Gas Evolution Rate Research Articles

Mechanism of gas evolution from the cathode of lithium-ion batteries at the initial stage of high-temperature storage

The evolution of gas in lithium-ion batteries (LIBs) at a charged state is one of the main problems in the industry because it causes significant distortion or swelling of the batteries. The mechanism of the gas-generating reaction related to the cathode at a charged state of LIBs was investigated. A side reaction between the electrolyte solution and free lithium compounds, such as Li2CO3 or LiOH in the cathode, is considered as the main cause of gas evolution at early stages of the storage test. Both Li2CO3 and LiOH generated CO2 mainly by a HF-mediated reaction, but the evolution of CO2 could be triggered by addition of H2O without a fluorine source for LiOH. Ni-based cathode materials generated more gas than conventional LiCoO2 at the initial stage because they contain more free lithium compounds, but the rate of gas evolution slowed down with time, suggesting that Ni-based active materials might be more appropriate for reducing long-term gas evolution in LIBs if the free lithium compounds could be removed effectively from the surface.

Effect of Reclamation on the Skin Layer of Ductile Iron Cast in Furan Molds

The paper presents the results of investigations of the influence of the quality of molding sand with furan resin hardened by paratoluenesulfonic acid, on the formation of microstructure and surface quality of ductile iron castings. Within the studies different molding sands were used: molding sand prepared with fresh sand and molding sands prepared with reclaimed sands of a different purification degree, determined by the ignition loss value. Various concentrations of sulfur and nitrogen in the sand molds as a function of the ignition loss were shown in the paper. A series of experimental melts of ductile iron in molds made of molding sand characterized by different levels of surface-active elements (e.g., sulfur) and different gas evolution rates were performed. It was shown that there exists a significant effect of the quality of the sand on the formation of the graphite degeneration layer.

Supported F-Doped <I>α</I>-Fe<SUB>2</SUB>O<SUB>3</SUB> Nanomaterials: Synthesis, Characterization and Photo-Assisted H<SUB>2</SUB> Production

Supported fluorine-doped alpha-Fe2O3 nanomaterials were synthesized by Plasma Enhanced-Chemical Vapor Deposition (PE-CVD) at temperatures between 300 and 500 degrees C, using a fluorinated iron(II) diketonate-diamine compound as a single-source precursor for both Fe and F. The system structure, morphology and composition were thoroughly investigated by various characterization techniques, highlighting the possibility of controlling the fluorine doping level by varying the sole growth temperature. Photocatalytic H2 production from water/ethanol solutions under simulated solar irradiation evidenced promising gas evolution rates, candidating the present PE-CVD approach as a valuable strategy to fabricate highly active supported materials.

Hydrogen and carbon monoxide generation from laser-induced graphitized nanodiamonds in water

Nanodiamonds (ND) were found to generate hydrogen (H2) and carbon monoxide (CO) from water at a remarkable rate under pulsed laser (532 nm) irradiation. The transformation of diamond structure into graphitic layers takes place to form an onion-like carbon structure. The CO generation suggests the oxidative degradation reaction of graphitic layers, C + H2O → CO + 2H(+) + 2e(-), which produced a unique laser-induced reaction: C + H2O → CO + H2. Au, Pt, Pd, Ag, and Cu nanoparticles on the ND enhance both gas evolution rates (~2 times for Au) and graphitization and, specifically, Au was found to be the most efficient amongst other nanoparticles. The enhancement effect was ascribed to effective charge separation between the metal nanoparticles and ND. The Au-ND hybrid on the reduced graphene oxide produced consistently a greater photocurrent than the ND upon visible light irradiation.

Plasmon-enhanced near-infrared-active materials in photoelectrochemical water splitting

We report the near-infrared-driven photoelectrochemical water splitting using a ZnO nanorod-array decorated with CdTe quantum dots and plasmon-enhanced upconversion nanoparticles. The plasmon enhanced the intensity of the upconversion emission, which improved the photocurrent and the gas evolution rate of the photoelectrochemical reaction greatly.

Semiconductor photo-electrochemical solar cells based on admixing of nano-materials for renewable energy

We studied a new type of TiO2-WO3 admixed septum-based semiconductor photo-electrochemical (SC-SEP, PEC) solar cell for photo-electro chemical measurement and hydrogen production. The SC-SEP cell in the configuration of SCE/1 M NaOH/TiO2 (ns)/Ti/H2SO4 + K2SO4/PtCE, PtWE showed photo-voltage and photo-current of 0.72 V and 8.6 mA/cm2, respectively, whereas the SC-SEP cell employing WO3 admixed TiO2 (ns) photo-electrode with the configuration: SCE/1 M NaOH/TiO2(ns)-WO3/Ti/H2SO4 + K2SO4/PtCE, PtWE, showed photo-voltage and photo-current of 0.96 V and 15.6 mA/cm2, respectively. The hydrogen gas evolution for the SC-SEP cell based on TiO2 (ns)/Ti photo-electrode was found to be 8.2 l/h/m2, while the WO3-modified ns-TiO2 exhibited a higher hydrogen gas evolution rate of 13.8 l/h/m2. The improved performance of new photo-electrode is due to improved spectral response of WO3 for the hydrogen gas evolution kinetics.

Investigations of the Quality of The Reclaim of Spent Moulding Sands with Organic Binders

Abstract Modern investigation methods and equipment for the quality estimation of the moulding sands matrices with organic binders, in their circulation process, are presented in the paper. These methods, utilising the special equipment combined with the authors investigation methods developed in the Faculty of Foundry Engineering, AGH the University of Science and Technology, allow for the better estimation of the matrix quality. Moulding sands systems with organic binders require an in-depth approach to factors deciding on the matrix technological suitability as well as on their environmental impact. Into modern methods allowing for the better assessment of the matrix quality belongs the grain size analysis of the reclaimed material performed by means of the laser diffraction and also the estimation of the moulding sand gas evolution rate and identification of the emitted gases and their BTEX group gases content, since they are specially hazardous from the point of view of the Occupational Safety and Health.

Role of Heat Transfer in Early Stage Decarburization of DRI in Slag

The gas generation from reactions between direct reduced iron (DRI) pellets and steelmaking slags is known to take place in two stages; (1) the reaction of FeO and carbon within DRI, i.e., pellet internal reaction, followed by (2) the reduction of slag FeO with DRI carbon at the pellet–slag interface, if any carbon remains from the first step. To understand the controlling mechanism of the reaction between FeO and C inside DRI, the rate of the gas release and the temperature of pellets suspended in a slag-free atmosphere were quantified. The results were used to determine the apparent thermal conductivity of DRI that showed values of approximately 0.5 to 2 W.m−1.K−1 for a temperature range of 573 K to 1273 K (300 °C to 1000 °C). Furthermore, it was found that the experimental gas evolution rates are consistent with the values predicted by a heat–transfer based model, confirming that the FeO-C reaction within pellet is controlled by the rate of heat transfer from the slag to the DRI pellet.

Water Electrolysis Using Water-Absorbing Porous Electrolyte Consisting of a Sulfonated Nanotitania Proton Conductor

A sulfonated nanotitania proton conductor based on hydrous titania was applied to water electrolysis as a hydrogen production method from electricity. Hydrous titania in the form of nanoparticles was used as a water absorbing porous electrolyte to allow water transport to the anode via electrolyte part of the water electrolysis cell. Overpotential of the porous electrolyte cell in water was lower than that of the Nafion 117 membrane. Evolution of hydrogen and oxygen by electrolysis were confirmed although the rates of gas evolution were smaller than those calculated from Faraday’s law.

Are Uncatalyzed Bromate Oscillators Truly Gas-Free?

Gas evolution is a common byproduct of chemical oscillations but is seldom treated as anything but a complication. Its precise quantification is usually underestimated, and if not obvious enough, gaseous products are easily neglected completely. Reported herein is how evolution of gas from uncatalyzed bromate oscillators with pyrocatechol, pyrogallol, and 1,4-cyclohexanedione was measured by a high-precision batch-mode gasometric method, and the data obtained with unprecedented time resolution are presented. Even though within this completely closed arrangement of measurement no oscillations in rate of gas evolution were observed, it is verified that neither of the substrates can be considered totally free of gas production. Nevertheless, the amount of gas evolved from 1,4-cyclohexanedione was confirmed to be very small, and near negligible, if only oscillatory phase is of interest. Conversely, under identical conditions, the peak rates of gas evolution from the other substrates were reached much sooner, and even though the results in all three cases suggest some extent of suppression of gas production by oscillations, as much as 1 equiv of gas in total can be produced from the phenols, especially from pyrogallol, where the degradation was measured to be approximately twice as extensive. Greater caution is, therefore, recommended whenever the gas-free nature of these oscillators is considered.

Kinetics of methoxy-NNO-Azoxymethane hydrolysis in strong acids

The kinetics of methoxy-NNO-azoxymethane (I) hydrolysis in concentrated solutions of strong acids (HBr, HCl, HClO4, and H2SO4) has been investigated by a manometric method. The gas evolution rate is described by the equation corresponding to two consecutive first-order reactions, with the rate constant of the second reaction considerably exceeding the rate constant of the first reaction, i.e., k 2 {ie17-1} k 1. The temperature dependences of k 1 (s−1) in 47.59% HBr in the temperature range from 60 to 90°C and in 64.16% H2SO4 between 80 and 130°C are described by Arrhenius equations with IogA= 12.7 ± 1.5 and 13.6 ± 1.4 and E a = 115 ± 10 and 137 ± 10 kJ/mol, respectively. The parameters of the Arrhenius equation for the rate constant k 2 for the reaction in 64.16% H2SO4 between 80 and 130°C are IogA= 9.1 ± 2.5 and E a = 91 ± 18 kJ/mol. An analysis of the UV spectra of compound I in concentrated H2SO4 shows that I is a weak base \( (pK_{BH^ + } \approx - 6) \). The rate-determining step of the hydrolysis of I is the attack of the nucleophile on the carbon atom of the MeO group of the protonated molecule of I. The resulting methyldiazene dioxide decomposes via a complicated mechanism to evolve N2, NO, and N2O. The pseudo-first-order rate constant k 1 of the reaction at 80°C depends strongly on the acid concentration and on the type of nucleophile (Br−, Cl−, or H2O). The relationship between k 1 and the rate constant k of the bimolecular nucleophilic substitution reaction (SN2) is given by the linear equation log\( [k_1 /(C_H + C_{Nu} )] = m^ \ne m*X_0 + \log (k/K_{BH^ + } ) \), where \( C_{H^ + } \) and C Nu are the concentrations of H+ and nucleophile, respectively; X 0 is the excess acidity; and m ≠ and m* are coefficients. The Swain-Scott equation log\( (k_{Nu} /k_{H_2 O} ) = ns \), where n is the nucleophilicity factor and s is the substrate constant (s = 0.72), is applicable to the rate constants k of the SN2 reactions of the protonated molecule of I with Br−, Cl−, and H2O.

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H2 and CO2 are larger in steam gasification.

Water-Splitting Photoelectrolysis Reaction Rate via Microscopic Imaging of Evolved Oxygen Bubbles

Bubble formation and growth on a water-splitting semiconductor photoelectrode under illumination with above-bandgap radiation provide a direct measurement of the gas-evolving reaction rate. Optical microscopy was used to record the bubble growth on single-crystal strontium titanate immersed in basic aqueous electrolyte and illuminated with UV light at 351/364 nm from a focused argon laser. By analyzing the bubble size as a function of time, the water-splitting reaction rate was determined for varying light intensities and was compared to photocurrent measurements. Bubble nucleation was explored on an illuminated flat surface, as well as the subsequent light scattering and electrode shielding due to the bubble. This technique allows a quantitative examination of the actual gas evolution rate during photoelectrochemical water splitting, independent of current measurements.

Assembly of Core−Shell Structures for Photocatalytic Hydrogen Evolution from Aqueous Methanol

We present a layer-by-layer assembly approach for the construction of core−shell structures with photocatalytic activity for hydrogen evolution from aqueous methanol. Submicrometer silica spheres and ultrasonicated (TBA, H)Ca2Nb3O10 and PA2K2Nb6O17 nanosheets are used as the building blocks to assemble core−shell structures with single and double (homostacked and heterostacked) nanosheet layers via sequential electrostatic coupling with poly(diallyldimethylammonium) chloride (PDDA). The lateral nanosheet distribution on the SiO2 spheres is observed with SEM while the stacking is directly observed with TEM. Diffuse reflectance UV/vis spectra reveal the nanosheet absorbance edge at ∼350 nm. All core−shell structures are active for photocatalytic H2 evolution from aqueous methanol solution with gas evolution rates comparable or smaller than observed for individually dispersed nanosheets. Heterostacks were more active than homostacks, with the latter being comparable to single layers (at equal mass). Loading ...

Effect of pH on the in vitro corrosion rate of magnesium degradable implant material

Magnesium (Mg) has been recently advocated as a potential metallic material for degradable bone plates. The corrosion behavior of Mg in body fluids at different pH values, however, has not been fully studied. The pH value of the body fluid at the location of bone fracture changes during the course of recovery, and study of the effect of pH on the corrosion rate of Mg provides important information in the development and design of Mg implants. In the present study, the corrosion behavior of Mg in Hanks' solution (a simulated body fluid) at pH value ranging from 5.5 to 8.0 was studied via monitoring the rate of hydrogen gas evolution. The experimental results show that the pH value has very large effect on the corrosion rate in Hanks' solution within the range 5.5 to 8.0. The corrosion rate (penetration rate) at pH 5.5 exceeds 800 μm per day, which is extremely high. On the other hand, it drops to about 6 μm and 3 μm per day at pH 7.4 and 8.0, respectively. The corrosion behavior of Mg at different pH values was also studied using electrochemical methods, including potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS).

A simple automated system for measuring soil respiration by gas chromatography

An automated dynamic closed chamber system for CO(2) sampling and analysis was developed for the measurement of soil respiration under laboratory conditions. The system is composed by a gas chromatograph linked to a fully computerised sampling system composed by 16 sample jars and 2 multiposition valves. Besides CO(2), the system can automatically and simultaneously measure CH(4), N(2)O and other gases of environmental interest. The detection limits of the system for CO(2), N(2)O and CH(4) were 2, 1 and 4ppmv, respectively. The accuracy of the system, expressed as percent bias, was -0.88, -0.94 and -3.17% for CO(2), N(2)O and CH(4), respectively, with relative standard deviation of 0.42, 0.68 and 0.61%. Measurement of CO(2) evolved following acidification of a known amount of reagent grade CaCO(3) showed a standard recovery of 96.8+/-2.5% reached within 30s after acidification. A linear response of CO(2) respiration was obtained for a wide range of operative conditions (5-60min accumulation time, 10-80g soil sample size, 10-60mLmin(-1) air flow rate, 15-25 degrees C temperature of incubation) demonstrating the flexibility of the system, which allows for the measurement of soil samples characterised by different rates of gas evolution. Moreover, the results obtained with soil samples showed that within the above conditions the proposed system is not affected by potential limitations of static closed chamber systems such as CO(2) dissolution in the soil solution, reduced rate of CO(2) diffusion from soil to headspace and CO(2) inhibition of microbial activity. The system was also capable to detect significant changes in N(2)O emissions from soil amended with different amounts of glutamic acid. The automatic and frequent measurements provided by the system make possible an accurate description of the dynamics of gas evolution from soil samples under laboratory conditions.

An Experimental Study of the Coking Process

The coking process includes two dynamic and isothermal steps. In this process, some factors control the coke formation kinetics. In this research, effects of some important and effective parameters of feed on the quality of petroleum coke were studied. Two hydrocarbon residue feeds; Cracked Fuel Oil (CFO) and Styrene Monomer Tar (SMTAR) were used at 500°C with atmospheric pressure of nitrogen used as an inert gas. Rate of weight loss and gas evolution from these feeds were considered by data of thermal analysis TG (thermogravimetry) and DTG (derivative thermogravimetry). Based on the results, CFO was assigned as the better feed. After selecting better feed, simultaneous thermogravimetry-differential analysis (TG-DTA) was used to study the pyrolysis kinetics of CFO. Samples were heated in a TG-DTA apparatus in nitrogen atmosphere at a temperature range of 37-600°C. The activation energy (Ea) and pre-exponential factor (A) were calculated from the experimental results by using a three stage Arrhenius-type kinetic model and showed that CFO pyrolysis kinetics at temperature ranges 37-285, 320-450 and 467-600°C follows first, second and first order kinetics, respectively. Attentive to temperature increase and reaction progress, activation energy and pre-exponential factor indicated different values at each stage. Also, kinetics of the isothermal step of coke formation was studied during heating of CFO. Samples were reacted in a tube furnace at 450°C and with nitrogen atmosphere. The kinetics of coke formation for petroleum residue was followed by solvent extraction (insolubility in hexane (HI), toluene (TI)) and a development of TI approximate to apparent first order kinetics. The rate constant at this temperature was calculated and it was also observed that the coke formation had been started at a temperature below 450°C.

A Simple Method of Gas Evolution Measurement Suitable for Analysis of Batch Oscillating Reactions: Briggs−Rauscher System with Acetone Revisited

A high-precision batch-mode technique of gasometric measurement, employing weighing of liquid displaced by the gas, is proposed and supported by a detailed protocol for correct evaluation of the experimental data acquired. Results of measuring the gas production in the Briggs-Rauscher reaction with acetone, recorded following the procedures suggested, and precautions to be taken to enhance their reproducibility are discussed, and a previously undetected structure of the gas evolution rate peaks is reported.

Elucidation of the interaction among cellulose, xylan, and lignin in steam gasification of woody biomass

AbstractThe reaction mechanism for gas and tar evolution in the steam gasification of cellulose, lignin, xylan, and real biomass (pulverized eucalyptus) was investigated with a continuous cross‐flow moving bed type differential reactor, in which tar and gases can be fractionated according to reaction time. In the steam gasification of real biomass, the evolution rates of water‐soluble tar (derived from cellulose and hemicelluloses) and water‐insoluble tar (derived from lignin) decrease with increasing reaction time. It was found that the evolution of water‐soluble tar occurs earlier than in the gasification of pure cellulose, indicating an interaction of the three components. The predicted yield of water‐insoluble tar is substantially less than that of real biomass. This implies that the evolution of tar from the lignin component of biomass is enhanced, compared with pure lignin gasification, by other components. The gas evolution rate from real biomass is similar to that predicted by the superposition of cellulose, lignin, and xylan. © 2008 American Institute of Chemical Engineers AIChE J, 2009

Kinetics and Mechanism of Decarburization and Melting of Direct-Reduced Iron Pellets in Slag

An experimental study was conducted to understand the decarburization and melting behavior of direct-reduced iron (DRI) pellets in SiO2-Al2O3-CaO-MgO-FeO slags with various FeO concentrations (10 to 25 wt pct) and basicities (Bs), ranging from 1.5 to 2.5. The behavior of the pellet in slag was observed using the X-ray fluoroscopy technique; the rate of decarburization was simultaneously measured with a constant volume pressure increase technique. The study shows that the decarburization of DRI in slag at 1600 °C takes place in two stages. The first stage is the reaction between the FeO and the carbon inside the pellet, which is controlled by heat transfer from the slag to the pellet; the second stage involves the decarburization reaction between the FeO in the slag and the remaining carbon in the DRI. The kinetics of this stage is determined by the mass transfer of FeO in the slag and is strongly dependent on the FeO concentration. Depending on the physicochemical properties of the slag and the rate of gas evolution, the DRI may sink through, float inside the slag, or remain on top before complete decarburization.