Modified Combustion Process Research Articles

Single step auto-igniting combustion technique grown CeO2 and Ni-doped CeO2 nanostructures for multifunctional applications

In the present study, pristine and Ce1-xNixO2(x = 0.1) nanoparticles are grown by low cost modified combustion process. The surface morphology and phase pureness of the pristine and Ce1-xNixO2(x = 0.1) nanostructures is achieved by Scanning Electron Microscopy (SEM) and powder X-Ray Diffraction (XRD) techniques. The closed and open mode Z-scan studies reveal that these synthesized nanostructures possess excellent reverse saturation absorption behaviour, which can be utilized for optical limiting applications in defence and healthcare systems. By analyzing the photocatalytic properties against Eosin Yellow dye, the degradation efficiency of synthesized samples is found to be 91% and 93% respectively. Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopic (EIS) are the techniques which help to study the electrochemical properties of the synthesized materials for electrode materials of supercapacitor. From GCD, the specific capacitance of pristine and Ce1-xNixO2(x = 0.1) is 305 and 446 F g-1 respectively. Even after 2000 GCD cycles, the cyclic stability and coulombic efficiency of Ce1-xNixO2(x = 0.1) remains at 96.1% and 97.5%, while for pure CeO2 it is 88.3% and 91% respectively.

Synthesis and characterization of nano NiZrO3 for optical and dielectric applications

Abstract Nanocrystalline semiconducting NiZrO3 is prepared via a modified combustion process. The X-ray diffraction pattern shows that the so formed nanopowder is single phase and has an orthorhomb...

Synthesis of nano Lead Tungstate (PbWO4) by Single Step Modified Combustion Process and Characterization for their application as LTCC and Optical Material

NanostructredScheelitePbWO4were synthesized through a single step modified auto-ignition combustion technique. The X-ray diffraction, Fourier transform Raman and infrared spectroscopy studies revealed that the as-prepared samples were phase pure and the average crystallite size was ∼49 nm. PbWO4 crystallizes in tetragonal structure. The particle size and morphology of the sample was studied using transmission electron micrograph. The optical properties of the sample were studied using Ultraviolet-visible and photoluminescence spectra. The samples showed a maximum transmission in the visible regions but poor transmittance in the ultraviolet region. The optical band gap of the samples calculated using the Kubelka-Munk method was 3.87 eV, suggesting their semiconducting behavior. The photoluminescence spectra recorded on the samples showed that nano PbWO4 has visible luminescence. The thermal stability of the sample at elevated temperatures has been studied using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). No substantive weight loss were observed for the samples in the temperature range 50-900oC. The PbWO4 samples were sintered to 98% relative density at very low temperature of 787oC without using any sintering aid. The microstructure of the sintered pellets observed by Scanning Electron Micrograph (SEM) showed that the pellets were well sintered with minimum porosity. The dielectric constant (εr) of the sintered PbWO4 sample was recorded using an LCR meter in the range 50 Hz to 5 MHz and showed a value of 86 at 1 MHz with a loss factor of 10-2. The calculated temperature coefficient of dielectric constant is negative. The low sintering temperature, dielectric constant, low loss factor and negative temperature coefficient make the sample ideal for low temperature co-fired ceramic, electronic substrate materials as well as suitable for various optical applications such as UV filters, transparent films for window layers on solar cells, anti-reflection coatings, scintillators, detectors.

Synthesis and characterisation of MoO3 and WO3 nanorods for low temperature co-fired ceramic and optical applications

Nanorods of MoO3 and WO3 are synthesized through a single step modified combustion process. The X-ray diffraction, Fourier transform Raman and infrared spectroscopy studies reveal that the as-prepared samples are phase pure, where MoO3 crystallizes in orthorhombic and WO3 in monoclinic structure. The transmission electron micrograph show elongated nano rods of the samples. The calculated optical band gaps of the samples suggest that these materials are semiconductors. The samples showed maximum transmission in the visible regions but poor transmittance in the ultraviolet region. The photoluminescence spectra recorded on the samples showed that WO3 has no visible luminescence, but exhibited strong ultraviolet emission whereas MoO3 showed blue emission. The MoO3 and WO3 samples are sintered to above 90 % relative density at temperatures 725 and795 °C, respectively without using any sintering aid. The dielectric constants (er) of the sintered samples are 8 and 6 for MoO3 and WO3, respectively. The calculated temperature coefficient of dielectric constant is negative. The low sintering temperature, dielectric constant, low loss factor and negative temperature coefficient make the sample ideal for low temperature cofired ceramic, electronic substrate materials as well as suitable for various optical applications such as UV filters, transparent films for window layers on solar cells, anti-reflection coatings, scintillators, detectors.

Optical and Dielectric Properties of Nano GdAlO3

Nano perovskite-type structure as denoted by ABO3 (A= RE) have been popular targets of fundamental investigations since they exhibit a wide variety of physical properties depending upon the chemical composition, defects and small changes in atomic arrangements. Nanocrystalline GdAlO3 is synthesized through a modified combustion process. The X-ray diffraction study shows that the nanopowder is single phase with orthorhombic structure and belongs to the space group Pnma. The FT-IR spectral analysis confirms that the as-prepared powder itself is phase pure. The UV-Vis spectrum analysis reveals that the material is a wide band gap material with band gap of about 5.7eV along with good transmittance in the visible region which makes it suitable for transparent conducting oxide films for window layers on solar cells. Refractive index of the sample as a function of photon energy is also measured. The high value of optical conductivity in the visible region indicates that nano GdAlO3 is ideal for the fabrication of solar cell panels. Photoluminescence spectrum at the excitation wavelength 260nm is also recorded and analyzed. The dielectric constant, loss factor and conductance are studied in the radio frequency region. The conductance is very small at radio frequencies and is of the order of 10-6Ω-1 in the MHz frequency range. The low conductance and loss factor confirm its suitability as a promising candidate for application as substrate and electronic packing materials.

Structral, Optical and Dielectric Characterization of Nanocrystalline AMo0.5W0.5O4 (where A=Ba,Sr and Ca) Prepared by Single Step Modified Combustion Technique

Nanocrystalline AMo0.5W0.5O4 (A= Ba, Sr, Ca) have been synthesized through a modified combustion process. The X-ray diffraction studies have revealed that the samples are single phase and possess tetragonal structure. Raman spectra showed that the Ag modes of [MoO4]2− and [WO4]2− are split up into two well distinguished peaks while that of Bg and Eg modes of the tetrahedral units superimposed to form single strong peaks. Corresponding Au and Eu modes are registered in FTIR spectra. Vibrational analysis also confirms the long range order of lattice structure. The nanocyrstalline AMo0.5W0.5O4 are found to be excellent photo luminescent materials with strong blue and green emission. Blue emission is attributed to [WO4]2− and green emission responds to [MoO4]2− units. Thus we can fine tune the emission wavelength from blue to green region by varying the composition. These nanocrystals could be sintered at a relatively low temperature in the range 830-875oC for 3h to a high density. The SEM image of the sintered material indicates high densification of the material. The room temperature dielectric constant (ɛr) and of the sintered pellet at 5MHz were above ∼12 and attains a maximum value of ∼15. The low sintering temperature, moderate dielectric constant, low loss factor t makes nano AMo0.5W0.5O4 excellent composition for low temperature cofired ceramics, substrate material, and electronic packing materials, besides numerous optical applications.

Nanocrystalline scheelite SrWO4: a low temperature co-fired ceramic optical material-synthesis and properties

Nanocrystalline strontium tungstate (SrWO4) is synthesized through a single step modified combustion process. The X-ray diffraction, Fourier transform Raman and Infrared spectroscopy studies reveal that the as-prepared powder is single phase and possess tetragonal structure. The transmission electron microscopic investigations have shown that the particle size of the as prepared powder is in the range 18–22 nm. The optical constants are estimated from the UV–Visible studies and calculated optical band gap is 4.28 eV. The sample showed maximum transmission in the visible regions but poor transmittance in the ultraviolet region. The photoluminescence spectra recorded at different temperatures showed intense blue emission. The nanocrystalline SrWO4 obtained by the present combustion method was sintered to 95 % density at a relatively lower temperature of 810 °C for 3 h. The dielectric constant (er) and loss factor (tan δ) of the sintered SrWO4 pellets at 5 MHz measured at room temperature were 9.9 and 6.29 × 10−3 respectively. The experimental results obtained in this work demonstrate the application of SrWO4 as UV filters, transparent films for window layers on solar cells, anti-reflection coatings, scintillators, detectors and for low-temperature co-fired ceramic applications.

Optical and dielectric properties of SrMoO4powders prepared by the combustion synthesis method

In this paper, we report on the obtention of nanocrystalline <TEX>$SrMoO_4$</TEX> synthesized through modified combustion process. These powders were characterized by X-ray diffraction, Fourier Transform Raman and Infrared Spectroscopy. These studies reveal that the scheelite-type <TEX>$SrMoO_4$</TEX> crystallizes in tetragonal structure with I41/<TEX>${\alpha}$</TEX> (N#88) space group. Transmission electron microscopy image shows that the nanocrystalline <TEX>$SrMoO_4$</TEX> powders have average size of 18 nm. The optical band gap determined from the UV-V is absorption spectra for the as prepared sample is 3.7 eV. These powders showed a strong green photoluminescence emission. The samples are sintered at a relatively low temperature of <TEX>$850^{\circ}C$</TEX>. The morphology of the sintered pellet is studied with scanning electron microscopy. The dielectric constant and loss factor values obtained at 5 MHz for a well sintered <TEX>$SrMoO_4$</TEX> pellet has been found to be 9.50 and <TEX>$7.5{\times}10^{-3}$</TEX> respectively. Thus nano <TEX>$SrMoO_4$</TEX> is a potential candidate for low temperature co-fired ceramics and luminescent applications.

Towards achieving nano-structured sintered ceramics with high stability for SOFC applications: Ce&lt;SUB align=right&gt;1&amp;minus;xM&lt;SUB align=right&gt;xO&lt;SUB align=right&gt;2&amp;minus;&amp;delta;, M = Gd, Sm: interesting examples

Through selected examples, we have demonstrated the importance of using nanoparticles of oxides to obtain nanostructured sintered ceramics at low sintering temperatures. For this purpose, we have prepared two series of single doped ceria solid solutions of the general formulae Ce1−xMxO2−δ, where M = Gd and Sm and x = 0.05-0.2 using a modified combustion process, namely a mixed fuel process with a mixture of fuels, such as citric acid and glycine. Independent of the nature of the metal ions all the compositions formed doped Ce1−xMxO2−δ ceria in-situ with improved powder properties such as finer particle size and high surface area. Highly reactive powders that could achieve resultant sintered density of ≥98% of the theoretical density were achieved by this synthetic approach. Moreover, the sintered Ce1−xMxO2−δ powders exhibited enhanced densification and controlled grain growth and exhibited nano-sized grains in the sintered microstructures. A correlation could be established between the agglomerate size of the powders and the ultimate grain size of the sintered powder compacts. In addition, these powders have the potential of exhibiting substantial stability against reduction by retaining relatively high density over a wide range of temperatures. The cited examples clearly demonstrate an incremental increase in property, viz., enhanced sinterability of the particles due to nanosize effect.

Characterization, sintering and dielectric properties of nanocrystalline barium titanate synthesized through a modified combustion process

Nanocrystalline barium titanate has been synthesized through a modified combustion process in a single step for the first time. The as-prepared barium titanate powder is cubic perovskite with lattice constant a = 4.018 Å. The phase purity of the nanopowder was examined using thermo gravimetric analysis, differential thermal analysis and Fourier transform infrared spectroscopy. Transmission electron microscopic investigations have shown that the particle size of the as-prepared powder is in the range 20–40 nm. The agglomerate size distribution of the as-prepared powder was studied using atomic force microscopy. The nanoparticles of barium titanate were sintered to 97% of the theoretical density at a temperature of 1350 °C for 3 h. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant and loss factor of the sintered pellets at 1 MHz measured at room temperature were 1223 and 3.5 × 10 − 3 respectively.

Green chemistry-mediated synthesis of nanostructures of afterglow phosphor

Various nanostructures of SrAl 2O 4:Eu 2+, Dy 3+ (SAC) afterglow phosphor were prepared in a single-step reaction using a green chemistry-mediated modified combustion process. The evolution of hazardous NxOx gases during the customary combustion reaction was completely eliminated by employing an innovative complex formation route. Another fascinating feature of the process was that, a slight change in the processing conditions ensured the synthesis of either nanoparticles or nanowires. The photoluminescence spectrum of nanophosphor showed a slight blue shift in emission (∼511 nm) as compared to the bulk phosphor (∼520 nm). The afterglow (decay) profiles of SAC nanoparticles, nanowires and bulk phosphor were compared. The chemistry underlying the nanostructure synthesis and the probable afterglow mechanism were discussed.

Synthesis and characterization of Ba 2YSbO 6 nanoparticles through a modified combustion process

Nanoparticles of Yttrium Barium Antimonate (Ba 2YSbO 6), a complex perovskite ceramic oxide have been synthesized using an auto ignition combustion process for the first time. The particle size and properties of the nanocrystals have been characterized by X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba 2YSbO 6 and has a complex cubic perovskite (A 2BB'O 6) crystalline structure with lattice constant a = 8.402 Å. Transmission electron microscopy study has shown that the particle size of the as-prepared powder was in the range 20–50 nm. The nanocrystals of Ba 2YSbO 6 synthesized by the combustion technique could be sintered to 97% of the theoretical density at a temperature of 1550 °C for 4 h. The combustion synthesis has a definite advantage that the phase pure Ba 2YSbO 6 nanopowder could be obtained by a single step process without the need of a calcination step.

Sinter-active nanocrystalline CeO2 powder prepared by a mixed fuel process: Effect of fuel on particle agglomeration

A modified combustion process, namely a mixed fuel process making use of a mixture of two fuels, such as citric acid and glycine has been developed to prepare nanocrystalline ceria powders. The effect of the mixed fuel and the different fuel to oxidant ratios on the decomposition characteristics of the gels were investigated by simultaneous thermal analysis experiments. It was established from various characterization techniques that the ceria powder prepared through the mixed fuel process has got the optimum powder characteristics, namely, a surface area of 33.33 m2/g and a crystallite size of 14 nm compared to the powders produced through the combustion process using a single fuel like glycine or citric acid. Such powders when sintered at 1250°C resulted in pellets with densities in the range of 94–96% of theoretical density. In this paper, we have carried out systematic studies on the sintering of ceria powders prepared by different approaches. The sintered ceramic from mixed fuel batch, exhibited and retained relative density more than 95% up to 1250°C and this data clearly underscores the ability of this process in developing ceria ceramics with increased stability against reduction.

Synthesis of nanocrystals of long persisting phosphor by modified combustion technique

Synthesis and characterization of nanocrystalline long persistent SrAl2O4:Eu2+, Dy3+ phosphor via a modified combustion process has been presented in this paper. In this synthesis process, a mixture of respective metal nitrates, flux and combustible agent (urea/camphor) were thermally treated with slight modification at 400–600°C for about 5min. It resulted in low-density voluminous mass as compared to a sintered material by conventional solid-state method. The present work reports the changes made in the combustion process to achieve the homogenous incorporation of dopants and large-scale production of the nanophosphor in a short interval of time. The samples have been characterized for nanophase, structural and luminescent properties.

Barium Holmium Zirconate, A New Perovskite Oxide: II, Synthesis as Nanoparticles through a Modified Combustion Process

Nanoparticles of barium holmium zirconate, a new complex perovskite ceramic oxide, has been synthesized using a modified self‐propagating combustion process. The solid combustion products obtained were characterized by X‐ray diffraction (XRD), electron diffraction, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, particle size analysis, surface area determination, and high‐resolution transmission electron microscopy. The XRD and electron diffraction studies have shown that the as‐prepared powder is phase pure Ba2HoZrO5.5 and has a complex cubic perovskite (A2BB′O6) structure with a lattice constant a= 8.428 Å. The transmission electron microscopic investigation has shown that the particle size of the as‐prepared powder was in the range 4–16 nm with a mean grain size of 8.2 nm. The nanoparticles of Ba2HoZrO5.5 obtained by the present method could be sintered to 98% theoretical density at 1500°C.

Synthesis of nanoparticles of barium lanthanum hafnium oxide by a modified combustion process.

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba2LaHfO5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO3, La2O3, and HfO2 that had been heated at 1200 degrees C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba2LaHfO5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba2LaHfO5.5 synthesized by the present combustion technique could be sintered to > 97% of the theoretical density at a relatively low temperature of 1425 degrees C. Scanning electron microscopic studies on the sintered Ba2LaHfO5.5 samples showed that the final grain size of the sintered specimen was < 500 nm.