Bogdan Viorel Neamţu

Stability of Phases in Ball-Milled Zinc Ferrite/Iron Composite Produced by Spark Plasma Sintering

Three milling modes have been used for the synthesis of zinc ferrite/iron composite/nanocomposite powders. A partial or total reaction between zinc ferrite and iron (followed by the formation of zinc oxide and iron oxide) appears in the composite compact during Spark Plasma Sintering (SPS), for sintering temperature range of 400 to 550°C. Low sintering temperature led to a good preservation of zinc ferrite and iron when a composite powder obtained in low energetic milling mode was used. The milled powders and sintered compacts were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy, and energy dispersive X-ray spectrometry (EDX). The milling mode and sintering parameters influence on the stability of phases of composite/nanocomposites powder and compacts were investigated and discussed.

Effect of Process Control Agents on the FeSiB Powder Amorphisation by Wet Mechanical Alloying

Result of research concerning the influence of milling conditions on the amorphisation of the Fe75Si20B5 (at.%) alloy is presented. Amorphous powder of Fe75Si20B5 (at.%) was prepared by dry and wet mechanical alloying (MA) route starting from a mixture of Fe, Si and B elemental powders. The mixture was wet/dry milled up to 50 hours. Benzene, oleic acid and ethanol were used as process control agents (PCA) in order to investigate the influence of their chemical composition on the powder amorphisation. The evolution of the powder crystalline structure, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) as well as magnetic measurements versus temperature and field. It is proved that the chemical composition of the PCA (especially the carbon content) plays an important role in the amorphisation process induced by wet MA.

Synthesis of the Nanocrystalline/Nanosized NiFe2O4 Powder by Ceramic Method and Mechanical Milling

The polycrystalline nickel ferrite - NiFe2O4 has been obtained by ceramic route starting from a stoichiometric mixture of oxides (NiO and α-Fe2O3 powders). The obtained NiFe2O4 was subjected to high energy ball milling. The formation of NiFe2O4 by ceramic method and also the evolution of the powder during milling were studied by X-ray diffraction. The mean crystallite size of the NiFe2O4 continuously decreases with the increasing of the milling time and for all the milling time it is in nanometric range. The particles sizes are drastically reduced by milling process. For the milled samples, the particles size is ranging from tens of microns to few nanometers. The powder morphology and local chemical homogeneity were investigated by scanning electron microscopy (SEM) and respectively by energy dispersive x-ray spectrometry (EDX).

Effect of Sintering Parameters on the Stability of Phases of the ZnFe2O4/α-Fe Nanocomposite

The ZnFe2O4/α-Fe nanocomposite powders were obtained by ball milling starting from ZnFe2O4 powder synthesized by classical ceramic method and commercial iron powder. Two way of milling were used for the synthesis of the ZnFe2O4/α-Fe nanocomposite. In both cases after milling process the phases are relatively uniformly distributed in material and zinc ferrite mean crystallite size decreases from micrometric range up to 11 nm for the first milling mode and up 48 nm for second milling mode. The ZnFe2O4/α-Fe nanocomposite powders were compacted by Spark Plasma Sintering method (SPS). During sintering a reaction between nanocomposite phases occurs, thus leading to the formation of ZnO and FeO. The evolution of the powders during milling and stability of the nanocomposite phases was investigated by X-ray diffraction. The powders and compacts morphology and local chemical homogeneity were investigated by scanning electron microscopy (SEM) and respectively by energy dispersive x-ray spectrometry (EDX). The influence of the sintering parameters on the stability of nanocomposites phases is studied.

Zinc Ferrite Powder Synthesized by High Energy Reactive Ball Milling

The nanocrystalline zinc ferrite (ZnFe2O4) powder was synthesized by high energy reactive ball milling (RM) in a planetary mill. As starting materials a mixture of commercial zinc oxide (ZnO) powder and iron oxide (Fe2O3) powder was used. The starting mixture was milled for different periods of time, up to 30 h. The milled powders were annealed for 4 h at 350 oC in order to eliminate the internal stress and to finish the solid state reaction of ferrite formation. Zinc ferrite formation was investigated by X-ray diffraction. The obtained powder has a mean crystallite size of 12 nm after 20 h of milling. Using scanning electron microscopy (SEM) the particle morphology was studied. Particles size range of the powders was also determined using a laser particle size analyser.

Magnetic and thermomagnetic studies of the formation of the Rhometal powders by high energy mechanical milling

Nanocrystalline Rhometal (36Ni64Fe, wt. %) powders have been obtained by mechanical alloying under argon atmosphere. The initial mixture was milled up to 20 h. In order to eliminate internal stresses and to improve the solid state reaction annealing at 350 °C was performed for 4h. The alloy formation is obtained after 8 h of milling. A mean crystallite size of 10 ± 4 nm is obtained after 20 hours of milling. The magnetization values for the as-milled samples are between that of the starting sample and that of the as cast one. The evolution of the magnetization versus the milling time is discussed. The thermomagnetic analysis shows the Curie temperatures confirming the alloy formation by milling. As a result of the solid state reaction by milling means, a continuous decrease of the magnetization with increasing the temperature is recorded, similarly to the behaviour of the classical cast alloy.

Synthesis and characterisation of Al2O3/Ni-type composites obtained by spark plasma sintering

ABSTRACT This paper presents the influence of sintering on the structure, morphology and compressing strength of alumina/nickel composite compacts obtained by spark plasma sintering (SPS). Al2O3/Ni composites were prepared by SPS in argon atmosphere at temperatures in the range of 1000–1200 –C with a holding time of 2, 5 and 10 minutes. The heating rate was 200  C min−1. These composites have been characterised by X-ray diffraction, SEM and EDX. The relative density and compressive strength of the as-obtained compacts were determined. The results showed that the alumina particles are uniformly dispersed in a quasi-continuous Ni network, and there was no sign of phase changes during sintering. The maximum strength of the alumina/nickel composite with a content of 75 vol. − Al2O3 and 25 vol. − Ni was about 240 MPa for the samples sintered at 1200 C for 10 minutes. Special block from the conference RoPM2017 guest edited by Ionel Chicinas, Technical University, Cluj-Napoca.

Nanocrystalline/Nanosized Fe3O4 Powder Obtained by Mechanosynthesis

Nanocrystalline/nanosized magnetite - Fe3O4 powder was obtained by mechanical milling of well crystallized magnetite obtained by ceramic method starting from stoichiometric mixture of commercial hematite - Fe2O3 and iron - Fe powders. The mean crystallites size of the magnetite is decreasing upon increasing the milling time down to 6 nm after 240 minutes of milling. After 30 minutes of milling an undesired hematite phase is formed in the material. The amount of this phase increases upon increasing the milling time. In the early stage of milling (up to 30 minutes) the existence of nanometric particles (mean size below 100 nm) is noticed. The d50 median diameter decreases first (up to 5 minutes of milling) and after that, an increase follows for milling times up to 120 minutes. Saturation magnetization decreases upon increasing the milling time and is more difficult to saturate. X-ray diffraction, laser particle size analysis and magnetic measurements have been used for powder characterization.

Composite Compacts of Fe/Fe3O4 Type Obtained by Mechanical Milling-Sintering-Annealing Route

Fe/Fe2O3 composite powders were obtained by mechanical milling of iron and hematite up to 120 minutes in a high energy planetary ball mill. The particles size decreases by mechanical milling upon the formation of the Fe/Fe2O3 composite particles. After 120 minutes of milling the median particles size is at 7.2 μm. The Fe/Fe3O4 type composite were obtained by reactive sintering in argon atmosphere at 1100 °C of the Fe/Fe2O3 composite powders milled for 60 and 120 minutes. After sintering a FeO-wüstite residual phase is formed and this phase is eliminated by applying a subsequent annealing at a temperature of 550 °C. The sintered compact before and after annealing is composed by a quasi-continuous iron matrix in which are embedded iron oxides clusters (Fe3O4 and FeO before annealing and Fe3O4 after annealing). The iron oxide clusters are analogous with the Widmanstatten structure observed in steels before and after annealing. The materials have been investigated using laser particle size analysis, optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction.

Synthesis of Fe75Si20-xB5Mx (M=Ti, Ta or Zr) Powders by Wet Mechanical Milling

Amorphous Fe75Si20-xB5Mx powders with M= Ti, Ta or Zr and x = 0 and 5 were synthesized by wet mechanical alloying, using benzene as a surfactant. The thermal stability of the Fe-Si-B alloy increases by introducing transition metals. The replacement of 5% Si with Ti, Ta or Zr leads to an increase of the crystallization temperature. It was found that the replacement of 5% Si with Zr increases the crystallization temperature with 115 °C, and also reveals a glass transition temperature around 580 °C.