Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Utilizing electromagnetic wave energy – ion – or plasma
Reexamination Certificate
2001-01-29
2004-05-25
Stoner, Kiley (Department: 1725)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Utilizing electromagnetic wave energy, ion, or plasma
C505S238000, C505S511000, C505S737000, C505S818000, C428S701000, C428S702000, C428S930000, C427S062000, C204S192240
Reexamination Certificate
active
06740624
ABSTRACT:
The present invention relates an apparatus and a method of spraying to form a coating on flat or curved substrates, for example, either as part of the direct formation of metallic or ceramic coatings such as superconductive or piezo-electric layers or for the production of targets for sputtering magnetrons having coatings which are precursors of such layers.
TECHNICAL BACKGROUND
From EP-A-286 135 it is known to flame spray complex ceramic materials onto a substrate such as a tape to form a superconducting layer. It is suggested to pre-heat the substrate to temperatures above 540° C. and to cool the coating slowly. It is further recommended to treat the coating in an atmosphere containing one of the components of the superconducting ceramic. An oxy-acetylene flame is used for the flame spraying. Thickness of up to 3 mm are described.
It is also known from U.S. Pat. No. 5,196,400 to plasma spray a coating onto a target for use in a sputtering magnetron to sputter a Y—Ba—CuO superconductor coating. Deposition of only a thin target coating of 0.5 mm is reported.
The production of superconducting powders using flame spraying is reported in U.S. Pat. No. 5,140,005. An oxy-acetylene flame is used. It is tacitly accepted that the high temperature of the flame changes the stoichiometric ratios of the components and that this has to be compensated by increasing the more volatile components in the original mixtures. U.S. Pat. No. 5,045,365 describes a method of cooling a oxy-acetylene flame-sprayed substrate with water. Without special precautions, water cooling is unsuitable for superconductors due to the water vapour produced.
EP-A-355 736 describes production of flat targets with metal oxides up to a layer thickness of 3 mm. WO 98/0833 describes the production of <20 micron thick layers of superconducting metal oxide mixtures.
The article by Murakami et. al. “Rapidly Solidified Thick Deposit Layers of Fe—C—Mo Alloys by Flame Spraying” describes up to 1.5 mm thick rapidly cooled thick layers of Fe—C—Mo alloys by flame spraying. Special precautions were taken to produce dense layers, e.g. direct application of cryogenic gas on the coating during application.
EP-A-586 809 describes the metal spraying application of a layer of relatively homogeneous material (nickel coated silicon) which is much easier to handle than the heterogeneous oxide mixtures contemplated by the present invention. Layer thicknesses of up to 8 mm are described but 3 to 5 mm is preferred. Various layers are proposed including a Ni—Al layer for improving adhesion between the deposited layer and the substrate. A Ni—Al adhesion promoter is known from DE-A-33 18 828.
Plasma spraying of superconducting materials is described in EP-A-2887 11 up to a thickness of 250 micron.
It is an object of the present invention to provide an apparatus and a method of spraying heterogeneous metal oxides to form a ceramic coating on flat or curved substrates.
It is a further object of the present invention to provide an apparatus and a method of spraying heterogeneous metal oxides to form a thick walled ceramic coating on flat or curved substrates which is structurally sound.
It is a further object of the present invention to provide an apparatus and a method of spraying to form a thick walled coating of a superconducting ceramic material.
It is still a further object of the present invention to provide an apparatus and a method of spraying suitable for forming a thick walled ceramic coating on flat or curved targets to be used in a sputtering magnetron.
It is still another object of the present invention to provide a method of producing a (magnetron) vacuum sputtering target as well as the target itself with improved thermal and electrical conductivity and high mechanical strength using a spraying process employing dedicated powder formulations.
SUMMARY OF THE INVENTION
One aspect of the present invention is to provide a substrate with a coating of a combination of metal oxides having a thickness greater than 3 mm more preferably greater than 5 mm and most preferably greater than 8 mm. Preferably, the coating is deposited by spraying, e.g. flame or plasma spraying. Preferably, the substrate is cylindrical and is more preferably is suitable as a cylindrical target substrate for a sputtering magnetron. The combination of oxides preferably comprises at least a superconductive precursor or a superconductor. The thermal conductivity of the deposited material is preferably between 1 and 5 Wm
−1
K
−1
. When deposited on a steel substrate the thermal conductivity of the composite preferably lies within the range 25 to 125 Wm
−1
K
−1
. These values are particularly preferred for YBa
2
Cu
3
O
7
coatings. Preferably, an adhesion promoter layer is applied onto the substrate before application of the coating of the metal oxide combination. The adhesion promoter may be a layer of Ni—Al or a layer of an In-alloy, for example. The deposited coating is preferably impact resistant, e.g. withstands impact of a 0.036 kg steel ball from a height of 2 meters. Preferably, about 20% or up to 30% of a noble metal is included in the oxide material to improve electrical and thermal properties of the deposited layer. The noble metal is preferably silver. The noble metal may in included as a salt or oxide, e.g. silver nitrate or silver oxide, in the material to be sprayed. Preferably, the electrical resistivity of the deposited layer is lower than 15×10
−6
Ohm.m, more preferably lower than 10×10
−6
and most preferably less than 5×10
−6
Ohm.m. Values below 1×10
−6
Ohm.m can be achieved. Up to 30% of a noble metal such as silver may be added to lower the resistivity. These values are particularly preferred for YBa
2
Cu
3
0
7
coatings.
The electrical, thermal and mechanical properties of the coating deposited in accordance with the present invention should be sufficient that the deposited layer can be applied to a suitable substrate by means of a sputtering magnetron preferably at a static sputtering deposition speed of at least 5 nm/minute, more preferably, at 20 nm/minute and most preferably at at least 40 nm/minute.
When a superconductor precursor or a superconductive material is deposited, at least 10% of the coating is in the superconducting phase, more preferably 15%. This may be assisted by a subsequent limited thermal treatment, e.g. 3 hours and 940° C., after deposition.
The present invention also includes a method of depositing by spraying a superconductor precursor layer onto a cylindrical target for a sputtering magnetron, the layer having a thickness of at least 3 mm, and at least 10% of the layer being in a superconductive phase. The present invention also includes a method of depositing by spraying a layer onto a substrate, the layer having a thickness of at least 5 mm, and the coating comprising metal oxides.
In accordance with one aspect of the present invention a flame spraying apparatus is provided for depositing a metal oxide combination onto a substrate to produce a coating thereon, comprising: a burner for producing a flame; an inlet for feeding material to be sprayed through the flame, the flame imparting a temperature to the material to be sprayed of 1500° C. or less, preferably 1200° C. or less. Preferably the temperature imparted may be a little higher than the melting point of the powder to be sprayed, e.g. 600 to 1000° C. for some metal oxides. Preferably, the thickness of the deposited coating is greater than 3 mm more preferably greater than 5 mm and most preferably greater than 8 mm.
Another aspect of the present invention is to provide a flame spraying apparatus for depositing a metal oxide combination onto a substrate to produce a coating thereon, comprising: a flame spraying gun; and a cooling system for the substrate, the cooling system including a device for bringing a cryogenic fluid into contact with the substrate. Preferably, the thickness of the deposited coating is greater than 3 mm more preferably greater than 5 mm and most preferably greater than
Hoste Serge
Persyn Frans
Van Driessche Isabel
Barnes & Thornburg
Cooke Colleen P.
Stoner Kiley
Universiteit Gent
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