Carbonizing (metalworking)

Carbonization or coaling refers to the covering of the surface of electrodes made of sheet metal or wire mesh of electron tubes with a thin, blackening carbon coating .

A PL802, the blackened screen grille is clearly visible .

The creation of this layer can be done by

• Precipitation of soot from flames ,
• Application of finely divided carbon mixed with a binding agent (e.g. Aquadag ) on the mostly roughened metal substrate with subsequent heating under vacuum to 700–950 ° C, advantageous for substrates made of nickel ,
• thermal decomposition  of hydrocarbons

can be achieved.

The surfaces treated in this way have an increased radiation of the thermal energy introduced by the anode power loss . Are carbonized u. A. Anodes , grids or cooling wings in amplifier or small transmitter tubes.

Carbonized surfaces are not very smudge-proof and costly to degas . From the 1940s onwards, anodes treated in this way have been almost completely replaced by P2 iron , a surface roughened by an aluminum-iron reaction.

literature

• Werner Espe: Materials science of high vacuum technology . 1: Metals and metallically conductive materials. VEB Deutscher Verlag der Wissenschaften, Berlin 1957.