DIY Vacuum Flanges for the 1200°C Tube Furnace 

3:43 I made an error: It's 22.4L/Mol, not 22.4Mol/L. Sorry for the confusion.

I think you might be getting a stress riser where the end of the tube meets your metal plug. The atmosperic pressure ends up bearing on a very small area. You could put an o ring there as padding. And make sure there is tolerance for the metal to expand. This is a 1 bar pressure seal so you could leave the o rings a bit proud and it will still seal. If the metal plug heats up enough to put two opposing point loads on the inside of that glass hoop - you're hooped!

Hi. Verry nice video. I have some experience using tubular funaces in our lab. Though we are not using it for Silicone manipulation but for chemical syntheis. We are using a self made compression flange as well and I think our design is much simpler to make. If you are still interested I can share the design with you. Some other comments. If you start using gas flow I suspect that your O-Rings will melt . Even with massflowcontrollers, you have a significant heat transfer to the outgoing end at lest when you are using the furnace for days or weeks like we do regulary. I even had FFKM O-Rings melt on me! Also be aware that the glowing quarz tube creates significant UV-Radiation over 900°C wich will go into your flanges and heat them up eventually. Also if you wand to use Argon or other gases sure you will need a primary reduction valve but after that a needle valve and a buble counter with silicone oil on the other end will give you relativly fine controll over the gas flow. It might be enough for you. Finaly please!!! do not heat you quarz tube over 1100°C for longer than an hour. If you go longer you will reach the strain point of the Quarz wich basically creats a silicone oxide cristal growth chamber. Basically the glass will start to realine into its natural cristal structure on the surface of your tube wich creates strain over time, wich will eventually brake the tube. I have lost so many tubes because unknowing scientists were doing yust that.

You should try to make an end cap with 2 tubes, one goes to the vacuum pump and the other goes to an argon tank. Just saying

You could calibrate the thermocouple result, by comparing it to the inside thermocouple. I believe it should correlate to the inside temperature linearly, so calibration would be easily doable

Adding a vacuum reservoir tank and valve inline with the pump would allow you to "precharge" the vacuum system while firing the furnace, and save you those 2-3 minutes of time it takes to draw everything down, perhaps thinning the oxide layer a bit more.

Can one of the big chip manufacture please please get this lad sponsored and offer him tours through a production facility it would be great to see how much a guy like this gets out of such a hands on tour.

I was thinking, once sealed with gas fittings, if this could be used as a Catalytic Reactor for things like Ethanol to Ethane (Similar to @HyperSpacePirate ) , CO2 Methanation, The Haber Process, and *maybe* Fischer Troph? Granted pressure/temp requirements are probably different so this may be a bit of a…PIPE DREAM, but I figured using an existing, and well made, device would be easier!

It will never be as accurate, and it might suffer from confounding circumstances, but you should be able to run a series of heating and cooling cycles, collecting temperatures from both thermocouples, and develop a calibration curve that makes the permanently installed thermocouple useful. As long as this tube survives this means you could potentially make it workable, while still having access to both ends, if say you wanted a setup with gas inlet at one end, and the vacuum pump on the other, or you wanted to develop a cap that somehow lets you push and pull the boats while they're already under modified atmosphere

Can't wait for the next one, really happy I found your channel :)

This kind of project (making your own silicon chips) absolutely isn't in my wheelhouse, but I'm so down for all this problem solving you do on the channel. These videos are such a good demonstrations on how to tackle complex problems and how to be resilient in the face of constantly "failing" towards success.

Small note, although probably insignificant: EDIT: this might be a larger problem because depending on the wires used, you end up measuring the furnace temperature in reference to the flange. See sub-comments. Usage of thermocouple extension wire is recommended in this case as the termination point temperature is for sure above the board reference temperature. On the other hand if you are fine with having 50K uncertainty (I'm assuming the flange is 50C above ambient), it should be fine. In presence of temperature gradients (which in case of a furnace end cap will for sure be the case) you should not solder thermocouple leads as it creates a unpredictable set of thermocouples at the soldering point. Depending on how precise you want to go, the optimal solution is to use a specially designed thermocouple wire (for given thermocouple type) and spot welding it to the thermocouple tail, a mechanical connection can also work. At the board, the connection point is less critical if you can guarantee that there are no thermal gradients, but type-compensated connectors are also available.

A lot of excellent problem-solving again. I loved your vacuum development process. I was sad that you got caught out by the scam-like nature of modern glass, specifically that of faux borosilicate. Pyrex especially (which I don't know if you were using but is relevant) built a business of trust in the 20th century that their glassware was made of the high-quality material, but around the turn of the millennium, started allowing more use of their name on regular, low-quality glass. Even today, people are surprised when their Pyrex dishes shatter under normal, medium-temperature conditions because they'd owned other Pyrex dishes from 25+ years ago that had survived for so long. It's no doubt that most lab equipment companies now are more than happy to allow consumers to assume they're made of materials that had become standard but are instead no more robust than a $3 glass coffee carafe. But enough of my ranting. I love watching your processes.

Suggestion if you ever rebuild the thermocouple assy: instead of using an epoxy paste like the JB weld, use an epoxy liquid. There won't be as many entrained bubbles (you can improve on this a lot more if you use your vacuum pump to pull the micro bubbles out too), but you will have a much smoother surface finish. This is important because oxygen will be diffusing from the surface of the epoxy in a good vacuum. The liquid epoxy also reduces the risk of a leak along the solid wires. If you end up using stranded wire for something the liquid can flow between the strands and still give a pretty good seal (though you might want to spread the strands a bit). Keep up the good work. BTW: I have gotten that HPLC going and I still plan on running that PCB resist you sent me on it to see what happens, but I will want to get a bad column to run it on first so I don't risk a good one.

Can you check if termal diference is constant if it is you can just add the the diference

failure due to cold o-rings... RIP

The JB weld should definitely be fine outgassing-wise at these temperatures. I'm not sure if you said so, but make sure those threaded connections are sealed with either teflon tape (if they are NPT) or epoxy. Looks really good!

You're doing much hard, accurate and smart work...

20:15 I think someone else mentioned this, but depending on how hard of a vacuum you intend to pull this *could* be an issue. There are Vacuum Rated Epoxies/RTV Silocones for Vacuum Use if i remember correctly…granted for a price. That “Faraday Wax” someone on-RU-vid made may be worth a look, that and/or a less “witches brew” and moreso just “this fraction of paraffin wax” or something type recipe may be neat. GRANTED “if it ain’t broke don’t fix it”, and the build is already coming along great! Just thought I’d throw this out there in case you didn’t already know about that and “virtual leaks” and all that. Keep up the great work!

Any ideas on how to get compression fittings without a lathe? Or are you pretty much just stuck having to buy them

Idk why people keep saying borosilicate glass has such a high "melting point" It is higher than normal glass. But much lower than quarz glass. You even showed in the video that you can melt it with a normal torch ;D

Outstanding video as always. Great job on the clamps. 👍

Argon welding gas is cheap

Hey, great video again! Few suggestions below, but definitely include lathe work videos and keep up the amazing work! You can create an offset calibration curve for the external thermocouple, this is how many lab furnaces operate, as the hot spot is not usually very large and you're planning on putting the sample in the middle of it, giving a temperature offset anyway! I do this in my lab furnace which reaches 1500C so those radiation issues are massive. For your thermocouples, just buy thermocouple extension wire of whatever type you want, then use an acetylene torch (or spot welder) to melt the two wires together. Bam, now you have any length you like without any issues, and can shorten very easily (cut and remelt). Either a vacuum charger, or nitrogen/argon flush of the tube while loading might help remove some oxide growth. You could use your blank end to provide the flush?

I would really enjoy a full video about machining the end cap fittings :) And as always, really well made video. Keep up the great work!

Man, this project is sick! I can't believe it doesn't get more views, especially with how well laid-out and well-explained it all is. Keep up the good work!

Fascinating work. Ive used quartz rod for a clock pendulum due to its exceptionally low thermal expansion, nice work on the end caps. Hope the heatshring on the thermocouples doesn't leak vacuum, you can get ceramic feedthroughs but also glue lined heatshrink .

Usually most welding supply shops sell small Argon bottles for hobbyist that doesn't cost that much. Argon setup for this purpose is 200 dollars max.

You could measure internal temperature by knowing relation between temperatures of internal to external couple. Should be something similar to multiplying your external thermal couple temperature by 2 point something and then adding couple of degrees, a simple linear regression or can be any other kind of regression. Or it doesn't have to be linear you could just record temperature readings plot the results and see the actual relation yourself then just use the interpolation.

Why not leave the vacuum pump running while the furnace is heating up? There is such a low mass of hot air in there left anyway it won't damage your pump and you get a even better vacuum. Also there are small 1L Argon bottles with 100 Bar for like 25$. The trick is to just get a cheap valve for them and use it to fill a balloon. Now you have a nice low pressure gas for flushing :) 2 or 3 Flushes and your vacuum is free of oxygen. You can do Argon flushing for under 100$, of cause not pretty but this is science not a beauty contest 😄

I would add rubber grommets to the wire passthru holes, where you used glassfibre tubing. Timestamp 8:00

3D-Prints are even with 100% Infill not airtight. Trying to fix that is not worth the hustle.

O-rings and low temperatures, I think I’ve heard that before

Did you use thermocouple wire for that lead? If you used regular wire that means your cold junction is at the end of the tube, and that will mess up the cold junction compensation.

Great series. Please show the lathe work next time.

Even the cleanest welding argon 5.0 can have impurities in some bottles. I had troubles with arc stability during aluminum TIG welding. I was prepared to send the machine for servicing, but after receiving advice to change the bottle, I was able to weld properly again.

You need to be using thermocouple extension wire of the same type as your thermocouple. Using soldered copper wire for your thermocouple cable will likely throw off your temps fairly significantly, as right now your cold junction is at the end of the flange. You'll have an error roughly equivalent to the temperature different between the flange and your thermocouple input, which is probably somewhere in the range of 20-80 kelvin of error

Can you do a workshop tour? I would be really interested in how you use your mill and lathe...

May be you can flush out the oxygen within the tube with argon before vacuuming to reduce oxygen or connect argon to the end of the tube so that if leak is present, it takes argon other than air. By the way, when I saw the test tube started melted that easily with butane torch, I was sure it will be melted in the furnace 🤭🤭

Thanks for sharing all of these DIY semiconductors content! I couldn't find any source on internet, which shows whole process keeping it simple and at the same time comprehensively discussing the topic. Just watched all videos on your channel and now patiently looking forward for updates on project. I also hope for some mosfets, because they're what's really used because of their energy effieciency. You could even make SSD like memory with NANDs if you will be able to grow floating gate on SiO2 to hold charge and therefore store data and another SiO2 layer on top of that for insulation and finally gate contact on top to change state of memory:)

Wow, such a nice video and so well presented! Thanks for the insights on glass seals. Now that you have a vacuum tube furnace, you could try putting some H2 inside, that would actually reduce any oxides, and even if your substrate was not clean enough, you could "clean" it in-situ! Also, for the external thermo-couple, yes, it doesn't see the same amount of infrared radiation, but doesn't it get due it heat diffusion at some point up to the temperature? If not, you could actually calibrate it, knowing what you get from the internal one, and not throw it away. Anyways, very fond of your channel, best regards.

Never use a sodium silicate as separating layer between heating wire and quartz, because fused silica is not immune and will react with it on surface creating some kind of soda glass with much lower melting point than a quartz. As heating for operating 1200deg C only option is Kanthal A1( and equivalents ) in ribbon form , not a wire . Another thing is quartz (or fused silica ) can work up to max 1000 deg C for exdended period of time , higher temperature cause recrystalization of quartz , tube became opaque and very fragile.

Why don’t you just flow some argon into the tube then pull the vacuum? This will displace any regular atmosphere temporarily… So whatever gas is left is mostly just argon (or nitrogen if you choose N2 instead, but I’m unsure of silicon reactivity with nitrogen)… there is also some argument to flow nitrogen or argon near the end caps so whatever does leak in from vacuum is still inert… this fixes all the expensive fittings issues and just increases the effectiveness of your current system…

18:25 - Interested on making these compression tube fittings. Can you explain in more detail how this compression implementation for the fittings works? Thanks

"it was slightly colder than before and the o-rings were firmer as a result" NASA management: "Write that down! write it down!"

Purge the pipe with a tiny trickle of argon gas. You can get the Oxygen content into the ppb atmospheric equivalent range with argon purge and simple vacuum.

could you combine the two appraoches - flush with non-oxygen, and create a moderate vacuum - and do you need to use oxygen - could nitrogen be a cheaper flush?

I'm a sucker for any machine video especially if it involves trying to prevent leaks. Do it

No, go with the argon method. I hope he changes his mind, i must watch the rest. Well, i think i would have gone the argon method but it seemed to work well with vacuum also. Interesting and good video, thanks for sharing this stuff.

The part costs 500 but I have some lathe laying around in the corner of the garage, and I built it for 10 bucks.

An even better method of sealing the quartz tube is a simple cap with a rubber washer in it. It's easy to remove when off and the stronger the vacuum, the harder it pulls the cap on and compresses the tube end to end.

I saw a Video from breaking taps about copper metalization with a Diode laser you can use that to make the conductive traces on the silicon

15:18 Wait I’ve seen this one before…

Beautiful machining, very impressive

Wow nice, you are a smart boy my friend! 🙌🏻🙏🏻 love to see what people are up to! You getting a new subscriber!👍🏻

I like what you are doing, please continue.

orings must rattle on the shaft, glass filled teflon so cool!

Need not to worry about O ring temperature just put a wet cloth

Damn, you are such an inspiring person man! Really loving what you do and breaking the limits of what a single person can as hobby! Please don't get discouraged because of less views and following, you will surely get the fame you deserve one day.

Youve now got a good vacuum system, and a hot furnace. I hear the sounds of CVD.

So.... What are you going to make? Looks like you could make some MOSFETS in that thing...

3:44 The 22.4 number comes from something else! It's the INVERSE! It's how many liters one mole of gas occupies!

That region is DOPE!!

why not first haphazardly flush the device with an intert gas, then vacuum the device. You should end up with nearly no oxygen.

You have a typo in your thumbnail. It says "Furance" instead of "Furnace"

If you make heatsinks and clamp them on the tube right before your flanges, then you can prevent the heat being conducted all the way to the O-rings. Just in case if it ever becomes a problem.

isnt the nicely homemade compression flange on backwards? it looks like the o-ring sealing part wont make much difference? whats keeping the seal between the end of the glass tube and the big open gap between the halves of the compression fitting?

love you videos you have gaven me alot of adias

You can use argon for much cheaper. I live in the US and got an argon setup for my lab. I have a 10 ish lb cylinder and I got it from airgas for like $200 ish and the regulator setup for like another $200 because I have both a flow regulator and a pressure regulator for pressurized inert atmospheres. It’s totally doable for not that much. Also if you want to get even cheaper, look up argon wine preservation. There are setups with decent sized cylinders for around 200$ for everything. One more thing, what vacuum pump are you using?

Nice oven upgrade, was kinda hoping for a flow setup but going vacuum/batch is still plenty good in 90% of cases. As others have mentioned the math for V(O2) is off, also im pretty sure the unit is written mol. I have never seen Mol before.

I feel you have over-estimated the cost of argon by a lot. You rent most of it from the welding supplier, and the rest can be bought for cheap from China.

In my lab we have to work with oxygen free atmospheres in tube furnaces, though in my case the furnace tube is alumina so that we can reach 1500 degC. One of the simplest ways to go is to use what is called a test plug. It is an expandable rubber stopper with a gas feedthrough. That works fine, but oxygen does still get in, so we would place a dish of titanium sponge in a hot, but not too hot zone of the tube upstream of the sample. This did a nice job reacting with any oxygen that would get in. But in the end, I bought two weldable quick connect flanges and used a liquid engine gasket compound to make an airtight seal between the flange and the tube. This holds vacuum very well. But with all that said, flowing argon at a slight positive pressure is not very expensive really and works way better than vacuum to keep oxygen out. The $1,000 for argon and a regulator is way overpriced unless you are talking about buying a large gas cylinder.

wouldn't making a thread around the whole inner/outer piece be better for this? then you wouldn't have to worry about tightening the 4 bolts too much one by one, or not equally tightening them

Purge the cylinder with argon before puling a vacuum.

My big comment might've gotten nuked by the auto filter system, see if it ended up in the other thing

I think if you purge your system few times with inert gas before final evacuation there will be even less oxygen left in there

feels so wrong when you keep calling quartz tube "glass"

what kind of glue are you using to stick coil heater element? thank you

Very interesting. Nice work

Nice work on the flanges. Any concerns about their weight causing the tube to deflect?

This is amazing, man!

if glass sucks at tension, then how come fiberglass is so strong?

This “vacuum gauge digital reader” wher did you bay this one?

Thumbnail says furance instead of furnace

Well, now I know what I need to add to my (mental) design of a tube furnace lol

Can I have your help? This weekend I melted my expensive high borosilicate tube. Can you please point me to the aliexpress seller that you are using. I am from Portugal (europe) so buying from McMaster-carr is too expensive to ship to Portugal.

When pumping down to pressures much below about 1% of atmospheric pressure, the vast majority of the gas is water vapor and not residual nitrogen or oxygen unless there is a significant leak in the vacuum system.

Great adjustments learned a little bit good video

Could you add some material with a high surface to volume ratio that gets oxidized alongside the wafer and consumes the oxygen ? I'm thinking of copper dendrites

What's the resistance of a wafer that's just freshly out of the HF bath?

Argon does not need 2 regulators, all those for welding already include what you call secondary regulator. Also, since this is so wildly used for welding, it is dirt cheap. You can also use any hose you want, since you are not working with pressures. Note that you can turn on the vacuum pump seconds/minutes/hours before you actually need to use it. You do not need to turn it on right as you seal the vessel.

2:10 You are way overthinking the setup needed for argon. You don't need any kind of seal better than a bit of aluminum foil or any regulator other than the primary regulator on the tank; you just prevent oxygen from leaking in through the cracks, by flowing enough argon to ensure you're only leaking _out_ those cracks.

Also more machining videos please

9:15 you could test it at a variety of temperatures, measuring both its relation and its lag. if the lag is slow enough, the temperature difference isn't an issue, since you can fit a function to the relationship between them, to get one from the other. if it's mostly radiative, i don't think it would lag all that much, would depend on what contribution conduction makes to it.

Fascinating. Thank you for the great effort.

This is a pretty small volume. Thermal sputtering some titanium wire might get you a much better vacuum.

If you put something in the tube that reacts quickly and completely with oxygen maybe you could just use up all the oxygen. Like magnesium? That would happily react with the oxygen and form high temperature stable magnesium oxide with a 2500 C melting point

This is fascinating, would it be possible to add a material that sublimates into an inert gas either with temp rise or pressure drop to further remove oxygen ?

Great math around the residual oxygen at the vacuum level, but you can flush the tube with Argon and then pull the vacuum, which means there shouldnt be more than 1E-5 oxygen that was in the Argon, which should be much less. edit: P.S. great project and thanks for sharing.I wish they were longer and more detailed, I just love the combination of engineering, DYI and physics!

Now you could just flush the oxygen out with argon and then pull a vacuum, should work but might depend on how you plan to add the dopants. I've had some experience with tube furnace while making activated carbon using KOH and this flushing -> sealing method worked.