Transcript Value Added Ceramic Products from Fly Ash: A Review
Value Added Ceramic Products from Fly Ash: A Review
Swapan Kumar Das Chief Scientist
Refractories Division CSIR-Central Glass & Ceramics Research Institute Kolkata – 700032, India ICUFA Conference, Kolkata,January 10-11, 2013
Phase Analysis
Microstructure
SOME CONVENTIONAL USES
FLY ASH BRICKS CELLULAR LIGHT WEIGHT CONCRETE FLY ASH CEMENT ROADS, FILLS & EMBANKMENTS FILLING OF OPEN LAND AND MINES AGRICULTURE APPLICATIONS ASH BASED COMPONENTS FOR CONSTRUCTION INDUSTRY PAVEMENT BLOCK SUBSTITUTE OF CLINKER & NATURAL AGGREGATES WOOD SUBSTITUTE - DOORS & PANELS GRANITE SUBSTITUTE PAINTS & ENAMELS
NON CONVENTIONAL USES
WEAR RESISTANT TILES
REFRACTORY AGGREGATE
MODERATE HEAT DUTY REFRACTORY BRICK (IS 6)
TRADITIONAL PORCELAIN TILES
METAL MATRIX COMPOSITES (MMC)
GLASS CERAMICS
Fly Ash Based Wear Resistant Liner Background
Industrial material handling equipments used for transport of highly erosive and abrasive media particles undergoes
Heavy erosion PROCESS & abrasion by
Corrosion by CHEMICAL PROCESS MECHANICAL
BHEL and few private organizations in India manufacturing high alumina liners to provide a cost effective solution to such wear problem.
AUTHOR OF THIS PAPER SHARING HIS R&D EXPERIENCES OF BHEL, NML & CGCRI
“WEAR” IN MATERIAL
HANDLING
SYSTEM A Phenomena of removal of material from surfaces in relative motion by:
1. MECHANICAL PROCSS 2. CHEMICAL PROCESS EROSION ABRASION CORROSION
A SOLUTION TO THE WEAR PROBLEM USING CERAMIC LINER WHY CERAMICS?
Remarkable resistance to both sliding & impact abrasion
Exceptionally tough & harder than tool steel
Extraordinary durability
Low friction coefficient
Outlasts metal from ten to fifteen times
Lower cost : Performance ratio
RECOGNISED WEAR RESISTANT CERAMIC MATERIALS
Boron carbide
Silicon nitride
SIALON
Alumina (>85%)
Fused Cast
Basalt
AZS Sequential order of erosion rate: Boron Carbide
OPTIMUM SELECTION
BC
Si
3
N
4
Sialon
AZS
Basalt
NOT A COST EFFECTIVE SOLUTION Inhomogeneity in structure & presence of tapped cavities created from gas entrainment due to a high melt viscosity
MOST COST EFFECTIVE MATERIAL ALUMINA FAMILY (85 – 95% Al 2 O 3 ) FOR SLIDING ABRASION Crystal size : 2 – 16 micron FOR EROSION (IMPINGEMENT WEAR) Crystal size : 2-8 micron
Part Replacement of costly alumina by Fly Ash
Properties of Wear resistant liners (study at CSIR CGCRI) Properties Fly Ash Based Alumina Based Basalt
Fly Ash content 10% 20% 40% Al 2 O 3 85% Bulk Density, gm/cc App. Porosity (%) Moh’s hardness 3.38
0.8
9.0
2.85
0.5
9.0
2.75
0.3
~ 9 3.47
0.3
9.0
2.90
0.9
~ 9 Comp.
(kg/cm 2 ) strength >10000 >10000 >10000 >10000 2300 Abradability index 6.17
Erosion rate (vol.
loss, cc/kg erodent) 0.0135
Phase content Mullite, Corundum 14.10
0.0151
Mullite, Corundum 19.04
0.0162
16.72
0.0155
Mullite, Corundum Corundum, Mullite, 44.2
0.0985
View of some applications
View of some applications
Possible Waste Incorporated Batches
A Calcined alumina, basalt powder, iron ore tailing, clay and fly ash.
B Low grade bauxite, fly ash, clay, iron ore tailing and basalt powder.
S. K. Das, CSIR-CGCRI
Results of Different Batches
Properties Vitrification Temperature ( O C) % Linear Shrinkage Bulk Density (g/cc) % Water Absorption Abradibility index Cold Crushing Strength (Kg/cm 2 ) Mohs ’ Scale Hardness A 1275 15-17 2.85-2.90
<0.50
10-12 >4000 Closer to 8 S. K. Das, CSIR-CGCRI B 1275 18-20 2.80-2.85
<0.50
12-14 >4000 Closer to 8
A Comparison of the Abrasive Hardness of Different Materials
Material
Raw basalt
Cast basalt, vitreous
Cast basalt, Crystallized
Sintered basalt
Hard porcelain
Sintered corundum
90% Sintered alumina
Waste based ceramics (as presented in the current study)
Abrasive Hardness
* 700-900 750-800 1600-2700 2500-2900 1300-1400 4500-5000 4000-4500 3000-3500 * Measured by a wet grinding method using a load of 4.5 kg, at a velocity of 50meters/min. Abrasive materials used was 60 mesh SiC grains.
Areas of Waste Incorporated Liner Application
S. K. Das, CSIR-CGCRI
REFRACTORY AGGREGATE
Refractories -
withstand high load at higher temperatures.
Most
common refractories
are
alumina and silica.
Alumina, silica and their compounds are the prime candidate as refractory, except high basic environment,
Fly ash, containing mainly alumina and silica
, can also replace many of the refractory products if
iron oxide, lime and alkalis are negligible
in amount. Fly ash contains
these oxides
(harmful for any refractory item) to an extent of
15 to 25%.
Hence fly ash
can not be directly used
as refractory material. It can be
used in combination with alumina
replace part of costly alumina without deteriorating the properties.
and can
Aggregate Property (study at CSIR-CGCRI) Properties Fly Ash Kyanite
Fly Ash Use 28% - Bulk Density 2.81 3.13
(gm/cc) App. Porosity 0.35 0.43 (%) Refractoriness >1804 >1804 ( o C)
Aggregate as gel bonded self flow high alumina castable (study at CSIR-CGCRI)
Properties Aggregate amount Self flow value (%) Green Density (gm/cc) Fired Density (gm/cc) Green CCS (kg/cm 2 ) Fired CCS (kg/cm 2 ) 1400 o C MOR (kg/cm 2 ) Phase content Fly based ash 5% Fly ash +65% WTA Kyanite based 5% kyanite +65%WTA 78 2.98
2.96
440 950 62 Corundum, Mullite 83 2.96
2.94
430 980 65 Corundum, Mullite WTA based 70% WTA 80 3.00
2.98
450 1050 48 Corundum, Mullite
MODERATE HEAT DUTY REFRACTORY BRICK (IS 6)
Important not as hot face refractory but mainly as a
back up refractory lining.
Withstand temperature
up to 1300 o C
deterioration.
without any
Prevents heat loss
of the furnace and to
bear the load
.
Based on
fire clay
, which is a refractory grade clay material containing only the
alumino silicates
.
Fly ash, similar in composition
, can replace fireclay.
Non consistency in composition
and presence of
higher extent of iron and alkaline earth oxide
materials do not allow fly ash to be used singly.
Up to 40%
of fly ash can be successfully used in combination with fire clay materials for these bricks.
Properties of Fly Ash Based IS 6 Brick (study at CSIR-CGCRI)
Property IS Specification 30 min Alumina content (%) Bulk density (gm/cc) Apparent porosity (%) Specific gravity CCS (MPa) Refractories (ASTM No.) R. U. L.,Ta ( o C) PLCR (%), 1350 o C for 5 h 25 20 (min) 30 1300 1.0, max.
40% Fly Ash Based brick 33.4
1.99
22.3
2.59
30 >32 1340 Nil
TRADITIONAL PORCELAIN TILES
A
traditional porcelain quartz and feldspar.
batch consists of
clay,
Gradual depletion of good quality natural raw materials has increased the price of the product.
Alternative sources are being exploited.
Fly ash, alumino-silicate kaolinitic clays
partly. material, can replace the
Resemblance with clay in chemistry
and
inherently containing microcrystalline components
of
25 – 30%
like quartz and mullite, a replacement of
kaolinitic clay
by fly ash hardly affects the properties.
BACKGROUND….
Gradual depletion of natural minerals calls for alternative source for raw materials Converting industrial waste into wealth mitigating environmental pollution is a global need Industry require scientific understanding of the waste incorporated K 2 O-Al 2 O 3 -SiO 2 SYSTEM RESEARCH CHALLENGE FOR INDUSTRY
Fly Ash in Traditional Porcelain Tiles
Substitution of quartz
acts as a filler) by fly ash up to the in common porcelain tile (quartz
density and shrinkage 15%
showed an
increase
in and corresponding
decrease in porosity.
Again this can be
achieved at a lower temperature
the normal porcelain firing temperature.
than This is due to the
formation of low viscous glassy phase
in fly ash containing compositions, resulting
better sintering / densification
process. through liquid phase sintering
Addition of fly ash
also
increases
the amount of
mullite
the composition and reducing the free quartz content, thus increasing the strength of the sintered products. in
Better interlocking and uniform distribution
of smaller sized
mullite needle
crystals in a glassy matrix supports the evidence of this improvement.
Compositions studied
Normal porcelain 1.0
P % F ly a sh re pl PF10 aci ng q ua rtz PF5 FSP-2 FSP-1 FSP-3 PS5 % Sl ag re pla ci ng fe ld sp ar PS10 1.0
15 wt % Fly ash PF15 FSP-4 FSP-5 FSP-6 PS15 Slag
SEM of FA incorporated tile
Well developed mullite needles embedded in the matrix significantly enhanced the strength
Firing reduced temperature
Low cost of production
Utilized waste material
Microstructure of fly ash based tiles
Synergistic addition of FA and slag in porcelain
70 60 FSP-3 FSP-1 FSP-2 SP Addition of fly ash and blast furnace slag in the proportion of 1:1 and 1:2 beneficial 50 FP 40 30 NP R 2 1 2 O/R / O 3 4 5 6 2.3 2.4 2.5
2.9 3.0 3.1
2.6 2.7 2.8
SiO 2 /Al 2 O 3 3.2
Kausik Dana & Swapan Kr.Das, Ceramics International
, (in press, 2004)
View of Waste Based Tiles
METAL MATRIX COMPOSITES (MMC)
MMCs are
engineered materials
formed by the
combination of two or more materials
, at least
one
of which is a
metal.
MMCs have the advantages of
higher strength, density and stiffness density ratio
to monolithic metals.
compared They also
perform better
than the polymer matrix composites
at elevated temperatures
.
Use
of MMCs is
limited due to the cost
factor.
Fly Ash in MMC
Addition of potential of
fly ash
in cast aluminium (composite) have the
cost competitiveness application potential
. ,
lightness
and These composites are
suitable components, machine parts
for
automotive
and related industries. Dispersion of coal fly ash in common aluminium metal
improves the mechanical characteristics
as hardness.
3 vol%
of fly ash
in aluminium
metal
improves
the
abrasive wear resistance wear rate
of the composite of aluminium alloy,
decreased specific
with increasing load and sliding velocity. Specific abrasive wear rate decreased with increasing size of the abrading particles.
Friction coefficient
of the composite
decreased
with increasing time, load and size of the abrading particles.
Fly ash particles
in the composite
blunt the abrading SiC particles
, thus reducing the extent of ploughing.
Advantages of Fly Ash based MMCS
Use of fly ash metal composites can
reduce consumption of aluminium metal
.
the For automobile industries, it
reduces the weight
of the vehicle.
Correspondingly
improves mileage
of the vehicle.
In totality fly ash reduces the energy requirement for metal production, disposal hazards of fly ash, oil consumption, etc.
These composites are also important for foundries, manufacturing, transportation, construction, electrical and consumer goods industries.
GLASS CERAMICS
Glass ceramics are
polycrystalline solids
produced by
controlled crystallization of glass.
For glass ceramics it is important to
nucleate crystal
first
from a glassy melt
the and then
allow
to
grow
to specific size as per the requirement. Glass ceramics normally contain around
50 – 90% crystalline materials
by volume and the rest being a residual un-crystallized glassy phase.
Crystal type in the glassy matrix can be controlled by selection of the parent glass composition.
Final properties can also be tailored for specific application.
Fly Ash in Glass Ceramics
The chemical composition of fly ash is typical of the most common glassy ternary system (CaO-Al 2 O 3 SiO 2 ) and useful for glass ceramics.
Significant amounts of
transition metal oxides
present in fly ash,
act as nucleating agents
, for nucleation and crystallization. From the
disposal point metal ions
of view of the fly ash,
conversion to glass is beneficial
. As inorganic
glasses can incorporate large amount of heavy
inside the random network structure and the
chemical stability
of glass is
very high
against leaching in water. Again,
vitrification results in a very large reduction in volume
.
Glass Ceramics using only Fly Ash
Generally
melting
of
fly ash based glasses
is done around
1400 o C 650 – 750 o C
and and
growth nucleation
around between
850 – 980 o C
.
Temperatures
are
composition dependent
and can also be altered as per the requirement criteria. Generally
crystals of alkaline earth oxides
– alumina – silica system are nucleated in the fly ash based glass ceramics, namely
gehlenite
(Ca 2 Al 2 SiO
alumina
7 ),
anorthite
(CaAl 2 Si 2 O 8 ),
diopside-
[Ca (Mg, Al) (Si,Al) 2 O 6 ], etc.
Phase Analysis of Glass Ceramics using only Fly Ash
Phase Analysis of Glass Ceramics using only Fly Ash with varying heat treatment temperature
Properties Glass Ceramics using only Fly Ash (Other Author’s work)
Properties Density (gm/cc) Porosity (%) Water absorption (%) 850 2.03
o C 900 25.67
12.63
Compressive strength (MPa) 41.44
4 point strength (MPa) bending 19.96
2.07
o C 22.66
10.82
56.29
22.57
Electrical ( -cm)) resistivity Th. Exp. co- effficient ( a ) x10 -6 / o C 11.72
8.63
4.59
8.61
950 o C 1000 o C 1050 o C 2.17
2.26
2.21
19.29
7.41
53.96
11.76
5.18
38.75
11.92
5.87
31.31
17.00
3.23
9.19
12.09
2.95
9.18
11.99
1.05
10.21
Microstructure of glass ceramics using only Fly Ash, heat-treated at (a) 850 °C, (b) 900 °C, (c) 950 °C, (d)1000 o C and (e) 1050 o C for 2 h (Other Author’s work)
Fly Ash as a Component in Glass Ceramics
Utilization of fly ash up to certain extent as a
component in glass / glass ceramics
composition in combination with other oxides for the development of a specific glass ceramics is also important.
Addition of MgO, Al 2 O 3 and SiO 2
to fly ash can develop
cordierite based glass ceramic
, utilizing around
70% of fly ash
.
Cordierite-based glass-ceramics are important due to their good mechanical properties, low dielectric constant and low thermal expansion coefficient.
They are used as kiln furniture in white ware industry as well as in micro-electronic packaging industry.
Properties of Fly Ash Based Cordierite Glass Ceramics
Property Vickers Micro hardness (MPa) Fly ash based glass 4020 Fly ash based cordierite glass ceramics 6250 Industrial cordierite Density (gm/cc) 2.34
Bending (MPa) strength 65 Thermal Expansion co effficient ( a ) x10 -7 / o C 79 2.49
90 35 2.50
110 25
Phase Analysis of Fly Ash Based Cordierite Glass Ceramics
Summary & Conclusion
Utilization of fly ash has been successfully being practiced by various sectors and the extent of utilization is increasing with time.
However ever increasing generation of ash due to our higher dependence on power & electricity, using coal based thermal route, forcing us to develop new ways of utilizing the same. Use of fly ash up to 40% replacing alumina in wear resistant ceramic products shows no deterioration in properties. Use of fly ash up to 28% replacing alumina for the development of refractory aggregate, used in high alumina castable, shows no deterioration in the property, however an increase in the hot strength was obtained due to the presence of mullite in the composition from fly ash.
Summary & Conclusion
For automobile industries, it reduces the weight of the vehicle and the correspondingly improves mileage Utilization of fly ash up to 40% replacing fire clay in moderate heat duty refractory brick shows better properties than the specification in all the items. Use of fly ash up to 15% replacing quartz in traditional porcelain composition results better density, and strength at lower temperatures. This is due to liquid phase sintering of the product and presence of higher amount of mullite. Use of fly ash in metal (aluminium) matrix composite improves the abrasive wear resistance, decreases specific wear rate. This application can reduce the consumption of aluminium metal in automobile industries and can reduces the weight of the.
Summary & Conclusion
Use of fly ash for glass ceramic material helps in many ways. Chemical composition of fly ash is typical to glassy ternary system (CaO-Al 2 O 3 -SiO 2 ). Presence of transition metal oxides act as nucleating agents, for nucleation and crystallization. Conversion to glass is beneficial for disposal. As it can incorporates large amount of heavy metal ions and has very high chemical stability. Again, vitrification results in a very large reduction in volume.
Fly ash can be used solely or in combination with other oxides for manufacturing of glass ceramics. The properties are no way inferior than the conventional products.
Fly ash with other waste can be utilized to make hard ceramics as a liner material.