Zirconia dispersion for use in forming nano ceramics

Abstract

This invention relates to an aqueous dispersion of nanoparticles, the nanoparticles comprising, on an oxide basis: (a) 85-100 wt % ZrO.sub.2+HfO.sub.2, (b) 0-15 wt % Y.sub.2O.sub.3, and (c) 0-2 wt % Al.sub.2O.sub.3, wherein the dispersion has a polydispersity index of 0.10-0.17. The invention also relates to a method of forming a ceramic article comprising the steps of: (a) pouring the aqueous dispersion into a mould, (b) drying the aqueous dispersion in the mould to form a green body, and (c) sintering the green body to form the ceramic article.

Claims

1. An aqueous dispersion of nanoparticles, the nanoparticles comprising, on an oxide basis: (a) 85-100 wt % ZrO.sub.2+HfO.sub.2; (b) 0-15 wt % Y.sub.2O.sub.3; (c) 0-2 wt % Al.sub.2O.sub.3; and wherein the dispersion has a polydispersity index of 0.10-0.17, a nanoparticle content of 20-65 wt %, and a crystallite size of 10-20 nm.

2. The aqueous dispersion of nanoparticles of claim 1, wherein the polydispersity index of the dispersion is 0.11-0.16.

3. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a Z-average particle size of 30-60 nm.

4. The aqueous dispersion of nanoparticles of claim 1, wherein the nanoparticles comprise, on an oxide basis, 0.5-10 wt % Y.sub.2O.sub.3 and 0-1 wt % Al.sub.2O.sub.3.

5. The aqueous dispersion of nanoparticles of claim 1, wherein any second or subsequent peak in particle size distribution by intensity of the dispersion has an intensity of 0-15%.

6. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a PDI width of 10-20 nm.

7. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a particle size distribution as measured by intensity having a d10 value in a range of 25-40 nm.

8. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a particle size distribution as measured by intensity having a d50 value in a range of 35-60 nm.

9. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a particle size distribution as measured by intensity having a d90 value in a range of 60-100 nm.

10. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion comprises 0.5-6 wt % of a dispersant based on oxide content.

11. The aqueous dispersion of nanoparticles of claim 10, wherein the dispersant is an amino acid.

12. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a viscosity of <100 cPs.

13. The aqueous dispersion of nanoparticles of claim 1, wherein an amount of each of Fe, Cr, Ni and Ce in the dispersion is individually <20 ppm.

14. The aqueous dispersion of nanoparticles of claim 1, wherein the dispersion has a zeta potential of 20-50 mV.

15. An aqueous dispersion of nanoparticles, the nanoparticles comprising, on an oxide basis: (a) 85-100 wt % ZrO.sub.2+HfO.sub.2; (b) 0.5-15 wt % Y.sub.2O.sub.3; (c) 0-2 wt % Al.sub.2O.sub.3; and wherein the dispersion has a polydispersity index of 0.10-0.17 and a crystallite size of 10-20 nm.

16. The aqueous dispersion of nanoparticles of claim 15, wherein the dispersion has a nanoparticle content of 20-65 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This invention will be further described by reference to the following Figures, which are not intended to limit the scope of the invention claimed, in which:

(2) FIG. 1 shows a graph of particle size distribution by intensity for Example 1 and Comparative Example 10,

(3) FIG. 2 shows a graph of particle size distribution by intensity for Example 1 and Comparative Examples 13,

(4) FIG. 3 shows a TEM image of dried particles of Example 1,

(5) FIG. 4 shows XRD overlays of Examples 4-9 showing the elimination of monoclinic phase in the materials, and

(6) FIG. 5 shows a the green bodies of Example 1 (left) and Comparative Example 10 (right) showing the difference in green density.

DETAILED DESCRIPTION

Examples

(7) Nanodispersions were prepared as set out below. The dispersions were tested as set out below, with the results shown in Tables 2, 3 and 4 below.

(8) Solids Content

(9) A small portion of each was placed in an evaporation dish and put in a pre-heated oven set to 130 C. The dispersions were dried overnight until a constant weight was obtained. The solids content was obtained via the following equation:
% solids of dispersion=(dry weight of dispersion (g)/initial weight of dispersion (g))100
Particle Size

(10) Particle size measurements were made using a Malvern Zetasizer Nano ZS instrument, model ZEN3600, using a red laser of wavelength 633 nm. Each sample was first diluted to 0.5 wt. % using deionised water. 1 ml of the diluted sample was then placed in a DTS0012 disposable cuvette. The cuvette was loaded into the instrument and allowed to equilibrate to 25 C. A standard operating procedure (SOP) was created with the following parameters set: material refractive index 2.20, and material absorption value of 0.01 units. The dispersant refractive index (in this case, the continuous phase, ie water) was 1.33 and the dispersant viscosity was 0.8872 cP. The instrument was set to automatically adjust the laser position and attenuator settings to obtain the best measurement of particle size. A backscattering angle of 173 was used. The method of Dynamic Light Scattering (DLS) was used to calculate the particle size. A total of three measurements were taken with the cuvette being inverted between measurements. The three measurements were then averaged to give a final particle size result. The Z-average size or cumulant mean is a mean calculated from the intensity distribution and the calculation is based on assumptions that the particles are mono-modal, mono-dispersed and spherical. The polydispersity index (PDI) is a measure of the breadth of the particle size distribution and is calculated along with the Z-average size in the cumulant analysis of the intensity distribution. The PDI width is calculated by taking the square root of the PDI and multiplying this by the Z-average. The calculations for the Z-average size, polydispersity index and PDI width are defined in the ISO 22412:2017 Particle size analysisby Dynamic Light Scattering (DLS).

(11) Zeta Potential and Conductivity

(12) Zeta potential and conductivity measurements were made using a Malvern Zetasizer Nano ZS instrument, model ZEN3600. Each sample was first diluted to 0.5 wt. % using deionised water and placed in a DTS1070 disposable folded capillary cell. The cell was loaded into the instrument and allowed to equilibrate to 25 C. A standard operating procedure (SOP) was created with the following parameters set: material refractive index 2.20, and material absorption value of 0.01 units. The dispersant refractive index was 1.33, the dispersant viscosity was 0.8872 cP and the dielectric constant was 78.5. The instrument was set to automatically adjust the number of runs taken and was set to take five sets of measurements with a thirty second delay between measurements. The five measurements were then averaged to give the final zeta potential and conductivity.

(13) XRD/Crystallite Size

(14) A small portion of each sample was placed in an evaporation dish and placed in a pre-heated oven set to 130 C. The sols were dried overnight until a constant weight was obtained. The dry mass was ground in a pestle and mortar and passed through a 250 micron sieve to create a uniform powder. The powder samples were loaded into a sample holder where a generous portion of powder was placed in the holder. The powder was pressed down firmly using a microscope slide to create a level surface, with any excess powder being removed. The samples were analysed via powder X-ray diffraction (XRD) using a Bruker D8 Advance with a Copper K radiation source (A=1.5418 ) over a scan range of 10-85 degrees, a 2theta with a step size of 0.015 degrees 2theta and a 0.2 second duration per step with a 1 mm divergence slit. The recorded diffraction patterns were analysed using the Diffract Eva software to determine crystallite size by using the Scherrer method, K=0.9 and selecting the area between 26.0-33.0 degrees 2theta. Topas software was used to determine phase analysis whereas the default monoclinic, tetragonal and cubic structures were loaded into the software and each scan run against the defaults. Note tetragonal and cubic phases are reported combined in the examples.

(15) Viscosity Measurements

(16) Viscosity measurements were collected using the DIN 53019 coaxial cylinder30 mm diameter and loaded with 20 ml of sample. Each sample was left to equilibrate to 20 C. by placing it in a water bath for thirty minutes before running the measurement. Measurements were carried out using a Bohlin Visco 88 Viscometer. Ten measurements would be taken at 200 s.sup.1 shear rate with an average being calculated. This procedure was carried out for all samples by diluting a small portion of the sols with deionised water to a solids content of 55.0 wt %. The measured solids content as described above was used to calculate the dilution to ensure all samples were tested under equivalent solids loadings.

Example 1

(17) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738 a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an total oxide content of 25% by weight. This dispersion had a starting particle size of 1.4 microns measured via laser diffraction. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear (>1,000,000 s.sup.1) in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide (ie 2 wt % relative to the weight of the oxide). The final concentration was increased to 56.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 43.7 nm, a PDI of 0.140 and a PDI Width of 16.4 nm. The powder XRD results gave a crystallite size of 12 nm and a phase analysis of 1.4% monoclinic and 98.6% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.748 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 2

(18) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 58.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 46.8 nm, a PDI of 0.142 and a PDI Width of 17.6 nm. The powder XRD results gave a crystallite size of 12 nm and a phase analysis of 0.9% monoclinic and 99.1% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.720 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 3

(19) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 59.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 42.8 nm, a PDI of 0.122 and a PDI Width of 15.0 nm. The powder XRD results gave a crystallite size of 12 nm and a phase analysis of 1.5% monoclinic and 98.5% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.710 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 4

(20) An aqueous dispersion of a zirconium hydrous oxide was prepared by taking XZ02732, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 100:0:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 45.0 nm, a PDI of 0.115 and a PDI Width of 15.3 nm. The powder XRD results gave a crystallite size of 14 nm and a phase analysis of 32.9% monoclinic and 67.1% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.732 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 5

(21) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02733, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 98.2:1.8:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 46.1 nm, a PDI of 0.139 and a PDI Width of 17.2 nm. The powder XRD results gave a crystallite size of 13 nm and a phase analysis of 22.1% monoclinic and 77.9% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.749 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 6

(22) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02734, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 96.4:3.6:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 42.4 nm, a PDI of 0.140 and a PDI Width of 15.8 nm. The powder XRD results gave a crystallite size of 13 nm and a phase analysis of 7.1% monoclinic and 92.9% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.750 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 7

(23) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02735, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.7:5.3:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 58.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 45.2 nm, a PDI of 0.116 and a PDI Width of 15.4 nm. The powder XRD results gave a crystallite size of 14 nm and a phase analysis of 2.3% monoclinic and 97.7% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.725 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 8

(24) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02736, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 92.9:7.1:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2.25 wt % on oxide. The final concentration was increased to 56.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 44.4 nm, a PDI of 0.159 and a PDI Width of 17.7 nm. The powder XRD results gave a crystallite size of 11 nm and a phase analysis of 0.8% monoclinic and 99.2% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.731 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Example 9

(25) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02737, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 91.2:8.8:0, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under high shear in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2.5 wt % on oxide. The final concentration was increased to 59.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 43.5 nm, a PDI of 0.152 and a PDI Width of 17.0 nm. The powder XRD results gave a crystallite size of 11 nm and a phase analysis of 0.6% monoclinic and 99.4% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.733 g/cm.sup.3. All of the green bodies survived de-binding and sintering at 1150 C. for 2 hours to form a crack free ceramic piece.

Comparative Example 10

(26) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under low shear (50,000 s.sup.1) in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 73.2 nm, a PDI of 0.226 and a PDI Width of 34.8 nm. The powder XRD results gave a crystallite size of 11 nm and a phase analysis of 3.9% monoclinic and 96.1% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 3.040 g/cm.sup.3. Upon de-binding, all of the green bodies fractured inside of the furnace.

Comparative Example 11

(27) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged at >80 C. and subjected to at least 24 hours mixing under lower shear (35,000 s.sup.1) in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 93.3 nm, a PDI of 0.208 and a PDI Width of 42.6 nm. The powder XRD results gave a crystallite size of 11 nm and a phase analysis of 4% monoclinic and 96.0% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.881 g/cm.sup.3. Upon de-binding, all of the green bodies fractured inside of the furnace. This comparative example demonstrates the importance of using high shear mixing when preparing the dispersions of the invention.

Comparative Example 12

(28) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged and subjected to milling for 1 hour as per patent U.S. Pat. No. 9,822,039 B1 Comparative Example 1, in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 39.2 nm, a PDI of 0.180 and a PDI Width of 16.6 nm. The powder XRD results gave a crystallite size of 14 nm and a phase analysis of 6.0% monoclinic and 94.0% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.881 g/cm.sup.3. Upon de-binding, small cracks appeared inside the ceramic. Upon sintering at 1150 C. for 2 hours, the cracks propagated and the ceramics split into multiple pieces. This comparative example demonstrates the importance of the ageing and mixing techniques used when preparing the dispersions of the invention.

Comparative Example 13

(29) An aqueous dispersion of an yttrium doped zirconium hydrous oxide was prepared by taking XZ02738, a material grade from Luxfer MEL Technologies with a ratio of oxides of zirconium:yttrium:aluminium of 94.45:5.3:0.25, which was made up to 500 g using deionised water to give an active content of 25% by weight. This dispersion was aged and subjected to milling for 2 hours as per patent U.S. Pat. No. 9,822,039 B1 Comparative Example 1, in the presence of an amino acid dispersant (3-aminopropanoic acid), added at 2 wt % on oxide. The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion, measured via DLS, was a Z-Ave of 30.3 nm, a PDI of 0.181 and a PDI Width of 13.0 nm. The powder XRD results gave a crystallite size of 13 nm and a phase analysis of 2.4% monoclinic and 97.6% tetragonal/cubic phase. A green body was prepared by following the method of Example 1 of US 2016/0095798 A1, resulting in a green density of 2.873 g/cm.sup.3. Upon de-binding, small cracks appeared inside the ceramic. Upon sintering at 1150 C. for 2 hours, the cracks propagated and the ceramics split into multiple pieces. This comparative example is the same as Comparative Example 12 except that the milling time is 2 hours.

(30) The compositions of the nanodispersions are summarised in Table 1 below:

(31) TABLE-US-00001 TABLE 1 Sample ZrO.sub.2 + HfO.sub.2 Y.sub.2O.sub.3 Al.sub.2O.sub.3 Name wt % wt % wt % Example 1 94.45 5.3 0.25 Example 2 94.45 5.3 0.25 Example 3 94.45 5.3 0.25 Example 4 100 0 0 Example 5 98.2 1.8 0 Example 6 96.4 3.6 0 Example 7 94.7 5.3 0 Example 8 92.9 7.1 0 Example 9 91.2 8.8 0 Comparative 94.45 5.3 0.25 Example 10 Comparative 94.45 5.3 0.25 Example 11 Comparative 94.45 5.3 0.25 Example 12 Comparative 94.45 5.3 0.25 Example 13

(32) TABLE-US-00002 TABLE 2 Pk 1 Pk 2 Pk 1 Pk 2 Mean Mean Area Area Pdl Solids Zeta Sample Z-Ave Int Int Int Int D(i)10 D(i)50 D(i)90 D(i)95 D(i)99 Width % @ Potential Name (d.nm) Pdl (d.nm) (d.nm) (%) (%) (nm) (nm) (nm) (nm) (nm) (d.nm) 130 C. pH (mV) Example 1 43.7 0.140 50.5 0 100 0 28.0 46.4 79.5 90.9 116 16.4 56.0 4.5 38.7 Average Example 2 46.8 0.142 54.7 0 100 0 29.3 51.1 86.9 98.4 119 17.6 58.0 4.0 40.1 Average Example 3 42.8 0.122 47.0 0 100 0 31.2 45.3 66.1 73.3 86.4 15.0 59.5 4.2 40.2 Average Example 4 45.0 0.115 50.5 0 100 0 31.3 48.0 74.5 83.2 100 15.3 57.5 3.3 41.5 Average Example 5 46.1 0.139 53.5 0 100 0 32.1 50.6 79.4 89.4 107 17.2 57.5 4.2 40.2 Average Example 6 42.4 0.140 49.9 0 100 0 27.2 45.1 75.6 87.7 162 15.8 57.0 3.9 31.9 Average Example 7 45.2 0.116 48.6 0 100 0 32.7 47.0 67.4 74.6 86.8 15.4 58.0 4.0 37.0 Average Example 8 44.4 0.159 51.6 0 100 0 26.6 48.7 81.9 91.1 110 17.7 56.5 4.3 39.7 Average Example 9 43.5 0.152 48.6 0 100 0 29.5 45.9 72.7 81.2 99.5 17.0 59.5 4.2 36.1 Average

(33) TABLE-US-00003 TABLE 3 Pk 1 Pk 2 Pk 1 Pk 2 Mean Mean Area Area Pdl Solids Zeta Sample Z-Ave Int Int Int Int D(i)10 D(i)50 D(i)90 D(i)95 D(i)99 Width % @ Potential Name (d.nm) Pdl (d.nm) (d.nm) (%) (%) (nm) (nm) (nm) (nm) (nm) (d.nm) 130 C. pH (mV) Comparative 73.2 0.226 104.4 36.7 79.1 20.9 34.8 90.7 148 164 194 34.8 57.0 4.1 44.7 Example 10 Average Comparative 93.3 0.208 118.7 38.7 88.9 11.1 49.5 108 174 192 232 42.6 57.0 4.0 43.1 Example 11 Average Comparative 39.2 0.180 46.8 15.9 91.6 8.4 24.7 43.8 66.2 73.4 86.3 16.6 57.0 4.4 43.7 Example 12 Comparative 30.3 0.181 33.0 0 100 0 21.9 32.0 46.1 50.0 57.6 13.0 57.5 4.5 45.6 Example 13

(34) TABLE-US-00004 TABLE 4 Sample Name Viscosity/cP Example 1 4.6 Example 2 9.3 Example 3 7.6 Example 4 8.9 Example 5 4.5 Example 6 9.1 Example 7 5.8 Example 8 10.9 Example 9 9.7 Comparative Example 10 135 Comparative Example 11 176 Comparative Example 12 8.4 Comparative Example 13 9.6

(35) In relation to the figures, FIG. 1 compares particle size by intensity graphs for Example 1 and Comparative Example 10. This shows a monomodal peak of smaller size for Example 1 compared to the bimodal and larger size peak for Comparative Example 10. FIG. 2 shows a similar comparison for Examples 1 and Comparative Example 13. In this case, this shows the larger size peak achieved by Example 1.

(36) FIG. 3 shows a TEM image of the dried particles obtained in Example 1. This confirms that the particle size distribution is close to that measured by DLS, as well as highlighting the narrow distribution of the particles.

(37) The XRD overlays in FIG. 4 show the crystallinity of the nanoparticles of the invention. The arrows in FIG. 4 indicate the reduction in the 28 2theta peak relating to the monoclinic phase as the level of Y.sub.2O.sub.3 is increased through Examples 4-9.

(38) FIG. 5 is a photograph of green bodies formed in accordance with Example 1 (left) and Comparative Example 10 (right). As is clearly indicated, the left disc is wide and thin, whereas the right one is taller and narrower. Also, the green body formed by Comparative Example 10 had a crack in it, indicated by the circle in FIG. 5. This is understood to be due to the packing of the particles in the respective green bodies. The left disc (Example 1) has a narrower particle size range (essentially, more particles of a similar size). These particles pack together leaving voids in the green body for moisture/organics to escape during drying. This allows the green body to dry quicker and retain its shape. In contrast, the right disc (Comparative Example 10) has a bimodal particle size distribution, allowing smaller particles to fit into the voids around the larger particles. This means that the green body dries slower, the outside of the disc drying first whilst the middle retains moisture and then contracts. This results in a taller, narrower disc.