We've been experimenting with Multi-Etch and have some new data to show for our efforts. We tested heated as well as room temperature Multi-Etch on additional grades of titanium and on NiTiNol and retested many metals we did in the past.
We have two subjects to cover: using Multi-Etch on different titanium alloys and reusing etch baths.
Will this product work on a titanium alloy? Not sure of the exact composition. When etching polished pieces, should the items be as close to polished already or will Multi-Etch affect the polished finish? What kind of depth will the etching do? Will I see difference in color on different titanium grades?
Multi-Etch will remove the oxide layer from all grades of titanium including alloys such as 6Al4V (generally known as 6/4 or grade 5) although we have not tested all of the alloys.
Do all your polishing/finishing, bead blasting, wire brushing, etc. prior to dipping in heated Multi-Etch. Adjust etch times for polished material as it will make the titanium matte if left in too long. Seven to ten seconds should be sufficient if you're etching to anodize. We've found that over three minutes will dull the polished finish. But if you left it in longer than three minutes, it will produce a satin finish, i.e., something between matte & polished. This all applies to heated Multi-Etch.
Check out our etch depth table. The longer you leave the titanium in Multi-Etch, the deeper the etch. Generally, for 6/4 titanium you can expect .0005" depth per 5 minutes in heated Multi-Etch.
There are a couple of alloys including 11 and 17 that have palladium in them. We haven't tested those but believe the etching will be slower because of the palladium.
You won't see any difference in the colors from grade to grade.
If I used my Multi-Etch one day, can I reuse it the next? Do you just place a lid on the solution? How long can it be exposed to air. Does the exposure to air affect its efficacy?
You can reuse the solution until it is no longer working for you. Put a lid on it to prevent evaporation but even if uncovered, it will not affect the efficacy. We have found the unused solution gets stronger after a couple of weeks or so. We have tested the unused solution up to a year after mixing it, and it still works fine. As always, it's best to pour out the smallest amount you need for a given job, keeping the rest of your solution uncontaminated. But then you can keep using what you poured out until it no longer works.
Sometimes it’s handy to prepare a titanium piece with Multi-Etch and then protect the piece in a way that allows you to set it aside and anodize later.
One simple way is to Multi-Etch the piece, rinse, and then store in a tank of DI or distilled water. We’ve found this lasts at least 2-3 days, and probably longer.
A second way is to Multi-Etch and then “base coat” your titanium part with 8-10 volts. Those parts can then be stored dry and the base coating will protect the piece for a long time. We’ve stored pieces that way for years and been able to anodize them in the same brilliant colors we can produce when we are working with freshly Multi-Etched pieces. The only drawback with base-coating is that there will be a light tan on the piece, so if you need part of the piece to remain the natural color of titanium, base coating won’t work for you.
A third way that works on flat pieces is to Multi-Etch the piece and then cover and apply anodizers’ tape on the flat piece, burnishing thoroughly to make sure you cover the whole piece completely. You should cut the tape big enough to fold over the edges.
The concept with these three methods is to prevent the formation of the oxide layer that Multi-Etch is designed to remove.
We often stress the importance of using and storing Multi-Etch in plastic containers, never in metal or glass. First time users will receive dry Multi-Etch powder in a plastic gallon jug. This jug is meant to have distilled or deionized water added to make a gallon of regular strength or 1/2 gallon of double strength Multi-Etch. You can pour 150–160°F water into the jug to mix the solution.
When using heated Multi-Etch in either a double boiler or in a custom tank, there are a number of types of plastics that can be used. For small users (one gallon or less,) you can find suitable plastic containers at big box or grocery stores. Look on the bottom of containers to see a number inside a triangle. Most of these containers will have a number 5, for polypropylene. These can withstand up to at least 212°F.
For those of you building your own containers, several other plastics besides #5 can be used:
#2 white polyethylene can be heated to 160°F. This is what our Multi-Etch jugs are made of.
#3 PVC--upper thermal limits are 140°F for type 1 and 158°F for type 2
#7 is usually polycarbonate and can be heated to 212°F but #7 does include other plastics so sometimes means a type other than polycarbonate.
If you will run larger tanks of 5-20 gallons, we recommend IPEC Global who can construct complete customized systems which can include tanks for cleaning, rinsing, Multi-Etching, rinsing, and anodizing.
Since Multi-Etch is not as aggressive as hydrofluoric acid, it excels in removing amounts of titanium as thin as fractions of a micron. This allows for precise removal of material that is difficult to achieve with the blunt action of hydrofluoric acid.
For example, a U.S. laboratory uses Multi-Etch to fine-tune their microwave chambers. Multi-Etch is also used with several particle accelerators in the U.S. and Europe to remove minute amounts of titanium. Besides being able to achieve these precision operations, Multi-Etch, in whatever way it is used, is vastly safer than hydrofluoric acid.
Contact us today to see whether Multi-Etch will fulfill your application needs.
Long time friends, Bruce and Christine Senchesen, who are new Multi-Etch users sent us the following questions.
My start setup will be the crock pot deal. How critical is the temperature if it varies within the 120–160°F range?
Answer: “The temperature range is not critical. In fact, you really do not need a thermometer at all if you're using fresh etchant. Upon heating the solution you'll notice, as it heats up, a fine bloom of bubbles. Use that as an indicator of when to etch. But you won't see the bubbles if you reheat the same bath so it would be helpful to time the heating when you're using fresh etchant so you will know how long to heat if you reheat the same bath.”
Also, your instructions call for a non-metallic thermometer. I can't seem to find one.
Answer: “I actually use a metal probe type thermometer, Ashcroft 0°F - 220°F, available at Hardware stores. I use it for spot checking the temperature and it's OK that it's metal if you are just spot checking. Some companies leave thermometers in their bath all the time and in those cases, a non-metallic probe is required.”
I loved the bite from HF to erase scratches and was wondering if I took the pieces to be sandblasted, what material would be best to get similar finish before Multi-Etching?
Answer: “The bite is not like Hf--it will maintain whatever finish is on there unless you etch more than 3 minutes. Blasting with glass beads, wire brushing, belt sanding (which makes the ti resemble nb in brightness,) scotch pads, etc. will all be helpful. I've never tried blasting with ‘sand’ so, not sure about that. I like the coarse glass beads, 40-60 mesh.”
Added note: Do not blast with aluminum oxide; it will prevent good color. Similarly, if you use wire brushing, be sure to thoroughly clean with Simple Green before etching.