Amorphous Alumina Thin Films Deposited on Carbon Microfibers As Interface Layer for Thermal Oxidation Barriers

Abstract

Carbon microfibers make a promising candidate as textile reinforcement for high temperature composites provided that their limitation of thermal oxidation over 670 K in air is overcome. As such, this study explored the potential of atomic layer deposition (ALD) for the deposition of a substrate-nanolaminate interface layer for the design of a refractory oxygen barrier coating applied to individual carbon microfibers within a woven fabric. To this end, amorphous aluminum hydroxide was deposited at 350 K in a flow-type thermal ALD reactor operating at a pressure of 1.8 Torr, yielding a growth per cycle (GPC) of 1.0 Å/cycle. The conformal aspect of the amorphous films was found to be well preserved below a thickness of 45 ± 5 nm, above which reorganization of the substrate surface by junction of the previously deposited layers resulted in a uniform deposition. Furthermore, a minimal thickness of 20 ± 2 nm was required to obtain self-standing films following the thermal oxidation of the carbon microfibers. Indeed, thermal treatment at 1380 K of the coated woven fabric induced multiple occurrences of neat cracks in the aluminum oxide films, attributed to the increased rigidity and mismatch between the respective thermal expansion coefficients. The dense network of nanograins of aluminum oxide was further characterized by using 4D-STEM, revealing multiple phases and orientations.

A flexible precontact CNT-Al2O3 fiber sensor resistant to extreme temperatures

“…In all the nanoscale structures of ceramic materials, the one-dimensional structure with a large aspect ratio, with the advantages of high surface area, low density, excellent mechanical properties and multifunctionality, is one of the main structures of ceramic materials with flexibility. Among the various preparation processes, electrospinning, 17–19 blow spinning, 16,20 chemical vapor deposition (CVD) 21,22 and atomic layer deposition (ALD) 23,24 are suitable options to accomplish this task. For example, a large-area flexible TiO 2 nanofiber network is prepared by the extended electrospinning method, and the flexible pressure sensor based on the ceramic network can withstand high temperatures up to 370 °C.…”

“…Among the various preparation processes, electrospinning, [17][18][19] blow spinning, 16,20 chemical vapor deposition (CVD) 21,22 and atomic layer deposition (ALD) 23,24 are suitable options to accomplish this task. For example, a large-area flexible TiO 2 nanofiber network is prepared by the extended electrospinning method, and the flexible pressure sensor based on the ceramic network can withstand high temperatures up to 370 °C.…”