Refractory properties research

Thermal properties and electrical conductivity of refractory materials

1.1 Thermal expansion

The GB/T7320 standard has two definitions: the coefficient of linear expansion (relative rate of change of sample length between room temperature and test temperature, expressed in %), and the average coefficient of linear expansion (the temperature of the sample is increased by 1 ° C between room temperature and test temperature). The relative rate of change, in units of 10-6/°C).

GB/T7320 standard measurement principle: the sample is heated to the specified test temperature at the specified heating rate, the change of the length of the sample with the increase of temperature is measured, and the linear expansion rate and the specified temperature of the sample with the increase of temperature are calculated. The average linear expansion coefficient of the range and plot the expansion curve.

1.2 Thermal conductivity

The thermal conductivity is defined as the amount of heat transferred per unit area of the material along the direction of heat flow per unit temperature gradient per unit time.

The principle of determining the thermal conductivity is: according to the basic principle of the stable heat conduction process of the Fourier one-dimensional plate, the flow of the heat flow flowing through the central calorimeter after passing through the hot surface of the sample longitudinally to the cold surface in the one-dimensional temperature field per unit time at steady state is determined. The amount of heat absorbed. The heat is proportional to the thermal conductivity of the sample, the temperature difference between the hot and cold surfaces, and the area of the heat absorption surface of the central calorimeter is inversely proportional to the thickness of the sample.

The physical meaning of thermal conductivity refers to the amount of heat passing through a unit of vertical area per unit time under a unit temperature gradient. Thermal conductivity is a physical indicator of the thermal conductivity of a refractory material, and its value is equal to the heat flux density divided by the negative temperature gradient.

1.3 heat capacity

Any substance heats up when heated, but the heat required to heat up 1 °C for different substances of the same quality is different. It is usually expressed by the amount of heat (KJ) required to heat 1 kg of material at normal pressure to raise the temperature by 1 ° C, which is called heat capacity (also called specific heat capacity).

1.4 Conductivity

Refractory materials (other than carbonaceous and graphite products) are poor conductors of electricity at room temperature. As the temperature increases, the electrical resistance decreases and the conductivity increases. The increase is particularly remarkable at temperatures above 1000 ° C, such as heating to a molten state, which exhibits a large electrical conductivity.