CORROSION-RESISTANT PERMANENT MAGNET FOR AN INTRAVASCULAR BLOOD PUMP

Abstract

This invention is directed to a corrosion-resistant permanent magnet, to a method for producing a corrosion-resistant permanent magnet, and to an intravascular blood pump comprising the magnet. The magnet is surrounded by a composite coating, the composite coating comprising, in the order recited, a first metal oxide layer, a metal layer, a second metal oxide layer, a linker layer, and a layer formed from poly(2-chloro-p-xylylene). In an alternative embodiment, a further metal layer and, optionally, a further metal oxide layer may be provided between the second metal oxide layer and the linker layer. In a further alternative embodiment, the metal layer may be omitted, and a further layer structure comprising at least one metal oxide layer, a linker layer, and a layer formed from poly(2-chloro-p-xylylene) may be provided instead.

Claims

1. A corrosion-resistant permanent magnet comprising a magnet body and a composite coating provided on and covering surfaces of the magnet body, the composite coating comprising, in the order recited, a first metal oxide layer in physical contact with the magnet body, a metal layer, a second metal oxide layer, a linker layer, and a layer formed from poly(2-chloro-p-xylylene).

2. The magnet of claim 1, wherein the magnet body is a rare earth metal iron boron permanent magnet.

3. The magnet of claim 2, wherein the magnet body is a sintered magnet body having Nd.sub.2Fe.sub.14B crystals and a neodymium iron boron material surrounding the Nd.sub.2Fe.sub.14B crystals, said neodymium iron boron material being richer in neodymium than the Nd.sub.2Fe.sub.14B crystals.

4. The magnet of claim 1, wherein the metal of the metal layer is aluminum or titanium or an alloy of aluminum or titanium.

5. The magnet of claim 1, wherein the oxide of the first metal oxide layer is Al.sub.2O.sub.3 or TiO.sub.2 or a mixed oxide of Al.sub.2O.sub.3 and TiO.sub.2.

6. The magnet of claim 1, wherein the oxide of the second metal oxide layer is Al.sub.2O.sub.3 or TiO.sub.2 or a mixed oxide of Al.sub.2O.sub.3 and TiO.sub.2.

7. The magnet of claim 1, comprising a further metal layer and, optionally, a further metal oxide layer between the second metal oxide layer and the linker layer, wherein the metal layer is in physical contact with the first metal oxide layer, the second metal oxide layer is in physical contact with the metal layer, the further metal layer is in physical contact with the second metal oxide layer, the further metal oxide layer, if present, is in physical contact with the further metal layer, the linker layer is in physical contact with the further metal layer or, if present, the further metal oxide layer, and the poly(2-chloro-p-xylylene) layer is in physical contact with the linker layer.

8. The magnet of claim 7, wherein the metal of the further metal layer is aluminum.

9. The magnet of claim 1, wherein the metal layer is omitted, and the composite coating further comprises, in the order recited, on the layer formed from poly(2-chloro-p-xylylene), a third metal oxide layer, a further linker layer, and a further layer formed from poly(2-chloro-p-xylylene).

10. The magnet of claim 9, further comprising an intermediate metal oxide layer between the layer formed from poly(2-chloro-p-xylylene) and the third metal oxide layer.

11. The magnet of claim 9, wherein the oxide of the first metal oxide layer is Al.sub.2O.sub.3 and the oxide of the second metal oxide layer is TiO.sub.2, or the oxide of the first metal oxide layer is TiO.sub.2 and the oxide of the second metal oxide layer is Al.sub.2O.sub.3, or the oxides of the first and second metal oxide layers are Al.sub.2O.sub.3, or the oxides of the first and second metal oxide layers are TiO.sub.2, and/or wherein the oxide of the third metal oxide layer is TiO.sub.2 or Al.sub.2O.sub.3.

12. The magnet of claim 10, wherein the oxide of the intermediate metal oxide layer is Al.sub.2O.sub.3 or TiO.sub.2, and is different from the oxide of the third metal oxide layer.

13. A method for producing a corrosion-resistant permanent magnet, the method comprising providing a non-magnetized magnet body, forming a first metal oxide layer on surfaces of the magnet body, forming a metal layer on the first metal oxide layer, forming a second metal oxide layer on the metal layer, optionally, forming at least one further layer on the second metal oxide layer, forming a linker layer on the second metal oxide layer or, if present, on the at least one further layer, forming a layer of poly(2-chloro-p-xylylene) on the linker layer, and magnetizing the magnet body.

14. The method of claim 13, the method comprising forming the at least one further layer, wherein the at least one further layer is a further metal layer.

15. The method of claim 14, further comprising forming a further metal oxide layer on the further metal layer.

16. The method of claim 13, wherein the oxide of the first metal oxide layer and/or the oxide of the second metal oxide layer is the oxide of claim 5.

17. The method of claim 13, wherein the metal of the metal layer is the metal of claim 4.

18. The method of claim 14, wherein the metal of the further metal layer is the metal of claim 8.

19. A method for producing a corrosion-resistant permanent magnet, the method comprising providing a non-magnetized magnet body, forming a first metal oxide layer on surfaces of the magnet body, forming a second metal oxide layer on the first metal oxide layer, forming a linker layer on the second metal oxide layer, forming a layer of poly(2-chloro-p-xylylene) on the linker layer, optionally, forming an intermediate metal oxide layer on the poly(2-chloro-p-xylylene) layer, forming a third metal oxide layer on the poly(2-chloro-p-xylylene) layer or, if present, on the intermediate metal oxide layer, forming a further linker layer on the third metal oxide layer, forming a further layer of poly(2-chloro-p-xylylene) on the further linker layer, and magnetizing the magnet body.

20. The method of claim 19, wherein the oxide of the first metal oxide layer is Al.sub.2O.sub.3 and the oxide of the second metal oxide layer is TiO.sub.2, or the oxide of the first metal oxide layer is TiO.sub.2 and the oxide of the second metal oxide layer is Al.sub.2O.sub.3, or the oxides of the first and second metal oxide layers are both Al.sub.2O.sub.3 or are both TiO.sub.2, and/or the oxide of the third metal oxide layer is TiO.sub.2 or Al.sub.2O.sub.3.

21. The method of claim 19, comprising forming the intermediate metal oxide layer, wherein the oxide of the intermediate metal oxide layer is Al.sub.2O.sub.3 or TiO.sub.2, and is different from the oxide of the third metal oxide layer.

22. An intravascular blood pump comprising an electric motor, wherein the electric motor comprises the permanent magnet of claim 1.

Description

[0207] The present invention will be further explained with reference to the accompanying drawings, wherein

[0208] FIG. 1 is a schematic longitudinal section of an exemplary embodiment of an intravascular blood pump.

[0209] FIG. 2 is a schematic sectional view of a portion of a magnet according to the first embodiment of the present invention,

[0210] FIG. 3a is a schematic sectional view of a portion of a magnet according to the second embodiment of the present invention,

[0211] FIG. 3b is a schematic sectional view of a portion of another magnet according to the second embodiment of the present invention,

[0212] FIG. 4a is a schematic sectional view of a portion of a magnet according to the third embodiment of the present invention,

[0213] FIG. 4b is a schematic sectional view of a portion of another magnet according to the third embodiment of the present invention,

[0214] FIG. 5a is a schematic representation of an exemplary single-piece magnet according to the present invention,

[0215] FIG. 5b is a partial sectional view showing a detail of the magnet illustrated in FIG. 5a, and

[0216] FIG. 6 is a schematic top view of an exemplary segmented magnet according to the present invention.

[0217] The drawings are not to scale. They should not be construed as limiting the invention in any manner.

[0218] The intravascular blood pump 10 illustrated in FIG. 1 has been described above. The pump is conventional in construction, but comprises a corrosion resistant permanent magnet 1 according to the present invention.

[0219] In the pump of FIG. 1, the magnet 1 is rod-shaped, the opposing front faces being flat and parallel to each other. While the composite coating according to the present invention may effectively protect a magnet body having sharp edges as illustrated in FIG. 1 against corrosion over an extended period of time, it is preferred in the present invention to use a magnet body having a shape as illustrated in FIGS. 5 and 6. The individual layers of the composite coating completely extend over each previously applied composite coating layer.

[0220] FIG. 2 is a schematic sectional view of a portion of a magnet 1 having a composite coating 15 according to the first embodiment of the present invention. In the case of the exemplary magnet illustrated in FIG. 2, the composite coating 15 is formed on a surface 19′ of a non-magnetized magnet body 19. Composite coating 15 comprises a first aluminum oxide layer 42 formed by atomic layer deposition on surface 19′ of magnet body 19. An aluminum layer 43 is deposited by physical vapor deposition on surface 42′ of aluminum oxide layer 42. A second aluminum oxide layer 44 is deposited by atomic layer deposition on surface 43′ of aluminum layer 43. The first aluminum oxide layer 42, the aluminum layer 43 and the second aluminum oxide layer 44, in combination, constitute the inorganic layer 41 of composite coating 15. A linker layer 46 is formed on surface 44′ of the second aluminum oxide layer 44, and firmly bonds the organic layer 47 to the second metal oxide layer 44. The organic layer 47 of composite coating 15 consists of Parylene C and covers surface 46′ of the linker layer 46.

[0221] In the case of the exemplary magnet illustrated in FIG. 2, the first aluminum oxide layer and the second aluminum oxide layer each have a thickness of 100 nm, the aluminum layer has a thickness of 4 μm, the layer formed from Parylene C has a thickness of 15 μm, and the linker layer is a monolayer.

[0222] FIG. 3a is a schematic sectional view of a portion of a magnet 1 having a composite coating 16 according to the second embodiment of the invention. In the case of the exemplary magnet illustrated in FIG. 3a, the composite coating 16 is formed on surface 19′ of a non-magnetized magnet body 19. Composite coating 16 comprises a first metal oxide layer 52 consisting of titanium oxide. The first metal oxide layer 52 is deposited by atomic layer deposition on a surface 19′ of the magnet body 19 to a thickness of 100 nm. A metal layer 53 consisting of titanium is deposited by physical vapor deposition on surface 52′ of the first metal oxide layer 52 to a thickness of 4 μm. On surface 53′ of metal layer 53, a second metal oxide layer 54 is deposited by atomic layer deposition to a thickness of 100 nm. The second metal oxide layer consists of a mixture of aluminum oxide and titanium oxide. A plating layer 55 is provided on a surface 54′ of the second metal oxide layer 54. The plating layer 55 is an aluminum metal layer and has a thickness of about 15 μm. The first metal oxide layer 52, the metal layer 53, the second metal oxide layer 54 and the further metal layer 55, in combination, constitute an inorganic layer 51. A linker layer 56 is formed on surface 55′ of the further metal layer 55, and firmly bonds the organic layer 57 to the further metal layer 55. The organic layer 57 of composite coating 16 consists of Parylene C and covers surface 56′ of linker layer 56.

[0223] FIG. 3b shows a magnet 1 similar to the magnet shown in FIG. 3a, however, with a further metal oxide layer 58 provided on aluminum metal layer 55. In the embodiment illustrated in FIG. 3b, the further metal oxide layer 58 is a native aluminum oxide layer having a thickness of approximately 3 nm, i.e. a passivation layer formed upon exposure of the aluminum metal layer to air.

[0224] FIG. 4a is a schematic sectional view of a portion of a magnet 1 having a composite coating 18 according the third embodiment of the invention. In the case of the exemplary magnet illustrated in FIG. 4a, the composite coating 18 comprises a first layer structure 17 and a second layer structure 17′.

[0225] The first layer structure 17 comprises an inorganic layer 61 consisting of a first metal oxide layer 62 and a second metal oxide layer 64, an organic layer 67, and a linker layer 66 provided between the second metal oxide layer 64 and the organic layer 67. The second layer structure 17′ is provided on the first layer structure 17, and comprises an inorganic layer 71 consisting of a third metal oxide layer 74, an organic layer 77 and a linker layer 76 provided between the third metal oxide layer 74 and the organic layer 77.

[0226] The first metal oxide layer is an aluminum oxide layer having a thickness of 100 nm, formed by atomic layer deposition on surface 19′ of magnet body 19. The second metal oxide layer is a titanium oxide layer having a thickness of 10 nm, formed by atomic layer deposition on surface 62′ of the first metal oxide layer. Linker layer 66 is a monolayer formed on surface 64′ of the second metal oxide layer, and organic layer 67 is a layer formed from Parylene C on surface 66′ of linker layer 66. The Parylene C layer has a thickness in a range from 1 to 2 μm.

[0227] The third metal oxide layer 74 is a titanium oxide layer having a thickness of 10 nm, formed by atomic layer deposition on surface 67′ of the first organic layer 67. A linker layer 76 is provided on surface 74′ of the titanium oxide layer, and a further Parylene C layer 77 is formed on surface 76′ of linker layer 76. This outermost Parylene C layer has a thickness of about 13 μm.

[0228] FIG. 4b shows a magnet 1 similar to the magnet shown in FIG. 4a, however, an additional (intermediate) metal oxide layer 72 is provided between organic layer 67 and third metal oxide layer 74. Therefore, the second layer structure 17′ comprises an inorganic layer 71 consisting of the intermediate metal oxide layer 72 and a third metal oxide layer 74, an organic layer 77 and a linker layer 76 provided between the third metal oxide layer 74 and the organic layer 77. The intermediate metal oxide layer 72 is an aluminum oxide layer having a thickness of 20 nm, formed by atomic layer deposition. As for the rest, the same applies as in the case of the embodiment illustrated in FIG. 4a above. The first layer structure and the second layer structure comprise layers made from the same materials (while in other embodiments, the materials may be different), but having different thicknesses.

[0229] In the embodiments illustrated in FIGS. 4a and 4b all linker layers are monolayers and are identical.

[0230] FIG. 5a shows a single-piece magnet 1 having a rod shape and a bore or channel extending therethrough in a longitudinal direction. During use of the magnet in an intravascular blood pump 10 as illustrated in FIG. 1, the channel receives the motor shaft 25. The opposing front faces 4 of the magnet are tapered towards the channel. The magnet 1 is provided with a composite coating according to the invention at the outer surfaces 2 exposed to the fluid flowing in gap 26 and the tapered front faces 4. The inner surfaces 3 adjacent to the motor shaft 25 may or may not be coated. Edge 5 at the transition between the outer surface 2 and the front surface 4, as well as edge 6 at the transition between front surface 4 and the inner surface 3, are coated. The edges are soft, thus facilitating the formation of a well-adhering uniform coating. “N” and “S” indicate the north pole and the south pole of the magnet.

[0231] FIG. 5b is a partial sectional view along the dash-dot line in FIG. 5a. FIG. 5b shows the region of the magnet within the loop in FIG. 5a. FIG. 5b clearly shows the soft edges 5, 6.

[0232] FIG. 6 shows a segmented magnet 7. The magnet illustrated in FIG. 6 has four segments 8, 8′. Segments 8, which are opposite to one another, have the same magnetic polarity, as indicated by “N” in the top view of FIG. 6, and segments 8′, which are also opposite to one another, have the same magnetic polarity, as indicated by “S” in the top view of FIG. 6. As a result, adjacent segments 8, 8′ have opposite magnetic polarity.

[0233] Segments 8, 8′ have, analogously to the single-piece magnet shown in FIG. 5, inner surfaces, outer surfaces, opposing front faces, edges at the transition between the outer surfaces and the front surfaces, and edges at the transition between the front surfaces and the inner surfaces. The front faces are designated 4′, and the edges are designated 5′ and 6′, respectively, in correspondence to the designations in FIG. 5. In addition, segments 8, 8′ have side surfaces 9, 9′, separated by gaps in the drawing. Of course, when the magnet is in use, side surfaces 9, 9′ contact each other. All surfaces of each segment of the magnet may be completely covered by the inventive composite coating, but side surfaces 9, 9′ which are not exposed because they contact each other, and the inner surfaces which are not exposed because they contact the motor shaft, do not need to be coated. Preferably all edges of all segments are soft edges.

[0234] Identical cylindrical non-magnetized Nd.sub.2FeB.sub.14B sintered magnet bodies having a length of 12 mm and a diameter of 2.8 mm were coated (after washing, but without removal of the phosphate coating) with different coatings, magnetized, and subjected to corrosion testing in an aqueous solution containing 0.9 weight % sodium chloride at 60° C. In this test corrosion proceeds about 3.75 times faster than at room temperature in a solution of 5% to 40%, by weight, glucose in water for injection.

[0235] The following coatings proved to be particularly advantageous as regards the desired combination of excellent corrosion resistance and minimum rate of rejects: Magnets according to the first embodiment having a first metal oxide layer and a second metal oxide layer formed by ALD to a thickness of 100 nm, a metal layer formed by PVD to a thickness of 4 μm, and a Parylene C coating formed to a thickness of 15±2 μm. The best magnets had (a) Al.sub.2O.sub.3 as a first and a second metal oxide layer and aluminum as a metal layer, (b) Al.sub.2O.sub.3 as a first and a second metal oxide layer and titanium as a metal layer, (c) TiO.sub.2 as a first and a second metal oxide layer, and titanium as a metal layer, (d) Al.sub.2O.sub.3 as a first metal oxide layer, a mixture of Al.sub.2O.sub.3 and TiO.sub.2 as a second metal oxide layer, and titanium as a metal layer, and (e) TiO.sub.2 as a first metal oxide layer, a mixture of Al.sub.2O.sub.3 and TiO.sub.2 as a second metal oxide layer, and titanium as a metal layer. Biasing during PVD appeared to improve coating quality.

[0236] Magnets according to the second embodiment having a first metal oxide layer formed by ALD to a thickness of 100 nm, a second metal oxide layer formed by ALD to a thickness of 100 nm, a metal layer formed by PVD to a thickness of 4 μm, a further metal layer (aluminum) formed by plating to a thickness of 15 μm±3 μm, and a Parylene C coating formed to a thickness of 15±2 μm.

[0237] The best magnets had (a) Al.sub.2O.sub.3 as the first metal oxide layer and the second metal oxide layer, and aluminum as the metal layer, (b) TiO.sub.2 as the first metal oxide layer, a mixture of Al.sub.2O.sub.3 and TiO.sub.2 as the second metal oxide layer, and titanium as the metal layer, and (c) TiO.sub.2 as the first and the second metal oxide layer, and iron as the metal layer.

[0238] Magnets according to the third embodiment having Al.sub.2O.sub.3 as the first metal oxide layer, formed by ALD to a thickness of 100 nm, TiO.sub.2 as the second metal oxide layer, formed by ALD to a thickness of 10 nm, a Parylene C coating formed to a thickness of 1 to 2 μm, Al.sub.2O.sub.3 as the intermediate metal oxide layer, formed by ALD to a thickness of 20 nm, TiO.sub.2 as the third metal oxide layer formed by ALD to a thickness of 10 nm, and a Parylene C coating formed to a thickness of 13±2 μm.

[0239] In each case, linker layers and further linker layers, where applicable, were formed from an alcoholic solution (water/ethanol; acetic acid to achieve a pH of about 5 to 6; concentration of silane about 1%; reaction time about 5 minutes) containing silane A-174. Evaporation of the alcohol yielded essentially monolayers. Parylene C coatings were formed by plasma deposition.