Magnetic ball

1 . A sintered bead comprising the following crystalline phases, as percentages by weight on the basis of the crystalline phases and for a total of 100%:

stabilized zirconia: complement to 100%;

monoclinic zirconia: ≤20%;

4% ≤magnetic constituent ≤22%;

crystalline phases other than stabilized zirconia, monoclinic zirconia and magnetic constituent: <10%;

the magnetic constituent being selected from magnetic spinels, magnetic garnets, magnetic hexagonal ferrites and their mixtures;

excluding the magnetic constituent, the sintered bead comprising CeO 2 and optionally Y 2 O 3 in contents such that 3% ≤CeO 2 ≤17.5% and 1.5% ≤Y 2 O 3 +(CeO 2 )/3.5≤5%, as molar percentages on the basis of the sum of ZrO 2 , CeO 2 and Y 2 O 3 .

2 . The sintered bead as claimed in claim 1 in which, excluding the magnetic constituent, CeO 2 ≤16%, as molar percentages on the basis of the sum of ZrO 2 , CeO 2 and Y 2 O 3 .

3 . The sintered bead as claimed in claim 2 , in which 5% ≤CeO 2 and CeO 2 ≤15%, as molar percentages on the basis of the sum of ZrO 2 , CeO 2 and Y 2 O 3 .

4 . The sintered bead as claimed in claim 1 in which, excluding the magnetic constituent, Y 2 O 3 +(CeO 2 )/3.5 is more than or equal to 2% and less than or equal to 4%.

5 . The sintered bead as claimed in claim 1 , in which the zirconia is entirely stabilized with CeO 2, or in which the stabilized zirconia is entirely stabilized with CeO 2 and Y 2 O 3 .

6 . The sintered bead as claimed in claim 1 , in which more than 90% of the stabilized zirconia is present in the form of quadratic zirconia, as a percentage by weight on the basis of the stabilized zirconia.

7 . The sintered bead as claimed in claim 1 , having a monoclinic zirconia content, as a percentage by weight on the basis of the total quantity of the crystalline phases, of less than or equal to 10%.

8 . The sintered bead as claimed in claim 1 , wherein the magnetic constituent content is more than or equal to 5% and less than or equal to 18%, as percentages by weight on the basis of the crystalline phases.

9 . The sintered bead as claimed in claim 1 , wherein the magnetic constituent content is more than or equal to 7% and less than or equal to 15%, as percentages by weight on the basis of the crystalline phases.

10 . The sintered bead as claimed in claim 1 , in which the magnetic constituent is selected from magnetic spinels, magnetic hexagonal ferrites and their mixtures.

11 . The sintered bead as claimed in claim 1 , in which

excluding oxygen and for more than 90% of its mass, said magnetic spinel is constituted by iron and zinc and copper, by iron and copper and aluminum, by iron and nickel, by iron and cobalt, by iron and copper, by iron and zinc, by iron and magnesium, by iron and manganese, by iron and nickel and zinc, by iron and nickel and zinc and copper, by iron and manganese and zinc, by iron and manganese and zinc and aluminum, by iron and lithium and zinc and by nickel and manganese, by iron and zinc and lithium, by iron and zinc and copper and aluminum and calcium, and their mixtures; and/or

the magnetic hexagonal ferrite is selected from a M-type hexagonal ferrite, a W-type hexagonal ferrite and their mixtures, and/or

if the magnetic constituent is not selected from magnetic spinels, magnetic hexagonal ferrites and their mixtures, said magnetic garnet is selected from garnets comprising iron.

12 . The sintered bead as claimed in claim 1 , in which

0.2% ≤Al 2 O 3 ≤2%, Al 2 O 3 being expressed as excluding the magnetic constituent; and/or

CaO≤1.5%, CaO being expressed as excluding the magnetic constituent.

13 . The sintered bead as claimed in claim 1 , having

a size of less than 10 mm and more than 0.01 mm, and

a sphericity of more than 0.85.

14 . Powdered sintered beads comprising more than 90%, as percentages by weight, of sintered beads in accordance with claim 1 .

15 . A method for extracting beads and/or fragments of beads in accordance with claim 1 , said method comprising the following step:

1). applying a magnetic field to said beads and/or said fragments of beads, in a manner such as to attract said beads or said fragments of beads.

16 . A method for grinding, dispersing, homogenizing a material, said method comprising the following steps:

1) mixing a material to be ground, to be dispersed, to be homogenized, with beads and/or fragments of beads in accordance with claim 1 , in order to obtain a charge;

2) purifying the charge by applying a magnetic field to said beads and/or said fragments of beads, in a manner such as to attract said beads or said fragments of beads, the magnetic field being applied to said charge.

17 . A method for extracting beads or fragments of beads in accordance with claim 1 from a surface of a substrate on which said beads or said fragments of beads are lying, said method comprising the following steps:

1) projecting said beads and/or fragments of beads onto a surface to be treated by means of a projection apparatus;

2) recovering said beads or said fragments of beads by applying a magnetic field to said beads and/or said fragments of beads, in a manner such as to attract said beads or said fragments of beads, the magnetic field being applied to said substrate surface.

18 . The powdered sintered beads in accordance with claim 14 , wherein said powdered sintered beads are configured as any one of a grinding medium, a dispersion medium, a homogenizing medium or a medium for the treatment of surfaces.

19 . A method according to claim 17 , wherein the substrate surface is the surface to be treated and/or a surface of said projection apparatus.