free spirit
more tea vicar?
ok. so this is the bit that's bothering them?When ignited in a DSC device the chips exhibit large but narrow exotherms occurring at approximately 430 °C,
Their elemental analysis shows that the chips contain zinc, presumably because they're actually the pulverised remnants of the galvanised steel framework for the partition walls and ceiling hangers etc.
as I said above, Zinc dust has an auto ignition temperature of 460 deg C, though this ignition temperature is dependent upon the particle size, so smaller particles would ignite at lower temperatures.. so I would strongly suspect that it's the zinc that is igniting at the lower temperatures, then raising the temperature sufficiently for the iron to burn. Plus there's a fair amount of carbon in there as well, and magnesium.