Materials Science Forum
ISSN: 1662-9752, Vol. 878, pp 108-113
doi:10.4028/www.scientific.net/MSF.878.108
© 2017 Trans Tech Publications, Switzerland
Submitted: 2016-08-12
Accepted: 2016-09-07
Online: 2016-11-10
Characterisation of Silicon Carbide from Dark Red Meranti Wood
NOOR LEHA ABDUL RAHMAN1,a,*, KOAY MEI HYIE2,b, ANIZAH KALAM3,c,
TENG WANG DUNG4,d, HUSNA ELIAS5,e
1,3,5
Mechanical Engineering Department, Universiti Teknologi MARA,
40450 Shah Alam, Selangor, MALAYSIA
2
Faculty of Mechanical Engineering, Universiti Teknologi MARA, 13500 Permatang Pauh,
Pulau Pinang, Malaysia
2
SIRIM Berhad, Persiaran Dato‘ Menteri, Seksyen 2,40700 Shah Alam, Selangor, MALAYSIA
a
noorleha3585@salam.uitm.edu.my,bhyie1105@yahoo.com,canizahkalam@salam.uitm.edu.my,
d
wdteng@sirim.my,ehusnaelias@gmail.com
Keywords: Silicon carbide, Dark red meranti, pyrolysis, infiltration
Abstract. Porous biomorphic silicon carbide is a promising ceramic materials for used in wide
variety of applications especially in filtration and separation. Wood derived silicon carbide retains
the heterogeneous structure of initial wood. Silicon carbide ceramic was derived from Dark Red
Meranti wood precursor in this study. The derivation process was prepared by reaction between
liquid silicon and carbon preform. The carbon preform was obtained via pyrolysis process at 850 C
in Argon gas flow atmosphere. This process was followed by Si infiltration at 1500 C for different
holding hours. The density was determined using Archimedes method. SEM was performed to
observe their microstructures while the compositions and phase analysis were analysed by EDX and
XRD respectively. Thermogravimetric analysis showed that a major weight loss of about 60% of
carbon perform due to the decomposition of cellulose and lignin.XRD results revealed the presence
of SiC and excess of silicon. It was found that conversion efficiency of carbon into SiC has been
improved when the holding time was increased.
Introduction
Porous ceramic mimicking the biological structure has been extensively used in last decade in
wide variety of applications due to their unique properties. The lightweight and open porosity of
porous ceramic make it interesting for applications such as catalyst support, hot gas or molten metal
filters, biomedical, construction and automotive industry[1].It is expected that the growing
population in the worlds every year would increase the demand in silicon carbide usage such as in
owing to its excellent in wear resistant, corrosion resistant, high permeability and thermal resistant
Woods have different microstructure and variety in pore distribution. The abundant choice of
microstructure and sources provide a low cost of production. Hence, wood is one of the best choices
to be used as a precursor for production of porous silicon carbide.
Wood is a solid material derived from woody plant which is classified into hardwood and
softwood. Softwood contains close-packed rectangular cells of the same size, generally has one type
of pore in axial plane. Conversely, hardwood contains closed-packed tubular cells of different sizes
from a few micrometers to about one hundred micrometers. Hardwood microstructures have three
types of pores which are vessel, fibers and rays. Vessels provide a transport of nutrients and water
whereas fibers and rays are used as a storage and strength promoter[2]. Three major constituents of
wood are cellulose (a polymer glucosan), hemicellulose (a polysaccharide producing wood sugars),
and lignin (a multi-ring organic compound)[3-4].The existent of these three components form an
insoluble network which is difficult to be separated. The only simple way to convert lignocellulosic
materials is by pyrolysis[5]. Pyrolysis is a thermal degradation of an organic material in inert
atmosphere or without free oxygen. The temperatures that commonly applied is in the range of 500

C to 800 C, where the products are gasses, oil and charcoal[6].
A number of research have been done on converting woods into silicon carbide with different
kinds of typical Mediterranean species such as pine [7],beech [8], eucaplitus[9] and oak [10].
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Materials Science Forum Vol. 878
109
Generally, different origin of woods with different climates and topology may contribute to the
different pore distribution and size. These variablesare the main factors to affect the optimum
conversion of Si into SiC using wood as the precursor.
In this study, Dark Red Meranti from the tropical rainforest was chosen as a carbon precursor.
This wood is classified as light hardwood and mainly used in interior furniture, plywood and
boatbuilding[11]. The objective of this work is to fabricate porous silicon carbide by silicon melt
infiltration. Dark Red Meranti was converted into SiC by infiltration of molten silicon into carbon
perform, which was fabricated from pyrolysis process.The infiltration was performed at 2 and 3
hours, respectively in order to analyse the reaction of Si during carbon conversion into SiC.
Methods and Materials
Dark Red Meranti was selected as a precursor to fabricate SiC ceramic. The wood sample was first
prepared by cutting into rectangular shape of 100 mm x 25 mm x 20 mm. Then, the sample was
oven dried for 20 hours at 110 C to remove the moisture. The woods sample was then pyrolysed in
a tube furnace with an argon flow.Two stages of heating were done to avoid cracking of samples.
The first stage involved a heating to 500 C at 1°C/min for 30 minutes. The second stage involved a
heating to 850 C with 2 C /min and held for 1 hour. The pyrolysed wood was then packed in
excess silicon powders and heated up to 1500 C for 2 hours and 3 hours holding times,
respectively. Finally, the sample was subjected to leaching process in mixture of hydrofluoric acid
and nitric acid (HF + NHO3) to remove excess silicon.
Thermogravimetric analysis was performed by a thermal analyzer (Model Netzsch TG 209 F3)
under flowing nitrogen gas at flow-rate of 100ml min-1 with heating rate of 10 oC min-1 from room
temperature to 1000 C. Alumina powders was used as a reference sample to determine the mass
loss during pyrolysis. Density was measured by Archimedes method (ASTM C373-88) whereas
Scanning Electron Microscope (SEM-Hitachi S-2500) operated at 20kv and 20mA was used for
microstructure analysis. The phase composition was determined by X-ray Diffraction (XRD) on a
Rigaku Ultima III) X-ray diffractometer using Cu K radiation produced at 35kV and 20mA and
Energy-dispersive X-ray spectroscopy(EDX)with a detector attached to the same SEM.
Results and Discussion
The pyrolysis of wood would decompose cellulose, hemicellulose, lignin and volatile that leaves
behind a carbon preform porous structures. This process leads to the major weight loss
approximately 70% depends on the variation of pore size and orientation as well as different in
percentage of wood shrinkage [13]. However, the wood still retained their original structure.
The infiltration of carbon preform with liquid silicon involves packing of carbon preform in
excess silicon powders and heating up to above melting temperatures of silicon. The conversion of
carbon into SiC can be expressed as:
C(solid) + Si(liquid)SiC(solid)
(1)
During infiltration, some carbon preform was converted into SiC by filling up the pore with liquid
silicon and few pores were not completely filled. The formation of SiC were from capillary effect
and reactive wetting [12]. The driving forces from both factors led to the infiltration of silicon into
small and large pores followed by reaction of carbon with liquid Si. The formation of SiC layer
occurred very fast which was less than 2 seconds. The primary layer of SiC occurred at the surface
of the pore structure [10]. The final resulted SiC composed of crystalline SiC and unreacted
carbon.The existence of excess Si in the sample can be removed by leaching process with
hydrofluoric acid and nitric acid according to:
3Si + 12HF+4HNO3 3SiF4 +4NO +8H2O
(2)
SiO2 (s) +6HF(l) H2SiF6(l) + 2H2O (l)
(3)
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Advanced Materials Design and Mechanics IV
TGA Analysis
Figure 1 shows the thermogravimetric analysis of dark Red Meranti heated until 1000C. The test
indicated that there were three stages of decomposition. The initial stage involved the removal of
moisture contents at 100C until 180C which resulted in weight lost about 10%. The second stage
of decomposition process occurred at around 280C-500C where the major weight loss of about
60% was due to decomposition of cellulose and lignin [13].
Figure 1: TGA curve of Dark Red Meranti wood
The final stage of decomposition was found at a slow and minimal weight loss. At this stage, the
residual mass of Dark Red Meranti was about 12.44%. The temperature above 600C was the stage
where the graphitic carbon forming, which is necessary for infiltration process[14].Generally, the
mechanism in the conversion of wood into carbon is quite similar to other kinds of wood. However,
some differences may exist due to differences in cell wall structure of different wood samples [15].
Density
Table 1 shows the densities of wood, carbon and resulting SiC product at three different holding
times. The density was slightly increased as holding time increasing from 2 hours to 3 hours. The
final density is quite low which indicated that the transformation rate of carbon into silicon carbide
was slow. Some of the large pores may not completely fill with silicon. Thus, the final density of
resulted SiC is only 0.98 gm/cm3. The theoretical density of silicon is 2.33gm/cm3 and 3.21gm/cm3
for silicon carbide[16].
Table 1: Density of Red Meranti wood in different heating process
Wood
Dark Red
Meranti
Raw
0.778
Pyrolysed carbon
0.583
After infiltration(holding time)
2 hours
3 hours
0.86
0.98
SEM /EDX analysis
The SEM images of resulted porous SiC are shown in Figure 24(a-d). It can be seen that the
structure of the original wood template was retained. The formation of crystalline Si at the surface
sample is clearly visible. The resulted Si/SiC filled some pores and covered up the whole surface
Materials Science Forum Vol. 878
111
and few of SiC formed and filled at pore wall. However, there are some of pore does not filled by
molten silicon. This is because the capillary effect is higher in smaller pores. The liquid silicon from
the larger pore was extracted into small pores until the pressure equilibrium is reached [8] as can be
seen in Figure 2(d).It is concluded that the pore size is one of the important factor for optimum
infiltration to occur. If pore diameter is too small, the SiC formed at the surface could 100
block
µm and
restricted further infiltration process inside the pore walls. Otherwise too large pore could leave
unreacted carbon as SiC not fully converted [17].Therefore, the pore size should be ideal for
optimum reaction to occur. Besides, another factor that could be considered in Si infiltration
included contact angle and surface tension [18].
Figure 2 (c) shows an image after 3 hours etching at the surface whereas Figure 2 (d) at the cross
section. The pores are clearly visible in acid etched sample. It could be observed that from the
Figure 2 (d), the small pore was eliminated due to crystalline formation of SiC. After leaching, the
crystalline SiC are still remain inside the sample. The composition of Si as showed in Table 2, is
39.64 wt% and 25.56wt% at surface and cross section, respectively. This content is corresponding
to SiC compound and could be proven by XRD. The amount of Si was increased as the holding
time increasing from 2 hours to 3 hours which is about 41.07 wt.% to 76.83 wt.%.
a
b
SiC
c
Pores
d
SiC
SiC
100µm
100µm
SiC
100µm
Pores
100µm
Figure 2: SEM images of SiC (a) at 2 hours infiltration, (b) at 3 hours infiltration,
(c) surface of etched sample and, (d) cross section of etched sample
Table 2: Composition of resulted SiC
Element (wt.%)
2 hrs
3 hrs
Etched surface
Etched inside Pores
C
44.93
23.17
60.36
74.44
Si
55.07
76.83
39.64
25.56
Figure 3 shows the XRD patterns of carbon preform and resulting SiC. It can be seen that carbon
is amorphous with a broad peaks at around 22 and 44. The major crystalline phase is SiC at 2=
35.6,41.4,59.9and 75.5 while 2= 28.4, 47.3 and 56.1are corresponds to Si peaks. It is
clearly seen that the intensity of SiC in 3 hours holding time is much higher than 2 hours holding
time which indicating that the amount of SiC in 3 hours are greater than 2 hours . It was also found
that the major Si peak disappears after leaching as shown in Figure 5(d). The major peaks
correspond to SiC and C. The existence of carbon peak in the pattern after etching showed that there
was a residual carbon that does not completely converted into SiC during infiltration.
112
Advanced Materials Design and Mechanics IV
:SiC
:Si
:C
Intensity (arb.unit)
d
c
b
a
20
30
40
50
2θ (degree)
60
70
80
Figure 3: XRD patterns of (a) carbon preform, (b) infiltration for 2 hours,
(c) infiltration for 3 hours, and (d) etched SiC
Conclusions
Biomorphic silicon carbide was fabricated by silicon melt infiltration of pyrolyzed Dark Red
Meranti as carbon precursor. The microstructures of carbon perform and biomorphic SiC were
retained. Density of the resulted SiC was slightly increased when the infiltration time was increased.
In addition, as the SiC increase, the crystallinity of the sample was also increased. The process of
leaching away the residual Si in the sample and the final amount of fabricated SiC is only about 30
%from a total volume of carbon scaffold. The excess silicon content in the pore channel was
smaller compared to the surface of the carbon template. The formation of SiC layer was one of the
factors that was responsible for reducing wetting angle between solid and liquid .Thus, the
penetration of silicon is low at the end of pore channel. The SiC growth results in clogging of small
pores thus prevent the additional of Si liquid penetrate into the pores. This would stop the reaction
between carbon and silicon.
Acknowledgements
The authors would like to thank Research Management Institute UiTM (Grant FRGS :600RMI/FRGS 5/3 (52/2015) and Ministry of Higher Education Malaysia for financial support..In
addition, the author
would
like to thank both Ministry of Education (MOE) and
UniversitiTeknologi MARA for her PhD sponsorship.
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