X-ray or gamma ray systems or devices – Source – Target
Patent
1986-01-28
1988-03-15
Fields, Carolyn E.
X-ray or gamma ray systems or devices
Source
Target
378143, 378125, 378129, H01J 3510, H01J 3508
Patent
active
047318058
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE ART
The invention relates to X-ray tubes and, in particular, it deals with a rotary anode for an X-ray tube and with an X-ray tube having a rotary anode.
STATE OF THE ART
Known in the art is a rotary anode for an X-ray tube, comprising a disc having a blackening coating on the surface consisting of aluminum oxide and titanium dioxide (cf. FRG Pat. No. 2443345, Apr. 5, 1979), the coating being deposited to the disc surface of the method of plasma spraying.
The oxide coating features a low radiation factor which is about 0.3 because the oxides used for producing the coating are of white colour and an increase in the radiation factor of the anode having such a coating is only due to the roughness of fused particles. In addition, the oxide coating exhibits a low heat conductance.
To produce a strong coating of oxides, methods other than the plasma spraying method cannot be used. The use of this technique requires, however, use of sophisticated equipment and high temperatures which are above the melting point of the coating material so that the process of coating application is accompanied by breaking of structure and fusion of powder particles, hence, by impairment of characteristics of both raw materials and the resultant coating.
Internal stresses on the surface of the rotary anode caused by heat shocks during application of the coating and owing to a substantial difference between coefficients of thermal expansion of the materials of the disc and coating result in cracks appearing in the coating and in particles of the coating separating therefrom during rotation of the anode.
During operation, the oxide coating is capable of releasing oxygen which is a part of the oxides thus creating unfavorable conditions for operation of a cathode.
In view of the abovesaid, use of the prior art anode in X-ray tubes results in a comparatively low power and short service life of X-ray tubes.
Service life was prolonged and power of X-ray tubes were increased by improving the radiation factor of the surface of the rotary anode during operation of the X-ray tube through the employment of a rotary anode having a disc made of a molybdenum alloy containing carbon and having a focus path region of tunsten or a tungsten alloy having a double-layer blackening coating on its surface. The outer, basic layer of the surface in this prior art anode consists of several oxides or of a mixture of several metals and several oxides, and the intemediate layer disposed between the disc and the basic layer, which is 10 to 200 .mu.m thick, is made of molybdenum and/or tungsten (cf. French patent application No. 2521776, publ. Aug. 19, 1983).
Properties of the coating (strength and radiation factor) in such anode were stabilized during operation of the X-ray tube owing to the provision of the intermediate high-melting metal which partly compensates for a difference between physico-mechanical properties of the materials of the disc and basic coating layer.
In spite of advantages of this design, it does not make possible to improve characteristics of X-ray tubes having such anode to a substantial extent because of the drawbacks inherent in rotary anodes having blackening coating containing the oxides as described above.
In addition, the process of manufacture of the prior art anode is complicated since it involves application of several layers and, hence, is highly expensive.
SUMMARY OF THE INVENTION
The invention is based on the problem of providing a rotary anode for an X-ray tube having a coating with a composition and structure which feature high mechanical strength and radiation factor, also providing an X-ray tube having such anode, the X-ray tube being such that its higher power and longer service life should be ensured in operation.
This problem is solved by that in a rotary anode for an X-ray tube, comprising a disc having its surface which has, at least partially, a blackening coating containing a metal, according to the invention, the blackening coating comprises a sintered porous composition of titanium grains, main
REFERENCES:
patent: 3737699 (1973-06-01), Gager
patent: 4271372 (1981-06-01), Geldner
patent: 4320323 (1982-03-01), Magendans et al.
patent: 4637042 (1987-01-01), Braun
Andruschenko Lev G.
Boyarina Maiya F.
Filatov Oleg V.
Kupriyanov Valery N.
Sergeev Jury S.
Fields Carolyn E.
Hynds Joseph A.
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