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Author: Subject: Homebuilt 1300°C tube furnace
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[*] posted on 21-6-2008 at 19:54


Pre-oxidising is a good idea, a friend of mine that salvaged and restored old pottery kilns ,to sell to potters without much money, did that. They also applied a thin layer of a zirconium silicate based wash over the resistance wire before the final buttoning up, the layer is too thin to affect the radiative properties but enough to reduce the occurance of shorts from coil creep.

You might try building a box of backing board (usually calcium silicate based) around the tube furnace, with spacers/supports for the tube cut from some of the board. Most of this type of product is good up to 1100 C, and is low density giving good insulating properties. This makes the outside of the kiln square, which is easy to build a metal shell for.

Alternatively, or in addition, to backing board you could put on an outer layer of castable insulation, something like Kastolite light weight.
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[*] posted on 24-6-2008 at 13:28


Earlier I reported that the insulation used in my tube furnace was 8 pcf (lb/ft3) Kaowool. Upon further questioning of my vendor I find out that it is actually 8 pcf Superwool 607. This has a classification temperature of 1100C and a heat conductivity at 982C of 0.28W/(m-K).
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[*] posted on 6-10-2008 at 19:52


Hey Stefan, congratulations on your success! I also started building a tube furnace following your design. I'm really staying on the cheap side this time, which is always a good challenge for me. Used professional furnaces of comparable power can be bought for the amount you spent so far, if not less, although the fun and the learning experience are of great value too.

My tube is 30cm (12") long sillimanite; my heating coil is probably much like yours (so rogue, it took me two days to wind it all up, leaving about 2mm between successive turns); instead of the alumina coating I used some gypsum-based protective mixture... it might get brittle when heated, but the kaowool will be tightly bound around it by then. I plan on avoiding the oven pipe (way overpriced, for my liking); instead I'll place decreasingly heat-resistant layers of mineral fibers going from the core out; I still have to decide about an external case. An orientable stand would clearly come in handy. About that, you could mirror a Newton telescope mount to get a firm but versatile stand.

So far, my major concern is the temperature control. Kiln thermocouples are on sale at pottery supply stores here for well over $100. You said you built your own because the one that came with your PID had silicon insulation that wouldn't take your working temperature. My question is, is there a particular reason why you couldn't just remove this silicon (and, if necessary, replace it with ceramic fiber tape or similar) and go without? Or is this silicon worked inextricably into the construction of the sensor?

One more thing. It seems customary to place the sensor inside the chamber. This way you have no control on the temperature of the wire, which could easily pass the limit in case of quick heating, assuming a hundred or more degrees temperature gradient across the tube wall.
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[*] posted on 7-10-2008 at 08:35


It doesn't need to be Kanthal-wire. At welding-supply they sell Cr/Ni-wire (for stainless-steel-welding), by the kg. I paid for 1 kg 30 EUR, several years ago, in a hardware store. Probably can be got much cheaper ...
This Ni/Cr-wire (0.6 mm2) has a resistance of 3 Ohm when cold, and this doubles up to 1000 [Celsius]. It withstands at least those 1000 Celsius for quite a while, and I numerous times repaired my furnace with self-made-windings of this wire (which fails whenever some carbonate-melt gets out and fuses to a glass with the ceramics of the furnace).
Usually after many hours of 900-1000 [Celsius] the wire seems still like fresh, when it was within clay, but when on air it has a lifetime of maybe several 100 hours only.
It helps to glow it (electrically) before trying to make any windings of it (using a slow drilling engine), because it's much softer then.

I usually calculate the necessary wire-amount by the Stefan-Boltzmann-law of emission (assuming only radiation-emission cools the wire), constrainted to the desired electrical data, so the wire is only 100 [Celsius] hotter than the desired furnace-temperature, thereby the furnace-temperature may be optimally high.

Besides only 500 [Celsius] are necessary for Fe-vitriole-decomposition, according to other threads here.
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[*] posted on 7-10-2008 at 17:56
Automatic temperature control


Quote:
Originally posted by chief
This Ni/Cr-wire (0.6 mm2) has a resistance of 3 Ohm when cold, and this doubles up to 1000 [Celsius].


This means that at constant voltage, the power is halved. Correct me if I'm wrong, but this effect, common of most metallic conductors to some extent, causes the temperature and current to eventually reach an equilibrium dependent only on the voltage and the response rate of temperature to emitted power (which in turn depends on the physical construction, materials, content of the chamber etc). It would then be possible to calibrate the temperature by adjusting the constant voltage and get rid of an electronic controller, as long as the changes in the thermic properties of the reactants are negligible during the reaction. It would suffice to interpolate a few data about the equilibria and print out a table of T to V :cool:

[Edited on 7-10-2008 by jarynth]
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[*] posted on 7-10-2008 at 20:20


I learned two things running and rebuilding my kiln many times over the years. one is the importance of keeping the kiln airtight until it has cooled to a minimum temperature. The other is to coat my heating coils with a thin coat of ITC-100. In other words the most important factor was keeping oxygen away from the hot metal coil as much as is humanly possible. I also noticed an amazing increase in heating VS power efficiency and a decent increase in acheivable temperatures inside my kiln by coating every possible area inside the kiln with a nice thick coating of ITC-100 HT Ceramic Coating.

ITC-100 HT Ceramic Coating
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[*] posted on 7-10-2008 at 22:50


Yes, the power decreases with tempoerature, and this does self-limiting. But as the power decreases, with thermal losses increasing (with temperature), the last 100-200 degrees [Celsius] are reached quite slowly; best ist: Heat up with full voltage, then change the voltage to hold the the temp.
This can be done by using a transformer with several windings, to add up the voltages as needed: {1,2,4,8,16,32,65,128}-Volt-windings allow every voltage between 1 and 256 V, to the accuracy of 1 V ...
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[*] posted on 7-10-2008 at 23:44


When I said "heating VS power efficiency" I meant the ITC-100 acts like a heat mirror, in that thermal radiation losses through the bricks went down quite significantly. This allowed for lower "ON" cycle times while maintaining Cone 10 or hotter temperatures for many hours.
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[*] posted on 8-10-2008 at 02:58


Just to share 2 Ideas (not from me, but tricks of the trade) on reaching really high temoeratures:
==> up to 1700 [Celsius]: Mo-wire around Al2O3-ceramic-tube [also commercially available as furnaces]
==> up to 3000 [Celsius]: Wo-tube, current directly through the tube

The latter may be adapted,using cheaper stainless-steel-tubes (limited lifetime, but throw-away available from hardware-stores), which should hold up to 1300 [Celsius] too; then it would be only a matter of contacting them, wrapping some isolating-mat (even maybe rockwool) around them. Since the resistance rises with temperature the electrical power would be dissipated within the isolated zone, contacting therefor should be easy enough (if necessary through welding).
As power-supply: One thick additional secondary winding around the welding-transformer, eg. . Within such stainless-steel-tubes then, at lower temp., even pressure-experimentation could be done (catalysts in the tube, have fun making HNO3 etc.), since in the hardware-store there are also other stainless-steel-components available,usually to make waterpipe-connections etc. .

Maybe someone could succeed in Fischer-Tropsch-gasolining from coal-water (50 Bar, 200 [Celsius]) ?
[Edited on 8-10-2008 by chief]

[Edited on 8-10-2008 by chief]
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[*] posted on 9-10-2008 at 07:52


There was a thread on this somewhere, but here is a useful link upon reaching 1300 [Cels]within the microwave (700 W) within less than 5 minutes (!):
http://alp.dillingen.de/chemiekongress/doc/Workshopergebniss...

(usinc "activated carbon" as susceptor, maybe charcoal will work too ?)
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[*] posted on 21-10-2008 at 15:16


Surplus sales are great aren't they. I just scored a 340 meter roll of 2mm diameter Kanthal A-1 and a half dozen
Omega 150mm long quartz sheathed dual type K element
furnace thermocouples with Watlow solid state micro-controllers . Yeee ha! yipppee !
All of it is new unused but ancient stockroom surplus, all
of it for about eighty bucks :D One of the thermocouples alone lists for three times that :D Also got a few slightly used 95mm X 400mm mullite tubes. Let's see, now for what would these things be good ? Any ideas :P


[Edited on 21-10-2008 by Rosco Bodine]
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[*] posted on 25-10-2008 at 08:21


How did the old chemists reach the 1300 [Cels] ??
==> charcoal, with air-blowing
The to-be-decomposed material would before the heating be made to a dough, then dried as little spheres, so it wouldn't fly away as dust ...

Then these spheres would be mixed with the coal, the coal would be heated via air-stream, and the reaction would occur.

Now: With the "hot-air-gun"one may reach the extra 500 degrees above the usual coal-temperature, and it goes into white-glowing ! I do this every day now to start the fire in the oven ...
It's definately a high-temp heat-source to blow charcoal with the 10-$ hot-air-blowing-thing.

[Edited on 25-10-2008 by chief]
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[*] posted on 20-5-2009 at 20:05
Extreamly simple mini 600*C tube furnace.


If theres one thing I love more then chemistry thats tinkering with junk left over in my garage. Seeing some heating elements in an old hairdryer gave me the idea to see just how hot these elements could get a tube furnace.

My first attempt was to take some of the wire and wrap it around some glass tubing I had laying around. This was a big mistake. Within seconds the glass tubing almost
turned into a puddle. This gave me enough incentive to move along but since I did not have any quartz tube around I used 1" hard copper tubing. To prevent the wire from shorting out on the copper I preped the tubing with pieces of scrap pink insulation that had been diped into clay that was turned into a slip. This was allowed to dry overnight and the wire element was wraped aroung about 5 inches of the pipe and held in place with clay and insulation. More layers of insulation where built up and was toped off with a piece of metal flue pipe. The ends where coated with spackling compounds to hold the fiberglass insulation in place and to ensure a good low oxygen enviroment for the heating element.

Lastly as seen in the picture a dimmer switch was used to control the flow of electricity thru the circuit.

Here is a photo of the over all tube. It may have took me no more then two to two and one half hours of work to finish this little piece of crap but once she was fired up I was honestly impressed. In a matter of ten to fifteen minutes the temperature measured it reached a blistering 600 degrees Celsius and was held there for a matter of one half hours or so. This was done with the dimmer switch only half way up so I feel I could eak a few extra hundred degrees or more out of this thing if I allowed it to crank all the way up. Also since the tube is copper alot of loss is comming off the ends.
Over View


Side View



Pyrometer


Sadly the camera had trouble focusing on the numbers but what you are looking at here is the needle of my pyrometer resting directly on 600 degrees Celsius. It did raise a little above this and was slowly going up but for now I will call the limit as 600 even though I know it will surpass that number with ease.


Now....

What is one to do with such a creation?

I have considered Adapting the ends for a feed and exit tube to attach to and filling the tube with Cu powder in an attempt to synthesis formaldahyde and acetaldahyde and see how that goes. Could this same thing perhaps be used to oxidise BnOH to benzaldahyde? I already thought it was neat to stick A piece of Polystyrene in one end cap it off and watch liquid cracked styrene monomers to come out of the tube and condense on a cold glass.

Any other suggestions on how to play with this thing before I push it to its possible breaking point? Or melting point for that matter:D.

~Sedit





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[*] posted on 21-5-2009 at 17:29


Nice work!
Electric heat is capable of much more, but this is a good start.
Acetaldehyde and formaldehyde production is a good idea for this temperature range.
A carrier for the catalyst instead of plain copper powder would be a good idea. You could, for example, soak pumice in copper nitrate solution, dry, and heat to decompose it to CuO.
This gets reduced once the alcohol is passed over it at elevated temperature.
A copper wire mesh could also be a good catalyst.
About benzyl alcohol dehydrogenation- try it if you can get benzyl alcohol.

And try to move on and make a furnace that can reach 1000°C. With this, you can decompose sodium pyrosulfate.




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[*] posted on 22-5-2009 at 00:26


Hi, it seems that a limiting factor to making a truly useful tube furnace is the rarity/cost of a quartz glass tube. I notice that in most bar heaters (those cheap 1kw varieties) the resistance wire is wound inside some type of opaque glass tube which considering the temperature they get to must be quartz glass? While all the tubes I have seen are only in the order of 10mm diameter they could be useful for smaller reactions. Also someone recently told me that some of the bigger industrial sized light bulbs have sizable quartz glass tubes that may be serviceable.

If these tubes are too small for the actual “tube” they could be used as small reaction vessels when inserted into a metal tube furnace not unlike Sedit’s copper furnace.

Anyone here considered these options?

AB
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[*] posted on 22-5-2009 at 06:45


Quote: Originally posted by barbs09  
it seems that a limiting factor to making a truly useful tube furnace is the rarity/cost of a quartz glass tube. I notice that in most bar heaters (those cheap 1kw varieties) the resistance wire is wound inside some type of opaque glass tube which considering the temperature they get to must be quartz glass?
Costly, somewhat, but rare, not at all. You can order, off the shelf, for less that $50, a four foot length (standard) of 25mm ID medium wall quartz tube for less that 50 USD. (Sample vendor.) That's enough for 2-4 reaction tubes, depending on what length you need. Quartz can be cut with a diamond saw, such as is used to cut tile. Fire polishing of cut ends is possible with an oxyacetylene flame.

The opaque tube might have been quartz, as opaque varieties are used in heaters. More commonly opaque heater tubes are mullite, which is a bit less expensive. Mullite is also used for reaction tubes, though.
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[*] posted on 22-5-2009 at 11:55



Hello,

I think the glass tube that Barbs09 is referring to would be more accurately described as translucent as opposed to opaque. The ceramic (probably Alumina) tubes with a 'thread' on the outside for the Nichrome wire to sit in are not what he is referring to (I think).
I have wondered what exactly the translucent glass tubes were made from. The wire is wound in a coil on the inside of these tubes.
They can be had from the dumpster.

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[*] posted on 22-5-2009 at 12:18


The translucent or opaque tubes from heaters are made from quartz glass. They are sometimes a lesser quality of quartz glass, an opalescent one which contains many small air bubbles and is cheaper to produce, but is equal in properties to clear quartz glass except for the transparency.




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[*] posted on 23-5-2009 at 02:21


Hi thanks for your replies. The opaquely translucent ;) tubes I am familiar with also have fine striations parallel to the long axis of the tube which I guess could be extrusion marks.

Watson.fawkes thanks for the heads up on the availability and reasonable price of a good-sized quartz tube. I will look into this but I bet they are not so available/cheap in New Zealand:(

Also when winding Nichrome around a tube can anyone see any problems with twisting wires together if I don’t have on continuous length? Obviously I can’t solder them. I would imagine it would be much less than ideal due to localised resistance etc..

Regards, AB
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[*] posted on 23-5-2009 at 03:11


Quote: Originally posted by chloric1  

2. The design of your furnace is based on 230V as a power source. Wouldn't it be OK to use half the length of simular wire, different size tubing, make this suitable for use with 120 V source current?

P=IV and V=IR, so R=V²/P. That means that if you're using half the voltage and want the same power, you actually need 1/4 (ie 1/2²) of the resistance
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[*] posted on 23-5-2009 at 04:40


Hello,

Often wondered about sterilization lamps. Are the glass in them quartz, (in order to transmit the UV). They would be very expensive to buy just to scavange the tube but they must be replaced on a regular basis (not just when they are blown) so they may be available for zilch if you knew where to look.

There are also 'sun lamps' like here. You get four tubes (I presume they are quartz). You could just pinch one of the tubes for the good cause and give the remaining three legged sun-maker to the wife to alleviate any SAD syndrome she may be suffering from!

I presume regular sun tanning lamps (as you see in sun tanning shops) are not made from quarts but are just similarish to regular flouresent tubes.

Dann2
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[*] posted on 23-5-2009 at 08:57


Quote: Originally posted by barbs09  
Also when winding Nichrome around a tube can anyone see any problems with twisting wires together if I don’t have on continuous length? Obviously I can’t solder them. I would imagine it would be much less than ideal due to localised resistance etc..
You can't solder, but you can weld them. Twist together, flux with a little paste made of borax and water. Put under regular power. Local resistance of a "bad" joint (before welding) provides the heat. Let cool down, wash off and neutralize the flux.
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[*] posted on 23-5-2009 at 09:36


Garage chemist I really like the idea of the pumice copper catalyst. I was going to just take the fine powder copper I got from precipitating CuCl solution with zinc and grind that together with sand to give surface area but your idea is way better.

After a little time to mess around with the thing it has proven to be a steady 600 degrees Celsius. This is caused more then likely due to heat loss thru the copper tuding itself and since I have a kiln next time I fire it up I will make some high alumina porcelain tubes for use with it instead of copper. The fact that I have seen it liquify the clay around the wires means that without the heat loss due to the copper extreamly high temperatures should be achieved. Im going to attempt to insulate the copper once I get the end plugs on for attachments but I have to find my high temp epoxy before I can do that.

Mind you all this was just tossed together pretty much on a whim so im impressed with its handling and wounder how long a life time it will prove to have. I only used partial of the elements that a hair dryer has but welding them like is mentioned above is a good idea because it will give me more working surface for any reactions to take place.

Question: Is this a high enough temperature to produce Keten? It produces a nice red glow which should be enough for acetone pyrolysis but am unsure if other factors come into play there.





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[*] posted on 13-12-2009 at 09:14


Today I am 'playing' with electric heating.
First of my goal is to familiarize myself with this concept and see how far I could push some scratch that was lying around.

Materials available:
Old toaster
Flowerpot
old ceramic vase
Thermocouple
Sand

What did do:
Took apart the toaster and used 2 parts, the first was a glow wire and the second was the current limiter ( the part where you can set the amount of carbon you want on your toast )
4 spirals were found in parallel, I decided to use one for this test.
If course I tested if the single spiral would hold up when cut off from the rest, it did without burning.

Then I took the vase and spiralled the wire around it (about 1,5 meters of wire)
The vase is about 40 cm in length and 12 cm in width.
Only 15 cm was used for the spiral.
The vase was placed in a big flowerpot and surrounded with dry sand.

Test:
The juice was turned to about 20 % and I waited to see if the construction would hold up.
A temperature of 280 degrees was measured on the inner wall.
The power was further upped to about 40 percent and a temp of 360 degrees was measured.
(outside temp climbed to 100 deg C )

Finally the temp was slowly increased to 100% and a temp of 630 degrees was measured , it was still climbing but to coating of my thermocouple wire started to melt so fast that I had to stop.
(anyone any suggestions to fix this problem)
surprisingly the outside of the flowerpot only measured 140 degrees.

Anyway.
I found out that sand is a quite good insulation material and that even such a simple and primitive construction could reach such enormous temp within a short time spawn.
The temp that could be reached with all 4 of the wire's and better insulation is yet to be tested.
This all without paying a single dime (except for the electricity)
Ill report further tests if anyone would like that.



[Edited on 13-12-2009 by User]




What a fine day for chemistry this is.
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[*] posted on 13-12-2009 at 12:07


The "standard" insulation for high temperature thermocouple wires is braided glass/silica/asbestos substitute up to their limits, then little ceramic hollow tubes (long ones for rigid support, short ones for flexibility) threading a wire up through the holes up to the thermocouple wire limit. A two-foot-long (60 cm, more or less) ceramic type K probe without wiring (spot weld your current wire to it) costs $8.50 3859K56 from <a href="www.mcmaster.com">McMaster-Carr</a>. Fully fabricated ones with 304 stainless steel covering the probe cost $30 or so with cord and plug.

A truly cheap person with a Dremel tool and a small carbide bit might take broken pieces of pottery and drill pairs of holes in them to make improvised insulating beads.
I haven't seen unglazed ceramic beads for sale anywhere lately...


[Edited on 13-12-2009 by densest]
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