Robust,fire-resistant,and thermal-stable SiZrNOC nanofiber membranes with amorphous microstructure for high-temperature thermal superinsulation

Ceramic nanofibers with robust mechanical properties,high-temperature resistance,and superior thermal insulation performance are promising thermal insulators used under extreme conditions.However,developing of ceramic fibers with both low solid thermal conductivity(λs)and low infrared radiation thermal conductivity(λr)is still a great challenge.Herein,according to the Ioffe-Regel limit theory,we report a novel SiZrNOC nanofiber membrane(NFM)with a typically amorphous structure by combining the electrospinning method and high-temperature pyrolysis technique in a NH3 atmosphere.The prepared SiZrNOC NFM has a high tensile strength(1.98±0.09 MPa),excellent thermal stability(1100℃in air),and superior thermal insulation performance.The thermal conductivity of SiZrNOC NFM was 0.112 W·m^(−1)·K^(−1) at 1000℃,which is obviously lower than that of the traditional ceramic fiber membranes(>0.2 W·m^(−1)·K^(−1) at 1000℃).In addition,the prepared SiZrNOC NFM-reinforced SiO2 aerogel composites(SiZrNOCf/SiO2 ACs)exhibited ultralow thermal conductivity of 0.044 W·m^(−1)·K^(−1) at 1000℃,which was the lowest value for SiO2-based aerogel composites ever reported.Such superior thermal insulation performance of SiZrNOC NFMs was mainly due to significant decreasing of solid heat conduction and thermal radiation by the fancy amorphous microstructure and high infrared shielding compositions.This work not only provides a promising high-temperature thermal insulator,but also offers a novel route to develop other high-performance thermal insulating materials.

Effect of Rare Earth and Transition Metal Elements on the Glass Forming Ability of Mechanical Alloyed Al–TM–RE Based Amorphous Alloys

The present work aims to compare the amorphous phase forming ability of ternary and quaternary Al based alloys （Al86Ni8Y6, Al86GNi6Y6Co2, Al86NigLa6 and Al86Ni8Y45La15） synthesized via mechanical alloying by varying the composition, i.e. fully or partially replacing rare earth （RE） and transition metal （TM） elements based on similar atomic radii and coordination number. X-ray diffraction and high resolution transmission electron microscopy study revealed that the amorphization process occurred through formation of various intermetallic phases and nanocrystalline FCC Al. Fully amorphous phase was obtained for the alloys not containing lanthanum, whereas the other alloys containing La showed partial amorphization with reappearance of intermetallic phases attributed to mechanical crystallization. Differential scanning calorimetry study confirmed better thermal stability with wider transformation temperature for the alloys without La.

Effect of Oxygen on Microstructure Evolution and Glass Formation of Zr-based Metallic Glasses

The effect of oxygen on the microstructure evolution and glass formation of Zr-based bulk metallic glasses（BMGs）was studied in detail.It was found that oxygen did not form oxides or dissolve in glass matrix,but induced the precipitation ofα-Zr which has the high affinity and solubility of oxygen in the Zr-based bulk metallic glass（ZrBMG）.With the precipitation ofα-Zr,the remaining melts contain much lower oxygen content and have strong glass formation,resulting in the formation ofα-Zr/BMG composite.The findings provide an important insight into the mechanism of the oxygen on glass formation,and give us a useful guideline to avoid the oxygen detrimental for designing new BMGs.