Hiden Analytical (United Kingdom)

Reference gas adsorption isotherms are useful for validating equilibrium data obtained from various techniques and for ensuring that experimental systems are operating correctly. In this work, we extend an interlaboratory study on a NIST reference zeolite (Na-Y, RM8850) to two additional temperatures above and below the original 298.15 K, validating the results via independent measurements using two different techniques. Volumetric experiments on a novel Adsorption Differential Volumetric Apparatus (ADVA-270) were carried out at The University of Edinburgh, and gravimetric experiments were performed at Hiden Isochema using a proprietary XEMIS microbalance. Both techniques provided highly accurate results and an excellent match between the two independent measurements using less than 150 mg of sample. Absolute equilibrium data were modelled using a Langmuir-virial isotherm to obtain an accurate concentration dependence of the heat of adsorption.

To assess the performance of an adsorbent for a particular gas separation, and for process design, it is necessary to determine multicomponent gas adsorption equilibria, either experimentally or from predictions based on models or theory. The experimental techniques commonly used for this purpose, however, are time-consuming and typically require large samples. In this article, we describe a new approach, called the Integral Mass Balance (IMB) method, which combines the controlled flow of a gas mixture with in situ gravimetric measurement and gas composition analysis using quadrupole mass spectrometry. The IMB method allows very rapid equilibrium multicomponent gas adsorption measurements to be performed on samples weighing only a few grams. The method is demonstrated and validated by performing binary O2/N2 adsorption measurements on a commercial 5A zeolite, at ambient temperature and a total pressure of 0.915 MPa. Excellent agreement with previously published data was found, using a 3.5 g sample, with a measurement time of only 4 h for a 20 point isotherm. In contrast, other techniques of equivalent accuracy would require around 20 days of experimental effort to collect a comparable amount of data. Selectivities were also calculated and shown to agree with previously published results. In principle, the technique could readily be extended to measure gas adsorption from ternary or higher mixtures.

The authors present a quantitative secondary ion mass spectrometry (SIMS) analysis of the useful ion yield of magnesium dopant in a gallium nitride matrix. A quadrupole SIMS instrument was used to analyze an Mg-doped GaN sample grown by metal organic chemical vapor deposition. Oxygen (O2+) was used as the primary ion beam and its energy was varied in the range from 0.5 to 5 kV with and without oxygen flooding near the sample. The results of the analysis can be used to determine the primary beam energies for optimal magnesium sensitivity.

The original version of this article was published open access. Unfortunately, due to a technical issue, the copyright holder name in the online version (HTML and XML) is incorrectly published as “Springer Science+Business Media, LLC, part of Springer Nature 2018”. Instead, it should be “The Author(s) 2018”.

Current–voltage characteristics within the temporal pulse were recorded in high-power pulsed magnetron sputtering discharges for different target materials. These curves allowed identifying at a first glance the existence of separated plasma regimes clearly differentiated by the plasma conductivity and by the spatial arrangement of the plasma emission. We could establish that regimes of high plasma conductivity are univocally associated to the self-organization of the plasma in well-defined ionization zones. As the applied power is gradually increased, the high conductivity regime is abruptly replaced by a regime of high current and low plasma conductivity, associated to homogeneous plasma emission.

In this chapter we introduce the main gas sorption techniques applied to the characterisation of the hydrogen sorption properties of potential hydrogen storage materials. We begin with volumetric techniques, with a focus on the commonly used manometric (Sieverts’) method, but also cover some of the alternative approaches, such as the flowing and differential volumetric methods. We then describe the gravimetric technique, including a discussion of vacuum microbalances and the requirements for high pressure hydrogen operation. Thermal desorption techniques are then covered, including Thermogravimetric Analysis (TGA) and Thermal Desorption Spectroscopy (TDS), in which the temperature-programmed desorption of hydrogen can be detected in a number of ways, including quadrupole mass spectrometry. The chapter concludes with a practical comparison of the different gas sorption measurement techniques.

In this chapter we examine the hydrogen sorption properties of materials, considering both the parameters that are of prime practical engineering importance, and the thermodynamic and kinetic properties of interest for future materials development. We begin with the practical storage properties, such as the reversible storage capacity, including definitions of the gravimetric and volumetric capacities and the total and excess adsorption for adsorptive hydrogen storage, the long term cycling stability, gaseous impurity resistance, and the ease of activation. The thermodynamic properties, including the enthalpy of molecular hydrogen adsorption and the enthalpy of hydride formation or decomposition are then covered. We then discuss the kinetics of hydrogen adsorption and absorption, including parameters such as the activation energy, hydrogen diffusion coefficient and the apparent rates of absorption or desorption, which can be used to characterise the time-dependent sorption and desorption properties of materials. The latter part of the chapter then considers both equilibrium and kinetic models that can be used to describe experimental data.

In this contribution RF excited atmospheric pressure glow discharges are investigated in He–water mixtures in a parallel metal plate reactor by mass spectrometry. Positive and negative ion fluxes to the electrode are investigated as a function of varying water concentration and discharge power. The dominant positive ions are H3O+ (and its clusters), OH+, O+, , , HeH+, and . Negative ions are detectable from a concentration of 900 ppm water in He onwards. Coinciding with the emergence of the negative ions, there is a drop in positive ion flux to the mass spectrometer and a significant increase in applied voltage indicating increasing electron loss by attachment and ion loss by mutual (three and two body) positive–negative ion recombination. The dominant negative ions are OH− and its clusters. The negative ion flux increases with increasing water concentration. Positive and negative ion cluster formation increases with decreasing discharge power and increasing concentration of water vapour at constant power. It is shown that the size of the sampling orifice of the inlet of the mass spectrometer is important for sampling atmospheric pressure active plasmas due to the presence of the narrow sheath.

Spectral analysis of the vacuum conditions within the JET tokamak provides unique challenges due to the complex interactions of Hydrogen, Deuterium and Tritium with the large amounts of Carbon forming the plasma facing first wall. Overlapping masses and low resolution of the quadrupole Residual Gas Analyzer (qRGA) means discrimination of individual species is not possible operating in a conventional mode. Baking the vessel to temperatures in excess of 300 degrees Celsius further complicates an already difficult task.