Structural and electrical properties of Ti doped α-Fe2O3

In this work we have analyzed the effects of Ti doping on structural and electrical properties of α-Fe2O3. When the amount of added Ti (5 wt.%TiO2) was within the solubility degree and XRD, SEM and EDS analysis revealed a homogenous hematite structure, with lattice parameters a= 5.03719(3) Å, c=13.7484(1) Å slightly increased due to incorporation of Ti into the rhombohedral hematite lattice. Higher amounts of Ti (10 wt.%TiO2) resulted in the formation of pseudobrookite, besides hematite, confirmed by SEM and EDS analysis. Studies of electric properties in the temperature range 25-225oC at different frequencies (100 - 1Mz) showed that Ti doping improved electrical conductivity. Impedance analysis was performed using an equivalent circuit, showing one relaxation process and suggesting dominant grain boundary contribution. [Projekat Ministarstva nauke Republike Srbije, br. III45014 i br. III43008

Optimized production route of WC powder pre-alloyed with Ta for fine grained cemented carbides

Powders of hexagonal (W,Ta)C were produced following a two-step carburization process with (W,Ta)(2)C powder as an intermediate product XRD measurements indicate that higher temperatures during the first carburization step increase the fraction of Ta in the (W,Ta)(2)C structure where lower temperatures during the second carburization step seems to increase the fraction of Ta in the (W,Ta)C structure. Lower temperatures during the carburization steps increase the fraction of Sigma 2 WC/WC grain boundaries and cause the formation of what is interpreted as Sigma 4 boundaries. The (W,Ta)C powders can be successfully used to produce fine grained WC-Co based cemented carbides. The pre-alloying with Ta appears to have a softening effect on the material

Analysis of WC with increased Ta doping

WC powder with increased Ta doping has been produced. Tungsten and tantalum metal powders were cocarburized to yield a mixture of cubic and hexagonal carbide. The carburization was made through a two-step carburization process with (W,Ta)(2)C powder as an intermediate product. X-ray diffraction analysis showed that the lattice parameters of the hexagonal phase in the fully carburized powder were larger than those of pure WC indicating the formation of a mixed crystal carbide, (W,Ta)C. The powder with the largest lattice parameters was investigated in detail. A method to produce atom probe tomography specimens of this powder was developed. The largest Ta solubility, expressed as Ta/(Ta + W), was 0.086 which is more than four times higher than what previously has been observed. In addition, it was found with electron backscatter diffraction that the (W,Ta)C grains had a large fraction of Sigma 2 grain boundaries as well as a small fraction of what was suggested as Sigma 4 grain boundaries. (C) 2015 Elsevier Ltd. All rights reserved

A study of magneto-crystalline alignment in sintered barium hexaferrite fabricated by powder injection molding

Barium hexaferrite permanent magnets were produced by powder injection molding. Starting barium hexaferrite powder was prepared from a Fe2O3 and BaCO3 powder mixture by calcination followed by milling. The feedstock for powder injection molding was prepared by mixing barium hexaferrite powder with a low viscosity binder. Magnetic alignment was achieved by applying a high intensity magnetic field to the melted feedstock during the injection process. Green samples (with and without magnetic alignment) were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering conditions were optimized in order to achieve a maximum energy product value. Magneto-crystalline aligning in barium hexaferrite was studied on both green and sintered samples using X-ray diffraction, scanning electron microscope (SEM) and magnetic measurements (hysteresis-graphs). All measurements were made both in a parallel and perpendicular direction to the aligning magnetic field. The obtained results confirmed magneto-crystalline alignment

CO Oxidation on Technological Pd-Al2O3 Catalysts: Oxidation State and Activity

The specific CO oxidation activity of palladium versus palladium oxide is still controversially discussed. In this study, 5 wt. % Pd-gamma-Al2O3 catalysts were utilized to investigate the effect of the palladium oxidation state on the CO oxidation activity. Comprehensive in situ and ex situ characterization of different alumina supported PdOx (x = 0-1) phases (by HR-TEM, XRD, and FTIR spectroscopy), combined with kinetic measurements and DFT calculations of CO adsorption, allowed us to assess the catalytic activity of the different PdOx (x = 0-1) species: Supported Pd-0 and substoichiometric PdO

Sintered strontium hexaferrite shaped by injection moulding in unidirectional magnetic and electromagnetic field

Strontium hexaferrite permanent magnets were produced by powder injection molding (PIM). The feedstock for powder injection molding was prepared by mixing strontium hexaferrite powder with a "Solvent system" organic binder. Injection was performed in the cylindrical cavity of the mold both for isotropic and anisotropic green samples. Diametrical alignment was attained using high energy permanent magnets embedded in the mold (unidirectional magnetic field), while axial magnetic alignment was done by DC current passing through a solenoid placed around the cavity (electromagnetic field). Green samples (with and without magnetic alignment) were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering conditions were optimized in order to achieve maximum energy product. Magneto-crystalline aligning in strontium hexaferrite was studied on both green and sintered samples using X-ray diffraction, scanning electron microscopy (SEM) and magnetic measurements (hysteresisgraphs). All measurements were made in the direction parallel to the aligning magnetic field. The obtained results confirmed a high degree of magneto-crystalline alignment

Properties of MnZn ferrites prepared by powder injection molding technology

In this work, manganese zinc ferrite components were manufactured by powder injection molding-PIM technology. A fine powder consisting of Mn1-xZnxFe2O4 with small addition of hematite alpha-Fe2O3 as used in mass ferrite production was mixed with an organic binder (Solvent System) to form ferrite feedstock for powder injection molding-PIM technology. Excess of Fe2O3 was present in the starting powder in order to suppress conversion of Fe3+ to Fe2+ ions which would lower the permeability. The ferrite feedstock was injected in a mold with a cavity shaped like a small cylinder with a hole on the main axis. Injection molded samples were then solvent and thermally debinded and sintered in different atmospheres: air, argon and nitrogen. The starting powder, injected green samples and sintered samples were characterized using X-ray diffractometry, scanning electron microscopy, thermogravimetry, differential thermal analysis as well as by magnetic measurements. Rietveld refinement of measured X-ray patterns was done to detect possible phase transformations of Fe2O3 to other iron oxides through reduction by binder residues (carbon) at elevated temperatures during thermal debinding and sintering. Finally, the magnetic properties were measured by hysteresis graph and mutually compared for the injected samples that were sintered in air, argon and nitrogen. The obtained magnetic characteristics where found to be comparable with commercial samples prepared by traditional sintering technology

Structural and electrical properties of Ti doped α-Fe2O3

In this work we have analyzed the effects of Ti doping on structural and electrical properties of α-Fe2O3. When the amount of added Ti (5 wt.%TiO2) was within the solubility degree and XRD, SEM and EDS analysis revealed a homogenous hematite structure, with lattice parameters a= 5.03719(3) Å, c=13.7484(1) Å slightly increased due to incorporation of Ti into the rhombohedral hematite lattice. Higher amounts of Ti (10 wt.%TiO2) resulted in the formation of pseudobrookite, besides hematite, confirmed by SEM and EDS analysis. Studies of electric properties in the temperature range 25-225oC at different frequencies (100 - 1Mz) showed that Ti doping improved electrical conductivity. Impedance analysis was performed using an equivalent circuit, showing one relaxation process and suggesting dominant grain boundary contribution. [Projekat Ministarstva nauke Republike Srbije, br. III45014 i br. III43008