aluminum vacuum preparation

by:AAG     2020-11-04
Are you trying to make complex components for ultra-high vacuum (UHV)?
Are you upset about banning the use of anything other than the 304 series stainless steel in your room?
Now switch to cheap, light, machined high aluminum and believe it can be properly prepared for the vacuum according to the procedure described here.
In fact, let\'s cut into the topic now and introduce the program!
In following this procedure, you will follow a similar approach to CERN and Stanford Linear Accelerator SLAC, which operates the Large Hadron Collider, the survey commissioned by the American vacuum Association reported aluminum cleaning procedures for the two companies.
While the program here is very similar in principle to the program used by CERN and SLAC, the exact concentration I chose was set by the practice used during the JILA anooxidation process, A joint venture between the University of Colorado and the National Institute of Science and Technology, the Institute of Laboratory Astrophysics, and the National Institute of Standards and Technology.
Anode Oxidation begins with etching and cleaning, just like vacuum preparation.
By keeping the same concentration used on the anode oxidation line, I ensured the later practicality of these chemicals.
In addition, some concentrations used in large laboratories are quite extreme as they need to be cleaned with portable sprayers as these ingredients are not suitable for bathing.
Usually, we are taught to be afraid of aluminum due to the oxide layer of aluminum.
Aluminum is highly reactive to oxygen, so that once squeezed in forging, aluminum quickly forms an oxide layer when cooled.
Unlike iron, which slowly forms an oxide, then breaks and exposes more iron to oxidation, the oxide of aluminum can be dense, firm and protect the metal from further oxidation.
Unfortunately, the alumina layer is usually very thick according to the UHV standard (
Dozens of nanometers)
, Dirty, porous, difficult to clean, especially when the oxide is formed when the molten aluminum is squeezed in the rolling mill.
Even if formed during the cold processing of the workshop, oil and other contaminants may be trapped in the oxide layer.
To make matters worse, the studio ultrasonic cleaning procedure for the preparation of ultra-high vacuum materials is too aggressive for aluminum, which causes the pitting of the oxide layer and increases the pores. The solution?
Chemical etching is several microns away from the aluminum surface, completely stripping the existing oxide layer formed during processing or extrusion.
The new oxide layer formed immediately after etching will be very dense and thin (angstroms)
, No holes, because it is formed directly in the oxygen in the atmosphere at cold uniform temperature and low pressure.
After several cleaning steps, aluminum has been prepared for the extra high pressure, and since the oxide layer is permanent, there is no rush to send the parts into a vacuum.
In fact, now the vacuum chamber is actually made of aluminum, with lower pressure compared to steel.
The company is selling aluminum rooms and their reason is why it is better than steel.
All the information I just provided was collected from discussions with the chemists and mechanics, collected from the very useful comments I started at the bottom of page 2031 of the same survey article I linked in the intro, as well as various information profiles on the aluminum processing company website.
The chemicals used here are the standard stock of any chemical supplier, except for the etching powder, although the etching powder is usually used for etching marks on glass, which may be easier to obtain than you think.
Unless there is a shop near you that has done something similar, it is difficult to find large stainless steel tanks, as in my case.
The choice of gloves may be safer than nitrile, but not as strong as the shoulder length rubber.
I use nitrile most of the time and when I think there is a chance to get splashed during the cleaning process, I should use rubber.
Prepare the etchant bath first because it takes a long time to heat.
Install the 40-liter stainless steel silo above the hot plate to make the hot plate firmly contact the silo, but the bearing does not exceed about 25 pounds.
I implemented this with some of the large aluminum blocks I found in the storeRoom stocking area.
The blocks are cut from the same extrusion, so they are ideal for providing elevated but flat mounting structures.
Make sure you put the trash can on the floor near the front of the fume hood.
It is not suitable for the interior, but in this way, smoke can be discharged through the hood as long as the front is opened.
Carefully measured in 35 liters of tap water.
There is no need for cleaner water, as the compounds we add will completely dwarf any impurities.
I only had a 1 liter beaker on my hand, so it took 15 minutes.
Save time if you can find a larger container.
To do this, just measure five to rise to a larger container and mark it with sharpie, and now you have a larger measuring container.
I hope I thought so before!
Before installing the temperature probe for the heating plate, when you proceed to the next step, just burn East West Point to a full explosion.
At 4kJ/kgC, it takes 140 s/C * 45C = 1 3/4 hours to increase the bath tank to 70C with a 1 KW heater without loss of convection. Now mix in 0.
973 kg sodium hydroxide pellets, so as to obtain a 1. 39 mol/L or 5. 5% solution.
Sodium hydroxide (40g/mol)
It\'s a strong, caustic base, so wear gloves and don\'t splash.
Be sure to weigh the particles under the fume hood, because the dust generated when you pour the particles will aggravate your lungs. (
Believe me, I understand this through hard work.
It didn\'t really hurt, it just made me catch my breath in my throat and it might have hurt a bit that night).
Sodium hydroxide does not completely dissolve until you increase the temperature of the bath, but this is not a very hot reaction, so when it is heated and dissolved later, you don\'t have to worry about splashing or blistering.
Now go back and assemble the Teflon probe.
I did this with some of the chemical installation frames I found.
After inserting the probe, turn off the hot plate and turn it back on and set it to 70 °c.
You may want to trace the thermocouple as the Corning style hot plate will not tell you the current temperature and will only tell you if it is at the target temperature.
You also need to stir once in a while, otherwise a large temperature gradient will be generated.
Make sure the tub is mostly covered and then proceed to the next step.
We will use the secondary safety box as the main container for our acid removal
This is acceptable in the short term.
Long term storage only needs secondary containment.
Start with 12.
5 liters of water into the warehouse, and then slowly add 5 liters of 70% nitric acid, so that you can get a concentration pool of 20%. (
In fact, I didn\'t explain the increase in acid density, so this actually gives 25. 3% solution)
This is a kind of dilution that puts heat very much, so it is very important to avoid local boiling water and splashing acid.
It is also important to avoid heating the bath to more than 80 degrees Celsius, a softener for high density polyethylene in the secondary containment bin.
I was slow enough to add a 2.
5 liters of pot in 5 minutes.
When the dilution is strongest, I can see that when I pour water, the steam coil flows out of the water.
It is a good idea to monitor the temperature when pouring wine.
After adding half of the acid, my bath liquid rose to more than 30C and finally reached 40C.
Actually, let\'s check: 70% HNO 3, weight 70%, so 70g HNO 3 in 100g solution.
The density is 1.
413, so there are. 7*1.
413 = 989 gm/L, or 15.
7mol/L divided by HNO 3 of 63g/mol mass.
In addition, 70g in 30g water means that the molar concentration is 37mol/kg.
Now after 12.
5 liters of water, we have 989*5 = 4. 945 kg HNO 2. 12+12. 5 = 14. 62 kg of water. This is a 5. 37 m (mol/kg)
Solution, or 25. 3%.
In this table, we find that the new density is 1. 15 gm/L.
Now, looking at the dilution heat, I found that the dilution heat should be 15kJ/mol between the first two columns of the table.
We will not dilute to infinity, we will only dilute to 25. 3% (5. 37 m)
, Where the dilution heat is 1. 4kJ/mol.
That means we should release 13.
6 kJ/mol acid, we have 78.
5mol, so 1068kJ.
Now, water should rise by a C degree per 4 kilojoules/kg * 17.
5 kg = 70kJ, or 15C.
Of course, the specific heat of acid is different, 1.
7kJ/kgC, but this is a small correction: 14. 6*4 + 4. 95*1. 7 = 66.
8kJ/C, so 16C replaces 15C from 1068kJ.
Hooray, my final temperature measurement for 40C is consistent with the initial temperature of 24C, a little hot for tap water, but within the possible range.
Effective chemistry!
We are now adding diammonium fluoride.
It is exciting to open the Multi-Packaging Chemicals of sigma aldrich.
I could have used a less pure grade, but I wanted to see what this chemical looks like in pure form, and its cost is a stupid change relative to my experimental budget ($70).
This chemical is a sticky, flaky substance, almost like the real big snowflake you can find in a high-altitude dance (
No kidding, I \'ve seen it completely by 3-
In Boulder, there are 5mm full slices.
Before moving here from the East Coast, I thought the whole paper snowflake was just an art.
No, they really do).
Dilution is also very released if you scroll down the link, about 20kJ/mol, but only 25g, we are talking about 7. 3kJ.
This means that it is safe to dump it directly into a huge bathtub without any heating trouble, but this chemical is very dangerous in other ways.
If you follow this link, it talks about anything that fluoride causes from burning to heart failure to death.
We have to be in de-
Smut bath in order to remove silicon from smut formed after etching.
Since silicon is almost always a minority component of aluminum alloy, Silicon will exist.
I use a lot less fluoride than the national lab because I know my aluminum grade (6061)
The silicon content is much lower than some others.
At CERN, they use hf as their fluoride, but it is a little safer for diammonium(
Maybe because it\'s solid at room temperature, I\'m not sure).
Find some steel welding wiring and install a way to dip your parts into etchant and de-smut.
If your parts are useful for anything, they must have some kind of screw hole or other feature that you can use.
Good luck if you have to etching the perfect sphere or something.
Maybe just like they did for the dead Easter egg.
But if your corner is stuck in the Etudes, you\'re in trouble.
Etchant will eat the aluminum completely until the solution is no longer basic and at this point you have to add more sodium hydroxide particles or handle a lot of waste safely and start over.
Place a DI Bath near de-very close
Smu acid so you can put the parts directly into the DI after their acid bath instead of taking them to the sink and dropping the acid all the way.
You may also want to do the same for your etchant bath as you will rinse between etching and de-etchingsmutting.
I didn\'t do this because my etching bath was right next to the sink in the fume hood.
Dry the run to make sure you have a great way to schedule everything right.
I used a lab timer like the one shown, which is great because it starts counting as soon as it finishes the countdown so you know how long it\'s been running out of the timer.
Now is the time to actually execute the program.
When you are immersed in etching, there will be some brief moments where nothing has happened, perhaps because the solution has not passed through the oxide layer yet, or because the aluminum is going to heat a little.
Soon, however, intense bubbling will begin.
Make sure to move the parts to help with the etching even.
There are some marks in my first part, and I think it might be because I didn\'t do that.
A minute later, lift the part.
It will look ugly and it will send out threatening steam!
Rinse it thoroughly in the faucet before continuing the acid leaching.
Start your timer for five minutes
Soaked in acid.
In ten seconds you will see that this part is getting clean in acid, but if any few ingredients fall off slower, please wait patiently and move this part occasionally.
Transfer to your DI bucket after the time is over.
Be careful, make sure that the attachment you use to soak is immersed in the washed DI water more deeply than the acid.
Otherwise, acid will remain on the attachment to burn you or damage your parts.
After soaking, rinse very thoroughly in DI water and keep yourself flush for a long time.
Most DI faucets are a bit slow so be patient.
Make sure your parts are completely dry now!
I didn\'t do this for some of my parts because the nitrogen tank ran out and the filtered compressed air line was temporarily closed and I didn\'t want to fix it either.
I am very sorry because a few drops of DI sitting on the part can seriously change color and probably destroy the thin and dense oxide layer I am trying to make.
Transfer 35 liter etching slots to two 20 liter waste trucks.
Make sure they are high density polyethylene, so 70C liquids are safe as high density polyethylene begins to soften only above 80C.
Do not try to cool the bath, otherwise sodium hydroxide will settle out as salt.
You don\'t want to come into contact with salt or scrape or clean it up.
Be sure to pour slowly with a big funnel.
I wear shoulder long gloves for this part because it is the easiest to spill or splash. Turn 17.
In the same way, 5 liters of Acid Bath were sent to the remaining 20 liters of waste cars, and long shoulder gloves were worn.
Rinse the bath tank clean, and then use the acid bath for secondary sealing.
In my case, these chemicals will soon be permanently installed as part of the aluminum anode oxidation line, as there will usually be etching and de-corrosion before the anode is oxidizedsmutting.
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