US2329317A - Method of conditioning anodes - Google Patents

Description

Sept. 14, 1943. z J. ATLEE METHOD OF CONDITIONING \ANODES Filed March 19, 1941 succession-ptelectricali loads ofv progressively PatentedSept. 14,1943 I invention; rlates i ri general-to electronics wa mb ip i ti ar i n es vx1e!wierators, the inyention pertaining especialiy; to the conditioning of jx -ray generatorifpr u se, I

.An important object. oi -the :imiention :is to Pmv m e hediqt'p due n rximv generators; in 1 conditionfor service 33y ispbm itting the se nerato'r- }.to aginggand e'or ciitioiling@processes during theiabrication ofthesame morder that the finishedjproductqmay/have; ciesiredi operating' characteristics, including the abil'ityoato resist deterioration .w en m operation .under highloadicbnditionsi, I a Another important obiectis to iproiiigle. an :im proved oltechnique for 1 aging an ,xraya e eramr to the; en'qtha't awe/parts thereof. andis e -iany the anode,;may ibe' c oliditioried .to'ir'esjistj cieterio ration, particularly. through the .de' ielobmei' t lof cracks therein when exposed to high'ter'nperzituregencountereddngtkie operation of the gem I k v I H H I 1 Y anodednservic'e,iandtanaaging step to improye1 the gram, structure' of the anode material to fur:

orator, H N Another important :object isc-tofpmvide. v:m

aging, technique for anodes, in order to improve 7 the 'g'rain structure of the-- constituent --anode'rnaterial so that the may be rendered highly resistant to crackingmnder-tm destruetive forees applied thereto pwhen in sewice as -a flnishedgX-raygenezator. H I ;sAnothe1-' important :object toj prov de an X-ray "generator I embodying an "amide and we theggeneratonbyisuceessivelyi polishing theanode prior m itheassembly ithereor 1 in the glenc ratqrn aging :the polished anode and: 1 the gnerator by l exposing ,it",t:aiter. assemb 1y in the generator; toa

creasing intensity as a part'ota process 'foreon dition-ing the ,generatoz :forgservi'ce; a; further object beingito age the-"anode duringthe EVQGWK tion' of ,the;.generator; thereby. cmiserving' menum'gmovmeym improyed Aarmcaiit; v 15 artifcularly I for 3.0 condition the anode. duringv vthe 1 construction of facturing time, andktaQrqvide'getterirrg adapted tmt unc tion 'dumingathe agingn'operatien i-ng anode,c-an owectfofthefihireritioh eifi o employ fcommon jevaporabiemedium Q i I seneratcriembodying-ta s atio ary ian der bir ati st iJ i sfi he to accomplish, getteringn 1A X ray' generators; by,sulijecting theg anode, and

especially target thereof; -,to -;e1'ectro1ysis' .to polish Lthe same i in rorrier t a p i 't 'ac w further object, being tjo pr me (an .anode having improved instructui e derived by aging the anode priorl piaingfit inserv' ice;asti11 further has been polished. H 7 Another important objectistm we i;t anodeiin servicep 7' i I imother important. ob ct a to prov idean inl-l a polishing operation ltoi'tihibit" cracking of the ther erdiicecrackingtendencies; v

' These A and numerous other cimpor'tant,objects,

advantageagand inherent 'f irijc'tions-qo f Ithe =in'f,-

il ention willflbec'dnie' apparentgias jgtfilinverition is more 1111 .31 understood from the ronowingld;

'sclos'esif "a," preferred "Figure 1' isisetional viewthrogghfan'X-ray:

generator embodying ia'i'roltating anode; Figure 21s a plan yiewfor theend of of the generator shown in 'F1gfi1 I;

.Figure 3 is a'fl""e'n1a rged sectional-viewtakensubstantiajl ly-al oifi'gthe1ine;3 3 in"Figure 1; t Figure 4' is. a sectionalj view taken substantially along;thetline-AAQ?in'FigureB; a

tFigm'e:.:5,iisa. sectional jview through an X-eray :Figumge fie-js -a sectional; yiew taken substantiail y ong -theline 8, i masthe ine ial-fi ure 31a 'M-v 1T il st a it ain a oni thei in a v 1: 1 4is m r mzii ti e l qeefand:.

ther important object ,of t he -mventi on object Th me st-t ,aii d afterl h same 1 V V V .o i iiide ditioning technique fQIflQgilQdBS, embodyingthe t p polishing th e sar nmpreferably by elec-os tromiq action; inrorde proved anode conditioning,'inethod; iernp'odyin g t e" a .chanically secured "to said re-entrant portions.

The invention has great value in providing X-ray generators having unusually fine operat-f ing characteristicsat high temperature under relatively heavy load, and results'in the ability to produce unusual X-rayintensity from. a generator of relatively small sizewithoutdestructive effect in the generator. l 1' It should be understood that,X,-ray generators function to produce X-rays 'i'ri response to'the mechanical working of the target material to providea fibrous grain structure. I

Electronic action on the target, when in service, with incidental localized heating, changes the grain structure of the target material, which eventually becomes a line crystalline structure, de-

spite pre-treatment of the material by mechanical working. This changein structure, in accordance with my present inventiomis accomplished, without cracking the target, by means of anaging process whereby the development of the grain structure is caused to take place slowly. If the crystalline grain structure is thus developed successfully without cracking; thendanger'of cracking the anodein service is substantially eliminated. u

. I have discovered that the successful developmentof a satisfactory grain structure maybe ac- ;complished witha greater degree of success by activation of the anode by electronic action pro'- 1 i duced by the operationof the cathode C. This electronic action comprijses theimpin'gement of electrons emitted by the cathode upon 'a' .target H forming apart of the anode,-su'ch electronic impingement resultingfin thegeneration of relatively large quantities" of heatgwhich is dissipated thence through the body of the anode and 'out+ wardly of *theenvelope-through the anode support structure}; which extendsjjhrough a Sealed opening in theenvel ope walls. When in opera: tion, the'temperature of the generator, and particularly of the anode, may be of the order of 500 centigrade.

The intensity of X-rays produced is a function of the energy applied to the. anode,"the greater the energy applied, the vmore intense'is" there-1 sulting X-ray production; The more energy, however, that is applied on the anode, the.higher is theoperating temperature towhich the anode I is subjected; 'It ,is desirablefialso, to produce X-rays ina sharply defined beam in order to obtain sharp shadow definition. on a film or screen; or in applying the ;X -ra'ys to a;:desire'd spot for therapy purposes. For this reason,,it is necessary to accomplish electron impingement on the anodeon a small focal spotin the target, since the smaller the spot, the gre ter isthe defi-J nition accomplished in the resulting X1-ray beam. The maximum amount' of energy which may be applied on a focal spot or area,'with0ut melting .or cracking the same, is dependent primarily upon the target material ariditsfability to, resist cracking underitheinfluen'c'e offthe temperature developed through electronic impingement at the focal spot, which ordinarily-151a localized are'ain the target face.-;

Because of its high melting point-high atomic weight and ease of procurement, tungsten is commonly used as a target material for X-ray tubes, although numerous other materials are available. Oi all presently known materials,"however, tung-, seen has the greatest, ability --to"resist cracking under the influen'ceo'ffhigh temperatures! 1 The productionbi tubes to meetthedema'nd for high I capacityunits has {resulted in a tendency toward ahigher incidence o'f tube failure due to cracking of; the targ'et in' service.{ 'Material available for use intargets; includingtungstemhas a definite crystalline grain str ucture, andthe tendency toward target cracking may be minimized by relatively small 1 first polishinglltheLtarget in order to eliminate even small 'fissuresand other irregularities in the suriace of the target, forby eliminating suchirregularities, I find that. I am able to greatly reduce targeticracking, apparently because cracks-start as a result of surface irregularities in the target, even'though such irregularities may b of minute proportions. In any event, I have found that the higher the polish initially given to gthe'fl target the less is the cracking tendency; F

' 'In;keepingwith'these deductions, tubes built inaccordance with my' presen't invention are constructed'by first finishing'the-anode' Ff, including its embedded target 1' I to final form by a carefulv machining operation, the anode and target being finishedas smoothly'.as"possib le mechanical means. The completed anodefis then] given a mirror polish by subjecting it to electrolytic ac-' tion in a suitable bath, andwhere copperanodes having tungstentargets'arecbncerned, itlhasfbeen found that optimum chemical concentration. for anodic polishing by electrolysis comprises an aqueous solution ofsodium hydroxide and sodium carbonateflnthe following proportions. 5

l I Grams per liter of wat'er Sodium hydroxide (NaQH)' Sodium carbonate is presentprimarily as acuiton the tungsten may be increased rent carrier and'has little, if any,-action upon the tungsten target, butitspresence in the solution, is advisable to reduce heating.. Furthermore, by having sodium carbonate present in the solu-'' tion the minimum .concentrationof thesodium hydroxide polishingagent can be used, whichfin general, tends to produce the-best results The temperature 'at -which satisfactorypolishing 'is obtained is somewhat critical, andfor'thisreason, it is desirable to maintain -the solution at a tem perature of 1 between, 20? and 30 centigrade. the temperature of the polishing bath exceeds the stated limit, the actionof the polishing inedium toa degree resultingm a tendency to etch the surface ofthe target when a: standardsolutionan electrical current densityarelemployed Polishing is accomplished bypassing, a elec trical current through-the :anodeiand the poli ing solutionin which-it is suspended for'*a"prede termined time interval. {The :current; density is critical and should beestablished according to the standard solution and temperaturebeingused; Qptimum results with thesolution at the concentration and temperature herein disclosedare ace complished at a current density oi approximately amperes per square foot, maintained for a.

atooperateugn 1 i n Removal of gases iromithe envelope is accom y vby heating the. electrodes to a h'gh period of the; order of ten minutes until a satis factory polish is- 'accbmplishedi-" It"'is important that the anode be not-immersed imorin Contact I with, the solution for more than a} few' secondsv without application 5 of electrical current, since contact with the solution in the absence of an electric current will result in etching of the target.

The' copper of the anode has a tendency to a oxidize as a result of the electrolytic polishing ac tion'; i Oxidation of the copper'producesa black coating'thereon; whichmay be readily removedby immersing: the anode in a 25 %r' hydrochloric :acid

solution without rimpairing theipolish. A aj i t t a node; has :been' mirrdripblished as aforesai'd, itis assembled and sealed. in:,operative p'ostio'rr in the envelope 0, together vwith thercath ode? C; and;.-.the;tube' is conditioned forioperation by first removingvall gas present withinthe-'ena ve1ope'O,-and=a1so-any gas occluded in the anode and; cathode and in the material'aof. the: envelope itself. ;If such occluded gases are-notw substan-J tially; entirely removed, they will gradually be releasediwithin the envelope and, impairythe ex hausted condition at which thev devi'ce is designed pushed; y bak n o o h wis at ti he,

entire device at a temperature shortofthe softennected with a suitable exhausting'apparatus; H emperature 'of initially warming-ins ances we temperature oftheordr 6:100 Centigradein oruer'toirender' I the'f'targ'ee material 'd-uctild and minimize-the, dang' of sta ting cracks duringtheiaging'proci a ns' in o t e';.e1ia s,-w 1 t e ve e 9 1 :1

mo alof cluded sa es ay a o beaq a l ed he e c n bo dmen enbyplaei zths electrodes in a. ,ma net 'fiel uc atin tir quenc 'e o i he o ra q'f e n myv, According torthepresent invention, however li prerer to heat the electrodes by y electronxboi iie b dme t and thersb q omp i the e in 0?:

he. a de s pa t of the tnba q tieeiesH991 ess, although aging of the anode to develop a sati t o a -Stru tur fi e em sl vc vm plishedafter occiudedgases have been completely vxnere'lyfja' heat exposureaccompli'shed minute or twoj-thetub -1 operated"'duringia t6 secondilntervaL.

'For practical purposes, the agingsprocessl pref; erably is started with electrical energy-applies? tions or load'shots of thebrder of-"orie-ihalf of the v ratedfcapacity or thetube; and although thetina v vention 'ls riot limited-t0 any particular' schedule; thefollowing aging s'chedulehas-been found sa isiactoryior tubes' -rated for 'operatio atlfi k 500' milliamperes" {for second v 1 Application 1 -Milliamps./shot" time/shot 1-; 1 (seconds ging process consists energy' exposures' or shots,' -the *fir'st energy for 'a t'wentysecond peridd for thelpurpose H 4 ithe initial warming 1 and 'before the anode has 2. chance t s given twelve successive sepond eiiposiir sat 75- 'kv, pi "and 300 rn illiiam- 'pe'rs; with 9; 4.5 second; test p'er-iodn' betweeni exposures. Then the tube is subjected:to thirty' exhaustedfroni -the envelope and the'electrods.

Whet er b not aq m h dr ng, he emov l 9l, as s the-a ps? aging Pro e s a sists in applying energy onthe anode by electronic} 7 b ar m t a sume smania ym d l being gradually increased until thetube-issub jected to loads substantiallyinexce'ssof itsrated capacity. In this rnanner, the target material, is

, caused to; crystallize slowly I andithje seaminduced b y the rearrangement of the molecular amperes; wit st periods of 1.5 seconds between tex bsuresi" r structure, of the material as a resultfoffc'rystallizai he t a f minim m whereby cracking is prevented. r r I 11 node preferably is e't16suaqn m restiperiod after'eachloadapplication; 'eaeh'loadmgvcomprismgv a. a p N a applied; on the anode during a predeterm ned time interval. Y The, jloadingsfand times are; of

course, determined by' the size and capacity of during the aging process,buttheitube is given'a a predetermined'ainouiit of ene y the tubebeing treatedand are proportional to the" ratedcapacityofthe tubelf W I The rating ofan Xraytubeis ordinarilydeter mined ass. functions; theehcrgy required to melt'thej tar 1 s s d d I 7 tube isfrated for operationjat voltage andeurrent values sufficient" to impress on 'the anode only a predetermined fraction'qf the energy required to melt" the anodji'ii'aterialf Thus, for ten-second operation} a'tube may be rated to operate 'at volt get"mfa terial, and; consequently, a

m'illiah'ipere's; with 511. rest period between expesures; andgnnany; to sixty 'exposure'syoffone ation=at- 10o I); and 300* milli' 'The' foregomg'aging process is designed to allow the crystalline structure of the target materialto ag row slowly in-lorder to condition the tar-' I get for full i load operation withoutt destructive cracking After the aging process has been: ac

complishedythe tube is-Ljteste'dby subjecting it tolla' series of over-load test exposures,which; fora 'tubeuated at RV. piand 500'mi1llamperes'for second,"may comprise twenty-six exposures of-{ rsec'ondeach at kv. p. and 500rnil1iamperes;

with a' 'io'r'ty two second restperiod between ex po'sures; followed by fifty-fourtes't exposures,

each of second auratmnmmokv; p: and 500' mi'lliamper'e's, with aforty-tWo second'rest period d between exposures. I i.

then" aging the, anode, I have been able 'substan -Afterzall impurities, including occludedfgases and other impurities, have been re ovedoom th -fenvelope, the exhaust 'connection may be seMdotlQ asat l3 ,and as a final clea'nmp step; I a {suitable gettering material 'inay volatiliz'ed within the enveiopein order to form'end products of the: gettering material'and any tracea ot gas 1 or other impurities that may remaini-in i th en age a and current se im nt to" releasefenergy at -the;

anode e'quaiio 6p of tar et eltip ener y, so

of target melting energy during fi-s conwoper velopefisuch end products being: inert and'dn-T. noc'uousiaind remaining within, the @envelope dur.-.; ing 'itheiservicexlife;of the'tube' inithev formi-foti'a' ationand '90%' of ftarget elatingreneg -iwme Rest period between 3 seconds) I I ana30o mi11i-- f ar'rl-peres', 'each shotllastingftwtf seconds, with a restfperiod-"foi 17.5 seconds :be'tween" loadings; Thereafter; the" tube" is subjected to twenty, one

'mitiohot deposit up'onftheijactive Surfaces of the electrodes All ,"'of -th'e"metallic vapor. produced I i @1113 "a, 1drtion the fgettering 'mqterielg the ree nidinin gf u'n ised- "orti0n' ofiihegettering material from the foregoing descriptioiifqandfit is obi ious 4:1

I The ini entionfishereby claimed-' e's followsz R r in'i'xthei anode ianfdl: progressively increasing' the" 1 ,te'nding. portion. 2.670)? the electrode; support, and the other gen' d being cfonnectedrwith- {the a con- The foregoing arrangementiof'thegettering -5 equipment withina' .oonfined chember in'ainelee- Ftrode efreotivelyipreventsather escape of' any get -s terln'g tend produ'ct'srand insures againstlthe iordu-ri'ngm rthe vgett'ering :operetion aimpingesvupon 'eleo'trod'e surfaces withini ther ohax'nber I1. 1.] The vaporized-jgttrln g 'maltriailrcondenses upon such "surfaoes' immedi'a;te1y= i1pon impingingii-therefon 1 so. I that littld if anyvapor may 1 escape-Iron! within one e1etrodeduring the gettering"{operation. If "any vaiior shoi 'ld esoapej ifi rnush do so :through 'th' nriulai'vooning'elround tfie seail-wfliandinto 'emote "fro1'n 'the iactive elebtrode "surrace'smn ny' y'apoi' 'thus entering :the pocket Swill be'oor'rie condensed upon'ythe surfeoes thereof, whichare rel'atively cool;

e g'et-tering} material: -33 on, a 'oonduc'tofend' evaporating -t'he"'sem 2 heating "the hoseem eleetrioallyg'l amablejtocontrm the mean 6f getterin vepo'r produced -Iat any d 12 m'oiyifirovide'f a suitebleflexoess' of thaLtQaiffier'finitially oondi- I "t'io'nmg the tube to "operation by -ifevaporatin'g ay: bef us'ed lat r m nr evaporating {additional tering{mater-m1 remem-u {result [of f-the opereltion of damning-bearing maro- *'II1 lthiS W81 3 7,' Toan perform terihg andiubrio'atingoperniirvals uhn gthe service nr or t e 11 is thou'ghtthat t'heii yention'enditsnume roils attendentadvantages will be fully iln'der'stood The inthodof'oonditioningthe' moireaiser I electron flow device for s'eryice hioh cons ists in agin t-heanoa b sgili esii 'at s'iicoessive intervene to 'lofid ns *conipi'ising eleot rlbel' energy r progr" siVeIyHnoreLsing intensity. 3 The method of eonaitiam rriema e or {an leo ron. flow-device for service which consists in I se is during an "extended treatment periodic succe's sive' electrical :load shots inifi'iixlly of; theiiorde'r releasing aless than one half. .anode' @r'neltirign energy; I

hoiild-become ce s ry, I I

lzanodei material gby h wtment e i pm r s treatmentzperiod pro resses I 10;: @The ime hod pf conditioning ,t;h f an el'ectromflow device torinhibit oragking v. mciual rahea'nin i the; anodeit'o promoteslow icrystali growth'in" the anodematerialibydissipatingvelectrical energydn w Witspreceding'i shot 1 11711- Theiniethodrl o ec'inciitioningv the anode: of I Lainodeof "theg'anoderto promotejslo'weflsfiallQtOWh in the I a ode m er a bvid ss at z ectjr a n r y "the; anode inihe v for n 'of -energyshots; released at intervals during an .extendedrtreatmeni; period i with correspondingrest'periods between shots.-

Thei met h od oi eondi-tioning the anode of. an electron fiow device anode mat'ejrial by dissipating eleotrioal energy Lin the-a od infoh ifu rm ot energy shots 'of pro- -gressivelyincreesing energy:inigensity releesed' a t intervalsrduring ,g-n extended; treatment period ewith corresponding-rest periods betw' n shots i; I I no ei el ctr fl wld yi' r sz. nh bi ifi fi 11g :fherof I i z wh oh-c n st ina raduall he .8 anode. to promote} slowyorystal growih" in the,

dissipating K electrioal energy. T

t The method o f reon ditioning th in the imod v 1 1th fjq iilpf: en yfih i j r se at; intervals during xtended preatmeniip'eriod 'withvgcorresponding i iiesipgpelgipds 7 between shots, .and increasing the energy aluev oi -th I shots (at intervals during the ,tregljarnent period.

.18. T -h met 'Qdy ipnd bi ni th :wde'bifn: i QIYiCe whi h s s s nie i du he t n t e I ,erm5 fl-eni v sho j jrfl'ea d atintervals during angextended treatment period with corresponding rest periodsbetween shots;

and d reasineihe; re ist periods between shots as ins service -which consists in g'radually.: heating the anode to promote'slow crystal growth invthe ano m teri l -b rdi s a n r l i al en r y r ,theganode ii n j the?i'forrnv oi energy shots released I V f a in v ls' i ri -an e en edtrea ment e i d' 1 ,with=corresponding rest periods;l-betyvenTshots and; inoreasing fche energy valu'e ofi the shots-while we ns s, as t e decreasingbthe rest-(period, be

in .service which consistsg,

the: .a-node a'the' form'rof energy shot'szg-releesed at-iintervals during an e'xtendedxitrea/cmeni;v period each eres t-period-being:of

i-inten's'itryio'f. the shots unt ihth'e same a-re of the order-of intensityimex'cess o the maximum serv- I "ice loading:gofzohe,aujioIde;i;

' 44: Thiegmethod oi-gconditioningith flelectronifiow de ice; for; service whioh consistsvin fsubjecting ib; initially at, suoeessiye intervals, to electrical load shots}, of the order releasing less -than onehaIf ,anode melting energy in the anode I I and-z' he ea te t C 8. $i i d: shots, 'Qf :i e I creased-intensity andfinelly subjecting the-anode to load shots-Io"irelease energ-y;in thefgnode in .excesswof -Ithe ener y to which it is iesigned to be subjected in service; whereby to I pr oin'o e' slow "crystal; r wth inf 5 16513 0 8 material m obtain, -:a qrystzal s ru dtu red h r in 1 1 t rt inh i .oraokingnofithe, anodewhen heated :inservioe. a; 4 rrhei: method oi eonditioni .-;the" nodeof an electron fiowfdeyicejao inhibit; scraokinggihelje I II I I I inhibit oracking thereof I in seryice whiehconsists in gradually heeting the I anode; to. promote; sloweerystgl grow t h in the h I I I g ,ihe of r I alnvelectronz fiowrde ce to inhibit necking-thereof inhibit the tendency of the material to crack when heated in service, and finally allowing the anode to cool at a rate such as to preserve the crack resisting crystal structure produced by the in excess of the energy to which itis designed to be subjected in service whereby to promote slow crystal growth'inthe anode material to obtain a crystal structure therein adapted to inhibit cracking of the anode when heated in service and then allowing the anodeto, cool at a' rate such as to preserve the crack resisting crystal structure.

24. The method of conditioning the anode of an electron flow device to inhibit cracking thereof in service which consists in aging the same by gradually heating the anode up to a temperature of the order of five hundred degrees centigrade to vpromote slow crystal growth inthe anodemate: rial by dissipating electrical energy in the anode in the form of energy shots released atintervals during an extended treatment period with cor of in service which consists in first polishing the surfaces of the anode to mirror smoothness whereby to eliminate surface 'irregularities and I then aging the anode byprogressively increasing the temperature thereof gradually to promote slow crystal growth'intheanode material and thereby develop crack resisting crystal structure responding rest periods between successive shots, I

and finally allowing the anode to coolat a rate such as to preserve the cracking resisting crystal structure developed in the anode by the aging process. t, V

25. The method of conditioning the-anode of an electron flow device to inhibit cracking theretherein, andiinally allowing the anode to cool at a rate such as to preserve't he crack resist ing'crystal structure.

26. The; method ,of conditioning the rotary anode of an X-ray tube for service which consists in pre-forming the anode with an internal pocket and a mirror polish onthe active internal surfaces thereof, assembling the anode in operative position in the X-ray tube with anode" bearings in the pocket, evacuating the tube to clean up occluded gases, rotating the anode in the tube while evaporating a metallic getterlng medium in the anode pocket for preliminary gettering purposes and directing the vaporized.

medium andcondensingthe same uponthe anode bearings to form thereon alubricating alloy, subjecting the active polishedsurfaces of the anode to an aging process comprisinga series of electrical energy load shots of progressively'increasing intensityapplied on the anode'at intervals during an extended treatment period, whileflthe anode is'rotating, in order'to promoteslow crystalgrowth' in the anode to develop crack resisting crystal structure therein, evaporating additional quantities of the ,metallic "gettering medium in the anode pocket forfinal gettering f purposes and then allowing the anode to cool at a rate'such as to 'preservethe crack resistin l crystal structure produced by the aging process.

, i 'ZEDlATLEE,

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