Aqueous Combustion Synthesis Research Articles

Magnesium ferrichromate nanoparticles: an efficient and recyclable catalyst in the synthesis of pyrano[2,3-c]pyrazole derivatives

Magnetically separable magnesium ferrichromate nanoparticles (MgFeCrO4 NPs) were synthesized by aqueous combustion synthesis (ACS) using glycine as the fuel. The as-synthesized powder was characterized using XRD, FTIR, SEM–EDX and SQUID techniques. Rietveld refinement studies inferred the single-phase cubic structure of the nanoferrite. Using Williamson–Hall plot, the lattice strain and the crystallite size were evaluated. Small value of lattice strain is indicative of absence of strain in the crystal lattice. The M–O bonding at the tetrahedral as well as the octahedral position was confirmed by FTIR Spectroscopy. Morphological investigations demonstrated sphere-like nanostructures with 50–100 nm particle size using SEM. Absence of any impurity in the EDX spectrum suggests formation of extremely pure MgFeCrO4 NPs. The room temperature magnetization was studied using vibrating sample magnetometer, and the nanoferrite exhibits superparamagnetic behaviour. The pyrano[2,3-c]pyrazole derivatives were synthesized in water/ethanol solvent system using MgFeCrO4 NPs heterogenous catalyst. A very short reaction time, maximum yield, easy method of separation of product and environmentally safer and milder reaction conditions are some of the advantages of our work along with the retention of catalytic activity up to five cycles. Synthesis of chromene derivatives using magnetically separable magnesium ferrichromate (MgFeCrO4).

Combustion Synthesized Ceria Powder and its Characterization

Using aqueous combustion synthesis route the ultrafine ceria powder is produced with the help of glycine and nitrate, nitrate utilized as an oxidizer and glycine as a fuel. Using balancing equation with required molar ratios both fuel and oxidizer mixes together in deionized water. Viscous liquids containing glycine and ceric ammonium nitrate gets auto-ignited and resulted in voluminous ceria powder. Characterization is carried out on ceria powder after calcinations process. The resulted powder obtained in the present investigation is in the nano range.

Aqueous combustion synthesis of aluminum oxide thin films and application as gate dielectric in GZTO solution-based TFTs.

Solution processing has been recently considered as an option when trying to reduce the costs associated with deposition under vacuum. In this context, most of the research efforts have been centered in the development of the semiconductors processes nevertheless the development of the most suitable dielectrics for oxide based transistors is as relevant as the semiconductor layer itself. In this work we explore the solution combustion synthesis and report on a completely new and green route for the preparation of amorphous aluminum oxide thin films; introducing water as solvent. Optimized dielectric layers were obtained for a water based precursor solution with 0.1 M concentration and demonstrated high capacitance, 625 nF cm(-2) at 10 kHz, and a permittivity of 7.1. These thin films were successfully applied as gate dielectric in solution processed gallium-zinc-tin oxide (GZTO) thin film transistors (TFTs) yielding good electrical performance such as subthreshold slope of about 0.3 V dec(-1) and mobility above 1.3 cm2 V(-1) s(-1).

Manufacturing Wear-Resistant 10Ce-TZP/Al2O3 Nanoparticle Aluminum Composite by Powder Metallurgy Processing

Aluminum matrix composites (AMCs) are candidate materials for total joint arthroplasty, dental prostheses, cutting tools, and biomedical gadgets owing to their strength, machinability, dimension accuracy, and wear resistance. A novel method for manufacturing new generation of AMCs by addition of 10Ce-TZP(tetragonal zirconia polycrystal)/Al2O3 nanoparticles to aluminum via powder metallurgy is devised. Aqueous combustion synthesis is used for dispersoid production and milling–compaction–sintering for AMC fabrication. Effects of 10Ce-TZP/Al2O3 content on hardness, erosion, and wear resistance are investigated. Scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and pin-on-disk analyses are used to explore worn interface, morphology, mechanism of abrasion, and resistance to wear. By addition of 7 wt% dispersoid, considerable increase in hardness and resistance to wear are achieved.

Supported cobalt catalysts by one-pot aqueous combustion synthesis for catalytic phenol degradation

Cobalt oxides (Co) and Al2O3-, SiO2-, and TiO2-supported cobalt oxide catalysts were prepared by an aqueous combustion method using urea and glycine as fuels. Their catalytic performance in activation of OXONE® for phenol degradation in aqueous solution was investigated. It was found that unsupported Co oxide and supported Co oxide presented different mechanisms in activation of OXONE® for phenol degradation. The supported Co catalysts presented higher activity in activation of OXONE® for phenol degradation due to higher dispersion of Co3O4 on the supports and Co(II) coordination sites. The major oxidizing radicals were identified to be SO4- by competitive radical reactions. The Co oxides synthesized from urea or glycine showed a similar activity; however, the supported Co catalysts prepared by glycine fuel exhibited better activity than those prepared by urea. For Al2O3-, SiO2-, and TiO2-supported Co catalysts, Co/TiO2 presented a higher activity in phenol degradation compared with Co/SiO2 and Co/Al2O3. But, Co/SiO2 showed the best stability among the catalysts. Total organic carbon could be reduced by 80%, 72%, and 45% on Co/TiO2, Co/SiO2, and Co/Al2O3, respectively, at 30ppm phenol. Phenol degradation was found to follow the zero-order kinetics. The causes of deactivation were investigated, and the regeneration methods were proposed.

Nanocrystalline BaAl2O4 powders prepared by aqueous combustion synthesis

In order to achieve BaAl2O4 formation via combustion synthesis, two types of recipes were designed: single fuel recipes (urea, glycine, β-alanine or hexamethylenetetramine) and innovative fuel mixture recipes (urea+glycine, urea+β-alanine and urea+hexamethylenetetramine respectively). No combustion reactions were noticed in the case of single fuel recipes based on urea or hexamethylenetetramine. The only crystalline phase present in the case of the powders obtained in such a way was unreacted Ba(NO3)2. Glycine and β-alanine generated smoldering reactions, leading to the formation of black powders, which consist of Ba(NO3)2, BaCO3 and traces of BaAl2O4 (in the case of β-alanine). Fuel mixture recipes proved to be better than single fuel recipes, yielding BaAl2O4 as main crystalline phase. The specific surface area of the resulted powders ranges between 2.0 and 3.9m2/g. The urea and glycine fuel mixture was the most efficient yielding BaAl2O4 with an average crystallite size of 60nm.

Nanopowders of lanthanide ferrites and aluminates for production of ceramics

Nanopowders of lanthanide aluminates and ferrites were obtained by aqueous combustion synthesis. Scanning electron microscopy and specific surface area measurement made clear that the morphology and size of powder particles depended on the glycine: nitrate ratio in the initial mixture. The obtained powders consisted of aggregates of particles with the sizes of several nanometers. XRD analysis of the calcined powders did not reveal the presence of phases of individual oxides of rare earth elements (REE), aluminum, or iron, which indicated the completeness of solid state reactions.

Aqueous combustion synthesis and characterization of ZnO powders

New organic fuels (β-alanine, valine, zinc acetate and acrylamide) have been successfully tested for the preparation of nanocrystalline ZnO powders via aqueous combustion synthesis. In all cases, ZnO resulted directly from the combustion process and no subsequent annealing was required. Properties of the as-prepared ZnO powders were investigated and it was found that morphology, specific surface area, crystallite size and cumulative volume of pores are determined by the used fuel. A correlation has been found between the total volume of generated gases, adiabatic temperature, the amount of ZnO and the characteristics of the resulting powders. Largest surface area (42.0 m 2 g −1) and smallest ZnO crystallite size (21 nm) were obtained for acrylamide.

Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

Unaggregated La0.82Sr0.18MnO3 + δ perovskite nanoparticles with a mean crystallite size of 22 nm were successfully synthesized through an aqueous combustion process (Glycine Nitrate Process, GNP) which takes advantage of exothermic, fast and self-sustaining chemical reactions between metal nitrates and glycine as a suitable organic reducing agent. The influence of G/N molar ratio on the phase purity, crystallite size and manganese valency was screened. Fuel-rich conditions were selected to improve chelation of the cations in acidic pH and ensure an accurate control of the cationic composition. Fast calcination was optimized to enhance crystallinity of the nanoparticles and subsequent milling step was performed to favour their desaggregation. The manganite nanoparticles were thoroughly characterized by X-ray diffraction (XRD), elemental chemical analysis, Mohr salt titration and transmission electron microscopy (TEM). According to a process derived from the Stober's method, they were uniformly coated with a 5 nm thick silica shell, as evidenced by TEM, infrared spectroscopy, ζ potential measurements and dynamic light scattering experiments. Preliminary heating experiments in a ac magnetic field showed these core@shell nanoparticles fulfill the requirements for self-controlled magnetic fluid hyperthermia, considering their size (20–70 nm) and their maximum heating temperature (43 °C) which is controlled by the Curie temperature of the magnetic cores.

Effect of Fuel Choice on the Aqueous Combustion Synthesis of Lanthanum Ferrite and Lanthanum Manganite

High‐surface area, nanocrystalline powders of two closely related peroviskite oxides, LaFeO3 and LaMnO3, were produced by aqueous combustion synthesis using two different fuels. LaMnO3 powders synthesized using glycine fuel had a higher surface area and a smaller crystallite size than when synthesized using ethylene glycol fuel. However, the opposite was observed for LaFeO3 powders, where a higher surface area and a smaller crystallite size was obtained using ethylene glycol. The effect of the fuel type on the powder properties was attributed to the combustion characteristics, such as the rate of temperature increase and maximum measured temperature, and the mode of combustion synthesis. The lower surface area LaFeO3 and LaMnO3 powders had higher rates of temperature increase, which is characteristic of a volume combustion synthesis mode. The high‐surface area LaFeO3 powder produced using ethylene glycol fuel, in contrast, had a lower rate of temperature increase, representative of a self‐propagating high‐temperature synthesis mode. Differential thermal analysis showed that the mode of combustion correlated to the delayed reaction of the iron nitrate oxidizer with the ethylene glycol fuel. For the combustion synthesis of multication complex oxides, each fuel–oxidizer reaction is important for predicting the combustion characteristics and the resulting powder properties.

Structure and properties of electrocodeposited Cu–CeO 2 nanocomposite thin films

Electrocodeposition of ceria particles along with copper from acidic electrolytes has been achieved by using pulse plating technique. The ceria particles are synthesized by the aqueous combustion synthesis route with glycine as the fuel and ceric ammonium nitrate as the oxidizer. The nanocomposite thin films have been characterized by XRD, SEM and TEM. The microhardness of the composites is evaluated and compared with that of pure copper deposited under the same conditions. The microhardness of the copper matrix is enhanced from 0.67 to 1.45 GPa due to the presence of reinforcement. The volume fraction of the reinforcement is estimated to be 7–10% and particles are uniformly distributed in the copper matrix.

Aqueous combustion synthesis and characterization of zirconia–alumina nanocomposites

Abstract The zirconia–alumina nanocomposite powders with 3–48 mol% of alumina are prepared by aqueous combustion synthesis technique using stoichiometric amounts of aluminium nitrate, zirconyl nitrate and glycine. The nanopowders are compacted uniaxially and sintered at 1000 °C temperature in a muffle furnace. Thermodynamic modeling of the combustion reaction shows that, as the alumina content increases, the amount of gases produced increases with a decrease in the adiabatic flame temperature. The green and sintered densities of cold press composite powders decrease with an increase in the mol% of alumina.

Pulsed co-electrodeposition and characterization of Ni-basednanocomposites reinforced with combustion-synthesized, undoped,tetragonal-ZrO2 particulates

Nanostructured nickel matrix composites reinforced with nanosized, undoped, tetragonalzirconia has been synthesized by cathodic pulsed electrodeposition. The reinforcement issynthesized by the aqueous combustion synthesis route with glycine as the fuel and zirconylnitrate as the oxidizer. The reinforcement and composite have been characterized by XRD,TEM and SEM coupled with EDS. The microhardness and thermal stability(Kissinger method) of the composite are evaluated. These values are comparedwith those of pure nickel deposited under the same conditions. The results showthat the microhardness of the nickel matrix is enhanced by the presence of thereinforcement from 450 to 575 VHN. Also the strengthening due to grain sizeeffects and dispersion strengthening effect are evaluated individually and theinterparticle separation is estimated to be around 85 nm. The volume fraction of thereinforcement is estimated to be 12–15% and the particles are uniformly distributed andmonodispersed in the nickel matrix. The thermal stability of the composite isbetter than that of pure nickel in contrast to some of the reported literature.

Aqueous Combustion Synthesis and Characterization of Nanosized Tetragonal Zirconia Single Crystals

Nanocrystalline zirconia powder has been synthesized by an aqueous combustion synthesis route using glycine as fuel and nitrate as oxidizer. The powders have been prepared by using different glycine to zirconyl nitrate molar ratios (G/N). The powders produced with different G/N ratios have been characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to determine the parameters resulting from powder with attractive properties. The theoretical combustion temperature (Tad) has been calculated for different G/N ratios, and it is correlated with powder characteristics. An attempt is also made to explain the stability of tetragonal zirconia on the basis of extrinsic factors such as the morphology of nanocrystallites. Nanocrystalline metastable tetragonal zirconia (∼25 nm) powder (TZ) with disc-shaped morphology has been produced with a weak agglomeration in fuel deficient mixtures.

Novel perovskite-based catalysts for autothermal JP-8 fuel reforming

Autothermal reforming is an attractive method for on-site production of hydrogen for use in proton exchange membrane (PEM) fuel cells. The use of liquid hydrocarbons as feedstock, however, remains a challenge as these fuels cause severe coking of the currently available catalysts. In this work, cerium- and nickel-substituted LaFeO3 perovskites were investigated as potential low cost coking resistant catalysts for autothermal reforming of a JP-8 fuel surrogate. The high surface area complex oxides were prepared using aqueous (solution) combustion synthesis at fuel-rich conditions and characterized by BET and XRD techniques. The catalysts exhibited excellent stability during autothermal reforming at 775∘C and 1 atm, with near-equilibrium hydrogen yield even at high GHSV values (130,000h-1). The addition of cerium significantly improved coking resistance, attributed to improved oxygen ion conductivity, resulting in carbon oxidation on the catalyst surface.

High throughput evaluation of perovskite-based anode catalysts for direct methanol fuel cells

Liquid feed direct methanol fuel cells (DMFC) are promising candidates for portable power applications. However, owing to the problems associated with expensive Pt-based catalysts, viz., CO poisoning, a promising approach is to use complex oxides of the type ABO 3 (A = Sr, Ce, La, etc. and B = Co, Fe, Ni, Pt, Ru, etc.). In the current work, a variety of ABO 3 and A 2BO 4 type non-noble and partially substituted noble metal high surface area compounds were synthesized by an effective and rapid aqueous combustion synthesis (CS). Their catalytic activity was evaluated by using “High Throughput Screening Unit”—NuVant System, which compares up to 25 compositions simultaneously under DMFC conditions. It was found that the Sr-based perovskites showed performance comparable with the standard Pt–Ru catalyst. Further, it was observed that the method of doping SrRuO 3 with Pt influenced the activity. Specifically, platinum added during aqueous CS yielded better catalyst than when added externally at the ink preparation stage. Finally, it was also demonstrated that the presence of SrRuO 3 significantly enhanced the catalytic properties of Pt, leading to superior performance even at lower noble metal loadings.

Combustion Synthesis and Luminescent Properties of Eu3+‐Activated Cheap Red Phosphors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel Ferrimagnetic Iron Oxide Nanopowders

Because of their scientific and technological utility, magnetic properties of fine-particle systems have assumed great importance in recent years. Maghemite (γ-Fe2O3) and magnetite (Fe3O4) are commonly used in magnetic inks, as catalysts, and as ferrofluids for biomedical uses. In the current work, we report a novel one-step process for the synthesis of different iron oxide phases, including maghemite and magnetite, using the aqueous combustion synthesis technique. The method involves a self-sustained reaction between an oxidizer (e.g., metal nitrate) and a fuel (e.g., glycine or hydrazine). Using this approach, for the first time, spherical, nanoscale (6−10 nm) iron oxide particles with excellent ferrimagnetic properties were synthesized. While the samples have particle sizes of <10 nm, they exhibit ferrimagnetic behavior at room temperature, as opposed to super-paramagnetism, as reported previously by numerous workers. Further, particularly for Fe3O4, the coercivity values are exceptionally high (213 Oe), indicating stable magnetization.

Combustion synthesis and luminescent properties of Eu 3+-activated cheap red phosphors

Aqueous combustion synthesis has been successfully extended to prepare Eu 3+-activated cost-effective and cheap red phosphors LnMAlO 4, where Ln = La or Y and M = Ca or Sr, having K 2NiF 4 structure. Thus, aqueous solution of corresponding metal nitrates, ammonium nitrate and urea with exact quantity calculated based upon O/F ratio have been heated at 525 °C. This process lasted for less than 5 min and led to the formation of voluminous white powder. These phosphors have been characterized by powder XRD, color under 254 nm wavelength and luminescence. All the compounds are crystalline and these compounds exhibit red color under 254 nm radiation. Luminescence studies have been carried out on these cheap red phosphors.

Oxidizer−Fuel Interactions in Aqueous Combustion Synthesis. 1. Iron(III) Nitrate−Model Fuels

Aqueous (solution) combustion synthesis of iron oxide is investigated using iron(III) nitrate nonahydrate and three model fuels, each containing one specific functional group. The investigated ligands, in order of experimentally determined reactivity, are −NH2 > −OH > −COOH, where only the amino group triggers a vigorous combustion reaction. On the basis of the experimental findings, a reaction mechanism for iron oxide synthesis is proposed. During the first step, nitric acid is released during thermal decomposition of iron(III) nitrate. Subsequently, two reactions occur: nitric acid reacts with the amino group in a fast exothermic redox reaction, and it also decomposes thermally to release oxygen. The latter may react with carbon available in the fuel and thus increase the overall process exothermicity.