Development of nano indium tin oxide (ITO) grains by alkaline hydrolysis of In(III) and Sn(IV) salts

Indium tin oxide (ITO) nano powders of different compositions (In: Sn = 90: 10, 70: 30 and 50: 50) were prepared by heat treatment (300-450°C) of mixed hydroxides of In(III) and Sn(IV). The hydroxides were obtained by the reaction of aq. NH₃ with mixed aq. solutions of In(NO₃)₃ and SnCl₄. FTIR and TG/DTA studies revealed that powders existed as In(OH)₃H₂O—SnO₃H₂H₂O in the solid state and then they transformed to In₂O₃—SnO₂ via some metastable intermediates after 300°C. Cubic phase of In₂O₃ was identified by XRD for the oxides up to 30% of Sn. Particle size measurements of the solid dispersed in acetone and SEM study for microstructure showed that the oxides were in the nano range (55-75 nm) whereas the size range determined from Debye-Scherrer equation were 11–24 nm.     

Some X-ray photoelectron spectroscopic measurements on Passivated Tin in some neutral media

Some ESCA measurements have been carried out on the anode film formed on BDH Sn foil by the potentiodynamic technique up to 2.5 V (SCE) in (i) phosphate buffer, pH 6.7, (ii) 0.1 M KCl, 0.1 M Na₂SO₄, pH 6.6, in order to identify the elements, and possibly also some compounds, present in the film. The results in phosphte buffer indicate the presence of: (i) Sn(II) and Sn(IV) oxides and hydroxides, (ii) tin phosphate species probably (HPO₄)^2?, (H₂PO₄)^?, and insoluble phosphate complexes and (iii) evidence is given for the formation of soluble Sn species containing OH or phosphates before the beginning of passivity. The results in chloride solutions indicate the presence in the anode film of Sn, O and Cl in various states of combination such as: (i) Sn(II) and Sn(IV) species (oxides, chlorides and some hydroxides, (ii)) adsorbed oxygen and water, and (iii) basic or oxysalts or complexes involving Sn, O, Cl, and K. The results in Na₂SO₄ solutions indicate the presence in the film of Sn, O, S, and Na in the form of: (i) Sn(II) and Sn(IV) oxides and hydroxides, (ii) Na₂SO₄, other un- identified S species, and possibly also traces of PbS (from traces of Pb present in the Sn foil), (iii) adsorbed oxygen and water, and (iv) basic or oxysalts or complexes involving Sn, Na, O, sulphate and other unidentified S species.     

Sorption of Sr on clay minerals modified with ferrocyanides and hydroxides of transition metals

The sorption properties toward strontium of bentonitic clays modified with Fe(II) and Cu(II) ferrocyanides and Ti(IV), Sn(IV), and Sb(V) hydroxides were studied. The sorption properties of modified bentonites significantly surpass those of the natural mineral. The sorption equilibrium is attained in 2 h. The most efficient sorbent is the bentonitic clay modified with titanium hydroxide, with which K _d reaches 3.2 × 10⁴.     

Formation of perovskite-related structures CaMO3 (M = Sn, Ti) by mechanical milling

Nanoparticle calcium stannate (CaSnO₃) and calcium titanate (CaTiO₃) have been prepared by the mechanical milling of mixtures of calcium(II) oxide with tin(IV) oxide or titanium(IV) oxide. The formation of calcium titanate (CaTiO₃) is more easily achieved by milling calcium(II) oxide with the rutile modification of titanium (IV) oxide than with the anatase form.     

Adsorption of platinum(IV) and palladium(II) from aqueous solution by thiourea-modified chitosan microspheres

The chitosan microparticles were prepared using the inverse phase emulsion dispersion method and modified with thiourea (TCS). TCS was characterized by scanning electron microscope (SEM), the Fourier transform infrared (FT-IR) spectra, sulfur elemental analysis, specific surface area and pore diameter. The effects of various parameters, such as pH, contact time, initial concentration and temperature, on the adsorption of Pt(IV) and Pd(II) by TCS were investigated. The results showed that the maximum adsorption capacity was found at pH 2.0 for both Pt(IV) and Pd(II). TCS can selectively adsorb Pt(IV) and Pd(II) from binary mixtures with Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). The adsorption reaction followed the pseudo-second-order kinetics, indicating the main adsorption mechanism of chemical adsorption. The isotherm adsorption equilibrium was well described by Langmuir isotherms with the maximum adsorption capacity of 129.9 mg/g for Pt(IV) and 112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and Pd(II) decreased with temperature increasing. The negative values of enthalpy (ΔH°) and Gibbs free energy (ΔG°) indicate that the adsorption process is exothermic and spontaneous in nature. The adsorbent was stable without loss of the adsorption capacity up to at least 5 cycles and the desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H₂SO₄ eluent was used. The results also showed that the preconcentration factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the recovery was found to be more than 97% for both precious metal ions.     

Mössbauer lattice parameters of mixed tin fluoride α-Sn2F6

Mössbauer resonance measurements using the 23.8 keV γ-transition in ^II9Sn have been carried out on the mixed tin fluoride Sn^IISn^IVF₆ over the temperature range 4.2 ⩽ T ⩽ 378 K.From the temperature dependence of the isomer shift it is possible to extract the effective vibrating masses, i.e. M_eff = 178 amu for Sn(II) and M_eff = 298 amu for Sn(IV). The lattice temperatures calculated from the temperature dependence of the area of the resonance peak are 166 K and 211 K for Sn(II) and Sn(IV) respectively. Using M_eff leads to lattice temperatures of 139K (Sn(II)) and 133 K (Sn(IV)). The recoilless fractions at 293 K are 0.15 for Sn(II) and 0.31 for Sn(IV).     

Removal of Fe(II) from tap water by electrocoagulation technique

Electrocoagulation (EC) is a promising electrochemical technique for water treatment. In this work electrocoagulation (with aluminum as electrodes) was studied for iron Fe(II) removal from aqueous medium. Different concentration of Fe(II) solution in tap water was considered for the experiment. During EC process, various amorphous aluminum hydroxides complexes with high sorption capacity were formed. The removal of Fe(II) was consisted of two principal steps; (a) oxidation of Fe(II) to Fe(III) and (b) subsequent removal of Fe(III) by the freshly formed aluminum hydroxides complexes by adsorption/surface complexation followed by precipitation. Experiments were carried out with different current densities ranging from 0.01 to 0.04 A/m². It was observed that the removal of Fe(II) increases with current densities. Inter electrode distance was varied from 0.005 to 0.02 m and was found that least inter electrode distance is suitable in order to achieve higher Fe(II) removal. Other parameters such as conductivity, pH and salt concentration were kept constant as per tap water quality. Satisfactory iron removal of around 99.2% was obtained at the end of 35 min of operation from the initial concentration of 25 mg/L Fe(II). Iron concentration in the solution was determined using Atomic absorption spectrophotometer. By products obtained from the electrocoagulation bath were analyzed by SEM image and corresponding elemental analysis (EDAX). Cost estimation for the electrocoagulation was adopted and explained well. Up to 15 mg/L of initial Fe(II) concentration, the optimum total cost was 6.05 US$/m³. The EC process for removing Fe(II) from tap water is expected to be adaptable for household use.     

Synthesis and characterization of tin(IV) phenyl phosphonate in nano form

An inorgano-organic ion exchanger, Sn(IV) phenyl phosphonate, has been synthesized in amorphous form. Further, an attempt has been made to synthesize Sn(IV) phenyl phosphonate in the nano form. The materials have been characterized for elemental analysis (ICP-AES), thermal analysis (TGA), X-ray analysis and FTIR spectroscopy. Chemical resistivity of these materials has been accessed in acidic, basic and organic solvent media. Catalytic activity has been studied and compared by using esterification of ethylene glycol as a model reaction wherein glycoldiacetate has been prepared. The transport properties of these materials have been explored by measuring specific proton conduction at different temperatures using SOLARTRON DATASET impedance analyser over a frequency range 1 Hz-1 MHz. It has been observed that Sn(IV) phenyl phosphate in the nano form behaves as a better Bronsted catalyst and proton conductor as compared to the amorphous form.     

Post-synthetic treatments on NixMnxCo1 − 2x(OH)2 for the preparation of lithium metal oxides

A series of hydroxides Ni_xMn_xCo_(1−2x)(OH)₂ for x = 0.00–0.50 were prepared. These hydroxides were used as the precursors in the synthesis of electrochemical active lithiated mixed metal oxides, LiNi_xMn_xCo_{(1 − 2x)}O₂. The traditional co-precipitation method was used to synthesize the hydroxides and the effect of different post-synthetic treatments were tested. The solutions after co-precipitation of the hydroxides were heated under hydrothermal or microwave assisted hydrothermal conditions at 180 °C. All samples were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. We observed that the hydroxides undergo oxidation to an oxyhydroxide phase as the stoichiometry varies during their synthesis and with post-synthetic treatments. As the concentration of Ni and Mn increases in the sample, a mixture of both hydroxide and oxyhydroxide phases is obtained. SEM images demonstrate a sintering effect on the hydroxide particles after post-synthetic treatment, while XRD measurements on these samples show an increase in crystallinity and reduced turbostratic disorder. The oxides synthesized from these precursors demonstrate similar electrochemical performance with one another.     

Microalloying of molybdenum disilicide with magnesium through mechanical and field activation

Utilizing a two-step method of mechanical and field activation, the heretofore-unachieved goal of incorporating Mg on the Si sub-lattice of MoSi₂ was successfully demonstrated. Mechanical activation was done through high-energy ball milling and field activation was achieved through the use of the spark plasma sintering (SPS) method. The incorporation of Mg was verified by a variety of techniques including XRD, SEM, and EDS.     

Phase composition and pore structure of nanoparticulate tin oxides prepared by AC electrochemical synthesis

The effect of current density and sodium chloride concentration in solution on the phase composition and pore structure of the products of ac electrolysis of metallic Sn has been studied using X-ray diffraction, thermogravimetry, differential scanning calorimetry, electron microscopy, and low-temperature nitrogen adsorption measurements. The results demonstrate that the synthesis products consist of tin(II) and tin(IV) oxides and hydroxides, whose percentages depend on electrolysis conditions, and have a large specific surface area and mesoporous structure. The average particle size ranges from 10 to 30 nm.     

Crystallographic and magnetic properties of Fe-doped SnO<Subscript>2</Subscript> nanopowders obtained by a sol–gel method

We prepared Sn_1?x Fe _x O₂ (x = 0, 0.03, 0.05, 0.10, and 1.0) nanoparticles by the polymeric precursor method based on the modified Pechini process. Two types of starting reactants for both tin and iron were explored: Sn(II)/Fe(II) and Sn(IV)/Fe(III) precursors. Thermogravimetric analysis revealed that the precursor powders prepared from Sn(IV) have higher excess in ethylene glycol in comparison to precursor samples prepared from Sn(II). XRD patterns for those samples prepared from Sn(IV) and Fe(III) were adequately fitted by introducing only the cassiterite phase of SnO₂. Micro-Raman spectra also support these findings, and additionally it is found that the presence of iron broadened and reduced the intensities of the principal bands. ¹¹⁹Sn Mössbauer spectra indicated only the presence of Sn⁴⁺, whereas RT ⁵⁷Fe Mössbauer spectra suggested the presence of two Fe³⁺ sites located at different distorted sites. On the other hand, micro-Raman and ⁵⁷Mössbauer spectrometry showed the formation of hematite as impurity phase for those samples with iron concentrations above ~5 at.%, prepared from Fe(II) and Sn(II) precursors. In addition, their XRD patterns revealed larger average grain sizes for the cassiterite phase of SnO₂ in comparison to those samples prepared from Sn(IV) and Fe(III).     

The aqueous solution-gel synthesis of perovskite Pb(Zr1−x,Tix)O3 (PZT)

Starting from a novel water-based Zr(IV)-peroxo-citrato solution, an entirely aqueous solution-gel synthesis of Pb(Zr_0.53,Ti_0.47)O₃ (PZT) was carried out. Because of the tendency of Zr⁴⁺-ions to hydrolyze and condensate extensively in water, the Zr⁴⁺-ions had to be chemically modified by reaction with hydrogen peroxide and citric acid in a two-step precursor synthesis. A transparent amorphous PZT gel precursor was obtained by evaporating the solvent (water). This resulted in a network of cross-linked ammonium-carboxylate bonds that holds Zr(IV)-peroxo-citrato, Ti(IV)-peroxo-citrato and Pb(II)-citrate complexes. By combining complementary thermal analysis techniques such as HT-DRIFT (high-temperature diffuse reflectance Fourier-transform infrared spectroscopy), TGA-MS (thermogravimetrical analysis online coupled to mass spectrometry) and DTA (differential thermal analysis) insight in the decomposition mechanism of the PZT gel was gained. Three major regions could be distinguished; consecutively the non-coordinative matrix surrounding the metal ion complexes, the precursor complexes and the remaining organic matrix are being decomposed. The phase formation of crystalline perovskite PZT was investigated in situ by means of HT-XRD (high-temperature X-ray diffraction). It shows that sublimation of PbO leads to the phase segregation of a Zr-rich PZT phase when a stoichiometric PZT precursor is used. Single phase perovskite PZT however can be obtained at low temperature (∼610 °C) when a 16 % lead excess is applied.     

Ion-exchange studies of ‘organic–inorganic’ nano-composite cation-exchanger: Poly-o-anisidine Sn(IV) tungstate and its analytical application for the separations of toxic metals

The separation of Hg(II) from aqueous solutions was studied using Poly-o-anisidine Sn(IV) tungstate nano-composite cation exchanger. This nano-composite material was synthesized via sol–gel mixing of Poly-o-anisidine with the inorganic precipitate of Sn(IV) tungstate, providing a new class of organic–inorganic nano-composite cation exchanger with good ion-exchange capacity, better chemical and thermal stability than most of the Poly-o-anisidine based exchanger reported so far. The ion-exchange capacity and ion-exchange behaviors of the nano-composite were also carried out to understand the ion-exchange capabilities. Its selectivity was examined by achieving some important binary and tertiary separations of metal cations on its column indicating its utility in environmental pollution control. This new exchanger was successfully applied for quantitative determination and separation of Hg(II) from a synthetic mixture of metal ions.     

Electrochemical Studies on the passive behaviour of tin in different buffer solutions

The effect of pH on the passivity of Sn has been investigated in buffered (phthalate-borate, and citrate phosphate buffer series), and in unbuffered phosphate solutions, using the cyclic voltammetric technique. Two anodic peaks; the first being more pronounced than the second, and on cathodic peak have been observed in the two buffer series at different scan rates and pH values. The anodic and cathodic peak current densities (I_p) and potentials (E_p) are functions of the scan rate (v) and the pH value. Plots of I_p against v^1/2 yield straight lines at each pH value. The effect of pH on I_p for the first anodic peak shows a shallow minimum in the near neutral and slightly alkaline range at all scan rates. Straight lines are also observed between E_p and v^1/2, the extrapolation of which to v = 0 gives the spontaneous (no polarization) oxidation or reduction potentials (E′ and E″). The absence of polarization effects in E′ and E″ make them the most suitable values for comparison with thermodynamic data. Therefore, the two straight lines obtained between E′ and E″ on one hand and the pH on the other hand to give an estimate of (i) the slope (dE°/dpH), and (ii) the value of E° at pH - 0 (from intercept). Comparison of the two experimental values with all available thermodynamic data for Sn(II) and Sn(IV) oxides and hydroxides shows that: (i) the first anodic peak represents the formation of Sn(OH)₂ from Sn and OH^?, (ii) the second anodic peak represents the formation of Sn(OH)₄ directly from Sn and OH^?, and (iii) the cathodic reduction peak correponds to the reduction of Sn(IV) oxidized species to Sn. The results in citratephosphate buffer have been treated in the same manner. However, the result of (dE°/dpH) and E° at pH = 0 deviate from thermodynamic data, because of the possible participation of other anodic reactions such as the formation of soluble Sn compounds, Sn complexes, and incorporation of anions in the anodic film.     

A comparative study of dip coating and spray pyrolysis methods for synthesizing ITO nanolayers by using Ag colloidal sol

Indium tin oxide (ITO) films were deposited on glass substrates by dip-coating and thermal pyrolysis methods. Sn (IV) is often used in the spray method as a precursor salt, but in this research we have employed a new procedure that uses Sn (II) and In(NO₃)₃ for preparation of transparent conductive thin films. Then, colloidal Ag was deposited on the ITO layers in order to compare the two synthesis methods, and the structural and electrical properties of the resultant films were investigated by FESEM, XRD, and four-terminal resistometry. The obtained films are polycrystalline with a preferred orientation of (200). The XRD patterns of the films indicate that in both films, the Sn phase is crystallized separately from In₂O₃. The presence of a Sn peak and the overall low intensity of XRD peaks suggest relative crystallization of ITO structure. For this reason, Ag films were deposited by dip coating method using a colloidal sol. By analyzing the XRD patterns of Ag-ITO films after eliminating the Sn peak, the increased intensity of the peaks confirmed the relatively good crystallization of the ITO films. The results show that the films with a sheet resistance as low as 2 × 10^?2 Ω·cm, which is beneficial for solar cells, were achieved.     

Diffusion of tin (IV) in silicate glazes and glasses

The diffusion coefficients of Sn(IV) in an aluminosilicate glass and a commercial glaze have been measured from 809 to 1505° C. Two experimental techniques have been used. In one method, single crystals of SnO₂ were embedded in either the powdered glass or sealed into a bar of the glass. After the diffusion anneal, the Sn(IV) concentration profile was determined by EPMA. In the other method, radioactive ¹¹³Sn was used as a tracer and the profile determined by measuring the X-ray emission. The results gave a good agreement between the two methods. The diffusion coefficients in the glaze ranged from 7×10^–20 m² sec^–1 at 809° C to 1.9×10^–14 m² sec^–1 at 1250° C and in the glass, from 5.6×10^–15 m² sec^–1 at 1307° C to 1.6×10^–11 m² sec^–1 at 1505° C.     

Sorption of lead(II) onto gel spheres of zirconium hydroxide

Adsorption of Pb(II) from nitric acid solution onto gel spheres of zirconium hydroxide and of a solid solution of zirconium and calcium hydroxides was studied. The Pb(II) distribution coefficient on zirconium hydroxide gel spheres at pH 6.0 ± 0.2 is high, 4 × 10⁴ cm³ g^?1. For the gel spheres of a solid solution of zirconium and calcium hydroxides, the distribution coefficient is appreciably lower, but the sorption capacity is considerably higher. These features are due to formation of a solid solution of lead and zirconium hydroxides in the course of sorption.     

The effects of hydroxide gel drying on the characteristics of co-precipitated zirconia-hafnia powders

Mixed zirconia-hafnia (Hf_0.25Zr_0.75O₂) powders of fine particle size and narrow particle-size distribution can be prepared via co-precipitation routes using mixed zirconium and hafnium salts as the starting materials. The characteristics of the resultant zirconia-hafnia powders are dependent strongly on the dehydration route by which the co-precipitated hydroxide gels are dried. Zirconium-hafnium hydroxide gels are formed when zirconium and hafnium oxynitrates are co-precipitated in an ammonia solution of pH 10.5. The co-precipitated hydrous gels were dried by three very different routes including organic solvent dehydration, microwave drying, and conventional infrared heating lamp drying. The dried hydroxides were then calcined at various temperatures in the temperature range 550–1150 °C, followed by ball milling to remove large soft-particle agglomerates. The resultant zirconia-hafnia powders were characterized for crystallite size, particle size, particle-size distribution, particle morphology, and the degree of powder agglomeration, using experimental techniques such as X-ray diffraction, BET surface area, differential thermal analysis, thermo-gravimetric analysis, sedigraph, scanning and transmission electron microscopy. Hard particle aggregates, which cannot be effectively eliminated using ball milling, occur in the zirconia-hafnia powders processed via either the microwave drying or conventional infrared heating lamp drying routes. In contrast, the organic solvent dehydration route resulted in an almost aggregate-free powder of fine crystallite and particle sizes. Therefore, the zirconia-hafnia powder processed via the organic solvent dehydration route exhibited high sinterability on sintering at 1300 °C.     

Processes to produce superconducting Nb3Sn powders from Nb-Sn oxide

The superconducting compound Nb₃Sn was produced by the reduction of the oxides or hydroxides of niobium and tin. The procedure consists of the following three steps; (i) preparation of the mixed oxides or hydroxides, (ii) direct alloy reduction, and (iii) homogenizing heat treatment of the reduced metal powders. For mixing the two oxides, two methods were tried: the simultaneous precipitation from the aqueous solution and the solidification of the molten oxides. These mixed oxides were reduced by ca!ciunn or magnesium vapour in the temperature range 973 to 1373 K. After calcium or magnesium oxide was removed by leaching the fine compound powder had an A-15 type crystal structure, but showed a relatively low superconducting critical temperature (T _c). The isothermal annealing improvedT _c to 18.0 K.