Protection upgraded
SurTec® 680
Chromiting – Chromitierung®
Thick Layer Passivation for Zinc and Zinc Alloys
Properties
liquid concentrate, based on chromium(III)
exceeds the requirements for yellow chromates according to DIN 50 021 SS
produces coatings of a clear, green, slightly iridescent colour
long service life, even with feed-back of rinsing water
layer fulfils all requirements of ELV, RoHS and WEEE when following
the recommended process sequence (see "application")
world-wide patent: Europe 0 907 762; Japan 3597542; USA 6,287,704
IMDS-number: 900896
Application
SurTec 680 can be used in rack or barrel application. The process includes
the following products:
SurTec 680 Chromiting Concentrate contains chromium(III), cobalt
and the complexing agent in the correct relations
SurTec 680 K Salt is the Corrective Salt which is added in case
of rising zinc contents in the bath to complex the excessive zinc
SurTec 680 C Cobalt Solution is a cobalt containing additive
which is only added for maintenance, according to analyses
make-up values: SurTec 680 12.5 %vol
SurTec 680 K Salt if necessary
SurTec 680 C only for correcting the Co content
analytical values: SurTec 680 12.5 %vol
cobalt 2.5 g/l (> 1.5 g/l)
(for make-up concentrations of 12.5 %vol SurTec 680)
make-up: Steps for make-up:
1. Fill in the calculated amount of SurTec 680.
2. Dilute with tap water up to the final volume
(hot tap water is possible).
3. Check the pH-value and adjust it if necessary.
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temperature: 60°C (55-80°C)
pH-value: 1.8 (1.8-2.0)
adjust with nitric acid resp. with sodium carbonate (Na2CO3)
application time: 60 s (30-90 s)
tank material: steel with heat- and acid-resistant plastic coating
heating: necessary, out of acid-resistant material (e.g. Teflon, glass)
agitation: rack or (low) air agitation
hints: As last step before Chromiting we recommend an acid dip in 0.5 %vol nitric
acid (conc.), especially for parts plated in alkaline electrolytes. For zinc/
nickel plated parts, an acid dip in hydrochloric acid is necessary (pH 2).
Due to the high working temperature of the Chromiting a partial or even
total feed-back of the rinsing water is possible. We would be pleased to
calculate the optimal process conditions for your line in accordance with
your throughput and your requirements – please contact us!
In lines with recycled feed-back rinsing water, the precipitated zinc sludge
must be removed out of the Chromiting bath (by sedimentation tank or
filtration).
For rack applications it is recommended to install water spray nozzles
above the Chromiting bath, to rinse the parts as they exit the Chromiting
solution for preventing flash drying of bath solution on the warm parts.
SurTec 680 has a potentially unlimited service life; the limiting factor
is the iron concentration. With increasing iron content firstly the
visual appearance and later the corrosion resistance will be affected.
SurTec 680 already contains a certain amount of iron inhibitor. In case
of high throughput of incompletely zinc plated parts (hollow parts, e.g.
tubes), an addition of SurTec 660 B Iron Inhibitor is recommended in order
to extent the service life (see product information sheet SurTec 660 B).
SurTec 660 B has no negative effect on the zinc removal and on the
efficiency of an ion exchanger.
Additionally we recommend for bathes with high input of iron the
installation an ion exchange system. The specific ion exchange resin
SurTec 680 IAT is able to remove iron selectively out of the passivation
bath, without disturbing the passivation process (see product information
sheet SurTec 680 IAT).
recommended process sequence:
1. zinc or zinc alloy process
2. cascade rinsing
3. activation in nitric acid, pH 1.4-2.0
4. Chromiting SurTec 680
5. cascade rinsing
6. optional: sealing (e.g. SurTec 555 or SurTec 555 S)
7. hot air drying (70-85°C)
The rinsing methods have to be adapted to the plating line.
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Maintenance and Analysis
Check the pH-value regularly. Analyse and adjust the concentration of SurTec 680 regularly.
Strong dosages of SurTec 680 K Salt may lead to reduced cobalt concentrations. To increase
the cobalt content, add SurTec 680 C Cobalt Solution (thereby 10 ml/l SurTec 680 C is exactly
equivalent to 1 g/l cobalt). SurTec 680 Chromiting Concentrate can also be used for raising the
cobalt content: 50 ml/l SurTec 680 is exactly equivalent to 1 g/l cobalt.
Sample Preparation
Take a sample at a homogeneously mixed position and let it cool down to room temperature.
If the sample is turbid, let the turbidity settle down and decant or filter the solution.
SurTec 680 – Analysis by Titration
reagents: sulfuric acid (conc.) p.a.
ammonium peroxodisulfate p.a.
0.1 N silver nitrate solution
potassium iodide p.a.
0.1 N sodium thiosulfate solution (= 0.1 mol/l)
starch solution (1 %)
procedure: 1. Pipette exactly 2 ml bath sample into a 250 ml beaker.
2. Acidify with 3 ml conc. sulfuric acid and mix by slight rotation
(sample becomes clearly green).
3. Dilute with approx. 50 ml deionised water.
4. Add 15 ml silver nitrate solution.
5. Add 2 g ammonium peroxodisulfate.
6. Cover the beaker with a watch glass, heat the sample up on a
heating plate and boil it slightly (!) for 20 min (sample slowly
becomes clearly yellow).
7. After cooling to room temperature, wash down the drops
from the watch glass and from the beaker’s walls, using
small amounts of deionised water.
8. Dilute with deionised water to approx. 100 ml.
9. Add 2 g potassium iodide (colour changes to milky light brown).
10. Titrate with 0.1 mol/l sodium thiosulfate solution until the
sample becomes milky pale yellow.
11. Add several ml of starch solution (change to milky dark grey).
12. Continue to titrate until the colour fades to milky pale green.
calculation: consumption in ml · 1.083 = %vol SurTec 680
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SurTec 680 – Analysis by Photometry
equipment: spectrophotometer or
filter photometer with 560 nm filter unit (± 50 nm)
100 ml volumetric flask, 10 ml pipette, 1 cm cuvette
reagents: hydrochloric acid (½ conc.) p.a.
procedure: Prepare a standard solution (laboratory standard with 12 %vol in
dilution 1:10 - prepare freshly at least every 3 month, see ”possible
errors”):
Pipette 10 ml half conc. hydrochloric acid into a 1000 ml volumetric
flask. Add 12 ml SurTec 680 Chromiting Concentrate, fill up with
deionised water and mix well.
Before each sample measurement, fill the standard solution into a
1 cm cuvette and measure it photometrically at 560 nm against water.
Note the absorbance ES.
Sample measurement:
1. Pipette 10 ml of the filtrated bath sample into
a 100 ml volumetric flask.
2. Add about 1 ml half conc. hydrochloric acid.
3. Fill up with deionised water and mix well.
4. Fill this solution into a 1 cm cuvette.
5. Measure the cuvette in the photometer at 560 nm.
6. Note the absorbance EP.
calculation: EP / ES · 12 = %vol SurTec 680
possible errors: Bath turbidity simulates a higher concentration, therefore
the sample should be filtrated.
High amounts of iron impurities lead to wrong results.
Use the standard solution not longer than max. 3 month.
SurTec 680 – Analysis by AAS
equipment: atomic absorption spectrometer (AAS)
wave length: 357.9 nm
1000 ml volumetric flask, 1 ml pipette
reagents: acetylene/synth. air
chromium standard solutions: 5, 10, 20 ppm
hydrochloric acid (conc.) p.a.
procedure: Prepare a 1:1000 dilution:
1. Pipette 10 ml hydrochloric acid into a 1000 ml volumetric flask.
2. Add 1 ml bath sample and mix shortly.
3. Wait 5 min before filling up.
4. Fill up with deionised water and mix well.
5. Calibrate the AAS with the chromium standards and directly
after this measure the prepared dilutions.
calculation: measured value in ppm · 1.25 = %vol SurTec 680
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possible errors: The pipette has to be clean and should be rinsed with bath
solution before it will be used for the bath sample.
If the reaction time of hydrochloric acid with the bath sample is
to short, chrome has no good configuration for AAS measurement.
The result will be too low.
Warm up the AAS lamp for 10-15 min (see AAS instructions).
Calibration has to be done before each measurement.
Older AAS lamps can leave the linear measurement range.
Cobalt – Analysis by AAS
equipment: atomic absorption spectrometer (AAS)
wave length: 240.7 nm
slit: 0.2 nm
reagents: hydrochloric acid (½ conc.) p.a.
cobalt standard solutions
procedure: Prepare a 1:500 dilution:
1. Pipette 1 ml bath sample into a 500 ml volumetric flask.
2. Add 5 ml hydrochloric acid.
3. Fill up to 500 ml with deionised water and mix well.
4. Measure against cobalt laboratory standards by AAS.
calculation: measured value in ppm · 0.5 = g/l cobalt
correction: rise by 1 g/l cobalt = addition of 10 ml/l SurTec 680 C
or 50 ml/l SurTec 680
Technical Specification
(at 20°C) Appearance Density (g/ml) pH-value (conc.)
SurTec 680 liquid, dark grey to violet 1.475 (1.45-1.50) 1.8 (1.6-2.0)
(at 12.5 vol%)
SurTec 680 K Salt salt, white 0.900 (0.70-1.10) kg/l -
SurTec 680 C liquid, dark red, clear 1.235 (1.21-1.26) 5.7 (4.8-7.0)
note: In SurTec 680 Chromiting Concentrate, there is a slight settling possible
that will not impair its function.
Consumption and Stock Keeping
The consumption depends heavily on the drag-out. To determine the exact amounts of
drag-out, see SurTec Technical Letter 11.
For each litre dragged out solution, 125 ml of SurTec 680 concentrate has to be added;
best is a dosage of SurTec 680 based on throughput.
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In order to prevent delays in the production process, per 1,000 l bath the following amounts
should be kept in stock:
SurTec 680 210 kg
SurTec 680 K Salt 60 kg
SurTec 680 C 30 kg
Product Safety and Ecology
Classification and designation are noted in the Material Safety Data Sheets (according to the
European legislation). The safety instructions and the instructions for environmental protection
have to be followed in order to avoid hazards for people and environment. Please pay attention
to the explicit details in our Material Safety Data Sheets.
Warranty
We are responsible for our products in the context of the valid legal regulations. The warranty
exclusively accesses for the delivered state of a product. Warranties and claims for damages
after the subsequent treatment of our products do not exist. For details please consider our
general terms and conditions.
Further Information and Contact
If you have any questions concerning the process, please contact your local technical
department.
For further information and contact details please visit our homepage:
http://www.SurTec.com
24 May 2016/DK, SiD
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Trouble Shooting
problem possible cause remedy
slight white clouds in/on a) if the clouds are already check the quality of the parts, the pre-
the Chromiting layer visible on the plated zinc treatment and the zinc plating process
(after activation)
b) insufficient rinsing and drying check the pH-value of the activation (≤ 2);
conditions shorten the rinsing times: in total < 2 min;
check the pH of the last rinse (best: 5-6);
optimize the drying process:
first cold drying (air blow),
then dry 10-15 min at 60-80°C
c) pH-value of the Chromiting correct the pH with nitric acid to pH 1.8
bath is too high
d) loss of complexing agent add SurTec 680 K Salt in steps of 1 g/l
SurTec 680 K Salt (high zinc (for 1 g/l zinc add 2 g/l SurTec 680 K Salt)
contents lead to precipitation
of complexing agent)
yellowish Chromiting layer content of iron in the bath is find out the source of the iron
too high contamination and prevent it;
further dissolution of iron can be reduced
by adding SurTec 660 B;
for continuous input of iron we
recommend the installation of an ion
exchange system (SurTec 680 IAT)
pale colour of the working parameters of the check concentration, pH-value, agitation
Chromiting layer, Chromiting are not correct temperature and application time - and
bad corrosion protection correct these parameters if necessary
discolouration of the a) inadequate storage conditions high humidity, high temperatures and salts
Chromiting layers on the part’s surface impair the
after 1-4 weeks Chromiting layers
b) too thin zinc layer possible migration of base metal cations
can lead to discolouration
=> increase the plating time
c) metal impurities in the zinc keep the electrolyte free from metal
bath or the Chromiting bath impurities;
for the Chromiting bath: use the ion
exchange SurTec 680 IAT for eliminating
metal impurities
d) in case of using a sealer: dilute the sealing bath;
be aware that it is not too adjust the pH-value as low as possible
alkaline and that the resulting
layer is not too thick
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