Phase transformation of FeCr2O4 to (Fe,Cr)2O3 solid solution pigment powders: Effect of post-heating temperature

Iron chromite powders were synthesized via solution combustion route using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, as well as glycine–urea, glycine–citric acid, and glycine–ethylene glycol mixtures as fuels. The effect of postheating at different temperatures on the structure, molecular, microstructure, and chromatic properties of powders and tiles colored by in-glaze powders was studied. The X-ray diffraction patterns showed that as-synthesized powders were obtained in crystalline FeCr₂O₄ phases moreover, postheating of the powders led to d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution phase regardless of fuel type. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase of as-synthesized particles. Fourier transform infrared analysis illustrated that the band positions of octahedral M–O and tetrahedral M–O bonds were shifted due to Fe cations movement from their position and lattice shrinkage by increasing of post-heating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles were formed from porous spongy FeCr₂O₄ particles due to oxidation and phase transformation during the postheating. Furthermore, chromatic properties of the samples were represented. The color properties of the pigments showed that the formation of brown pigments is provided with the phase transformation from FeCr₂O₄ to (Fe,Cr)₂O₃ at a temperature of up to 750°C. Moreover, increasing the color purity to this temperature is related to the removal of residual carbonaceous matters. The chromatic properties of the glazed tiles colored using the pigments showed that postheating between 250 and 500°C led to more brown appearance.     

Synthesis of (Fe,Cr)2O3 solid solution pigment powders for ink application

Iron chromite pigment was synthesized via solution combustion using iron(III) nitrate nonahydrate and chromium(III) nitrate nonahydrate as starting materials, and glycine, urea, citric acid, and ethylene glycol as fuels. The effect of postheating temperature on the structure, microstructure, and chromatic properties of the synthesized powders was also studied. X-ray diffraction patterns showed that the as-synthesized powders were amorphous to crystalline FeCr₂O₄ phases, depending on fuel type. Moreover, regardless of the fuel type, postheating led to the d-space shift and oxidation and formation of (Fe,Cr)₂O₃ solid solution. Phase transformation of FeCr₂O₄ to (Fe,Cr)₂O₃ solid solution was observed at 500/750°C depending on the dominant phase present in the as-synthesized particles. Fourier transform infrared analysis illustrated a shift in the band position of octahedral M–O and tetrahedral M–O bonds due to the movement of Fe cations and the lattice shrinkage by increasing the postheating temperature. Moreover, scanning electron micrographs showed that Fe_0.7Cr_1.3O₃ semispherical fine particles consisted mainly of porous and spongy FeCr₂O₄ particles due to the oxidation and phase transformation during postheating. According to chromatic measurements, the ink prepared by using the powders synthesized in the presence of glycine and post-heated at 500°C showed reddish-brown color which could be considered a promising candidate for tile decoration application. Furthermore, rheology studies revealed that the prepared ink showed non-Newtonian shear thinning behavior.     

Solution combustion synthesis of cerium oxide nanoparticles as corrosion inhibitor

In this study, combustion synthesis of cerium oxide nanoparticles was reported using cerium nitrate hexahydrate as starting material as well as urea, glycine, glucose, and citric acid as fuels. The influence of fuel type on structure, microstructure, band gap, and corrosion inhibition was investigated. X-ray diffraction (XRD) patterns and scanning electron microscopy micrographs showed that CeO₂ nanoparticles with different morphologies were obtained depending on the fuel type. Microstructural changes from unreacted gel to sponge-like morphologies were resulted by varying the fuel type from urea, glycine, and glucose to citric acid. In addition to Ce–O bonds, Fourier transform infrared analysis showed carbon bonds of carbonaceous compositions from incomplete combustion which were declined during combustion reaction. Furthermore, corrosion analyses showed that samples synthesized using urea fuel released the most Ce⁺⁴ ions and could have better protection than other samples.     

燃烧法制备铝酸铜色料的研究

以三水合硝酸铜、九水合硝酸铝和甘氨酸为原料,采用燃烧法制备了铝酸铜(CuAl₂O₄)棕色色料。采用SEM、XRD、FT-IR、TG-DTA和UV-Vis等测试手段,研究了煅烧制度和铜铝摩尔比(Cu/Al)对色料物相组成、微观结构、呈色性能的影响。结果表明,当Cu/Al摩尔比为1∶2.4,煅烧温度为1 100 ℃(不进行保温)时,可以得到呈色性能最佳的CuAl₂O₄色料,其色度值为L^*=46.22、a^*=24.43、b^*=27.09。     

Chromium incorporated nanocrystalline cobalt ferrite synthesized by combustion method: Effect of fuel and temperature

Nanocrystalline CoCrFeO₄ samples were prepared by Cost effective and low temperature combustion method using different fuels as glycine, urea and polyvinyl alcohol and the effect of temperature on their physical properties has been studied. The thermal study of the precursor gels was done by using Thermogravimetric and Differential thermal analysis (TG-DTA). Occurrence of the cubic spinel phase for the samples was confirmed by the Rietveld analysis of X-ray diffraction (XRD) data. The refinement results also confirm that the cationic distribution over the tetrahedral and octahedral sites in the spinel lattice of samples is partially inverse. The magnetic studies indicate a superparamagnetic behaviour, showing an increase in the blocking temperatures with the particle size in case of all fuels. All the samples showed ferromagnetic behaviour and the nanoparticles prepared by using glycine as a fuel were found to have largest crystallite size and relatively stronger A–O–B interaction compared to others. Magnetization measurements exhibit non-collinear ferrimagnetic structure for the samples.     

Facile,scalable synthesis of nanocrystalline calcium zirconate by the solution combustion method

Single phasic nanocrystalline CaZrO₃ powder has been synthesized by glycine nitrate solution combustion method around 300 °C using nitrate as oxidant and glycine as fuel. The as prepared product obtained as a result of combustion itself is crystalline and nearly single phasic CaZrO₃ confirmed by X-ray diffraction (XRD). The product calcined at 600 °C reveals carbonate free single phasic orthorhombic structured CaZrO₃. To study the impact of oxidant to fuel ratio (O/F) and ignition temperature, a systematic variation of O/F and ignition temperature of combustion reaction has been investigated by analyzing the products through XRD in each case. These products have been characterized by XRD, Fourier Transform Raman spectroscopy, Thermal Analysis (TGA/DTA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Raman Spectrum reveals single phasic nanocrystalline perovskite CaZrO₃. Spherical shaped particles were observed through SEM. TEM results also confirm the particles to be in nano regime (30–90 nm).     

A comparative study of hydroxyapatites synthesized using various fuels through aqueous and alcohol mediated combustion routes

Nano-sized calcium hydroxyapatite, [Ca₁₀(PO₄)₆(OH)₂] has been synthesized by the sol–gel combustion method using calcium nitrate and di-ammonium hydrogen phosphate as precursors in the aqueous medium. Triethyl phosphite was used as a phosphate precursor for alcohol mediated combustion. The aqueous and alcohol media were employed for the investigation of combustion synthesis in the presence of various fuels such as urea, glycine, alanine, hydrazine and hexamine. The metal-to-fuel ratio in the synthesis was maintained at 1 to facilitate complete combustion and the Ca/P ratio was maintained at 1.67 to aid the stoichiometric formation of hydroxyapatite. The combustion products were calcined at 800 °C for 10 h and were characterized by powder XRD, FT-IR, HR-SEM and HR-TEM techniques. All the five fuels used under the alcohol mediated combustion, resulted in forming phase pure hydroxyapatite; whereas the aqueous mediated combustion method yielded biphasic calcium phosphate containing Ca₁₀(PO₄)₆(OH)₂ and β-TCP depending on the nature of the fuel.     

Effect of propellant on the combustion synthesized Sr-doped LaMnO3 powders

Lanthanum strontium manganite (LSM) powders of composition La_0.7Sr_0.3MnO₃ are good candidates for cathode application in solid oxide fuel cells. This paper reports the synthesis of LSM powders from nitrate precursors by the combustion method, using two different propellants (urea and glycine) and varying the propellant/nitrate ratio. Thermogravimetric analysis (TGA) revealed two or three decomposition stages of the as-synthesized samples, with complete burn out of organics at about 850–900 °C. X-ray diffraction (XRD) patterns showed formation of only LSM phase for the sample synthesized with excess of urea, whereas SrCO₃ and MnCO₃ phases were also found for the samples prepared from glycine. The powder is better crystallized when a homogeneous gel is formed before burning. The crystallite size calculated using the Scherrer equation is in the range of 15–20 nm. Scanning electron microscopy (SEM) revealed the presence of agglomerates, formed by fine particles of different shapes.     

Combustion synthesis of PZN-10PT nanopowders

Discussed is the influence of the fuel and water employed in combustion synthesis of single-phase (perovskite) PZN-10PT nanopowder with an x = 0.10 composition. Pb(NO₃)₂, Zn(NO₃)₂ · 6H₂O, (NH₄NbO(C₂O₄)₂), and C₈H₂₀O₄Ti were used as cation precursors while urea, glycine, glycine/urea (50/50 ratio), and tetraformal triazine (TFTA), as fuels. Two sets of precursors (denoted as set-1 and set-2) were used with each of these fuels, and four different fuels: without and with the addition of 250 mL of water. The results indicated that the highest percentage of perovskite phase in the PZN-10PT nanopowders was obtained using an urea/glycine mixture as a fuel. When the urea/glycine mixture was added to the solution containing cations precursors, the two fuels form a gel in aqueous solution, this gel contributes not only to obtain homogeneously mixed in the starting material but also aids explosive combustion leading to a high-temperature reaction within a shorter period of time, which is a condition that favors the formation of metastable PZN-10PT nanopowders.     

Effects of the fuel type and fuel content on the specific surface area and magnetic properties of solution combusted CoFe2O4 nanoparticles

In this work, the different fuels (citric acid, glycine and urea) at the various fuel to oxidant ratios (ϕ=0.5, 0.75, 1 and 1.25) were used for solution combustion synthesis of CoFe₂O₄ nanoparticles. The phase evolution, microstructure, specific surface area and magnetic properties of the solution combusted CoFe₂O₄ nanoparticles were investigated by X-ray diffraction, thermal analysis, electron microscopy, adsorption-desorption isotherms and vibrating sample magnetometry techniques. The specific surface area of the combusted products decreased with the increase of fuel to oxidant ratio (ϕ), irrespective of the fuel type. However, the specific surface area for the glycine fuel was higher than the others, due to the higher combustion rate for releasing gaseous products. Furthermore, the solution combusted CoFe₂O₄ powders by the glycine fuel exhibited the higher saturation magnetization (63.6 emu/g) on account of their higher crystallinity and particle size.     

Retention of high dielectric constant sodium beta alumina via solution combustion: Role of aluminum ions complexation with fuel

In the present study, solution combustion technique has been explored to synthesize Sodium β-alumina (SBA; NaAl₁₁O₁₇) powder and thin films. Three fuels namely urea, glycine and citric acid have been used to seek the feasibility of synthesizing crystalline SBA powder at low temperature. Also, the effect of nature of fuels used as well as calcination treatment on phase evolution and morphology of the as-combusted powder was investigated. Thermal analysis and X-ray diffraction studies suggest the formation of crystalline SBA powder at temperature as low as 259 °C, using urea in the combustion reaction whereas other fuels resulted in amorphous SBA phase and this variation in phase was found due to difference in exothermicity of the fuel used. Thermodynamic and spectroscopic analyses showed that the exothermicity of fuel depends on various factors like (i) standard heat of formation of fuel and (ii) the complexation offered by fuel to metal cations. Furthermore, sodium β-alumina thin film capacitor (metal-insulator-metal) was also fabricated using urea via spray combustion synthesis. The sodium β-alumina thin film showed a high dielectric value (ε_r) of ~21.     

Impregnated active layer combustion synthesis of nano MgFe2O4 using green template

Nano-Magnesium ferrite (MgFe₂O₄) powders have been prepared by a modified combustion synthesis method named impregnated active layer combustion (IALC). The effects of five important parameters such as main fuel to oxidizer ratio (F/O), main fuel type, added fuel type, template type and main fuel (Added F/MF) to the added fuel ratio have been studied using Taguchi design. Xylitol, D-mannitol, ethylene diamine tetra acetic acid (EDTA) and diethylene triamine penta acetic acid (DTPA) were used as fuels. Besides, waste newspaper and Platanus orientalis leaf (POL) were used as new green templates. Samples were characterized by XRD, XRF, SEM, TEM, BET and VSM analyses. Results showed that the average crystallite size of the sample prepared under optimized condition (mixture of Xylitol and DTPA as fuel, POL as template, and Added F/MF ratio of 0.75) was 17.66?nm. The result was confirmed by TEM. The saturated magnetization of the optimum sample was 21?emu/g and the specific surface area was 15.377?m²/g.     

Color parameters of Y2Cu2O5 green-blue nanopigments fabricated by the sol-gel combustion method and their efficiency for coloring the glazed tiles

Non-toxic Y₂Cu₂O₅ nanopigments were synthesized by sol-gel combustion method and the effects of synthesis parameters on their chromatic properties have been studied. The chromatic properties of the samples were studied by UV-vis reflectance spectroscopy and the L^*a^*b^* coordinates were evaluated using the CIE Lab1976 color scales. The results showed that the chromatic properties of nanopigments were changed by altering the synthesis conditions such as pH and the molar ratio of the fuel to oxidizer. Also some Y₂Cu₂O₅ micro sized pigments were synthesized by solid state reaction and the measurements showed that the chromatic properties of the nanopigments were slightly bigger than those of the large particles indicating that the nanopigments were more stunning. Using DTA analysis it was found that the nanopigments were very stable in the temperature range of 50–950 °C. The measurements of a^* and b^* showed that the nanopigments are also very stable in glazes.     

Effect of fuel type on structural and physicochemical properties of solution combustion synthesized CoCr2O4 ceramic pigment nanoparticles

Due to importance and wide applications, CoCr₂O₄ ceramic pigment nanoparticles were synthesized via low-temperature solution combustion route by different fuels including ethylenediamine/oxalic acid, ethylenediamine/citric acid, oxalic acid/citric acid and ethylenediamine/oxalic acid/citric acid. Physicochemical properties of the synthesized samples were determined by different techniques such as fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) and color/optical properties were evaluated based on CIELAB system by spectrophotometer. Moreover, thermodynamic considerations of combustion reactions for CoCr₂O₄ nanopigments formation in terms of calculated adiabatic flame temperature and enthalpy of combustion reaction were studied. The Comparison of results and data showed that cobalt chromite pigment nanoparticles synthesized by using ethylenediamine/citric acid and ethylenediamine/oxalic acid/citric acid fuels exhibited higher purity, smaller crystallite size and lower degree agglomeration.     

Effect of fuel type on the microstructure and magnetic properties of solution combusted Fe3O4 powders

Porous magnetite (Fe₃O₄) powders were synthesized by solution combustion method using the glycine and urea at different fuel to oxidant ratios (ϕ). The combustion behavior depended on the fuel type as characterized by thermal analysis. The structure and phase evolution investigated by X-ray diffraction method showed nearly single phase Fe₃O₄ powders which were achieved only by using the glycine fuel at ϕ=1. The specific surface area and porous structures of the as-combusted Fe₃O₄ powders were characterized by N₂ adsorption-desorption isotherms and scanning electron microscopy, respectively. The surface area using the glycine fuel (62.6 m²/g) was higher than that of urea fuel (42.5 m²/g), due to different combustion reactions. Magnetic properties of the as-combusted powders were studied by vibration sample magnetometry which exhibited the highest saturation magnetization of 74 emu/g using the glycine fuel at ϕ=1 on account of its high purity and large crystallite size.     

Solution combustion synthesis of FeCr2O4:Zn,Al pigment powders

FeCr₂O₄:Zn,Al pigment powders were prepared via a solution combustion synthesis method. Effects of Zn and Al dopants and less/extra Fe content on the structure, molecular bonds, and optical properties of powders were studied. Results showed that addition of dopants as well as extra/less content of Fe led to weaker combustion and consequently lower X-ray diffraction peak intensities, lattice parameters, and differential thermal analysis peak intensities. Moreover, Fourier transform infrared analysis illustrated that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies with moving away from stoichiometry. In addition, scanning electron micrographs showed that in all samples, porous spongy microstructures were formed with highly flake-like agglomerated particles. Furthermore, there was a significant difference between the powder samples and the tiles colored with in glaze powders due to the partial dissolution of pigments in contact with the molten glaze of tiles. In comparison to the tile colored with the stoichiometric FeCr₂O₄ pigments without dopants, the color difference (ΔE) in the tiles colored by the iron chromite pigments doped with Zn and Al dopants and less/extra Fe content reached the high values as large as ΔE = 36.19. The solar reflectance values (R_s) in near-infrared region were above 50% in all samples. Near 80% R_s in the tile colored by the iron chromite pigment doped with 3 mol% Zn and the yellowish brown appearance (L* = 43.44, a* = 6.77, b* = 18.38, c* = 19.59, h = 69.79) showed that the sample was a good candidate for cool building materials such as roof tiles.     

Influence of the Fuel Used in the Microwave Synthesis of Cr2O3

The synthesis and physico-chemical characterization of chromium oxide (Cr₂O₃) is reported. Samples were prepared by a novel microwave technique using two different fuels, i.e., tetraformaltrisazzine (TFTA) and urea. The physical characterization of the synthesized chromium oxides was achieved using XRD, IR, Raman, BET surface area and pore size distribution (PSD) techniques. The XRD and IR and Raman spectroscopy studies reveal that crystalline Cr₂O₃ is the only phase formed. The XRD, surface area and particle size analysis reveal that the samples prepared using TFTA as the fuel possess a larger surface area, smaller crystalline size, smaller particle size and larger pore diameter. Both samples were calcined at 600°C for 6 h so that they could be used for the catalytic oxidation of LPG. Catalytic runs on the Cr₂O₃ samples revealed that the two samples possess different activity and selectivity. The Cr₂O₃ sample prepared by using TFTA as the fuel gave rise to more dehydrogenation and cracking compared to the sample prepared by using urea as the fuel, which gave more combustion products.     

Influence of heating approach (microwave vs. muffle furnace) and fuel in auto-combustion design of nanostructured Ca2Mn3O8 as support for efficient and reusable catalyst used in green fuel production

In this article, MgO/Ca₂Mn₃O₈ nanocatalyst was used for the first time in the transesterification process for the production of green fuel from sunflower oil. Besides, the synthesis of layered nanostructured Ca₂Mn₃O₈ was done for first applied by combustion route as well. The effects of two heating sources including muffle furnace and microwave irradiation, and also various fuels including urea, glycine, and ethylene glycol were investigated on the characteristics of calcium-manganese oxide (Ca₂Mn₃O₈) as the support of the nanocatalysts loaded by MgO as active phase. The synthesized samples were characterized by different analyzes such as AFM, HRTEM, FESEM, FTIR, EDX, XRD, and BET-BJH. The nanocatalyst produced by the microwave irradiation combustion method and urea fuel scored the best performance. This nanocatalyst had the highest specific surface area (46.4 m²/g), and better pore size distribution, too. The roughness of this sample was reported at 5.1 nm in the range of 2 μm. It was found that the optimum sample has converted 96.7% of the oil extracted from sunflower seed to fatty acid esters that are gained by transesterification of fats with methanol. This sample exhibited better reusability in the same operating conditions in proportion to the sample synthesized with muffle furnace in twelve runs, which justified the positive influence of microwave irradiation on the catalytic properties.     

Nanocrystalline Cr2O3 and amorphous CrO3 produced by solution combustion synthesis

The synthesis of chromium oxides by solution combustion synthesis was investigated. Ammonium dichromate, glycine, urea and ammonium nitrate dissolved in aqueous solution were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. Amorphous CrO₃ and crystalline Cr₂O₃ were synthesized. The results suggest that glycine is a better complexing/combustible agent for ammonium dichromate than urea. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The smallest crystallite size (≈20 nm) of Cr₂O₃ was obtained with glycine as fuel/complexant agent in fuel-lean mixtures. The highest specific surface area (63 m²/g) was observed with urea in fuel-rich mixtures, forming amorphous CrO₃.     

燃烧法制备纳米ZnO及光催化降解甲基橙的研究

分别以甘氨酸和柠檬酸为燃料,Zn（NO3）2为氧化剂,采用燃烧法制备纳米ZnO粉体并采用模拟太阳光进行甲基橙光催化降解研究。XRD和SEM表征样品表明,燃烧法能简单、快速制备纳米ZnO粉体。研究表明,燃烧剂和氧化剂的配比以及反应温度对制备的纳米ZnO降解甲基橙效果有较大影响。Zn（NO3）2与甘氨酸之比为0．2～0．5（物质的量比）,反应温度为5000C;Zn（NO3）2与柠檬酸之比为1．5,反应温度为600℃进行反应制备得到的纳米ZnO降解甲基橙效果较好。降解实验的结果表明,纳米ZnO能有效地光催化降解甲基橙染料。以柠檬酸为燃料制备的ZnO样品,在1h内对10mg·L^-1甲基橙溶液的降解率为90％。