particles although nanotubes may form at higher hab than those described in the present system see fig1 the range of equivalence ratios that could support nanotube growth can therefore potentially extend from 1 7 to 1 0 equivalence ratios of 1 9 and higher are dominated by soot like structures displaying clustered networks of primary particles of either metallic or carbon encapsulated metal centers with the occasional nanotube within this matrix it is interesting to note that within the formation window range relatively u2018 clean u2019 nanotubes are formed at the lower equivalence ratios while an increasing level of encrusting with disordered carbon is observed on the nanotubes as the equivalence ratio increases a continuum of morphologies is apparent ranging between clean nanotubes at low equivalence ratios through to an increasing proportion of soot like material as the equivalence ratio increases a competition between carbon precipitation pathways is likely with one pathway leading to filamentary or tube structures and the other to disordered carbon clusters this observation is consistent with the nanotube formation mechanism and how this would relate to a flame environment as fuel equivalence ratio increases from unity the level of excess carbon available in the flame gases increases so one would also expect an increasing potential to form carbon nanotubes this trend is tempered as the sooting equivalence ratio limit is reached and.