Ceramic Grains and Method for Their Production

Abstract

The disclosure herein relates to a method for preparing ceramic grains comprising: making a slurry comprising inorganic particles and a gelling agent; making droplets of the slurry; introducing the droplets in a liquid gelling-reaction medium wherein the droplets are gellified; deforming the droplets before, during or after gellification; drying the gellified deformed droplets, thereby obtaining dried grains and sintering the dried grains, thereby obtaining the ceramic grains.

The disclosure herein further relates to ceramic grains obtainable by a disclosed method.

Claims

1. Method for preparing ceramic grains comprising making a slurry comprising inorganic particles and a gelling agent; making droplets of the slurry; introducing the droplets in a liquid gelling-reaction medium wherein the droplets are gellified; deforming the droplets before, during or after gellification by impacting the droplets on a deformation mechanism arranged for deforming the droplets upon receiving of the droplets; drying the gellified deformed droplets, thereby obtaining dried grains and sintering the dried grains, thereby obtaining the ceramic grains.

2. Method according to claim 1, wherein the droplets are introduced in the gelling-reaction medium by letting them fall through air or another gaseous atmosphere into the gelling-reaction medium.

3. Method according to claim 1, wherein the deformation mechanism is present at the surface of the gelling-reaction medium or in the gelling-reaction medium.

4. Method according to claim 3, wherein the deformation mechanism comprises a perforation, a grating, a grid, or a mesh.

5. (canceled)

6. (canceled)

7. Method according to claim 1, wherein the gelling agent is an anionic polymer, and wherein the gelling-reaction medium comprises a multivalent cation which reacts with the anionic polymer, thereby gellifying the droplets.

8. (canceled)

9. (canceled)

10. (canceled)

11. Method according to claim 1, wherein the slurry comprises particles of a silicate; carbide particles; nitride particles; boride particles; or calcium carbonate particles.

12. Method according to claim 11, wherein the grains comprise 30-100 wt. % aluminium oxide.

13. Method according to claim 12, wherein the grains comprises 50-90 wt. % aluminium oxide, 0-50 wt. % zirconium oxide, the sum of both of the aluminium oxide and the zirconium oxide being 70-100 wt. %.

14. (canceled)

15. (canceled)

16. Sintered ceramic grains, wherein the grains have a striated or grooved surface.

17. Sintered ceramic grains according to claim 16, wherein the grains comprise alpha-alumina, wherein the alpha-alumina content of the grains being in the range of 50-90 wt. %, wherein the grains further contain an amorphous phase forming less than 30 wt. % of the total weight of the grains, wherein the grains contain silicon dioxide, wherein the grains have on average a sphericity, defined as shortest projected size to longest projected size, in the range of 0.65-0.80, as determined by a Camsizer.

18. Sintered ceramic grains according to claim 17, wherein the grains comprise 50-85 wt. % alumina, 7-40 wt. % zirconia and 3-30 wt. % other component(s).

19. (canceled)

20. Sintered ceramic grains according to claim 16, wherein the alpha-alumina content is 50-70 wt. %.

21. (canceled)

22. (canceled)

23. (canceled)

24. Sintered ceramic grains according to claim 16, comprising a rare earth metal oxide, wherein the rare earth metal oxide is yttrium oxide or calcium oxide.

25. Sintered ceramic grains according to claim 24, wherein the rare earth metal oxide comprises yttrium oxide and has a yttrium content, expressed as its oxide, of 0.3-5 wt. %.

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. Open-porous ceramic structure formed of a three-dimensionally interconnected network of ceramic grains according to claim 16, wherein the grains are joined to each other with a binding agent, wherein a packing of the grains provides for open pores between the grains, which pores are Tillable by a liquid metal.

34. (canceled)

35. Metal-ceramic composite wear component made of an open porous ceramic structure according to claim 33 and a metal matrix surrounding at least a part of the ceramic structure.

36. Method for preparing a wear component according to claim 35, comprising: providing a ceramic structure according to claim 33; filling the open pores of the ceramic structure with liquid metal; and allowing the liquid metal to solidify, thereby forming the wear component.

37. Comminution device comprising a wear component according to claim 36, wherein the comminution device is a grinding device or crushing device.

38. (canceled)

39. Method for treating a material, comprising introducing the material in a device according to claim 37 and subjecting the material to a comminution step wherein the wear component is contacted with the material.

40. (canceled)

41. Abrasive cut-off tool, made from ceramic grains according to claim 16.

42. (canceled)

43. (canceled)

44. (canceled)

Description

COMPARATIVE EXAMPLE

[0146] A batch of ceramic grains produced by melting, quenching and then crushing were commercially obtained from Saint-Gobain (CE) comprising 75 wt. % alumina and 23 wt. % zirconia (including HfO.sub.2),

REFERENCE EXAMPLE 1

[0147] Grains were provided using the methodology of EP 930 948. They had the following composition: [0148] Aluminum Oxide 75.0% [0149] Zirconium Oxide 23.0% [0150] Titanium Oxide 0.10% [0151] Silica 0.30% [0152] Iron Oxide 0.30% [0153] Sodium Oxide 0.08% [0154] Calcium Oxide 0.10% [0155] Magnesium Oxide 0.03% [0156] Sulphur 0.06%

EXAMPLE 1

[0157] Grains were prepared as follows (conditions are ambient, typically about 20-30 C. unless specified otherwise) Raw material mixtures of metal oxide particles and silicate particles were prepared having the following composition.

TABLE-US-00001 Raw materials Wt. % Al.sub.2O.sub.3 75.5 ZrSiO4 23 Y.sub.2O.sub.3 1.5

[0158] A slurry of the raw material mixture in water was prepared. The water contained about 1 wt. % dispersing agent Dolapix CE64. The content of raw materials was about 72 wt. %. The particles in the slurry were ground in an attritor, until a slurry was obtained wherein the d.sub.50 of the particles was about 0.6 m.

[0159] A 5 wt. % aqueous solution of gelling agent (sodium alginate) was added to the slurry to obtain a slurry containing about 0.7 wt. % alginate and about 65 wt. %), inorganic particles, based on the total dry weight of the slurry.

[0160] The resultant slurry was pumped through a nozzle (3 mm aperture) positioned at a height of 10 cm above the gelling-reaction medium (an aqueous solution of 0.3 wt. % calcium chloride dehydrate).

[0161] The gelling medium was present in a reaction bath that was provided with tilted plates having a grid on the upper surface upon which the slurry droplets impacted. The plates were partially submerged in the liquid medium, such that falling droplets impacted on the plates and were allowed to slide into the liquid medium.

[0162] The gelled particles were removed from the reaction medium after about 1 hour and dried in hot air (up to 80 C.) until the residual water content was about 1%.

[0163] The dried particles were sintered.

[0164] The grain composition after sintering is indicated in the table below.

TABLE-US-00002 Chemical composition of the grains Wt. % Al.sub.2O.sub.3 75 ZrO.sub.2 (+HfO.sub.2) 15.5 Y.sub.2O.sub.3 1.5 SiO.sub.2 7.5 CaO 0.5

[0165] Sintering temperature and dwell time are indicated in the Table below.

[0166] The sizes distribution (d.sub.10, d.sub.50, d.sub.90) and the sphericity of a sample of the produced grains (Ex 1) and the comparative grains (CE) were determined with a Camsizer.

[0167] Hardness of the grains was determined as follows by Vickers indentation with a load of 49 N (ASTM C 1327).

[0168] Crystallographic composition can be determined by X-ray diffraction (XRD), by the reconstruction of the diffraction spectrum based on the theoretical individual diffraction spectrum and atomic structure of the different crystallographic phases (Rietveld method).

[0169] Results are shown in the Table below.

TABLE-US-00003 Ex1 CE Manufacturing Sintering (direct Melting, quenching process size and shape) then crushing Sintering or 1480 2000 Melting temperature ( C.) Dwell time 2.5 (hrs) Density 3.87 4.6 D10 (mm) 1.462 1.072 D50 (mm) 1.666 1.461 D90 (mm) 1.881 1.875 Sphericity 0.796 0.671 Hardness 13.5 GPa 16-18 GPa Alpha-Al.sub.2O.sub.3 56.7 61 ZrO.sub.2 tetragonal 9.6 33 ZrO.sub.2 tetragonal 2.6 1 prime ZrO.sub.2 monoclinic 2 4 ZrC 1 Mullite (3 Al.sub.2O.sub.32 13.6 SiO.sub.2) Spinel (MgAl.sub.2O.sub.4) Amorphous 15.4 phase.sup.1 Tqc 86 89 .sup.1The amorphous phase has been measured using Rietveld method by adding a known amount of a reference crystalline material (quartz) to the sample.

[0170] Binocular view photographs of whole grains (FIG. 1.1), optical microscope views of polished cross-sections (FIG. 2.1) and electronic microscope views (FIG. 3.1, scale bar is 10 m; FIG. 4.1; scale bare is 10 m) were made of the grains.

[0171] Comparative images were made of grains of the Comparative Example (FIGS. 1.2, 2.2, 3.2 and 4.2 respectively).

[0172] The electronic microscope views were made after etching the grains by the following procedure: Mirror polishing of the grains embedded in a resin matrix. Removing some grains from the resin, then thermal etching (under air, 20 min at a temperature 50 to 100 C. below the sintering temperature) in an electric furnace.

[0173] The whitish parts are zirconia.

[0174] The darker parts alumina/mullite/spinel/anorthite/amorphous phase.

EXAMPLE 2

[0175] 3D-open porous ceramic structures (having a structure as shown in FIG. 5) were made of the grains of Example 1, 2 and the Reference Example 1 (two structures for each type of grains). The procedure was as follows: the grains were mixed with 4 wt. % of mineral glue comprising sodium silicate, alumina powder and water. The grains with the glue were poured inside a mould of the desired design. The mould and contents were heated to 100 C. until all water had evaporated. Then the ceramic structure was removed from the mould.

EXAMPLE 3

[0176] Ceramic metal wear components (impellers for vertical shaft impactors) were made as follows: the ceramic structures obtained according to Example 2 were individually placed into a sand mould, the liquid metal was poured onto the structure and allowed to cool down.

EXAMPLE 4

[0177] Both the pair of impellers made with the grains according to the invention (Ex 1) and the pair of impellers made with the grains of Reference Example 1 were weighted and thereafter mounted on the same table of a Vertical Shaft Impactor crusher, to ensure that all impellers were tested under the same conditions. The crusher was used to crush porphyry stones. After 19 hours of operation and 2,470 metric tons of crushed material, the impellers were dismounted and weighted again.

[0178] It was visually noticeable that the impellers according to the invention were less worn. Moreover, a comparison of the weight losses indicated that the wear of the impellers according to the invention was 15% lower.

EXAMPLE 5

[0179] Two 3D-open porous ceramic structures for preparing an anvil of a VSI crusher were made of the grains prepared based on the methodology as described in Example 1.

[0180] The grains had the following composition: [0181] Aluminum Oxide 38.4% [0182] Zirconium Oxide 54.0% [0183] Silicon oxide 3.8% [0184] Yttrium oxide 3.10% [0185] Calcium oxide 0.60%

[0186] The ceramic structures were made as follows: the grains were mixed with 4 wt. % of mineral glue comprising sodium silicate, alumina powder and water. The grains with the glue were poured inside a mould of the desired design. The mould and contents were heated to 100 C. until all water had evaporated. Then the ceramic structure was removed from the mould.

REFERENCE EXAMPLE 2

[0187] Grains were provided using the methodology of EP 930 948. They had the following composition: [0188] Aluminum Oxide 60.0% [0189] Zirconium Oxide 39.0% [0190] Titanium Oxide 0.15% [0191] Silica 0.35% [0192] Iron Oxide 0.15% [0193] Sodium Oxide 0.03% [0194] Calcium Oxide 0.09% [0195] Magnesium Oxide 0.02%

[0196] Two ceramic structures of the same design as the structure of Example 5 were made using the grains of the Reference Example, using the same method.

EXAMPLE 6

[0197] From the ceramic structures of Example 5 and the ceramic structures of the Reference Example 2, ceramic metal wear components (anvils for vertical shaft impactors) were made as follows: the ceramic structures were individually placed into a sand mould, the liquid metal (an iron alloy) was poured onto the structure and allowed to cool down.

[0198] Further two anvils were made of metal of the same metallurgic composition but without ceramics (full metal anvils)

[0199] All six anvils were weighted and thereafter mounted on the same ring of a VSI crusher, to ensure that all anvils were tested under the same conditions. The crusher was used to crush river gravel. After 60 hrs of operation the anvils were removed and weighted again.

[0200] In this test, no improvement was visible with respect to wear resistance for the anvils made with the grains from the Reference Example 1, compared to the full metal anvils. However, it was visually noticeable that the anvils made with grains according to the invention (Example 4) were less worn. Moreover, a comparison of the weight losses indicated that the wear of the anvils according to the invention was 50% lower than for the anvils of the reference examples or the full metal anvils.