Degrease the sample of parts in an organic solvent, dry thoroughly and weigh to an accuracy of 1 in 10000: them totally Immerse the parts in the requisite stripping solution and tum them over to allow free access to all surfaces. After the effervescence has ceased, remove the parts, wash immediately in running water and wipe with a soft cloth t remove any loose deposits. Immerse in clean acetone, remove, dry thoroughy and reweigh.
A stripping solution consists of
--- hydrochloric acid (1,16 g/ml ≤ p ≤ 1,18 g/ml): 800 ml
--- distilled water: 200 ml
--- antimony trioxide: 20 g
Calculate the batch average thickness of coating, in micrometres, using the following
formula:
Batch average thickness = K(m0 - m1 )/A
where
K is a factor dependent on the density of the deposit metal (K = 10000/p
cm3/g);
m0 is the original mass, in grams, of the sample;
m1 is the final mass, in grams, of the sample;
A is the total area, in square centimetres, of the parts of the sample.
Values of K are as follows:
--- for cadmium, K = 1160, assuming a mass density of rho = 8.6g/cm3 for
cadmium;
--- for zinc, K = 1410 assuming a mass density of p = 7.1g/cm3 for zinc.
Degrease the sample of parts in an organic solvent, dry thoroughly and weigh to an
accuracy of 1 in 10000.
If the batch of fasteners has been chromium-plated, remove the chromium by immersing and
stirring them in stripping solution A, which dissolves the chromium in less than 2 min,
after which time there should be no appreciable gassing. The parts shall be removed
without delay and rinsed in water, prior to stripping the nickel by the method given in
either below.
Stripping solution B (see D.2.2), maintained between 75 deg * C and B * 5 deg * C will completely strip 7.5mu*m of nickel in 30 min. provided the parts are tumed over The copper undercoat which also stripped will be as if it were nickel, provided it does not exceed 0.5mu*m in thickness.
Stripping solution C (see D.2.2), maintained between 80 deg * C and 90 deg * C will
completely strip 2,5 µm in about 10 min and complete removal of the nickel will be
indicated by the absence of further gassing. Parts are usually suspended in the solution
on thin copper wire.
As soon as the nickel coating has completely dissolved, remove the parts, wash well with
water wipe and dip in clean acetone. Dry and reweigh as before.
The stripping solutions consist of one of the following:
a) Stripping solution A
--- antimony trioxide: 120 g/l
--- hydrochloric acid (p > 1.16 g/ml) to make up to a one litre solution
b) Stripping solution B
--- sodium meta-nitrobenzene sulfonate: 65 g
--- sodium hydroxide: 10 g
--- sodium cyanide: 100 g
Make up to a one litre solution with water
c) Stripping solution C
--- orthophosphoric acid (p = 1.75 g/ml)
NOTE: It is dangerous for water to come into contact with the hot acid; water lost by
evaporation should be replaced only wa the solution has cooled.
Proprietary chemical stripping solutions for nickel may be used provided it can be shown
that there is only neglig attack on the base metal (ie. less than 0,5 µm of base metal
being removed).
Calculate the batch average thickness of coating, in micrometres, using the following
formula:
Batch average thickness = K x (m0 - m1)/A
where
K = 10000/p = 1120, assuming the mass density of nickel p = 8.9g/cm3;
m0 is the original mass, in grams, of the sample;
m1 is the final mass, in grams, of the sample;
A is the total area, in square centimetres, of the parts of the sample.
The surface area A can be evaluated according to informative annex G.