micro-raman spectroscopy of carbonized semifusinite and fusinite

International Journal of Coal Geology 87 (2011) 253–267

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International Journal of Coal Geology

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Micro-Raman spectroscopy of carbonized semifusinite and fusinite

R. Morga ⁎Institute of Applied Geology, Silesian University of Technology, Akademicka 2, 44-100 Gliwice, Poland

⁎ Tel.: +48 606437074; fax: +48 322372290.E-mail address: [email protected].

0166-5162/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.coal.2011.06.016

a b s t r a c t
a r t i c l e i n f o
Article history:Received 5 December 2010Received in revised form 16 June 2011Accepted 29 June 2011Available online 5 July 2011

Keywords:CoalInertiniteSemifusiniteFusiniteRaman spectroscopyHeating experiment

The purpose of the study was to present application of micro-Raman spectroscopy for examination of coalmacerals and to characterize the internal structure of semifusinite and fusinite heated at 400–1200 °C, in anargon atmosphere. Examination was performed on inertinite concentrates prepared from three samples ofsteam and coking bituminous coals (Rr=0.98–1.42%) from the Upper Silesian Coal Basin of Poland. Fusiniteand semifusinite, as well as reactive and non-reactive forms of the latter maceral differ in terms of structuralproperties, as inferred from the Raman-derived parameters. Behavior of both macerals under heat-treatmentis determined by their structural and chemical properties. Carbonization causes rebuilding of macromolecularnetwork of semifusinite and fusinite resulting in the growth of polyaromatic units and, in case of the formermaceral, also increases in structural organization. This is followed by significant reflectance increase.Semifusinite carbonized at 1200 °C has larger coherent domains and they are more ordered than in fusinite,which results in higher reflectance value. The AD3+D4/AALL ratio may be used as a measure of inertinitereactivity. Significant relationships between random reflectance (Rr) of semifusinite and fusinite and theID1/IG ratio and position of most Raman bands (G, D1, D2 and D3) for the studied temperature range werefound.

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1. Introduction

Raman spectroscopy is a widely used method for characterizationof structure of graphite and different carbonaceous materials (Beny-Bassez and Rouzaud 1985; Beyssac et al., 2003; Cuesta et al., 1994;Ferrari and Robertson, 2000; Guedes et al., 2008; Jawhari et al., 1995;Knight andWhite, 1989; Kwiecińska et al., 2010; Nemanich and Solin,1979; Reich and Thomsen, 2004; Sadezky et al., 2005; Schwan et al.,1996; Tuinstra and Koenig, 1970; Zickler et al., 2006 and manyothers). Less frequently it is applied for coals, coal macerals andproducts of their processing (Bustin et al., 1995; Chabalala et al., 2010;Dong et al., 2009; Green et al., 1983; Guedes et al., 2010; Johnson et al.,1986; Li et al., 2006; Malumbazo et al., 2010; Marques et al., 2009;Nestler et al., 2003; Quirico et al. 2005; Sheng, 2007; Wagner, 1982;Zaida et al., 2007; Zerda et al., 1981). A broad review of Ramanspectroscopy as a tool for coal structure analysis was presented byPotgieter-Vermaak et al. (2009).

In the first-order Raman spectrum of perfect crystalline graphiteone narrow band (G band) at 1580 cm−1 occurs (Nemanich and Solin,1979; Tuinstra and Koenig, 1970). It corresponds to the stretchingvibration mode with E2g symmetry in the graphite aromatic layers.When other carbonaceous materials are concerned, the G band mayalso have its origin in condensed benzene rings (Li et al., 2006;

Schwan et al., 1996). Ferrari and Robertson (2000) remarked thatthis mode is found at all sp2 sites, not only those in the rings. Whendisorder in the graphite structure occurs, the D1 band (1350–1380 cm−1) appears and its intensity rises with increasing dis-order intensity. The D1 band was related to graphitic lattice vibrationmode A1g, and attributed to in-plane defects between the BasicStructural Units (BSUs) or occurrence of heteroatoms (Beny-Bassezand Rouzaud, 1985; Green et al., 1983; Rouzaud et al., 1983; Tuinstraand Koenig, 1970). Schwan et al. (1996) connected the D1 band alsowith condensed benzene rings, and Li et al. (2006) suggested thataromatics having six or more fused benzene rings will contribute tothe D1 band. Tuinstra and Koenig (1970) noted that the ratio of theD1 band and G band intensities (ID1/IG) is inversely proportional tothe in-plane crystallite size (La). Ferrari and Robertson (2000) andZickler et al. (2006) found that for Lab2 nm Tuinstra and Koenig'sequation is no longer valid. Furthermore, Ferrari and Robertson(2000) showed that in such case the D1 band intensity is proportionalto the probability of finding a sixfold ring in the cluster, that is,proportional to the cluster area. Thus, in amorphous and disorderedcarbons the development of the D1 band indicates ordering and isproportional to La. This is consistent with earlier conclusions drawnby Dillon et al. (1984). Usually, in Raman spectra of coal and coalmacerals other bands are also observed. The D2 band (1620 cm−1)makes a shoulder on the G band, and also corresponds to a graphiticlattice mode E2g. It is observed in imperfect graphite, soot and otherdisordered carbonaceous materials (Cuesta et al. 1994; Green et al.,1983; Sadezky et al., 2005; Sze et al., 2001). According to Beyssac et al.

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254 R. Morga / International Journal of Coal Geology 87 (2011) 253–267

(2003) the D2 band is always present when the D1 band is presentand its intensity decreases with increasing degree of organization.In some cases the G and D2 bands are difficult to be resolved (Guedeset al., 2010). A broad D3 band (1460–1530 cm−1) is present only inpoorly ordered carbonaceous materials. It originates due to inter-stitial defects outside the plane of aromatic layers, like tetrahedralcarbons (Beny-Bassez and Rouzaud, 1985; Rouzaud et al., 1983). Itis attributed to organic molecules, fragments or functional groupsforming randomly distributed disordered (“amorphous”) carbonphase (Cuesta et al., 1994; Jawhari et al., 1995; Sadezky et al.,2005). Schwan et al. (1996) connected the D3 band with semi-circle ring stretch vibration of benzene or condensed benzenerings. Li et al. (2006), analyzing brown coal chars suggested threebands (1540 cm−1, 1465 cm−1 and 1380 cm−1) between the G andD1 bands. They argued that all these band represent small aromaticring systems having 3–5 fused benzene rings as well asmethylene andmethyl group. Guedes et al. (2010) proposed two bands (1520 cm−1

and 1450 cm−1) within this spectral region. Gong et al. (2009)suggested the D3 band reflects the active sites (edge carbons) incoal. The other band typically observed in coals is the D4 band(1200 cm−1). It occurs in the spectra of very poorly organizedmaterials such as soot and chars (Beyssac et al., 2003; Sadezky et al.,2005) and it is assigned tomixed sp2–sp3 or sp3-rich carbon structuressuch as alkyl–aryl C–C structures, and also nanocrystalline orhexagonal diamond (Li et al., 2006; Schwan et al., 1996). It was alsoassociatedwith the occurrence of the active sites in coal (Bar-Ziv et al.,2000; Livheh et al., 2000). The D3 and D4 band are still present incokes of low degree of structural organization (Urban et al., 2003).Both Li et al. (2006) and Guedes et al. (2010) introduced also otherbands at 1230–1260 cm−1, 1060–1090 cm−1 aswell as at 1680 cm−1.

The purpose of this study was to present application of micro-Raman spectroscopy for examination of coal macerals and to char-acterize and compare the internal structure of semifusinite andfusinite before and after heat-treatment at 400–1200 °C, in an argonatmosphere. Semifusinite is a maceral, which in part is reactive inthermal processing of coal. Taylor et al. (1998) distinguished threeforms of this maceral: reactive, semi-reactive and non-reactive. Thehigher the semifusinite reflectance, the lower is its reactivity. Forpractical purposes semifusinite is divided into reactive and non-reactive. Conventionally, one third of the total amount of semifusinitein a given coal sample is considered reactive (Schapiro et al., 1965).Fusinite is a non-reactive maceral. Raman spectroscopy may be auseful method enabling differentiation between more and lessreactive coal macerals as well as making it possible to predict theirbehavior during thermal processing.

2. Experimental procedures and analytical methods

Examination was performed on inertinite concentrates preparedfrom three samples of the bituminous coal from seam 505–505/1(Namurian B; samples 1 and 3) and 405/1 (Westphalian A; sample 2)in the Upper Silesian Coal Basin of Poland. Vitrinite reflectance Rr ofthese coals was: 0.98% (sample 1 — steam coal), 1.07% (sample 2 —

coking coal) and 1.42% (sample 3 — coking coal). Selected propertiesof the parent coals are summarized in Table 1. The concentrates wereobtained by gravity separation in the mixture of toluene and

Table 1Selected properties of the parent coals used in the study.

Sample Vdaf% Rr% Vitrinite% Liptinite% Inertinite% Mineralmatter%

1 — steam coal 30.41 0.98 54 6 38 22 — coking coal 24.75 1.07 65 2 30 33 — coking coal 20.47 1.42 55 1 43 1

tetrachloroethylene. Coal, after grinding to the fraction of b0.1 mmwasmixed with the liquid and separated in centrifuge. The separationproducts were dried and demineralized in hot HCl, as the mostfrequent minerals in the inertinite fraction were carbonates. Theconcentrates obtained from samples 1 and 3 contained 80% inertinite,and the concentrate from sample 2 — 83% inertinite (Table 2). Theother part of the concentrates consisted of vitrinite (15–17%) andsmall amounts of mineral matter (pyrite, clays). About 300 mgsamples of each concentrate was heated in a Carbolite pipe oven attemperature of 400, 500, 600, 800, 1000 and 1200 °C for 1 h in anargon atmosphere. The heating commenced at room temperatureand increased at a rate of 60 °C/min. Micro-Raman examinationwas carried out with the use of Horiba-Jobin-Yvone spectrometer(excitation line λ0=514 nm) with a total of 30 grains of semifusiniteand fusinite in each mount. Spectral range was 800–2000 cm−1, andresolution of 2 cm−1. During each measurement four acquisitions of10 s were co-added. Measurement area was 2×2 μm. Deconvolutionof the spectra was performed in the range of 800–1800 cm−1 withthe use of GRAMS 32 software, following the method presented bySadezky et al. (2005), which is most commonly applied for exam-ination of coals, soot and related materials. Four Lorentzian (G, D1, D2and D4 band) and one Gaussian (D3 band) lines were used (Fig. 1).Goodness of fit was checked by χ2 test. Several structural parameterswere determined: position of the Raman bands and their FWHMs aswell as structural ratios such as: ID1/IG and ID2/IG (both calculated asthe band height ratios), and AG/AALL, AD1/AALL, AD2/AALL, AD3/AALL andAD4/AALL (all calculated as the area ratios). Measurements of meanreflectance (Rr) of semifusinite and fusinite in concentrates before andafter heating were carried out according to PN-ISO 7404-5:2002, withthe use of a Zeiss microscope Axioskop, in immersion oil (no=1.518at 23 °C).

3. Results

3.1. Concentrates before heat-treatment

Spectra of semifusinite in concentrates before heating (Fig. 2)are characterized by similar average position of the G (1588 cm−1),D1 (1353 cm−1) and D2 (1610–1611 cm−1) bands (Figs. 3a–5a).Position of the other two bands is more scattered. They are: D3 (1458–1468 cm−1) and D4 (1241–1250 cm−1) (Figs. 6a and 7a). In mostof the spectra weak band probably associated with the occurrenceof C_O bonds (1704–1709 cm−1) is found (Fig. 2) (Li et al., 2006).The FWHM values of these bands as well as the values of structuralratios are shown in Figs. 8a–19a. For fusinite position of each Ramanband is the following: G band — 1588–1590 cm−1, D1 — 1342–1349 cm−1, D2— 1610 cm−1, D3— 1484–1490 cm−1 andD4—1227–1242 cm−1 (Figs. 3b–7b). In part of the spectra band due to carbonylgroup is also present (1703–1706 cm−1). Figs. 8b–19b show therespective bandwiths and the values of the structural ratios. Meanreflectance (Rr) of semifusinite in concentrates before heating is 2.12–2.20% (sr=0.25–0.42%), while that of fusinite 2.71–3.20% (sr=0.20–0.40%) (Fig. 20).

Table 2Petrographic composition of the inertinite concentrates.

Concentrate V% L% I% MM% Sf% F% Ida% Ma% Mi% Fu%

Steam coal 1 17 – 80 3 52 3 38 5 2 –

Coking coal 1 15 – 83 2 54 12 28 4 1 1Coking coal 2 16 – 80 4 49 7 32 8 4 –

Abbreviations: V — vitrinite, L — liptinite, I — inertinite, MM — mineral matter, Sf —semifusinite, F — fusinite, Id — inertodetrinite, Ma — macrinite, Mi — micrinite, Fu —

funginite.a Includes inertinite fragments originated due to crushing of coal.

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Fig. 1. Deconvolution of the Raman spectra according to Sadezky et al. (2005).

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255R. Morga / International Journal of Coal Geology 87 (2011) 253–267

Based on reflectance and morphological features, semifusiniteoccurring in the raw inertinite concentrates was divided into reactiveand non-reactive forms. Spectra of reactive semifusinite differs fromthose of non-reactive one by higher frequencies of the D1 and D4 bandposition and lower frequency of the D3 band position, higher FWHMsof the G, D1 (the steam coal sample excepting), D3 and D4 bands aswell as lower values of the ID1/IG, ID2/IG and AD1/AALL ratios but highervalues of the AG/AALL, AD3/AALL and AD4/AALL ratios. The maindifferences are presented in Table 3. Spectra of semifusinite fromthe steam coal (sample 1) compared with those of the semifusinitefrom the coking coal (samples 2 and 3) are characterized by highervalues of the G and D1 band FWHMand AD1/AALL ratio and lower valueof the AD4/AALL ratio (Figs. 8a, 9a, 16a and 19a). Position of the D4 peakis moved to the lower frequencies (Fig. 7a). Structural parameters

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Raman shift [cm-1]

Fig. 2. Raman spectra of semifusinite before and after heat-treatment at 400–1200 °C.

Fig. 3. Position of the G band for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.

determined for semifusinites and fusinites coming from the sameseam (sample 1 and 3) only partly are in good agreement. Fusinitespectra compared with those of semifusinite in each sample differs

Table 3Comparison of the selected Raman-derived structural parameters determined forreactive and non-reactive semifusinite in the concentrates before heating.

Sample G bandFWHM

D1 bandposition

D3 bandposition

ID1/IG

ID2/IG

AD1/AALL

AD3+D4/AALL

1-reactive sf 71.3 1354.0 1465.2 0.80 0.66 0.42 0.243.9 3.6 25.4 0.10 0.11 0.06 0.06

1-non-reactive sf 71.1 1352.4 1470.8 0.88 0.71 0.48 0.194.9 5.2 17.3 0.10 0.12 0.07 0.05

2-reactive sf 69.5 1357.3 1447.0 0.74 0.85 0.33 0.336.4 5.4 5.4 0.06 0.18 0.04 0.04

2-non-reactive sf 62.7 1348.0 1471.7 0.96 0.93 0.42 0.265.4 3.8 27.6 0.22 0.13 0.08 0.06

3-reactive sf 68.6 1354.3 1455.1 0.73 0.68 0.37 0.285.8 4.0 12.9 0.09 0.17 0.04 0.03

3-non-reactive sf 65.4 1349.6 1465.3 0.94 0.89 0.40 0.266.3 4.2 13.2 0.19 0.19 0.04 0.03

Explanation: In the upper line of each rowmean values of structural ratios are given; inthe lower line of each row (in italics) standard deviations are presented.


mainly by the position of the D1 and D4 bands shifted to the lowerfrequencies and position of the D3 band moved to the higherfrequencies, lower G, D2 and D4 band FWHMs, higher values of theID1/IG, ID2/IG and AD1/AALL ratios as well as lower AG/AALL ratio (Figs. 4,6–8, 10, 12–14 and 16). Taking into account the model proposed byFerrari and Robertson (2000), based on the ID1/IG ratio and position ofthe G band, the structure of the examinedmacerals can be determinedas intermediate between typical for amorphous carbon and nano-crystalline graphite.

The XRD measurements carried out by Xie et al. (1991),Malumbazo et al. (2010) and also those, being in progress, performedby the author of this study, show that in-plane size of coherentdomains (crystallites) (La) in the studied macerals is on average ca.1.0–1.4 nm and increases upon heat-treatment. Taking into consid-eration relationship between ID1/IG ratio and La determined forLab2 nm (Ferrari and Robertson 2000; Zickler et al. 2006), and higherID1/IG ratio for fusinite than semifusinite obtained in this study(Fig. 13), it can be concluded that before heating fusinite has largercoherent domains than semifusinite. La size for the reactivesemifusinite is lower than that of the non-reactive type. The FWHMof the G band for fusinite is lower and the FWHMof the D band similar

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Fig. 4. Position of the D1 band for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.

or lower as that of semifusinite. The same relation occurs betweennon-reactive and reactive semifusinite. However, the stack height(Lc), as concluded from the ID2/IG ratio (Sze et al., 2001), is lower forfusinite than semifusinite. As it is known, Lc increases with coal rank,attaining the maximum at the transition from bituminous coals toanthracites, and decreases again as coalification proceeds. The sametrend is also observed in the first stages of bituminous coalcarbonisation (Marsh 1973; Van Krevelen, 1993). So, the differencebetween the two macerals observed here may result from highertemperature in which fusinite was formed.

In comparison with the results showed by Guedes et al. (2010),who deconvoluted spectra following the method introduced by Liet al. (2006), the D1 band position determined for fusinite is movedto slightly higher frequencies and the D1 band FWHM is also higher.On the other hand, position of the G band is shifted to the lowerfrequencies with similar FWHM value. The values of ID1/IG ratio forfusinite agree with those found in the present study. The G band-widths for semifusinite and fusinite obtained here are similar or lowerfrom those presented for inertinite by Zerda et al. (1981), possiblybecause the authors did not consider the D2 band, whereas theD1 band FWHM is similar or slightly higher. Position of the D1 bandboth for semifusinite and fusinite shows similarity to those of soot(Sadezky et al., 2005) and anthracites C (at higher FWHM values) asdetermined by Marques et al. (2009). Positions of the D3 and D4band as well as their respective FWHMs for fusinite are in goodagreement with the values of these parameters found for anthracite C(Marques et al., 2009). This may suggest some similitudes in internalstructure of fusinite and semianthracites or anthracites, which waspreviously communicated by Blanc et al. (1991). The D3 and D4 bandswere connected with the occurrence of active sites (Bar-Ziv et al.,2000; Gong et al., 2009; Livheh et al., 2000) and, consequently,combustion reactivity of chars which can be evaluated by the ID3+D4/IG ratio (Gong et al., 2009). Following this idea, the sum of AD3/AALL

and AD4/AALL ratios (AD3+D4/AALL) was analyzed. For all samplesexamined in this study AD3+D4/AALL ratio is higher for semifusinitethan fusinite (Figs. 18 and 19).What is more, reactive semifusinite hashigher AD3+D4/AALL ratio than non-reactive semifusinite (Table 3).For semifusinite and fusinite from the coking coals the ratio is higherthan that of these macerals from the steam coal. Therefore, AD3/AALL

and AD4/AALL ratios, or the sum of them, might be indicative of higherreactivity of a maceral, and used as a reactivity measure. This needs,however, further investigation. The values of AD3/AALL ratio are closeto those obtained by Sonibare et al. (2010) for the Nigerian bitu-minous coals.

3.2. Heat-treated concentrates

Fig. 2 shows changes in the Raman spectra of semifusinite withincreasing temperature of heating. Changes in the values of Ramanspectral parameters have similar character for both examinedmacerals. However, for fusinite they usually start at higher temper-ature and havemore limited range, which reflects more heat-resistantstructural framework of this maceral.

Position of the G band (Fig. 3) in the semifusinite and fusinitespectra is stable in the lower temperatures of heat-treatment, andat 800 °C or 1000 °C it moves to the higher wavenumbers. The D2band (Fig. 5) shifts to the higher frequencies beginning with 600 °C(the steam coal sample) or 800 °C (the coking coal samples). Positionsof the D1, D3 and D4 bands for both macerals at lower temperaturesgenerally move to the lower frequencies, and at 800 °C–1000 °C jumpbackwardly to the higher frequencies (Figs. 4, 6 and 7). A weakcarbonyl band at 1680–1705 cm−1 disappears at 800 °C.

The G band FWHM of semifusinite and fusinite (except of cokingcoal sample 3) is similar during the whole experiment (Fig. 8). Atthe temperature range of 500–600 °C slight decrease of the param-eter value for semifusinite was ascertained. The D1 band FWHM of

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semifusinite (Fig. 9a) decreases at 600 °C, and at 800 °C significantlyrises, while at 1200 °C decreases again or does not change. That offusinite (Fig. 9b) has similar value during the whole experiment(the steam coal sample) or also increases considerably at 800 °C(the coking coal samples). The D2 band FWHM (Fig. 10) increaseswith increasing temperature both for semifusinite and fusinite, moststrongly at 800 °C. The D3 band FWHM (Fig. 11) rises significantlyat 600 °C, and at 800 °C and above it systematically decreases for bothmacerals. The D4 band FWHM of semifusinite (Fig. 12a) decreases at800 °C and at higher temperatures has similar value (the steam coalsample) or increases again (the coking coal samples). When fusiniteis concerned (Fig. 12b), the value of this parameter is on similar levelin the whole temperature range or increases at highest temperaturesof heating. A shift in the D3 band position to higher wavenumbers,and the D4 band to the lower wavenumbers, together with thedecrease in the FWHM of the two bands at 1000 °C was also found incoke by Urban et al. (2003). As in the present study, high standarddeviations for the D3 and D4 band positions and FWHMs, especiallyfor high-temperature chars, were reported by Zaida et al. (2007). Isnoteworthy that for semifusinite from the coking coals heated at800 °C, position of the D3 and D4 band as well as their respective

FWHMs is close to those of anthracite A, at almost the same randomreflectances (5–5.5%) of bothmaterials, as presented byMarques et al.(2009).

Similar, as in the present study, variation of the D1 band positionand the G band position and FWHM for pyrolyzed wood wasdescribed by Zickler et al. (2006). However, the D1 band FWHMcontinuously decreased with the temperature increase. Bar-Ziv et al.(2000) also found increase in the G and D1 bandwith for thebituminous South African coal heated to 900 °C and their subsequentdecrease at higher temperatures. On the contrary, Chabalala et al.(2010) demonstrated decrease in the bandwidth during heating ofsimilar inertinite-rich coal up to 1000 °C. Guedes et al. (2008)reported for inertinitic chars that the D1 band was located at muchlower frequencies and had lower FWHM as macerals examined in thisstudy heated at 800–1000 °C. The G band position was similar, atslightly lower FWHM values (the D2 band was not considered).Johnson et al. (1986) inversely correlated the D1 band FWHMwith Laof coherent domains in coke heated at 500–1900 °C, and Cuesta et al.(1994) found that this parameter is the most useful for describing thedegree of organization of disordered materials. According to Ferrariand Robertson (2000), broadening of the D1 band is correlated to adistribution of clusters with different order and dimensions. Ring

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Fig. 8. The G band FWHM for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.


orders other than six tend to decrease the peak height and increase itswidth. Thus, strong increases in the FWHM of the D1 and G bandsobserved both for semifusinite and fusinite at 800 °C imply increase instructural disorder and a variety of ring orders and dimensions, whiledecrease in the value of the former parameter at 1200 °C— increase inthe structural organization.

The information about the less distorted aromatic rings is in the D1band intensity (peak height) and not in width, which depends on thedisorder (Ferrari and Robertson 2000). Therefore, the ID1/IG peakintensity ratio is more informative for the disordered carbons thanthe area ratio of these bands. At the lower temperatures of heating(400–600 °C) the values of ID1/IG ratio calculated for semifusinite(exception — the coking coal sample 2) and for fusinite to remainalmost unchanged (Fig. 13). At 800 °C the ID1/IG ratio significantly risefor bothmacerals. Following observationsmade byDillon et al. (1984),Ferrari andRobertson (2000) aswell as Zickler et al. (2006), increase inthe ID1/IG ratio at Lab2 nm indicates growth of coherent domainsduring heat-treatment both in semifusinite and fusinite. Increase inthe ID1/IG ratiowithin the temperature range, as used in this study,wasalso reported by Chabalala et al. (2010) for chars originated frominertinite-rich coals, by Zaida et al. (2007) for chars prepared fromcellulose fibers as well as by Theodoropoulou et al. (2004) for the

resin/biomass composites pyrolyzed up to 1000 °C. Zickler et al.(2006) found an increase in the ID1/IG area ratio as a result of woodpyrolysis at 400–1000 °C. The rate of increase of the ID1/IG ratio fromthe values obtained for the concentrates before heating to thosedetermined for the concentrates heated at 1200 °C is much higherfor semifusinite than fusinite (98–181% and 47–117%, respectively),reflecting different reactivity of these macerals. Much higher rate ofthe ID1/IG ratio increase was found for semifusinite from the cokingcoal concentrates (samples 2 and 3; 181% and 140%, respectively) thanfor semifusinite from the steam coal concentrate (sample 1 — 98%).

The coefficient of variation (CV) may be used as a brief measureof heterogeneity of a given population. It is interesting to note thatthe CV value calculated for the ID1/IG ratio of semifusinite from thecoking coals is the highest (~20%) when the raw concentrates areconcerned. With progressive heating the CV value decreases, reachingminimum (~8–15%) at 600 °C. This is when the semifusinite popu-lation is most homogenous, taking La into account. This suggests thatdimensions of coherent domains in more reactive semifusinite(characterized by lower La size before heating) become similar tothose in the non-reactive form. The CV value for semifusinite from thesteam coal before heating is about 15%, increasing up to 35% at 800 °C(the strongest heterogeneity). At the highest temperatures of heating

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 1400100

120

140

160

180

200

220

240

F 1 F 2 F 3

0 200 400 600 800 1000 1200 1400120

140

160

180

200

220

a

b

T [oC]

T [oC]

D1

band

FW

HM

[cm

-1]

D1

band

FW

HM

[cm

-1]

Fig. 9. The D1 band FWHM for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 140035

40

45

50

55

60

65

70

75

F 1 F 2 F 3

0 200 400 600 800 1000 1200 140030

35

40

45

50

55

60

65

70

75

80

D2

band

FW

HM

[cm

-1]

D2

band

FW

HM

[cm

-1]

T [oC]

T [oC]

a

b



the CV value is similar for all the samples (~20%), like in the con-centrates before heating.

The ID2/IG ratio calculated for semifusinite increases during heat-treatment, attaining the maximum, when 800 °C is reached, and at1000–1200 °C decreases (Fig. 14a). Changes determined for fusinitestarts at higher temperature and they are of lesser intensity (Fig. 14b).Sze et al. (2001) suggested that the ID2/IG ratio (measured as theband area ratio) should be inversely proportional to the thicknessof coherent domains (Lc — the stack height) in soot. Thus, theinitial increase in the ID2/IG ratio, observed in this study, may beindicative of the decrease in Lc in semifusinite and fusinite, and thefurther decrease in the ID2/IG ratio would reflect growth of a stackheight at 1000–1200 °C. This is consistent with observations made byMalumbazo et al. (2010), based on XRD analysis of a char obtainedfrom inertinite-rich coal and those of Sheng (2007) in his Ramanresearch on pyrolysis of the Chinese low-rank coals at 910–1500 °C.Decrease in Lc for carbonized coals during resolidification and itssubsequent increase was also communicated by Marsh (1973), VanKrevelen (1993) and Marzec (1997). Increase in the La and Lc size ofcoherent domains in the South African semifusinite-rich coal, heatedat 900–1400 °C, was also demonstrated by Senneca et al. (1998).

Rouzaud et al. (1983) found an increase in the number of aromaticlayers in a stack for thick carbon films heated at 1000 °C and above. Asthe ID2/IG ratio of semifusinite heated to the temperature between500 °C and 600 °C attains, on average, similar level as that of rawfusinite from the same coal, the ratio might be indicative of conditions(temperature range) in which both macerals were formed.

The AG/AALL ratio determined for semifusinite significantly de-creases at 800 °C and above, and increases again at 1200 °C or stays atsimilar level (Fig. 15a). When fusinite is concerned changes followsimilar trend but they are of lesser range (Fig. 15b). Change observedat 800 °C is a result of relative increase in the area of the other Ramanbands, such as D1 and D3. It is connected with the rebuilding ofmacromolecular network in semifusinite and, with smaller intensity,also in fusinite. Increase in the ratio value, ascertained for semifusiniteat 1000–1200 °C, might indicate ordering of the structure. Similarprocess was described for chars by Sheng (2007), beginning with theheating temperature of 900 °C.

The values of AD1/AALL ratio are stable at lower temperatures ofheat-treatment, and at 800 °C they increase, after that remaining atsimilar level to the final heating temperature (Fig. 16a). Changesobserved for fusinite have the same character but they are morelimited (Fig. 16b). Increase in the AD1/AALL ratio is due to overall

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 1400100

120

140

160

180

200

220

240

260

F 1 F 2 F 3

0 200 400 600 800 1000 1200 1400120

140

160

180

200

220

240

D3

band

FW

HM

[cm

-1]

D3

band

FW

HM

[cm

-1]

T [oC]

T [oC]

a

b


Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 140060

80

100

120

140

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180

200

220

240

260

280

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F 1 F 2 F 3

0 200 400 600 800 1000 1200 140040

60

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320

D4

band

FW

HM

[cm

-1]

D4

band

FW

HM

[cm

-1]

T [oC]

T [oC]

a

b



increase in the D1 band intensity and FWHM, which reflects increasein La size of coherent domains, on one hand, and increase in variety ofcluster orders and dimensions due to condensation and recombina-tion reactions, on the other. The latter may result from rebuilding ofmacromolecular network, accompanied by increase in the in-planedefects. Similar changes of the AD1/AALL ratio were observed byRouzaud et al. (1983) for the heat treated thick carbon films.

The AD2/AALL ratio for semifusinite slightly increases at lowertemperatures of heating, and beginning from 800 °C (coking coalconcentrates) or 1000 °C (steam coal concentrate) significantly de-creases (Fig. 17a). For fusinite the parameter value remains initially onpractically the same level, and considerably decreases at 800 °C or1000 °C (Fig. 17b). These observations follow conclusions drawn inthe section describing variation in the ID2/IG ratio.

The AD3/AALL ratio for semifusinite increases at 500–600 °C, andat higher temperatures decreases, rising slightly once again (thecoking coal concentrates) at 1200 °C (Fig. 18a). In the case of fusiniteit attains the maximum at 600 °C (the steam coal concentrate) orremains on similar level during the whole experiment (the cokingcoal concentrates) (Fig. 18b). The initial change reflects intensificationof interstitial defects between the aromatic layers or coherentdomains (Beny-Bassez and Rouzaud, 1985; Rouzaud et al., 1983).

This might be connected with the plastic stage, and formation andoccurrence of the mobile component. At 800–1000 °C these in-terstitials are partly eliminated due to condensation and recombina-tion reactions which lead to formation of new polyaromatic unitsof different order and size, contributing to existing, or constitutingnew, aromatic layers within the coherent domains, as concluded fromaccompanying increase in the D1 band FWHM, the ID1/IG (La increase)and ID2/IG ratio (Lc increase). Such variation in the AD3/AALL ratiofollows the trend observed by Rouzaud et al. (1983) for the thickcarbon films, although the maximum values are found at lowertemperature. The observed variation of the AD3/AALL ratio alsocorresponds with the increase and subsequent decrease in thenumber of active sites (edge carbons) (Gong et al., 2009). Weakerchanges of the ratio observed for fusinite are another indication ofhigher thermal resistance of this maceral. Similar changes describedby the ID3/IG area ratio for cellulose chars were previously reportedby Zaida et al. (2007).

The AD4/AALL ratio calculated both for semifusinite and fusiniteremains stable at lower temperatures of heating and at 800 °C con-siderably decreases (Fig. 19). Such change results from the thermaldecomposition of mixed sp2–sp3 carbon structures such as alkyl–arylC–C structures and ethers, which is more intense for semifusinite

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8I D

1/I G

I D1/

I G

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

T [oC]

T [oC]

a

b

Fig. 13. The ID1/IG ratio for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

I D2/

I GI D

2/I G

T [oC]

T [oC]

a

b

Fig. 14. The ID2/IG ratio for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.


than fusinite. It also suggests decrease in the number of active sitesboth in semifusinite and fusinite due to increase of polyaromatic units.At 1200 °C slight increase in the value of the ratio is observed forsemifusinite. Kawakami et al. (2005) found decrease in the AD3+D4/AALL ratio for a bamboo charcoal heated at 1000–1200 °C. For a woodcharcoal such change was observed at higher temperature.

Mean reflectance (Rr) of semifusinite starts rising at 500 °C, and inthe case of fusinite at 600 °C (Fig. 20). At 800 °C a significant jump inthe Rr values is observed and semifusinite reflectance surpasses that offusinite. A second considerable increase is found at 1200 °C for bothmacerals from the coking coals. Finally, reflectance of semifusinite andfusinite in the steam coal concentrate is 6.56% and 5.96%, respectively,while in the coking coal concentrates it is much higher. The highest inthe case of sample 3–9.41% and 8.32%, respectively. These values arehigher than those obtained by Taylor et al. (1998) for the non-reactiveisotropic inertinite in coke. The rate of the overall reflectance increaseis much higher for semifusinite (209–327%) than fusinite (120–260%),which reflects difference in reactivity of these macerals. Increase inthe reflectance value results from the H/C atomic ratio decrease (VanKrevelen, 1993) and, generally, follows the trend known from heat-treated anthracite, coke and reference carbon examination (Rouzaudand Oberlin, 1989; Taylor et al., 1998).

After heat-treatment at 1200 °C spectra of semifusinite in allexamined concentrates are characterized by similar position of the D1band as well as similar values of the D1 band FWHM, AD1/AALL ratio,AD2/AALL ratio and AD4/AALL ratio (Figs. 4a, 9a, 16a, 17a and 19a).Spectra of semifusinite from the same seam (sample 1 and 3) havealso similar position of the G band as well as AG/AALL ratio (Figs. 3a and15a). Semifusinite from the steam coal (sample 1) differs fromsemifusinite from the coking coal (samples 2 and 3) by significantlylower D1, D2 and D3 and D4 band FWHM. Position of the D4 band ismoved to the higher frequencies and the AD3/AALL ratio is lower(Figs. 7a, 9a–12a and 18a). Spectra of fusinite heated at 1200 °C havesimilar values of the AD2/AALL and AD3/AALL ratios (Fig. 17b and 18b).For fusinite from the same seam (samples 1 and 3) also similarposition of the G band, the D3 band FWHM as well as the values of ID2/IG and AG/AALL ratios were ascertained (Fig. 3b, 11b, 14b and 15b).Spectra of fusinite from the steam coal (sample 1) compared to thoseof fusinite from the coking coal (samples 2 and 3) have lower D2 bandFWHM (Fig. 10b). After heating at 1200 °C semifusinite differs fromfusinite principally by the position of the G and D1 bands moved tothe higher frequencies, higher values of the ID1/IG ratio and AD3+D4/AALL ratio, lower values of the ID2/IG ratio and lower G band FWHM(Figs. 3, 4, 8, 13, 14, 18 and 19).

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

AG

/AA

LLA

G/A

ALL

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

T [oC]

T [oC]

b

a

Fig. 15. The AG/AALL ratio for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.2

0.3

0.4

0.5

0.6

0.7

0.8

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

AD

1/A

ALL

AD

1/A

ALL

T [oC]

T [oC]

a

b

Fig. 16. The AD1/AALL ratio for semifusinite (a) and fusinite (b) before and after heat-treatment at 400–1200 °C.


4. Discussion

4.1. Effect of the heat-treatment on structural and spectralcharacteristics of semifusinite and fusinite

Summarizing the results, decreases in the FWHMs of the G andD1 bands found at 400–600 °C for semifusinite, indicate slight re-ordering of its structure. This is due to softening of more reactive partof this maceral, leading to greater mobility of polyaromatic layers andtheir partial alignment. As a result, reflectance value starts rising.Increase in the ID2/IG ratio reflects the decrease in the stack height ofthe domains (Lc). The AD3/AALL ratio growth at 500–600 °C indicatesintensification of interstitial defects, which is probably connectedwith formation and occurrence of themobile component. For fusinitesall these changes are much weaker or not observed. Coherentdomains in this maceral are larger but stronger bonds inhibit theirmobility and growth at lower temperatures of heating. At 800 °Cusually strong increases in ID1/IG, ID2/IG and AD1/AALL ratio as well asthe FWHM of the G and D1 bands occur. Position of the G band movesto the higher frequencies and AD4/AALL ratio decreases. These changesdetermined both for semifusinite and fusinite, although less intense,reflect more or less significant rebuilding of macromolecular network

of these macerals and intensification of different kinds of structuraldefects. Aryl–alkyl structures decompose under the influence ofheating. Condensation and recombination reactions of the cleavedbonds or hydrogen with clusters lead to the formation of newpolyaromatic units of different order and size. Coherent domains growalong the a-axis. This is a reason for the reflectance jump found forboth macerals, which is a typical feature (Komorek and Morga,2007; Morga, 2010). Structural features of semifusinite conform tothose of fusinite, which is concluded from similarity of the valuesof most spectral parameters for these macerals in each sample. At800–1000 °C the AD3/AALL ratio for semifusinite decreases, whichindicates partial elimination of interstitial defects. At 1000–1200 °Cfurther increase in the ID1/IG ratio, decrease in the FWHM of the D1band and decrease in the ID2/IG as well as further shift of the G band tothe higher frequencies occur in case of semifusinite. This suggestsincrease in structural organization. Smaller aromatic units are partlydecomposed or coalesce into larger aromatic units, which leads toincrease in La size. This is reflected by further reflectance increase. Thedisorder within the coherent domains weakens and their stack height(Lc) increases. Similar, although much weaker changes, are found forfusinite. Finally, carbonized semifusinite has larger coherent domainsboth in terms of their diameter (La) and stack height (Lc) and they are

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18A

D2/

AA

LLA

D2/

AA

LL

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

T [oC]

T [oC]

a

b


Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

F 1 F 2 F 3

0 200 400 600 800 1000 1200 14000.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

AD

3/A

ALL

AD

3/A

ALL

T [oC]

T [oC]

a

b



more ordered than in fusinite from the same coal, which results inhigher reflectance value.

4.2. Differences between semifusinite and fusinite

The difference between fusinite and semifusinite behavior duringheat treatment is determined by the structural and chemicalproperties of these macerals before heating. Like for many othercarbonaceous materials, the crucial question here is the size ofcoherent domains (the larger they are, the smaller fluidity) as well ascontent of oxygen acting as a cross-linker and proportion of highlydisordered material (such as aliphatic moieties, hydrocarbon mole-cules), which contributes to higher fluidity, playing a role of asuspensive medium and allowing better packing of aromatic layers(Kidena et al., 2002; Rouzaud, 1990; Van Krevelen 1993). Rouzaudet al. (1988) found a correlation between O/H ratio of a coal and thesize of molecular orientation domains in resulting cokes. The authorsalso observed that for a given coal, inertinite has the highest O/H ratioof all the macerals. High oxygen content and low hydrogen contentof inertinite-rich coals (semifusinite abundant) was communicated byBorrego et al. (1997). According to Stach et al. (1982), fusinisationproduces substances with relatively low hydrogen content and, for

the same H/C ratio, a higher O/C ratio than in vitrinite. Taking intoaccount division of carbonaceous materials, based on their graphitiz-ability (Emmerich, 1995; Franklin, 1951), fusinite belongs to non-graphitizing carbons. It contains relatively large coherent domains(thus the highest reflectance) but which are misoriented (thus itsisotropy). It usually has relatively high O/C and low H/C ratios (Blancet al., 1991; Diessel, 1992) and it is more aromatic than semifusinitefrom the same coal (Morga, 2010). Therefore, abundance of cross-linking bonds at a very low content of a mobile phase precludessoftening and inhibits increase of coherent domains. Alteration of thestructure requires high activation energy, and it starts at 600–800 °C,which corresponds well with the results of the FTIR examination,presented elsewhere (Morga, 2010). Rouzaud and Oberlin (1989)concluded that functional groups in non-graphitizing carbons (so,fusinite as well) are firmly fixed upon BSUs, hence H/C and O/C ratiosdecreased significantly not earlier as the temperature of 800–1000 °Cwas reached. Increase in the diameter (La) and height (Lc) of thecoherent domains and, consequently, the reflectance value of fusiniteis limited, and follows the trend known from examination of othernon-graphitizing carbons (Emmerich, 1995; Rouzaud and Oberlin,1989). In contrast, semifusinite has smaller coherent domains as wellas lower degree of aromaticity and condensation (Morga, 2010), and

Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14000.00

0.02

0.04

0.06

0.08

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F 1 F 2 F 3

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0.04

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0.18

0.20

AD

4/A

ALL

AD

4/A

ALL

T [oC]

T [oC]

b

a


Sf 1 Sf 2 Sf 3

0 200 400 600 800 1000 1200 14001

2

3

4

5

6

7

8

9

10

11

Rr [%

]R

r [%

]

F 1 F 2 F 3

0 200 400 600 800 1000 1200 1400

T [°C]

T [°C]

2

3

4

5

6

7

8

9

10

a

b

Fig. 20. The mean reflectance (Rr) of semifusinite (a) and fusinite (b) before and afterheat-treatment at 400–1200 °C.


the amount of mobile hydrogen is higher than in fusinite (Maroto-Valer et al., 1998). According to Diessel (1992) semifusinite “posseslower H/C and higher O/C ratios than vitrinite without reaching theextreme values of fusinite”. Reactive part of this maceral has smallestcoherent domains, among the examined components, but, similarly tovitrinite, they may be oriented to some extent due to stress actingduring coalification. This pre-orientation, as it happens in vitrinites,may play important role in subsequent alignment of these domains.Reactive semifusinite undergoes softening which allows highermobility of polyaromatic layers and their coalescence, and conse-quently, growth and alignment of aromatic layers. Such mechanismwould be similar to that occurring in a coke formation from the highrank coking coals (Fortin and Rouzaud, 1994). Thus, reactivesemifusinite may act as a partially graphitizing or even graphitizingcarbon. The number of coherent domains most probably remainsstable during heating, what changes are their dimension along thea-axis (La) and c-axis (Lc — the stack height) as well as a number ofaromatic layers in a stack (Emmerich, 1995; Rouzaud and Oberlin,1989). Compared to fusinites and reactive semifusinite, non-reactivesemifusinite has coherent domains of intermediate size, which in aparent coal are disoriented. Also intermediate is its aromaticity andcondensation. Therefore, this type of semifusinite does not soften

(similarly to fusinite) or may be partially melted, in such case beingsometimes called semi-reactive (Taylor et al., 1998). Consequently, it isalso a non-graphitizing carbon, however, having less rigid macromo-lecular network, more able for rebuilding than fusinite. It is importantto note that fine grinding of coal, necessary for maceral separation,may improve elimination of the metaplast and, in the result, limit thegrowth of coherent domains (Rouzaud et al., 1988). Thus the degree ofstructural re-organization in the examinedmacerals would be stronger,when the whole coal samples are carbonized.

Fusinite and, following many authors, at least major part ofsemifusinite is a result of incomplete combustion (Bustin and Guo,1999; Guo and Bustin, 1998; Jones et al., 1991; Scott and Glasspool,2007; Scott and Jones, 1994). Based on models created by Jones et al.(1991), Scott and Jones (1994) as well as Scott and Glasspool (2007),mean reflectance values for semifusinite obtained in this study wouldsuggest the average temperature of formation at about 400–450 °C.Fusinite described here originated due to wildfires, in which the flametemperature was above 500 °C. This is when the main structuralfeatures of the examined fusinite and non-reactive semifusinite wereformed, as they change little during coalification (Stach et al., 1982;Borrego et al. 1997). Only reactive semifusinite could have beensubjected to more important chemical-structural alteration. Changesof reflectance and some of the Raman structural parameters (such as

Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1584 1586 1588 1590 1592 1594 1596 1598 1600 1602

G band position [cm-1]

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6I D

1/I G

Sf 1: r = 0.963, p = 0.0005Sf 2: r = 0.732, p = 0.0616Sf 3: r = 0.800, p = 0.0309F 1: r = 0.923, p = 0.0030F 2: r = 0.900, p = 0.0057F 3: r = 0.838, p = 0.0186

Fig. 21. Relationship between the G band position and the ID1/IG ratio for semifusiniteand fusinite before and after heat-treatment at 400–1200 °C.

a

b

Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 10

Rr [%]

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

I D1/

I G

Sf 1: r= 0.968, p = 0.0003Sf 2: r = 0.957, p = 0.0007Sf 3: r = 0.930, p = 0.0024F 1: r = 0.896, p = 0.0063F 2: r = 0.877, p = 0.0096F 3: r = 0.932, p = 0.0023

Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 10

Rr [%]

1584

1586

1588

1590

1592

1594

1596

1598

1600

1602

G b

and

posi

tion

[cm

-1]

Sf 1: r = 0.982, p = 0.00009Sf 2 :r = 0.891, p = 0.0071Sf 3: r = 0.953, p = 0.0009F 1: r = 0.915, p = 0.0038F 2: r = 0.849, p = 0.0157F 3: r = 0.887, p = 0.0077

Fig. 22. Relationship between the reflectance value (Rr) and the ID1/IG ratio (a) andrelationship between the reflectance value (Rr) and theGbandposition (b) for semifusiniteand fusinite before and after heat-treatment at 400–1200 °C.


the ID1/IG and ID2/IG ratio) occur after heating semifusinite at 400–500 °C and fusinite at 600–800 °C. This suggests that the ID1/IG ratioand ID2/IG ratio, could play a role of thermometers, indicatingtemperature at which fusinite and, at least, non-reactive semifusinitewere formed. This requires, however, further examination.

4.3. Relationships between reflectance and spectral parameters

It was found that many significant relationships (correlationcoefficient r≥0.75, p-valueb0.05) exist between the parameterscalculated from the Raman spectra. Among others, there is usually agood correlation between the G band position and the ID1/IG ratio,showing that shifting the G band to the higher frequencies is followedby an increase in the ID1/IG value (Fig. 21). Both for semifusinite andfusinite the ID1/IG ratio also shows strong correlations with the D2band position and its FWHM. For semifusinite the ID1/IG ratio is alsocorrelated with the D1 band FWHM as well as the AG/AALL (negativecorrelation) and AD1/AALL ratios. Important correlations for semifusi-nite exist between the D1 band FWHM and the position of the D2 andD3 bands, the D3 band FWHM as well as the AD1/AALL, AD2/AALL

(negative correlation) and AD4/AALL (negative correlation) ratios.

a

b

Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 10

Rr [%]

Rr [%]

1340

1345

1350

1355

1360

1365

1370

1375


Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 101606

1608

1610

1612

1614

1616

1618

1620

1622

1624

1626

1628

1630

1632

1634

Sf 1: r = 0.981, p = 0.0001 Sf2: r = 0.981, p = 0.0001 Sf 3: r = 0.957, p = 0.0007 F 1: r = 0.987, p = 0.00003 F 2: r = 0.818, p = 0.0246 F 3: r = 0.919, p = 0.0034

D2

band

pos

ition

[cm

-1]

D1

band

pos

ition

[cm

-1]

Fig. 23. Relationship between the reflectance value (Rr) and the D1 band position(a) and relationship between the reflectance value (Rr) and the D2 band position (b) forsemifusinite and fusinite before and after heat-treatment at 400–1200 °C.

a

b

Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 10

Rr [%]

30

35

40

45

50

55

60

65

70


Sf 1 Sf 2 Sf 3 F 1 F 2 F 3

1 2 3 4 5 6 7 8 9 10

Rr [%]

1420

1440

1460

1480

1500

1520

1540

1560

1580


D2

band

FW

HM

[cm

-1]

D3

band

pos

ition

[cm

-1]

Fig. 24. Relationship between the reflectance value (Rr) and the D2 band FWHM (a) andrelationship between the reflectance value (Rr) and the D3 band position (b) forsemifusinite and fusinite before and after heat-treatment at 400–1200 °C.


Many important correlations exist for AD1/AALL ratio and suchstructural parameters as the D2 and D3 band positions and FWHMsand AG/AALL and AD4/AALL ratios. For fusinite such correlations areweaker. Both for semifusinite and fusinite strong correlationsbetween their random reflectance (Rr) and the ID1/IG ratio, positionof the G, D1, D2 and D3 bands as well as the D2 band FWHM werefound (Figs. 22–24). For semifusinite only reflectance is wellcorrelated with the AD1/AALL ratio. The results of the study showthat importance of such parameters as the AD1/AALL, AD3/AALL, AD4/AALL

(AD3+D4/AALL) and ID2/IG ratios or the D2 band position and its FWHMin Raman examination of coal macerals should be investigated deeper.Increase in the D1 and G band area ratio with increasing fusinitereflectance was also found by Guedes et al. (2010).

5. Conclusions

Raman spectroscopy gives broad insight in the internal structure ofsemifusinite and fusinite before and after heat-treatment. It enablesdifferentiation between more and less reactive coal macerals andmakes it possible to predict their behavior during thermal processing.Diameter of coherent domains (La) increases with transition fromreactive semifusinite to non-reactive semifusinite and then to fusinite.

Behavior of both macerals under heat-treatment is determined bytheir structural and chemical properties before heating. At 400–600 °Cslight re-ordering of semifusinite structure occurs, which is reflectedby reflectance increase. At 600 °C content of highly disorderedmaterial increases, which intensifies interstitial defects. At 800 °Crebuilding of macromolecular network of both macerals takes place.Recombination and condensation reactions lead to the formation ofnew polyaromatic units of different order and size. Coherent domainsgrow but they are strongly disordered. This is reflected by thereflectance jump found for both macerals. At 1000–1200 °C increasein structural organization, accompanied by further reflectance in-crease are found in semifusinite. Changes observed for fusinite aremore limited. Semifusinite heated at 1200 °C has larger coherentdomains and they are more ordered than in fusinite, which results inhigher reflectance value. The AD3+D4/AALL ratio may be used as ameasure of inertinite reactivity in bituminous coals, being higher forsemifusinite than for fusinite. For both studied macerals strong linearcorrelations between their random reflectance (Rr) and the ID1/IGratio, position of the G, D1, D2 and D3 bands as well as the D2 bandFWHM in the studied temperature range were found.

Acknowledgments

The study was financially supported by theMinistry of Science andHigher Education of Poland grant no. 3631/B/T02/2008/35 and by theSilesian University of Technology grant no. BW-475/RG-0/2008.

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micro-raman spectroscopy of carbonized semifusinite and fusinite

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