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Abstract  

Thermal decomposition of metal-organic precursors for the mixed oxide BaBiO3 was studied using TG and EGA. Precursors produced by polyesterification of bifunctional acids with ethylene glycol (Pechini process) decomposed about 100°C higher than those without the diol. BaCO3 was identified by IR and XRD as a reaction intermediate. EGA proved that the amount of BaCO3 was below 10% of the total barium, and that the barium exists mainly as a nitro-compound up to 650°C. Phase-pure BaBiO3 with a moderately high surface area (1.4 m2/g) could be synthesised from a citrate precursor by the Pechini process at around 850°C.

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Abstract

Nanocrystalline ferrite with the composition: Mn0.6Zn0.4Fe2O4 was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol–gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 °C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn0.68Zn0.32Fe2O4.

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Abstract  

The hydroxide, oxalate and citrate precursors of the metal oxides such as γ-Fe2O3, (MnZn)Fe2O4, Cu(K)Fe2O4, BaTiO3, La(Sr)MnO3, La(Sr)AlO3, La/Gd(Ca/Ba/Sr)CoO3, and anatase TiO2 on modifications with the hydrazine decompose at low temperatures give single phase oxides of superior properties, while the complexes without such modification require higher temperatures for achieving the phases. The hydrazine released at lower temperatures reacts with the oxygen in the atmosphere, N2H4+O2→N2+2H2O; ΔH=−625 kJ mol−1, and liberates enormous energy that is sufficient for the oxidative decomposition of the complexes now devoid of hydrazine. Such extra energy is not available in the case of the precursors without such modifications. The reaction products of hydrazine oxidation provide desired partial pressure of moisture needed for the stabilization of γ-Fe2O3. Also, the nitrogen that is formed in the reaction of hydrazine with oxygen gets trapped in the lattice of TiO2 giving yellow color nitrogen doped TiO2−xNx photocatalyst. Thus, hydrazine method of preparation has many advantages in the preparation of metal oxides of superior properties.

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Abstract  

Glasses of composition expressed by the following general formula xCaO·(1−x)SiO2 (0.30≤x≤0.50) can be prepared by means of the sol-gel route starting from tetramethylorthosilicate and calcium nitrate tetrahydrate They are all difficult to prepare by means of the traditional technique of quenching the melt, because of the high liquidus temperature,T 1 t that in the case ofx=0.3 glass isT 1=1650°C. The DTA apparatus appears a valuable tool for defining the procedure necessary to obtain the glass through the sol-gel route. The glassx=0.3 is bioactive. The experimental results suggest that the gel structures, such as obtained at room temperature, are very similar; only at high temperature do the reactions of hydrolysis and polycondensation go to completion and the structural units characteristic of each glass are obtained.

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Abstract  

Sodium zirconium phosphate [NaZr2P3O12], a potential ceramic matrix for fixation of high level nuclear waste, was synthesized by heating the mixture of sodium carbonate [Na2CO3], zirconyl nitrate hydrate [ZrO(NO3)25H2O] and ammonium dihydrogen phosphate [NH4H2PO4] in air, in a resistance heated furnace and a microwave heating system respectively in the temperature range 450 to 650C. The mixture heated for 1 h in a resistance furnace at 450C yielded a poorly crystalline NaZr2P3O12 [NZP]. Increasing the temperature to 650C produced a highly crystalline product. The same mixture heated in a microwave oven at 450C for 1 h however, yielded the most crystalline NZP. In an alternate method, the mixture of sodium dihydrogen phosphate (NaH2PO4), zirconium dioxide (ZrO2) and diammonium hydrogen phosphate [(NH4)2HPO4] heated in resistance furnace at 650C for the same period did not react in air. It also did not yield the pure product at 450C when heated in microwave assembly for 1 h.

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] Ghosh S. , Dasgupta , S. , Sen , A. , Maiti H. S. ( 2005 ) Low-temperature synthesis of nanosized bismuth ferrite by soft chemical route . J Am Ceram Soc 88 ( 5 ) 1349 – 1352 . [27

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.10.013 . 26. Ghosh , S , Dasgupta , S , Sen , A , Himadri Sekhar Maiti , HS . 2005 Low temperature synthesis of bismuth ferrite nanoparticles by a ferrioxalate precursor method . Mater Res Bull. 40 : 2073 – 2079 . 10.1016/j

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. 2. Verma , S , Karande , J , Patidar , A , Joy , PA 2005 Low-temperature synthesis of nanocrystalline powders of lithium ferrite by an autocombustion method using citric acid and glycine . Mater Lett 59 : 2630

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these methods require very high temperature and prolonged heating period to get a desired product. Now a days microwave heating method is used as alternative low temperature synthesis method [ 6 – 8 ]. In our laboratory we have synthesized mixed oxides

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Preparation of nanoparticles of oxides by the citrate–nitrate process

Effect of metal ions on the thermal decomposition characteristics

Journal of Thermal Analysis and Calorimetry
Authors: S. Banerjee, A. Kumar, and P. Sujatha Devi

–nitrate combustion process which was first developed for the low temperature synthesis of phase pure perovskites and superconducting oxides, and later extended for the synthesis and large-scale production of other multi component oxides with diverse properties [ 30

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