1. Overview of electrode paste roasting process
According to the observation of small-scale tests, taking special paste as an example, the sintering process can be roughly represented in the following table.
The main roasting process is completed in the range of 400 ~ 800 ℃. During the small-scale test, because the paste surface is not high and the exhaust conditions are good, a large amount of gas escapes. In production practice, the upper liquid electrode paste hinders the upward movement of the gas. Except that a part of the gas is discharged from the small holes ablated when the electrode shell passes through the copper tile, most of the gas is further cracked into free carbon at 800 ~ 900 ℃ and filled in the pores of the electrode.
2. Determination of specific resistance during baking of electrode paste
Place the corundum crucible containing the electrode paste sample in the silicon carbide rod electric furnace, raise the temperature at the rate of 100 ℃ per hour, measure the resistance value of the electrode paste at the corresponding temperature through a pair of metal plates pre processed into the electrode paste with an electric bridge, calculate and correct with the container coefficient calibrated with 0.1N potassium chloride standard solution in advance, and then * the specific resistance value of the electrode paste at this temperature.
Through this experiment, we can see the following problems:
(1) In the past, although it was known that the conductivity of electrode paste was poor before burning, it was still used to regard electrode paste as a conductor. Conclusions can be drawn from the measurement results; Electrode pastes before 400 ℃ are basically insulators. Taking standard pastes and special pastes as examples, their specific resistance at low temperature is very large, and it is impossible for current to pass through under the working conditions of electric furnaces.
In order to prove this problem, we used a plastic tube with a diameter of 100m/m and a length of 300m/m to put electrode pastes with different particle sizes, connect the power supply at both ends, control the voltage value with a voltage regulator, and record the voltage based on the current of 25 mA passing through the line.
According to the particle size, the electrode paste column with a diameter of 100 m/m and a length of 300 m / M needs a voltage of 140 ~ 260 volts to start the current flow, which shows the poor conductivity.
(2) From the test results of special paste and standard paste, it can be seen that the difference between the two is that the special paste has a lower specific resistance value before 500 ℃, while it gradually tends to be the same after 500 ℃. Examples of specific resistance changes during baking of standard paste and special paste are shown in the table below. It can be seen that the sealed paste is significantly better than the standard paste at low temperature. Therefore, the crucible is small, and there are few electrode paste samples (1100 grams) for each roasting, so the characteristics of special paste, such as fast heat conduction speed and strong self sintering ability, are not easy to show in small-scale tests. However, considering that graphitized coke with good heat transfer is mostly used in the formula of special paste, its thermal conductivity is certainly better than that of standard paste in the sintering process, so the advantage of using special paste under the condition of electric furnace production will be more prominent than that of small-scale test