Experimental Characterization of the Thermal Conductivity and Microstructure of Opacifier-Fiber-Aerogel Composite

Abstract

Due to their high-porosity, nanoporous structure and pores, aerogel materials possess extremely low thermal conductivity and have broad potential in the thermal insulation field. Silica aerogel materials are widely used because of their low thermal conductivity and high temperature resistance. Pure silica aerogel is very fragile and nearly transparent to the infrared spectrum within 3–8 μm. Doping fibers and opacifiers can overcome these drawbacks. In this paper, the influences of opacifier type and content on the thermal conductivity of silica fiber mat-aerogel composite are experimentally studied using the transient plane source method. The thermal insulation performances are compared from 100 to 750 °C at constant pressure in nitrogen atmosphere among pure fiber mat, fiber mat-aerogel, 20% SiC-fiber mat-aerogel, 30% ZrO2-fiber mat-aerogel and 20% SiC + 30% ZrO2-fiber mat-aerogel. Fiber mat-aerogel doped with 20% SiC has the lowest thermal conductivity, 0.0792 W/m·K at 750 °C, which proves that the proper type and moderate content of opacifier dominates the low thermal conductivity. The pore size distribution indicates that the volume fraction of the micropore and mesopore is also the key factor for reducing the thermal conductivity of porous materials.

Effects of the Heat Treatment in the Properties of Fibrous Aerogel Thermal Insulation

“…From these results, we could expect that heat treatment in such materials causes either a crystallization process or the growth of the grains. In Reference [45], it was stated that the different types of measurements carried out on fiber aerogel samples are very important, as they support each other. Reference [46] stated that the artificial aging of insulation materials and their investigations with different methods are very important.…”

Preparation and characterization of novel nano‐Al2O3/SiO2‐based composites for energy‐saving

“…As an opacifier, SiC can effectively suppressed high-temperature radiation, and the effect was more obvious as the temperature increased. 17 For example, when the porosity is 89.6%, as temperature increases from 200 to 800 • C, thermal conductivity value of nano-Al 2 O 3 /SiO 2 -based composites increases from .06 to .072 W/(m K). From Figure 7, we can see that a negative correlation was found between porosity and thermal conductivity.…”

“…A possible explanation for this might be that as the temperatures rose, nano-Al 2 O 3 /SiO 2 -based composites continuously absorbed radiant energy, resulting in an increase in radiant heat and ultimately an increase in thermal conductivity. As an opacifier, SiC can effectively suppressed high-temperature radiation, and the effect was more obvious as the temperature increased 17. For example, when the porosity is 89.6%, as temperature increases from 200 to 800 • C, thermal conductivity value of nano-Al 2 O 3 /SiO 2 -based composites increases from .06 to .072 W/(m K).…”

Thermally Conductive Self-Healing Nanoporous Materials Based on Hydrogen-Bonded Organic Frameworks

“…Comparison of thermal conductivities of various porous materials such as aerogels, MOFs, − zeolites, − COF-5 (through-plane measurement), and ABTPA HOF (this work) as a function of mass density. Generally, zeolites have higher thermal conductivities since they have relatively higher mass densities as compared to other porous solids.…”

“…43 This arrangement allows large flexibility in the dynamic movement of the organic building blocks and the free rotation of the anthracene units made possible by the hydrogen-bonded 2D square lattice. As such, this provides a potential avenue for an adaptive framework by introducing an overall responsive behavior of Comparison of thermal conductivities of various porous materials such as aerogels, 12 MOFs, 13−17 zeolites, 18−21 COF-5 (through-plane measurement), 3 and ABTPA HOF (this work) as a function of mass density. Generally, zeolites have higher thermal conductivities since they have relatively higher mass densities as compared to other porous solids.…”