United States Patent 1191 1111 3,982,148 Kaplan et al. 1451 Sept. 21, 1976

[541 HEAT RADIATING COATING AND 3,819,971 6/1974 Kaplan et a1 ...... 313/330 METHOD OF MANUFACTURE THEREOF 3,869,6343,821,581 6/19743/1975 HollandKonieczynski et al. et...... a1 ...... 313/330 [75] Inventors: Richard B. Kaplan, Hollywood; Sebastian Gonnella, Arleta; Walter FOREIGN PATENTS OR APPLlCATlONS M. Abrams, Van Nuys, ail of Calif. 947,998 8/1956 Germany ...... 313/330 [73] Assignee: Ultramet, Pacoima, Calif. Primary Examiner—Sax?eld Chatmon, Jr. [22] Filed: May 7, 1975 Attorney, Agent, or Firm—Edwin A. Oser [21] Appl. No.: 570,281 [5 7 ] ABSTRACT A heat radiating coating of for a refractory [52] U.S. Cl ...... 313/330; 313/40; core which may be used for a rotating X-ray anode, 313/41; 313/309; 313/351; 427/65; 427/160; power tube or the like. The coating is characterized by 313/55 a multiplicity of needle-like radiation-re?ecting ele [51] Int. Cl.2 ...... 1101.1 35/08 ments disposed adjacent to each other. The needles [58] Field of Search ...... 313/330, 309, 351, 336, have such steep angles that incoming radiation is sub 313/40, 41, 55; 427/35, 36, 65, 58,160 stantially absorbed thereby by repeated re?ection. Since the coating has a high radiation absorption coef [56] References Cited ?cient it has a corresponding high emissivity on the UNITED STATES PATENTS order, of 0.9 at elevated temperatures. A process is dis 2,071,696 2/1937 Jonas ...... 313/40 closed for depositing such a heat radiating coating of 2,607,016 8/1952 Kennebeck ...... 313/351 X rhenium by chemical vapor deposition. 3,174,043 3/1965 Dyke et al...... 313/309 X 3,453,478 7/1969 Shoulders et a1, ...... 313/336 X 5 Claims, 4 Drawing Figures

\\\\\\\\\\\\\\\\\\\\\\ US. Patent Sept. 21, 1976 3,982,148 3,982,148 1 pentachloride. The rhenium hexa?uoride reaction is HEAT RADIATING COATING AND METHOD OF carried out at 800°C and for the MANUFACTURE THEREOF ' at about I000°C. However, none of these prior coatings have a really high emissivity, where the maximum pos BACKGROUND OF THE INVENTION 5 sible emissivity is 1.0 as in a perfect black body radia This invention relates generally to a heat radiating tor. In other words, the actual emissivity is less than one coating for a refractory core and a method of manufac third of the theoretical emissivity. ture thereof, and particularly relates to such a coating It is accordingly an object of the present invention to suitable, for example, for the rotating anode of an provide a coating consisting of rhenium for a refractory X‘ray tube, high power tubes and the like, and capable core which has superior heat radiating properties, that of withstanding the high vacuum and high temperatures is an emissivity on the order of 0.9. encountered in such environments. Another object of the present invention is to provide For many applications such as high power tubes‘and such a coating which consists of radiation re?ecting X-ray tubes, it is imperative to have a material capable needle-like elements which due to their steep angles of radiating heat with high efficiency-For example, in will re?ect radiation out of the coating to provide a an X-ray tube of the type having a rotating anode, the high degree of radiation and a correspondingly high electron beam bombards a track on the anode which in emissivity. turn radiates the X-rays. However, most of the incom A further object of the present invention is to provide ing energy is transformed into heat. Hence the ef?— a process of depositing such a heat radiating coating of ciency of the reradiation of heat from the anode deter 20 rhenium by the vapor deposition of the rhenium in the mines how often the tube can be pulsed or how much form of a halogenide of rhenium. energy can be applied thereto as a function of time. For example, for modern X-ray techniques rapid and SUMMARY OF THE INVENTION repetitive exposures are required to obtain'the desired A heat radiating coating for a refractory core in ac 25 results. This is particularly true of angiography or cine cordance with the present invention consists of a layer radiography. Similar considerations apply for high of rhenium having a thickness of no less than about 25 power tubes. microns. They layer further has a heat radiating emis In the past various materials capable of withstanding sivity on the order of 0.9 at a temperature on the order high temperatures have been used, for example, vfor the 30 of I000°C (Centigrade). The coating may cover all or anode or the anode coating of X-ray tubes. Generally, part of the refractory core. For example, it may be such materials as tungsten and rhenium or composites desired to provide a different material or coating for thereof have been proposed. These materials not only the focal track of a rotating X-ray anode. The coating are capable of withstanding high temperatures, but are ‘ further consists of a multiplicity of needle-like radia also good X-ray emitters due to their high atomic num- ‘ 35 tion-re?ecting elements disposedrgadjacent to each bers. ' other. The needle-like elements have such steep angles For example, the US. Pat. No. 3,649,355 to Hennig that incoming radiation is substantially absorbed describes a process for coating a refractory core for the purpose of providing a rotating X-ray anode. It is pro thereby by re?ection and accordingly the coating will ,posed that tungsten or tungsten alloys are deposited similarly reradiate heat coming from the core by a from a gaseous phase and such vapor deposition. to 40 reciprocal process. Due to its radiation absorbing char produce tungsten coatings is generally known. The acter the coating appears black to the naked eye while ‘refractory core may, for example, consist of graphite or nevertheless the needles re?ect radiation. When other suitable materials. . viewed through a low powered microscope, the individ‘ The US. Pat. No. 2,863,083 to Schram also discloses ual needles appear as highly re?ecting surfaces. anodes for X-ray tubes. Speci?cally, it is proposed to 45 A process is also described for depositing such a heat make the anode either entirely of rhenium or to pro radiation coating of rhenium from a halogenide of rhe vide it with a coating of rhenium. One of the processes nium such as rhenium pentachloride or rhenium hexa recommended is the chemical vapor deposition of rhe ?uoride. - nium by decomposing a halogenide of rhenium such as The .novel features that are considered characteristic rhenium pentachloride at a temperature between 500 50 of this invention are set forth with particularity in the and 1500°C (centigrade) in vacuum. However, the appended claims. The invention itself, however, both as emissivity of such a coating disclosed by Schram is no to its organization and method of operation, as well as more than about 0.3. It is also proposed by Schram that additional objects and advantages thereof, will best be the non-focal surface be blackened by a known process understood from the following description when read not further speci?ed, apparently in an effort to increase 55 in‘connection with the accompanying drawing. the heat radiation properties of the coating. _ BRIEF DESCRIPTION OF THE DRAWING The anode may consist of a refractory core, for‘ex ample molybdenum or graphite. In some cases an inter FIG. 1 is a cross-sectional view of a rotatable anode mediate layer is provided between the outer rhenium of an X-ray tube embodying the coating of the present coating and the refractory core and the intermediate invention; . layer may, for example, consist of tungsten or the like. FIG. 2 is a schematic greatly enlarged view of two of Reference is also made to the prior US. Pat. to Kap the needle-like elements of the coating of the invention lan et al. No. 3,819,971. This patent dealswith a com showing the path of a light ray entering the structure; posite anode for X-ray tubes where the coating is re FIG. 3 is a cross-sectional view similar to that of FIG. tained to the core by means of scoring the surface of 65 I but with the coating omitted at the focal track of the the core or similar means. This patent also discloses a anode; and process for the chemical vapor deposition of rhenium, FIG. 4 is a reproduction of a microphotograph of for example. from rhenium hexa?uoride or rhenium 2000 X enlargement of the coating of the present in 3,982,148 vention illustrating the needle-like elements above re re?ect radiation and appears as highly re?ective tiny ferred to. ~ mirrors. I V _ Because, of thcneedle-like structure required the DESCRIPTION OF THE PREFERRED coating 12 should have a thickness no less than about EMBODIMENTS 25 microns so that the'needles can form the proper Referring now to FIG. 1 there is illustrated a conven aspect ratioaln general, it is desired to have as thin a tional anode for a rotating anode of an X-ray tube coating as possible because rhenium‘is an expensive provided with the coating of the invention. Thus, the metal. Actually, the coating may be as thick as 250 anode includes a refractory core' l0having a_ central microns. For example, the patent to Schram above aperture 11 through which may pass a rod and a screw, referred to suggests a coating of a thickness of 10 mi the rod being connected to a motor for rotating the crons which isnot thick enough to permit the needle anode. The refractory core 10 may, for example, con like structure of the coating of the invention to form. sist of molybdenum, tungsten, or a composite of rhe The coating of the present invention may be depos nium, tungsten and molybdenum. Instead ofa metal the ited in the following manner. A gaseous mixture of core may consist of other refractory materials such as rhenium pentachloride and argon may be introduced graphite or a ceramic such, for example, as silicon - into a vacuum chamber or the, reaction may take place carbide, boron carbide or boron nitride. In some cases at atmospheric pressure in a reaction chamber. The it may be desirable to provide an intermediary layer reaction ‘chamber contains a heated substrate or refrac between .the refractory core 10 and the outer core 12 tory core upon which the coating is to be applied. The not illustrated. Such an intermediary layer may, for core or substrate is heated to a temperature in the example, consist of tungsten or similar materials. How range between about 900°C and about 1100°C. This ever, the term refractory core is meant to include both temperature range is within the temperature range the core and an intermediary layer if present. where the reaction takes place viz 850° to 1400°C. Accordingly, the following reaction takes place: In accordance with the present invention the core 10 25 is provided with an outercoating 12 which consists of rhenium and which 'has certain properties which make it uniquely suitable for use in high power tubes and Optionally the reaction may take place in the presence X-ray tubes. In particular, the coating has a very low 'of argon or another . _ vapor pressure and is capable of withstanding the high For reasons of speed'and- economy it is usually de vacuum, as well as the high temperatures encountered sired to maintain the reaction efficiency as high as in such tubes. possiblefHowever, in accordance with the present The coating ‘consists of a multiplicity of needle-like invention the reaction efficiency is held at no more radiation-re?ectingelements of the type illustrated in than about 60%. This, of course, means that there must the electron photomicrograph of FIG. ‘4. It is these be an excess of the rhenium pentachloride. . needle-like elements which give the coating its unique These conditions are essential for the deposition of a properties. As shown schematically in FIG. 2, there are rhenium coating with the properties previously enu two adjacent needles l4 and 15 with relatively steep merated. Normally, as explained, it is desirable to angles. A light ray l6 entering the valley between the maintain the reaction ef?ciency as high as possible. two needles l4, 15 is successively reflected down 40 Furthermore, the usable deposition temperature range wardly until it is ?nally absorbed. Assuming, ‘for exam is much wider than that appropriate for the growth of ple, that thesurfaces re?ect 70% of the impinging light, ‘ the needle-like structure. then 30% of the light is absorbed as heat. Because the Instead of carrying out the reaction with rhenium ' incoming light my 16 is successively re?ected down pentachloride, other halogenides of rhenium may be ward, less and less- light remains to be re?ected so that 45 .used for the vapor deposition. Thus, the reaction may substantially all of the light is eventually absorbed. also be carried out with rhenium hexa?uoride and hy This is the reason that the emissivity is on the order of drogen in which the reaction procedure is as follows: 0.9. In any black body or near ideal black body a high heat absorption corresponds to a high emissivity of heat. This phenomenon is well understood from basic 50 physics. Substantially all-of the light which impinges at . As will be seen from reaction (2) hydrogen ?uoride an angle between 90° and say 20° to a horizontal plane forms and the pure rhenium remains and is deposited. is thus substantially re?ected until completely ab This process is generally carried out in the same man sorbed. Conversely, the heat of the anode. is substan -ner.with a reaction efficiency of no more than about tially completely rcradiated. Thus referring again to 55 60%, that is with an excess of rhenium hexa?uoride. FIG. 2 when the coating is heated the’hcat radiation In order for the reaction to take place and the needle will be re?ected as shown by the light ray 16 except like structure to form the substrate is heated to a tem that the direction of travel is reversed. Instead of 'the perature between about 750° and about 900°C. Actu light ray ‘being partially absorbed during each re?ection ally, this reaction can take place over a temperature additional heat radiation will emerge at each re?ection range of 500° to l50()°C; Nevertheless, the temperature point, thereby to increase the emissivity. This process is range is limited in accordance with the present inven particularly efficient at the elevated temperature at ‘tion to produce the desired results. which the coating is to be used. This is true because Referring now to FIG. 3, there is illustrated a modi-. most of the heat is radiated in the form of visible light ?ed anode in accordance with the present invention. 65 and infrared. ' v ‘ The anode again comprises a refractory core 10 having Due to its light absorbing character the coating ap a central aperture 11 and a coating 12. However, the pears black to the naked eye. However, when viewed focal track 20 has not been covered with the coating of under a light microscope the needle-like structure does rhenium and instead some other material may be used. 3,982,148 Thus, the focal track may, for example, be covered consisting of a layer of rhenium having a thickness with a layer of tungsten or a composite of tungsten and of no less than about 25 microns, said coating hav rhenium. It will be understood that the coating 12 of ing a needle-like structure with closely adjacent the present invention will reradiate most of the heat radiation-re?ecting needles having relatively steep introduced, for example, into the focal track 20 of the angles, so that outgoing radiation is reflected be anode. Similar considerations apply for the anode of a tween adjacent needles and heat is radiated at an high power tube. overall emissivity on the order of 0.9. It will also be understood that instead of omitting the 3. The process of depositing a heat radiating coating rhenium coating of the invention at the focal track 20, of rhenium on a refractory core, the process compris it is feasible to deposit tungsten or tungsten-rhenium ing the steps of: over the initial coating 12 which has not been illus a. introducing a vapor of rhenium pentachloride into trated. a reactor; ' There has thus been disclosed a heat radiating coat b. heating the refractory core to a temperature be ing consisting ofa layer of rhenium with unique proper tween about 900" and about 1 100°C while carrying ties. The rhenium layer consists of needle-like radia out the reaction at an efficiency of no more than tion-re?ecting elements. As a result the heat radiation about 60%; and emissivity is on the order of 0.9. The coating entirely or c. depositing a layer of rhenium having a thickness no partially covers a conventional refractory core. A less than about 25 microns, whereby the deposited vapor deposition process has been disclosed for provid coating is characterized by a needle-like structure ing such a coating with these unique properties. The having a radiation-re?ecting surface capable of process may, for example, be carriedout with a halo! either absorbing heat radiation or reradiating it genide of rhenium such as rhenium pentachloride or with an emissivity on the order of 0.9. rhenium . 4. The process de?ned in claim 3.wherein a noble gas What is claimed is: 1 is added to the vapor of rhenium pentachloride. l. A heat radiating coating for a refractory core, said 25 5. A process of depositing a heat radiating coating of coating consisting of a layer of rhenium having a thick~ rhenium on a refractory core, the process comprising: ' ness of no less than about 25 microns and a heat radiat— a. introducing rhenium hexa?uoride and hydrogen ing emissivity on the order of 0.9, said coating covering into a reaction chamber; at leasta portion of the core and consisting of a multi b. heating the refractory core to a temperature be 3h o plicity of needle-like radiation-reflecting elements dis tween about 750° and about 900°C; and posed adjacent to each other and at such steep angles c. carrying out the reaction at an ef?ciency of no that outgoing radiation is reflected until substantially more than about 60% until a layer has been depos all heat is released from the core. ited no less than about 25 microns thick, whereby 2. A rotating X-ray anode comprising: 35 the thus obtained coating is characterized by a a. a core of refractory material having approximately I needle-like structure having a radiation-re?ecting the shape of a disk; and surface capable of absorbing or emitting radiation b. a heat radiating coating provided over at least a with a high ef?ciency. portion of the surface of said core, said coating * * * * *

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