The remaining iron-depleted surface is high in chromium and sometimes nickel also which reacts with air to form stable passive metal oxide layer. Titanium alloys do not contain iron, and therefore the surface does not need an acid treatment to enable formation of a passive metal oxide layer.
If the surface is or may have been contaminated with iron from an external source, then that iron can become rust down the road if it is not removed. Since it's fundamentally the same task as passivating stainless steel removing iron from the surface we use the same process nitric or citric acid treatment and tend to use the same terminology. I hope you can see now that putting it in terms of "undoing the passivation" or "negating the passivation" is not really accurate.
For a non-ferrous alloy like titanium, it doesn't really matter what the history is. If you have an iron-free surface, and then contaminate it with iron, you create the possibility of surface rust unless that iron is removed via an acid passivation treatment. It is extremely destructive to use a carbon steel wire brush on anything that isn't also carbon steel.
In your case, even a stainless steel wire brush, regardless of whether or not it sets up a rust problem, would be contaminating your titanium surface with not-titanium material. Since you did not describe your application or the nature of the foreign object damage that needs to be cleaned, I cannot say what is or isn't potentially a problem for you here.
The FOD is non-metallic bonding material that nestles in some of the bores as part of the assembly process. This material is quite robust in that in some cases it is the only means of securing the details to the assembly.
The assembly is a non-critical flight part that is ITAR controlled. I understand that the "passivation" cannot be undone, but it seems to me that introduction of a steel, whether it is carbon, or stainless might contaminate the fittings to the extent that they no longer would meet the requirement of the customer that the titanium be "passivated" certified at the time that the customer takes possession.
Thank you for your expertise in this subject matter and of course, your time. Darryl, Well, again you use the term "undoing the passivation". If you want to think of it that way, you can. It's sort of similar to saying that your pet dog "undid his bath" by rolling in the mud. Most people would just say he "got dirty". So, if I can make sense of all that properly, this is a titanium part that is getting glued into place, and some of the glue is getting into some holes, so they clean out the holes with a steel wire brush.
I would think this to be one of those ounce of prevention vs pound of cure situations. Could an addition be made to the standard assembly procedure involving some sort of temporary plugs to keep the holes clear and clean? Assuming of course that it would be futile to merely give a dire warning against using too much glue near the holes.
Neutralization Employ a neutralizing procedure for product designs where acidic liquid could be trapped e. Rinsing and Drying A thorough water rinsing process and drying process are essential. Specific methods are left to the cognizant engineering organization. Citric 5: Other combinations of temperature time and concentration of citric acid with or without chemicals to enhance cleaning, accelerants or inhibitors capable of producing parts that pass the specified test requirements.
Immersion bath to be controlled at pH of 1. A table of recommended nitric acid passivation methods is provided in the Appendix that correlates Nitric 1 through 5 methods to the specific stainless steel alloy grade. No such reference is provided in the specification for Citric 1 through 5 methods. It is uncommon that descaling is required in passivation of titanium or other medical grade components. Again, "passivation" of titanium is for removing contaminant iron that may otherwise turn into surface rust later on, in a similar fashion to the removal of surface iron from stainless steel during passivation.
So the same general procedures used for stainless apply to titanium as well. Citric acid is NOT dangerous to titanium. Hi, I work in the orthopaedic medical device industry. We currently passivate all products -- this includes non stainless steel products such as Titanium. I know the chemistry about removal of free iron and formation of an oxide layer, the later of which will not happen on Ti. Basically does anyone have any info on passivation of non ferrous metals in the medical device industry.
Does it need to be done? Know any standards? What is it for? I ask as our products are plasma coated and are shot blasted, cleaned, passivated and then coated.
I am looking to change the passivation to before shot blasting - or getting rid of altogether on Ti products. I think one reason is that if any ferrous tooling is used by mistake, the passivation will remove any iron contamination, which would mean it is OK to passivate before shot blasting.
Another reason may be any iron impurity bought to the surface of the Ti by shot blasting will be removed, in which case it's not OK to passivate before shot blasting. I have never been able to detect any free iron on the surface of Ti using copper sulphate. Can anyone help?
Cheers Jim. Considering that Ti will oxidize with time in air, I would be a bit surprised if a strong oxidizing acid would not give at least a minor coating. If you are shot blasting with steel shot, passivation before blasting would be a waste of time. I would find the use of steel shot a bit disturbing. Review the applicable ASTM standards. You will see that talk of the "passivation" of Ti and its alloys is something of a misnomer.
Acid processing of Ti is more oriented to the removal of undesirable "alpha case" and surface contaminants, as opposed to the use of the term "passivation" in the context of stainless steels. Dave, I always thought that removal of "alpha case" required a fluoride containing acid.
It seems to me that there have been topics in the past where "passivation" of Ti was required. It sure seemed to me that it was NOT the normal use of the word "passivation". The topic of 'what does passivation mean? Some seem to think it means the formation of an enhanced layer of passive oxides on a stainless steel surface.
Today, citric acid has improved with new formulations for biocides which prevent organic growth in solution. These new advancements have allowed smaller manufacturers which had little to no experience with chemical handling to bring their passivation process in-house. Citric passivation vs. Parts can be processed in as little as 4 minutes when using citric acid, compared to 20 minutes minimum with nitric acid. As with nitric acid, it is important to maintain a balance between temperature, immersion time and acid concentration with citric acid passivation, to avoid the challenges of runaway corrosion known as flash attack.
For more details on citric passivation, please see our page on Citric Acid Passivation , including the Compatibility Guide for various grades of stainless steel.
The following chart provides a summary of the key differences between nitric vs citric passivation. To learn more about nitric vs citric passivation industry standards and specifications , please see our page " What is Passivation?
Today, many companies are taking a second look at citric acid due to its ease of chemical handling, disposal and overall safety for employees, all of which are more challenging when going with nitric acid passivation vs citric acid passivation.
Best Technology works closely with many companies in the aerospace and medical device industries and has successfully assisted these companies with converting from nitric to citric acid. Often it is as simple as talking with the end customer and showing them the equivalency of the types of passivation. This system can handle it all.
This 3-in-1 system offers 3 different automated passivation options:. A key advantage of an automated passivation system is that it is designed to run as a closed-loop system, so the operator is not exposed to chemicals like nitric acid. Best Technology is a recognized industry leader in passivation equipment , systems, tanks and lines.
Our automated passivation equipment is particularly well-suited for nitric acid passivation, due to reduced worker interaction with hazardous chemicals. Whether it's citric acid or nitric acid passivation, Best Technology can provide a system that's right for your company.
0コメント