Phase Reaction Products Research Articles

(Invited) Following Energy Transduction from Light Absorption to Product Formation in Photoelectrocatalysis

The ability to track how energy is transduced and transported in its various forms is critical to achieve a full understanding of key factors to optimize photoelectrocatalysis. Toward this end, we employ various forms of in situ optical scattering and reflectance microscopy that reveal the spatiotemporal evolution of both photogenerated charge carriers in semiconductor photoelectrodes on ultrafast time scales and electrochemical products as they diffuse from an electrode with sub-mM sensitivity and sub-ms time resolution. Thermal transport can also be resolved to clarify dissipation and thermal management. I will show structure-transport relationships in candidate photoelectrode transition metal oxides and show how a related approach also enables investigation of solution phase reaction products and their transport, even as a function of electrode irregularities.

Preparation and properties of alkali-activated fly ash-waste brick porous building materials

This study explores the development of sustainable porous building materials through the alkali-activation of fly ash and waste clay brick powder. Utilizing Class F fly ash and brick powder from demolished buildings, a series of alkali-activated mortars with varying brick powder replacements (0 % to 50 % by mass) were formulated and analyzed. The results reveal that a 10 % brick powder replacement optimizes the compressive strength, reaching 73 MPa at 28 days, attributed to enhanced nucleation and calcium-rich gel formation. However, higher brick content reduces strength due to the dilution of key reactive materials, with a 50 % replacement leading to a strength of 27 MPa. Porosity increases proportionally with brick content, achieving a maximum of 42 % at 50 % replacement, suggesting potential applications in insulation-centric scenarios. Microstructural analysis confirms the formation of a porous network and identifies the phase compositions and reaction products. This research demonstrates the potential of repurposing construction waste into efficient and environmentally friendly building materials, contributing to waste reduction and offering a greener alternative to traditional practices.

Atomic structure of nanocrystalline and amorphous ASR products

Limited information about the atomic structure of amorphous and nanocrystalline alkali–silica reaction (ASR) products is available. Here, reactive molecular simulations were employed to construct a model of these products based on defective shlykovite. To introduce disorder into the models, various annealing temperatures (ranging from ambient to temperatures above silicate dissolution) were tested. Structures obtained from annealing at 700 K reproduced the main peaks observed experimentally in X-ray diffraction patterns of “ASR-P1” phase, a nanocrystalline or amorphous alkali–silica reaction product recently identified in synthetic and field concrete. Pair distribution functions and structure factors computed for this structure also compared well with previous data reported for “amorphous” ASR products. These results demonstrate that what was previously considered “amorphous” ASR products might be related to nanocrystalline defective shlykovite structures.

Insight into the Structure and Redox Chemistry of [Carbonatotetraamminecobalt(III)] Permanganate and Its Monohydrate as Co-Mn-Oxide Catalyst Precursors of the Fischer-Tropsch Synthesis

[Carbonatotetraamminecobalt(III)] permanganate monohydrate was synthesized first in the metathesis reaction of [Co(NH3)4CO3]NO3 and NaMnO4 in aqueous solution. Its thermal dehydration at 100 °C resulted in phase-pure [Co(NH3)4CO3]MnO4 (compound 1). Compounds 1 and 2 (i.e., the hydrated form) were studied with IR, far-IR, and low-temperature Raman spectroscopies, and their vibrational modes were assigned. The lattice parameters were determined by powder X-ray diffraction (PXRD) and single crystal X-ray diffraction (SXRD) methods for the triclinic and orthorhombic compounds 1 and 2, respectively. The detailed structure of compound 2 was determined, and the role of hydrogen bonds in the structural motifs was clarified. UV studies on compounds 1 and 2 showed the distortion of the octahedral geometry of the complex cation during dehydration because of the partial loss of the hydrogen bonds between the crystal water and the ligands of the complex cation. The thermal decomposition consists of a solid phase quasi-intramolecular redox reaction between the ammonia ligands and permanganate anions with the formation of ammonia oxidation products (H2O, NO, N2O, and CO2). The solid phase reaction product is amorphous cobalt manganese oxide containing ammonium, carbonate (and nitrate) anions. The temperature-controlled thermal decomposition of compound 2 in toluene at 110 °C showed that one of the decomposition intermediates is ammonium nitrate. The decomposition intermediates are transformed into Co1.5Mn1.5O4 spinel with MnCo2O4 structure upon further heating. Solid compound 2 gave the spinel at 500 °C both in an inert and air atmosphere, whereas the sample pre-treated in toluene at 110 °C without and with the removal of ammonium nitrate by aqueous washing, gave the spinel already at 300 and 400 °C, respectively. The molten NH4NO3 is a medium to start spinel crystallization, but its decomposition stops further crystal growth of the spinel phase. By this procedure, the particle size of the spinel product as low as ~4.0 nm could be achieved for the treatments at 300 and 400 °C, and it increased only to 5.7 nm at 500 °C. The nano-sized mixed cobalt manganese oxides are potential candidates as Fischer-Tropsch catalysts.

Gas Additives for Silicon Anode Lithium-Ion Batteries

While many organic liquid and electrolyte salt formulations have been explored to improve the stability of lithium-ion batteries, less research has been done to determine the role of evolved gasses in the performance of commercial Li-ion battery chemistries, let alone novel combinations of gas additives that may affect the solid-electrolyte interphase (SEI) formation and evolution.[1,2] Many gases are generated during Li-ion battery cycling, any of which could have possible beneficial or harmful effects on performance. Currently, only the effect of carbon dioxide (CO2) gas addition to Li-ion batteries with Si anodes has been studied.[3-4] In addition to CO2, ethylene gas (C2H4) is a promising additive for Si anode systems because it is a precursor in polyethylene polymerization reactions, nCH2=CH2 --> [-CH2-CH2-]n. In addition, polyethylene oxide (PEO) has been observed in the Si-anode SEI and contributes to its passivation while maintaining flexibility.[5] Therefore, creating polyethylene and increasing PEO concentration in situ via ethylene gas doping may yield an improved SEI and more-stable battery.This work investigates the potential of gas-phase additives, including CO2 and C2H4, to improve the performance of Si anodes for Li-ion batteries. The pressure decay of the gasses at different starting pressures dissolving in GenF3 electrolyte (1.2 M LiPF6 in 3:7 wt:wt ethylene carbonate to ethyl methyl carbonate + 3 wt% fluoroethylene carbonate) was monitored to determine the saturation concentration of dissolved gas. The experimental pressure decay curve was fit to a model and extrapolated to predict the final pressure at equilibrium.[6] The relationship between partial pressure and concentration of dissolved gas in GenF3 at equilibrium was plotted and a curve was drawn to determine the Henry’s law constant. Varying volumes of gas were injected into battery pouch cells containing Si nanoparticle anodes and LiFePO4 (LFP) cathodes to pressurize them to different pressures. Electrochemical cycling and subsequent multi-phase analyses, including vibrational spectroscopy and X-ray characterization of the SEI surface layer and GC-MS/FID were conducted to determine the impact of gas doping on the capacity, SEI, and gas phase reaction products.

Steam oxidation of ytterbium disilicate environmental barrier coatings with and without a silicon bond coat

AbstractThe current generation of multilayer Si/Yb2Si2O7 environmental barrier coatings (EBCs) are temperature limited by the melting point of Si, 1414°C. To investigate higher temperature EBCs, the cyclic steam oxidation of EBCs comprised of a single layer of ytterbium disilicate (YbDS) was compared to multilayered Si/YbDS EBCs, both deposited on SiC substrates using atmospheric plasma spray. After 500 1‐h cycles at 1300°C in 90 vol%H2O‐10 vol%air with a gas velocity of 1.5 cm/s, both multilayer Si/YbDS and single layer YbDS grew thinner silica scales than bare SiC, with the single layer YbDS forming the thinnest scale. Both coatings remained fully adherent and showed no signs of delamination. Silica scales formed on the single layer coating were significantly more homogeneous and possessed a markedly lower degree of cracking compared to the multilayered EBC. The single layer EBC also was exposed at 1425°C in steam with a gas velocity of 14 cm/s in an alumina reaction tube. The EBC reduced specimen mass loss compared to bare SiC but formed an extensive 2nd phase aluminosilicate reaction product. A similar reaction product was observed to form on some regions of the bare SiC specimen and appeared to partially inhibit silica volatilization. The 1425°C steam exposures were repeated with a SiC reaction tube and no 2nd phase reaction product was observed to form on the single layer EBC or bare SiC.

Liquid-solid phase reaction products formation in the diffusion welded joints made between Ti-6Al-4 V and AISI304L with brass interlayer

Abstract Liquid-solid phase reactions taken place at Ti-6Al-4 V-brass interface and brass-AISI304L stainless steel are presented in the current study. The liquid–solid phase reaction products formed in the diffusion welded (DW) samples made between Ti-6Al-4 V and AISI304L with brass interlayer were characterized with microscopy, energy dispersive X-Ray analysis and X-ray diffraction technique. Diffusion welding was performed by maintaining temperature 875, 900, 925 ⁰C and pressure 4, 8 and 12 MPa and welding time 20 and 40 min. Diffusion of ‘Cu’ and ‘Zn’ from the brass interlayer into base metals, and elements such as ‘Ti’, ‘Fe’, ‘Cr’, ‘Al’, ‘V’, ‘Ni’, ‘Mn’, ‘Si’ and ‘C’, diffused from the base metals into brass interlayer was observed. The maximum hardness values for the sample welded at 925 ⁰C, 12 MPa and 40 min were 595.2 VHN at the AISI304Lside and the Ti-6Al-4 V side, it was 612.4 VHN.

Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide

Four simulated waste streams relevant to the vitrification of Hanford nuclear waste were studied to evaluate the removal kinetics of technetium-99 (Tc) and co-mingled Cr(VI) during treatment with solid ferrous hydroxide (Fe(OH)2(s)). Simulants treated with Fe(OH)2(s) were reacted for 24 h and sub-sampled periodically to monitor Tc and Cr removal. Solution sample analysis during the reaction was coupled with solid phase characterization, for example, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), to establish influence of the solid phase product on Tc and Cr removal rates. Based on these results, the majority of Tc and Cr removal occurs within the first 5 min of simulant contact with Fe(OH)2(s). However, the order in which Tc and Cr are completely removed from each simulant depends on the simulant chemistry, the preferred reduction pathway, and the solid phase product, for example, magnetite (Fe3O4) versus goethite (α-FeOOH). Low pH and low Cr concentrations favor rapid Tc removal, with XRD and XAS confirming that Fe3O4 readily incorporates reduced Tc(IV) into its structure. High pH, high Cr concentrations, and the presence of other co-mingled constituents favor heterogeneous removal of Tc early in the reaction (<1 h) with removal rates often faster than those determined for Cr. At reaction times of >1 h, Tc removal slows as homogeneous removal of Cr begins to dominate, concurrent with an increase in the formation of FeOOH as the solid phase reaction product. These results suggest that for complex, high pH waste streams, Tc removal within the first hour after Fe(OH)2(s) treatment is necessary for complete Tc reduction and improved mineral immobilization.

Phase evolution and reactivity of Pr2NiO4+δ and Ce0.9Gd0.1O2-δ composites under solid oxide cell sintering and operation temperatures

In developing a new compositae air electrode for Solid Oxide Cells (SOCs) it is essential to fully understand the phase chemistry of all components. Ruddlesden-Popper type electrodes such as Pr2NiO4+δ have previously been proposed as attractive alternatives to conventional La0·6Sr0·4Fe0·8Co0·2O3-δ/Ce1-xGdxO2-δ compositae air electrodes for both fuel cell and electrolyser modes of operation. However, Pr2NiO4+δ have been shown to have limited stability, reacting with a Ce1-xGdxO2-δ interlayer to form a Ce1-x-yGdxPryO2-δ (CGPO) phase of unknown stoichiometry. Additionally, Pr2NiO4+δ are known to decompose to Pr4Ni3O10 ± δ under certain conditions.In this work detailed understanding of the chemical reaction between Pr2NiO4+δ and Ce0.9Gd0.1O2-δ (CGO10) under normal solid oxide cell fabrication and operating temperatures was obtained, identifying the composition of the resulting CGPO phase reaction products. It is shown that, in addition to the unreacted CGO10 present after sintering the compositae at 1100 °C for up to 12 h, a series of CGPO chemical compositions were formed with various Ce, Gd and Pr ratios depending on the relative distance of the doped ceria phases from the Pr2NiO4+δ phases. The extent of the chemical reaction was found to depend on the sintering time and the contact area of the two phases. Further thermal treatment of the resulting products under SOC air electrode operating temperature (800 °C) resulted in the initiation of Pr2NiO4+δ decomposition, forming Pr4Ni3O10 ± δ and Pr6O11 with no detectable change in the composition of previously formed Pr-substituted ceria phases. It is apparent that the Pr2NiO4+δ/CGO10 compositae is unsuitable as an air electrode, but there is evidence that the decomposition products, Pr4Ni3O10 ± δ and Ce1-x-yGdxPryO2-δ are stable and suitable candidates for SOC electrodes.

In English

Reliability and profitability of NPP operation of any type to a large extent depend on the reliable operation of the system of its pipelines. From literary sources is shown that the most dangerous zone, in terms of erosion wear, is a pipeline fluctuation. Solving the problem of erosion wear of the zone of the twists of the pipelines is possible by gas phase depositing protective coatings based on boron carbide, which slow down the cavitation processes of wear. This paper presents the results of studies on the production of a cavitation-resistant coating based on boron carbide by hydrogen reduction of boron trichloride BCl 3 and toluene C 7 H 8 . Boron carbide was carried out on a plant with a horizontal flow-type reaction chamber. The principle of its operation consists in passing through the reaction chamber of the vapor-gas flow of reagents entering the chemical reaction on the surface of the heated substrate located inside the reaction chamber. Solid phase reaction products form an increasing condensate layer on the substrate surface and gaseous products are removed from the reaction chamber and neutralized. Trichloride boron BCl 3 and toluene C 7 H 8 were selected as reagents. Carrying gas and activator was hydrogen H 2 . Deposition was carried out on the austenitic steel substrate. It was shown that morphology of the surface is characterized by grapple-scraped globules. X-ray spectral studies have shown that the distribution of elements is uniform, this indicates that when austenitic steel is heated, no significant changes in properties occur. Diffractometric studies have shown that coating contains grain of Fe 2 B iron boride and Fe 7 C 3 iron carbide. measurement microhardness have shown that from the center of the substrate to the side of the coating is increased in double. Destruction of samples under the influence of cavitation was studied on the installation of ultrasound cavitation. The cavitation zone was formed between the end of the emitter, which is connected with an ultrasonic generator of UZG-3 0.4 type, and the surface of the test specimen installed in water having the temperature of 293 K. For comparison, the kinetic curve of the destruction of the standard A18H10T austenitic steel and a boron carbide-based sample is given. Under the same test conditions, the nature of the kinetic curves is different. A sample with a carbide-borne coating is 2.5 times less cavitation wear than austenitic steel.

Polymetallic Ore Concentration Middlings Nitric Acid Leaching Kinetics

The purpose of this work is the kinetic evaluation of reactions occurring during nitric acid leaching of pollymetallic sulfide middlings, for the most complete translation of copper, zinc and sulfur in solution and concentration of precious metals in residue. Methodology is pollymetallic sulfide middlings nitric acid leaching kinetics were studied using mathematical methods such as the experimental data numerical differentiation. Relevance/value is the main sulfide minerals kinetic characteristics were obtained for the studied materials, including the rate of the process, order of reaction, the rate constant for the forward and reverse reaction. Findings are the rate of the process is limited by kinetics. The calculated values of kinetic parameters showed that the process kinetics are influenced by such factors as the nature of leachable sulfide, nitric acid concentration, the surface area of the solid sulfide, the system approaches equilibrium at saturation of the liquid phase reaction products.

Reaction path and product analysis of sodium-water chemical reactions using laser diagnostics

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a coolant because of its excellent heat transport capability and a large safety margin to the boiling point (1153K) at the atmospheric pressure. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow caused by a breach of heat transfer tubes. Therefore, the study on sodium-water chemical reactions is of importance for safety of SFR. The purpose of this study aims to clarify the gas phase sodium-water reaction path and reaction products quantitatively. The counter-flow diffusion experiment device was employed to analyze the reaction path and reaction products using laser diagnostics. sodium (Na), sodium dimer (Na2), water (H2O), sodium hydroxide (NaOH), sodium oxides (Na2O and NaO) and hydroxyl radical (OH) were measured using Raman spectroscopy, absorption spectroscopy, photo-fragmentation spectroscopy and laser induced fluorescence in the reaction field for the sodium-water vapor, sodium-oxygen and sodium-hydrogen reaction. Based on the measurement results by absorption spectroscopy, it was revealed that the sodium-oxygen reaction was faster than that of sodium-water. It was indicated that sodium-hydrogen reaction did not react noticeably with sodium from the measurement result as well. The main product of sodium-water reaction was determined to be NaOH and the sodium oxide was not notably measured compared with NaOH from the results by photo-fragmentation spectroscopy. The sodium oxide concentration ratio to NaOH was determined 2% with standard deviation of 3%. Its reaction path was also discussed using sodium-water, sodium-oxygen and sodium-hydrogen reaction analyses.

Guaiacol Hydrodeoxygenation over Platinum Catalyst: Reaction Pathways and Kinetics

Guaiacol represents a large fraction of lignin derived pyrolysis bio-oils. It was shown in our prior work that Pt has higher activity and stability for guaiacol hydrodeoxygenation as compared to other noble metal catalysts. In the present study, further theoretical and experimental investigations were conducted to reveal the reaction pathways and kinetics. For Pt/C catalyst in a fixed-bed reactor, the main liquid phase reaction products were phenol, catechol and cyclopentanone. Because cyclopentanone was typically not observed in the prior literature, a pathway for its formation was proposed and supported by density functional theory (DFT) calculations. By varying the space velocity, kinetic data was acquired in the temperature range 275 to 325 °C. The rate constants and activation energies for each subreaction in the network were obtained based on the power-law model.

Electrochemical method for wet removal of phosphine

The removal of phosphine (PH3) was studied with an electrochemical approach using a Ti/SnO2 anode. The effects of the current density, O2 content, gas flow rate, temperature, and type of electrolyte on the PH3 removal were investigated. The liquid phase reaction products were detected by ion chromatography. It was observed that PH3 was effectively removed in the electrochemical reactor and phosphate (PO43−) existed in solution after reaction. Increasing current density, oxygen content and reaction temperature can enhance the removal of PH3. 0ver 85% PH3 was removed with an operation condition of current density of 53.05 mA/dm2, 65°C, 4.6 vol % O2 and gas flow rate of 200 mL/min in 0.1 mol/L Na2SO4 aqueous solution. Chosen Na2SO4 as electrolyte, removal efficiency remained stability and it would be conducive to the recovery of phosphate (PO43‐). The gas flow rate influence is remarkably clear in the reactor where it was evident that the most efficient gas flow rate toward a 90% PH3 removal was reached at 50 mL/min. Electrochemical oxidation will be a potential method for the PH3 removal because of its low cost, long duration removal efficiency and the valuable hydrogen byproduct produced. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1640–1646, 2015

Abiotic U(VI) reduction by aqueous sulfide

Reactions with aqueous sulfide are important in determining uranium (U) geochemistry under sulfate reducing conditions. This paper reports on abiotic reduction of U(VI) by aqueous sulfide under a range of experimental conditions using batch reactors. Dissolved U concentration was measured as a function of time to study the effects of chemical variables including pH, U(VI), S(−II), total dissolved carbonate (CARB=H2CO3*+HCO3−+CO32−), and Ca2+ concentration on the U(VI) reduction rate. Solid phase reaction products were characterized using X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. The chemical variables had impacts on the solid phase U(VI) reaction products as well as the reduction rates by aqueous sulfide. The solid U reaction product at circumneutral pH was identified as uraninite (UO2+x(s)). Under basic pH conditions, whether a precipitate occurred depended on Ca2+ and CARB concentrations. U(VI) reduction was faster under higher S(−II) concentrations but was slowed by increased dissolved Ca2+ or CARB concentration. In the absence of dissolved CARB and Ca2+, a rapid decrease in dissolved U concentration occurred at circumneutral pH, while virtually no decrease was observed at pH 10.7 within the experimental timeframe of two days. The U(VI) reduction rate was proportional to the total concentration of free uranyl plus its hydrolysis complexes even at minor to trace concentrations. Dissolved Ca2+ and CARB slow abiotic U(VI) reduction by forming stable Ca–U(VI)–carbonato soluble complexes that are resistant to reaction with aqueous sulfide. U(VI) reduction was slow in a synthetic solution representative of groundwater at a uranium mill tailings site. This study illustrates that abiotic U reduction by aqueous sulfide can significantly vary under typical ranges of chemical conditions in groundwater and newly demonstrates the importance of dissolved Ca2+ in the abiotic U(VI) reduction by aqueous sulfide. The results contribute to our understanding of the impact of sulfate reducing conditions on U speciation in groundwater systems undergoing bioreduction conversion of U(VI) to less mobile U(IV) solid phases.

Toluene destruction over nanometric palladium supported ZSM-5 catalysts: influences of support acidity and operation condition

The effects of catalyst physicochemical property and operation condition on toluene destruction over Pd/Z-x (Z: ZSM-5; x: n Si/Al) were extensively studied. The support acidity has important impact on active phase dispersion and reaction product desorption. Pd/Z-25 shows the highest catalytic activity with toluene complete conversion at 220 °C, which is about 60 °C lower than that of Pd/Z-300. Both Pd loading and space velocity are key experimental factors determining toluene oxidation activity. The water vapor has a significant negative effect on the oxidation reaction, especially for the catalyst with higher Al content. The activity of the used Pd/Z-25 could not regain its initial level after removal of water vapor due to the formation of coke. Pd0 and Pd2+ species have a synergetic effect on toluene oxidation, and the catalytic activity is primarily correlated to the support acidity, the active phase dispersion, and the CO2 desorption capability.

E203 レーザ計測技術を用いたナトリウム-水化学反応場の反応経路解析(OS8 軽水路・新型炉・原子力安全(4))

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. Therefore, the study on sodium-water chemical reactions is of importance for security reasons. This study aims to clarify the gas phase sodium-water reaction path and reaction products Na, Na_2, H_2O, and reaction products in the counter-flow sodium-water reaction field were measured using laser diagnostics such as Raman scattering and photo-fragmentation. The main product in the sodium-water reaction was determined to be NaOH and its reaction path was discussed using Na-H_2O elementally reaction analysis.

A statistical description of the evolution of cloud condensation nuclei activity during the heterogeneous oxidation of squalane and bis(2-ethylhexyl) sebacate aerosol by hydroxyl radicals

The heterogeneous reaction of hydroxyl radicals with chemically reduced organic aerosol comprised of either squalane or bis(2-ethylhexyl) sebacate are used as model systems to examine how cloud condensation nuclei (CCN) activity evolves with photochemical oxidation. Over the course of the reaction, the critical super-saturation evolves both by the formation of new oxygen functional groups and by changes in aerosol size through the formation of gas phase reaction products. A statistical model of the heterogeneous reaction reveals that it is the formation, volatilization, solubility, and surface activity of many generations of oxidation products that together control the average changes in aerosol hygroscopicity. The experimental observations and model demonstrate the importance of considering the underlying population or subpopulation of species within a particle and how they each uniquely contribute to the average hygroscopicity of a multi-component aerosol. To accurately predict changes in CCN activity upon oxidation requires a reduction in the surface tension of the activating droplet by a subpopulation of squalane reaction products. These results provide additional evidence that surface tension-concentration parameterizations based on macroscopic data should be modified for microscopic droplets.

The statistical evolution of multiple generations of oxidation products in the photochemical aging of chemically reduced organic aerosol

The heterogeneous reactions of hydroxyl radicals (OH) with squalane and bis(2-ethylhexyl) sebacate (BES) particles are used as model systems to examine how distributions of reaction products evolve during the oxidation of chemically reduced organic aerosol. A kinetic model of multigenerational chemistry, which is compared to previously measured (squalane) and new (BES) experimental data, reveals that it is the statistical mixtures of different generations of oxidation products that control the average particle mass and elemental composition during the reaction. The model suggests that more highly oxidized reaction products, although initially formed with low probability, play a large role in the production of gas phase reaction products. In general, these results highlight the importance of considering atmospheric oxidation as a statistical process, further suggesting that the underlying distribution of molecules could play important roles in aerosol formation as well as in the evolution of key physicochemical properties such as volatility and hygroscopicity.

Fabrication of particle dispersed inert matrix fuel based on liquid phase sintered SiC

In the present work, liquid phase sintered SiC (LPS-SiC) was proposed as an inert matrix for the particle dispersed inert matrix fuel (IMF). The fuel particles containing plutonium and minor actinides were substituted with pure yttria stabilized zirconia beads. The LPS-SiC matrix was produced from the initial mixtures prepared using submicron sized α-SiC powder and oxide additives Al 2O 3, Y 2O 3 in the amount of 10 wt.% with the molar ratio 1Y 2O 3/1Al 2O 3. Powder mixtures were sintered using two sintering methods; namely conventional high temperature sintering and novel spark plasma sintering at different temperatures depending on the method applied in order to obtain dense samples. The phase reaction products were identified using X-ray diffraction (XRD) and microstructures were investigated using light microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) techniques. The influence of powder mixing methods, sintering temperatures, pressures applied and holding time on the density of the obtained pellets was investigated. The samples sintered by slow conventional sintering show lower relative density and more pronounced interaction between the fuel particles and matrix in comparison with those obtained with the fast spark plasma sintering method.