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Neutron reflectometry has been used to study liquid metal-ceramic interfaces in situ. A high-temperature facility designed and commissioned for use on the SURF reflectometer at the ISIS beamline, Rutherford Appleton Laboratory, is described. Results from a study of two Sn-Ti alloys on sapphire up to 1173 K are presented and the interfacial composit...
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... a common-sense approach to the expected interfacial chemistry allows one to limit the number of variables used and a realistic description of the reflection profile in terms of compounds present at the interface can be made. Table 1 shows the neutron scattering length density values of a range of compounds which might be expected at the interface between Sn-Ti alloys and Al 2 O 3 (sapphire). The negative scattering length of Ti ensures that all the likely interfacial compounds expected (sub-stoichiometric oxides of titanium) will show good contrast in reflection. ...
Citations
... [8][9][10][11][12][13][14][15][16][17][18][19] In many different areas of materials science, it has been used to study stimuli-dependent effects at interfaces, including temperature and pressure. [20][21][22][23][24] There have been many such studies probing solid-liquid interfaces, including studies probing the interface between liquid metals and sapphire to temperatures of 900 ○ C. [25][26][27][28] The system described in these works allows for the introduction of thin metal foils into a sample region defined by a graphite block held in contact with the sapphire substrate. The system is then placed inside of an evacuated fused silica tube and heated via a clam-shell tube furnace. ...
In this work, we describe the design and development of an in situ neutron reflectometry cell for high temperature investigations of structural changes occurring at the interface between inorganic salts, in their molten state up to 800 °C, and corrosion resistant alloys or other surfaces. In the cell, a molten salt is confined by an annular ring of single crystal sapphire constrained between the sample substrate and a sapphire plate using two gold O-rings, enclosing a liquid salt volume of 20 ml, along with a dynamic cell volume to accommodate expansion of the liquid with heating. As a test case for the cell, we report on an in situ neutron reflectometry measurement of the interface between a eutectic salt mixture of MgCl2–KCl (32:68 molar ratio) and a single crystal sapphire substrate at 450 °C, resulting in the formation of a 60 Å layer having a scattering length density of 1.72 × 10⁻⁶ Å⁻². While the origin of this layer is uncertain, it is likely to have resulted from the salt reacting with an existing impurity layer on the sapphire substrate.
This chapter discusses the main spectroscopic techniques that have been developed or adapted for the study of the chemistry of liquid/solid interfaces at the molecular level. It begins with a review of the use of infrared absorption spectroscopy to the interrogation of liquid/solid interfaces and provides an overview of other vibrational spectroscopies, in particular, Raman scattering spectroscopy and sum frequency generation. The chapter introduces the use of UV–vis spectroscopies and acoustic‐based techniques. It then focuses on the use of X‐rays and neutrons to extract electronic information about the liquid/solid interface. The potential use of techniques such as X‐ray photoelectron spectroscopy and nuclear magnetic resonance and electron spin resonance spectroscopies for the characterization of liquid/solid interfaces is briefly surveyed. The chapter also provides a discussion on the approaches available for the acquisition of spatially resolved information on liquid/solid interfaces, including optical and scanning microscopies.
Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties. As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools. One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal. The joining of engineering ceramics to metals is not always easy. There are two main considerations. The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond. The second consideration is the mismatch in the coefficient of thermal expansion. In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either as a consequence of operating conditions or from the joining procedure itself, failure can occur. The plethora of joining processes available will be reviewed in this article, placing them in context from both an academic and commercial perspective. Comment will be made on research reporting advances on known technology, as well as introducing ‘newer’ technologies developed over the last 10 years. Finally, reviews and commentary will be made on the potential applications of the various joining processes in the commercial environment.
Neutron reflection spectroscopy has been used to characterise the composition of interfaces between liquid Sn-Ti alloys and Al2O3. The reflectivity profiles for both 1% and 3% Ti alloys are consistent with the presence of a layer approximately 2 nm thick at the liquid/solid interface, showing extensive segregation of Ti. The composition of this layer is not pure Ti but shows a greater Ti content than any known Ti oxide composition. In all interfaces exposed to liquid metals at elevated temperature (including pure Sn) there is a layer of thickness 20–100 nm on the alumina surface with slightly lower neutron scattering length density than pure alumina. This is interpreted as evidence for surface roughening of the Al2O3 surface during exposure to the liquid metal.
A study was conducted to demonstrate probing techniques for liquid and solid interfaces at the molecular level. Investigations revealed that new approaches were needed to study liquid or solid interfaces at a molecular level. Some electron-based surface-science techniques were adapted to probe liquid and solid interfaces by minimizing the paths that the probing particles needed to travel through the liquid phase. The use of techniques based on light or other electromagnetic radiation for surface analysis had more potential to achieve these objectives. The potential use of techniques, such as X-ray photoelectron spectroscopy and nuclear magnetic and electron spin resonance spectroscopies for the characterization of liquid and solid interfaces was investigated. Investigations revealed that infrared (IR) absorption spectroscopy was the most commonly used technique for the molecular-level characterization of such liquid and solid interfaces.
