Ana Cristina F. M. Costa

Effect of heating conditions during combustion synthesis on the characteristics of Ni0.5Zn0.5Fe2O4 nanopowders

Ni-Zn ferrite powders were synthesized by combustion reaction. The effect of external conditions of heating on the characteristics of the resulting powders was evaluated. Two synthesis routes were studied. The first involved preheating on a hot plate at 300°C and subsequently heating in a muffle furnace at 700°C (RCPM). In the second route the powders (RCP) were heated directly to 600°C on a hot plate until self-ignition occurred. The resulting RCP products were evaluated before and after attritor milling in order to reduce the size and increase the uniformity of particles and/or agglomerates. The resulting powders were characterized by X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), helium pycnometry, sedimentation and transmission electron microscopy (TEM). The results showed that it was possible to obtain Ni-Zn ferrite powders using both routes and that the second route (RCP) was the most favorable in terms of obtaining powders with high surface area. The efficiency of the grinding was confirmed by the reduction of the size of the particles.

Combustion synthesis, sintering and magnetical properties of nanocristalline Ni-Zn ferrites doped with samarium

An investigation was made of combustion synthesis to uniformly incorporate small amounts of samarium additive into nanocrystalline Ni0.5Zn0.5Fe2 − xSmxO4 (0.0 ≤ x ≤ 0.1) nanopowders (≈26–20 nm particle size). The effect of the addition of the rare-earth ion samarium on the microstructure, relative density and magnetic properties of the Ni-Zn ferrite obtained by combustion reaction was studied. The samples were uniaxially compacted by dry pressing, sintered at 1200°C/2 h, and characterized by bulk and apparent density, XRD, SEM and magnetic properties. The nanopowder samples without additive displayed an average grain size of 2.87 μm, while the addition of 0.05; 0.075 and 0.1 wt% Sm was found to inhibit grain growth, decreasing the average grain size to 0.77; 0.68 and 0.62 μm, respectively. The relative density was found to increase with the addition of samarium (>98.00% of the theoretical density). The samples without additive showed higher hysteresis parameter values.

Combustion Synthesis: Effect of Urea on the Reaction and Characteristics of Ni-Zn Ferrite Powders

The purpose of this study was to evaluate the effect of the urea content (fuel) on the reaction and the characteristics of Ni-Zn ferrite powders obtained by combustion synthesis. Several batches were prepared with different fuel contents, ranging from the stoichiometric composition between 20 and 100% (excess), while the desired molar proportion of the metal precursors was kept constant. The solutions were heated on a hot plate and then transferred to a muffle furnace preheated to 700°C, in which ignition took place. The resulting powders were characterized by XRD, BET, SEM, and sedimentation, aided by rotation measured through an optic light. The crystalline hematite (α-Fe2O3) and Ni-Zn ferrite phases were present in all the compositions studied, and the appearance of the agglomerates varied from soft to hard with increasing urea content. The increased urea content, which promoted a longer flame time, influenced the growth and/or formation of hard agglomerates. After sintering at 1200°C/2 h using the stoichiometric composition, only the spinel structure Ni-Zn ferrite, with homogeneous microstructure, was present.

Ferritas Ni-Zn: síntese por reação de combustão e sinterização

This work presents the study of the synthesis for combustion reaction and sintering of Ni-Zn nanometric ferrite powders. The ef fect of the concentration of Zn 2+ in the system Ni1-xZnxFe2O4 was investigated. The resulting powders of the combustion were characterized by DRX, BET, MEV, picnometry of helium and sedimentation (Horiba). Uniaxially pressed samples were sintered with constant heating rate (TCA) of 5.0 oC/min from 600 oC to the temperature of 1200 oC, in a horizontal dilatometer. The compact ones were characte rized by scanning electron microscopy. The results show that was possible to obtain Ni-Zn ferrite powders with particle size among 18 nm using combustion reaction synthesis. During sintering of the nanometric powders it was observed three different stages, whic h were identified through the Theory of Bannister. The addition of Zn 2+ didn’t modify the sintering mechanism in the three stages. For the initial and final stages the predominant mechanism was for viscous flow, attributed to the structural rearrangement of the nano particles and for the intermediate stage the mechanism was volumetric diffusion.