Note: Descriptions are shown in the official language in which they were submitted.
GAS LASER CATHO~E AND PROCESS ~OR MAKI~G SAME
~ he present invention relate~ to quantum electronios
and~ more specifical~y, it relate~ to cathode3 of ga~ e.g.
CO~=, laser~ and pro~e~s~ for making same.
It i~ known that in a ga~ laser and, in p~rticular,
~2 1~9er u~e is made of cathode~ man~actured from metal~,
since met~ls (nickel~ platinum and t;he like~ ~re :re~pon-
~ible for the ba3io propertie~ o~ the c~thod~s - electrical
conductivity and emittivity of electrons. However~ the~e
cathode~ do ~ot provida ~or long-term operation of la3er~
d~e to their sputtering un~er the ef~ect of ionio bombard-
ment ~d interactio~ with the components of the workin~
ga~ mlxture.
Known in the ar~ i~ a cathode for a gas la~er ~haped
a~ ~ thin-w~llad (Qbout 0.7 mm) cylindrical ~leeve from a~
electroconducting emitting materi~l - GoVar (alloy of Ni
28%, Co - 18%, Fe ~ 54%)~
This ¢athode, llke other metal cat~odes, undergoe~
~puttering under the effect o~ ion bombardment, which re-
sult~ in a changed compo3ition of the working ga9 mixture,
a rapid decrea2e of the radiation power~ thu~ limiting the
~ervice life OI the in~trument to a period not exceeding
500 hour~ .
Al~o known are cathode~ for electro-ion instruments
:erom ¢arbide.~ of r~fractory metal~ having emis~ion proper-
tie~ and a h:lgh electrical conductivity.
As compared to metals9 carbide~ OI mlmerou~ refracto-
ry metal~ are in~ignificarltly ~pu-ttered under the oo~di-
tions o~ ion bombardment and ~ub~tantially do no-t react
with acti~e component~ of the gas mixture of C02 laser~
Articleæ from carbide~ ncluding cathode~, are gene-
r~lly manufactured by method~ o~ powder metallurgy - com-
pre~ion-moulding and ~inte:rin~ However~ the manufacture
o~ relatively thi~-walled ~0.5-0~8 mm) ca.thodes f'or ga~
la~er~ by these method~ i~ hindered ~ue to brittlenes~ of
carbides ~
Known in the art i~ a proce~s for the ma~u~acture of
~rticles, including cathode~ of carbides of refractory
metals which comprises heating of a graphite blarlk in an
atmo~phere of tantalum or niobium pentachloride and argon
bs~ed on the interaction of graphite with a metal halide
at a .high temperature with the formation of a carbide coat-
ing. ~lowever, manufacture of cathode~ for ga~ lasers by
thi~ proce~ doe~ not re~ult in a noticeable e:~tens~ on OI
the service li~e o~ la~er~, si~ce the ~raphite ~ub~trat~
actival~ interact~ with the gas medium of the laser thu~
hindering a full-~cope utili~ation of useful propertie~ of
the carbide ~ e,
Al~o known in the art i~ a proces~ for produci~g ar-
ticle~ (cathode~, in particular) from carbides of refracto-
ry metal~: compri~ing heating o:E a metal blank in a char~3e
from a powder-like graphite in the atmo~ph~re of argon
including tantalum and niob:lum which process is based on
di~u~ion-type car~urization~ However, the manu~acture o-f
cathode~ for gas la~er~ by this process is lnef~icLent due
to the pre~en~e o~ an active met~l b~se a~fecting the ga~
medium compo~ition~
It i~ an object of the present inventlon to lower the
rate of qputtering of the gas laser cathode und~r the ef-
fect o~ ion bombar~mont, ~tabilize the lQ~ar ga~ medium com~
po~ition during lt~ operatlon and, hence, exten~ion of.the
deYice ~3ervlc8 li~f9.
It is another object of the pres@nt invention to pro-
vide a proce~ for the manufacture of ~uch cathade for a
g~B laser.
~ he present invention resides in that in a gas laser
cathode ~haped as a sleeve from an el~ctroconducting emit~
ting r.laterial, according to the present inventionl the
Ye iB made three layered from ~arbide~ of metal~ of
~ide subgroup of Group V of the Periodic System ~ith e~ter-
nal layer~ o~ the composition MeC0.74_0.95
layer o~ the composition ~eC0 92 0 98 re3pectiYely, or from
a ~emicarbide ~leC0 5.
~ he pre~ent invention also resides in that in a pro-
ce~ for m~king a cathode comprlsing heating of a graphite
blank in ~n atmosphere of tantalum or niobium pentachloride,
accordi~g to the pre~ent invention, the graphlte blank is
heated to a temperature within the range o~ from 2 9 300 to
2.500C and malntained ~t this temperature for a period of
from 5 to 8 hour~.
In another embodiment of the pre~ent invention, in a
process for the manu~acture o~ a cathode comprising heating
of a tantalum or niobium blank in a charge of powder like
graphite; according to the present invention, the cathode
blank is heated to a temperature within the range of ~rom
29000 to 2,200C and maintained at this temperature for a
period o~ from 5 to 10 hour~
A ~as laser cathode produced by the proc~ss according
to the present invention ~eatures low sputtering, ~tability
in a ga~ medium, hlgh mechanical ~trength, high electrical
conductivity and emission characteri~tic~. These advantage~
of the cathode aGcording -to the pre~ent invention make it
po~ible to extcnd the ser~ice life of ga~ lasers by as
much a8 about 10 times~
:~he embodiment~ of th~ proces~ ~or the manufacture of
a gas laser ¢athode according to the present inventio~ are
simpla in practicing and en~ble the production o~ thi~-wal-
led (005Y tO 0.7 mm) mechanically durable ~tructure~ of
cathodes~
rrhe pre~ent invention will be further illu~trated by
the deqcription of its embodiments and the accompanying
drawingl wherein the ga~ laser cathode aocording to the
prese~t invention is shown in elevatio~0
'rhe ga~ la~er cathode according to the present inven-
tion is shap~d as a cylindrical sleeve with its wall~
having a three~lay~r ~ tructure and m~Lde from carbide3 of
metals o.ê ~ide qubgroup OI Group V of the Periodic System.
Extern~l layers 1 have the compo~ition MeC0 7~ 0 95, ~nd
inn.er layer 2 ha~3 the composition MeC0 92 o 9~3 respecti~ely
or is mads OI a ~emicarbide MeC0 51 The ratio OI thickne~-
~es OI the layers 1-2~ el,ected within the range o:f
from 1 :1 ,1 to 1 :0025 :1 . These par~meters are e~plained by
the rLeces~ity of comb:i.ning the woxking p:ropextie~ oY the
cathode (low rate of sput terin,g" ~tability i:~ a gas medium,
and the like) aIld its mechanical strength a3 a structurs,1
member o* the la~erO
As ha~ been shown experlmentally, the requi:red worki~g
properties of the cathode a:re ensured by the compo~ition o~
0~74_0~95j herefore the composition of
the extern~l carblde layer~ 1 should not go beyond the
range speciI ied hereinbe:~ore .
~ he required mecha:clical strength of the cathode i~
eIl~ured ~y the inner l~yer 2 o~ a cellular ~t:ructure of
ta~talum or niobium monocarbide of an approprlate compo~i-
tion ~lthin the rarlge of from MeC0 92 to MeC0 9E~ or ~rolll a
tantalum or niobium semicarbide MeC0 5 (at a composition
of the exter~al layers of M~Co .~3 to 0 .95 )
Vi~Go~ity than monoc~rbides.
The ratio oY thicknes~es of the layers OI fro~ 1
to 1:0.25:1, a~ it ha~ been found experimentally, en~ure~
the required mechanical strength of the cathode a~
~tructural member of the laser.
The proces~ ~or making the ~as la~er cathode accord-
i~g to the pre~ent inve~tion can be per~ormed in two embo-
diment~.
-- 6 --
Accordin~ to a fir~t embodiment of the proce~ for themanufacture of a cathode 9 as a base use i~ made of a hollow
graphita blank with a wall -thicknes~ ~lightly ~maller th~n
the w~ hickness of the final cathocleO ~he bla~k i9 heat
ed in a mixture of vapour~ o~ tantalum or niobium penta~
chloride and argon (1~5 to 2 g/l of argon) to a temper~ture
within the range of from 2,300 to 2,500~C and maintained at
this temperature for a period of from 5 to 8 hours. ~he pro-
ces~ temperature and duration~ the starting blank thickne~s
~nd concentration of pent~ohloride are ~elected ~o as to
en~ure the occurrence of the proce~s of carbidlzation with
the formatio~ of a three-layer carbide ~tructure of the re-
quired composition and ratio between ths layer thickne~se~
~ he t~ree-layered structure of the ~athode is ensured
by thAt at the ~elected proGe~ parameter~ in the entire
surface of the graphite blank there i~ ~imultaneously ~or~-
ed a den~e aarbide layer ~external) and further growth of
the carbide can be effect~d only through the agency of dif-
fu~ion o~ carbon from the inner graphite m~trix which at a
¢~rtain proces~ ~tage i9 converted into a loo~en~d ~truc-
ture and pentachloride penetrate~ thereinto along lt~ inter-
grain face~ to convert thi~ structure into carbide rein-
~orci~g the inner layers. At the proce~s temperature below
2,300C too den~e exter~al layer~ are formed, which hindex
sharply the carbidization proces~ and make it impo~3ible
to obtain the required re~ult within an acceptable time.
At a temperature exceeding 2,500C there oc¢urs formation
of 100~3e c~rbide layers due to occurrence o~ the reaction
i:~ bulk. The ~tar-ting thickne~s oE th}~ blank i~ ~elected
by c~lculating the den~ity of carbide o~ tantalum or nio-
bium and experimental corre¢tion.
Si~ce the conditions of the proce~ ~or tha manu~
tur~ of cathodes with the required parameters are lnterre
lated, the time of carbidization i~ ~ound experimentally
f rom the d~ta of met~llographic ~-ray structural analy~i~
of the final cathode~ and change~ in the weighk of the gra-
phite blank after carbidization~ ~he above-specified time
period o~ 5 to 8 hour~ ensures complete con~er~ion o~ ~ra-
phite into the carbide ~tructure.
Specific condition~ of the fir~t embodiment of the
proce~ according to the pre~ent invention and parameter~
of the resulti~g cathodes are shown in Table hereinbelow.
In ~nother embodiment of the proces~ ~or the manu~ac-
ture o~ cathodes according to the pre~e:nt in~ention, a me-
tal blank (OI tantalum or niobium respectively) with a
wsll thioknes~ slightly ~maller than the wall thicknes~ o*
the final cathode i9 heated in a charge of powder-like gr~-
phite in an inert medium to a temperature withi~ the range
of ~rom 2,000 to 2,200C and maintained at thi3 temperature
for 5 to 10 hour~. The process conditio~ nd the bl~nk
thiokne~3 are ~elected ~o as to ensure occurre~ce o~ the
carbidization process with the ~ormation o~ ~ three l~yered
carbide ~truc-ture of the requirod composition and thicknes~
ratio.
-- 8 --
~.~4~
~ he three~layered cathod~ st~cture in this ca3e i~
ensured by that c~rbidiæation of meta:Ls o~ the ~ide sub-
~roup of Group V o~ the Periodic Sy~tem proceed~ in accord-
a~ce with ~he Me-C st~te diagram~ i.e~ in extern~l layer~
contacting ~ith carbon a monocarbide MeC~ is formed7 where-
in ~ can hava meanings close to the upper limit of monoge-
neity of the carbide, while the inner l~yer i~ tran~formed
into a semicQrbide at long residenc~ times~
~ ctual process rates depend on ~umerous parameter~ and
cannot be ca].culated th~ retlcQlly with the required accu~
racy. ~or thi~ rea~on9 it is neoe~sary to carry out e~peri-
mental verification of the proce~s condition~ and parame
ter~ o~ the cathodes obtained. At a temperature below
2,000C the carbidization process i~ ~harply decelerated,
the result bei~g a consider~bly extended carbidization time.
At a temper~ture above ~9200C the prooes~ of carbidization
i~ accompa~ied by the formation of defect~ in the growing
carbide la~er~ and by changes in the cathode ~hape due to
inter~l stresse~ and pla3tic deforn~tion. In the manu~ac-
ture of cathodes ~rom niobium oarbide the process tempera-
ture i3 maintained within the range of from 2~000 to
2,100~C, in the case of tantalu~ carbide the proce~ tempe-
rature i~ maintained within the range of from 2,100 to
2,200~. Since all the conditions of the procc~ for the
manufacture of cathode~ with the required parameter~ are
interrelated, the proce~s duration i~ an overall factor
and its value~ are found experimentally on the basi~ of
me-tallographic ana].yqis. ~he process d~ration increa~e3
wi-th lowering o~ the temperature and decreasing thicknes~
of the ilmer layer of the composition llleG10 5. Since ~emicar-
bides of tan-talum and niobium have a very .n~rrow range o-
~homogeneity and a hexagonal lattice, variations in -the semi-
carbide composition could not be establi~hed from the X-ray
an~lysi~ data~
Particular condition~ of the second embodiment of the
proce~ accordi.~g to the pre~ent inventionL and parameter~
of -the re~ulting cathodes are shown in Table 2 h.ereinbelo~.
~ est3 were carried out of sealed C02 lasers with dif~
derent cathodes produced according to the present invention
and having the parame-ter3 sho~n in Tables 1 and 2, For the
purpo~e of comparison a ~ealed C02 laser with a metallic
(covar) cathode o~ a ~imilar s~ape was a1~o tested.
~ he tests have shown that the use o~ cathode~ produced
f~om tantalum or niobium carbide by the proce~ according
to the present invention make~ it possible to e~tend the
service li~e of sealed C02 lasers ~rom 500 (for covar
cathode) to 10,000 hours and over.
At the same -time, the obtaining a maximum po~ible
value of a unit power of radiation per unit wa~elength and
maintaining it substantially constant with time are
ensured. It ha~ also been found that limitation to the
service li~e is impo~ed not by the ini~luence o~ the catho-
de, but o~ ot;her factors, the elimination of which must
bring about i.'urther exten~ion of the 3er~ice li~e of gas
laser~ .
- ~0 -
T a b 1 e
NoO Blank Proce~s Parameters of -the obtained
matsrial parameter~ ca~hode~
Tempe Dura- Penta- Layer E~ter~al Inner
rature~tion, ~hlorlda thick~ layer layer
~C hours concen- ~e~s compo~i- compo~i-
tration, ratio tion tion
g/l OI
argon
2 3 4 5 6 7 8
1 G.raphite 2~500 5 2 1 0.5:1 TaC~07~ TaC0~92
2Ditto 2,300 8 2 1:1:1 T~Co 9~TaC0 98
3Dit~o 29400 .6 1.5 1:0.5:1 ~bCoo74~bC0.92
4Dltto 2,300 8 1.5 1:1:1 NbCo.92~C0.98
T ~a~ b l e 2
___
1 2 3 4 5 6 7 8
1Niobium 2,000 4 - 1:0,5:1 ~bC0.95~bC0.5
2 ~ant~lum 2,200 8 _ 1:0.25:1 TaCa 8 TaC0 5
3 ~iobium 2,100 5 - 1:0,3:1 ~bCo 9~bCo 5
4 ~antalum 2~100 10 - 1Ø5:1 TaCo.85 TaaOo5
Th~s, the advantage o~ t~e gaa la~er cathode produ¢e~
by the proce~ according to the pre~ent invention reside~
in an e~ten~ion by a~ much a~ ~everal times of the servi~e
life of ga~ la~ers. Thls applie~ not only to C02 lasers~
but to many other g~9 la~ers in which ~puttering of the
cathc)de i~ o~` princ.ipal importance, for example, to C0
la~ers~ helium-neon la~er3, and the like.
