An Open Call to Ceramic Engineers- Reverse Engineering Biscotto di Sorrento

[scott123]

At various times, this forum has seen potters and ceramic engineers contribute, and, while we don't seem have any among our active ranks at the moment, I'm starting this thread in case someone with these skills either becomes active again, joins as a new member or finds it through Google.

A domestically produced, durable, low conductivity (<.6 W/m-K) ceramic material with very high resistance to thermal shock would be profitable. Wood fired oven builders would scramble for it, which would drive some sales, but it would also have a large appeal to gas deck oven pizzeria owners with heat imbalances at high temps.

Extremely low conductivity is the next frontier for hearth materials.  It won't be all that useful for home oven bakers, but, for WFO owners and commercial deck oven owners, it will be a game changer.

Get to work.  We're waiting

[henkverhaar]

How about sintered alumina ceramics ?

Would make for one expensive oven...

;-)

[scott123]

I have a sintered alumina plate that was given to me by a crucible manufacturer.  The resistance to thermal shock, is, as far as I can tell, unparalleled, but the conductivity is just too high.

[henkverhaar]

I have a sintered alumina plate that was given to me by a crucible manufacturer.  The resistance to thermal shock, is, as far as I can tell, unparalleled, but the conductivity is just too high.

Ah, too bad. You can always use it as an expensive sharpening stone... I have a few custom sintered alumina objects that exploit its hardness: a fishing hook hone and a fur rake (google 'ceramiscrape' if you're interested).

I would guess that most alternative technical ceramics also have an 'unacceptable' conductivity then; most of the materials that I'm aware of do, like SiC, TiN, TiC, WC, etc. Probably also Fe3C, although I doubt whether that is even available in pure form (it's usually present as carbides in high speed steel).

[scott123]

All the materials that I'm aware of have relatively high conductivity as well. Except for maybe asbestos, which is definitely not a component of Biscotto di Sorrento.

I can only assume that air is part of the Italian's equation.  It can only be part, though, since too much air introduces both thermal and physical weakness.

If one of the people who have access to a lone piece of this material could measure it and weigh it, the density should give us part of the picture.

[shuboyje]

I don't know if you saw my post in the other thread about this, but I really don't think there is anything magical about making biscotto.  The Neapolitans have been making it for hundreds of years.  I've done the calculations, and it would take 100's of tons of pressure to dry press a slab for a quarter of an oven.  Obviously they didn't have that ability, so the tiles are slab formed.  From what I've read the probably method is a slab formed clay body is pounded into a mould with a huge mallet and then the excess is wire cut.  The hammering is supposed to  stop the tile from warping.  I've found references to a refractory clay made from half fire clay half crush hard brick formed this way that would probably be my starting point if I was gonna try.  Tiles made like this would be much less dense then dry pressed firebrick, and would be much less conductive.  They may not be identical to Biscotto but I think they would be close enough.

[scott123]

Jeff, common brick has a thermal conductivity, according to this site:

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

of .6 to 1.  Fireclay is, generally speaking, 1 and up. I'm not sure you can combine brick and fireclay and end up with less than .6 W/m-K without adding a considerable amount of air, and air would have these things spalling/crumbling pretty quickly in the harsh environment of a WFO. Do Italians/domestic places with Italian ovens cool their decks with wet mops? A wet mop would wreak havoc on an airy fireclay and common blended brick.

Edit: I did some research and found out that dry pressing is popular for firebricks. Some firebrick can be extruded, though, and I'm not sure a wet process would leave enough additional air to drop the conductivity to Biscotto numbers, and, like I said, if it did leave a lot of air, I don't think it would be thermally durable.

Could Biscotto be a high air wet process firebrick with common brick aggregate?  Maybe, but I still think you're looking at either thermal fragility or excessive conductivity with this route.

[henkverhaar]

All the materials that I'm aware of have relatively high conductivity as well. Except for maybe asbestos, which is definitely not a component of Biscotto di Sorrento.

I can only assume that air is part of the Italian's equation.  It can only be part, though, since too much air introduces both thermal and physical weakness.

So you're thinking space shuttle ceramic tiles, eh? (over 90% air, pretty fragile...)

[shuboyje]

Some oven floor tiles domestically are pressed at 8500 PSI.  From my research I don't think you will find dry pressed firebrick under 1500 PSI.  You really don't think the difference in density between this and something slab formed will make a difference in the conductivity? 

I really don't see Italians a couple hundred years ago developing some sort of specialized process to produce low conductivity floor tiles.  It is much more likely they used their standard processes for working with ceramics and adjusted the oven and the pizza to work with that. 

As for thermal shock resistance and fragility, there are people building metal melting foundry's this way that are fired in place that are running at 3000F with no issues.  Firing them in a kiln and putting them in a 1000F oven should be nothing.   

[PizzaJerk]

I have been in deep thought about this subject also. How about the "insulating" type fire brick?
http://www.ktrefractories.com/CeramicFiberProducts/InsulatingFireBricks.htm

[scott123]

Some oven floor tiles domestically are pressed at 8500 PSI.  From my research I don't think you will find dry pressed firebrick under 1500 PSI.  You really don't think the difference in density between this and something slab formed will make a difference in the conductivity?

Alright, I just put around 4 hours researching firebricks in hopes that I could find a wet process that produced a .6 W/m-K or higher level of conductivity, and not only could I not find it, I found a hammer process fireclay brick that clocks in between .18 and .3

http://www.gistconpro.com/507-Farabi.pdf

Here are the figures converted to W/m-K:

Fire clay bricks made from local (Mymensingh) clay Fire clay bricks made from local (Mymensingh) clay with grog Fire clay bricks made from dressed clay Fire clay bricks made from dressed clay with grog

0.18714996 0.26000028 0.27758484 0.30061224

Grrrr  

Bangledesh, from this particular firebrick perspective, feels a bit like it could be Italy 50-100 years ago.

If someone reads this and has a kiln, at this point, I'll concede that this is the method to try first, but, until I see a finished product being quench tested, I'm still skeptical about a wet process firebrick.

If you look at the compression and density figures, this falls slightly lower than fibrament.  While fibrament is a chemical bond and this is heat/partial vitrification, I think the basic building blocks involved are similar enough to make a comparison.  Right now, the only materials that we're familiar with that clock in with more air/lower density than fibrament are quarry tiles, and quarry tiles are notorious for being all over the map when it comes to resistance to thermal shock.  Quarry tiles frequently have issues in the relatively even heat of a home oven.  A WFO is many times more stressful.

And thermal shock resistance has very little to do with peak operating temps. I can take a piece of glass, heat it to around 400, plunge it into ice water and it will shatter.  Kilns do operate at temperatures far above where we're working at, but they're taken to these temps over a matter of days, specifically to avoid the issues with dramatic changes in temp. Thermal shock resistance is the ability of a tile to have a red hot ember sitting on one half of it and nothing on the other half, and yet the tile will still be able to handle the thermal expansion on the hot side, and lack of thermal expansion on the cooler side. It's a tile that can take being pre-heated to 850 and then, in an instant, being lowered to 212 with the introduction of wet dough.These are areas where low conductivity/low density/high air (yet still high abrasion resistance) materials typically fail.

[scott123]

I have been in deep thought about this subject also. How about the "insulating" type fire brick?
http://www.ktrefractories.com/CeramicFiberProducts/InsulatingFireBricks.htm

So you're thinking space shuttle ceramic tiles, eh? (over 90% air, pretty fragile...)

When I mentioned 'durable' in my first post, I should have said 'high abrasion resistance.'  Insulating bricks are too soft to bake pizza on- and they may have too low of a heat transfer.  Assuming Craig's .3-.6 W/m-K Biscotto numbers are correct, that's imo, exactly where we want to be. Any lower than that and the bottom won't cook.

[norma427]

Scott,

I sure don’t know much about ceramics, but will just throw this out there to see what you think.  http://www.baileypottery.com/kilnfurniture/carbidekilnshelves.htm 

http://kilnshelf.com/Websites/kilnshelf/Images/Kiln%20Shelf%20Options%20by%20Schran.pdf

Norma

[shuboyje]

Here's an easier method Scott.  A member at fornobravo has been experimenting with foam additives to make insulating concrete with good results.  How about using this foam in lower quantities to make calcium alumni ate based tiles with the exact conductivity you want via trial and error?

[scott r]

forgive me if you guys already know this, or its obvious,  but I have heard numerous people who work with, own, or sell real neapolitan ovens talk about how fragile and quick to wear down the biscotto de sorrento is.    Simply having an oven operator thats not gentle with their peel could cause it to need replacing in just a few years.    Of course, in a home environment it would take a lot longer than that to wear down and become hard to manage.  I am speaking of a commercial setting.   

[dellavecchia]

forgive me if you guys already know this, or its obvious,  but I have heard numerous people who work with, own, or sell real neapolitan ovens talk about how fragile and quick to wear down the biscotto de sorrento is.    Simply having an oven operator thats not gentle with their peel could cause it to need replacing in just a few years.    Of course, in a home environment it would take a lot longer than that to wear down and become hard to manage.  I am speaking of a commercial setting.   

Yes, I have also heard this as well. The common practice of slapping the turning peel on the floor, either out of dramatic flourish or dispersing ash, is very detrimental to the biscotto.

John

[TXCraig1]

I've seen the wear/breakdown first hand in the SF ovens at Vesta.

[PizzaJerk]

So could it be said that the when the conductvity levels get relatively to extremely low, not only does it become almost impossible to cook on but also the durability of the material becomes suceptible?

I think something that would fit all criteria of ideal conductivity levels, durability etc. would no doubt have to be custom. What would be the ideal mixture in your mind Scott?

I've seen the wear/breakdown first hand in the SF ovens at Vesta.

In your opinion, when it finally breaks down to a point of no longer being usable, what is the protocol in such a case?

[dellavecchia]

In your opinion, when it finally breaks down to a point of no longer being usable, what is the protocol in such a case?

The floor is removed and replaced I believe. There is a mechanism for getting the pieces back in - I do not know the specifics though.

John

[TXCraig1]

The floor is removed and replaced I believe. There is a mechanism for getting the pieces back in - I do not know the specifics though.

John

This is correct. I can only guess that the new pieces must fit through the door. That would necessitate that a replacement floor has more than the original four pieces.