Research advancements and challenges in the design and fabrication of glass to metal seals for solar receiver tube applications

Glass to metal joints has a vast field of application due to their distinct properties in terms of electric conductivity, thermal conductivity, transparency, emissivity, reflectivity, coefficient of thermal expansion (CTE), density, wettability, and crystalline structure. This wide diversification in their properties makes this combination very useful in the special application like concentrated solar receiver tubes (CSRT), etc. This challenge becomes bigger when such seals are subjected to a very high temperature range, ultra-high pressure or ultra-high vacuum, and also gone through repeated number of thermal cycling over a period of time, as may be in the case of CSRT. Hence how to prepare a good quality seal for such constraints, study and control of many factors are essential covered such as seal design, oxidation layer thickness, manufacturing method, temperature and time of making seal, surface roughness, and residual stresses in glass, etc., that has been vigorously studied and reported in this paper.