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Uranium dioxide (UO

Combustion synthesis in uranyl nitrate-acetylacetone-2-methoxyethanol solutions was used to deposit thin UO2 films on aluminum substrates to investigate the irradiation-induced restructuring processes. Thermal analysis revealed that the combustion reactions in these solutions are initiated at ∼160 °C. The heat released during the process and the subsequent brief annealing at 400 °C allow the deposition of polycrystalline films with 5-10 nm UO2 grains. The use of multiple deposition cycles enables tuning of the film thicknesses in the 35-260 nm range. Irradiation with Ar2+ ions (1.7 MeV energy and a fluence of up to 1 × 1017 ions/cm2) is utilized to generate a uniform distribution of atomic displacements within the films. X-ray fluorescence (XRF) and alpha-particle emission spectroscopy showed that the films were stable under irradiation and did not undergo sputtering degradation. X-ray photoelectron spectroscopy (XPS) showed that the stoichiometry and uranium ionic concentrations remain stable during irradiation. The high-resolution electron microscopy imaging and electron diffraction analysis demonstrated that at the early stages of irradiation (below 1 × 1016 ion/cm2) UO2 films show complete amorphization and beam-induced densification (sintering), resulting in a pore-free disordered film. Prolonged irradiation (5 × 1016 ion/cm2) is shown to trigger a crystallization process at the surface of the films that moves toward the UO2/Al interface, converting the entire amorphous material into a highly crystalline film. This work reports on an entirely different radiation-induced restructuring of the nanoscale UO2 compared to the coarse-grained counterpart. The preparation of thin UO2 films deposited on Al substrates fills an area of national need within the stockpile stewardship program of the National Nuclear Security Administration and fundamental research with actinides. The method reported in this work produces pure, robust, and uniform thin-film actinide targets for nuclear science measurements.

Solution combustion synthesis (SCS) utilizes exothermic self-propagating reactions to prepare nanoscale materials that can be used widely in energy, electronics, and biomedical technologies and other applications. SCS is a specific variety of a more general combustion synthesis (CS) method. Investigations of the thermodynamics, kinetics, and the mechanisms of SCS reactions, are not as well studied as the other CS processes. This work reports on a systematic study of the thermodynamics and kinetics of SCS reactions involving Ni(NO3)2, an oxidizer, and either glycine (C2H5NO2) or hexamethylenetetramine (HMT, C6H12N4) as fuels. A thermodynamic modeling approach, based on the Gibbs free energy minimization principle, is applied to the simultaneous calculations of the adiabatic temperatures and compositions of the equilibrium products. Our calculations reveal the influence of fuel-to-oxidizer ratio, amount of water, and the oxygen in air on the combustion temperature under adiabatic conditions and the composition of the resulting products. We have, in turn, measured the combustion temperature and phase composition of products and compared them with the calculations. Variations of drying times for the solutions yield precursor gels with varying water contents. This approach enables the manipulation of combustion parameters and confirms the use of calculated activation energies for reactions using the Merzhanov-Khaikin method. The results show that SCS reactions in fuel-lean solutions producing NiO have higher activation energy in contrast to reactions with fuel-rich solutions that form Ni. Reduction of activation energies due to the increase in the fuel-to-oxidizer ratio could be related to the observed change of the rate-limiting stages of the endothermic decomposition of the individual reactants to the exothermic decomposition of coordinate compounds formed between the reactants.

Cesium lead iodide with cubic perovskite structure (α-CsPbI3) is gaining significant interest in photovoltaic applications due to its excellent absorbance of the visible solar light and other attractive optoelectronic properties. However, the synthesis of stable α-CsPbI3 poses a significant challenge. Mechanochemical synthesis is emerging as a suitable method for the preparation of cesium lead halides. This work investigates the ball milling-induced synthesis of cesium lead halides perovskite phase using halide mixing or doping approaches. The synthesis in the CsI + PbI2, CsBr + PbBr2, CsBr + PbI2, and CsI + PbI2 + NdI3 mixtures and halide exchange reactions in the CsPbBr3 + 3KI and CsBr + PbBr2 + 3KI systems are investigated to elucidate the mechanism of this process. Then, CsPb(I1−xBrx)3 and CsPb(1−y)NdyI3 materials with different x and y ratios are prepared, and their stability is probed in the air using light absorption spectroscopy. These results suggest that Nd doping is more efficient in the stabilization of the perovskite structure than partial replacement of iodine with bromine. Microstructure observations reveal the existence of two different product formation mechanisms depending on the mechanical properties of reactants. The results reveal that the milling temperature has a significant impact on the reaction kinetics. The produced particles nucleate and grow at the reactant interface and retard the synthesis reaction by creating a diffusion barrier. Extended milling reduces the product particle size and creates fresh contact between reactants, thus facilitating reaction completion.

Microwave-assisted hydrothermal synthesis followed by high-temperature (1050 °C) calcination was used to prepare pure and cerium-doped zinc orthosilicate (Zn2SiO4) pigments. Nanoscale Zn2SiO4 and Ce–Zn2SiO4 powders were blended with potassium silicate (K2SiO3) and then applied to the aluminum substrate to obtain thermoregulating coatings. Electron beams with different energies were used to irradiate nanoscale pigment powders and coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM) were used to characterize the phase composition, morphology, and atomic-level structure of materials. The diffuse reflectance and absorption measurements of materials before and after irradiation indicated that Ce–Zn2SiO4-based coatings exhibit better radiation resistance compared to pure Zn2SiO4. Simple and straightforward preparation, as well as high radiation resistance, make Ce–Zn2SiO4-based thermoregulating coatings excellent candidates for space vehicles.

Combustion synthesis in uranyl nitrate-acetylacetone-2-methoxyethanol solutions was used to deposit thin UO

This work presents results of macro, micro, and nanoscale surface characterization for a set of Roman denarii, ranging from 136 BCE to 240 CE, using large-scale X-ray fluorescence (XRF) mapping, particle-induced X-ray emission (PIXE) spectroscopy, focused-ion-beam-assisted scanning electron microscopy (FIB-SEM) with energy dispersive spectroscopy (EDS). The combination of XRF and PIXE, with varying beam energies, allowed for visualization and quantification of individual elements as a function of the surface distribution. These results helped to select suitable areas for FIB-SEM-EDS analysis. The edges of selected coins were polished to image the inner composition and surface morphology of the coins using a backscattering electron (BSE) imaging method and EDS mapping. Nanosized lamellas extracted from the coins were investigated by transmission electron microscopy (TEM) as well. The combination of these methods enabled the surface, the subsurface, and volume composition of these coins to be probed to better understand their production methods, their surface treatment methods, and their corrosion. The results also provide evidence that a particular surface treatment method, amalgam silvering, had been used to make authentic Roman coins as early as the third century CE.

Nickel oxide reduction by methane is of particular importance in catalysis, extractive metallurgy, and clean power generation technologies. Despite extensive investigations of the NiO + CH4 reaction, many questions remain about its kinetics and molecular and structural transformation mechanisms. This work reports the reduction kinetics of bulk polycrystalline NiO by CH4 using a new calorimetric method. The method permits rapid, controllable heating of the NiO/Ni wires and continuous data (electrical power, the electrical resistivity of the wire, and temperature) acquisition with a frequency of 10 kHz. The method also allows arresting and preservation of the structure of the sample by programmed termination of electric power in thin specimens. This approach, coupled with ex situ electron microscopy, allows determination of the reaction rate and tracking of the ongoing structural transformations. The mechanism of NiO reduction by methane is suggested based on direct correlations between reaction kinetics an...

A single-step method for the preparation of metastable e-Fe3N nanoparticles by combustion of reactive gels containing iron nitrate (Fe(NO3)3) and hexamethylenetetramine (C6H12N4) in an inert atmosphere is reported. The results of Fourier transform infrared spectroscopy (FTIR) and thermal analysis coupled with dynamic mass spectrometry revealed that the exothermic decomposition of a coordination complex formed between Fe(NO3)3 and HMTA is responsible for the formation of e-Fe3N nanoscale particles with sizes of 5-15 nm. The magnetic properties between 5 and 350 K are characterized using a superconducting quantum interference device (SQUID) magnetometer, revealing a ferromagnetic behavior with a low-temperature magnetic moment of 1.09 μB/Fe, high room temperature saturation magnetization (∼80 emu/g), and low remanent magnetization (∼15 emu/g). The obtained value for the Curie temperature of ∼522 K is close to that (∼575 K) for bulk e-Fe3N reported in the literature.

Here, we report on a size-controlled synthesis of highly crystalline germanium particles, via the self-sustained reaction of GeO2 with Zn, Mg, and NaBH4. The thermodynamic analysis suggests that the GeO2 + 2Zn and GeO2 + NaBH4 systems are characterized by moderate heats of reaction (−121 and −204 kJ per mole of Ge, respectively), while GeO2 + 2Mg exhibits a much higher reaction enthalpy (−623 kJ). Magnesium reduction has been found not to be suitable for the preparation of germanium crystals due to the high reaction temperature, which exceeds 2000 °C. The partial substitution of Zn by Mg, however, enables increasing the overall reaction temperature in the low caloric GeO2 +Zn system. By using different reducers and their mixtures, the reaction temperature was optimized to be in the 600–1100 °C range. Such temperature modifications allow for control of the germanium particle sizes, ranging from 200 nm to 2 mm. Thermal analysis of the reacting mixtures and electron microscopy examination of the products indicates that dissolution-precipitation is the dominant formation mechanism of the germanium crystals in the GeO2 + Zn system. The higher reaction temperatures in the GeO2 + Zn + Mg and GeO2 + NaBH4 systems cause melting, and subsequent coalescence of the primarily precipitated germanium resulting in much larger particles.

Using glucose (C6H12O6) and copper nitrate (Cu(NO3)2) as fuel and oxidizing agent respectively, CuO/Cu2O/C composites with different carbon contents were successfully prepared by the solution combustion synthesis method. The as-obtained CuO/Cu2O nanoparticles exhibited uniform spherical morphology and, by changing the amount of fuel and ambient temperature, carbon was synthesized in-situ with content ranging from 3 to 36 wt%. The electrochemical performance of the CuO/Cu2O/C anode in Li-ion batteries was investigated systematically, demonstrating >400 mAh g−1 capacity at 20 mA g−1 current density and highly stable cycling performance with capacity 260 mAh g−1 after 600 cycles at current density 0.2 A g−1. This performance is attributed to the synergistic effect of anodes porous structure, conducting carbon coating and two-component CuO/Cu2O structure. Owing to the inexpensive and facile solution combustion synthesis method and the resulting high electrochemical performance, the CuO/Cu2O/Carbon composite is a promising anode material for application in Li-ion batteries.

A simple and efficient microwave-assisted preparation of ReB2-based material is reported utilizing ammonium perrhenate (NH4ReO4), magnesium boride (MgB12) reactants and carbon as an absorber of microwave irradiation. The investigation of microwave irradiated NH4ReO4 +MgB12 +C mixtures, thermal analysis results and electron microscopy examination reveals that NH4ReO4 decomposition produces ReO3 at early stages of the process. The ReO3 then exothermically reacts with MgB12 forming the nanoscale Re3B phase, which converts into ReB2 upon further irradiation. The coupling of microwave energy with exothermic reactions significantly accelerates the formation of ReB2. The product primarily consists of ReB2 as well as B4C and minor carbon phases. Structural characterization reveals that the average particle size of ReB2 is ~ 50 nm.

Energy production in Type Ia x-ray bursts depends on a number of nuclear reactions that become efficient in a hot environment (up to 2 GK). Model sensitivity studies have been performed in an effort to better identify the reactions that have the largest effect, but these efforts are hampered by the high level of complexity of the astrophysical model and large nuclear physics uncertainties. In a recent study, the $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction was found to significantly affect the energy generation in x-ray bursts. This manuscript reports the first study of the $^{24}\mathrm{Mg}(\ensuremath{\alpha},{p}_{1,2}\ensuremath{\gamma})^{27}\mathrm{Al}$ reaction at energies relevant for x-ray bursts. The branches to the $^{27}\mathrm{Al}$ excited states increase to a small degree the estimates of the total astrophysical $^{24}\mathrm{Mg}(\ensuremath{\alpha},p)^{27}\mathrm{Al}$ reaction rate.

Nucleosynthesis in the first generation of massive stars offers a unique setting to explore the creation of the first heavier nuclei in an environment free of impurities from earlier stellar generations. In later generations of massive stars, hydrogen burning occurs predominantly through the CNO cycles, but without the carbon, nitrogen, and oxygen to catalyze the reaction sequence, first stars would have to rely on the inefficient $pp$ chains for their energy production. Observations of second and third generation stars show pronounced abundances of carbon and oxygen isotopes, which suggests a rapid conversion of the primordial abundances to heavier elements. While the triple-alpha-process primarily facilitates this conversion, there are alternative reaction sequences, such as $^{2}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{6}\mathrm{Li}(\ensuremath{\alpha},\ensuremath{\gamma})^{10}\mathrm{B}(\ensuremath{\alpha},n)^{13}\mathrm{N}$, that may play a significant role. To study such alternate reaction pathways for production of carbon and heavier nuclei, a number of new measurements are needed. In this work, new measurements are reported for the $^{10}\mathrm{B}(\ensuremath{\alpha},n)^{13}\mathrm{N}$ reaction, extending the cross section down to 575 keV incident $\ensuremath{\alpha}$-particle energy. The measurements were made using a state-of-the-art deuterated liquid scintillator and a spectrum unfolding technique. An $R$-matrix analysis was performed in order to facilitate a comparison of the underlying nuclear structure with the reaction measurements. An unexpected upturn is observed in the low-energy $S$ factor that indicates the presence of a new low-energy resonance. A revised reaction rate is determined that takes into account the present data as well as other previous measurements from the literature that were previously neglected.

A high-speed electrothermography approach is applied to investigate the mechanism and kinetics for nanostructured Al/Ni foils. Application of the Kolmogorov–Johnson–Mehl–Avrami and adiabatic thermal explosion models reveal that the activation energy for nucleation appears to be much higher than that for the reaction. It is shown that formation of intermetallic nuclei is the limiting step that defines the ignition characteristics of the foils at temperatures below 500 K, while the process is reaction-limited at higher temperatures. Nucleation is also shown to play an important role during rapid (∼10 m/s) propagation of the combustion (reaction) wave along the Al/Ni foils. These findings suggest new approaches for controlling the ignition and combustion processes for nanostructured reactive materials.

In this work, we report a liquid-phase reduction method to prepare porous non-supported amorphous nickel catalysts with high surface areas (65–250 m 2 /g). A highly crystalline face center cubic Ni (fcc-Ni) catalyst with 110 m 2 /g surface area was also prepared by frontal crystallization of the amorphous nickel catalyst. The catalytic activity and stability of these catalysts for ethanol decomposition was investigated at different time on stream (TOS) to understand structural transformations occurring at the early stages of catalyst activation-deactivation. Activity vs. TOS results obtained at 473 K show that on the amorphous catalysts the conversion increases from about 50% to 60–75% reaching a steady value at ∼30 h TOS, which remains constant during the observed 96 h of TOS. The fcc-Ni catalyst initially exhibits a higher conversion (∼85%), however, it quickly deactivates to a conversion in the similar range as the amorphous catalysts. It is also shown that BET surface areas of amorphous catalysts decreases during hydrogen pretreatment at 473 K due to crystallization, grain growth, and sintering. The structure of amorphous catalysts continuously refines to form a combination of fcc-Ni and hexagonal close-packed nickel (hpc-Ni) phases, as well as nickel carbide (Ni 3 C) and carbon layers that stabilize catalytic activity. The structure of the fcc-Ni catalyst remains unchanged during the 96 h TOS experiment indicating that carbon deposition might cause its initial deactivation. At 523 K, the amorphous catalyst shows 100% conversion, which remains constant during 96 h of TOS, while the fcc-Ni crystalline catalyst initially exhibits 95% conversion and then slowly deactivates to ∼80% at 96 h TOS. Thus at 523K the stabilized amorphous catalyst does not deactivate under the same TOS compared to the crystalline fcc-Ni catalyst, showing that the active sites on these catalysts are different. The findings of this work suggest that the liquid-phase reduction method can be used to prepare active and stable catalysts for reactions involving decomposition of alcohols and hydrocarbons to produce hydrogen.

Here, we report a simple and scalable synthesis strategy of metal (Ni or Cu) nanoparticles uniformly distributed inside a mesoporous silica matrix. This method involves incorporation of metal nitrates and citric acid in a stable silica gel through controlled hydrolysis of tetraethyl orthosilicate. Combustion of dried gels with ammonium nitrate in an inert gas atmosphere enables preparation of highly porous Ni/SiO2 and Cu/SiO2 nanomaterials with tunable metal content (∼5–30 wt.%). This approach also allows for independent tuning of the metal nanoparticle size (from 2 to 50 nm) and textural parameters, such as surface area (50–600 m2/g), average pore size (3–8 nm), and pore volume (0.05–0.6 cm3/g) of the materials during the one-step combustion. This new approach also enables uniform incorporation of metal nanoparticles within a porous silica matrix. This feature allows for synthesis of encapsulated stable ultra-small metallic nanoparticles with unusual properties. We tested Ni/SiO2 nanoscale materials with different textural parameters as catalysts in the ethanol decomposition reaction. The catalysts exhibited high activity toward hydrogen generation for ∼100 h. The relevant links between the textural parameters and stability of the catalysts are revealed. Characterization of the spent catalysts showed no structural changes, indicating superior stability over long periods of time. We also used spark plasma sintering (SPS) of Ni/SiO2 and Cu/SiO2 nanoscale materials to fabricate porous (70–80%) compact samples. These materials exhibited significantly low thermal diffusivity, which makes them attractive for thermal management applications. We also showed that the simple preparation method allows for production of large batches of final product, such as 10–50 g, in laboratory conditions.

The exothermic reactions in the ZrF4−Mg-Si and ZrF4-Al-Si systems are investigated by a fast temperature recording (thermocouple) technique, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). A quenching method is used to arrest the combustion process and conduct a layer-by-layer analysis of the products by x-ray diffraction (XRD) and electron microscopy. Two seemingly similar reactive systems exhibited considerably different combustion characteristics, composition, and morphology. Based on these investigations, we propose and discuss phase formation mechanisms at the early stages for each system. Three different pathways involving the reaction of ZrF4 with other reagents and the Mg2Si intermediate are identified to occur in the ZrF4−Mg-Si system. Contrary to the complex mechanism in the ZrF4−Mg-Si system, the early stage of the combustion process for the ZrF4-Al-Si system involves the interaction of ZrF4 with Al-Si eutectic melt. The exothermic reaction between reduced solid Zr and Si melt is the primary heat-generating step for both systems in spite of substantial differences in the early stages of the reactions. The silicon content in the reactive mixtures governs the phase composition of products. The ZrSi2 phase, with a high growth rate, forms first on the Zr particle surfaces and then grows by a reactive diffusion mechanism. The ZrSi2+Zr reaction produces silicon-lean phases (e.g., ZrSi) when the silicon supply is limited. The combustion temperature also has a considerable influence on the phase compositions of the products. High combustion temperature in the ZrF4+2Mg+Si mixture enables the formation of multiphase products (α-ZrSi and β-ZrSi), whereas the relatively lower temperatures in the 3ZrF4+4Al+3Si mixture yields a single-phase α-ZrSi. Lower combustion temperatures also make the ZrF4-Al-Si system more advantageous for the preparation of zirconium silicides.

The combustion phenomenon is characterized by rapid self-sustaining reactions, which can occur in the solid, liquid, or gas phase. Specific types of these reactions are used to produce valuable materials by different combustion synthesis (CS) routes. In this article, all three CS approaches, i.e. solid-phase, solution, and gas-phase flame, are reviewed to demonstrate their attractiveness for fabrication of zero-, one-, two-, and three-dimensional nanostructures of a large variety of inorganic compounds. The review involves five sections. First, a brief classification of combustion synthesis methods is given along with the scope of the article. Second, the state of art in the field of solid-phase combustion synthesis is described. Special attention is paid to the relationships between combustion parameters and structure/properties of the produced nanomaterials. The third and fourth sections describe details for controlling material structures through solution combustion synthesis and gas-phase flame synthesis, respectively. A variety of properties (e.g., thermal, electronic, electrochemical, and catalytic) associated with different types of CS nanoscale materials are discussed. The conclusion focuses on the most promising directions for future research in the field of advanced nanomaterial combustion synthesis.

Cross sections for 34 proton-induced nuclear reactions on isotopically enriched molybdenum ($^{92,94\ensuremath{-}98,100}\mathrm{Mo}$) leading to production of $^{92}\mathrm{Tc}$, $^{93\mathrm{m}}\mathrm{Tc}$, $^{93\mathrm{g}}\mathrm{Tc}$, $^{94\mathrm{m}}\mathrm{Tc}$, $^{94\mathrm{g}}\mathrm{Tc}$, $^{95\mathrm{m}}\mathrm{Tc}$, $^{95\mathrm{g}}\mathrm{Tc}$, $^{96\mathrm{m}+\mathrm{g}}\mathrm{Tc}$, $^{97\mathrm{m}}\mathrm{Tc}$, $^{99\mathrm{m}}\mathrm{Tc}$, $^{101}\mathrm{Tc}$, $^{91(\mathrm{m}+\mathrm{g})}\mathrm{Mo}$, $^{93\mathrm{m}}\mathrm{Mo}$, $^{99}\mathrm{Mo}$, $^{89\mathrm{m}}\mathrm{Nb}$, $^{89\mathrm{g}}\mathrm{Nb}$, $^{91\mathrm{m}}\mathrm{Nb}$, $^{92\mathrm{m}}\mathrm{Nb}$, $^{95\mathrm{m}}\mathrm{Nb}$, $^{95\mathrm{g}}\mathrm{Nb}$, $^{96}\mathrm{Nb}$, and $^{97\mathrm{m}+\mathrm{g}}\mathrm{Nb}$ were measured in the energy range 8--19 MeV with the activation method using individual irradiations. The experimental data were compared with published data from natural abundance and isotopically enriched targets as well as with the predictions of the nuclear reaction code talys. Special attention was given to the medically relevant $^{100}\mathrm{Mo}$($p,2n$)$^{99m}\mathrm{Tc}$ and $^{100}\mathrm{Mo}$($p,pn$)$^{99}\mathrm{Mo}$ as well as nine reaction cross sections that had not previously been measured in this energy range.

The National Ignition Facility (NIF) provides the opportunity to study nuclear reactions under controlled conditions at high temperatures and pressures at a level never before achieved. However, the timescale of the deuterium-tritium (DT) implosion is only a few nanoseconds, making data collection and diagnostics very challenging. One method that has been proposed for obtaining additional information about the conditions of the implosion is to activate a dopant material using the $\ensuremath{\alpha}$ particles produced from the DT fuel as a diagnostic. The yield of the activated material can give a measure of the mixing that occurs in the capsule. One of the reactions that has been proposed is $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ as it produces a radioactive reactant product with a convenient half-life of $\ensuremath{\approx}10\phantom{\rule{0.16em}{0ex}}\mathrm{min}$. Although this reaction has several advantages for the application at hand, it has not seen much study in the present literature, resulting in large uncertainties in the cross section. Furthermore, for the current application, the cross section must be well characterized. With this motivation, the $^{10}\mathrm{B}(\ensuremath{\alpha},n)\phantom{\rule{0.16em}{0ex}}^{13}\mathrm{N}$ cross section has been remeasured for $2.2l{E}_{\ensuremath{\alpha}}l4.9\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ with the angle-integrated ground-state cross section reported for the first time. The present results, combined with previous measurements, allow for a determination of the cross section to a significantly higher degree of accuracy and precision than obtained previously and are shown to be consistent with thick-target measurements. Preliminary calculations are performed to test the feasibility of this reaction as a diagnostic for a NIF implosion.

Combustion synthesis (CS) of advanced materials is an energy-saving and efficient approach, which can occur in the solid, liquid, and gas phases. CS can be accomplished in two different modes. First is a self-propagating mode. In this case, the reactive media are locally preheated by an external source to the ignition temperature, at which point reaction is initiated in this layer. The “hot” reacted layer preheats and ignites the next “cold” layer and thus combustion front self-propagates along the reactive mixture resulting in the formation of the desired solid product. Second is the volume combustion synthesis mode. In this case, the entire reactive media are uniformly heated by some external source to ignition temperature, and reaction starts at each point of the media essentially uniformly, again leading to the production of valuable materials. The maximum synthesis temperature is limited by the thermodynamics of the considered systems, and is in the range of 500K–4000K. It is important that after “ignition” no external heat sources are required. Hence, CS is an energy-efficient method. The rate of the temperature change at the self-ignition stage is very high (103–106 K/s), which defines unusual extremely nonequilibrium conditions for the material fabrication and facilitates the formation of crystalline nanomaterials with unique morphology, including one- and two-dimensional nanostructures. In this chapter, we briefly review the CS processes taking place in solid and liquid phases that allow controlling the structure and properties of one- and two-dimensional nanomaterials. Some fundamental principles for controlling the morphology and dimensionality of CS products are also reviewed.

Microwave-assisted synthesis of carbon-supported Mo 2 C and WC nanomaterials was studied. Two different routes were utilized to prepare MoO 3 (WO 3 ) - C precursors that were then subjected to microwave irradiation in an inert atmosphere. The effect of synthesis conditions, such as irradiation time and gas environment, was investigated. The structure and formation mechanism of the carbide phases were explored. As-synthesized nanomaterials exhibited catalytic activity for hydrous hydrazine (N 2 H 4 ·H 2 O) decomposition at 30–70 ° C. It was shown that the catalyst activity significantly increases if microwave irradiation is applied during the decomposition process. Such conditions permit complete conversion of hydrazine to ammonia and nitrogen within minutes. This effect can be attributed to the unique nanostructure of the catalysts that includes microwave absorbing carbon and active carbide constituents.

A mechanically induced solid-state reaction method for the synthesis of organic–inorganic hybrid perovskites, such as methylammonium lead iodide (CH3NH3PbI3) is reported. The perovskites were synthesized both in bulk and Al2O3-supported forms. The phase- and structural-formation mechanisms of such perovskites are also investigated. The experiments suggest that diffusion of PbI2 into CH3NH3I crystals is a rate-limiting step of the reaction process. It is also shown that water (humidity) significantly influences the reaction kinetics. UV–Vis–NIR absorption and photoluminescence spectroscopies indicate that the band edge and emission characteristics of the as-fabricated materials strongly depend on their particle size.

The synthesis of amorphous Ni (a-Ni) using a liquid-phase chemical reduction approach is reported. Detailed structural analysis indicates that this method allows for efficient fabrication of high surface area (210 m2/g) amorphous Ni nanopowder with low impurity content. We investigated the self-propagating exothermic waves associated with crystallization of Ni from the amorphous precursor. Time-resolved X-ray diffraction indicates that amorphous nickel crystallizes in the temperature range 445–480 K. High-speed infrared imaging reveals that local preheating of compressed a-Ni nanopowder triggers a self-sustaining crystallization wave that propagates with velocity ∼0.3 mm/s. The maximum temperature of crystallization wave depends on the sample density and can be as high as 600 K. The Kissinger approach is used to determine the apparent activation energy (55.4 ± 4 kJ/mol) of crystallization. The self-diffusion activation energy of Ni atoms in a-Ni is ∼60 kJ/mol, determined through molecular dynamics (MD) si...

We present complementary multiscale X-Ray Fluorescence (XRF) mapping and Raman spectroscopy to analyze pigments in a rare medieval Breton manuscript. Once a codex of 129 parchment leaves in the Bergendal Collection (olim MS 8), the manuscript was sold at auction and then subsequently dismembered page-by-page. The leaves were then disseminated on the open market by the biblioclast. The analysis was performed on 12 illustrated leaves (samples) out of the 92 which were recovered by Rare Books and Special Collections at the University of Notre Dame. The combination of elemental mapping with molecular spectroscopy permits an unprecedented analysis of the illuminations in the manuscript. XRF scanning provides both elemental analysis of large-scale objects as well as microscopic examination of individual pigment particles. The XRF mapping indicates distinctive elemental distributions within specific regions of interest. Raman spectroscopy of these selected areas identifies the molecular composition of the pigments. This combination of analytical techniques provides an in-depth characterization of the Breton manuscript on the macro, micro- and molecular levels. The results from different leaves confirm that pigments and inks of illustrated leaves belong to the same palette. The results also show the pigments utilized in illustrations, text, and borders are identical indicating that the manuscript was prepared in a single setting, by a single artisan or a small number of artisans working closely.

The tantalum–carbon reactive system possesses a high energy of reaction with an adiabatic combustion temperature of 2743 K, which is significantly below the melting points of the reactants, as well as any intermediate phases and final products. It was suggested that a combustion wave could propagate in Ta+C mixtures solely owing to a solid–solid reaction. However, this combustion process has never been shown to occur without gas-assisted transport. Here, we report preparation of highly pure and pore-free Ta/C composite particles, which were used for experimental validation of the solid-flame. Preparation of these composite particles involves short term high-energy ball milling (HEBM) of tantalum and carbon powders. High-resolution microscopy coupled with three-dimensional reconstruction techniques were used to characterize the volume nanostructure of mechanically fabricated composite particles. It was quantitatively shown that the particles have nano-scale mixing of the reagents and possess high contact surface area between tantalum and carbon. Experiments revealed that the ignition temperature of as fabricated composite particles is 1243 ± 15 K and maximum combustion temperature was shown to be 2487 ± 50 K, which is well below any possible solid–liquid transitions. Utilizing results obtained with composite particles prepared under different HEBM conditions, it is shown that carbon diffusion through the tantalum grain boundaries and subsequent formation of a Ta(C) solid solution defines low temperature ignition of mechanically fabricated particles. The high surface area contact between the Ta and C nano-scale reagents allows the reaction to propagate in a self-sustained manner, owing solely to a solid-state diffusion mechanism.

Reactions that populate the 15N system have implications for nucleosynthesis through the 11B(α, n)14N and 14N(n, p)14C reactions and the 14N(n, p)14C reaction is also a key component in modeling atmospheric 14C production. A convenient characteristic of this system is that the α-particle, proton, and neutron separation energies are all within ≍1 MeV of one another. Further, it has been observed that 11B+α, 14N+n and 14C+p induced reactions all populate many of the same resonances near their reaction thresholds. This strongly facilitates the simultaneous analysis of data for all three of these entrance partitions using a global R-matrix analysis, which in turn provides a method of comparing the consistency among the different experimental measurements. In this work, a new measurement has been performed for the 11B(α, n)14N reaction, which gives a more accurate description of the cross section, in particular over an important interference region. This new data is combined with results from previous measurements, which populate a similar excitation energy range in the 15N system, to produce a global fit that includes 11B(α, n)14N reaction data for the first time.

The influence of high-energy (1.6 MeV) Ar2+ irradiation on the interfacial interaction between cerium oxide thin films (∼15 nm) with a SiO2/Si substrate is investigated using transmission electron microscopy, ultrahigh vacuum x-ray photoelectron spectroscopy (XPS), and a carbon monoxide (CO) oxidation catalytic reaction using ambient pressure XPS. The combination of these methods allows probing the dynamics of vacancy generation and its relation to chemical interactions at the CeO2/SiO2/Si interface. The results suggest that irradiation causes amorphization of some portion of CeO2 at the CeO2/SiO2/Si interface and creates oxygen vacancies due to the formation of Ce2O3 at room temperature. The subsequent ultra-high-vacuum annealing of irradiated films increases the concentration of Ce2O3 with the simultaneous growth of the SiO2 layer. Interactions with CO molecules result in an additional reduction of cerium and promote the transition of Ce2O3 to a silicate compound. Thermal annealing of thin films exposed to oxygen or carbon monoxide shows that the silicate phase is highly stabile even at 450 °C.

The preparation, characterization, activity, and stability of a Ni–Al2O3 catalyst derived from reduction of a Ni–Al layered double hydroxide precursor (LDH, Ni6Al2(OH)16(CO3)0.75(OH)0.25·4H2O) are reported in this paper. In-situ X-ray adsorption spectroscopy shows that reduction of Ni from the LDH precursor to form a highly loaded 80% Ni–Al2O3 catalyst (Ni–Al2O3–LDH) is faster than reduction of a 10% impregnated Ni–Al2O3 alumina (Ni–Al2O3–I) catalyst. The reduced Ni–Al2O3–LDH catalyst exhibits highly dispersed Ni nanoparticles (3–5 nm) distributed on top, partially embedded nanoparticles, and some encapsulated in the Al2O3 matrix. The nanoparticles impregnated on alumina (Ni–Al2O3–I) are larger (∼7–15 nm) and appear on top of the alumina support. Conversion vs time on stream (TOS) results during ethanol decomposition at 250 °C on Ni–Al2O3–LDH exhibits only a slight deactivation during 100 h TOS, while the Ni–Al2O3–I catalyst shows rapid deactivation with no conversion after 2 h TOS. X-ray photoelectron spectroscopy shows that the carbon content increases up to 48% after 100 h TOS on the Ni–Al2O3–LDH catalyst, while a similar increase occurs after 2 h TOS on the Ni–Al2O3–I catalyst. TEM shows that after 100 h TOS either a thin layer of amorphous carbon or carbon nanotubes forms on Ni on top of the alumina matrix and on partially embedded Ni nanoparticles on the Ni–Al2O3–LDH catalyst. Total surface area of the Ni–Al2O3–LDH catalyst increased during TOS, which may be suplying fresh surface Ni from the encapsulated Ni nanoparticles that sustain the high activity.

We studied the reduction kinetics of bulk NiO crystals by hydrogen and the corresponding structural transformations in the temperature range of 543–1593 K. A new experimental approach allows us to arrest and quench the reaction at different stages with millisecond time resolution. Two distinctive temperature intervals are found where the reaction kinetics and product microstructures are different. At relatively low temperatures, 543–773 K, the kinetic curves have a sigmoidal shape with long induction times (up to 2000 s) and result in incomplete conversion. Low-temperature reduction forms a complex polycrystalline Ni/NiO porous structure with characteristic pore size on the order of 100 nm. No induction period was observed for the high-temperature conditions (1173–1593 K), and full reduction of NiO to Ni is achieved within seconds. An extremely fine porous metal structure, with pore size under 10 nm, forms during high-temperature reduction by a novel crystal growth mechanism. This consists of the epitaxia...

We have investigated the effect of accelerated ion beam irradiation on the structure and reactivity of multilayer sputter deposited Al/Ni nanomaterials. Carbon and aluminum ion beams with different charge states and intensities were used to irradiate the multilayer materials. The conditions for the irradiation-assisted self-ignition of the reactive materials and corresponding ignition thresholds for the beam intensities were determined. We discovered that relatively short (40 min or less) ion irradiations enhance the reactivity of the Al/Ni nanomaterials, that is, significantly decrease the thermal ignition temperatures (Tig) and ignition delay times (τig). We also show that irradiation leads to atomic mixing at the Al/Ni interfaces with the formation of an amorphous interlayer, in addition to the nucleation of small (2-3 nm) Al3Ni crystals within the amorphous regions. The amorphous interlayer is thought to enhance the reactivity of the multilayer energetic nanomaterial by increasing the heat of the reaction and by speeding the intermixing of the Ni and the Al. The small Al3Ni crystals may also enhance reactivity by facilitating the growth of this Al-Ni intermetallic phase. In contrast, longer irradiations decrease reactivity with higher ignition temperatures and longer ignition delay times. Such changes are also associated with growth of the Al3Ni intermetallic and decreases in the heat of reaction. Drawing on this data set, we suggest that ion irradiation can be used to fine-tune the structure and reactivity of energetic nanomaterials.

In recent years progress in the materials research field has been associated with the discovery of graphene and other two-dimensional atomic crystals. Those materials uniquely combine many exceptional properties, which make them highly attractive for a variety of applications. Despite significant advancement in synthesis and processing, the relevance of those materials is essentially driven by progress in their production. In the past 3 years, several unique inexpensive combustion-based approaches have been developed to prepare the nanomaterials. This article specifically aims to be an overview of current trends and as a perspective of combustion synthesis of 2D-crystals. We summarized the benefits of extreme combustion conditions for atomic-scale processing and integration of these materials for advanced energy applications.

Solution combustion synthesis (SCS) reactions take place in homogeneous solutions of metal containing oxidizers (metal nitrates) and fuels, such as water-soluble organic amines, acids, and amino-acids. These redox reactions are completed within a short time (seconds) with maximum temperatures as high as ∼ 1500°C. High temperatures favor formation of crystalline nanoscale materials, including binary and complex oxides, metals, alloys, and sulfides. A combination of combustible reactive solutions with hard and soft templates provides new possibilities for the development of novel nanoscale materials with tailored structure and properties.

Solution combustion synthesis (SCS) is a relatively new method for catalyst preparation. It uses elements of conventional preparation approaches and involves its own unique techniques. SCS-derived catalysts can be categorized into two major groups: bulk and supported. The evident advantages of combustion reactions to prepare solid catalysts include utilization of straightforward and rapid techniques and the ability to control the catalyst microstructure by changing the combustion conditions. One of the most significant advantages relates to the preparation of doped complex catalysts with the highest possible structural homogeneity. Combustion synthesized catalysts exhibit high stability towards deactivation.

Two-dimensional (2D) materials are layered crystalline solids that have strong bonding in one crystal plane while the neighboring atomic planes are held together by much weaker van-der-Waals forces. Graphene and its structural derivatives are typical 2D materials. These crystalline solids have attracted great attention because of their electronic, thermal, optical, and mechanical properties. 2D materials show great potential to be integrated into electrochemical energy storage devices (batteries and supercapacitors) and solar water splitting technologies and to be used as hydrogen storage materials.

Solution combustion synthesis (SCS) is typically used to produce nanostructured oxides and bulk metallic materials for a variety of application including catalysis. Here, we report in situ, one-step SCS of high surface area (155 m2/g) Ni catalysts supported on fumed silica (SiO2). Time-resolved X-ray diffraction is used to investigate the dynamics of phase formation during combustion of nickel nitrate–glycine–ammonium nitrate reactive gels impregnated onto porous SiO2. It is shown that highly dispersed nickel nanoparticles (5 nm) formed in the reaction front are followed by their rapid oxidation by air oxygen. To prevent the undesired oxidation process, the synthesis was conducted in an inert atmosphere (argon, helium). It is demonstrated that low concentration oxygen impurity (less than 0.001 wt %) in the inert gas passivates the Ni nanoparticles through the formation of a thin amorphous oxide layer. The thus prepared Ni/SiO2 supported catalyst possesses high activity during the ethanol decomposition tow...

A template-assisted combustion-based method is developed to synthesize the ultrasmall (below 5 nm) α-Fe2O3 nanoparticles. The iron and ammonium nitrate are used as oxidizers, glycine as a “fuel” and mesoporous silica (SBA-15) as a template. Because of the ultralow sizes and high crystallinity, the combustion-derived α-Fe2O3 nanoparticles exhibit superparamagnetism in the temperature range of 70–300 K. The high specific surface area (132 m2/g) of α-Fe2O3 indicates the important role of surface magnetic spins resulting in remarkably high magnetization (21 emu/g) at 300 K.

A simple, surfactant-free liquid-phase reduction of Cu, Ni and Fe salts (e.g. nitrates, chlorides) was used to prepare nanostructured FeNi/Cu catalysts for hydrous hydrazine (N2H4·H2O) decomposition. The synthesis of nanomaterials includes reduction of copper salt using N2H4, followed by rapid reduction of iron and nickel salts by NaBH4. The catalysts were characterized by XRD, BET, TEM, XPS, XANES/EXAFS techniques and their activity and selectivity was studied during hydrous hydrazine decomposition at temperatures ranging from 300 to 345 K. The selectivity to hydrogen increases to ∼100% with increasing temperature up to ∼345 K. The catalytic performance of these materials depends on the structure of NiFe layer formed over a Cu core, which may be controlled by changing of NiFe/Cu mass ratio. Investigation of the catalytic performance for bi- and tri-metallic materials show that main active metal is nickel but a NiFe alloy could be responsible for the increased selectivity. Alloying of nickel with iron coupled with a favorable dispersion on copper nanoparticles remarkably enhances the catalytic conversion and selectivity of hydrogen evolution.

Due 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).

In this work, we examined several modifications of solution combustion synthesis (SCS) method to produce new nanoscale non-oxide phases (nitrides, intermetallics, and alloys). In particularly two approaches were outlined: (i) so-called, catalytic SCS, where existence of one metal promotes reduction during combustion; (ii) synthesis by using media, which contains both reactive solution and solid metals, i.e. combination of solution and heterogeneous combustion.

The mechanism of structural transformation during combustion of nickel nitrate (oxidizer)–glycine (fuel) system is investigated by using different in situ techniques, including time-resolved X-ray diffraction (TRXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) with dynamic mass spectrometry (MS), and high-speed infrared thermal imaging. It is shown that for initial compositions with a relatively large fuel-to-oxidizer ratio (φ), pure Ni phase forms directly in the combustion front. For fuel-lean conditions, only NiO phase can be detected. Analysis of the obtained data, including transmission and scanning electron microscopy (TEM–SEM) studies of the quenched reaction fronts, allows us to suggest the intrinsic mechanism of pure metal formation in the investigated system. It is shown that the combustion front propagates because of the reaction between N2O and NH3, which are the products of decomposition of the oxidizer and fuel. The excess of NH3 gas produced in fuel-rich condi...