katodiset

Katodiset is a term referring to the cathodes in various electrochemical and electronic devices. In electrochemistry, the cathode is the electrode where reduction takes place. The sign of the cathode depends on the type of cell: in galvanic (voltaic) cells it is the positive electrode, while in electrolytic cells it is the negative electrode. The opposing electrode is the anode, where oxidation occurs.

In galvanic cells such as a Daniell cell, reduction occurs at the cathode, for instance copper ions reduced to copper metal on the copper electrode. In electrolytic cells, electrical energy drives a non-spontaneous reaction; the cathode attracts cations and is connected to the negative terminal.

In electroplating, the object to be plated is made the cathode; metal ions are reduced at its surface, forming a metal layer, while the anode dissolves to replenish ions.

In vacuum tubes, the cathode is a heated source of electrons (thermionic emission); electrons emitted by the cathode are attracted to the anode, enabling current through the tube. In cathode ray tubes and certain diodes, the terms reflect the direction of electron flow.

Materials for cathodes vary by application: metals such as copper or nickel in electrochemistry; coated or impregnated tungsten, graphite, or lanthanum hexaboride in vacuum devices.

The term derives from Greek kathodos, meaning “the way down,” via historical usage in German and English. See also anode, electrochemistry, thermionic emission, cathode ray tube.