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Abstract  

Sol–gel auto combustion process was employed to synthesize nanosized Mn–Zn ferrite at different pH values (<1, 5, 6, 7, 8 and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective combustion was observed at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH < 1 showed localized burning. Thermogravimetric (TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air) of powders P1 and P6 synthesized at pH < 1 and pH 6 were also determined. B–H loop results showed that calcined powder C6 was more ferromagnetic than C1 due to fully developed spinel phase and larger particle size.

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Abstract  

The objective of present research was to sinter nanosized Mn–Zn ferrites (MZF) at low temperature (≤1,000 °C) by avoiding the formation of nonmagnetic phase (hematite). For this purpose, MZF powder was synthesized by sol–gel auto combustion process at 220 °C and further calcined at 450 °C. In calcined powder, single phase (spinel) was confirmed by X-ray diffraction analysis. Pellets were pressed, having 43% of the theoretical density and showing 47 emu gm−1 saturation magnetization (M s). Various combinations of heating rate, dwelling time and gaseous environment were employed to meet optimum sintering conditions at low temperature (≤1,000 °C). It was observed that sintering under air or N2 alone had failed to prevent the formation of nonmagnetic (hematite) phase. However, hematite phase can be suppressed by retaining the green compacts at 1,000 °C for 180 min in air then further kept for 120 min in nitrogen. Under these conditions, spinel phase (comprising of nano crystallites), 90% of theoretical density and 102 emu gm−1 of saturation magnetization has been achieved.

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involves many stages and it is energy-consuming [ 1 – 3 ]. In recent years research into the synthesis of Mn–Zn ferrites by chemical methods: sol–gel and sol–gel auto-combustion [ 4 – 9 ], hydrothermal [ 10 , 11 ], co-precipitation [ 12 ] and

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10973-010-0719-7 . 17. Waqas , H , Qureshi , AH . Influence of pH on nanosized Mn–Zn ferrite synthesized by sol–gel auto combustion process . J Therm Anal Calorim . 2009 ; 98 : 355

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. 32. Waqas , H , Qureshi , AH . Low temperature sintering study of nanosized Mn-Zn ferrites synthesized by sol-gel auto combustion process . J Therm Anal Calorim . 2010 ; 100 : 529 – 535 . 10.1007/s10973

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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

. 10.1016/S0955-2219(02)00191-7 . 20. Waqas , H , Qureshi , A-H . Low temperature sintering study of nanosized Mn–Zn ferrites synthesized by sol–gel auto combustion process . J Therm

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Molecular dynamic simulation sintered magnets soft magnetic sol–gel auto-combustion

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