SIGNIFICANCE OF ACTIVATION ENERGY IN PROCESS METALLURGY MASTER OF TECHNOLOGY

SIGNIFICANCE OF ACTIVATION ENERGY IN PROCESS METALLURGY  MASTER OF TECHNOLOGY
SIGNIFICANCE OF ACTIVATION ENERGY IN PROCESS
METALLURGY
THESIS SUBMITTED TO
NATIONAL INSTITUTE OF TECHNOLOGY,
ROURKELA
FOR THE AWARD OF THE DEGREE
OF
MASTER OF TECHNOLOGY
IN
METALLURGICAL AND MATERIAL ENGINEERING
BY
SANJAY RAJ
Roll No.: 211MM1366
DEPARTMENT OF METALLURGICAL AND MATERIALS
ENGINEERING,
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
May-2013
SIGNIFICANCE OF ACTIVATION ENERGY IN PROCESS
METALLURGY
THESIS SUBMITTED TO
NATIONAL INSTITUTE OF TECHNOLOGY,
ROURKELA
FOR THE AWARD OF THE DEGREE
OF
MASTER OF TECHNOLOGY
IN
METALLURGICAL AND MATERIAL ENGINEERING
BY
SANJAY RAJ
Roll No.: 211MM1366
Under the supervision of
Prof. U.K.Mohanty
&
Prof. S.K.Sahoo
DEPARTMENT OF METALLURGICAL AND MATERIALS
ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
May-2013
DEPARTMENT OF METALLURGICAL AND MATERIALS
ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
ORISSA, INDIA - 769008
CERTIFICATE
This is to certify that the thesis entitled “SIGNIFICANCE OF ACTIVATION
ENERGY IN PROCESS METALLURGY”, submitted to the National
Institute of Technology, Rourkela by Mr. SANJAY RAJ, Roll No.
211MM1366 for the award of Master of Technology in Metallurgical and
Materials Engineering, at the National Institute of Technology, Rourkela, is an
authentic work carried out by him under supervision and guidance. The
experimental work and analysis of results are original work of the student and
have not been presented anywhere for the award of a degree to the best of our
knowledge.
Prof. U.K. Mohanty
Department of Metallurgical and
Materials Engineering
National institute of technology
Rourkela – 769008
Prof. S.k.sahoo
Department of Metallurgical and
Material Engineering
National Institute of Technology
Rourkela – 769008
ACKNOWLEDGEMENT
It is an honour for us to present this project which has helped us in enhancing
our practical and theoretical skills in various metallurgical aspects. We wish to
Express our deep sense of gratitude to Prof. B.C.Ray, HOD, Metallurgical and
Materials Engineering NIT Rourkela for giving us an opportunity to work on
this project.
I am highly indebted to my guide Prof. U.K .Mohanty, Prof. S.k.sahoo, for his
Consistent encouragement, guidance and support to carry out and complete this
Project,
I would be highly obliged to extend our thanks to Mr. Uday Kumar Sahu for
his immense support and help rendered while carrying out our experiments,
Without which the completion of this project would have been at stake.
I would like to express my sincere gratitude to all the faculty members and staff
of the department for their unflinching support, inspiration, and cooperation and
providing me with all sort of official facilities in various ways for the
completion of the thesis work.
I would also like to thank all my friends & my seniors, for extending their
technical and personal support and making my stay pleasant and enjoyable.
At last but not the least; I remain really indebted to my family, my parents
instilled strength especially at times when life was tough and supported me
Throughout my difficulty period with endurance, with much love, I would like
to thank my younger brothers and sister and who with their kind and
encouraging words provided me with strong moral support.
Sanjay raj (211mm1366)
National Institute of Technology
Rourkela
Date: 2013-05-22
CONTENTS
Page No.
Abstract..........................................................................
List of Figure..................................................................
List of Tables..................................................................
Chapter-1
I
II
III
Introduction....................................................................
1
1.1 Introduction.........................................................
1.2 Objective.............................................................
2-3
3
Chapter-2
Literature Survey...........................................................
4
2.1 Introduction of blast furnace...............................
2.2 Blast Furnace Operation......................................
5-7
7
2.2.1. Reactions in the Upper Zone................
2.2.2. Reactions in the Middle Zone..............
2.2.3. Reactions in the Lower Zone................
2.3 Blast Furnace Slag.............................................
8
8
9
10
2.4.0
2.4.1
2.4.2
2.4.3
2.4.4
2.3.1. General Overview................................
10
2.3.2. Forming methods of Slag.....................
11-12
2.3.3. Slag Composition.................................
12-13
2.3.4. Slag Viscosity.......................................
14
2.3.5. Calculation of viscosity........................
15
2.3.6. Flow Characteristics of slag.................
15
Activation Energy..........................................
16
Activation energy of blast furnace slag..........
16-17
Factor affecting of activation energy..............
17-18
Methods of estimation of activation energy...
18-22
Available Literature on Estimation of Activation Energy-22, 23
Chapter-3
EXPERIMENTAL.........................................................
3.1. Sample Preparation............................................
3.2. Experimental Apparatus.....................................
3.2.1. Planetary Ball Mill..............................
3.2.2. TG-DSC..............................................
3.2.3. High temperature viscometer..............
3.2.4. High Temperature Microscope............
3.2.5. XRD Phase Analysis...........................
3.2.6. SEM Analysis.....................................
3.3. Experimental Procedure....................................
25
26
27-30
27
28
28
29
30
30
31-35
Chapter-4
RESULTS AND DISCUSSION......................................
36
4.1 RESULT......................................................................
4.1.1 Activation energy calculation...........................
4.1.2 Viscosities Measurements................................
4.1.3 XRD Analysis...................................................
4.1.4 Flow characterisation of blast furnace slag.......
4.1.5 Microstructure Analysis by SEM......................
37
37-43
43-44
44
45
46
4.2 DISCUSSION..............................................................
47
Chapter-5
CONCLUSION.................................................................
5. Conclusion............................................................
48
49
FUTURE SCOPE.............................................................
49
REFERENCES.................................................................
50-52
Abstract
A study of thermal behaviour, thermal degradation kinetics, and effect of composition on
flow characterisation of blast furnace slag is important to Understanding the flow
characteristics of blast
furnace (B/F)
slag. It
is an important
parameter
for
efficiency/productivity of a blast furnace. In the present study flow characteristics of five
different B/F slag (C/S: 1.04, 1.192, 1.107, 1.101, and 1.189) were investigated. This study
was predominantly based on the estimation of activation energy. The activation energy was
estimated using two methods: differential scanning calorimetry (DSC) and High temperature
viscometer. DSC of different slag were measured at 30-1300oC @ 2o, 4o, 6o, 8o and 10oC/min.
Activation energy was estimated from such DSC plots using Kissinger and Ozawa methods.
It was observed that activation energy is largely dependent on C/S ratio of B/F Slag – The
activation energy decreases with increase in C/S ratio. The flow characteristics of different
B/F slag were also investigated by high temperature heating microscope, X-ray diffraction
(XRD) and scanning electron microscope (SEM). The estimated IDT (initial deformation
temperature), ST (softening temperature), HT (hemispherical temperature) and FT (fusion
temperature) of different B/F slag was shown in table. Phase analysis of XRD and SEM
micrographs support the results of flow characteristics measured by heating microscope.
Keywords: Activation Energy, DSC, Viscosity, B/F slag, heating rate, XRD.
i
List of Figures
Figure no 2.1: Schematic diagram showing Blast Furnace Process.
Figure no 2.2: Schematic sectional diagram of the internal zones in a blast furnace.
Figure no 3.1: Coning and Quartering.
Figure no. 3.2: A four station Planetary Ball Mill
Figure no.3.3: Simultaneous Thermo Analysis (TG-DSC or TG-DTA) in wide temperature
range
Figure no.3.4: VIS 403 Rotating High Temperature Viscometer.
Figure no 3.5: Pictorial view of Leitz heating microscope.
Figure no 3.6: X-ray Diffraction Machine
Figure no.3.7: Scanning electron microscopic Machine (SEM).
Figure no. 4.1: DSC curves of powdered slag samples (a), (b), (c), and (d).
Figure no 4.2: Activation Energy vs. C/S ratio plot.
Figure no 4.3: Plot between Activation Energy vs. MgO%
Figure No-4.4.Viscosity vs. Temperature graph.
Figure no 4.5: .XRD pattern of slag sample.
Figure no 4.6- flow characteristic image of sample observed through Leitz Heating
Microscope
Figure 4.7 (a) SEM micrographs at 500 magnifications of powder sample, (b) SEM
micrographs at 500 magnification of sample no 1 whose C/S ratio is 1.192.
ii
LIST OF TABLES
Table 2.1: Chemical Composition of Industrial Blast Furnace Slag.
Table 2.2: Comparative values of viscosity of some liquids
Table 3.1: Chemical composition (wt. %) of different blast furnace slag
Table 4.1: Peak temperature of different obtained from DSC curve.
Table 4.2: Different DSC analysis plots by (a) Kissinger (b) Ozawa methods for the blast
furnace slag studied
Table 4.3.Tabulation of Activation Energy by different methods and C/s ratio
Table 4.4: Tabulation of Activation Energy and MgO% by different methods
iii
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Chapter-1
INTRODUCTION
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1. INTRODUCTION
The iron and steel slag that is generated as a by-product of iron and steel manufacturing
processes can be broadly categorized into blast furnace slag and steelmaking slag .Iron and
steel slag refers to the metal manufacturing slag [1,2] that is generated during the process of
manufacturing iron and steel products.
Literature study reveals blast furnace slag which is recovered by melting separation from blast
furnaces [3] that produce molten pig iron. It consists of non-ferrous components, contained in
the iron ore together with limestone as an auxiliary materials and ash from coke (CaO, SiO2,
MgO, Al2O3, TiO2, FeO, K2O,).Approximately 290 kg of slag is generated for each ton of pig
iron. When it is rejected from blast furnace, the slag is in molten at a temperature of
approximately 1,5000c. Depending on the cooling method used, it is classified either as aircooled slag or granulated slag.
During iron making the blast furnace is a complex high temperature counter current reactor in
which iron bearing materials (ore, sinter/pellet) and coke are alternately charged along with a
suitable flux to create a layered burden in the furnace. The iron bearing material layers start
softening and melting in the cohesive zone under the influence of the fluxing agents at the
prevailing temperature which greatly reduces the layer permeability that regulates the flow of
materials (gas/solid) in the furnace. It is the zone [1] in the furnace bound by softening of the
iron bearing materials at the top and melting and flowing of the same at the bottom. A high
softening temperature coupled with a relatively low flow temperature would form a narrow
cohesive zone lower down the furnace. This would decrease the distance travelled by the liquid
in the furnace there by decreasing the Silicon pick-up On the other hand the final slag that
trickles down the Bosh region to the Hearth in the furnace should be a short slag that starts
flowing as soon as it softens. Thus activation energy [4, 5] behaviour of blast furnace slag is
important parameter to evaluate the flow characteristics of slag.
Activation Energy detects the stability of main constituents. A lower value of that energy
(constituents’ energy) put the relative value of Activation Energy. Activation energy gives an
idea about the optimum reaction conditions in process chemistry, it gives an idea about thermal
stability and the expected lifetime of a slag to be kept at a certain temperature or it provides
information in quality research. The activation energy of the thermal decomposition [6]
reaction of the relative bond strengths within the molecules studied.
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Keeping the above in mind, to obtain objective of this experiment we collected Blast furnace
slag from Rourkela steel plant contained at different heat (over a time period) and then
determined the chemical composition of slag. In addition to employing three different
experimental methods used to determine the activation energy of blast furnace slag.
Firstly used generalised Kissinger and Ozawa equation [7], which is derived from Arrhenius
Equation, apply a range of approximations for the temperature integral. In which a simplified
assumption that the transformation rate during a reaction is the product of two functions, one
depending solely on the temperature, T, and the other depending solely on the fraction
transformed ᾀ. It calculated with the help of DSC measurements instruments at slow heating
rates (2, 4, 6, 8, 100C/min.). Other than this methods Ozawa [8] method applied to analytical
study of Activation Energy of slag. And also plotting the graph between Activation Energy vs.
C/S ratio and also vs. MgO % this gives idea about variation of Activation Energy with these
values Second phase of the experiment involve calculation of activation energy of slag by
viscosity meter machine which depends upon the viscous property of the slag. Viscosity of slag
increases by the presence of silica and alumina whereas the presence of calcium oxide reduces
the viscosity which is function of temperature of melt [9].
Next work in this project is to analyse crystallization behaviour of diffused slag of different
chemical composition. It related with Activation Energy of slag. We therefore tested by several
determination techniques XRD for phase analysis, SEM for morphological study, High
Temperature Heating Microscope to determine flow temperature of slag .the quality or
consistency of a slag and identified the unknown materials in slag.
1.2 Objective
Objective of this work is to measure the activation energy of the blast furnace slag, collected
from different sources with varied chemical composition and to correlate the activation energy
with the chemical composition of the slag. This would provide a basis of understanding the
variation of activation energy of the slag. Objectives of this thesis are 1. Determination of Activation energy of blast furnace slag by two techniques.
A. TG-DSC.
B. Viscosity measurements by High Temperature Viscometer.
2.
Phase Analysis by X-ray Diffraction Techniques (XRD) to understand the variation in
activation energy.
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Chapter-2
LITERATURE SURVEY
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2.1 Introduction of Blast Furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial
metals, generally iron. The blast furnace is fundamentally a vertical steel shaft or stack varying
in height from 24 to 33 meters with a diameter at the hearth of about 8.5 meters. Generally the
total volume for production of pig iron is more than 1400 cubic meters. And steel structural
cylinder is lined with hard-fired alumina refractory brick to a depth of approximately 1.2
meters. The total weight of the furnace is approximately 9000 metric tons. The blast furnace
has charging arrangements at the top and a means of running off the pig iron and slag at the
bottom.
Element of blast furnace construction- the main unit consists of
(1) The hearth (Lower section ),
(2) The bosh (Middle section),
(3) The stack and charging mechanism (Upper section).
The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into
liquid iron called "hot metal". The blast furnace is a huge, steel stack lined with refractory
brick, where iron ore, coke and limestone are dumped into the top, and preheated air is blown
into the bottom. The raw materials require 6 to 8 hours to descend to the bottom of the furnace
where they become the final product of liquid slag and liquid iron. These liquid products are
drained from the furnace at regular intervals. The hot air that was blown into the bottom of the
furnace ascends to the top in 6 to 8 seconds after going through numerous chemical reactions
[3]. Once a blast furnace is started it will continuously run for four to ten years with only short
stops to perform planned maintenance.
The sources of iron are its ores in which iron is contained mainly as its oxides such as hematite
(Fe2O3) or magnetite (Fe3O4) and sometimes in small proportions as hydroxides and
carbonates. Hematite constitutes the largest portion of all the ores used for blast furnace iron
making. When pure, hematite contains about 70% and magnetite about 72.4% of iron. But in
actuality, the iron content of the ores ranges from 50-65% for rich ores and 30-50% for lean
ores and the remainder is gangue which consists mostly of silica and alumina as well as minor
amounts of moisture and chemically- combined water.
Iron Ore processing for the Blast- Before introducing the blast furnace reaction it is
important to know the Iron Ore Processing for the Blast Furnace. It is based on flowing steps
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Mining Iron Ore – Ores have been produced subsequently wherever erosion exposed suitable
structures to the particular conditions of climate, topography, tectonic stability required for the
long process. Mining iron ore begins at ground level. Taconite is identified by diamond drilling
core samples on a grid hundreds of feet into the earth. Taconite rock comprises about 28
percent iron; the rest is sand or silica. These samples are analyzed and categorized so that
mining engineers can accurately develop a mine plan.
Crushing the Ore - The crude taconite is delivered to large gyrator crushers, where chunks as
large as five feet are reduced to six inches or less. More than 6,000 tons of taconite can be
crushed in one hour. The crushed material is transferred by belt to an ore storage building,
which holds up to 220,000 tons of taconite. An apron feeder sends the ore to the concentrator
building for grinding, separating, and concentrating.
Concentrating - The crude taconite is now roughly the size of a football or smaller. A series of
conveyor belts continuously feed the ore into the large 27-foot-diameters, semi-autogenously
primary grinding mills. Water is added at this point to transport it (94 percent of the water is
recycled, while the rest is lost through evaporation .The product is called “filter cake”, and is
now ready for mixing with the Binding agent .Once the filter cake is complete; it is deposited
into a surge bin. It then travels onto a feeder belt and from there to a conveyor where betonies,
a bonding agent, are added. Betonies are clay from Wyoming used to help iron ore concentrate
stick together when rolled into pellets. About 16 pounds of Betonies are added to every ton of
iron ore concentrate. Small amounts of limestone (1%) are also added and mixed with the
concentrate at this point. Limestone is added to meet the requirements of steel customers in the
blast furnace process.
Palletizing - A pellet plant contains a series of balling drums where the iron ore concentrate is
formed into soft pellets, in much the same manner that one rolls a snowball, to make a pellet
about the size of a marble (between 1/4" and 1/2"). Pellets are screened to meet the size
specification, with undersized or oversized pellets crushed and returned to the balling drums.
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Figure 2.1: Schematic diagram showing Blast Furnace Process.
2.2 Blast Furnace Operation
In blast furnace operation, the charge components ore, flux, and cock are carried in successive
layers and in carefully calculated proportions to the top of the furnace [3]. They are introduced
into the furnace through the bell valves and the stack is loaded to a height 1.8 to 3 meters above
the valve system. Air is preheated to about 1000oC in heaters attached to the furnace. It is then
blown in through vents spaced around the furnace near its lower end, leaving enough space for
the slag and molten iron to collect in the bottom below them. It is this blast of air that gives
furnace its name.
The blast furnace operates on a counter current principle; the charge moves slowly down in the
furnace and current of gas that reacts with this charge moves upward. This operation is
reduction smelting.
Blast furnace reaction gives three zone reactions [10].
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2.2.1 Reactions in the lower zone
In the Bosh area of the furnace where the burden starts to soften and melt, direct reduction of
the iron [and other] oxides and carbonization by the coke occurs at 1,000-1,600 C. Molten iron
and slag start to drip through to the bottom of the furnace Between the bosh and the hearth are
the tuyeres [water cooled copper nozzles] through which the blast combustion air, preheated to
900-1,3000C, often enriched with oxygen is blown into the furnace [3, 10].
Immediately in front of the tuyeres is the combustion zone, the hottest part of the furnace,
1,850-2,200 C, where coke reacts with the oxygen and steam in the blast to form carbon
monoxide and hydrogen [as well as heat] and the iron and slag melt completely.
Fe + CO = Fe + CO2
C +CO2 = 2CO
Lower zone [10] is higher temperature zone in which reduction of Si and Ti occurs while the
oxides of Mg, Ca and Al are highly stable such that they are reduced to a negligible amount. At
the high temperature the reduction of Mn from its monoxide takes place which is quiet difficult
and Cr and V behaves in similar manner as Mn.
MnO+ C = Mn + CO
SiO2 + 2C = Si + 2CO
S + CaO + C = CaS + CO.
2.2.2 Reactions in the Middle Zone.
In the Middle part of the blast furnace, indirect reduction of the iron oxides (wustite) by
carbon monoxide and hydrogen occurs take place at 700-1,000 C.
The ratio of CO/CO2 gas is 2.3, a value exhibiting equilibrium with Fe-FeO (Eq.) The indirect
reduction will be more if the height of this Zone (800-1000°C temperature zone) is large since
the contact time is longer between gas/solid.
This zone may occupy 50-60% of the furnace volume. The extent of this zone is important
because the Wustite should be given as much opportunity as possible for getting reduced
indirectly. Another reaction of importance which occurs in the middle zone is the water-gas
shift reaction:
CO2 + C = 2CO – 41210 cal.
CO + H2O = CO2 + H2
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2.2.3 Reactions in the Upper Zone.
In the upper or preheating zone of the furnace, free moisture is driven off from the burden
materials and hydrates and carbonates are disassociated. The temperature of the gas ascending
from the middle zone falls rapidly from 800-10000C to 100-2500C and that of solids rises from
ambient to 8000C in this zone Carbon deposition and Partial or complete reduction of hematite
and magnetite to their lower oxides occurs
2CO = CO2 + C.
Figure 2.2: Schematic sectional diagram of the internal zones in a blast furnace.
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2.3 Blast Furnace Slag
2.3.1. General OverviewBlast furnace slag as “the non-metallic product consisting essentially of silicates and alumino
silicates of calcium and other bases that is developed in a molten condition simultaneously with
iron in a blast furnace ” Iron and steel slag refers to the type of metal manufacturing slag that is
generated during the process of manufacturing iron and steel products. The term "slag"
originally referred to slag produced by metal manufacturing processes, however it is now also
used to describe slag that originates from Molten waste material when trash and other
substances are disposed of at an incinerator facility.
In the production of iron, the blast furnace is charged with iron ore, flux stone (limestone
and/or dolomite) and coke for fuel. Two products are obtained from the furnace: molten iron
and slag. The slag consists primarily of the silica and alumina from the original iron ore,
combined with calcium and magnesium oxides from the flux stone. It comes from the furnace
in a molten state with temperatures exceeding 1480°C (2700°F).
It play important role as they protect the metal and remove undesirable impurities. Usually a
liquid slag layer covers the molten metal and carries out the following functions [3].
(i)
It seals off the metal from oxygen and prevents oxidation
(ii)
It removes undesirable elements (e.g. S, P) from the metal
(iii)
It helps to remove non-metallic inclusions (e.g. by flotation etc)
(iv) It reduces the heat losses from the metal surface and prevents the “skull formation” and
(v) In the continuous casting of steel liquid slag infiltrates continuously between the metal and
mould and it provides both lubrication and control of the heat extraction
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2.3.2. Forming methods of Slag
There are four distinct methods [2, 3] of processing the molten slag. Which is air cooled,
expanded, pelletized and granulated. Each of these methods produces a unique slag material.
This is given below of this topic.
1. Air-Cooled slag (Atmospheric cooling)
Air-Cooled Blast Furnace (ACBF) Slag as defined in ASTM C 125 [2] is: “The material
resulting from solidification of molten blast-furnace slag under atmospheric conditions.
Subsequent cooling may be accelerated by application of water to the solidified surface.”The
solidified slag characteristically has a vesicular structure with many non-connected cells.
ACBF slag crushes to angular, roughly cubical pieces with a minimum of flat or elongated
fragments. The rough vesicular texture of slag gives it a greater surface area than smoother
aggregates of equal volume and provides an excellent bond with Portland cement and high
stability in bituminous mixtures.
2. Expanded slag (Controlled water cooling)
Controlled quantities of water are used to accelerate the solidification process of molten blast
furnace slag, resulting in a low density material. The solidified expanded slag is crushed and
screened for use as a lightweight structural aggregate. It is angular and cubical in shape, with
negligible flat or elongated particles. Due to the action of the water and resulting steam on the
solidification process, the open cellular structure of the particles is even more pronounced than
particles of air cooled blast furnace slag.
3. Pelletized (Accelerated cooling)
In the pelletizing process, a molten blast furnace slag stream is directed onto an inclined
vibrating feed plate where it is quenched with water. The addition of water at this stage causes
the slag to foam. While in this expanded pyroplastic state the slag stream flows from the feed
plate onto a revolving finned drum. As the drum rotates, the fins repeatedly strike the slag
stream with sufficient force to propel the slag into the air, dispersing it and forming spherical
droplets. These droplets, or slag pellets, freeze rapidly to a solid state as they are launched
through the air away from the pelletizer. It has a unique internal cellular structure within each
slag pellet. This cellular structure (many voids only detectable with the aid of an electron
microscope) is contained within a smooth spherical skin. The combination of these
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characteristics leads to the formation of a low density aggregate, with diverse applications as a
construction material [3].
4. Granulated (Water quenching)
The most common process for granulating blast furnace slag involves the use of high water
volume, high pressure water jets in direct contact with the molten blast furnace slag at a ratio of
approximately 10 to 1 by mass. The molten blast furnace slag is quenched almost immediately,
forming a material generally smaller than a #4 sieve.
2.3.3. Slag Composition
The principle constituents of blast furnace slag are silica, alumina, calcium and magnesia
which comprise 95% of slag’s total makeup. Minor elements include manganese, iron and
sulphur compounds as well as trace quantities of several others. Analysis of most blast furnace
slags falls within the ranges that are shown below. The major oxides do not occur in free form
in the slag. In air-cooled BF slag, they are combined to form various silicate and
aluminosilicate minerals such as melilite, merwinite, wollastonite, etc., as found in natural
geological forms. In the case of granulated and pelletized slag, these elements exist primarily
as glass. The chemical composition [11] of slag from a given source varies within relatively
narrow limits since raw materials charged into the furnace are carefully selected and blended
The major constituents of the slag include the following,
Major elements are:
 SiO2
–
32-42% ,
 Al2O3 –
7-16% ,
Minor elements are:
S
FeO
–
1-2%
–
1-1.5%
 CaO
–
32-45% ,
MnO –
0.2-1.0%
 MgO
–
5-15% ,
TiO2 –
1.01%
K2O+Na20 –
1%
Trace Oxides –
0.5%
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In this project work I have taken 5 sample of blast furnace slag in which slag constituents are.
Sample
SiO2
Al2O3
CaO
MgO
TiO2
Na2O
K2O
Fe2O3
C/S
1
31.86
16.92
38
10.23
0.7
0.98
0.48
0.66
1.192
2
33.25
16.31
36.84
10.56
0.82
1.1
0.52
0.54
1.107
3
32.48
17
35.78
11.88
0.55
1.1
0.52
0.6
1.101
4
31.08
17.04
36.96
11.22
0.5
1.8
0.88
0.40
1.189
5
34.32
16.58
36.2
9.57
0.55
1.36
0.82
0.53
1.054
Table2.1. Chemical Composition of Industrial Blast Furnace Slag
2.3.4. Slag Viscosity
Viscosity involves transporting one layer of liquids over another layer i.e. flow phenomena. In
the study of blast furnace slag various important phenomena occurs such as the heat transfer,
mass transfer and the chemical reactions between the slag and metal. And it depends on the
flow phenomena of the slag hence study of viscosity is important [12]. Slag viscosity also
determines the slag-metal separation efficiency, and subsequently the metal yield and impurity
removal capacity.
In blast furnace iron making process, slag viscosity is a very important physical property,
because it influences the furnace operation in many ways. The viscosity of the slag affects the
degree of desulphurization, coke consumption, smoothness of operation, gas permeability, heat
transfer etc.
The blast furnace slag behaves as a Newtonian fluid due to the presence of shear stresses
applicable on the slag [13, 14]. This shear stress is the iconic and molecular structure that
governs the viscosity of the blast furnace slag. Viscosity of a slag is strongly influenced by the
chemical composition, structure and the temperature. Thus, for smooth furnace operation, it is
always advisable to have a low viscosity slag which helps in smooth transport of ions from the
slag and metal interface to the liquid slag [15].
The calculation of viscosity by Arrhenius equation [16] mainly depends on temperature and
chemical composition.
ή =A.exp (E/RT).
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Where ή is called the kinematic viscosity of slag and has the dimensions of L2 t-1. The
kinematic viscosity is also referred to as the momentum diffusivity of the fluid, i.e. the ability
of the fluid to transport momentum. In the metric system, the unit of viscosity is the Poise
(1P=1 g cm-1 s-1), which is subdivided to 100 centipoise (cP). And A = Pre – exponential
term. E= Activation energy for viscous flow. R = Gas constant. T=Temperature, in absolute
scale.
Slag viscosity is a transport property that relates to the reaction kinetics and the degree of
reduction of the final slag. The viscosity of the slag controls the aerodynamics such as the gas
permeability and the heat transfer this in turn affects the efficiency of the blast furnace.
The viscosity of the blast furnace slag governs the reaction rates in the furnace by its effect on
the diffusion of ions through the liquid slag to and from the slag metal interface.
A process of depolymerisation lowers the viscosity of the slag. An increase in basicity
decreases the viscosity of the blast furnace slag breaking the three dimensional silicate network
in to discrete anionic groups thereby causing depolymerisation.
The component of slag namely silica and alumina increase the viscosity whereas the presence
of calcium oxide reduces the viscosity. The melting zone of slag determines the cohesive zone
of blast furnace and hence the fluidity and melting characteristics of slag play a major role in
determining the blast furnace productivity.
Fluid
Density ( Kgm-3)
Temperature
Viscosity
(0C)
(Kgs-1 m-1)
1550,
6.70×10-3
7.21×103
1600
6.10×10-3
7.16×103
High-iron slag
1200
3.50×10-1
4.50×103
Low-iron slag
1500
5.00×10-1
3.50×103
Molten iron
Table 2.2 Comparative standard values of viscosity of some liquids
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2.3.5: Calculation of viscosity
In our experimental work calculation of viscosity of blast furnace slag is done by VIS 403
Rotating High Temperature Viscometer which has viscosity range 101-108dPas, Max
Temperature 1700oC, crucible material-PtAu5%, max speed-800 rpm, Torque range 0150mNm, and Atmosphere -air or inert gas, purge gas.
2.3.6: Flow Characteristics of Blast Furnace Slag
High temperature microscope is used to determine flow characteristics of slag sample. It has
got four characteristics temperatures to be studied:

Initial deformation temperature (IDT) - Initial deformation temperature is the
temperature at which the first rounding up of the edges of the cube-shaped sample
specimen takes place. In fact this is the temperature at which the first sign of the change
in shape appears. Rheologically this temperature symbolizes the surface stickiness of
the slag.

Softening Temperature (ST):- It is the temperature at which the outline of the shape
of the sample starts changing and is reported as the temperature at which the sample
shrinks by one division or the temperature at which the distortion of the sample starts.
Rheologically this temp symbolizes the start of plastic distortion.

Hemispherical Temperature (HT):- It is the temperature at which the sample has
fused down to hemispherical shape and is measured as the temp at which the height of
the sample is equal to the half of its base length. This is defined as the fusion point or
the melting point in Germen Industrial Standards 51730 [10]. Rheologically this
temperature symbolizes the sluggish flow of the slag.

Flow Temperature (FT):- It is the temperature at which the sample liquefies and is
reported as the temperature at which the height of the sample is equal to one-third of the
height that it had at HT (hemispherical temperature). Rheologically this temperature
symbolizes the liquid mobility of the slag.
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2.4.0 Activation energy and its importance
In reaction point of view Activation energy is a term introduced in 1889 by the Swedish
scientist Svante Arrhenius that is defined as the minimum energy that must be input to a
chemical system, containing potential reactants, in order for a chemical reaction to occur.
Activation energy may also be defined as the minimum energy required starting a chemical
reaction. The activation energy of a reaction is usually denoted by Ea and given in units of
kilojoules per mole.
The Arrhenius equation gives the quantitative basis of the relationship between the activation
energy [4] and the rate at which a reaction proceeds. From the Arrhenius equation, the
activation energy can be expressed as
Where A is the frequency factor for the reaction, R is the universal gas constant, T is the
temperature (in Kelvin), and K is the reaction rate coefficient [17].
In metallurgical point of view the activation energy give the idea about thermal decomposition
reaction of the relative bond strengths within the molecules studied.
The additional energy required to break the bond and to start the reaction is also called
activation energy.
In another point of view the content E, called activation energy, is often interpreted as the
energy barrier opposing the reaction.
2.4.1: Activation energy of blast furnace slag
Slag is the by-product of steel making process in which the component of the pig iron and
steel-scrap are modified in order to produce steel.
During production of pig iron it should be important to know the idea about the activation
energy of blast furnace slag in following point of view.
 It play important role in adhesion of ash particles to the walls of a reactor,
 It give an idea about solidification of slag,
 Slag and metal separation temperature and time calculation,
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 Calculation of heat content change of slag,
 Representation of endothermic and exothermic reaction [18].
 It gives the idea about recrystallization temperature [18].
 Energy barrier of slag flowing properties,
 Movement of flow units involves breaking of Si-O bonds (Heat of dissociation) [19].
 Time taken to the reaction of slag formation [17].
 Viscosity property of slag [20].
 The energy required to move one layer of silicate group with respect to the other layer
.i.e. the number of ionic bonds which have to be broken or distorted in order to enable
the group to move,
 It gives the melting point of slag [21].
 It gives the idea about nucleation and grain growth [22].
2.4.2: Factor affecting the activation energy
Activation energy of blast furnace slag affected by

Temperature - At the high temperature region of furnace, slag initially has highly
active i.e. have more energy of slag practical means have less activation energy
,similarly those practical which has less temperature has more activation energy. This is
due to the Increase in speed of particles do there are more successful collisions with
particles having the required activation energy.

Concentration and pressure - If the concentration or pressure of a slag is high, there
will be more particles within a given space and therefore collision of particle more, so
the rate of reaction also increases which give flow characteristics of slag is high means
activation energy become less.
 Physical state - for the calculation of activation energy of slag, particle size must be in
power shape because if one of the slag particles is in large shape then the reaction can
only take place on the surface of the solid which will not give correct result in
calculation of activation energy of slag. The smaller the size of the slag particles, the
greater the area that the reaction can take place is high.

Composition of the slag.
Within the range of compositions study, the net-work
breaking ability of Mg, Al, Ca, Si oxides are different which give the different
activation energy.
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2013
Percentage of CaO - Those slag sample which has more percentage of CaO is more
basicity [21] so it also increase the liquidus temperature (Tliq )[4] of the slag and thereby
reduce the amount of liquid slag formation which result in high activation energy of
slag.

Structure of melted slag - Since thermodynamics gives a description of bond strength
which is related with activation energy of slag.
 Basicity of slag - Some slag have a highly basicity (CaO/SiO2 >2) and consequently the
Si4+ ions are predominantly in the form of monomers. Which give the high activation
energy of slag [2].

Surface tension – These properties predominantly depend upon surface and not on the
bulk, in mixtures, the constituents with the lowest surface tension (slag containB2O3)
will tend to occupy the surface layer. When there are more than two surface-active
components in the slag (CaF2 and B2O3) there will be competition for the surface sites
which alter the activation energy of slag.
2.4.3: Numerical Methods of Estimation of Activation Energy
A general objective of the analysis and prediction of thermally activate reactions is the
derivation of a complete description of the progress of a reaction that is valid for any thermal
treatment as a [23, 24]

Isothermal by linear heating and

Non-isothermal treatment
Many researchers make the simplifying assumption that the transformation rate during a
reaction is the product of two functions, one depending solely on the temperature T, and the
other depending solely on the fraction transformed, α
(1)
Temperature dependent function follows Arrhenius type dependency,
KT = k0 exp
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The quantity α is the degree of conversion, f(α) is a mathematical function whose form depends
on the reaction types and KT is the temperature dependent rate constant , K0 is pre exponential
factor , E is the activation energy and R is the gas constant, 8.314 J/mol K .
From (1) and (2) this give basic equation is,
(3)
For isothermal conversion:
It has been known that for analysis linear heating experiment (heating at constant rate), highly
accurate and reliable activation energy analysis methods [25] can be obtained by applying
accurate approximations of the temperature integral so from equation no. (3) Is integrated by
separation of variables.
Where Tf is the temperature at an equivalent (fixed) state of transformation, to be the start
temperature of the linear heating experiment, and β is the heating rate. The integrals on the
right hand side are generally termed temperature integrals (or ‘Arrhenius integral’). We can
write Eq. 4 as:
(5)
Where I(To), I(Tf) are the temperature integrals on the right hand side of Eq. 4. The derivation
proceeds by noting that of the last two terms, one is much smaller than the other
And hence I (To), the smaller term in above equation (5) so we can neglect
Thus it follows that,
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Through applying a suitable approximation for the temperature integral on the right of the latter
equation a range of well-known and lesser known isoconversion methods for activation energy
analysis can be derived [25]. These methods include the Kissinger method [26], the Kissinger–
Akahira–Sunose (KAS) method [21, 27] (also termed the generalised Kissinger method), All of
these methods involve the plotting of 1/Tf vs. a logarithmic function which depends on the
heating rate and often the temperature and all of these methods neglect the last integral term in
Eq. 4 ( I(To) in Eq. 5).
The general equation is:
Where k is a constant depending on the approximation of the temperature integral employed
[28], and A and C are constants. For the above mentioned methods k equals to 0 (FWO
method), 2 (KAS method) and 1.9 to 1.95 for the methods by Starink [26].
From equation (7) we determine the activation energy E and linear fit intercept C which gives
frequency factor.
Another method related with isothermal conversion.
When we consider f( ) = (1
)n, where n is called the reaction order in analogy with
homogeneous reactions. When we start from isothermal measurements at different
temperatures, we can calculate Ea and A from resulting straight line when using logarithmic
form of equation (3).
–
This calculation is repeated for different values of n and the value that gives the highest
correlation coefficient is considered to be the best value. The slope and onset give us –Ea/R and
ln K, respectively.
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For Non-isothermal conversion:
For linear heating rate
, considered for non isothermal measurements,
The basic equation
can be written as
,
Restricting the function to f ( ) = (1
)n
Taking logarithms on both sides we get
–
Kofstad [39] transforms this equation to
a/RT
(10)
The value of “n” gives the best correlation coefficient for the resulting straight line is used, and
from the slope we can calculate the activation energy E a.
Ingraham and Marrier [10] complicate the formulae by suggesting that the frequency factor
A is a linear function of temperature (A=A/
T), but they restrict the value of n = 0, zero
order reaction, so equation (9) can then be transformed to
/
(11)
The methods of Kofstad , INgraham and Marrier give us a value of n ,
These three methods use one single measurement and allow us to calculate E a from the slope of
straight line for a range of value of .
Here, it should be noted that changing the heating rate and thus the temperature at which the
reaction takes place can change the reaction mechanism and thus the activation energy.
Therefore methods based on only a single run (one heating rate) are disapproved of by most
researchers.
Modulating heating rates
In modulating heating rate methods, a sinusoidal temperature is superimposed on top of a
conventional heating profile. This working methods is equivalent to temperature – modulated
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DSC, and as a fact, both techniques were devised by Mike reading. The rate of weight loss
responds to the temperature oscillations and the use of discrete Fourier transformation allows to
calculate the kinetics parameters Ea and A on a continuous basis, making possible the study of
the decomposition kinetics as a function of time, temperature and conversion factor, without
any assumptions about the reaction mechanism (Model free calculations). The software
calculates Ea on the basis of the following equation,
Ea = R(T2
A/ 2)L
2A/
(12)
Where Ea, R and T have their normal meaning, A/ is the temperature amplitude of the applied
sinus profile and L for peak and valley differentiation,
2.4.4: Available Literature on Estimation of Activation Energy of blast
furnace slag.
The calculation and the meaning of activation energy is always a subject for animated
discussions at thermal analysis meeting. All this interested lies in the fact that the value of the
activation energy can give an idea about the optimum reaction conditions, thermal stability, and
the expected lifetime of a slag to be kept at a certain temperature. So reaction kinetics has
always been a point of interest for researcher: as early as 1889 S. Arrhenius won first Nobel
Prize in chemistry and in this field many more researchers worked.
Borham, B. M. et al [17] studied the urea nitrate by differential thermal analysis (DTA) curves
using the Murray and White equation and various other reaction rate equations and An average
activation energy ΔE‡ of 31.7 ± 10.0 kcal/mole was calculated and they have shown that These
results illustrate the pronounced effect of self heating on calculation of activation energies. The
Kissinger method of calculating the reaction order developed for endothermic DTA peaks
produced good results when applied to the present DTA study.
Moynihan, C. T., et al [20]. Studied the activation energy ΔH for structural relaxation in the
glass transition region which determined from the heating rate dependence of the glass
transition
temperature Tg or
the
cooling
rate
dependence
of
the
limiting
fictive
temperature T′f measured using DSC or DTA.
Keuleers, R. R., J. F. Janssens, et al [23] comparison the effective methods for calculation of
activation energy for the thermal decomposition of chemical compounds They have studied for
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the comparative study of different measurement and calculation procedures for the thermal
decompositon of Mn(Urea)2Cl2.
Starink, M. J, et al studied the Model-free iso-conversion methods which were most reliable
methods for the calculation of activation energies of thermally activated reactions and a large
number of these isoconversion methods have been proposed in the literature [24]. Type A
methods such as Friedman methods make no mathematical approximations, and Type B
methods, such as the generalised Kissinger equation [4]. And they found that accuracy of
determination of transformation rates is limited, and type B methods will often be more
accurate than type A methods.
Homer E. Kissinger et al [18] studied the Variation of Peak Temperature with Heating Rate in
Differential Thermal Analysis and found that Changes in heat content of the active sample are
indicated by deflections shown by a line representing the differential temperature. It is
conventional to represent an endothermic effect by a negative deflection and an exothermic
effect by a positive deflection. The deflections, whether positive or negative, are called peaks.
Masashi Nakamoto et al [29] studied the viscosity of molten slag with low melting point to
develop an improved blast furnace operation at lower temperature such as 1673 K. They
measured the viscosities of molten CaO- SiO2-MgO-Al2O3 slag by rotating cylinder method
and compared with the results of the model developed. They showed that slag with composition
35% Al2O3-43.1% CaO-7.5% MgO-14.4% SiO2 has melting temperature below 1673 K and
has a viscosity less than 0.6 Pa.s below 1673 K.
Y.S. Lee et al [15] studied the influence of MgO and Al2O3 contents on the viscosities of blast
furnace slag containing FeO. The viscosities of CaO-SiO2-Al2O3-MgO-FeO slag were
measured under conditions of C/S 1.35-1.45, 10-18% Alumina, 3.5-10% MgO and 5% FeO.
They found that on increasing Al2O3 content, the viscosity of the slag increased at fixed C/S
and MgO content. The viscosity of the slag showed a minimum value at around 7% MgO at
temperatures above 1723 K. However, it was not significantly changed with varying MgO
content.
Wang, Zhong-jie, et al, [30] studied the crystallization process of glass ceramics prepared
from a mixture which was composed of nickel slag, blast furnace slag and a small amount of
quartz sand. The crystallization behaviour was studied by differential scanning calorimetry
(DSC), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM).
They found shown that the radial crystals were observed when the glass was heated up to
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820 °C. By XRD analyzing, the spherical crystals and radial crystals were likely to be the
crystals of Diopside (CaMg(Si,Al,Fe)2O6) and Hedenbergite (CaFe(Si,Al,Fe)2O6).
D. Ghosh V.A. Krishnamurthy, et al [31] studied the application of optical basicity to
viscosity of high alumina blast furnace slag. In which he found that Experimental
measurement of slag viscosity requires high temperature equipment and is time consuming
and Viscosity of a slag is strongly influenced by the chemical composition, structure and the
temperature and found that The basic oxides namely lime, magnesia, titania are the providers
of oxygen, act as network breakers and result in depolymerisation of the melt.
Gan, Lei, et al [9] studied the continuous cooling crystallization kinetics of molten blast furnace
slag. Activation Energy obtained is much higher during cooling than that yielded during heating.
Result show that akermanite and gehlenite are the major minerals in the continuous cooled
crystalline blast furnace slag were investigated by means of X-ray diffraction
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Chapter-3
EXPERIMENTAL DETAILS
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3. Experimental
3.1. Sample Preparation:
Coning and quartering sampling technique used, which is the reduction in size of a granular or
powdered sample, by forming a conical heap which is spread out into a circular, flat cake. The
cake is divided radically into quarters and two opposite quarters are combined. The other two
quarters are discarded. The process is repeated as many times as necessary to obtain the
quantity desired for some final use (e.g. as the laboratory sample or as the test sample). If the
process is performed only once, coning and quartering is no more efficient than taking alternate
portions and discarding the others. [32]
Figure3.1. Coning and Quartering [29]
After Coning and quartering, I did ball milling for forming fine particle size. These mills are
also referred as centrifugal mills and are used to grind samples into colloidal Fineness by
generating high grinding energy. Here used 300 rpm of revolution and taken 30 minutes for
each sample.
For calculation of viscosity, sample preparation start with preheating of sample in air blow
furnace which heated sample up to 300oC then it cooled by which it removed moisture and
after this it formed fine particle through planetary ball milling.
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3.2. Experimental Apparatus
3.2.1 Planetary Ball Mill
These mills are also referred as centrifugal mills and are used to grind samples into colloidal
Fineness by generating high grinding energy
This apparatus used for sample preparation to form fine powder of industrial blast furnace slag
in the experimental process of DSC. Fig.3.2. Represents a four stationed planetary mill
presented by Gilson Company. The samples are placed in one of the vile and numerous balls
are added as shown. The vile is covered by the cover plate and then it is mounted in the
machine. Once the viles are mounted and secured, the machine is functional. The bowls are
independent of the rotatable platform and the direction of rotation of the bowls is opposite to
the direction of the rotatable platform. Due to alternate addition and subtraction of the
centrifugal forces, the grinding balls rolls halfway in the vile and then thrown across the viles
and then impacting the opposite walls at very high speeds. Here used 300 rpm of revolution
and taken 30 minutes for each sample.
Figure 3.2- A four station Planetary Ball Mill
3.2.2. Differential scanning calorimetry (TG-DSC).
By using Thermo gravimetric Analyzers STA 409 PC Luxx, Netzsch, Germany, We have
studied the thermal analysis of blast furnace slag which gives us peak temperature of phase
changed slag.
The Specification of these equipments is,
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Sensitivity:
0.001 mg
Mass variation measurement ranges:
±20 mg, ±200 mg, ±2000 mg
Accuracy:
1% of measurement range
Peak load:
18 g
Temperature range:
25 - 1500°С
Rate of temperature change:
0.1 - 50°С/min
Atmosphere:
neutral, oxidative, reducing
In this experimental work we have taken mass of slag sample 20mg, temperature range 25 to
1350oC and rate of temperature change 2,4,6,8,10oC/min.
Figure 3.3 Simultaneous Thermo Analysis (TG-DSC or TG-DTA) in wide temperature range
3.2.3. High temperature viscometer
For calculation of viscosity of blast furnace slag we have used High temperature viscometer
which is shown in fig. no.3.4, the main purpose of calculation of viscosity is to analyse flow
characteristics of liquid slag. And also calculate activation energy of blast furnace slag by
viscometer.
This machine has viscosity range 101 -108 dPas, Max Temperature 1700oC,crucible materialPtAu5%,max speed-800 rpm, Torque range 0-150mNm, Atmosphere -air or inert ga ,purge gas.
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Figure 3.4: VIS 403 Rotating High Temperature Viscometer.
3.2.4. High Temperature Microscope
The Heating Microscope method is adopted for recording the characteristic temperatures. A
picture of the Leitz heating microscope is shown in Fig.7.The sample, in the form of a 3 mm
cube, is heated in an electric furnace in the microscope assembly. The shape change of the
sample as a result of heating is shown by me. A grid-division which is simultaneously observed
with the sample and the temperature to which the sample is being heated facilitate
identification of the four characteristic temperatures
Figure No. 3.5: Pictorial view of Leitz heating microscope
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3.2.5. X-ray diffraction (XRD)
X-ray diffraction technique was used to identify the different phases (elemental
phase/intermetalic phase/crystalline phase/non-crystalline phase) present in the coating. XRD
analysis was done by using Panalytical MPD system. Here Ni- filtered Cu-Kα radiation used in
X- Ray Diffractometer. d- Values obtained from XRD patterns were compared with the
characteristics d-spacing of all possible values from JCPDS cards to obtain the various X-ray
peaks. Obtained d-spacing based on the equation;
n
2dsin
Where,
crystal.&
= Wavelength of characteristic x-rays., d=Lattice inter-planar spacing of the
= x-ray incident angle.
Figure 3.6: X-ray Diffraction Machine.
3.2.6. Scanning electron microscopic Machine (SEM).
By using JEOL JSM-6480 LV scanning electron microscope (SEM), microstructure of raw
power of blast furnace slag before heating and plasma sprayed coated specimens after heating
(diffusion) were studied. The surface morphology as well as the coating – substrate interface
morphology of all coatings was observed under the microscope. Here SEM mostly using the
secondary electron imaging. By the use of this Machine we showed particulates and size of the
powder slag sample, and exhibition of melting formation an incongruent mass.
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Figure 3.7.Scanning electron microscopic Machine (SEM).
3.3: Experimental Procedure
The experimental procedure is divided in ‘Five’ parts, the aim being to determine the
Activation energy of blast furnace slag and correlate the chemical composition of slag for
proposing the flow characteristics that would give slag behaviour with blast furnace. The five
part of experimentation include the following,
3.3.1. Collected five Blast Furnace slag from Rourkela steel plant contained different heat.
3.3.2. Determined the chemical composition by adopting the conventional methods. This is
given in table no3.1.
Sample
SiO2
Al2O3
CaO
MgO
TiO2
Na2O
K2O
Fe2O3
C/S
1
31.86
16.92
38
10.23
0.7
0.98
0.48
0.66
1.192
2
33.25
16.31
36.84
10.56
0.82
1.1
0.52
0.54
1.107
3
32.48
17
35.78
11.88
0.55
1.1
0.52
0.6
1.101
4
31.08
17.04
36.96
11.22
0.5
1.8
0.88
0.40
1.189
5
34.32
16.58
36.2
9.57
0.55
1.36
0.82
0.53
1.054
Table 3.1: Chemical composition (wt.%) of different blast furnace slag.
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3.3.3. For Estimation of Activation energy of blast furnace slag we have done two
measurements.
A. DSC in which different methods have applied,
I.
II.
Kissinger method.
Ozawa method.
B. Viscosity measurements to examine the validity of the measurement by using DSC.
DSC (Differential Scanning Calorimetry) ANALYSYS
For calculation of Activation Energy of slag DSC analysis has to be done. Firstly we have done
sampling of B.F. slag which gave uniformity and fineness of slag sample which is given in
section 3.1and 3.2.1. After sampling of slag we took 20mg of sample for this analysis, this
sample placed in the alumina crucible which has also weighted 180mg after this alumina
crucible placed in Thermo gravimetric Analyzers STA 409 PC Luxx, Netzsch, Germany. This
apparatus shown in 3.2.2;
Before starting of analysis we have done stabilisation of equipment and crucible for 30 min.
And then open correction file of machine to finding out correction factor for different heating
rate (2, 4, 6, 8,100C/min.) of the sample.
The DSC furnace temperature is controlled by a cam-driven program controller. A current
interrupter in the cam motor circuit allows any heating rate up to about 25 0C/min.
The differential scanning is measured between the centres of the active and reference sample.
The reference sample is
-aluminium oxide. The DSC and Temperature are recorded on the
same chart by a multipoint recorder. A typical pattern of sample has shown in figure no 9, 10,
11, and 12.
Each of the five sample materials were run in DSC in the alumina crucible holder at about
heating rate 2, 4, 6, 8, 100C/min. After finding the DSC curve of sample we have applied two
methods for calculation of Activation Energy which have derived from Arrhenius equation is
I.
II.
Kissinger method.
Ozawa method.
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Calculation based on Kissinger equation wasLn ( /Tp2) = Ea/RTp
Where
Constant.
is heating rate in K/min.
Tp is peak point temperature in (k) at melting point of slag,
R is universal Gas constant = 8.314 J/mol-k,
Ea is Activation Energy in KJ/mole
Now Graph plotted between Ln ( /Tp2) in Y axis, and 1/Tp in X axis and we obtained slope
which is equal to
Ea/R, from this we get Activation energy Ea (KJ/mole).
Calculation based on Ozawa equation –
Ln
Where
= −Ea/Tp R + constant.
is heating rate in K/min. Tp is peak point temperature in (k), R is universal Gas
constant = 8.314 J/mol-k, Ea is Activation Energy in Kj/mole.
Now Graph plotted between Ln ( ) in Y axis, and 1/Tp in X axis and we obtained slope which
is equal to
Ea/R, from this we get Activation energy Ea (kj/mole).
VISCOSITY ANALYSIS
Viscosity involves transporting one layer of liquids over another layer i.e. flow phenomena.
The mobility of ionic species present in the slag determines it viscosity.
Experimental procedure for calculation of viscosity of slag start with sampling, for this Sample
No 3 (C/S=1.101) was prepared as fine particle, then sample placed in platinum crucible and
then this crucible place in furnace where it heated up to 1400 oC for complete melting and after
it cooled in open atmosphere. Then it was found that it reduced by volume with 60% of the
crucible after it was ready for placement in viscosity measurement instrument.
This analysis part consists of the VIS 403 Rotating High Temperature Viscometer which has
shown in 3.2.3, the fused power slag which was in platinum crucible placed in furnace chamber
of viscometer which is attached with thermocouple gives reading of heating temperature. All
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these equipments were connected with computer programmer. The sample material was run
with heating, holding and cooling temperature. All this time and Temperature of slag sample
were given in the computer programmer.
We have given heating range up to 10000C then holding for 5 min. And again heating up to
14000C.After heating we got the slag fully converted in liquid form so after this stage rotor of
this instrument rotated manually for free rotational test and then operating system gives a
command for cooling and slow down the position of rotor which goes downward with slow
motion and then rotor rotate at the speed 100rpm. After this experiment we obtain viscosity of
slag during cooling with cooling rate 50C/min.
The calculation of viscosity by this instrument based on Arrhenius equation [16] mainly
depends on temperature and chemical composition.
ή =A.exp (E/RT).
Where ή is viscosity of slag during cooling (d pas), E is Activation Energy , R is universal Gas
constant =8.314 J/mole, T is Temperature in Kelvin
3.3.4 HEATING MICROSCOPE ANALYSIS
Flow characteristics measurements of the sample are carried out by this experiment. Specially
this experiment is carried out to have a chance of the Tp (melting point) as defined from DSC
and from HT (hemispherical temperature).Sampling for heating microscope is the same
procedure as DSC sampling has taken.
Analysis part consists of the high temperature microscopy shown in figure no- (Leitz heating
microscope) was used for flow characteristics temperature measurement. The powdered slag is
prepared in the form of small cubic shapes for this measurement. They are mounted in the
heating microscope. The sample gets heated gradually and deformation takes place. This
deformation defines the flow characteristics of the slag in the form of IDT (initial deformation
temperature), ST (softening temperature), HT (hemispherical temperature) and FT (fusion
temperature). There is a control of heating rate, water is used as coolant and there is a camera
attached to take photographs of different characteristics temperature of slag when required.
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3.3.5 XRD ANALYSIS
Phase Analysis of sample was carried out by using X-pert MPD system (PAN Analytical) Xray Diffraction Techniques (XRD).Which is shown in figure no-8.
Sample for this instrument were taken same as DSC analysis. In XRD analysis both powder
sample and fussed powder sample were taken and this was placed in sample holder of XRD
machine where it was operated in scanning range 10-90O( ) and step speed 30C/min. Here Nifiltered Cu-Kα radiation used in X- Ray Diffractometer. This range of XRD applied for all five
samples for getting Phase analysis.
3.3.6 SEM ANALYSIS
SEM were carried out to understand fusion behaviour of the slag sample, this is carried out by
SEM (JEOL-JSM840) machine. This has been shown in figure no 9.
Prior to Microscopy analysis the fused samples were mounted on a metal stub with carbon
paint. In a vacuum evaporator the samples were thin coated with palladium-gold under vacuum
of 0.01 torr to make the surface conducting for viewing through SEM. The mounted specimens
were studied by SEM (JEOL-JSM840).
Microstructures of the sintered specimens were analyzed using a scanning electron
microscope. The system set up is shown in the fig. No... Scanning electron microscope was
used to study the micro structural feature of samples as it has a much greater resolution power
compared to the optical microscope. In SEM, a hot tungsten filament electron gun, under
vacuum emits electrons; which pass through a series of electromagnetic lenses. The sample is
then bombarded with a fine beam of electrons. The acceleration potential ranges from 1-30
KV. A part of the beam is reflected back as back-scattered electrons. The electron beam
produced by tungsten filament is of 50μm in diameter. Images formed from the secondary
electron beam were studied in the extrinsic mode of SEM. While the images obtained appear
very real and as if they were photographed by ordinary means, the apparent illumination is a
function of particle emission. These particles emitted are termed secondary electrons, and their
detection via detector is displayed on a scanning TV display. A bright image will be the result
of high secondary electron emission, while the primary influence on high emission is the
surface structure of the specimen. The end result is therefore brightness associated with surface
characteristics and an image that looks very much like a normally illuminated subject.
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Chapter-4
RESULTS AND DISCUSSION
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4.1 Results
4.1.1 Activation energy calculation
Thermal analysis of blast furnace slag is carried out by DSC (Differential Scanning
Calorimeter) measurement to determine the crystallization mechanism as mentioned in Section
(2.4.3).
Figure 4.1-shows four DSC curves of finely powdered blast furnace slag sample
whose C/S ratio 1.192., 1.107, 1.101, and 1.189 respectively.
(b)
(c)
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(c)
(d)
Figure 4.1 DSC curves of four powdered slag samples: (a) sample 1, (b) sample 2, (c) sample 3
and (d) sample 4. At different heating rates (@ 2, 4, 6, 8, and 10oC/min.).
Calculation of Activation Energy by DSC is based on two different methods which have
derived from Arrhenius equation this is
1. Kissinger method: -
Ln ( /Tp2) = Ea/RTp
2. Ozawa method: -
Ln
Constant
= −Ea/Tp R + constant.
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Calculation of Peak Temperature from DSC curve of different sample. At different heating
rate. The glass-transition temperature, Tg, was determined as the point of intersection of the
straight-lines extending from the tangents of the DSC curves in the region of the baseline shift.
Some similar features of each thermo gram are apparent: (a) a reversible endothermic peak at
beginning of crystallization temperature, corresponding to the glass-transition temperature, Tg;
(b) exothermic events with maxima in the range of 1000 to 1100°C, indicating crystallization,
Tc; (c) endothermic events at about 1280±1315°C, involving the melting of some crystal
phases, Tp (K).
(0C/min)
Wo(mg)
T(min.)
Tp (k)
Tp(k)
Tp(k)
Tp(k)
Heating
sample 1
sample 2
Sample 3
Sample 4
rate
C/S=1.192
C/S=1.107
C/S=1.101
C/S=1.18
2
25.00
287
1468.8 K
1472.1 K
1466.6 K
1466.6K
4
25.00
199.5
1473.2 K
1471.6 K
1466.2 K
1469.2K
6
25.00
170.3
1474.2 K
1473.5 K
1467.7 K
1469.5K
8
25.00
155.75
1474.8 K
1474.4 K
1467.6 K
1471.3K
10
25.00
147
1476.8 K
1476 K
1468.7 K
1471.2K
Table 4.1: Peak temperature of different obtained from DSC curve.
Table 4.2: Estimation of A.E. using, (a) Kissinger & (b) Ozawa method for different blast
furnace slag.
Sample No.
Ozawa method
Kissinger method
and C/S ratio
Sample 1,
C/S=1.192
A.E= 3732.50 KJ/mole.
A.E = 3755.35 KJ/mole.
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sample 2
C/S=1.107
A.E = 5569.50 KJ/mole
A.E = 5596.90 KJ/mole
A.E = 9202.43 KJ/mole
A.E = 9221.72 KJ/mole
sample 3
C/S=1.101
sample 4
C/S=1.189
A.E = 5758.52 KJ/mole
A.E = 5815.31 KJ/mole
The activation energy for crystallization is an important kinetic parameter for the determination
of thermal stability of the amorphous phase. Based on the results of the exothermic peak shift
in DSC measurements conducted at different heating rates, the value of activation energy was
calculated using Kissinger [18] and Ozawa [33] equations.
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The dependence of crystallization temperature on heating rate was used to determine the
associated activation energy by means of Kissinger equation ln( /Tp2 )=−Eac/RTp + constant
and Ozawa equation Ln =−Eac/Tp + constant
Where
is the heating rate, Tp is the peak temperature in DSC scans, R is gas constant having
value 8.3145 J.mol-1.K-1 with slope −Eac/R=B, where B is a constant.
Data on heating rate and peak temperature was plotted in terms of 1000/Tp vs ln( /Tp2) for
Kissinger equation and 1000/Tp vs ln
for Ozawa equation, as shown in
table no 4,
respectively. The linear fit of the data resulted in slope, (A.E)/R = B. The value of the slope B
was measured from the plots. Putting the values of R and B, activation energies for the first
stage crystallization by Kissinger and Ozawa methods designated as (A.E−K) and (A.E−O)
were calculated and the results are summarized in Table 4.2.
Relation of Activation Energy vs. C/S value of slag:
From the given tabulation value and plot between Activation Energy vs. C/s ratio gives the
conclusion that As the C/S ratio increases the Activation Energy values decreases and so
viscosity of slag decreases.
Due to increase of c/s value basic oxide namely lime, magnesia provide oxygen, act as
network breakers and result in depolymerisation of the melt there by decreasing the viscosity .
C/S value of slag
A.E by Kissinger methods A.E
Kj/mole
by Ozawa
methods
Kj/mole
1.101
9202.43
9221.72
1.107
5569.50
5596.90
1.189
5758.52
5815.31
1.192
3732.50
3755.35
Table 4.3.Tabulation of Activation Energy and C/s ratio by different methods
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Figure 4.2: Activation Energy vs. C/S ratio plot.
From this plot we found that as the C/S ratio of slag increases Activation Energy decreases.
So also viscosity of slag decreases and hence flow characteristics of increases.
Relation between Activation Energy and MgO% value of slag
Here we have given table which give the relation between Activation Energy and MgO% as
calculated by Kissinger and Ozawa methods
MgO%
A.E by Kissinger methods
A.E by Ozawa methods
Kj/mole
Kj/mole
10.23
3732.50
3755.35
10.56
5569.50
5596.90
11.22
5758.52
5815.31
11.88
9202.43
9221.72
Table 4.4: Tabulation of Activation Energy and MgO% by different method
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Figure 4.3: Plot between Activation Energy vs. MgO%
This plot also shows that as the MgO% increases Activation Energy increases up to 10.56% of
MgO contain and then it does not show any significant variation till 11.2% MgO. Beyond
11.22% MgO the Activation Energy again shows an abrupt increase with increase of MgO
percentage.
4.1.2 VISCOSITY MEASURMENTS
In our experimental work calculation of viscosity of blast furnace slag is done by VIS 403
Rotating High Temperature Viscometer which has viscosity range 101-108dPas, Max
Temperature 1700oC,
In viscosity measurement rate of cooling from liquid phase has adopted 50C/min.
The calculation of viscosity by Arrhenius equation [16] mainly depends on temperature and
chemical composition.
ή =A.exp (E/RT).
Where ή is viscosity of slag during cooling (d pas), E is Activation Energy , R is universal Gas
constant =8.314 J/mole, T is Temperature in Kelvin .
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Figure 4.4.Viscosity vs. Temperature graph.
The calculation of viscosity of blast furnace slag has done by the Arrhenius equation .From the
given plot of viscosity we obtained viscosity 2.95d pas at 1299.3 0C of slag sample 3. Which
chemical composition is given in table no1.
From this value we have calculated logarithmic value of slag viscosity and this gives the
Activation Energy 3906.1002 KJ/mole. Which is approximately same value is as obtained from
DSC analysis.
4.1.3 XRD ANALTSIS
Phase analysis is carried out by using X-ray Diffraction pattern.
Figure4.5 XRD pattern of slag sample.
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Phase analysis of diffused Blast Furnace Slag gives Idea about change of chemical
composition during crystallization temperature which is given in fig no 14. Where G is
Gehlenite
(Ca2Al2SiO7),A
is
Akermanite
(Ca2MgSiO7),
and
M
is
Melilite
(Ca,Na)2(Al,Mg,Fe)(Si,Al)2O7 is major constituents
4.1.4 Flow characterisation of blast furnace slag.
The flow characteristics of 5 blast furnace slag samples were measured using the High
Temperature Microscope. The flow characteristics give four characteristics temperature, viz.
Initial Deformation Temperature (IDT), Softening Temperature (ST), Hemispherical
Temperature (HT) and Flow Temperature (FT). The flow characteristics of the sample no 1 is
represented in fig no 15.
Initial shape
IDT
ST
HT
FT
000 OC
804 OC
920 OC
1380 OC
1385 OC
Figure 4.6: flow characteristic image of sample.
The flow characteristics of 5 blast furnace slag samples measured by High Temperature
Microscope have the same value of Hemispherical Temperature (HT).As obtained by the DSC
value of slag melting temperature Tp.
Sampe
HTOC
FT OC
FT-ST ˚C
920
1380
1385
465
816
910
1378
1384.8
474.8
1.101
810
894
1379
1390
496
17.04
1.189
800
889
1370
1386
497
16.58
1.054
795
870
1374
1382
512
IDTO
STO
C
C
1.192
804
16.31
1.107
11.88
17
31.08
11.22
34.32
9.57
CaO
SiO2
MgO
%
%
%
1
38
31.86
10.23
16.92
2
36.84
33.25
10.56
3
35.78
32.48
4
36.96
5
36.2
no.
Al2O3%
C/S
Table 4.5: Composition and flow characteristics of blast furnace slag sample obtained.
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4.1.5 Microstructure:
Fig. 4.7(a) shows the scanning electron microscopic images of the powder blast furnace sample
and Fig.4.7 (b) shows the scanning electron image of diffused blast furnace slag sample from
this image we have observed particulate and size of slag sample before diffusion and after
diffusion which gave average value of powder slag sample was 22 micrometer. And we have
also shown the exhibition of melting forming an incongruent mass. This is shown in figure 4.7
(a) and (b).
(a)
(b)
Figure 4.7(a) SEM micrographs at 500 magnifications of powder sample, (b) SEM
micrographs at 500 magnification of sample no 1 whose C/S ratio is 1.192.
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4.2 Discussion
The Activation Energy values obtained in the present case are found to be very high. This is
true when any of the two equations are used .Similar observations are reported by Lei Gan, Lei,
et al [9]. Which reports the Activation Energy of crystallization of Blast Furnace Slag, They
got a value of 1021-1969KJ/mol, as against 457.5KJ/mol for B.F. slag as reported by Francis et
al [34]. And 125.4-627 KJ/mol for CaO-MgO-Al2 O3-SiO3 slag as reported by J.Williamson et
al [35].The obtained high value are attributed to the difference of crystallization mechanism as
adopted by the different phases identified in the XRD plot & similar reasons may hold for the
present case. For example if we consider the XRD plot for slag no 3. We find the major
constituents phases are Gehlenite, Akermanite and Melilite [36]. All the phases have
tetrahedral unit cells. But the volume of the unit cells is different. While Gehlenite unit cell has
a volume of 300.3[Ao]3, Akermanite unit cell has volume of 307.22[Ao]3, and Melilite
303.27[Ao]3, the basic unit cell which also is tetrahedral, has a volume of 173.39[A o]3 [37]. The
above explains that the formation of the different unit cells of different phases by the presence
of different constituents lime CaO, MgO etc. In to the silicate tetrahedral network while
breaking the silicate network which accounts for the lower value of the Activation Energy of
viscous flow, might have also been responsible for the rise of the Activation energy by
consisting a stress in the silicate unit cell [38, 39].
The activation energy calculated by viscometer has the approximate same as the DSC
activation energy of sample 3.and we get variation of activation energy with the change the
value of C/S ratio. This is due to increase of c/s value basic oxide namely lime, magnesia
provide oxygen, act as network breakers and result in depolymerisation of the melt there by
decreasing the viscosity of the slag so also decreasing the activation energy of slag [40]. In this
present work we observed that as the MgO% increases Activation Energy increases up to
10.56% of MgO contain and then it does not show any significant variation till 11.2% MgO.
Beyond 11.22% MgO the Activation Energy again shows an abrupt increase with increase of
MgO percentage.
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Chapter-5
CONCLUSION
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5. Conclusions
1. Methods adopted for the calculation of activation energy gave identical values by DSC
analysis.
2. The values of activation energy obtained by DSC analysis also matched with the results
of viscosity measurement.
3. As the C/S ratio increases the Activation Energy decreases.
4. As the MgO percentage increases the Activation Energy increases up to 10.56% of
MgO and then after 11.22% of MgO abruptly increases Activation Energy.
5. The calculated value of Activation Energy was much higher may be due to lattice strain
in the silicate structure.
FUTURE SCOPE
The study may be continued for more number of blast furnace slag with variation of C/S ratio
and MgO%, to estimate and correlate activation energy of blast furnace slag. Estimation of
activation energy by viscosity measurement has not been completed in the present study; this
may be characterized extensively. It also required to estimate activation energy of pure oxides
to understand the large values of activation energy (as predicted in the present study). Also
activation energy of crystallization and viscous flow may be examined to understand such large
values of activation energy.
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