Chemical Reactivity and Oxidation Resistance

The M +iX layers are chemically quite stable. By comparison, because the A-group atoms are relatively weakly bound, they are the most reactive species. For example, heating Ti3SiC2 in a C-rich atmosphere results in the loss of Si and the formation of TiCx [113]. When the same compound is placed in molted cryolite [114], or molten 

A1 [115] essentially the same reaction occurs, namely that the Si escapes and TiC forms. 

In some cases, such as Ti2lnC, simply heating in vacuum at 800 °C results in a loss of the A-group element and the formation of TiC [48]. 

In general, the oxidation of the MAX phases occurs according to reaction (II)  

Given the close structural and chemical similarities between the MAX and their corresponding MX phases, it is not surprising (as discussed above) that these two classes of compounds share some common attributes and properties. For example, they are both metal-like conductors dominated by d-d bonding their phonon conductivities are both susceptible to the presence of vacancies and the TCEs of the ternaries track those of the binaries, to name a few. 

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