As-combusted Powders Research Articles

Activation of bismuth aluminate for obtaining near infrared emission

New results on NIR emission in Bi2Al4O9 phosphors activated with Cr3+, Er3+or Nd3+ are presented. These phosphors were prepared by a simple two step method consisting of combustion followed by annealing at 800C. Annealing step was necessary to obtain powders with good crystallinity; as-combusted powders being amorphous. Host sensitization was observed in all the phosphors. An excitation band around 279 nm corresponds to bandgap excitation of the host1So→ 3P1 transition of the Bi3+ ion, while that at 360 nm to the defect absorption. Apart from the excitation in these host related bands, characteristic excitations also produced intense emission lines. It is suggested that these phosphors can be useful for making low cost NIR sources needed in various applications.

Electromagnetic microwave absorption properties of high entropy spinel ferrite ((MnNiCuZn)1−xCoxFe2O4)/graphene nanocomposites

High entropy spinel ferrite (HEF) nanoparticles were synthesized by solution combustion method as high-performance microwave absorbers. The structural, microstructural, magnetic and microwave absorption properties of (MnNiCuZn) 1−x Co x Fe 2 O 4 powders (x = 0.05, 0.1, 0.2, and 0.3) were studied as a function of Co contents by modern characterization methods including X-ray diffractometry, Raman spectroscopy, electron microscopy, vibrating sample magnetometry, and vector network analyzer. The as-combusted powders were single phase with the space group of F d 3 ¯ m . The cation distributions showed that the fraction of Fe 3+ cations in (A) sites decreased with the substitution of Co cations. The (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 nanoparticles (~30–70 nm) were dispersed on the graphene sheets. The coercivity increased from 94 to 225 Oe with the Co contents, while the saturation magnetization slightly changed in the range of 67–71 emu/g. The saturation magnetization and coercivity of the (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 /graphene composite powders were lower than those of (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 powders due to their smaller particle size. The (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 /paraffin composite sample at the mass fraction of 70 wt.% showed the maximum reflection loss of −27 dB at the matching thickness of 5.3 mm in Ku band. The interfacial relaxation and ferromagnetic resonance were determined as main dielectric and magnetic loss mechanisms, respectively. By compositing the (MnNiCuZn) 0.7 Co 0.3 Fe 2 O 4 powders with graphene, the maximum reflection loss of −16 dB at the matching thickness of 4.5 mm in Ku band was obtained at the lower mass fraction of 30 wt.% because of the higher dielectric loss of graphene.

CTAB-assisted solution combustion synthesis of LiFePO4 powders

Cetyltrimethylammonium bromide (CTAB) was used as fuel in solution combustion synthesis of LiFePO4 powders at various fuel contents (ϕ = 1, 2, and 3). Both conventional and microwave heating methods were applied for ignition of the precursor solution. The slow combustion reaction rate characterized by thermal analysis guaranteed the direct formation of the LiFePO4 phase. Phase evolution studies by X-ray powder diffraction showed that nearly single-phase LiFePO4 powders were obtained at higher fuel contents. The as-combusted powders were calcined at 700 °C for removing the impurity phases. The specific surface area of conventionally combusted powders (137 m2/g) was slightly higher than that for microwave heating, as measured from nitrogen adsorption–desorption isotherms. The higher discharge capacity (91 mAh/g) and higher rate capability were obtained by the microwave-combusted LiFePO4 powders due to their higher crystallinity and lower electrode resistance, as confirmed by electrochemical impedance spectroscopy.

Photocatalytic performances of BiFeO3 powders synthesized by solution combustion method: The role of mixed fuels

Abstract Single phase BiFeO3 powders were prepared by solution combustion synthesis method for visible photodegradation of organic pollutants. The effects of mixed fuels on the combustion behavior, phase evolution, structure, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffraction, infrared spectroscopy; electron microscopy, and diffuse reflectance spectroscopy techniques. The as-combusted powders are composed of BiFeO3 phase together with impurity Bi2Fe4O9 and Bi24Fe2O39 phases which were almost eliminated by following the calcination at 600 °C. Particle size decreased from 700 nm to 250 nm using the mixture of fuels due to the decrease in combustion temperature. The BiFeO3 powders can absorb a wide range of visible light with band gap energy in the range of 1.88–2.17 eV. About 100% of methylene blue was photodegraded during 100 min visible light irradiation in the presence of BiFeO3 powders prepared by urea fuel.

Solution Combustion Synthesis of BiFeO3 Powders Using CTAB as Fuel

Nearly pure BiFeO3 powders were synthesized by the solution combustion method using cetyltrimethylammonium bromide as fuel at various fuel to oxidant ratios (φ). Phase evolution, morphology, magnetic and optical properties were characterized by thermal analysis, infrared spectroscopy, x-ray diffractometry, electron microscopy, photoluminescence and diffuse reflectance spectroscopy techniques, respectively. An impurity Bi24Fe2O39 phase appeared while increasing the fuel content. Magnetization of the as-combusted BiFeO3 powders increased from 0.5 emu/g to 11.1 emu/g on account of the decrease in particle size and appearance of the impurity phase with the increase of φ values. Visible light absorption and band gap energy depended on the purity and morphology, being tunable by fuel content. About 85% of methylene blue was photodegraded in the presence of the powders prepared by φ = 0.5 under visible light irradiation.

Solution combustion synthesis of nickel sulfide composite powders

Nickel sulfide powders were synthesized through solution combustion method using a suitable combination of thiourea fuel as reducing/sulfidizing agent with glycine fuel as auxiliary reductant agent. Effects of fuel contents on the combustion behavior, phase evolution, microstructure and optical properties were investigated by infrared spectroscopy, thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. Single phase NiS2 powders were formed using thiourea fuel at higher content, while a mixture of nickel sulfide phases was appeared in the presence of glycine fuel. The amount of different sulfide phases was considerably dependent on the thiourea content. Particle size of the as-combusted powders increased with the increase of thiourea; while the existence of glycine fuel together with thiourea led to the bulky microstructure. Maximum photodegradation (~ 56%) of methylene blue was achieved by as-combusted powders at a thiourea fuel to the oxidant molar ratio of 1, as a consequence of their high ability of light absorption.

Solution Combustion Synthesis of Fe3O4 Powders Using Mixture of CTAB and Citric Acid Fuels

Magnetite (Fe3O4) powders were synthesized by solution combustion method using a mixture of cetyltrimethylammonium bromide (CTAB) and citric acid fuels at various fuel to oxidant ratios (ϕ = 0.5, 1, 1.5, and 2). Phase evolution investigated by x-ray diffraction method showed single-phase Fe3O4 powders were only formed at ϕ = 1 using mixture of fuels, while impurity α-Fe2O3 phase together with magnetite phase was completely disappeared at ϕ = 2 for CTAB fuel alone. The specific surface area and porous structures of the as-combusted Fe3O4 powders were characterized by N2 adsorption-desorption isotherms and scanning electron microscopy techniques, respectively. The specific surface area using the mixture of fuels (37 m2/g) was higher than that of CTAB fuel alone (32 m2/g). Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry method. The highest saturation magnetization of 83 emu/g was achieved by mixture of fuels at ϕ = 1, due to the high purity and large particle size.

Solution combustion synthesis of CoFe2O4 powders using mixture of CTAB and glycine fuels

Cobalt ferrite (CoFe2O4) powders were synthesized by solution combustion method using a mixture of cetyltrimethylammonium bromide (CTAB) and glycine fuels. The combustion behavior, phase evolution, microstructure, specific surface area, and magnetic properties were investigated by thermal analysis, infrared spectroscopy, X-ray diffractometry, nitrogen adsorption–desorption, electron microscopy, and vibrating sample magnetometry techniques. Single-phase CoFe2O4 powders were achieved by mixing of CTAB and glycine fuels, regardless of fuel content, while the impurity Co3O4 and α-Fe2O3 phases together with CoFe2O4 phase were disappeared at higher amounts of CTAB fuel. Bulky microstructure of the as-combusted powders using CTAB fuel with specific surface area of 43 m2/g was transformed to foamy and porous structure (196 m2/g) by means of the mixture of CTAB and glycine fuels. Furthermore, the solution combusted CoFe2O4 powders using mixture of CTAB and glycine fuels exhibited the higher saturation magnetization due to their higher crystallinity and particle size.

Magnetic properties of Li0.5Fe2.5O4 nanoparticles synthesized by solution combustion method

In this research, lithium ferrite (Li0.5Fe2.5O4) powders were prepared by solution combustion synthesis using glycine and citric acid fuels at various fuel to oxidant molar ratios (ϕ = 0.5, 1 and 1.5). Phase evolution, microstructure and magnetic properties were characterized by thermal analysis, infrared spectroscopy, X-ray diffraction, electron microscopy and vibration sample magnetometry techniques. Single-phase lithium ferrite was formed using glycine fuel at all fuel to oxidant ratios, while some impurity α-Fe2O3 phase was appeared using citric acid fuel at ϕ ≥ 1. The phase and crystallite size mainly depended on the combustion rate through fuel type. Bulky microstructure observed for citric acid fuel was attributed to its slow combustion, while the fast exhausting of gaseous products led to spongy microstructure for glycine fuel. The highest saturation magnetization of 59.3 emu/g and coercivity of 157 Oe were achieved for the as-combusted powders using glycine fuel.

Effect of fuel type on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Porous magnetite (Fe3O4) powders were synthesized by solution combustion method using the glycine and urea at different fuel to oxidant ratios (ϕ). The combustion behavior depended on the fuel type as characterized by thermal analysis. The structure and phase evolution investigated by X-ray diffraction method showed nearly single phase Fe3O4 powders which were achieved only by using the glycine fuel at ϕ=1. The specific surface area and porous structures of the as-combusted Fe3O4 powders were characterized by N2 adsorption-desorption isotherms and scanning electron microscopy, respectively. The surface area using the glycine fuel (62.6m2/g) was higher than that of urea fuel (42.5m2/g), due to different combustion reactions. Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry which exhibited the highest saturation magnetization of 74emu/g using the glycine fuel at ϕ=1 on account of its high purity and large crystallite size.

Synchrotron X-ray absorption spectroscopy study of disordered cation distribution of nanosized zinc ferrite powders

The zinc ferrite (ZnFe2O4) powders of various nanoparticle sizes were synthesised at different milling times (0 to 24 h) of the as-combusted powders. The non-equilibrium site occupancy of zinc (Zn2+) and ferric (Fe3+) ions was investigated through Zn and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. The XRD and SEM strongly confirm the particle size of these ferrites decreasing with the increasing milling time. Compared with the bulk specimen of zinc ferrite, both XANES and EXAFS spectra of zinc ferrite powders clearly exhibit the large translocation of Zn2+ ions from the tetrahedral (A) sites to the octahedral (B) sites and the opposite translocation of some of Fe3+ ions without affecting the long-range structural order. Moreover, the curve-fitting analysis of Zn and Fe K-edge EXAFS spectra indicates that the degree of inversion increases as the particle size decreases resulting in significant differences in the magnetic behaviours.

Effect of Neodymium and Samarium on the Properties of Bismuth Titanate Ceramics

This paper reported the doping effect on BIT by two different rare-earth compounds i.e. Nd and Sm, each at different mole content (0.25, 0.5, 0.75 and 1.0 mol). The so-called single-step combustion synthesis was used to produce the as-combusted powders, whereby the intermediate calcination step was then eliminated. This method was able to sinter the samples at temperature as low as 1000°C for 3 h. The entire ceramics were characterized for phase detection and stability, microstructure and dielectric properties. It was found that the single phase BIT was successfully formed with Nd and Sm doping. However, little content of pyrochlore phase was detected in the sample with Sm doping particularly at high mole content. (0.5 to 1.0 mol). Besides, a remarkable decrease in the grain size with better microstructure was observed particularly at high mole content (1.0). The improvement in microstructure led to the increase in dielectric constant with low dielectric loss.

Synthesis and Characterization of Nanosized Dy-Doped of Ceria Developed by Microwave Assisted Combustion Route

Nanosized Ce1-xDyxO2-x/2 (DDC, x = 0.05—0.25 mol%) were synthesized by combustion routes induced by microwaves (MS) and compared with the same composition prepared by conventional (CS) method. The conventional and microwave sintering routes were also used to consolidate the pellets. The samples were characterized by X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and AC impedance spectroscopy. The as-combusted powders prepared by microwaves were found to be pure oxides with low crystallinity, and exhibited excellent sintering behavior. Highly dense DDC pellets with fine and homogeneously grown grains (400 nm) were achieved by microwave, while conventionally densified pellets had average grain size of 1100 −1400 nm. The ionic conductivity measured for pellet sintered by MS at 1050°C for 1 h is, σ550°C = 7.42 × 10−2 S/cm, Ea = 0.86 eV, and for CS at 1300°C for 5 h, is σ550°C = 9.79 × 10−3 S/cm, Ea = 1.05 eV.

Synthesis of cobalt-doped bismuth vanadate by combustion-synthesis: Influence of fuel on phase content and morphology

Cobalt (15 at.%) doped bismuth vanadate, Bi4(V0.85Co0.15)2O11-δ (BICOVOX0.15), is known to have high oxygen ion conduction in the medium temperature range (400–600 °C). Small grain size may be important in stabilizing the highly conductive and disordered γ-phase at lower temperature. In this article, we report for the first time the synthesis of highly porous nanoscale BICOVOX powders by a solution combustion technique. The effects of fuel-to-oxidizer ratio, and postcombustion heat treatment temperature and time on the phase content and microstructure of the powders were investigated. As-combusted powders were revealed to be a mixture of Bi2O3, BiVO4, and γ-BICOVOX phases that were converted to phase pure γ-BICOVOX during heat treatment.

Synthesis and properties of SDC powders and ceramics for low temperature SOFC by stearic acid process

Ce0.8Sm0.2O1.9 (SDC) powders were prepared by a novel solution combustion process using molten stearic acid as dispersive medium and reducing agent. The powders prepared with the molar ratio of \( {\text{NO}}^{ - }_{{\text{3}}} \) to stearic acid at 1:1.5 exhibited a narrower distribution in sizes and the average agglomerate size is about 157 nm. The non-agglomerated particles are in the range 10–40 nm. The as-combusted powders prepared by the present method were pure oxides powder with low crystallinity, which exhibited excellent sintering properties, easily achieving high dense SDC ceramics with lager grains (0.85 μm).

Mechanochemical Reduction of V 2O 5

The reduction of V 2O 5 using Mg, Al, and Ti as reductants during mechanical milling in a ball mill has been studied. With all three reductants, a combustion reaction was observed after milling for a critical ignition time. Using Mg as the reductant, the ignition time was found to increase with decreasing collision energy. However, the combustion event could not be associated with a critical degree of microstructural refinement or a reduction of the ignition temperature. With both Mg and Al reductants TEM examination of the as-combusted powders showed the presence of nanoscale single crystal smoke particles, similar to those formed by gas evaporation techniques.