NOBLE-METAL POWDER AND THE USE THEREOF FOR PRODUCING COMPONENTS

Abstract

The present invention relates to a powder composed of spherical noble-metal particles having a particle size distribution with a d.sub.10 value of ≧10.0 μm and a d.sub.90 value of ≦80.0 μm.

Claims

1. Powder composed of spherical noble-metal particles having a particle size distribution with a d.sub.10 value of ≧10.0 μm and a d.sub.90 value of ≦80.0 μm.

2. Powder according to claim 1, wherein the noble metal is a platinum-group metal, gold or silver or an alloy composed of at least two of the aforementioned noble metals.

3. Powder according to claim 2, wherein the platinum-group metal is platinum, iridium, palladium, ruthenium, rhodium or osmium or an alloy composed of at least two of the aforementioned platinum-group metals.

4. Powder according to claim 1, wherein the noble-metal particles contain elements which are not noble metals in a proportion of not more than 0.1% by weight.

5. Powder according to claim 1, wherein the d.sub.90 value and the d.sub.10 value differ by at least 15 μm.

6. Powder according to claim 1, wherein the d.sub.10 value is within the range from 10.0 to 35.0 μm, and/or the d.sub.90 value is within the range from 40.0 to 80.0 μm.

7. Powder according to claim 1, wherein the noble metal is iridium, the d.sub.10 value is within the range from 20.0 to 30.0 μm, the d.sub.90 value is within the range from 40.0 to 80.0 μm, and the difference between the d.sub.90 value and the d.sub.10 value is at least 20 μm.

8. Powder according to claim 1, wherein the powder satisfies the following condition:
F/ρ.sub.TH≦0.30 s/(50 cm.sup.3) where F is the flowability of the powder in s/(50 g), determined in accordance with DIN EN ISO 4490:2014-11, and ρ.sub.TH is the theoretical density in g/cm.sup.3 of the noble metal forming the noble-metal particles.

9. Powder according to claim 1, wherein, based on the number of noble-metal particles, at least 80% of the noble-metal particles satisfy the following condition:
0.8≦d.sub.min/d.sub.max≦1.0; where d.sub.min and d.sub.max are the minimum diameter and the maximum diameter, respectively, of a noble-metal particle.

10. Powder according to claim 1, wherein the noble-metal particles have a mean crystallite size ≧200 nm.

11. Powder according to claim 1, obtainable via an atomization of liquid noble metal, preferably a gas atomization, a plasma atomization, a centrifugal atomization or a crucible-free atomization, and optionally a classification carried out after the atomization.

12. (canceled)

13. Component which is obtainable from the powder according to claim 1, via an additive manufacturing process and which has a porosity of less than 10%.

14. Additive manufacturing process for producing a component, comprising the following steps: (a) applying the powder according to claim 1, in the form of a first layer to a substrate in a construction space, (b) at least partially melting the powder of the first layer using high-energy radiation and allowing solidification of the melted powder, (c) applying a further layer of the powder to the first layer, (d) at least partially melting the powder of the further layer using high-energy radiation and allowing solidification of the melted powder, and (e) repeating steps (c) and (d).

Description

EXAMPLES

[0060] A) Methods of Measurement

[0061] The parameters used in the present invention were determined in accordance with the following methods of measurement.

[0062] Particle Size Distribution and the d.sub.10 and d.sub.90 Values Thereof

[0063] Particle size distribution was determined by laser diffraction using the instrument “Sympatec Helos BR/R3”. Measurement range: 0.9-175 and 4.5-875.

[0064] The dispersion system used for dispersing the powder particles:

[0065] RODOD/M dry dispersion system with VIBRI vibratory feeder (with Venturi nozzle). Sample amount: approximately 5 g.

[0066] Wavelength of the laser radiation: 632.8 nm.

[0067] Evaluation done via Mie theory.

[0068] The particle sizes are obtained as a mass distribution, i.e. within the scope of the present invention, what is determined is the particle size distribution in the form of a mass distribution cumulative curve.

[0069] The d.sub.10 and d.sub.90 values can be read off from the particle size distribution measured by laser diffraction (mass distribution).

[0070] Flowability of the Powder

[0071] Determined in accordance with DIN EN ISO 4490 by means of a Hall flowmeter from Impact Innovations.

[0072] The values for the theoretical density of the noble metals (for normalizing flowability to density) can be taken from relevant standard works. For example, the theoretical density of iridium is 22.56 g/cm.sup.3, that of gold is 19.32 g/cm.sup.3, that of silver is 10.49 g/cm.sup.3, that of PtRh20 is 18.71 g/cm.sup.3, and that of PtIr50 is 22.05 g/cm.sup.3.

[0073] d.sub.min and d.sub.max of the Noble-Metal Particles

[0074] Minimum (d.sub.min) and maximum diameter (d.sub.max) of the particles were determined by optical image analysis as follows:

[0075] Following ISO 9276-1, ISO 9276-6 and ISO13320, the morphology and shape of the particles was determined using a QICPIC image analysis system (Sympatec GmbH System-Partikel-Technik Germany). The dry feeding of the particles was carried out using compressed air and the QICPIC-connected RODOS/L (0.50 63.0 mm) unit. The measurement area was set to M6, covering particles having a diameter from 5 to 170 μm. Additional parameters were: image frequency=450 Hz, VIBRI feed rate=20%, funnel height=2 mm, inner diameter of the dispersion pipe=4 mm, pressure: 1 bar. FERET_MIN (minimum diameter d.sub.min) and FERET_MAX (maximum diameter d.sub.max) were determined. As a measure of the sphericity of a particle, the ratio of the minimum diameter d.sub.min to the maximum diameter d.sub.max was used in a first approximation.

[0076] Mean Crystallite Size

[0077] X-ray powder diffraction diffractograms were measured using a STADI P two-circle diffractometer from Stoe & Cie in transmission. The measurement was done using Cu K.sub.α1 radiation. For the calibration, the NIST standard Si (640 d) was used. The 2-theta position of a reflection was determined on the basis of its peak maximum.

[0078] The diffraction reflections of the X-ray powder diffraction diffractogram were mathematically fitted using Stoe pattern-fitting software and the full widths at half maximum (FWHM) of the diffraction reflections were determined.

[0079] The measured values were corrected with respect to the instrument standard LaB6 NIST (660 b).

[0080] The mean crystallite size was determined using the Stoe software. To this end, the Scherrer equation was applied to the (111) reflection. As is known to a person skilled in the art, the Scherrer equation is as follows:

d=(K*λ)/(β*cos θ)

where

[0081] d is the mean crystallite size,

[0082] K is a dimensionless shape factor,

[0083] λ is the wavelength of the X-radiation,

[0084] β is the full width at half maximum of the reflection, measured in radians,

[0085] θ is the diffraction angle.

[0086] A value of 1.0 was taken for K.

[0087] Porosity

[0088] Porosity is the result of the following equation:

Porosity P (in %)=(1−(ρ.sub.geo/ρ.sub.th))×100% [0089] where [0090] ρ.sub.geo is the geometric density of the component and ρ.sub.th is the theoretical density of the component.

[0091] Geometric density can be ascertained according to Archimedes' principle, for example using a hydrostatic balance. The theoretical density of the component corresponds to the theoretical density of the noble metal from which the component is formed.

Relative density D.sub.rel (in %) is the result of (ρ.sub.geo/ρ.sub.th)×100%. Thus: P=1−D.sub.rel

[0092] Composition of the Noble-Metal Particles

[0093] Determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0094] B) Production of Powders Composed of Spherical Noble-Metal Particles and the Use Thereof for the Production of Noble-Metal Components by Additive Manufacturing

[0095] Using various noble metals, noble-metal powders were produced via an atomization process. Ir powder, PtRh20 powder, PtIr50 powder, Ag powder and Au powder were produced.

[0096] Examples 1-4 and comp. ex. 1-3: powder particles consist of iridium

[0097] Example 5 and comp. ex. 4: powder particles consist of PtRh20 alloy

[0098] Example 6 and comp. ex. 5: powder particles consist of PtIr50 alloy

[0099] Example 7 and comp. ex. 6: powder particles consist of silver

[0100] Example 8 and comp. ex. 7: powder particles consist of gold

[0101] Both in the examples according to the invention and in the comparative examples, the powders were produced in each case by induction melting of the starting material and gas atomization (EIGA (electrode induction melting gas atomization)) using argon. This process yields spherical powder particles.

[0102] Thereafter, the powders obtained via the atomization process were classified by sieving. Sieving was done using the instrument Retsch AS 200. Sieves of 20 μm, 45 μm, 63 μm and 140 μm mesh size were used and sieving was carried out for 2-5 minutes using an amount of approximately 100 g at different amplitudes.

[0103] The d.sub.10 and d.sub.90 values of the classified powders were determined. In addition, flowability, crystallite size and crystallinity of the powders were measured.

[0104] From these powders, a component was produced in each case in an additive manufacturing process. The same process parameters were always used. The component was produced by selective laser melting (SLM). Machine: machine from ConceptLaser, model MLab.

[0105] The quality of the application of powder (i.e. of the powder layers introduced into the construction space) was assessed on the basis of the number of visually identifiable imperfections (e.g. mark due to coarse particles or clumps) per 30 application operations on an area of 50 cm.sup.2.

[0106] Geometric density and relative density (i.e. quotient from geometric density and theoretical density) were determined for the components obtained.

[0107] The results for the powders consisting of iridium particles and for the iridium components produced therefrom are combined in table 1.

TABLE-US-00001 TABLE 1 Properties of the iridium powders and of the components produced therefrom Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. ex. 1 Comp. ex. 2 Comp. ex. 3 d.sub.10 [μm] 22.46 28.34 11.8 12.4 136.96 9.3 4.2 d.sub.90 [μm] 48.15 67.25 47.5 67.5 292.79 46.9 68.6 Flowability 3.5 3.1 3.8 4.1 6.9 Not 6.9 (s/50 g) measurable* Flowability Very good Very Good Good Moderate Poor Moderate good Flowability, 0.16 0.14 0.17 0.18 0.31 0.31 [s/cm.sup.3] normalized to density Crystallite 306 320 291 310 171 191 160 size [nm] Quality of 0-1 0-1 1-2 1-2 2-4 4-10 2-4 application of powder Density after 21.91 21.89 21.84 21.83 20.82 19.8 20.82 additive manufacturing [g/cm.sup.3] Density after 97.12 97.03 96.81 96.76 92.29 87.77 92.29 additive manufacturing [%] *Powder got stuck in the funnel.

[0108] Quality of the application of powder: number of visually identifiable imperfections (e.g. mark due to coarse particles or clumps) per 30 application operations on an area of 50 cm.sup.2 assessed, i.e. the lower the value, the better the quality of the application of powder

[0109] As demonstrated by the results in table 1, only the iridium powders with d.sub.10 value ≧10.0 and d.sub.90 value ≦80.0 allow the realization of a high flowability with high quality of application of powder at the same time and the production of a component of low porosity (i.e. high relative density) via an additive manufacturing process.

[0110] As shown in particular by example 3 (d.sub.10 value: 11.8 μm; d.sub.90 value: 47.5 μm) and comparative example 2 (d.sub.10 value: 9.3 μm; d.sub.90 value: 46.9 μm), a d.sub.10 value of less than 10 μm leads abruptly to a significant deterioration both in flowability and in the quality of the applied powder layer.

[0111] The results for the PtRh20 powders and for the PtRh20 components produced therefrom are combined in table 2.

TABLE-US-00002 TABLE 2 Properties of the PtRh20 powders and of the components produced therefrom Ex. 5 Comp. ex. 4 d.sub.10 [μm] 12.3 148.5 d.sub.90 [μm] 65.7 307.5 Flowability [s/50 g] 4.5 6.5 Flowability Good Moderate Flowability, [s/cm.sup.3] 0.24 0.35 normalized to density Quality of application 0-1 2-4 of powder Density after additive 18.5 17.6 manufacturing [g/cm.sup.3] Density after additive 98.88 94.07 manufacturing [%]

[0112] The results for the PtIr50 powders and for the PtIr50 components produced therefrom are combined in table 3.

TABLE-US-00003 TABLE 3 Properties of the PtIr50 powders and of the components produced therefrom Ex. 6 Comp. ex. 5 d.sub.10 [μm] 13.1 106.2 d.sub.90 [μm] 66.4 293.4 Flowability [s/50 g] 3.4 6.8 Flowability Good Moderate Flowability, [s/cm.sup.3] 0.15 0.31 normalized to density Quality of application 0-1 2-4 of powder Density after additive 21.98 20.8 manufacturing [g/cm.sup.3] Density after additive 99.7 94.3 manufacturing [%]

[0113] The results for the Ag powders and for the Ag components produced therefrom are combined in table 4.

TABLE-US-00004 TABLE 4 Properties of the Ag powders and of the Ag components produced therefrom Ex. 7 Comp. ex. 6 d.sub.10 [μm] 15.3 128.5 d.sub.90 [μm] 65.7 307.5 Flowability [s/50 g] 3 6.6 Flowability Good Moderate Flowability, [s/cm.sup.3] 0.29 0.63 normalized to density Quality of application 0-1 2-4 of powder Density after additive 10.35 9.5 manufacturing [g/cm.sup.3] Density after additive 98.67 90.56 manufacturing [%]

[0114] The results for the Au powders and for the Au components produced therefrom are combined in table 5.

TABLE-US-00005 TABLE 5 Properties of the Au powders and of the Au components produced therefrom Ex. 8 Comp. Ex. 7 d.sub.10 [μm] 27.3 4.9 d.sub.90 [μm] 51.6 196.5 Flowability [s/50 g] 3.2 5.9 Flowability Good Moderate Flowability, [s/cm.sup.3] 0.17 0.31 normalized to density Quality of application 0-1 2-4 of powder Density after additive 19.1 17.8 manufacturing [g/cm.sup.3] Density after additive 98.86 92.13 manufacturing [%]

[0115] The results in tables 2-5 demonstrate too that only the noble-metal powders with d.sub.10 value ≧10.0 and d.sub.90 value ≦80.0 allow the realization of a high flowability with high quality of application of powder at the same time and the production of a component of low porosity (i.e. high relative density) via an additive manufacturing process.