Bonding mechanisms of bonding agents for refractory materials
The bonding agents for refractory materials have different bonding mechanisms depending on the chemical properties of the bonding agent. There are six typical binding mechanisms. Generally speaking, a binding agent has its specific binding mechanism, but sometimes several binding mechanisms also exist at the same time. This is very important for the material design, and sometimes special requirements can be achieved through a certain bonding mechanism with different bonding mechanisms.
(1) Hydration combination
The binding effect is generated by the hydration reaction between the binder and water at normal temperature to generate hydration products. For example, all types of cement are bonded through the hydration bonding mechanism and give the material strength.
(2) Chemical bonding
With the aid of a binding agent and a coagulant, or a chemical reaction between the binding agent and the refractory material at normal temperature, or a chemical reaction upon heating, a compound with a binding effect is formed to form a bond. For example, when sodium silicate (water glass) binding agent is added with sodium silicate coagulant, it will react to form an aqueous solution SiO2: nH2O, which will be dehydrated to form a siloxane (Si-O-Si) network structure, resulting in a stronger Combined effect.
With the addition of a catalyst or a cross-linking agent, the binding agent undergoes polycondensation to form a network-like structure to generate binding strength. For example, novolac resin plus methyltetramine undergoes polycondensation bonding through a crosslinking reaction under heating conditions.
(4) Ceramic bonding (sintering bonding)
Adding additives or metal powders that can reduce the sintering temperature to the refractory material can greatly reduce the temperature at which the liquid phase appears, and promote the solid-liquid reaction at low temperatures to produce low and medium temperature sintering bonds.
(5) Adhesive (adhesive) bonding
Binding occurs by virtue of one or more of the following physical effects: one is the adsorption, including physical and chemisorption, and the binding is based on the intermolecular interaction force-Van der Waals force; the second is the diffusion effect That is, under the action of the thermal movement of the material molecules, the binding agent and the molecules of the bound substance mutually diffuse, and a diffusion layer is formed at the interface to form a strong bond; the third is the electrostatic effect, that is, the binding agent is bonded There is an electric double layer at the interface of the object, which is combined by the electrostatic attraction of the electric double layer.
By adding a coagulant, the microparticles (colloid particles) are coagulated to form a bond.