[Stoves] "Vom Pyrolysekocher zur terra preta" Workshop 11-12.06. --> Clay TLUDs

[Anand Karve]

Dear Stovers,
the discussion on making clay TLUD brought back to me memories from 1980s
and 1990s when our Institute participated in a programme called National
Programme on Improved Cookstoves. The impoved cookstoves in those days were
always fabricated using clay. Our Institute used to conduct annually some
600 training programmes for village artisans. The training consisted of
preparing good quality clay, assembling the mold into which the clay was
filled, and dismantling the mold without breaking the cookstove. Each state
in India had an annual target to fulfill.  The programme failed in my state
(Maharashtra, which is highly industrialised), because the urban life style
was the role model for the rural people and therefore the villagers wanted
LPG stoves and not wood burning clay stoves!   We are still in the business
of selling wood burning stoves, but nowadays our stoves are metallic and
our clients are almost exclusively urban householders, who want to  use a
wood burning stove, occasionally, just for the fun of it.
Yours
A.D.Karve

***
Dr. A.D. Karve

Chairman, Samuchit Enviro Tech Pvt Ltd (www.samuchit.com)

Trustee & Founder President, Appropriate Rural Technology Institute (ARTI)

On Wed, May 4, 2016 at 9:53 PM, Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

> Dear Julien and Rebecca
>
>
>
> The matter of the impact of silica on the cracking tendency of ceramic
> components is central to making stoves that survive.
>
>
>
> I have worked on this with CermaLab of Pretoria for ProBEC and the result
> are still available at the ProBEC website.
>
>
>
> The suppression of the silica transition from state A to B, which happens
> at 573°C, crack glass and ceramic. This transition can be smoothed to take
> place over a larger range of temperature (with glass it is almost
> instantaneous) by adding various ingredients and optimising the firing
> temperature.
>
>
>
> The addition of lithium is a common approach, so lithium petalite is one
> solution. We used a mix that included 55% lithium petalite in one project.
> Lithium carbonate is much better by very expensive.
>
>
>
> The transition is also accomplished by adjusting the chemistry of the clay
> (which could include all sorts of biomass) so as to bind the silica. This
> is what happens with a baldosa tile made the traditional Aztec way. I found
> that the free silica content of a baldosa tiles was essentially zero even
> though the silica content was more than 50%.
>
>
>
> There is a book by Hugh Allen available on line (1991, ATI) about how to
> make improved Kenyan jiko stoves. It is the ‘poor man’s way’ to develop a
> clay body – what to do when you have no access to a lab (XRF, XRD) and you
> want to use what is available.  I think we can do better with more modern
> understandings + Hugh’s advice which is iterative and takes about a year.
>
>
>
> Thermal shock resistance is not only from suppressing the silica
> transition, or having a low thermal expansion coefficient. It also should
> be strong enough to have a good service life. Not a lot of information on
> making domestic stove ceramics is available because people who work out how
> to do it keep the knowledge secret.
>
>
>
> I someone wants to embark on a research project into this for a particular
> location they can contact for some pointers.
>
>
>
> Regards
>
> Crispin
>
>
>
>
>
>
>
>
>
> Dear Rebecca;
>
> Thanks for sharing your experience with rice hulls.  You have saved me
> some trouble.
>
> Rice hulls were worth testing, because they are plentiful, whereas sawdust
> is harder to come by.
>
> I have seen papers were rice hulls were used in bricks, but I have
> wondered if they would work in refractory materials because some forms of
> silica expand over a narrow temperate range and cause microcracks.  A
> diagram of the phenomenon can be found here:
>
> http://www.thaiceramicsociety.com/spaw/uploads/images/quartz%20inversion.jpg
>
> Rice hulls can contain 20% silica, but I don't know what chemical
> structure silica in raw hulls, or pyrolyzed hulls.  The surface of rice
> hulls may be impervious to clay particles.  The exterior surface of plants
> is usually coated with wax to prevent water loss.
>
> By contrast, particles of sawdust will expand when added to wet clay, and
> clay particles can form electrostatic bonds with glucose monomers.
> Pyrolyzed, there is a little ash remaining.
>
> Would rice hulls work better if they were pretreated, such as by exploding
> them in boiling water?
>
> Something else worth trying is "paper clay" where soaked and pulverized
> waste paper is mixed in with the clay.  In some countries, waste paper is
> abundant in the form of politicians' election posters ;-}
>
>
>
> Of the organic matter added to the clay body, a herbivore manure, and
> straw or fibrous material is a common component.  The manure provides fiber
> and makes the green clay easier to work.  The fiber reinforces the outer
> walls of the stove body against cracking.   Fiber can be added as straw or
> retted plant stems.
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
>
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20160505/a786ba1f/attachment.html>