Combustion Of Precursors Research Articles

Influence of Co over magnetically benign Zn ferrite system and study of its structural, dielectric, superparamagnetic and antibacterial efficacy

A series of nano-sized Co-Zn ferrite, CoxZn1-xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) was synthesized by precursor combustion method. The phase purity, composition, surface area, and oxidation states of corresponding metal ions were confirmed by using the techniques such as X-ray powder diffraction, infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, inductive coupled plasma-atomic emission spectroscopy, Brunauer–Emmett–Teller surface area measurement, and X-ray photoelectron spectroscopy. The transmission electron microscopy analysis revealed cuboidal shaped ferrite particles with 20−30 nm size. The dielectric studies with change in frequency and temperature, and magnetization studies with a change in temperature and applied field, exhibited marked enhancement with cobalt content in the ferrites. The transition from paramagnetic to superparamagnetic nature with rising cobalt content was observed in our investigation based on magnetization and supported by Mössbauer studies. The synthesized ferrites also revealed good antimicrobial activity against gram-negative E. coli ATCC 8439.

Correlation between Structural and Transport Properties of Ca-Doped La Nickelates and Their Electrochemical Performance

This work presents the results from a study of the structure and transport properties of Ca-doped La2NiO4+δ. La2−xCaxNiO4+δ (x = 0–0.4) materials that were synthesized via combustion of organic-nitrate precursors and characterized by X-ray diffraction (XRD), in situ XRD using synchrotron radiation, thermogravimetric analysis (TGA) and isotope exchange of oxygen with C18O2. The structure was defined as orthorhombic (Fmmm) for x = 0 and tetragonal (I4/mmm) for x = 0.1–0.4. Changes that occurred in the unit cell parameters and volume as the temperature changed during heating were shown to be caused by the excess oxygen loss. Typical for Ruddlesden–Popper phases, oxygen mobility and surface reactivity decreased as the Ca content was increased due to a reduction in the over-stoichiometric oxygen content with the exception of x = 0.1. This composition demonstrated its superior oxygen transport properties compared to La2NiO4+δ due to the enhanced oxygen mobility caused by structural features. Electrochemical data obtained showed relatively low polarization resistance for the electrodes with a low Ca content, which correlates well with oxygen transport properties.

Streamers Variability Investigation of a Radio-Frequency Corona Discharge in an Optical Access Engine at Different Speeds and Loads

Engine research community interest in the Radio-Frequency corona-based ignition systems is currently gaining in importance mainly due to their capability to ensure robust combustion at challenging operating conditions such as very lean mixture and/or high EGR dilution. The benefits of Corona low-temperature plasma foster the early flame development thanks to combustion precursors production and to a more energetic and volumetric discharge, resulting in a larger amount of involved mixture. The corona discharge generates ionizing waves, named streamers, whose temporal and spatial variability in orientation, length and branching can affect the combustion onset and, therefore, the engine cycle-to-cycle variability. In this work, the discharge natural luminosity of a RF corona igniter, characterized by four tips electrodes, was recorded in an optically accessible engine via high-speed camera detection. A preliminary statistical analysis of the spatial and temporal streamer variability was performed by operating in motored conditions. Four different engine speeds and two different loads were explored in order to deeply investigate the streamer behaviour at diverse engine operating conditions. A comparison between a motored and a lean operating condition is also proposed to analyse, at a specific engine speed, the mixture influence on the streamers propagation before the start of the combustion.

Electrochemical response of carbon doped LiFePO4 olivine nanoparticles: Cobalt doping and temperature calcination effects

We report the preparation of carbon-coated cobalt-doped olivine nanoparticles (LiFe 1-x Co x PO 4 /C) by the citrate gel precursor combustion method at different calcination temperatures. This work reveals side effects of cobalt doping, and temperature calcination in the structure, carbon coating characteristics and electrochemical performance of olivine nanoparticles. First, we report the effects of active material/carbon ratio and surface load of active material on the electrochemical properties by evaluating discharge capacity values, reversibility and faradaic efficiency. Once cathode preparation conditions were optimised, information on relevant parameters such as diffusion coefficient of lithium ions can be obtained from the analysis of electrochemical results. Values of diffusion kinetic parameters determined from cyclic voltammetry were compared with those obtained from electrochemical impedance spectroscopy. Optimal electrochemical responses were observed from electrodes prepared with a 75% of active material and surface loads of 2 mg. cm −2 . Since all samples presents a similar crystalline size domain, we can conclude that differences in electrochemical performance can be attributed to the amount and structural features of the carbonaceous coating of the olivine crystals, despite of the fact that we are dealing we a very complex system when considering the cathode preparation.

Comparative study of samarium-doped ceria nanopowders synthesized by various chemical synthesis routes

This article presents various chemical synthesis techniques to form samarium-doped ceria (SDC) nanopowders that can be used as electrolyte materials for fabricating solid oxide fuel cells (SOFC). Ce0.8Sm0.2O2-δ powders were prepared by three chemical synthesis routes: glycine nitrate precursor combustion, co-precipitation and sol-gel. SDC pellets were formed using uniaxial and isostatic pressing approaches and sintered at 1200 °C for 5 h. Crystal and thermal features, chemical functional groups were investigated by X-ray diffraction (XRD), combined thermogravimetric and differential thermal analysis (TG/DTA) and Fourier transform infrared (FT-IR) analysis methods. It is shown that the crystallization of the samples synthesized by combustion method starts at the comparably low calcination temperature (171.42 °C) as compared to the samples obtained by sol-gel and co-precipitation methods (391.94 °C and 368.05 °C respectively). The structural and morphological properties of all the samples were analysed via Scanning (SEM) and Transmission (TEM) electron microscopies that have shown very dense structures with no intergranular pores. Impedance (IS) spectroscopy analysis shows three types of processes, which appeared in the structures that include grain, grain boundary, and response from platinum electrodes. The obtained results show that the pellet synthesized by combustion synthesis route has higher total conductivity value 3.04∙10−2 S∙cm−1at 800 °C and the lowest activation energy comparing to co-precipitation and sol-gel.

Synthesis and characterization of Ni0.7−xMnxZn0.3Fe2(C4H2O4)3·6N2H4 (x = 0.1–0.6): A precursor for the synthesis of nickel–manganese–zinc ferrites

Spinel ferrites are the technologically important materials whose application ranges from the environmental, bio-medical to the smart devices. The properties of the ferrite can be tuned by varying the particle size of the different metal ion substituted in the core of the ferrite. In the present studies, we have successfully prepared sparingly investigated Ni0.7−xMnxZn0.3Fe2O4 (x = 0.1–0.6) ferrite series by precursor combustion method using nickel–manganese–zinc–iron fumarato–hydrazinate as precursor. These metal fumarato–hydrazinate precursors burn auto-catalytically, once ignited with a burning splinter, to form metal ferrites. The detailed study of these precursors was carried out using TG–DTA, IR, CHN analysis, isothermal mass loss and total mass loss studies. The experimental hydrazine content as well as contents of C, H, N, Ni, Mn, Zn and Fe of the precursors matched exactly with the theoretical values. The thermal analysis of the precursors suggest mainly two major steps decomposition. The XRD patterns and the IR spectra of the ferrites obtained by burning these precursors confirmed the single-phase cubic nature of these ferrites. The resistivity studies indicate decrease in resistivity with increase in Mn2+ content of the ferrites. The Curie temperature also shows the same trend.

A correlation story of syntheses of ZnO and their influence on photocatalysis

The crystallinity, surface morphology, porosity and band structure of semiconducting catalytic materials greatly influence their photocatalytic efficiency. Here, the semiconducting ZnOs were synthesized with three different synthetic routes of precipitation, solution combustion and direct calcination of precursor. All the synthesized catalysts were characterized thoroughly by X-ray diffraction, Field emission scanning electron microscopy, diffuse reflectance spectroscopy, Brunauer–Emmett–Teller surface area and photoluminescence. The synthesized catalysts show different nano-crystallinity, morphology, surface properties and band structure depending on the synthetic methods. All the synthesized catalysts were explored for photocatalytic degradation of methylene blue under visible and UV light illumination. The correlation between the physical properties and catalytic efficacy were established. The complete mechanism for the photocatalytic degradation of methylene blue was also proposed. The typical band structure and the longer life of excitons due to the presence of defects in solution combustion synthesized ZnO overpowered the other physical properties in influencing the visible and UV light assisted methylene blue degradation. This work shades light on the key controlling factors of a photocatalytic reactions and provides simple strategy for the development of efficient photocatalysts for solar energy conversion applications in solving energy crisis and environmental pollution problems.

Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes.

Evolved stars are a foundry of chemical complexity, gas and dust that provides the building blocks of planets and life, and dust nucleation first occurs in their photosphere. Despite their importance, the circumstellar regions enveloping these stars remain hidden to many observations, thus dust formation processes are still poorly understood. Laboratory astrophysics provides complementary routes to unveil these chemical processes, but most experiments rely on combustion or plasma decomposition of molecular precursors under physical conditions far removed from those in space. We have built an ultra-high vacuum machine combining atomic gas aggregation with advanced in-situ characterization techniques to reproduce and characterize the bottom-up dust formation process. We show that carbonaceous dust analogues formed from low-pressure gas-phase condensation of C atoms in a hydrogen atmosphere, in a C/H2 ratio similar to that reported for evolved stars, leads to the formation of amorphous C nanograins and aliphatic C-clusters. Aromatic species or fullerenes do not form effectively under these conditions, raising implications for the revision of the chemical mechanisms taking place in circumstellar envelopes.

Effect of local ordering around Th4+ ions in glycine-nitrate precursor gel on the powder characteristic of gel-combusted ThO2

In the present study, influence of local environment around Th4+ ions in the precursor gel on the powder characteristics of combusted product (ThO2) is investigated in detail. Partial crystallization of Th4+ complexes having different number of glycine and NO3− species in glycine-thorium nitrate aqueous gel has been confirmed by DSC and SAXS studies. Further, combining SAXS and FT-IR results with existing speciation studies, it is inferred that, varying concentrations of mono- and hexanuclear Th4+-glycine-NO3- complexes are formed in the precursor gel depending upon the fuel to oxidant ratio (F:O). Lower F:O values lead to predominance of hexanuclear Th4+-glycine-NO3- complexes with excess NO3− ions in its vicinity while higher F:O value (F:O = 1.25) results in predominant formation of monocular Th4+-glycine-NO3- complexes. Combustion of gel consisting of mononuclear complexes leads to smaller ThO2 crystallites as compared to hexanuclear complexes as the Th4+--Th4+ distances are larger in the former compared to the latter. The above mentioned complex species are responsible for the observed bimodal crystallite size distribution in nanocrystalline ThO2 powder prepared upon combustion of gel precursor.

Structural and magnetic properties of nanosized CoxZn(1-x)Fe2O4 (x= 0.0, 0.5, 1.0) synthesized via autocatalytic thermal decomposition of hydrazinated cobalt zinc ferrous succinate

Nanocrystalline monophasic cobalt substituted zinc ferrite with general formula CoxZn(1-x)Fe2O4 (x = 0.0, 0.5, 1.0) were synthesized by precursor combustion method. The precursors namely, hexa-hydrazine cobalt zinc ferrous succinate with formulae CoxZn(1-x)Fe2(C4H4O4)3.6N2H4 (x = 0.0, 0.5, 1.0) were characterized by IR, CHNS, ICP-AES analysis, and their thermal studies were carried out by TG-DTA, TG-DTG, and isothermal mass loss studies. The ‘as prepared’ Co–Zn ferrites obtained by auto-catalytic thermal decomposition of precursors, on initial ignition, were characterized by XRD, IR, EDAX, TEM, and SEM. The SAED and XRD studies confirmed the formation of crystalline single phase nano Co–Zn ferrites. The morphology of these ‘as prepared’ ferrites was studies by TEM analysis which confirmed the particles to be in the nanometer range (20–30 nm). The increase in cobalt concentration resulted in reduced lattice parameter. The electrical resistivity declined while the Curie temperature surged with a decreased zinc concentration in ‘as prepared’ Co–Zn ferrites. The magnetization studies with the applied field at 300 K and 50 K displayed a gradual increase in magnetization values with the rise in cobalt content while confirming the super-paramagnetic nature of Co–Zn ferrite nano-system.

Insights of cobalt doping on carbon-coated LiFePO4 olivine nanoparticles prepared by citric acid combustion route as cathodes for lithium batteries

Here, we report the preparation of carbon-coated cobalt-doped olivine nanoparticles (LiFePO4/C) by the citrate gel precursor combustion method. The major contribution of this work is to reveal insights and side effects of cobalt doping, not only in the structure, microstructure, and electrochemical performance of olivine nanoparticles, but also in the consequences on the carbon coating characteristics. Our structural and microstructural studies by means of several instrumentation techniques revealed that the presence of low amounts of cobalt during the synthesis leads to the apparent formation of more porous channels in the carbon coating. In consequence, the electrochemical characterization showed an enhancement in the capacity and diffusion constants for cobalt-doped LiFePO4/C samples in comparison with cobalt-undoped samples.

Induced effects of Zn+2 on the transport and complex impedance properties of Gadolinium substituted nickel-zinc nano ferrites

Abstract We report on the preparation and transport properties of Gadolinium substituted Ni ( 1 - x ) Zn x Gd y Fe ( 2 - y ) O 4 ( 0 ⩽ x ⩽ 1 , y = 0.1 ) nano particles using low temperature citrate precursor combustion method. The Rietveld refinement of PXRD data suggests the crystal structure of sample belongs to Fd-3m space group with an octahedral occupation of Gd+3 ions. FESEM micrographs show the existence of porosity in the samples. The dielectric studies reveal the good dielectric behaviour with high dielectric constant in Zn+2 substituted sample (x = 0.4). An increase in a . c conductivity observed in the Zn+2 substituted sample due to the hopping mechanism. The impedance spectroscopy of the samples shows the existence of high grain boundary resistance and an alternate switching of dielectric relaxation from non-Debye to Debye type. The activation energies and Curie temperature estimated using D. C. conductivity measurements drop linearly with an increase in Zn+2 concentration. We attribute the observed transport properties mainly to the hopping of Fe+2 ↔ Fe+3 ions.

A Novel Reddish Orange Luminescent Material Sr3B2O6:Sm3+

The Sm3+ doped Sr3B2O6 phosphors were synthesized using a solution combustion synthesis method followed by heating of the precursor combustion ash at 1000°C in air. The synthesized phosphors were characterized by powder XRD. The photoluminescence properties of Sm3+-doped Sr3B2O6 were investigated at room temperature. The photoluminescence spectra at room temperature show the f–f transitions typical of Sm3+. The emission spectrum of Sr3B2O6:Sm3+ exhibited four sharp emission peaks corresponding to 4G5/2 → 6H5/2 (563–572 nm), 4G5/2 → 6H7/2 (598–614 nm), 4G5/2 → 6H9/2 (647–666 nm), and 4G5/2 → 6H11/2 (705–714 nm) transitions of Sm3+. The relation between the charge transfer band of Sm3+ ion and the host composition was discussed.

A novel foam combustion approach for the synthesis of nano-crystalline cobalt oxide powder

This article focuses on the nano-crystalline tricobalt tetraoxide (Co3O4) synthesis using the combustion method. The fabrication process involves the combustion a mixture of cobalt nitrate as oxidized and expanded polystyrene (EPS) as a novel fuel. The effects of fuel/oxidizer ratio on the phases formed, Co3O4 as a major phase and CoO as an impurity, and the Co3O4 crystallite size have been addressed. Based on the thermal analyses data (TGA and DTA), which follow the phase changes during the heat treatment of the parent fuel/oxidizer precursor, the different parent precursors have been calcined at 500 °C. Characterization of the formed solids has been performed using various tools (XRD, FT-IR, SEM, TEM, and XPS). It was concluded that the EPS content, in the combustion precursor mixtures, is a key parameter that controls the phase features of the prepared nanomaterials. CoO impurity was detected for the solids with EPS > 4 wt%. The crystallite size, morphology, and the surface elemental concentration are influenced by changing the EPS content. The activity of the different powders towards hydrogen peroxide decomposition has been evaluated at the 35–50 °C temperature range.

A novel method to synthesize vanadium nitride nanopowders by ammonia reduction from combustion precursors

Vanadium nitride (VN) has many applications ranging from structural materials to electrode material owing to its high hardness, excellent wear resistance, high electrical and thermal conductivity and high-temperature stability. The conventional synthesis methods are often plagued by high temperature (above 1000 °C) and long reaction times. In the paper, VN nanopowders are firstly synthesized by a large-scale, low-temperature and short-time solution combustion synthesis-based method. Firstly, vanadium dioxide (VO2) precursors are prepared through ultrafast (within one minutes) solution combustion synthesis method. During the subsequent ammonia reduction process, the VN nanopowders are successfully obtained at 700 °C for 2 h. In the investigation, the phase transformations and microstructures of precursors during ammonia reduction procedure have been studied in detail. The as-prepared VN nanopowders are composed of nanoparticles with particles sizes ranging from 30 to 40 nm and possess mesoporous structures. Upon evaluating the VN nanopowder as an anode material for lithium ion batteries, it displays good electrochemical performances and exhibits high reversible capacity of 634 mAh g−1 at 0.1 A g−1 after 250 cycles.

The physical properties and electrochemical performance of Ca-doped Sr2MgMoO6-δ as perspective anode for solid oxide fuel cells

The double perovskites Sr2-xCaxMgMoO6–δ with x = 0, 0.25, and 0.5 were obtained by combustion of organometallic precursors and were shown to have a tetragonal structure with the crystalline lattice parameters a = b = 5.569, c = 7.923, 7.899, 7.885 A, respectively. Calcium doping was found to improve the conductivity and decrease the activation energy values. At x = 0.5, the temperature dependence of the total conductivity has a metallic-like behavior under reducing conditions. The electrical conductivity for Sr1.5Ca0.5MgMoO6−δ was about 25 and 30 S/cm at 800 and 500 °C, respectively. Besides, the enhancement of the calcium content lead to the reduction in the area specific resistance of the Sr2−x Ca x MgMoO6−δ anode. In conjunction with the electron paramagnetic resonance study, the experimental data on the electrical conductivity demonstrated that calcium doping is accompanied by an enhanced electron component under reducing conditions. The magnetic susceptibility revealed the coexistence of itinerant electrons and paramagnetic centers in calcium-rich molybdate Sr1.5Ca0.5MgMoO6−δ.

High-temperature defect thermodynamics of nickel substituted double-perovskite cobaltite PrBaCo2−xNixO6−δ (x = 0.2)

The double perovskite praseodymium cobaltites PrBaCo2−xNixO6−δ, where 0.1 ≤ x ≤ 0.3, were obtained by combustion of organo-metallic precursors and shown to have a tetragonal structure with the crystalline lattice parameters a ≈ 3.91 and c ≈ 7.63 Å consistent with electron compensation 2Co3+ = Ni2+ + Co4+ of Ni2+ impurity centers. The oxygen content (6 – δ) vs. log(pO2) dependencies were measured by a coulometric titration technique for x = 0.2 at 650–950 °C and oxygen pressure variations within 10−10 – 0.6 atm. The reductive decomposition of the cobaltite is found to take place at δ = 1.13. The experimental data were utilized in order to derive partial thermodynamic functions of oxygen that govern defect equilibration. The oxygen partial enthalpy ΔH¯O and entropy ΔS¯O are found to exhibit strong changes near (6 – δ) = 5. The observed behavior is explained in frameworks of the defect formation model, which involves reactions of charge disproportionation of Co3+ cations, oxygen exchange with the gas phase and oxygen disordering over O2 and O3 structural positions.

Infrared gas phase study on plasma-polymer interactions in high-current diffuse dielectric barrier discharge

A roll-to-roll high-current diffuse dielectric barrier discharge at atmospheric pressure was operated in air and Ar/N2/O2 gas mixtures. The exhaust gas from the discharge was studied using a high-resolution Fourier-transform infrared spectrometer in the range from 3000 to 750 cm−1 to unravel the plasma-polymer interactions. The absorption features of HxNyOz, COx, and HCOOH (formic acid) were identified, and the relative densities were deduced by fitting the absorption bands of the detected molecules. Strong interactions between plasma and polymer (Polyethylene-2,6-naphthalate, or PEN) in precursor-free oxygen-containing gas mixtures were observed as evidenced by a high COx production. The presence of HCOOH in the gas effluent, formed through plasma-chemical synthesis of COx, turns out to be a sensitive indicator for etching. By adding tetraethylorthosilicate precursor in the plasma, dramatic changes in the COx production were measured, and two distinct deposition regimes were identified. At high precursor flows, a good agreement with the precursor combustion and the COx production was observed, whereas at low precursor flows an etching-deposition regime transpires, and the COx production is dominated by polymer etching.

Modelling winter organic aerosol at the European scale with CAMx: evaluation and source apportionment with a VBS parameterization based on novel wood burning smog chamber experiments

Abstract. We evaluated a modified VBS (volatility basis set) scheme to treat biomass-burning-like organic aerosol (BBOA) implemented in CAMx (Comprehensive Air Quality Model with extensions). The updated scheme was parameterized with novel wood combustion smog chamber experiments using a hybrid VBS framework which accounts for a mixture of wood burning organic aerosol precursors and their further functionalization and fragmentation in the atmosphere. The new scheme was evaluated for one of the winter EMEP intensive campaigns (February–March 2009) against aerosol mass spectrometer (AMS) measurements performed at 11 sites in Europe. We found a considerable improvement for the modelled organic aerosol (OA) mass compared to our previous model application with the mean fractional bias (MFB) reduced from −61 to −29 %. We performed model-based source apportionment studies and compared results against positive matrix factorization (PMF) analysis performed on OA AMS data. Both model and observations suggest that OA was mainly of secondary origin at almost all sites. Modelled secondary organic aerosol (SOA) contributions to total OA varied from 32 to 88 % (with an average contribution of 62 %) and absolute concentrations were generally under-predicted. Modelled primary hydrocarbon-like organic aerosol (HOA) and primary biomass-burning-like aerosol (BBPOA) fractions contributed to a lesser extent (HOA from 3 to 30 %, and BBPOA from 1 to 39 %) with average contributions of 13 and 25 %, respectively. Modelled BBPOA fractions were found to represent 12 to 64 % of the total residential-heating-related OA, with increasing contributions at stations located in the northern part of the domain. Source apportionment studies were performed to assess the contribution of residential and non-residential combustion precursors to the total SOA. Non-residential combustion and road transportation sector contributed about 30–40 % to SOA formation (with increasing contributions at urban and near industrialized sites), whereas residential combustion (mainly related to wood burning) contributed to a larger extent, around 60–70 %. Contributions to OA from residential combustion precursors in different volatility ranges were also assessed: our results indicate that residential combustion gas-phase precursors in the semivolatile range (SVOC) contributed from 6 to 30 %, with higher contributions predicted at stations located in the southern part of the domain. On the other hand, the oxidation products of higher-volatility precursors (the sum of intermediate-volatility compounds (IVOCs) and volatile organic compounds (VOCs)) contribute from 15 to 38 % with no specific gradient among the stations. Although the new parameterization leads to a better agreement between model results and observations, it still under-predicts the SOA fraction, suggesting that uncertainties in the new scheme and other sources and/or formation mechanisms remain to be elucidated. Moreover, a more detailed characterization of the semivolatile components of the emissions is needed.

Thermodynamic analysis of defect equilibration in double perovskites based on PrBaCo2O6–δ cobaltite

The double perovskite praseodymium cobaltite lightly doped with yttrium Pr0.9Y0.1BaCo2O6–δ (PYBCO) was obtained by combustion of organo-metallic precursors and shown to have a tetragonal structure with the crystalline lattice parameters a=b=3.903 and c=7.621Å. The PYBCO composition occurs remarkably stable as show coulometric titration measurements of oxygen content (6–δ) in the oxygen pressure range 10–13–0.21atm and at temperatures variations within 650–950°С. The experimental data were utilized in order to derive partial thermodynamic functions of oxygen that govern equilibration of defects in PYBCO. The oxygen partial enthalpy ΔH¯O(δ) and entropy ΔS¯O(δ) both experience strong changes near (6–δ)=5. The observed behavior of ΔH¯O(δ) and ΔS¯O(δ) is explained in frameworks of the defect formation model, which involves reactions of charge disproportionation of Co3+ cations, oxygen exchange with the gas phase and oxygen disordering over O2 and O3 structural positions. The verification of the suggested approach is carried out by comparison with independently obtained thermochemical data.