CN113727956A

CN113727956A - Zirconia dispersion for forming nanoceramics

Info

Publication number: CN113727956A
Application number: CN201980091355.7A
Authority: CN
Inventors: W.怀斯曼
Original assignee: Magnesium Elektron Ltd
Current assignee: Magnesium Elektron Ltd
Priority date: 2019-02-05
Filing date: 2019-02-05
Publication date: 2021-11-30
Anticipated expiration: 2039-02-05
Also published as: JP7330277B2; JP2022521369A; WO2020161451A1; WO2020161451A9; CN113727956B; EP3921292A1

Abstract

The invention relates to the aqueous content of nanoparticlesA dispersion, said nanoparticles comprising, in oxide basis: (a)85-100 wt% ZrO₂+HfO₂(b) 0-15% by weight of Y₂O₃And (c)0-2 wt.% Al₂O₃Wherein the dispersion has a polydispersity index of 0.10 to 0.17. The present invention also relates to a method of forming a ceramic article comprising the steps of: (a) pouring the aqueous dispersion into a mold, (b) drying the aqueous dispersion in the mold to form a green body, and (c) sintering the green body to form a ceramic article.

Description

Zirconia dispersion for forming nanoceramics

Technical Field

The present invention relates to an aqueous dispersion of zirconia particles, optionally comprising yttria and alumina, for forming nanoceramics.

Background

Nanoceramics are ceramics with an average grain (grain) size in the range of 1-200 nm. The advantages of nanoceramics are known and include their exhibiting greatly improved mechanical and optical properties and other phenomena not exhibited by conventional submicron ceramics. Work by Binner et al (US 2011/0230340 a1) states that yttrium doped zirconia ceramics having an average grain size of 190nm or less exhibit hydrothermal resistance as well as excellent wear resistance properties. These enhanced properties make nanoceramics excellent materials for a wide range of applications including use in: in the electronics industry, in cell phone housings, glass and watch cases, in the abrasives market via tougher abrasive materials (wearables), and in the healthcare market, for example, in implants. One application of nanoceramics including zirconia is as dental (dental) ceramic materials. For example, US2016/0095798a1 and US 9,820,917B 1 relate to zirconia dental ceramics formed from a suspension of zirconia nanoparticles and gels made from such suspensions. The ceramics described in these documents are said to have translucency, opalescence and desirable physical properties. US2016/0095798a1 also contains a substantial discussion of earlier patents related to zirconia dental articles and patents, patent applications and journal articles in the more general field of zirconia ceramics and processing methods.

The process for forming a zirconia dental article described in US2016/0095798a1 comprises the steps of: (i) forming a zirconia nanoparticle suspension into a suitable shape to form a wet zirconia green body, (ii) drying the wet green body to produce a zirconia green body, (iii) heating the zirconia green body to a zirconia brown body, and (iv) sintering the zirconia brown body to form an opalescent zirconia sintered body.

A problem with drying nanomaterials such as those described in US2016/0095798a1 and US 9,820,917B 1 is that the particles may agglomerate and no longer possess the true nanoparticle properties. In order to try and overcome this problem, US2016/0095798a1 mentions in example 6 that the suspension is dried for 15 days to slow down the process. This process is not only time consuming but also expensive (if the part is damaged during a lengthy drying period).

A potential problem with this extended drying process is that when a dense green body has been formed, de-greasing (resin removal) must occur to remove any organics or volatiles from the ceramic. Dense green bodies will result in smaller voids in the material and if they are not large enough to allow organics or volatiles to escape, pressure can build up within the green body and cause cracks and damage in the resulting ceramic.

It is desirable to minimize the number of damage in the resulting ceramic to reduce the manufacturing cost of the zirconia nanoceramic. Accordingly, methods and materials for reducing the rate of damage to zirconia dental ceramics are continually being sought.

Disclosure of Invention

The invention relates to an aqueous dispersion of nanoparticles comprising, in terms of oxides:

(a) ZrO amounting to 85 to 100% by weight₂+HfO₂，

(b)0-15 wt.% Y₂O₃And are and

(c)0-2 wt.% Al₂O₃，

Wherein the dispersion has a polydispersity index of 0.10 to 0.17.

It is desirable to adjust the inventive dispersion to have defined particle size properties to suppress the particle packing (pack) pattern when forming the green body. Thus, the green density of the material will be lower than conventional ceramics.

In the inventionHerein, the term "nanoparticle" is used to refer to a particle that: in the particles, one or more external dimensions are in the size range of 1nm to 100nm for 50% or more of the particles in the number (number) size distribution. At the time of writing, this is a recommended definition of nanomaterials, such as "Association RECOMMENDATIONs for nanomaterial definition on 10.2011, 18 (Commission record of 18)^thOctober 2011 on the definition of nano materials) (2011/696/EU) ".

Generally, a dispersion is a system in which solid particles are dispersed in a continuous phase having a different composition. The term "dispersion" as used in connection with the present invention is intended to refer to a system in which solid nanoparticles are dispersed in a liquid phase or medium (in this case, water). The dispersion may optionally include additives such as surfactants to increase the stability of the dispersion. Such additives are known to those skilled in the art. The term "nanodispersion" is used to refer to a dispersion of nanoparticles. The dispersion of the present invention may be defined as a colloid, i.e. a dispersion of particles having at least one dimension in the size range of 1nm to 1 μm. More particularly, a dispersion may be defined as a colloidal sol, i.e., a colloid in which the dispersed phase is a solid and the continuous phase is a liquid.

In the context of the present invention, the term aqueous is used to refer to dispersions in which the liquid phase may comprise at least 75 wt% water, more particularly at least 90 wt% water, even more particularly at least 95 wt%. In some embodiments, the liquid phase may comprise at least 98 wt% water, more particularly substantially 100 wt% water. The liquid phase may need to include a solvent such as an organic solvent and particularly a polar solvent such as an alcohol.

In some embodiments, it may be beneficial to add a suitable dispersant to the dispersion, particularly for high solids content (e.g., > 35% by weight) dispersions. Suitable dispersing agents are those capable of providing electrostatic repulsion between nanoparticles, steric interaction between particles, or electro-steric repulsion between particles. Examples of such dispersants include amino acids such as glycine (2-aminoacetic acid), alanine and its isomers (2-aminopropionic acid, 3-aminopropionic acid) and valine and its isomers (D-2-amino-3-methylbutyric acid, L-2-amino-3-methylbutyric acid). In particular, the dispersant may be 3-aminopropionic acid.

In particular, the dispersion may comprise from 0.5 to 6% by weight, more particularly from 1.0 to 4.0% by weight, even more particularly from 1.5 to 3.0% by weight, of dispersant (based on the oxide content).

In particular, the nanoparticles may comprise, calculated as oxide, 90 to 100% by weight of ZrO₂+HfO₂. More particularly, the nanoparticles may comprise, calculated as oxide, 0.5-10 wt.% Y₂O₃More particularly 1-9 wt% Y₂O₃. In particular, the nanoparticles may comprise, calculated as oxide, 0-1% by weight of A1₂O₃More particularly 0-0.5% by weight of A1₂O₃。

More particularly, the dispersion can have a nanoparticle content of 0.5 to 65 wt.%, more particularly 10 to 63 wt.%, even more particularly 20 to 62 wt.%. In some embodiments, the dispersion may have a nanoparticle content of 50-60 wt%. This may also be referred to as solids content. The solids content can be varied by techniques such as dilution, evaporation, membrane filtration, microfiltration, centrifugation. More particularly, the technique may be dilution, evaporation or membrane filtration.

In particular, the dispersion may have a polydispersity index of 0.11 to 0.16. More particularly, the polydispersity index (PDI) can be measured by Dynamic Light Scattering (DLS).

More particularly, the dispersion may have a pH of 1 to 7, even more particularly 2 to 6, more particularly 3 to 5.

In particular, the dispersion may have a Z-average particle size of 30-60nm, more particularly 35-55nm, even more particularly 40-50 nm. In particular, the Z-average particle size can be measured by Dynamic Light Scattering (DLS).

More particularly, the dispersion may have a zeta potential of 20 to 50mV, even more particularly 25 to 45mV, more particularly 30 to 42 mV.

More particularly, any secondary or sub-peak (substequent peak) in the particle size distribution of the dispersion by intensity may have an intensity of 0-15%, even more particularly 0-10%. In connection with the present invention, the term "secondary or secondary peak" is used to refer to any peak in the particle size in intensity distribution as measured by Dynamic Light Scattering (DLS) except the highest intensity peak. The percentage is a measure of the area under the peak, i.e., if there are two peaks, peak 1 has an area of (100-x) and peak 2 has an area of x.

In particular, the dispersion may have a PDI breadth of 10-20nm, more particularly 12-18 nm. More specifically, the PDI width may be measured by Dynamic Light Scattering (DLS).

More particularly, the dispersion may have a particle size distribution, measured by intensity, having a d10 value in the range of 25-40nm, even more particularly in the range of 26-34 nm.

In particular, the dispersion may have a particle size distribution, measured by intensity, having a d50 value in the range of 35-60nm, more particularly in the range of 45-53 nm.

More particularly, the dispersion may have a particle size distribution, measured by intensity, having a d90 value in the range of 60-100nm, even more particularly in the range of 65-90 nm.

In particular, d10, d50, and d90 can be measured by Dynamic Light Scattering (DLS).

In particular, the green density of the green body formed from the dispersion of the invention by following the method of example 1 in US2016/0095798 is preferably such that<2.800g/em³And even more preferably<2.760g/cm³. These green density figures are lower than the green densities often obtained by forming green bodies from powders. Without wishing to be bound by any theory, it is believed that this increases the survival rate of the green body during drying.

In particular, the dispersion may have<100cP, more particularly<30cP, even more particularly<Viscosity of 20 cP. More particularly, the viscosity can be used for 200s^-1The shear rate of (2) is measured at 20 ℃.

According to a further aspect of the present invention, there is provided a solid metal oxide obtainable by drying the above dispersion. In particular, the metal oxide may be in the form of a powder. More particularly, the drying may be carried out at 130 ℃ until a substantially constant mass is reached. In particular, the powder may be obtained by milling.

In particular, the nanoparticles may comprise a monoclinic phase and a tetragonal/cubic combined phase when measured by powder X-ray diffraction (XRD) at 2-theta between 10 ° and 85 °.

In particular, the crystallite (crystallite) size of the nanoparticles may be 10-20nm, more particularly 10-15 nm.

In particular, the nanoparticles may comprise a monoclinic phase and a tetragonal/cubic phase when measured by raman spectroscopy.

It is desirable to control the level of minor components in ceramics, especially when used as precursors for color-conscious dental implants. In some embodiments, it may be desirable to control minor ingredients in the dispersion, such as Fe, Cr, Ni, Ce, Co, Mn, Er, Pr, Nd, Tb, Cu, Bi, and compounds thereof, such as oxides. More particularly, the respective amounts of these minor ingredients in the dispersion may be <20ppm, even more particularly <10ppm, respectively. Since all of them add color to the sintered ceramic. More particularly, it may be desirable to control the levels of Fe, Cr, Ni and Ce in the dispersion. In particular, the respective amounts of these minor ingredients in the dispersion may be <20ppm, more particularly <10ppm, respectively. It may also be desirable to control the amount of other elements in the dispersion, such as Na, K, S, N, C, Cl, Si and Ti, especially Na, Cl, Si and Ti, in order to avoid detrimental sintering effects. More particularly, the respective amounts of these components in the dispersion may be <200ppm, even more particularly <100ppm, respectively.

In a further embodiment, the present invention relates to a method of forming a ceramic article comprising the steps of:

(a) the aqueous dispersion as described above is poured into a mould,

(b) drying the aqueous dispersion in the mold to form a green body, and

(c) sintering the green body to form the ceramic article.

In particular, step (c) may comprise the step of grinding and/or polishing the ceramic article after sintering. In some embodiments, the method may include, between steps (b) and (c), the step of pre-sintering the green body to remove any dispersant and form a pre-sintered body. Step (c) will further comprise sintering the pre-sintered body to form a ceramic article. More particularly, the method may comprise a step of shaping (shaping) the pre-sintered body after the pre-sintering step but before step (c).

In particular, the composition of the nanoparticles of the present invention can be varied to make ceramics for a range of applications. Undoped ZrO₂Nanoparticle dispersions have filtration applications and non-temperature sensitive (thermosensitive) applications. Y is₂O₃Doped ZrO₂Nanoparticle dispersions offer a wide range of uses from structural applications such as wear parts and abrasives to functional applications such as oxygen sensors and fuel cells. Thus, to control the identity of the material with respect to its crystal structure while retaining the desired Z-average particle size and polydispersity index (PDI), Y in the nanoparticle dispersion is controlled₂O₃Levels are useful.

The invention will be further described with reference to the following figures, which are not intended to limit the scope of the claims of the present invention, in which:

figure 1 shows a graph of the particle size distribution by intensity for example 1 and comparative example 10,

FIG. 2 shows a graph of the particle size distribution by intensity for example 1 and comparative example 13,

figure 3 shows a TEM image of the dried particles of example 1,

FIG. 4 shows an XRD stack of examples 4-9 showing the elimination of monoclinic phases in the material, and

fig. 5 shows the green bodies of example 1 (left) and comparative example 10 (right), showing the difference in green density.

Examples

The nanodispersions were prepared as set forth below. The dispersions were tested as set forth below, with the results shown in tables 2, 3 and 4 below.

Solids content

A small portion of each was placed in an evaporation dish and placed in a pre-heated oven set at 130 ℃. The dispersion was dried overnight until a constant weight was obtained. The solids content is obtained via the following equation:

solid% of dispersion (dry weight of dispersion (g)/initial weight of dispersion (g)) x 100

Particle size

Particle size measurements were performed using a Malvern Zetasizer Nano ZS instrument model ZEN3600, using a red laser at a wavelength of 633 nm. Each sample was first diluted to 0.5 wt% using deionized water. Then 1ml of the diluted sample was placed in a DTS0012 disposable tube. The tube was loaded into the instrument and allowed to equilibrate to 25 ℃. The Standard Operating Program (SOP) is formed from the following set of parameters: the material refractive index was 2.20, and the material absorption value was 0.01 units. The dispersant refractive index (continuous phase, i.e., water in this case) 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 particle size measurements. A backscattering angle of 173 ° was used. Particle size was calculated using the Dynamic Light Scattering (DLS) method. A total of three measurements were taken with the cuvette flipped between measurements. The three measurements were then averaged to obtain the final particle size result. The Z-average size or cumulative average is the average calculated from the intensity distribution and the calculation is based on the following assumptions: the particles are monomodal, monodisperse and spherical. The polydispersity index (PDI) is a measure of the breadth of the particle size distribution and is calculated in the cumulative analysis of the intensity distribution along with the Z-average size. The PDI width is calculated by taking the square root of the PDI and multiplying it by the Z-average. The calculations for Z-average size, polydispersity index and PDI breadth are defined in ISO 22412: 2017 "Particle size analysis-by Dynamic Light Scattering (DLS)".

Zeta potential and conductivity

Zeta potential and conductivity measurements were made using a Malvern Zetasizer Nano ZS instrument model ZEN 3600. Each sample was first diluted to 0.5 wt% using deionized water and placed in a DTS1070 disposable folded capillary cell. The cell was loaded into the instrument and allowed to equilibrate to 25 ℃. The Standard Operating Program (SOP) is formed from the following set of parameters: the material refractive index was 2.20, and the material absorption value was 0.01 units. The refractive index of the dispersant was 1.33, the viscosity of the dispersant was 0.8872cP, and the dielectric constant was 78.5. The instrument is set to automatically adjust the number of runs taken and to acquire five sets of measurements with a thirty second delay between measurements. The five measurements were then averaged to obtain the final zeta potential and conductivity.

XRD/crystallite size

A small portion of each sample was placed in an evaporation dish and placed in a pre-heated oven set at 130 ℃. The sol was dried overnight until a constant weight was obtained. The dried material was ground in a mortar and pestle and passed through a 250 micron screen to produce a uniform powder. The powder sample was loaded into a sample holder, where most of the powder was placed in the holder. The powder was compacted down using a microscope slide to create a horizontal surface, with any excess powder removed. The samples were analyzed by powder X-ray diffraction (XRD) using Bruker D8 Advance with a copper K α radiation source (λ ═ 1.5418A) with a scan range of 10-85 degrees, 2 θ step size of 0.015 degrees and a time duration of 0.2 seconds per step, a divergence slit of 1 mm. The recorded diffraction patterns were analyzed using diffrac Eva software to determine crystallite size by using the Scherrer (Scherrer) method, K0.9 and selecting an area between 26.0-33.0 degrees 2 θ. The phase analysis is determined using Topas software, while default monoclinic, tetragonal and cubic structures are loaded into the software and each scan is run against the default values. Note that in each of examples and comparative examples, tetragonal phase and cubic phase are reported in combination.

Viscosity measurement

Viscosity measurements were collected using a DIN 53019 coaxial cylinder-30 mm diameter and loaded with 20ml samples. Before the measurements were taken, each sample was equilibrated to 20 ℃ by placing it in a water bath for thirty minutes. Measurements were performed using a Bohlin Visco 88 viscometer. Will be in 200s^-1Ten measurements were taken of the shear rate and the average was calculated. This procedure was carried out for all samples by using a small portion of the solDeionized water to a solids content of 55.0 wt.%. The dilution was calculated using the solids content measured as described above to ensure that all samples were tested at equivalent solids loading.

Example 1

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (grade of materials from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give a total oxide content of 25 wt%. The dispersion had a starting particle size of 1.4 microns as measured via laser diffraction. The dispersion is aged at > 80 ℃ and subjected to high shear (> 1,000,000 s)^-1) Mixing was carried out for at least 24 hours in the presence of an amino acid dispersant (3-aminopropionic acid) added at 2% by weight calculated on oxide (i.e. 2% by weight with respect to the weight of oxide). The final concentration was increased to 56.0% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 43.7nm, a PDI of 0.140 and a PDI breadth of 16.4 nm. The powder XRD results give a crystallite size of 12nm and a phase analysis of 1.4% monoclinic phase and 98.6% tetragonal/cubic phase. The green body was prepared by following the method of example 1 of US2016/0095798a1, yielding 2.748g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 2

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). Membrane filtration was used to increase the final concentration to 58.0% solids. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 46.8nm, a PDI of 0.142 and a PDI breadth of 17.6 nm. Results of powder XRD gaveA crystallite size of 12nm and phase analysis of 0.9% monoclinic phase and 99.1% tetragonal/cubic phase was obtained. A green body was prepared by following the procedure of example 1 of US2016/0095798A1, yielding 2.720g/em³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 3

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). Membrane filtration was used to increase the final concentration to 59.5% solids. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 42.8nm, a PDI of 0.122 and a PDI width of 15.0 nm. The powder XRD results give a crystallite size of 12nm and a phase analysis of 1.5% monoclinic phase and 98.5% tetragonal/cubic phase. The green body was prepared by following the method of example 1 of US2016/0095798A1, yielding 2.710g/em³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 4

An aqueous dispersion of hydrous zirconia was prepared by: XZO2732 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 100: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 45.0nm, a PDI of 0.115 and a PDI breadth of 15.3 nm. The powder XRD results gave a crystallite size of 14nm and a monoclinic phase sum of 32.9%Phase analysis of 67.1% tetragonal/cubic phase. The green body was prepared by following the method of example 1 of US2016/0095798A1, yielding 2.732g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 5

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2733 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 98.2: 1.8: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 46.1nm, a PDI of 0.139 and a PDI breadth of 17.2 nm. The powder XRD results give a crystallite size of 13nm and a phase analysis of 22.1% monoclinic phase and 77.9% tetragonal/cubic phase. A green body was prepared by following the procedure of example 1 of US2016/0095798A1 to yield 2.749g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 6

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2734 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 96.4: 3.6: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 42.4nm, a PDI of 0.140 and a PDI width of 15.8 nm. The powder XRD results gave a crystallite size of 13nm and a phase analysis of 7.1% monoclinic and 92.9% tetragonal/cubic phases. A green body was prepared by following the procedure of example 1 of US2016/0095798A1 to yield 2.750g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 7

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2735 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.7: 5.3: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). Membrane filtration was used to increase the final concentration to 58.0% solids. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 45.2nm, a PDI of 0.116 and a PDI breadth of 15.4 nm. The powder XRD results give a crystallite size of 14nm and a phase analysis of 2.3% monoclinic phase and 97.7% tetragonal/cubic phase. A green body was prepared by following the procedure of example 1 of US2016/0095798A1 to yield 2.725g/em³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 8

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2736 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 92.9: 7.1: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2.25% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 56.5% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 44.4nm, a PDI of 0.159 and a PDI breadth of 17.7 nm. The powder XRD results give a crystallite size of 11nm and a phase analysis of 0.8% monoclinic phase and 99.2% tetragonal/cubic phase. Green body pass follow US2016Prepared by the method of example 1 of/0095798A 1 to yield 2.731g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Example 9

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2737 (material grade from Luxfer MEL Technologies with a zirconium to yttrium to aluminum oxide ratio of 91.2: 8.8: 0) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and subjected to mixing under high shear for at least 24 hours in the presence of 2.5% by weight, calculated as oxide, of an added amino acid dispersant (3-aminopropionic acid). Membrane filtration was used to increase the final concentration to 59.5% solids. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 43.5nm, a PDI of 0.152 and a PDI breadth of 17.0 nm. The powder XRD results give a crystallite size of 11nm and a phase analysis of 0.6% monoclinic phase and 99.4% tetragonal/cubic phase. The green body was prepared by following the method of example 1 of US2016/0095798A1 to yield 2.733g/cm³Green density of (2). All green bodies survived degreasing and sintering at 1150 ℃ for 2 hours to form crack-free ceramic pieces.

Comparative example 10

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and at low shear (50,000 s)^-1) The following is subjected to mixing for at least 24 hours in the presence of 2% by weight, calculated as oxide, of added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 73.2nm, a PDI of 0.226 and a PDI breadth of 34.8 nm. The powder XRD results give a crystallite size of 11nm and a phase analysis of 3.9% monoclinic phase and 96.1% tetragonal/cubic phase. The green body was made by following US2016/0095798A1 prepared by the method of example 1 to yield 3.040g/cm³Green density of (2). Upon degreasing, all green bodies are broken inside the furnace.

Comparative example 11

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged at > 80 ℃ and at lower shear (35,000 s)^-1) The following is subjected to mixing for at least 24 hours in the presence of 2% by weight, calculated as oxide, of added amino acid dispersant (3-aminopropionic acid). The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 93.3nm, a PDI of 0.208 and a PDI width of 42.6 nm. The powder XRD results give a crystallite size of 11nm and a phase analysis of 4% monoclinic phase and 96.0% tetragonal/cubic phase. The green body was prepared by following the procedure of example 1 of US2016/0095798A1 to give 2.881g/em³Green density of (2). Upon degreasing, all green bodies are broken inside the furnace. This comparative example demonstrates the importance of using high shear mixing when preparing the inventive dispersions.

Comparative example 12

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged and milled for 1 hour in the presence of 2% by weight, calculated as oxide, of added amino acid dispersant (3-aminopropionic acid) according to patent US 9,822,039B 1 comparative example 1. The final concentration was increased to 57.0% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 39.2nm, a PDI of 0.180 and a PDI breadth of 16.6 nm. The powder XRD results give a crystallite size of 14nm and a phase analysis of 6.0% monoclinic and 94.0% tetragonal/cubic phases. The green body was made by following US2016/0095798A1 prepared by the method of example 1 to give 2.881g/em³Green density of (2). Upon degreasing, small cracks appear inside the ceramic. Upon sintering at 1150 ℃ for 2 hours, cracks propagated and the ceramic broke apart into pieces. This comparative example demonstrates the importance of the aging and mixing technique used in preparing the inventive dispersions.

Comparative example 13

An aqueous dispersion of yttrium-doped hydrous zirconia was prepared by: XZO2738 (material grade from Luxfer MEL Technologies with an oxide ratio of zirconium to yttrium to aluminum of 94.45: 5.3: 0.25) was taken and made up to 500g with deionized water to give an active content of 25 wt%. The dispersion was aged and ground for 2 hours in the presence of 2% by weight, calculated as oxide, of added amino acid dispersant (3-aminopropionic acid) according to patent US 9,822,039B 1 comparative example 1. The final concentration was increased to 57.5% solids using membrane filtration. The final particle size distribution of the dispersion as measured via DLS was a Z-average of 30.3nm, a PDI of 0.181 and a PDI breadth of 13.0 nm. The powder XRD results give a crystallite size of 13nm and a phase analysis of 2.4% monoclinic phase and 97.6% tetragonal/cubic phase. A green body was prepared by following the method of example 1 of US2016/0095798A1 to give 2.873g/cm³Green density of (2). Upon degreasing, small cracks appear inside the ceramic. Upon sintering at 1150 ℃ for 2 hours, cracks propagated and the ceramic broke apart into pieces. This comparative example is the same as comparative example 12 except that the milling time is 2 hours.

The composition of the nanodispersions is summarized in table 1 below:

sample name	ZrO₂+HfO₂By weight%	Y₂O₃By weight%	Al₂O₃By weight%
				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 example 10	94.45	5.3	0.25
				Comparative example 11	94.45	5.3	0.25
Comparative example 12	94.45	5.3	0.25
				Comparative example 13	94.45	5.3	0.25

TABLE 1

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

TABLE 4

With respect to the figures, fig. 1 compares the particle size by intensity plots of example 1 and comparative example 10. This shows that example 1 is a unimodal of smaller size compared to the bimodal and larger size peak of comparative example 10. Figure 2 shows a similar comparison of example 1 and comparative example 13. In this case, this shows that a larger size peak is achieved by example 1.

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, and that a narrow distribution of particles is highlighted.

The XRD stacking in fig. 4 shows the crystallinity of the nanoparticles of the present invention. The arrows in FIG. 4 indicate at Y₂O₃The 282 theta peak associated with the monoclinic phase decreased as the level increased through examples 4-9.

Fig. 5 is a photograph of green bodies formed according to example 1 (left) and comparative example 10 (right). As clearly shown, the left disk is wide and thin, while the right disk is taller and narrower. Also, the green body formed by comparative example 10 had cracks (shown by circles in fig. 5) therein. This is believed to be due to the filling of the particles in the respective green bodies. The left disc (example 1) has a narrower particle size range (essentially, more particles of the approximate size). These particles fill together, leaving voids in the green body for moisture/organics to escape during drying. This allows the green body to dry more quickly and retain its shape. In contrast, the right disk (comparative example 10) had a bimodal particle size distribution, allowing smaller particles to fit into the voids around the larger particles. This means that the green body dries slowly, the outer part of the disc drying first while retaining moisture in the middle and then shrinking. This results in a higher, narrower disc.

Claims

1. An aqueous dispersion of nanoparticles, said nanoparticles comprising, in oxide:

(a)85-100 wt% ZrO₂+HfO₂，

(b)0-15 wt.% Y₂O₃And are and

(c)0-2 wt.% Al₂O₃，

Wherein the dispersion has a polydispersity index of 0.10 to 0.17.

2. An aqueous dispersion of nanoparticles as claimed in claim 1 wherein the dispersion has a polydispersity index of 0.11 to 0.16.

3. An aqueous dispersion of nanoparticles as claimed in claim 1 or claim 2 wherein the dispersion has a nanoparticle content of 0.5-65 wt%.

4. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the dispersion has a Z-average particle size of 30 to 60 nm.

5. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the nanoparticles comprise 0.5-10 wt% Y calculated as oxide₂O₃And 0-1 wt.% Al₂O₃。

6. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein any sub-peak or sub-peak in the particle size distribution of the dispersion by intensity has an intensity of 0-15%.

7. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the dispersion has a PDI width of 10-20 nm.

8. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the intensity-measured particle size distribution of the dispersion has a d10 value in the range of 25-40 nm.

9. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the intensity-measured particle size distribution of the dispersion has a d50 value in the range of 35-60 nm.

10. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the dispersion has a particle size distribution, measured by intensity, with a d90 value in the range of 60-100 nm.

11. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the dispersion comprises 0.5 to 6% by weight of dispersant calculated on oxide content.

12. An aqueous dispersion of nanoparticles as claimed in claim 11 wherein the dispersant is an amino acid.

13. An aqueous dispersion of nanoparticles as claimed in any one of the preceding claims wherein the dispersion has a viscosity of <100 cP.

14. An aqueous dispersion of nanoparticles according to any one of the preceding claims wherein the amount of each of Fe, Cr, Ni and Ce in the dispersion is <20 ppm.

15. A method of forming a ceramic article comprising the steps of:

(a) pouring the aqueous dispersion of any one of claims 1 to 14 into a mold,

(b) drying the aqueous dispersion in the mold to form a green body, and

(c) sintering the green body to form a ceramic article.