Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Cobalt oxide nanopowder synthesis using cellulose assisted combustion technique

Cobalt oxides nanopowders were prepared using novel cellulose assisted combustion synthesis and solution combustion synthesis techniques. The synthesis conditions were optimized to produce high surface area cobalt oxide nanopowders. Effect of precursors ratio on product properties (such as crystalline structure, nanoparticle size, surface area etc.) were studied and compared for the two methods. Thermodynamic calculations along with TGA/DTA studies were used to understand the synthesis mechanism leading to cobalt oxide formation. The synthesized nanopowders were characterized using various materials characterization techniques such as XRD, SEM and TEM.     

High-porosity TiAl foam by volume combustion synthesis

Preparation of high-porous TiAl foam by volume combustion synthesis (VCS) was investigated. It is shown that the optimum conditions for pore formation are attained when gas evolution coincides in time with melting of the reactants.      

Synthesis of BSCF perovskites using a microwave-assisted combustion method

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−Δ (BSCF) perovskite-type oxide was synthesized using a microwave-assisted combustion method. Following about 10 min of exposure to microwave, the combustion reaction was self-ignited and it produced a porous powder. For comparison, BSCF perovskite powders were also synthesized by conventional heating. Two different fuel types were used in the two heating methods. The crystalline BSCF powders were characterized using scanning calorimetry and thermogravimetry (DSC/TG), X-ray diffraction (XRD), BET surface area measurement, scanning electron microscopy (SEM), and dilatometric analysis. The microwave heating method resulted in a powder with nanometric crystallites, submicrometric particles, and a specific surface area of 9.93 m²/g, which corresponds to a BET diameter of approximately 100 nm. The dilatometric analysis showed that the microwave-synthesized BSCF powder has the maximum sintering rate at 970 °C, but the sintering process initiates at lower temperatures.     

Accelerated crystallization of CuAlO2 delafossite phase by controlling thermal regime during solution combustion synthesis

In the present study, for the first time, CuAlO₂ delafossite phase was successfully obtained through a one-step solution combustion synthesis (SCS) process. Moreover, in order to accelerate CuAlO₂ crystallization, two-step process, i.e. SCS followed by heat-treatment (different thermal regimes: continuous and discontinuous) without controlling the atmospheric oxygen, was applied. In the two-step process, heating time duration needed for the crystallization of CuAlO₂ was lowered to 30 min at 1100 °C by exerting SCS on the mixture of starting materials. It was found that different thermal regimes can highly affect the formation of CuAlO₂ phase. Furthermore, according to the SEM and TEM studies, it was revealed that the resultant powders have a flaky-shape morphology with lamellar structure.     

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 study of salt-assisted solution combustion synthesis of magnesium aluminate and sintering behaviour

We synthesized nano MgAl₂O₄ with a ~80?nm particle size by salt-assisted solution combustion synthesis using LiCl as salt. Nano MgAl₂O₄ produced by conventional solution combustion synthesis commonly exhibits poor uniformity in terms of size with partially sintered particles and a high degree of agglomeration, leading to poor sinterability. It was found in this study that the use of the salt-assisted solution combustion method has successfully lowers the degree of agglomeration with uniform particle size and morphology, demonstrating superior sinterability. Conventional sintering in air atmosphere at 1550?℃ of MgAl₂O₄ obtained by salt-assisted solution combustion followed by calcination at 700–1100?℃ yielded up to 94% of relative density, while the conventional solution combustion method could not match this. In addition, using the spark plasma sintering technique, fully dense (over 99%) submicrometer (~340?nm) transparent polycrystalline MgAl₂O₄ with elevated mechanical properties (~16.6?GPa) was achieved. The salt-assisted solution combustion method could be effectively used for fully dense material, but can be further developed for various nano oxide materials where high dispersion with a low degree of agglomeration is preferred.     

Transparent AlON ceramics by nitriding combustion synthesis precursors and pressureless sintering method

Fine AION powders (D₅₀ = 607 nm) with high sintering activities were synthesized by a high-efficiency solution combustion-based method, and a high-transmittance AlON ceramics can be achieved by a subsequent sintering process. Moreover, the influences of various aluminum resources (Al(NO₃)₃, AlCl₃ and Al₂(SO₄)₃) on the morphology of precursors and nitride-functionalized products have been studied in detail. Using Al(NO₃)₃ as aluminum source resulted in more active precursors and was beneficial for the preparation of ultrafine AlON powders. Then, single-phase AlON powders were obtained by calcining precursors at 1700 °C for 10 min, while residual Al₂O₃ was observed in the calcined products synthesized by other two aluminum sources. As a result, transparent AlON ceramics with high in-line transmittance of 85.9% at 2 μm were obtained. This research provides valuable reference for rapid preparation of AlON powders and transparent ceramics.     

Solution combustion synthesis of CeFeO3 under ambient atmosphere

Polycrystalline CeFeO₃ was prepared with almost single phase purity of 93% by a solution combustion synthesis (SCS), but contrarily to all other reports, CeFeO₃ could be obtained under ambient atmosphere. The perovskite-type phase was gained at 400 °C from a solution containing stoichiometric amounts of metal nitrates and by using glycine as fuel. For comparison, CeFeO₃ was also prepared under inert atmosphere by a conventional, oxalate-based high-temperature solid-state reaction. The products were structurally characterised by X-ray powder diffraction (XRD), and the lattice parameters were determined from subsequent Rietveld refinements. Since solution combustion is often referred as the method delivering nano-sized ceramics, the morphological characteristics of the products obtained through the two different synthesis methods were compared by scanning electron microscopy (SEM). Furthermore, the particle sizes were determined by laser diffraction analysis.     

Preparation of BaTiO3 nanopowders by the solution combustion method

Barium titanate was synthesized by the method of exothermal combustion in solutions using barium nitrate, titanium dioxide (TiO₂) and titanyl nitrate (TiO(NO₃)₂) as sources of titanium and barium and reducing agents such as glycine (C₂H₅NO₂), carbamide (СН₄N₂O) and glycerol (C₃H₅(OH)₃). In an effort to form a barium titanate phase, the materials synthesized using titanium dioxide were subjected to additional calcination at 800 °С. With titanyl nitrate the use of glycine and carbamide enabled carrying out a single-step synthesis of barium titanate. The obtained materials have pseudo-cubic lattice and are characterized by high stability of properties in a wide range of temperatures and frequencies of the electromagnetic field.     

Nano-sized plate-like alumina synthesis via solution combustion

Nano-sized plate-like alumina is an important inorganic material in catalytic, ceramic and electronic applications due to its unique two-dimensional structure and properties, while its facile synthesis is still under investigation. In this work, nano-sized alumina plate was synthesized by solution combustion method with glycine and polyvinyl alcohol as composite fuels for the first time. The calcination temperature during solution combustion process was optimized as confirmed by XRD, FT-IR, TG-DSC, Raman, ²⁷Al MAS NMR, SEM, TEM, and N₂ physisorbtion. Obtained alumina displayed special nano-sized plate morphology and porous structure. It was further adopted as support for cobalt acetate and used as catalyst for selective oxidation of cyclohexane. This work develops a facile approach to synthesize two-dimensional plate-like alumina for catalytic application.     

Fast synthesis of Na2Ti3O7 system synthesized by microwave-assisted hydrothermal method: Electrical properties

Sodium titanate Na₂Ti_nO_2n+1 (2 ≤ n ≤ 9) is a well-known semiconductor that exhibits interesting electrical properties allowing numerous applications, such as: electrodes for solid-state batteries. In this work, we reported a novel, fast and simple route to produce sodium titanate (Na₂Ti₃O₇ - NT) structures at low temperature and short time, by using microwave-assisted hydrothermal method. The NT powder synthesis was performed at 200 °C for 1 h and 4 h. Afterward, the as-synthetized powders were sintered to 900 °C for 1 h. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance spectroscopy. It was identified a phase mixture of the polymorphs Na₂Ti₃O₇ and Na₂Ti₆O₁₃ with elongated rod-like morphology. Both samples showed a majority Na₂Ti₃O₇ (≥95%) crystalline phase, as confirmed by Rietveld refinement. After ceramics sintering the total dc conductivity values between of 10^-6 S/cm and 10^-7 S/cm were achieved.     

An investigation of fuel precursors and calcination temperature to obtain mayenite (Ca12Al14O33) powders by solution combustion synthesis

The influence of the fuel (glycine, urea, citric acid and sucrose) and calcination temperature used to obtain calcium aluminate in the mayenite phase assisted by solution combustion synthesis (SCS) is the central point of this work. Thermal gravimetric analysis helps to establish the calcination temperatures used (1100, 1200 and 1300 °C). Using the X-ray diffraction technique (XRD) and complementary analyses, such as Raman spectroscopy, the specific surface area and laser granulometry, it was possible to elucidate the behavior and relationship of the fuel and heat treatment on the phase formation, crystallite size and powder crystallinity. Glycine showed better performance than other fuels, with the lowest calcination temperature, obtaining pure mayenite with nanometric crystallite size in all calcination ranges. Thus, it was observed that the type of fuel has an influence on obtaining pure mayenite, as well as the calcination temperature, and glycine reveals the best performance.     

微波辅助溶液燃烧法制备MgAl_2O_4粉体

将硝酸镁、硝酸铝、尿素按物质的量比为1 2 6.66制得透明混合前驱液,用低温燃烧技术与微波加热技术相结合的方法制备了高纯度、低团聚的镁铝尖晶石(MgAl2O4)粉体。研究了燃烧反应过程中,微波输出功率(200、400、600、700 W)对Mg Al2O4粉体晶体结构、形貌及比表面积的影响。结果表明:微波高效加热方式导致燃烧反应瞬间产生大量气体,促进了Mg Al2O4超细颗粒的形成。同时,随着微波输出功率的增加,尿素氧化加速,利于MgAl2O4晶粒的生长发育。在微波功率700W,微波时间2 min的条件下,可制备结晶完整,粒度分布均匀(平均晶粒尺寸为56.03 nm)的Mg Al2O4粉体。     

Solution combustion synthesis of ZnO powders using CTAB as fuel

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using cetyltrimethylammonium bromide (CTAB) as fuel. The effects of fuel to oxidant ratios (? = 0.5, 0.75, 1 and 1.5) on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy, and diffuse reflectance spectrometry techniques. The slow decomposition rate of CTAB guaranteed the direct formation of single phase and well-crystalline ZnO powders regardless of fuel content. The specific surface area of the as-combusted ZnO powders with platelet particles increased from 21 ± 1 to 35 ± 2?m²/g with fuel content. The band gap energy also increased from 2.99 to 3.13?eV due to the decrease of particle size. The as-combusted ZnO powders at ? = 1.5 exhibited the highest photodegradation (~69%) of methylene blue under ultraviolet light irradiation, due to their good crystallinity and smaller particle size.     

Solution combustion synthesis of ZnO powders using mixture of fuels in closed system

Single phase ZnO powders with wurtzite structure were synthesized by solution combustion method using various amounts of mixed glycine-citric acid fuel in the presence (open system) and absence (closed system) of air oxygen. Phase evolution, microstructure and optical properties were investigated by thermal analysis, X-ray diffractometry, electron microscopy and Raman, photoluminescence (PL) and diffuse reflectance spectrometry techniques. Rapid combustion reaction in closed system led to weak crystallinity, as confirmed by deep-level emissions in PL spectra. Larger spherical particles (~200?nm) were synthesized in open system at ? =?1. The as-combusted ZnO powders in closed system exhibited higher photocatalytic activity under ultraviolet irradiation, due to their higher adsorption capacity of methylene blue on ZnO surface. Photodegradation rate increased with the increase of fuel content in as-combusted ZnO powders produced by open route as a result of the reduction of particle size and band gap energy.     

Solution combustion synthesis (SCS) of chrome alumina as a high temperature pink pigment

In this article, one step synthesis of the chrome alumina pink pigments is investigated. Results indicated that adjusting ignition parameters such as the fuel type (glycine, citric acid, and urea) and the oxidizer to fuel ratio, is the essential factor to obtain the straight corundum structure of the pigment. According to this, chrome alumina pink pigment was just synthesized by the urea fuel in 1.8 oxidizer to fuel (O/F) ratio. The effect of ignition parameters on the morphology was also studied. The microstructure was changed from ultra‐fine irregular agglomerates to sponge‐like flakes by the change in the fuel type from citric acid to urea. Colorimetric characteristics confirmed the relationship between the formation of the corundum structure and one step synthesis of the pink pigment. The pink color of synthesized pigments was comparable with commercial purplish pink pigments of tiles.     

Solution combustion synthesis of new metal borophosphates (Fe1-xCrx)2B(PO4)3: Structural,thermal, surface,and magnetic properties

The new borophosphates were successfully synthesized by solution combustion synthesis assisted with glycine. The obtained materials were systematically characterized by Fourier-transform infrared spectroscopy, X-ray powder diffraction, UV–visible spectroscopy, thermogravimetric analysis, scanning electron microscopy, Brauner-Emmett-Teller surface area, and magnetometry. The Rietveld refinements indicated that Fe₂B(PO₄)₃ is a hexagonal, space group P63/m with a = b = 8.029 and c = 7.408. As Cr substitutes the Fe atoms, there is a significant decrease in the lattice parameters. When all Fe atoms are replaced by Cr, Cr₂B(PO₄)₃ is formed and the structure turns out to be a trigonal, space group P3 with a = b = 7.950 and c = 7.360. The materials are thermally stable and demonstrate paramagnetic behavior at room temperature. The magnetization increases as the iron content increases because of the high magnetic moment of the iron ion. Temperature-dependent magnetic measurements reveal that Fe₂B(PO₄)₃ has a Néel transition at 30 K and the Néel temperature decreases with Cr substitution.     

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).     

Preparation of hollow SiC spheres by combustion synthesis

Hollow spherical β-SiC was successfully prepared in argon by combustion synthesis using Si powder and polytetrafluoroethylene (PTFE) powder. The phase composition and morphology of spherical products can be controlled by adjusting the Si/C₂F₄ molar ratio (M_Si/(C2F4)). When M_Si/(C2F4) = 3, the phase content of β-SiC is the highest (up to 85.54%), and hollow spherical products obtained; When M_Si/(C2F4) ≥ 5, the Si/SiC microspheres are solid. The synthesis mechanism of hollow β-SiC microspheres is as follows: Si particles react with PTFE releasing heat. Then unreacted Si absorbs heat to form liquid phase microspheres, which is equivalent to the core template to form β-SiC microspheres by reaction with cracked C. Meanwhile, the silicon diffuses from the core to the shell to form the cavity. This method can synthesize the hollow spherical β-SiC in a simple way without prearranged spherical template and long synthesis cycle.