Temperature Conductivity and Conductivity

Temperature conductivity is the ability of the material to have the same temperature tendency in the process of heating or cooling, that is, the transfer rate of temperature.

The temperature conductivity is expressed by thermal diffusivity (also known as thermal conductivity):

λ / (pcp)

In the formula = thermal diffusivity, m ~ 2 ≤ s;

λ = thermal conductivity, W / (m ≤ K);

P = bulk density, kg/m3;

Cp= isobaric mass heat capacity, J / (kg*K)

The higher the value of refractory, the higher the propagation speed of internal temperature and the smaller the temperature difference everywhere under the same external heating or cooling conditions, so it determines the size of the internal temperature gradient when the material is hot and cold.

The thermal diffusivity of materials is an important parameter to analyze and calculate the unstable heat transfer process. The temperature distribution of intermittent kiln wall and the calculation of heat storage should be used.

The thermal diffusivity of the material is related to its thermal conductivity and volume density. There is no test method for determining thermal diffusivity in the current national standard of refractories.

Conductivity refers to the ability of a material to conduct electricity. The resistance (also known as resistance or resistance coefficient, which represents the resistance of the material to the current when the current passes through the material) is usually used to indicate that the greater the resistance of the material, the lower the electrical conductivity of the material. The relationship between resistance and temperature is as follows:

p=AeB/T

In the formula p = resistance;

T = absolute temperature;

B = constant related to material properties.

At room temperature, general refractories (except carbon refractories) are bad conductors of electricity. With the increase of temperature, the resistance decreases and the conductivity increases. Impurities, pores and atmosphere in refractories all have effects on their conductivity. The impurity content is high and the resistance is also high. The resistance of refractories increases with the increase of porosity, the porosity is high and the conductivity decreases. However, at high temperature, the effect of porosity on resistance will weaken or even disappear.

Graphite has good conductivity. Conductive refractories mainly refer to carbon-containing refractories with graphite as conductive material, such as Mgo-C, Mgo-Cao-C, Al2O3-C and so on. In carbon-containing refractories, the amount and particle size of graphite have an effect on the resistance of the materials. In Mgo-C brick, when the amount of graphite is between 5% and 12%, the resistance decreases rapidly with the increase of graphite content, while when the amount of graphite is between 12% and 20%, the decrease of resistance is smaller, and the selection of graphite less than 0.147mm is more beneficial to improve its conductivity. Sex. In addition, because the anisotropy of graphite conductivity and its distribution orientation cause the anisotropy of electrical conductivity of Mgo-C brick, attention should be paid to the orientation of graphite in brick when forming and using graphite refractory.

The normal temperature resistance of carbon-containing refractory products is measured according to the standard YB/T173-2000 test method of Chinese black metallurgy industry. the principle is that the resistance of the sample is measured directly by DC double-arm bridge, and the resistance is calculated according to the length and average cross-section area of the sample. The formula is as follows:

P=R*A/L

In the formula, P = the resistance of the sample, Ω * m;

R = the resistance of the sample, Ω;

A = the average cross section area of the sample, m2;

L = the length of the sample, m.