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 .3http://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
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.