Solid-phase Oxidation Research Articles

Comparison of Hydrogen Generation Rate between CORA-13 Test and MELCOR Simulation: Clad Solid-Phase Oxidation Models Using Self-Developed Code MYCOAC

To better understand the MELCOR oxidation and degradation models, past work compared the MELCOR model to a CORA experiment (CORA Test 13). These MELCOR analyses specifically focused on fuel bundle heatup and clad oxidation when compared to CORA test data. The comparison allowed the authors to investigate differences between hydrogen generation data and simulation results. Several potential reasons were considered for hydrogen generation rate differences, including MELCOR input power, heat transfer modeling, the clad solid-phase oxidation model, and the gaseous steam diffusion model. This work focuses on the possible uncertainty in the clad oxidation models used in MELCOR. First, the MELCOR nodalization approach for the CORA test was reviewed. Then, the temperature history and spatial variation were examined. One main focus was to consider other clad solid-phase oxidation models to compare the MELCOR models. This was accomplished by developing a separate model, MYCOAC, using MELCOR temperature predictions as input. Finally, the mass transfer resistance of steam diffusion to the clad surface was examined and found to be a small effect. While the Baker-Just solid-phase oxidation model showed better agreement with CORA data at low temperatures, the conclusion in this paper is that the oxidation models are not the major source of uncertainty in hydrogen generation rate differences. Future work will focus on heat transfer modeling of the CORA test.

Thermogravimetric analysis of InCl3 sublimation at atmospheric pressure

This paper presents a thermogravimetric approach to evaluate the vapor pressure of low-volatility inorganic compounds such as CuCl and InCl3 under atmospheric conditions. The thermogravimetric analysis (TGA) approach is inherently more straightforward than alternatives such as torsion studies and mass spectrometry. Vapor pressures are evaluated using the Clausius–Clapeyron relationship between the vapor pressure and sublimation (or vaporization) enthalpy at a given temperature. Despite the relative simplicity of TGA, the highly hygroscopic nature of InCl3 demands some caution in the data analysis. Especially at high temperature, a solid-phase oxidation product In2O3 remains as a residual mass. Water is found to be the oxidation agent, with the residual proceeding through a solid-phase InOCl intermediate. However in the relatively low temperature range of interest oxidation is found to be negligible, with the gas-phase sublimation product being In2Cl6. This paper reports sublimation enthalpies and vapor pressures as functions of temperature in the range 570≤T≤640K and atmospheric pressure.

Development of cladding oxidation analysis code [COAC] and application for early stage severe accident simulation of AP1000

Clad oxidation is an important phenomenon which can affect core degradation under severe accident conditions. The oxidation process always coincides with cladding material embrittlement. The energy released from the oxidation of cladding material can accelerate the accident process, and the hydrogen released from oxidation may threaten the integrity of vessel. As a consequence, the high temperature clad solid-phase oxidation model research and its code development play an important role in reactor safety analysis. To push the research on this region, a clad solid-phase oxidation analysis code (COAC) is developed by Xi'an Jiaotong University. To verify the quality of COAC, CORA-13 is used as a benchmark. The results show that COAC does produce expected values. COAC is then applied to AP1000 severe accident calculations. In this case, the station blackout accident (SBO) is modeled. The response of fuel rods under varying natural circulation conditions while coolant pump idle time is calculated. The calculations show that the oxidation of cladding can delay fracturing, and protect its integrity. Meanwhile, the performances of other oxidation models are explored in this paper.

Physics of the solid-phase oxidation and reduction of metals

The transfer of electric charges and mass in the crystal lattice of an oxide is analyzed. The massand electrotransport in oxides are shown to be caused by ionic displacements; to be interrelated; and to occur via scattering of charged ionic vacancies, which form at the surface of contact of oxide with a reducing or oxidizing medium. A general physical model is developed to describe metal reduction and oxidation. This model is based on the universal principle of equality of the number of elementary charge carriers, namely, electrons and protons, in any phase and the contingency of mass- and electrotransport in an ionic crystal lattice.

Investigation of the thermo-oxidation mechanism of acrylic-urethane-silicone/amino-silane based topcoat

Silicone acrylic-urethane/amino-silane coatings are considered as promising candidates for use as a topcoat in high-temperature engineering applications. However, under these conditions, their functional properties can be affected, and it is well known that the loss of functional properties is related to modification of the chemical structure.The main objective of this first study is to identify the main criteria for degradation and establish a mechanism of degradation. For this purpose, the thermo-oxidative ageing of the topcoat is studied at the molecular scale using FTIR coupled with chemical treatments, TGA, and SPME/GC-MS.These complementary techniques allow the study of both the solid and gas phases and provide evidence for a more comprehensive degradation mechanism of this topcoat. The results show that degradation occurs on the labile hydrogen atoms located on the tertiary carbon of the acrylate group and on the α-position of the ester and amide. The solid phase oxidation products were identified as anhydrides and amides, whereas volatile products such as lactones and siloxanes were identified in the gas phase.

Chemism and kinetics of the oxidation of zinc-calcium oxysulfide

The sequence of phase transformations and the kinetics of the solid-phase (heating to 1273 K) oxidation of zinc-calcium oxysulfide CaZnSO with air are determined by thermodynamic, thermogravimetric, mass spectrometric, and X-ray diffraction analyses. The oxidation process is shown to be accompanied by the formation of the CaSO4 and ZnO phases depending on the heating conditions, as well as by the formation of CaO with SO2 evolution. The two-stage oxidation of CaZnSO is interpreted by the Avrami-Erofeev kinetic equations with activation energies of 190 and 422 kJ/mol.

Regularities of the formation of iron(III) nanocrystalline particles during the oxidation of iron(II) compounds in a neutral medium

The regularities of the formation of iron(III) oxide hydroxides as nanocrystalline particles via oxidation of iron(II) compounds in a near-neutral pH region were studied by potentiometric titration, electron microscopy, chemical analysis, and X-ray diffraction. The oxidation process comprises two steps. The first step produces Fe(II)-Fe(III) hydroxo salts having a “green rust” structure in the form of nanocrystalline particles shaped as hexagons. The second step produces anisotropic nanocrystalline particles of iron(III) oxide hydroxides via the dissolution-oxidation-precipitation mechanism and via solid-phase oxidation. The oxidation of chlorine-containing suspensions helps the formation of single-phase nanocrystalline lepidocrocite, while oxidation in the presence of sulfate ions yields nanocrystalline goethite.

Molecular Basis of Glucagon-like Peptide 1 Docking to Its Intact Receptor Studied with Carboxyl-terminal Photolabile Probes

The glucagon-like peptide 1 (GLP1) receptor is a member of Family B G protein-coupled receptors and represents an important drug target for type 2 diabetes. Despite recent solution of the structure of the amino-terminal domain of this receptor and that of several close family members, understanding of the molecular basis of natural ligand GLP1 binding to its intact receptor remains limited. The goal of this study was to explore spatial approximations between specific receptor residues within the carboxyl terminus of GLP1 and its receptor as normally docked. Therefore, we developed and characterized two high affinity, full-agonist photolabile GLP1 probes having sites for covalent attachment in positions 24 and 35. Both probes labeled the receptor specifically and saturably. Subsequent peptide mapping using chemical and proteinase cleavages of purified wild-type and mutant GLP1 receptor identified that the Arg(131)-Lys(136) segment at the juxtamembrane region of the receptor amino terminus contained the site of labeling for the position 24 probe, and the specific receptor residue labeled by this probe was identified as Glu(133) by radiochemical sequencing. Similarly, nearby residue Glu(125) within the same region of the receptor amino-terminal domain was identified as the site of labeling by the position 35 probe. These data represent the first direct demonstration of spatial approximation between GLP1 and its intact receptor as docked, providing two important constraints for the modeling of this interaction. This should expand our understanding of the molecular basis of natural agonist ligand binding to the GLP1 receptor and may be relevant to other family members.

Solid-phase oxidative halodecarboxylation of β-arylacrylic acids with the ceric ammonium nitrate—alkali halide system

The solid-phase oxidation of cinnamic, 4-methoxy- and 3,4-dimethoxycinnamic acids with Ce(NH4)2(NO3)6—MHal system leads to β-halostyrenes. Similar procedure in the absence of a metal halide results in a cleavage of the C=C bond giving the corresponding benzaldehydes.

Chemiluminescence in the solid-phase reaction of powdered XeF2 and Na4XeO6 · nH2O with U(OH)4 · nH2O

Reactions of solid-phase oxidation of U(OH)4 · nH2O with Xe compounds to U(VI), accompanied by intense chemiluminescence, were revealed and examined. The reactions are typically complete within ∼60 min at 20°C, i.e., are much faster than oxidation of crystalline U(IV) salts, e.g., U(SO4)2 · nH2O. The reactions of U(OH)4 · nH2O with XeF2 and Na4XeO6 · nH2O substantially differ in the chemiluminescence kinetics: In the former case, there is a chemiluminescence intensity splash, followed by a smooth decay, while in the latter case the luminescence flames up from the initial moment after mixing and passes through one, and then through another, maximum. A complex kinetics of both reactions can be due, in particular, to successive oxidation of U(IV) to U(VI) via formation of intermediate U(V) and Xe(I) species. The chemiluminescence spectrum of U(OH)4 · nH2O is observed in the 440–580 nm range and falls within the UO 2 2+ ion emission region. Despite the differences in the chemiluminescence spectra of the solid compound and UO 2 2+ aqua ion, hydroxo complexes of U(VI), formed from oxidation of U(IV), were identified as chemiluminescence emitters. In the discovered solid-phase chemiluminescence reactions, an important role is played by water of crystallization and coordinated water.

The genesis of CO 2 and CO in the thermooxidative degradation of polypropylene

Using a set of three isotactic polypropylene samples that had been individually labeled with carbon-13 at each of the three positions in the monomer unit, we conducted experiments to determine the position of origin of carbon monoxide and carbon dioxide that arise during thermal oxidation of this polymer. By GC–mass-spectral analysis, we find that 2/3 of the CO 2 derives from the C(1) [methylene] carbon and the remaining 1/3 comes from the C(2) [tertiary] carbon, with none coming from the C(3) [methyl group] carbon. The CO also comes mainly from the C(1) [methylene] carbon (≥80%). This is in contrast to the solid-phase oxidation products, which have been found (by C-13 NMR on these same labeled PP materials) to originate predominantly (80–85%) from oxidation at the C(2) [tertiary] carbon. These results can be understood in terms of the free-radical reactions that underlie the polypropylene oxidation chemistry.

Insights into Oxidation Pathways, from Gaseous Products of Polypropylene with Selective Isotopic Labeling

Polymer degradation mechanisms are exceedingly complex, but their understanding is fundamental to improving material durability. We have initiated selective isotopic labeling as a means of tracking oxidation chemistry, and chose polypropylene (PP) to test this approach, since it has a simple structure (three unique carbon sites along the chain), and is of commercial importance. There has in fact been much interest in the stability of PP, and many prior studies have contributed to the ongoing development of understanding its degradation processes. In recent work, we applied ^(13)C NMR to examine the solid-phase oxidation products of isotopically labeled PP; in this Communication, we begin identifying the volatile products.

A macromolecular oxidant, the N,N-dichlorosulfonamide for removal of residual nitrites from aqueous media

Nitrites are highly harmful compounds. They are extremely undesirable in surface and municipal water. The permissible content in natural water is very low and should not exceed 0.01 mg of NO 2 - / dm 3 . In this instance a redox copolymer, a macromolecular analogue of Dichloramine T (i.e. a macroporous S/DVB copolymer containing –SO 2NCl 2 groups) was used for the removal of nitrite ions from aqueous solutions by its oxidation to achieve the less toxic nitrates. The resin was prepared starting from Amberlyst 15 by a three-step transformation of the sulfonic – via chlorosulfonyl and sulfonamide – to the N, N-dichlorosulfonamide groups. The resulting copolymer contained 8.2 meq of active chlorine/g and showed strong oxidizing properties. It was employed in batch and flow processes for treatment of NaNO 2 solutions containing 115 and 230 or 460 mg of NO 2 - / dm 3 . The effects of various parameters on the reaction course have been studied (mole ratio of reagents, pH of the reaction media, flow rate in the column processes). The solid phase oxidation carried out in a dynamic regime provided the drive to bring the reaction to completion. Thus, nitrite free effluents (<3.0 μg/dm 3) were obtained in the column processes. The reaction of nitrite oxidation by means of this heterogeneous oxidant was fast, and therefore the permissible flow rate was highly satisfactory – close to 20–25 bed volumes/h. Under the examined reaction conditions, 1 mol of NO 2 - ions was oxidized by 1 mol of active chlorine, thus the oxidation capacity of the resin was nearly 200 mg NO 2 - / g of the copolymer. The N, N-dichlorosulfonamide copolymer is very useful for the purification of neutral solutions from nitrites. The copolymers redox potentials determined here and the complex redox titration measurements which have been carried out, prove why the macromolecular oxidant shows varied reactivity, depending on the solution’s pH.

Arsenic Speciation in As(III)- and As(V)-Treated Soil Using XANES Spectroscopy

Arsenic (As) is a toxic trace element that occurs naturally in groundwater and soils. Understanding the reactions of arsenite (As(III)) and arsenate (As(V)) with soil and mineral surfaces is critical for predicting the fate and transport of As in the environment and developing better ways to remediate As-contaminated areas. This investigation uses X-ray absorption near edge spectroscopy (XANES) to evaluate the solid phase oxidation state and mineral surface binding sites in three agricultural soil samples from California, USA by fitting linear combinations of XANES spectra derived from several synthetic and well characterized As(III)- and As(V)-treated model compounds (Fe and Al metal hydroxides and aluminosilicate illite clay mineral). The results suggest that As(III) is either partially or completely oxidized to As(V) when reacted with soil in an aqueous, batch reaction. The As(III)-treated Aiken soil was composed of 60% As(III) attached to surfaces similar to lepidocrocite (γ-FeOOH)) and 40% As(V) attached to aluminosilicate (illite). The Fallbrook soil completely oxidized As(III) and the product was As(V) adsorbed on Al hydroxide (gibbsite, γ-Al(OH)3) (62%), illite (16%), and lepidocrocite (γ-FeOOH) (22%). The reaction of As(III) with Wyo soil resulted in 42% As(III) adsorbed on surface similar to goethite and 58% As(V) adsorbed on lepidocrocite. Arsenic(V) adsorption on soil resulted in stable As(V) surface complexes that were well described by XANES spectra from As(V) adsorption complexes on gibbsite, illite, and lepidocrocite.

Uranyl-based heterogeneous catalyst for the selective oxidation of benzylic alcohols to form corresponding carbonyl compounds

Uranyl ions (O U O) 2+ immobilized in mesoporous MCM-41 are found to serve as highly active heterogeneous catalyst for the formation of benzaldehyde in liquid–solid-phase oxidation of benzylic alcohols, using tert-butyl hydrogen peroxide ( t-BuOOH) as an oxidant. The benzoic acid was formed on subsequent oxidation of benzaldehyde and therefore its yield increased with the increasing contact time. The solvent employed as a reaction medium influenced the catalyst activity considerably, and the best results were obtained using ethyl acetoacetate as the solvent. In the repeated cycles of activity measurements, fairly reproducible results were achieved after an initial decrease in the activity because of the partial leaching of uranyl ions.

Screening the importance of soil micro-organisms on radionuclides mobility

In surface soils, the native physical and chemical properties of the abiotic components control most of the sorption-desorption processes. Moreover, micro-organisms may significantly modify the speciation of trace elements and/or radionuclides and subsequently determine their fate, to a large extent. Micro-organisms, mainly bacteria and fungi, develop many strategies that may affect indirectly or directly the behaviour of trace elements. Due to their activity, changes in the pore-water composition, e.g. pH, redox-potential, may occur in relation with organic acid production or solid phase alteration, reduction or oxidation of metallic oxi-hydroxides, and mineralization of organo-metallic complexes. Micro-organisms may also directly modify the speciation of radionuclides as a result of bio-accumulation in living cells, biosorption on cellular components, direct reduction or oxidation, biomethylation, etc. Each one of these microbial processes may either increase or decrease radionuclide mobility, depending on the element, the soil reactivity and the environmental conditions. The resulting effect of these processes is still poorly known. This literature review intends to present a comprehensive overview of the role of micro-organisms on radionuclide mobility. It aims at classifying these elements, regarding to their potential sensitivity to these microbial processes. It summarizes the theoretical effect of these mechanisms, resulting in a potential increase or decrease of the solid-liquid distribution. The environmental significance of such processes for various biogeochemical radionuclides cycles still remains to be confirmed by experiments. (This study is part of a research program supported by Andra).

Pu(V)O2+ Adsorption and Reduction by Synthetic Hematite and Goethite

Changes in aqueous- and solid-phase plutonium oxidation state were monitored over time in hematite (alpha-Fe2O3) and goethite (alpha-FeOOH) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Solid-phase oxidation state distribution was quantified by leaching plutonium into the aqueous phase and applying an ultrafiltration/solvent extraction technique. The technique was verified using oxidation state analogues of plutonium and sediment-free controls of known Pu oxidation state. Batch kinetic experiments were conducted at hematite and goethite concentrations between 10 and 500 m2 L(-1) in the pH range of 3-8. Surface-mediated reduction of Pu(V) was observed for both minerals at pH values of 4.5 and greater. At pH 3 no adsorption of Pu(V) was observed on either goethite or hematite; consequently, no reduction was observed. For hematite, adsorption of Pu(V) was the rate-limiting step in the adsorption/reduction process. In the pH range of 5-8, the overall removal of Pu(V) from the system (solid and aqueous phases) was found to be approximately second order with respect to hematite concentration and of order -0.39 with respect to the hydrogen ion concentration. The overall reaction rate constant (k(rxn)), including both adsorption and reduction of Pu(V), was 1.75+/-2.05 x 10(-10) (m(-2) L)(-2.08) (mol(-1) L)(-0.39) (s(-1)). In contrast to hematite, Pu(V) adsorption to goethite occurred rapidly relative to reduction. At a given pH,the reduction rate was approximately independent of the goethite concentration, although the hydrogen ion concentration (pH) had only a slight effect on the overall reaction rate. For goethite, the overall reaction rates at pH 5 and pH 8 were 6.0 x 10(-5) and 1.5 x 10(-4) s(-1), respectively. For hematite, the reaction rate increased by 3 orders of magnitude across the same pH range.

The solid-phase oxidation of steroidal alkenes with potassium permanganate and metal salts

The oxidation of steroidal alkenes by potassium permanganate and metal salts in the solid phase gives epoxides with a stereochemistry that can differ from that obtained by the use of per-acids.

Solid Phase Oxidation of Alcohols and Benzyl Halides to Carbonyls Using Bromate Exchange Resin.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solid Phase Oxidation of Alcohols and Benzyl Halides to Carbonyls Using Bromate Exchange Resin

Aromate exchange resin prepared by a simple elution technique and used for the biphasic oxidation of alcohols and benzyi halides to corresponding carbonyl compounds.