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A series of Z n 0.5 C o 0.25 C u 0.25 H o 0.037 F e 1.963 O 4 (ZCCHF)/Graphene nanoplatelets (GNPs) nanocomposites (where GNPs = 0 wt%, 1.25 wt%, 2.5 wt%, 3.75 wt%, 5 wt%) were prepared via sol-gel auto-combustion (SGAC) method followed by bath sonication and studied their structural, morphological, optical, dielectric, and magnetic properties. The structural analysis confirmed a single-phase crystal matrix of all the as-prepared nanocomposites. The optical analysis revealed that the energy bandgap (E g) lies within the range of 1.57 eV–1.62 eV. The dielectric analysis showed that the improvement in the dielectric constant (ε ′) and reduction in dielectric tangent loss (tan δ d) with increasing GNPs concentration from 0 wt% to 5 wt%. The real part of permeability (μ ′) was improved and magnetic tangent loss (tan δ M) was reduced with the addition of GNPs. Magnetic properties were studied at different temperatures (5 K, 300 K, and 400 K), and observed high saturation magnetization (M S), and coercivity (H C) at a low temperature (at 5 K). The low M S , and H C values were observed at high temperatures (300 K and 400 K). The combination of improved dielectric and tunable magnetic properties makes ZCCHF/GNPs nanocomposites promising candidates for applications in spintronics, high-frequency magnetic devices, and advanced electronic systems. [Display omitted] • The ZCCHF SFs and ZCCHF/GNPs nanocomposites were synthesized using a sol-gel auto-combustion (SGAC) method followed by bath sonication. • XRD analysis revealed a single-phase crystal structure and the tunable energy bandgap ranges from 1.57 eV to 1.62 eV. • The maximum dielectric constant and minimum dielectric tangent loss were found for ZCCHF/5 wt%GNPs nanocomposites. The nanocomposite with 5 wt%GNPs reveals the highest magnetic permeability around 0.995. The minimum magnetic tangent loss and skin depth was found for ZCCHF/5 wt%GNPs nanocomposites. • The saturation magnetization is lower across all temperatures with GNPs incorporation and the microwave operating frequency was 14.21 GHz at 300 K for ZCCHF/5 wt%GNPs nanocomposites. • The study highlights the multifunctional potential of ZCCHF/GNPs nanocomposites in promising candidates for a broad range of advanced technological applications. [ABSTRACT FROM AUTHOR]

Agricultural waste availability implies the possibility of recovering energy as biomass. The collateral effect is the production of ashes that, in some cases, have the potential to be reused in the manufacture of cement, mortar, and concrete. This article presents the study of the auto-combustion (unlike all previous studies) of corn (maize) straw (stems and leaves). The auto-combustion temperature was monitored, and the obtained corn straw ash (CSA) was characterized by means of X-ray fluorescence, X-ray diffraction, thermogravimetry, and scanning electron microscopy. Finally, the behavior of ground CSA was analyzed in both the fresh state by measurement of workability on the spreading table and the hardened state by compressive strength measurement on mortars in which 10% of ordinary Portland cement (OPC) was replaced with CSA. These values were compared to both a control mortar (OPC) and a mortar in which OPC was partially replaced with 10% limestone filler. Ashes showed adequate pozzolanic reactivity because, at 90 curing days, the compressive strength of the mortars with 10% replacement of OPC with CSA was practically equal (98% of the strength) to the control mortar without pozzolan replacement. The auto-combustion of biomass is a process that can be easily available, and the results on pozzolanic reactivity of CSA are satisfactory. The auto-combustion could be used by low-income communities to reduce Portland cement clinker use and to recover waste. [ABSTRACT FROM AUTHOR]

Cobalt zinc chromium ferrites, which have been doped with chromium Co0.4Zn0.6-xCrxFe2O4 (x = 0.05, 0.10, 0.15, 0.20) (CZC) nanoferrites, are employed by the auto-combustion route. The magnetic and dielectric characteristics of Co–Zn nanoferrites were improved by Cr3+. Analysis using XRD, FTIR, and FESEM reveals the cubic spinel phase for CZC nanoferrites. SEM reveals a lot of clustering. The ferrite samples have cluster form with a spherical shape in the range 54.64–73.38 nm, as seen by the FESEM results. TEM studies show agglomeration. The Cr3+ concentration determines the magnetic properties of specimens. Ms declines from 62.38 emu/g to 42.59 emu/g by increasing Cr3+. For all samples, a frequency-dependent evaluation of the dielectric properties, including dielectric constant, dielectric loss, and ac conductivity, is performed. On the basis of Koop's theory, the Maxwell-Wagner polarization procedure, and the movement of electrons, the fluctuation of dielectric features at frequencies between 50 Hz and 108 Hz has been mentioned. The dielectric constant and dielectric loss tangent decreased with increasing frequency. The conduction of ferrite samples is influenced by the grain boundaries. Both recording media and high-frequency devices can benefit from using these nanoferrites. [ABSTRACT FROM AUTHOR]

Pure Lanthanum Ferrite (LaFeO3) nanoparticles and Lanthanum Magnesium Ferrite (LaMgxFe1-xO3) nanocomposites have been prepared by the sol-gel auto-combustion method. The structural and morphological properties were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) spectroscopy. Powder XRD studies revealed that the samples are pure orthorhombic perovskite crystals with a size of around 20-50 nm. The FT-IR spectra of pure and composites was confirmed the formation perovskite structure. It has been discovered that composites material functions as an electrode in supercapacitors after its electrical characteristics have been examined by galvanostatic charging and discharging (GCD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) with a 2 M KOH electrolyte. [ABSTRACT FROM AUTHOR]

Herein we report the effect of the Cr3+ content on the distinctive features of the first-ever auto-combustion-synthesis-produced Cr3+ doped ZnO nanoparticles utilizing leucine as the fuel. To assess the impact of fuel and Cr3+ content on the structural, optical, and luminescence characteristics, as-synthesized powders were systematically examined using powder XRD, UV–Visible, and Photoluminescence spectroscopy. Structural studies show that the exothermicity of the redox mixture containing oxidizer and fuel combination leads to the development of polycrystalline, single-phase, and nanosized particles. XRD analysis shows that, reduced crystallite size with Cr3+ content. In contrast, other characteristics like lattice parameters, unit cell volume, strain, and dislocation density, were shown to increase linearly with Cr3+ concentration up to 7 mol%. Additionally, it is seen that the predicted Urbach energy values rise as Cr3+ is added to the ZnO host matrix, indicating that the substitution of Cr3+ for Zn in the host ZnO lattice has increased structural disorder. In contrast to the other samples, the 5 mol% Cr3+ doped ZnO sample exhibits the emission near the white region according to the PL emission measurements. Furthermore, the photocatalytic activity of the as-prepared Cr3+ doped ZnO NPs was examined. It was found that the as-prepared samples exhibit outstanding photocatalytic activity in the visible wavelength region against Malachite Green (MG) dye. Among all, 9 mol% Cr3+ doped ZnO has shown the maximum 95.4% degradation against MG dye. All the investigated results conclude that the produced Cr3+ doped ZnO nanoparticles could be exploited in a variety of upcoming optoelectronic and photocatalytic applications. [ABSTRACT FROM AUTHOR]

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

The present paper reports the structural, dielectric and ac electrical properties of nanoparticles of mixed polycrystalline spinel ferrite ternary compound Mn0.6Co0.2Ni0.2Fe2O4 synthesized by using the citrate-gel auto-combustion technique. The standard characterization techniques such as EDAX, XRD and FTIR were primarily employed to confirm the elemental stoichiometry, crystallized single-phase, IR-functional groups. These measurements ascertained the formation of monophasic and pure ferrite compound. The powder X-ray diffraction analysis was done to determine the lattice constant(0.8420 nm), crystallite size(21 nm), X-ray density (5.16 g/cm3), distribution of cations among the tetrahedral and octahedral sites of spinel lattice(with iron-Fe3+ distribution ratio among A and B sites is 0.25), bond angles and bond lengths. The theoretical lattice constant is found to be 0.8422 nm. The nature and position of the IR-bands were observed through FTIR spectroscopy. The high-frequency band v1 (A-site vibrations) lies at 563.07 cm-1 while the low-frequency band v2 (B-site vibrations) lies at 462.59 cm-1. The force constants for the tetrahedral site (kt) and octahedral site (ko) were deduced 1.33 x 10² N/m and 1.27 x 10² N/m, respectively. Frequency dependence of dielectric constant and tangent loss has been explained by the Maxwell Wagner model and Koop's theory. The Jonscher's power low was used to describe the ac conductivity measurements. The Nyquist and cole-cole plots indicated presence of grain contribution in the conduction mechanism. [ABSTRACT FROM AUTHOR]

Mn0.8Zn0.2Fe2O4 ferrites were successfully prepared via a recycling process of spent Zn–C batteries (SZCBs) using sol–gel auto-combustion techniques and different fuels, including citric acid and sucrose chitosan, gelatin, and egg-white. The cost of this recycling technology, as well as the used fuels, have both economic and environmental advantages, facilitating many promising industrial applications. XRD confirmed single-phase formation with average crystallite sizes in the range from 15 to 55 nm. The appropriate cation distribution, elucidated using structural parameters, indicated the preferential occupancy of Zn+2 ions only by the A-sites while Mn+2 and Fe+3 ions preferentially occupy both A and B-sites. TEM images exhibited cubically agglomerated particles with wide size distribution. VSM indicated a wide range of magnetization values (51.0–19.8 emu/g) depending on the preparation route, suggesting the impact of the fuel used. The prepared ferrite using citric acid showed the highest value, while that prepared using egg-white indicated the lowest one. The obtained coercivities indicated soft magnetic materials with a decreasing behavior by increasing sizes. The ac-conductivity indicated semiconducting characteristics with a noticeable improvement in the conductivity than that of the bulk ferrite. The temperature dependence of the ac-conductivity showed a transition from ferro- to paramagnetic by increasing temperature. The estimated Curie temperatures (TC) indicated an improvement in the magnetic characteristics. In addition, the frequency dependence of ac-conductivity indicated a change in the conduction mechanism from the electron hopping to polaron type by increasing temperature. The very high dielectric values obtained in the order of 105 at low frequency warrant their application at low frequencies. Highlights: Mn0.8Zn0.2Fe2O4 ferrites were prepared from spent Zn-C batteries with different fuels. The entire ferrites were prepared using environment-friendly auto-combustion routes. Ferrites were characterized using XRD, TEM, and VSM. The different obtained properties were investigated and discussed. [ABSTRACT FROM AUTHOR]

The importance of water is so high that new methods and materials are constantly being developed to increase freshwater quality. For this purpose, to investigate the unique properties of double perovskites in the photocatalytic process, novel Tb2CoMnO6 nanoparticles were synthesized using the sol-gel auto-combustion method. In this method, maltose, cellulose, and Date syrup were used as fuel. Two different ratios of maltose were tested to investigate the effect of fuel content on size and morphology. The synthesized particles in the presence of maltose in an equal ratio to the precursor were selected as the optimal sample by using different analyses such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Other properties of optimal nanoparticles were investigated using transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM) and diffuse reflectance analysis (DRS) analysis. These nanoparticles were used to investigate the photocatalytic properties under UV light in the aqueous solution of Eriochrome black T, Rhodamine B, Thymol blue, and Acid red dyes. The results of the photocatalytic process showed 70% discoloration for the Eriochrome Black T. Three compounds, include Ethylenediaminetetraacetic acid, 1,4-Benzoquinone, and Benzoic acid, were used as scavengers to investigate the mechanism of the photocatalytic process. The results showed that the mechanism of the photocatalytic process proceeds through superoxide radicals, which Benzoquinone scavenges.

In this paper, BaLa‌xGdxFe12-2xO19 (x=0.2, 0.4, 0.6 and 0.8) were synthesized via sol-gel auto-combustion method. Fourier transform infrared spectroscopy (FTIR) of samples was represented that the bands at 400 and 500 cm-1 were related to the formation of hexaferrite phase. The (x-ray diffraction) XRD patterns were matched exactly with the structure of barium hexaferrite. (Field emission scanning electron microscopy) FESEM were represented the hexagonal shapes of all products. Magnetic analysis of barium hexaferrite were investigated by (vibrating sample magnetometer) VSM. The saturation magnetization of all samples decreased by increasing dopant’s substitution due to the different occupation sites of dopants instead of Fe3+ (64 to 36.56 emu/g) in the hexaferrite structure. The coercivity increased because of its reverse relation with saturation magnetization (5010 to 5500 Oe). Microwave absorption properties of samples was investigated by (vector network analyzer) VNA. The maximum value of reflection loss was -7.8 db at 10.4 GHz frequency in 3mm thickness for x=0.4 sample.

In this article, MgO/Ca 2 Mn 3 O 8 nanocatalyst was used for the first time in the transesterification process for the production of green fuel from sunflower oil. Besides, the synthesis of layered nanostructured Ca 2 Mn 3 O 8 was done for first applied by combustion route as well. The effects of two heating sources including muffle furnace and microwave irradiation, and also various fuels including urea, glycine, and ethylene glycol were investigated on the characteristics of calcium-manganese oxide (Ca 2 Mn 3 O 8) as the support of the nanocatalysts loaded by MgO as active phase. The synthesized samples were characterized by different analyzes such as AFM, HRTEM, FESEM, FTIR, EDX, XRD, and BET-BJH. The nanocatalyst produced by the microwave irradiation combustion method and urea fuel scored the best performance. This nanocatalyst had the highest specific surface area (46.4 m2/g), and better pore size distribution, too. The roughness of this sample was reported at 5.1 nm in the range of 2 μm. It was found that the optimum sample has converted 96.7% of the oil extracted from sunflower seed to fatty acid esters that are gained by transesterification of fats with methanol. This sample exhibited better reusability in the same operating conditions in proportion to the sample synthesized with muffle furnace in twelve runs, which justified the positive influence of microwave irradiation on the catalytic properties. [ABSTRACT FROM AUTHOR]

Iron oxide (Fe2O3) nanoparticles were prepared by combination of sol-gel autocombustion and ultrasonic irradiation. The XRD pattern reveals that the crystallite size of sample is 36.7 nm and the phase identification shows hematite, syn has been crystalized. The morphology of the sample investigated by FESEM showed that particle size of the sample was about 76 nm. The optical property of Fe2O3 investigated by DRS showed that there may exist three energy band gaps in iron oxide nanoparticles . FT-IR technique was used to determine the functional group of product. In agreement to XRD results, the result of FT-IR revealed no organic residue in product. Photo catalyst nanoparticles were immobilized on the surface of glass slide using Doctor Blade method. Photocatalytic degradation of reactive red 4 (RR4) was investigated under UV light using iron oxide nanoparticles as catalyst. The kinetic of RR4 degradation under UV light irradiation in the presence of Fe2O3 as photocatalyst, and rate constant was determined. Experiments exhibited that Fe2O3 nanoparticles decomposed 52% of azo dye RR4 in solution duration 135 min. The photo catalytic reaction kinetic of RR4 degradation in the presence of Fe2O3 nanoparticles followed Langmuir-Hinshelwood model with the rate constant of about 0.005 min-1.

LaFeO 3 was prepared via simple, economical and environmentally friendly auto-combustion methods using different fuels, including citrate, urea, sucrose, egg whites, gelatin and chitosan. The prepared ferrites were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high resolution transmission electron microscopy (HRTEM), vibrating sample magnetometry (VSM) and electrical measurements to study the impact of the synthetic routes on the various properties. XRD showed the formation of a single orthorhombic phase, except for the samples prepared via egg white, gelatin and urea methods, which indicated a secondary La 2 O 2 CO 3 phase. The FT-IR and TEM studies confirmed the formation of the phase. Differential thermal analysis-thermogravimetry techniques (DTA-TG) were used to characterize the auto-combustion process up to ferrite formation. The obtained unsaturated magnetization for all of the samples suggested the presence of anti-ferromagnetic ordering in addition to weak ferromagnetic ordering. The egg white method showed higher magnetization (1.78 emu/g), while the urea and chitosan methods indicated lower magnetization (0.13 emu/g). The coercivity measurements confirmed the presence of ferromagnetic/anti-ferromagnetic interfaces with higher values than those reported in the literature. The AC-conductivity measurements indicated semiconducting characteristics and exhibited a change in the conduction mechanism from hopping to polaron conduction by increasing the temperature. LaFeO 3 prepared via the egg white method indicated an anti-ferromagnetic/paramagnetic transition at approximately 715 K. The dielectric measurements confirmed the AC-conductivity results and exhibited values higher than those reported in the literature. [ABSTRACT FROM AUTHOR]

Abstract It is extremely desirable but challenging to develop a facile synthesis to directly prepare permanent magnet foam with high coercivity (H c) and low mass density to meet the requirements of advanced magnets in modern industry. In this work, we developed a facile strategy to synthesize cobalt ferrite foam by solution combustion method and subsequently annealing treatment. The structure and magnetic properties of the foams can be influenced by the ratios of glycine to nitrate (G/N), Co content and annealing treatment temperatures. The increase in the mean grain sizes within the single domain range gives rise to an enhancement in coercivities. The highest H c of ∼3 kOe with an ultra-low mass density of ∼45 mg/cm3 can be successfully obtained by controlling the preparation process. The work opens up a new way to prepare ultra-light Fe-based oxides for magnetic and catalytic applications. Highlights • Foam-like porous Co x Fe 3- x O 4 was prepared by facile auto-combustion method. • The effects of glycine to nitrate ratios and Co content were studied. • Ultra low mass density ∼45 mg/cm3 and large coercivity ∼3 kOe were obtained. [ABSTRACT FROM AUTHOR]

Abstract Palm oil mill effluent (POME) is a serious and expensive environmental problem in Malaysia. In this paper, CaFe 2 O 4 is introduced as a novel photocatalyst for the degradation of POME under visible light irradiation. Two synthesis routes, auto-combustion and co-precipitation, and two calcination temperatures 550 °C and 700 °C were used to produce four CaFe 2 O 4 catalysts AC550, AC700, CP550 and CP700. CP550 exhibited the greatest photocatalytic degradation at 56% chemical-oxygen-demand (COD) removal after 8 h of irradiation which dropped to 49% after three consecutive cycles indicating reasonable conversion and high recyclability. BET analysis indicated CP550 had the highest S BET (27.28 m2/g) and pore volume (0.077 cm3/g) which dropped precipitously for CP700 upon increasing the calcination temperature to an S BET of 9.73 m2/g and pore volume of 0.025 cm3/g due to annealing which created a smoother surface area as evidenced by the SEM images. UV–Vis DRS indicated CP550 had the highest band-gap (1.52 eV) which is likely due to the presence of a highly crystalline pure CaFe 2 O 4 phase compared to the other products which existed as a mixture of Fe oxidation states evidenced by the XRD data. The PL spectra for all catalysts indicated significantly lower recombination rate for both CP550 and CP700. Introduction of IPA into the reaction mixture to eliminate hydroxyl radicals resulted in a diminishing of COD removal from 56% to 7% proving hydroxyl radicals to be the primary reactive species responsible for photodegradation of POME. Highlights • Visible light-active CaFe 2 O 4 was synthesized to treat POME. • Auto-combustion and co-precipitation were employed to produce CaFe 2 O 4. • Scavenging studies showed OH. as a responsible radical to degrade POME. • Recyclability studies showed a mere 7% reduction in POME degradation. [ABSTRACT FROM AUTHOR]

Pure phase spinel ferrite nanoparticles (Mn0.5Zn0.5Fe2O4) were one-step synthesized by the sol-gel auto-combustion method at low temperature. The structural characteristics, morphology and thermal decomposition were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), TG-DSC analyzer, respectively. The results indicate that pure phase Mn0.5Zn0.5Fe2O4 ferrite nanoparticles of about 60nm in diameter can be directly synthesized after auto-combustion of the nitrate-citrate xerogel under the conditions of pH=7.0, R=1:1 and C(CA)=0.7 mol/L. The obtained nanoparticles show the diameter increases and the diffraction peak narrows but the strength increases after calcined at 400℃ which improves the crystal structure.

M-type barium hexaferrite (BaFe _12 O _19 ) particles are synthesized by using sol-gel auto-combustion reaction for microwave absorption study in X-band. Three different materials namely BaNd _0.02 Fe _11.98 O _19 (Nd2), BaNd _0.04 Fe _11.96 O _19 (Nd4) and BaNd _0.06 Fe _11.94 O _19 (Nd6) have been developed by varying doping of neodymium in barium hexaferrite. The synthesis of particles has been confirmed using SEM micrographs and XRD diffraction pattern. The hysteresis study is carried out for saturation magnetization using vibrating sample magnetometer (VSM). As the doping concentration of neodymium increases, the saturation magnetization of the material is decreased from 47.272 emu g ^−1 to 16.479 emu g ^−1 . The vector network analyzer (VNA) is used for complex permittivity and complex permeability measurements of the developed materials. Nd4 material shows highest values of permittivity and permeability losses among other developed materials. From the complex permittivity and complex permeability, the reflection loss results of the developed materials have been calculated. The maximum reflection loss of −33.17 dB was obtained for 2.2 mm pallet of BaNd _0.04 Fe _11.96 and −10 dB bandwidth reaches 2.94 GHz.

Undoped and Ba and Ag-doped SrTiO3-based nanopowders (NPs) were successfully grown by a modified auto-combustion method. An optimum ratio of citric acid and nitric acid was used as the polymerization agent and fuel. The X-ray diffraction (XRD) results revealed that the products were crystalline with cubic and tetragonal structures. The particle aggregation state, nanoparticles size distribution, morphology and electrical properties were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), atomic force microscopy (AFM) and ultraviolet–visible (UV–vis) were studied, respectively. Using the X-ray peak broadening and size–strain plot (SSP) method the crystallite sizes and lattice strain of the samples were investigated. The UV–vis absorption spectra revealed that the band gap of the STO-based has a strong absorption peak which lies in the UV region.

Di-phase ceramic composites, with general formula xNi 0.7 Zn 0.3 Fe 2 O 4 – (1-x)BaTiO 3 (x = 0.9, 0.7, 0.5, 0.3, 0.1), were prepared by a mixing method. X-ray analysis, for powder and ceramics, indicated the formation of ferrite and barium titanate phases without the presence of the impurities. SEM analysis indicated that the composite morphology contained two types of grains, polygonal and rounded. Homogeneous microstructure and the smallest grain size were obtained in ceramics with 70% of barium titanate. The electrical properties of these materials were investigated using impedance spectroscopy, dielectric and ferroelectric measurements. The NZF-BT(30-70) composite has shown better electrical properties in comparison to other investigated ceramics, confirmed by dielectric and ferroelectric data analysis. Saturation magnetization and coercive field decreased with the increase of the content of ferroelectric phase. [ABSTRACT FROM AUTHOR]

Chemically derived auto-combustion technique is employed to synthesize the Zn0.95−xFe0.05AlxO (x = 0, 0.03, 0.05, 0.07) nano-crystallites. The salient similarities between variations in lattice parameters, crystallite size, morphology, electrical resistivity and saturation magnetization designated a strong association between these properties. X-ray diffraction studies of all compositions revealed the phase pure wurtzite crystal structure with space group P63mc. The lattice parameters and crystallite size are changed with doping of Al attributed to the diversity in the size of ionic radii. Scanning electron micrographs revealed that Al doping affects the size and shape of grains in synthesized compositions. Temperature dependent electrical resistivity shows a decreased trend with the rise of temperature, confirming the semiconducting nature of compositions. The lower resistivity and enhanced saturation magnetization values in Al doped compositions correspond to the increase in density of carriers. Carrier mediated RKKY interactions are found to enhance magnetization.

A series of solids was synthesized by the incorporation of Ni and Mo active species on delaminated clay with novel acidic properties, by impregnation and auto-combustion. The resulting solids were characterized by X-ray fluorescence, X-ray diffraction (XRD), textural analysis by N 2 physisorption, temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and, in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Decane hydroconversion was used to evaluate the potential of the materials as hydrocracking catalysts for vacuum bottoms. XRD was used to confirm modification of the material and good active phase dispersion. TPR revealed an important decrease in the reduction temperatures with auto-combustion method. Low-temperature reducible species play a key role in the catalytic performance for decane hydroconversion. [ABSTRACT FROM AUTHOR]

(Bi0.5 Na0.5 )TiO3 ceramic was prepared by dry auto-combustion method using urea as a fuel. It was shown that the phase composition of the synthesized powder depends on the amount of urea. The X-ray diffraction study confirmed that single phase rhombohedral structure with space group R3C was obtained in the powder calcined at 700 °C when 25 wt.% of urea was added, but secondary phases were observed with higher addition of urea. Pellets have been formed from the single phase powder and sintered at 1100 °C for 2 and 3 hours. The effect of sintering conditions on the structural and dielectric behaviour was studied in detail. The scanning electron micrographs of pellets showed dense structure with well-defined rectangular grains having larger size after longer sintering time. The temperature and frequency dependence dielectric study of the sintered samples showed two dielectric peaks attributed to the factors caused by the phase transitions from ferroelectric to antiferroelectric and antiferroelectric to paraelectric phase. The dielectric constant and the diffuse phase transition behaviour increases with increase in sintering time.

In this research, NiFeO-based composite nanopowder with 0.8, 1, 1.35, 1.7 fuel-to-oxidant (F/O) ratios was synthesized by sol-gel auto-combustion method. Changes in phase constituents, microstructure and magnetic properties due to changes in F/O ratios were evaluated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM) techniques. XRD and Raman spectroscopy results show the presence of NiFeO, FeNi, α-FeO and NiO phases. The amount of nickel ferrite was increased, while the amount of FeNi was decreased with increasing F/O ratio from 0.8 to 1.35. Mean crystallite sizes of the samples are in the range of 40-46 nm. FESEM studies depicted the formation of NiFeO particles coexisting with FeNi phase. Changes in F/O ratios alter the saturation magnetization values from 37 to 60 emu/g as a result of changes in FeNi and NiFeO amounts. Coercivity values are in the range of 135-177Oe. Graphical Abstract: In this research nano-sized NiFeO powders with 0.8, 1, 1.35, 1.7 Fuel to Oxidant (F/O) ratios were synthesized by sol-gel auto-combustion method. FESEM studies depicted the formation of NiFeO particles coexisting with FeNi phase. Changes in F/O ratios alter the saturation magnetization values from 37 to 60emu/g as a result of changes in FeNi and NiFeO amounts. Coercivity values are in the range of 135 to 177Oe.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Monocristales de ( (1 - x)Pb(Zn1=3Nb2=3)O3-xPbTiO3-PZN-xPT ) con estructura perovskita, muestran excelentes propiedades dieléctricas, ópticas y electrostrictivas en composiciones cerca al contorno de fase morfotrópico (CFM), x 0;09. La preparación de cerámicas con composiciones cercanas al CFM por métodos convencionales, conduce a cerámicas con estructura pirocloro. En este trabajo, polvos de ((1 - x)Pb(Zn1=3Nb2=3)O3-xPbTiO3-PZN-xPT) con x = 0;10 fueron sintetizados por el método de reacción por combustión. Como combustibles fueron usados: CO(NH2)2, C2H5NO2, CO(NH2)2=C2H5NO2 y C4H16N6O2. El resultado indica que el mayor porcentaje de fase perovskita (70 %) fue obtenido usando CO(NH2)2= C2H5NO2 (razón 50=50). Esta fase es mantenida al sinterizar la muestra a 1000 C en atmósfera de nitrógeno. MSC: 74E15, 74E40, 74N15 PACS: 80.81

In the present work we have illustrated the physics of the electrical characteristics of nanocrystalline La 1− x Pb x FeO 3, (0 ⩽ x ⩽ 0.2) powder prepared using auto-combustion synthesis. The effect of lead doping on the dielectric, impedance and ac conductivity characteristics of lanthanum ferrite has systematically been investigated. The synthesized powders were phase pure and crystallized into centro-symmetric Pnma space group. As compared to pure LaFeO 3 ceramics (dielectric constant ∼ 14,000), the dielectric constant is grossly increased (∼30,000) in Pb doped LaFeO 3 . The temperature dependence of dielectric constant of 10.0 at.% Pb doped LaFeO 3 exhibits dielectric maxima similar to that observed in ferroelectric ceramics with non-centrosymmetric point group. For La 0.8 Pb 0.2 FeO 3 ceramics, the frequency dependence of the dielectric constant and loss tangent at various temperatures (300–450 K) exhibit typical colossal dielectric constant (CDC) like behavior. From the impedance spectroscopy we have estimated the grain and grain boundary resistance and capacitance of Pb doped LaFeO 3 that follow a small polaron hopping conduction model. Long range movement of the charge carriers govern the CDC behavior. [ABSTRACT FROM AUTHOR]

A series of Y and Fe co-doped Ca 3− x Y x Co 4− y Fe y O 9+ δ (0 ⩽ x ⩽ 0.3, 0 ⩽ y ⩽ 0.1) samples synthesized by auto-combustion reaction and followed by a spark plasma sintering (SPS) processing with the effects of Fe and Y doping on the high temperature (RT to 800 °C) thermoelectric properties were systematically investigated. For the Fe-doped system ( x = 0, y ⩽ 0.1), the electrical resistivity ( ρ ) decreased over the whole measured temperature range, while the Seebeck coefficient ( S ) remained almost the same. For the co-doped system, at any fixed Fe doping content, both ρ and S tended to increase with increasing Y dopants, however, the effect is more substantial on ρ than on S , particularly in the low temperature regime. In contrast to ρ and S, the in-plane thermal conductivity ( κ ) is only slightly influenced by Y and Fe substitutions. Among all the investigated samples, the co-doped sample with x = 0.1 and y = 0.03 showed a decrease of ρ , enhanced power factor over the measured temperature range, and improved ZT at 800 °C as compared to un-doped Ca 3 Co 4 O 9+ δ . [ABSTRACT FROM AUTHOR]

Nanosized powders of compositions, Bi 0.8 Er 0.2 O 1.5 (ESB) and Ce 0.85 La 0.15 O 1.925 (CLO) have been prepared using citrate–nitrate auto combustion method. ESB added CLO (ECLO) samples have been prepared by mixing nanosized CLO powder with 0.5, 1, 2 and 3 wt.% of ESB. X-ray diffraction patterns confirm that all the samples are single phase having cubic fluorite structure similar to CeO 2 . Density of Ce 0.85 La 0.15 O 1.925 increases with increasing ESB content. All the samples have been sintered at 1350 °C. All the ECLO samples have density more than 97% of the theoretical value. Field emission scanning electron microscope images show dense microstructure with distinct grains and grain boundaries. Impedance measurements have been made in the temperature range 200–700 °C in air. Addition of ESB increases the conductivity of the bulk as well as of grain boundaries. Ce 0.85 La 0.15 O 1.925 with 0.5 wt.% of ESB exhibits the maximum conductivity 1.41 × 10 −2 S cm −1 at 600 °C of all the compositions. This value is one order of magnitude higher than the conductivity of Ce 0.85 La 0.15 O 1.925 (1.99 × 10 −3 S cm −1 ). [ABSTRACT FROM AUTHOR]

Co-Mn-Mg-Al oxides were synthesized using auto-combustion and co-precipitation techniques. Constant ratios were maintained with (Co + Mn + Mg)/Al equal to 3.0, (Co + Mn)/Mg equal to 1.0 and Co/Mn equal to 0.5. The chemical and structural composition, redox properties, oxygen storage capacity and oxygen mobility were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), temperature-programmed reduction of hydrogen (H2-TPR), oxygen storage capacity (OSC), oxygen storage complete capacity (OSCC) and isotopic exchange, respectively. The catalytic behavior of the oxides was evaluated in the total oxidation of a mixture of 250 ppm toluene and 250 ppm 2-propanol. The synthesis methodology affected the crystallite size, redox properties, OSC and oxide oxygen mobility, which determined the catalytic behavior. The co-precipitation method got the most active oxide in the oxidation of the volatile organic compound (VOC) mixture because of the improved mobility of oxygen and ability to favor redox processes in the material structure. [ABSTRACT FROM AUTHOR]

MnMgAlO x mixed oxides were prepared by means of the auto-combustion methodology using glycine/nitrate ratios of 1.0, 0.56 and 0.2; and M 2+ /M 3+ = 3.0 and Mn 2+ /Mg 2+ = 1.0 ratios. Additionally, MnMgAlO x oxide was obtained from the hydrotalcite-type precursor by the traditional co-precipitation method. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (H 2 -TPR), temperature programmed desorption (O 2 -TPD), textural analysis, scanning electron microscopy (SEM) and their catalytic performances were evaluated in the total oxidation of two volatile organic compounds (VOCs) representative of aromatic compounds (toluene) and of esters (ethyl acetate). The manganese mixed oxides resulting from the auto-combustion exhibited a chemical composition similar to that of the oxide obtained by thermal decomposition of the hydrotalcite with ∼36% of manganese loading. The mixed oxides obtained by both methodologies were active in the VOC oxidation. However, the mixed oxides synthesized by the auto-combustion methodology with stoichiometric and rich fuel conditions, showed better performance in the oxidation of toluene and ethyl acetate. The fuel/oxidizer ratio determined the redox properties, specific area and the catalytic performance of the materials in the oxidation of VOCs. Using the auto-combustion method was possible to obtain mixed oxides with a high manganese load which showed lower size particle (4–7 nm) and better structural stability than the mixed oxide obtained by the co-precipitation method (34 nm). The auto-combustion allowed for the obtaining of mixed oxides in very short synthesis times (∼5 h) with equal or superior catalytic properties as the oxide obtained by the co-precipitation method probably due to the maximization of the properties of the materials, where the decrease of the particle sizes and the improvement of the active phase distribution and oxidation-reduction properties are favorable for the improvement of catalytic performances. [ABSTRACT FROM AUTHOR]

Mixed oxides of manganese, cobalt and their mixture were synthesized by auto-combustion and co-precipitation methodology maintaining a constant M 2+ /Al 3+ ratio of 3.0, which is characteristic of the oxides obtained from the thermal decomposition of hydrotalcite-type precursors (in manganese oxides M 2+ = Mg + Mn, in cobalt oxides M 2+ = Mg + Co and in manganese-cobalt oxides M 2+ = Mg + Mn + Co). The catalysts were characterized by the following techniques: X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 adsorption, temperature-programmed reduction (H 2 -TPR), temperature programmed desorption of oxygen (O 2 -TPD) and 18 O isotope exchange. All of the materials were evaluated for the catalytic oxidation of two organic compounds of different reactivities: toluene and 2-propanol. It was observed that the joint participation of the absorbed oxygen species on the surface and the lattice oxygen atoms are responsible for the catalytic activity of the materials. However, the redox properties and the oxygen mobility play a determining role in the oxidation of the two volatile organic compounds (VOCs), with the oxygen mobility playing a more significant role in the cobalt oxides, whereas the redox properties are fundamental in the manganese oxides and in the Co and Mn mixture. The existence of a cooperative effect between the Co and Mn oxides is demonstrated when the co-precipitation method is used for the synthesis of the mixed oxide. This effect is not observed when auto-combustion is used for the synthesis; therefore, the autocombustion manganese oxide is the most active catalyst in the oxidation of the two VOCs by this methodology. [ABSTRACT FROM AUTHOR]

Undoped and Ba and Ag-doped SrTiO 3 -based nanopowders (NPs) were successfully grown by a modified auto-combustion method. An optimum ratio of citric acid and nitric acid was used as the polymerization agent and fuel. The X-ray diffraction (XRD) results revealed that the products were crystalline with cubic and tetragonal structures. The particle aggregation state, nanoparticles size distribution, morphology and electrical properties were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), atomic force microscopy (AFM) and ultraviolet–visible (UV–vis) were studied, respectively. Using the X-ray peak broadening and size–strain plot (SSP) method the crystallite sizes and lattice strain of the samples were investigated. The UV–vis absorption spectra revealed that the band gap of the STO-based has a strong absorption peak which lies in the UV region. [ABSTRACT FROM AUTHOR]

((1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3-(1-x)PZN-xPT) single crystals with perovskite structure near to the morphotropic phase boundary (MPB), x~0, 09, exhibit unusual large dielectric and piezoelectric constants. Preparation of PZN-PT ceramics with composition near to the MPB using conventional methods leads to ceramics with pyrochlore structure. In this paper, ((1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3-PZN-xPT) powders with x = 0; 10 were synthetized by the combustion reaction method. CO(NH2)2, C2H5NO2, CO(NH2)2=C2H5NO2 y C4H16N6O2 were used as fuels. Results show that a maximum of 70% of perovskite phase was obtained using CO(NH2)2= C2H5NO2 (in relation 50=50). The afore mentioned phase is preserved when sintering the sample at 1000°C, during 4h on nitrogen atmosphere. [ABSTRACT FROM AUTHOR]

Abstract: A CoFe2O4/cetyl trimethylammonium bromide (CTAB) nanocomposite has been fabricated by a sol–gel auto-combustion method. Characterization of the material revealed the composition of the crystalline phase as CoFe2O4 while FT-IR confirmed the presence of CTAB on the nanoparticles. From X-ray line profile fitting, average crystallite size was estimated to be 22±6nm. SEM analysis showed a porous sheet-like morphology with internal nanosize grains of about 30nm. The room temperature coercive field (H c ) of the CoFe2O4/CTAB nanocomposite was found to be 1045Oe which is close to the previously reported room temperature values for bulk CoFe2O4. The H c was observed to decrease almost linearly with the square root of the temperature (√T) according to Kneller's law. From the linear fit of H c versus √T, the zero-temperature coercivity (H c0) and superparamagnetic blocking temperature (T B ) of the CoFe2O4/CTAB nanocomposite were found to be ∼9.1kOe and ∼425K, respectively. The remanence magnetization (M r ), the reduced remanent magnetization (M r /M s ), and the effective magnetic anisotropy (K eff ) decrease with increasing temperature. The M r /M s value of 0.6 at 10K higher than the theoretical value of 0.5 for non-interacting single domain particles with the easy axis randomly oriented suggests the CoFe2O4/CTAB nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model. [Copyright &y& Elsevier]

The γ-Al2O3 nanocrystallites were synthesized successfully by combination of sol-gel auto-combustion process and ultrasonic method. The overall process involves three steps: formation of homogeneous sol at 50 °C; formation of dried gel at 90 °C, and experiments revealed that Al2O3 dried gel derived from glycine (as fuel) and nitrates sol exhibits self propagating combustion at 400 °C that it is ignited in air. After auto-combustion process, the Al2O3 nanopowders were calcined at 1100 °C. Also, aluminum alloy matrix composites reinforced with 0.75 and 1.5 vol.% γ-Al2O3 nanoparticles were fabricated via stir casting method. Fabrication was performed at 850 °C temperatures. The resulting composites were tested for their nanostructure and present phases. Based on the obtained results, optimum amount of reinforcement and casting temperature were determined by evaluating the density, hardness and compression tests of the composites. [ABSTRACT FROM AUTHOR]

Abstract: This study presents an original approach to the improvement of advanced oxidation process (AOP) efficiencies through the design of highly active catalysts. Then, removal of phenol was obtained under mild conditions by catalytic wet peroxide oxidation (CWPO) process over silica supported micropore and/or mesopore confined copper oxide nanoparticles. The materials, i.e. y wt.% CuO (y ranging from 4 to 10) on SBA-15 exhibiting different pore structure properties, were entirely characterized. In this study, we took advantage from the evolution of the micropore fraction in the mesoporous silica with the autoclaving temperature of synthesis. While only mesopore nanocasted copper oxide nanoparticle formed when the support exhibits only mesoporosity, micropore silica confined nanoparticles other formed the two supports exhibiting both micropores and mesopores. In this case, mesopore nanocasted nanoparticles can be only observed when copper oxide loading reaches 10wt.%. As a consequence, the copper active surface is suggested to be higher when copper incorporates interconnected micropores, without limited pore plugging issued from mesopore confined nanoparticle formation. For the phenol removal reaction, all the materials are exhibiting interesting activity, with a complete conversion of phenol and almost 60–80% of mineralization obtained in less than 2h at 60°C. Nevertheless, the results showed that the increase in copper loading up to high values is not needed to achieve high mineralization degree, due to the typical morphology of the materials, i.e. confinement of nanoparticles inside micropores or mesopores. In addition, the prepared materials allow a continuous use in reaction with leaching of active phase (≤4.4mgL−1) which also results in no water post-purification for cation removal as in the case of the classical homogeneous Fenton process. [Copyright &y& Elsevier]

Nanocrystalline ZrO2 with particle size of about 38 nm was directly synthesized by sol-gel auto-combustion method. The overall process involved three steps: formation of homogeneous sol at 50-55°C; formation of dried gel at 110°C, and combustion of the dried gel at 400°C. Experiments revealed that ZrO2 dried gel derived from glycine (Fuel) and nitrate sol exhibited self propagating combustion at 400°C that it was ignited in air. The auto-combustion was considered as a heat-induced exothermic oxidation-reduction reaction between nitrate ions and carboxyl group. After auto-combustion, products were calcined at 650°C. ZrO2 nano particle were incorporated into the A356 aluminum alloy by a mechanical stirred at 850°C and after that, cylindrical specimens were cast. After preparing the samples, mechanical properties were measured. The results of microstructure, compression and hardness tests indicated that addition of ZrO2 nano particulates to aluminum matrix composites improved the mechanical properties. Also, Based on experiments, it was revealed that the presence of ZrO2 reinforcement led to significant improvement in hardness and compressive strength. [ABSTRACT FROM AUTHOR]

Abstract: A series of the as-burnt and the burnt Cu/ZnO catalysts were prepared by a sol–gel auto-combustion method using metal nitrates with the mole ratio of Cu/Zn=1/1 (noted as M, M=Cu+Zn) and citric acid (noted as CA). When the xerogels were burnt in the argon atmosphere, H2 and CH4 which were came from the decomposition of the citric acid, were the reducing agents and were used in the redox process for synthesizing metallic Cu from Cu2+ in the chelated compound. The XRD patterns revealed that all the as-burnt catalysts with different M/CA molar ratios were converted into pure Cu and ZnO species. TPR analysis of the as-burnt catalyst illustrated that almost no hydrogen was consumed. It proved that Cu2+ in the chelated compound was absolutely reduced to metallic Cu in the as-burnt catalyst. The effects of M/CA molar ratio on the properties of catalysts were studied by TG-DTA, FT-IR, Raman spectrum, XRD, SEM-EDS, BET, and N2O chemisorption techniques. The activity of the as-burnt catalysts without reduction was investigated for low-temperature methanol synthesis from syngas containing CO2 using ethanol as a promoter at 443K and 5.0MPa for 12h. The total carbon conversion increased with increasing the content of citric acid and reached a maximum for the as-burnt Cu/ZnO catalyst C0.8 with M/CA=1/0.8, and then decreased. The variation trend was in accordance with that of the copper (Cu0) surface area. Comparing with the burnt catalyst C0.8-air after reduction, the methanol selectivity of the as-burnt Cu/ZnO catalyst was much lower owing to lower hydrogenation activity of the ethyl formate. The as-burnt catalyst C0.8 was also used in continuous low-temperature methanol synthesis at 443K and 5.0MPa for 40h. The total carbon conversion was stable after 15h and no obvious deactivation during 40h reaction, but the methanol selectivity was still not high. [Copyright &y& Elsevier]

Abstract: Using spent alkaline Zn–Mn batteries as raw material, Mn–Zn soft magnetic ferrite nanoparticles are prepared by multi-step processes including acid leaching, chemical treatment of battery iron shells and citrate-nitrate precursor auto-combustion. Acid leaching and chemical treatment mechanisms are investigated. Dried gels thermal decomposition process, auto-combustion, phase composition, morphological and magnetic properties of as-prepared Mn–Zn ferrite nanoparticles are characterized by thermogravimetric and differential thermal analysis, X-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer. Synthesized Mn–Zn ferrite nanoparticles (Mn0.5Zn0.5Fe2O4) have pure ferrite phase, larger saturation magnetization (M s =60.62emug−1) and lower coercivity (H c =30Oe) compared with the same composition ferrites prepared by other techniques due to better crystallinity. Mn–Zn ferrite nanoparticles synthesis method presents a viable alternative for alkaline Zn–Mn batteries recycling. [Copyright &y& Elsevier]

Abstract: Quasi-single magnetic domain M-type barium hexaferrite powders have been synthesized via sol–gel auto-combustion route, followed by secondary heating treatment at 800°C for 4h, using barium nitrate, ferrite nitrate, ammonium nitrate, citric acid, and ammonia solution as the starting materials. The auto-combustion producing powders were γ-Fe2O3 and BaCO3 with aid of additional ammonium nitrate to increase the combustion temperature. The influences of the citric acid to metal ions (CA/M) and pH values on the gel auto-combustion, the phase compositions of the synthesized powders and their magnetic properties have been studied. The results showed that the chelation of barium and ferrite ions were important for the phase formation of barium hexaferrite: the phase compositions of the synthesized powders changed from a multi-phased mixture to a single phase of M-BaFe12O19 for the gradually complete complexing of barium and iron ions with citrate as the pH values and CA/M increased. The resulting powders demonstrated that various magnetic properties mainly depended on the variation in phase composition, sintering adhesion between grains and grown-up of crystalline sizes. With CA/M=1.5, pH 7, the synthesized powders had a particle size distribution in the range of 100–200nm and a saturation magnetization of 58.0emu/g at 12kOe. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

• Ce 1− x La x O 2−δ (x = 0 − 0.1) solid solutions showed linear increase in ionic conductivity with La3+ • Ea is 1.49, 0.94, 0.87 and 0.70 eV for x = 0, 0.01, 0.03, 0.05 and 0.1 composition. • LDC showed highest ionic conductivity of 1.01 × 10−2 S cm−1 at 750 °C. • Electronic and ionic transference numbers are 0.20 and 0.80 at 700 °C for x = 0.1. • 0.05 LDC showed the OCV of 0.81 V and max. power density of 41 mWcm−2. [Display omitted] La-doped CeO 2 nanoparticles of composition Ce 1− x La x O 2−δ (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 − 750 °C. The Ce 0.90 La 0.1 O 2−δ (0.1 LDC) and Ce 0.95 La 0.05 O 2−δ (0.05 LDC) showed a maximum conductivity of 8.89 × 10−3 and 8.32 × 10−3 S cm−1 at 700 °C, respectively. The σ t of 0.1 LDC = 1.01 × 10−2 S cm−1 at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO 2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm−2 at 650 °C using hydrogen as fuel. [ABSTRACT FROM AUTHOR]

The present study elucidates the synthesis of magnesium ferrite magnetic nanocrystallites via hydroxylation–condensation reaction followed by an auto-combustion process. Nanocrystallites with diameter of 3–7 nm were successfully formed via this method. The ignition temperature of the redox reaction was apparently improved to 200°C by the modification of the pH of the metal aqueous solution. The crystallite size was altered by varying the hydrolysis parameters. The XRD analysis of the as-synthesized powder confirms the formation of a single-phase MgFe2O4 spinel structure. Importantly, the crystalline particles were obtained at low temperature without further calcination. The thermodynamic behavior of the precursor was characterized by DTA-TG. TEM observations showed the morphology and crystal structure of the nanocrystallites. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of nano-sized La9.33Ge6O26 powders with apatite-type structure by sol–gel auto-combustion method has been investigated. The details of gel''s auto-combustion were investigated by DTA-TG and the structure of as-synthesized powders from auto-combustion was charactered by XRD and TEM. The results show that single phase La9.33Ge6O26 powders with average size of ∼50nm can be directly synthesized by sol–gel auto-combustion. The as-synthesized powders exhibited high sinter activity, it can be sintered to 94% of its theoretical density at 1150°C for 4h, about 200°C lower than the sintering temperature for the powder derived from traditional solid reactions. The La9.33Ge6O26 electrolyte sintered at 1150°C for 4h has relatively high oxide ionic conductivities (σ 750°C =0.01S/cm), moderate thermal expansion (TECs=9.82×10−6 K−1, between room temperature and 1000°C) and low electrical activation energy (E a =1.02eV). [Copyright &y& Elsevier]

Abstract: A nitrate–citrate–silica gel was prepared from metallic nitrates, citric acid, and silica powder by sol–gel process, and it was further used to synthesize Ni0.5Zn0.5Fe2O4/5wt% SiO2 nanocomposites by auto-combustion. The effect of pH on the formation of NiZn ferrite/SiO2 and thermal properties of gel precursors was studied by XRD, IR, EPR, TGA and DTA techniques. The results revealed that the ratio of the citrate ion to the nitrate ion is directly related to the pH of the solution. The pH in the starting solution affects the combustion process, and then determines the particle size of the as-synthesized powder. The EPR parameters (peak-to-peak linewidth, g factor, and spin number) increased with increasing pH, whereas the spin–spin relaxation time () decreased. The thermal stability and enthalpy of the decomposition process in air decreased with increasing pH, whereas the enthalpy in nitrogen increased. Moreover, the activation energy () of thermo-oxidative degradation of the gel precursor at pH 3 was much lower than the gel precursor at pH 5 and 7, and that increased with increasing pH. [Copyright &y& Elsevier]