SYNTHESIS OF LiFePO4 NANOCRYSTALS IN THE ION-LIQUID MEDIUM USING MICROWAVE HEATING

The liquid-phase method of synthesis of lithium iron(II) phosphate (LiFePO4) in the medium of choline chloride and diethylene glycol under the action of microwave heating is proposed. With a power of microwave radiation of 920 and 1150 W, a nanocrystalline LiFePO4 without impurities was obtained. Obtained samples of microwave processes contain amorphous phase and require long annealing resulting in nanocrystalline LiFePO4/C composites with small impurities Li3PO4, Li3Fe2(PO4)3, Fe2O3. For samples obtained in the choline chloride with diethylene glycol microwave heating characteristic is lamellar morphology – the same as for LiFePO4 obtained by thermal heating, but in the case of using microwave irradiation plates are smaller. This indicates that the reaction mechanism of LiFePO4 synthesis does not change in the microwave synthesis, but the reaction rate is significantly increased (up to 6 times faster than thermal synthesis). Using the Raman spectroscopy, the nature of the carbon coating on the crystal of LiFePO4 was studied. The Raman spectra of the LiFePO4/C composites obtained from an annealed powder with glucose and malic acid have pronounced D (~ 1340 cm-1) and G (~ 1600 cm-1) peaks, as well as two additional bands at ~ 1200 and ~ 1520 cm-1 obtained after the expansion of main peaks. The ratio of peak intensities of lines D and G (ID/IG) has a value of 1.06 for the material obtained after glucose carbonation and 1.01 for LiFePO4/C composites annealed with malic acid, which correlates with the results of other investigations of the carbon coating LiFePO4 (ID/IG ~ 1-3) That means the choice of an organic precursor does not affect the nature of the carbon coating (ID/IG ~ 1). Capacity of cathode material based on LiFePO4/C composites is ~ 130 mAh/g for a current of 0.1C.

SYNTHESIS OF Cu1.6Bi4.6S8 COMPOUND FOR THERMOELECTRIC APPLICATION

<p class="AMSmaintext">In this work, Cu_1.6Bi_4.6S₈ thermoelectric compound was synthesized using high energy milling and heat treatment. The starting mixture include Cu, Bi and S elemental powders at the stoichiometry ratio of the formula Cu_1.6Bi_4.6S₈ were ball milled in a planetary ball mill and heat treated in an electric furnace. The results shown that after 10 hours of milling, a compound identified as Cu_3.21Bi_4.79S₉ was formed. The 16h milled powder was heat-treated at 350, 400 and 450ºC for 1 hours at a heating rate of 8 ºC/minute, XRD of the annealed powder reveals that the Cu_3.21Bi_4.79S₉ obtained fully transformed into Cu_1.6Bi_4.6S₈ after being heat treated at 400ºC. Meanwhile, Bi₂S₃ was found in the powder being annealed at 350ºC. The 5h milled powder was also annealed at 400ºC for 1 hours at a heating rate of 2 and 8 ºC/minute, XRD analysis show that Cu_1.6Bi_4.6S₈ was also formed in the heat-treated powder with the heating rate of 2 ºC/min.</p>

Sintering of AISI M2 Tool Steel Processed in High-Energy Planetary Mill

This work aimed to evaluate the effect of pre-sintering annealing heat treatments and sintering times in AISI M2 high-speed steel powders processed by high energy milling. Turning chips were obtained from an AISI M2 drill bit that was annealed during 2 hours at 900°C, under argon atmosphere, before machining. Subsequently, the chips were milled during 10 hours in a high energy planetary mill with a power ratio of 10:1, also under argon atmosphere. Half of the powder mass was annealed at 650oC during 30 minutes under argon atmosphere after milling. Three different samples were prepared, consisting of: non-annealed powder, annealed powder and a mixture 1:1 of annealed and non-annealed powders. All powders were compacted by uniaxial pressing before sintered. Compressibility curves were obtained for all samples. Sintering process was conducted at 1200°C during 1, 2 and 3 hours and samples were cooled inside the furnace. The annealed powder sample presented the best compactation behavior, due to its restored ductility, followed by the 1:1 mixture of annealed and non-annealed powders. The microstructure of sintered samples displayed a ferritic matrix surrounded by carbide networks at grain boundaries. Higher sintering times resulted in carbon impoverishing, leading to lower volume fractions of carbides and hence reducing its hardness. Non-annealed powders showed higher dependency of sintering time to reduce their porosity. The best results were obtained for the annealed powder with shorter sintering time, since it presented low volume fraction of porosities and smaller grain sizes.

Comprehensive characterization of BiFeO3 powder synthesized by the hydrothermal procedure

In this paper, bismuth ferrite (BFO) particles synthesized by controlled hydrothermal process, where the particles of small sizes and with high purity were obtained. Structural analysis showed that non-annealed powder can be perfectly fitted to rhombohedral space group R3c and contains a very small amount of secondary phase, whereas the final product (annealed at 800?C) represents single-phase perovskite powder with high crystallinity. HRTEM analysis confirmed existence of twin stacking faults, which are responsible for enhanced magnetic properties. EPR measurements suggested existence of electrons trapped by vacancies or defects. It has been proposed that existence of Fe3+?OV defect complex could be generated at elevated temperatures followed by formation of trivalent Fe ions, which intensely provide local 3d moments.

Characterization of 14YWT As-Atomized, Milled, Milled and Annealed Powders and HIP Consolidated Alloys

ABSTRACTNanostructured ferritic alloys (NFA) are Fe-Cr based ferritic stainless steels containing an ultrahigh density of very stable Y-Ti-O nanofeatures (NFs) that provide dispersion strengthening and radiation damage resistance for candidate Generation IV and future fusion reactor materials. This work is a small and focused part of a larger collaboration to produce large best practice NFA heats. The powders analyzed were rapidly solidified from a melt containing Fe-14%Cr, 3%W, 0.4%Ti and 0.2%Y by gas atomization in Ar, Ar/O, and He atmospheres. Note this represents a different processing path from conventional NFA production where metallic powders are mechanically alloyed with Y2O3 by ball milling. Electron probe microanalysis (EPMA), atom probe tomography (APT), transmission electron microscopy (TEM) and small angle neutron scattering (SANS) were used to characterize the powders in the as-atomized, ball milled and ball milled and annealed conditions. EPMA showed the Y is heterogeneously distributed and phase separated in all the as atomized powders, but attritor milling for 20 to 40 h is required to mix the Y. Milling also creates a significant quantity of O as well as N contamination. Subsequent powder annealing treatments, typically at 1150°C, result in the precipitation of a high density of NFs. All the annealed powder variants show a bimodal grain size distribution, but TEM and APT show NFs in both large and small grains. Reducing O content added during milling of the Ar atomized powders increased the precipitate size and decreased the number density, adversely affecting the hardness.

Thermoluminescence Properties of Novel La2O3 Phosphor Obtained by Solution Combustion Synthesis

Thermoluminescence (TL) of La2O3 is reported for the first time. Novel La2O3 phosphor was obtained by solution combustion synthesis (SCS) in which a redox combustion process between lanthanum nitrate and urea at 500 °C is accomplished. The powder samples obtained were annealed at 900 °C during 2 h in air. X-Ray Diffraction (XRD) results showed the hexagonal phase of La2O3 for annealed powder samples. The TL glow curve obtained after exposure to beta radiation of these samples, displayed two maxima located at ˜ 101 °C and ˜ 200 °C, and a shoulder at ˜ 247 °C. Results from experiments such as dose response and fading showed that annealed La2O3 powder obtained by SCS is a promising material for radiation dosimetry applications.

EFFECT OF MILLING TIME ON MECHANOCHEMICAL SYNTHESIS OF TiO2 NANOPARTICLES

Titanium dioxide nanoparticles have great potential for use in photocatalytic applications, cosmetics, white pigments and so on. In this paper, the effect of milling time on particle size, morphology and phase composition of TiO 2 nanoparticles, prepared by mechanochemical method, was investigated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). TiO 2 nanoparticles were prepared by the use of high energy ball milling of titanyl sulphate ( TiOSO 4) and NaCl powders as the starting mixture in different milling durations. The milled powder was annealed at 700°C for 30 min. The NaCl powder, used as the diluent phase, was removed by washing the annealed powder with distilled water. It was found that with increasing milling time, decrease in the size of equiaxed spherical particles and increase in temperature of anatase to rutile transformation ( A → R ) can be observed.

The Effect of Alloying Elements on the c/a Ratio of Magnesium Binary Alloys

In order to clarify the effect of alloying elements on the axial ratio of magnesium binary solid solutions, the solid solutions of Mg-Al, Mg-Zn, and Mg-Li with various concentrations were casted and homogenized. Synchrotron X-ray diffraction patterns were then obtained from annealed powder samples and analyzed using the Rietveld method. The effects of solutes concentration on lattice parameters were explained on the basis of atomic size difference and valence electron effect, which changes electron overlap of magnesium. It has been found in this study that Al and Li raise and reduce the c/a ratio, respectively, while Zn has no effect on the c/a ratio.