Evaluation of sample cell materials for aqueous solutions used in quasi-elastic neutron scattering measurements

Abstract

For quasi-elastic neutron scattering (QENS) studies, sample cells made of pure or alloyed aluminium are frequently employed. Although the Al surface is protected by a passivating film, this film is not robust. Therefore, when the sample is an aqueous solution, chemical interactions between the Al surface and sample, promoted by corrosive entities such as chloride ions and certain conditions of pH, can compromise the integrity of the cell and interfere with the experiment. In this study, the corrosion susceptibilities of Al and its alloys were investigated by subjecting them to various treatments; the results were compared with those of other candidate materials with low chemical reactivity. This work showed that alloys with higher Al content and boehmite-coated surfaces are resistant to corrosion. In particular, for Al, the resistance is due to a reduction in the contact area achieved by reducing the surface roughness. QENS measurements of empty sample cells made of these materials revealed two results: (1) the profile of the cell fabricated with a copper-free Al alloy showed a minor dependence on the scattering vector magnitude Q and (2) reducing the real surface area of Al effectively suppresses its scattering intensity, while boehmite coating strengthens the scattering. Cells fabricated with Mo, Nb and single-crystal sapphire can be used as alternatives to Al because of their low scattering intensity and reduced dependence on Q.

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“…The inner diameter of the outer cylinder was 14 mm, the outer diameter of the inner cylinder was 13 mm, and the wall thicknesses of both the inner and outer cylinders were 0.25 mm. The arithmetic mean roughness, R A , of each cylinder was approximately 0.28 µm (which is the same as that of the regular machining surface in the literature [ 27 ]). By loading the liquid sample into the gap between these cylinders (the space created by the inside of the outer cylinder and the outside of the inner cylinder), the sample was formed into an annular shape.…”

“…The sample container comprised outer and inner cylinders made of aluminum (Al 1070) [ 27 ]. The inner diameter of the outer cylinder was 14 mm, the outer diameter of the inner cylinder was 13 mm, and the wall thicknesses of both the inner and outer cylinders were 0.25 mm.…”

“…The covered ranges of the scattering vector Q (in Å −1 ) and energy transfer E (in meV) were 0.13 < Q < 1.7 and −0.01 < E < 0.02, respectively. The exposure times were approximately 3.9 h. The acquisition and analysis of data were the same as in a previous paper [ 27 ]. The data were obtained after subtracting the background profile of the instrument and correcting for detector efficiency using a vanadium standard.…”

“…For aqueous samples, chemical reactions between aluminum and water should be considered. The chemical reactions between the aluminum cell and the aqueous sample were previously summarized, demonstrating that the reaction with aluminum can not only corrode the sample cell, but also change the sample conditions (water concentration and/or ionic environment, and/or pH) [ 27 ]. It should be noted that these changes could affect the stability of the sample, thereby deteriorating the quality of the resulting scattering profile.…”

“…It should be noted that these changes could affect the stability of the sample, thereby deteriorating the quality of the resulting scattering profile. To overcome this problem, we adopted a boehmite coating of aluminum cells, which is expected to be corrosion-resistant over a wide temperature range [ 27 , 28 ]. To further suppress cell-derived incoherent scattering, a boehmite coating with deuterium oxide (D 2 O) was used in this study.…”