Rama Krushna Panda

Hydrothermal preparation and characterization of boehmites

Boehmites (Al2O3·xH2O, 1<x<1.5) have been prepared hydrothermally from Al(NO3)3·9H2O and urea. Effect of temperature on preparation was studied in the range of 160°–220°C. No precipitation of boehmite was observed until the attainment of ∼160°C at which temperature a partly amorphous gel started precipitating. With the increase in temperature, transformation of the amorphous precipitate into crystalline boehmites took place as indicated by the X-ray diffraction (XRD) patterns. From the weight loss studies of the samples prepared at different temperatures and for different reaction time intervals, the value of x was estimated to vary between 1.3 and 1.5. The Fourier transform infrared (FTIR) spectra of samples obtained at 180°, 200° or 220°C showed 25–40 cm−1 upward shift in the –OH stretching and bending vibrations assigned to boehmites. γ-Alumina obtained by subsequent calcination of boehmite at 725°C was also characterized by XRD.

Effect of anions during hydrothermal preparation of boehmites

Boehmites were precipitated hydrothermally from different inorganic aluminum salt solutions under similar conditions using urea as the precipitating agent. It was observed that the hydrolysis of Al2ŽSO4.3starts at a lower temperature due to formation of hydroxy sulfates in comparison to AlCl3and AlŽNO3.3 solutions. The boehmite obtained from Al2ŽSO4.3 has a lower water content, and a higher surface area than the boehmites obtained either from AlCl3or AlŽNO3.3. The boehmite obtained from Al2ŽSO4.3was lighter giving lower tap density value. Depending on the nature of anion present during synthesis, the TG-DTA showed the endothermic peak between 460 and 480 8C, characteristic of transformation of boehmite to g-Al2O3. No other phase transformation occurred up to 1000 8C, indicating enhanced thermal stability of g-Al2O3 prepared through the present hydrothermal route. q2002 Elsevier Science B.V. All rights reserved.

Characterisation of fine polycrystals of metastable η-alumina obtained through a wet chemical precursor synthesis

Abstract An inexpensive and easy wet chemical synthesis is described which involves a mild base hydrolysis of an aqueous solution of aluminium sulfate with aqueous hydrazine hydrate solution as the hydrolysing precipitant, leading to the preparation of the basic aluminium sulfate (BAS) precursor. Heat treatment of the BAS precursor produces η-alumina (η-Al 2 O 3 ) when calcined at 900°C for 2 h; high temperature calcination at 1200°C of the precursor or of the above-mentioned calcined material leads to the formation of the thermodynamically stable α-alumina (α-Al 2 O 3 ). The alumina phases have been characterised by FTIR, X-ray diffraction, particle size measurements, electron micrography, weight-loss measurements and TGA-DTA analysis.

Preparation of barium hexa-aluminate through a hydrothermal precipitation–calcination route and characterization of intermediate and final products

Abstract A high surface area (∼22 m 2 /g) micro-sized (0.3–2 μ) barium hexa-aluminate powder was prepared by the calcination (at 1400 °C for 2 h) of hydrothermally prepared precursors of orthorhombic barium carbonate and boehmite. The precursors were obtained by a hydrothermal treatment (at 180 °C, for 1 h) of aqueous solutions of barium and aluminum nitrates of appropriate compositions in the presence of aqueous urea as the neutralizing precipitant. Results of XRD, TG-DTA and SEM measurements suggest the most probable reaction sequence for the preparation of barium hexa-alumnate ceramic powder as: (i) the hydrothermal precipitation of orthorhombic BaCO 3 and boehmite (γ-AlOOH) precursors from the aqueous Ba and Al nitrates in the presence of urea, (ii) the formation of an interim mixture of γ-Al 2 O 3 , BaCO 3 and Ba–β 1 -alumina in the temperature range of 800–1200 °C, and finally (iii) the formation of a ceramic powder corresponding to the composition BaO·6Al 2 O 3 having β-alumina type structure at ∼1400 °C. The final material did not show presence of any other crystalline phases like alumina, baria, barium mono-aluminate and tri-barium mono-aluminate phases.

Transition-metal chalcogenide materials. Quick and convenient methods of synthesis of crystalline nickel(II) disulfide

Abstract Quick, convenient and low-temperature methods of preparation of crystalline nickel (II) disulfide (NiS2) are reported, employing precursor-synthetic routes in the reaction of solid oxodihydroxonickel(IV) with an alkali-metal or ammonium polysulfide or with thioacetamide in the presence of ammonium acetate/ammonium hydroxide, both in the solid state and in small volumes of aqueous suspensions. Relative advantages of these methods over reported ones are discussed.

Solid state electroactive materials: synthesis and solid state electroactivity of some new materials derived from tris(2,2′-bipyridine-N,N′-dioxide)iron(III)-(IV) and hexacyanoferrate(II)-(III)

Abstract The synthesis of new solid electroactive materials of mixed-valent multinuclear inorganic backbones, derived from tris(2,2′-bipyridine- N , N ′-dioxide)iron(III) tris(2,2′-bipyridine- N , N ′-dioxide)iron(IV), hexacyanoferrate(II) and hexacyanoferrate(III) in the presence of perchlorate and/or chloride salts of sodium and/or potassium, are reported. The solid state cyclic voltammetry results show that thin powder layers of some of these solid materials possess good conducting properties ( i.e. varying degrees of electron conduction and/or ion conduction) at room temperature as a result of simultaneous electron and ion transport capabilities generated during redox.

Solid-state electroactive materials. Synthesis and solid-state electroactivity of some new materials derived from tris(2,2′-bipyridine-N,N′-dioxide)nickel(II)/ zinc(II)/cadmium (II)/mercury(II) and hexacyanoferrate(II)/(III)☆

Abstract New solid electroactive materials of mixed-valent multi-nuclear inorganic backbones, derived from the title complexes in the presence of perchlorate and/or chloride salts of sodium and/or potassium, have been synthesized. Results on solid-state cyclic voltammetry show that thin powder layers of some of these solid materials possess significant conducting properties (i.e. electron conduction and/or ion conduction) at room temperature because redox transitions in them are accompanied by simultaneous electron and ion transport.

Kinetics and mechanism of the reaction between 4-t-butylphenolate anion and tetrahydroxoargentate(III) in aqueous alkaline media

The reaction of [Ag(OH)4]– with 4-t-butylphenolate (L–) follows a biphasic absorbance change, each phase exhibiting pseudo-first-order kinetics under limiting conditions of the silver(III). A subsequent, slow, and very small absorbance increase (t0.5 > 1 h) is accompanied by the precipitation of metallic silver. In the [L–] range 0.5 × 10–3– 10 × 10–3 and [OH–] range 0.12–1.2 mol dm–3 at 25 °C and in aqueous medium, the pseudo-first-order rate constant for the initial, faster phase, Kf(in s–1), corresponds to the first one-electron transfer from L– to the initial silver(III) species and obeys the relation (i). The pseudo-first-order rate constant for the second, kf=(0.330 ± 0.09)+(1.26 ± 0.09)× 103[L–]+(2.64 ± 0.28)× 102[L–]/[OH–](i), slower phase, Ks(in s–1), represents the second one-electron transfer from L– to an intermediate silver(II) species produced as a result of the first one-electron transfer and satisfies an [OH–]-independent expression (ii). The kf and ks values are not influenced by the ionic strength (0.3–1.2, ks=(1.46 ± 0.02)× 102[L–]/{1 +(56.0 ± 3.5)[L–]}(ii) mol dm–3) of the medium nor by the presence of added pyrophosphate or silver(I) ions. Kinetic and spectral results are interpreted as suggesting that each of the processes mentioned most probably proceeds by a substitution-controlled mechanism at the silver centre.

Kinetics of oxidation of hydrazine and of t-butylhydrazine using tris(dimethylglyoximato)nickelate(IV) in the presence of added Cu2+(aq)

The kinetics of the oxidation of hydrazine and t-butylhydrazine using tris(dimethylglyoximato)-nickelate(IV), [Ni(dmg)3]2–, in the presence of added Cu2+(aq), and in the pH range 5.0–7.0 at 35 °C and I= 0.25 mol dm–3in aqueous medium, follow pseudo-first-order and pseudo-zero-order disappearance of the NiIVcomplex, respectively. Results of the Cu2+(aq)-promoted oxidation of hydrazine by [Ni(dmg)3]2–, are consistent with a probable scheme involving pH-dependent equilibrium formation of intermediate adducts between the NiIV and CuII–hydrazine complex species present in the solution and subsequent rate-determining electron transfer(s) to the adduct(s) from the hydrazine species in the presence of H+. Results of the Cu2+(aq)-catalyzed oxidation of t-butylhydrazine are interpreted in terms of a probable mechanism involving a rate-determining decomposition of the 1 : 1 intermediate complex between the CuII and t-butylhydrazine species in the solution, with a concomitant electron transfer. While the oxidation of hydrazine leads to nitrogen, the main products of the t-butylhydrazine oxidation are nitrogen and t-butyl alcohol.

Kinetics and mechanism of oxidation of hydrazine by tri-iodide ion in aqueous acidic media

The kinetics of oxidation of hydrazine (L) by I3– follows a pseudo-first-order rate law in aqueous acetic acid–sulphuric acid media in the range [H+] 2.0–1.58 × 10–3 mol dm–3. The pseudo-firstorder rate constants (kobs.) exhibit: (1) at [H+]= 0.9 mol dm–3 a linear dependence on [L]o at low [L]o, with a tendency to a limiting value at high relative [L]o; (2) a decreasing and complex trend in [I–] and in [H+]; (3) a decreasing trend with decreasing dielectric constant of the medium; and (4) negligible dependences on the ionic strength of the medium, on added Cu2+(aq), and on added ethylenediaminetetra-acetate. The results are interpreted in terms of a mechanism which envisages (a) negligible reactivities of I3– and of HL+ predominant in the medium, (b) an inner-complex mechanism of electron transfer (i.e. a 1 : 1 σ-charge-transfer co-ordination prior to the electron transfer) involving I2 and L, and (c) an encounter reaction between IOH and L. Mechanistic ambiguities of some earlier reports of the same reaction are explained.