Increasing H2O Concentration Research Articles

Exploring NH3 combustion in environments with CO2 and H2O via reactive molecular dynamics

In existing power units such as internal combustion engines and gas turbines, the combustion of ammonia mixed with hydrocarbon fuels can effectively enhance the combustion intensity of ammonia. In the duel-fuel combustion scenario, the effect mechanism of the main components of combustion exhaust gas i.e., CO2 and H2O on ammonia combustion is still unclear and needs to be studied. Therefore, this paper uses reactive molecular dynamics simulations to study the combustion and emission processes of ammonia in environments with CO2 and H2O. The effects of the diverse gas environments (N2/O2, O2/CO2, and O2/CO2/H2O environments), high CO2 levels, varying H2O proportions, and O2 concentrations on ammonia combustion and emission were systematically explored. It was found that ammonia consumption was accelerated in the O2/CO2/H2O environments compared to N2/O2 environments, resulting in more NH2, H2, and H2O production. The effect of high CO2 concentration on ammonia oxidation was mainly related to temperature. The simulations found that the high CO2 concentration inhibited ammonia consumption at T < 2800K while enhancing it at T ⩾ 2800K. In addition, the high CO2 concentration could inhibit NO production under stoichiometric conditions but promote the conversion of nitrogen-containing intermediates to NO with the oxidizing capacity of CO2 enhanced significantly under extremely high temperature conditions. It was found that the increasing content of H2O molecules in the environment promoted NO production and inhibited CO production under stoichiometric conditions. In addition, the reaction paths for the conversion of HNO and HNO2 molecules into NO molecules were significantly enhanced with increasing H2O concentration. The increase in oxygen concentration can promote OH radical production and NO formation at high temperatures.

Experimental study on the structure and reactivity of char in pressurized O2/H2O atmosphere

Pressurized O2/H2O combustion is regarded as a promising high-efficiency CCS technology. In this study, char combustion in a pressurized O2/H2O atmosphere was performed with a pressurized horizontal tube furnace. The effects of pressure (0.1–1.3 MPa) and H2O concentration (0–60%) on char conversion, char physicochemical structure and reactivity were investigated by means of XPS, Raman, temperature-programed desorption and TGA tests. The results show that both pressurization and H2O can promote char conversion and facilitate the formation of carbon‑oxygen bonds on the char surface. Pressure mainly affects the consumption and generation of micropores, while the effect of H2O on the pore structure has no obvious selectivity. Pressurization reduces the relative content of CC, while H2O has the opposite effect. At low pressure (0.1–0.7 MPa) and low H2O concentration (0–40%), pressurization and H2O can promote the formation of C(O) on the surface of char. The reactivity of char first decreased and then increased with increasing pressure and increasing H2O concentration.

Modeling of single-particle char combustion under O2/H2O conditions: Effects of temperature and steam concentration

In this study, the single-particle char-O2/H2O combustion kinetic model was modified based on the one-dimensional unsteady mass and heat transfer equation coupled with the Maxwell–Stefan multicomponent diffusion coefficient. Numerical simulations of char-O2/H2O combustion at different reaction temperatures and H2O concentrations were performed. The simulation results show that the average temperature of a char particle decreases with increasing H2O concentration, and the particle temperature is higher in the inner layer than in the outer layer. Without H2O, O2 consumption in the boundary layer accounts for 50% of the total O2 consumption at different temperatures. Higher temperatures and H2O concentrations promote competition for O2 by homogeneous reactions in the boundary layer. Char-O2/H2O combustion is simultaneously controlled by O2 external diffusion and internal diffusion. Control by O2 internal diffusion is hardly affected by the H2O concentration. The contribution of the gasification reaction to carbon consumption increases with increasing temperature and H2O concentration. Increasing the H2O concentration three-fold from 5% increases the contribution of the gasification reaction to carbon consumption 1.96-fold at 1373 K, but only 1.25-fold at 1673 K.

Oxymethylene Ethers: Quantifying the Effect of Fuel Chain Length and Water Emulsification on Emissions and Combustion in a Heavy-Duty Diesel Engine via Linear Regression Analysis

Due to the nature of diffusive combustion, diesel engines display a distinct trade-off between nitrogen oxide (NOX) and particulate matter (PM). Since emission regulations become ever stricter, the relevance of dissolving this trade-off increases steadily as it hinders engine development from achieving ultralow emission levels. Seeking new opportunities to approach the problem, the modification of fuel properties has gained much attention. In particular, oxygenated fuels reduce particle emissions drastically, while having little adverse impact on NOX. Similarly, water (H2O) emulsification of diesel is commonly reported to reduce both NOX and PM. Both methods appear very promising, yet only few investigations were conducted in an effort of combing the benefits of the two. With this work, the authors provide a detailed study on combustion and emissions for both neat oxymethylene ethers (OME2-OME5) and an H2O-emulsified OME mixture (OMEmix). By varying injection pressure and fuel properties (i.e., fuel chain length/H2O fraction in OMEmix) separately, the sole impact of altered fuel on the investigated measurands (NOX, carbon dioxide [CO2], combustion speed, cylinder pressure, heat release) could be distinguished and quantified on the basis of a linear regression analysis. It was found that the impact of fuel properties does not interact with varied operating conditions (i.e., rail pressure); thus the impact of altered fuel (chain length, H2O content) onto the measurands is nearly constant. With respect to NOX, the effect of increased fuel chain length (−0.73 g/kWhi with an increase in chain length of one) was found to be approximately twice as pronounced when directly compared with increasing H2O concentration (−0.41 g/kWhi with a 1% increase in H2O share). It was found that CO2 emissions are directly correlating to a rising fuel chain length (approx. +23 g/kWhi with an increase in chain length of one). The latter also affects the combustion process (i.e., combustion speed, max. heat release, max. cylinder pressure) in near-linear correlation. Contrary to the impact of neat OMEn chain length, an additional H2O share in OMEmix barely affected the combustion process.

Reaction process and characteristics for coal char gasification under changed CO2/H2O atmosphere in various reaction stages

During the operation of industrial gasifier, the concentrations of CO2 and H2O in gasification media vary with the change of stages, causing the gasification process being affected accordingly. Therefore, dividing the gasification process into different stages to study the effect of multi-stage switching atmosphere is significant. The conversion rate, reaction characteristics and reaction process for the gasification of Xiaolongtan (XLT) coal char in different atmospheres (CO2/H2O/N2) switching in the early, middle and late reaction stages were investigated using thermo-gravimetric analysis (TGA). The results indicated that the average reaction rate of coal char with H2O was approximately 3 times that of CO2. Increasing H2O concentration improved the reaction and conversion rate of coal char, which was the most obvious in the early stage. With the H2O concentration increasing from 0 to 95%, the increment of conversion rate in the early, middle, and late stages were 7.13%, 4.40%, and 3.92%, respectively. Thus, considering the problem of H2O corrosion in practical production, the H2O concentration could be appropriately increased in the early stage to improve efficiency. Compared with the random pore model, the shrinking core model fitted the gasification process of coal char better in a highly reactive 95% H2O/5% N2 atmosphere.

A study of the effect of H2O on char oxidation during O2/H2O combustion using reactive dynamic simulation

In present work, the effect of H2O on the oxidation of char during O2/H2O combustion is investigated by reactive molecular dynamics simulation (ReaxFF MD). The simulation results show that H2O promotes the overall carbon conversion of char, which is consistent with the experimental results. By analyzing the distribution of H2 yield, the contributions of the char-H2O gasification reaction to the overall carbon conversion at different temperatures are quantitatively determined. The activation energy of char-H2O gasification reaction obtained from ReaxFF MD simulations is 199 kJ/mol. The contributions of the oxidation reactions to the overall carbon conversion in O2/H2O combustion are also obtained. The results show that the carbon oxidation is enhanced by the reactivity of H2O. The effect mechanism of H2O on char oxidation is revealed by analyzing the distributions of OH radicals·H2O significantly increases the concentration of OH radicals through the reaction of H2O with O radicals. Then, the contribution of H2O to the oxidation rate of char at different char conversions in O2/H2O combustion is quantitatively determined based on the assumption that char oxidation and char gasification reactions occur at separate active carbon sites. Finally, the effect of H2O concentration on the contribution of H2O to the oxidation rate of char is investigated. The results show that the oxidation rate contributed by H2O is enhanced with increasing H2O concentration.

Direct CO2 conversion to syngas in a BaCe0.2Zr0.7Y0.1O3- δ-based proton-conducting electrolysis cell

Electrolysis of steam and CO2 is considered to be a promising instrument for energy storage via sustainable H2 and hydrocarbon production. A model electrolysis cell was assembled using a thick BaCe0.2Zr0.7Y0.1O3-δ (BCZY27) electrolyte and two distinct electrodes, i.e., a (H2-cathode) porous Pt layer; and (steam-anode) a composite made of 60 vol. % La0.8Sr0.2MnO3-δ (LSM) and 40 vol. % BCZY27. The as-sintered steam electrode was catalytically-activated with Pr6O11-CeO2 nanoparticles. The cell was characterized by means of voltamperometry and impedance spectroscopy. Different operation parameters were analyzed: temperature; water concentration in the anode chamber; and H2 and CO2 concentration in the cathode chamber. Increasing H2O concentration (in the anode) and presence of CO2 (in the cathode) positively affected the electrode performance giving rise to lower cell overpotential and, consequently, substantial improvement in Faradaic efficiency. The high electrolyte thickness and the non-optimized Pt cathode limited the range of current density and the achieved peak power densities. The Faradaic efficiency for water electrolysis reached a value of 39% at 10.4 mA/cm2, as determined by the analysis of the H2 production. During co-electrolysis, the CO2 reaction was fostered by co-feeding a minimum H2 amount. CO formation took place through the reverse water gas shift (RWGS) reaction. When the current density was applied, CO2 conversion increased due mainly to the non-Faradaic electrochemical modification of catalytic activity (NEMCA effect) that allowed for the improvement of CO2 hydrogenation kinetics.

Effects of water addition on soot properties in ethylene inverse diffusion flames

The effects of H2O addition on the evolutions of soot morphology, nanostructure, and oxidation reactivity were investigated in ethylene inverse diffusion flames. The thermophoretic sampling and transmission electron microscopy (TEM) analysis were used to evaluate the soot morphological characteristics including primary particle diameter, projected area of agglomerates, and fractal dimension. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were utilized to gain the nanostructure and crystallite features and thermogravimetric analyzer (TGA) was adopted for oxidation reactivity by analyzing the soot collected via quartz plate sampling. A reduction in soot production was found with increasing H2O concentration, which illustrated an inhibition effect of H2O on soot formation. The soot morphology evolutions further demonstrated that H2O addition could decrease soot inception process from the reduced sizes of primary particles and agglomerates, and fractal dimension. The HRTEM and XRD results showed that the increasing H2O addition led to larger fringe length, lower fringe tortuosity, and smaller interlayer spacing of soot, which indicated a higher carbonization degree in soot nanostructure. The soot oxidation reactivity was slightly reduced with H2O addition.

Study of the flue gas characteristics and gasification reaction of pulverized coal combustion in O2/CO2/H2O atmosphere

ABSTRACTThe impacts of O2 and H2O on the combustion characteristics of pulverized coal in O2/CO2/H2O atmosphere were studied. The gasification reaction ratio was calculated from the components of flue gas. The competition exists between C-CO2 and C-H2O reactions under rich CO2 atmosphere. At various H2O concentrations, the differences were found in generation amounts of CO and H2 in flue gas. At O2 concentrations <10%, C-CO2 reaction decreased while C-H2O reaction increased with increasing H2O concentration; while at O2 concentration >30%, H2O showed no obvious specific patterns of effects. The gasification ratio was reduced as coal ranks increase.

Effect of CO2 and H2O on the combustion characteristics and ash formation of pulverized coal in oxy-fuel conditions

The combustion characteristics and ash formation of pulverized coal under different atmospheres (O2/N2, O2/CO2 and O2/H2O/CO2) were investigated using an isothermal thermal analysis system. The burning rate in O2/N2 was faster than that in O2/CO2 due to differences in the physical properties between N2 and CO2 at 800 °C. The effect of CO2 gasification was enhanced with increasing temperature; as a result, the overall reaction rate in O2/CO2 approached and exceeded the combustion rate in O2/N2. However, the effect of gasification was weakened by increasing O2 concentration, and the overall reaction rate in O2/CO2 decreased and eventually lagged the combustion rate in O2/N2. Because of the distinct physical properties of H2O, the burning rate in O2/CO2/H2O was lower than that in O2/N2 but higher than that in O2/CO2 at 800 °C. At a low O2 concentration, the influence of CO2 and H2O gasification was enhanced with increasing temperature; thus, the overall reaction rate in O2/H2O/CO2 was higher than that in O2/CO2. Moreover, the burning rate in O2/H2O/CO2 increased slightly with increasing H2O concentration. However, higher O2 concentrations weakened the effect of gasification, leading to similar burning processes under different atmospheres. The XRD analysis of the ash samples showed that CO2 and H2O had no significant effect on the transformation of main minerals.

Effects of H2O in the Feed of Sulfur Recovery Unit on Sulfur Production and Aromatics Emission from Claus Furnace

An increase in the exploitation of sour reservoirs with a high content of acid gas (mainly H2S and CO2) and the enforcement of stringent emission standards have triggered demand for high sulfur recovery efficiency in sulfur recovery units (SRUs). The high amount of H2O that is present in feed gases to the SRU can act as a diluent in the thermal section of the SRU and can also pose operational difficulties and have substantial chemical effect on the equilibrium-limited reactions of sulfur production and the destruction of impurities. This paper explores the role of H2O (0–12% in the furnace feed) in sulfur recovery and in the fate of undesirable aromatics, COS, and CS2 in the thermal section using a detailed reaction mechanism and industrial SRU operating parameters. An increasing H2O concentration in the feed decreased the sulfur recovery efficiency in the thermal section significantly, as the equilibrium conversion of H2S to sulfur was affected. The higher H2O concentrations increased the concentrations ...

Effects of H2O on NO Emission during Oxy-coal Combustion with Wet Recycle

This study investigated the characteristics of NO emissions during oxy-coal combustion with wet-recycle, especially in the presence of high H2O concentrations. The oxy-combustion was carried out using two types of coal, namely Leiyang (LY) anthracite and Zhundong (ZD) bituminous coals, inside a 24 kW drop tube furnace under different O2/CO2/H2O atmospheres. The results showed that the NO conversion increased with decreasing CO2 concentration from 70% to 30% and decreased with increasing H2O concentration from 10% to 40%. Under the experimental conditions employed in this study, the fuel-N conversion for both LY and ZD coals under the oxy-coal wet recycled combustion was lower than that under the oxy-coal dry recycled combustion. The results indicated that H2O and CO2 showed a competitive effect on NO emissions, though both of them have positive effect on NO reduction. In order to investigate the effects of H2O/CO2 on recycled NO, oxy-coal combustion experiments were also performed with the initial additio...

Arsenic antisite and oxygen incorporation trends in GaAs grown by water-mediated close-spaced vapor transport

Close-spaced vapor transport (CSVT) provides a plausible path to lower the costs of GaAs deposition as it uses only solid precursors and provides precursor utilization in principle approaching 100%. However, the use of H2O as a transport agent causes O to be incorporated in CSVT films, and O has been associated with a number of electrically active defect centers in GaAs, which decrease minority carrier lifetimes. Using deep-level transient spectroscopy, we study the effect of H2O concentration and substrate temperature on electron trap concentrations in n-type GaAs. We find that the most-prominent O-related center (ELO) typically has a much higher concentration than the center usually associated with As antisites (EL2), but that overall defect concentrations can be as low as those in films deposited by common vapor phase techniques. The trends with increasing H2O concentration suggest that ELO is most likely a defect complex with two As antisites. We also consider the optimal conditions for achieving high growth rates and low defect concentrations using CSVT. The results of this study have implications for the future CSVT growth using halide transport agents, where the ELO defect would be eliminated but EL2 might have a higher concentration.

Effects of H2O Gasification Reaction on the Characteristics of Chars under Oxy-Fuel Combustion Conditions with Wet Recycle

This work aims to clarify the potential effects of the H2O gasification reaction on the characteristics of chars under oxy-fuel combustion conditions with wet recycle. Chars of a Chinese sub-bituminous coal were prepared in a fluidized-bed/fixed-bed reactor at 1350 K under CO2/N2, H2O/N2, and CO2/H2O atmospheres. Structures of the chars undergoing some extent of gasification were characterized with a micro-Raman spectrometer, Fourier transform infrared spectrometer, and the N2 adsorption technique. Char combustion reactivity was also obtained in a thermogravimetric analyzer to reveal the effects of structure changes on the char combustion reactivity in oxy-fuel combustion. The results indicate the H2O gasification reaction can really take place and accelerate the char consumption in CO2/H2O, but the effect extent is lower than that in H2O/N2. The H2O gasification reaction would affect the chemical structures of the char with increasing H2O concentration in CO2/H2O, and different phenomena are observed for...

Effects of water, depth and temperature on partial melting of mantle-wedge fluxed by hydrous sediment-melt in subduction zones

This study investigates the partial melting of variable bulk H2O-bearing parcels of mantle-wedge hybridized by partial melt derived from subducted metapelites, at pressure–temperature (P–T) conditions applicable to the hotter core of the mantle beneath volcanic arcs. Experiments are performed on mixtures of 25% sediment-melt and 75% fertile peridotite, from 1200 to 1300°C, at 2 and 3GPa, with bulk H2O concentrations of 4 and 6wt.%. Combining the results from these experiments with previous experiments containing 2wt.% bulk H2O (Mallik et al., 2015), it is observed that all melt compositions, except those produced in the lowest bulk H2O experiments at 3GPa, are saturated with olivine and orthopyroxene. Also, higher bulk H2O concentration increases melt fraction at the same P–T condition, and causes exhaustion of garnet, phlogopite and clinopyroxene at lower temperatures, for a given pressure. The activity coefficient of silica (ϒSiO2) for olivine-orthopyroxene saturated melt compositions (where the activity of silica, aSiO2, is buffered by the reaction olivine+SiO2=orthopyroxene) from this study and from mantle melting studies in the literature are calculated. In melt compositions generated at 2GPa or shallower, with increasing H2O concentration, ϒSiO2 increases from <1 to ∼1, indicating a transition from non-ideal mixing as OH− in the melt (ϒSiO2 <1) to ideal mixing as molecular H2O (ϒSiO2 ∼1). At pressures >2GPa, ϒSiO2 >1 at higher H2O concentrations in the melt, indicate requirement of excess energy to incorporate molecular H2O in the silicate melt structure, along with a preference for bridging species and polyhedral edge decorations. With vapor saturation in the presence of melt, ϒSiO2 decreases indicating approach towards ideal mixing of H2O in silicate melt. For similar H2O concentrations in the melt, ϒSiO2 for olivine-orthopyroxene saturated melts at 3GPa is higher than melts at 2GPa or shallower. This results in melts generated at 3GPa being more silica-poor than melts at 2GPa. Thus, variable bulk H2O and pressure of melt generation results in the partial melts from this study varying in composition from phonotephrite to basaltic andesite at 2GPa and foidite/phonotephrite to basalt at 3GPa, forming a spectrum of arc magmas. Modeling suggests that the trace element patterns of sediment-melt are unaffected by the process of hybridization within the hotter core of the mantle-wedge. K2O/H2O and H2O/Ce ratios of the sediment-melts are unaffected, within error, by the process of hybridization of the mantle-wedge. This implies that thermometers based on K2O/H2O and H2O/Ce ratios of arc lavas may be used to estimate slab-top temperatures when (a) sediment-melt from the slab reaches the hotter core of the mantle-wedge by focused flow (b) sediment-melt freezes in the overlying mantle at the slab-mantle interface and the hybridized package rises as a mélange diapir and partially melts at the hotter core of the mantle-wedge. Based on the results from this study and previous studies, both channelized and porous flow of sediment-melt/fluid through the sub-arc mantle can explain geochemical signatures of arc lavas under specific geodynamic scenarios of fluid/melt fluxing, hybridization, and subsequent mantle melting.

Probing the status of felsic magma reservoirs: Constraints from the P–T–H2O dependences of electrical conductivity of rhyolitic melt

Electrical conductivity of rhyolitic melts, combined with magnetotelluric data, can provide important constraints for the physicochemical conditions of active felsic magma reservoirs. Previous experimental investigations are limited to low H2O concentration (<3 wt% H2O) and low pressure (<0.2 GPa for hydrous melts). We here report new results from electrical conductivity measurements of peralkaline rhyolitic melts with 4.7 wt% Na2O and 0.1–7.9 wt% H2O at 868–1665 K and 0.5–1.0 GPa in piston cylinder apparatuses using sweeping-frequency impedance analyses. Logarithmic electrical conductivity (σ) is found to correlate linearly with H2O concentration and reciprocal temperature, and the influence of H2O has been considerably underestimated by previous work. The negative pressure effect on electrical conductivity appears to attenuate with increasing H2O concentration. Based on the new data, we develop the following electrical conductivity model for peralkaline rhyolitic melts under conditions up to 1665 K, 1.0 GPa, and 8 wt% H2O:log⁡σ=2.983−0.0732w−3528−233.8w+(763−7.5w2)PT where σ is electrical conductivity in S/m, T is temperature in K, w is H2O concentration in wt%, and P is pressure in GPa. According to the Nernst–Einstein relation, this conductivity model can also be applied to metaluminous and peraluminous rhyolitic melts by scaling down according to the diffusivity and concentration of Na+ (the primary charge carrier). With the new model, we suggest that the highest electrical anomaly beneath the Tianchi volcano corresponds to a melt fraction of ∼9% if the melt contains 5 wt% H2O, or to a melt fraction of ∼32% for 2 wt% H2O. Similarly, the magma reservoir beneath the Taupo volcanic zone, New Zealand is inferred to contain a fully molten rhyolite with 7.5 wt% H2O or 36% water-saturated melt with 10 wt% H2O.

Coupled Interactions between Volatile Activity and Fe Oxidation State during Arc Crustal Processes

Arc magmas erupted at the Earth’s surface are commonly more oxidized than those produced at mid-ocean ridges. Possible explanations for this high oxidation state are that the transfer of fluids during the subduction process results in direct oxidation of the sub-arc mantle wedge, or that oxidation is caused by the effect of later crustal processes, including protracted fractionation and degassing of volatile-rich magmas. This study sets out to investigate the effect of disequilibrium crustal processes that may involve coupled changes in H2O content and Fe oxidation state, by examining the degassing and hydration of sulphur-free rhyolites. We show that experimentally hydrated melts record strong increases in Fe3+/∑Fe with increasing H2O concentration as a result of changes in water activity. This is relevant for the passage of H2O-undersaturated melts from the deep crust towards shallow crustal storage regions, and raises the possibility that vertical variations in fO2 might develop within arc crust. Conversely, degassing experiments produce an increase in Fe3+/∑Fe with decreasing H2O concentration. In this case the oxidation is explained by loss of H2 as well as H2O into bubbles during decompression, consistent with thermodynamic modelling, and is relevant for magmas undergoing shallow degassing en route to the surface. We discuss these results in the context of the possible controls on fO2 during the generation, storage and ascent of magmas in arc settings, in particular considering the timescales of equilibration relative to observation as this affects the quality of the petrological record of magmatic fO2.

Influence of co-feeds additive on the photo-epoxidation of propylene over V–Ti/MCM-41 photocatalyst

In this work, the effects of co-feed species, namely, H2O or H2, on the photocatalytic epoxidation of propylene over V–Ti/MCM-41 are examined. A promoting effect on the C3H6 consumption rate is found under 0.6kPa H2O co-feed when the PO (propylene oxide) formation rate is not proportionally promoted, resulting a slightly decreased PO selectivity. With increasing H2O concentration, the reaction activity decreases and this can be attributed to surface site blocking by excess H2O. The presence of H2O also increases the stability of photocatalyst during reaction. Similar observation of the enhanced C3H6 consumption rate and the improved stability is found when 5.6kPa H2 is used as co-feed. We found that the catalyst stability is improved when the AA (acetaldehyde) is increased. This suggests that AA accumulation on the catalyst surface may lead to surface fouling and the observed deactivation. The presence of H2O or H2 co-feed, which can lead to hydroxyl radical (OH•), may impose a shift in the production formation of photocatalytic reaction.

Mixed electrical conduction in a hydrous pantellerite glass

Electrical conductivity measurements were carried out on pantelleritic trachyte glasses containing up to 3.5wt.% dissolved H2O. At temperatures below about 700K, we find evidence for small polaron conduction due to the presence of both ferrous and ferric iron in the glass. At the higher temperatures of the investigation (up to 973K), a marked change in the conductivity–temperature relation is observed, which suggests that an ionic conduction mechanism becomes the dominant means of charge transport. In the ionic conduction regime, conductivity increases with increasing H2O concentration. Activation energies are similar for both the anhydrous and hydrous glasses, indicating that the conductivity is controlled by sodium diffusion even for the highest H2O concentration examined. A slight variation in activation energy is observed depending on the H2O concentration, which is most likely associated with the depolymerising effect of dissolved water on the silicate network structure. At low temperatures, we find a dramatic effect of fO2 on the conductivity that supports an electronic conduction mechanism based on small polaron hopping between Fe3+ and Fe2+ sites. This electronic pathway controls the overall electrical conductivity in these alkali-rich glasses at temperatures exceeding 500°C if conditions remain anhydrous at an oxygen fugacity of 0.2atm.

Evaluation of Performance of InGaN/GaN Light-Emitting Diodes Fabricated Using NH3 with Intentionally Added H2O

We investigated the performance of InGaN/GaN light-emitting diodes (LEDs) fabricated using NH3 with intentionally added H2O. The H2O concentrations in NH3 were assessed quantitatively using an optical analyzing system. The oxygen concentration in the active layer was measured by secondary ion mass spectrometry and observed to increase with increasing H2O concentration. In addition, the oxygen was predominantly incorporated in InGaN well layers rather than in GaN barrier layers. The performance of LEDs markedly deteriorated with increasing H2O concentration. It was found by current–voltage measurement that oxygen in the multi quantum well layer increases leakage current.