Hot‐air aging failure mechanisms of carbonyl iron powder/methyl vinyl silicone rubber microwave‐absorbing materials

Abstract

A rubber microwave‐absorbing material was prepared by compounding methyl vinyl silicone rubber (VMQ) and 45 vol% carbonyl iron powder (CIP). When used in a high‐temperature environment at long periods, the material undergoes thermal aging and rapid degradation. This work mainly aimed to investigate the thermal behavior and aging failure mechanisms of such material during hot‐air aging at 200°C. The mechanical and electromagnetic properties were measured with an electronic tensile testing machine and a network analyzer, respectively. Results indicate that CIP was oxidized by oxygen in the aging process and produced reactive oxygen species, which catalyzed the cross‐linking of VMQ. The increased cross‐linking density changed the mechanical properties and enhanced the thermal stability of the CIP/VMQ composite‐absorbing material. Thermal aging gradually penetrated the surface and proceeded into the interior of the material. The microwave‐absorbing properties deteriorated after hot‐air aging.

Thermal aging properties of flame retardant silicone rubber based on melamine cyanurate

“…With aging time prolonged (to 2016 h), both the size and amounts of the holes obviously increased. This phenomenon was mainly attributed to small molecules escaping from FRSR surface and generate some degraded small molecules 32 . Compared with FRSR, no holes were observed on the surface of SR without MCA (figure S1), which furtherly confirmed the decomposition of MCA in FRSR materials.…”

“…Both the tensile strength and elongation at break were significantly decreased. At the initial stage, the downtrend was more obvious, which was mainly due to the degradation of bulky SR materials under thermal‐oxidative aging 31,32 . With aging time increased, the decreased tendency was slowed down, but the elongation at break continuously declined.…”

“…The increased hardness can been explained by the increased reaction density between free radicals arising from the breakage of chemical bond of SR under attack of heat and oxygen. As previous literature reported, factors such as light, heat and external force could activate the generations of free radicals, which was easily react with each other to form “inorganic silicon” or large particles, thus leading to the increase of the hardness of the materials 32,33 …”

“…At the initial stage, the downtrend was more obvious, which was mainly due to the degradation of bulky SR materials under thermal-oxidative aging. 31,32 With aging time increased, the decreased tendency was slowed down, but the elongation at break continuously declined. The deterioration in tensile properties after aging was normally related to both the molecular chain scission and the coexisted cross-linking between radicals and oxygen.…”

“…As previous literature reported, factors such as light, heat and external force could activate the generations of free radicals, which was easily react with each other to form "inorganic silicon" or large particles, thus leading to the increase of the hardness of the materials. 32,33 Since flame retardant property was provided by the incorporation of MCA, the retention of MCA in the SR matrix was quite important during the long-term thermal aging process. The surface and fracture surface microstructure of aged sample at varied periods were observed by SEM.…”