ZIRCONIUM OXIDE POWDER FOR THERMAL SPRAYING

Abstract

The present invention relates to zirconium oxide powder for thermal spraying and a method for its manufacture. Furthermore, the present invention relates to thermal insulation layers, which are obtained using the zirconium oxide powder according to the invention.

Claims

1. Zirconium oxide powder (ZrO.sub.2) for thermal spraying comprising yttrium oxide (Y.sub.2O.sub.3), ytterbium oxide (Yb.sub.2O.sub.3) and gadolinium oxide (Gd.sub.2O.sub.3), wherein the content of yttrium oxide is 0.01 to 2.5 percent by weight relative to the total weight of the powder.

2. Zirconium oxide powder according to claim 1, consisting of, in each case relative to the total weight of the powder: yttrium oxide (Y.sub.2O.sub.3): 0.01 to 2.5 percent by weight, ytterbium oxide (Yb.sub.2O.sub.3): 5.0 to 20.0 percent by weight, gadolinium oxide (Gd.sub.2O.sub.3): 5.0 to 20.0 percent by weight, optionally hafnium oxide (HfO.sub.2): 0.1 to 3 percent by weight, optionally other components: 0.1 to 7.9 percent by weight, and as the rest zirconium oxide (ZrO.sub.2) and unavoidable impurities.

3. Zirconium oxide powder according to claim 1, wherein the content of yttrium oxide is 0.1 to 2.4 percent by weight relative to the total weight of the powder.

4. Zirconium oxide powder according to claim 1, wherein the content of ytterbium oxide is 5.0 to 20.0 percent by weight relative to the total weight of the powder.

5. Zirconium oxide powder according to claim 1, wherein the content of gadolinium oxide is 5.0 to 20.0 percent by weight relative to the total weight of the powder.

6. Zirconium oxide powder according to claim 1, wherein the powder contains 1.0 to 2.0 percent by weight yttrium oxide, 8.0 to 12.0 percent by weight ytterbium oxide and 8.0 to 12.0 percent by weight gadolinium oxide.

7. Zirconium oxide powder according to claim 1, wherein the powder has other components in a quantity from 0.1 to 7.9 relative to the total weight of the powder.

8. Zirconium oxide powder according to claim 7, wherein the other components are selected from the group consisting of silicon compounds, aluminium compounds, alkaline earth oxides, lanthanum oxide (La.sub.2O.sub.3), iron oxide (Fe.sub.2O.sub.3), titanium dioxide, alkali metal oxides, oxides of radioactive elements, chlorides and organic compounds and mixtures thereof.

9. Zirconium oxide powder according to claim 7, wherein the other components in total are contained in quantities from 0.1 percent by weight to 7.0 percent by weight relative to the total weight of the powder.

10. Zirconium oxide powder according to claim 1, wherein the powder has a nominal particle size of 22/5 m to 300/75 m, determined according to EN 1274.

11. Zirconium oxide powder according to claim 1, wherein the proportion of zirconium oxide in the monoclinic phase is less than 4.0 percent by weight relative to the total weight of the powder.

12. Method for manufacturing a zirconium oxide powder according to claim 1, comprising the following steps: a) providing starting materials comprising zirconium oxide, yttrium oxide, ytterbium oxide and gadolinium oxide, wherein the content of yttrium oxide is 0.01 to 2.5 percent by weight relative to the total weight of the mixture; b) high-temperature treatment of the starting materials from step a) to obtain a stabilised zirconium oxide powder; c) cooling of the powder obtained in step b).

13. Thermal insulation layer obtainable by using a zirconium oxide powder according to claim 1.

14. Thermal insulation layer according to claim 13, wherein the thermal insulation layer has a porosity of 2 to 30 area percent.

15. Thermal insulation layer according to claim 13, wherein it is a thermal insulation layer for turbine blades, guide vanes of turbines and combustion chambers of turbines.

16. A method comprising coating the zirconium oxide powder according to claim 1 on high-temperature components.

17. Method for manufacturing a thermal insulation layer according to claim 13, wherein the thermal insulation layer is produced by means of a thermal spraying process.

Description

EXEMPLARY EMBODIMENTS

[0063] The present invention will be illustrated by means of the following examples, wherein these should not be understood as limiting the inventive concept, i.e. as restrictive.

Example 1 (Comparative Example)

[0064] An 8YSZ plasma spray powder with a nominal particle size or grain size distribution according to DIN EN 1274:2005-02 of 90/10 m was produced by the method agglomeration/sintering of the individual oxides Y.sub.2O.sub.3 and HfO.sub.2-containing ZrO.sub.2. According to chemical and physical analysis, this powder had the following properties:

[0065] Y.sub.2O.sub.3 7.68%, HfO.sub.2 1.91%

[0066] MgO 13 ppm, CaO 330 ppm, Fe.sub.2O.sub.3 130 ppm, Al.sub.2O.sub.3 1200 ppm, SiO.sub.2 1150 ppm

[0067] U.sub.2O.sub.3+ThO.sub.2 530 ppm

[0068] Sieve analysis (percentages by weight):

TABLE-US-00001 >106 m 0% 106/75 m 11.7% 75/45 m 49.1% <45 m 39.2

[0069] Grain distribution parameters using laser diffraction (Microtrac X100):

[0070] D90: 92 m, D50 55 m, D10 26 m

[0071] Proportion of monoclinic phase: <1 vol %

[0072] The plasma spray powder was processed with a plasma spray system F4 using the following setting:

[0073] Argon 35 l/min, hydrogen 10 l/min, electrical power 35 kW

[0074] Conveying gas 3 l/min, conveying 80 g/min

[0075] Nozzle: 8 mm, spray distance 120 mm

[0076] A porosity of 7% (area percent) was determined on the spray layer by means of image processing. FIG. 1 shows that the spray layer has the typical structure of a spray layer of agglomerated/sintered spray powders.

[0077] The thermal conductivity in the spray layer was determined by means of the laser flash method at temperatures from room temperature up to 1200 C. The results are shown in Table 1.

Example 2 (According to the Invention)

[0078] A plasma spray powder with a nominal particle size or grain size distribution according to DIN EN 1274:2005-02 of 125/45 pm was produced by the method agglomeration/sintering of the individual oxides Y.sub.2O.sub.3, Yb.sub.2O.sub.3, Gd.sub.2O.sub.3 and HfO.sub.2-containing ZrO.sub.2. According to chemical and physical analysis, this powder had the following properties:

[0079] Y.sub.2O.sub.3 1.64%, Yb.sub.2O.sub.3 10.19%, Gd.sub.2O.sub.3 10.10%, HfO.sub.2 1.64%

[0080] MgO, CaO, Fe.sub.2O.sub.3, Al.sub.2O.sub.3, SiO.sub.2 each <0.0100%

[0081] U.sub.2O.sub.3+ThO.sub.2<100 ppm

[0082] Remainder ZrO.sub.2

[0083] Sieve analysis:

TABLE-US-00002 >125 m 0.8% 125/106 m 7.1% 106/90 m 13.8% 90/53 m 100% remainder 53/45 m 14.1% <45 m 3.6%

[0084] Grain distribution parameters by means of laser diffraction (Microtrac X100):

[0085] D90: 109 m, D50 73 m, D10 51 m

[0086] Proportion of monoclinic phase: <1 vol %

[0087] The plasma spray powder was processed with a plasma spray system F4 using the following setting:

[0088] Argon 35 l/min, hydrogen 10 l/min, electrical power 35 kW

[0089] Conveying gas 3 l/min, conveying 80 g/min

[0090] Nozzle: 8 mm, spray distance 120 mm

[0091] A porosity of 8 +/1% (area percent) was determined in the spray layer by means of image processing. FIG. 2 shows that the spray layer also has the typical structure of a spray layer made of agglomerated/sintered spray powders.

[0092] The thermal conductivity at temperatures from room temperature up to 1200 C. was determined in the spray layers from examples 1 and 2 by means of the laser flash method. The results are shown in Table 1. A reduction in the thermal conductivity of between 7.7% (1200 C.) and 16.5% (500 C.) compared with the reference layer from Example 1 is achieved depending on the measuring temperature.

TABLE-US-00003 TABLE 1 Example 1 (comparison) Example 2 Thermal conductivity Thermal conductivity Temperature [ C.] [W/mK] [W/mK] 25 1.344 1.124 100 1.288 1.093 200 1.232 1.061 300 1.193 1.037 400 1.109 0.947 500 1.104 0.922 600 1.112 0.959 700 1.115 0.984 800 1.174 1.050 900 1.256 1.138 1000 1.416 1.251 1100 1.633 1.483 1200 1.726 1.594

[0093] As can be seen from Table 1, the thermal insulation layer produced from the powder according to the invention has a significantly reduced thermal conductivity compared with the layer produced from the comparison powder. The reduced thermal conductivity is particularly evident at higher temperatures, which has a positive effect particularly in applications in the high-temperature range.

[0094] Since the zirconium oxide powders in Examples 1 and 2 have different compositions and thus different melting behaviour, the particle size of the powder 1 was deliberately chosen to be smaller in order to compensate for the lower degree of melting and the resulting higher layer porosity of powder 1 by way of a finer particle size. As can be seen from the measured values for porosity, this has also succeeded, due to which the measured values for the thermal conductivity of the resulting coatings only permit conclusions to be drawn about the intrinsic thermal conductivity of the coating materials.