(1) Field of the Invention
The present invention relates to an anode paste for use in the electrolytic furnace for aluminum, and particularly, relates to an anode paste for use in Soderberg-type electrolytic furnace for aluminum.
(2) Description of the Prior Art
The anode paste for use in the anode of Soderberg-type electrolytic furnace for aluminum is usually prepared by pulverizing cokes such as calcined pitch cokes or petroleum cokes to obtain pulverized cokes as an aggregate, adding a suitable amount of a binder such as tar pitch to the aggregate, kneading the thus formed mixture to be a paste-like state, and solidifying the paste-like mixture into a briquette-like shape. The thus prepared anode paste is put into the electrolytic furnace from the upper part of the anode in an amount corresponding to the amount of consumption thereof at the lower surface of the anode and then the anode paste constitutes the baked carbon anode while gradually moving downwards with the consumption of the anode by the electrolysis.
As the important items in the performance of carbon anode formed by baking the paste during the electrolysis shown above, the following three points are mentioned.
(1) The carbon anode should have high electrical conductivity. PA1 (2) The amount of consumption of carbon by electrolysis should be small. PA1 (3) The contact between the spike and the anode should be favorable (there are occasions where anode carbon cracks due to the thermal expansion of the spike and to the contraction of the anode paste during the baking step to make the contact between the spike and the carbon poor.).
(a) On the following two reactions, the amount of consumption of carbon due to the secondary reaction should be small (in other words, the secondary reaction difficultly occurs). EQU Al.sub.2 O.sub.3 +3/2C.fwdarw.2Al+3/2CO.sub.2 (primary reaction) EQU C+CO.sub.2 .fwdarw.2CO (secondary reaction) PA2 (b) The amount of anode carbon which disintegrates as a floating carbon on the surface of electrolytic bath should be small.
Usually, the above-mentioned performances of the anode depends on the composition of the aggregate, the composition of the binder, the amount of them and the like. However, the relationship between the performance of the anode and such a factor has not been satisfactorily clarified.
The present inventors have made studies on the anode paste which is able to maintain the above-mentioned performances as the anode in suitable state, and as a result, have found that the anode of extremely favorable performances can be formed by maintaining the particle size-distribution of the aggregate in a specified range, and have attained the present invention.