As the lightest structural materials, magnesium (Mg) alloys play a significant role in vehicle weight reduction, aerospace, military equipment, energy saving, and emission reduction. However, the poor corrosion resistance of Mg alloys has become a bottleneck restricting its wide application. Developing a good surface protective coating can effectively improve the corrosion resistance of Mg alloys. The silane-based sol-gel coating technology has been widely used in the corrosion protection of Mg alloys in recent years due to its advantages of simple process, accessible tailoring of film composition and structure, and excellent corrosion resistance. Whereas the synthesis of sol-gel coatings includes the hydrolysis and dehydration process, which may inherently contain micron or nano defects in the coatings, thereby making it detrimental to the anti-corrosion effect. Therefore, in order to enhance their protection against corrosion, the appropriate modification of sol-gel coatings has become a current research hotspot. This review is based on the modification methods of silane-based sol-gels on the surface of Mg alloys, which are divided into four categories: bare sol-gel, nanoparticles, corrosion inhibitors, and sol-gel-based composite coatings. The modification methods and corrosion protection mechanism are discussed respectively, and the application, development, and research strategies of silane-based sol-gel coatings are included.

Tungsten-based scandate dispenser cathodes are promising next-generation thermionic electron sources for vacuum electron devices, due to their excellent emission performance at temperatures lower than those required for conventional cathodes. There has been a significant recent effort to understand scandate cathode performance and to characterize the tungsten and other materials on the emitting surface, primarily via the study of cathodes before and after emission testing. Moreover, these scandate cathodes have typically been characterized at room temperature only. In situ observations of scandate cathodes is challenging, as these devices are thermionic emitters that operate in a high-vacuum environment, and because the sizes of relevant material features range from the micron (2.0 µm) to the nanometer (<50 nm diameter) length scales. In the current study, a series of in situ heating experiments was conducted on un-activated impregnated scandate cathode fragments, utilizing a micro-electro-mechanical system-based heater chip in a scanning electron microscope, enabling the real-time observation of cathode material evolution at elevated temperature (up to 1200 °C) under a pressure of 10⁻⁶ to 10⁻⁷ mbar. This study revealed how impregnant materials grow and migrate within the cathode matrix at elevated temperatures, and these observations are key to a thorough understanding of the behavior of scandate cathode materials. It also enabled direct observation of the incipient faceting of tungsten surfaces at high temperature while surrounded by impregnant materials. These are the first in situ observations of scandate cathode material evolution in relevant environmental conditions and at sufficiently high resolution to provide insights into the morphological and phase changes that occur in the near-surface regions of scandate cathodes.