Metal hydride differential scanning calorimetry as an approach to compositional determination of mixtures of hydrogen isotopologues and helium

Abstract

Gaseous mixtures of diatomic hydrogen isotopologues and helium are often encountered in the nuclear energy industry and in analytical chemistry. Compositions of stored mixtures can vary due to interactions with storage and handling materials. When tritium is present, it decays to form ions and helium -3, both of which can lead to further compositional variation. Monitoring of composition is typically achieved by mass spectrometry, a method that is bulky and energy-intensive. Mass spectrometers disperse sample material through vacuum pumps, which is especially troublesome if tritium is prese nt. Our ultimate goal is to create a compact, fast, low-power sensor that can determine composition with minimal gas consumption and waste generation, as a complement to mass spectrometry that can be instantiated more widely . We propose calorimetry of metal hydrides as an approach to this, due to the strong isotope effect on gas absorption, and demonstrate the sensitivity of measured heat flow to atomic composition of the gas. Peak shifts are discernible when mole fractions change by at least 1%. A mass flow restriction results in a unique dependence of the measurement on helium concentration. A mathematical model is presented as a first step toward prediction of the peak shapes and positions. The model includes a useful method to compute estimates of phase diagrams for palladium in the presence of arbitrary mixtures of hydrogen isotopologues. We expect that this approach can be used to deduce unknown atomic compositions from measured calorimetric data over a useful range of partial pressures of each component.If composition could be measured by a method that is more compact and lower power, without consuming or dispersing the sampled gas, it will be possible for a gas handling system to report composition at more sampling © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ bw fig2 bw fig3 bw fig4 bw fig5l bw fig5r bw fig6l bw fig6r bw fig7l bw fig7r bw fig8l bw fig8r bw fig9 bw fig10l bw fig10r bw fig11l bw fig11r bw fig12l bw fig12r bw fig13l bw fig13r bw figs1 bw figs2 baseline-h2.tif bw figs3 onset-vanthoff.tif bw figs4 curve baseline.tif bw figs5 const p vary h d.tif bw figs6bl sensitivity fix h add more d pct.tif bw figs6br sensitivity fix d add h pct.tif bw figs6tl sensitivity fix d add more h.tif bw figs6tr sensitivity fix h add d pct.tif bw figs7 ternary.tif

Microwatt-Resolution Calorimeter for Studying the Reaction Thermodynamics of Nanomaterials at High Temperature and Pressure

“…Figure b shows the enthalpy of hydrogenation per mole of adsorbed H 2 , which spans a range from −33.44 to −41.94 kJ/mol-H 2 . This value is also in agreement with previous studies that mostly rely upon indirect measurement of the enthalpy of hydrogenation using an isotherm method and Van’t Hoff’s relation, clustered within −28 to −40 kJ/mol-H 2 depending on Pd particle size and measurement technique. ,,, The results are also in agreement with past calorimetric measurements, which report a wide range for the enthalpy of hydrogenation of Pd (−32 to ∼−60 kJ/mol-H 2 ). ,, In Figure b, the enthalpy of hydrogenation shows no significant trend as a function of temperature; however, a decrease in the absolute value of enthalpy of hydrogenation with the reaction pressure is observed. This effect can be explained based on the variation of equilibrium H/Pd ratio as a function of reaction pressure, where some previous studies have reported that the enthalpy of hydrogenation is higher at lower H/Pd ratios as a result of highly exothermic dissociative chemisorption of H 2 molecules on the Pd surface. , …”

“…21,22,29,30 The results are also in agreement with past calorimetric measurements, which report a wide range for the enthalpy of hydrogenation of Pd (−32 to ∼−60 kJ/mol-H 2 ). 7,23,31 In Figure 10b, the enthalpy of hydrogenation shows no significant trend as a function of temperature; however, a decrease in the absolute value of enthalpy of hydrogenation with the reaction pressure is observed. This effect can be explained based on the variation of equilibrium H/Pd ratio as a function of reaction pressure, where some previous studies have reported that the enthalpy of hydrogenation is higher at lower H/Pd ratios as a result of highly exothermic dissociative chemisorption of H 2 molecules on the Pd surface.…”

Comparison of Designs of Hydrogen Isotope Separation Columns by Numerical Modeling

“…Q rxn is the product of the reaction rate and the reaction enthalpies described in our prior work. , Different enthalpies are used for absorption and desorption. The reaction rate applies to the pore volume instead of a power per unit length, so we multiply it by the pore area A pore as indicated in Scheme .…”

“…To determine the equilibrium gas-phase concentrations for a given solid-phase composition and temperature, we use a model built by multiple authors several decades ago, − summarized by Lässer, and applied by us to gas mixtures. , The approach is to equate the chemical potentials of each gas-phase isotopologue with the sum of its two constituent isotopes absorbed in the solid, while also relating chemical potentials to partial pressures, solid-phase mole fractions, and temperature. This yields a function of partial pressure versus solid-phase composition that, for an intermediate range, unphysically decreases in equilibrium pressure as the solid-phase content increases.…”

“…We adopt the overall approach of refs and , combined with a model of equilibrium absorption and desorption partial pressures for each isotopologue in palladium derived by Lässer . We have previously applied this absorption–desorption model to zero-dimensional models of thermally driven gas–solid reactions. , By examining the predicted hydrogen isotope concentrations in the gas and solid phases as a function of position and time, we observe that both TCAP and SMB can separate isotopes starting from a totally uniform spatial distribution, although only SMB can achieve regions of nearly pure H 2 , D 2 , and T 2 in just a few cycles.…”