B. Vishwanadh

Copper(I) 2-pyridyl selenolates and tellurolates: Synthesis, structures and their utility as molecular precursors for the preparation of copper chalcogenide nanocrystals and thin films

The complexes, [Cu{EC(5)H(3)(R-3)N}](4) (E/R = Se/Me or Te/R; R = H or Me) were isolated by the reaction between CuCl and NaEC(5)H(3)(R-3)N and were characterized by elemental analyses, uv-vis and NMR ((1)H, (13)C) spectroscopy. The crystal structures of [Cu{SeC(5)H(3)(Me-3)N}](4) and [Cu(TeC(5)H(4)N)](4) revealed that the molecules are tetrameric in which each copper atom lies at the vertex of the tetrahedron and each face of the tetrahedron is capped by the bridging pyridylchalcogenolate ligand. Thermal behavior of these complexes was studied by thermogravimetric analysis. Depending on reaction conditions, thermolysis gave both stoichiometric and non-stoichiometric copper chalcogenides, which were characterized by XRD, EDX, SEM, TEM and SAED techniques. These precursors were used for the preparation of nanocrystals and for deposition of thin films of copper chalcogenides by AACVD (Aerosol Assisted Chemical Vapor Deposition).

Diorganotin(IV) 4,6-dimethyl-2-pyrimidyl selenolates: synthesis, structures and their utility as molecular precursors for the preparation of SnSe2 nano-sheets and thin films

The complexes of composition [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Me, Et, nBu or tBu) have been isolated by the reaction of R2SnCl2 with NaSeC4H(Me-4,6)2N2. The treatment of [R2Sn{SeC4H(Me-4,6)2N2}2] with R2SnCl2 afforded chloro complexes [R2SnCl{SeC4H(Me-4,6)2N2}] (R = Me, nBu or tBu). These complexes were characterized by elemental analyses and NMR (1H, 13C, 77Se, 119Sn) spectroscopy. The molecular structures of [tBu2Sn{SeC4H(Me-4,6)2N2}2] and [tBu2SnCl{SeC4H(Me-4,6)2N2}] were established by single crystal X-ray diffraction analyses. Thermolysis of [R2Sn{SeC4H(Me-4,6)2N2}2] (R = Et, nBu or tBu) in oleylamine (OLA) afforded the nanocrystalline hexagonal phase of SnSe2. Thin films of SnSe2 were deposited on silicon wafers by AACVD of [tBu2Sn{SeC4H(Me-4,6)2N2}2]. The nanostructures and thin films were characterized by solid state diffuse reflectance spectroscopy, XRD, EDX, SEM and TEM techniques. The solid state diffuse reflectance measurements of the nanosheets showed direct and indirect band gaps in the ranges of 1.76–2.30 eV and 1.38–1.49 eV, respectively, which are blue shifted relative to bulk tin selenide.

Size induced modification of boron structural unit in YBO3: systematic investigation by experimental and theoretical methods

Nanocrystalline YBO3 (∼4–8 nm) was prepared using polyol method. Structural features of these nanoparticles have been investigated jointly by experimental and theoretical methods and compared with corresponding bulk phase of YBO3. The symmetry around Y3+ has been examined by photoluminescence measurements of Eu3+ doped YBO3 sample, while the local structure around boron has been probed through 11B MAS-NMR studies. XRD and photo-luminescence investigations reveal that YBO3 nanoparticles are structurally distorted in comparison to their bulk counterpart. Judd–Ofelt analysis shows that local environment around Y3+/Eu3+ is more polarizable in nanoparticles. 11B MAS-NMR studies confirmed that contrary to bulk phase where only BO4 units are present, nanoparticles of YBO3 have both BO3 and BO4 structural units in almost equal proportion. DFT calculation also predicts the existence of both BO3 and BO4 structural units in YBO3 nanoparticles where BO3 units are primarily distributed on surface of the nanoparticles. We expect that such nanoparticles, rich in unsaturated boron oxides on the surface, will help in the synthesis of inorganic–organic hybrid phosphors for next generation flexible display devices.

Diorganotin(IV) 2-pyridyl and 2-pyrimidyl thiolates: synthesis, structures and their utility as molecular precursors for the preparation of tin sulfide nanosheets

The complexes of composition, [R2Sn(2-SC5H4N)2] (R = Me (1) or Et (2)), [Et2SnCl(2-SC5H4N)] (3) and [R2SnCl{SC4H(Me-4,6)2N2}] (R = Me (4), Et (5)) were prepared and characterized by elemental analyses and NMR (1H, 13C, 119Sn) spectroscopy. The molecular structures of [Et2Sn(2-SC5H4N)2] (2), [Me2SnCl{SC4H(Me-4,6)2N2}] (4) and [Et2SnCl{SC4H(Me-4,6)2N2}] (5) were established unambiguously by single crystal X-ray diffraction analyses. The central tin atom acquires a skew trapezoidal bipyramidal configuration in the former (2) while distorted trigonal bipyramidal geometry in the latter two complexes (4 and 5), respectively. Thermolysis of diethyltin complexes [Et2Sn(2-SC5H4N)2] (2) and [Et2SnCl{SC4H(Me-4,6)2N2}] (5) in oleylamine (OLA) afforded orthorhombic phase SnS nano-sheets of thickness 30–80 nm which were characterized by solid state diffuse reflectance spectroscopy, XRD, EDX, SEM and TEM techniques. The solid state diffuse reflectance measurements of the nanosheets showed direct and indirect band gaps in the ranges of 1.61–1.90 eV and 1.46 eV, respectively which are blue shifted relative to bulk tin sulfide [Eg (direct) = 1.3 eV and Eg (indirect) = 1.1 eV].

Aluminide formation on Alloy 800 by plasma spraying and heat treatment

ABSTRACT Specimens of Fe–Ni–Cr based Alloy 800 were subjected to atmospheric plasma spraying using aluminum powder. Quantitative microscopic analysis of as-sprayed specimen revealed formation of aluminum-rich oxygen-containing layer (∼100 µm) on the uppermost surface, while adjoining layer (∼25 µm) comprising oxygen-rich Fe–Ni–Cr–Al-containing phase. Microscopy with quantitative analysis of as-sprayed + heat-treated (at 1273 K) substrate revealed formation of FeAl type layer (∼80 µm) on the uppermost surface with an Al-rich intermediate layer (∼25 µm) adjacent to substrate. Knoop hardness number was obtained as 764 (±20), 477 (±10), and 210 (±10) for FeAl layer, Al-rich intermediate layer, and substrate, respectively. During scratch tests at 2, 4, and 6 N loads, friction coefficient for the aluminides was recorded in the range of ∼0.05–0.15, while that was ∼0.18 for the substrate. Scratched surfaces at 2 and 4 N load tests revealed neither cracking nor peeling off at aluminides or interfaces indicating good adherence, whereas cracking occurred at aluminides during 6 N load test. Penetration depths for the aluminides were recorded as lower than that of the substrate during the scratch tests. X-ray photoelectron spectroscopy on thermally oxidized FeAl layer revealed formation of Al2O3 type oxide on the surface.

Intermetallics and Alloys for High Temperature Applications

Potentials of intermetallics for high temperatures were realized in the early 1900s. But initial attempts from time to time failed due to inadequate ductility as well as poor high-temperature creep strength exhibited by the intermetallic phases. From these early attempts three main ideas germinated. First, addition of ternary elements can improve properties of intermetallic phases dramatically. Second, introduction of new phases not only can change properties but also allow tailoring of the microstructure according to the demand of the application requirements. Third, combining brittle phase along with a ductile matrix it is possible to develop a composite material that encompasses the inherent limitations of the intermetallic phases. Based on these points, a new series of alloys and phases were developed. These recent developments and innovations are summarized in this chapter. The first part of the chapter is devoted to various intermetallic phases, which are under active consideration, and the second part of the chapter is focused on the development of refractory metal-based alloy and high-entropy alloy systems.

Electrosynthesis and characterization of nanocrystalline UO2 coating from aqueous alkaline electrolyte

In this study, UO2 coating was deposited by direct current (DC) electrolysis from an aqueous electrolyte containing UO2(NO3)2 as source of uranium. Deposition parameters such as electrolyte pH, temperature and current density were optimized in order to obtain a smooth adherent UO2 coating on metallic substrates. The effect of pH, temperature and current density on the deposition rate and on faradic current efficiency (CE) was studied in detail. The study revealed that the control over pH of the electrolyte was more important in comparison to temperature and current density to obtain a smooth deposition of UO2 from this uranyl nitrate–oxalate complex electrolyte. Grazing incidence X-ray diffraction (GI-XRD) of the as-deposited coating with a broad peak confirmed amorphous to ultra-nanocrystalline deposition. Upon vacuum annealing at higher temperature, the as-deposited coating transformed into nanocrystalline fcc UO2 with the appearance of sharper (111), (220), (220), (222) XRD reflections. The average grain size obtained was 13.2 nm for the sample annealed at 700 °C. In the presence of air, the fcc UO2 coating was transformed largely into the hcp U3O8 phase with a small percentage of hcp UO3 at temperatures higher than 400 °C. The surface morphology of the as-deposited coating showed a granular morphology with the appearance of few cracks. Upon annealing at 700 °C, the film showed a network of cracks throughout the surface with numerous pores inside the UO2 matrix. Composition analysis by EDS of the film confirmed the presence of uranium and oxygen. Cross-sectional FESEM analysis of the focused ion beam (FIB) cut samples confirmed deposition of a 6 μm thick UO2 coating. Upon annealing at 700 °C, it converted into a highly porous UO2 coating with improved adhesion with the substrate.

A study on reaction kinetics and development of silicide coatings on Nb–1Zr–0.1C alloy by molten salt technique

In this study a molten salt technique has been used to produce silicide coating on Nb–1Zr–0.1C alloy using a NaCl–KCl–NaF–Na2SiF6–Si melt. Molten baths having different concentrations of Si in the metallic state produced silicide coating whereas those molten baths which were devoid of metallic Si could not produce any coating. Structural and chemical characterization of the coated samples by scanning electron microscopy (SEM) and X-ray diffraction (XRD) have shown that the uniform coating had NbSi2 as a major phase. Depending upon the composition of the salts, post experiment examination by X-ray photoelectron spectroscopy (XPS) technique and ion chromatography revealed the presence of varying relative concentrations of various states of silicon, F− and the etched Nb. Based on the analysis of these results it was elucidated that the presence of Si2+ is a prerequisite for silicide coating on the Nb alloy. A mechanism of silicide coating formation on Nb alloy by the molten salt technique has been proposed in the present study.