Citrate-gel Combustion Method Research Articles

Structural Elucidation, IR spectroscopy and DC electrical conductivity of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via a low-temperature citrate gel combustion method

In the present work, we report the detailed Powder XRD Rietveld refinement and elucidation of structural factors of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites. The Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via low-temperature citrate gel combustion technique for the various levels of Gd3+ ion concentration (y = 0.0, 0.1, 0.15 and 0.20). The generated structural factors signify the dependence on the concentration of Gd3+ ions. The prepared samples were found to crystallize in the Fd-3m space group and also identified their occupancies; some of the Fe3+ ions of the octahedral site at the 16d position will be replaced by Gd3+ ions. The lattice constant and crystallite size dropped to a low value for y = 0.1, and then, later, noticed the small increment. The crystallite sizes of the sample are to fall in the range of 26.1 nm–37.6 nm. The cation distribution among the tetrahedral (AII) and octahedral sites (BII) has been estimated. The obtained values correlate with Gd3+ ion concentration, and the radius variation of AII and BII sites signifies the migration of Fe3+ ions from the BII site to the AII sites. The force constant of Metal-Oxygen bonds was determined from the infrared spectrographs; the force constant was found to be relatively low with the BII site. The DC electrical conductivity infers the semiconducting nature and distinct phase of conductivity, which is attributed to the magnetic phase change due to temperature. The magnetic curie temperatures of the sample are obtained by the Arrhenius plot, which signifies the dependence of Gd3+ion concentration.

PANI-wrapped BaFe12O19 and SrFe12O19 with rGO composite materials for electromagnetic interference shielding applications

We report electromagnetic interference (EMI) shielding efficiency in the PANI-wrapped BaFe12O19 and SrFe12O19 with rGO composites. Barium and strontium hexaferrites were synthesized using the nitrate citrate gel combustion method. These hexaferrites were polymerized in situ with aniline. The PANI-coated ferrite-based composite materials were developed along with reduced graphene oxide (rGO) in acrylonitrile butadiene styrene (ABS) polymer, and their shielding effectiveness was assessed in X-band frequency range (8.2–12.4 GHz). The reflection (SER) and absorption (SEA) mechanism of shielding effectiveness was discussed with the different rGO concentrations. The results reveal that 5 wt% of rGO with PANI-coated barium and strontium hexaferrite polymer composites exhibit shielding efficiency of 21.5 dB and 19.5 dB, respectively, for 1 mm thickness composite. These hexaferrite polymer-based composite materials can be used as an attractive candidate for EM shielding materials in various technological applications.

Effect of Ni2+ substitution on magnetic, optical and electrical properties of SrFe2O4

Citrate gel combustion method is used for the synthesis of Ni2+ substituted strontium ferrite Sr1-xNixFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8). The characterization of synthesized material is done by different techniques. Fourier transform Infra-red (FT-IR) spectra revealed the inverse spinel structure and showed slight shift in spectrum. X-ray diffraction (XRD) patterns demonstrated the orthorhombic phase of spinel formation with trace of secondary phase impurity of SrCO3. Scanning electron microscopy (SEM) images showed agglomeration of particles. The effect of Ni2+ substitution in SrFe2O4 on structural, magnetic, optical and direct current (DC) electrical resistivity properties are investigated. Room temperature vibrating sample magnetometer (VSM) studies indicated increase in trend of saturation magnetization (Ms) and remanence magnetization (Mr) with increase in content of Ni2+ ion. The squareness ratio (SQR) Mr/Ms for SrFe2O4 is found to be 0.5752, while for remaining samples it is found to be less than 0.5 which demonstrated multi domain to single domain transition. Variation of band gap energy with Ni2+ substitution is reported with the help of ultra-violet diffuse reflectance spectra (UV-DRS). Temperature dependent DC electrical resistivity by two probe method measurement obeyed Arrhenius equation and revealed the typical semiconducting behavior of the samples. The change in slope of line observed in resistivity due to ferrimagnetic to paramagnetic transition in all samples attributed strong exchange interaction between the outer and inner electrons. Activation energy (Ea) for ferri and paramagnetic region is calculated. For ferrimagnetic region the Ea is found to increase with increasing Ni2+ content while, in paramagnetic region for Ni2+ substituted samples the Ea is found to be greater than 0.2 eV which inferred the hopping motion of small polarons are responsible for conductivity. The complex impedance spectra revealed the information about conduction mechanism.

Optical properties of Sr3Gd(PO4)3: Eu3+ phosphors for white LED sources

The SGPEux phosphors of composition Sr3Gd(1–x)(PO4)3:xEu3+ were synthesized by modified citrate-gel combustion method for white LED sources. The optimum conditions of synthesis were obtained from thermogravimetric and differential scanning calorimetry. The synthesized phosphors were crystallized into BCC structure with JCPDS No. 29–1301. The presence of various bonds due to stretching and bending vibrations of different functional groups were studied through Fourier transform infrared spectroscopy. The morphology was examined using high-resolution scanning electron microscopy. The luminescence analysis was carried out through photoluminescence excitation and emission studies. The charge transfer band and f-f transitions of Gd3+ and Eu3+ ions cause a transfer of energy from Gd3+ to Eu3+. A suitable excitation wavelength for efficient luminescence was selected as 273 nm by studying the emission properties at different excitations. The quenching in luminescence noticed beyond 2.0 mol% was assigned to non-radiative transitions at higher Eu3+ concentrations. The analysis of colour perception and colour temperature of emitted luminescence was studied using chromaticity coordinates evaluated from the emission spectra. The observed results suggest that the 2.0 mol% of Eu3+ doped SGPEu phosphor has more proficiency to design new class of w-LED sources.

Influence of catalyst synthesis methods on anti-coking strength of perovskites derived catalysts in biogas dry reforming for syngas production

This study examined biogas dry reforming using perovskite-derived catalysts over the temperature range of 650–850 °C. Citrate-gel combustion and co-precipitation methods were used to prepare perovskites (LaCoO3 and LaNiO3). These perovskites were converted into metal-supported catalysts by reduction process. Also, impregnation was applied for the synthesis of 30 wt% Ni/La2O3 and 10 wt% Ni/Al2O3. X-ray diffraction and high-resolution transmission electron microscopy confirmed that the average particle size of Ni or Co was smaller in the combustion method over co-precipitated method. Citrate-gel combustion method favors La2O2CO3 phase, whereas co-precipitation method prefers La(OH)3 phase in the support. Although the biogas dry reforming condition used in this study (CH4/CO2 = 1.5) is much severe for coke deposition than conventional dry reforming condition (CH4/CO2 = 1.0), the catalyst derived from perovskite LaNiO3 by citrate-gel combustion method showed outstanding performance among examined catalysts. The La2O2CO3 phase self-regenerates and oxidizes carbon from the nickel sites continuously. The high anti-coking strength was attributed to the highly dispersed nickel nanoparticles, La2O2CO3 species, and low acidity confirmed by NH3-TPD. Therefore, the citrate-gel combustion method is an alternative to conventional methods for biogas dry reforming.

Deep reddish-orange emitting Sr3Gd(PO4)3: Sm3+ phosphors via modified citrate-gel combustion method

The photoluminescence properties of different concentrations of Sm3+ activated Sr3Gd(PO4)3 phosphors synthesized by modified citrate gel-combustion method were investigated for white light emitting diode (w-LED) applications. The studied phosphors were characterized through powder x-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), photoluminescence excitation, emission and lifetime studies. The PXRD profiles confirmed the body centred cubic structure of undoped and Sm3+ -doped phosphors. The SEM studies showed the distribution and agglomeration of particles. The characteristic emission transitions such as 4G5/2 → 6H5/2 (∼561 nm), 4G5/2 → 6H7/2 (∼598 nm), 4G5/2 → 6H9/2 (∼645 nm) and 4G5/2 → 6H11/2 (∼705 nm) were noticed at their respective positions when excited at 403 nm wavelength. The highest luminescence intensity was found for 1.0 mol% of Sm3+ doped phosphors at 403 nm excitation showing luminescence quenching and it was ascribed to dipole-dipole interaction type of energy transfer among the excited Sm3+ ions at higher concentrations. The reddish-orange color of emitted luminescence was examined by evaluating the chromaticity coordinates. The experimental results confirm the potentiality of studied phosphors for w-LED applications.

Utilizing the Oxygen Carrier Property of Cerium Iron Oxide for the Low-Temperature Synthesis of 1,3-butadiene from 1-butene

Low-temperature oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene is one of the challenging reactions in the polymer industry. Towards this a highly dispersed cerium iron oxide was synthesized by citrate gel combustion method and employed for the synthesis of 1,3-butadiene (BD) from 1-butene. The reaction was carried out at low temperature under an oxygen-free atmosphere in a continuous flow mode fixed bed reactor. A decrease in the lattice parameters observed from PXRD and high-resolution TEM analysis proved that iron occupies cerium sites in the crystal lattice. XPS, TPR, and oxygen uptake studies quantified the nature and abundance of different oxygen species. ODH was observed through consuming lattice oxygens. The vacancies generated could be filled by re-oxidation with an external supply of oxygen which will restore the catalytic activity demonstrating the Mars van Krevelen mechanism.

Processing and characterization of Ba0.5Sr0.5Fe12O19/Y3Fe5O12 nanocomposite ferrites towards permanent magnet applications

A one-step citrate-gel combustion method was employed to process (Ba0.5Sr0.5Fe12O19)1-x/(Y3Fe5O12)x nanocomposite ferrites with different compositions (x = 0.1, 0.2, 0.3, and 0.4). The morphological, structural, thermal, and magnetic properties of the as-synthesized samples were investigated with respect to their structural, thermal, and magnetic properties using field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and vibration sample magnetometer (VSM), respectively. The FESEM micrographs revealed homogeneous distribution of hard and soft magnetic phases throughout the sample. The XRD results confirmed the crystallization of both BSFO and YIG as hard and soft magnetic phases, respectively, without any other secondary phases. The TGA/DSC curve confirmed the phase formation of the nanocomposite material around 1100 °C with a total weight loss of ~ 63%. The magnetic hysteresis loops of as-synthesized ferrite nanocomposites demonstrated a single-phase behavior due to the existence of strong inter-grain exchange coupling between the hard and soft magnetic phases. The single peak in switching field distribution (SFD) curves of synthesized nanocomposite ferrite were observed for all the compositions. Maximum values of coercivity (6090 Oe), saturation magnetization (54 emu/g), and energy product (19.5 kJ/m3) were achieved for the BSFO0.9/YIG0.1 composition. The results of the present study suggest that the magnetic parameters such as those derived from the nanocomposite ferrites are superior as compared with that of those obtained for the constituent YIG and BSFO phases.

Ferrimagnetism, exchange bias and spin-glass property of disordered La2CrNiO6

A B-site disordered double perovskite La2CrNiO6 is synthesized by citrate-gel combustion method. The material is showing an orthorhombic Pbnm crystal structure which doesn’t change upon cooling to 15 K and with an applied field of 50 kOe. Upon cooling from room-temperature to 15 K, a nearly linear dependence in the volume of the crystal structure with temperature is observed until 100 K, which is around the ferrimagnetic transition temperature of the material. The disordered Cr and Mn introduced inhomogeneous magnetic interactions, leading to Griffiths-like phase (GP) and spin glass state in the material. The material shows an exchange bias effect, owing to the GP and spin glass state. Mott’s variable range hopping is the conduction mechanism of the insulating disordered double perovskite La2CrNiO6.

Microwave-assisted citrate gel-combustion synthesis of nanocrystalline urania

A systematic investigation on the microwave-assisted citrate gel-combustion synthesis of nanocrystalline urania powders is being reported for the first time. Nanocrystalline urania powders were synthesized by microwave-assisted citrate gel-combustion method by using citric acid as a fuel and nitrate as an oxidizer. The fuel to nitrate ratio (R) was varied from 0 to 1 (0, 0.1, 0.25, 0.5, 0.75 and 1.0). It was observed that at a particular stoichiometric ratio (R = 0.1), auto ignition reaction takes place resulting in a porous product. The as-prepared powders were calcined and further reduced under flowing hydrogen. All these powders were characterized for the phases present viz., X-ray diffraction (XRD), size distribution of pores, transmission electron microscopy (TEM), specific surface area (SSA), thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) and infrared spectroscopy. It was observed that the microwave-derived powders with an R-value of 0.1 had the lowest bulk density, highest SSA and highest total pore volume. Upon calcination and reduction, the total pore volume decreased. The specific surface area of the calcined powders was the lowest and that of the as-prepared powders was the highest while that of the hydrogen-reduced powders was in between. An opposite trend was observed with the X-ray crystallite size (XCS). The microwave-derived nanocrystalline urania powders showed a lower SSA, higher XCS, higher lattice strain, higher residual carbon and lesser total pore volume than their hot plate derived counterparts. This is probably due to the influence of microwave which accelerates the reaction leading to faster grain coarsening.

Magnetization sign reversal, exchange bias, and Griffiths-like phase in orthorhombic perovskite Pr2FeMnO6

Abstract The perovskite Pr2FeMnO6 has been synthesized by citrate-gel combustion method. The material has an orthorhombic crystal structure with Pbnm space group. The presence of Fe3+ and Mn3+ cations in the material are confirmed by XPS analysis. A magnetization sign reversal is observed for the material at low-temperatures in low applied magnetic fields. When the applied field or temperature is increased, the negative magnetization got diminished. Such a sign reversal of magnetization is observed for the material as a result of the interaction between components of paramagnetic Pr3+ and Mn3+ moments opposite to the component of the ferromagnetic Fe3+ moment or the anti-aligned Fe-rich regions to that of Mn-rich regions containing with Pr3+. Negative exchange bias is also exhibited by Pr2FeMnO6 below 200 K which can be ascribed to the Dzyaloshinskii-Moriya interaction and magnetic exchange anisotropy. A high-temperature magnetic transition at TC = 576 K is identified for the material from the thermomagnetic data. From the detailed analysis of the thermomagnetic data, the presence of ferromagnetic short-range correlations is observed far above the TC, which suggests a Griffiths-like phase with Griffiths temperature at TG = 681 K.

Temperature-dependent phase transition: Structural and magnetic properties of Ba0.5Sr0.5Fe12O19-CoFe2O4 nanocomposites

Ba0.5Sr0.5Fe12O19(hard)-CoFe2O4(soft) nanocomposite ferrites synthesized using the citrate-gel combustion method was subjected to different annealing temperatures (Ta) (700 °C, 800 °C, 900 °C, and 1000 °C), and the resultant structural and magnetic properties were investigated. The microstructural characterization of nanocomposites via X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) analysis at first revealed the dominance of soft phases annealed at 700 °C and then showed the presence of hard phases at 900 °C. Lattice vibrational analysis again showed a clear distinction between the bands corresponding to Ta at 700 °C and 900 °C. An increase in saturation magnetization (MS) and coercivity (HC) was observed upon increasing the Ta. A good combination of MS (56.9 emu/g) and HC (3.3 kOe) was obtained at Ta = 900 °C. In addition, high-temperature magnetic studies confirmed the dominance of soft phase with Curie temperatures of 592 °C and 480 °C for the samples annealed at 700 °C and 900 °C, respectively. Combining these facts, a detailed mechanism involving the domination of spinel plates and hexagonal layers was drawn. The magneto crystalline anisotropy was evaluated and showed a maximum for Ta at 900 °C. The extent of exchange coupling between the hard and soft phases was further analyzed by switching field distribution curves and is discussed in detail.

Elektrohemijsko ponašanje resintetisanog katodnog materijala iz potrošenih litijum jonskih baterija u organskom elektrolitu

The excessive use of Li-ion batteries has resulted in the growing necessity of developing a recycling procedure for them, particularly stemming from their negative impact on the environment as well as the fact that the natural-ore metals contained in them can be replaced. This work presents a re-synthesis of cathode material obtained from spent Li-ion batteries using the co-precipitation method in order to recycle it. The structure of the re-synthesized metal was characterized by XRD and the morphology by SEM. The chemical content of the spent cathode material was determined by FAAS. In order to prove functionality, the electrochemical behaviour was examined in a 1M solution of LiClO4 in propylene carbonate by galvanostatic charging and discharging. Since the initial capacity of the re-synthesized material was 70.6 mAh g-1 when the current of charging/discharging was 100 mA g-1, the fade of capacity was 13% after the initial five cycles. The electrochemical properties of the re-synthesized material were then finally compared to the material re-synthesized by the citrate gel combustion method.

Synthesis, structure and thermoelectric properties of $$\mathrm{La}_{1-x}\mathrm{Na}_{x}\mathrm{CoO}_{3 }$$ La 1 - x Na x CoO 3 perovskite oxides

Monovalent ion doped lanthanum cobaltate $$\hbox {La}_{1-x}\hbox {Na}_{x}\hbox {CoO}_{3 }$$ ( $$0 \le x \le 0.25$$ ) compositions were synthesized by the nitrate–citrate gel combustion method. All the heat treatments were limited to below 1123 K, in order to retain the Na stoichiometry. Structural parameters for all the compounds were confirmed by the Rietveld refinement method using powder X-ray diffraction (XRD) data and exhibit the rhombhohedral crystal structure with space group R-3c (No. 167). The scanning electron microscopy study reveals that the particles are spherical in shape and sizes, in the range of 0.2–0.5 $$\upmu $$ m. High temperature electrical resistivity, Seebeck coefficient and thermal conductivity measurements were performed on the high density hot pressed pellets in the temperature range of 300–800 K, which exhibit p-type conductivity of pristine and doped compositions. The X-ray photoelectron spectroscopy (XPS) studies confirm the monotonous increase in $$\hbox {Co}^{4+}$$ with doping concentration up to $$x = 0.15$$ , which is correlated with the electrical resistivity and Seebeck coefficient values of the samples. The highest power factor of $$10~\upmu \hbox {W~mK}^{-2 }$$ is achieved for 10 at% Na content at 600 K. Thermoelectric figure of merit is estimated to be $${\sim }1 \times 10^{-2}$$ at 780 K for 15 at% Na-doped samples.

Structural and magnetic properties of multiferroic Y2NiMnO6 double perovskite

ABSTRACTThe double perovskite Y2NiMnO6 is prepared by a citrate-gel combustion method. The structural, magnetic and dc transport properties of Y2NiMnO6 are investigated systematically. A monoclinic crystal structure having space group P21/n is identified for the material from XRD. Magnetic structure is characterized by isothermal and thermomagnetic studies. The material possesses a ferromagnetic transition at 88 K. The dynamic magnetic structure of the material is analyzed using the ac susceptibility data. Resistivity data suggests the semiconducting behavior of the material. The work provides well advancement in researchers on potential material for spintronic applications.

A potential green emitting citrate gel synthesized NaSrBO3:Tb3+ phosphor for display application

A potential green emitting NaSrBO3:Tb3+ (1–9mol%) phosphor was synthesized by a citrate gel combustion method. X-ray diffraction patterns confirmed the monoclinic phase of the phosphor. The phosphor emitted intense green emission under near-UV and electron excitation due to the characteristic transitions 5D4→7F6(488nm),5D4→7F5(544nm),5D4→7F4(586nm) and 5D4→7F3(622nm) of Tb3+ ions. The optimal molar concentration of Tb3+ ions was found to be 6mol%, after that concentration quenching occurred. The dipole-dipole interaction was found to be accountable for energy transfer between the Tb3+ ions. X-ray photoelectron spectroscopy was carried out to analyze the chemical states of the elements and suggest that terbium was mostly presented in the (+3) valance state in the phosphor. The approximated Commission Internationale de l′Eclairage coordinates for the PL (0.31, 0.61) and CL (0.33, 0.57) were found to be very close to the well-known green emitting phosphor. The obtained results suggest that the studied phosphor could be an ultimate choice for green emission in display applications.

Combustion synthesis and characterisation of Eu<SUP align="right">3+</SUP>-activated Y<SUB align="right">2O<SUB align="right">3 red nanophosphors for display device applications

Europium activated yttrium oxide red phosphors have gathered more attention because of their good luminescent characteristics, acceptable atmospheric stability, reduced degradation under applied voltages, and lack of hazardous constituents. In order to achieve improved luminescent properties of Y2O3:Eu3+, the synthetic methods are playing an important role. In the present study, Eu3+ (2 mol %) doped Y2O3 nanophosphors were synthesised by the facile nitrate citrate gel combustion method at relatively low temperature and shorter duration (700°C for 2 h). Further samples were characterised by powder X-ray diffraction (XRD) technique. The morphology and particle size of the phosphors were studied by scanning electron microscope (SEM), UV reflectance spectroscopy and Raman spectroscopy. The photoluminescence measurements of the Y2O3:Eu3+ particles showed red emission peaks at 610-612 nm (5D0 → 7F2). CIE chromaticity diagram and CCT calculations confirmed that these nanophosphors can act as a red component in the fabrication of white light emitting diodes (WLEDs) for display and other optical device applications.

A study on the extent of exchange coupling between (Ba0.5Sr0.5Fe12O19)1−x(CoFe2O4)x magnetic nanocomposites synthesized by solgel combustion method

One step citrate gel combustion method followed by high temperature annealing was employed for preparing (Ba0.5Sr0.5Fe12O19)1−x(CoFe2O4)x (x=0.1, 0.2, and 0.3) composite ferrite powders. The powders were subjected to annealing at 800°C in order to decisively study the phase evolution of the combined hard and soft ferrites. Thermogravitry (TGA)/differential scanning calorimetry (DSC) analysis exhibited three stages of decomposition in the precursor gels combined with an exothermic peak at 210°C. X-ray diffraction (XRD) analysis confirmed that the diffraction peaks were perfectly indexed to the hexagonal magnetoplumbite structure of Ba0.5Sr0.5Fe12O19 and the cubic spinel structure of CoFe2O4. Fourier transform infrared spectroscopy (FT-IR) analysis for the samples showed a Co–O stretching vibration accompanied with Co–O–Co or Fe–O–Fe bands at 1220cm−1. The morphology of the samples were examined by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). The crystallinity of a selected sample was evaluated by using the high resolution transmission electron microscope (HR-TEM) and selected area electron diffraction (SAED) pattern. It confirmed the presence of planes comprising the hard and soft phases in the synthesized nanocomposites. The magnetic parameters like saturation magnetization MS, remanent magnetization MR, squareness ratio SR, coercivity HC and magnetic moment µB were evaluated using hysteresis by employing vibrating sample magnetometer (VSM). Maximum HC of 4.7kOe and MS of 60.4emu/g were obtained for (Ba0.5Sr0.5Fe12O19)0.9(CoFe2O4)0.1. Switching field distribution curves were analysed by using the demagnetization curve. The exchange coupling between the hard and soft phases were analysed by the dM/dH plots and it indicated the exchange coupling first increased with the increase in the concentration of spinels and then decreased. The possible comparison of exchange coupling between the hard and soft phases has been discussed in detail.

Influence of Co-substitution on the structural and magnetic properties of nanocrystalline Ba0.5Sr0.5Fe12O19

One-step citrate gel combustion method followed by annealing (800°C/2h) was employed to synthesize cobalt substituted barium strontium hexaferrite with a chemical composition of Ba0.5Sr0.5Fe12−xCoxO19 (x=0, 0.5, 0.7, and 0.9). A combination of thermo-gravimetric analysis and differential scanning calorimetry was employed to understand the thermo-chemical behavior of Ba0.5Sr0.5Fe12O19. X-ray diffraction (XRD) was used to evaluate the hexagonal phase evolution for the barium strontium ferrite nanopowders and a formation of secondary phase: α-Fe2O3 is evident for the Ba0.5Sr0.5Fe12O19. Raman spectroscopy confirmed the presence of different sublattices of Fe3+ present in the hexaferrite structure. Fourier transform infrared spectroscopy demonstrated the usual stretching vibrations of tetrahedral and octahedral M–O bands. The morphology and chemical composition of the samples were analyzed by transmission electron microscopy and field emission scanning electron microscopy attached with energy dispersive X-ray analysis, respectively. Selected area electron diffraction studies showed the nanocrystalline nature of the samples. The magnetic parameters such as saturation magnetization MS, coercivity, HC and remanent magnetization, MR were estimated from the hysteresis loops. Maximum value of MS (70.5emu/g) was obtained for the Ba0.5Sr0.5Fe11.5Co0.5O19 nanoparticles. A possible growth mechanism on the crystallization of Ba0.5Sr0.5Fe12O19 hexagonal platelets during the citrate gel combustion synthesis is highlighted.

Bulk synthesis of nanocrystalline urania powders by citrate gel-combustion method

Bulk quantities (60 g) of nanocrystalline (nc) free flowing urania powders with crystallite size ranging from 38 to 252 nm have been synthesized for the first time by the citrate gel combustion method. A systematic study of the influence of the fuel (citric acid) to oxidant (nitrate) ratio (R) on the characteristics of the urania powders has been carried out for the first time. Mixture with an “R” value of 0.25 exhibited a vigorous auto-ignition reaction. This reaction was investigated with Differential Scanning Calorimetry (DSC) and in-situ thermogravimetry coupled with differential thermal analysis and mass spectrometry (TG-DTA-MS). The bulk density, specific surface area, X-ray crystallite size, residual carbon and size distribution of particles of this powder were unique. Microscopic and microstructural investigation of selected samples revealed the presence of nanocrystals with irregular exfoliated morphology; their Electron Energy Loss Spectra testified the covalency of the U–O bond.