A review on silica aerogel-based materials for acoustic applications

Silica aerogels are popular in terms of production volume and real-world applications. Although the current market growth rate is driven exclusively by thermal insulation, aerogels may also be attractive for acoustic applications with the potential in aiding sound absorption/insulation. This paper is a summary of the acoustics related studies of silica aerogel-based products. It introduces silica aerogels, some acoustic characterization methods, and reviews systematically the available data on sound absorption/insulation of silica aerogels, polymer-silica aerogel composites, nonwoven-silica aerogel blankets, and aerogel renders/glazing. The work identifies areas where further research is required, including experimental and theoretical work on the physics of sound absorption in mesoporous materials, and more systematic and standardized evaluations of the acoustic properties of aerogel and aerogel-composites. Aside from this call to action, the opportunities and barriers for the commercialization of silica aerogel products for acoustic applications are presented

SiO2 glass density to lower-mantle pressures

The convection or settling of matter in the deep Earth’s interior is mostly constrained by density variations between the different reservoirs. Knowledge of the density contrast between solid and molten silicates is thus of prime importance to understand and model the dynamic behavior of the past and present Earth. SiO2 is the main constituent of Earth’s mantle and is the reference model system for the behavior of silicate melts at high pressure. Here, we apply our recently developed x-ray absorption technique to the density of SiO2 glass up to 110 GPa, doubling the pressure range for such measurements. Our density data validate recent molecular dynamics simulations and are in good agreement with previous experimental studies conducted at lower pressure. Silica glass rapidly densifies up to 40 GPa, but the density trend then flattens to become asymptotic to the density of SiO2 minerals above 60 GPa. The density data present two discontinuities at ∼17 and ∼60  GPa that can be related to a silicon coordination increase from 4 to a mixed 5/6 coordination and from 5/6 to sixfold, respectively. SiO2 glass becomes denser than MgSiO3 glass at ∼40  GPa, and its density becomes identical to that of MgSiO3 glass above 80 GPa. Our results on SiO2 glass may suggest that a variation of SiO2 content in a basaltic or pyrolitic melt with pressure has at most a minor effect on the final melt density, and iron partitioning between the melts and residual solids is the predominant factor that controls melt buoyancy in the lowermost mantle

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

Anomalous density, sound velocity, and structure of pressure-induced amorphous quartz

The study of quartz and other silica systems under pressure is one of the most prolific domains of research over the past 50 years because of their applications in material science and fundamental relevance to planetary interiors. The characterization of the amorphous state is essential for the comprehension of pressure-induced amorphization of minerals, the metamorphism observed in shocked materials, and the study of melt structures under pressure. Here, we measured in situ, under static compression the density, sound velocities, and electronic structure of quartz as it passes through its pressure-induced amorphization transition. The transition pressure could be derived from the abrupt increase in density and sound velocity at 24 GPa, and from strong changes in the silicon L2,3 edge and oxygen K edge between 22 and 27 GPa observed in x-ray Raman scattering data, confirming previous results from x-ray diffraction. Above this pressure, our data show an anomalous behavior in density, sound velocity, and electronic fine structure compared to the cold compressed glass and other silica polymorphs. The pressure-induced amorphous quartz has a lower density relative to that of the compressed glass, consistent with the lower average coordination inferred from a different signature in the Si L2,3 and O K electronic absorption edges measured by x-ray Raman scattering spectroscopy. This behavior sheds light on the pressure limit of tetrahedral units in SiO2 components and the existence of polyamorphism in network-forming materials, and highlights the possibility to discriminate between different amorphous states with x-ray Raman scattering spectroscopy

Multiple assembly strategies for silica aerogel-fiber combinations – a review

Silica aerogels have a unique structure that makes them promising materials for variable applications. However, they are brittle due to weak inter-particle necks, and also expensive. Combining aerogel with fibers can not only enhance the mechanical/insulation properties, but also reduce dust release, and ease practical application. The majority of review articles in this field have been on the aerogel/textile systems' application or on textile impregnation in silica sol utilizing the sol–gel technique, with a few papers also addressing the use of aerogel as filler. This review for the first time highlights all strategies to assemble silica aerogel with textile materials. For sol–gel approaches, the fibers can be impregnated in a silica precursor sol to form the aerogel in situ between the fibers, but the sol itself can also be spun into aerogel fibers. Other strategies employ pre-formed silica aerogel, mixed in polymer or solvent matrices/slurries, to form aerogel injected blankets, aerogel-filled material coated fibers, and aerogel-filled composite fibers. Aerogel particles-filled textile packages have also been proposed. The emerging activities on simulations of aerogel-fiber combinations are reviewed. The advantages/disadvantages of various approaches are evaluated, and the current market situation and an outlook for the future of the field are summarized

Structural control on bulk melt properties: Single and Double quantum 29Si NMR spectroscopy on alkali-silicate glasses

International audienc

Structural control on bulk melt properties: Single and Double quantum 29Si NMR spectroscopy on alkali-silicate glasses

International audienc

Speciation data on CaO-SiO2 and CaO-Al2O3 systems at the glass transition temperature

International audienc

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