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The Structure of Black Chromium

I have recently prepared a review paper on black chrome for the Institute of Metal Finishing (UK). I have not been able to find any references to the actual structure of the deposit and I am curious to know exactly what black chrome consists of. The elemental composition is approximately 60% chromium, 35% oxygen and some hydrogen. This suggests that the deposit consists mainly of oxides of chromium. However, as far as I am aware, the only oxide of chromium which is black is chrome (IV) oxide and this is ferromagnetic! Black chromium is non magnetic although the percentage of chromium and oxygen in the deposit does suggest an empirical composition of approximately CrO₂. I would be grateful if anyone could help out here or point me in the direction of some references.

Thanks,

Dr. Trevor Pearson, MIMF
- U.K.
1996

I have a lot of papers regarding black chromium. A lot of research has been done in Australia and I have most of them but not on the computer. If you send me your address I can mail it for you.

Most papers (including NASA's report) state that 75% is metallic chromium and 25% Cr₂O₃. X-ray and auger indicated that black chrome surface exists as a porous finely structured medium with small particles embedded in a chromium oxide dielectric matrix.

On the other hand I found an article stating that the non metallic component of black chrome is predominantly a hydroxide rather than an oxide. Sara

Sara Michaeli
Tel-Aviv-Yafo, Israel
1996