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Transmission electron microscopic studies of morphology and crystallography of particulate emissions in smokes
185
Forensic Science International, 32 (1986) 185-192 Elsevier Scientific Publishers Ireland Ltd.
TRANSMISSION ELECTRON MICROSCOPIC MORPHOLOGYANDCRYSTALLOGRAPHYOF PARTICULATE EMISSIONS IN SMOKES
STUDIES
OF
B.B. ARORA Police Forensic
Science Laboratory,
Rajasthan,
Jaipur-302016 (India)
(Received March 24, 1986) (Revision received June 26, 1986) (Accepted July 4, 1986)
Summary Arson, sabotage and suicide involving fire are topical problems in forensic science. Transmission electron microscopic (TEM) studies of the morphology and crystallography of particulate carbon from smoke deposits from various fuels were carried out to try to identify the fuel from the soots. Samples of particulates from the combustion of a variety of fuels were examined using bright field TEM for the morphology and selected area diffraction for the composition and structure. Several distinct characteristics were identified. The particles consist of quasispherical subunits of carbon forming chains or clusters. The shape and size of these spherules, the degree of their agglomeration and their crystallinity exhibit quantifiable variations conspicuous enough to identify the parent fuel. The scope of applications is discussed briefly. Key Words: Fuels; Identification
from soots; Transmission
electron
microscopy
Introduction Soot primarily consists of elemental carbon [1,2] which is swept along in the gaseous phase of the smoke. A survey of literature reveals that, though much is available on the study of carbon as well as the analysis of liquid fuels and their remnants in the charred materials, there is an acute paucity of information on the particulate exhausts of domestic fuels and fires. In a previous study [3], the morphology and crystallography of various phases of carbon viz amorphous, turbostratic, graphite and diamond were examined with transmission electron microscopy (TEM). Each phase was found to have a distinct character and their particles could be distinguished from charcoal dust, mould and other similar fine black matter. Ueyama et al. [4], Basu and Ferriss [5] and several others including Walten et al. [6], have examined muzzle deposits and gun shot residue and other fine particles using scanning electron microscopy. In this paper, TEM studies of soots are introduced. The work is restricted to the broad morphological and crystallographical characteristics of particulate carbon-the primary component of smoke of common organic fuels. The samples were recovered from sweeps of smoke deposits generated from liquid 0379-0738/86/$03.50 c 1986 Elsevier Scientific Publishers Printed and Published in Ireland
Ireland Ltd.
186 petroleum gas, spirit, kerosene, wood, cotton and mineral coal under normal combustion conditions. Thus the soots came from a range of gaseous, liquid and solid fuels. The study of paper soot was also undertaken to gather general data on characterisation features. Following the principal morphological and crystallographical characteristics observed, i.e. the shape and size of the subparticles forming the particles, their mode of agglomeration, the crystallinity and the internal structure it will be observed that soot particles exhibit distinct characteristics which could be correlated with the parent fuel. Materials
and methods
TEM has been preferred for the examination of soots because: (i) its conventional mode exhibits the highest resolution; (ii) its selected area diffraction (SAD) mode enables the determination of the composition as well as the internal structure of a specific particle/sub-particle; (iii) the sampling technique is simple as no conductive coating is required to dissipate the charge build up resulting from the incident electron beam; and (iv) it is easier to preserve the sample integrity because the copper grids on which the particles are loaded can be inserted directly into the electron microscope. The bright field transmission electron micrography was carried out to examine the morphology of particles and selected area diffraction studies were made for studying the internal structure of the samples with the TEM model 802 (AEI, U.K.). The measurements of intensity and dimensions of the SAD patterns were recorded with a Carl Zeiss Microdensitometer G II. Representative soot samples generated from liquid petroleum gas, spirit (ethanol), kerosene, wood, rags (cotton) and coal were collected in the form of sweeps or smears respectively from gas burners, spirit lamps, kerosene stoves, open hearth domestic fire-places and a loco railway engine workshop shed. The tars and resins associated with the samples were separated by leaching with benzene and the fluffy carbon was further dispersed by stirring in distilled water under low energy ultrasonic action. The inorganic contaminants or urban dust settled to the bottom and were removed. The particles were finally transferred to 3 mm copper grids previously coated with a thin film of Formvar and mounted on glass fibre mats. A number of grids were prepared from each soot which were thoroughly examined with the TEM to ensure that the analysis was representative and no preference was given to any specific ensemble. Discussion
of results and scope
The bright field transmission electron micrographs of the soots originating from LPG, ethanol, kerosene, coal, wood, cotton and paper obtained under normal combustion and cooling conditions are reproduced in Figs. la4a and 5(a,b&7(a,b) and their SAD patterns are shown in Figs. lb4b and 5c-7c. The micrographs reveal that a soot particle consists of a cluster/chain of smaller quasi-spherical sub-units (spherules) and the size and shape of spherules, their
Fig.1. (a) Bright field transmission electron micrograph magnification. (b) SAD pattern of LPG soot sub-particle.
showing
LPG soot particles
at 40,000
Fig.2. (a) Bright field transmission electron micrograph showing ethanol soot particles magnification. (b) SAD pattern of ethanol soot sub-particle.
at 40,000
Fig.3. (a) Bright field transmission electron micrograph showing kerosene soot particles at 40,000 magnification. (b) SAD pattern of kerosene soot sub-particle.
188
Fig. 4. (a) Bright field transmission electron micrograph showing mineral coal soot particles 40,000 magnification. (b) SAD pattern of mineral coal soot sub-particle.
Fig.B(a).
at
Fig. 5(b).
Fig. 5(c). Fig. 5. (a) Bright field transmission electron micrograph showing wood soot particles at 6,300 magnification. (b) Bright field transmission electron micrograph showing wood soot particles at 40,000 magnification. (c) SAD pattern of wood soot sub-particle.
Fig. 6(b)
Fig. 6(a).
Fig. 6(c). Fig.6 (a) Bright field transmission electron micrograph showing cotton soot at 6,300 magnification. (b) Bright field transmission electron micrograph showing cotton soot at 40,000 magnification. (c) SAD pat,tern of cotton soot sub-particle.
number density in a particle and their mode of agglomeration vary from fuel to fuel. The morphology further shows that for a particular soot generated from a single hydrocarbon, the size of spherules is uniform whereas, for those generated from fuels containing a mixture of hydrocarbons, there exists a spherule size distribution. In the case of wood, cotton and paper (Figs. 5a,b7a,b), the spherule size remains almost uniform and there is a strong tendency to retain the pre-existing preferred fibrous configuration of the parent fuel. The average sizes of spherules measured from TEM are summarised in Table 1. The spherules generated from ethanol are found clustered most densely, whereas those from the coal form branched chain-like short dispersed agglomerates. There is a positive indication of the formation of monodispersive spherules, though in a very small number in the soot of coal. The SAD study of soots shows that particles are made up of carbon and as there are no hkl reflections in the patterns (Figs. lb-4b and 5c-7c), they are not
Fig. 7(a).
Fig. 7(b).
Pig. 7(c). Fig.7. (a) Bright field transmission electron micrograph showing paper soot at 6,300 magnification. (b) Bright field transmission electron micrograph showing paper soot at 40,000 magnification. (c) SAD pattern of paper soot sub-particle.
crystalline. In crystalline materials, atoms exhibit systematic regular threedimensional orientation which produce sharp hkl dot reflections. However, the broad asymmetrical hk bands indicate the existence of a weak two-dimensional crystalline order of the carbon atoms. Thus the particles are not entirely amorphous for with the latter atoms occupy random positions and there exists no repeat distances and orderliness. They present rather a turbostratic organisation with atoms occupying positions more or less in planes which are stacked randomly. As seen from the SAD patterns, the degree of crystallinity varies from fuel to fuel, it being highest for the cotton and wood soots which produce sharp rings and least for ethanol and paper soots which give diffused halos. Broad physical trends of the particle character are summarised in Table 1. It is observed that soots generated from LPG, spirit, kerosene, coal, wood,
191 TABLE
1
BROAD PHYSICAL Fuel
TRENDS
OF CARBON
Spherule size distribution in nm Major component
Minor component
LPG Ethanol
15, 40 10
30
Kerosene Coal Wood
50 60 20
40 20 -
Cotton
15
25
Paper
5-15
SOOT PARTICULATES Nature of agglomeration
Degree of crystallinity
Large clusters Compactly packed very large clusters Medium large clusters Small branched clusters Large branched chain clusters in fine filament configuration Large branched chain clusters in fibrous configuration Gel formation in fibrous configuration
Medium high Relatively lowest Medium low LOW
Relatively
highest
Relatively
highest
Low
cotton and paper under similar normal combustion and cooling conditions exhibit distinguishable morphological and crystallographical features as observed with TEM. With the limited data obtained as far it has been possible to correlate the characterisation features of the soot with the parent fuel in an attempt to trace its origin. The study can contribute significantly to the investigation of crimes involving fire, specially where the scene of occurrence is found to be either disturbed or the fuel remnants are not available. It can further help in ascertaining whether a particular article was exposed to a specific smoke. Acknowledgements The author expresses gratitude to Prof. K.L. Chopra, (Indian Institute of Technology, New Delhi) for providing experimental facilities in his TEM laboratory. The author also wishes to thank Dr. V.D. Vankar for useful discussions and appreciates the co-operation of Mr. V.D. Arora (TEM Lab., I.I.T. New Delhi). References 1 W.C. MC Crone and J.G. Delly, The Particle Atlas, 2nd edn., Ann Arbor Science Publishers, 1972. 2 J.B. Donnet and A. Voet, Carbon Black, Dekker, N.Y., 1976. 3 B.B. Arora, The crystallography and morphology of carbon, National Symposium on Instrumentation, Indian Institute of Technology, New Delhi, India, Nov. 1983.
192 4 M. Ueyama, R.L. Taylor and T.T. Noguchi, SEM/EDS analysis of muzzle deposits at different target distances. Scanning Electron Microsc., I 367-372. technique for rapid search of gunshot residue 5 S. Basu and S. Ferriss, A refined collection particles. Scanning Electron Microsc., I (1980) 375-364. 6 G.M. Walten, R.S. Nesbitt, A.R. Calloway and G.L. Laper, Particle analysis for detection of gunshot residue, II. Occupational and environmental particles. J. Forensic Sci., 24 (1979) 425-430.
Forensic Science International, 32 (1986) 185-192 Elsevier Scientific Publishers Ireland Ltd.
TRANSMISSION ELECTRON MICROSCOPIC MORPHOLOGYANDCRYSTALLOGRAPHYOF PARTICULATE EMISSIONS IN SMOKES
STUDIES
OF
B.B. ARORA Police Forensic
Science Laboratory,
Rajasthan,
Jaipur-302016 (India)
(Received March 24, 1986) (Revision received June 26, 1986) (Accepted July 4, 1986)
Summary Arson, sabotage and suicide involving fire are topical problems in forensic science. Transmission electron microscopic (TEM) studies of the morphology and crystallography of particulate carbon from smoke deposits from various fuels were carried out to try to identify the fuel from the soots. Samples of particulates from the combustion of a variety of fuels were examined using bright field TEM for the morphology and selected area diffraction for the composition and structure. Several distinct characteristics were identified. The particles consist of quasispherical subunits of carbon forming chains or clusters. The shape and size of these spherules, the degree of their agglomeration and their crystallinity exhibit quantifiable variations conspicuous enough to identify the parent fuel. The scope of applications is discussed briefly. Key Words: Fuels; Identification
from soots; Transmission
electron
microscopy
Introduction Soot primarily consists of elemental carbon [1,2] which is swept along in the gaseous phase of the smoke. A survey of literature reveals that, though much is available on the study of carbon as well as the analysis of liquid fuels and their remnants in the charred materials, there is an acute paucity of information on the particulate exhausts of domestic fuels and fires. In a previous study [3], the morphology and crystallography of various phases of carbon viz amorphous, turbostratic, graphite and diamond were examined with transmission electron microscopy (TEM). Each phase was found to have a distinct character and their particles could be distinguished from charcoal dust, mould and other similar fine black matter. Ueyama et al. [4], Basu and Ferriss [5] and several others including Walten et al. [6], have examined muzzle deposits and gun shot residue and other fine particles using scanning electron microscopy. In this paper, TEM studies of soots are introduced. The work is restricted to the broad morphological and crystallographical characteristics of particulate carbon-the primary component of smoke of common organic fuels. The samples were recovered from sweeps of smoke deposits generated from liquid 0379-0738/86/$03.50 c 1986 Elsevier Scientific Publishers Printed and Published in Ireland
Ireland Ltd.
186 petroleum gas, spirit, kerosene, wood, cotton and mineral coal under normal combustion conditions. Thus the soots came from a range of gaseous, liquid and solid fuels. The study of paper soot was also undertaken to gather general data on characterisation features. Following the principal morphological and crystallographical characteristics observed, i.e. the shape and size of the subparticles forming the particles, their mode of agglomeration, the crystallinity and the internal structure it will be observed that soot particles exhibit distinct characteristics which could be correlated with the parent fuel. Materials
and methods
TEM has been preferred for the examination of soots because: (i) its conventional mode exhibits the highest resolution; (ii) its selected area diffraction (SAD) mode enables the determination of the composition as well as the internal structure of a specific particle/sub-particle; (iii) the sampling technique is simple as no conductive coating is required to dissipate the charge build up resulting from the incident electron beam; and (iv) it is easier to preserve the sample integrity because the copper grids on which the particles are loaded can be inserted directly into the electron microscope. The bright field transmission electron micrography was carried out to examine the morphology of particles and selected area diffraction studies were made for studying the internal structure of the samples with the TEM model 802 (AEI, U.K.). The measurements of intensity and dimensions of the SAD patterns were recorded with a Carl Zeiss Microdensitometer G II. Representative soot samples generated from liquid petroleum gas, spirit (ethanol), kerosene, wood, rags (cotton) and coal were collected in the form of sweeps or smears respectively from gas burners, spirit lamps, kerosene stoves, open hearth domestic fire-places and a loco railway engine workshop shed. The tars and resins associated with the samples were separated by leaching with benzene and the fluffy carbon was further dispersed by stirring in distilled water under low energy ultrasonic action. The inorganic contaminants or urban dust settled to the bottom and were removed. The particles were finally transferred to 3 mm copper grids previously coated with a thin film of Formvar and mounted on glass fibre mats. A number of grids were prepared from each soot which were thoroughly examined with the TEM to ensure that the analysis was representative and no preference was given to any specific ensemble. Discussion
of results and scope
The bright field transmission electron micrographs of the soots originating from LPG, ethanol, kerosene, coal, wood, cotton and paper obtained under normal combustion and cooling conditions are reproduced in Figs. la4a and 5(a,b&7(a,b) and their SAD patterns are shown in Figs. lb4b and 5c-7c. The micrographs reveal that a soot particle consists of a cluster/chain of smaller quasi-spherical sub-units (spherules) and the size and shape of spherules, their
Fig.1. (a) Bright field transmission electron micrograph magnification. (b) SAD pattern of LPG soot sub-particle.
showing
LPG soot particles
at 40,000
Fig.2. (a) Bright field transmission electron micrograph showing ethanol soot particles magnification. (b) SAD pattern of ethanol soot sub-particle.
at 40,000
Fig.3. (a) Bright field transmission electron micrograph showing kerosene soot particles at 40,000 magnification. (b) SAD pattern of kerosene soot sub-particle.
188
Fig. 4. (a) Bright field transmission electron micrograph showing mineral coal soot particles 40,000 magnification. (b) SAD pattern of mineral coal soot sub-particle.
Fig.B(a).
at
Fig. 5(b).
Fig. 5(c). Fig. 5. (a) Bright field transmission electron micrograph showing wood soot particles at 6,300 magnification. (b) Bright field transmission electron micrograph showing wood soot particles at 40,000 magnification. (c) SAD pattern of wood soot sub-particle.
Fig. 6(b)
Fig. 6(a).
Fig. 6(c). Fig.6 (a) Bright field transmission electron micrograph showing cotton soot at 6,300 magnification. (b) Bright field transmission electron micrograph showing cotton soot at 40,000 magnification. (c) SAD pat,tern of cotton soot sub-particle.
number density in a particle and their mode of agglomeration vary from fuel to fuel. The morphology further shows that for a particular soot generated from a single hydrocarbon, the size of spherules is uniform whereas, for those generated from fuels containing a mixture of hydrocarbons, there exists a spherule size distribution. In the case of wood, cotton and paper (Figs. 5a,b7a,b), the spherule size remains almost uniform and there is a strong tendency to retain the pre-existing preferred fibrous configuration of the parent fuel. The average sizes of spherules measured from TEM are summarised in Table 1. The spherules generated from ethanol are found clustered most densely, whereas those from the coal form branched chain-like short dispersed agglomerates. There is a positive indication of the formation of monodispersive spherules, though in a very small number in the soot of coal. The SAD study of soots shows that particles are made up of carbon and as there are no hkl reflections in the patterns (Figs. lb-4b and 5c-7c), they are not
Fig. 7(a).
Fig. 7(b).
Pig. 7(c). Fig.7. (a) Bright field transmission electron micrograph showing paper soot at 6,300 magnification. (b) Bright field transmission electron micrograph showing paper soot at 40,000 magnification. (c) SAD pattern of paper soot sub-particle.
crystalline. In crystalline materials, atoms exhibit systematic regular threedimensional orientation which produce sharp hkl dot reflections. However, the broad asymmetrical hk bands indicate the existence of a weak two-dimensional crystalline order of the carbon atoms. Thus the particles are not entirely amorphous for with the latter atoms occupy random positions and there exists no repeat distances and orderliness. They present rather a turbostratic organisation with atoms occupying positions more or less in planes which are stacked randomly. As seen from the SAD patterns, the degree of crystallinity varies from fuel to fuel, it being highest for the cotton and wood soots which produce sharp rings and least for ethanol and paper soots which give diffused halos. Broad physical trends of the particle character are summarised in Table 1. It is observed that soots generated from LPG, spirit, kerosene, coal, wood,
191 TABLE
1
BROAD PHYSICAL Fuel
TRENDS
OF CARBON
Spherule size distribution in nm Major component
Minor component
LPG Ethanol
15, 40 10
30
Kerosene Coal Wood
50 60 20
40 20 -
Cotton
15
25
Paper
5-15
SOOT PARTICULATES Nature of agglomeration
Degree of crystallinity
Large clusters Compactly packed very large clusters Medium large clusters Small branched clusters Large branched chain clusters in fine filament configuration Large branched chain clusters in fibrous configuration Gel formation in fibrous configuration
Medium high Relatively lowest Medium low LOW
Relatively
highest
Relatively
highest
Low
cotton and paper under similar normal combustion and cooling conditions exhibit distinguishable morphological and crystallographical features as observed with TEM. With the limited data obtained as far it has been possible to correlate the characterisation features of the soot with the parent fuel in an attempt to trace its origin. The study can contribute significantly to the investigation of crimes involving fire, specially where the scene of occurrence is found to be either disturbed or the fuel remnants are not available. It can further help in ascertaining whether a particular article was exposed to a specific smoke. Acknowledgements The author expresses gratitude to Prof. K.L. Chopra, (Indian Institute of Technology, New Delhi) for providing experimental facilities in his TEM laboratory. The author also wishes to thank Dr. V.D. Vankar for useful discussions and appreciates the co-operation of Mr. V.D. Arora (TEM Lab., I.I.T. New Delhi). References 1 W.C. MC Crone and J.G. Delly, The Particle Atlas, 2nd edn., Ann Arbor Science Publishers, 1972. 2 J.B. Donnet and A. Voet, Carbon Black, Dekker, N.Y., 1976. 3 B.B. Arora, The crystallography and morphology of carbon, National Symposium on Instrumentation, Indian Institute of Technology, New Delhi, India, Nov. 1983.
192 4 M. Ueyama, R.L. Taylor and T.T. Noguchi, SEM/EDS analysis of muzzle deposits at different target distances. Scanning Electron Microsc., I 367-372. technique for rapid search of gunshot residue 5 S. Basu and S. Ferriss, A refined collection particles. Scanning Electron Microsc., I (1980) 375-364. 6 G.M. Walten, R.S. Nesbitt, A.R. Calloway and G.L. Laper, Particle analysis for detection of gunshot residue, II. Occupational and environmental particles. J. Forensic Sci., 24 (1979) 425-430.