Citrate-nitrate Combustion Method Research Articles

Carbonates formed during BSCF preparation and their effects on performance of SOFCs with BSCF cathode

Series of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) samples have been prepared by modified citrate-nitrate combustion method from the precursor solutions with different pH values and citrate/metal ion ratios. The XRD results reveal that BSCF oxide free of impurity phases can be obtained from a precursor solution with a suitable pH value and a suitable C/M value, whereas CO2-TPD profiles show that there are minor carbonates species present in all BSCF samples, but the amount of these carbonates varies with the pH and C/M values of precursor solutions. The current density–voltage characteristics indicate that carbonates in the BSCF samples reduce the cell performance. The electrochemical impedance spectra (EIS) show that carbonates in BSCF lead to increases in ohmic and polarization resistances. High performance is achieved on the cell with a cathode using a pure BSCF calcined under O2 flow at 900 °C.

Combustion synthesis and thermal expansion of RE6UO12 (RE = Dy and Tb)

Citrate–nitrate combustion method was adopted for the synthesis of RE6UO12 (RE = Dy and Tb). These compounds were characterized by X-ray diffraction. Thermal expansion coefficient of these compounds were measured in the temperature range of 298–1,273 K by high temperature X-ray powder diffractometry (HT-XRD) and compared with other rare earth compounds reported in the literature. There was no observed phase transition in Dy6UO12, but Tb6UO12 showed a second-order phase transition at 670 K which was confirmed using differential scanning calorimeter. The average volume thermal expansion coefficient of Dy6UO12 in the temperature range of 298–1,273 K is (29.82 ± 4.02) × 10−6 and that of Tb6UO12 in the temperature range of 298–673 K is (13.76 ± 2.64) × 10−6 K−1.

Synthesis and electrical properties of Ce1−xGdxO2−x/2 (x = 0.05–0.3) solid solutions prepared by a citrate–nitrate combustion method

Ce1−xGdxO2−x/2 (GDC) powders with different Gd3+ contents (x=0.05–0.3) were prepared by a simple citrate–nitrate combustion method. The influence of the Gd3+ doping content on the crystal structure and the electrical properties of GDC were examined. Many analysis techniques such as thermal analysis, X-ray diffraction, nitrogen adsorption analysis, scanning electron microscopy and AC impedance analysis were employed to characterize the GDC powders. The crystallization of the GDC solid solution occurred below 350°C. The GDC powders calcined at 800°C showed a typical cubic fluorite structure. The lattice parameter of GDC exhibited a linear relationship with the Gd3+ content. As compared with that sintered at other temperatures, the GDC pellet that sintered at 1300°C had a high relative density of 97%, and showed finer microstructure. The conductivity of GDC was firstly increased and then decreased with the increase of the Gd3+ content. The sintered GDC sample with the Gd3+ content of 0.25 exhibited the highest conductivity of 1.27×10−2Scm−1 at 600°C.

Synthesis and sintering of indium tin oxide nanoparticles by citrate-nitrate combustion method

Spherical indium tin oxide (ITO) nanoparticles were synthesized by combustion method using citric acid as fuel and nitrates as oxidizer. The obtained ITO nanoparticles were characterized by TG-DSC, FT-IR, XRD, BET, TEM, and SEM. The ITO nanoparticles grew steadily with the increase of heat treatment temperature, and the 700°C calcined particles had a crystallite size of 25.3 nm and a specific surface area of 26.1 m2·g−1. The avoidance of chlorine ions in the synthesis process decreases particle agglomeration and promotes powder densification. The 900°C sintered pellet had a density of 67.6% of theoretical density (TD) and increased steadily to 97.3% for the 1400°C sintered ceramics, respectively.

Magnetic and dielectric properties of mixed spinel Ni–Zn ferrites synthesized by citrate–nitrate combustion method

Abstract Mixed Ni x Zn 1− x Fe 2 O 4 ( x = 0.1, 0.2, 0.3, 0.4 and 0.5) systems were prepared by a chemical combustion route. This method involves the addition of aqueous nickel nitrate, zinc nitrate, ferric nitrate as oxidizing agents and fuel citric acid as a reducing agent to form a homogeneous redox mixture. The product materials on calcination to 700 °C for 2 h produces nanocrystalline Ni–Zn ferrite with the corresponding average grain size ranging from 53 nm to 71 nm with varying composition. The room temperature magnetization measurements showed that the saturation magnetization ( M s ) of Zn ferrite increases with Ni content. Temperature dependent DC resistivity measurements reveal the semiconducting behavior for all the samples. Room temperature dielectric properties viz.; relative dielectric permittivity ( ɛ r ), dielectric loss (tan δ ) and AC conductivity ( σ AC ) for all the samples were studied as a function of applied frequency in the range from 20 Hz to 1 MHz. These studies indicate that the relative dielectric permittivity for all the samples shows usual dielectric dispersion which is due to the Maxwell–Wagner type interfacial polarization. The AC conductivity measurement suggests that the conduction is due to small polaron hopping.

Preparation and properties of the CoFe 2O 4–Nb–Pb(Zr,Ti)O 3 multiferroic composites prepared in situ by gel-combustion method

Di-phase magnetoelectric composites formed by magnetic CoFe 2O 4 and ferroelectric Nb–Pb(Zr,Ti)O 3 were prepared by citrate–nitrate combustion method technique by using Nb–Pb(Zr,Ti)O 3 template powders prepared by mixed oxides. Pure di-phase powder composites with a good crystallinity were obtained after the calcination step. The purity was maintained by sintering at temperature of 1100 °C/2 h, which ensured limited reactions at interfaces, while by sintering at 1250 °C/2 h, small amounts of secondary phases resulted. The method allowed to produce di-phase ceramics with homogeneous microstructures and a very good mixing of the two phases. The dielectric and magnetic investigations at room temperature confirmed the formation of composite ceramics with both dielectric and magnetic properties at room temperature, with permittivity and magnetization resulted as sum properties from the parent Pb(Zr,Ti)O 3 and ferrite phases.

Thermal expansion and heat capacity of Gd 6UO 12(s)

Gd 6UO 12(s) was synthesized by citrate–nitrate combustion method. Thermal expansion measurements of this compound were carried out in the temperature range of 298–1273 K by high temperature X-ray powder diffractometry and compared with other rare earth compounds of similar stoichiometry reported in literature. Heat capacity of Gd 6UO 12(s) was also measured by differential scanning calorimetry in the temperature range of 330–720 K. Enthalpy, entropy and free energy functions for Gd 6UO 12(s) were computed.

Citrate-oxide method to prepare SrBi 4Ti 4O 15 powders and ceramics

SrBi 4Ti 4O 15 (SBTi) powders were synthesized by citrate-oxide method. Oxides and carbonates were used as starting materials to replace other expensive soluble salts in citrate–nitrate combustion method. Attempts have been made to understand the synthesis process with the help of thermogravimetric (TG) and differential scanning calorimetry (DSC) of the samples. XRD results showed that the pure phase SBTi powders were obtained at 500 °C for 2 h, which was much lower than the calcination temperature (800–850 °C) required in solid-state reaction. The SBTi ceramics sintered at 1180 °C for 1 h exhibited a relative density of 93.7% and a piezoelectric coefficient of 19 pC/N. This sintering temperature was lower 50 °C than that required in solid-state reaction. The research results indicate that the citrate-oxide method is an efficient, quick and simple method for mass production of ceramic oxide powder.

Photoinduced decomposition of BaFeO 3 during photodegradation of methyl orange

Photodegradation of methyl orange under UV light irradiation has been studied over a photocatalyst BaFeO 3 prepared by the citrate–nitrate combustion method. Both X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy have revealed the decomposition of the structure of BaFeO 3 after the photocatalytic experiment. The photoinduced decomposition of BaFeO 3 is due to the existence of unstable iron ions in BaFeO 3. X-ray photoelectron spectroscopy (XPS) indicates that the valence state of iron ions in BaFeO 3 changes after the photocatalytic experiment. SEM observation shows that the morphology of BaFeO 3 does not change under UV light irradiation. It is indispensable to select a suitable element for the B-site in order to synthesize photostable perovskite photocatalysts.

Structure and photocatalytic property of perovskite and perovskite-related compounds

Perovskite (ABO 3) and perovskite-related (brownmillerite, A 2B 2O 5) compounds were prepared by citrate–nitrate combustion method. Crystal structure was verified by X-ray diffraction. Absorbency was determined by UV–vis spectrophotometer. FTIR was also used to determine whether the decoloration of methyl orange solution was caused by photocatalysis. SEM was used to compare the morphology of the samples prior to and after photocatalysis. Calcination temperature of the samples was maintained at 450 °C for 2 h and 800 °C for 4 h. It was supposed that the presence of different photocatalytic properties among synthesized perovskite (ABO 3) and perovskite-related (brownmillerite, A 2B 2O 5) compounds was derived from structural differences among those materials; moreover, transition-metal ions (Fe 3+ and Co 2+) in oxygen coordinated octahedra were the main source of photocatalytic abilities and alkaline-earth metal ions (Ca 2+, Sr 2+ and Ba 2+) play important roles in stabilizing perovskite structure. And photocatalysis has no influence on the morphology of the sample.