Akash Satapathy (107CR016) in partial fulfillment of the requirements for the award of a Bachelor of Technology Degree in Ceramic Engineering at National Institute of Technology, Rourkela is an authentic work carried out by him under my supervision and guidance. To the best of my knowledge, the matter contained in this thesis has not been submitted to any other University/Institute for the award of any Degree or Diploma. I would also like to thank IFGL Refractories for the help and support in conducting experiments and providing raw materials.
I am also grateful to the research fellow in the Department of Ceramic Technology for helping in laboratories and analyses. Self-flow casting has been prepared that fixes the distribution coefficient q at 0.21 in the continuous particle size distribution model as proposed by Dinger-Funk. High alumina cement and silica sol were used at 4 wt% and 6 wt% as binder and water was used until self-flowing consistency was achieved in the castable mixture.
INTRODUCTION
GENERAL INTRODUCTION
Since the early 1960s, the availability of purer calcium aluminate cements (CACs) with higher alumina content has made the unformed refractories system cleaner and made it possible to use them for various high-temperature applications (2). Among various binders, calcium aluminate cement is the commonly used hydraulic binder in refractories, but the presence of CaO in the cement results in low-melting phases in Al2O3 and Al2O3-SiO2 refractory system [1, 2]. Other important concerns for cementitious castings are the curing and dewatering steps, which must be performed carefully to reduce explosive spalling [1].
A significant increase in the life and performance of alumina-based castings has been made possible by reducing the cement content, thereby avoiding/reducing the formation of liquid phase at application temperatures, which in turn improves corrosion resistance and creep strength. Further development work resulting in a new bonding system with superfine materials produced through the sol-gel route appeared in industry, opening a new horizon for refractory technologists. So in a refractory system, formation of a three-dimensional network gel structure from a sol surrounding the refractory aggregates results in strength of the system upon drying.
LIETRATURE REVIEW
- CASTABLE AND PARTICLE SIZE DISTRIBUTION
- SELF FLOW CASTABLE
- SILICA SOL BASED CASTABLE
- CEMENT BASED CASTABLE
They may contain metallic, organic or ceramic fiber materials.‖Application of a monolithic is entirely based on its chemical composition and particle size distribution. The need for packing is that it decides that the pourable is vibrable/self-flowing mass and optimal packing requires less water for placement. The dispersion factor dictates the particle size distribution and the flow behavior of the castable material.
Fine and superfine oxide powders increase the packing of the cast material by filling the voids and forming a viscous suspension that keeps the coarse particles or aggregates far enough apart that the cast material flows under its own weight due to the effect of gravity. Also fine and fine particles tend to be spherical, so they also improve the flow property of the cast material. The yield stress indicates the minimum stress required to cause deformation in the flow process of the cast material.
If the castable potential energy exceeds the yield stress, the flow process occurs and it stops as soon as Epot = Eyyield. In reality, the casting continues to deform even after equilibrium is reached between the castable potential energy and yield stress. This is due to the transformation of some castable potential energy into the kinetic energy during the flow process.
Colloidal silica is a water stable suspension when mixed with castable increases the drying speed and sinterability of the product. Colloidal silica is self-dispersing in nature due to spherical size and nanometric size. To destabilize the colloidal silica suspension and then increase the probability for bond-forming collisions, MgO sinter was added.
MgO favors anionic reaction mechanisms on its surface by withdrawing hydrogen ions from Si-OH groups, giving a higher siloxane bond formation, which increases the colloidal silica gelation rate.
EXPERIMENTAL PROCEDURE AND CALCULATION
BATCH FORMULATION
The water required for pouring cement-based cast materials increases with the increase in the high content of alumina cement due to the increase in the content of CaO in the composition. In Figures 4 and 5, XRD analysis shows that the main phase present in the sol-based casting is alumina and the other phase present is mullite. In Figures 6 and 7, the XRD analysis shows that the main phase present in the cement-based cast is aluminum and the other phase present is grossite.
At 110°C, 4% cement-based castable shows more bulk density than 6% cement-based castable due to high porosity in the oven-dried samples, as the water required for casting 6% cement-based castable is higher than 4% cement-bound castable. 4% solar-based castable shows lower bulk density than 6% solar-based castable due to high porosity in the oven-dried samples, as required water for casting 6% solar-based castable is lower than 4% solar-based castable. The cement-based casting compound shows shrinkage at both 950°C and 1550°C, while the solar-based casting compound shows shrinkage at 950°C and expansion at 1550°C.
As more liquid is formed at 1550°C with 6% cement-based castable material than with 4% cement-based castable material, higher compaction and better pore removal occur. Both 4% and 6% sol-based castings exhibit shrinkage at 950°C and then gradually reveal that expansion may be due to mullite phase formation in the composition. When a larger amount of mullite is formed at 1550°C in the case of a 6% sol base castable than a 4% sol base castable, it shows higher expansion.
At 110°C, the cement-based castable shows higher strength than the solar-based castable due to the presence of hydrated bonding phases, which provide strength to the castable. 6% cementitious castable gives higher strength than 4% cementitious castable due to greater amount of the hydraulic binder. Sun-based casts show lower strength than cement-based casts, as no bonding phases are present.
At 1550°C, the cement-based cast shows higher strength than the solar-based cast due to significant densification, which gives higher strength.
SAMPLE PREPARATION
CHARACTERIZATION
The physical bulk density of the sample was measured using the linear dimensions of the sample. Volume shrinkage = (VB - VA)/VA * 100 VB= Volume of sample after firing VA= Volume of sample before firing.
RESULTS AND DISCUSSION
RAW MATERIAL CHARACTERIZATION
Formulated particle size distribution gives CPFT v/s particle size plot on a log-log scale as shown below:-. There is an abrupt change in the slope of the plot due to the high content of fines (28.8. From the XRD analysis of the high alumina cement binder as observed in Figures 2 and 3, it was found that CaO.2Al2O3 (CA2) was the main phase and the other phase was CaO.Al2O3 (CA).
SAMPLE CHARACTERIZATION
Mullite can be formed due to the reaction between fine alumina particles and SiO2 originating from sol in the matrix phase. The bulk density increases gradually for cement-based castable material due to the gradual removal of pores and compaction, and that of sol-bonded castable material decreases due to gradual expansion due to the formation of the mullite phase. Sol-bonded castings exhibit higher bulk density than cement-bonded castings because less water is required for casting.
The cold crushing strength value gradually increases for all casting compositions with increasing temperature. Unlike the theoretical estimate, the cement-based strength is low at 110 °C than at 950 °C, as the main phase present in HAC is CA2, which exhibits poorer hydraulic behavior and therefore gives low strength at 110 °C. The initial strength of the salt-bonded casting was found to be lower than that of the cement-bonded cast due to the coagulation bonding mechanism of the salt compared to the chemical hydrate bonding in those containing cement.
However, the cementitious ones showed relatively lower initial strength values, may be due to the presence of a greater amount of less hydratable gross phase (CA2) and less degree of CA phase in the cement with high alumina content. Mullite phase exists in the sol-bonded casting material due to the reaction between silica particles from the sun and fine alumina present in the matrix at high temperatures, and the sol-bearing casting materials showed expansion or lower shrinkage values. Only grossite is found beyond the corundum phase in XRD of cement-bonded cast, may be due to unreacted grossite phase from cement with high alumina content or due to the formation of grossite phase by.
PROPERTIES
CONCLUSION
The effect of the binder and its amount on the self-liquid castable alumina with high alumina content, with a partition coefficient q of 0.21 according to the continuous particle size distribution model proposed by Dinger-Funk, has been studied.
Pandolfelli, Processing of no cement self-flowing high alumina refractory castable material by matrix rheological control. Iler, "The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry," New York, Wiley, 866p (1979). Ghatak, ―Effect of synthetic mullite aggregate prepared by hydroxyl hydrogel method on sol-bonded clay-based mullite castable‖, American Ceramic Society Bulletin (www.ceramicbulletin.org) 84 [11] p.
The use of particle size distribution in the development of refractory casting material, presented at the XXV ALAFAR Congress, San Carlas De Bailocke, Argentina, 1-4 December 1996, Elkem Refractory. Cambier, Belgian Ceramic Research Centre, Mons, Belgium, ― Refractory castings: an overview‖ cfi/Ber.DKG 84(2007) No.6. Rafael Salomão, Marina Rojas Ismael, Victor Carlos Pandolfelli, Federal University of São Carlos – Materials Engineering Department ― Hydraulic binders for refractory castings: mixing, hardening and drying‖ cfi/Ber.DKG 84(2007) No.9.
21.Z.Li, G.ye, P.R.China, Luoyang Institute of Refractories Research Paper on Refractories Subrata Banerjee, Answer Technology Inc, Wheaton, Illinois, USA Featured Article - Versatility of Gel-bond Castable/Pumpable Refractories. Mrs.) K.M.Parker and J.H.Sharp Dept. Pandolfelli – colloidal silica as a nanostructure binder for refractory castings' Refractories application and news, part 11, number 4.
