Note: Descriptions are shown in the official language in which they were submitted.
:~398~7
3-10-78 1 PH~ 77-012
Oxide cathode and method of manufacturing powder mel.allur-
gical nickel for such a cathode.
The invention relates to ~ oxi~7e cathode comp.Lisin~
a cathode support which consists substantial~y of po~der
metall.urg;.cal ni.ckeI which nic~el comprises a reductor :rOr
the emissive coatlng which coati~.~ is provided on the
support and which consists of ~ compound of at ].east one
~lkal:ine earth metal and oxygen, in ~hich support a
heating element is provided
: The in~ention also relates to an electric discharge
tube ~taving such an oxide c.athode al~d to a method of
~nanufact~ring ~owde:r metallur~rical nickel for the ~support
of such an o~ide cathode.
Such oxide cathodes have a very wi.de fiel(l of
ap~lic~tion. They may be used, for e~-ample, ;n elect.roll
tubes, di.spl.ay tubes, T.V. oamera. tubes, transttlittin~r tu~es,
klys~on~, ma~netrons, and the like.
Such an oxide cathode :is known from Pbllip* ReseclrL^h
: ~eports 26, 519-531~ 1971. The oxide la-yer descr:i.be~ :i.n
I saic. reports comprises in-ter alla BaO (bari.um o~i~e). T}~e
reductol used consists of one or ~cre oi` the elements .~l,
C, Mgr, Si. or Zr, whleh el.ements reduce a part of the 13~.0 to
Ba. Th~ reductlon of the BaO takes pl.ace :in t.llat t:~.te
~educto:r ~i~fuses from tht-.~ nick.el S11~0:1'~ stril~ in th.
l~yer o~ B~O on the ~upport u:nder ,'he inf`~ence c~f tlle
thexltla1. eneI~ry of tlle hecater elemell.', and re~llce~ $1~ere
2S th~ B~O to free ~ rhic3l d.:ifru~3 to the ~1rf~ee oi` the
, '
q~
11398Z7
.
3-'l0-'7~ ~ P~Q 77-~lZ
, layer of Ba0 and f`orn]s -cherQ a l~onoat.om:ic surface layer o.t`
¦ low work function.
¦ Cathode support stri.p consistin~ of nicke~. containingr
an acti~ator element such as Al, C, Mg, Si or Zr, has bee
made by a powder r~etallurgy method in ~rhich ~I mixture o~`
the consti.tuent powders is compressed to form a blocl~, the
~ compressed block is sintered, ~nd the sinccred :Lllgot i5
f rolled. 'l`his method recluiros a. po~rerful press, ~rhich is
¦ expensive, and the centre of tlle ingot is rclatively porou.s.
'~ l0 It i5 necessary to si.Il1;er ]~rge in.gots at :relati~rely higl
temperatures :~or a lon~ -timeS Por examplo at 1300C ~or
48 hour~, in order -to recluce the porosity of the cellcre of
the ingot. However, such a process is not suitable h-ithout
taking troublesome precautions .such as encaps~ .t;:ing the
ingQt when the activator element i~s ~agllc~ium, ~rhich i~
volatile and has a bolling ~oint o:f 1'l00C.
~ isadvan.tagre of kn.own ox;de cathoclcs UsiIlg known
.~ catllode supr~ort nickel strip is that the quan-tity of` free
ba:riun~ available when the cathocle is first operated i.5
20 reduced consi.d.erably by ga3 residue~ in the electrQn tube'
in which the cathocle is used,'~hich residues form c0l1lpouuds.
' w:it'h the free bariun~. Thl3 is terrlled tlle poisoi~lr!g of thc
cathodeO Such poisoni.n.g gas r~sidue~s are :formed not only as
a result of i.nsuffic:ient evaCuati.Qn Or or leaks in the
25 elect.ron tube ( a ~rood vacuum of` 10 7 mm llg still meanC
10~9 mol o~ ~as I)er cm3) 'lut ~llso Qs a re~u'lt of hoati~
i and evvlutio.rl o~ ga.~e~s I':rom componotlts ill tlj.e tube. More-
.3 over, the cat'hode~poisoning gases can be ~ormed UpO-l im~act
of electrvlls ~ith materials and thc g~s may b~ rcleased
30 from the glass ~ra.ll o~ the electron lub~ A3 already said,
~ ca-thode poisoni.ng occurs i.n particular at the begir~ning of
it the opcration of the cal.hode so t~ t the tl~bc i.n which sai~
, cathode ic;ll.sec' i.nitially shows a pOOI Operati.Orl as a
j resul.t o~ a poGr cathode em-ission.
J 35 :C-I ;.s the-leroré~ the o~ject'o:~ the in~rention to
pro~r:ide an oxicle cat~lode whlc~rl at the~ beë~inn:i.r~ of` the
. operatio~l of said caihocle i.s cc~ls:iclerabl~r les_ xe.ls:iti.-~-c to
poisonirlg ~ncl which, whe:n used i.n a tubc, ra~ y ~chic~re~
, . ~ .
:1~39827
¦: 3-10-78 3 PHQ 77-012
I
j ' a good emiss:ion.
i ~ccording to ~he invention, such a cathode of the
kind descrlbed in the I`irst ~aragraph is characterized in
! that the reductor i 5 distribut~3d i.nhonlogeneou~ly through
the nickel ol` t~le ~upport a.nd Iorms islailds ha.~-.r;g a high
reductor concentration ill th.e surface of the support.
The activator element diPfuses from th.e intelior of
the cathode support as a reslllt of a conc~ntratlon gra~ient
~ of the aGti~ating elemt3nt being set u~ between the oxide-
T 1U bearlng sur*ace o~ the cathode .support arld tlle inte:rlor of
¦ the cathode s~pport as a result of a reaction between bari~
oxide and the activati~lg element at the surface o~` the
cathode support. Thus free barium -which was lost by reacticn
with gas residues in the electron tube is replaced.
~ 15 Diffusion occurs at acceptable~ rates as a result of` the
i high temperature of -the ca-thode support duriIlg oparation
of the cathode. The nickel coating surroundj.ng the
i particles oP an allo~r of` ni.ckel and an activator element
ma~.es it possible to si.nter the compacted strip at high
20- speeds and low temperatures, and makes the sintoring process
casier to control.
When magnesium is used as an activator el~3ment, it is
introduced into tne powder mixture in the form of nickel-
~: control particles of` a ni.ckel-magnesium alloy, for example
25 containing '15~, b~ wei~ht of magnesi.um co-tecl w:;tll ~uch a
th.icklless of lliolcc~l t'hat the m~gne,s:Lum ~ontent. of tho
l eoated partlo:L~ , 2$ hy we:L.~,rht,. B~r lntroducing the
¦ magnesium ln this manller, the ni.ckel-mag-.resium alloy i3
protected Prom oxi.dation by traces oi` o~rgen which are
30 inevitab~.y present in the si.nterlng ~1,mos~here. I~ is
oon~en.:i.enl; to i.ncorporate al.umini,urn when used in tho nlix-tu~
in the ~o-Lm oP a nlccl~,ol--aluminlu.n al3.oy contai.nin~, f`or
ex~mple 5~ ~y weight c.P .~luminill~. When the .lc~i~r~to:r
el.ement i..s ma~n~sium, -the magnesium contenl o~ e n.cliol.
3~ .strip m~y b~ f'rom 0.03 to 0015,~'. by weightO kT~len tlle nic~e:L
st,r:ip i;lClU~ alumlni.~in-l, t~e alu:nir.iulTI c:ontent o~` the
nicl~.el strip ma.y be f':rom 0~01 t~ 0.10G~ we~
11398Z7
3-10-78 4 P~IQ 77-012
Comn1ercially available carbonyl nickel powder consists of
more than 99% by weight,of` nickel, together with trace
impurities. Small quantities o~ other elements, such as
tungsten, may be included in the mixture in order to
improve the n1echanica:L properties of the nic1~elst.:rip.
The nickel-coated particles of the alloy of nickel
with an acti.va1;or element a.re thorou~hly mixed with carbo- -
nyl nicl~el powder and any ot'her ingredients of the mixture~
A strip i.s -then rolled from the mixture, the th:icknr3ss of`
th.e compact,od .strip bei11g ~roverned by the apparatus
avallable. Thc compact~d st,rip is the~ sintered, and the
sin-tered strip is then rolled so as to reduce the thickness
of the stri.p to a desired value~ l`he rolled strip ma)r be
a3lnealed ii` desired.
- l5 An embodiment of the invention ~ill now be described
with reference to the drawin.g in ~hich
Fig~lre 1 is a sectional clevat:ion of an oxide cathode,
I~`igur~ 2 is a sectional elevation of a kno~rn cathode
support bc3aring a bariulr.-calcium-stron1;ium oxide layer,
~igure 3 is a sectio3lal elevation of a cal,hode
support nickel strip made by a method a~cording to thr_
invention bcaring a barium-calcium-strorti1lm o~ide layer,
Fi.gure 4 is a plan ~rie~ of a disc of a cathode
support. ~ickel strip made 'by a method according to the
invention.
'Fi~ure 5 is a. schemal;ic slde cl.evl.tion of an ~p1~ara
tllS usc3d to makQ a sintered compncted strlp by ~ m~thoc~
a~cording to the inventlon, and
Figure 6 is a plan vie~ of the rollers of t'.he
apparatu~ sh.o~n in Fi.~ure 5.
Fi~,r~lre 1 shows an oxide~ cathode consistin~ of a
support 1 made of the strip made by the metr.od described
w:itll rcfereJ;ce -to Figrures 5 and ~ ~ecllred -to cl cathode
s'ha.~ 2. A heatcr ele-rllen~ ~ i.s sit:uate~i below t,he suppor~
1. The s~ ort. 1 bears a laye- ~ ol` (BaCaSr~0. This layer
4 is o1~taiil~d ~ spra.yl~g .1 suspens:ion oi' b~rium-ralciu~
: st.rontium carl~onat~ onto the support 'I and con.verti11g t'he
CarbO31ate il~CO (~aCa~r)0 by hea,.tir~
1~398Z7
i
1 3-10--7~ 5 ~HQ 77-012
i l~igure 2 sllows a part of a p.rior art support 1
I bearing an emissive layer 4. This prior art support was
produced from a casting of an or a high temperature sintere~
powder metallurgy alloy of nickel ancl an ac-tivator element
5 which is shown as dots homogeneous1y distributed in t~le
nickel of` the support and the activator e]ement diffllses
into the emissive la~er 4 durin.g ope:ration of the ca~nc,de.
en the emissi~re layer 4 ha.s been F~olsonec1~ the I~aO i.n
this cathod~ is not reduced suffi.c.i.ently ral~idly so that
th~ emission of the cathode cont;inues at a lower level than
was t~le case before poisoning.
Fi~ure 3 shows a part of the support 1 according to
the i.n~entlon bearing the emissi.~Te layer 4. Th~ activator
elemel1ts 6 Mg and Al are present in the n~ckel of the sup-
i l~ port and at the surface of the support in a loca].l.y ~
conceIltrated form so that the supporting consisting of
po-~der raetallurgical nicke]. colnprises I.i. 0.05 to o.oc~
by weigllt of Mg an.d from 0.01 to 0.05~ by we~ hi; of A.l~
~ A.s a :esult of thls being localiy concentrated it initially
:~ 1 20 di.. ff1lses con.siderably more rapidly i.n-to the emissive layer4 a.nd can rapidly replenish the Ba which has been lost ;-lS
a result of poisoning.
Figure 4 is a plan view of ~.he support 1 according
to tlle irl~cntion in which the islands 6 havin~ a high
con.c~ntrati.oIl of activa1;or elemen-t are si1.uated. l~
be ob~i.ous that the cat;llode n.iclcel may also be used in
other cath.od.e oonstrllctio.ns, and ~cl;i~at()r olcrncnts an~l
1' a.lka].i.. ne earth motal oxidos other than those de~cribsd may
b~ usedO
Now a method for mallllfactuLin~ n1etal].l.lr~ical nic1~l
i for su.ch a cathode wi1l be describ6d.
A magn~sl-ml-nickel a.lloy corl1;a:inin~ 15,~, by wei.gh1; o:t`
j ma~lles:L~ Ti in the .forl~ of lu.nps was crushed9 ~round and
1 s-ie~Je~ I;he matsri.al p~s~in~ a 350 mesh (mcshe~s pcr illCI' )3~ s:ievc beir~l~ coll.ected. ~rhi.5 minu~ ~50 mesn IriatcriLtl ~.~as
coated w:ith a t.~ic.n~s.s of ni.ckel suc1~. tha~ t~e Inclg-rl~s1.u~
content Or t~;le coace~ particles 1~a; 2~o ~y ~Tei~ht. Thc
part-~c.~os w~re coat;ed ~i.th nic~;~l in an autoc1ave by tlle
.
: .
,,
:, .. ~ .. .. . .. . . .. .. . ........ , .. ~ .. ... .
1~39827
3- iO-1 ~)7~ 6 PHQ 77-012
reductiLon of an aqueous ar~nonlaea . solution eol~taining
n.~ekel. sll~phate and amrllonium slllpha.t~ heated to 175C,
the au ,;oealve eontai.ning an over-pressure of 350 lbs/in2
o:f h-~7drogGn.
1~ master Dlixt;ure consis ting oI` equal weigh.ts of
tungsten powder and carbonyl. nick~al powder having average
particle ~sizes of 3/um was prepared. All alunl-lniun~-nlcke].
(52/~l~3 by weight) ~:~owrlGr was sleved through a I-()O mesh
sieve and t.he rni.l~us IIOC mesh :fraetion w~s use-l.
A m~ tu~e \~as pri3parod consistilng of
80 g o:f thc3 ll:icke~ l-coa ted magne~sillm-lli.cke:l. alloy
parti.cles
1 . (:'j g C!:~ th~a n1intl.s 1loo mesh alumillium-nic3~el. alloy
powder
80 ~ o:L` th~ tungsten arid ea-.rborl~_ niekel master
mix-l;ure
1 ælTO g o:E` earbonyl nickel po~del .
This mi:~ture eor~a:Lns 0.08 ~ llg, 0,04 % by woig~nt
Al arl.d 2 G~ y we igh t W .
Re:ferring -to l?igures 5 and 6 o:L` the dr~3wings, po~rder
mixture 1 0 was fed i~to a h.opper 11 I`rc,m l~Thi.Ch the powder
pQ,ssed i.lltO a o.6 rr!rn wide gap 12 bet~eerl t~-To 15G mn~
~liameter rollers 13, 14 xu.nning in th(3 hori~,ontal plan~.
The eoJrpacted stri.p 15 l~as.sed over suppor-t rollers 16, 1 ~
and læ b~3fc-re enterLn~ a mu:Erle tube 19 o:f a muI:E:le furn~ce
ZO l.n whieh the strip 15 l~as si.nte:led. .Puret dry h5~clrogre
wa~ passed throuT~r~h th.e muf:fle ttub~3 1~3 ~llcl t.h~ st;r.ip
passed l;hl ou~r,h t;he lu:r]lace at ~ueh a r at.c~ t llat: a peak
tenll~t3ral:uro o:~ 1050~C wa~s appli.ed :Eor 3 m:L~ .tos, Thc
s-lntc3r~ed s~tr.:ip 21 em~r~in~ rrorn ~t~ e n~ f.fle tUb? 1~3 w~
J;~ 011~ 1 Go(,) Itlm d:~arl~et~ SpO~ I 2'> ~ ~rll~3 sillte c`e~' s~ i
~as 0. 7 ~ t~li.C~:' arld ~ra~; SUbs(?r~L~:(37:ltLs~ I`OLleCi to ~i~e a
fll,xl thlcl~ne~ of 100/u~n~ Thi.~; 100/un; strip I a~ nsi3c~ lo
rnali.f3 t~ 3 oxi.~r2 Cat'rlOQ'3 suppox~t~
., . ~ . ~
