[Stoves] Phosphate bonding of clay and other speculations

[Crispin Pemberton-Pigott]

Dear Friends

One of the great things about an internet discussion group is that you can say things that are wa-a-a-y wrong and no one will fire you for it.  Now how about this idea:

I have been looking at how ceramic stoves are assembled at the microscopic level and all things considered, I don't think many of the stoves we see are very 'ceramic' at all.  There are strong phosphate bonds - strong chemical bonds which are pretty heat resistant.  I am suggesting that several 'traditional' approaches to making clay products are (mostly) phosphate bonded.

Consider this:  people add cow dung to clay to improve the 'performance'.  It is usually assumed with some degree of support that the reason the clay lasts longer in a stove is that the holes produced by the fibres make it into a more flexible and insulative.  Suppose the real reason was that the phosphates in the dung are creating a stronger product that is not really held together by melted clay minerals (ceramic bonds) but by chemical ones.

And this: people add a variety of things to clay to make it 'better' and the secret ingredient may in fact be phosphate, added accidentally, creating a stronger product.

And this: making 'clay bricks' from ant hill soil (which is full of dried, fresh grass and biomass, works (makes a decent brick) when the product is fired at temperatures far too low to be ceramic-bonded.  I suggest it is the phosphates in the biomass creating a chemical, not ceramic bond.

So....how about we try making 'ceramic' stove parts deliberately salted with phosphates?  The insulative bricks used in the 6-brick Rocket Stoves could be made just as easily, but they would be a lot stronger (resist their inherent nature to disintegrate from thermal shock) if phosphates were added.

What natural processes form them?  What are the readily available sources of phosphates?  

Grass
Fertilizer (I was thinking of artificial fertilizer which is widely available?
Dung
The raw materials for detergents
Phosphoric acid (sounds dangerous)
What about laundry soap?  Omo? Tide?
Bat guano
Chicken 'litter'
Rabbit manure

Instead of using ground charcoal, which has no phosphates at all, how about using hammer-milled fresh dried grass?  Powdered hay.  Make the porus structure using something that releases phosphates as it burns.

If there is a lot of phosphate in chicken manure, it could be mixed into the brick or ring material and when burned, would provide both little air pockets as well as phosphate bonding.

I suspect that a careful look at the chemistry of traditional ceramics would repeatedly pitch up natural sources of phosphates that are making chemical bonds in low temperature clay products like terracotta.  The traditional 'bisquit firing' might just by a slight phosphate bonding, not a very low temperature ceramic bond.

What's really going on?

Ponderingly yours
Crispin