Authors:G. Chuah, S. Jaenicke, K. Chan, S. Khor, and J. Hill
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.
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.
Authors:K. Rane, H. Uskaikar, R. Pednekar, and R. Mhalsikar
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.
Authors:A. Buri, A. Costantini, G. Laudisio, R. Fresa, M. Catauro, and F. Branda
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,T1t that in the case ofx=0.3 glass isT1=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.
Authors:A. Naik, N. Thakkar, S. Dharwadkar, K. Singh Mudher, and V. Venugopal
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.
Authors:Xuehang Wu, Wenwei Wu, Xuemin Cui, and Sen Liao
Ghosh , S , Dasgupta , S , Sen , A , Himadri Sekhar Maiti , HS . 2005 Lowtemperaturesynthesis of bismuth ferrite nanoparticles by a ferrioxalate precursor method . Mater Res Bull. 40 : 2073 – 2079 . 10.1016/j
Authors:A. P. Surzhikov, T. S. Frangulyan, S. A. Ghyngazov, and E. N. Lysenko
Verma , S , Karande , J , Patidar , A , Joy , PA 2005 Low-temperaturesynthesis of nanocrystalline powders of lithium ferrite by an autocombustion method using citric acid and glycine . Mater Lett 59 : 2630
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 lowtemperaturesynthesis method [ 6 – 8 ]. In our laboratory we have synthesized mixed oxides
Authors:S. Banerjee, A. Kumar, and P. Sujatha Devi
–nitrate combustion process which was first developed for the lowtemperaturesynthesis 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