Combustion Synthesis Process Research Articles

Thermodynamic Analysis and Synthesis of Metallic Molybdenum Powder via the Solution Combustion Synthesis Process

ABSTRACT This study investigates the production of metallic molybdenum powder through the solution combustion synthesis (SCS) method. Despite thermodynamic challenges posed by potential back-oxidation under equilibrium conditions, the non-equilibrium nature of SCS facilitates the formation of metallic molybdenum. Experimental evidence suggests that Mo6+ actively participates as an oxidizer in the process, leading to the reduction of Mo6+ to Mo4+. Subsequent reduction of MoO2 is primarily driven by reactions with methane, a byproduct of the SCS process. Characterization of the gel precursor reveals the formation of a molybdenum-citric acid dimer. The resulting molybdenum powder exhibits a semi-amorphous structure with a developed specific surface area and low metallic impurity content but contains a significant amount of residual organic compounds. While heat treatment does not effectively remove these impurities, future research efforts should focus on developing purification strategies to minimize organic contamination.

Synthesis of high purity Ti2AlC MAX phase by combustion method through thermal explosion mode: Optimization of process parameters & evaluation of microstructure

Obtaining high-purity MAX-phase powders is a challenging issue. Therefore, in this article, the effects of two key parameters, including mechanical activation time (1, 2, and 3 h), and preheating temperature (800 and 1000 °C) were investigated on the formation mechanism of Ti2AlC MAX phase using mechanically activated (assisted) self-propagating high-temperature synthesis (MA-SHS) combustion method through thermal explosion mode. For this aim, a powder mixture of titanium, aluminum, and carbon with a stoichiometry ratio of (2:1:1) was used. Differential thermal analysis (DTA) was carried out to evaluate the effect of mechanical activation and preheating temperature of the formation temperature of the target MAX phase. Subsequently, the microstructural, phase analysis, chemical composition, and determination of surface chemical states studies were carried out through scanning electron microscopy (SEM), X-ray energy distribution spectroscopy (EDS) transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectric spectroscopy (XPS), respectively. DTA results illustrated that applying mechanical activation alters the formation temperature, which leads to an increase in the purity of the MAX phase. The quantitative measurements were carried out using the Rietveld method to determine the purity of the achieved MAX phase. The results indicated that samples subjected to 2 h of mechanical activation at a preheat temperature of 1000 °C exhibited to contain 96.1 % of Ti2AlC MAX phase, which is the highest value among other specimens and the lowest amount of secondary and oxide phases (3.9 % of TiC) during the combustion synthesis process compared to other samples.

The effect of carbon addition on the synthesis process and the physical/electrocatalytic properties of FeTiO3 nanopowder produced by solution combustion synthesis method

The FeTiO3 nanopowder is a vital engineering material known for its exceptional performance in energy generation, storage, electrochemical sensors, and catalysis. However, synthesizing FeTiO3 nanopowder with high crystallinity and phase purity typically requires specialized equipment and controlled heat treatment due to the instability of Fe2+ ions. Using the one-step solution combustion synthesis (SCS) method, FeTiO3 nanopowder withe high crystallinity were successfully produced utilizing basic equipment. Additionally, the influence of carbon additives on phase transitions, as well as the physical and physicochemical properties of the synthesized powder, was examined. XRD results indicate that increasing the amount of fuel, particularly glycine, creates a stable environment for the crystallization of FeTiO3 nanoparticles. Moreover, enhancing the carbon content in precursor solutions with urea enhances reduction conditions and boosts the stability of FeTiO3 in the final product. The presence of carbon additives in glycine-fuel samples leads to unfavorable outcomes by increasing the levels of TiO2 and Fe3O4 undesirable phases. Incorporating additive carbon into the urea-synthesized precursor solution resulted in a particle size increase exceeding 50 nm and raised the combustion temperature by a minimum of 230 °C. Furthermore, the presence of 15 wt% additive carbon in the sample synthesized with glycine improved the specific surface area of particles from 2.44 m2/g to 18.41 m2/g. Obtained results have shown that achieving high crystallinity of FeTiO3 nanopowder is feasible through a one-step solution combustion synthesis process. This can be accomplished by carefully choosing the synthesis conditions, such as the type and quantity of fuel, along with the carbon additive.

Multi-site synergistic hydrogen evolution reactions on porous homogeneous FeCoNiCu high-entropy alloys fabricated by solution combustion synthesis and hydrogen reduction

A combination process of solution combustion synthesis and hydrogen reduction was proposed to prepare porous homogeneous FeCoNiCu high-entropy alloys (HEAs) for hydrogen evolution reaction (HER). Solution combustion synthesis was herein employed to obtain the multiple composite oxide precursor with tunable molar ratio of elements and pore structure, as well as uniform element distribution. The generated bulk porous HEAs composed of single-phase solid solution were achieved by hydrogen reduction of the oxide precursor at optimal temperature. The porous structure and specific surface area of oxide precursor and reduced HEA could be adjusted by varying the mass ratio of metal nitrates to glycine and the reduction temperature. The prepared FeCoNiCu0.5 HEA with enriched porosity and high specific surface area showed high catalytic activity and excellent electrochemical stability during alkaline HER. Density functional theory (DFT) calculation revealed the electronic interaction between Fe, Co, Ni and Cu elements facilitated the efficiency for H* adsorption and H2 desorption, and enhanced the catalytic activity of the Co/Ni sites. This work provided an approach to develop porous high-entropy alloy catalysts for HER and other applications.

High-Entropy Spinel Oxide Ferrites for Battery Applications.

Four different high-entropy spinel oxide ferrite (HESO) electrode materials containing 5-6 distinct metals were synthesized by a simple, rapid combustion synthesis process and evaluated as conversion anode materials in lithium half-cells. All showed markedly superior electrochemical performance compared to conventional spinel ferrites such as Fe3O4 and MgFe2O4, having capacities that could be maintained above 600 mAh g-1 for 150 cycles, in most cases. X-ray absorption spectroscopy (XAS) results on pristine, discharged, and charged electrodes show that Fe, Co, Ni, and Cu are reduced to the elemental state during the first discharge (lithiation), while Mn is only slightly reduced. Upon recharge (delithiation), Fe is reoxidized to an average oxidation state of about 2.6+, while Co, Ni, and Cu are not reoxidized. The ability of Fe to be oxidized past 2+ accounts for the high capacities observed in these materials, while the presence of metallic elements after the initial lithiation provides an electronically conductive network that aids in charge transfer.

Stabilization of metastable γ-co: Combustion synthesis and rapid processing

This study reports a novel method for stabilizing the metastable γ-Co phase, which has a face-centered cubic structure. This phase is known for its challenging synthesis due to its tendency to transform into the stable hexagonal-closed packed (ε-Co) allotrope. Combustion synthesis and a rapid pressure-less sintering approach overcome the traditional barriers to γ-Co preparation. The combustion process involves exothermic reactions in a solution of cobalt nitrate hexahydrate and hexamethylenetetramine, generating enough heat to increase the synthesis temperature above the γ↔ε phase transition temperature (∼690 K). Rapid cooling of the solid product by gases is critical to preventing the reverse transition to ε-Co, thus stabilizing the γ-Co phase with a minimal amount of the stable phase. Thermal analysis has demonstrated that the decomposition of cobalt nitrates hexahydrate leads to the formation of cobalt oxides. These oxides are then reduced to Co by methane (CH4) and hydrazine (N2H4), released during hexamethylenetetramine decomposition. Kinetic data analysis shows that the rate-limiting step in forming Co is the CH4 (or N2H4)-mediated reduction of CoO. When subjected to rapid pressure-less sintering at 1275 K, the combustion synthesized materials consolidate into compact samples with a relative density of ∼90 % and micrometer-size grains. High-resolution electron microscopy investigation shows increased lattice dislocation due to the ε→γ transition at high-temperature processing. Prepared γ-Co exhibits a higher nanohardness and Young's modulus than ε-Co prepared by slow melt solidification and rolling methods.

Plasma‐catalytic CO2 methanation over NiO/bentonite catalysts prepared by solution combustion synthesis

AbstractA solution combustion synthesis (SCS) process to prepare nickel catalyst over bentonite (NiO/Ben) is reported. Compared to the traditional impregnation method, NiO/ben produced by SCS has smaller nickel particle size and higher dispersion. With a metal loading of 20 wt%, the afforded NiO/Ben demonstrates excellent catalytic activity for CO2 methanation in a dielectric barrier discharge reactor. In certain discharge conditions (H2:CO2 ratio of 5 in feed gas, discharge input power of 45 W, and gas hourly space velocity of 11 320 h−1), CO2 conversion and CH4 selectivity are as high as 55.8% and 84.6%, respectively. Under the conditions of plasma configuration, the strong interaction between the nickel species and the support plays an important role in the CO2 methanation process.

Fabrication of MAX‐Phase Composites by Novel Combustion Synthesis and Spontaneous Metal Melt Infiltration: Structure and Tribological Behaviors

In this work, a new scheme is developed and experimentally tested for fabricating family of MAX–metal composites. This scheme combines the combustion synthesis (CS) process to obtain a porous MAX‐phase skeleton and process of metal melt infiltration spontaneously, which is then used to fabricate Ti3SiC2–TiC–Sn and Ti3SiC2–TiC–(Sn–Pb) composites. The resultant composite samples have an uneven density along the length, which steadily decrease from the point of contact of the sample with the molten tin to the opposite edge. Existence of Ti3SiC2, TiC, Sn, and (Sn and Pb) phases in the composite samples is confirmed using X‐ray diffraction and energy‐dispersive spectroscopy analyses. Comparative tribological characterizations are performed on fabricated Ti3SiC2–TiC–Sn and Ti3SiC2–TiC–(Sn–Pb) composite samples. Herein, these results are compared against standalone Sn and Sn–Pb samples as baseline and reveal major differences in friction and wear mechanisms due to addition of select MAX phases via novel CS process. As a whole, in the present study, a novel synthesis process is established to fabricate MAX‐phase composites and its enhanced tribological behavior and wear mechanisms which can have plethora of applications ranging from aerospace, automotive to biomedical sectors, are validated.

MO2C/C Nanocomposites Prepared by a Solid-Flame Combustion Synthesis Process for the Hydrogen Evolution Reaction

MO₂C/C Nanocomposites Prepared by a Solid-Flame Combustion Synthesis Process for the Hydrogen Evolution Reaction

Combustion synthesis of Eu2O3 nanomaterials with tunable phase composition and morphology

Combustion reactions in europium nitrate – acetylacetone – 2-methoxyethanol solutions and gels were investigated to produce europium (III) oxide (Eu2O3) nanocrystalline materials and thin films. Thermal analyses of solutions indicated that the 2-methoxyethanol solvent also acts as a fuel in the absence of acetylacetone. Adding acetylacetone increases the overall heat of the reaction. Thermal analysis results revealed that the slow oxidation of unburned hydrocarbon residues follows the primary combustion reaction. Time-temperature profile measurements of the bulk combustion synthesis process in air and nitrogen atmospheres enabled the extraction of the maximum reaction temperature and the heating and cooling rates in the combustion zone. Several direct correlations exist between measured combustion parameters and the phase composition of the products. Combustion in air results in mixed-phase cubic and monoclinic nanocrystalline Eu2O3. Increasing the acetylacetone concentration in solutions increases the synthesis temperature and decreases the quantity of cubic Eu2O3. The reaction of solutions in a nitrogen atmosphere or diluted with Eu2O3 provides control of the product phase composition and reduces the quantity of the monoclinic phase. Transmission electron microscopy imaging shows that the Eu2O3 end products are highly porous aggregates of nanocrystalline particles. Electrospraying of reactive solutions onto different substrates followed by short annealing makes the preparation of Eu2O3 materials with diverse morphologies possible.

Electrochemical properties of NiO–Ni electrocatalyst synthesized via solution combustion for methanol oxidation in alkaline media

Transition metal oxides have been recently considered as the anode catalyst in direct methanol fuel cells to reduce the anodic overpotential of methanol electrooxidation in alkaline media. In this work, the NiO–Ni catalyst is synthesized via solution combustion synthesis process to reach an appropriate nanomorphology with high effective surface area and electrocatalytic activity. The influence of the fuel type (glycine and urea) and the fuel to oxidizer (F/O) ratio are investigated. The composition and phase analysis, crystallite size, particle size, specific surface area, and morphology of the nanoparticles are assessed. Moreover, electrochemical characteristics of the products are evaluated. The catalytic activity of the product towards methanol oxidation is found to vary with the fuel type and F/O ratio. The dependence of the oxidation current on the adiabatic temperature and morphological characteristics of the product is discussed. It is found that solution combustion synthesis is a confident technique that provides a considerable improvement in catalytic performance. Moreover, it is concluded that samples with dominant NiO show lower onset potential and higher current density. Synthesis by glycine in the most explosive condition (i.e., F/O = 0.83) results in more desirable catalytic activity.

Effect of particle size and shape of diluent on the reaction process of combustion synthesis of α‐Si3N4 powder

Abstractα‐Si3N4 powder was prepared by combustion synthesis using different particle sizes and shapes of Si3N4 diluent. The effects of different diluents on combustion temperature, phase composition, and microstructure of the product were investigated. The role of diluents in combustion synthesis is discussed. When no ammonium salt was added, because of the higher reaction temperature, the phase transformation of the fine particle diluent with the best barrier effect was also enhanced, and the α content of the product was the lowest. When the ammonium salt is added, the liquid phase Si content decreases at high temperatures, the lower reaction temperature and the Si3N4 generated before Si melting make the barrier effect of the diluent fully play. Finally, Si3N4 powder with 86% α content was synthesized by combustion with 2 μm Si3N4 diluent.

Impact of fuel quantity on luminescence properties of Sr3Al2O6:Eu by combustion synthesis

The photoluminescent behavior of Eu-doped Sr3Al2O6 obtained by highly efficient solution combustion synthesis is reported. In order to understand the influence of the fuel on the synthesis, the stoichiometric quantity and an excess of fuel were evaluated. By adjusting the amount of fuel, different luminescence responses were obtained, allowing europium cations incorporation into the Sr3Al2O6 lattice to serve as effective luminescence activators in such a short time during the rapid combustion synthesis process. The higher amount of fuel in the presence of the oxidizing agent produced Sr3Al2O6:Eu particles with higher phosphorescence brightness, owing to the increase of the reduction process from Eu3+ to Eu2+. The synthesized phosphor showed an intense band emission centered at 515 nm and could be excited over a broad spectral range in the UV-visible region. Particles having nanostructured flake-type morphology were obtained, which was considered a micro-nanofunctional candidate for practical applications.

Two-dimensional photocatalyst with highly efficient and stable visible light photocatalytic activity

Hex ammonium molybdate (AHM), ammonium nitrate (NH4NO3), and glycine were used as the precursors in a microwave-assisted solution combustion synthesis (WSCS) process to create foam-like MoO2 nanoparticles. Methodically investigated was the effect of the glycine/NH4NO3 ratio (=0.25, 0.50, 0.75, 1.0 and 1.25) on the finished goods. The findings indicate that the final morphologies and phases of the products are virtually influenced by the value of Φ. MoO2 nanoparticles measuring 20 to 30 nm can be successfully composited under the condition of Φ=0.50 to produce a foam-like result. The photocatalytic activity of foam-like MoO2 nanoparticles was tested with several pollutants. The results show that foam-like MoO2 nanoparticles have good degradability and stability. The photocatalytic mechanism and fabrication mechanism of foam-like MoO2 has been presented in detail. Using foam-like MoO2-based photocatalyst materials for energy transfer and environment protection is supported by this research.

Two-dimensional photocatalyst with highly efficient and stable visible light photocatalytic activity

Hex ammonium molybdate (AHM), ammonium nitrate (NH4NO3), and glycine were used as the precursors in a microwave-assisted solution combustion synthesis (WSCS) process to create foam-like MoO2 nanoparticles. Methodically investigated was the effect of the glycine/NH4NO3 ratio (=0.25, 0.50, 0.75, 1.0 and 1.25) on the finished goods. The findings indicate that the final morphologies and phases of the products are virtually influenced by the value of Φ. MoO2 nanoparticles measuring 20 to 30 nm can be successfully composited under the condition of Φ=0.50 to produce a foam-like result. The photocatalytic activity of foam-like MoO2 nanoparticles was tested with several pollutants. The results show that foam-like MoO2 nanoparticles have good degradability and stability. The photocatalytic mechanism and fabrication mechanism of foam-like MoO2 has been presented in detail. Using foam-like MoO2-based photocatalyst materials for energy transfer and environment protection is supported by this research.

Combustion synthesis of SiC/Al2O3 composite powders with SiC nanowires and their growth mechanism

SiC/Al2O3 composite powders with SiC nanowires were synthesized using a one-step combustion synthesis method taking silica fume (SiO2), aluminum powder (Al) and carbon black (CB) as raw materials, while ferrocene (C10H10Fe) was used as the catalyst. The calculated results for the relationship between the equilibrium phase and temperature of the Al–SiO2–C system show that SiC and Al2O3 are the only equilibrium phases in the system. In addition, the effects of C10H10Fe on the combustion synthesis process and products were studied. It was found that with increasing catalyst content, the amount of residual Si in the products first decreases and then increases, the combustion temperature first increases and then decreases, and the nanowire content continues to increase. For an optimal amount of C10H10Fe of 0.75 wt%, almost no residual Si is observed in the product, while the combustion temperature (Tc) is high (2104 K), the SiC nanowire content is relatively high, and the nanowire aspect ratio is large. In addition, two growth mechanism models for SiC nanowires: VS and VLS were validated.

In silico study and experimental evaluation of the solution combustion synthesized manganese oxide (MnO2) nanoparticles

An innovative system was proposed to overcome the major problem of particles' agglomeration during the solution combustion synthesis (SCS) process by using external oxygen sources, named OSCS. The effect of self-sustained exothermic SCS and OSCS process parameters on the structural properties and antioxidant activity of β-MnO2 nanoparticles were investigated theoretically and experimentally. According to ab-initio molecular dynamic (AIMD), molecular dynamic (MD) simulations and experimental results, the crystallographic parameters, kinetic of phase transformation, thermal stability, microstructure, and the super-lattice defects of SCS and OSCS synthesized β-MnO2 nanoparticles relied on the high established vacuum during the process. Interestingly, the specific surface area (SBET) of the OSCS products was increased ∼ 4 times, and particle size and band-gap (Eg) were significantly decreased. The results showed the synthesized β-MnO2 nanoparticles were non-toxic with a high potential against free radicals; the calculated adsorption energy of O2 on the (110) surface of the standard and SCS synthesized β-MnO2 was about 0.19 and 6.85 eV, respectively.

Interference of oxygen during the solution combustion synthesis process of ZnO particles: Experimental and data modeling approaches

In the present study, the ratio of reducing to oxidizing (F/O) elements as an indicator for maximum oxygen interference during the solution combustion synthesis (SCS) process of ZnO particles was determined using simple mathematical calculations. The obtained result was called special point (S.P). To interpret the role of S.P in the SCS reactions, ZnO particles were synthesized in the presence of citric acid, hexamine, hydrazine, and urea with various F/O values (0.75, 1, 1.25). The correlations between the S.P, physicochemical properties of the synthesized ZnO powders, and density functional theory (DFT) predictions were investigated. X-ray diffraction results, band-gap values, oxygen vacancy data, DFT results, and S.P points demonstrated the direct relation of these parameters. According to the S.P idea, it can be affirmed that the structural defects, particle size, optical band-gap (Eg = 3.06), the color of the products, the magnetic properties (0.2 emu/g), and the antibacterial inhibitory (15.625 µg/mL) of the synthesized particles were controlled via the interference of O2 during the synthesis process. In fact, the S.P investigation was suggested that the reaction rate of the combustion synthesis process could regulate the properties of ZnO particles.

Thermal Analysis of Metal-Organic Precursors for Functional Cu:ΝiOx Hole Transporting Layer in Inverted Perovskite Solar Cells: Role of Solution Combustion Chemistry in Cu:ΝiOx Thin Films Processing.

Low temperature solution combustion synthesis emerges as a facile method for the synthesis of functional metal oxides thin films for electronic applications. We study the solution combustion synthesis process of Cu:NiOx using different molar ratios (w/o, 0.1 and 1.5) of fuel acetylacetone (Acac) to oxidizer (Cu, Ni Nitrates) as a function of thermal annealing temperatures 150, 200, and 300 °C. The solution combustion synthesis process, in both thin films and bulk Cu:NiOx, is investigated. Thermal analysis studies using TGA and DTA reveal that the Cu:NiOx thin films show a more gradual mass loss while the bulk Cu:NiOx exhibits a distinct combustion process. The thin films can crystallize to Cu:NiOx at an annealing temperature of 300 °C, irrespective of the Acac/Oxidizer ratio, whereas lower annealing temperatures (150 and 200 °C) produce amorphous materials. A detail characterization study of solution combustion synthesized Cu:NiOx, including XPS, UV-Vis, AFM, and Contact angle measurements, is presented. Finally, 50 nm Cu:NiOx thin films are introduced as HTLs within the inverted perovskite solar cell device architecture. The Cu:NiOx HTL annealed at 150 and 200 °C provided PVSCs with limited functionality, whereas efficient triple-cation Cs0.04(MA0.17FA0.83)0.96 Pb(I0.83Br0.17)3-based PVSCs achieved for Cu:NiOx HTLs for annealing temperature of 300 °C.

Characteristics of Porous YAG:Ce Nano-Powders Phosphor Fabricated by a Solution Combustion Synthesis.

A cerium-doped YAG (Y₃Al5O12) phosphor is used as a rare-earth element phosphor for blue light absorption and yellow light emission for a white light source. A solution combustion synthesis, which is a method for producing nano-powder, is a reaction that is spontaneous ignition by reaction heat released through oxidation/reduction reaction between metal nitrate and fuel. Since the reaction speed is fast and it does not go through a separate firing process, it is a method of easily synthesizing nano-powder by simple process. In this study, YAG:Ce nano-powders were prepared by using various fuels in the combustion synthesis method. Depending on the kind of the additive fuel, the reaction of the combustion synthesis process was different, and the shape of the powder particles according to the fuels was also different. The agglomerated particles of nanoparticles were observed and the characteristics of YAG:Ce powders synthesized under various conditions were analyzed.