Coefficient of thermal expansion is a physical quantity that measures the degree of expansion of an object when it is heated. The expansion of solid material per unit temperature rise and per unit length is called coefficient of expansion. The linear expansion coefficient can be divided into linear expansion coefficient (along the length direction) and volume expansion coefficient. According to the directivity of the test sample, the CTE along the axial direction of the electrode and the CTE along the radial direction of the electrode can be determined respectively.
Detection method: put the 8mm×50mm sample into the quartz tube in the furnace of the linear expansion instrument. Both ends of the sample are covered with a quartz cone. Insert the thermocouple into the temperature measuring hole, cover the furnace, close the thermocouple switch, and adjust the temperature indication to room temperature. Adjust the temperature and expansion coordinates respectively, switch on the thermocouple, and pass nitrogen into the electric furnace. The cooling system is connected to the cooling water, and the electric furnace is powered, and the temperature is raised at 3℃/min. The quartz jacking rod of the linear expander is connected with a reflector. When the sample is expanded, the jacking rod drives the reflector to rotate to change the Angle of the light point, and the mirror projects the moving light point onto the cassette negative. When the temperature reaches 600℃, the power supply of the electric furnace is turned off. When the temperature drops to 100℃, nitrogen is stopped, and the cooling water is closed.
► The linear expansion coefficient is calculated as follows:
Alpha = (L2 - L1)/KL0 (600-100) + alpha quartz
Where is the average linear expansion coefficient of the sample at the temperature of 100 ~ 600℃, 1/℃. L0 is the sample length at room temperature, mm; L1 is the sample length at 100℃, mm; L2 is the sample length at 600℃ (mm); K is the amplification factor of the dilatometer; Alpha quartz refers to the average linear expansion coefficient of quartz at 100 ~ 600℃, 0.618×10-6/℃-1.
► In addition, there is a simple and practical dilatometer, widely used in China carbon plant, the principle of the instrument is the same as the above method, the electric furnace is vertical, with a digital thermometer to measure the temperature, with a micrometer thimble on the quartz rod to measure the expansion of samples at different temperatures. The instrument does not use nitrogen and cooling system. The calculation formula is as follows:
Alpha = (L2 - L1)/L0 (600-100) + alpha quartz
The symbolic meaning in the formula is the same as the preceding one.
►Graphite electrode features: graphite electrode thermal expansion coefficient