after quenching in liquid nitrogen. From a morpho-structural point of view, the annealing treatment improves homogeneity, with respect to pristine samples, and influences secondary phase precipitate morphology. Regarding superconducting properties, a key role of the cooling procedure is assessed: controlled cooling leads in fact to a significant improvement of high field behaviour with respect to the melted material, while quenched samples are characterized by a worsening of the superconducting properties. Despite the overall worsening, however, the quenched samples show evidence of the presence of superconducting phases characterized by a remarkably high critical temperature (Tc > 18 K), observed for these materials only in films or under pressure.

Superconducting properties of the Fe(Se,Te) system are directly related to its microstructure. However, in the framework of a not well assessed phase diagram, a large spread of chemico-physical and functional properties is reported for compounds characterized by similar overall chemical compositions. This is in particular observed in materials produced by melting routes, where chemical inhomogeneities and multiple phases are commonly obtained. Both composition and morphology of these inhomogeneities seem to play a role in the behaviour of the superconducting phases, pointing out the need to assess the dependence of phase composition and therefore of the material performance on the sample thermal history. In this work, the effect of different post-synthesis annealing treatments is studied. A melting route has been adopted to synthesize polycrystalline samples, subsequently subjected to thermal treatments at different temperatures. Morphology and microstructure were characterized by means of x-ray diffraction and microscopy techniques. The superconducting properties have been evaluated by means of electrical and magnetic measurements. It is observed how microstructure, chemical composition and morphology of the obtained products strictly depend on the annealing temperature. Moreover, a crucial role of the cooling step is evidenced: in fact, a rapid cooling procedure from high temperature leads to the formation of high temperature (Tconset > 19 K) superconducting phases, but the overall bulk superconducting performance is negatively affected. Other annealing treatments can promote instead an enhancement in the critical current at high fields with respect to pristine sample, suggesting that a careful engineering of a post-synthesis thermal step can represent a useful tool to optimize the material properties.

The present work investigates the effect of heat treatments in air on the surface and structure of titanium hydride (TiH2) and hydrogen desorption. TiH2 has been heated in air at 440 and 540 °C for increasing time up to 180 min. to obtain the samples representative of 12 different oxidation conditions. The samples have been then examined by Temperature Programmed Desorption (TPD), X-Ray Diffraction (XRD) and Photoelectron Spectroscopy (XPS). Experimental results are presented and discussed.

This study is focused on the phase separation phenomena in Fe(Se,Te) materials. In particular, it investigates the effect of a high temperature and long time annealing treatment on morphostructural and superconducting properties of bulk samples. The synthesis of Fe(Se,Te) compounds was carried out through a melting route, and the materials were characterized in their morphostructural and magnetic properties. The obtained compounds possess a high degree of inhomogeneity due to dendritic precipitates of secondary phases in a superconducting tetragonal matrix. The high temperature annealing treatment induces a morphological evolution of the material and leads to the structuration of two distinct superconducting phases.

In this work we report the crystallization of iron chalcogenides compounds starting from a Fe(Se0.5Te0.5) solid pellet. The synthesis process is carried out at 675 degrees C using a molten chloride salts mixture and permitted to obtain well defined and easily separated hexagonal and tetragonal crystals, characterized by Fe-3(Se0.43Te0.57)(4) and Fe1.02Se0.41Te0.59 compositions respectively. The obtained tetragonal compound exhibits superconductivity at 14 K with critical current density of similar to 10(5) A/cm(2) at 5 K.

In the effort to unveil the relations between synthesis conditions, morpho-structural features and superconducting properties of (11)-type iron-based superconductors, this study is focused on FeSe0.5Te0.5 materials obtained from high-temperature melts and different cooling rates. Crystalline and chemical composition are evaluated by means of XRD and SEM analyses, highlighting the formation of complex multiphase structures: the obtained results suggest that high-temperature nucleating phases may play a key role in the observed phase separation. Superconducting properties, evaluated by magnetization measurement and dc electrical resistance in different magnetic field conditions up to 18 T, highlight the low homogeneity of the superconducting phases, reflecting the microstructural observation. © 2002-2011 IEEE.

In spite of their favourable chemical characteristics, using AB5 alloys as fixed bed for hydrogen storage devices requires proper management of a number of technological aspects. Among these, the mechanical stability of metal particle grains under hydrogen cycling and the overall thermal conductivity of the material bed constitute crucial features. We developed by High Energy Ball Milling HEBM a mechanically stable silica-based AB5 composite with enhanced thermal conductivity. Here, focusing on the material’s physical-chemical properties, we report on the silica-AB5 composite development and characterization. Particularly, we studied the material consolidation process, the resulting composite morphology and the system behaviour under hydrogen loading/unloading cycling.

The transformation of mixed sodium manganese ferrite into manganese ferrite induced by carbon dioxide was investigated. The reaction was performed in controlled conditions at different temperatures (600 °C and 800 °C). Transformation kinetics were followed in terms of powder composition evolution and weight gain by in-situ high temperature X-ray diffraction and thermogravimetric analysis respectively. Differently than expected by the reaction stoichiometry, the comparative analysis of the obtained experimental results reveals that sodium carbonate and manganese ferrite compounds formation is asynchronous. A mechanism describing mixed sodium manganese oxide transformation into manganese ferrite following sodium extraction by carbon dioxide is proposed and discussed.

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be prepared from peroxy lithium titanate solution (stabilized with citric acid) by a modified INCT (Institute of Nuclear Chemistry and Technology) variant of the sol–gel process. The process consists of the following main steps: (I) formation of aqueous phase emulsion in 2-ethylhexanol-1; (II) gelation of emulsion drops by extraction of water with partially dehydrated EH; (III) filtration and washing with carbon tetrachloride or acetone; (IV) non-destructive thermal treatment. The medium size particles can be used for increasing pebble bed density by infiltration them into bed larger spheres (1 mm diameter). The tritium release from sol–gel process preparation of Li2TiO3 microspheres was found very close to that observed for other traditional material however, the new process is more efficient than other processes because of the morphology of the sintered specimens.

Application of Li 2 TiO 3 pebbles was proposed in the Japanese and European blanket design of a fusion reactor. The wet process and direct sol–gel methods are most advantageous from viewpoints of low-cost mass fabrication, reprocessing of lithium-bearing solution and removal of radioactive isotopes. Previously, the target density (80–85% T.D.) of Li 2 TiO 3 pebbles was achieved in the preliminary fabrication test; however, the grain size of Li 2 TiO 3 pebbles was larger than 5 μm and low sphericity. Therefore, the fabrication tests of Li 2 TiO 3 pebbles by the direct-wet process were continued, focusing the effects on dissolving process of Li 2 TiO 3 , dropping of the solution into coagulant and drying/calcinating and sintering processes of the droplet for high sphericity and decreasing the cracks of Li 2 TiO 3 pebble surface.

Nanostructured MnFe 2 O 4 was prepared by high-energy ball milling of a stoichiometric mixture of MnO and Fe 2 O 3 powders and characterized by XRD, TEM and TGA techniques. The ball milling process leads to strained nanocrystals with an average size of about 5 nm, agglomerated in sizes of about 100 nm. It was used with mechanically activated Na 2 CO 3 to produce hydrogen from water in the temperature range 973–1073 K. At 1023 K the mixture shows a hydrogen production five times higher than that obtained with manganese ferrite prepared by thermally activated solid-state reaction.

Nanocrystalline MnFe 2 O 4 particles were synthesized by a high-energy ball milling technique, starting from a manganosite (MnO) and hematite (α-Fe 2 O 3 ) stoichiometric powder mixture. The mechanosynthesis process was performed at room temperature both in hardened steel and in tungsten carbide vials. X-ray powder diffraction quantitative phase analysis by the Rietveld method was used to study the chemical transformations promoted by the milling action. The nanocrystalline MnFe 2 O 4 spinel phase begins to appear after 10 h of milling and reaches its maximum content (≈0.8 molar fraction) after 35 h of milling. A prolonged milling time induces a dramatic contamination of the powder mixture, when hardened stainless steel was adopted, due to metallic iron originating from vial and balls debris. Ball milling is able to induce a redox reaction between Fe III and metallic iron, transforming the MnFe 2 O 4 spinel phase into a wustite type (Fe, Mn)O phase. The yield of the hydrogen production reaction on synthetised materials is reported.

Lithium titanate (Li2TiO3) has attracted the attention of many researchers because of good tritium recovery at low temperature, chemical stability, low tritium inventory, etc. In this work, the effects of TiO2 doping of Li2TiO3 on the resistance to the environmental attack in air and hydrogen reduction under Ar+0.1%H2 flow were examined. Based on the results, the TiO2 doping (from 3.7 to 30 wt%) was found to improve the resistance to the environmental attack for very long exposure times in air at room temperature. The hydrogen reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 °C and that of Li4Ti5O12 was higher in the temperature range from 800 to 950 °C.

The rate of tritium release from Li2TiO3 pebbles was examined by post irradiation thermal desorption spectroscopy (the Temperature Programmed Desorption (TPD) method). Pre-treatments before and even after irradiation were found useful to gain insight on the behavior of these pebbles at different temperatures, as good spectrum de-convolution is achieved and kinetic parameters for the rate determining pseudo-first-order steps can be estimated. We show the results concerning Li2TiO3 pebbles bed specimens developed in the frame of the European fusion technology program.

The application of Li2TiO3 pebbles (diameter: 0.2–2 mm, density: 80–85%T.D., grain size

Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

A process for obtaining Li 2 CO 3 from Li 2 TiO 3 powder by wet chemistry was developed. This is considered useful in view of the recovery of the 6 Li isotope from lithium titanate breeder burned to its end of life in a fusion reactor. The process was optimized with respect to the chemical attack of titanate and the precipitation of carbonate from aqueous solutions to get a powder with chemical and morphological characteristics suitable for its reexploitation in the fabrication of Li 2 TiO 3 pebbles. Reprocessing was also planned to adjust the 6 Li concentration to the desired value and to obtain a homogeneous distribution in the powder batch. Further development concerning reprocessing of sintered Li 2 TiO 3 pebbles is in progress exploiting the results obtained with lithium titanate powders.

Medium sized spherical particles of Li2TiO3 (with diameters below 100 μm) can be fabricated by a classical, inorganic sol-gel process, from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li : Ti molar ratio (MR) = 2; (5) thermal treatment at 1200°C. This temperature can be significantly lowered (to 750°C) by chemical treatment of chloride precursors (gels or starting solution TiCl4) with aq. ammonia or better with nitric acid. Tritium release from sol-gel made Li2TiO3 micro-spheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.

The reduction of Li 2 TiO 3 to Li 2 TiO 3− x at 800 °C by He+H 2 (0.1%) purge gas was studied with Li 2 TiO 3 pebbles. The evolution of O-vacancy concentration ( x ( t )) allowed extrapolation to the steady-state value x ( t →∞)=0.0096 which was found to be independent from the material microstructure, while the process rate and its mechanism were found to depend on the grain size, porosity and sintering temperature of the pebbles. The temperature of tritium removal from the so-treated (reduced) pebbles was found to be higher than those from the oxidized (stoichiometric) ones, the increase of x being accompanied by an increase in the population of more energetic tritium trap sites at the grain boundary interface of the material. However, this phenomenon should not be of concern under ‘normal’ breeding blanket operating conditions.

A model has allowed us to perform the analysis of the tritium inventory and permeation in the international thermonuclear experimental reactor (ITER) breeding blanket under the hypothesis of steady state conditions. Li 2 ZrO 3 (reference) and Li 2 TiO 3 (alternative) have been studied as breeding materials. The total breeder inventory assessed is 7.64 g for the Li 2 ZrO 3 at reference temperature. The model has also been used for a parametric analysis of the tritium permeation. At reference temperature and purge helium velocity of 0.01 m/s, the HT partial pressure is ranging from 10 to 30 Pa in the breeder and 1.5×10 −3 Pa in the beryllium. At 0.1 m/s of purge helium velocity, the HT partial pressure is reduced of one order by magnitude in the breeder and becomes 5×10 −5 Pa in the beryllium. The tritium permeation into the coolant for the whole blanket is ranging from 100 to 250 mCi per day for purge helium velocity of 0.01 m/s. The analysis of the tritium inventory and permeation for the alternative Li 2 TiO 3 breeding material has been carried out too. The tritium inventory in the breeder is in the range from 6 to 375 g larger than in Li 2 ZrO 3 by about a factor 5; the tritium permeation into coolant is comparable to the Li 2 ZrO 3 one. This analysis provides indications on the influence of the operating parameters on the tritium control in the ITER breeding blanket; particularly the control of the tritium inventory by the temperature and the tritium permeation by the purge gas velocity.

YBa 2 Cu 3 O 7−δ was synthesised using a solution method. The coprecipitation of the stoichiometric amounts of nitrate solution of yttrium, barium and copper was performed using a mixture of NaOH, Na 2 CO 3 and H 2 C 2 O 4 in a molar ratio 5:1:1 as precipitation agent. The as-obtained precursors have a copper deficiency of 0.1 with respect to the nominal stoichiometry of the starting solution. The mechanistic study of the product formation has revealed that in these atomically mixed precursors the individual components have a different behaviour with respect to those in a mechanical mixture. The final products was obtained after heat treatment at 950°C for 6 h in oxygen atmosphere. The product was analyzed by XRD, SEM, EDXS and four probe DC resistivity measurements. The as-synthesised YBCO has shown good superconducting properties T c ( R = 0) = 90.5 K and ΔT = 1 K. This method was used with success in the fabrication of YBCO target for laser ablation.

Spherical powders of hydroxyapatite with particle diameters below 100 μm were prepared using the water extraction variant of the sol-gel process. A freshly prepared solution of calcium acetate and phosphoric acid (molar ratio Ca/P = 1.67) was emulsified in dehydrated 2-ethyl-1-hexanol. Drops of the emulsion were solidified by extraction of water with this solvent. The process was carried out continuously. The separated gel particles were calcined to hydroxyapatite particles with preservation of the spherical shape. This process was studied using differential thermal analysis, thermal gravimetric analysis, X-ray diffraction analysis and infrared spectroscopy. During thermal treatment, the formation of calcium carbonates is observed first. Above 400°C, the formation of hydroxyapatite starts and then at 580°C formation of carbonate hydroxyapatite starts. The last step, decomposition to hydroxyapatite, proceeds above 750°C.

Hydrogen production by water-splitting thermochemical cycle based on manganese ferrite/sodium carbonate reactive system is reported. Two different preparation procedures for manganese ferrite/sodium carbonate mixture were adopted and compared in terms of material capability to cyclical hydrogen production. According to the first procedure, conventionally synthesized manganese ferrite, i.e., high temperature (1250°C) heating in Ar of carbonate/oxide precursors, was mixed with sodium carbonate. The blend was tested inside a temperature programed desorption reactor using a cyclical hydrogen production/material regeneration scheme. After a few cycles, the mixture resulted rapidly passivated and unable to further produce hydrogen. An innovative method that avoids the high temperature synthesis of manganese ferrite is presented. This procedure consists in a set of consecutive thermal treatments of a manganese carbonate/sodium carbonate/iron oxide mixture in different environments (inert, oxidative, and reducing) at temperatures not exceeding 750°C. Such material, whose observed chemical composition consists of manganese ferrite and sodium carbonate in stoichiometric amounts, is able to evolve hydrogen during 25 consecutive water-splitting cycles, with a small decrease in cyclical production efficiency.

Thin films of YBa 2 Cu 3 O y have been grown in situ on (100) SrTiO 3 and (100)MgO, by pulsed excimer laser evaporation from a stoichiometric target. The substrate temperature was adjusted at 750°C by using a CO 2 laser as the heating source and the oxygen partial pressure during the deposition was about 0.3 mbar. The samples have been patterned in the shape of lines 0.2 mm long and of widths between 5μm and 20μm. DC transport critical currents have been investigated as a function of temperature and of applied magnetic field up to 6T.

The rate of tritium release from Li-ceramics, measured by in-situ and out of pile tests, is reported. The data are related to the nature (LiAlO2 vs. Li2ZrO3) and the microstructure of the materials, as well as to the helium purging gas composition (hydrogen vs. water-hydrogen mixtures). Li2ZrO3 releases tritium much better than LiAlO2. In both cases the rate constant is proportional to the grain size. Moist helium is confirmed to be an effective tritium removing sweeping gas.

The mechanical properties (compressive and bending strengths, sound velocity) have been determined for gamma-LiAlO/sub 2/ pellets produced by different processes at various porosities. A correlation between nondestructive measurements and mechanical strength has been obtained.

The gamma-LiAlO/sub 2/ ceramic material is the reference candidate for the solid breeder option of the Next European Torus Program. The experiments and methodologies developed in Italy to produce high surface area gamma-LiAlO/sub 2/ powders to be compacted by cold pressing and sintering at 70 to 90% of the theoretical density, keeping a near fully open porosity is presented. The lithiating step was assessed for the Li/sub 2/CO/sub 3/ and Li/sub 2/O/sub 2/ precursors reacting with Al/sub 2/O/sub 3/ having submicron grain size. Sol-gel methodologies were also developed for the gamma-LiAlO/sub 2/ preparation by which very high surface area ceramic grade powders were obtained.

It is well known that the oxygen content exherts a critical role in determining the electrical characteristics of the perovskite cuprate superconductors. However, the formal oxidation state of copper in the compounds as well as the mechanism of oxygen incorporation in their structure, are still a matter of discussion. In this work, we propose two possible disorder equilibria in the 400°C to 525°C temperature range and attempt to substantiate them by experimental evidence.

Titanium oxide and titanates based on Ba, Sr and Ca were prepared from commercial solutions of TiCl4 and HNO3. The main preparation steps for the sols consisted of elimination of chloride anions by distillation with nitric acid and addition of metal hydroxides for the titanates. Resulting sols were gelled and used to (1) prepare irregularly shaped powders by evaporation; (2) produce by a dipping technique thin films on glass, Ag, or Ti substrates; and (3) produce spherical powders (diameters

Transport properties as: normal state resistance, transition temperature and critical current density in weak applied field, of ceramic YBa 2 Cu 3 O y samples, sintered under different conditions, have been investigated. Sintering temperatures ranging from 900°C to 970°C have been used. For each temperature the sintering time has been determined by monitoring the sample resistance in situ during the process. The slope of the R vs T dependence has a maximum value for a sintering temperature between 920°C and 930°C. Although the samples sintered at 900°C have a lower density, they exhibit the highest current density.