Salt-assisted Combustion Synthesis Research Articles

Combustion Synthesis of Aluminum Oxynitride in Loose Powder Beds.

This paper describes combusting loose powder beds of mixtures of aluminum metal powders and aluminum oxide powders with various grain sizes under various nitrogen pressure. The synthesis conditions required at least 20/80 weight ratio of aluminum metal powder to alumina powder in the mix to reach approximately 80 wt% of γ-AlON in the products. Finely ground fused white alumina with a mean grain size of 5 μm was sufficient to achieve results similar to very fine alumina with 0.3 μm grains. A lower nitrogen pressure of 1 MPa provided good results, allowing a less robust apparatus to be used. The salt-assisted combustion synthesis upon addition of 10 wt% of ammonium nitrite resulted in a slight increase in product yield and allowed lower aluminum metal powder content in mixes to be ignited. Increasing the charge mass five times resulted in a very similar γ-AlON yield, providing a promising technology for scaling up. Synthesis in loose powder beds could be utilized for effective production of relatively cheap and uniform AlON powder, which could be easily prepared for forming and sintering without intensive grounding and milling, which usually introduce serious contamination.

Enhancing the electrocatalytic properties of LaMnO3 by tuning surface oxygen deficiency through salt assisted combustion synthesis

In this work, we report a detailed investigation on the salt assisted combustion synthesis of LaMnO3 perovskite catalyst for improving the electrochemical properties through agglomeration control and enhanced oxygen defects for fuel cell and battery applications. The main challenge in conventional solution combustion synthesis (SCS) is the nanoparticle agglomeration that masks the active sites in catalysts. Herein, we follow a salt assisted solution combustion synthesis route to synthesize LaMnO3 perovskites (LaMnO3-SA) with a lower level of agglomeration and investigate its application for oxygen electrocatalysis. Through an effective incorporation of salt in the redox combustion mixture, the surface area of the particles doubled along with an improved pore size and pore volume distribution. The surface analysis by x-ray photoelectron spectroscopy indicated the formation of more surface oxygen defects with the introduction of inert salt that helps the absorption of oxygenated species during electrochemical process. Remarkably, LaMnO3-SA showed superior characteristics in terms of limiting current density, onset potential and half wave potential displaying enhanced bifunctionality towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The mass activity of LaMnO3-SA was almost double and kinetic current density was threefold the value at -0.25 V in comparison to the traditional SCS LaMnO3. This work demonstrates that active sites accessible for oxygen electrocatalysis in solution combustion synthesis can be enhanced through the introduction of an inert salt during the synthesis.

Characterization of Amorphous Boron Powders Prepared by Salt-assisted Combustion Synthesis

Characterization of Amorphous Boron Powders Prepared by Salt-assisted Combustion Synthesis

Submicron LaB6 powders with high purity prepared in large scale by salt-assisted combustion synthesis

LaB6 powders were synthesized in large scale by salt-assisted combustion synthesis (CS) with different NaCl diluent contents. The variety of phases, particle size and purity of the powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscope (TEM). With increase of NaCl content, the adiabatic combustion temperature of the reaction system linearly declines, the average particle size of leached products decreases, the impurity phases are easier to remove, and the products purity enhances obviously. When NaCl content is 40 wt%, the purity of the superfine powders of LaB6 is more than 98 wt%, and the average particle size is 380 nm.

Simple salt-assisted combustion synthesis of Nd2Sn2O7–SnO2 nanocomposites with different amino acids as fuel: an efficient photocatalyst for the degradation of methyl orange dye

Highly photocatalytically active Nd2Sn2O7–SnO2 nanocomposites have been prepared through a simple salt-assisted combustion approach. NaCl as dispersing agent and different amino acids as fuel and capping agent have been utilized to prepare Nd2Sn2O7–SnO2 nanocomposites for the first time. The as-obtained Nd2Sn2O7–SnO2 nanocomposites have been analyzed by TEM, FT-IR, UV–Vis, EDX, FESEM, and XRD. According to the FESEM and XRD investigations of the as-synthesized nanocomposites, it was found that grain size, shape and purity of the nanocomposites are controlled by setting the factors such as the tin source and amino acid type. Additionally, the photocatalytic behaviour of Nd2Sn2O7–SnO2 nanocomposites was evaluated by photodegradation of methyl orange dye.

Effect of Carbon Content on Morphology, Size and Phase of Submicron Tungsten Carbide Powders by Salt-assisted Combustion Synthesis

Abstract The diluent NaCl was introduced into the WO 3 -Mg-C-Na 2 CO 3 system to prepare submicron tungsten carbide (WC) powders via salt-assisted combustion synthesis. The products were analyzed by SEM, EDS and XRD, and the effects of C content on morphology, average particle size and phase composition of the products were studied. Results show that on basis of the m = 0.125 (the number of moles of Na 2 CO 3 ), when the number of moles of carbon in raw material increases from l =2 to 2.25 and 2.5, before leaching, the product is made up of a small number of large size particles and a large number of small size particles; after leaching, samples are composed of aggregates of submicron particles, and the sintering phenomenon between particles is very weak, indicating low degree of aggregation. Particle size distribution of leached product almost falls into the normal distribution, and the particle sizes range from 200 nm to 350 nm. Under the condition of l =2.25, a main target product is WC, and the content of by-products W 2 C is extremely few. That is, k = 2.0 (the number of moles of NaCl), m = 0.125, and l =2.25 are the process conditions for single-phase WC synthesis.

Fabrication of AlN particles and whiskers via salt-assisted combustion synthesis

High-quality AlN ceramic particles and whiskers were synthesized via salt-assisted combustion with the addition of AlN and NaCl, KCl, or MgCl2 to the raw Al powders. The experiments were carried out at nitrogen pressures between 0.2 and 1.0MPa. The results show that 20–30mass% salt is required to achieve complete nitridation of Al. The sensible and latent heats of these salts afford effective heat absorption during the reaction, which greatly reduces the amount of diluent AlN required compared with the conventional combustion synthesis of AlN. In addition, AlN particles are obtained when NaCl or KCl is added, whereas irregular whiskers are obtained with MgCl2.

Fabrication of mixed α/β-SiAlON powders via salt-assisted combustion synthesis

High-quality Y- and Ca-α/β-SiAlON and α-SiAlON ceramics were synthesized via salt-assisted combustion synthesis from Si, Al, and metal oxide (Y2O3 and CaO) with the addition of NaCl and MgCl2 under a nitrogen pressure of 1MPa. NaCl and MgCl2 were employed as they act as excellent diluents that effectively absorb the reaction heat through melting and evaporation. We found that the type of metal chlorides employed significantly affected the α/β ratio and the morphology of the product, with the use of NaCl affording high α/β ratios and equiaxed morphologies, while the use of MgCl2 resulting in low α/β ratios and elongated grains. The results of this work suggest that high-purity α/β-SiAlON composite products of intended α/β ratios can be successfully fabricated by controlling the initial metal chloride content.

The Effect of Silicon Powder Characteristics on the Combustion of Silicon/Teflon/Viton Nanoenergetics

AbstractDue to its thin passivation layer, potentially good aging characteristics, and ease of surface functionalization nanoscale silicon (Si) may offer some advantages over nanoaluminum as a reactive fuel in nanoenergetic compositions, particularly with fluorine‐based oxidizers. Currently, Si nanopowder can be quite expensive and the quality of commercial powders has been found to vary drastically. As a result limited efforts have focused on the role of specific surface area, active content, morphology, and dominant particle size of the powder have on the combustion performance. In this work we report the effect of such characteristics on the combustion of silicon (Si)/polytetrafluoroethylene (Teflon)/FC‐2175 (Viton) (SiTV) nanoenergetics. A cost effective combustion synthesis route, salt assisted combustion synthesis, was used to produce several Si powders and these were directly compared to commercial nanoscale Si powders. Reactive mixtures of SiTV were burned at atmospheric conditions and burning rates, combustion temperatures, spectral intensities, and effective plume emissivities were measured. Measured combustion temperatures ranged from 1664 to 2380 K and were limited by Si powder active content. This was found to drive plume emissivity and maximum spectral intensity, which had values ranging from 0.10 to 0.55 for effective plume emissivity and 17.6 to 48.1 kW m−2 sr−1 μm−1 for maximum spectral intensity. Burning rates ranged from 0.7 to 3.4 mm s−1 and were found to be dependent on the dominant particle size of the powder. Powders synthesized with salt assisted combustion resulted in comparable burning rate, plume emissivity and maximum spectral intensity to porous Si powder (Vesta Ceramics).

Morphology control of β-SiAlON via salt-assisted combustion synthesis

A facile salt-assisted combustion synthesis of β-SiAlON and systematic characterization of the endothermic effects of addition of KCl, MgCl 2 , and CaCl 2 were investigated under a nitrogen pressure of 1 MPa. Single-phase products containing crystals with different shapes were obtained. The results indicated that the metal chlorides act as perfect diluents that effectively absorb the reaction heat via their melting and evaporation, which occur in the same temperature ranges as the two stages of the exothermic processes. In addition, the products exhibited different morphologies when the type or amount of metal chlorides was changed. The results of this work suggest that single-phase β-SiAlON could be fabricated with the intended morphology by simply adding different kinds of metal chlorides.

Salt-assisted combustion synthesis of β-SiAlON fine powders

A novel method of producing submicron-size β-SiAlON powders by combustion synthesis using NaCl as a diluent was proposed. The combustion synthesis was carried out with the raw materials Si, SiO2, and Al powders, and varying amounts of NaCl under a nitrogen pressure of 1 MPa. Phase compositions and particle morphologies of the synthesized powders were analyzed. The results revealed that as the z-values increased, the amount of NaCl needed to complete the reaction increased, which in turn decreased the particle size of the product. With small z-values, single-phase products were obtained; however, with large z-values, NaCl and unreacted Si remained in the products due to the large amount of liquid phase. NaCl acted not only as a diluent by absorbing the heat generated by the reaction but also as a diffusion barrier between β-SiAlON particles, which greatly limited the growth of β-SiAlON crystals.

A Convenient Method for Preparing Well-Dispersed Er<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> Nanocrystals

Well-dispersed fluorite Er2Zr2O7 nanocrystals have been successfully prepared by a convenient salt-assistant combustion method. The effects of calcinations temperature and salt category on the characteristics of the products were investigated by XRD and TEM. The thermal treatment temperature has an important effect on crystal size and lattice distortion of the nanocrystals. The experiment showed that the introduction of salt in the combustion synthesis process resulted in the formation of well-dispersed Er2Zr2O7 nanocrystals. The average size was 30 nm and was in agreement with the XRD result, which indicated that the nanocrystals were uniform in particle size distribution. Moreover, the possible formation process in the salt-assisted combustion synthesis was also analyzed.

Salt-assisted combustion synthesis of silicon nitride with high α-phase content

This paper presents the results showing the effect of adding varying amounts of additives, such as NH 4Cl, NaN 3, and NaCl on the ratio of α/β-Si 3N 4 prepared by nitridation of micrometer size silicon powder by combustion synthesis. The nitridation process was performed under 6.0 MPa pressure of nitrogen, and the content of α/β-Si 3N 4 in the final product was examined using intensity of the peaks in the XRD patterns. The resultant was a mixture of α-Si 3N 4 and β-Si 3N 4, where a rapid increase of α-phase was found after addition of NaCl. In the optimized synthesis conditions, micrometer size Si 3N 4 powder with ∼90% of α-phase was obtained. The reaction mechanism is discussed with respect to the combustion temperature and the amount of NaCl.

Molten salt-assisted combustion synthesis and characterization of MoSi2 and MoSi2-Si3N4 composite powders

Abstract The possibilities of the synthesis of submicron MoSi2 and MoSi2–Si3N4 composite powders were investigated using inorganic salt-assisted combustion synthesis method. Combustion laws in the MoO3–3Mg–2Si–NaCl and Mo–5Si–NaCl–Si3N4–N2 systems were studied. The main factors influencing the combustion parameters, phase composition and microstructure of products for both these systems were determined experimentally. Optimum synthesis conditions of submicron MoSi2 and MoSi2–Si3N4 composite powders containing 30–40 wt.% of molybdenum disilicide were determined. Compacting conditions for 30 wt.% MoSi2–70 wt.% Si3N4 composite using the hot pressing technique were found. Compact samples 20 mm in diameter were obtained. Microstructure, phase and chemical compositions of the dense samples were studied.

자전연소합성법에서의 알칼리염을 이용한 WC 분말의 제조

Tungsten carbide powder was synthesized by SHS (self-propagating high-temperature synthesis). Except WO₃, each concentration of raw material (WO₃, Mg, NaCl, Na₂CO₃, C) was investigated. Final product was characterized by XRD and SEM. X-ray data demonstrated that the NaCl+Na₂CO₃ combined mixture has superiority in the WC formation process. Single phase and submicrometer WC powder was synthesized at the temperature below 1600℃. The role of sodium salts in combustion process was discussed, and chemical mechanism of WC formation was proposed. WC powder prepared by salt-assisted combustion synthesis has a size 0.2~3 μm and low agglomeration degree.

Novel Salt-Assisted Combustion Synthesis of High Surface Area Ceria Nanopowders by An Ethylene Glycol-Nitrate Combustion Process

A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area ceria nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion sunthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ∼ 6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m 2·g −1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m 2·g −1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.

Salt-assisted combustion synthesis of highly dispersed perovskite NdCoO 3 nanoparticles

Highly dispersed perovskite NdCoO 3 nanoparticles with an average particle size of about 9 nm have been successfully prepared by a novel salt-assisted combustion process. The effects of NaCl content and calcination temperature on the characteristics of the products were investigated by XRD, TEM and BET nitrogen adsorption. The facile introduction of NaCl in the conventional combustion synthesis process was found to result in the formation of well-dispersed perovskite nanoparticles and increase specific surface area of the resultants from 1.70 to 43.22 m 2·g − 1 . A mechanism scheme was proposed to illustrate the possible formation processes.

Combustion synthesis of WC powder in the presence of alkali salts

This paper deals with the formation of tungsten carbide sub-micrometer powders from WO3+Mg+C+sodium salts (NaCl, Na2CO3) system by combustion synthesis technique. The powders were characterized by XRD and FESEM. X-ray data demonstrate the superiority of the NaCl+Na2CO3 combined mixture in the WC formation process. Single phase, sub-micrometer WC powders were synthesized at temperatures as low as 1600 °C. The roles of sodium salts in combustion process were discussed and chemical mechanism of WC formation was proposed. WC powder produced by salt-assisted combustion synthesis technique has a size 0.2–3 μm, crystalline shape and low agglomeration degree.