Value Added Ceramic Products from Fly Ash: A Review

1. 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

2. Phase Analysis

3. Microstructure

4. 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

5. NON CONVENTIONAL USES • WEAR RESISTANT TILES • REFRACTORY AGGREGATE • MODERATE HEAT DUTY REFRACTORY BRICK (IS 6) • TRADITIONAL PORCELAIN TILES • METAL MATRIX COMPOSITES (MMC) • GLASS CERAMICS

6. Fly Ash Based Wear Resistant LinerBackground Industrial material handling equipments used for transport of highly erosive and abrasive media particles undergoes Heavy erosion & abrasion by MECHANICAL PROCESS Corrosion by CHEMICAL PROCESS 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

7. A Phenomena of removal of material from surfaces in relative motion by: EROSION 1. MECHANICAL PROCSS ABRASION 2. CHEMICAL PROCESS CORROSION “WEAR”IN MATERIAL HANDLING SYSTEM

8. A SOLUTION TO THE WEAR PROBLEM USING CERAMIC LINERWHY 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

9. RECOGNISED WEAR RESISTANT CERAMIC MATERIALS • Boron carbide • Silicon nitride • SIALON • Alumina (>85%) • Fused Cast • Basalt • AZS Sequential order of erosion rate: Boron Carbide <Silicon Nitride<Sialon<Alumina<AZS<Basalt

10. OPTIMUM SELECTION NOT A COST EFFECTIVE SOLUTION Inhomogeneity in structure & presence of tapped cavities created from gas entrainment due to a high melt viscosity • BC • Si3N4 • Sialon • AZS • Basalt

11. MOST COST EFFECTIVE MATERIALALUMINA FAMILY(85 – 95% Al2O3)FOR SLIDING ABRASIONCrystal size : 2 – 16 micronFOR EROSION (IMPINGEMENT WEAR)Crystal size : 2-8 micron

12. Part Replacement of costly alumina by Fly Ash

13. Properties of Wear resistant liners (study at CSIR-CGCRI)

14. View of some applications

15. View of some applications

16. Possible Waste Incorporated Batches S. K. Das, CSIR-CGCRI

17. Results of Different Batches S. K. Das, CSIR-CGCRI

18. A Comparison of the Abrasive Hardness of Different Materials * 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.

19. Areas of Waste Incorporated Liner Application S. K. Das, CSIR-CGCRI

20. 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 and can replace part of costly alumina without deteriorating the properties.

21. 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 (oC)

22. Aggregate as gel bonded self flow high alumina castable (study at CSIR-CGCRI)

23. 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 1300oC without any deterioration. • 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.

24. Properties of Fly Ash Based IS 6 Brick (study at CSIR-CGCRI)

25. TRADITIONAL PORCELAIN TILES • A traditional porcelain batch consists of clay, quartz and feldspar. • Gradual depletion of good quality natural raw materials has increased the price of the product. • Alternative sources are being exploited. • Fly ash, alumino-silicate material, can replace the kaolinitic clays partly. • Resemblance with clay in chemistry and inherently containing microcrystalline components like quartz and mullite, a replacement of 25 – 30% of kaolinitic clay by fly ash hardly affects the properties.

26. 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 incorporatedK2O-Al2O3-SiO2 SYSTEM RESEARCH CHALLENGE FOR INDUSTRY

27. Fly Ash in Traditional Porcelain Tiles • Substitution of quartz in common porcelain tile (quartz acts as a filler) by fly ash up to 15% showed an increase in the density and shrinkage and corresponding decrease in porosity. • Again this can be achieved at a lower temperature than the normal porcelain firing temperature. • This is due to the formation of low viscous glassy phase in fly ash containing compositions, resulting better sintering / densification through liquid phase sintering process. • Addition of fly ash also increases the amount of mullite in the composition and reducing the free quartz content, thus increasing the strength of the sintered products. • Better interlocking and uniform distribution of smaller sized mullite needle crystals in a glassy matrix supports the evidence of this improvement.

28. Compositions studied

29. SEM of FA incorporated tile • Well developed mullite needles embedded in the matrix significantly enhanced the strength • Firing temperature reduced • Low cost of production • Utilized waste material

30. Microstructure of fly ash based tiles

31. Synergistic addition of FA and slag in porcelain • Addition of fly ash and blast furnace slag in the proportion of 1:1 and 1:2 beneficial Kausik Dana & Swapan Kr.Das, Ceramics International , (in press, 2004)

32. View of Waste Based Tiles

33. 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 compared to monolithic metals. • They also perform better than the polymer matrix composites at elevated temperatures. • Use of MMCs is limiteddue to the cost factor.

34. Fly Ash in MMC • Addition of fly ash in cast aluminium (composite) have the potential of cost competitiveness, lightness and application potential. • These composites are suitable for automotive components, machine parts 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 abrasivewear resistance of aluminium alloy, specific wear rate of the composite decreased 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 SiCparticles, thus reducing the extent of ploughing.

35. Advantages of Fly Ash based MMCS • Use of fly ash metal composites can reduce the consumption of aluminium metal. • 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.

36. GLASS CERAMICS • Glass ceramics are polycrystalline solids produced by controlled crystallization of glass. • For glass ceramics it is important to nucleate the crystal first from a glassy melt 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.

37. Fly Ash in Glass Ceramics • The chemical composition of fly ash is typical of the most common glassy ternary system (CaO-Al2O3-SiO2) 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 of view of the fly ash, conversion to glass is beneficial. As inorganic glasses can incorporate large amount of heavy metal ions 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.

38. Glass Ceramics using only Fly Ash • Generally melting of fly ash based glasses is done around 1400oC and nucleation around 650 – 750oC and growth between 850 – 980oC. • 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 (Ca2Al2SiO7), anorthite (CaAl2Si2O8), diopside-alumina [Ca (Mg, Al) (Si,Al)2O6], etc.

39. Phase Analysis of Glass Ceramics using only Fly Ash

40. Phase Analysis of Glass Ceramics using only Fly Ash with varying heat treatment temperature

41. Properties Glass Ceramics using only Fly Ash (Other Author’s work)

42. Microstructure of glass ceramics using only Fly Ash, heat-treated at (a) 850 °C, (b) 900 °C, (c) 950 °C, (d)1000oC and (e) 1050oC for 2 h(Other Author’s work)

43. 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, Al2O3 and SiO2 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.

44. Properties of Fly Ash Based Cordierite Glass Ceramics

45. Phase Analysis of Fly Ash Based Cordierite Glass Ceramics

46. 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.

47. 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.

48. 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-Al2O3-SiO2). • 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.

49. Thank You