PROCESS FOR THE PRODUCTION OF AN ULTRA-LIGHT MINERAL, AND USE OF THE RESULTING MINERAL FOAM AS A REFRACTORY MATERIAL

Abstract

A process for the production of a mineral foam suitable for its use as refractory material includes (i) separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry comprises water (W), an aluminate cement (C) and a lithium salt; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; (iii) adding lithium salt during or after stage (ii); (iv) casting the slurry of foamed cement and leaving it to set.

Claims

1. A method for the production of a mineral foam suitable for its use as refractory material comprising the following steps: (i) separately preparing a slurry of cement and an aqueous foam, wherein the cement slurry comprises water (W), an aluminate cement (C) and a first part of lithium salt; (ii) contacting the slurry of cement with the aqueous foam to obtain a slurry of foamed cement; (iii) adding a second part of lithium salt during or after step (ii); (iv) casting the slurry of foamed cement and leaving it to set.

2. The method according to claim 1, wherein the aluminate cement comprises aluminium oxide and mullite.

3. The method according to claim 1, wherein the aluminate cement does not contain a source of calcium sulfate.

4. The method according to claim 1, wherein the amount of lithium salt added in step (i) is comprised between 0.05 and 1.5% in weight of dry lithium salt by weight of cement.

5. The method according to claim 1, wherein in step (iii) an aqueous solution comprising the lithium salt is added.

6. The method according to claim 1, wherein step (iii) is performed after step (ii) and before step (iv).

7. The method according to claim 1, wherein the total amount of lithium salt is added in an amount of 0.05-2.5% in weight of dry lithium salt by weight of cement.

8. The method according to claim 1, wherein the lithium salt is lithium carbonate, lithium sulfate, lithium hydroxide, or mixtures thereof.

9. The method according to claim 1, wherein the aqueous foam prepared in step (i) have bubbles and the D50 of the bubbles is less than or equal to 400 m.

10. The method according to claim 1, wherein the cement slurry in step (i) has a water/cement ratio (weight/weight ratio) comprised between 0.1 and 0.25.

11. The method according to claim 1, wherein the cement slurry comprises a water reducer.

12. The method according to claim 1, wherein the slurry of foamed cement comprises a retarder.

13. The method according to claim 1, wherein the cement slurry comprises at least one supplementary mineral component.

14. A mineral foam obtained or obtainable according to the process of claim 1, comprising 0.05-2.5% in weight of dry lithium salt by weight of cement.

15. The mineral foam obtained or obtainable according to claim 14 having a density comprised between 20 and 2000 kg/m.sup.3.

16. A method comprising utilizing the mineral foam according to claim 14 as a refractory material.

17. An element of a refractory system comprising the mineral foam according to claim 14.

18. The method according to claim 2, wherein the sum of the weight percentages of aluminium oxide and mullite is comprised between 20 and 90% by weight relative to the total cement weight.

19. The method according to claim 4, wherein the amount of lithium salt added in step (i) is comprised between 0.1 and 1.0%, the percentages are expressed in weight of dry lithium salt relative to the weight of cement.

20. The method according to claim 7, wherein the total amount of lithium salt is added in an amount of 0.1-2.0% in weight of dry lithium salt by weight of cement.

21. The method according to claim 13, wherein the supplementary mineral component is selected from silica, silica fume, alumina, aluminosilicates including mullite and andalusite, zircon and zirconia, metakaolin, or mixtures thereof.

Description

EXAMPLES

[0124] Materials

[0125] A laboratory formulation of a mineral binder, hereafter called refractory binder, was used, with the following composition:

TABLE-US-00001 Refractory aggregate - Mullite (Max size 5 mm) 50 wt.-% Calcium aluminate cement (SECAR71 from Imerys) 10 wt.-% Silica fume 15 wt.-% Corundum (Max size 5 mm) 25 wt.-%

[0126] The aluminium oxide content is around 70 wt.-% in SECAR 71 and around 100 wt.-% in corundum.

[0127] The salt added to stabilise the mineral foam is lithium carbonate, which was used as a powder of at least 99 wt.-% purity supplied by the company Sigma-Aldrich.

[0128] The foaming agent used is MAPEAIR L/LA supplied by the company MAPEI, having a solids content of 26 wt.-%.

[0129] Tap water was used in all of the examples.

[0130] Equipment

[0131] The Rayneri mixer: [0132] A Turbotest mixer (MEXP-101, model: Turbotest 33/300, Serial No.: 123861) supplied by the company Rayneri, which is a mixer with a vertical axis.

[0133] Pumps: [0134] A pump having an eccentric screw conveyer Seepex of the type MD 006-24, commission no. 244920. [0135] A pump having an eccentric screw conveyer Seepex of the type MD 006-24, commission no. 278702.

[0136] Foamer: [0137] A foamer comprising a bed of glass beads of the type SB30 having a diameter of 0.8-2.5 mm filled up in a tube having a length of 100 mm and a diameter of 12 mm.

[0138] Static Mixer: [0139] A static mixer comprised of 32 helicoidal elements of the type Kenics having a diameter of 19 mm and referred to as 16La632 at ISOJET.

[0140] Preparation of Cement Slurry

[0141] For preparing one liter of slurry having a water/cement ratio of 0.15, the following composition was used:

TABLE-US-00002 TABLE 1 Amount Weight percentage wt.-% Refractory binder 2112.4 g 86.83 Lithium carbonate 3.6 g 0.148 Tap water 316.9 g 13.03 Total 2432.9 g 100

[0142] The cement slurry has been prepared by using the mixer Rayneri Turbotest 33/300, into which tap water has first been introduced. While mixing at 1000 rpm, the solid components have progressively been added. The cement slurry was then mixed for two additional minutes.

[0143] Preparation of the Foaming Solution

[0144] A foaming solution, i.e. an aqueous solution containing the foaming agents, was prepared using the following amounts of materials.

[0145] For one litre of foaming solution:

TABLE-US-00003 MAPEAIR L/LA 25 g TAMOL 731 A (from DOW) 2 g Tap water 973 g

[0146] The foaming solution was pumped by means of a volumetric pump having an eccentric screw conveyor Seed TM MD-006-24 (commission no: 278702).

[0147] This foaming solution was introduced into the foamer through the bed of beads by means of pressurized air (1-6 bar) and a T-junction. The aqueous foam was produced in a continuous way at a rate of 8 litres per minute, having a density of 45 kg/m.sup.3.

[0148] Lithium Carbonate Salt

[0149] Lithium carbonate in powder form provided by Sigma Aldrich was used, with a purity of at least 99 wt.-%.

[0150] The salt was used to prepare an aqueous solution with a concentration of 1.67 g of lithium carbonate per 100 g of solution.

[0151] Preparation of the Fresh Mineral Foam

[0152] The aqueous foam as previously obtained, was brought into contact with the cement slurry each other in a static mixer and a slurry of foamed cement was obtained. The flow rate of the aqueous foam into the static mixer is of 377 g per minute.

[0153] The slurry rate is adjusted to obtain the target density of 500 kg/m.sup.3.

TABLE-US-00004 TABLE 2 Targeted dry foam density (kg/m.sup.3) 400 500 600 Calculated wet density (kg/m.sup.3) 442 540 640 Flow rate of aqueous foam (g/min) 377 370 377 Slurry flow (g/min) 3714 3992 4259

[0154] The aqueous solution of lithium carbonate was injected at a position located at two thirds of the length of the static mixer at a rate of 20 g per minute.

[0155] Preparation of Mineral Foam Cubes

[0156] The slurry of foamed cement was poured into cubes made of polystyrene having a dimension of 101010 cm. Three cubes have been prepared for each slurry of foamed cement. The cubes have been demoulded after 1 day and stored 7 days at a relative humidity of 100% and a temperature of 20 C. The cubes were then dried at a temperature of 45 C. until a constant weight is obtained.

[0157] Analysis of the Mineral Foams

[0158] The stability of the foams has been measured by visual inspection of the cubes before demoulding. A foam has been described as stable, if the cube kept its height of 10 cm after setting. A foam has been described as unstable, if the cube has slumped during its setting. Each test was carried out on 3 cubes of 101010 cm. The results show a similar performance among the 3 cubes. As the case may be, the results are the mean value of 3 cubes.

[0159] A column has been considered stable if the density between the lower section and the upper section does not differ by more than 5 kg/m.sup.3.

[0160] Refractory Properties of the Mineral Foam

[0161] The refractory properties of the foams are reported in the table below.

TABLE-US-00005 TABLE 3 English units Metric units Bulk density 23.7 lbs/ft.sup.3 378 kg/m.sup.3 Maximum service temperature 2200 F. 1200 C. Thermal 73 F./23 C. 0.81 BTU- 0.12 W/m- conductivity 750 F./399 C. 1.14 in/hr- 0.16 K 1469 F./799 C. 2.26 ft.sup.2 0.33 2188 F./1198 C. 4.34 0.62 2694 F./1479 C. 6.82 0.98 Cold 450 F./232 C. 39 PSI 0.3 MPa crushing 700 F./371 C. 31 0.2 strength Apparent porosity 84.8 %