## Homebuilt 1300°C tube furnace - Lò ống 1300 độ

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### Homebuilt 1300°C tube furnace - Lò ống 1300 độ

Homebuilt 1300°C tube furnace
Tự chế Lò ống 1300°C

I completed my new powerful tube furnace. Look here for pictures:
http://www.versuchschemie.de/ptopic,168531.html#168531
You can see that I have successfully taken it to 1300°C (2370°F- thats above the maximum continuous use temp for quartz glass!) already before I put it into a casing.

As you can see, the construction is ridiculously simple. It can be thrown together and put into use on a single day.
No cements or castable refractories are used.

The core of the furnace is a ceramic tube, 500mm long, 40mm OD, 32mm ID. The ceramic is called "pythagoras" and is good up to 1400°C (some sources say 1500°C), it is also absolutely gastight (even high-vacuum tight).
14,7m of 1mm Kanthal A1 wire (1,8 ohm per meter, giving about 2000W of power at 230V) is wound onto the tube and covered with a paste of equal parts MgO (dead-burned magnesia) and Al2O3.
Phần lõi của lò là ống gốm: dài 500mm, đường kính ngoài OD 40mm và đường kính trong ID 32mm. Loại ống này được gọi là "pythagoras" và chịu nhiệt lên đến 1400°C (một vài nơi nói là nhiệt độ lên đến 1500°C), loại vật liệu này là kín khi (có thể dùng cho chân không). Dây đốt là Kanthal A1 đang sợi 1mm và dài 14.7m (điện trở là 1.8 ohm/m, có công suất 2000W với điện áp 230V)

After drying, it is surrounded by two layers of 1400°C aluminum silicate-zirconia 25mm ceramic fiber blankets held in place by wire.
It is put into a 120mm ID sheet metal pipe (the fiber blankets have to compressed somewhat for it to fit into the pipe- a larger pipe would have been better, but I couldnt find one).

The power is regulated by a thyristor circuit (commercial dimmer module), a 60W incandescent light bulb is put in parallel to the furnace to serve as a crude indicator of power.

Temperature is measured by a selfmade Type K (Nichrome-nickel) thermocouple connected to a multimeter with a temperature measurement option.
The lifetime of such a thermocouple is limited above 900°C (but can be taken to 1350°C for short periods of time)- a Type S (Pt-PtRh) thermocouple would be a much better choice, but is very expensive.

I have a 20cm long quartz test tube with ground glass joint that fits into the furnace. This can be used to take substances to temperatures far higher than what can be reached by a bunsen burner.

Such a tube furnace is able to provide extreme heat for every application in the lab where a gas burner fails miserably.
The prime example for such an application is: SYNTHESIS OF PHOSPHORUS.

I am mostly interested in the production of sulfur trioxide from ferric sulfate in this tube furnace, as well as carbon disulfide from sulfur vapor and charcoal and ketene from acetone.

==========================
What kind of "solvent" is used with MgO and Al2O3 to form a paste? Is it water or something else?
Yes, the MgO+Al2O3 is made into a paste with water.
Brauer recommends this mix for coating the wire, I found that it doesnt adhere at all after drying, but used it anyway.

I posted the important information from the german text in the first post. If questions remain, feel free to ask.

EDIT: I forgot to mention, the 4cm of insulation that I used is pretty thin. The outer sheet metal tube gets hot quickly (over 100°C). You need to place the furnace on a heat-resistant support, like a few ceramic tiles or bricks, otherwise a wooden table may char.
If you can get a suitable larger sheet metal tube, using a third layer of ceramic fiber blanket would be a very good idea.

The furnace still reaches 1000°C in just 10 minutes at full power with my current design, and takes less than 50% power to stay stable at 1100°C.
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Nice work gc! I love the simplicity of your design. I am surprised that your furnace pipe OD is only 120mm (4.7 inches)! That means your insulation thickness is 40mm (1.6") maximum. Unbelievable!

This should open up the home chemist's ability make all kinds of useful reagents.

I have a couple questions. Your Pythagorus tube is 500mm long, with 450mm heated. Will you still be able to use your 20cm quartz tube w/ground glass fittings? Do you just insert the quartz tube and connect to borosilicate glass tubing on both ends, or what? Will you need to use supporting saddles for your quartz tube or will it center itself adequately?
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Magpie, the kaowool is indeed a very good insulator.
However, the 4cm are really less than optimal. The furnace gets really hot on the outside, well over 100°C. It still has no problems reaching 1300°C though.

The quartz test tube I am talking about is closed on one end, and has a ground glass joint on the other side. It will be inserted into the furnace at one end and connected to e.g. a condenser for product vapors. Yes, the top 5cm of the test tube will be in the unheated zone then, but you have to have a temperature gradient zone to protect the joint from the furnace heat.
I also have a 10cm quartz extension tube with two joints.
The test tube will not be centered in the ceramic tube, the heat distribution is even. The temperature at the bottom of the tube is nearly the same as at the top due to heat transfer via radiation.

I also have a 70cm long quartz pipe that is open at both ends, with two joints. This can be used for continuous flowing gas reactions like ketene synthesis or CS2.

Fleaker, I would prefer to leave the phosphorus synthesis to you if you can build a tube furnace too. I can simply buy red P, so I would rather sublimate this.
Also, I havent read up as much on the different raw materials from which P can be made as some other members here, like Polverone and BromicAcid, and probably you as well.

Currently, I have a bowl of agricultural FeSO4 sitting around for it to oxidise in air. Guess what that makes when I put it in the furnace.

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I baked the coating of MgO-Al2O3 mix after drying by running power through the wire without insulation. It became really powdery and fragile after that, I think it would be better to not bake it and just pack it into the fiber blanket as it is and then heat it up.
Dont use sodium silicate as binder, this attacks Kanthal wire above 1000°C and makes it oxidise very fast. You need to be really careful about what you put in contact with the wire. SiO2 attacks it as well, so you cant use a quartz tube instead of a ceramic one.

With 120V, your best bet would be to use a thicker wire that has half the resistance per meter of the 1mm one so that you get 2000W as well.
If you use the same wire as me and make it half as long to get the same power, you will have a special problem: the surface loading of the wire will be too high, e.g. the wire temp will exceed 1400°C and melt even if the inside of the tube is still far below 1300°C because the wire surface is too small to transfer all that power to the tube.

Look in Brauer in the section about tube furnaces. It explains the problem and gives maximum surface loadings for heating wire.
I already exceeded the maximum surface loading strongly with my current design- but only at full power, and the furnace is always run with reduced power through the dimmer.
Especially at high temperatures one must not heat at full power- as a general rule, dont ever give full power to the furnace when it already is above 1100°C. If you need 1300°C for your experiment, you need to increase the temperature slowly and gradually above 1100°C.

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That is very good to know. Platinum and rhodium are both trading at all time high prices, and even a few inches of wire are very expensive. I have maybe a 11g piece of 50cm long Pt wire, but no PtRh alloy wire, and that will be troublesome to procure. My main concern with connecting a type S to a type K is that the business end might conduct enough heat to melt the connections. How would one connect the type S from the center of the tube ( BTW, that is the best place for thermocouple, it is most representative of horiz. chamber temp.) to the cheap type K? That is a problem I think, otherwise it would be great: type K is very cheap, type S, damn expensive. Len, you seem to know what you're doing with electronics, how would you solve the conduction problem?

I am very interested in building a tube furnace for home that is about 75 cm/30 inch in length with a 6 cm inner diameter. Originally I planned on using a fused alumina tube and heating it with molybdenum disilicide elements but it would cost me about $1200 to do that. It would give me 1750*C though, suitable for many things! Yet for really cheap, about$50, I can buy some A1 kanthal that uses 240V in series, 14.5 amp, and 3500 watts. I think that would be sufficient, the furnace won't heat as fast as garage chemist's but it will still be plenty powerful. A1 Kanthal is good til about 1450C/2550F. This would also mean that I could use a cheap mullite tube or silimantite tube. Probably under 200 dollars I would think. I think I would want a PID and some sort of stand so I can make the furnace vertical as well.

I have several hundred square feet of kaowool and plenty of Al2O3 and MgO, so that's no problem.

My biggest question is, how one would make a clamshell design? It would be difficult because you would not be able to just wrap the wire around the tube, plus you would need to have the tube cut in half.

Despite the evident construction problems, they are still very convenient--quick cool downs, allows easily introducing reaction system, best part I think is that it could make for easier ''zoning'' of the tube furnace.
That's another question for you electronics wizards: how would I make one end of the tube 500*C, while the other end would be 1000*C? I know I would need some sort of insulating barrier in between, but how do I control current supply to the elements, do I run several heating element circuits?
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Beautiful! Great work!;)

I am very pleased that your project became such a success. So my design has proved to be workable even with somewhat different components.

Using the ITC-100 paste was a very good choice, I see. My Al2O3/MgO mix became very powdery and flaked off in some spots. If I wanted to build another tube furnace, I would definately not use this again (I'd probably use calcium aluminate cement, even though this would be good to 1250°C only).
ITC-100 does not seem to be easily available here.

A question: what kind of heatup rates did you get with your furnace on full power? I get over 100°C/min at low temperatures, and at 1000°C still 60°C/min.
You said you got 1°C/min at over 1200°C- I think mine still heats up much faster at those temperatures!
Does your alumina tube + ITC-100 have such a large heat capacity, or are there other reasons, like heat loss?

My mullite tube has quite a low thermal conductivity. I remember alumina ceramic having a much higher conducitvity. Does this lead to increased heat loss at the ends?
The free ends of the ceramic tube on my furnace stay below 600°C (no visible glow) even at 1250°C inside the furnace.
Is that different with your alumina tube?
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Posts: 60
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### Re: Homebuilt 1300°C tube furnace - Lò ống 1300 độ

When ordering elements please have this info handy: