Fire-resistant calcium sulphate-based products

Abstract

The present invention provides calcium sulphate-based product having reduced shrinkage after exposure to high temperatures, the product comprising gypsum, a pozzolan source (e.g. in an amount between 4-27 wt %) and a metal salt additive (in an amount between 0.5 and 10 wt %). The pozzolan source may be selected from a kaolinitic clay material, fly ash, rice husk ash, diatomaceous earths, volcanic ashes and pumices, micro-silica, silica fume and silicone oil. The metal salt additive may be a metal salt which decomposes between a temperature of 300-500 C. to yield a metal oxide, e.g. magnesium nitrate.

Claims

1. A gypsum wallboard comprising: gypsum, a pozzolan source, and a metal salt, wherein: the gypsum is provided in an amount of 40% or greater based on a total weight of the gypsum wallboard, the metal salt is selected from nitrate and hydrogen carbonate salts of calcium, magnesium, copper, zinc, iron and aluminum, and carbonate and chloride salts of copper, zinc, iron or aluminum; and the metal salt is provided in an amount of between 0.5 wt % and 10 wt % based on the weight of the gypsum, the pozzolan source and the metal salt.

2. The gypsum wallboard according to claim 1, wherein the pozzolan source is included in an amount between 4 wt % and 27 wt % (based on the weight of the gypsum, the pozzolan source and the metal salt).

3. The gypsum wallboard according to claim 1, wherein the wt % of pozzolan source and wt % metal salt are equal.

4. The gypsum wallboard according to claim 1, wherein the pozzolan source is selected from a kaolinitic clay material, fly ash, rice husk ash, diatomaceous earths, volcanic ashes and pumices, micro-silica, silica fume and silicone oil.

5. The gypsum wallboard according to claim 1, wherein the metal salt decomposes between a temperature of 300 C.-500 C. to yield a metal oxide.

6. The gypsum wallboard according to claim 1, wherein the metal salt is a magnesium salt.

7. A gypsum wallboard formed by a process comprising: drying an aqueous slurry containing gypsum, a pozzolan source, and a metal salt additive, wherein: the gypsum is provided in the gypsum wallboard in an amount of 40% or greater based on a total weight of the gypsum, the pozzolan source and the metal salt additive, the metal salt additive is selected from nitrate and hydrogen carbonate salts of calcium, magnesium, copper, zinc, iron and aluminum and carbonate and chloride salts of copper, zinc, iron or aluminum, and the metal salt additive is included in the slurry in an amount between 1 wt % and 15 wt %.

8. The gypsum wallboard according to claim 7, wherein the pozzolan source is included in the slurry in an amount between 5 wt % and 30 wt %.

9. A calcium sulphate-based composition for use in forming a gypsum wallboard by drying an aqueous slurry of the calcium sulphate-based composition, the calcium sulphate-based composition comprising: gypsum, a pozzolan source, and a metal salt, wherein: the gypsum is provided in the gypsum wallboard in an amount of 40% or greater based on a total weight of the gypsum wallboard, the metal salt is selected from nitrate and hydrogen carbonate salts of calcium, magnesium, copper, zinc, iron and aluminum and carbonate and chloride salts of copper, zinc, iron or aluminum, and the metal salt is included in the slurry in an amount between 1 wt % and 15 wt %.

10. The calcium sulphate-based composition according to claim 9, wherein the pozzolan source is included in an amount between 5 wt % and 30 wt %.

11. The calcium sulphate-based composition according to claim 9, wherein the wt % of pozzolan source and wt % metal salt are equal.

12. The calcium sulphate-based composition according to claim 9, wherein the pozzolan source is selected from a kaolinitic clay material, fly ash, rice husk ash, diatomaceous earths, volcanic ashes and pumices, micro-silica, silica fume and silicone oil.

13. The calcium sulphate-based composition according to claim 9, wherein the metal salt decomposes between a temperature of 300 C.-500 C. to yield a metal oxide.

14. The calcium sulphate-based composition according to claim 13, wherein the metal salt is a magnesium salt.

15. A method of forming a gypsum wallboard by drying an aqueous slurry comprising the composition according to claim 9.

16. A gypsum wallboard comprising: gypsum, a pozzolan source, and a metal salt additive, wherein: the gypsum is provided in an amount of 40% or greater based on a total weight of the gypsum wallboard, the metal salt additive is selected from calcium nitrate and salts of magnesium, copper, zinc, or iron, and the wt % of pozzolan source and wt % metal salt additive are equal.

17. The gypsum wallboard according to claim 16, wherein the pozzolan source is selected from a kaolinitic clay material, fly ash, rice husk ash, diatomaceous earths, volcanic ashes and pumices, micro-silica, silica fume and silicone oil.

18. The gypsum wallboard according to claim 16, wherein the metal salt decomposes between a temperature of 300-500 C. to yield a metal oxide.

19. The gypsum wallboard according to claim 18, wherein the metal salt is a magnesium salt.

Description

EXAMPLES

(1) Sample formulations having the amounts of metal salt, pozzolan source and calcined gypsum shown in Table 1 below were prepared (for all but Example 23) by mixing the metal salt with 140 g of water at 40 C. The pozzolan source and calcined gypsum were dry blended and added to the water/salt mixture. The resulting mixture was blended by hand for 30 seconds to form a slurry. For example 23, the silicone oil and metal salt were added to 140 g of water at 40 C. and then the calcined gypsum was added to the solution to form a slurry which was blended by hand for 30 seconds. Wt % amounts (based on the dry ingredients) of each component in the slurry are shown below in brackets.

(2) The slurry was poured into a cylindrical silicone mould (height 25 mm, diameter 12 mm) and dried overnight (minimum 12 hours) at 40 C.

(3) TABLE-US-00001 TABLE 1 Summary of sample formulations Pozzolan Metal source/g salt/g Sample Stucco/g (wt %) (wt %) (wt %) Control 1 200 0 0 Control 2 180 (90) 20 (10) 0 Kaolin Control 3 140 (70) 60 (30) 0 Kaolin Control 4 200 (91) 0 20 (9) Control 5 200 (93) 0 16 (7) Control 6 200 (92) 0 19 (8) Control 7 200 (91) 0 20 (9) Control 8 200 (91) 0 20 (9) Control 9 180 (90) 20 (10) 0 Rice husk ash Control 10 180 (90) 20 (10) 0 Silicone oil Control 11 180 (90) 20 (10) 0 Micro-silica Control 12 180 (90) 20 (10) 0 Diatomaceous earth Example 1 180 (81.8) 20 (9.1) 20 (9.1) Mg nitrate (hexahydrate) Kaolin Example 2 140 (63.6) 60 (27.3) 20 (9.1) Mg nitrate (hexahydrate) Kaolin Example 3 180 (89.1) 20 (9.9) 2 (1.0) Mg nitrate (hexahydrate) Kaolin Example 4 195 (96.5) 5 (2.5) 2 (1.0) Mg nitrate (hexahydrate) Kaolin Example 5 195 (95.1) 5 (2.4) 5 (2.4) Mg nitrate (hexahydrate) Kaolin Example 6 180 (87.8) 20 (9.8) 5 (2.4) Mg nitrate (hexahydrate) Kaolin Example 7 190 (92.7) 10 (4.9) 5 (2.4) Mg nitrate (hexahydrate) Kaolin Example 8 180 (83.3) 20 (9.3) 16 (7.4) Cu nitrate (tetrahydrate) Kaolin Example 9 140 (64.8) 60 (27.8) 16 (7.4) Cu nitrate (tetrahydrate) Kaolin Example 10 180 (82.6) 20 (9.2) 18 (8.3) Ca nitrate (tetrahydrate) Kaolin Example 11 140 (64.2) 60 (27.5) 18 (8.3) Ca nitrate (tetrahydrate) Kaolin Example 12 180 (81.8) 20 (9.1) 20 (9.1) Fe (III) nitrate (nonahydrate) Kaolin Example 13 140 (63.6) 60 (27.3) 20 (9.1) Fe (III) nitrate (nonahydrate) Kaolin Example 14 180 (81.8) 20 (9.1) 20 (9.1) Al nitrate (nonahydrate) Kaolin Example 15 140 (63.6) 60 (27.3) 20 (9.1) Al nitrate (nonahydrate) Kaolin Example 16 180 (81.8) 20 (9.1) 20 (9.1) Zn nitrate (hexahydrate) Kaolin Example 17 140 (63.6) 60 (27.3) 20 (9.1) Zn nitrate (hexahydrate) Kaolin Example 18 180 (89.1) 20 (9.9) 2 (1.0) Mg chloride (hexahydrate) Kaolin Example 19 195 (96.5) 5 (2.5) 2 (1.0) Mg chloride (hexahydrate) Kaolin Example 20 195 (95.1) 5 (2.4) 5 (2.4) Mg chloride (hexahydrate) Kaolin Example 21 180 (87.8) 20 (9.8) 5 (2.4) Mg chloride (hexahydrate) Kaolin Example 22 180 (82) 20 (9) 20 (9) Mg nitrate (hexahydrate) Rice husk ash Example 23 180 (82) 20 (9) 20 (9) Mg nitrate (hexahydrate) Silicone oil Example 24 180 (82) 20 (9) 20 (9) Mg nitrate (hexahydrate) Micro-silica Example 25 180 (82) 20 (9) 20 (9) Mg nitrate (hexahydrate) Diatomaceous earth
Linear Shrinkage

(4) Linear shrinkage was measured using a Netzsch dilatometer. The samples were heated to 1000 C. at a rate of 5 C./min. The shrinkage was measured in-situ using a transducer having a resolution of 8 nm.

(5) The dilatometer results are shown in Table 2.

(6) TABLE-US-00002 TABLE 2 Pozzolan Metal Stucco/wt % source/wt % salt/wt % in slurry in slurry in slurry (wt % in (wt % in (wt % in Shrinkage (%) Sample product) product) product) 500 C. 750 C. 900 C. 950 C. 1000 C. Control 1 100 0 0 1.8 3.6 7.13 18 Off scale Control 2 90 (91.4) 10 (8.6) 0 1.59 2.50 3.10 5.11 8.03 Control 3 70 (73.5) 30 (26.5) 0 1.6 2.7 3.46 6.48 8.59 Control 4 91 (92.2) 0 9 (7.8) 0.02 0.12 0.17 2.84 6.51 Control 5 93 (93.7) 0 7 (6.3) 0.24 1.54 12/9 Off Off scale scale Control 6 92 (92.6) 0 8 (7.4) 0.26 2.84 9.05 9.08 9.1 Control 7 91 (92.2) 0 9 (7.8) 0.6 0.7 3.6 7.7 12.3 Control 8 91 (92.2) 0 9 (7.8) 0.7 0.4 0.4 0.9 3.5 Control 9 90 (91.4) 10 (8.6) 0 1.7 2.6 3.5 7.7 10.4 Control 90 (91.4) 10 (8.6) 0 1.3 2.2 2.4 3.2 4.6 10 Control 90 (91.4) 10 (8.6) 0 2.0 3.4 4.8 9.4 11.7 11 Control 90 (91.4) 10 (8.6) 0 1.8 2.6 3.5 6.2 8.5 12 Ex. 1 81.8 (84.2) 9.1 (7.9) 9.1 (7.9) 0.13 0.02 0.04 0.13 0.69 Mg(NO.sub.3).sub.2 Ex. 2 63.6 (67.5) 27.3 (24.4) 9.1 (8.1) 0.22 0.23 0.7 1.52 1.85 Mg(NO.sub.3).sub.2 Ex. 3 89.1 (90.7) 9.9 (8.5) 1.0 (0.8) 1 1.11 1.36 3.34 6.07 Mg(NO.sub.3).sub.2 Ex. 4 96.5 (97.1) 2.5 (2.1) 1.0 (0.8) 1.25 1.41 1.42 2.19 12.4 Mg(NO.sub.3).sub.2 Ex. 5 95.1 (95.9) 2.4 (2.1) 2.4 (2.1) 0.74 0.61 0.77 1.3 12.8 Mg(NO.sub.3).sub.2 Ex. 6 87.8 (89.5) 9.8 (8.4) 2.4 (2.1) 0.18 0.022 0.16 0.24 1.45 Mg(NO.sub.3).sub.2 Ex. 7 92.7 (93.8) 4.9 (4.2) 2.4 (2.1) 0.32 0.068 0.13 0.39 6.95 Mg(NO.sub.3).sub.2 Ex. 8 83.3 (85.6) 9.3 (8.0) 7.4 (6.4) 0.19 0.03 0.29 0.04 1.49 Cu(NO.sub.3).sub.2 Ex. 9 64.8 (68.6) 27.8 (24.8) 7.4 (6.6) 0.47 0.38 0.52 0.99 1.5 Cu(NO.sub.3).sub.2 Ex. 10 82.6 (84.9) 9.2 (8.0) 8.3 (7.2) 0.3 0.01 0.3 0.24 0.72 Ca(NO.sub.3).sub.2 Ex. 11 64.2 (68.0) 27.5 (24.6) 8.3 (7.4) 0.49 0.52 0.04 0.52 1.01 Ca(NO.sub.3).sub.2 Ex. 12 81.8 (84.2) 9.1 (7.9) 9.1 (7.9) 0.75 0.64 0.92 1.0 1.42 Fe(NO.sub.3).sub.3 Ex. 13 63.6 (67.5) 27.3 (24.4) 9.1 (8.1) 0.47 0.34 0.42 0.68 0.99 Fe(NO.sub.3).sub.3 Ex. 14 81.8 (84.2) 9.1 (7.9) 9.1 (7.9) 0.78 0.5 0.32 0.3 0.36 Al(NO.sub.3).sub.3 Ex. 15 63.6 (67.5) 27.3 (24.4) 9.1 (8.1) 0.82 0.93 0.79 0.80 0.79 Al(NO.sub.3).sub.3 Ex. 16 81.8 (84.2) 9.1 (7.9) 9.1 (7.9) 0.47 0.31 0.86 2.07 4.43 Zn(NO.sub.3).sub.2 Ex. 17 63.6 (67.5) 27.3 (24.4) 9.1 (8.1) 0.05 0.1 0.07 0.6 0.87 Zn(NO.sub.3).sub.2 Ex. 18 89.1 (90.7) 9.9 (8.5) 1.0 (0.8) 0.5 0.4 0.07 1.2 1.4 MgCl.sub.2 Ex. 19 96.5 (97.1) 2.5 (2.1) 1.0 (0.8) 0.58 0.63 2.64 7.4 8.69 MgCl.sub.2 Ex. 20 95.1 (95.9) 2.4 (2.1) 2.4 (2.1) 0.49 1.45 5.51 8.89 10.61 MgCl.sub.2 Ex. 21 87.8 (89.5) 9.8 (8.4) 2.4 (2.1) 0.3 0.3 0.5 0.1 0.1 MgCl.sub.2 Ex. 22 82 (84.2) 9 (7.9) 9 (7.9) 0.04 0.04 0.15 1.85 4.23 Mg(NO.sub.3).sub.2 Ex. 23 82 (84.2) 9 (7.9) 9 (7.9) 0.95 1.42 1.38 1.52 1.95 Mg(NO.sub.3).sub.2 Ex. 24 82 (84.2) 9 (7.9) 9 (7.9) 0.41 0.31 0.2 0.7 8.8 Mg(NO.sub.3).sub.2 Ex. 25 82 (84.2) 9 (7.9) 9 (7.9) 0.03 0.01 0.02 0.07 1.92 Mg(NO.sub.3).sub.2

(7) The results show that a combination of pozzolan source and a metal salt can help reduce shrinkage after exposure to elevated temperatures. Results are most pronounced when greater than 5 wt % of pozzolan source is used in the slurry (greater than 4 wt % in the product) and when greater than 1 wt % metal salt is used in the slurry (greater than 0.5 wt % in the product). Results where an equal amount of pozzolan source and metal salt are used are particularly pronounced.