[Terrapreta] wood torrefaction: from hard to brittle

[Gerald Van Koeverden]

Nick,

The torrefying of wood results initially in hardened wood, like that  
used by Amerindians for arrow and spear points.  At what point in the  
process does torrefied wood become so soft it can be broken up with  
bare hands?  Is this a result of long-term exposure to the same heat,  
or to higher heats than that used for fire-hardening??

"By careful fire hardening, the willow tip can be made virtually as  
hard as steel. The willow is also soft enough to insert larger harder  
thorns through the tip, then fire hardening the willow tip to shrink,  
make the thorns virtually unremoveable."

http://outdoorhelp.org/fishing/q-2365272.html



A few quotes from your writings on the "Stoves" listserve:

"Why don't you torrefie the wood first at a temperature of 280 degrees
celsius then you can break it with your bare hands, THE SIZE REDUCTION
COSTS ARE NEARLY ZERO THAT WAY.
With a simple grinding mechanism you get every size you want."


"Still have to add some thing to my explication concerning the use of
 >charcoal versus activated charcoal. I would use torrefied wood  
because its
 >easy to grind into avery fine powder and the slurry you can form  
adding
 >water and melassa from sugarcane is easy to apply by spray to the  
soil. (
 >cheaper and better use of the raw material)
 >The volatiles in the torrefied wood will be eaten up slowly by adapted
 >bacteria and will leave the pure carbon structure which will have wide
 >pore diameter spectrum and a enormous surface for the adsorbtion of
 >mineraals and water. But torrefaction should be at a temperature of at
 >least 300 degrees over prolonged time to garantie the carbonisation  
of the
 >lignin and the transformation into volatiles of the cellulose and
 >hemicellulose."




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