Abstract:The structure of perhydropolysilazane (PHPS)-derived silica (PDS) waterproof thin layers synthesized by curing at 60 • C for 1 h and allowed to stand for 48 h at 20 • C on various kinds of substrates was studied. Neutron reflectivity (NR) analysis suggested that uniform PDS thin layers were synthesized on the substrates, and the density of the layers varied depending on the type of substrate. Additionally, since the change in PDS density is correlated with the pK a value of the OH group on the substrate, it can be suggested that the acidity of the substrate would be one of the main factors determining the density of the coated PDS thin layers. For the water penetration structure study, NR analysis revealed that the depth of water penetration into the PDS layers was below 500 Å, and the hydration number of the SiO 2 molecule was estimated to be 8.0-9.0. From these results, we concluded that water penetration occurred by the formation of water-pool structures in the PDS layers, and the randomly formed nano-air holes lead to a reduction in the probability of water penetration into the deep regions of the PDS layers.
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.
The structures of a SiO 2 layers synthesized using perhydropolysilazane [PHPS, labeled as SiO 2 (PHPS)] on both Si and Fe/Si substrates were studied using Fourier transform infrared spectroscopy (FT-IR) and neutron reflectivity (NR) analysis. The FT-IR results revealed that no unreacted PHPS remained and that the primary component of the SiO 2 (PHPS) layer could be considered to be SiO 2 . The NR analysis suggested that a uniform SiO 2 (PHPS) layer was synthesized on the Si and Fe/Si substrate and that the density of this SiO 2 (PHPS)layer was lower than that of natural SiO 2 . In addition, the density of the SiO 2 (PHPS) layer was altered by varying both the thickness and the type of substrate used. These results indicated that the variation in the density of the SiO 2 (PHPS) layer depended on the efficiency of cross-linking reaction between the silazane oligomers in the PHPS coating.
The spin‐contrast‐variation neutron reflectometry technique was developed for the structural analysis of multilayer films. Polarized‐neutron reflectivity curves of film samples vary as a function of their proton polarization (PH). The PH‐dependent reflectivity curves of a polystyrene monolayer film were precisely reproduced using a common set of structural parameters and the PH‐dependent neutron scattering length density of polystyrene. This result ensures that these curves are not deformed by inhomogeneous PH but can be used for structural analysis. Unpolarized reflectivity curves of poly(styrene‐block‐isoprene) films were reproduced using a flat free‐surface model but PH‐dependent polarized reflectivity curves were not. The global fit of the PH‐dependent multiple reflectivity curves revealed that holes with a depth corresponding to one period of the periodic lamellae of microphase‐separated polystyrene and polyisoprene domains were produced on the surface of the films, which agrees with the microscopic results. In this manner, the spin‐contrast‐variation neutron reflectometry technique determines the structure of multiple surfaces and interfaces in a film sample while excluding the incorrect structure that accidentally accounts for a single unpolarized reflectivity curve only.
Quasielastic neutron scattering studies frequently employ aluminum (Al) or Al alloys as sample cells. Due to the increasing incident-neutron flux, this research area has experienced continuous expansion; thus, the rate of acquiring data for dilute conditions has increased considerably. One such research topic is water-containing systems. In this study, we investigated the effect of temperature on Al and found that Al corrosion occurs even in a low temperature atmosphere. This was attributed to the different thermal expansion coefficients of Al as a base substrate and Al oxide as a passivating film.
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