Hypocrystalline ceramic aerogels for thermal insulation at extreme conditions

Abstract

Thermal insulation under extreme conditions requires materials that can withstand complex thermomechanical stress and retain excellent thermal insulation properties at temperatures exceeding 1,000 degrees Celsius1–3. Ceramic aerogels are attractive thermal insulating materials; however, at very high temperatures, they often show considerably increased thermal conductivity and limited thermomechanical stability that can lead to catastrophic failure4–6. Here we report a multiscale design of hypocrystalline zircon nanofibrous aerogels with a zig-zag architecture that leads to exceptional thermomechanical stability and ultralow thermal conductivity at high temperatures. The aerogels show a near-zero Poisson’s ratio (3.3 × 10−4) and a near-zero thermal expansion coefficient (1.2 × 10−7 per degree Celsius), which ensures excellent structural flexibility and thermomechanical properties. They show high thermal stability with ultralow strength degradation (less than 1 per cent) after sharp thermal shocks, and a high working temperature (up to 1,300 degrees Celsius). By deliberately entrapping residue carbon species in the constituent hypocrystalline zircon fibres, we substantially reduce the thermal radiation heat transfer and achieve one of the lowest high-temperature thermal conductivities among ceramic aerogels so far—104 milliwatts per metre per kelvin at 1,000 degrees Celsius. The combined thermomechanical and thermal insulating properties offer an attractive material system for robust thermal insulation under extreme conditions.

Electrospinning-Based Biosensors for Health Monitoring

“…When the jet is flying in the air, the solvent evaporates and the final solute is deposited on the receiving plate to form nanofibers. Figure 2 is a schematic diagram of the working principle of electrospinning [ 22 , 23 ]. The whole electrospinning equipment mainly includes three parts: a high voltage supply device, an injector and a receiving board.…”

Flexible-in-rigid polycrystalline titanium nanofibers: a toughening strategy from a macro-scale to a molecular-scale

“…One recent research study demonstrated that the structural resilience of ZrO 2 nanofibers can be optimized by embedding ZrO 2 nanocrystallites into an amorphous zircon matrix. 13 Upon loading, the relatively flexible zircon would lubricate the brittle ZrO 2 nanocrystallites and allow more deformations to dispersive stress. As an alternative tactic, the grain growth in oxide nanofibers can be effectively hampered by coating an Al 2 O 3 shell outside the surface via co-axial electrospinning, therefore enhancing their thermal and mechanical stability.…”

Medium-entropy ceramic aerogels for robust thermal sealing

“…The working environments of sealing materials are usually very harsh, 5,6 such as high temperatures over 1000 °C, large thermal shocks and highfrequency vibrations in spacecras, furnaces, engines, etc., requiring materials with high thermomechanical properties and low thermal conductivity (k) to guarantee the system safety. Due to the low k, low density (r) and excellent re/corrosion resistance, ceramic aerogels [7][8][9][10][11][12][13][14] are attractive candidates for thermal sealing. However, the brittle nature and crystallizationinduced pulverization of ceramic aerogels oen lead to severe strength degradation and structural failure under dynamic loads, sharp thermal shocks or high-temperature exposure in hypersonic vehicles, spacecras, internal combustion engines, etc.…”

“…10,11,24 The oxidation resistance and thermal expansion coefficient can be improved by elemental composition selection 25 and structural design. 7 However, it is more difficult to suppress the crystal growth and phase transition induced pulverization of ceramic materials when the system energy exceeds the crystalline barrier at high temperatures. 10,11 A potential strategy to simultaneously enhance the mechanical and thermal properties is to increase the degree of congurational entropy in material design.…”