This study simulated the short circuit of copper wires at ambient atmosphere, we scrutinized the microstructures of FCABs. The experimental results showed that the FCABs can be divided into the non-oxygen-permeated and the oxygen-permeated arc beads, two different molten marks.
6.1 Non-Oxygen-Permeated FCABs
From the non-oxygen-permeated FCABs experiment performed at ambient atmosphere, we studied the FCABs located 1 cm away from the load end of wires having diameters from 0.1 to 1.2 mm. The total undercooling (∆T0) of the melted bead grown out of the thermal dendrite was inversely proportional to the wire diameter. The thermal dendrite growth velocity (ν) was inversely proportional to the square of the wire diameter. The primary spacing of the dendrite (λ) is proportional to the wire diameter. Therefore, the total undercooling (∆T0) of the melt of an arc bead, as well as the growth velocity (ν) of thermal dendrite increased upon decreasing the diameter of the wire. Thus, decreasing the diameter of the wire increased the cooling rate of the FCAB melt. Our aim for this study was to obtain evidence for FCABs from various perspectives of materials science and to derive a corresponding mathematical model. Indeed, we successfully deduced several interacting physical properties: the primary spacing of thermal dendrite (λ), the growth velocity (ν), and the total undercooling (∆T0) in the FCAB all with respect to the diameter of the copper wire.
6.2 Oxygen-Permeated FCABs
According to the XRD results from the solidification of the Cu-dendrites, the growth of high-index planes with higher surface energy are quicker than low-index planes, thus leaving the low-index｛111｝plane in the final solidification of Cu-dendrites. Therefore, the cuprous oxide surface layer and the microstructure constituents of solutal Cu-dendrites and Cu- κ eutectic structure are the characteristic feature, as well as the fingerprint of the FCABs permeated by oxygen, for the short circuit of copper wire occurs at an ambient atmosphere before fire.
Comprehensive conclusions, instead of visual inspection or empirical rule, the microstructure of FCABs can be analyzed precisely by using FIB-SEM and TEM. As a result, convincing scientific evidences can be provided in court.
Through the establish FCABs module verified scientifically, it effectively enhances the evidential power in judicial fire investigations.
This study would expect to attract the administration attention for the molten mark with the sentiment that throws a sprat to catch a whale. We are to anticipate that this issue may remind the administration to continue studying the relation of the wire length to FCAB, and FRAB identification etc. problems.
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Tables
Table 2-1 Dendrite crystal structure observed by Seki et al. [21]
Bead
No Dendrite Crystals (%)
Dendrite Cu Crystals (%)
Dendritic Cu2O Crystals (%)
FCAB 57 38 5
FRAB 92 8 0
Table 4-1 Interplanar spacings of dendrite specimens calculated from the electron diffraction pattern.
Spot Calculated Interplanar Distance (Å )
Standard Interplanar
Distance (Å ) Crystalline Plane (hkl)
1 1.2728 1.2780 ̅ ̅
2 2.0859 2.0880 ̅ ̅
3 1.8034 1.8080
4 2.0864 2.0880
Table 4-2 Average primary spacings (λɑve), growth velocities (νs), and the temperature differences due to heat flow (∆TtS) of thermal dendrites of copper arc beads obtained from wires of various diameters.
Parameter Correspondind Datum
Diameter of
Wire (mm) 0.1 0.2 0.4 0.6 0.8 1.2
λɑve (μm) 0.83 ± 0.17 1.85 ± 0.36 3.59 ± 0.70 5.92 ± 0.95 8.43 ± 1.41 11.83 ± 1.61 νs (μm/s) 3.58 × 106 8.95 × 105 2.24 × 105 9.94 × 104 5.59 × 104 2.48 × 104
∆TtS (K) 10.09 5.04 2.52 1.68 1.26 0.85
Table 4-3 Interplanar spacings of dendritic surface precipitate specimens calculated from the electron diffraction pattern.
Spot Calculated Interplanar Distance (Å )
Standard Interplanar
Distance (Å ) Crystalline Plane (hkl)
1 3.0147 3.0200
2 2.4478 2.4650
3 4.3151 4,2690
4 2.4537 2.4650 ̅ ̅
Figures
Fig. 2-1 NFPA 921 defines the appearance morphology of FMMs [8].
(a)
(b)
Fig, 2-2 NFPA 921 defines the appearance morphology of EMMs [8].
(a)
(b)
Fig. 2-3 Oxgen concentration profiles shown in the patent by MacCleary and Thaman [24, 25].
Electron Energy (EV)
Fig. 2-4 AES profiles the surface of FCAB by Anderson [26].
Distance below surface (nm)
Fig. 2-5 Elements profiles the surface of FCAB by Anderson [30].
Atom concentration (%)
Fig. 2-6 Elements profiles the surface of FRAB by Anderson [30].
Atom concentration (%)
Distance below surface (nm)
Fig. 2-7 Oxygen solubility in liquid and solid copper as a function of temperature, averaged from the compiled reference by Howitt [31].
Solubility (ppm)
Temperature (°C
Fig. 2-8 Raman spectra obtained from carbonized residue remaining in the molten marks of field samples (a), (b), (c): FCAB, (d): FRAB by E. P, Lee et al.
[37].
(a)
(b)
Fig. 2-9 (a) FCAB Carbon depth profile, (b) FCAB Chlorine depth profile,
(c) FRAB Carbon depth profile, (d) FRAB Chlorine depth profile, by C. Y.
Chen et al. [38]
(c)
(d)
Short-circuit experiment
FCABs samples preparation FCABs Classification
FCABs with non-faceted surface FCABs with faceted surface
XRD SEM
FIB
TEM EDS Metallograhy
Modulus built
XRD SEM TEM
FIB
EDS
Modulus built
Fig. 3-1 Schematic diagram of the flow char with experiment
Fig. 3-2 Short-circuit experiment: (a) schematic diagram; (b) FCAB samples.
Load side 110volt Power side
Short circuit site
(remove insulation)
PVC insulating sleeve Copper wire
1 cm
(a) (b)
Load siteFig. 3-3 XRD diffractometer (PANalytical, Almelo, The Netherlands).
Fig 3-4 SEM (Seiko SMI3050SE dual-beam FIB-SEM hybrid system, Oyama, Japan). with attached EDS (METEK, Gloucestershire, UK, 5 ≤ Z ≤ 92).
Fig. 3-5 TEM(FEI Tecnai G2 20 S-Twin, Hillsboro, OR, USA).
20 30 40 50 60 70 80 90 Cu(111)
Cu(200)
Cu(220)
Intensity (arb. unit)
2 (deg.)
Fig. 4-1 X-ray diffraction (XRD) analysed the non-faceted surface FCABs at 1.2mm wire diameter.
Fig. 4-2 Microstructures of the non-faceted surface FCAB at 1.2mm wire diameter observed through focused ion beam SEM (FIB-SEM) and the sampling of a transmission electron microscopy (TEM) specimen.
Heat flow
Kev
Fig. 4-3 TEM analysis of primary crystallites of the non-faceted surface FCAB at 1.2mm wire diameter : (a) energy dispersive spectroscopy (EDS)
spectrum; (b) TEM bright-field image; (c) dark-field image and (d) diffraction pattern along the [011] direction.
4
(a) (b)
Heat flow
Fig. 4-4 Growth of primary trunk of thermal dendrites in a melted bead (anti-parallel to the heat flow direction); (a) schematic diagram of the thermal dendrites; (b) metallographic photo of thermal dendrites in arc bead of 0.6mm wire.
Fig. 4-5 Cross-sectional metallographic analyses of arc beads of copper wire with diameters of (a) 0.1, (b) 0.2, (c) 0.4, (d) 0.6, (e) 0.8, and (f) 1.2 mm, used a metalloscopy.
10 20 30 40 50 60 70 80
Cu(111)
Cu2O(311)
Cu2O(220)
Cu2O(111)
Intensity (arb. unit)
2 (deg.) Cu2O(110)
Fig. 4-6 XRD microanalysis of the faceted surface FCABs of 1.2mm wire diameter.
(a) (b)
Sampling
6 μm
2 1 3
4
(d)
(e)
(f)
(c)
Fig.4-7 Microscopic photos of the faceted surface FCAB at 1.2mm wire diameter (a) Faceted surface layer observed through FIB-SEM, (b) sampling region of TEM specimen on the faceted surface layer, (c) EDS spectrum, (d) TEM bright field image, (e) Dark field image and (f) Corresponding diffraction pattern along [ ̅ ̅] direction.
Fig. 4-8 TEM analysis of the eutectic phase of faceted surface FCAB at 1.2mm wire diameter (a) Microstructure of the eutectic phase and the sampling of TEM specimen, (b) EDS spectrum of the matrix, (c) TEM bright field of the matrix, (d) Dark field of the matrix, (e) Corresponding diffraction pattern of the matrix along [ ̅ ] direction, (f) EDS spectrum of the rod-shaped phase, (g) TEM bright field of the rod-shaped phase, (h) Dark field of the rod-shaped phase, (i) Corresponding diffraction pattern of the rod-shaped phase along [ ̅ ̅] direction.
Sampling
(a) (b)
Fig. 4-9 Analysis of the dendrite tipped with precipitate of the faceted surface FCAB at 1.2mm wire diameter (a) Microstructure of the dendrite tipped with precipitate observed by FIB-SEM and the sampling of TEM specimen, (b) Schematic diagram of dentdritic growth, (c) EDS spectrum
of the dendrite, (d) TEM bright field of the dendrite, (e) Dark field of the dendrite, (f) Corresponding diffraction pattern of the matrix along [001] direction, (g) EDS spectrum of the precipitate phase, (h) TEM bright field of the precipitate phase, (i) Dark field of the precipitate phase, (j) Corresponding diffraction pattern of the Cu2O phase along [110] direction.
Fig. 4-10 Schematic microstructure of FCAB permeated by oxygen.
Unmelted wire Solutal dendrite
Eutectic
Oxide layer
Fig. 5-1 Schematic representation shows the thermal dendrite growth initiated by perturbation at the solid–liquid interface, and the corresponding temperature curve in front of the dendrite tip.
Rs
Z’
y
π r*
Rc
∆Tt
∆T0
z
Ti Tm
∆TR
Tl
T
Fig. 5-2 Relationship between the primary spacing of thermal dendrites and the diameter of the wire
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0 2 4 6 8 10 12 14 16
Primary spacing (um)
Diameter of wire (mm) Primary spacing
Linear Fit of Primary spacing
Fig. 5-3 D-ν relation between the wire diameter and the growth rate of thermal dendrite at marginal stability.
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0 0.5 1 1.5 2 2.5 3 3.5
4x 106 Dendrite Growth Rate as a Function of Wire Diameter
D(mm)
V(um/sec)
Fig. 5-4 D-Δ ts relation between the wire diameter and the temperature difference due to heat flow at marginal growth stability.
0 0.2 0.4 0.6 0.8 1 1.2 1.4
0 2 4 6 8 10 12
Undercooling in Arc Bead Melt as a Function Wire Diameter
D(mm)
ΔTt(K)
Fig. 5-5 Relationships among the values of ΔT0, R, and ν, of the thermal dendrites obtained from various wire diameters (D) during different growth stages [72].
Initial stage
2nd Stage
3rd stage Final stage
ΔT0 (K)
Fig. 5-6 In Cu-O phase diagram, Cu-κeutectic point Xo=0.017 (at T=1339K) [75].
誌 謝
感謝實驗室的學長與學弟妹，陪我一起打拼的日子，這段時間有苦、有