SLURRY FOR SUSPENSION PLASMA SPRAYING, METHOD FOR FORMING RARE EARTH ACID FLUORIDE SPRAYED FILM, AND SPRAYING MEMBER

Abstract

Provided is a slurry for suspension plasma spraying, which is a spray material used for suspension plasma spraying in an atmosphere including an oxygen-containing gas, contains 5-40 mass % of rare earth fluoride particles having a maximum particle diameter (D100) of 12 μm or less, and contains one or more types of solvent selected from among water and organic solvents. A rare earth acid fluoride-containing sprayed film, in which process shift and particle generation hardly occur, can be stably formed on a base material by carrying out suspension plasma spraying in an atmosphere including an oxygen-containing gas. A spraying member provided with this sprayed film exhibits excellent corrosion resistance to halogen-based gas plasma.

Claims

1. A suspension plasma spraying slurry for use as a spray material for suspension plasma spraying in an atmosphere containing an oxygen-containing gas, the slurry comprising 5 to 40% by weight of rare earth fluoride particles having a maximum particle size (D100) of up to 12 μm and at least one solvent selected from water and organic solvents.

2. The slurry of claim 1, further comprising up to 3% by weight of an anti-agglomerating agent of an organic compound.

3. The slurry of claim 1, further comprising up to 5% by weight of at least one microparticulate additive selected from the group consisting of rare earth oxides, rare earth hydroxides, and rare earth carbonates.

4. The slurry of claim 1 wherein the rare earth element is at least one element selected from the group consisting of yttrium (Y), gadolinium (Gd), holmium (Ho), erbium (Er), ytterbium (Yb), and lutetium (Lu).

5. The slurry of claim 1 wherein the suspension plasma spraying is atmospheric suspension plasma spraying.

6. A method for forming a sprayed coating of rare earth oxyfluoride, comprising the step of suspension plasma spraying the slurry claim 1 as a spray material to a substrate in an atmosphere containing an oxygen-containing gas.

7. The method of claim 6 wherein the suspension plasma spraying is atmospheric suspension plasma spraying.

8. The method of claim 6 wherein the sprayed coating contains a rare earth oxyfluoride as main phase.

9. The method of claim 6 wherein the rare earth oxyfluoride is at least one rare earth oxyfluoride selected from the group consisting of ReOF, Re.sub.5O.sub.4F.sub.7, Re.sub.6O.sub.5F.sub.8, and Re.sub.7O.sub.6F.sub.9 wherein Re is a rare earth element.

10. The method of claim 6 wherein the sprayed coating is a mixture of a rare earth oxyfluoride, a rare earth oxide, and a rare earth fluoride.

11. A sprayed article comprising a substrate and a sprayed coating deposited thereon and containing a rare earth oxyfluoride as main phase.

12. The sprayed article of claim 11 wherein the rare earth element is at least one element selected from the group consisting of yttrium (Y), gadolinium (Gd), holmium (Ho), erbium (Er), ytterbium (Yb), and lutetium (Lu).

13. The sprayed article of claim 11 wherein the rare earth oxyfluoride is at least one rare earth oxyfluoride selected from the group consisting of ReOF, Re.sub.5O.sub.4F.sub.7, Re.sub.6O.sub.5F.sub.8, and Re.sub.7O.sub.6F.sub.9 wherein Re is a rare earth element.

14. The sprayed article of claim 11 wherein the sprayed coating is a mixture of a rare earth oxyfluoride, a rare earth oxide, and a rare earth fluoride.

15. The sprayed article of claim 11 wherein the sprayed coating has a thickness of 10 μm to 150 μm.

16. The sprayed article of claim 11 wherein the sprayed coating has a porosity of up to 1%.

Description

EXAMPLES

[0043] Examples and Comparative Examples are given below by way of illustration and not by way of limitation.

Examples 1 to 7 and Comparative Examples 1 and 2

[Preparation of Rare Earth Fluoride Particles and Slurry for Examples 1 to 7]

[0044] A rare earth fluoride having a rare earth compositional ratio as shown in Table 1 or 2 was prepared by mixing 1 kg of a rare earth oxide (previously prepared in the rare earth compositional ratio) with 1.2 kg of acidic ammonium fluoride powder and firing the mixture in a nitrogen atmosphere at 650° C. for 2 hours. The rare earth fluoride was ground on a jet mill and passed through an air classifier, whereby a fraction of rare earth fluoride particles having a maximum particle size (D100) as shown in Table 1 or 2 was obtained. The particle size distributions (D100 and D50) and BET specific surface area of rare earth fluoride particles are shown in Table 1 or 2. The particle size distribution of particles was measured by laser light diffractometry and the BET specific surface area of particles was measured by an automatic surface area analyzer Macsorb HM model-1280 (Moumtech Co., Ltd.). (Hereafter, the same methods were applied in the measurements.) Their oxygen and fluorine concentrations (or contents) are also shown in Table 1 or 2. Particles were analyzed for oxygen concentration (or content) by an inert gas fusion infrared absorption spectroscopy using an elemental analyzer THC600 (LECO Corp.) and for fluorine concentration (or content) by dissolution ion chromatography. (Hereafter, the same methods were applied in the measurements.)

[0045] An anti-agglomerating agent and microparticulate additive (in Examples 3 to 5) in Table 1 or 2 were added to the rare earth fluoride, and a solvent in Table 1 or 2 was further added. The mixture was admitted into a nylon pot with nylon balls of diameter 15 mm where it was milled for about 2 hours. The mixture was passed through a sieve of 500 mesh (opening 25 μm), obtaining a rare earth fluoride slurry.

[Preparation of Yttrium Oxyfluoride Particles and Slurry for Comparative Example 1]

[0046] Yttrium oxyfluoride was prepared by mixing 1 kg of yttrium oxide with 1.2 kg of acidic ammonium fluoride powder and firing the mixture in a nitrogen atmosphere at 650° C. for 4 hours. The yttrium oxyfluoride was ground on a jet mill and passed through an air classifier, whereby a fraction of yttrium oxyfluoride particles having a maximum particle size (D100) as shown in Table 1 or 2 was obtained. The particle size distributions (D100 and D50) of yttrium oxyfluoride particles are shown in Table 1 or 2. Their oxygen and fluorine concentrations (or contents) are also shown in Table 1 or 2.

[0047] An anti-agglomerating agent in Table 1 or 2 was added to the yttrium oxyfluoride and a solvent in Table 1 or 2 was further added. The mixture was admitted into a nylon pot with nylon balls of diameter 15 mm where it was milled for about 2 hours. The mixture was passed through a sieve of 500 mesh (opening 25 μm), obtaining an yttrium oxyfluoride slurry.

[Preparation of Yttrium Fluoride Particles for Comparative Example 2]

[0048] Yttrium fluoride was prepared by mixing 1 kg of yttrium oxide with 1.2 kg of acidic ammonium fluoride powder and firing the mixture in a nitrogen atmosphere at 650° C. for 2 hours. The resulting yttrium fluoride was ground on a jet mill, to which polyvinyl alcohol (PVA) as a binder was added to form a slurry. The slimy was granulated by means of a spray dryer and fired in a nitrogen atmosphere at 700° C. for 4 hours, obtaining yttrium fluoride particles having a maximum particle size (D100) as shown in Table 1 or 2. The particle size distributions (D100 and D50) of yttrium fluoride particles are shown in Table 1 or 2. Their oxygen and fluorine concentrations (or contents) are also shown in Table 1 or 2.

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 Rare earth flouride (Gd.sub.0.9Lu.sub.0.1)F.sub.3 YF.sub.3 (Y.sub.0.93Yb.sub.0.05)F.sub.3 YF.sub.3 GdF.sub.3 Content in slurry 25 wt % 30 wt % 25 wt % 25 wt % 20 wt % D100 (μm) 11 8 10 9 5 D50 (μm) 3 1.8 2.4 3 1 BET (m.sup.2/g) 1.8 1.7 2.1 2.8 3.8 O concentration 0.2 wt % 0.3 wt % 0.8 wt % 1.2 wt % 1.8 wt % F concentration 27.0 wt % 38.7 wt % 39.0 wt % 37.7 wt % 24.8 wt % Anti-agglomerating poly- polyethylene- polyethylene- poly- nonionic agent carboxylate imine- imine- carboxylate surfactant polymer- based based polymer- based anionic anionic based anionic surfactant surfactant anionic surfactant surfactant Content in slurry 0.5 wt % 0.05 wt % 0.5 wt % 0.5 wt % 1 wt % Microparticulate none none Y.sub.2O.sub.3 Y(OH).sub.3 Gd.sub.2O.sub.3 additive Content in slurry — — 3 wt % 3 wt % 3 wt % D50 (μm) — — 0.01 0.01 0.05 Solvent water: water water water: isophorone ethyl DMDG = cellosolve = 4:1 (vol) 4:1 (vol)

TABLE-US-00002 TABLE 2 Example Comparative Example 6 7 1 2 Rare earth YF.sub.3 YF.sub.3 YOF YF.sub.3 fluoride Content in 30 wt % 30 wt % 30 wt % — slurry D100 (μm) 9 10 10 75 D50 (μm) 2.5 3 1.8 30 BET (m.sup.2/g) 9.8 0.6 — — O concen- 0.2 wt % 0.5 wt % 12.5 wt % 0.05 wt % tration F concen- 38.7 wt % 38.1 wt % 13.3 wt % 39.1 wt % tration Anti- polyethylme- sionionic pclyvinvl none agglomerating imine- surfactant alcohol agent based (PVA) anionic surfactant Content in 0.905 wt % 0.01 wt % 5 wt % — slurry Micro- none none none none particulate additive Content in — — — — slurry D50 (μm) — — — — Solvent IPA: butanol: water none ethyl butyl cellosolve = cellosolve 3:1 (vol) acetate = 2:1 (vol)

[Formation of Sprayed Coating, and Preparation of Sprayed Article]

[0049] On an aluminum substrate, an yttrium oxide undercoat of 150 μm thick was formed by atmospheric plasma spraying. Onto the undercoated aluminum substrate, a sprayed coating having a thickness in Table 3 or 4 was formed by using the slurry in each of Examples 1 to 7 and Comparative Example 1 or particles in Comparative Example 2 and atmospheric suspension plasma spraying (Examples 1 to 5 and Comparative Example 1) or atmospheric plasma spraying (Comparative Example 2) under the conditions in Table 3 or 4. For thermal spraying, Examples 1, 4 and 5 and Comparative Example 2 used a thermal spray equipment Triplex (Oerlikon Metco AG) and Examples 2, 3, 6 and 7 and Comparative Example 1 used a thermal spray system CITS (Progressive Surface Inc.).

TABLE-US-00003 TABLE 3 Example 1 2 3 4 5 Thermal spraying process SPS Current (A) 440 440 440 440 480 Voltage (V) 180 230 230 160 100 Power (kW) 79 101 101 70 48 Atmosphere air atmosphere and normal pressure Plasma gas 3 gases 3 gases 4 gases 4 gases 4 gases Ar (L/min) 80 150 50 50 100 H.sub.2 (L/min) 70 60 50 10 10 He (L/min) 0 0 30 10 50 N.sub.2 (L/min) 120 60 120 80 70 Coating thickness (μm) 30 60 50 80 100

TABLE-US-00004 TABLE 4 Comparative Example Example 6 7 101 2 Thermal spraying process SPS plasma spraying Current (A) 440 440 440 480 Voltage (V) 230 230 230 100 Power (kW) 80 80 101 48 Atmosphere air atmosphere and normal pressure Plasma gas 2 gases 3 gases 4 gases 3 gases Ar (L/min) 160 150 80 50 H.sub.2 (L/min) 0 10 20 10 He (L/min) 0 0 20 0 N.sub.2 (L/min) 60 50 80 10 Coating thickness (μm) 100 100 200 150

[Evaluation of Physical Properties of Sprayed Coating]

[0050] The sprayed coating was scraped off the sprayed article and analyzed by X-ray diffractometry. From the X-ray diffraction profile, phases of which each sprayed coating was composed were identified and the intensity ratio of their highest peak was determined. The sprayed coating was analyzed for oxygen and fluorine concentrations (or contents). Coatings were analyzed for oxygen concentration (or content) by an inert gas fusion infrared absorption spectroscopy using an elemental analyzer THC600 (LECO Corp.) and for fluorine concentration (or content) by dissolution ion chromatography. The porosity of the sprayed coating was determined by image analyzing an electron microphotograph in cross section of the coating. The surface hardness of the sprayed coating was measured by a Vickers hardness tester AVK-C1 (Mitutoyo Corp.) The results are shown in Table 5 or 6.

[Evaluation of Corrosion Resistance of Sprayed Coating]

[0051] Each sprayed article on its coating surface was masked with masking tape to define masked and unmasked (exposed) sections before it was mounted on a reactive ion plasma tester. A plasma corrosion test was performed under conditions: frequency 13.56 MHz, plasma power 1,000 W, etching gas CF.sub.4 (80 vol %)+O.sub.2 (20 vol %), flow rate 50 sccm, gas pressure 50 mTorr (6.7 Pa), and time 12 hours. After the test, the masking tape was stripped off. Any step formed between the exposed and masked sections due to corrosion was observed under a laser microscope. The step height was measured at 4 points, from which an average was computed to determine a height change as an index of corrosion resistance. The results are shown in Table 5 or 6.

TABLE-US-00005 TABLE 5 Example 1 2 3 4 5 Phases detected Gd.sub.5O.sub.4F.sub.7 1.1 Y.sub.5O.sub.4F.sub.7 0.9 Y.sub.5O.sub.4F.sub.7 0.6 Y.sub.6O.sub.5F.sub.8 0.4 Gd.sub.2P.sub.4F.sub.7 0.4 by X-ray GdOF 0.2 YOF 0.2 YOF 0.8 YOF 0.8 GdOF 0.8 diffractometry GdF.sub.3 0.6 YF.sub.3 0.4 YF.sub.3 0.3 YF.sub.3 0.2 GdF.sub.3 0.2 and the intensity Gd.sub.2O.sub.3 0.2 Y.sub.2O.sub.3 0.2 Y.sub.2O.sub.3 0.4 Y.sub.3O.sub.3 0.2 Gd.sub.2O.sub.3 0.5 ratio of the highest peak of each phase O concentration   2 wt %  3 wt %  6 wt %  8 wt % 10 wt % F concentration  21 wt % 33 wt % 26 wt % 23 wt %  7 wt % Porosity (vol %) 0.5 0.2 0.2 0.6 0.8 Vickers hardness 400 420 380 380 360 Hv Height change 4 3 2 5 7 (μm)

TABLE-US-00006 TABLE 6 Example Comparative Example 6 7 1 2 Phases detected Y.sub.5O.sub.4F.sub.7 0.6 Y.sub.6O.sub.5F.sub.8 0.8 YOF 0.2 YF.sub.3 0.8 by X-ray YOF 0 YOF 0 Y.sub.2O.sub.3 0.8 diffractometry YF.sub.3 0.5 YF.sub.3 0.4 and the intensity ratio of the highest peak of each phase O concentration  0.7 wt %   1 wt % 15 wt %  0.2 wt % F concentration 37.5 wt % 36.6 wt %  8 wt % 38.9 wt % Porosity (vol %) 0.3 0.3 1 3 Vickers hardness 420 390 185 250 Hv Height change 1 3 25 15 (μm)

[0052] In Examples 1 to 7, sprayed coatings were formed by atmospheric SPS of the slurry of rare earth fluoride particles having a maximum particle size (D100) of up to 12 μm. The rare earth fluoride particles were oxidized during thermal spraying, and a rare earth oxyfluoride coating was eventually formed. The sprayed coatings contained rare earth oxyfluorides as the main phase. It is demonstrated that the sprayed coating is a dense coating having a low porosity, high hardness and corrosion resistance. Sprayed coatings in Examples 1 to 5 which are used water slurry have comparatively increased oxygen content, and Sprayed coatings in Examples 6 to 7 which are used organic solvent slurry show limited increase of oxygen content.