[Stoves] Re-firing a Baldosa tile improves its thermal performance dramatically

Crispin Pemberton-Pigott crispinpigott at outlook.com
Fri Jan 2 14:02:56 CST 2015


Dear Friends

 

I just located this old file from ProBEC showing a test of the Baldosa tile
sample picked up at ETHOD ins 2008 (thanks to Dean S).

 

It shows that after firing 'properly' to over 800 C there is a grate change
in the thermal expansion characteristics. While the expansion coefficient is
not particularly low, there is a dramatic suppression of the S curve typical
of the silicon transformation at 573 degrees that is the main cause of most
ceramic/clay stove fracturing.

 

The main discovery from the XRF and XRD analysis was that there is no free
silica in the Baldosa tile (once fired well).

 

This may be of interest to stove producers in Central and South America who
have access to traditional Baldosa tile production knowledge. The absence of
a 573° silicon phase change from A to B condition implies there is virtually
no free silica in the final fired product.

 

The results are plotted against a lower expansion product containing a
medium-level lithium content (?4%) additive from Bikita Mina in Zimbabwe
that (very unusually) contains no iron.

 

The expansion measurement/trace was made with a Dilatometer but you can do
it as well with any sample, an oven and a digital caliper.

 

Regards

Crispin

 

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