Release Of Oxygen Gas Research Articles

Impact of Nickel on Next-Generation Li-Rich Oxide Cathodes for Li-Ion Batteries

As developments in lithium-ion batteries have focused on improving energy density, cycle life, and reducing cost, an important class of layered oxides with excess lithium, Li[Li,Ni,Mn,Co]O2, has been heavily studied as a next-generation electrode material. However, our limited understanding of the underlying electrochemical mechanisms hinders our ability to mitigate the negative impacts of these mechanisms, preventing commercialization. Previous studies have shown that these materials show a myriad of simultaneous mechanisms including changes in the nickel oxidation state, reversible oxygen redox accounting for capacities exceeding the theoretical limit1, oxygen gas release decreasing cycle efficiency2, as well as structural transformations leading to voltage fade3. Due to this complex mixture of electrochemical processes, model systems have been used extensively to observe these processes one at a time.This work on model systems is continued here by studying materials that show both nickel and oxygen redox but no structural transformations during cycling. This builds on work performed on Li-Fe-Sb-O and Li-Fe-Te-O where oxygen gas release was found to reduce Fe during charging of the electrode, an unexpected observation that had not been seen in other materials4. Given the use of nickel rather than iron in next-generation materials, herein we use Li-Ni-Sb-O and Li-Ni-Te-O as model systems to better understand the electrochemical contribution of Ni and O during cycling. The materials have been studied using extensive electrochemical tests, ex-situ powder X-ray diffraction, online electrochemical mass spectrometry, X-ray absorption near-edge spectroscopy and X-ray photoemission spectroscopy. Results show limited oxygen release from the particle surfaces only, coupled with a marked contrast between the nickel oxidation states at the surface (XPS) and those of the bulk of the particles (XANES). XPS data also demonstrates a slight reduction in surface nickel during oxygen gas release, confirming that the mechanism identified with Li-Fe-Sb-O does in fact occur in Ni-containing materials, though this is limited to the particle surface. Given that a great deal of work is currently being done to maximize the amount of nickel in next-generation electrode material, the consequences of nickel use in Li-rich oxides observed here are of high importance to further our understanding of the limitations of these materials that are currently preventing their commercialization. 1. McCalla, E. et al, Science 2015, 350 (6267), 1516.2. Jung, R. et al, Journal of The Electrochemical Society 2017, 164 (7), A1361-A1377.3. Gallagher, K. G et al, Electrochemistry Communications 2013, 33, 96-98.4. McCalla, E. et al, Journal of the American Chemical Society 2015, 137 (14), 4804-4814.

Influence of Composition and Nano-Scale Morphology on Enhancing the Acid Mediated Oxygen Evolution Electrocatalysis of Earth Abundant and Low PGM Containing Transition Metal Oxide Solid Solution Oxide Anodes

Acid mediated proton exchange membrane based water electrolysis (PEMWE) is currently at the forefront amongst various hydrogen production approaches for harvesting clean and sustainable hydrogen fuel.1-4 In the present study density functional theory (DFT), based calculations were used to rationalize the thermodynamics and kinetics of OER. Accordingly, we identified and fabricated theoretically predicted earth abundant metal oxide (e.g. MnO2 and SnO2) based solid solution electrocatalysts comprising low precious group metal (PGM-Ir) as solute and 10 wt. % anionic dopant (F) [(Mn,Ir)O2:F, (Sn,Ir)O2:F] in one-dimensional (1D) architectures (nanorods and nanotubes)1, 5. The as-synthesized (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F systems demonstrated superior OER electrocatalytic performance (Fig. 1A-B) in comparison to the state-of-the art IrO2 and 2D thin films of corresponding compositions. The (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F anodes (at 1.45 and 1.5V, respectively) exhibited significantly lower charge transfer resistance (Rct ~ 2.5 and 4.2 Ω cm2, respectively). Furthermore, the systems exhibited higher electrochemically active surface area (ECSA ~ 704 and 38 m2g-1, respectively) and higher mass activity (40 and 21 Ag-1, respectively). In addition, they displayed significantly lower over-potential (200 and 285 mV, respectively) to deliver the benchmark current density of ~ 10 mAcmgeo 2 in comparison to pristine IrO2 and 2D thin films compositions of (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F. Such excellent OER performance of these systems is indeed attributed to the modified electronic structures of MnO2 and SnO2 following solid solution formation with IrO2 with incorporation of F. Additionally, the attributes of 1D nanostructures contribute to the improvement in electrochemical performance. These include high active specific surface area, high aspect ratio (L/D), high active-site densities, high roughness factor, lower charge transfer resistance (Rct) and high electronic conductivity with the presence of 1D channels, lattice planes with fewer crystal boundaries, presence of sufficient porosity and open space between the adjacent 1D channels enabling rapid release of oxygen gas. Durability tests conducted for 24h in 1N H2SO4 display minimal current density loss, indicating good electrochemical stability. Therefore, the as-synthesized 1D low PGM containing (Mn0.8Ir0.2)O2:10F and (Sn0.8Ir0.2)O2:10F electrocatalyst systems demonstrate promise as high performance and potentially low cost acid assisted PEM water splitting electrocatalyst systems. Results of these studies will be presented and discussed. Acknowledgements: Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) is acknowledged.

An investigation onto Cd toxicity to freshwater microalga Chlorella sorokiniana in mixotrophy and photoautotrophy: A Bayesian approach

Aquatic ecosystems are composed by a myriad of dissolved organic materials that can be assimilated by microalgae, while they can perform photosynthesis, this is refereed as mixotrophy. However, ecotoxicological tests usually consider only the photoautotrophic metabolism. This research investigated the ecotoxicological differences between photoautotrophy and mixotrophy in Chlorella sorokiniana exposed to cadmium (Cd). Chlorophyll a, photosynthetic efficiency (Fv/Fm), cell viability, biochemical composition and pH were used to monitor possible toxic effects at 72 h cultures. Glucose (1 g.L−1) was used as organic carbon source. To evaluate the probability of the photoautotrophic culture being more affected by Cd than the mixotrophic one, Bayesian statistical analysis was performed. The photoautotrophic cultures were more affected by Cd than the mixotrophic ones, with reduction of all evaluated parameters, except for protein concentration. However, in mixotrophic cultures, no changes in protein concentration and proteins:carbohydrates ratio were observed, and chlorophyll a, Fv/Fm and cell viability were only affected at the high Cd concentrations (range ln −11.5 to −9.4). However, both mixotrophy and photoautotrophy had the same probability of having the carbohydrates concentration affected by Cd. We conclude that the microalgae in mixotrophy were more resistant to the Cd than in photoautotrophy. In addition, we showed that under photoautotrophy Fv/Fm decreased linearly as Cd concentration increased, but in mixotrophy no effect was observed up to 10−5 molL−1 Cd, after which it decreased. We rationale that the reduced photosynthetic capacity under mixotrophy can end up reducing the release of oxygen gas, which can compromise the entire aquatic ecosystem.

Engineering oxygen nanobubbles for the effective reversal of hypoxia

Hypoxia, which results from an inadequate supply of oxygen, is a major cause of concern in cancer therapy as it is associated with a reduction in the effectiveness of chemotherapy and radiotherapy in cancer treatment. Overexpression and stabilization of hypoxia-inducible factor 1α (HIF-1α) protein in tumours, due to hypoxia, results in poor prognosis and increased patient mortality. To increase oxygen tension in hypoxic areas, micro- and nanobubbles have been investigated by various researchers. In the present research, lipid-shelled oxygen nanobubbles (ONBs) were synthesized through a sonication method to reverse hypoxic conditions created in a custom-made hypoxic chamber. Release of oxygen gas from ONBs in deoxygenated water was evaluated by measuring dissolved oxygen. Hypoxic conditions were evaluated by performing in vitro experiments on MDA-MB231 breast cancer cells through the expression of HIF-1α and the fluorescence of image-iT™ hypoxia reagent. The results indicated the degradation of HIF-1α after the introduction of ONBs. We propose that ONBs are successful in reversing hypoxia, downregulating HIF-1α, and improving cellular conditions, leading to further medical applications.

Insight into the Relationship between Transition Metal and Anionic Redox As Found in Simple Li-Rich CuO-Li2O Composite Cathode Materials

Conventional lithium ion battery cathode materials derive their capacity exclusively from transition metal cation redox. Many recent studies on novel Li-rich cathode materials have found substantial reversible anionic redox that shows promise to greatly enhance battery capacity. Unfortunately, this anionic (oxygen) redox contribution to the charge compensation of lithium extraction and insertion typically results in cathode degradation and oxygen gas release. While previous studies have emphasized methods such as the doping of 4d or 5d transition metals to stabilize the formation of peroxo-like species, the mechanism of anionic redox in relation to the transition metals present is still largely unknown. This study employs simple Li-rich cathode materials as a model for further understanding of the mechanism of anionic redox. Here we have synthesized a number of materials including simple 3d transition metal (e.g., Cu) doped lithium oxide to more closely examine the relationship between oxygen redox and the transition metal present in the cathode material. The materials studied contain a high ratio of lithium to transition metal to probe the maximum anionic redox activity. We will discuss our results in which galvanostatic measurements are combined with quantitative gas evolution analysis, in addition to ex-situ resonant inelastic X-ray scattering and X-ray photoelectron spectroscopy on cycled electrodes, to continue to clarify the required conditions for anionic redox in lithium ion battery cathode materials.

Synthesis and Electrochemical and Structural Investigations of Oxidatively Stable Li2MoO3 and xLi2MoO3·(1 – x)LiMO2 Composite Cathodes

The structural evolution of Li2MoO3 during electrochemical delithiation/lithiation is reported. Li2MoO3 undergoes an irreversible crystalline to amorphous transformation which starts during the first delithiation step and gradually proceeds throughout subsequent cycles. This observation is supported by complementary data obtained from X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The amorphization does not prevent reversible Li storage, and the Li2MoO3 cathodes exhibit initial capacities of 147 mAh/g (corresponding to 0.87 Li cycled per formula unit) at an average operating potential ∼2.5 V vs Li/Li+ with reasonably good cycling stability (81% capacity retention after 50 cycles). In-situ mass spectrometry studies reveal the amorphization of Li2MoO3 does not involve the release of oxygen gas even when charged to very positive potentials (i.e., 4.8 V vs Li/Li+). The Li storage properties and excellent oxidative stability of Li2MoO3 make it a promising candidate to ...

Roles of Ultrasound on Hydroxyl Radical Generation and Bauxite Desulfurization from Water Electrolysis

Roles of ultrasound on the hydroxyl radical generation from water electrolysis were examined in this work. Results indicated that the ultrasound could not only strengthen the mass transfer of liquid phase, but also could improve the electron gain and loss for hydroxyl ion, and thus improve the hydroxyl radical generation. Results from ESR signal indicated that, ultrasonic strengthened hydroxyl radical formation from water electrolysis in whatever in alkaline or acidic solution. Ultrasound improved the equilibrium potential and current of OER, indicating that ultrasound inhibited the thermodynamics conditions in OER. Ultrasound inhibited the oxygen gas release, and thus resulting in the increase in the amount of hydroxyl radicals. The Rct of OER increased with ultrasound addition, while the Rs for water electrolysis decreased. Whatever platinum (Pt) or nickel (Ni) electrode, bauxite electrolysis desulfurization all were improved by ultrasound, and the desulfurization of Ni under ultrasound was higher than Pt without ultrasound. That is, electrolysis desulfurization with Ni electrode in presence of ultrasound could replace electrolysis desulfurization with Pt electrode in absence of ultrasound.

Enabling the high capacity of lithium-rich anti-fluorite lithium iron oxide by simultaneous anionic and cationic redox

Anionic redox reactions in cathodes of lithium-ion batteries are allowing opportunities to double or even triple the energy density. However, it is still challenging to develop a cathode, especially with Earth-abundant elements, that enables anionic redox activity for real-world applications, primarily due to limited strategies to intercept the oxygenates from further irreversible oxidation to O2 gas. Here we report simultaneous iron and oxygen redox activity in a Li-rich anti-fluorite Li5FeO4 electrode. During the removal of the first two Li ions, the oxidation potential of O2− is lowered to approximately 3.5 V versus Li+/Li0, at which potential the cationic oxidation occurs concurrently. These anionic and cationic redox reactions show high reversibility without any obvious O2 gas release. Moreover, this study provides an insightful guide to designing high-capacity cathodes with reversible oxygen redox activity by simply introducing oxygen ions that are exclusively coordinated by Li+. It is challenging to exploit anionic redox activity to boost performance of battery electrodes, especially for anti-fluorite structures. Here the authors report simultaneous anionic and cationic redox in Li5FeO4, which enables its high capacity and eliminates the undesired oxygen gas release.

Seamlessly Conductive 3D Nanoarchitecture of Core–Shell Ni‐Co Nanowire Network for Highly Efficient Oxygen Evolution

Electrochemical splitting of water is an attractive way to produce hydrogen fuel as a clean and renewable energy source. However, a major challenge is to accelerate the sluggish kinetics of the anodic half‐cell reaction where oxygen evolution reaction (OER) takes place. Here, a seamlessly conductive 3D architecture is reported with a carbon‐shelled Ni‐Co nanowire network as a highly efficient OER electrocatalyst. Highly porous and granular Ni‐Co nanowires are first grown on a carbon fiber woven fabric utilizing a cost‐effective hydrothermal method and then conductive carbon shell is coated on the Ni‐Co nanowires via glucose carbonization and annealing processes. The conductive carbon layer surrounding the nanowires is introduced to provide a continuous pathway for facile electron transport throughout the whole of the integrated 3D catalyst. This 3D hierarchical structure provides several synergistic effects and beneficial functions including a large number of active sites, easy accessibility of water, fast electron transport, rapid release of oxygen gas, enhanced electrochemical durability, and stronger structural integrity, resulting in a remarkable OER activity that delivers an overpotential of 302 mV with a Tafel slope of 43.6 mV dec−1 at a current density of 10 mA cm−2 in an alkaline medium electrolyte (1 m KOH).

X-ray Computed Tomographic Investigation of the Porosity and Morphology of Plasma Electrolytic Oxidation Coatings.

Plasma electrolytic oxidation (PEO) is of increasing interest for the formation of ceramic coatings on metals for applications that require diverse coating properties, such as wear and corrosion resistance, low thermal conductivity, and biocompatibility. Porosity in the coatings can have an important impact on the coating performance. However, the quantification of the porosity in coatings can be difficult due to the wide range of pore sizes and the complexity of the coating morphology. In this work, a PEO coating formed on titanium is examined using high resolution X-ray computed tomography (X-ray CT). The observations are validated by comparisons of surface views and cross-sectional views of specific coating features obtained using X-ray CT and scanning electron microscopy. The X-ray CT technique is shown to be capable of resolving pores with volumes of at least 6 μm(3). Furthermore, the shapes of large pores are revealed and a correlation is demonstrated between the locations of the pores, nodules on the coating surface, and depressions in the titanium substrate. The locations and morphologies of the pores, which constitute 5.7% of the coating volume, indicate that they are generated by release of oxygen gas from the molten coating.

Reversible Li-Intercalation through Oxygen Reactivity in Li-Rich Li-Fe-Te Oxide Materials

Lithium-rich oxides are a promising class of positive electrode materials for next generation lithium-ion batteries, and oxygen plays a prominent role during electrochemical cycling either by forming peroxo-like species and/or by irreversibly forming oxygen gas during first charge. Here, we present Li-Fe-Te-O materials which show a tremendous amount of oxygen gas release. This oxygen release accounts for nearly all the capacity during the first charge and results in vacancies as seen by transmission electron microscopy. There is no oxidation of either metal during charge but significant changes in their environments. These changes are particularly extreme for tellurium. XRD and neutron powder diffraction both show limited changes during cycling and no appreciable change in lattice parameters. A density functional theory study of this material is performed and demonstrates that the holes created on some of the oxygen atoms upon oxidation are partially stabilized through the formation of shorter O-O bonds, i.e. (O2)n– species which on further delithiation show a spontaneous O2 de-coordination from the cationic network and migration to the now empty lithium layer. The rate limiting step during charge is undoubtedly the diffusion of oxygen either out along the lithium layer or via columns of oxygen atoms.

A multi-step reaction model for ignition of fully-dense Al-CuO nanocomposite powders

A multi-step reaction model is developed to describe heterogeneous processes occurring upon heating of an Al-CuO nanocomposite material prepared by arrested reactive milling. The reaction model couples a previously derived Cabrera-Mott oxidation mechanism describing initial, low temperature processes and an aluminium oxidation model including formation of different alumina polymorphs at increased film thicknesses and higher temperatures. The reaction model is tuned using traces measured by differential scanning calorimetry. Ignition is studied for thin powder layers and individual particles using respectively the heated filament (heating rates of 103–104 K s−1) and laser ignition (heating rate ∼106 K s−1) experiments. The developed heterogeneous reaction model predicts a sharp temperature increase, which can be associated with ignition when the laser power approaches the experimental ignition threshold. In experiments, particles ignited by the laser beam are observed to explode, indicating a substantial gas release accompanying ignition. For the heated filament experiments, the model predicts exothermic reactions at the temperatures, at which ignition is observed experimentally; however, strong thermal contact between the metal filament and powder prevents the model from predicting the thermal runaway. It is suggested that oxygen gas release from decomposing CuO, as observed from particles exploding upon ignition in the laser beam, disrupts the thermal contact of the powder and filament; this phenomenon must be included in the filament ignition model to enable prediction of the temperature runaway.

Unipolar resistive switching mechanism speculated from irreversible low resistance state of Cu2O films

We observed cathode-interfaced electroreduction and a variation of oxygen content in an irreversible low resistance state of highly oriented cuprous oxide (Cu2O) films. These local microstructural and stoichiometric changes in hard breakdown of film allow speculation on the unipolar resistive switching mechanism: formation of metallic filaments originating from generation/migration of oxygen ions (O2−) from the cathode and release of oxygen gas through the anode. Based on the as-proposed switching model, endurance switching properties could be modulated from tens up to over 104 switching cycles by controlling ambient gas or the interface between Cu2O and anode.

Thermoanalytical study of the polymorphism and melting behavior of Cu2V2O7

We have developed a procedure for the synthesis of phase-pure α- and β-Cu2V2O7. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu2V2O7 (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu2V2O7, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu2V2O7, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu2V2O7, CuVO3, and other compounds.

Degradation of some ceria electrolytes under hydrogen contact nearby anode in solid oxide fuel cells (SOFCs)

This work is concerned with thermodynamic analysis of the stability of some ceria electrolytes under contact with hydrogen gas nearby anode in fuel cells. It was considered the following types of ceria-electrolytes: pure ceria, strontium-doped ceria, calcium-doped ceria and calcium-bismuth-doped ceria. The equilibrium Log (pH2O/pH2) vs. T diagrams were constructed for x = 0.1 and 0.01, where x is the fraction of initial ceria converted to Ce2O3 (proportional to the ratio between activities of Ce3+ and Ce4+ in the ceria electrolyte, which is proportional to the fraction of electronic conduction in the electrolyte at a given temperature). The predictions of the diagrams are as follows: (a) Ce1.9Ca0.1Bi0.8O5.1 and Ce0.9Sr0.1O1.9 are less stable than pure ceria for the whole temperature range (from 0 to 1000 °C); (b) Ce0.9Ca0.1O1.9 is more stable than pure ceria below about 650 °C for x = 0.1 and below about 400 °C for x = 0.01; (c) at each temperature in the considered range the pressure ratio pH2O(g)/pH2(g) has to be higher than thermodynamically predicted in order to keep CeO2 stable in the electrolyte contacting hydrogen gas. Thermodynamic predictions are entirely capable of explaining experimental data published on the subject (irreversible cell degradation in the case of SrO-doped ceria; weight loss from doped-ceria electrolyte above 700 °C; oxygen gas release during sintering of ceria).

Safe Scale-Up of Oxidation by Hydrogen Peroxide in Flammable Solvents

Oxidation of species by hydrogen peroxide gives rise to the potential to release oxygen, which in the presence of flammable solvents can lead to an explosion risk due to the extreme sensitivity to ignition of the resulting oxygen-enriched atmosphere. The release of oxygen gas in the form of bubbles from the liquid can produce an electrostatic field, which is capable of igniting sensitive flammable atmospheres in larger-scale operations. A method of inerting the system can be applied which makes the atmosphere nonflammable and the reaction safe, whilst minimising solvent losses. A practical scale-up from laboratory flask to pilot scale of 150 kg demonstrated that solvent losses, whilst significant, are not a barrier to production of fine chemical intermediates on a commercial scale.

Improvement in critical current densities of long length AgCu-sheathed Bi-2212 round wires

In order to avoid an injurious effect of release of oxygen gas during heat treatment on critical current densities ( J c) of AgCu-sheathed Bi-2212 round wires in long length, a modified heat treatment process has been developed. In this modified process, only a schedule of heat treatment for the partial melting and slow cooling process has been changed, instead of increased atmospheric pressures. A transport J c of about 2×10 4 A/cm 2 (critical current of 160 A) at 4.2 K and 10 T has been obtained for a wire 1.5 m in length, using the modified process. This value corresponds to about 80% of J c's of a few cm long wires, while J c's of long length wires heat treated by the conventional process are reduced to about 30% of short length wires. Relations between transport J c properties and microstructures such as the size and distribution of voids have been investigated, using X-ray radiography.

Synthesis of (Li,Mn) ferrites by reaction of ultrafine γ-Fe 2O 3 with LiMn 2O 4 spinel at 650°C

(Li,Mn) ferrites (LMFs; Li yMn 2yFe 3−3yO 4+δ, y = 0.27–0.75, δ = 0.01–0.04) were synthesized by solid-state reaction of ultrafine maghemite (γ-Fe 2O 3) with lithium manganese spinel (LiMn 2O 4) at 650°C. For y ≤ 0.5, the LMFs were synthesized in a He gas stream; for y > 0.5, the LMFs were formed in an air stream at 650°C. In the formation of LMF (y = 0.44), release of oxygen gas was observed at 460 and 650°C in a He gas stream. The oxygen release at 460°C was accompanied by the reaction of LiMn 2O 4 with γ-Fe 2O 3, and the release at 650°C was due to the reaction of the formed LMF and α-Fe 2O 3. The deviation of lattice constant from Vegard’s Law was largest at y = 0.5, where all Mn ions were trivalent.

Flashchain Theory for Rapid Coal Devolatilization Kinetics. 7. Predicting the Release of Oxygen Species from Various Coals

The release of oxygen from any coal primarily involves only three mechanisms: the shuttling of oxygen as an element in tar molecules; the simultaneous release of CO2, H2O, and small amounts of CO when labile bridges are converted into char links; and the release of CO from the residual oxygen in nascent char links at high temperatures. This modeling study characterizes these processes for heating rates from 0.5 to 104 K/s, temperatures to 1550 K, and pressures from 0.1 to 1 MPa. Evaluations against a database compiled from the behavior of 27 coal samples representing ranks from lignite to anthracite demonstrate that CO2, H2O, and CO yields plus the oxygen contents of tar and char can be predicted within useful tolerances throughout this domain. With Flashchain, no additional parameters or rate expressions are required to quantitatively predict the contributions from tar shuttling from any coal at any operating conditions. And the release rates of CO2, H2O, and low-temperature CO release are set equal to the previously evaluated formation rates of char links. Only one reaction rate expression (but no hypothetical ultimate yield parameter) is required to predict the yields and evolution rates of CO at high temperatures. This modeling approach departs from multiple, independent conversion channels for each gas product and instead recognizes the conversion of labile bridges into refractory char links as the fundamental process underlying the release of most of the oxygen-bearing noncondensible gases. As consequences of this premise, (a) oxygen is shuttled away in tars and simultaneously released as CO2 and H2O at all heating rates; (b) oxygen gas yields, especially H2O and CO yields, diminish in tandem with enhanced tar yields for faster heating rates or lower pressures; and (c) the onset of oxygen gas release shifts to higher temperatures for coals of progressively higher rank, particularly for low volatility coals. Production rates of high-temperature CO accelerate rapidly after the end of tar evolution, overtaking the production of CO2 and H2O from all coal types. CO is released over narrower temperature ranges for coals of progressively higher rank.

Radiolytic Aspects in Boiling Water Reactor Primary Systems: Results from Numerical Simulations and Statistical Regression Analyses

Dependencies of radiolytic aspects on geometric and operational conditions of boiling water reactor (BWR) primary systems were studied for normal operation or for hydrogen alternate water chemistry (HAWC) by using a computer simulation code AQUARY. Statistical regression analyses were applied to those calculated results and a great many close correlations were found among radiolytic concentrations. In the course of the study, it was discovered that residence time and energy deposition rate in th downcomer had a critical effect on HAWC. A set of simple estimation formulas for radiolytic conditions was proposed for normal BWR operation, and the following prediction formulas were proposed for the oxygen gas release rate and oxygen concentration in the recirculation line under HAWC: R0 = R0 exp (-0.00985 C* /SUB H/ ) and C02 = 191.3 exp (-0.0483 C /SUB H/ ).