Application Prospect Analysis Of Hydraulic Alumina in Amorphous Refractories
Feb 14, 2023
Theoretical basis
Hydraulic alumina in the condition of water, can be hydrated into a gel, has good bonding performance, hydraulic alumina before hydration of the basic morphology of hydraulic alumina and raw material similar to aluminum hydroxide, but the degree of crystallization is very low, hydration of hydraulic alumina is a kind of colloidal substance, the combination between particles is a close combination, can not see the boundary between small particles, It shows that after hydration, it is a kind of colloidal substance, and some cracks are formed on the surface of the particles due to drying and dehydration. Therefore, the hydration and hardening property of hydraulic alumina can be used as the bonding agent of amorphous refractory
Advantages of hydraulic alumina as binder
In the bond used by amorphous resistant materials, each bond has certain advantages and disadvantages, especially in the use of the impurity elements introduced in the use of binders, have a great impact on the performance of refractory materials, such as in the introduction of a bond containing calcium oxide, by Al2O3-SiO2-CaO, at high temperature, CaO can react with Al2O3 and SiO2 in the material to produce two low melting point compounds: anorthite (Cao-Al2O3-2sio2, melting point 1553℃) and anorthite (2CaO· Al2O3-sio2)
, melting point 1593℃). For the multicomponent system such as Al2O3-SiO2-CaO- (Fe2O3, TiO2, Na2O, K2O, etc.), liquid phase can appear at about 1300℃, so that the thermal strength and load softening temperature of the material is reduced. CaO can also react with iron to form Fe2O3-CaO compounds, reducing the high temperature properties of the material. Therefore, the introduction of calcium oxide should be minimized in some high-grade amorphous refractories, so as to improve the high temperature performance of refractories.
The hydrate formed by hydraulic alumina after hydration is alumina hydrate. At high temperature, alumina hydrate will undergo a series of dehydration and phase transition process, and finally form stable α-alumina. α-alumina itself is a kind of refractory material with good performance. At the same time, reduction reaction will not occur, so it is a kind of amorphous refractory binder with good development prospect.
