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Abstract  

The metal complex, [Ni(en)2(H2O)2](NO3)2 (en = ethylenediamine), was decomposed in a static furnace at 200 °C by autogenous decomposition to obtain phase pure metallic nickel nanocrystallites. The nickel metal thus obtained was studied by XRD, IR spectra, SEM and CHN analysis. The nickel crystallites are in the nanometer range as indicated by XRD studies. The IR spectral studies and CHN analyses show that the surface is covered with a nitrogen containing species. Thermogravimetric mass gain shows that the product purity is high (93%). The formed nickel is stable and resistant to oxidation up to 350 °C probably due to the coverage of nitrogen containing species. Activation energy for the oxidation of the prepared nickel nanocrystallites was determined by non-isothermal methods and was found to depend on the conversion ratio. The oxidation kinetics of the nickel crystallites obeyed a Johnson–Mehl–Avrami mechanism probably due to the special morphology and crystallite strain present on the metal.

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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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Journal of Thermal Analysis and Calorimetry
Authors:
S. K. Durrani
,
K. Saeed
,
A. H. Qureshi
,
M. Ahmad
,
M. Arif
,
N. Hussain
, and
T. Mohammad

YAG with a homogeneous distribution of dopant at 900 °C suggested that this synthesis temperature is rather low for such kinds of ceramics. The average size of nano-crystallites was determined from the broad diffraction lines of X-ray patterns

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