Citrate Nitrate Gel Research Articles

Nitrate-Citrate Sol-gel Synthesis of Phase Pure Nd3+ doped Nanocrystalline Yttrium Aluminum Garnet

Phase pure nanopowders of undoped and neodymium ( Nd 3+)-doped yttrium-aluminum-garnet(YAG) was synthesised by sol-gel process using nitrate-citrate gel method. Complete crystallisation of YAG was studied using Fourier transform infra-red spectroscopy (FTIR) and x-ray diffraction (XRD). Complete phase formation took place at 900 OC for 2 h. The average primary particle size calculated was ~25 nm. Transmission electron microscopy (TEM) showed particles in the range of ~25 nm to 30 nm. Nd -dopant concentration levels of 2 and 4 atomic per cent were studied. Using XRD data the cell parameters of Nd (0, 2 and 4 atomic per cent):YAG were calculated and it was found to increase with increase in dopant concentration. Defence Science Journal, 2011, 61(3), pp.214-218 , DOI:http://dx.doi.org/10.14429/dsj.61.438

Preparation of nanoparticles of oxides by the citrate–nitrate process

Abstract This paper reports preparation of nanoparticles of oxides by the citrate–nitrate process and the effect of metal ions on the thermal decomposition characteristics of the corresponding citrate–nitrate gel precursors. In order to understand the effect of metal ions on the thermal decomposition characteristics of the precursors, we have prepared a series of single component oxides such as MO, where M = Zn, MO2, where M = Sn, Ce, Zr, and M2O3 where M = Al, Fe, Bi. In all the cases the citrate to nitrate ratio was fixed at 0.3. In order to ascertain the decomposition characteristics of the gel samples, TG/DTA studies were performed on the dried gel samples. After complete physico-chemical characterization of the precursors and the calcined products, it could be concluded that the nature of decomposition of the precursors depends largely on the nature of the metal ions. Finally, the advantages of the citrate–nitrate process such as its high degree of reproducibility, its potential for large-scale produ...

Influence of chromium substitution on structural and magnetic properties of BaFe 12O 19 powder prepared by sol–gel auto combustion method

The nanocrystalline Cr 3+ substituted barium hexaferrite having generic formula BaFe 12− x Cr x O 19 (where x = 0.00, 0.25, 0.50, 0.75, and 1.00) samples were synthesized by sol–gel auto-combustion technique. The precursors were prepared by using stoichiometric amounts of Ba 2+, Fe 3+ and Cr 3+ nitrate solutions with citric acid as a chelating agent. The metal nitrate to citric acid ratio was taken as 1:2 while pH of the solution was kept at 8. The thermal decomposition of nitrate–citrate gels of as-prepared powder was investigated by TG/DTA. The as-prepared powder of BaFe 12− x Cr x O 19 was sintered at 900 °C for 8 h. The sintered powder was characterized by XRD, EDAX, SEM and VSM technique. The pure barium hexaferrite shows only single phase hexagonal structure, while for the samples at x = 0.25, 0.50, 0.75 and 1.00 shows α-Fe 2O 3 peaks with M-phase of barium hexaferrite. The lattice parameters ( a and c) decreases with increase in chromium content x. The particle size obtained from XRD data is in the range of 30–40 nm which confirms the nanocrystalline nature of the samples. The magnetic properties were investigated by means of vibrating sample magnetometer (VSM) technique. The saturation magnetization ( M s), remanence magnetization ( M r), coercivity ( H c) and magneton number ( n B) decreases with increase in chromium content x.

Preparation and characterization of perovskite REFeO 3 nanocrystalline powders

Combustion of nitrate-citrate gel was employed to prepare REFeO 3 (RE=Y, La and Gd) nanocrystalline powders. The samples were characterized with X-ray diffraction (XRD) analysis, thermal analysis (TG/DTA) and transmission electron microscopy (TEM). LaFeO 3 crystallites were directly obtained by the sol-gel combustion process, and orthorhombic YFeO 3 and GdFeO 3 were formed when annealed at 800 °C. The investigation of magnetic properties showed that YFeO 3 and LaFeO 3 exhibited ferromagnetic behavior, while GdFeO 3 presented paramagnetic coupling. It was suggested that the Fe sublattice governed the magnetization process in YFeO 3 and LaFeO 3. The dominance of paramagnetic component from Gd was observed in GdFeO 3.

Characterization and preparation of nanocrystalline MgCuZn ferrite powders synthesized by sol–gel auto-combustion method

Nanocrystalline Mg–Cu–Zn ferrite powders were successfully synthesized through nitrate–citrate gel auto-combustion method. Characterization of the nitrate–citrate gel, as-burnt powder and calcined powders at different calcination conditions were investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that the combustion process is an oxidation–reduction reaction in which the NO3− ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature resulted in increasing the crystallite size of Mg–Cu–Zn ferrite powders. VSM measurement also indicated that the maximum saturation magnetization (64.1 emu/g) appears for sample calcined at 800 °C while there is not much further increase in Ms at higher calcination temperature. The value of coercivity field (Hc) presents a maximum value of 182.7 Oe at calcination temperature 700 °C. TEM micrograph of the sample calcined at 800 °C showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 °C for 4 h presents the initial permeability (μi) of 405 at 1 MHz and electrical resistivity (ρ) of 1.02 × 108 Ω cm.

Synthesis and structure–property relations in xCuO–(1−x)Bi2O3 (0.5⩽x⩽0.9) (C1–C5: x=0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the x CuO–(1 − x )Bi 2 O 3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ∼0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g -matrix elements g || > g ⊥ > g e for the glasses C1–C5 at 4.2 K are due to the Cu 2+ (3d 9 ) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O 1/2 –CuO 4/2 –O 1/2 ] having D 4h symmetry. IR spectroscopic results show the presence of octahedron [BiO 6/2 ] 3− and [CuO 6/2 ] 4− units and pyramidal [BiO 2/2 O] − unit in the glasses.

Influences of Precursors Molar Ratio and Basic Agent on Processing of Nickel–Zinc Ferrite Nanopowders by a Sol-Gel Auto-Combustion Method

In the present investigation, nickel-zinc ferrite nanocrystalline powder has been prepared by a sol-gel auto-combustion technique using a gel including citric acid as a reductant and nitrates as oxidants. The results showed that the nitrate citrate gels exhibit a self- propagating behavior after ignition in air. The effects of Fe/(Ni, Zn) molar ratio and the kind of the basic agent on the thermal decomposition of the gels, and phase constitution, crystallite size, and morphology of the resultant powders were investigated by differential thermal analysis, thermo gravimetric analysis, X-ray diffraction, and transmission electron microscopy techniques. The results also revealed that in the presence of ammonia as a pH adjusting agent and Fe/(Ni, Zn) molar ratio of 2, the smallest crystallite size of nickel-zinc ferrite as 27 nm could be obtained directly after auto-combustion without the postcalcination process.

Synthesis of nanocrystalline wollastonite powders by citrate–nitrate gel combustion method

Wollastonite was synthesized for the first time by a citrate–nitrate gel combustion method using citric acid as a reductant/fuel and nitrate as an oxidant. The yielding powders calcined at 650 °C for 2 h were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N 2 adsorption measurements (BET). The XRD data revealed that the resultant product was a pure phase of wollastonite without any other impurities. The SEM and BET results showed that the product was highly porous with a relatively high specific surface area of 40.69 m 2 g −1. The average grain size calculated from BET measurements of calcining powders is found to be 50.7 nm.

Influence of zinc substitution on magnetic and electrical properties of MgCuZn ferrite nanocrystalline powders prepared by sol–gel, auto-combustion method

The ferrite compositions Mg 0.80− x Cu 0.20Zn x Fe 2O 4 with x = 0.5, 0.55, 0.60 and 0.63, were synthesized through nitrate–citrate gels auto-combustion method. The autocatalytic nature of the combustion process has been studied by thermal analysis (DTA and TG) of the dried gels. The as-burnt powders were calcined at 800 °C for 1 h and then pressed ferrite parts were sintered at 900 °C for 4 h. The as-burnt powders and calcined powders were characterized with respect to phase identification, grain size and lattice parameter determination using X-ray diffraction. The sintered ferrites have been investigated for their electrical and magnetic properties such as saturation magnetization, initial permeability, AC-resistivity, dielectric constant, dielectric loss tangent as a function of zinc content. The initial permeability, saturation magnetization, dielectric constant and dielectric loss were found to increase and AC-resistivity was decreased with Zn substitution for Mg. The powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.

Thermodynamic studies on LnCoO 3(s) (Ln = Dy, Ho) by solid-state electrochemical cells

Ternary oxides, DyCoO 3(s) and HoCoO 3(s) have been synthesized by citrate–nitrate gel combustion method and characterized by X-ray powder diffraction method. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) have been measured using solid oxide galvanic cell technique employing yttria-stabilized zirconia (YSZ) and calcia-stabilized zirconia (CSZ) as solid electrolyte tubes, respectively. The standard molar Gibbs energies of formation of DyCoO 3(s) and HoCoO 3(s) were calculated from the measured e.m.f. data and are given as: Δ f G m ° ( DyCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1211.3 + 0.2449 ∗ ( T K ) , ( 1013 K ≤ T ≥ 1167 K ) , Δ f G m ° ( HCo O 3 , s , T ) kJ mo l − 1 ( ± 4 ) = − 1237.8 + 0.2590 ∗ ( T K ) . ( 964 K ≤ T ≥ 1102 K ) , A set of self consistent thermodynamic functions for LnCoO 3(s) (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho) has been computed from available experimental data in the literature.

Luminescence of Nanocrystalline Tb3Al5O12 : Ce3 + Phosphors Synthesized by Nitrate-Citrate Gel Combustion Method

-doped nanocrystalline terbium aluminum garnet (, ) phosphors were successfully synthesized in low temperature by nitrate-citrate gel combustion method using microwave irradiation as a heating source. The pure TAG phase was obtained after calcining at for . The prepared nanocrystalline phosphors showed a broad peak at , and the maximum doping concentration of for the highest emission intensity was at . The temperature dependence on photoluminescence properties of the prepared phosphors was investigated from , and the activation energies for thermal quenching was determined by Arrhenius fitting. The experimental results clearly indicate that prepared nanocryatalline has great potentials for a down-conversion yellow phosphor in white light emitting diodes.

Influence of Different Calcination Conditions on the Microstructure and Phase Constitution of Nickel-Zinc Ferrite Nanocrystalline Powders Prepared by a Sol-Gel Auto-Combustion Method

In this work, nickel-zinc ferrite nanocrystalline powder has been prepared by a sol-gel autocombustion technique using nitrate-citrate gel obtained from metal nitrates and citric acid solution. Characterization of the nitrate-citrate gel, as-burnt powder and calcined powder at different calcination conditions were investigated by using XRD, FTIR and SEM techniques. The results revealed that the nitrate-citrate gel exhibits a self-propagating behavior after ignition and showed that the different calcination conditions affect the crystallite size of the synthesized powder as well as its phase constitution.

Linear Combination of Atomic Orbitals Approximation in Nanocrystalline Yittria-Stabilized Zirconia Synthesized by Citrate–Nitrate Gel Combustion Process

Nanocrystalline yittria-stabilized zirconia (YSZ) compounds with yittria concentration varying between 8 and 12 mol% have been synthesized by gel combustion method followed by heat treatment at 550°C. The YSZs are found to posses stable face centered cubic structure at room temperature by X-ray diffractometry. The lattice parameter ‘a’ showed an increasing trend with increasing concentration of yittria. The crystallite size estimated by Scherrer method was in the range of 7–10 nm. Band gap studies showed an increasing trend with increasing yittria concentration and are found to be consistent with respective lattice parameters following the tight binding approximation or linear combination of atomic orbitals approximation.

Effect of citrate to nitrate ratio on the decomposition characteristics and phase formation of alumina

This paper reports the effect of the variation of citrate to nitrate ratio on the thermal decomposition characteristics of alumina precursor and the properties of nanocrystalline alumina synthesized using this auto-ignition process. The technique involves the auto-ignition of a citrate-nitrate gel occurring between Al(NO3)3 and citric acid to yield an ash powder that upon calcination at 1373 K produced α-alumina. The auto-ignition was restricted to a particular range of citrate to nitrate ratio in the gel. The resulting powder exhibited large surface area (40–50 m2 gm−1) and fine crystallite size. It was established from various characterization techniques that the alumina powder prepared with a C/N ratio of 0.3 has got the optimum powder characteristics compared to the rest of the batches, thus establishing the importance of maintaining a stoichiometric or near stoichiometric C/N ratio. The process has a higher degree of reproducibility and a good potential for large-scale production of alumina.

Thermodynamic Studies on SrFe12O19(s), SrFe2O4(s), Sr2Fe2O5(s) and Sr3Fe2O6(s).

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Heat capacities, order–disorder transitions, and thermodynamic properties of rare-earth orthoferrites and rare-earth iron garnets

Rare-earth orthoferrites, RFeO 3, and rare-earth iron garnets (RIGs) R 3Fe 5O 12 ( R=rare-earth elements) were prepared by citrate–nitrate gel combustion method and characterized by X-ray diffraction method. Isobaric molar heat capacities of these oxides were determined by using differential scanning calorimetry from 130 to 860 K. Order–disorder transition temperatures were determined from the heat capacity measurements. The Néel temperatures ( T N) due to antiferromagentic to paramagnetic transitions in orthoferrites and the Curie temperatures ( T C) due to ferrimagnetic to paramagnetic transitions in garnets were determined from the heat capacity data. Both T N and T C systematically decrease with increasing atomic number of R across the series. Lattice, electronic and magnetic contributions to the total heat capacity were calculated. Debye temperatures as a function of absolute temperature were calculated for these compounds. Thermodynamic functions like C p , m o , S m o , H o, G o, ( H T o - H 0 o ) , ( H T o - H 298.15 K o ) , - ( G T o - H 298.15 K o ) / T , Δ f H m o , and Δ f G m o have been generated for the compounds RFeO 3(s) and R 3Fe 5O 12(s) based on the experimental data obtained in this study and the available data in the literature.

Heat capacities of RCoO 3(s) (R = La, Nd, Sm Eu, Gd, Tb, Dy and Ho) by differential scanning calorimetry

Ternary oxides, RCoO 3(s) (R = La, Nd, Sm Eu, Gd, Tb, Dy and Ho), have been prepared by citrate–nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these compounds have been measured in the temperature range from 130 to 850 K using a heat flux type differential scanning calorimeter. Heat capacity versus temperature plots for these compounds indicated broad humps in the temperature range from 450 to 780 K suggesting electronic transitions in these compounds accompanied by large entropy increments. The transition temperatures showed increasing trend with decrease in ionic radii of the lanthanide ion.

Synthesis of mixed-conducting oxide SrFeCo0.5O y powder by auto-combustion of citrate–nitrate gel

Mixed-conducting oxide SrFeCo0.5Oy powders have been synthesized by auto-combustion of citrate–nitrate gel. The resulting powder is pure, homogeneous and possesses a reasonably fine particle size. Attempts have been made to understand the combustion process with the help of Differential Thermal Analysis (DTA) of the sample. The XRD, SEM and TEM studies on these powders confirmed that the method produces powder had greater composition uniformity, lower residual carbonate levels and smaller particle sizes.

Characteristics of barium hexaferrite nanocrystalline powders prepared by a sol-gel combustion method using inorganic agent

Nanocrystalline particles of barium hexaferrite were synthesized by a sol-gel combustion route using nitrate-citrate gels prepared from metal nitrates and citric acid solutions under various Fe/Ba molar ratios of 10, 11 and 12. Sodium hydroxide was used as a pH-adjusting agent. The results revealed that the formation temperature of barium hexaferrite is influenced by Fe/Ba molar ratio; the Fe/Ba molar ratio of 12 is more favorable. For sample synthesized with a Fe/Ba molar ratio of 12, barium hexaferrite started to form at 800 °C and fully formed at 1000 °C. The results also showed that the coercivity of the samples decreases as the Fe/Ba molar ratio increases from 10 to 12, whilst the saturation magnetization increases.

Preparation of Mn–Zn ferrite nanoparticles from chemical sol–gel combustion method and the magnetic properties after sintering

Nano-size Mn–Zn particles were synthesized by the sol–gel combustion method. These particles were prepared from metal nitrates and citric acid. The combustion process is an oxidation–reduction reaction in which the NO 3 – ion is oxidant and the carboxyl group is reductant. The thermal analysis of nitrate–citrate gels and the phase evolution of dried gel, as-burnt powder and sintered sample were investigated by DTA/TG and XRD techniques, respectively. SEM was also used to characterize the microstructure of the products. The effect of sintering temperature on the magnetic properties of the sample ferrite such as initial permeability ( μ i) and hysteresis loop also investigated.