Validation and development of an electroplating process to deposit a black chromium coating from a trivalent chromium electrolyte

University essay from Uppsala universitet/Tillämpad materialvetenskap

Author: Josefin Sjöberg; [2016]

Keywords: ;

Abstract:

SAAB AB coats a part of their magnetron with black chromium to

enhance its ability to radiate thermal radiation. Today an

electrodeposition process that has hexavalent chromium as its main

component is used, but hexavalent chromium is carcinogenic and

will be prohibited. This project examines if an electrolyte based

on trivalent chromium can result in a black chromium coating.

The project was divided into in four experimental parts:

investigation of the adhesion on copper, the effect on color if

copper was added to the electrolyte and investigation of the

process parameters with and without cooling of the electrolyte.

It was concluded that a black chromium coating can be deposited

from a trivalent electrolyte. Heating the sample after plating and

addition of iron or copper in the electrolyte darkens the color

but addition of copper can not produce a coating on copper

substrates with good adhesion.

To examine how the coating thickness and emissivity vary with the

current density, electrolyte temperature and plating time, the

coatings thickness and emissivity were measured for different

settings. It was shown that the coating thickness increased with

plating time and current density until a critical value was

reached and the coating started to peel off. No correlation

between the emissivity and process parameters could be shown. It

is suggested that further experiment are conducted to investigate

if a variation in pH- value effects the emissivity. Based on the

results and conclusions it is recommended that the addition of

iron to the electrolyte is further examined.

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