Table 3 shows the average primary particle sizes estimated from the TEM and BET results, and the crystallite sizes obtained from the XRD analysis. The estimated sizes for the primary particles were below than 10 nm in all cases. The crystalline size coincides with primary particle size indicating single crystallinity of the particles. The size difference between aluminium oxide and Fe doped aluminium oxide particles was negligible. The formation of small primary particles with high surface area is typical for FSP and is due to the high enthalpy of the flame and rapid cooling in FSP. Table 3 lists the average diameter of aggregates (davg) estimated from the TEM images. The produced particles were loosely agglomerated as shown in the TEM images (see Fig. 5). Formation of aggregate is common for particles synthesized with FSP method due to coagulation and sintering, and the electrostatic attraction between the particles.