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. 2021 Feb 8;11:3316. doi: 10.1038/s41598-021-82806-z

Figure 2.

Figure 2

(a) Infrared spectra of Zhengzhou soil heated to various temperatures and mixed with potassium ferricyanide as an internal standard. Mass ratio (mIS/mS) is equal to one for all samples. All spectra are normalized to the peak absorbance value of the internal standard (AIS, located at wavenumber 2120 cm−1). The normalized height of the soil samples’ main absorption peak (at 1035 cm−1) decreases steadily as the firing temperature is increased from 150 to 900 °C (see inset plot); (b) Infrared spectra of quartz and of albite feldspar heated to various temperatures and mixed with potassium ferricyanide as an internal standard. For both quartz and albite, the normalized height of the main absorption peak (at 1080 cm−1 and 1016 cm−1, respectively) remains constant as firing temperature is increased.

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