Sodium hexametaphosphate (SHMP) is used in refractory materials to improve their strength, load-bearing capacity, and resistance to abrasion and high temperatures: 

• Bonding: SHMP is used in refractory mixes along with other phosphate salts, such as sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), or sodium acid pyrophosphate (SAPP), to provide bonding in the finished ceramic product. 
• Dispersing: SHMP can act as a dispersing agent in the precursor slurries. 

Rheology: Adding SHMP to the mix water of MgO/SiO2 cement pastes and mortars can improve their rheology and properties. This can lead to the production of materials with high strength, high density, and low porosity.