Dispersion-hardened precious-metal alloy

Abstract

Methods of making dispersion-hardened platinum compositions include A) producing a melt having at least 70 wt. % platinum, up to 29.95 wt. % of one or more of rhodium, gold, iridium and palladium, between 0.05 wt. % and 1 wt. % of oxidizable non-precious metals in the form of zirconium, yttrium and scandium, and, as the remainder, platinum including impurities, wherein the ratio of zirconium to yttrium in the melt is in a range of from 5.9:1 to 4.3:1 and the ratio of zirconium to scandium in the melt is at least 17.5:1, B) hardening the melt to form a solid body, C) processing the solid body to form a volume body, and D) oxidizing the non-precious metals contained in the volume body by a heat treatment in an oxidizing medium over a time period of at least 48 hours at a temperature of at least 750 C.

Claims

1. A method for producing a platinum composition comprising the following chronological steps: A) producing a melt having at least 70 wt. % platinum, up to 29.95 wt. % of one or more of rhodium, gold, iridium and palladium, between 0.05 wt. % and 1 wt. % of oxidizable non-precious metals in the form of zirconium, yttrium and scandium, and, as the remainder, platinum including impurities, wherein the ratio of zirconium to yttrium in the melt is in a range of from 5.9:1 to 4.3:1 and the ratio of zirconium to scandium in the melt is at least 17.5:1; B) hardening the melt to form a solid body; C) processing the solid body to form a volume body; and D) oxidizing the non-precious metals contained in the volume body by a heat treatment in an oxidizing medium over a time period of at least 48 hours at a temperature of at least 750 C.

2. The method of claim 1, wherein during the oxidation in step D), the oxygen is diffused through the solid body and cubic zirconia stabilized by yttrium oxide and/or scandium oxide is transported by means of oxygen ion conduction.

3. The method of claim 1, wherein during the oxidation in step D), dispersion hardening is carried out by yttrium-oxide-stabilized and/or scandium-oxide-stabilized zirconia particles precipitated from the metal matrix of the solid body.

4. The method of claim 1, wherein during the processing in step C), the solid body is reshaped and a volume form is produced in a targeted manner.

5. The method of claim 1, wherein the time period for oxidation in step D) is chosen depending on the thickness of the material to be oxidized owing to the average diffusion length of the oxygen such that the greater the material thickness, the longer the time period for oxidation is chosen.

6. The method of claim 1, wherein the time period of at least 48 hours in step D) relates to a metal sheet having a thickness of 0.5 mm and the time period for oxidation increases for thicker metal sheets.

7. The method of claim 1, wherein during the oxidation in step D), at least 70% of the zirconium, yttrium and scandium are oxidized to zirconium oxide (ZrO.sub.2), yttrium oxide (Y.sub.2O.sub.3) and scandium oxide (Sc.sub.2O.sub.3).

8. The method of claim 1, wherein during the oxidation in step D), at least 50 mol. % of the oxides of the non-precious metals created are cubic zirconia stabilized with yttrium oxide and/or scandium oxide.

9. The method of claim 1, wherein during producing the melt in step A), a melting metallurgy process is performed; and during processing the solid body in step C), the solid body is rolled out.

10. The method of claim 1, wherein during the oxidation in step D), a heat treatment is performed in an oxidizing medium such that the non-precious metals contained in the platinum composition are completely oxidized.

11. The method of claim 1, wherein after the oxidation in step D), the ratio of yttrium oxide to scandium oxide in the platinum composition in the volume body is in a range of from 2.6:1 to 10:1.

12. The method of claim 1, wherein after the oxidation in step D), between 8.0 mol. % and 10.0 mol. % of the oxides of the volume body are yttrium oxide.

13. The method of claim 1, wherein after the oxidation in step D), between 1.0 mol. % and 3.0 mol. % of the oxides of the volume body are scandium oxide.

14. The method of claim 1, wherein during producing the melt in step A), a melt is produced having at least 80 wt. % platinum and/or containing at least 1 wt. % rhodium, gold, palladium or iridium.

15. The method of claim 1, wherein after the oxidation in step D), a volume body is obtained containing between 5 wt. % and 20 wt. % rhodium and no gold, iridium or palladium, except for impurities, or containing between 2 wt. % and 10 wt. % gold and no rhodium, iridium or palladium, except for impurities.

16. The method of claim 1, wherein after the oxidation in step D), a volume body is obtained having a creep strength of at least 500 h at 1400 C. under a load of 20 MPa.

17. The method of claim 1, wherein after the oxidation in step D), a crucible for crystal growing, a semi-finished product, a tool, a tube, a stirrer, a fiberglass nozzle, a temperature sensor or a component for producing or processing glass is produced from the volume body.

18. The method of claim 1, wherein during the oxidation in step D), at least 90% of the zirconium, yttrium and scandium are oxidized to zirconium oxide (ZrO.sub.2), yttrium oxide (Y.sub.2O.sub.3) and scandium oxide (Sc.sub.2O.sub.3).

19. The method of claim 1, wherein during the oxidation in step D), at least 80 mol. % of the oxides of the non-precious metals created are cubic zirconia stabilized with yttrium oxide and/or scandium oxide.

Description

COMPARATIVE EXAMPLE 1

(1) 10 wt. % rhodium, 1830 ppm zirconium, 295 ppm yttrium, 50 ppm scandium and the remainder platinum including usual impurities.

(2) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 7.5 mol. % Y.sub.2O.sub.3 (yttrium oxide), 2.5 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(3) The oxidation of the non-precious metals of the 3 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of 27 days, >90% of the non-precious metals in the metal sheet were oxidized. The metal sheet was then ductility-annealed at 1400 C. for 6 hours and thermomechanically processed as disclosed in WO 2015/082630 A1. As a result, a creep strength of 3 hours is brought about at 1400 C. and 20 MPa and a creep strength of 50 hours is brought about at 1600 C. and 9 MPa.

COMPARATIVE EXAMPLE 2

(4) 10 wt. % rhodium, 1830 ppm zirconium, 295 ppm yttrium, 50 ppm scandium and the remainder platinum including usual impurities.

(5) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 7.5 mol. % Y.sub.2O.sub.3 (yttrium oxide), 2.5 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(6) The oxidation of the non-precious metals of the 3 mm thick metal sheet takes place in the air at 1000 C. After an oxidation time of 9 days, >90% of the non-precious metals in the metal sheet were oxidized. The metal sheet was then ductility-annealed at 1400 C. for 6 hours and the metal sheet was thermomechanically processed as disclosed in WO 2015/082630 A1. As a result, a creep strength of 0.5 hours is brought about at 1400 C. and 20 MPa and a creep strength of 3 hours is brought about at 1600 C. and 9 M Pa.

EXAMPLE 3 (INVENTION)

(7) 10 wt. % rhodium, 2770 ppm zirconium, 546 ppm yttrium, 63 ppm scandium and the remainder platinum including usual impurities.

(8) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 9.0 mol. % Y.sub.2O.sub.3 (yttrium oxide), 2.0 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(9) The oxidation of the non-precious metals of the 3 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of just 19 days, >90% of the non-precious metals in the metal sheet were oxidized. The metal sheet was then ductility-annealed at 1400 C. for 6 hours and the metal sheet was thermomechanically processed as disclosed in WO 2015/082630 A1. As a result, a creep strength of over 500 hours is brought about at 1400 C. and 20 MPa and a creep strength of over 1000 hours is brought about at 1600 C. and 9 MPa.

EXAMPLE 4 (INVENTION)

(10) 10 wt. % rhodium, 2770 ppm zirconium, 546 ppm yttrium, 63 ppm scandium and the remainder platinum including usual impurities.

(11) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 9.0 mol. % Y.sub.2O.sub.3 (yttrium oxide), 2.0 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(12) The oxidation of the non-precious metals of the 3 mm thick metal sheet takes place in the air at 1000 C. After an oxidation time of just 6 days, >90% of the non-precious metals in the metal sheet were oxidized.

(13) By optimizing the molar composition, i.e. the molar ratio of the oxide-forming non-precious metals, and by increasing the total quantity of oxide-forming non-precious metals (from 2150 ppm to 3400 ppm), the invention succeeds in reducing the oxidation time in the solid body by >25% while simultaneously improving the high-temperature properties.

EXAMPLE 5 (INVENTION)

(14) 10 wt. % rhodium, 2710 ppm zirconium, 511 ppm yttrium, 65 ppm scandium and the remainder platinum including impurities. A circular blank of 200 g was produced by means of arc melting.

(15) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 8.6 mol. % Y.sub.2O.sub.3 (yttrium oxide), 2.2 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(16) The oxidation of the non-precious metals of the 2 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of just 10 days, >90% of the non-precious metals in the metal sheet were oxidized. The metal sheet was then ductility-annealed at 1400 C. for 6 hours and the metal sheet was thermomechanically processed as disclosed in WO 2015/082630 A1. As a result, a creep strength of over 500 hours is brought about at 1400 C. and 20 MPa and a creep strength of over 1000 hours is brought about at 1600 C. and 9 MPa.

COMPARATIVE EXAMPLE 6

(17) 10 wt. % rhodium, 1870 ppm zirconium, 313 ppm yttrium, 33 ppm scandium and the remainder platinum including usual impurities. A circular blank of 200 g was produced by means of arc melting.

(18) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 7.8 mol. % Y.sub.2O.sub.3 (yttrium oxide), 1.6 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(19) The oxidation of the non-precious metals of a 2 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of 20 days, >90% of the non-precious metals in the metal sheet were oxidized. The metal sheet was then ductility-annealed at 1400 C. for 6 hours and the metal sheet was thermomechanically processed as disclosed in WO 2015/082630 A1. It results in a creep strength analogously to comparative example 1.

(20) For the further comparison, three additional comparative tests were carried out in which a combination of scandium oxide and niobium oxide (Nb.sub.2O.sub.5) instead of yttrium oxide and scandium oxide was introduced into the platinum composition for stabilizing the oxygen-ion-conducting cubic zirconia phase.

(21) The platinum compositions described in the following were produced by circular blanks having individual weights of 200 g each being produced by arc melting. In this way, 3 different platinum compositions containing 10 wt. % rhodium, 200 ppm scandium and variable proportions of niobium were produced. A 2 mm thick metal sheet of the platinum composition was produced by rolling and tempering.

(22) The proportion of the oxidized non-precious metals in the platinum composition was then determined by quantitative IR spectroscopy.

COMPARATIVE EXAMPLE 7

(23) 10 wt. % rhodium, 1800 ppm zirconium, 80 ppm niobium, 200 ppm scandium and the remainder platinum including usual impurities.

(24) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 2.0 mol. % Nb.sub.2O.sub.5 (niobium oxide), 10.0 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(25) The oxidation of the non-precious metals of the 2 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of 20 days, only 39% of the non-precious metals in the metal sheet were oxidized.

COMPARATIVE EXAMPLE 8

(26) 10 wt. % rhodium, 1800 ppm zirconium, 40 ppm niobium, 200 ppm scandium and the remainder platinum including usual impurities.

(27) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 1.0 mol. % Nb.sub.2O.sub.5 (niobium oxide), 10.0 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(28) The oxidation of the non-precious metals of the 2 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of 20 days, only 42% of the non-precious metals in the metal sheet were oxidized.

COMPARATIVE EXAMPLE 9

(29) 10 wt. % rhodium, 1800 ppm zirconium, 20 ppm niobium, 200 ppm scandium and the remainder platinum including usual impurities.

(30) This corresponds to a mole fraction of the oxide of the non-precious metal in the oxidized state of the platinum composition of 0.5 mol. % Nb.sub.2O.sub.5 (niobium oxide), 10.0 mol. % Sc.sub.2O.sub.3 (scandium oxide) and the remainder ZrO.sub.2 (zirconia).

(31) The oxidation of the non-precious metals of the 2 mm thick metal sheet takes place in the air at 900 C. After an oxidation time of 20 days, only 36% of the non-precious metals in the metal sheet were oxidized.

(32) The oxidation time in comparative examples 6, 7 and 8 was therefore considerably worse than in comparative example 5. This shows that a direct conclusion cannot be drawn on the oxidizability or oxidation time of the platinum composition from the oxygen ion conductivity of the oxides.

(33) The measurements show that, for the platinum composition, there is no simple connection such that an oxide having high ion conductivity would bring about an acceleration of the oxidation process. Accordingly, the selection of non-precious metals according to the invention in the platinum composition according to the invention results in surprising success.

(34) The features of the invention disclosed in the above description, as well as in the claims, drawings and exemplary embodiments, may be essential both individually and in any combination for realizing the invention in its various embodiment forms.