Research ArticleMATERIALS SCIENCE

Ultralight and fire-resistant ceramic nanofibrous aerogels with temperature-invariant superelasticity

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Science Advances  27 Apr 2018:
Vol. 4, no. 4, eaas8925
DOI: 10.1126/sciadv.aas8925
  • Fig. 1 Structure design and cellular architectures of CNFAs.

    (A) Schematic illustration of the fabrication of CNFAs. (B) XPS spectrum of CNFAs for all elements. a.u., arbitrary unit. (C) A CNFA heated by a butane blowtorch without any damage. (D) An optical image of CNFAs with diverse shapes. (E) An optical image showing a 20-cm3 CNFA (ρ = 0.15 mg cm−3) standing on the tip of a feather. (F to H) Microscopic structure of CNFAs at different magnifications demonstrating the hierarchical nanofibrous cellular architecture. (I) STEM-EDS images of a single nanofiber with corresponding elemental mapping images of Si, O, Al, and B, respectively. (J) Schematic showing the three levels of hierarchy of the relevant structures.

  • Fig. 2 Multicycle compressive properties of the CNFAs.

    (A) Compressive σ versus ε curves during loading-unloading cycles with increasing ε amplitude. (B) A 500-cycle fatigue test with compressive ε of 60%. (C) Young’s modulus, energy loss coefficient, and maximum stress versus compressive cycles. (D) The Poisson’s ratio of the CNFAs versus ε. Inset: SEM observations of the CNFAs under compression and release, focusing on a small piece (<1 mm). (E) Sketch of the inversion of the nanofibrous cell walls under compression. SEM images showing the curvature radius of (F) a single cellular cell and (G) a single nanofiber. (H) Schematic illustration of the microstructure of a bent silica nanofiber. (I) A set of real-time images showing that CNFAs can rebound a steel ball at high speed. (J) The frequency dependence of the storage modulus, loss modulus, and damping ratio for CNFAs (oscillatory ε of 3%). (K) The relative Young’s modulus of selected cellular aerogels with low densities.

  • Fig. 3 Mechanical properties of the CNFAs over a wide range of temperature.

    (A to C) Storage modulus, loss modulus, and damping ratio of the CNFAs versus angular frequency (0.1 to 10 Hz) at temperatures from −100° to 500°C, with an oscillatory ε of 3%. (D) Compression and recovery work of the CNFAs after treatment at various temperatures for 30 min. (E) XRD patterns of CNFAs after treatment at 1000°, 1200°, and 1400°C for 30 min. (F) SEM images of CNFAs after treatment at 1200° and 1400°C for 30 min. Compression and recovery process of the CNFAs in the flame of (G) an alcohol lamp and (H) a butane blowtorch.

  • Fig. 4 Thermal insulation properties of the CNFAs.

    (A) The thermal conductivities of the CNFAs as a function of density. (B) Thermal conductivity versus maximum working temperature for aerogel-like materials. (C) An optical image of the CNFAs on the large scale for thermal insulation applications. (D) Thermal insulation capacity of the CNFAs compared with those of Fe, SiO2, and Al2O3 materials for protecting fresh petals from withering. (E) Optical and infrared images of CNFAs on a 350°C heating stage for 30 min. (F) Optical and infrared images of CNFAs exposed to a butane blowtorch for 120 s.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/4/eaas8925/DC1

    fig. S1. Fabrication of electrospun SiO2 nanofibers.

    fig. S2. Homogenization of nanofibers.

    fig. S3. Morphology of homogenized nanofibers.

    fig. S4. The freezing of nanofiber dispersions.

    fig. S5. Magnified XPS spectrum.

    fig. S6. The ultralow density of the CNFAs.

    fig. S7. Compressibility of the CNFAs with a density of 0.15 mg cm−3.

    fig. S8. SEM images of the nanofibrous cell walls.

    fig. S9. Micro-orientation and macro-isotropic structure of CNFAs.

    fig. S10. Mechanical properties of the CNFAs upon different orientation.

    fig. S11. EDS mapping of junctions between nanofibers.

    fig. S12. Shear mechanical properties of CNFAs.

    fig. S13. Tensile mechanical properties of CNFAs.

    fig. S14. Elastic resilience of CNFAs with different structures.

    fig. S15. Amorphous character of the CNFAs.

    fig. S16. Effect of fiber diameter on the structure of CNFAs.

    fig. S17. Effect of fiber diameter on the mechanical properties of CNFAs.

    fig. S18. Effect of lamellar spacing on the structure and properties of CNFAs.

    fig. S19. Elasticity of a PU foam.

    fig. S20. Elasticity of CNFAs with a wide range of densities.

    fig. S21. The temperature at the position of the CNFAs upon flames.

    table S1. The relevant densities and thermal conductivities of CNFAs and other insulation materials.

    Supplementary Methods

    Supplementary Discussions

    movie S1. Compression and recovery processes of CNFAs.

    movie S2. Fast recovery of CNFAs by rebounding a steel ball.

    movie S3. Compression testing in the flame of an alcohol lamp.

    movie S4. Compression testing in the flame of a butane blowtorch.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Fabrication of electrospun SiO2 nanofibers.
    • fig. S2. Homogenization of nanofibers.
    • fig. S3. Morphology of homogenized nanofibers.
    • fig. S4. The freezing of nanofiber dispersions.
    • fig. S5. Magnified XPS spectrum.
    • fig. S6. The ultralow density of the CNFAs.
    • fig. S7. Compressibility of the CNFAs with a density of 0.15 mg cm−3.
    • fig. S8. SEM images of the nanofibrous cell walls.
    • fig. S9. Micro-orientation and macro-isotropic structure of CNFAs.
    • fig. S10. Mechanical properties of the CNFAs upon different orientation.
    • fig. S11. EDS mapping of junctions between nanofibers.
    • fig. S12. Shear mechanical properties of CNFAs.
    • fig. S13. Tensile mechanical properties of CNFAs.
    • fig. S14. Elastic resilience of CNFAs with different structures.
    • fig. S15. Amorphous character of the CNFAs.
    • fig. S16. Effect of fiber diameter on the structure of CNFAs.
    • fig. S17. Effect of fiber diameter on the mechanical properties of CNFAs.
    • fig. S18. Effect of lamellar spacing on the structure and properties of CNFAs.
    • fig. S19. Elasticity of a PU foam.
    • fig. S20. Elasticity of CNFAs with a wide range of densities.
    • fig. S21. The temperature at the position of the CNFAs upon flames.
    • table S1. The relevant densities and thermal conductivities of CNFAs and other insulation materials.
    • Supplementary Methods
    • Supplementary Discussions

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Compression and recovery processes of CNFAs.
    • movie S2 (.mov format). Fast recovery of CNFAs by rebounding a steel ball.
    • movie S3 (.mp4 format). Compression testing in the flame of an alcohol lamp.
    • movie S4 (.mp4 format). Compression testing in the flame of a butane blowtorch.

    Files in this Data Supplement:

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