Refractory castables bonding

Gitzen WH, Hart LD. Explosive spalling of refractory castables bonded with calcium aluminate cement. Bull Amer Cer Soc 1961 40(8) 503 -507, 510. 

S. Mukhopadhyay, et al., In situ spinel bonded refractory castable in relation to co-precipitation and sol-gel derived spinel forming agents. Ceram. Int. 29(8), 857-868 (2003). 

Ahari KG, Lee WE, Habesch S. Spinel formation in cement-free castable bond systems. Proc. 44th Inti. Coll, on Refractories, Refractories in Steelmaking, Aachen, Germany, 2001 160-163. 

As mentioned, refractory castables are combinations of refractory aggregates, matrix components, bonding agents, and admixtures. The proportions of each component used vary in each castable composition to achieve the desired physical and chemical properties and characteristics for the intended castable application. The general range of component quantities in a refractory castable is shown in Table 2. 

Refractory castables must set or harden at room temperature. Either water or another catalyzing agent must activate the bonds used in castables. After... 

Regular Castables. These are hydraulically bonded refractory castables containing cement however, they do not contain a deflocculant. 

Chemically Bonded Castables. These refractory castables contain one or more chemical bonds. After the addition of water or a suitable mixing liquid and an intensive mixing, they start setting mostly due to a neutralization process. By this it should be stressed that a clear differentiation between a chemically bonded castable and a deflocculated one of the NCC type is hardly possible. This can be also traced back to the fact that the nature of bonds has not been investigated in detail, respectively classified, so far. 

The bond is ensured by the hydration of an aluminous refractory cement added to the product. This cement is made up of a mixture of calcium aluminates which are hydrated in the presence of water at low temperatures, by provoking hardening of the material. It therefore refers to a cold binding method. Irrespective of its content high (around 30%), low (around 2% to 10%) or ultra low (less than 2%), this cement is considered to be the typical binder for refractory castables. 

Castable refractories consist of course and fine grains with suitable bonding cement. After mixing with water, these are poured in place using molds or pouring forms. 

No-Cement Castable. Alumina and aluminosilicate castable refractories which do not contain hydraulic setting cement and in which the bonding agents contribute no significant amount of lime (CaO). The product might contain up to 0-2% total lime (CaO) on a calcined basis as contributed by the aggregate. (ASTM C401-91). 

Plascast. A clay-bonded castable refractory which is claimed to combine... 

In the aluminum industry, melting furnaces are made entirely out of monolithic refractories. The heating chamber is lined with high-alumina castable, while sections that are in direct contact with the metal are made from phosphate-bonded plastic refractory. 

Castable and plastic refractories are the two types of liners most commonly used. The plastic varieties incorporate phosphate as a chemical bond-... 

Due to the recent development of sol-gel bonded refractories (2), the high-temperature properties of castable/pumpable refractories have improved significantly since the high-temperature phases are no longer low-melting. It forms muUite only at higher temperatures (since there is no CaO or MgO) and thus provides better properties at elevated temperatures. 

Baneijee S. Versatility of gel-bond pumpable/castable refractories. ALAFAR XXVin Congress, Aruba, 1999 13-24. 

Fuhrer M, Hey A, Lee WE. Microstructural evolution in seff-forming spinel/calcium aluminate-bonded castable refractories. J Euro Ceram Soc 1998 18(7) 813-820. 

The abrasion loss from a material is highly dependent upon its density and porosity, the angle of impact, and the grain size and nature of the abrading media. Variation also exists between the outer skin of a refractory material and its interior, and tests take this into account. The abrasion loss generally decreases for fired refractories with increasing temperature as the material softens. However, for castable refractories, abrasion loss increases at elevated temperatures as the hydraulic bond is lost, but reduces again as a ceramic bond is formed (8). 

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