Trying an insulating refractory material

[jdelaney44]

I've decided to give a go with some EP kaolin, aluminum oxide, zirconium silicate, sawdust, and millet seed. The blend was about this by calculations:

32 lbs EPK
13 lbs aluminum oxide
5 pounds zirconium silicate
~ 1 pound saw dust
~ 10 pounds millet

I ran short of Aluminum Oxide so I substituted zirconium silicate for the balance.

The sawdust & millet was intended to be about 20% by volume. This along with whatever air gets trapped in the mix will provide gaps that should create the insulation properties once the compound is dried & fired. Frankly I am now feeling like I should have gone to 50% on the sawdust & millet. I want to let these panels dry and fire them to see how they look compared the the walls of my kiln.

The dry mix before dry blending



The mix after water & some machine mixing with a 1/2 inch eletric drill and a mud mixing attachment



Here's what it looked like after being pressed in the mold



It's drying now. The shrinkage has been about 3/16 in. in 24 hours. That was enough to get it out of the forms. Total shrinkage after firing is supposed to be 11% - 12%.

Oh, dry any flat clay item on something like Hardie board or drywall. These materials tend to pull water out of the bottom of the piece and continue to dissipate the water. If you don't use something like that, the top dries way faster than the bottom and it starts to cup.

Hopefully the sawdust will keep it from cracking. Once it's dry it goes in the kiln to be fired as close to cone 10 as I can get it. That will burn out the sawdust and the millet. If all works according to what I've been able to research, this will yield an insulating ceramic panel.

Actually, it will probably have to go into the kiln for a day or so at 180 - 200 degrees until the water stops coming off it. The last thing you want in clay as it approached 1000 degrees is water. I've had this happen before and lost the piece with the water in it and several pieces next to it.

I have no idea if this is going to work for me as it has for others before me. We shall see. Keep you posted.

[Fosterob]

Panels look good so far, let us know how they turn out.
Rob

[Dodge]

What is EPK?
Thanks,
Scott

[pkrankow]

EPK is a particular grade of kaolin for pottery. Looks like an interesting project, hope it turns out!

Phil

[Bigred1o1]

please keep us updated on how this goes i have been toying with the idea of trying to do some bricks in a pit fire so i am really interested in seeing how your recipe goes

[MattBower]

I have played with homemade castables from ceramics. I found the experience very frustrating. The problem tends to be getting them hot enough to vitrify properly in situ in a forge or furnace. The outer layers generally don't get hot enough to fire, and that creates all kinds of internal stresses. But all castable refractories are basically ceramics, so if you overcome the firing problem (and the tendency to crack as they dry) there's no reason they can't work. Good luck. I'll be interested to see how it goes.

[jdelaney44]

Thanks for the comments!

Today I broke up the slabs and increased the seed content. I added about double the seed that was in there. The slabs have been re-cast and are drying again. This time I over filled the forms a bit, put a piece of plywood over them and beat them with a 5 lb. compo cast type hammer to consolidate it better. Then I screeded it off. Pix to follow.

The millet had begun to sprout by this morning! LOL! Just the surface. The deep stuff was not doing anything. This was supposed to be hulled millet. I guess that's not enough to stop it from germinating. It was growing some nice mold too. Interesting.

EPK is EP Kaolin. I'm just figuring all this out so this is what I know. Kaolins are clays that seem to be found in areas where sedimentary coastal ocean floor has pushed up. I found three major formation here in the U.S. and apparently there are several in China as well. The EP Kaolin is produced by Edgar Minerals in Florida. It has the highest content of Aluminum Oxide that I have found available commercially.

It comes in a 50 lb. bag. It's very fine from ball milling. If you want "fire clay" this is the best I think you can find. It's cheap too. Like $7 - $8 a 50 lb. bag.

The other two Kaolin sites I found are in Kentucky and close to where I live in Amador County west of Sacramento CA. However, those sites are a little lower in aluminum oxide content.

With regard to the firing of a non-setting ceramic like this. Yes, if you were firing it in-situ there would be all those problems. I fortunately have an electric ceramics kiln. I've been giving this some thought. How does one without a kiln pull this off? Not sure yet. First I want to see if it works. If it works, then maybe it's worth exploring some options.

Possible solution:

A one time kiln out of mud and straw is a centuries old approach to firing ceramics. If one has already built a workable burner or three, it seems to me that a one time mud & straw kiln is possible. Maybe even throw in some wire mesh for good measure. If it's in the middle of the mix, it's not going to get hot enough to totally lose it's tensile strength. If one wants to get really old school you could fire it with wood.

[Bigred1o1]

http://www.google.com/url?sa=t&rct=j&q=firing%20bricks&source=web&cd=3&ved=0CEMQFjAC&url=http%3A%2F%2Fwww.aprovecho.org%2Flab%2Fpubs%2Frl%2Fstove-design%2Fdoc%2F14%2Fraw&ei=nYajTtC-BKP30gGy7IXwDQ&usg=AFQjCNG3jEgItkxUpJ2p8EDElI3Tf6A_Wg&cad=rja
i hope that link works it is a pdf file i came across years ago on third world brick making there is a incredible coal fired one in india that it talks about
but over all i thought it might give people some ideas
i did a small workshop on making bricks with kids a few years back and it was based off of the bootstrap idea that you could make your own bricks to then build a better kiln out of to make better bricks in
all done using local clays and materials

[DDTedder]

Wow, making your own fire brick/wall compound? ~Very interesting, thanks~ I hadn't really considered this angle...

[MattBower]

Possible solution: A one time kiln out of mud and straw is a centuries old approach to firing ceramics. If one has already built a workable burner or three, it seems to me that a one time mud & straw kiln is possible. Maybe even throw in some wire mesh for good measure. If it's in the middle of the mix, it's not going to get hot enough to totally lose it's tensile strength. If one wants to get really old school you could fire it with wood.

Firing temps for these types of very pure ceramics tend to be extremely high, though.

[Bob S]

http://www.google.com/url?sa=t&rct=j&q=firing%20bricks&source=web&cd=3&ved=0CEMQFjAC&url=http%3A%2F%2Fwww.aprovecho.org%2Flab%2Fpubs%2Frl%2Fstove-design%2Fdoc%2F14%2Fraw&ei=nYajTtC-BKP30gGy7IXwDQ&usg=AFQjCNG3jEgItkxUpJ2p8EDElI3Tf6A_Wg&cad=rja i hope that link works it is a pdf file i came across years ago on third world brick making there is a incredible coal fired one in india that it talks about but over all i thought it might give people some ideas i did a small workshop on making bricks with kids a few years back and it was based off of the bootstrap idea that you could make your own bricks to then build a better kiln out of to make better bricks in all done using local clays and materials

neat link.

[MattBower]

http://www.google.co...Tf6A_Wg&cad=rja

Fascinating PDF. Thanks for that.

[Bigred1o1]

glad i could help its odd but there is not as much ready info on brick making out on the web as one might think

[jdelaney44]

That PDF is pretty cool. Thanks for sharing!

Failure is mine! Arrrgh!

I did a test firing today on a small piece. It was hand built so it wasn't as dense as the panels that are still drying. As is past 500 degrees it was a cracked pile of black stuff. The clay had shrunk in past the seeds. Black, charred seeds were on the surface. The whole thing was black. I looked like a pile of ash.


At about 900 it turned white and I had some hope it might vitrify into something eventually. I increased the target to cone 7.

At about 1250 it caved in on itself. It looks like a gross flaky gray pastery. You could see flames from the organics continuing flame off. I shut it down at this point. Why waste the power?

Oh, and man it reeked. Fennel does not burn nicely. Maybe THAT's why sawdust is the normal solution.

It's cooling. There is a red hot core still. I'm holding out hope that has consolidated into something.

Well, this should be interesting ... I'm not even going to begin to speculate until I can see it up close.

[Bigred1o1]

oddly i have to say i would like to see a photo of the end product
as well i am thinking the density of the fennel and the caloric content were probably your undoing
still i am hoping i can benefit from your processes
so please keep up the posts

[pkrankow]

Seems like you may have fired too fast. You probably want to stop at about 500F until it is done charring all the way through. While the organic matter is charring it is producing much more gas than after it is fully charred. Then it will be dry and only carbon remaining so the amount of gas produced will decrease. It will continue producing gas until all the carbon is used.

Since this is a failure you can make some grog for the next mix to reduce shrinkage. Break this learning experience down to a fine mixture with a hammer and add it to your next batch.

I'd like to see pictures too.

Phil

[Frosty]

A topic dear to my heart!

I've never heard of anyone using seed to make voids in ceramics. I can think of a few problems# First, being seeds hold moisture tenaciously so it'd be much harder to get them sufficiently dry for a ceramic shell. Secondly What's the burnoff temp of the oil? Millet seeds carry a pretty high % of oil and it has to go somewhere. Fennel is darned high in oil. Thirdly, Sprouting is going to be an issue too, seed doesn't need to be near the surface to sprout and sprouts will not only stress the mix but cause the equivalent of cold shuts.

I'm thinking you pushed firing too fast, especially considering the seed. Next time hold at 230f. for at least 5 hrs. This will drive off all the hygroscopic moisture, remember this blend of clays is extremely fine grained, in the area o 2 microns by4 or smaller, this will produce a very moisture resistant barrier. It is NOT going to dry quickly and most certainly not going to be ready for even 400-500f. for a long time.

I'd put another hold at 400f. this is below most "dry" materials ignition point, 451f being paper's. No oxygen you say? It may not allow moisture to exit easily but air is a lot more sneaky so you have to drive it off. It'll leave reasonably quickly though, shortly after the heat reaches the 400f range.

Once you've done a proper hygroscopic drying cycle bisque fire it! Have you talked to a ceramics shop about going straight from green dry to high temp firing? It's pretty much an autodestruct move.

I dong know if a cone 7 is hot enough to fire zirconia, it's far below the vitrification temp, FAR below. Heck, I don't know if cone 12 will do it. I don't know about zirconia silicicate though. What I've been hearing about is zirconia oxide which has a vitrification temp in excess of 4,500 . . . CELCIUS! Can you say 10,000f +?

Phil has been making his own for a while now so I'm sure he has the ratio down far better than I do.

High alumina clay will make a much more flux resistant liner and the zirconia doesn't seem to notice at all.

By all means keep the failed liner and crush it into grog. Grog is one important item missing from your refractory clay mix. The organics, sawdust, seed, etc. will not prevent checking, shrink or heat, the organics HOLD moisture and will draw it. Grog or sand will provide vent avenues so moisture and pressure can vent. Grog also provides a little flex for the finished product, making it less brittle in use and allows it to expand and shrink with temps, during firing and in use.

Mixing comes to mind now. What I've had the best success with (before I just bought refractory that is) is to mix the cement elements first, the clays. Next I added the grog I'd soaked in water a while. I tried a number of things to make insulating voids and saw dust worked as well as any I tried. I dampened the saw dust almost wet.

The wet components provided all the moisture for the mix, if I got it right that is. Dampening the grog and organics instead of adding them dry made combining the water with the clay much easier. Clays tend to be hygroscopic and hydrophilic in the extreme. So, when you put a bunch of damp sawdust in a batch of dry clays the clay will suck the moisture out of the sawdust in hours. Then you need to cover it and let it set a day or at least over night to equalize the moisture content. This is called tempering the clay.

On this last bit of trickyness, if you dampen the zirconia flour before mixing each particle will be evenly coated with clay and be bonded into the liner if only in a matrix instead of as a component of the fired ceramic itself.

I find making these kinds of things require properly tempering the clays. You do NOT want a wet mix! If it's wet like pottery clay it will shrink check as it dries. You only want just enough moisture to make it hold it's shape when rammed or squeezed hard. Testing is pretty much the same as for green sand, take a handful and squeeze it HARD. If anything sticks to your hand it's too wet, add more clay or let air dry and retemper. (sealed container over night) If it doesn't stick try breaking it, it should break cleanly without crumbling or leaving dust on your hands, if either condition exists it needs a LITTLE more moisture. And I mean a LITTLE, as little as 1/4 cup can take dry to much too wet so think a couple tablespoons as a large addition. RE-temper it and test it again in a couple days.

Repeat till you get it as close as you can. Then RAM it into the form, strike, screeding is for wet work like concrete but that's semantic niggling not a serious correction from me. <grin> Let it dry, put a light bulb over/under it if it's humid. And leave it dry a day longer than you're SURE it's dry.

First fire is to drive off hygroscopic moisture, 230f for 5hrs to over night. Next firing is the pre-burnout firing, under 400f. Then Bisque fire it. Lastly fire the stuffings our of it, go as high a cone as you can afford.

Lastly, that's just my opinion I could be wrong. Best of luck, I buy my hard refractories and they're high phosphate or phosphate bonded to resist fluxes. It's just SOoooo much easier than trying to make my own.

Frosty the Lucky.

[jdelaney44]

Posting here too - http://redwagonforge.blogspot.com/

Can anyone tell me the trick to easily posting images here?

[jdelaney44]

Well if I don't want a wet mix, then I am WAY off. Ok, well, I am where I am.


<a href=" title="IMG_3818 by Total Slack 44, on Flickr"><img src="http://farm7.static.flickr.com/6215/6313572715_8250ffb24f.jpg" width="500" height="333" alt="IMG_3818"></a>



IMG_3798 by Total Slack 44, on Flickr



IMG_3802 by Total Slack 44, on Flickr

1.) These are some of the larger chunks.
2.) The whole pile in the kiln after I was picking through it. It was a more consolidated pile
3.) Some larger chuncks with the lens cap for a sense of scale

So, I've been drying the slabs. One I put in the kiln last weekend for about 16 hours at 150 degrees F. No problems. So I've got the other two in there now. I put the first one in the kitchen oven at 170 this evening. There's still some moisture coming off it. I can feel it and smell it a little. Not much but it's not totally dry. So ... that's going to take some time.

No sprouts! I got sprouts in the dark of the garage on the first batch. So either re-mixing it or letting it bake in the sun suspended that process. It was pretty warm last week. Not sure if cooking the first slab at 150 killed the seeds or not. That would not seem to he hot enough, but maybe.

I think the hold might be better around 300. I noticed on the last round that the seeds started to char at 350. The carbon you see above formed at 500. When I let it soak at 500, it was totally black. The white material was on the outside at around 900 - 1000. The black material was in the core of the pile. When I shut it down, the carbon, or whatever was still burning. There was flame coming out of the pile like you get with charcoal. That's pretty much what I had at that point. Charcoal mixed with clay.

Your comment about the oil is an interesting thing. That oil might plasticize before it burns. Not sure what that does for me though.

Grog / silica sand. Yes. I feel I need a larger aggregate in there some place.

The next couple of tries are going to be small batches. I don't know WHAT I was thinking going for a full batch all at once. Anyway, I'm going to stick with this for a bit before I cave and just buy the castable.

[jdelaney44]

Link to the pictures. Sorry. The photo upload features on this site suck!

1.

2.

3.

[jdelaney44]

Oh, regarding temps & old kiln designs. I think as that PDF points out, wood fired kilns can get very hot. As I understand it, the matter is getting energy into the kiln at a rate that exceeds how fast it's escaping. I've read about several wood fired kilns where the ash from the wood burning in the early stages of the firing becomes the glaze. These firings can take a couple days and constant tending by a small team.

[jdelaney44]

Had the slabs in the kiln at 160 F for ~15 - 16 hours Saturday and ~11 hours Sunday at 160 F. Then took them up to 190 F for about ~5 hours. So far no cracks in the one I can see which is the oldest one. Started the kiln again this morning at 09:55 with a 190 F setting.

Also posting here - http://redwagonforge.blogspot.com/

Frosty, I wanted to make sure I understood what you were saying about bisque-ing. Yes, I'm pretty familiar with bisque-ing. Although I probably can't spell it. The 3 - 4 clays I have used in the past are usually bisqued in the 1300 - 1900 F range. I have put green ware in that was too green to have it explode around 900 - 1000. I was actually trying to bisque the trial piece.

Were you saying that I needed to let it "soak" at ~400 - 500?

Recommendations vary with respect to soak temps & time to drive off moisture. My friend Aaron who is a potter gets really agressive with it. But he throws really thin walls and I think he is used to short dry times and fewer issues with thick clay bodies, that are too wet like this.

I also did some more reading. The book "Hands In Clay" give a good overall treatment of the firing process and the stages. Apparently there is a "quartz" transition range around 441 F. This fits with your gut feel of a soak in the 400 - 500 F range. This is where the impure silicates begin to change out of a crystalline state. In plastics I learned this as the "glass transition temperature". It was were the cross linkages in thermo plastics started to break apart. At that point the plastic started to become flexible.

"Hands In Clay" also discussed fluxes. I'm convinced I need one or more fluxes. There is a % of fluxing material in the EPK and Zircopax plus. More math here I guess.

Another observation with respect to porosity. I said the carbon saturated the matrix above just in passing. When I enlarged the pictures I could see that it really did. That tells me that this mix is WAY more porous that I ever imagined. At the molecular level the combustion by products are oozing everywhere.

Thinking that through, maybe I need another soak time at around 350 or where ever that seed carburizes at. Frosty made the good point about the oil in the seed. That may carburize around 300 or so.

Well anyway, this IS too much, but I do want to see what it takes to get the seeds to work if I can. If I can get one bisqued and fully fired at cone 10 it'll be interesting to see if the big pockets insulate well.

[jdelaney44]

Frosty, I just read your post again. We are in total agreement. Thanks for getting me thinking more clearly. Phil, thanks for the tip on the grog. My friend Aaron said the same thing as soon as he saw the stuff. He want's me to keep going on this as he may have some artistic application for the concept. Everyone else, thanks for the comments & interest. It helps in overcoming a big failure like this one.

Man I was bummed!

[MattBower]

Can I make a suggestion for an alternative to seeds and sawdust? I know some mad scientist types who use ceramics to line casting furnaces, and they like to add styrofoam beads to the mix for insulation. Styrofoam is very low in density, so the beads burn out quickly and don't offgas nearly as much as the denser stuff. And they don't leave fluxes behind. Some guys shred styrofoam with a wire wheel, in a trash bag. I've tried it, and it was extremely messy.

[pkrankow]

Toasting the seed will solve the sprouting problem...

Phil