The acoustical properties of tetraethyl orthosilicate based granular silica aerogels

Available data suggests that granulated aerogels can be of interest in terms of their sound absorption performance in the audio frequency range. However, there is still no thorough understanding of the complex physical phenomena which are responsible for their observed acoustical properties. This work is an attempt to address this gap through advanced material characterization methods and mathematical modelling. Aerogel samples are produced through a two-step, acid-base sol-gel process, with sol silica concentration and density being the main variables. Their pore structure is carefully characterized by nitrogen sorption analysis and scanning electron microscopy. The acoustical properties of hard-backed granular silica aerogels are measured in an impedance tube and the results predicted accurately with the adopted theoretical model. Although silica aerogels have over 90% of open interconnected pores, this was neither reflected in the measured acoustical properties nor the parameter values predicted with the model. Novel results show that only a proportion of the micro and mesopores in the direct vicinity of the grain surface influenced the acoustical properties of aerogels. Further work in the hierarchical pore structure of aerogels is required to better understand the roles of different pore scales on the measured acoustical properties of a granulated aerogel

Optimized solder alloy for glass-to-metal joints by simultaneous soldering and anodic bonding

Strong glass/solder/metal seals were prepared between float glass, tin solder and Fe-Ni alloys by the Activated Liquid Tin Solder Anodic Bonding (ALTSAB) process that combines classical anodic bonding with a liquid solder to ensure a near perfect contact between the bonding surfaces. The optimization of the Al content of the solder enables the production of glass/solder/metal joints without pre-treatment of the metal or glass surfaces. Strong glass/solder bonds are formed by anodic bonding across the oxide/metal interface and strong solder/metal bonds are formed simultaneously by soft soldering. The combined process consists of two very different processes and the optimal solder composition represents the middle ground between the requirements for both interfaces. The glass/solder bond strength increases with increasing Al content at the expense of the solder/metal bond strength: solders with a very low Al content of 75 ppm constitute the best compromise and result in the strongest glass/solder/metal joints. The optimal solder composition was used to anodically bond Dilaton Fe-48 wt%Ni frames to the edge of 500 × 500 mm2 float glass panes for vacuum glazing applications

Large-scale anodic bonding mediated by a liquid tin solder

Large area seals were prepared between a metal foil frame (Fe-Ni alloy with 48 wt% Ni) and a 901 × 814 mm2 glass pane through the simultaneous application of activated liquid tin solder anodic bonding and soft soldering. An experimental facility including a liquid solder injector was built. Prototype seals were produced with tin solder alloys with variable Al contents and the hermiticity and interface integrity was determined. Solder alloys with an Al content of 112.5 ppm resulted in the strongest adhesion forces, broadly consistent with a previous study at the laboratory scale. The resulting prototypes consist of a bonded area of ∼450 cm2 along the perimeter of a 0.73 m2 glass pane and display consistently strong bonds for sections over a meter in length, demonstrating that activate d liquid solder anodic bonding is not restricted to small-area applications