STUDY ON SILICON CARBIDE PRODUCED

STUDY ON SILICON CARBIDE PRODUCED
STUDY ON SILICON CARBIDE PRODUCED
FROM RICE HUSK AS A REINFORCING AGENT
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Bachelor of Technology
In
Metallurgical & Materials Engineering
By
SIDHESHWAR KUMAR (107MM024)
BHAGIRATHI SINGH (107MM032)
Department of Metallurgical & Materials Engineering
National Institute of Technology
Rourkela
2011
~I~
STUDY ON SILICON CARBIDE PRODUCED
FROM RICE HUSK AS A REINFORCING AGENT
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
Bachelor of Technology
In
Metallurgical & Materials Engineering
By
SIDHESHWAR KUMAR (107MM024)
BHAGIRATHI SINGH (107MM032)
Under the Guidance of Prof. S. Sarkar
Department of Metallurgical & Materials Engineering
National Institute of Technology
Rourkela
2011
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NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
CERTIFICATE
This is to certify that the thesis entitled, " STUDY ON SILICON CARBIDE
PRODUCED FROM RICE HUSK AS A REINFORCING AGENT " submitted
by Sidheshwar Kumar (107MM024) and Bhagirathi Singh (107MM032), in
partial fulfillments for the requirements for the award of Bachelor of Technology
Degree in Metallurgical and Materials Engineering at National Institute of
Technology, Rourkela is an authentic work carried out by them under my
supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not been
submitted to any other University/Institute for the award of any Degree or
Diploma.
Date:
Prof. S. Sarkar
Dept. of Metallurgical and Materials Engineering
National Institute of Technology, Rourkela-769008
~III~
ACKNOWLEDGEMENT
We wish to express our deep sense of gratitude to Prof. S. Sarkar, our guide, for his consistent
encouragement, guidance and support to carry out and complete this project, and for giving us an
opportunity to work on this project.
We are sincerely grateful to Prof. B. B. Verma, Head of the Department of Metallurgical and
Materials Engineering, NIT-Rourkela, for providing all the necessary facilities in the department.
I would like to extend my sincere thanks to Prof. A. Basu, Prof. S. K. Sahoo, and Prof. D.
Chaira, for their guidance and help at different stages of the project.
We are also grateful to Dr. B. Mallick, Institute of Physics, Bhubaneswar, for their visionary
guidance and analysis techniques highly essential for our project.
We would be highly obliged to extend our thanks to Mr. Uday Kumar Sahu and Mr. Rajesh
Patnaik, for their immense support and help rendered while carrying out our experiments,
without which the completion of this project would have been at stake.
We would also like to thank all the staff members of MME Dept., NITR and everyone who in
some way or the other has provided us valuable guidance, suggestion and help for this project.
Date:
Sidheshwar Kumar (107MM024)
Bhagirathi Singh (107MM032)
B. Tech (Metallurgical and Materials Engineering)
National Institute of Technology, Rourkela-769008
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ABSTRACT
Now days, agricultural waste material are getting a wide exposure to the future generation of
material science world. Rice husk is one of them, and its global production is approximately 140
million tons, annually. In the majority of cases much of the husk produced from the processing
of rice is either burnt or dumped as a waste.
In the present work, an attempt has been made to synthesize the silicon carbide from rice
husk and consolidate the prepared silicon carbide with aluminum matrix and form a composite
by powder metallurgy route, this treatment of rice husk will act as a ‘resource’ for energy
production and simultaneously avoids its disposal problems. Following the powder synthesis and
consolidation with aluminum powder and sintering done at temperature of 5500 C with holding
time of 1 hr., extensive efforts have been undertaken for characterization by X-ray diffraction,
SEM and EDX, microstructural evolution by optical microscopy and other analysis as well as
assessment of mechanical properties like hardness under different loading conditions and wear
behavior variables like time, wear depth and sliding distance. The results suggest that preparation
of metal matrix composites of Al-SiC followed by conventional sintering method is a potential
way for synthesizing new high strength commercial MMCs by utilization of biomass resources.
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CONTENTS
Certificate
III
Acknowledgement
IV
Abstract
V
List of Figures
VIII
List of Tables
IX
CHAPTER 1
1
1. Introduction
2
1.1 Rice husk
2-3
1.2 Silicon carbide
3
1.2.1 Natural occurrences
3-4
1.2.2 Production
4
1.2.3 Structure and properties
4-5
1.2.4 Uses of silicon carbide
5
1.3 Metal matrix Composite
5
1.3.1 Processing of MMCs
7
1.4 Sintering
7
1.4.1 Steps in sintering
7-8
1.4.2 Densification parameter
8
1.5 Wear behavior
9
1.5.1 Types of wear
9
1.5.2 Effect of environment on abrasive wear
9
1.5.2.1 Abrasive
9
1.5.2.2 Temperature
9-10
1.5.2.3 Speed of contact
10
1.5.2.4 Load
10
1.5.2.5 Humidity
10
CHAPTER 2
11
2. Literature Survey
12-13
~VI~
CHAPTER 3
14
3. Experimental Details
15-19
3.1 Formation of silicon carbide from rice husk
15
3.2 XRD analysis
15-16
3.3 Scanning electron microscopy
16-17
3.4 Consolidation and sintering
17
3.5 Hardness measurement
18
3.6 Wear testing
19
CHAPTER 4
20
4. Result and Discussion
21-32
4.1 XRD analysis
21-22
4.2 Scanning electron microscopy
22
4.2.1 Silicon carbide
23-24
4.2.2 White ash
24-25
4.2.3 Aluminum silicon carbide composite
26-27
4.2.4 Pure aluminum
27-28
4.3 Hardness measurement
28-30
4.4 Wear behavior
30
4.4.1 Effect of sliding distance on wear depth
30-31
4.4.2 Effect on wear depth with time
31-32
CHAPTER 5
33
5. Conclusion
34
CHAPTER 6
35
6. Future Plan of Work
36
CHAPTER 7
37
7. References
38-39
~VII~
LIST OF FIGURES
Figure 1.1 Ideal sintering steps
Figure 1.2 Sintering stages
Figure 3.1 JEOL JSM - 6480LV scanning electron microscope
Figure 3.2 Vickers hardness testing machine
Figure 4.1 XRD plot of SiC produced from rice husk
Figure 4.2 XRD plot of white ash produced from rice husk
Figure 4.3 Scanned image of silicon carbide particles
Figure 4.4 EDX pattern of silicon carbide particle
Figure 4.5 Scanned image of white ash particle
Figure 4.6 EDX pattern of white ash
Figure 4.7 Scanned image of Al-SiC (1%) composite
Figure 4.8 EDX pattern of Al-SiC (1%) composite
Figure 4.9 Scanned image of pure aluminum
Figure 4.10 EDX pattern of pure aluminum
Figure 4.11 Comparison between pure Al and Al-SiC (1%) composite under different load
Figure 4.12 Plot between wear depth and sliding distance
Figure 4.11 Plot between wear depth and time of sliding
~VIII~
LIST OF TABLES
Table 1.1 Chemical analysis of rice husks
Table 1.2 Compositional analysis of rice husks
Table 1.3 Properties of major silicon carbide polytypes
Table 3.1 List of parameter used during XRD analysis
Table 3.2 Parameters used during SEM analysis
Table 3.3 Parameters used during compaction
Table 3.4 Comparison of different densities
Table 3.5 Parameters used during Vickers hardness testing
Table 4.1 Elemental analysis silicon carbide particle
Table 4.2 Elemental analysis of white ash
Table 4.3 Elemental analysis of Al-SiC (1%) composite
Table 4.4 Elemental analysis of pure aluminum
Table 4.5 Hardness under different load for pure aluminum
Table 4.6 Hardness under different load for Al-SiC (1%) composite
~IX~
CHAPTER 1
INTRODUCTION
~1~
1. INTRODUCTION
1.1 RICE HUSK
Rice husks (or rice hulls) are the hard protecting coverings of grains of rice. Rice husk is an
agricultural residue abundantly available in rice producing countries. Husk Produced is around
20% of total rice production. The annual rice production in India and the World is 150 MTs
(Million Tons) and 700 MTs, respectively, and hence husk produced in India and the World, the
amounts are generally approximately in the range of 30 MTs and 140 MTs, respectively. Rice
husk is generally not recommended as cattle feed since its cellulose and other sugar contents are
low means there is limited source of energy for body. Furfural and rice bran oil are extracted
from rice husk. Industries use rice husk as fuel in boilers and for power generation. Among the
different types of biomass used for gasification, rice husk has a high ash content varying from 18
– 20 %. Silica is the major constituent of rice husk ash and the following tables gives typical
composition of rice husk and rice husk ash. With such a large ash content and silica content in
the ash it becomes economical to extract silica from the ash, which has wide market and also
takes care of ash disposal. The dry analysis of rice husks are as follows:
Element Analysis
Mass Fraction %
Carbon
41.44
Hydrogen
4.94
Oxygen
37.32
Nitrogen
0.57
Silicon
14.66
Potassium
0.59
Sodium
0.035
Sulfur
0.3
Phosphorous
0.07
Calcium
0.06
Iron
0.006
Magnesium
0.003
Table 1.1 Chemical analysis of rice husks
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Compositions
Mass Fraction (%)
Silica (SiO2)
80 – 90
Alumina (Al2O3)
1 – 2.5
Ferric oxide (Fe2O3)
0.5
Calcium oxide (CaO)
1–2
Magnesium oxide (MgO)
0.5 – 2.0
Sodium oxide (Na2O)
0.2 – 0.5
Potash
0.2
Titanium dioxide (TiO2)
Nil
Loss on Ignition
10 – 20
Table 1.2 Compositional analysis of rice husks
1.2 SILICON CARBIDE
Silicon carbide (SiC), also known as carborundum, is a compound of silicon and carbon with
chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Grains of
silicon carbide can be bonded together by sintering to form very hard ceramics which are widely
used in applications requiring high endurance, such as car brakes, car clutches and ceramic plates
in bulletproof vests. Silicon carbide with high surface area can be produced from SiO2 contained
in plant material
[12]
. Silicon Carbide is potentially useful such as high temperature structure
material, because of its high hardness, high oxidation resistance, good thermal shocking
resistance etc. However, the production of high density ceramics by solid state sintering is
difficult due to the strong covalent nature of Si-C bond. The solid state sintering of SiC can be
performed at high temperature up to 22000 C.
1.2.1 NATURAL OCCURRENCES
Moissanite is natural form of Silicon carbide. When the first artificial moissanite reached the
jewelry market, it has been regarded as an excellent diamond substitute, with optical properties
exceeding those of diamond. Because it has its own unique appearance, it cannot be truly called a
diamond stimulant
[8] [10]
. Its ethical production, however, does make it a popular alternative to
diamonds.
~3~
Because of its hardness, it is useful for high-pressure experiments (e.g., using diamond anvil cell)
competing there with diamond. Large diamonds, used for anvils, are prohibitively expensive.
Therefore for large-volume experiments, much cheaper synthetic moissanite is a more realistic
choice. Synthetic moissanite is also interesting for electronic and thermal applications because its
thermal conductivity is similar to that of diamonds. High power SiC electronic devices are
expected to play an enabling and vital role in the design of protection circuits used for motors,
actuators, and energy storage or pulse power systems [13] [9] [18].
1.2.2 PRODUCTION
Due to the rarity of natural moissanite, silicon carbide is typically man-made. Most often it is
used as an abrasive, and more recently as a semiconductor and diamond simulant of gem quality.
The simplest manufacturing process is to combine silica sand and carbon in an Acheson graphite
electric resistance furnace at a high temperature, between 1600 and 2500 °C
[15] [6]
. Fine SiO2
particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess
carbon from the organic material.
1.2.3 STRUCTURE AND PROPERTIES
Silicon carbide exists in about 250 crystalline forms. The polymorphism of SiC is characterized
by a large family of similar crystalline structures called polytypes. They are variations of the
same chemical compound that are identical in two dimensions and differ in the third. Thus, they
can be viewed as layers stacked in a certain sequence. Alpha silicon carbide (α-SiC) is the most
commonly encountered polymorph; it is formed at temperatures greater than 1700 °C and has a
hexagonal crystal structure (similar to Wurtzite). The beta modification (β-SiC), with a zinc
blende crystal structure (similar to diamond), is formed at temperatures below 1700 °C [8].
Properties
Structure-3C (β)
Structure-4H
Structure-6H (α)
Crystal structure
Zinc blende (cubic)
Hexagonal
Hexagonal
Lattice constants (Å)
4.3596
3.0730; 10.053
3.0730; 15.11
Density (g/cm3)
3.21
3.21
3.21
Bandgap (eV)
2.36
3.23
3.05
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Bulk modulus (GPa)
250
220
220
3.6
3.7
4.9
Thermal conductivity
(W/(cm·K))
Table 1.3 Properties of major silicon carbide polytypes
Pure SiC is colorless. The brown to black color of industrial product results from iron impurities.
The high sublimation temperature of SiC (approximately 2700 °C) makes it useful for bearings
and furnace parts. Silicon carbide does not melt at any known pressure
[20]
. It is also highly inert
chemically. There is currently much interest in its use as a semiconductor material in electronics,
where its high thermal conductivity, high electric field breakdown strength and high maximum
current density make it more promising than silicon for high-powered devices [3] [12]. SiC also has
a very low coefficient of thermal expansion (4.0 × 10−6/K) and experiences no phase transitions
that would cause discontinuities in thermal expansion.
1.2.4 USES OF SILICON CARBIDE
 Abrasive and cutting tools
 Structural material
 Automobile parts
 Jewelry
 Electric and electronic systems
 Thin film pyrometry and heating elements
 Carborundum printmaking
 Graphene production
1.3 METAL MATRIX COMPOSITE
The matrix in a metal matrix composite (MMC) is usually an alloy, rather than a pure metal, and
there are three types of such composites [1]:
 Dispersion-strengthened, in which the matrix contains a uniform dispersion of very fine
particles with diameters in the range 10–100 nm,
 Particle-reinforced, in which particles of sizes greater than 1 μm are present, and
~5~
 Fiber-reinforced, where the fibers may be continuous throughout the length of the
component, or less than a micrometer in length, and present at any volume fraction.
Compared to monolithic metals, MMCs have:
 Higher strength-to-density ratios,
 Higher stiffness-to-density ratios,
 Better fatigue resistance,
 Better elevated temperature properties,
 Higher strength,
 Lower creep rate,
 Lower coefficients of thermal expansion, and
 Better wear resistance.
The advantages of MMCs over polymer matrix composites are [1] [2]:
 Higher temperature capability,
 Fire resistance,
 Higher transverse stiffness and strength,
 No moisture absorption,
 Higher electrical and thermal conductivities,
 Better radiation resistance,
 No out gassing,
 Fabric ability of whisker and particulate-reinforced MMCs with conventional
metalworking equipment.
Some of the disadvantages of MMCs compared to monolithic metals and polymer matrix
composites are [1] [3]:
 Higher cost of some material systems,
 Relatively immature technology,
 Complex fabrication methods for fiber-reinforced systems (except for casting),
 Limited service experience.
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1.3.1 PROCESSING OF MMCs
Accordingly to the temperature of the metallic matrix during processing the fabrication of
MMCs can be classified into four categories:
(a) Liquid phase processes,
(b) In – Situ Processes,
(c) Two phase (solid-liquid) processes.
(d) Solid state processes.
1.4 SINTERING
Sintering is a powder metallurgy route for the process of forming objects from a metal powder
by heating the powder at a temperature below its melting point, until its particles adhere to each
other. Sintering is a solid state process and traditionally used for manufacturing ceramic objects.
Most of the material exhibit sintering at homologous sintering temperatures between 0.5 Tm –
0.8 Tm range. With higher temperature, longer time, or smaller particles, the bond grows more
rapidly and densification becomes prominent.
1.4.1 STEPS IN SINTERING
Figure 1.1 Ideal sintering steps
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Where, ∆γ is change in surface energy and A is surface area.
The steps for sintering are as follows:
 Adhesion: This stage occurs when particle comes into contact.
 Rapid growth of the inter-particle neck.
 The pore structure becomes smooth and develops an interconnection, i.e. giving average
larger grains with few grains.
 Pores are get closed due to grain growth.
Ideally, when two particle of diameter of D are compacted and then sintered then the resultant
diameter of larger grain is 1.26*D [16]. These mentioned steps are shown in the below figure.
Figure 1.2 Sintering stages
The shown figure indicates that the pore structure changes during sintering, starting with
particles in the point contact. The pore volume decreases and the pore become smoother. As pore
spheroidization occurs, the pores are replaced by grain boundaries.
1.4.2 DENSIFICATION PARAMETER
Densification parameter is an important parameter for sintering operations. Ideally it should be
positive but in some cases of sintering it is found negative. The positive value of densification
parameter means there is increase in density due to sintering, i.e. sintered density should be
higher than green density. It is followed by formula given below:
Densification Parameter = (ρs
Where,
− ρg) / (ρTh − ρg)
ρs is the sintered density of material, ρg is the green density of material, and ρTh is the
theorectical density of material which has been calculated on ideal basis of material.
~8~
1.5 WEAR BEHAVIOUR
Perhaps the biggest in solving wear problems is that of anticipating the type(s) of wear to which
components will be subjected. Material can be removed from a solid surface in only three ways:
by melting, by chemical dissolution, or by the physical separation of atoms from the surface. The
last method can be accomplished either by the one-time application of a high strain or by cyclic
straining at lower magnitudes. Mechanical and chemical processes may operate separately or
together, such as abrasion in a corrosive medium [1] [4] [14].
1.5.1 TYPES OF WEAR
Depending on the nature of movement of the media following types wear has been classified as:
 Abrasive wear,
 Sliding and Adhesive wear,
 Corrosive wear,
 Oxidational wear
1.5.2 EFFECT OF ENVIRONMENT ON ABRASIVE WEAR
In addition to the properties of a material, the environment affects wear. As stated earlier,
abrasion loss rates are not intrinsic to a material. Environmental factors that affect abrasive
losses include, but are not limited to: the type of abrasive and its characteristics, temperature,
speed of contact, unit load of the abrasive on the material, humidity, and corrosive effects.
1.5.2.1 ABRASIVE
The hardness of the abrasive particles is important to the rate of abrasion of the subject material.
As the hardness of the abrasive exceeds that of the wear material, abrasive wear typically
becomes much worse .As the abrasive hardness exceeds the hardness of the material, it is able to
penetrate the surface and cut/remove material without having its cutting edges broken or
rounded.
1.5.2.2 TEMPERATURE
It might be expected that abrasive wear would increase as the temperature rises, because the
hardness and yield strength decrease. Instead, for aluminum and copper, when the temperature
was increased from ambient to 673 K, very little change in the abrasive wear rate was observed.
It has been proposed that the reason for this small change is that during abrasion, small areas are
adiabatically heated. At higher initial temperatures, the metal flow stress is reduced. This results
in less heating in the material during the abrasion process. The end result is that areas around the
~9~
material that is being removed have a similar temperature, independent of starting temperature,
and similar abrasion rates [2] [19].
1.5.2.3 SPEED OF CONTACT
The rate of abrasive wear has been found to slightly increase with increasing speed in the range
from 0 to 2.5 m/s (0 to 8.2 ft/s). This increase in wear may be attributable to frictional heating.
The effect is small, because all of the abrasion occurs in a near-adiabatic process. This should
result in nearly the same peak temperature rise, independent of speed, for the tiny volume of
material where the asperities are removing the material [4].
1.5.2.4 LOAD
When load causes fracture of abrasive particle then wear can increase. If the abrasive particle
points are rounded, wear will decrease.
1.5.2.5 HUMIDITY
The effect of atmospheric humidity on abrasive wear is far from clear, and contrary results exist.
Larsen- Basse studied the effect of atmospheric humidity on abrasive wear for a variety of pure
metals and steels. When using SiC abrasive, wear usually increased with increasing humidity, up
to 65% relative humidity. This increase is attributed to a moisture-assisted fracture of the SiC
abrasive particle, which resulted in fresh sharp edges to cut into the surface of the material.
~10~
CHAPTER 2
LITERATURE SURVEY
~11~
2. LITERATURE SURVEY
[1] C. Srinivasa Rao and G. S. Upadhyaya
[6]
have studied on the processing and mechanical
properties of 2014 and 6061 Al alloy-based power metallurgy composites containing up to 8
~01% of SIC in either particle or continuous fibre form. For consolidation of the green compacts,
liquid phase sintering under vacuum at 635°C was adopted. The addition of reinforcement
imparted improved densification such that particulate composites were better densified than the
fibrous ones. Relatively higher work hardening rates were observed in fibrous composites than in
the particulate ones. The ductility values of obtained porous particulate composites were similar
to those of the fully dense once reported in the literature.
[2] Huei-Long Lee, Wun-Hwa Lu and Sammy Lap-Ip Chan [7] have studied on the effects of
sintered porosity, volume fraction and particle size of silicon carbide particles (SiC& on the
abrasive wear resistance of powder metallurgy (P/M) aluminium alloy 6061 matrix composites.
Aluminium alloy 6061 manufactured following the same route was also included for direct
comparison of alloy 6061 manufactured following the same route was also included for direct
comparison. The results show that the beneficial effect of hard Sic, addition on wear resistance
far surpassed that of the sintered porosity in the P/M composites. The wear rates of composites
decreased as the amount of Sic, increased. Aluminium alloy composites reinforced with larger
SiC, size are more effective against abrasive wear than those reinforced with smaller SiC, size.
The wear rates of the P/M aluminium alloy and 10 vol.% SiC, composite were significantly
affected by the aging conditions. However, for the 20 vol.% SiC, composite, and for the
composites with large SiC, size, the aging effect on the wear rate of the composites was found to
be small.
[3] Lauri Kollo, Marc Leparoux, Christopher R. Bradbury, Christian Jäggi, Efraín
Carre˜no-Morelli, and Mikel Rodríguez-Arbaizar
[8]
have studied that planetary milling for
nano-silicon carbide reinforced aluminium metal matrix composites. High-energy planetary
milling was used for mixing aluminium powders with 1 vol.% of silicon carbide (SiC) nanoparticles. It was shown that mixing characteristics and reaction kinetics with stearic acid as
process control agent can be estimated by normalised input energy from the milling bodies. For
this, the additional parameter characterizing the vial filling was determined experimentally.
Depending on the ball size, a local minimum in filling parameter was found, laying at 25 or 42%
filling of the vial volume for the balls with diameter of 10 and 20mm, respectively. These
~12~
regions should be avoided to achieve the highest milling efficiency. After a hot compaction,
fourfold difference of hardness for different milling conditions was detected. Therewith the
hardness of the Al–1 vol.% nano SiC composite could be increased from 47HV0.5 of pure
aluminium to 163HV0.5 when milling at the highest input energy levels.
[4] P. K. Mishra, B. C. Mohanty, and B. B. Nayak
[9]
have studied that thermal plasma
synthesis of silicon carbide from boiler burnt rice husk. Thermal plasma technology has been
utilized for synthesis of powder silicon carbide, the burnt rice husk and wood charcoal being
processed in a different way. The product has been characterized by chemical analysis, XRD,
SEM and also particle size analyser. The yield was 60% which produced both α and β silicon
carbide. Based on microstructural study a mechanism has been proposed for formation through
liquid phase of SiC.
[5] U. Kalapathy, A. Proctor, J. Shultz
[10]
have studied that rice hull ash (RHA), a waste
product of the rice industry is its husk. The method based on alkaline extraction followed by acid
precipitation was developed to produce pure silica xerogels from RHA, with minimal mineral
contaminants. The silica gels produced were heated to 80oC for 12 hr to obtain xerogels. Silica
and mineral contents of xerogels were determined by energy dispersive X-ray (EDX) and
inductively-coupled plasma (ICP) emission spectrometers, respectively. Xerogels produced from
RHA had 93% silica and 2.6% moisture. The major impurities of silica produced from RHA at
an extraction yield of 91% were Na, K, and Ca. Acid washing prior to extraction resulted in
silica with a lower concentration of Ca (<200 ppm). However, final water washing of the xerogel
was more reactive in producing silica with lower overall mineral content (Na< 200 ppm and K<
400 ppm). X-ray diffraction patterns revealed the amorphous nature of silica xerogel.
[6] Kannigar Dateraksa, Kuljira Sujirote, and Pimpa Limthongkul
[11]
have studied on
pressureless sintering of nano-silicon carbide from rice husk. Silicon carbide obtained from
direct pryolysis of raw rice husk exhibited very fine microstructure, its sintering behavior may
resemble that of nano-silicon carbide. After milling the isostatic compaction done at 250 MPa
and then sintered at 1850o C for 6 hours and all analysis have been carried out. It is found that
prolonged sintering even at room temperature led at extensive grain growth. On the other hand,
SiC from rice husk which although composed of small grain SiC, but those grains are connected
together in the form of large agglomerate, therefore, required higher sintering temperature and
native porous structure of the rice huskstill remained for some extent after sintering.
~13~
CHAPTER 3
EXPERIMENTAL DETAILS
~14~
3. EXPERIMENTAL DETAILS
3.1 FORMATION OF SILICON CARBIDE FROM RICE HUSK
Rice husks (RH) were collected from a local rice mill with the husk dimension of 7-10 mm long,
1.5-2.0 mm wide and 0.10-0.15 mm thick. Dry raw rice husks were washed thoroughly with
water to remove the adhering soil and other contaminations present in them and then dried in the
sunlight for 24 hrs. These were designated as raw rice husk (RRH).
The chemical analysis of these washed RRH was carried out as shown in the flow chart.
Acid leaching was performed by treating the RRH with dilute HCl (1:1) in distilled water for 1
hour. It was then washed thoroughly with distilled water followed by treatment with dilute
ammonia solution (10 vol. %) for 1 hr to remove the traces of acid. The treated husk was taken
out and washed thoroughly in distilled water followed by drying in air for 24 hrs. About 5 g
samples of RRH and acid-treated rice husk (ARH) were taken in separate cylindrical alumina
crucibles and introduced into a muffle furnace for pyrolysis at different temperatures varying
from 7000 C to 11000 C at an interval of 1000 C for 2 hrs. Soaking time in static air, and weight
losses were measured after each pyrolysis by an electronic balance. Black ash (BA) and White
ash (WH), both the powders were prepared for further study.
3.2 XRD ANALYSIS
The XRD analysis conducted to detect the phases present in the silicon carbide and white ash,
which have been made from rice husk were studied by X-ray diffraction using a high resolution
PHILIPS X„Pert High Score program system, with Cu - Kα radiation (λ=1.54 A). The phases
formed were identified by insidious comparison of the recorded diffraction peaks with the ICDD
database. Instrumental broadening was correlated by using FWHM of Silicon standard. X-ray
Diffraction scans were conducted for phase present in the produced material.
Parameters
Value
Raw Data Origin
PHILIPS-binary (scan)
Start Position [°2Th.]
10.0100
End Position [°2Th.]
79.9900
Step Size [°2Th.]
0.0200
Scan Step Time [s]
0.6000
Scan Speed
2° (degree) per minute
Scan Type
Continuous
~15~
Anode Material
Cu
Voltage applied
30 kV
Current Flow
20 mA
Table 3.1 List of parameter used during XRD analysis
3.3 SCANNING ELECTRON MICROSCOPY
Microstructural characterization studies were conducted to examine distribution of reinforcement
throughout the matrix. This is accomplished by using scanning electron microscope. Silicon
carbide produced from rice husk, white ash and sintered composites of Al-1% SiC and pure
aluminum samples were metallographically polished prior to examination. Characterization is
done in etched conditions. Etching was accomplished using Keller‟s reagent. The SEM
micrographs of composites were obtained using the scanning electron microscope. The images
were taken in secondary electron (SE) mode. This analysis was done by a JEOL 6480 LV
scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) detector
of Oxford data reference system.
Figure 3.1 JEOL JSM-6480LV scanning electron microscope
~16~
Parameters
Value
Detector
Silicon
Accelerating voltage
15.00 ( kV )
Process time
5 seconds
Magnification
1000 X, 2500 X, 5000 X, 10000 X, 20000 X
Table 3.2 Parameters used during SEM analysis
3.4 CONSOLIDATION AND SINTERING
The pure aluminum powder of size 150µm has been taken and silicon carbide, made from rice
husk is mixed in mortar and then the mixed they were compacted by cold pressing hydraulic
machine of 10 mm diameter stainless steel dies with load of 3.2 tons, i.e. equivalent pressure is
400 MPa. The powders used for making cold compact weighs around 1.1 grams. The cold
compact is then sintered in a muffle furnace 100 C/min with slow heating rate up to at a
temperature of 5500 C with the holding time of 1 hour.
Parameters
Pure Aluminum
Al-1%SiC Composite
Temperature
250 C
250 C
Particle size of Al powder
150 µm
Not Calculated
Diameter of Die
10 mm
10 mm
Load Applied
400 MPa
400 MPa
Compaction Time
5 minutes
5 minutes
Weight of Green Pellet
1.0415 g
0.9050 g
Weight of Sintered Pellet
1.1003 g
0.9637 g
Table 3.3 Parameters used during compaction
Material
Theoretical
Green
Sintered
Densification
Density (g/cm3)
Density (g/cm3)
Density (g/cm3)
Parameter
Pure Aluminum
2.7000
2.6521
2.6641
0.2505
Al-1%SiC
2.7042
2.6524
2.6643
0.2297
Table 3.4 Comparison of different densities
~17~
3.5 HARDNESS MEASUREMENT
The specimens for hardness measurement were ground flat using a belt grinder. Sufficient care
was taken so that the opposite surfaces were flat and parallel to each other to ensure the accuracy
of measurements. Vickers microhardness tests were carried out on the Vickers Hardness testing
machine. The machine was calibrated using a standard test block of known hardness prior to the
hardness tests
[3] [4]
. At least ten readings were taken from each sample to get the mean value.
The microhardness was measured at minimum loads of 300 gf, 500 gf, and 1000 gf with a dwell
time of 10 seconds. The Vickers hardness has been calculated using expression:
HV =
1.854 P
d avg 2
Where, P is load in kgf (Kilogram Force) and davg =
d1 + d 2
; where, d1 and d2 are the lengths of
2
the and two indentation diagonals in millimeters. This hardness testing was done by a LECOLV700, Vickers Hardness Indenter having loading capacity range from 300 gf to30 kgf.
Figure 3.2 Vickers hardness testing machine
~18~
3.6 WEAR TESTING
A DUCOM–TR-208-M1, Ball on Plate Wear Tester, Bangalore made computerized pin on- disc
wear test machine was used for these tests. The wear testing was carried out at a different sliding
velocity with different normal loads. A cylindrical pin of size 1.1cm diameter and 2.1cm length,
prepared from composite casting, was loaded through a vertical specimen holder against
horizontal rotating disc. The rotating disc was made of Hardened carbon steel ball of diameter 50
mm and hardness of 64 HRC. The weights were measured before and after each test segment to
determine the abrasive wear loss of each sample.
Parameters
Value
Load Applied
500 g
Speed
10 rpm
Track Diameter
2 mm
Ball Diameter
4 mm
Testing Time
5 minutes
Table 3.5 Parameters used during Vickers hardness testing
~19~
CHAPTER 4
RESULT AND DISCUSSION
~20~
4. RESULT AND DISCUSSION
4.1 XRD – ANALYSIS
The phase analysis of silicon carbide (SiC) and white ash, which have been produced from rice
husk. The figures shown below are the XRD plots of both SiC and white ash. In the plot SiC all
the peaks are sharper, i.e. it represents the silicon carbide is in crystalline form and crystal sizes
have been calculated by the help of modified Scherrer formula and crystal size found in the range
of 118nm - 50nm. During phase analysis, it is found that all the sharper peaks are of SiC. But, in
the plot of white ash, there are one sharper peak of silicon oxide, i.e. material is almost
amorphous. The particle size of white ash is found in the range of 207nm – 35nm.
Silicon Carbide (SiC)
600
(111)
Crystal Size = 118nm - 50nm
Intensity (a. u.)
(110)
400
(446)
200
(114)
0
30
60
2 (Degree)
Figure 4.1 XRD plot of SiC produced from rice husk
~21~
300
White Ash
Intensity (a.u.)
Crystal size = 207nm - 35nm
200
100
0
30
2 (Degree)
60
Figure 4.2 XRD plot of white ash produced from rice husk
~22~
4.2 SCANNING ELECTRON MICROSCOPY
The chemical analysis of silicon carbide (SiC) and white ash, which has been produced from rice
husk, were studied under SEM (Scanning Electron Microscope) and further chemical analysis
has been done with the help of EDS (Energy Dispersive Spectroscopy).
4.2.1 SILICON CARBIDE
Figure 4.3 Scanned image of silicon carbide particles
Figure 4.4 EDX pattern of silicon carbide particle
~23~
Element App
Intensity Weight% Weight% Atomic%
Conc. Corrn.
Sigma
CK
11.49 0.3700
57.95
1.19
74.38
OK
1.76 0.5344
6.14
1.09
5.92
Si K
21.02 1.0922
35.90
0.96
19.71
Totals
100.00
Table 4.1 Elemental analysis silicon carbide particle
4.2.2 WHITE ASH
Figure 4.5 Scanned image of white ash particle
~24~
Figure 4.6 EDX pattern of white ash
Element App
Intensity Weight% Weight% Atomic%
Conc. Corrn.
Sigma
CK
12.86 0.4956
30.91
1.49
41.94
OK
33.96 0.8764
46.12
1.19
46.98
Si K
14.78 1.0138
17.36
0.50
10.07
Zr L
3.25 0.6905
5.61
0.55
1.00
Totals
100.00
Table 4.2 Elemental analysis of white ash
~25~
4.2.3 ALUMINUM-SILICON CARBIDE COMPOSITE
Figure 4.7 Scanned image of Al-SiC (1%) composite
Figure 4.8 EDX pattern of Al-SiC (1%) composite
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn.
Sigma
CK
0.59
0.2356
4.75
0.90
8.86
OK
11.51 1.0387
21.15
0.48
29.64
~26~
Al K
44.73 1.2008
71.01
0.79
59.02
Si K
1.06
3.09
0.17
2.47
0.6511
Totals
100.00
Table 4.3 Elemental analysis of Al-SiC (1%) composite
4.2.4 PURE ALUMINUM
Figure 4.9 Scanned image of pure aluminum
Figure 4.10 EDX pattern of pure aluminum
~27~
Element App Intensity Weight% Weight% Atomic%
Conc. Corrn.
Sigma
OK
7.38
1.0539
15.88
0.56
24.15
Al K
46.39 1.2513
84.12
0.56
75.85
Totals
100.00
Table 4.4 Elemental analysis of pure aluminum
Above figures and tables of SEM, show that there the silicon carbide particles, which have been
formed from rice husk and their chemical analysis by EDS also shows of silicon and carbon are
present in the provided sample. The SEM analysis for sintered pellets of pure aluminum and AlSiC (1%) composite have been done and shows the presence dispersed phase, i.e. silicon carbide
is homogeneously distributed in the matrix phase of aluminum and on the surface of the pellets
there are some white particles which are the traces of aluminum oxides (Al2O3), formed during
sintering process with atmospheric oxygen and pores in the grain boundaries are clearly visible
during the investigation.
4.3 HARDNESS MEASUREMENT
Applied Load
Diagonal
Diagonal
Vickers
Average
(in g)
(d1, in µm)
(d2, in µm)
Hardness
Hardness
165.3
172.9
19.5
165.6
172.7
19.4
164.9
172.1
19.6
165.2
173.4
19.4
164.5
173.1
19.5
201.5
205.9
22.3
201.9
206.1
22.2
202.4
205.1
22.3
202.0
205.8
22.3
201.7
206.5
22.3
269.4
271.5
25.4
270.0
271.9
25.3
269.6
271.6
25.3
300 g
500 g
1000 g
~28~
19.5
22.3
25.3
270.8
272.4
25.1
269.9
271.4
25.3
Table 4.5 Hardness under different load for pure aluminum
Applied Load
Diagonal
Diagonal
Vickers
Average
(in g)
(d1, in µm)
(d2, in µm)
Hardness
Hardness
151.0
149.8
24.6
151.6
149.9
24.5
152.4
148.7
24.6
151.8
150.3
24.4
150.0
150.1
24.7
176.8
176.8
29.7
175.6
176.9
29.8
176.3
176.5
29.8
177.1
176.2
29.7
176.9
176.0
29.7
252.2
249.6
29.5
250.8
248.2
29.8
251.1
249.1
29.6
253.2
247.9
29.5
250.0
248.7
29.8
300 g
500 g
1000 g
Table 4.6 Hardness under different load for Al-SiC (1%) composite
~29~
24.6
29.7
29.6
35
Pure Aluminum
Al-1%SiC Composite
Hardness (HV)
30
25
20
15
10
5
0
300 g Load
500 g Load
1000 g Load
Applied Load
Figure 4.11 Comparison between pure Al and Al-SiC (1%) composite under different load
Above plot shows the relation between applied load and hardness value (in HV Scale) sintered
pellets of pure aluminum and Al-SiC (1%) composite. It is seen that at low load, the hardness
value of both pellets show comparatively lesser value than harness at high loading conditions.
Another important observation is that hardness value of pure aluminum is lesser than hardness
value of Al-SiC (1%) composite in different loading conditions means increase in hardness due
to dispersed phase.
4.4 WEAR BEHAVIOR
4.4.1 EFFECT OF SLIDING DISTANCE ON WEAR DEPTH
Below figure shows the relation between sliding distance and wear depth of the composites at a
constant load of 4.9 N. The above figure clearly shows that change of wear depth initially high
and after a certain sliding distance the change of wear depth becomes constant. Like variation of
wear depth with load in the present case also increase in dispersed phase silicon carbide reduces
the wear rate.
~30~
Al-SiC (1%) Composite
Pure Aluminum
Wear Depth (X10^-6 m)
60
40
20
0
0
100
200
300
Sliding Distance
Figure 4.12 Plot between wear depth and sliding distance
4.4.2 EFFECT ON WEAR DEPTH WITH TIME
Below figure shows the relation between wear depth and time of the composites at a constant
sliding velocity 10 rpm. It is seen that as time of wear increases, there is increase in wear depth
and change in wear depth of composite is constant after sometime. The wear depth in case of as
pure aluminum sample is higher than in Al-SiC (1%) composite.
~31~
Pure Aluminum
Al-SiC (1%) Composite
Wear Depth (X10^-6 m)
60
40
20
0
0
100
200
Time (s)
Figure 4.11 Plot between wear depth and time of sliding
~32~
300
CHAPTER 5
CONCLUSION
~33~
5. CONCLUSION
The following conclusion may be drawn from the present work:
 The silicon carbide (SiC) powder can be synthesized from rice husk.
 The prepared SiC powder is almost crystalline particle is appeared.
 The produced white ash powder is almost amorphous and some crystalline particle of
silicon oxide appeared.
 The crystal size of prepared SiC powder is found to be 118-50 nm range.
 Cold compaction of pure Al and Al-SiC (1%) powders were done by hydraulic pressing
machine at high pressure, 400 MPa.
 There is increase in density of cold compacted pellets after sintering and densification
parameter is found to be 0.22-0.25.
 The hardness value of sintered pellet of pure aluminum and Al-SiC (1%) composite is
found to be in the range of 19-25 HV and 25-30 HV.
 Strengthening of composites is due to particle reinforcement, dispersion strengthening
and solid solution strengthening.
 The Al-SiC (1%) composite shows better wear resistance than pure Al, due to its superior
load bearing capacity.
 The wear resistance has improved significantly by addition of SiC.
~34~
CHAPTER 6
FUTURE PLAN OF WORK
~35~
6. FUTURE PLAN OF WORK
The following points may be concluded for future plan of work:
 Silicon carbide produced from rice husk can be scaled up to 100g for the further analysis.
 As prepared silicon carbide powder can be kept in liquid nitrogen, alone then it can be
mechanically ball milled for different timing and it‟s TEM, XRD, SEM and other
characterizations can be done.
 As prepared silicon carbide powder can be mechanically alloyed with aluminum/stainless
steel/copper or any other metal/alloys and it‟s TEM, XRD, SEM and other
characterizations can be done to find out the nano-metric dispersion size distribution of
SiC in the matrix.
 Above mentioned alloyed milled powders can be cold compacted at different pressure
ranges, 200-600 MPa.
 Sintering can be done under different atmosphere like hydrogen, nitrogen or argon etc.
and their impact on sintering density and densification parameter and sintering density
can be further improved up 99% by hot compacting/hot isostatic pressure (HIP) method.
 Oxidation resistance and corrosion resistance tests under different atmosphere can be
carried out.
 Above mentioned sintered pellets can be subjected to tensile, compression and impact,
hardness at high temperature tests.
 White ash having silica, produced from the process can be used for aluminum matrix
composite using stir-casting route, the produced MMC can be further characterized and
mechanical behavior like tensile strength, compressive strength, impact strength tests can
be done.
~36~
CHAPTER 7
REFERENCES
~37~
7. REFERENCES
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~38~
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~39~
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