New hypotheses on the mechanism of the deterioration of cordierite diesel filters in the presence of metal oxides

It is well known that the durability of the honeycomb structures made of cordierite, used as filters for diesel exhaust emissions, is affected by some components of the soot which can react with cordierite during regeneration cycles at high temperature (up to 1000 degrees C). Amongst all the components of the soot, sodium is particularly dangerous because of its destructive effect on the cordierite structure. The interaction between sodium carbonate and cordierite has been studied by means of FTIR spectroscopy and the following statements can be made: even if very slowly, the attack on cordierite has already begun at 500 degrees C and proceeds very quickly onwards from 600 degrees C; an amorphous phase is formed at 700 degrees C; at higher temperature, the amorphous phase crystallizes releasing sodium which, during cooling, reacts with carbon dioxide, yielding again sodium carbonate; this carbonate will act as sodium source in the following thermal regeneration cycles. During this study it has also been shown that the first attack is not determined by the sodium ion diffusion into the pseudo-zeolitic channels of the cordierite lattice.