How to make Soapstone ?

[Deleted]

Soapstone is composed of 30-80% of talc and secondary magnesite, serpentine, various chlorites
and amphiboles.
(Chlorite from Greek. Chloros = green)
(The name serpentine is thought to come from the greenish color being that of a serpent)

If it is to hard to be scratched with a knife blade (hardness of 5.5), it is not soapstone.

Soapstone has a better thermal conductivity than other rocks due
of its dense structure and mineral composition.
The high conductivity allows evenly and quickly warming.

The high thermal capacity of soapstone is the result of hydrate and magnesium content and softness.
Hydrogen has the highest specific heat (14300 J/(kg K)) of all elements.-
Lithium 3570 J/(kg K), Beryllium 1820 J/(kg K), Sodium 1230 J/(kg K), Magnesium 1020 J/(kg K),
Oxygen 919 J/(kg K), Aluminium 904 J/(kg K).
See: www.periodictable.com

The serpentine subgroup consists of antigorite, chrysotile and lizardite.
Chrysotile is a kind of asbestos, magnesium containing amphiboles and chlorites can be asbestos too.
Rocks from all three mineral groups can be geopolymerized.

Happy experimenting.

[Deleted]

Physical Properties of Soapstone:

soft and easy to carve
nonporous
nonabsorbent
resistant to acids and alkalis
low electrical conductivity
heat resistant
high specific heat capacity
high heat conductivity

Which of the properties would you consider most important, which least ?

[Deleted]

Magnesium phosphate cements in which insoluble magnesium phosphates are formed from
a mixture of magnesium oxide and a soluble phosphate eg.

Aluminum Dihydrogen Phosphate Al(H2PO4)3
Magnesium Dihydrogen Phosphate Mg(H2PO4)2
Sodium Dihydrogen Phosphate NaH2PO4
Potassium dihydrogen Phosphate KH2PO4
agricultural fertilizer 10-34-0 ammonium polyphosphate

Talc as raw material for cementitious products formulation.
ac.els-cdn.com/S2187076414000554/1-s2.0-S2187076414000554-main.pdf?_tid=c08da6ac-55b7-11e6-a407-00000aacb361&acdnat=1469816018_01c6d69e9a53c05f1ef4dba3c3597bdb

Talc-based cementitious products: Effect of talc calcination.
ac.els-cdn.com/S2187076415000652/1-s2.0-S2187076415000652-main.pdf?_tid=120a843a-55b5-11e6-be7d-00000aab0f6b&acdnat=1469814866_6afc5ed59ce5944b3c0384338343deaf

Special information Phosphate bonding.
www.zschimmer-schwarz.com/m/simon/zschimmer-schwarz/media/site/downloads/fachinfo/eng/Fach/E_FF_Phosphatbindung.pdf

Phosphate Bonding in Refractories
dspace.mit.edu/bitstream/handle/1721.1/77868/29893269-MIT.pdf?sequence=2

Refractory concretes of chemical bond with diverse aggregates.
www.sciencedirect.com/science/article/pii/S2211812812000582/pdf?md5=0f29385e96aa5d5f4ee12ab25159a6d1&pid=1-s2.0-S2211812812000582-main.pdf

[Deleted]

Nice info, karl !
It makes me think to the stone artifacts davidovits used to produce : www.geopolymer.org/fichiers_pdf/pyramid_chapt1.pdf
Do you have a recipe for the basic mix you use as a binder for the geopolymerization of stone ?

[Deleted]

The basic condition for chemical reactions is that the substances are not inert,
which means that there must be some mutual interest in a chemical marriage.

For fast chemical reactions solids should have a surface of 1/3-1/2 square meter per gram.
Solids should be amorphous, lacking the long-range order characteristic of a crystal,
and not hydrated as hydration makes solids more inert.
There are two kinds of surfaces influencing the chemical reactivity.
The Blaine surface is only influenced by particle shape and size.
The BET surface includes the accessible inner surface of solids.
If the Blaine surface is lage enoug a large inner surface can increase reactivity significantly.
With a total surface of several hundred square meters per gram eg. zeolithe,
chrystalinity and hydration may not longer be a hindrance for a chemical marriage.

The basic condition for making synthetic rocks from solids is that the solid is prone
to acidic or caustic attack and that the result of the chemical marriage is insoluble in water.

[Deleted]

It is no problem to make geopolymers with high talc and magnesium oxide content.
I have tested this with different pozzolans.
The resulting geopolymers distinctively feel like soapstone.

I have got some Anorthite a calcium, sodium feldspar with a fineness of 250 mesh
from pottery supply to test geopolymerisation of stone flour.
I have mixed 80% anorthite with 10% lye and 10% overaged trass cement, then added 40% talc
and to improve reactivity a small amount of powdered waterglass.
The mixture started to harden at ambient temperature after a few hours.
Due to the talc it will take longer to get to final strength than without.

[lawry]

Thank you for the lessons Karl. When I asked if we could make soapstone I really didn't expect so much information. It seems south Africa didn't have soapstone deposits. The next step for me is to get the talc and test it out. I have Fly Ash in abundance... What ratio do you think I should try out first? (Fly ash/talc)?

[Deleted]

Which of the properties of soapstone are the most important for you?

For high thermal conductivity fly ash is about the worst possible choice,
as the particles are hollow balls.
Fly ash geopolymers have thus a high porosity despite the low water demand.
Something dense, like grog or stone flour would be better.

With respect to thermal conductivity and capacity the answer is as little as possible fly ash.

High thermal conductivity and capacity require high density, which is difficult to achive with talc alone.
You will need some magnesium oxide, which can be stubstituted by fine corundum or silicon carbide powder.
A superplasticier will help too.

Talc can be activated with phosporic acid or a water soluble metal salt of it.
Magnesium phospate would be the best, some others I have listed above.
See also the papers listed above.

Also you could try mix talc with waterglass and phosporic acid or a water soluble salt of it.

Caustic burnt magnesiumoxide may cause explosive spalling if the mixture is not well mixed.

[lawry]

I like the thermal conductivity and heat capacity properties of soapstone. I got some silicon carbide (very expensive) that I added to the FA geopolymer as a aggregate.
I have halted my experiments for now until I get molds done for me by a professional. When I get the molds I will test the different mixes.
And I am also busy with a TLUD for heating project which is quite fun. It will keep me occupied while I wait for the molds

[Deleted]

lawry you may try acid activated clay instead of the fly ash.
donkey32.proboards.com/thread/2057/acid-activated-geopolymers

[jorgeenelpueblo]

Reading the links:
- Talc can be used to make cement.
- It is better to fire it to 900 C. so that Mg availability increases. This will make the cement stronger.
- The practical use of phosphates as binders is tricky.
- A long one from 1948.

Now: How to do soapstone? I was actually expecting to see a recipee here, with this headline... I though it could be doable at home. Any suggestions, anybody?

[coastalrocketeer]

Sounds like Geopolymerization might be a great way to make loose, friable asbestos from cleanup of old insulation and other materials safe for normal waste disposal, or even placing in your garden as a decorative rock!

[esbjornaneer]

I shot from the hip and made a test puck with burned/meta-fire clay and NaOH as the binder and baby powder (talc and purfume) as the aggregate, before having read and taken in all the details and papers from this thread. I have not performed all the tests on it yet but it is the lightest of my test samples yet.

Aug 22, 2016 13:36:47 GMT -8 @karl said:

High thermal conductivity and capacity require high density, which is difficult to achive with talc alone.
You will need some magnesium oxide, which can be stubstituted by fine corundum or silicon carbide powder.
A superplasticier will help too.

Talc can be activated with phosporic acid or a water soluble metal salt of it.
Magnesium phospate would be the best, some others I have listed above.
See also the papers listed above.

Now that I am taking the time to read properly I know I did it all wrong.
What amount/proportions of talc/MgO would you advice @karl ? What purity MgO product would be best, I am finding 80-98% purity animal feed grade (here)
Would this Magnesium phosphate be good?
What 'superplasticier' would you use?
Anything else to add to the mix?

Please would you give as detailed instructions as possible for proportions and procedure.
(My fire clay experiments are on hold as I am in the UK at the moment but can get the above 3 ingredients easily here to play with in my spare time.)

[Deleted]

Garden fertiliser have a far to low purity.
One would need industry grade Monomagnesium phosphate.

I've just done some rough testing to see if it is possible,
thus I have no specific recipes.

Try a sulphate free one like polycarboxylate ether superplasticizer.

You can also experiment with magnesium oxide and phosphoric acid or
monopotassium phosphate in a molar 1/1 ratio as a binder.

[esbjornaneer]

So reading the first scientific article I find they used:

90% Talc with 10% MgO increased compressive strength compared with 100% Talc (i.e. 90g talc + 10g MgO)
40% of dry matter weight as water (i.e. 40g water)
40% of talc+MgO dry weight as phosphate (potassium phosphate / potassium dihydrogenophosphate) (i.e. 40g phosphate)

Mar 2, 2018 7:52:36 GMT -8 @karl said:

Garden fertiliser have a far to low purity.
One would need industry grade Monomagnesium phosphate.

Can only find 'food grade' of this.

I've just done some rough testing to see if it is possible,
thus I have no specific recipes.

Can you tell if your testing mix was anything close to the above mix? What were your observations of your results?

Try a sulphate free one like polycarboxylate ether superplasticizer.

Here is a concrete superplasticiser that 'Contains polycarboxylate ether polymers' and is 'facilitated by the molecular structure of polycarboxylate ether-based technology' could it be of any use? And if so at what rate (it is used 1 litre to 100kg cement)? And when should it be added in the procedure?

You can also experiment with magnesium oxide and phosphoric acid or
monopotassium phosphate in a molar 1/1 ratio as a binder.

I have found this monopotassium phosphate is it appropriate for this use?
And in a molar 1/1 ratio it would mean MgO/KH2PO4=40/136.
(KH2PO4: 136.09g/mol
 MgO: 40.30g/mol)

Comparing their recipe, (MgO/KH2PO4=1/4=0.25), with your suggestion, molar 1/1 ratio (MgO/KH2PO4=40/136=~0.294), you advice slightly more MgO than they used. Would you recommend I still use 10%MgO/90%talc in the aggregate or 100% talc?

Their procedure was:

The cement pastes were prepared as follows:

In an acidic solution of potassium phosphate, a known amount of thermally treated talc and, if needed, MgO are added and thoroughly mixed during 5 min using a M&O mixer. The viscous paste obtained is used for samples molding and for setting time determination. ... The pastes in the mold are vibrated for 10 min on an electrical vibrating table (M&O, type 202, No. 106) to remove entrapped air bubbles. The samples are covered with a polyethylene bag and left for consolidation. The consolidated samples are kept at the ambient temperature (24–27 °C).

So they used no plasticiser. And if I understand correctly they mixed KH2PO4 and water, then added talc and MgO, no mention of binder pre-mix.

Comments please.