Refractories are the basic materials for the development of high-temperature industrial technology. To a certain extent, the quality and type of refractories play a key role in the development of high-temperature technology. Compared with shaped refractories, unshaped refractories have many advantages and do not require Preforming and firing, simple production process, short cycle, energy and material saving, convenient construction, high efficiency, safe use and wide application range, are the main direction of research and development in the refractory material material industry, and are also widely used in high temperature industries. It can be divided into castables, plastics, ramming materials, etc. according to the construction method.
 
The castable refractory material is a refractory material castable with good flow properties obtained after a certain proportion and particle gradation of aggregates, powders, binders and admixtures are first dry mixed and then wet mixed with water. It can be directly cast into a lining or prefabricated block, which has the advantages of convenient and flexible construction, shortened construction period, and reduced labor intensity.
 
The refractory material castable also has good construction performance and performance, and has been widely used in high temperature industries such as iron and steel metallurgy, petrochemical industry, etc. The binder used in the castable can bond the aggregate and fine powder particles together, so that the castable has The fluidity required for on-site construction and sufficient bonding strength after curing. The castable is a material that is directly used without high temperature sintering, so the binder has a great influence on its performance.
 
The binders in the castable can be divided into chemical binders, cohesive binders, hydration binders, etc. Among them, chemical binders include phosphoric acid or phosphate, sodium silicate or potassium silicate, phenolic resin plus hardener, etc. They are bonded by new compounds or polymeric bridges (cross-linking) generated by the chemical reaction between the binder and the refractory material (oxide aggregate) at room temperature or when heated. When used in materials, phosphoric acid, phosphates, silicates, etc. will decompose and release harmful gases (such as P2O5, SO2, etc.), which will not only corrode equipment and instruments, but also pollute the environment; in addition, most chemical binders When used in liquid form, impurities such as Na2O and K2O will be brought in, which will reduce the high temperature performance of refractory material castables.
 
Coagulation binders include clay micropowder, SiO2, AL2O3, TiO2, Cr2O3 and other oxide micropowders, silica sol, aluminum sol, and the like. Cohesion bonding is the bonding produced by the van der Waals force generated by the attractive and close contact between microparticles (colloidal particles).
 
Hydrated binders include calcium aluminate cement, hydrated alumina (also known as ρ-A12O3) and the like. The hydration binding agent will react with water to form hydration products after contacting with water at room temperature. Hydration binding is the combination generated by the hydration products generated after the binding agent meets water, so as to achieve the purpose of cementing particles. The most commonly used bonding system in refractory material castables. Among them, calcium aluminate cement is the most widely used because it can obtain higher strength of the castable in a short curing time of 24 hours. Compared with calcium aluminate cement, although hydrated alumina can make the castable have acceptable solidification time, but also makes the castable more sensitive to drying treatments and less strong. Hydrated alumina binder is mainly used in castables for unshaped refractories that require relatively low CaO content for some reasons.