Coating oxide (chemical blacking) in surface industry

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  • Chemical blacking flowsheet


General flowsheet for the surface treatment of metals & plastics:


Chemical blacking flowsheet.jpg

Literature: BAT for the surface treatment of metals & plastics, 2006


  • Typical parameters of the process


Process Temperature [°C] Heat transfer medium Residence time Chemicals Concentration Details Literature
Chemical blacking of steel 121-149 Sodium hydroxide and sodium nitrate or a mixture of sodium nitrate and sodium nitrite Sodium hydroxide: 75 wt% and sodium nitrate: 25 wt%; sodium nitrate: 12 wt% and sodium nitrite: 13 wt% BAT for the surface treatment of metals and plastics, August 2006
Chemical blacking of stainless steel 370 Molten sodium/porassium dichromate
60-90 Chromic acid and sulphate "Inox" process
125-130 NaOH/NaNO2 Black colouring of chromium nickel steel
Chemical blacking of copper 93-100 Sodium hydroxide and sodium chlorite Sodium hydroxide: 75 wt% and sodium chlorite: 25 wt%
Chemical blacking of brass 93-100 5-10 min Sodium hydroxide and sodium chlorite Sodium hydroxide: 85 wt% and sodium chlorite: 15 wt%



  • Energy losses from the surface area of heated process solutions


Energy losses from the surface area of heated process solutions.jpg

LITERATURE: BAT for the Surface Treatment of Metals and Plastics, May 2005


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