Study of the Microstructure of Solid Residues of Peat-Ore Compositions
Abstract Generated abstract
This study examines changes in the carbon microstructure of solid residues formed during heat treatment of peat and peat ore briquettes containing iron oxides. Samples were heated in a laboratory shaft furnace up to 1200°C, deashed, and analyzed by X-ray diffraction, with particular attention to the 002 band as an indicator of orientation and growth of carbon network packets. The results suggest that initial peat contains small, weakly ordered crystalline regions, that heating to 400 to 600°C destroys or fragments these regions, and that further heating promotes ordering and growth of coherent scattering regions. Addition of iron oxides appears to enhance development of the crystalline carbon structure, giving larger crystallite sizes than peat alone at 1000 and 1200°C.
Full Text
STUDY OF THE MICROSTRUCTURE OF SOLID RESIDUES OF PEAT–ORE COMPOSITIONS
N. G. Antonov, V. P. Zaryuto
(Presented by the Scientific-Methodological Seminar of the Organic Departments of the Faculty of Chemical Technology)
Changes in the atomic structure of peats during interaction with oxidizing agents in the processes of combustion, gasification, activation, and other technically important processes have a substantial influence both on the kinetics of these processes and on the properties of the solid residue.
The processes by which the structure of coke from peat is formed have been insufficiently studied. There are few data in the literature on the formation of the multilayer aromatic structure of peat cokes [1–2]. As a result of an X-ray study of the process of carbonization of peat, the authors of work [2] concluded that this process is characterized by the formation and subsequent growth of flat hexagonal networks of carbon atoms, similar to the atomic monolayer of graphite. The formation and growth of carbon networks can be traced quantitatively on X-ray patterns by the appearance and subsequent increase in the intensity of the interference bands 100 and 110. The process of mutual orientation and growth of packets of networks, which proceeds simultaneously with their growth, is indicated on the X-ray patterns by the 002 band.
The study of the process of orientation and growth of packets of carbon networks in peat–ore compositions during heating was carried out using the 002 band. For this purpose, peat and peat–ore briquettes made from high-moor peat (\(A^c\)—4.85%, \(V^r\)—85.93%, \(C^r\)—52.30%, \(H^r\)—6.43%, \(N^r\)—2.43%, degree of decomposition 20–25%) and iron oxides with an Fe\(_2\)O\(_3\) content in the peat–ore materials of 33.14% on a dry basis were subjected to heat treatment in a laboratory shaft furnace at a heating rate of 5°/min and with a one-hour holding period at the end of the coking interval. After heat treatment, the samples were crushed and de-ashed by the Radmacher method [3].
The investigation of the regions of coherent scattering of X-rays by the carbon of the solid residue was carried out on a DRON-1 unit, with a copper anode, anode voltage of 30 kV, and anode current of 20 mA. The determination of the size of the coherent scattering regions and the half-widths of the interference maxima was performed according to [4]. Crystals of annealed NaCl were used as the standard for determining the instrumental half-widths of the interference peaks.
The data obtained (Table 1, Figs. 1, 2) indicate that the initial peat has elements of crystalline structure, whose interference maxima on the X-ray patterns have a diffuse form and low intensity. This indicates that the region—
Table 1
Structural parameters of the solid residues of heat treatment of TIM and peat
| Sample | Treatment temperature, °C | $d$, Å | $l$, mm | $\beta \cdot 10^{-3}$ rad | $B$, deg | $\cos \theta_{\max}$ | $L_c$, Å | Note |
|---|---|---|---|---|---|---|---|---|
| Peat | initial | 3.4221—3.39 | 23 | 16.15 | 15.7 | 0.9738 | 90 | |
| Peat | 400 | — | — | — | — | — | <20 | |
| Peat | 800 | — | — | — | — | — | <20 | |
| Peat | 1000 | 3.4906—3.4686 | 39 | 27.80 | 27.5 | 0.9750 | 51.5 | |
| Peat | 1200 | 3.3890—3.3937 | 208 | 21.40 | 20.95 | 0.9739 | 67.5 | |
| TIM | initial | 3.4221—3.39 | 23 | 16.15 | 15.7 | 0.9738 | 90 | $b_{\mathrm{NaCl}} = 3.88 \cdot 10^{-3}$ rad |
| TIM | 800 | — | traces | traces | — | — | ∼20 | |
| TIM | 1000 | 3.3986—3.3866 | 170 | 21.3 | 20.93 | 0.9737 | 68 | |
| TIM | 1200 | 3.3913—3.3704 | 176 | 14.1 | 13.52 | 0.9736 | 104.5 |
coherent-scattering regions do not have constant parameters of the crystal lattice; their number is small and their size is slightly greater than 20 Å.
During heat treatment of peat and peat-ore materials up to 400–600°C, the disappearance of interference maxima is observed, which, apparently, is associated with the destruction and fragmentation of packets of networks into smaller ones. A further increase in temperature (above 800°C)
Fig. 1. X-ray diffraction patterns of peat. 1 — initial peat, M-1:1; 2 — 400°C, M-1:1; 3 — 800°C, M-1:1; 4 — 1000°C, M-1:2; 5 — 1200°C, M-1:2
Fig. 2. X-ray diffraction patterns of TPM. 1 — initial, M-1:1; 2 — 800°C, M-1:2; 3 — 1000°C, M-1:2; 4 — 1200°C, M-1:2
promotes ordering and growth of the coherent-scattering regions, with iron oxides, up to the investigated temperatures (1200°C), promoting the formation of the crystalline structure of carbon. Thus, if at a temperature of 1000°C the crystallites of peat without additions of Fe₂O₃ have an average size of about 51.5 Å, then with additions it is 68 Å, and at 1200°C, respectively, 67.5 and 104.5 Å.
-
The change in the microstructure of the carbon of peat-ore compositions has been studied.
-
The introduction of iron oxides promotes the formation of the crystalline structure of carbon.
LITERATURE
-
Riley, H. Blayden, and J. Gibson. Proceed. of Conference on Ultrafine Structure of Coals and Coke, BCURA, London, 1944, p. 176.
-
V. E. Rakovskii, F. A. Kaganovich, E. A. Novichkova. Chemistry of Pyrogenic Processes. Minsk, Publishing House of the Academy of Sciences of the BSSR, 1959.
-
W. Radmacher, P. Mohrhauer. “Brennstoff-Chemie,” 36, No. 15–16, 1955.
-
Ya. S. Umanskii. X-ray Diffraction of Metals and Semiconductors. Moscow, Metallurgiya, 1969.