Combustion Synthesis Reaction Research Articles

Characterization of NOx Release during Combustion Synthesis and Cyclic Reaction Performance of Cu-Based Oxygen Carriers Prepared with Citric Acid

Characterization of NO_<i>x</i> Release during Combustion Synthesis and Cyclic Reaction Performance of Cu-Based Oxygen Carriers Prepared with Citric Acid

Direct Production of Ferromolybdenum from Molybdenite by Combustion Synthesis Reaction in the Presence of Aluminum

In this research, a new method for the direct and in-situ production of ferromolybdenum alloy by the combined aluminothermic reduction of molybdenum sulfide (MoS) and iron oxide Fe2O3 has been introduced and its feasibility has been investigated. Also, in order to investigate the effect of the presence or absence of a desulfurizer on the chemical composition and purity of the product, lime (CaO) and magnesia (MgO) have been used as desulfurizers. Preliminary investigations showed that the heat of reduction of molybdenum sulfide by aluminum is very high. Their reaction can be carried out as a self-promoting combustion synthesis reaction (Self-propagating high-temperature synthesis). Also, preliminary results showed that increasing the amount of iron oxide in the composition of raw materials increases the heat produced by the reaction, which results in the melting of FERROMOLYBDENUM as a reaction product. In order to examine the synthesized phases and analyze the obtained results, the images taken by the scanning electron microscope (scanning electrode microscope) and the data obtained from the analysis (Energy-dispersive spectroscopy) were used. Also, X-Ray Diffraction Analysis was used to analyze the formed slag. The results indicate that the reaction carried out in the presence of magnesia as a desulfurizer is a more successful system in absorbing sulfur from the produced alloy.

Effect of the synthesis route on luminescence dynamics and thermographic properties of Sm3+ doped Ba2Mg(PO4)2 phosphor

The present study investigates the impact of synthesis routes on the structure, optical, and thermographic properties of Ba2Mg(PO4)2:xSm3+ (x = 2 mol.%) phosphor. The two techniques used for the synthesis were combustion synthesis (CS) and solid-state reaction synthesis (SSR). X-ray diffraction analysis confirmed a pure monoclinic phase with space group P21/n in both SSR and CS synthesized samples. The average crystallite size was 41 ± 0.19 nm for SSR and 21 ± 0.02 nm for CS phosphors. Using Fourier transform infrared (FTIR) analysis, the vibrational behavior of both synthesized phosphor samples was analyzed. Both samples displayed a bright orange-red photoluminescence (PL) emission, attributed to the 4G5/2→6H7/2 transition when excited with 403 nm light at room temperature. However, the intensity of PL emission was higher in the CS-prepared sample. The UV-Vis absorption measurements indicated several bands in both samples. The CIE coordinates were calculated for both samples and they corresponded to the shade of orange-red emission of the Sm3+ ions. The study also included an investigation into the temperature-sensing characteristics of the synthesized phosphors, which was performed in the 323–673 K temperature range. The fluorescence intensity ratio (FIR) technique was used to study the non-contact temperature sensing for both samples, and the CS-prepared phosphors exhibited the maximum value of absolute sensitivity (0.00629 K−1) and relative sensitivity (0.26 % K−1) at temperature 673 K. Overall, the results indicate that the CS method provides better results in terms of luminescence and temperature sensing characteristics compared to the SSR method.

Hardening Mechanism of Thick (Ti,Cr,V)N Composite Coatings with Multi-layer Nano-columnar Dendrites Microstructure

The 300 μm thick (Ti,Cr,V)N nanocomposite coatings were prepared by plasma spraying technique combined with combustion synthesis reaction of N and Ti-Cr-V reconstituted composite powders, and their microstructure and hardening mechanism were explored. The phases and microstructures were analysed by X-ray diffractometer, X-ray photoelectron spectroscopy and scanning electron microscopy, transmission electron microscopy, respectively, and a microhardness tester was employed to measure the microhardness. The main phase of the composite coating is (Ti,Cr,V)N solid solution, which has a multilayered structure of elongated columnar dendrites arranged in parallel, with different solidification positions resulting in crystal bundles possibly having different orientations. The composite coating has nanoscale fine crystals, as well as two typical strengthening models, "dislocation-TB" and "lattice distortion", which together contribute to the high hardness of the (Ti,Cr,V)N composite coating. The (Ti,Cr,V)N composite coating containing 10wt.% Cr has better surface morphology and the highest microhardness value (1844.80 HV0.5).

Combustion synthesis of high yield Ti3SiC2 from TiC0.67 with induction heating assistance

Combustion synthesis of Ti3SiC2 MAX phase was first reported more than 30 years ago, yet it has not become a widespread method, because of unavoidable presence of TiC as a by-product. Here we report high-purity Ti3SiC2 powders free of TiC by-products synthesized with a high yield using TiC0.67 and elemental powders as starting materials by combustion synthesis method with an induction heating (IH) assistance. By using IH assistance, ignition of the reaction and subsequent post-heating aimed to complete the reaction were done in one process. The addition of TiC0.67 was used to control the exothermic effect of the reaction and facilitate the reaction between three elements. Moreover, to improve the reactivity of the starting powders, a small amount of Al was added. As a result, TiC-free high-purity Ti3SiC2 powders were synthesized under IH ignition and post-heating at 1400 °C for 10 min in Ar flow. It was concluded that the combustion synthesis reaction can be effectively controlled using IH assistance, resulting in the product with a high yield. Furthermore, the addition of TiC0.67 provided a direct synthetic route of Ti3SiC2 without intermediate phases, and the addition of Al decreased the negative effects of oxygen in the starting powders. The present method bridges the advantages of the combustion synthesis method such as short time and low energy consumption and precise and fast control of heating conditions provided by IH, and is considered to be perspective for the synthesis of other MAX phases.

Crystal structure and photoluminescence of ZnSe and ZnSe:Mn nanocrystals obtained by combustion synthesis

ZnSe and ZnSe:Mn nanocrystals were obtained by combustion synthesis (self-propagating high-temperature synthesis) using current pulses to initiate a reaction with amplitudes of ∼35 A and ∼40 A. The magnitude of the amplitude of the current pulse affects the size of the nanocrystals, their phase composition, the ratio of the cubic and hexagonal phases, the degree of microstresses and the density of dislocations. The inclusion of Mn dopants into ZnSe has little effect on the nanocrystal morphology and strongly influences the morphology of polycrystals. An EPR spectrum of Mn2+ ions with a hyperfine structure constant A = 6.55 mТ and a g-factor g = 2.0055, which is due to Mn2+ ions in a cubic environment, was found in self-activated and doped ZnSe and ZnSe: Mn nanocrystals. It was found that increasing the amplitude of the current pulse, which initiates the combustion synthesis reaction, increases the intensity of the diffusion processes and more effective isovalent substitution of Zn2+ ions by Mn2+ ions in the crystal lattice of ZnSe nanocrystals. The photoluminescence spectra of ZnSe and ZnSe:Mn nanocrystals were investigated, and individual emission bands were detected in the integral spectra. There were three such individual bands in the photoluminescence spectrum of ZnSe nanocrystals. Their maxima were characterized using the following parameters: λ max = 592 nm (E = 2.095 eV), λ max = 543 nm (E = 2.282 eV), and λ max = 505 nm (E = 2.455 eV). Six individual emission bands were detected in the photoluminescence spectra of ZnSe:Mn nanocrystals with the parameters: λ max = 675. 5 nm (E = 1.835 eV), λ max = 642.5 nm (E = 1.929 eV), λ max = 613 nm (E = 2.022 eV), λ max = 583.5 nm (E = 2.124 eV), λ max = 550 nm (E = 2.255 eV), λ max = 528.5 nm (E = 2.345 eV). This paper discusses the nature of the centers of radiative recombination of individual bands.

Preparation and Characterization of In Situ (TiC-TiB2)/Al-Cu-Mg-Si Composites with High Strength and Wear Resistance.

This study involved the preparation and characterization of in situ (TiC-TiB2)/Al-4.7Cu-0.32Mg-0.44Si composites with excellent mechanical and abrasive wear properties. The composites were synthesized in an Al-Ti-B4C system by combining combustion reaction synthesis with hot-pressed sintering and hot extrusion. The in situ TiB2 and TiC particles were of multi-scaled sizes ranging from 20 nm to 1.3 μm. The TiB2 and TiC particles effectively increased the yield strength (σ0.2), ultimate tensile strength (σUTS), hardness (HV), and abrasive wear resistance of the composites. The 40 wt.% (TiC-TiB2)/Al-4.7Cu-0.32Mg-0.44Si composite exhibited the highest σ0.2 (569 MPa), σUTS (704 MPa) and hardness (286 HV), which were 74%, 51% and 110% higher than those of the matrix alloy, respectively. Compared with the matrix alloy, the abrasive wear resistance of the 40 wt.% (TiC-TiB2)/Al-4.7Cu-0.32Mg-0.44Si composite was increased by 4.17 times under an applied load of 5 N and Al2O3 abrasive particle size of 13 µm. Micro-ploughing and micro-cutting were the main abrasive wear mechanisms for the Al-Cu-Mg-Si alloy and the composites.

Self-propagating combustion synthesis of few-layer graphene for supercapacitors from CO and Mg

Graphene is considered as a promising electrode material for supercapacitors due to its large specific surface area, excellent electrical conductivity and so on. In this paper, few-layer graphene is prepared by self-propagating combustion reaction between CO and metal magnesium, using powder MgO as deposition template. Graphene with a high specific surface area of up to 928 m 2 g −1 replicates the morphological feature of powder MgO. Raman spectroscopy analysis demonstrates that the graphene layer decreases when the dosage of MgO template is increased. The specific capacitance of as-prepared sample exhibits the highest specific capacitance of 222 F g −1 at the current density of 1 A g −1 in EMI [TFSI] electrolyte. The sample demonstrates a "double high" performance with high specific energy density and high specific power density. A high energy density of 76.3 Wh kg −1 can be achieved at a specific power density of 1.75 kW kg −1 , and it can still remain 48.6 Wh kg −1 when the specific power density reaches a high level of 35 kW kg −1 . • Self-propagating combustion reaction synthesis graphene. • Synthesis graphene from CO and Mg. • Synthesized graphene has good structural properties. • Excellent capacitive performances in the electrolyte of EMI [TFSI].

Dissimilar joining of cemented carbide to low-carbon steel via combustion welding: Effect of process parameters on the interfacial microstructure and joint strength

An innovative method based on pressure-assisted combustion synthesis reactions in compressed powder mixtures of nickel and titanium was developed to join WC-Co cemented carbide to VCN-150 steel (Standard No. 1.6582). A specially-designed experimental setup was used for induction heating of the samples under uniaxial pressure in an argon atmosphere. Rapid heating of the samples provoked the exothermic reaction between Ni and Ti, resulting in the in-situ formation of an NiTi-based intermediate layer between the steel and carbide parts. XRD and SEM-EDS analyses as well as shear strength test were used to characterize the samples and evaluate the quality of the joint. XRD analysis showed NiTi as the main phase in the joining layer. It was found out that a decrease in Ni particle size led to an increase in the contact surfaces of the powders and intensity of the reaction, resulting in improved adhesion of the joining parts, decreased porosity within the interlayer, and increase in the average shear strength. Although increasing the thickness of the bonding layer resulted in more intensive reactions, higher liberated heat, and wider diffusion layers at the interface, it led to relatively weak joints due to a rise in the volume percentage of porosity. The most favorable results in welding were obtained by using fine particles of the reactants and minimum thickness of the green interlayer (2 mm). By increasing the applied force during the process to ~600 N, shear strengths up to ~77 MPa could be obtained.

Progress of porous Al-containing intermetallics fabricated by combustion synthesis reactions: a review

Recently, research on the preparation of porous Al-containing intermetallic compounds using combustion synthesis (CS) reaction in combination with a space holder process has been gradually increased, in order to improve the porosity and obtain the pore structures with controllable pore morphology and pore size. The reaction mechanism for the M–Al (M = Ti, Ni, Fe, Nb, and Cu) system is closely related to the state of aluminum (e.g., solid or liquid phase) and is greatly affected by processing parameters such as particle size, Al content, heating rate, compacting pressure, sintering temperature, content, and the type of pore-forming agents. Once the sintering temperature causes the appearance of one liquid phase in the reaction system, the remaining solid reactant quickly dissolves into the molten one to improve the surface contact and then generate considerable heat to complete the combustion reaction. Interestingly, the actual temperature change of the sample during the sintering process is accurately detected, and the transparent observation of the reaction state is also realized, which provides a new vision for further exploration of the reaction mechanism of other compounds.

Synthesis and photocatalytic investigation of ZnFe2O4 in the degradation of organic dyes under visible light

Zinc ferrites (ZnFe2O4), with spinel-like structure, were produced by combustion reaction synthesis in solution and heat-treated at temperatures of 400–1100 °C. The structural and chemical properties of the ZnFe2O4 samples were investigated by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), Field Emission Gun Scanning Electron Microscopy (FEG-SEM) with X-ray dispersive spectroscopy (EDS), and diffuse reflectance spectroscopy (DRS) in the ultraviolet (Uv–vis) region. The photocatalytic performance of this compound was investigated in order to evaluate the green malachite and rhodamine B dyes degradation under visible irradiation. The XRD patterns results reveal the presence of cubic ZnFe2O4 at all heat-treated temperatures and pure phase above 800 °C. The presence of spherical and porous agglomerate morphology was confirmed through SEM analysis. Absorption bands between 400 and 600 cm−1 in the infrared spectra confirmed the presence of the ferrite phase. Diffuse reflectance results on the ZnFe2O4 samples showed that absorption occurred in the visible light range. The best temperature of the photocatalytic degradation performance of the dyes was 400 °C. This was more pronounced for the green malachite dye when compared to rhodamine B due to secondary phases and smaller crystal sizes.

In-situ chemical reaction mechanism and non-equilibrium microstructural evolution of (TiB2 + TiC)/AlSi10Mg composites prepared by SLM-CS processing

The preparation of aluminum matrix composites (AMCs) by laser additive manufacturing (AM) technology has become an important means of improving performance of aluminum alloys. In this work, a novel in-situ synthesis method of selective laser melting combined combustion synthesis (SLM-CS) was used to prepare dual-phase reinforced AMCs. The feasibility of a B4C–Ti combustion synthesis reaction system to produce TiB2 and TiC ceramics by selective laser melting (SLM) was verified. AlSi10Mg alloy matrix composites with dual reinforcements were then fabricated by SLM, and systematic qualitative and quantitative phase analysis was carried out. The calculation results of the graphical-extrapolation method show that the lattice constant of α-Al matrix phase in the composites increases from 0.40466 nm to 0.40528 nm. The effects of a series of reactants with different chemical element composition ratios on the characteristics of melting process and non-equilibrium solidification microstructure were studied. The preliminary principles of the combustion chemical reaction under the rapid and continuous laser scanning were concluded from the theory and experiments results. In terms of mechanical properties, an appropriate amount of ceramic particles results in a significant improvement in the microhardness and elastic modulus, and yet composites prepared with a mixture powder amount greater than 0.7 wt % witnessing a clear drop in the tensile strength as well.

A new method of preparing high-performance high-entropy alloys through high-gravity combustion synthesis

A new method of high-gravity combustion synthesis (HGCS) followed by post-treatment (PT) is reported for preparing high-performance high-entropy alloys (HEAs), Cr0.9FeNi2.5V0.2Al0.5 alloy, whereby cheap thermite powder is used as the raw material. In this process, the HEA melt and the ceramic melt are rapidly formed by a strong exothermic combustion synthesis reaction and completely separated under a high-gravity field. Then, the master alloy is obtained after cooling. Subsequently, the master alloy is sequentially subjected to conventional vacuum arc melting (VAM), homogenization treatment, cold rolling, and annealing treatment to realize a tensile strength, yield strength, and elongation of 1250 MPa, 1075 MPa, and 2.9%, respectively. The present method is increasingly attractive due to its low cost of raw materials and the intermediate product obtained without high-temperature heating. Based on the calculation of phase separation kinetics in the high-temperature melt, it is expected that the final alloys with high performance can be prepared directly across master alloys with higher high-gravity coefficients.

Fuel-lean combustion synthesized cobalt catalysts for Fischer-Tropsch reaction

The present study investigates synthesis of liquid fuels and higher hydrocarbons via Fischer Tropsch (FT) reaction using combustion synthesis (CS) catalysts. The CS method employed citric acid (C6H8O7) as fuel with lean stoichiometry (ϕ = 0.3, ϕ = 0.6) for the catalyst synthesis. CS reactions at lean conditions can be easily controlled, and holds the structural integrity of the catalyst support, resulting in no loss of active sites. The fuel-lean conditions show decreased formation of cobalt aluminates, resulting in high catalyst reducibility and larger fraction of active sites. When tested at constant space velocity, the CS catalysts achieve CO conversion up to 88%, which is 57% higher than the wet impregnation (WI) synthesized catalysts. Furthermore, the variation of the equivalence ratio allows to tailor the catalyst properties and thereby control conversion and selectivity of the CS catalysts. CS(ϕ = 0.6) showed a C5+ selectivity 31% higher compared to the CS(ϕ = 0.3). The liquid fuel space time yield (STY) ranged from 0.13 to 0.30 (gC5+ gcat-1 h-1) and it increases in the following order: WI < CS(ϕ = 0.3) < CS(ϕ = 0.6). These results emphasize the effectiveness of the CS method for the synthesis of FT catalysts and show the effect of the lean-fuel stoichiometry on the catalyst properties and performance.

Fabrication and mechanical properties of (Mo0.9W0.1)(Si0.4Al0.6)2 composites reinforced by TiC

TiC-(Mo0.9W0.1)(Si0.4Al0.6)2 composites were prepared from Mo, W, Si, Al and TiC powders via self-propagating high-temperature synthesis and hot pressing. The propagation mode of the combustion synthesis reaction and the influence of different TiC contents (0, 5, 10, 15, 20, 25 and 30 vol%) on the mechanical properties of (Mo0.9W0.1)(Si0.4Al0.6)2 were investigated. The results showed that the combustion propagation mode was steady from 0.00 to 2.06 s and unsteady from 2.06 to 6.45 s. The composites were mainly composed of MoSi2 (C11b) and TiC. The bending strength, Vickers hardness, and fracture toughness of the 0–30 vol% TiC-(Mo0.9W0.1)(Si0.4Al0.6)2 composites were 270–433 MPa, 9.60–14.85 GPa and 6.40–9.73 MPa · m1/2, respectively. These results indicated that TiC doping could effectively improve the mechanical properties of (Mo0.9W0.1)(Si0.4Al0.6)2.

Effect of the residual water content in gels on solution combustion synthesis temperature

The composition of gels and xerogels, as well as their transformation during heating and dehydration, determine the thermochemistry of solution combustion synthesis reactions. An improved descriptive thermodynamic model of combustion processes was formulated on the basis of the investigated formation of complex compounds of metal ions with organic fuel (glycine, citric acid, urea, and PVA) in nitrate solutions. The intensity of SCS reactions was found to depend on the strength of Ni2+–ligand complexes. The effect of heat loss during combustion on the ΔTmax value was analyzed for the model system Ni(NO3)2·nH2O–Fuel–H2O. It was found the heat loss occurs due to the presence of various amounts of structurally-bound water in gels and xerogels before the combustion.

High-entropy transition metal diborides by reactive and non-reactive spark plasma sintering: A comparative investigation

The direct synthesis and consolidation by SPS (1950 °C, 20 min, 20 MPa) of high-entropy (Hf0.2Mo0.2Zr0.2Nb0.2Ti0.2)B2 from elemental powders resulted in a multiphase product. An increase of the heating rate determined a change of the mechanism governing the synthesis reaction from gradual solid-state diffusion to rapid combustion regime, while the final conversion degree was 67 wt.%. The sintered product displayed a non-uniform microstructure with the presence of 10–15 μm sized pores, due to volatilization phenomena occurring during the combustion synthesis reaction. In contrast, when the SPS process was preceded by powder synthesis via SHS, a homogeneous single-phase ceramic was obtained. Clear benefits are derived by the use of SHS, able to provide very shortly powders with elemental species very well intermixed, so that the obtainment of (Hf0.2Mo0.2Zr0.2Nb0.2Ti0.2)B2 during the subsequent SPS stage is strongly promoted. The resulting 92.5% dense product shows superior oxidation resistance with respect to individual borides prepared with the same method.

Magnesium Phosphate Cements/GNPs Composites by Combustion Synthesis and Acid-Base Reaction

Magnesium phosphate cements (MPC)/graphene nanoplatelets (GNPs) composites were fabricated by combustion synthesis and acid-base reaction. MgO/GNPs mixture powders were obtained by the combustion reaction between Mg powders and CO2 gas. The composites were prepared by mixing MgO/GNPs mixture powders with potassium dihydrogen phosphate (KH2PO4) using borax as retarder. The effect of GNPs content on mechanical and functional properties of the prepared MPC/GNPs composites was investigated. The results show that this MPC/GNPs cements mainly consisted of MgO and KMgPO4•6H2O. Moreover, the crystallinity of KMgPO4•6H2O in lower surface is better than the upper surface due to the difference of temperature. With incorporating small amounts of GNPs into MPC, the spectral absorptivity of the composite was improved to 0.95 in most spectral regions. Nevertheless, the compression strength shows little change with changing the GNPs content, which may be attributed to use coarse MgO powder as reactant. In virtue of short processing time and homogeneous distribution of GNPs, the novel fabrication provides a new route for preparing GNPs-cement based composites.

Combustion synthesis of single‐phase Al4SiC4 powder with assistance of induction heating

AbstractTernary aluminum silicon carbide Al4SiC4 is a promising material not only in refractory applications, but also in electronics and photocatalysis. However, synthesis of Al4SiC4 requires high‐temperature heat treatment for several hours. In this work, we describe a new, fast and effective method to synthesize single‐phase Al4SiC4 powder. Our method is based on combustion synthesis reaction of Al, Si and C initiated under high‐frequency induction heating. Heating program was optimized to prevent separation of melted aluminum and provide uniform initiation, propagation and completion of the reaction. As a result, pure‐phase Al4SiC4 powder was synthesized in few minutes. Temperature profile of a sample measured during heating process showed appearance of two exothermic peaks, thus confirming propagation of a two‐step combustion reaction. Induction heating provided capability to finely and readily control external heating rate, which is considered to be one of the key factors to reach high‐purity Al4SiC4.

Combustion synthesis of Hf-doped zirconolite-rich composite waste forms and the aqueous durability

Zirconolite is recognized as one of the most durable waste matrices for the disposal of high-level radioactive wastes (HLWs). In this study, HfO2 was employed as the surrogate of tetravalent actinides. Hf-bearing zirconolite-based composite waste forms (CaZr1−xHfxTi2O7) were rapidly prepared by combustion synthesis (CS) using CuO as the oxidant, where quick pressing (QP) was introduced to obtain densified samples. Similar as solid state reaction process, the Zr site of zirconolite can be totally occupied by Hf (x = 1.0) under the CS reaction. The original 2M zirconolite structure was maintained and a small amount of perovskite impurity phase was generated in the final products. The aqueous durability of representative sample (Cu-Hf-0.6) was tested, where the 42-day normalized leaching rates (LRi) of Ca, Cu, and Hf are 0.25, 3.10×10−2, and 1.11×10−8 g·m−2·d−1.