Spinel forming refractory compositions, their method of production and use thereof

1. A particulate composition for use in an alumina-magnesia spinel forming dry vibratable mix, the composition comprising, based on the total weight of the particulate composition:

from 95 to 99.9 wt % of a mixture of particulate Al 2 O 3 and particulate MgO; and

from 0.1 to 5 wt % binding agent,

wherein at least a portion of the particles of said mixture of particulate Al 2 O 3 and particulate MgO is present in the particulate composition as a coating of particles on the surface of other particles,

further comprising mineraliser particles as part of said coating, said mineraliser particles selected from the group consisting of B 2 O 3 , V 2 O 5 , TiO 2 , Y 2 O 3 , Fe 2 O 3 , CaO, NaCl, AlCl 3 , MgCl, LiF, ZnF 2 , BaF 2 , and CaF 2 .

2. The particulate composition of claim 1 , wherein the particulate composition has the following particle size distribution:

from 35 to 65 wt % of the particulate composition are particles having a particle size of 1 mm or above;

from 45 to 75 wt % of the particulate composition are particles having a particle size of 0.5 mm or above;

from 65 to 95 wt % of the particulate composition are particles having a particle size of 0.045 mm or above; and

binding agent,

wherein at least a portion of the particulate composition are first metal oxide particles selected from Al 2 O 3 , MgO, or both, and having a particle diameter of 0.25 mm or below, which are present in the particulate composition as part of a coating on second metal oxide particles selected from Al 2 O 3 and MgO and having a particle diameter of 0.5 mm or above.

3. The particulate composition of claim 1 , wherein substantially all of the particles present as part of the coating of metal oxide particles on the surface of other particles have a particle diameter of 0.25 mm or below and the other particles have a particle diameter of 0.5 mm or above.

4. The particulate composition of claim 2 , wherein some or all of said particles having a particle size of 0.25 mm or below are particles having a particle diameter of 0.045 mm or below.

5. The particulate composition of claim 2 , wherein said first metal oxide particles are Al 2 O 3 or a mixture of Al 2 O 3 and MgO, and said second metal oxide particles are MgO.

6. The particulate composition of claim 2 , wherein said first metal oxide particles are MgO or a mixture of MgO and Al 2 O 3 , and said second metal oxide particles are Al 2 O 3 .

7. The particulate composition of claim 1 , wherein the binding agent is selected from solid thermoplastic binding agents, thermohardening binding agents and liquid, thermo setting binding agents and liquid, and reacting binding agents.

8. A particulate composition for use in an alumina-magnesia spinel forming dry vibratable mix, the composition comprising, based on the total weight of the particulate composition:

from 95 to 99.9 wt % of a mixture of particulate Al 2 O 3 and particulate MgO; and

from 0.1 to 5 wt % binding agent,

wherein at least a portion of the particles of said mixture of particulate Al 2 O 3 and particulate MgO is present in the particulate composition as a coating of particles on the surface of other particles,

wherein the Al 2 O 3 comprises white fused alumina.

9. A method of producing the particulate composition of claim 1 , the method comprising the steps of, in order:

(i) providing (a) from 95 to 99 parts by weight of a mixture of particulate Al 2 O 3 and particulate MgO, and (b) from 1 to 5 parts by weight of a thermoplastic or thermosetting binding agent;

(ii) introducing particles from a portion of the provided mixture of particulate Al 2 O 3 and particulate MgO to be coated into a mixer;

(iii) starting the mixing operation;

(iv) introducing the provided binding agent into the mixer;

(v) introducing particles from another portion of the provided mixture of particulate Al 2 O 3 and particulate MgO to form part of a coating into the mixer; and

(vi) gradually reducing temperature in the mixer to below the melting or transition temperature of the thermoplastic or thermosetting binding agent,

wherein, prior to step (vi) the mixing was carried out at a temperature above the said melting or transition temperature.

10. A method of producing the particulate composition of claim 1 , the comprising the steps of, in order:

(i) providing (a) from 95 to 99.9 parts by weight of a mixture of particulate Al 2 O 3 and particulate MgO, and (b) from 0.1 to 5 parts by weight of a thermoplastic or thermosetting two-component binding agent;

(ii) introducing particles from a portion of the provided mixture of particulate Al 2 O 3 and particulate MgO to be coated into a mixer;

(iii) starting the mixing operation;

(iv) introducing a first component of the two-component binding agent into the mixer;

(v) introducing particles from another portion of the provided mixture of particulate Al 2 O 3 and particulate MgO to form part of a coating into the mixer; and

(vi) introducing a second component of said two-component binding agent into the mixer.

11. A method of producing the particulate composition of claim 1 , the method comprising the steps of, in order:

(i) providing (a) a mixture of particulate Al 2 O 3 and particulate MgO, and (b) a water-based suspension comprising from 50 to 89.9 wt % particles to form part of a coating, from 0.1 to 5 wt % of a binding agent and from 10 to 50 wt % water;

(ii) introducing particles from a portion of the provided mixture of particulate Al 2 O 3 and particulate MgO to be coated into a mixer;

(iii) starting the mixing operation;

(iv) introducing the water-based suspension into the mixer; and

(v) gradually reducing the temperature in the mixer to below 100° C.

12. The method according to claim 9 , wherein:

from 35 to 65 wt % of the total provided particulate composition are particles having a particle size of 1 mm or above;

from 45 to 75 wt % of the total provided particulate composition are particles having a particle size of 0.5 mm or above;

from 65 to 95 wt % of the total provided particulate composition are particles having a particle size of 0.045 mm or above; and

such that at least a portion of the particulate composition formed are first metal oxide particles selected from Al 2 O 3 , MgO, or both, and having a particle diameter of 0.25 mm or below, which are present in the particulate composition as part of a coating on second metal oxide particles selected from Al 2 O 3 and MgO and having a particle diameter of 0.5 mm or above.

13. The method of claim 12 , wherein said first metal oxide particles are Al 2 O 3 , and said second metal oxide particles are MgO.

14. The method of claim 12 , wherein said first metal oxide particles are MgO, and said second metal oxide particles are Al 2 O 3 .

15. The particulate composition of claim 8 , wherein the particulate composition has the following particle size distribution:

from 35 to 65 wt % of the particulate composition are particles having a particle size of 1 mm or above;

from 45 to 75 wt % of the particulate composition are particles having a particle size of 0.5 mm or above;

from 65 to 95 wt % of the particulate composition are particles having a particle size of 0.045 mm or above; and

binding agent,

wherein at least a portion of the particulate composition are first metal oxide particles selected from Al 2 O 3 , MgO, or both, and having a particle diameter of 0.25 mm or below, which are present in the particulate composition as part of a coating on second metal oxide particles selected from Al 2 O 3 and MgO and having a particle diameter of 0.5 mm or above.

16. The particulate composition of claim 8 , wherein substantially all of the particles present as part of the coating of metal oxide particles on the surface of other particles have a particle diameter of 0.25 mm or below and the other particles have a particle diameter of 0.5 mm or above.

17. The particulate composition of claim 15 , wherein some or all of said particles having a particle size of 0.25 mm or below are particles having a particle diameter of 0.045 mm or below.

18. The particulate composition of claim 15 , wherein said first metal oxide particles are MgO or a mixture of MgO and Al 2 O 3 , and said second metal oxide particles are Al 2 O 3 .

19. The particulate composition of claim 8 , wherein the binding agent is selected from solid thermoplastic binding agents, thermohardening binding agents and liquid, thermo setting binding agents and liquid, and reacting binding agents.