Inelastic neutron scattering from Tl2CaBa2Cu2O8

Coherent inelastic neutron scattering measurements have been carried out on the high temperature superconductors Tl₂CaBa₂Cu₂O₈ (Tl-2122,T _c =107 K) and YBa₂Cu₃O₇ (Y-123,T _c =92 K), at the Dhruva reactor at Trombay. The density of phonon states in Tl-2122 is enhanced at 6–17 meV and reduced at 40–70meV compared to that in Y-123.     

Recovery of 1 2 5Sb from Neutron-Irradiated 1 2 4Sn

Recovery of ^{1 2 5}Sb from metallic tin (96% enrichment with ^{1 2 4}Sn) irradiated in a nuclear reactor (specific activity 5 mCi g^{- 1}) was studied. Irradiated tin was dissolved in concentrated HCl with addition of H₂O₂ or Br₂; dissolution was monitored with ^{1 1 9 m} Sn tracer. The separation of ^{1 2 5}Sb and tin was studied using strongly basic (Dowex-50, AV-17), moderately basic (AN-2FN), and weakly basic (AN-31) anion exchangers with HCl, HCl + HBr, and HNO₃ eluents. In the case of strongly basic anion exchangers, the separation coefficients of ^{1 2 5}Sb from tin reached 10⁴-10⁵ in a single cycle. From for AN-31 weakly basic anion exchanger, tin was almost completely removed with 0.8 M HCl; the yields of tin and ^{1 2 5}Sb were 99 and 98%, and the content of ^{1 2 5}Sb in tin was no more than 0.1% of the initial activity.     

Cathodoluminescence from crystalline phases in a ZrO2-SiO2-CeO2 ceramic

The chemical composition of crystalline phases in a ZrO₂-SiO₂-CeO₂ ceramic was determined by electron probe x-ray microanalysis, and the luminescent properties of these phases were studied. The valence state of Ce in these phases was determined from cathodoluminescence data.     

Preparation of SiC ultrafine particles from SiH2Cl2 and C2H4 gas mixtures by a CO2 laser

Preparation of SiC ultrafine particles from SiH₂Cl₂-C₂H₄ mixtures by a CO₂ laser was investigated. The powders with specific surface area in the 8–150 m² g^–1 range were obtained by irradiating SiH₂Cl₂-C₂H₄ gas mixtures with a CO₂ laser at atmospheric pressure. X-ray diffraction of the products showed that silicon, SiC and free carbon were produced and the composition of the powders depended on the C₂H₄/SiH₂Cl₂ ratio. The reaction flame temperature changed from less than 1273 K to more than 3073 K with the laser power density and C₂H₄/SiH₂Cl₂ ratio. When SiH₂Cl₂ was irradiated with the CO₂ laser, the reaction temperature was less than 1273 K and silicon particles were formed. When the SiH₂Cl₂-C₂H₄ mixture was irradiated with a CO₂ laser, the reaction temperature was low (<1273 K) at low power density and low C₂H₄/SiH₂Cl₂ ratio, but it increased rapidly to around 3000 K at high laser power density and high C₂H₄/SiH₂Cl₂ ratio (>0.3). SiC was formed at both high and low reaction flame temperatures. It was considered that the rapid increase in the reaction flame temperature was caused by the initiation of exothermic reactions and the increase in laser absorption which was caused mainly by carbon particle formation. Hysteresis was observed between the reaction flame temperature and the power density of the laser beam. It was found that SiH₂Cl₂ underwent a disproportionation reaction on irradiation with the CO₂ laser, and silicon and SiC particles were formed through the various products of the disproportionation reaction. In particular, at low reaction flame temperature, the reactive species, such as SiH₄ and SiH₃Cl, produced by the disproportionation of SiH₂Cl₂ were considered to play an important role in the formation of silicon and SiC particles.     

Mullite formation from highly homogeneous mixtures of Al2O3 and SiO2

Mullite, 3A1₂O₃ · 2SiO₂, was synthesized by heat-treating homogeneous sol-gel-derived mixtures of A1₂O₃ and SiO₂ taken in stoichiometric amounts. To reduce the mullitization temperature, sols containing γ-AlOOH and SiO₂ nanoparticles (2 to 20 nm) were used in the preparation of the mullite precursors. A few samples were made using the products of hydrolysis of aluminum salts instead of the γ-AlOOH sol. The process parameters determining the homogeneity of the precursor mixtures were revealed. The preparation conditions ensuring mullite crystallization at temperatures between 1200 and 1250°C were found. The results are discussed in terms of the reaction between A1₂O₃ and SiO₂ during mullitization.     

Simple synthesis of MoS2 inorganic fullerene-like nanomaterials from MoS2 amorphous nanoparticles

The amorphous MoS₂ nanoparticles have been synthesized by a simple oxidation–reduction reaction in an aqueous solution. A series of products with different morphologies, such as MoS₂ nanospheres, inorganic fullerene-like nanospheres, nanorods and Mo bended rods, can be obtained by annealing the amorphous MoS₂ nanoparticles under N₂ atmosphere under 400–1200 °C. These products have been characterized by X-ray diffraction, field emission scanning electronic microscopy, transmission electron microscopy and high-resolution transmission electron microscopy in detail. The possible transformation mechanism for the structure has been discussed based on the experimental results. In addition, the optical properties of IF-MoS₂ have also been performed by UV–vis absorption spectroscopy.     

Multiparticle tunneling during field electron emission from Bi2CaSr2Cu2O8

An analysis of data on the experimental statistics of the field electron emission (FEE) from an oxide superconductor of the Bi₂CaSr₂Cu₂O₈ system reveals the multielectron tunneling effect. The spectral curves and statistical data obtained under various experimental conditions are considered, and possible mechanisms of the multiparticle tunneling are discussed.     

Preparation of porous supports in the SiO2-ZrO2-Na2O system from microspherical silica gels

Preparation of porous supports in the SiO₂-ZrO₂-Na₂O system was investigated using a commercially available silica gel as a starting material. The microspherical silica gel, impregnated with ZrOCl₂ and NaCl, was heated and subsequently washed with water. Porous supports, composed with sponge-like skeletons on the surface of the particles, were obtained owing to suppression of crystallization of the supports as well as their sintering. Similar supports were formed using a silica gel prepared from sodium silicate solution by the same procedure. In contrast, crystallization of silica proceeded in supports prepared by heating the mixture of silica gel and NaCl in the absence of ZrOCl₂. A new method for preparing the analogous supports was also investigated by heating a mixture of silica gel impregnated with ZrOCl₂ and Na₂CO₃ powder.     

Crystallization of nanosized Aurivillius phase Bi2W2O9 from amorphous precursor

Nanoparticles of bismuth layered Aurivillius phase, Bi₂W₂O₉, have been synthesized by annealing of precursor prepared by high energy milling in ball mill. The obtained powders have been investigated using the XRD, TEM, SEM, diffuse reflectivity, Raman and infrared spectroscopy. The results show that mechanochemical activation allows obtaining Bi₂W₂O₉ at much lower temperatures than those required in a conventional solid state reaction or synthesis through a complex organic precursor. As a result, material with smaller grain size can be obtained. Therefore this synthesis method is the best route to enhance photocatalytic activity of Bi₂W₂O₉. Our results also show that milling time has great impact on the crystallization mechanism. Bi₂W₂O₉ crystallizes easily already at 600 °C from precursor milled by 8 h. However, prolong milling time results in stabilization of an unknown phase or phases, which crystallize below 700 °C, and transform into the well-known Bi₂W₂O₉ phase after annealing at 750 °C.     

Lattice Transformation from 2D to Quasi 1D and Phonon Properties of Exfoliated ZrS2 and ZrSe2

Recent reports on thermal and thermoelectric properties of emerging 2D materials have shown promising results. Among these materials are Zirconium-based chalcogenides such as zirconium disulfide (ZrS₂), zirconium diselenide (ZrSe₂), zirconium trisulfide (ZrS₃), and zirconium triselenide (ZrSe₃). Here, the thermal properties of these materials are investigated using confocal Raman spectroscopy. Two different and distinctive Raman signatures of exfoliated ZrX₂ (where X = S or Se) are observed. For 2D-ZrX₂, Raman modes are in alignment with those reported in literature. However, for quasi 1D-ZrX₂, Raman modes are identical to exfoliated ZrX₃ nanosheets, indicating a major lattice transformation from 2D to quasi-1D. Raman temperature dependence for ZrX₂ are also measured. Most Raman modes exhibit a linear downshift dependence with increasing temperature. However, for 2D-ZrS₂, a blueshift for A1g mode is detected with increasing temperature. Finally, phonon dynamics under optical heating for ZrX₂ are measured. Based on these measurements, the calculated thermal conductivity and the interfacial thermal conductance indicate lower interfacial thermal conductance for quasi 1D-ZrX₂ compared to 2D-ZrX₂, which can be attributed to the phonon confinement in 1D. The results demonstrate exceptional thermal properties for Zirconium-based materials, making them ideal for thermoelectric device applications and future thermal management strategies.     

Preparation of glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems from metal alkoxides and their resistance to alkaline solution

Glass fibres of the ZrO₂-SiO₂ and Na₂O-ZrO₂-SiO₂ systems containing up to 33 wt% ZrO₂ were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO₂ content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm^–2 for the fibres containing 17 to 26 wt% ZrO₂, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO₂ showed higher resistance.     

Sorption of Np(V) on montmorillonite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between montmorillonite and solutions of MgCl₂ and CaCl₂ were determined experimentally. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is very fast within the first several hours after the start of the experiment and then decelerates, reaching the equilibrium in approximately two weeks. The constants of binary ion exchange NpO ₂ ⁺ -Mg²⁺ and NpO ₂ ⁺ -Ca²⁺ on montmorillonite determined by fitting the experimental results are $\log K_{NpO_2^ + - Mg^{2 + } } = 0.083 \pm 0.03$ and $\log K_{NpO_2^ + - Ca^{2 + } } = 0.106 \pm 0.014$ .     

The crystallisation of glasses from the ternary CaF2-CaAl2Si2O8-P2O5 system

A study of glasses from the ternary system CaF₂-CaAl₂Si₂O₈-P₂O₅ has been carried out. It has been shown that glasses with low phosphorus contents and high fluorite contents crystallise to fluorite. Fluorine reduces the glass transition temperature and is also required for the formation of fluorapatite (FAP). In the absence of fluorine in the glass no apatite phase is formed. Bulk nucleation of FAP is favoured for glasses with Ca:P ratios close to the apatite stoichiometry of 1.67 and with low crosslink densities. Thermal gravimetric analysis showed significant weight losses attributable to the formation of volatile silicon tetrafluoride to occur on crystallisation of the aluminium containing phases, anorthite and mullite, which supports the view that silicon tetrafluoride formation is hindered by fluorine bonding to the aluminium atoms of the glass network. Anorthite crystallisation always occurred by a surface nucleation mechanism and appeared to be favoured by the higher silicon to aluminium ratio in these glasses compared to previously studied glass compositions.     

In-situ Synthesis of Ti3AlC2/TiC-Al2O3 Composite from TiO2-Al-C System

Ti3AlC2/TiC-Al2O3 composite was synthesized by a combustion reaction in TiO2-Al-C system. The effect of the compositions in raw materials on the products was investigated. Ti3AlC2/TiC-Al2O3 composite was obtained at the molar ratio of TiO2:Al:C=3.0:5.0～5.1:1.8～2.0. The reaction path for the 3TiO2-5Al-2C system was proposed. Al3Ti, Ti2O3, TiO, and δ-Al2O3 are found to be transitional phases. Finally,Ti3AlC2/TiC-Al2O3 composite forms at ～900℃ of furnace temperature. The measured Vickers hardness,fracture toughness, and flexural strength of the nearly dense sample from 3TiO2-5Al-2C are 13.3±1.1 GPa,5.8±0.3 MPa.m1/2, and 466±39 MPa, respectively.     

Sorption of Np(V) on kaolinite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between kaolinite and solutions of MgCl₂ and CaCl₂ were determined experimentally at various concentrations of the electrolytes and Np. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is completely reversible. The sorption equilibrium is attained in approximately one week after the start of the sorption-desorption experiments. The constants of NpO₂ ⁺-Mg²⁺ and NpO₂ ⁺-Ca²⁺ binary ion exchange on kaolinite were determined by fitting the experimental results with an ion-exchange equation for the restricted sorption capacity: $\log K_{NpO_2^ + - Mg^{2 + } } = 1.26 \pm 0.08$ and $\log K_{NpO_2^ + - Ca^{2 + } } = 0.96 \pm 0.10$ . These constants describe well the experimental data at low Np concentrations (≤1×10^?6 M). The ion-exchange capacity of kaolinite, calculated from the experimental data on Np sorption from solutions (3.03×10^?4 g-equiv kg^?1 MgCl₂), somewhat differs from that in CaCl₂ solutions (2.15×10^?4 g-equiv kg^?1).     

Synthesis of WS2 and MoS2 fullerene-like nanoparticles from solid precursors

Inorganic fullerene-like WS₂ and MoS₂ nanoparticles have been synthesized using exclusively solid precursors, by reaction of the corresponding metal oxide nanopowder, sulfur and a hydrogen-releasing agent (NaBH₄ or LiAlH₄), achieved either by conventional furnace heating up to ∼900 °C or by photothermal ablation at far higher temperatures driven by highly concentrated white light. In contrast to the established syntheses that require toxic and hazardous gases, working solely with solid precursors permits relatively safer reactor conditions conducive to industrial scale-up.      

WS2 nanoflakes from nanotubes for electrocatalysis

Next-generation catalysts for water splitting are crucial towards a renewable hydrogen economy. MoS₂ and WS₂ represent earth-abundant, noble metal cathode alternatives with high catalytic activity at edge sites. One challenge in their development is to nanostructure these materials in order to achieve increased performance through the creation of additional edge sites. In this work, we demonstrate a simple route to form nanostructured-WS₂ using sonochemical exfoliation to break interlayer and intralayer bonds in WS₂ nanotubes. The resulting few-layer nanoflakes are ～100 nm wide with a high density of edge sites. WS₂ nanoflakes are utilized as cathodes for the hydrogen evolution reaction (HER) and exhibit superior performance to WS₂ nanotubes and bulk particles, with a lower onset potential, shallower Tafel slope and increased current density. Future work may employ ultra-small nanoflakes, dopant atoms, or graphene hybrids to further improve electrocatalytic activity.      

Fabrication of hollow glass microspheres in the Na2O-B2O3-SiO2 system from metal alkoxides

Hollow glass microspheres (HGS) for laser fusion targets were fabricated in the system Na₂O-B₂O₃-SiO₂ from NaOCH₃, B(OCH₃)₃ and Si(OC₂H₅)₄. Gel powders prepared from metal alkoxides and urea liberate H₂O, CO₂ and NH₃ gases, evolution of which takes place completely at about 500° C. The precursor of HGS is formed by the encapsulation of these gas components in the glass layer formed at the surface of the powder. HGS are produced from the gel powders having both a melting temperature lower than about 1000° C and a viscosity at that temperature lower than 10⁵ P. In the Na₂O-B₂O₃-SiO₂ system, the compositions from which HGS are produced are those containing 55–75 wt% SiO₂ and 0–20 wt% B₂O₃. HGS ranging from 100–500m diameter and 0.5–7.0m wall thickness are obtained by change of urea content.     

Alpha irradiated YNi2B2C studied from positron lifetime measurements

For YNi₂B₂C, a typical borocarbide superconductor, we have carried out positron annihilation lifetime measurements, before and after a 40 MeV -irradiation to a fluence of 2X10¹⁶ particles/cm². A 3-lifetime fit, giving improved variance, showed a third lifetime longer than 1 ns and of low (1 to 2%) intensity. This lifetime is due to positronium formation and o-Ps to p-Ps conversion in the porous samples. The irradiation increases the bulk lifetime. B, calculated from ₁ and ₂, from 181 ps to 213 ps.     

Synthesis of ZnTa2O6 from peroxide solutions

We have studied the formation of zinc metatantalate from peroxide solutions. The results indicate that the use of peroxide solutions enables stoichiometric ZnTa₂O₆ to be prepared. The crystal structure of the low-temperature phase of ZnTa₂O₆ forms at a calcination temperature of 700°C. The synthesized ZnTa₂O₆ powders have been characterized by X-ray diffraction, differential thermal analysis, thermogravimetry, and scanning electron microscopy.