Thermophysical and mechanical properties of zirconia fibrous ceramics for thermal protection

Abstract

Zirconia fibrous ceramics with high porosity (porosity=70-90%) were fabricated and investigated for high-temperature thermal protection applications. Two types of zirconia fibers, tetragonal and cubic phases, were compared. The results showed that the ceramics made of cubic-phase fibers had lower room-temperature thermal conductivity and lower mechanical strength. In addition, the effects of fiber diameter on the properties were also studied. Using the fibers with smaller diameter, the sample's thermal conductivity decreased, but the compressive strength also decreased slightly. It was found that the ceramics' room-temperature thermal conductivity and mechanical strengths varied with porosity linearly or exponentially, respectively. The ceramics' thermal expansion and thermal capacity in the range of RT~900 were measured. The high ℃ ℃ ℃ ℃ -temperature insulation performance was evaluated by back temperature tests. Finally, the porous ceramics were impregnated with aerogels. The room-temperature as well as high-temperature thermal conductivities both decreased. Therefore, the zirconia fibrous ceramics is a promising candidate for high-temperature insulation applications. Nomenclature ρ = density λ RT = room-temperature thermal conductivity λ HT = high-temperature thermal conductivity σ c = compressive strength σ t = tensile strength α = average linear thermal expansion C p = average thermal capability

Novel high entropy (Y0.2Sm0.2Gd0.2Er0.2Ho0.2)3NbO7 nanofibers with ultralow thermal conductivity

“…Figure 6B shows the thermal conductivities of 5RE 3 NbO 7 ‐900 fibrous ceramic and some typical thermal insulation materials. 5RE 3 NbO 7 ‐900 fibrous ceramic presented a lower thermal conductivity than mullite fibrous ceramics 21,45–47 and zirconia fibrous ceramics 48 with the same porosity (78.18 %, porosity), and closed to that of porous silica. Previous research suggested that porosity can reduce the effective heat carrying cross‐section, 18 slow down phonon velocity, and enhance effective phonon scatterings 49 .…”

“…(A) Typical fluorite unit cell and Cubic 5RE 3 NbO 7 unit cell, created by VESTA software. 51 (B) Thermal conductivity versus porosity of 5RE 3 NbO 7 ‐900 fibrous ceramic and typical thermal insulation materials 7,20,21,31,45–48,52–59 . (C) UV–Vis–NIR diffuse reflectance spectra of 5RE 3 NbO 7 ‐900 nanofiber, inserts are the magnification of the reflectance spectra in different wavelength ranges.…”

Improved oxidation resistance of high emissivity coatings on fibrous ceramic for reusable space systems

“…A typical concept for a RTPS structure comprises a high emissivity coating (HEC) on the surface of low thermal conductivity fibrous ceramic insulation, facilitating radiative cooling while minimizing heat conduction. In the past few years, fibrous ZrO2 ceramics have been the subject of increasing attention towards thermal insulation applications in ultra-high temperature environments because of their higher temperature stability relative to fibrous quartz or mullite ceramics [2]. Consequently, HEC materials with similarly high thermal stability are sought to complement fibrous ZrO2 insulation materials in RTPSs.…”