All of the room temperature spectra showed that the iron oxide content was not pure FeO. In pure FeO there is a distinctive ratio between the intensity of the two spectral components. This ratio, , should equal 1:1.88 (A:B).8.1 In all cases for the toner samples was greater than this. This indicated another iron oxide being present and comparison with the example spectra in Reference dacosta_95 shows this to be -FeO (maghemite). In this case we can use the areas of the two components to calculate the Fe/Fe ratio and the FeO/FeO ratio.
Taking as the the proportion of FeO to the whole (between 0, pure FeO, and 1, pure FeO)
Laporte supplied five samples for study: two of their own (L1 and L2) and three competiting brands (C1, C2 and C3). No information was given concerning the composition of any of the samples. The room temperature Mössbauer spectra obtained from these samples are shown in Figure 8.1 and the fitting parameters in Table 8.1.
Using Equations 8.2 and 8.3 the ratio of Fe to Fe can be calculated. These values are shown in Table 8.2. Rearranging Equation 8.1 to obtain the ratio of atoms, :, gives the relation
Mössbauer spectra were recorded from the same samples at . These spectra are shown in Figure 8.2.
At the samples are below the Verwey transition temperature, , of . The single B site component has now become two separate components for and ions. The hyperfine fields for Fe A sites and Fe B sites in magnetite and the Fe A and B sites all lie close to each other, meaning they overlap in the spectrum. This, combined with the broad linewidth of the Fe B site makes these data much less reliable for accurate assessment of area ratios than the room temperature spectra. Thus the final results were based on the room temperature fits only.
Dr John Bland, 15/03/2003