Effect of potassium on a model soot combustion: Raman and HRTEM evidences

Figures & data

Table 1. BET analysis (SA, m²/g) at different soot conversion values.

	SA (m^2/g)
Soot conversion (%)	Soot	K-soot
Fresh	90	75
8	153	—
11	219	81
20	246	185
40	367	286
50	330	—
60	270	—
64	—	580

Figure 1. Fringes extraction from Printex U HRTEM micrograph: (A) image selection; (B) filtered image; (C) threshold analysis; (D) skeletonized image (in the inset is shown the BSU parameters evaluated in the fringe analysis).

Table 2. Primary size distributions obtained by TEM measurements, XRD, and TEM crystallographic parameters (the mean interlayer spacing between carbon layers d₀₀₂ (nm), average height L_c (nm), and average width L_a (nm) of BSU) of soot and K-soot samples at different oxidation degrees.

				d002(nm)		Lc (nm)		La (nm)
Sample	Mean diameter (nm)	σ^− (nm)	σ+ (nm)	From XRD	From TEM	From XRD	From TEM	From TEM
Soot	22	7	11	0.368	0.379	1.11	1.02	0.78
K-soot	21	8	12	0.359	0.377	1.15	0.98	0.81
Oxidized soot—60%	20	9	15		0.371		1.25	1.18
Oxidized K-soot—64%	19	9	16		0.376		1.05	0.78

Figure 2. XRD measurement of unoxidized soot and K-soot samples.

Figure 3. TEM images of fresh samples. (A) Low magnification bright field TEM micrograph of fresh Printex U; (B) High resolution TEM of fresh Printex U; (C) Low magnification bright field TEM micrograph of fresh K-doped Printex U; (D) High resolution TEM of fresh K-doped Printex U. The insets in A and C report the primary particle size distributions of fresh Printex U and K-doped Printex U, respectively.

Figure 4. Raman spectra (632 nm excitation, 100 µW laser power) recorded over fresh Printex U and K-doped Printex U samples.

Figure 5. Raman spectra (632 nm excitation, 100 µW laser power) recorded over oxidized Printex U (A) and K-doped Printex U (B) samples under O₂ and O₂/NO₂ (oxidation state near 40% in both cases).

Figure 6. First-order Raman spectra of Printex U at different oxidation degrees (curve a = 0%, b = 20%, c = 40%, d = 50%, e = 60 %) under O₂/NO₂ at 200°C.

Figure 7. TEM images of partially oxidized samples (60% in the case of Printex U, 64% in the case of K-doped Printex U). (A) Low magnification bright field TEM micrograph of oxidized Printex U; (B) High resolution TEM of oxidized Printex U; (C) Low magnification bright field TEM micrograph of oxidized K-doped Printex U; (D) High resolution TEM of oxidized K-doped Printex U. Insets in B and D report the fringes extracted images of the areas indicated by the boxes. The area in the inset B (oxidized Printex U 60%) clearly exhibits a higher graphitization degree (higher La and Lc) in comparison to the inset D (oxidized K-doped Printex U 64%). The insets in A and C report the primary particle size distributions of oxidized Printex U 60% and K-doped Printex U 64%, respectively.

Figure 8. First-order Raman spectra of K-doped Printex U at different oxidation degrees (curve a = 0%, b = 10%, c = 15%, d = 20 %, e = 40 %, f = 64 %) under O₂/NO₂ at 200°C.