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Hexaferrite multiferroics: from bulk to thick films
摘要： We report studies of the structural and microstructural properties of Sr3Co2Fe24O41 in bulk form and as thick films. The precursor powders for the bulk form were prepared following the sol-gel auto-combustion method. The prepared pellets were synthesized at 1200 oC to produce Sr3Co2Fe24O41. The XRD spectra of the bulks showed the characteristic peaks corresponding to the Z-type hexaferrite structure as a main phase and second phases of CoFe2O4 and Sr3Fe2O7-x. The microstructure analysis of the cross-section of the bulk pellets revealed a hexagonal sheet structure. Large areas were observed of packages of hexagonal sheets where the separate hexagonal particles were ordered along the c axis. Sr3Co2Fe24O41 thick films were deposited from a suspension containing the Sr3Co2Fe24O41 powder. The microstructural analysis of the thick films showed that the particles had the perfect hexagonal shape typical for hexaferrites.
关键词： hexaferrite,microstructure,sol-gel auto-combustion,thick films,multiferroics
更新于2025-09-23 15:21:01
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Photoluminescence properties of Ca3B2O6: RE3+ (RE = Dy and Eu) phosphors for ecofrindly solid state lighting
摘要： The phosphors Ca3B2O6:Dy3+ and Ca3B2O6:Eu3+ were prepared by a combustion method. The phosphor was characterized for X- ray diffraction and photoluminescence. The XRD is well matched with the standard JCPDS. Ca3B2O6:Dy3+ phosphor shows two emission bands centered at 481nm and 577nm corresponding to transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 respectively. Eu3+ doped Ca3B2O6 phosphor gives emission centered at 588nm, 597nm, 614nm and 627 nm having excitation at 396nm. Concentration quenching effect was observed in both the phosphors. Photoluminescence results suggest that phosphor could be used as ecofriendly solid state lighting applications.
关键词： Combustion method,Borate,solid state lighting
更新于2025-09-23 15:21:01
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Flame Propagation Enhancement by Dielectric Barrier Discharge-Generated Intermediate Species
摘要： The interaction between nonthermal plasma (NTP) and fuel-air mixtures was studied both experimentally and by means of simulations, to elucidate their promotional effect on flame propagation. A promotional effect on flame propagation velocity was experimentally observed by generating a dielectric barrier discharge (DBD), prior to spark plug ignition of an n-heptane mixture in a high-pressure and -temperature environment, using a rapid compression and expansion machine (RCEM). A novel method of concentration calibration for mass-spectral analysis was conducted, to determine the intermediate species in the fuel-air mixtures passing through the DBD plasma. The effect of the intermediate chemical species on flame propagation was examined numerically using the PREMIX code, with the observed species being considered as initial additives in the calculations. The promotional effect was reproduced numerically with the addition of alkyl hydroperoxide to an n-heptane/air mixture; and the higher the temperature and leaner the mixture in the parameter region, the more pronounced was the effect. The promotional behavior was examined using reaction path analysis, on the basis of which enhanced low-temperature oxidation reactions, due to the dissociation of the alkyl hydroperoxide, were determined in pre-flame region.
关键词： dielectric barrier discharge,flame propagation velocity,Plasma-assisted combustion,low-temperature oxidation,isomerization
更新于2025-09-23 15:21:01
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Combustion synthesis and photoelectrochemical characterization of gallium zinc oxynitrides
摘要： We report a rapid combustion synthesis method for producing band gap tunable gallium zinc oxynitrides, a material of interest for water splitting applications. By varying the ratio of zinc and gallium, we can tune the band gap from 2.22 to 2.8 eV. Furthermore, nitrogen can be incorporated up to nearly 50% via replacement of oxygen without the need for high temperatures or an additional ammonolysis step. X-ray photoelectron spectroscopy (XPS) and EDX analysis suggests a preferential segregation of Zn to the surface of the as-synthesized particles, though the surface Ga/Zn molar ratio in the as-synthesized particles is correlated with the Ga/Zn molar ratio of the precursor materials. Photoelectrochemical measurements show that the oxynitride powders are photoactive under both AM1.5 and visible-only (k . 435 nm) irradiation. Hydrogen and oxygen were both evolved in half-reaction experiments under simulated AM1.5 irradiation without externally applied bias, although addition of an OER catalyst did not enhance the rate of oxygen formation, suggesting that intra- and interparticle recombination are signi?cant.
关键词： water splitting,photoelectrochemical,gallium zinc oxynitrides,band gap tuning,combustion synthesis
更新于2025-09-23 15:21:01
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Annealing Effect on the Structural, Optical and EPR Properties of UV Radiation Emitting Gd3+ Doped SrAl2O4 Host
摘要： An ultraviolet B (UVB) radiation emitting Gd3+ doped SrAl2O4 sample was synthesized by solution combustion. Powder x-ray diffraction, photoluminescence and electron paramagnetic resonance (EPR) techniques were used to characterize the as-prepared and annealed samples. The monoclinic phase of SrAl2O4 was identi?ed. It was observed that by employing thermal annealing, the photoluminescence properties of Gd3+ doped SrAl2O4 sample could be considerably improved. The photoluminescence studies disclosed that the sample emits UVB radiation caused by the 6P5/2 ? 8S7/2 and 6P7/2 ? 8S7/2 transitions of the Gd3+ ions under 273 nm excitation. EPR studies revealed the presence of Gd3+ in the low symmetry Sr2+ sites in as prepared samples, while in annealed samples the intensity of the signal reduced drastically.
关键词： EPR,Gd3+,SrAl2O4,Combustion,luminescence
更新于2025-09-23 15:21:01
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Analysis of combustion instability of hydrogen fueled scramjet combustor on high-speed OH-PLIF measurements and dynamic mode decomposition
摘要： This paper investigated the combustion instability of spanwise positions in a hydrogen fueled scramjet combustor with a cavity flame holder. High-speed OH-PLIF technique was performed on a direct-connect supersonic combustion facility, and dynamic mode decomposition (DMD) as postprocessing. Combustion instability was investigated by characterizing the dominant frequencies and growth factors. By changing the equivalence ratio of hydrogen, the peak frequencies of scramjet mode and ramjet mode were obtained. Scramjet mode tended to have small oscillation at 150e200 Hz reflected by negative growth factors due to the stable flame structure. At ram-to-scram transition, oscillations at 80 e120 Hz were remarkably enhanced due to the positive growth factors. In ramjet mode, the large differences of frequency characteristics in spanwise positions were observed. The dominant DMD modes near the cavity wall appeared to have negative growth factors leading to a stable flame with small oscillations. Besides, the characteristics of frequency-shift were affected by the positions of injector.
关键词： Combustion instability,Dynamic mode decomposition,Dominant frequency,High-speed planar laser-induced fluorescence of OH radicals,Supersonic combustion
更新于2025-09-23 15:19:57
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Parametric analysis on the combustion and thermal performance of a swirl micro-combustor for micro thermophotovoltaic system
摘要： A swirl micro-combustor which has strong capability to stabilize the flame has been developed and is promising to be used in micro thermophotovoltaic power generators in this work. Heat recirculation plays a requisite role in flame stability and thermal performance of micro combustors. Thus, the effects of three parameters (center inlet radius w1, swirler width w2, and step height w3) that determine the size and location of the recirculation zones in a premixed hydrogen/air flame are investigated numerically. The results show that inner recirculation zone and corner recirculation zone generated by a swirler are critical for stabilizing the flame. The parameter w1 has an insignificant influence on the thermal performance. Enlarging the inner recirculation zone by decreasing w2 provokes enhanced heat transfer, and increases the temperature level and temperature non-uniformity of combustor walls. The size of corner recirculation zone is increased by increasing w3, which raises the outer wall temperature uniformity. Based on the parametric analysis, the newly designed micro combustor possesses a high wall temperature level. Additionally, the energy output increment is between 9.1% and 14.2% at hydrogen mass flow rate of 0.0006 g/s when stoichiometric hydrogen/air ratio ranges from 0.6 to 1.4.
关键词： Thermal performance,Swirl micro-combustor,Micro thermophotovoltaic system,Recirculation zone,Micro combustion
更新于2025-09-23 15:19:57
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Effects of bluff-body on the thermal performance of micro thermophotovoltaic system based on porous media combustion
摘要： To improve thermophotovoltaic system efficiency, a porous media combustor with a bluff-body as the flame holder was proposed. A two-dimensional numerical simulation of premixed hydrogen/air combustion inside a planar porous media channel with the local thermal non-equilibrium model was conducted. Effects of the bluff-body flame holder on mean wall temperature and system efficiency were examined. By inserting the bluff-body, the blowout limits of the planar porous media combustor for ? = 0.6, 0.8, 1.0, 1.2 are increased by 33%, 19%, 12%, 20%, respectively. Numerical results show that the flame stabilization is dominated by flow and heat recirculation. Further analysis reveals the mechanism of heat transfer on flame stabilization due to three heat recirculation paths. Considering the view factor and the external quantum efficiency, the system efficiency with the bluff-body is increased by 14.72% as compared to the one without the bluff-body at ? = 0.8, vin = 4 m/s.
关键词： Wall temperature,Bluff-body,System efficiency,Micro thermo-photovoltaic system,Porous media combustion,Heat recirculation
更新于2025-09-23 15:19:57
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Combustion-processed NiO/ALD TiO2 bilayer as a novel low-temperature electron transporting material for efficient all-inorganic CsPbIBr2 solar cell
摘要： Low-temperature ALD TiO2 electron transporting layers (ETLs) are promising for all-inorganic perovskite solar cells (PSCs), such as the CsPbIBr2-based ones. However, the non-ideal interfacial level-alignment between ALD TiO2 and CsPbIBr2, as well as the concomitant defects in ALD TiO2 during preparation of upper CsPbIBr2 film severely limit the performance of final PSC. We report herein a new design of ETL by combining ALD TiO2 with low-temperature combustion-processed NiO. Although the underlying NiO layer has a p-type conductivity and is known as a hole transporting layer (HTL), the NiO/ALD TiO2 bilayer can serve as an ETL with fewer traps, larger conduction band minimum (CBM) offset with CsPbIBr2 film, along with the similar optical transmittance, in contrast with individual ALD TiO2 ETL. Consequently, the resulting optimized CsPbIBr2 PSC yields the superior efficiency of 9.71% and photovoltage of 1.272 V, both of which exceed those of the one based on individual ALD TiO2 ETL and even so-gel TiO2 ETL. Our work verifies the great applicability of NiO/ALD TiO2 ETL for CsPbIBr2 PSC and thereby explores a promising way to develop more low-temperature ETLs by combining conventional HTLs with ALD TiO2 layers.
关键词： NiO/TiO2 bilayer,ALD,Low temperature,All-inorganic CsPbIBr2 solar cells,Solution combustion,Electron transporting material
更新于2025-09-23 15:19:57
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In-situ measurement of potassium release during biomass combustion using laser-induced breakdown spectroscopy: effect of silicate on potassium release
摘要： In this study, an improved calibration method for the in-situ measurement of potassium (K), concentration in the flame field was developed using laser induced breakdown spectroscopy (LIBS). The temporal behaviors of K release and particle temperature were recorded simultaneously during biomass combustion. During combustion of raw willow wood, the majority of K was released during ash-cooking stage, followed by char combustion stage, only a small amount of K was released during the initial devolatilization stage. The results indicated during devolatilization stage K was released due to the decomposition of organic K. Char- K was subsequently converted to K2CO3 and most K2CO3 was subsequently released during final ash-cooking stage. In the case of rice straw combustion, K was mainly released during the initial devolatilization stage, most likely as KCl. The transformation of char-K and the K-Si reaction forming K-silicates mainly occurred during char combustion stage, K was found to be released slowly from K-silciates during ash-cooking stage. The combustion of willow wood with different Si contents demonstrated that Si significantly inhibited the K release during both char combustion and ash-cooking stage.
关键词： release,LIBS,biomass,combustion,Potassium,silicate
更新于2025-09-23 15:19:57