Electro-deoxidation of Ta2O5 in calcium chloride–calcium oxide melts

Tantalum oxide has been electro-deoxidised in a bath of CaCl₂-1wt%CaO to form tantalum. It was found that the reaction between the calcium oxide in the melt and the tantalum oxide takes precedence over any reduction process so that until the calcium tantalum oxide Ca₃(CaTa₂O₉) (equivalent to 4CaO·Ta₂O₅ or Ca₄Ta₂O₁₀) is formed, calcium ions are reduced to either form calcium metal or reduced calcium species. This eventually results in high electronic conductivity in the melt which means that, compared to the electro-deoxidation of oxides of similar stability to Ta₂O₅, the energy and current efficiencies are low. In addition, the vast changes in microstructure result in a structure that is extremely fragile so that the resulting tantalum can only be harvested as a fine powder.     

Structural characterization of nickel tantalum oxide synthesized by sol–gel spin coating technique

For the first time, crack-free, dense and transparent tetragonal NiTa₂O₆ single-phase structure thin films have been prepared by a sol–gel method using tantalum isopropoxide and nickel acetate. The formation of the NiTa₂O₆ phase starts from 750°C onwards. The complete tetragonal structure of NiTa₂O₆ forms on silicon(100) substrates at an annealing temperature of 850°C for 5 h. As the annealing temperature increased from 750°C to 950°C, we have not observed any kind of silicate phases due to silicon diffusion at the interface of Si and NiTa₂O₆ phase. Structural, morphological and elemental evolution of these NiTa₂O₆ thin films produced by the sol–gel synthesis were characterized by grazing incidence X-ray diffraction (GIXRD), tapping mode atomic force microscopy (TMAFM) and X-ray photoelectron spectroscopy (XPS), respectively.     

Surface tension of lead–bismuth eutectic melts with lithium

The temperature and concentration dependences of the surface tension of lithium alloys (up to 33.1 at %) on the basis of a eutectic melt of Pb_44.7Bi_55.3 are measured in the range from the liquidus temperature to 700 K. The margin of error of the experiments was ~2%. Lithium has a low surface activity in the Pb_44.7Bi_55.3 eutectic melt, which agrees with the criteria of the surface activity of components in binary liquid metal melts.     

Effect of calcium–silicon ratio on microstructure and nanostructure of calcium silicate hydrate synthesized by reaction of fumed silica and calcium oxide at room temperature

A C–S–H series with calcium–silicon ratio 0.6–3.0 was synthesized by pozzolanic reaction. Phase composition, nanostructural and morphological characteristics were determined using XRD, XRF, SEM and ²⁹Si NMR. Most of the samples were phase-pure, poorly crystalline C–S–H. Significant changes in the nanostructure of the C–S–H samples were observed when the calcium–silicon ratio reached values of 0.8, 1.0 and 1.5. At calcium–silicon ratio 0.8 the basal XRD peak began to develop, crosslinking between layers was seen below this ratio but not above, and there was a substantial decrease in mean silica chain length at this ratio. At calcium–silicon ratio 1.0 there was a pronounced microstructural change from granular to reticular and another substantial decrease in mean chain length (indicated by an abrupt increase in the Q¹ peak intensity and decrease in the Q² peak intensity). At calcium–silicon ratio 1.5 the basal XRD peak began to diminish again, the mean silica chain length decreased further, and isolated tetrahedra (Q⁰) were observed.     

Surface coatings of zinc oxide–tantalum pentoxide on multicrystalline Si solar cell as effective light harvester

One of the key elements to enhance the performance of solar cells was antireflective surface coatings. It can be employed through different deposition techniques such as spin coating, dip coating, blade coating, etc., In this research work, the coating materials such as ZnO, Ta₂O₅ and ZnO–Ta₂O₅ blends were coated over silicon solar cells through electrospraying technique. The performance of coated solar cells were evaluated using different characterization techniques. At the coating time of 90 min and input voltage supply of 17 kV, almost uniform thin films were attained. This was confirmed through FESEM and AFM analysis. The transmittance and power output characteristics of coated glass slides and Si solar cells were examined through UV–Vis spectroscopy and I–V source meter. In comparison with other solar cells, the ZnO–Ta₂O₅ blend (H3) coated cell exhibit uniform layer deposition and minimal light reflectance of 5%. The maximum power conversion efficiency was achieved for H3 solar cell of 17.7% (direct sunlight) and 19.6% (neodymium light source), due to increased transmittance of photons reaching the depletion region. The electrical resistivity of H3 solar cell was noted as 3.57?×?10^?3 Ω cm using four probe method, which was lesser than other solar cells. From the obtained experimental outcomes, ZnO–Ta₂O₅ blend coated solar cell reveal the maximum performance than other coated and uncoated solar cells. Hence, ZnO–Ta₂O₅ blends were found to be better antireflective material for attaining maximum output performance of solar cell.

     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

Microindentation creep of monophasic calcium–silicate–hydrates

Microindentation creep results for monophasic synthetic C–S–H (C/S = 0.6–1.5), 1.4 nm tobermorite, jennite and calcium hydroxide at 11%RH are reported. Creep results for well hydrated cement paste and C₃S ‘composite’ systems are also described. The significance of the co-linear behavior of creep modulus functions of indentation modulus and indentation hardness for C–S–H obtained by microindentation and nanoindentation methods is discussed. The porosity dependence of creep modulus and the general equivalence of density values determined by helium pycnometry and by calculations employing unit cell dimensions (obtained using X-ray crystallography techniques) are also discussed in terms of postulates for the existence of two types of C–S–H. Comment on the compatibility of the creep modulus data for 1.4 nm tobermorite and jennite with models of C–S–H present in cement paste is provided.     

Reduced graphene oxide–nickel oxide composites with high electrochemical capacitive performance

Reduced graphene oxide (RGO)–NiO composites have been fabricated by a simple solvothermal route starting with graphite oxide (GO). The morphology, composition and microstructure of the as-obtained samples are systematically characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, the electrochemical performances of composites were evaluated by cyclic voltammogram (CV) and galvanostatic charge–discharge. Interestingly, it was found that the electrochemical performance of the composites could be affected by the mass ratio between RGO and NiO. The composite with the mass ratio up to 79:21 (NiO:RGO) exhibits the highest specific capacitance of 576 F g⁻¹ at 1 A g⁻¹, which is much higher than that of pure NiO (240 F g⁻¹) and pure RGO (98 F g⁻¹). In addition, the cycling measurements showed that RGO–NiO composite exhibited excellent cycling stability with no decay in the available capacity over 1100 cycles. The enhancement in specific capacitance and cycling stability may be attributed to the increased electrode conductivity owing to RGO network, the increased effective interfacial area between NiO and the electrolyte, as well as the contact area between NiO and RGO.     

Thermophysicochemical Reaction of ZrCo–Hydrogen–Helium System

Nuclear fusion energy, which is clean and infinite, has been studied for more than half a century. Efforts are in progress worldwide for the demonstration and validation of nuclear fusion energy. Korea has been developing hydrogen isotope storage and delivery system (SDS) technologies including a basic scientific study on a hydrogen storage medium. An SDS bed, which is a key component of the SDS, is used for storing hydrogen isotopes in a metal hydride form and supplying them to a tokamak. Thermophysicochemical properties of the ZrCo–H\(_{2}\)–He system are investigated for the practical utilization of a hydriding alloy system. The hydriding reaction, in which \(\hbox {ZrCoH}_{\mathrm{x}}\) is composed as ZrCo absorbing hydrogen, is exothermic. The dehydriding reaction, in which \(\hbox {ZrCoH}_{\mathrm{x}}\) decomposes into ZrCo and hydrogen, is endothermic. The heat generated through the hydriding reaction interrupts the hydriding progress. The heat loss by a dehydriding reaction impedes the dehydriding progress. The tritium decay product, helium-3, covers the ZrCo and keeps the hydrogen from contact with ZrCo in the SDS bed. In this study, we designed and fabricated a ZrCo bed and its performance test rig. The helium blanketing effect on a ZrCo hydrogen reaction with 0 % to 20 % helium content in a gaseous phase and a helium blanket removal method were studied experimentally. In addition, the volumetric flow rates and temperature at the beginning of a ZrCo hydrogen reaction in a hydrogen or helium atmosphere, and the cooling of the SDS bed by radiation only and by both radiation and natural convection related to the reuse cycle, were obtained.     

Metastable microheterogeneity of melts in the Ga–Bi system with limited solubility of components in liquid state

A set of acoustic (using the pulse phase method for ultrasound velocity v _s measurement) and γ-absorption experiments with the Ga–Bi melts have been performed to clear the nature of their microinhomogeneity. Both methods allow determining υ _s and intensity of the penetrating γ-beam, I, at various distances, h, from the bottom of the measuring cell. Distinct υ _s(h) and I(h) dependences were discovered in one phase domain of the phase diagrams. It is clear that such inhomogeneity is connected with the chemical inhomogeneity of the melt which, in its turn, can exist if one of the components forms very large particles containing 10⁴–10⁵ atoms. The cupola-like borders of the domains where such inhomogeneity exists were fitted in the phase diagrams of the systems under investigation. The inhomogeneity has been confirmed in special acoustic experiments with superposition of ultrasound and low-frequency oscillation.     

Composition and properties of silver-containing calcium carbonate–calcium phosphate bone cement

The introduction of silver, either in the liquid phase (as silver nitrate solution: Ag(L)) or in the solid phase (as silver phosphate salt: Ag(S)) of calcium carbonate–calcium phosphate (CaCO₃–CaP) bone cement, its influence on the composition of the set cement (C-Ag(L) and C-Ag(S) cements with a Ca/Ag atomic ratio equal to 10.3) and its biological properties were investigated. The fine characterisation of the chemical setting of silver-doped and reference cements was performed using FTIR spectroscopy. We showed that the formation of apatite was enhanced from the first hours of maturation of C-Ag(L) cement in comparison with the reference cement, whereas a longer period of maturation (about 10 h) was required to observe this increase for C-Ag(S) cement, although in both cases, silver was present in the set cements mainly as silver phosphate. The role of silver nitrate on the setting chemical reaction is discussed and a chemical scheme is proposed. Antibacterial activity tests (S. aureus and S. epidermidis) and in vitro cytotoxicity tests (human bone marrow stromal cells (HBMSC)) showed that silver-loaded CaCO₃–CaP cements had antibacterial properties (anti-adhesion and anti-biofilm formation) without a toxic effect on HBMSC cells, making C-Ag(S) cement a promising candidate for the prevention of bone implant-associated infections.     

Whisker microcrystals on the surface of tantalum–cadmium alloy films

Technical Physics Letters - Whiskers crystals were discovered in the tantalum–cadmium (56.6 at % Cd) solid solutions formed by in-turn deposition of the superfine tantalum and cadmium...     

Properties of ductile cast iron nodularised with multiple calcium–magnesium based master alloy

Abstract

Austempered ductile iron (ADI) is gradually replacing many fabricated and forged steel components in engineering applications. One of its advantages is the combination of good castability, machinability, and mechanical properties with significant savings in cost and weight compared with equivalent steel components. A problem in the production of ADI is the use of expensive and dangerously reactive magnesium as a graphite nodulariser. There is a need to find cheaper, safer, and equally effective substitutes. Results of an investigation of the effectiveness of a multiple calcium–magnesium based master alloy nodulariser and the properties of the ductile iron and ADI produced are reported. Up to 96% nodularity could be obtained using a special Ca–CaC₂–Mg master alloy, compared with 98% using magnesium alone. The mechanical properties were also comparable.     

Structure and micro-nanomechanical characterization of synthetic calcium–silicate–hydrate with Poly(Vinyl Alcohol)

The principal phase of hardened Portland cement pastes is calcium silicate hydrate (C–S–H), which influences the physical and mechanical properties of construction materials. In this work calcium silicate hydrate (C–S–H) was synthesized, with the addition of Poly(Vinyl Alcohol) (PVA), for the development of C–S–H/polymer nanocomposites. Among the polymers available, PVA is indicated by the literature as one of the most viable for producing C–S–H/polymer complexes. However, no consensus exists regarding the kind of interaction. The resulting compounds were characterized by XRD, FT-IR, TGA, carbon content (CHN), TEM, SEM and elastic modulus and hardness were measured by instrumented indentation. The set of results presented do not confirm the intercalation of PVA in the interlayer space of C–S–H, but presented evidence of the potential for intercalation, since changes in the structure clearly occurred. A significant change in the micro-nanomechanical properties of C–S–H occurred in the presence of PVA.     

The formation of hydroxyapatite–calcium polyacrylate composites

Tetracalcium phosphate (TetCP, Ca₄(PO₄)₂O) reacts rapidly with polyacrylic acid (PAA). Complete reaction results in the formation of hydroxyapatite (HAp) and calcium polyacrylate. Consequently, this combination of reactants can react to form a dental cement. However, reaction occurs so rapidly that it would be difficult to achieve a homogeneous mixture of reactants suitable for use in restorations. In order to explore extending the working time, the effects of prehydrating the TetCP to form surface layers of HAp on the TetCP particles was explored. Prehydration was found to be an effective means of allowing workability. Therefore, the effects of the proportions of TetCP and PAA, with and without HAp filler, on cement properties were investigated. The extents of the reactions were investigated by X-ray diffraction analysis; the extents of PAA neutralization were studied by Fourier transform infra-red spectroscopy (FTIR); pore structures were determined by mercury intrusion porosimetry; microstructures were observed by scanning microscopy, and compressive strengths were determined. After curing for 17 days at room temperature PAA neutralization was almost complete; however, residual TetCP could be detected by X-ray diffraction and PAA by FTIR. As expected, the compressive strengths of the cements showed a dependence on the liquid (water+polymer)-to-solid (TetCP+HAp filler) used. The presence of HAp filler caused a significant decrease in compressive strength and increasing the proportion of HAp filler resulted in a decrease in the compressive strength. The characteristics of the load–deflection curves showed a dependence on the presence of HAp filler. In the absence of filler, two slopes were observed in the curves whereas a linear curve, typical of a ceramic, was observed when HAp filler was present. Mercury intrusion porosimetry (MIP) indicated the majority of the porosity was present in pores larger than 0.1 m. Porosity increased with increasing liquid-to-solids ratio and with an increasing proportion of HAp filler at a constant liquid-to-solids ratio. Microstructural observations indicated the effect of HAp filler on increasing porosity was the result of porosity present in the filler itself. Thus, poorly consolidated HAp filler contributed to increased porosity and reduced compressive strength. © 1999 Kluwer Academic Publishers     

Reaction of the superconductive oxide BaPb1−xBixO3 (BPB) with La2O3

Semiconductive BPB of x=0.4 became superconductive after it had been sintered with La₂O₃, and the maximum T_C is about 11 K. X-ray phase analysis shows that all samples consist of two or three phases, one of which is of BPB structure. Calculation of a, b, c and a_o of the BPB phase reveals that they all decrease as the amount of La₂O₃ increases. The observed and calculated T_C values are semi-quantitatively consistent with each other. This indicates that BPB does not form a single phase solid solution with La₂O₃ over a wide range, but La₂O₃ changes the ratio of Bi/Pb in the phase.     

Heterogeneous cycloaddition of styrene oxide with carbon dioxide for synthesis of styrene carbonate using reusable lanthanum–zirconium mixed oxide as catalyst

Clean Technologies and Environmental Policy - Development of environmentally benign green processes for utilization of carbon dioxide to synthesize value-added compounds using heterogeneous...