Enhancement of the self-healing ability in oxidation induced self-healing ceramic by modifying the healing agent

Abstract

The available temperature range of the self-healing induced by high temperature oxidation of SiC can be controlled by the particle size of the contained SiC particles. In this study, three types of alumina–SiC composites were prepared. The SiC particle sizes of the composites were 270, ∼30 nm, and less than 10 nm. The self-healing abilities were estimated by the strength recovery behavior at several temperatures. The use of nanometer-sized dispersed SiC particles as healing agent decreases the activation energy of the SiC oxidation obtained from the differential thermal analysis with several heating rates. This implies that smaller SiC particles can give rise to the oxidation at lower temperature. Moreover, the lowest temperature at which the cracked strength was completely recovered for 10 h was strongly affected by the SiC particle size. As the SiC particle size varied from 270 to ∼30 nm, the lowest temperature varied from 1300 to 950 °C. However, alumina composite containing SiC particles whose particle size is less than 10 nm cannot recover completely the cracked strength under every condition, because the space between crack walls cannot be filled with the formed oxide due to the small volume of SiC on the crack walls. Therefore, it was found that there is an optimal SiC particle size for endowing self-healing ability.

Generic principles of crack-healing ceramics

“…Similar thermodynamic considerations describe the size effect on the reduction of melting temperature of nanoscale particles [124], disorder-induced amorphization [125], and disorder induced melting of amorphous solids [126]. Experimental observation revealed significantly higher oxidation reaction rates when the particle size of the SiC repair filler dispersed in an Al 2 O 3 matrix was reduced to nanoscale [51]. Thus, apparent activation energies derived from DTA measurements of peak temperature for oxidation reaction, T p , at constant heating rates revealed a pronounced decrease with particle size from G * = 383 kJ/mol at d  270 nm to 268 kJ/mol at 30 nm to 197 kJ/mol at 10 nm, respectively.…”

“…The second term expresses the net force driving either crack advance (G c >G heal ) or regression (G c <G heal ).  is a constant having the status of an activation area for the kinetic crack motion [49] [50], significantly higher activation energies were reported for vapour-solid oxidation reaction (G * <400 kJ/mol), and solid state matter transport through viscous flow of an amorphous inter-granular phase (G * < 500 kJ/mol), surface diffusion (G * < 600 kJ/mol) and grain boundary diffusion (G * < 800 kJ/mol) [10,51,52]. Compared to the repair capacity of polymers and polymer composite materials which are able to regenerate cracks near ambient temperature or supported by UV radiation catalysis [7,53], repair reactions in ceramic materials therefore require elevated temperatures to overcome the high activation energy barrier.…”

“…Microcracks in crystalline SiO 2 (quartz) with a length of 100 µm and a width of 10 µm were completely healed by exposure to a water pressure of 200 MPa at 600 ℃ for 4 h [50]. Strength recovery by hightemperature oxidation induced crack healing with environmental oxygen at elevated temperatures was reported from a number of non-oxide ceramics as well as oxide ceramics loaded with SiC [26,30,34,[39][40][41]51,[69][70][71][72][73][74]. For example, annealing of SiC reinforced Al 2 O 3 nanocomposites in inert Ar atmosphere resulted in a strength increase of 50% relative to the unannealed specimen whereas annealing in air yielded a three-fold improvement in the indendation strength [69].…”

“…To overcome mismatch between crack volume and the amount of healing agent two approaches were proposed [51]: (i) use of elongated healing agents such as whiskers and fibers and (ii) reduction of crack opening by prestressing. Elongated healing agents would be more efficient than spherical shaped agents because of significantly lager production of reaction phase volume.…”

The effect of the TiC particle size on the preferred oxidation temperature for self-healing of oxide ceramic matrix materials

“…While the optimal healing temperature has been shown to vary significantly with the chemical composition of the healing particle and to a lesser degree of that of the matrix material, very few studies, with the exception of [8], performed a systematic study on the effect of particle size on the healing kinetics given a fixed composition for both the particle and the matrix. In their study, Nakao and Abe [8] measured the strength recovered by high-temperature oxidation of alumina containing 18 vol% SiC particles of size 270, 30 and 10 nm.…”