How to make Soapstone ?

[Deleted]

esbjornaneer said:

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)

You quote the second, not the first.
The first deals with raw talc the second with calcined talc.
The difference in reported strength is neglible.

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

Can only find 'food grade' of this.

Food grade is much more expensive.

karl said:
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?

I did the tests with phosphoric acid, calcined magnesium oxide and raw talc.
In anothe test I have replaced the MgO with nepheline syenite,
wich is much cheaper and easier to handle.
The results were similar to the results reported in the two papers.
The result with 30% nepheline syenite was the most satisfying.

karl said: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?

Superplasticiser are added to the mixing water.
Up to a few percent.

I have found this monopotassium phosphate is it appropriate for this use?

Far to expensive.
Look for monopotassium phosphate fertilizer.

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?

With 10% MgO you can expect an increase of compressive strenth of about 15% and about 35% with 20% MgO.
Nevertheless even with 20% MgO the strength remains rather low.

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.

Superplasticiser are used to increase compressive strenth by saving water.[/quote][/quote][/quote][/quote]

[Deleted]

Off topic:
BTW as you have mentioned to stay in the UK currently.
For private customers the UK is a paradise for some cheap pozzolans as geopolymer raw materials.
Shops for tratitional building materials are selling Argical M1000 metakaolin and Pulverised Fuel Ash (PFA),

If you are not traveling by air you can take quite a lot with you.

Argical M1000
www.mikewye.co.uk/product/argical-pozzolan/
www.chalkdownlime.com/argical-m1000-25kg-bag.html#.Wprde-YiGkA
cornishlime.co.uk/catalogsearch/result/?q=metakaolin

Pulverised Fuel Ash (PFA)
cornishlime.co.uk/pulverised-fuel-ash
www.roseofjericho.co.uk/product/pulverised-fuel-ash

[esbjornaneer]

Hmmm... I must be using the wrong sourcing of materials here then. The nepheline syenite comes in at the same price as MgO when including postage in the price. And the monopotassium phosphate I linked to above is actually cheaper than the fertilizer versions I find here in the UK. And this options seemed cheaper than the acid as I had to order 5litres of a 45% solution for more money. Not sure what I am doing wrong in my google searches.

And you say the strength remains low. Is it too low to use as the bell/bench of a RMH in your opinion? Compressive strength of soapstone come in the 10-40MPa range, which is more than is achieved with the talc in these papers. What would make a manufactured soapstone more suitable for use in the bell/bench (i.e. high thermal conductivity, high specific heat capacity, sufficient abration and compression resistance, with little heat expansion)?
Or should I look for other feedstock for a geopolymer for this use?

[Deleted]

Here I can get 1Kg of Haifa MKP™ - Mono Potassium Phosphate for about 5€, 10Kg for 35€ and 25Kg for about 53€.
Fertilizers are relatively cheap, else no farmer could afford them.

With talc as raw maretial one can achive only low density and strength.
Higher strength requires calcined or dead durned magnesium oxide.
One can try to mimic the properties of soap stone with other source materials.