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"CitriSurf® is a perfect and environmentally friendly alternative to passivating with nitric acid!"

Dieter Fuchs, Boehringer Ingelheim Pharma GmbH & Co. KG

Our answers to your questions about CitriSurf®

Question I must observe the ASTM 967A what should I take note of?
Answer The CitriSurf® method was developed to meet the requirements of the US ASTM967A standard and meets all requirements of this standard.
Question Can I use municipal water for rinsing?
Answer No, in addition to lime, municipal water also contains salts and chlorides. The lime leaves ugly "water stains", and the chlorides can negatively affect the formation of the passive layer.
Question Stainless steel forms a natural passive layer – is this not enough?
Answer The natural passive layer is much thinner and exhibits a much worse chromium to iron ratio than the passivation layer which can be produced by chemical or electrochemical methods. In addition, impurities must be removed with sulphur and carbon because they can lead to local chromium reduction. Burned surfaces as created by welds and laser markings do not form a natural passive film and will begin to rust after a short time.
Question Why do some instruments have dark-grey discolourations after passivation?
Answer This can appear when slag remnants of the forged part were not sufficiently removed or if there are faults in the hardened microstructure on the surface. Especially in hardenable steels (e.g. 1.4021), this effect is a sign of problems during hardening. The surface carbon can indeed be removed by pre-cleaning with KleerKleen®4002, but hardening problems cannot be ‘cured’ with this method.
Question Is it also possible to use pure citric acid, which is considerably cheaper than CitriSurf®?
Answer CitriSurf® also contains additional ingredients to ensure that the solution has a longer shelf life and that free iron particles are bound in the solution and that the degreasing process is intensified.
Question How long can the solution be used?
Answer If the parts that should be passivated have been pre-cleaned sufficiently, the solution will last three to four months. The concentration must be checked regularly. If the solution is contaminated by oil or other substances or starts to smell bad, it is time to renew the solution.
Question How can I easily check whether the solution is still effective?
Answer The density and thus the required concentration can be checked with a simple density meter (areometer). The areometer should be adjusted to the correct temperature.
Question What about disposal? Can I easily dispose of the used solution?
Answer The used solution must be disposed of like any other cleaner, according to local provisions. Remaining unused solution can be disposed of in the wastewater after being adequately diluted because CitriSurf® is not a hazardous or toxic solution.
Question Are plastics or other materials attacked when they come into contact with the solution?
Answer Aluminium, titanium and all kinds of stainless steel are not damaged or visibly altered. Plastics used
in medical technology are not attacked. Non-stainless steels may not be treated with CitriSurf®.
Question I passivated scissors with CitriSurf® and after that had the impression that the scissors were not as sharp. Did the acid dull the scissors?
Answer Since CitriSurf® does not ablate any material, but only removes the free iron ions from the uppermost molecule layers, the scissors cannot be dulled by CitriSurf®. If the instruments have not been oiled by instrument milk or similar product after passivation, the scissors may have been damaged through the dry movement. The same applies to instruments with box locks and other moving parts where metal rubs against metal.
Question Are solder joints attacked?
Answer Solder joints are not attacked nor will they become discoloured. For example, needle holders with
soldered inserts can be passivated without hesitation.
Question How can you make sure that an adequate passive layer has formed?
Answer The method has already been tested and verified several times using laboratory methods. The tests for the validation of the process can be carried out at NMI or similar laboratories. The cooking test can be used as a simple test for corrosion resistance. The salt spray test or the copper sulphate test can also be used.
Question Laser markings fade after passivation. Rust forms on the markings without passivation. How can we solve this issue?
Answer Laser markings superficially burn or temper the work piece on the surface, which causes the dark-grey (tempering) discolouration. An adequate passive layer cannot form at these points. It is only through passivation with high-alkaline pre-cleaning that the free iron components are removed, so that a new chromium oxide layer can form again. In case of too long passivation, the surface is restored to its original colour. Depending on the laser intensity and type of steel, you have to find a passivation cycle which ensures adequate corrosion protection while leaving the lettering legible. You may need to change the depth of laser engraving to achieve this. Markings performed with higher energy and stronger focusing have often led to better results. In most cases, passivation cycles of 12 to 15 minutes have been sufficient.
Question Can CitriSurf® also be used for pickling?
Answer with a pickling solution or pickling paste. The surface treated this way must, however, be treated with a passivation solution. Passivation is not a substitute for pickling.