AU2005324287B2

AU2005324287B2 - Foaming plaster

Info

Publication number: AU2005324287B2
Application number: AU2005324287A
Authority: AU
Inventors: Edgar Donald Knott
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-01-07
Filing date: 2005-12-16
Publication date: 2010-07-08
Anticipated expiration: 2025-12-16
Also published as: AU2005324287A1

Description

WO 2006/072126 PCT/AU2005/001908 TITLE FOAMING PLASTER FIELD OF THE INVENTION 5 The present invention relates to foaming plaster and a method of manufacture thereof. SUMMARY OF THE INVENTION In accordance with one aspect of the present invention there is provided a method of producing a foamed plaster, the method characterised by comprising the steps of: 10 (a) mixing plaster of Paris and calcium carbonate, the calcium carbonate being between 2% and 12% by weight of the plaster of Paris; (b) supplying water; and (c) adding phosphoric acid, the phosphoric acid reacting with the calcium carbonate to release gaseous carbon 15 dioxide, and the water providing water of hydration to the plaster of Paris to form gypsum. DESCRIPTION OF PREFERRED EMBODIMENTS In a preferred embodiment of the invention a building panel is formed using the 20 following method. A suitable calcium carbonate containing material is ground to a size of under 50 micron. Suitable calcium carbonate containing materials include limestone, marble, lime sands and coral sands. Preferably the material is predominantly calcium 1 WO 2006/072126 PCT/AU2005/001908 carbonate, with low levels of soluble salts of sodium and magnesium. The ground calcium carbonate is added to powdered plaster of Paris in such quantity that the resulting plaster of Paris and calcium carbonate mixture contains about 6% calcium carbonate by weight. 5 Surface sheeting materials, such as steel, aluminium or fibreglass sheets, are held in frames so as to create a cavity therebetween. The ends of the cavity are sealed by known means. The inner surfaces of the sheeting materials are preferably treated with a bonding agent such as an epoxy primer with glass or other fibre to increase the bond between 10 the sheeting and the plaster. The combined plaster of Paris and calcium carbonate mixture is then combined with 4%w/v phosphoric acid solution in a ratio of about two parts by volume plaster of Paris and calcium carbonate mixture to about one part by volume phosphoric acid solution. A frothing agent may also be added. The resulting suspension is then 15 sprayed or poured into the cavity. In an alternative embodiment, water is added to the mixture in the ratio of about two parts by volume plaster of Paris and calcium carbonate mixture to about one part by volume water. The resulting suspension is then sprayed into the cavity, using an appropriately designed spray head, along with concentrated phosphoric acid. 20 Preferably, the acid has a concentration of about 81% to 85% w/v. In both embodiments, the water present adds water of hydration to the plaster of Paris, thus forming gypsum. At the same time, the phosphoric acid reacts with the calcium carbonate in the limestone according the to the equation 3CaCO 3 + 2H 3

PO

4 -+ Ca 3 (PO4)2 +3H20 + 3CO2t 2 WO 2006/072126 PCT/AU2005/001908 in order to liberate carbon dioxide gas. The gypsum sets around the bubbles, forming a foamed plaster. It will be appreciated that the above proportions allow for a surplus of calcium carbonate so that when the reaction above is completed no free acid remains. The 5 hard, foamed plaster produced is comprised predominantly of gypsum together with small amounts of calcium phosphate and remaining calcium carbonate. It will be appreciated that calcium phosphate and calcium carbonate are relatively insoluble, thus allowing for a long life for the foamed plaster. One advantage of the present invention is that the phosphoric acid used during 10 formation of the foamed plaster forms an insoluble iron phosphate coating on any steel sheeting or reinforcing used in connection with the foamed plaster. It will be appreciated that the use of other acids may cause degradation of steel in contact with the foamed plaster. A further advantage of this method is that it is anticipated that over time the calcium 15 phosphate will react with fluoride and/or chloride in the resultant foamed plaster to form apatite, making the structure stronger, and with potentially soluble fluoride and chloride converted to relatively insoluble apatite . It will be appreciated that the method described hereinabove may be varied by the addition of stabilising or strengthening elements to the plaster mix, such as cement or 20 other pozzolanic materials or organic polymers, epoxies and the like. It will also be appreciated that the amount of foaming, and the size of the gaseous bubbles, may be controlled by careful selection of the sizing and amount of calcium carbonate, phosphoric acid and frothing agents used in the above process. It is anticipated that a 3 WO 2006/072126 PCT/AU2005/001908 quantity of calcium carbonate between 2% and 12% by weight of the plaster of Paris will yield a useful result. In another embodiment of the invention, foamed plaster blocks may be formed by combining the equivalent of 8% by weight calcium carbonate with plaster of Paris. 5 This mixture is then added in a ratio of about two to one by volume with about 5%w/v phosphoric acid, and the resulting the mix sprayed into a box mould. The reaction proceeds as above. When the foamed plaster blocks are formed they can then be cut to a required size. It will be appreciated that foamed plaster made according to the present invention is 10 particularly useful in acting as a fire retardant, and in insulating exposed steel beams on columns. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 4

Claims

1. A method of producing a foamed plaster, the method characterised by comprising the steps of: 5 (a) mixing plaster of Paris and calcium carbonate, the calcium carbonate being between 2% and 12% by weight of the plaster of Paris; (b) supplying water; and (c) adding phosphoric acid, the phosphoric acid reacting with the calcium carbonate to release gaseous carbon 10 dioxide, and the water providing water of hydration to the plaster of Paris to form gypsum.

2. A method of producing a foamed plaster as claimed in claim 1, characterised in that the calcium carbonate is about 6% by weight of the plaster of Paris.

3. A method of producing a foamed plaster as claimed in claim 1 or claim 2, 15 characterised in that the calcium carbonate is contained within a calcium carbonate containing material.

4. A method of producing a foamed plaster as claimed in claim 3, characterised in that the calcium carbonate containing material is limestone, marble, lime sands or coral sands. 20 5. A method of producing a foamed plaster as claimed in claim 3 or claim 4, characterised in that the calcium carbonate containing material is ground to a size of under 50 micron.

5 WO 2006/072126 PCT/AU2005/001908

6. A method of producing a foamed plaster as claimed in any preceding claim, characterised in that the water and phosphoric acid are supplied together as dilute phosphoric acid solution.

7. A method of producing a foamed plaster as claimed in claim 6, characterised 5 in that the dilute phosphoric acid solution has a concentration of about 6%w/v.

8. A method of producing a foamed plaster as claimed in claim 6 or claim 7, characterised in that the dilute phosphoric acid solution is supplied in a ratio of about two parts by volume plaster of Paris and calcium carbonate solution to about one part by volume dilute phosphoric acid solution. 10

9. A method of producing a foamed plaster as claimed in any one of claims 1 to 5, characterised in that the water is combined with the plaster of Paris and calcium carbonate before the phosphoric acid is added.

10. A method of producing a foamed plaster as claimed in claim 9, characterised in that the water is supplied in a ratio of about two parts by volume plaster of Paris 15 and calcium carbonate solution to about one part by volume water.

11. A method of producing a foamed plaster as claimed in claim 9 or claim 10, characterised in that the added phosphoric acid has a concentration of about 81% to 85% w/v

12. A method of producing a foamed plaster as claimed in any one of claims 9 to 20 11, characterised in that the combined water and plaster of Paris mixture are sprayed into a cavity together with a phosphoric acid spray.

13. A method of producing a building panel comprising the steps of holding surface sheeting materials in spaced arrangement so as to form a cavity therebetween; 6 WO 2006/072126 PCT/AU2005/001908 producing a foamed plaster according to the method of any one of claims 1 to 12, and supplying the foamed plaster into the cavity.

14. A method of producing a foamed plaster block, characterised in that n a foamed plaster produced according to claim 1 is sprayed into a box mould. 5

15. A method of producing a foamed plaster block as claimed in claim 14, characterised in that the calcium carbonate is about 8% by weight of the plaster of Paris.

16. A method of producing a foamed plaster block as claimed in claim 14 or claim 15, characterised in that the water and phosphoric acid are supplied together as an 10 about 5%w/v phosphoric acid solution.

17. A building panel produced according to the method of claim 13.

18. A foamed plaster block produced according to the method of any one of claims 14 to 16. 7