Development and interface characterization of unmatched glass-metal joint

An unmatched glass-metal joint between borosilicate glass and austenitic stainless steel SS 304 was developed for parabolic trough receiver tube application. 40SiO2-54B2O3-4Na2O-2Al2O3 material was used as the glass sealant to join the SS304 metal ring and borosilicate glass tube. The research work reported was carried out with objective of investigating the role of glass sealant, joint design and pre-oxidation conditions on the wettability and adhesion strength of the glass-metal joint. The work also aimed at analysing the types of oxides formed at the glass-metal joint interface. The pre-oxidation behavior of SS304 was studied by varying the pre-oxidation temperature and pre-oxidation time. The oxide formed on the surface of SS304 substrates were examined using x-ray diffraction and energy dispersive x-ray spectroscopy. During the glass-metal sealing process the oxides at the glass-metal interface were characterized using x-ray diffraction and scanning electron microscopy. In-situ wetting behavior of glass sealant 40SiO2-54B2O3-4Na2O-2Al2O3 over austenitic stainless steel SS 304 was examined using the in-house developed image acquisition system. The optimum condition for joining 40SiO2-54B2O3-4Na2O-2Al2O3 glass sealant with SS304 is obtained by pre-oxidizing metal specimen at 700 °C for 3 min, where optimum oxide layer mass gain of 5.8666 × 10−04 g/cm2 and optimum oxide layer thickness of 87.57 μm was achieved. The maximum strength of joint during adhesion test was measured around 2.57 N/mm2 (MPa) corresponding to pre-oxidation temperature of 700 °C and 3 min pre-oxidation time. The FeO and ((SiO2),AlNa(SiO4)) oxide phases were observed at the interface of glass and the metal during joining. During in-situ wettability analysis the contact angle between the glass sealant pallet and SS304 substrate was measured at different temperatures. The contact angle of the glass sealant pallet decreased during heating process and the contact angle increased as the glass sealant pallet cooled from sealing temperature.