Effect of silica sol of different routes on the properties of low cement castables
TL;DR: In this paper, the effect of different sources of such sols on the important physico-mechanical properties of the castables such as bulk density, apparent porosity, compressive strength, volume shrinkage and residual strength after spalling have been studied.
Abstract: Silica sols synthesized through different routes viz. inorganic, organic and ion-exchange routes, have been incorporated in the low cement alumina castable composition in various proportions and cast samples in the form of 2 inch cube briquettes were prepared. The cast briquettes after curing were subjected to heat treatment at various temperatures. The effect of different sources of such sols on the important physico-mechanical properties of the castables such as bulk density, apparent porosity, compressive strength, volume shrinkage and residual strength after spalling have been studied. Some of the selected samples were also subjected to microstructural evaluation. It is observed that silica sol synthesized through cation exchange routes has significant beneficial role on the properties of castable with 3% addition.
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TL;DR: In this paper, a comparison of different binding systems for refractory castables is shown and the benefits of replacing CAC or hydratable alumina by colloidal binders is discussed.
Abstract: Calcium aluminate cement (CAC) contents higher than 3 wt% in refractory castables can have some drawbacks in the various processing steps (mainly drying) and also in their refractoriness when in contact with SiO 2 . The use of colloidal silica as an alternative binder has been studied by many researchers in recent years and recently reports have also explored the use of colloidal alumina for the same purpose. This article reviews the recent developments in nano-bonded refractory castables focusing on the use of colloidal silica or alumina. In the first part of the paper, a comparison of different binding systems for refractory castables is shown. The benefits of replacing CAC or hydratable alumina by colloidal binders are discussed. In the second part, the advantages of colloidal silica/alumina as a refractory binder are highlighted. Meanwhile, the characterization techniques and functional mechanisms of these binders are presented in order to understand the behavior of these systems. Finally, in the last section, the challenges for suitable use of colloidal binders are discussed and the future direction of nano-structured refractory castables is outlined.
109 citations
Cites background from "Effect of silica sol of different r..."
...The literature also reports on the use of CAC as the setting agent of colloidal binders [42,69–71]....
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TL;DR: In this paper, the contributions of nanotechnology in selection of raw materials, the binders and choice of additives to improve the quality of refractory materials, and the future of nanotechnical research in refractories are reviewed.
Abstract: In recent times nanotechnology has drawn significant attention in the field of refractory research. Different nano-powders and colloidal suspensions have been utilized to improve the properties of refractory castables. Various studies have been carried out worldwide with nano scaled binders; such as, hydratable alumina (HA), colloidal alumina (CA), colloidal silica (CS), micro silica, etc.; to improve the thermo mechanical properties of refractory materials. Nano scaled additives are also being applied to reduce the energy consumption and to improve the densification process at lower temperatures. In this paper, the contributions of nanotechnology in selection of raw materials, the binders and choice of additives to improve the quality of refractory materials, and the future of nanotechnology in refractory research are reviewed.
34 citations
Journal Article•
TL;DR: In this article, it was found that colloidal silica is one of the best binders can substitute other binders such as cement in No Cement Castable (NCC) and Ultra Low Cement (ULCC) refractories.
Abstract: Colloidal silica bonded refractory castables have been developed recently. It was found that colloidal silica is one of the best binders can substitute other binders such as cement in No Cement Castable (NCC) and Ultra Low Cement Castable (ULCC) refractories. Also composition of colloidal silica with appropriate additives resulted in a gel form which makes the initial strength. Moreover, the nano size silica particles are extremely reactive in high alumina castables and may encourage the mullite formation in the microstructure. In the current study, four castables were prepared. The sample containing 6wt % microsilica was a reference, then microsilica was replaced by different amount of colloidal silica (2.5, 5, 7.5 wt %). Silica and water content was kept constant. It's concluded that the castables containing the optimum amount of silica sol shows remarkable increase in both castable fluidity and mechanical strength (CCS and MOR) in dried and sintered state. It was also found that nanosilica particles increase the rate of needle-shaped mullite formation during sintering at 1400°C. According to FTIR results, the addition of Calcium Aluminate Cement (CAC) to the silica sol may be responsible for the increment of siloxane bridges (Si-O-Si).
16 citations
Cites background from "Effect of silica sol of different r..."
...Formation of this phase in the presence of both silica sol and CAC also was reported in [13]....
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...Also mixing process will be better than in the CAC and HAB bonded refractories [5]....
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...It is can be explained by the reaction of nanosized silica particles with microfine alumina resulting in the formation of mullite needles network [4, 13]....
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...Furthermore, these gel-like structures can improve mechanical strength of the dried samples comparing to the castables containing CAC in which longer time is needed for the dissolution/precipitation process of cement....
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...Adding silica sol to refractory castable doesn’t produce any normal chemical products such as calcium aluminate hydrates in CAC bonded and alumina gel in hydratable alumina bonded (HAB) castable refractories....
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TL;DR: In this article, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated.
Abstract: The bonding system in low cement castables is achieved by the use of calcium aluminate cement, microsilica and reactive alumina. The lime/silica ratio critically impacts the liquid phase formation at high temperatures and subsequently the corrosion resistance and the mechanical and physical properties of the refractory. In the current study, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated. Alcoa Cup test was used to evaluate the corrosion resistance of the castables at 850 oC and 1160 oC. The study showed that an increase in the microsilica/cement ratio improves the physical and mechanical properties of the castable, but at the expense of the corrosion resistance. When a fixed amount of BaSO4 was added to the base refractory material, barium celsian along with glassy phase formation was observed to increase with the increase in the microsilica/cement ratio in the refractory. The presence of the glassy phases was noted to lower the positive effect of Ba-celsian formation on improving the corrosion resistance of the refractory. The observed results were validated using thermodynamic calculations which indicated that Ba-celsian phase was more resistant than Ca-anorthite for applications involving contact with molten aluminum.
13 citations
01 Jan 2010
TL;DR: In this article, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated.
Abstract: The bonding system in low cement castables is achieved by the use of calcium aluminate cement, microsilica and reactive alumina. The lime/silica ratio critically impacts the liquid phase formation at high temperatures and subsequently the corrosion resistance and the mechanical and physical properties of the refractory. In the current study, the effects of microsilica and cement contents on the corrosion resistance and the physical and mechanical properties of Andalusite Low Cement Castables (LCCs) refractories were investigated. Alcoa Cup test was used to evaluate the corrosion resistance of the castables at 850 ˚C and 1160 ˚C. The study showed that an increase in the microsilica/cement ratio improves the physical and mechanical properties of the castable, but at the expense of the corrosion resistance. When a fixed amount of BaSO 4 was added to the base refractory material, barium celsian along with glassy phase formation was observed to increase with the increase in the microsilica/cement ratio in the refractory. The presence of the glassy phases was noted to lower the positive effect of Ba-celsian formation on improving the corrosion resistance of the refractory. The observed results were validated using thermodynamic calculations which indicated that Ba-celsian phase was more resistant than Ca-anorthite for applications involving contact with molten aluminum.
13 citations
References
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Book•
01 Jan 1929
TL;DR: The first edition of the Applied Inorganic Analysis (AIA) was published in 1929 by the National Bureau of Standards (NBS) and the second edition appeared in 1953 by the same authors.
Abstract: The 1929 first edition of Applied Inorganic Analysis [1] was a classic of its time, commonly referred to as the " analyst's bible. " Co-authored by two Chief Chemists of the National Bureau of Standards, Gustav Ernst Fredrik Lundell and William Francis Hillebrand, the book represented the authors' comprehensive knowledge and broad practical experience. The 1953 second edition [2] was a thorough revision by Harry Aaron Bright and James Irvin Hoffman, who were Chief of the Analytical Chemistry Section and Assistant Chief of the Chemistry Division, respectively. Both editions of Applied Inorganic Analysis presented critical expositions of the chemical methods of analysis as applied to a broad range of complex matrices including metals, alloys, rocks, minerals, ores, ore concentrates, and glass. Each of the two editions stood alone as the authoritative single-volume reference for inorganic analysis for many years, and even today remains a valuable resource for pre-instrumental, classical methods of chemical analysis. The story of the development of this remarkable book began in 1878 after the young American chemist William Francis Hillebrand completed a course in metallurgy and assaying at the mining academy in Freiberg, Germany. Fully intent on returning to America and impressed with the opportunities for young chemists as assayers, he took this course in order to supplement the training in mineral analysis that he had received from Bunsen, under whom he had earned his Ph.D., magna cum laude, at the University of Heidelberg, in 1875. Upon returning, he failed to find suitable work in the East, so he made his way in 1879 to Leadville, Colorado, where he became the third partner in a small assaying firm. Samuel F. Emmons, an occasional customer who was in charge of the Rocky Mountain Division of the newly formed United States Geological Survey (USGS), offered Hillebrand a job as a chemist. Considering this offer to be the opportunity of a lifetime, he quickly accepted, remaining in the Denver laboratory of USGS until 1885, when he was transferred to the Washington USGS laboratory. During his 28 years at USGS, Hillebrand made more than 400 complete (for that day) analyses of various rock samples [3]. In 1897 Hillebrand wrote a 50-page introduction to USGS Bulletin No. 148 [4] on the methods of analysis of silicate rocks, and this was translated into German and published in Germany in 1899. In 1900 this material was rewritten and enlarged to 114 pages and issued …
677 citations
TL;DR: In this paper, a new colloidal processing method for near net shaping ceramic components is outlined, which relies on electrostatic stabilized ceramic suspensions and it’s destabilization by time delayed in situ reactions.
Abstract: A new colloidal processing method for near net shaping ceramic components is outlined. The Direct Coagulation Casting (DCC) process offers the opportunity to produce complex shaped components of high mechanical strength and high reliability at low costs. The process relies on electrostatic stabilized ceramic suspensions and it’s destabilization by time delayed in situ reactions. Enzyme catalyzed reactions may be used either to create salt at a constant pH or/and to shift the pH of the suspension to the isoelectric point of the powder. Different enzyme/substrate systems are outlined, suitable for different ceramic powders. The reaction kinetics of the liquid – solid transition can be controlled by the enzyme concentration and temperature. The mechanical properties of the resulting viscoelastic ceramic green bodies in their wet state are characterized by dynamic viscosity measurements as well as by their compressive strength. The resulting wet green strength is highest for fine particle suspensions with high solids loading. The wet green strength may be increased using alkaline swellable thickeners changing their conformation upon the enzymatic reaction. Ceramic processing routes are reported for alumina powders.
188 citations
"Effect of silica sol of different r..." refers methods in this paper
...Gauckler et al (1999) and Studart et al (2002) recently reported that coagulation mechanism involve the modification of the nature of forces acting among fine particles from typically repulsive to attractive forces....
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01 Jan 1992
TL;DR: The authors discute des mecanismes et des applications des liaisons hydrauliques, chimiques, ceramiques, adhesives et de coagulation dans les refractaires monolithiques.
Abstract: On discute des mecanismes et des applications des liaisons hydrauliques, chimiques, ceramiques, adhesives et de coagulation dans les refractaires monolithiques.
24 citations
Journal Article•
TL;DR: In this paper, the enzyme coagulated high-alumina castables were examined for their refractoriness and high-temperature properties for lowmelting-point eutectic phases.
Abstract: Examines the enzyme coagulated high-alumina castables. Enhancement on refractoriness and high-temperature properties for low-melting-point eutectic phases; Decrease on hydraulic binder content; Migration of fine particles in the castables during drying process..
5 citations
"Effect of silica sol of different r..." refers methods in this paper
...Gauckler et al (1999) and Studart et al (2002) recently reported that coagulation mechanism involve the modification of the nature of forces acting among fine particles from typically repulsive to attractive forces....
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TL;DR: In this article, a set of fundamental regularities of the thermodynamics of irreversible processes (nonequilibrium thermodynamics) is used to analyze the processes of structure formation in manufacturing new refractory concretes.
Abstract: With allowance for the approach developed preferentially in the works of Tsimmermanis and Shtakel'berg, a set of fundamental regularities of the thermodynamics of irreversible processes (nonequilibrium thermodynamics) is used to analyze the processes of structure formation in manufacturing new refractory concretes. Structure formation and hardening of concretes is phenomenologically realized as the formation of a capillary-porous structure in the process of changes in the free surface energy of the system, which serves as a measure for the strength, elastic, and other properties of the material. In this approach to thermodynamic analysis of structure formation the watering potential of a disperse system is treated as an analog of the Gibbs chemical potential. The notions of structural affinity and the degree of completeness of structure formation are introduced by analogy with chemical affinity and the degree of completeness of a chemical reaction.
5 citations
"Effect of silica sol of different r..." refers background in this paper
...The similar observation was also made by Pivinskii (1995)....
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