Refractories – Refractory Binders

Topics Covered

Background

Types of Bonds Formed in Monolithic Refractories

Calcium Aluminate Cements

Activated Aluminas

Background

The sole purpose of a refractory binder is to gel materials together in the green state. At elevated temperature binders then either dehydrate, volatise or sinter leaving behind a refractory material.

There are a number of binders which are commonly used for refractory applications, the most common of which is high alumina cement. They are always selected with the environment of the final application in mind.

Types of Bonds Formed in Monolithic Refractories

Table 1 summarises the types of bonds formed by the various refractory binders.

Table 1. Bonds formed by refractory binders.

Calcium Aluminate Cements

Calcium aluminate cements are the most common types of refractory binders. Following the addition of water they hydrate to form a network of hydrated species which bond the particulate materials together. During heating they dehydrate then undergo sintering, with the aggregate forming a strong ceramic bond.

Activated Aluminas

Activated aluminas or hydratable aluminas are used in ultra-low and cement-free castables. They consist of high surface area r-alumina species which are formed from partially calcined alumina hydrates. On the addition of water these materials will gel together in a cement-like action by forming alumina hydrates. One advantage of this system is that they do not introduce any calcia into the system, so the fired material will be more refractory. Often the hydration of activated aluminas can be slow and uncontrollable and small amounts of cement additions are required to trigger the reaction. 

Source: CERAM Research Ltd

For more information on this source please visit CERAM Research Ltd.