Chemically bonded phosphate ceramics and refractories result from reacting an acidified phosphate or phosphoric acid and a sparsely soluble metal oxide. Unique features of this highly versatile product have opened up a wide array of applications, from the typical porcelain applications to the more diverse applications of oil well cements, hazardous waste containment, spray-on housing materials and road repair. The functionality of phosphate salts ranges from providing bonding in the finished ceramic products to acting as dispersing agents in the precursor slurries.
ICL polyphosphates are used to prepare high solids clay slurries that flow readily into molds. Along with monopotassium phosphate (MKP), they also provide bonding in the refractory mix and increase the green strength of the refractory castings. Sodium hexametaphosphate (SHMP) is commonly used in this application, along with sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP) or sodium acid pyrophosphate (SAPP).
Phosphoric acid is an excellent bonding agent for high-alumina refractory products. The bond is formed by reaction of the acid with the alumina in the refractory aggregate yielding an aluminum phosphate cement. Magnesia, zirconia and carbon refractories can also be bonded with phosphoric acid. Phosphate-bonded refractories are generally superior in terms of strength, load-bearing, high-temperature stability and abrasion resistance.
Additional information on these and other ceramics applications are available from our technical service group.