[Stoves] Re: Improving longevity of steel stoves; Chiwicla-lining

[Crispin Pemberton-Pigott]

*This message was transferred with a trial version of CommuniGate(r) Pro*
Dear Friends

This revives an old conversation with several inputs from William Carr.  It 
was about improving the longevity of metal by various means and of course it 
drifted to ceramic liners and how to make them stronger.

I have been talking to a remarkable man called Rob Bartelink who is very 
experienced at making many types of modern ceramic materials.  One thing 
that came up again in conversation was the idea of increasing the strength 
of ceramics fired to low temperatures (like most real stoves made in the 
bush) by adding Na-hexametaphosphate otherwise known as calgonite - the raw 
material for that dishwasher powder in the shiny green pack.

I am asking anyone who want to get involved to try sourcing some calgonite-S 
(probably the only thing available) and mix 3 to 5% by weight into some of 
their regular known clay mix.  Otherwise treat it as normal.  It is likely 
you will have to reduce the amount of water in the mixture as calgonite is 
an anti-flocculant.

Then fire the resulting part to a temperature you know to be modest.  I am 
thinking 900 to 1000 or perhaps even less.  What do you get as a result? 
There is a phosphate bonding that is established with the aluminates - it 
starts above 600 or so.  The result should be an increase in strength.

I got a quote at about $2 per Kg for calgonite-S and $1 for something 
similar called sodium tri-polyphosphate which works the same way.

If you are reading this and are involved in low tech clay stoves, give this 
additive a try and see if you are impressed enough with the result to be 
willing to buy the material.  If, for example, it saves a great deal of 
firewood in a place like Malawi where it has to be purchased, it might be 
worth the cost of the additive if the result is a much better stove.

It might greatly increase the strength of light insulative bricks produced 
in a low temperature kiln.

I have not yet found any information on the high temperature at which the 
phosphate bonds are destroyed and ceramic bonding dominates.

What allows us to explore this material is that the temperatures which 
stoves reach while cooking are, from a ceramics industry point of view, 
quite modest.  If the stove parts don't heat up past 600 during their 
working life, there may not be a need to make ceramic bonds in the first 
place.

Best regards
Crispin