The formation of η-Al2O3 and ϴ-Al2O3 phases is typically observed at temperatures between 200 and 800 °C, while in the FSP the temperatures within the flame can be as high as 3000 K. However, the residence times at these temperatures are very short accompanied by rapid cooling which can lead to the formation of metaphases, e.g. γ-alumina. Thus, the crystallization is likely to be dictated by the fast cooling leading to the formation of η-alumina. Based on the data it can be assumed that the reactions/crystallization in the FSP used in the studies have been quenched around 600–800 °C which is the temperatures range for η-Al2O3 formation.