Rate Of Isotope Exchange Reaction Research Articles

Investigation of Hydrogen Isotope Exchange Reaction Rate in Mixed Gas (H2 and D2) at Pressure up to 200 MPa Using Raman Spectroscopy

Currently the problem of theoretical calculation and experimental determination of the isotopic exchange rate in mixes of hydrogen isotopes is open. There are a few experimental data on exchange rate constants that are rather discrepant. Of interest are experimental data on isotopic exchange rate in a gaseous mix of hydrogen isotopes at high pressures (thousands atmospheres). Raman spectroscopy is a relevant method for obtaining objective data on isotopic exchange rate in a gaseous mix of hydrogen isotopes, since it allows one to determine a gaseous mix composition without sampling in a real time. The paper describes equipment which allows registration of Raman spectra for gases under pressure up to 400 MPa and experimental data determining the constants of isotopic exchange rate in a protium-deuterium mix at pressures up to 200 MPa.

Investigation of Hydrogen Isotope Exchange Reaction Rate in Mixed Gas (H2 and D2) at Pressure up to 200 MPa Using Raman Spectroscopy

Investigation of Hydrogen Isotope Exchange Reaction Rate in Mixed Gas (H2 and D2) at Pressure up to 200 MPa Using Raman Spectroscopy

Study of isotope exchange reactions on ceramic breeder materials deposited with noble metal

Lithium orthosilicate is one of the candidate materials of the tritium-breeding blanket of the D–T fusion reactors. Tritium is released via the exchange reaction with sweep gases containing hydrogen. It is expected that the isotope exchange reaction is promoted by adding noble metals that possess catalytic functions. Thus, palladium was deposited in a sample of lithium orthosilicate, and the effect of catalyst on the rate of isotope exchange reaction on the sample surface was examined. It was found that the isotope exchange reaction proceeds faster even at lower temperatures over the breeder materials with a catalytic additive and its activation energy can be considerably lowered. This result suggests that the isotope exchange reaction can be promoted by the deposition of catalytic metals.

Modelling the budget of middle atmospheric water vapour isotopes

Abstract. A one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. In the troposphere, this isotope composition is determined by "physical'' fractionation effects, that are phase changes (e.g. during cloud formation), diffusion processes (e.g. during evaporation from the ocean), and mixing of air masses. Due to these processes water vapour entering the stratosphere first shows isotope depletions in D/H relative to ocean water, which are ~5 times of those in 18O/16O, and secondly is mass-dependently fractionated (MDF), i.e. changes in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O. In contrast, in the stratosphere and mesosphere "chemical'' fractionation mechanisms, that are the production of HO due to the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions considerably enhance the isotope ratios in the water vapour imported from the troposphere. The model reasonably predicts overall enhancements of the stable isotope ratios in H2O by up to ~25% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O in the mesosphere relative to the tropopause values. The 17O/16O and 18O/16O ratios in H2O are shown to be a measure of the relative fractions of HOx that receive the O atom either from the reservoirs O2 or O3. Throughout the middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. In the stratosphere the known mass-independent fractionation (MIF) signal in O3 is in a first step transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from poorly quantified isotope exchange reaction rate coefficients and kinetic isotope fractionation factors.

Enhancement of isotope exchange reactions over ceramic breeder material by deposition of catalyst metal

The deposition of catalyst metals in ceramic breeders could enhance the release rate of tritium due to the promotion of isotope exchange reactions taking place at the interface of the breeder surface and the sweep gas. In this work, the authors examined the effects of catalytic active metal deposited on lithium titanate on the isotope exchange reactions. With respect to the virgin lithium titanate, it was found that the rate of the isotope exchange reactions taking place on the surface is quite low. However, the deposition of palladium greatly increased the exchange reaction rate. The effect of the amounts of deposited palladium on the isotope exchange reaction rate was also investigated. The results indicate that the exchange reactions are still enhanced even if the amounts of deposited palladium are as low as 0.04%.

Isotope exchange reaction between tritiated water and hydrogen on SiC

SiC has been considered as a primary candidate material for a first wall component in future fusion reactor because it has been claimed that SiC has excellent high-temperature properties, good chemical stability and low activation. However, the behavior of tritium on SiC has not been discussed yet. In this study, tritium trapping capacity on the surface of SiC was experimentally obtained at the temperature range of 25–800 °C in consideration of tritium trapping to the experimental system. The capacity, which was independent of the water vapor pressure in the gas phase and the temperature, was determined as about 10 6 Bq/cm 2. The isotope exchange reaction rate between tritiated water in a gas phase and hydrogen on the surface was quantified at the temperature of 25, 500 and 700 °C in consideration of the behavior of tritium trapping at change of experimental condition by the numerical curve fitting method applying the serial reactor model. The reaction rate was observed to be constant as 3.48 × 10 −5 m/s. Additionally tritium release behavior from the surface of SiC in water vapor atmosphere was predicted and compared with that for graphite and stainless steel.

Tritium inventory in Li 2TiO 3 blanket

The tritium inventory in the Li 2TiO 3 blanket of a nuclear fusion reactor is discussed in this paper. The method of tritium inventory estimation was proposed by the present authors. The overall mass transfer coefficient of the isotope exchange reaction 1 between H 2 in the purge gas and tritium on grain surface of Li 2TiO 3 was obtained in this study. This equation shows that the rate of isotope exchange reaction 1 in the Li 2TiO 3 bed is much smaller than that was observed by the authors for Li 2O, LiAlO 2, Li 4SiO 4, and Li 2ZrO 3. This phenomenon is caused by a surface reaction that occurs at high temperature between Li 2TiO 3 and H 2 in the gas phase. It was observed that the color of Li 2TiO 3 surface was changed from white to black, and quartz tube was corroded by this reaction. Tritium inventory in the Li 2TiO 3 blanket estimated in this study is about ten times larger than for any other solid breeding blanket at 973 K. It must be also cared that most tritium is released as HTO in this case. The use of He with H 2 on purge gas of Li 2TiO 3 blanket gives contradictory effect.

Isotope Exchange Reaction Between Gaseous Hydrogen and Tritium on Li2TiO3 Grain Surface

Though litium ceramic materials such as Li2O, LiA1O2, Li2ZrO3, Li4SiO4, and Li2TiO3, are considered as the candidates for breeding materials in the blanket of a D-T fusion reactor, the release behavior of the bred tritium in these solid breeder materials has not been fully understood yet. We have pointed out that it is essential to understand such mass transfer steps as diffusion of tritium in the grain, absorption of water in the bulk of grain, and adsorption of water on the surface of grain, together with two types of isotope exchange reactions for estimation of the tritium inventory in a uniform solid breeder blanket under the steady-state condition. The rate of isotope exchange reaction-1 on Li2TiO3 is quantified in this study, where pebbles of Li2TiO3 from CEA, KHI, and NFI are used.It is observed in this study that the rate of isotope exchange reaction on Li2TiO3 becomes 2∼3 order smaller than other solid breeder materials when it is placed in the hydrogen atmosphere at high temperature. It is also observed that the color of Li2TiO3 changed to black in accordance with decrease of reaction rate.The observation obtained at the release experiment of bred tritium performed in Kyoto University Reactor that chemical form of tritium becomes HTO at the high temperature even when hydrogen of 100 Pa is added to the purge gas can be explained by decrease of isotope exchange reaction rate.Tritium inventory in the Li2TiO3 blanket in various conditions are also discussed in this paper.

Rate of Isotope Exchange Reaction Between Tritiated Water in a Gas Phase and Water on the Surface of Piping Materials

The system effect of tritium arises from the interaction of tritium in the gas phase with water on the surface of piping materials. It has been reported that the system effect can be quantified by applying the serial reactor model to the piping system and that adsorption and isotope exchange reactions play the main roles in the trapping of tritium. The isotope exchange reaction that occurs when the chemical form of tritium in the gas phase is in the molecular form, i.e., HT or T2, has been named isotope exchange reaction 1, and that which occurs when tritium in the gas phase is in water form, i.e., HTO or T2O, has been named isotope exchange reaction 2.The rate of isotope exchange reaction 2 is experimentally quantified, and the rate is observed to be about one-third of the rate of adsorption. The trapping and release behavior of tritium from the piping surface due to isotope exchange reaction 2 is also discussed. It is certified that swamping of water vapor to process gas is effective to release tritium from the surface contaminated with tritium.

Isotope exchange reaction on solid breeder materials

Lithium ceramic materials such as Li 2O, LiAlO 2, Li 2ZrO 3, Li 2TiO 3 and Li 4SiO 4 are considered to be as candidate for the tritium breeding material in a deuterium–tritium (D–T) fusion reactor. In the recent blanket designs, helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas to reduce tritium inventory and promote tritium release from the breeding material. In addition, the rate of isotope exchange reaction between hydrogen isotopes in the purge gas and tritium on the surface of the breeding material is necessary to analyze the tritium release behavior from the breeding materials. However, the rate of isotope exchange reactions between hydrogen isotopes in the purge gas and tritium on the surface of those materials has not been quantified until recently. Recently, the present authors quantified the rate of isotope exchange reaction on Li 2O and Li 2ZrO 3. The overall mass transfer coefficients representing the isotope exchange reaction between H 2 and D 2O on breeding materials or the same between D 2 and H 2O are experimentally obtained in this study. Comparison to isotope exchange reaction rates on various breeding materials is also performed in this study. Discussions about the effects of temperature, concentration of hydrogen in the purge gas or flow rate of the purge gas on the conversion of tritiated water to tritium gas are also performed.

Kinetic study of the isotope exchange reactions of malonic acid and its derivatives in various acidic D2O media using 1H NMR spectroscopy. Implication in the Belousov‐Zhabotinsky reaction

The kinetics of the isotope exchange reactions of RCH(COOH)2 (RH, D, Me, Et, Bu, and Ph) in D2O solution were studied by using 1H NMR spectroscopy. It was observed that the rate of isotope exchange reaction was inhibited by the presence of 1 M of DNO3, DCl, DBr or D2SO4 and catalyzed by the presence of 4 M of D2SO4. No inhibition effect was observed in the case of D3PO4. The effect of inorganic acids follows the order of D3PO4>D2SO4 ≫ (DNO3, DCl, DBr). The conjugated base (RCH(COOD)(COO−)) of RCH(COOD)2 plays an important role in the isotope exchange reaction. The presence of deuterium ion suppresses the generation of RCH(COOD)(COO−) ion from RCH(COOD)2 and inhibits the rate of isotope exchange. In general, the order of reactivity of RCH(COOH)2 toward isotope exchange with deuterium atom is RPh>(H, Br)>Me>(Et, Bu). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 455–461, 1999

Isotope exchange reaction on Li 2ZrO 3

Lithium meta-zirconate, Li 2ZrO 3, is considered as a strong candidate for the tritium breeding material in a D-T fusion reactor. The isotope exchange reaction rate between hydrogen isotopes in the purge gas and tritium on the surface of Li 2ZrO 3 has not been quantified yet, although helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas in the recent blanket designs. The mass transfer coefficient representing the isotope exchange reaction between H 2 and D 2O or that between D 2 and H 2O in the Li 2ZrO 3 is experimentally obtained as K F,ex1 = 1.60 × 10 2 exp(− 121[kJ/mol]/RT) in this work. Discussions about the effect of temperature, concentration of hydrogen in the purge gas or flow rate of the purge gas on the conversion of tritiated water to tritium gas, HT instead of H 2, are also performed.

Handling of Pt catalyst in H2-H2O equilibration method for D/H measurement of water.

In the H2-H2O equilibration method for D/H measurement of water samples, an improved handling of Pt catalyst was proposed. The catalyst was wrapped in a Teflon® filter to prevent dispersion of fine fragments of the catalyst. Despite a reduced rate of isotope exchange reaction, equilibrium was attained within 24 h at 25°C. A conventional unit for automatic CO2-H2O isotope exchange reaction can be used for this purpose.

Effect of 235UF6238UF6 Gas Mixing on the Kinetic Rate of the Isotope Exchange Reaction between 235U-Enriched UF5 Nanoparticles and Natural UF6 Gas.

Effect of 235UF6238UF6 Gas Mixing on the Kinetic Rate of the Isotope Exchange Reaction between 235U-Enriched UF5 Nanoparticles and Natural UF6 Gas.

The effect of electrode materials on the response of oxygen sensors and the electrode kinetics

The lowest limit of operation temperature for the solid electrolyte oxygen sensor was significantly reduced by using perovskite-type oxide electrodes and a ceria-based electrolyte. In particular, the sensor with the La 0.6Sr 0.4Co 0.98Ni 0.02O 3 electrode and (CeO 2) 0.8(SmO 1.5) 0.2 electrolyte exhibited theoretical e.m.f. even at 200 °C. The lowest limit of operation temperature of the oxygen sensor was closely related to the cathodic overpotential, the electrode conductivity and the rate of oxygen isotopic exchange reaction.

Hydrogen isotope exchange reaction rate in tritium and methane mixed gas

Hydrogen isotope exchange reaction rate in tritium and methane mixed gas, as induced by tritium decay and beta radiation, has been experimentally measured. Initially T2 gas was filled to 40 kPa and 20 kPa of CH4 gas was added. The mixed gas spectrum was analyzed periodically by laser Raman spectrometry. The first order HT and H2 formation rates and T2 and CH4 decay rates by hydrogen isotope exchange reaction were observed between 2.9·10−3 h−1 and 4.8·10−3 h−1. Although the estimated hydrogen isotope exchange reaction rate was 1/20–1/10 slower than the rate of H2+T2 mixed gases, it was nearly equivalent to the ion formation rate by tritium beta radiation. This suggested that isotopic hydrogen radicals formed via ionization would disappear in the presence of methane.

The hydrolysis products of cis-diamminedichloroplatinum(II) 7. The rate of the hydrogen isotope exchange reaction

The rate of the NH → ND exchange reaction for cis-PtCl 2(NH 3) 2, PtCl 2(en) and PtCl 2(tn) has been measured in succinate buffered D 2O. Samples of the complex were precipitated as the HgCl 2 adduct, at various times, and the extent of deuteration was estimated by IR spectroscopy. The rate of the reaction is proportional to the [OD −] and activation parameters for the three complexes ( I=0.1 M NaCl, 25.0 °C) in the order (NH 3) 2, (en), (tn) are: 10 4 k ex (M −1 s −1) = 135, 51.4, 3.64; ΔH ≠ (kJ mol −1) = 24.9, 21.2, 50.0; ΔS ≠ (J K −1 mol −1) = −44.1, −64.6, + 10.2.

Isotopic Exchange Between Barium Oxalate and Barium Ion in Aqueous Solution

Abstract The heterogeneous isotopic exchange reaction of precipitated barium oxalate in barium chloride solution has been studied using Ba-133 as tracer. The effect of barium chloride concentration on the rate of isotopic exchange reaction has been studied. It was found that the rate was controlled by surface mass reaction and particle diffusion process in the solid particle. The result also indicate that the effect of recrystallization can be neglected.

Comparison of Precious Metal Catalysts with Hydrophilic Porous Substrate for Tritium Cleanup System

Abstract Existence of the structure water in the hydrophilic porous substrate can give various effects on tritium behavior in a tritium recovery system consisted of precious metal catalyst bed and adsorption bed because the catalytic isotope exchange reaction or the isotope exchange reaction proceeds besides oxidation reaction or adsorption reaction. Properties of Pt catalysts loaded on various hydrophilic porous substrate are compared in this study. It is known from experiment that Pt-Alumina catalyst has the largest exchange capacity and that Pt-MS 5A catalyst has the largest total capacity because it has the effective adsorption capacity. For silica gel substrate, certain transport reaction of tritium in the substrate whose rate is rather slower than the rate of isotope exchange reaction is observed and it gives peculiar undesirable quality for silica gel to use in a tritium recovery system.

Comparison of precious metal catalysts with hydrophilic porous substrate for tritium cleanup system.

Abstract Existence of the structure water in the hydrophilic porous substrate can give various effects on tritium behavior in a tritium recovery system consisted of precious metal catalyst bed and adsorption bed because the catalytic isotope exchange reaction or the isotope exchange reaction proceeds besides oxidation reaction or adsorption reaction. Properties of Pt catalysts loaded on various hydrophilic porous substrate are compared in this study. It is known from experiment that Pt-Alumina catalyst has the largest exchange capacity and that Pt-MS 5A catalyst has the largest total capacity because it has the effective adsorption capacity. For silica gel substrate, certain transport reaction of tritium in the substrate whose rate is rather slower than the rate of isotope exchange reaction is observed and it gives peculiar undesirable quality for silica gel to use in a tritium recovery system.