Ceramic grains and method for their production

Abstract

The disclosure relates to sintered ceramic grains comprising 3-55 wt. % alumina, 40-95 wt. % zirconia and 1-30 wt. % of one or more other inorganic components. The invention further relates to a method for preparing ceramic grains according to the invention, comprising: making a slurry comprising alumina, zirconia; making droplets of the slurry; introducing the droplets in a liquid gelling-reaction medium wherein the droplets are gellified; drying the gellified deformed droplets.

Claims

1. A metal-ceramic composite wear component comprising: a ceramic structure formed of a three-dimensionally interconnected network of sintered ceramic grains in a metal matrix surrounding at least a part of the ceramic structure; said ceramic structure comprising sintered ceramic grains comprising 3-55 wt. % alumina, 40-95 wt. % zirconia, and one or more other inorganic components in a combined amount of 1-30 wt. %; said one or more other inorganic components comprising at least one component selected from the group consisting of rare earth metal oxides, alkaline earth metal oxides, silicates, carbides, nitrides, and borides; wherein the rare earth metal oxide represents 1-10 wt. % when present; and wherein the sintered ceramic grains are rounded and free of sharp edges.

2. The metal-ceramic composite according to claim 1, wherein the one or more other inorganic components includes a rare earth metal oxide comprising yttrium oxide.

3. The metal-ceramic composite according to claim 2, wherein an yttrium content of the sintered ceramic grains, expressed as yttrium oxide, is 6 wt. % or less.

4. The metal-ceramic composite according to claim 2, wherein an yttrium content of the sintered ceramic grains, expressed as yttrium oxide, is at least 1.5 wt. %, and wherein the one or more other inorganic components further includes 0-2 wt. % cerium, expressed as cerium oxide.

5. The metal-ceramic composite according to claim 1, wherein the sintered ceramic grains are spheroidal when observed at the macroscopic level.

6. The metal-ceramic composite according to claim 1, wherein the sintered ceramic grains have a striated or grooved surface.

7. The metal-ceramic composite according to claim 1, wherein the one or more other inorganic components includes a rare earth metal oxide, and a rare earth metal content of the sintered ceramic grains, expressed as rare earth metal oxide, is 1-5 wt. %.

8. The metal-ceramic composite according to claim 1, wherein the zirconia of the sintered ceramic grains has a tqc ratio in the range of 25-100%, wherein the tqc ratio is defined as: 100% multiplied by the sum of the weights of [tetragonal zirconia, tetragonal-prime zirconia, and cubic zirconia] divided by the sum of the weights of [tetragonal zirconia, monoclinic zirconia, tetragonal-prime zirconia, and cubic zirconia].

9. The metal-ceramic composite according to claim 1, wherein the sintered ceramic grains comprise a calcium content, expressed as calcium oxide, of 0.01-5 wt. %.

10. The metal-ceramic composite according to claim 1, wherein said one or more other inorganic components of the sintered ceramic grains further includes zirconium silicate.

11. The metal-ceramic composite according to claim 1, wherein the sintered ceramic grains are produced by a method comprising: making a slurry comprising alumina, zirconia and a gelling agent; making droplets of the slurry; introducing the droplets in a liquid gelling-reaction medium wherein the droplets are gellified, which liquid gelling-reaction medium preferably comprises at least one component selected from the group of rare earth metal ions and alkaline earth metal ions, which droplets are preferably introduced in the gelling-reaction medium by letting them fall deforming the droplets before, during or after gellification, preferably by impacting the droplets on a deformation mechanism arranged for deforming the droplets upon receiving of the droplets, which deformation mechanism preferably is present at the surface of the gelling-reaction medium or in the gelling-reaction medium; drying the gellified deformed droplets, thereby obtaining dried grains and sintering the dried grains, thereby obtaining the ceramic grains.

12. A comminution device selected from the group consisting of grinding devices and crushing devices comprising the metal-ceramic composite wear component according to claim 1.

13. An abrasive cut-off tool made from the metal-ceramic composite according to claim 1.

14. A composite armour made from the metal-ceramic composite according to claim 1.

15. A dredging pump and tool made from the metal-ceramic composite according to claim 1.

16. A flexible coated abrasive product having an abrasive surface provided with the metal-ceramic composite according to claim 1.

Description

COMPARATIVE EXAMPLE

(1) A batch of ceramic grains produced by melting, quenching and then crushing were commercially obtained from Saint-Gobain (CE) comprising: 59 wt. % alumina, 40 wt. % zirconia (including HfO.sub.2), and 0.80 wt. % yttrium oxide

Examples 1-3

(2) Grains of a different composition 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.

(3) TABLE-US-00001 Raw materials Ex1 Ex2 Ex3 Al.sub.2O.sub.3 38.5 39.8 14.9 ZrSiO4 11.7 Zr(Hf)O2 46.2 58.3 82.1 Y.sub.2O.sub.3 3.1 1.9 3.0 CaCO3 0.5

(4) A slurry of the raw material mixtures 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 0.25 μm.

(5) A 5 wt. % (Ex1) or 0.5 wt. % (Ex2 and Ex3) aqueous solution of gelling agent (sodium alginate) was added to the slurry to obtain a slurry containing about 0.7 wt. % (Ex1) or 1.1 wt. % (Ex2 and Ex3) alginate and about 65 wt. % (Ex1) or 35 wt. % (Ex2 and Ex3), raw materials based on the total dry weight of the slurry.

(6) 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 dihydrate (Ex1) or 2 wt % yttrium nitrate hexahydrate (Ex2 and Ex3).

(7) 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.

(8) 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%.

(9) The dried particles were sintered.

(10) The grain compositions after sintering are indicated in the table below.

(11) TABLE-US-00002 Chemical composition of the grains Ex1 Ex2 Ex3 Al.sub.2O.sub.3 38.5 39.5 14.8 ZrO.sub.2 (+HfO.sub.2) 54 58 81.7 Y.sub.2O.sub.3 3.1 2.5 3.5 SiO.sub.2 3.8 CaO 0.6

(12) Sintering temperature and dwell time are indicated in the Table below.

(13) The sizes distribution (d.sub.10, d.sub.50, d.sub.90) and the sphericity of samples of the produced grains (Ex1-Ex3) and the comparative grains (CE) were determined with a Camsizer®.

(14) The sizes distributions (d.sub.10, d.sub.50, d.sub.90) and the sphericity of samples of the produced grains (Ex1-Ex3) and the comparative grains (CE) were determined with a Camsizer®.

(15) Hardness of the grains was determined as follows by Vickers indentation with a load of 98 N (to be checked with ASTM C 1327).

(16) 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).

(17) TABLE-US-00003 Ex1 Ex2 Ex3 CE Manufacturing Sintering Sintering Sintering Melting, process (direct size (direct size (direct size quenching and shape) and shape) and shape) then crushing Sintering or 1450 1600 1540 2000 Melting temperature (° C.) Dwell time (hrs) 2.5 2.5 2.5 Density 4.74 4.99 5.62 4.6 D10 (mm) 1.436 1.428 1.444 1.072 D50 (mm) 1.714 1.686 1.695 1.461 D90 (mm) 2.031 2.004 1.964 1.875 Sphericity 0.743 0.734 0.766 0.671 Hardness 14 GPa 15 GPa 14 GPa 16-18 GPa α-Al.sub.2O.sub.3 34.7 39.5 14.8 61 ZrO.sub.2 tetragonal 36.9 49.5 69.2 33 ZrO.sub.2 tetragonal 7.3 9.5 14.5 1 prime ZrO.sub.2 monoclinic 3.1 1.5 1.5 4 ZrC 1 Mullite 3 (3Al.sub.2O.sub.3•2SiO.sub.2) Spinel (MgAl.sub.2O.sub.4) Amorphous 15 phase.sup.1 Tqc 93 97.5 98.2 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.

(18) Binocular view photographs of whole grains (FIGS. 1.1-1.3), microscope views of polished cross-sections (FIGS. 2.1-2.3) and electronic microscope views (FIGS. 3.1-3.3, scale bar is 10 μm; FIGS. 4.1-4.3; scale bare is 10 μm) were made of the grains.

(19) Comparative images were made of grains of Comparative Example 1 (FIGS. 1.4, 2.4, 3.4 and 4.4 respectively).

(20) 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.

(21) The whitish parts are zirconia.

(22) The darker parts alumina/mullite/spinel/anorthite/amorphous phase.

Example 4

(23) Two 3D-open porous ceramic structures for preparing an anvil of a Vertical Shaft Impactor (VSI) crusher were made of the grains prepared using the methodology as described in Examples 1-3.

(24) The grains had the following composition:

(25) TABLE-US-00004 Aluminum Oxide 38.4% Zirconium Oxide 54.0% Silicon oxide  3.8% Yttrium oxide 3.10% Calcium oxide 0.60%

(26) 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 1

(27) Grains were provided using the methodology of EP 930 948. They had the following composition:

(28) TABLE-US-00005 Aluminum Oxide 60.0% Zirconium Oxide 39.0% Titanium Oxide 0.15% Silica 0.35% Iron Oxide 0.15% Sodium Oxide 0.03% Calcium Oxide 0.09% Magnesium Oxide 0.02% Yttria 0.80%

(29) Two ceramic structures of the same design as the structure of Example 4 were made using the grains of the Reference Example, using the same method.

Example 5

(30) From the ceramic structures of Example 4 and the ceramic structures of the Reference Example 1, 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.

(31) Further two anvils where made of metal of the same metallurgic composition but without ceramics (full metal anvils).

(32) 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.

(33) In this application, 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.

Example 6

(34) One roller of a vertical roller mill was made with grains made with a method according to the invention, using the methodology as described in Examples 1-3. The grains had the following composition:

(35) TABLE-US-00006 Aluminum Oxide 14.8% Zirconium Oxide 81.7% Yttrium oxide 3.50%

(36) The ceramic structure for the roller was made using the same methodology as in Example 4. The ceramic-metal roller was made using the same methodology as in Example 5.

(37) Further, a ceramic reference roller (Reference Example 2) was made in the same manner, except that the grains described in Reference Example 1 were used to make the ceramic structure.

(38) Further, a roller of a vertical roller mill was made with the same metallurgical composition but without any ceramic grains to be used as a reference (full metal roller).

(39) The three rollers were weighted before and after the wear test.

(40) The three rollers were mounted in the same mill in a cement factory. They were thus subjected to the same operating conditions. After 3000 h of operation, the rollers were removed and weighted.

(41) It was observed that the ceramic reference was less worn than the full metal roller. Its weight loss was 22% less compared to the full metal roller. The roller according to the invention was visually less worn than both the other rollers. Moreover, the weight losses indicated that the wear is 80% lower. Thus the wear resistance of the roller made with the grains of the present invention was considerably better than the wear resistance of the roller of Reference Example 2.