Low-temperature Combustion Synthesis Research Articles

Polyacrylamide-assisted combustion-carbothermal synthesis of well-distributed SiC nanowires

SiC nanowires are produced by employing a novel synthesis process involving the carbothermal reduction reaction of Polyacrylamide (PAM)-assisted low-temperature combustion synthesis (LCS) precursors. PAM-assisted LCS mixtures with high specific surface area and fibers with various size are used as precursors. The precursors, derived from silicic acid (Si source), PAM (additive), nitric acid (oxidizer), urea (fuel), and glucose (C source) mixed solution, are prepared by PAM-assisted LCS method. The prepared precursors have exhibited a high contact area of reactants. The carbothermal reduction of these high specific surface area precursors results in the formation of pure and well-distributed SiC nanowires with a diameter of 50nm and a length of up to several micrometers. The effects of PAM contents and carbothermal reduction parameters on the production of SiC nanowires are discussed in detail. The precursors and corresponding carbothermal reduction products are investigated by FESEM, TEM, HRTEM, and XRD analyses.

Low-temperature combustion synthesis of cobalt magnesium ferrite magnetic nanoparticles: effects of fuel-to-oxidizer ratio and sintering temperature

The effects of glycine-to-nitrate molar ratio (G/N) and sintering temperature of 600 °C on the solution combustion synthesis of nanocrystalline Co0.8Mg0.2Fe2O4 (CMFO) are reported. The structural, morphological and magnetic properties of CMFO could be controlled by using different combinations of glycine fuel and metal nitrates and also sintering temperature. Thermodynamic considerations of the combustion processes show that the exothermicity, adiabatic flame temperature and the amount of gases released increase with increase in G/N. The auto-combusted and sintered powders obtained were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), thermo-gravimetric analysis–differential scanning calorimetry and vibrating scanning magnetometer measurements. SEM images of CMFO showed that the G/N ratio and sintering temperature had pronounced effect on the microstructure regarding density and porosity. The magnetization, crystallite sizes and crystallinity of the CMFO spinel phase increased with increase in G/N ratio and sintering temperature. Raman spectroscopic analysis showed that only the fuel-rich sample gave the five Raman active modes characteristic of a spinel structure. The obtained results were also discussed in comparison with ferrite system formed by different synthesis processes. XRD of CMFO auto-combustion powders prepared with different G/N ratios: (a) G/N = 2.22, (b) G/N = 1.48 and (c) G/N = 0.74.

Low Temperature Combustion Synthesis of TiC Powder Induced by PTFE

TiC powders were prepared at low temperature from the Ti-C system with polytetrafluoroethylene (PTFE) as a chemical activator. The reaction temperature, phase composition and morphology were determined via differential scanning calorimetry (DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to explore the reaction mechanism, respectively. The FESEM result shows that TiC powders with average particle size less than 100 nm are synthesized via low-temperature combustion synthesis at 530 °C by adding 3wt% PTFE into Ti-C system. Based on the most intensive diffraction peak (200) of the XRD pattern, the crystallite size of prepared TiC powders is calculated to be about 81 nm by the Scherrer formula, which is close to the average particle size observed from the FESEM image. It indicates that TiC particles consist of a single crystal as the result of fast, low-temperature, solid-state synthesis process. According to DSC results, the combustion synthesis mainly includes two reaction processes. Firstly, the initial reaction between titanium and PTFE particles releases a great amount of heat, and subsequently, the heat induced combustion reaction between titanium and carbon particles.

Low temperature combustion synthesis of nitrogen-doped graphene for metal-free catalytic oxidation

A mild synthesis method was developed to improve metal-free catalysis of graphene in catalytic oxidation by nitrogen modification, which can be easily tailored by varying calcination temperature.

Synthesis and luminescent properties of two different Y2WO6:Eu3+ phosphor phases

In this paper, two different Y2−xEuxWO6 phases were synthesized. The monoclinic phase was prepared via a conventional solid-state reaction, whereas the orthorhombic phase was obtained via a facile, low-temperature combustion synthesis method. X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy were used to characterize the resulting phosphors. The XRD results indicate the orthorhombic phase crystallized isostructurally with the Aurivillius Bi2WO6 phase, whereas the other polymorph crystallized isostructurally with Yb2WO6 in the monoclinic system. The SEM studies revealed both phases had a strong tendency to form agglomerates averaging nanometers in size. The photoluminescence emission spectra confirmed all of the samples were efficiently excited by near UV light and were dominated by the electric dipole transition 5D0→7F2. The orthorhombic Y2−xEuxWO6 excitation spectrum possessed a broad band across the entire UV region (220–400nm); therefore, Y1.86Eu0.14WO6 could be considered an efficient spectral converter material for use in dye-sensitized solar cells.

Two‐Step Carbothermal Synthesis of AlN–SiC Solid Solution Powder Using Combustion Synthesized Precursor

In the present work, a two‐step carbothermal reduction method is employed to prepare the AlN–SiC solid solution (AlN–SiCss) powders by using a combustion synthesized precursor. The precursor is prepared by low‐temperature combustion synthesis (LCS) method using a mixed solution of aluminum nitrate, silicic acid, polyacrylamide, glucose, and urea. The synthesized LCS precursor exhibits a porous and foamy uniform mixture of Al2O3 + SiO2 + C consisting of flaky particles. The carbothermal reduction in the LCS precursor is carried out in two steps. First, the precursors are calcined at 1600°C in argon for 3 h. Subsequently, the precursors are further calcined at 1600°C–1900°C in nitrogen for 3 h. The results indicate that the precursor calcined at and above 1850°C in nitrogen for 3 h yields the single‐phase AlN–SiCss powders. The synthesized AlN–SiCss powder exhibits near‐spherical particles with diameter of 200–500 nm. The experimental and thermodynamical results reveal that the formation of AlN–SiCss occurs via the diffusion of AlN into SiC by virtue of formation of a highly defective β′ intermediate during the second step reaction.

Comparison of photoluminescence properties of Gd2O3 phosphor synthesized by combustion and solid state reaction method

In this paper, we presented a comparison of Photoluminescence (PL) studies of Gd2O3 phosphor prepared by two synthesis methods, high temperature (1400 °C) solid state reaction and low temperature combustion synthesis. Both of these methods synthesized Gd2O3 phosphor successfully. Structural properties of Gd2O3 phosphor were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR). Scanning electron microscope (SEM), Energy dispersive X-ray analysis (EDX), and Transmission electron microscopy (TEM). The results obtained for both methods of preparation were compared. The photoluminescence (PL) properties of pure Gd2O3 were carried out over the range of 300 nm–650 nm. A PL emission band at UV region in between 318 and 370 nm along with blue, green and red emission was observed at 275 nm excitation.

EPR and optical investigations of LaMgAl11O19:Cr3+ phosphor

The LaMgAl11O19:Cr3+ phosphor has been prepared by a low-temperature combustion synthesis method. As-prepared combustion synthesized powder was characterized using powder X-ray diffraction (XRD), diffuse reflectance (DRS), electron paramagnetic resonance (EPR) and photoluminescence (PL) studies. The X-ray diffraction pattern reveals crystalline hexagonal phases. The UV–vis diffuse reflectance spectrum exhibits three broad bands characteristic of Cr3+ ions in octahedral symmetry. The EPR spectrum exhibits several resonance signals. The signals with the effective g values at g=4.84, 3.64 and 2.26 have been attributed to the isolated Cr3+ ions. The signal with the effective g value at g=1.94 has been attributed to exchange coupled Cr3+–Cr3+ ion pairs. The PL studies exhibit several bands characteristic of Cr3+ ions in octahedral symmetry.

Synthesis of titanium nitride nanopowder at low temperature from the combustion synthesized precursor and the thermal stability

Titanium nitride (TiN) nanopowder with uniform morphology was prepared combining low temperature combustion synthesis (LCS) and carbothermal reduction and nitridation method. The prepared TiN nanopowder were well-distributed spherical particles ranging from 30 to 50nm. According to the thermodynamic calculation, the temperature and the reaction atmosphere are important factors. In the experiment, the experimental temperature was set at 1000–1200°C and the nitrogen atmosphere with the partial pressure of 0.1MPa was purified by carbon. The phase and microstructure of the sample were characterized by XRD, SEM and FTIR. TG–DTA was adopted to investigate the reaction mechanism. The result showed that TiN was synthesized without intermediate phase formation at or above 1100°C. The lattice parameter of TiN synthesized at 1100–1200°C (a=4.240–4.241Å) agreed well with the theoretical value (a=4.241Å). Furthermore, TiN nanopowder exhibited good thermal stability and the oxidation started from 400°C in air.

Tungsten carbide synthesized by low-temperature combustion as gas diffusion electrode catalyst

Tungsten carbide powder, which is used as the catalyst for a gas diffusion electrode, has been prepared by low-temperature combustion synthesis for the first time. The average particle size of the prepared tungsten carbide is 200 nm, determined by X-ray diffraction and field-emission scanning electron microscopy. The effects of the carbon/tungsten (C/W) molar ratio on the formation of tungsten carbide and carbon content on the complete carbonization temperature are discussed. The optimal synthesis temperature is 1100 °C, and the optimal C/W molar ratio is 19/3. The electrocatalytic properties of tungsten carbide for the oxygen reduction reaction are evaluated through the use of polarization curves and electrochemical impedance spectroscopy in neutral and alkaline electrolytes. The current density of the tungsten carbide-based gas diffusion electrode is as high as 350 mA cm −2 at 0.4 V versus Hg/HgO. It is demonstrated that the tungsten carbide catalyst exhibits excellent electrocatalytic performance, comparable with that of Pt. • The WC particles of well-distributed and smaller size are produced by the LCS method. • The LCS method is a new direct reduction and carbonization method. • C/W mole ratio affects the formation of WC. • Carbon content affects the complete carbonization temperature.

Essence of superparamagnetism in cadmium ferrite induced by various organic fuels via novel solution combustion method

An attempt has been made to enumerate the myriads of successful applications of magnetic materials in nano-regime via low-temperature solution combustion synthesis of cadmium ferrite using different organic fuels such as urea, oxalyl dihydrazide (ODH), glycine and ethylene glycol giving rise to 1D nanorods and monodispersed spherical nanoparticles, thereby exploring their applicability in nanoelectronic devices such as high speed integrated circuits as well as in biomedical field as contrasting agents used in magnetic resonance imaging (MRI) with enhanced magnetization. Thus, with appropriate selection of organic fuel and precursors (metal nitrates), single phase, cubic structured cadmium ferrites have been synthesized as depicted from FTIR spectroscopy and XRD patterns with particle size lying in 12–27nm regime as rendered from TEM micrographs. Magnetic studies in the shadow of Mössbauer studies prelude to the emergence of superparamagnetism with non-saturation of M–H loop and negligibly small values of remanence as well as coercivity at room temperature, hence attributing to its single domain as well as soft magnetic character. Moreover, the room temperature dielectric measurements show dispersion behavior with increasing frequency corresponding to low dielectric losses, hence making them suitable for applications in high-frequency devices. Thus, solution combustion methodology was successfully used as a key step in the synthesis of CdFe2O4 with highly superparamagnetic and soft character, thereby leading to products with different morphologies in nano-regime.

Comparison of the photocatalytic degradation of trypan blue by undoped and silver-doped zinc oxide nanoparticles

Zinc oxide (ZnO) and silver doped zinc oxide (ZnO:Ag) nanoparticles were prepared using nitrates of zinc and silver as oxidizers and ethylene diaminetetraacetic acid (EDTA) as a fuel via low-temperature combustion synthesis (LCS) at 500°C. X-ray diffraction (XRD) pattern indicates the presence of silver in the hexagonal wurtzite structure of ZnO. Fourier transform infrared (FTIR) spectrum indicates the presence of Ag–Zn–O stretching vibration at 510cm−1. Transmission electron microscopy (TEM) images shows that the average particle size of ZnO and ZnO:Ag nanoparticles were found to be 58nm and 52nm, respectively. X-ray photoelectron spectroscopy (XPS) data clearly indicates the presence of Ag in ZnO crystal lattice. The above characterization techniques indicate that the incorporation of silver affects the structural and optical properties of ZnO nanoparticles. ZnO:Ag nanoparticles exhibited 3% higher photocatalytic efficiency than pure ZnO nanoparticles. ZnO:Ag nanoparticles show better photocatalytic activity for the degradation of trypan blue (TrB) compared to undoped ZnO nanoparticles.

ChemInform Abstract: Enhanced Luminescence by Monovalent Alkali Metal Ions in Sr2SiO4:Eu3+ Nanophosphor Prepared by Low Temperature Solution Combustion Method.

AbstractPorous and irregular shaped nanoparticles of Sr2SiO4:Eu3+ and Sr2SiO4:Eu3+:M+ (M: Na, K, Li) are prepared by low temperature combustion synthesis of an aqueous solution of metal nitrates and oxalyl dihydrazide as the fuel (muffle furnace, 500 °C, 5 min) followed by grinding and heating of the resulting powder (900 °C, 2 h).

Structural and luminescent properties of Eu3+-doped GdSrAl3O7 nanophosphor

Eu3+-doped GdSrAl3O7 nanophosphor with promising luminescent properties has been synthesized by low-temperature solution combustion synthesis. The structural properties examined by X-ray diffractometer, scanning electron microscopy, and transmission electron microscopy showed that pure tetragonal GdSrAl3O7: Eu3+ red nanophosphor having narrow size distribution in 50–55 nm range could be readily obtained at low temperature 550 °C. The photoluminescent excitation and emission spectra, life time, and concentration effect were studied in detail. Under excitation at 266 nm, Eu3+-doped GdSrAl3O7 nanophosphor revealed weak green emission and strong red emission attributed to 5D1 → 7F1–2 and 5D0 → 7F0–3 transitions of Eu3+ ion, respectively in the region of 525–700 nm. The red emission from 5D0 → 7F2 transition at 616 nm exhibits the highest intensity under the optimized concentration of 10 mol% after which the quenching mechanism became relevant. Quenching behavior of the europium in the GdSrAl3O7 host was explained by nonradiative cross-relaxation phenomenon. Moreover, Eu3+-doped GdSrAl3O7 nanophosphor can generate light from orange to deeper red by properly tuning the concentration of europium ions based on the energy transfer principle.

An electron paramagnetic resonance and optical study of Cr doped BaAl12O19 powders

The BaAl12O19 powders doped with Cr3+ ions have been prepared by a low-temperature combustion synthesis method. As prepared combustion synthesized powder was characterized using powder X-ray diffraction and energy dispersive analysis of X-ray methods. The diffuse reflectance spectrum exhibits three bands characteristic of Cr3+ ions in distorted octahedral symmetry. The EPR spectra exhibit signals with the effective g values at g=1.96, 2.27 and 4.85. The signals with the effective g values at g=2.27 and 4.85 have been attributed to the isolated Cr3+ ions. The signal at g=1.96 has been attributed to the exchange coupled Cr3+ ions. The excitation spectrum exhibits bands characteristic of Cr3+ ions in distorted octahedral symmetry. The ligand field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated from the excitation spectrum. The emission spectrum exhibits an intense band centered at 700nm (14,286cm−1) and this band has been attributed to 2Eg→4A2g transition.

Thermoluminescence properties of Mn-doped CaYAl3O7 phosphor irradiated with ultra-violet, mega-voltage and gamma radiation

Low temperature combustion synthesis was employed for the preparation of CaYAl3O7(Mn2+) phosphor. X-Ray diffraction (XRD) patterns were recorded to confirm the phase formation. Estimated particle size was found to be ~19.9nm by using the Debye Scherrer׳s formula. FTIR study confirms the formation of CaYAl3O7 compound, escape of nitrates and other organic products. Thermoluminescence (TL) glow curves of the prepared phosphor were recorded after exposing the sample with Ultra-violet (UV), 6-Mega-voltage (MV), 16-MV and Co-60(Cobalt-60, 1.25-MeV average gamma energy) radiation. Trapping parameters namely activation energy (E), order of kinetics (b) and frequency factor(s) of main peak, centered around 186°C in the sample irradiated with UV source for 20min, were determined using glow curve shape (Chen׳s) method. It has been observed that the TL peak intensity increases with increasing the exposure from UV source. Also with increases the energy of incident radiation a decrease in TL peak intensity were observed. This could be due to higher penetration power and less absorbance of incident beam in the phosphor material. Analysis suggests that possibility of utilizing this phosphor in futuristic low and high energy dosimetric applications as well as in solid state lighting devices.

Optimization of the low temperature combustion synthesis of Er3+ doped lead–natrium–yttrium–fluoride phosphor

The low-temperature combustion synthesis (LCS) method is the most popular method for the synthesis of ultrafine oxides and compound oxides. A kind of Er - Y - Pb - Na quaternary fluoride sensitive to 1.55 μm was synthesized by the LCS method and the synthesis conditions were optimized with orthogonal experiments. Intense upconversion emissions at 522 nm, 541.4 nm and 654.7 nm corresponding to the 2 H 11/2, 4 S 3/2 and 4 F 9/2 transitions to the 4 I 15/2 ground state were observed when excited by CW laser radiation at 1.55 μm. The effect of the carbamide amount on the phase formation and the luminescence intensity was analyzed. The product is of uniform particle size of ca. 40 nm, which is very outstanding for its reutilization in the infrared detection field.

Preparation and millimeter wave attenuation properties of NiFe2O4/expanded graphite composites by low-temperature combustion synthesis

Abstract In this paper, NiFe 2 O 4 /expanded graphite (EG) composites are successfully prepared by low-temperature combustion synthesis method. The morphology, structure and millimeter wave (MMW) attenuation properties of the NiFe 2 O 4 /EG composites are investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and MMV radar measurement device. The effects of fuel and stoichiometric ratio on the composites are also investigated. The results show that NiFe 2 O 4 /EG composites are uniform and have a good crystallinity. The composites possess better MMW attenuation properties than EG. The 3 and 8 MMW attenuation performances of NiFe 2 O 4 /EG composites are 8.5 dB and 14.6 dB, respectively.

Combustion synthesis and characterization of TaC, TaC/TaSi2, and TaC/TaB nanoparticles

Herein, we present the low-temperature solid-phase combustion synthesis of tantalum carbide (TaC), TaC/tantalum silicide (TaSi2), and TaC/tantalum boride (TaB) nanoparticles by the silicothermic reduction of potassium fluorotantalate (K2TaF7) in the presence of carbon, boron, and polytetrafluoroethylene (PTFE,11BJH, Barrett–Joyner–Halenda; HRTEM, high-resolution transmission electron microscopy; MMC, metal matrix composite; PFTE, polyfluorotetraethylene; PTFE; polytetrafluoroethylene; RF, radio frequency; SAED, selected area electron diffraction pattern; Tc, combustion temperature; TEM, transmission electron microscopy; Uc, combustion velocities; XRD, X-ray diffractometer. (C2F4)n). The temperature–time profiles of the combustion wave were measured by thermocouples and used to calculate the combustion parameters: temperature and wave velocity. The flame temperature was found to increase with the concentration of PTFE. Using high resolution transmission electron microscopy, a homogeneous distribution of highly crystalline nanoparticles was observed. The thermal–kinetic activation energy, the heat released during each of the individual reactions, and the chemical mechanism of the overall combustion process are discussed with respect to the final products.

Low-temperature solution combustion synthesis of high performance LiNi0.5Mn1.5O4

High-voltage LiNi0.5Mn1.5O4 spinels were synthesized by a low temperature solution combustion method at 400°C, 600°C and 800°C for 3h. The phase composition, structural disordering, micro-morphologies and electrochemical properties of the products were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and constant current charge–discharge test. XRD analysis indicated that single phase LiNi0.5Mn1.5O4 powders with disordered Fd-3m structures were obtained by the method at 400°C, 600°C and 800°C. The crystallinity increased with increasing preparation temperatures. XRD and FTIR data indicated that the degree of structural disordering in the product prepared at 800°C was the largest and in the product prepared at 600°C was the least. SEM investigation demonstrated that the particle size and the crystal perfection of the products were increased with increasing temperatures. The particles of the product prepared at 600°C with ~200nm in size are well developed and homogeneously distributed. Charge/discharge curves and cycling performance tests at different current density indicated that the product prepared at 600°C had the largest specific capacity and the best cycling performance, due to its high purity, high crystallinity, small particle size as well as moderate amount of Mn3+ ions.