Microwave-induced Solution Combustion Synthesis Research Articles

Fabrication, sintering behavior, and strength of tritium breeding ceramic pebbles with Pb addition

Lithium ceramics are regarded as potential candidates for tritium breeding in fusion reactors. Lead (Pb) was added to the ceramic to improve the strength and tritium release properties. The Li2TiO3-0.5Li4SiO4–Pb ceramic powders with the Pb contents of 5 wt% and 20 wt% were prepared by microwave-induced solution combustion synthesis. It was confirmed that the Pb was in the form of the Li2PbO3 phase in the powders. The Li2TiO3, Li4SiO4, and Li2PbO3 crystallites were composited at nanoscale level, which was confirmed by the transmission electron microscopy (TEM). During high-temperature sintering, the Li2PbO3 was transformed into PbO, which facilitated the densification process at low temperatures. The chemical state in the sintered body was characterized by X-ray photoelectron spectroscopy (XPS) with 3 keV Ar+ sputtering. The binding energies for Pb were 137.2 and 142.2 eV. There was almost no change in peak position during Ar+ sputtering, showing that Pb was firmly adherent with oxygen atoms. Besides, the as-synthesized powders were used for the pebble fabrication. The average crush load of Li2TiO3-0.5Li4SiO4–20%Pb pebbles sintered at 1223 K was 124 N, which was much higher than that without Pb addition. It was proved that the crush load increased almost linearly with the increase in the size of the pebbles. Thus, the bending strength of the sintered ceramic body was used to evaluate the mechanical properties. Further, the grain growth kinetics was studied. It was confirmed that the Pb addition reduced the activation energy of grain growth, which realized the densification of the ceramic pebbles at low temperatures.

A review on the synthesis of metal oxide nanomaterials by microwave induced solution combustion.

With the increasing awareness of environmental protection and health, the preparation of metal oxide nanomaterials by environmentally friendly methods is favored by more and more researchers both at home and abroad. The preparation of metal oxide nanomaterials by a microwave-induced solution combustion synthesis method can significantly reduce the reaction time, energy consumption, and the use of toxic chemicals, which is an energy-saving, environmentally friendly method for nanomaterials synthesis. In addition, the microwave-induced solution combustion synthesis (MISCS) method has many advantages such as fast reaction speed, high selectivity, small product size, and homogeneous composition. This paper briefly describes the mechanism of the MISCS and its advantages in the synthesis of metal oxide nanomaterials, the related studies on microwave-induced solution combustion synthesis of metal oxide nanomaterials, and the effects of process parameters on the microstructure and properties of metal oxide nanomaterials synthesized by MISCS. Furthermore, some technical difficulties facing the synthesis of metal oxide nanomaterials by MISCS are summarized, and the future direction has also been prospected.

Solution combustion synthesis of lithium orthosilicate as the tritium breeder: Effects of microwave power and fuel-to-oxidizer ratio on phase, microstructure and sintering

Lithium orthosilicate (Li4SiO4) is regarded as a candidate solid tritium breeding material for the fusion reactors, but the phase control and densification for this ceramic are difficult. Microwave-induced solution combustion synthesis (MSCS) offers an efficient and flexible route for preparing the tritium breeders in a single step. The combustion process can be effectively controlled by the microwave power output and the fuel-to-oxidizer ratio (ϕ), which can be taken advantage of for the phase control of the product. The results show that the combustion temperature increases linearly with the increase of the ϕ value, and the Li4SiO4 becomes the main product when the ϕ value is higher than 0.75. Lithium metasilicate (Li2SiO3) is detected in minimum quantities in the products, and its content can be reduced when the microwave power output is 1100 W, which can be further removed by calcination at 873 K for 2 h. The thermal analysis results show that the redox reaction between the LiNO3 and citric acid provides the heat for the combustion. The ceramic body can be sintered to 84% of the theoretical density at a low temperature of 1073 K, and the relative density is close to 96% with high purity at the sintering temperature of 1373 K.

Microwave-induced solution combustion synthesis and luminescent properties of nano-sized powders with different Nd concentrations

The nano-sized neodymium doped aluminum lutetium garnet (LuAG:Nd) phosphors well crystallized with particle size of around 100–130 nm were successfully synthesized via microwave-induced solution combustion method. The optimal crystallization temperature of LuAG:Nd was determined at 900 °C based on controlled trials. XRD results showed an obvious distortion in lattice parameters of LuAG, which could be confirmed by the shift of diffraction peak towards lower degrees with Nd concentration increasing. Another evidence for successful doping of neodymium was the absorption line at around 808 nm in the absorption spectra, which could result from the Nd3+ 4I9/2-4F5/2 transition. Furthermore, the near-infrared spectra showed that the quenching concentration of Nd3+ in prepared LuAG:Nd polycrystalline samples with the highest intensity of 1064 nm was at 5 mol%.

Spectroscopic study and enhanced thermostability of combustion-derived BaMgAl10O17:Eu2+ blue phosphors for solid-state lighting

Blue-emitting BaMgAl10O17:Eu2+ (BAM:Eu), suitable for applications in a next generation of Hg-free lamps based on UV LEDs, was prepared by a microwave induced solution combustion synthesis, using urea as combustion fuel and nitrates as oxidizers. Purity control of the as-synthesized blue phosphor was undertaken by a washing step followed by a reduction one. Structural and morphological properties of the outcoming phosphors have been considered. Synthesis process allows producing a well-crystallized and nanostructured BAM phase within only few minutes. The influence of reduction treatment on the relative amounts of Eu2+/Eu3+ in our samples has been investigated through an original study by magnetization and Mössbauer spectroscopy. Furthermore, a complete optical study has been carried out and allowed us to determine the europium localization in the three possible sites in BAM matrix. The percentage of Eu2+ increased twofold after the reduction treatment, entailing an increase in the luminescence efficiency upon UV excitation. Finally, temperature-dependent luminescence of combustion-derived powders has been studied till 170 °C and compared to that of commercial BAM:Eu. MISCS-derived phosphors present a higher thermal stability than commercial one: whereas the emission efficiency of this last was reduced by 64%, the one of combustion-derived BAM:Eu experienced an only 12% decline. Furthermore, while commercial BAM suffered from a severe blue-shift with increasing temperature, our phosphors keep its color quality with a good stability of the photometric parameters.

ICONE23-1090 SINGLE STEP FABRICATION OF NANO-SIZED Li4SiO4 BREEDER BY MICROWAVE-INDUCED SOLUTION COMBUSTION SYNTHESIS

Li_4SiO_4 (lithium orthosilicate) is a promising ceramic tritium breeder for the future D-T fusion reactor, which is also considered as a candidate material for Helium Cooled Pebble Bed Test Blanket Module (HCPB TBM) of China. Simple and efficient microwave-induced solution combustion synthesis (MSCS) approach was adopted to prepare Li_4SiO_4 powder by using lithium nitrate and tetraethyl orthosilicate as raw materials. In MSCS, microwave power is a key factor, which controls the combustion mode, flame temperature, phase composition, and microstructure of the product. The synthesized Li_4SiO_4 particles are homogeneous distributed with an average crystalline size of 20 nm when the microwave power is 1100 W. The Li_4SiO_4 powder shows comparable sinterability to the conventional solid state reaction, which reaches 89.2% of theoretical density at 1173 K with a small grain size of 2 μm.

Flash synthesis of Li2TiO3 powder by microwave-induced solution combustion

Nano-crystalline Li2TiO3 powder was prepared by a microwave-induced solution combustion synthesis (MSCS) route using urea as fuel. It is observed that combustion reaction, which did not occur by conventional heating, happened when microwave heating was induced. The as-synthesized Li2TiO3 powder exhibits a narrow size distribution. In MSCS, the total metal ion concentration (Cm) in the starting solution plays an important role. By changing Cm values in starting solution, SCS process including ignition time, combustion period and reaction rate can be controlled. The as-prepared powder could be sintered up to 92.6% of the theoretical density at 1223K.

Structural, morphological and optical investigations on BaMgAl10O17:Eu2+ elaborated by a microwave induced solution combustion synthesis

Abstract Blue-emitting Eu2+-doped barium magnesium aluminate (BaMgAl10O17:Eu2+) for advanced displays and lighting devices was prepared by a microwave induced solution combustion synthesis using urea as combustion fuel and nitrates as oxidizer. Purity control of as-synthesized blue phosphor particles was undertaken by modifying the fuel to oxidizer molar ratio. X-ray diffraction, scanning electron microscopy and photoluminescence were used to investigate powders crystallinity, particles size, morphology and luminescent properties, respectively. Fuel-rich urea reactions preferentially lead to pure phases compared to the powders synthesized with a stoichiometric fuel to oxidizer ratio. In both cases, we produce a nearly pure well-crystallized and nanostructured BaMgAl10O17:Eu2+. Photoluminescence measurements exhibit the characteristic blue emission of Eu2+ under UV light excitation however a weak red emission associated to Eu3+ is also detected.

A Rapid Microwave-Induced Solution Combustion Synthesis of Ceria-Based Mixed Oxides for Catalytic Applications

We have been exploring the utilization of a simple and fast microwave-induced solution combustion synthesis technique for the preparation of various ceria-based mixed oxides for different catalytic applications. In our comprehensive investigation, CeO2–SiO2 (MWCS), CeO2–TiO2 (MWCT), CeO2–ZrO2 (MWCZ) and CeO2–Al2O3 (MWCA) mixed oxides were synthesized by solution combustion synthesis method using microwave dielectric heating and employed for CO and soot oxidation applications. The intricate relationship between ceria and other supporting oxides has been explored with the help of various analytical techniques namely, X-ray diffraction (XRD), temperature programmed reduction/oxidation (TPR/TPO), temperature programmed desorption (TPD) of ammonia and CO2, Raman spectroscopy (RS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), BET surface area and thermogravimetry analysis (TGA) methods. XRD results revealed amorphous nature of the material in case of ceria-silica mixed oxide and formation of a specific cubic fluorite type Ce0.5Zr0.5O2 solid solution in the case of ceria-zirconia mixed oxide. Ceria-titania and ceria-alumina mixed oxides exhibited diffraction lines only due to crystalline ceria. Zirconia-based mixed oxide exhibited a lower reduction temperature and better redox properties compared to other samples. TPD of ammonia and CO2 results revealed superior acid–base properties for MWCS mixed oxide. TGA measurements indicated a complete combustion in all preparations. RS results suggested defective structure of mixed oxides resulting in the formation of oxygen vacancies. XPS results revealed that ceria-zirconia mixed oxide contained more Ce3+ compared to other oxides. Among all the mixed oxides, the MWCZ sample exhibited a higher oxygen storage capacity, and better CO and soot oxidation activities. All these interesting findings have been elaborated in this publication.

CO and ethanol dual selective sensor of Sm 2O 3-doped SnO 2 nanoparticles synthesized by microwave-induced combustion

In the present investigation, the influence of Sm 2O 3 on the sensitivity and selectivity of SnO 2-based sensors for selective detection of CO and C 2H 5OH in the presence of CH 4 is studied. SnO 2 doped with 2.0, 5.0 and 10.0 wt% Sm 2O 3 samples were prepared employing a microwave-induced solution combustion synthesis using tin chloride. The samples were characterized by SEM, EDS, XRD and BET. The results indicate that samarium oxide inhibits SnO 2 crystal growth and enhances both sensitivity and selectivity of the sensors to CO and ethanol in the presence of methane. Upon addition of 2.0 wt% Sm 2O 3, the crystallite size of SnO 2 reduces from 4.3 to 2.9 nm. As SnO 2 is doped with 5.0 wt% Sm 2O 3 a significant enhancement in response to CO and ethanol was observed at various temperatures. At 200 °C, the 5.0 wt% Sm 2O 3-doped SnO 2 sensor response to 300 ppm CO is 16 times higher than that to 300 ppm ethanol. On the contrary, 33 times higher response to ethanol is observed at 300 °C. The 5.0 wt% Sm 2O 3-doped sensor shows no response to methane up to 350 °C. This way, at different temperatures, the sensor is selective to either CO or ethanol in the presence of methane.

Characterization and photocatalytic activity of TiO2–M x O y (M x O y = SiO2, Al2O3, and ZrO2) mixed oxides synthesized by microwave-induced solution combustion technique

Titania–silica, titania–alumina, and titania–zirconia mixed oxides (1:1 molar ratio) were prepared by a microwave-induced solution combustion synthesis technique. The prepared materials were characterized by thermogravimetry/differential thermal analysis, X-ray diffraction (XRD), Raman spectroscopy, BET surface area, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopic (UV–Vis DRS), and Fourier transform infrared (FTIR) techniques to assess their physicochemical properties. Their photocatalytic activity for the degradation of phenol in aqueous solution under sunlight was studied. XRD and Raman studies revealed the presence of titania in the form of anatase phase in all the mixed oxides synthesized. The XRD studies further suggested that titania–zirconia contains an additional (Ti,Zr)O2 phase. UV–Vis DRS results reveal that all samples exhibit absorption maxima near visible region. FTIR results revealed the presence of Ti–O–Si linkages in the titania–silica sample, which are responsible for its higher activity in the photocatalytic degradation of phenol under sunlight.

Single step synthesis of nanosized CeO2–MxOy mixed oxides (MxOy = SiO2, TiO2, ZrO2, and Al2O3) by microwave induced solution combustion synthesis: characterization and CO oxidation

Various CeO2–MxOy (MxOy = SiO2, TiO2, ZrO2, and Al2O3) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO2–SiO2 and CeO2–TiO2 mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce0.5Zr0.5O2 were observed in the case of CeO2–ZrO2 sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce4+ ← O2− and Ce3+ ← O2− charge transfer transitions. XPS studies revealed the presence of cerium in both Ce3+ and Ce4+ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.

Quantitative effects of fuel on the synthesis of Ni/NiO particles using a microwave-induced solution combustion synthesis in air atmosphere

Microwave-induced solution combustion process for the synthesis of Ni and NiO powders were described. The exothermic redox reaction and the heat evolved from the reaction completely convert the precursors into their corresponding products at temperatures below 400 °C in an oxidizing atmosphere. The characteristics of synthesized powders were investigated with types and amounts of fuel. Nickel particles were directly synthesized through solution combustion synthesis with fuel-rich (Φe=0.65) composition in air atmosphere without further reducing calcinations process. In the fuel-lean composition range (Φe>1) and stoichiometric composition (Φe=1), only NiO phase crystallized from the precursor mixture without forming any intermediate phases. Primary crystallite size of the as-synthesized Ni and NiO were about 30 nm.