Effect of temperature on the service life of refractory

Temperature is one of the important factors that affect the life cycle of firebricks. Among the many factors that affect the life cycle of firebricks, these factors do not exist alone, but often appear in a comprehensive form.

The basic performance of refractory materials is to resist high temperature and have heat insulation. However, temperature will affect all damage, such as impurities, at lower temperatures will form a liquid phase, resulting in shrinkage, and resulting cracks. Bulk material

In addition, when the refractory comes into contact with the slag, it diffuses into the slag, and the diffusion rate (dn/dt) can be expressed by the following formula:

dn/dt=DS(ns-n)/δ (1)

Where, D is the diffusion coefficient; S is the contact area between the refractory and the slag; ns and n are the saturation concentration of refractory in molten slag and the concentration at time t, respectively. δ is the thickness of the diffusion layer.

The diffusion coefficient varies greatly at different temperatures, which has the following relations:

D=Aexp-(Q/RT) (2)

Where, A is a constant; Q is the diffusion activation energy; R is the gas constant and T is the temperature.

You plug equation 2-2 into equation 2-1

dn/dt=Bexp(-Q/RT) (3)

Where, B=AS(ns-n)/δ; Formula 2-3 indicates that when the refractory appears melt loss, the melt loss increases exponentially with the rise of temperature. For the general melting reaction rate (υ), it depends on the diffusion rate:

υ=dn/dt=Bexp(-Q/RT) (4)

Due to the Stokes-Einstein relation between viscosity and diffusion coefficient:

D = KT = 6 PI eta gamma (5)

Where, K is Boltzmann constant; γ is the radius of the migrating particle; η is the viscosity coefficient. This relation is derived from the simple case of spherical particles in a homogeneous medium and is not necessarily available in silicate and oxide systems. However, the inverse relationship between D and η is certain. Equations 2-3 and 2-5 show that the viscosity of the reactant decreases with increasing temperature. When the viscosity of the solution is reduced, the amount of invading slag increases, the reaction area expands, and the melting loss accelerates.

In actual use, it is found that in the glass kiln, the melting temperature rises by 1℃, the erosion of the refractory increases by 10%, and in the LD converter, the steel temperature increases by 30℃, and the damage of the refractory is doubled. All these circumstances show that the influence of temperature on melting loss is very large. In order to solve this problem, in addition to the basic raw materials, the structure of the refractory that is, the porosity and the pore size are also very important, but the most important thing is that the wetting Angle (θ) between the refractory and the slag should be at 90 ° C, so the use of non-wetting materials is more effective. Generally speaking, the wettability between carbon materials and slag is small, so the use of carbon coordination is effective. The example of temperature erosion of A, B, C3 bricks in Al2O3-SiC-C system is shown in Figure 13-2-1. The figure shows that the erosion of these three kinds of bricks is small, and the infiltration is also small, but the erosion increases with the rise of temperature. Therefore, when A kind of brick is not ideal, B kind of brick is designed; When B kind of brick can not meet the conditions of use, C kind of brick is designed.

The influence of temperature on the damage of refractory materials can also be cited as an example of MgO-C brick. As shown in FIG. 2, the coexistence zone of MgO-C system Narrows sharply at high temperatures, and it has been reduced to a line at 1700℃. When it exceeds 1800℃, the two can no longer coexist.