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Colour of electroless NiB bath and stability

Hello, I am a university student trying to develop electroless NiB coating.Previously I used nickel chloride as the source of nickel and Sod-Pot-Tartrate as complexant and the colour of bath was green and could be seen through. Instability could be understood when black particles appeared and transparency of bath was lost. But now I have changed my complexant to ethylenediamine(99%) and using a concentration of 60 g/l. The bath becomes dark purple and can't be seen through. Hence instability could not be understood as was previously possible although coating can be developed.
Hence I want to know whether is it normal that such a colour (dark purple) develops when using ethylenediamine or am I using it in excess ?

Suman Das
student - Kolkata, West Bengal, India
October 31, 2008

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Dear Suman Das,

When you use ethylenediamine as the complexing agent, it is normal to expect the dark purple colouration (Ni-ED complex). The extent of purple colouration depends on the ratio of Nickel/ED.

Instability of the bath can be observed from hydrogen evolution which would occur throughout the bath solution.

Since borohydride is a powerful reducing agent, addition of a suitable stabilizer is recommended.

T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
(ed.note Nov. 2017: The good doctor has a fascinating blog at https://advancementinscience.wordpress.com)
November 16, 2008

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November 30, 2008

Hello, I am a university student trying to prepare electroless Ni-B coatings. I studied your article "Electroless NiÿB coatings: preparation and evaluation of hardness and
wear resistance" and did exactly like you.
(Bath composition
Nickel chloride 30 g/l
Sodium borohydride 0.1 g/l
Ethylenediamine (98%) 90 g/l
Sodium hydroxide 90 g/l
Thallium acetate 16 mg/l
Operating conditions
pH 14
Temperature 95)

but my coatings are so porous.
could you tell where the problem is?

Donya Ahmadkhany
student - Tehran, Iran