Note: Descriptions are shown in the official language in which they were submitted.
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~ R 0~ TA~ATLU1
Bac~ round of the Inventlon
This inve~tion relates.to a method of platini~ d
~eat tr~ati~g tantalu~ and ~ore particularly ta~talum
S plugs to be us~-d as electrodes in th~ ~etection o faults
: in reacti~ vessel protective linings.
It is a co~mon practice to use prot~ctive layers
of glass enamel as an an~i~corrosive lining o~ ~e lnside
of reac~io~ veesels which ontai~ corro~i~e liqulds~
: lO I~ suc~ vessels~ a ~ault in the protectl~e llning can
: rea~}t in scr~ous corrosio~ o the vesse~ and i such
a ~ault re~ai~ u~detected o~ some time~ the vessPl
. may bec~e u~usable and irreparable~ ome cases~
: : the contents of the vessel may eve~ $eco~e co~tami~ated.
15 Thu8, it cs~n be~see~ that ~essels o~ this type must be
: conti~uously monitored agal~st~ damage to the protec~ive
lini~g.
: U.S. Paeene 39858,114 di~closes a ~h~d for de~ect
ng~aults i~ reaction ves~el li~ings~ The method de
20 ~scribed~in this patent involve$ dispos~ng a pIati~u~ ;: :-
electrode ~ a conductive mediu~ in the Yessel and ~easur-
ing any current flowing from the electrode to the iron
or steel wall of ~he reaction vesselO ht locations where
damage has occurred to the lining, the current flow
:~ 2; increases acco~rdingly. Th~ intensity of the current
delivered by the so formed Pt-~e cell indicates the degree
: of damage to the protective layer. The platinu~ metal
.~ . used as an~electrode in U.S. Patent 3~85g,114 is very
expensive~ It would thereore ~e worth~hile, lf possible,
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~o pla~e a tan~alum core with pla~iuum aud use lt as
an electrode. Such a~ electrode would have a platinum
~urface and tantal~m core aud ~ould be legs expe~siYe tha~
conve~tionally platinum plateA e:Lectrode ~ Ta~talu~ has
5 been chosen as a core materlal because It 19 cor~sio~
resistant and should the plati~um laye~ of the elec~rode
break dow~, the ta~talu~ will no~ ad~e~sely affect the
conte~ts of the vesselO It has been found I~ practIce~
however, that con~entionally plated pIatnlum layers on
ta~talu~ wear out rather quickly~ partj.cularly whe~ the
conte~s of the ~essel con~ain an ab~asiYe materi~l ~uch
as slurr~.
Obiec~s of the I~ventio~
~- Accordi~glyD it ls a~ ob~ect of this inYe~ti~ ~Q
prov~de a~ abrasion resistant pIatinum layer on th~ oute~
surface of a tantalum ~or~piece~
It is another ob~ect of this ~n~entlon to p~ovIde
method of platiniæi~ and heat treat~D~ a t~.ntalu~ ~70xk~
: piece.
It i-4; yet another ob~ect o this inventIon to provide
: au l~prcved ~lectrode ~r a reactio~ vesael fault f~der
; . o hi~h precis~o~ ~
: It is a ~urther ob~ect of the ~nYent~On tO p~nvide a
method of obtai~in~ a thi~ stable layer o plati~Lm on
. 25 : a ~antal~u workpiece. : .
It is yet another object of the ~nvent~on to provlde
.
~: an ine~pe~sive platinum electrode~ -
5u~ary of the Invention ~
These obj~cts and:other are accomplished i~ accordance
with the present invention by providing a no~el method nf
platinizing and heat treating a tantalum wo~kpiece~ The
surface of the workpiece is first cleaned and then
connected to the negatiYe lead of a æource of DC supply.
The positive lead of the DC suppl~ is then connected to a
piece of corrosion~resistant conductive metal, such as
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platinu~, and both metals i~mersed i~ a platinizing
solutioTl. A current is ~hen p~ssed through ~he ~-olutlon
and platinum blac~ is deposi~ed on the ta~talum workplece.
The tantalum workp~ece ls then removed from the platin-
i2ing solution and heated to a tempera~ure of about1050-1150C in a va~uum ~urnace~ os furnace contai~in~
an inert atmospbere, for a time suffic~e~ TO diffUe
the plati~um into the su~face of ~he ~antaluTn. Thi~ -
res~l~s in the for~atio~ of a ~an~alu~ workpiece whlch
contains a ~table outer layer of platinum dlffu~ed iTl
~he surface of the t~ntalum, Thi~ proce~s ~nay be utilized
to manufacture platinum coated parts ~uch ~ elec~rodes, -
electrical probes, and repair plugs for glass liT~ed
vessels.
It sho~ld be understood that ~aTltalum and tant~elum
base alloys ~h~ch may be plati~ized and heat ~reated
are included within the scope of this inVen~iOT~.. For
e~ample~ tantalum alloyed ~lth tuTlgs~en coTnpr~ses a
~uitable alloy which may be used in place of tantalum
i~ the.process o the present i~v~ntion.
: ~tailed IL~ tI~ f the Invention
Within ~his disclosure. the t~rms platinum plated :~
a~d platinized ~re speci~icaily distingulshed ~ro~ e~ch
other. Plati~um plating is carried out by co~ventional
methods. A ~ell cleaned tantalu~ workpiece i5 ~astened
in a chuck which i~ electrically charged~ A spo~ge dipped ¦.
in a platinum solution is held against the rotating
tantalum core~ The process is continued until the desired
thic~ness of platinum is formed o~ the surface of the
; 30 taDtalun.
In the platinizing and heat treatment process accord-
ing to the present invention, a platinum black powder
: coating is deposited on the tantalum workpiece by electro- j
lysis~ The coated woxkpiece is then placed in 2 fuxnace : ¦
35 which is heated to about 1050-1150C., This heat treat-
ment results in the diffusion of the platinum into the
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surface of the tantalum~ This dlffusion ~f the platinum
i~to the surfa~e of the tantalu~ results in a ta~talum
part containing a pla~inum surace which ls electrlcally
- and mechanically superior to pla~ed pla~num part~ ~
The process of the presen~ i~ven~i~n results i~ a s~able
platinum layer on the tan~alum sur~ace a~d makes the
electrode abrasion resistant. Fur~her~ the platinum
lsyer made according to the presant invention ~ ~hlnner
. tha~ con~en~ionally plated pla~inum l.ayers~
In a preferred embodime~t of the pr~sent ~-nven~ion
a ta~talum workpiece~ sultab~e ~or ul~lmate use as ~
electrode in ~he detectio~ of aul~5 in ~ reacti~ vessel,
iB sandblasted to ~e~der the surface clean a~d ree of
dlrt a~d grease. The tantalum c~re is i~ the orm o
: ~5 a one piece 5/8 inch fla~ head sc~e~ and compri~e3 ~0%
by ~e~ght tantalum a~d 10% b~ weight tungsten~ The core
is ~en brushed off and clea~ed with a 202 HCl ~o:Lution
and washed~ The core may be st4xed i~ distilled water
; if plati~izi~g is ~o be don~ at ~ later ~tag~
Th~ followi~g ~aterial9 an~ appar~tus wera u~ed
in the platinizing process:
. 1. Bea~er (200 ~1~ .
. 2. Plati~izi~g soluti~n ~lS0 ~1
- . 30 Slx Yolt DC powe~ source
. 25 ~ 4.~ Small strlp o~ pla~num metal
2 x 1 1/4 x 1/32 i~che~)
The platinizing solutio~ is prepared ln t~e beaker~
~: ~ The solution ccntain5 3 g~s of chloroplatlnic acid, 0.02 :~
~ ~ gms of lead aceta~e per 100 ml of distilled water. The
; 30 tantalum core described above is connected to the negative
lead of the 6Y DC power supply and the platinum strip
is connected to the positive lead o the 6V DC power
supply. Both the platinum strip and the tantalum core
are suspended in the solutio~ in the beaker~ Only the .
area of the tantalum that is to be platinized is immersed
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.~n the solu~ion~ The vol~age i9 th~n applied for ~ix
mi~utes during which time the platinu~ black i5 deposited
on thc tantalum core~ The tantalu~ electrodc ls ~hen
care~ully removed ~rom t~e solution and ~lnsed with dis-
~illed water. The platinum black deposi~.ed is dull blackand no~-adherent at this s~ag~a. The electrode ~s then
placed in a rack and placed in a ~urrlace main~ai~ed at
a vacuùm of about lO-6 mm of ~ercury a~d a temp~rature
of about 1150C or l/2.hour~ This heat treat~ent re~ults
i~ the platinum bei~ diffused into the surface of the
tantalu~ ~hich exhibits a dull gray appearance Option-
ally, the eantalu~ corè may b platinized and heat 'c~eated
~or a seco~d time in order to.form a more stable a~d
adherent platinum lay~
It has also bee~ found that the quallty of the plat-
inizing a~d heat t~ea~ed electrode is better when ~i~er
sand is used ~or blastingt rather than coarser. The
surace roughness of the ta~talum core after ~,andblasting
i was measured by ENGIS*roughness meter type 6102E tEngis
Equipment Co., ~orton Grove, Illlnois? and ~ound to be
30-38 micr~ inches. The surfaee roughness of the comple-
ted platinized and heat treated electrode was meaaured
as ~4-28 micro ~nches.
. . The addition of lead acetate or other approprla~e .
. 25 lead salt to the platini~ g solution promotes the adher- . -
ence of platinum to the tan~alum electrode, and is essen-
t~aI for adherence of platinum black to the tantalum
surface. ~ithout the prese~ce oX.a lead salt in the
. platinizing solution, thc depos.Lted platinum blac~ flalces
30 of the surface of the tantalum. ~arious vol~a~es from
about 3-2~ volts and ~aricd ti~e periods from about l/2
to 6 minutes were ound to be satisfactory for the platin-
i7in~, processes. Six vol~s for six minutes was found
j~ to be optimum from the vlewpoint of cost and eficiency,
. 35 but is not critical for the proccss. ~ligher volta~es
* T r a c~ e ma r k
cause excessive pla~inum deposi~ on ~he elect~ode and
lower voltag~s take l~nger times ~ orm a platinum
deposit on the elec~rode.
~or good quality electrode~ ~ is desiràbl~ durlng
the hea~ treatment 5~e.p to maj..Llt,ain ~lC ~urnace ~emper~
a,ure in the range of abont 105~-1150~ fo~ ~imes r~ngi~
f~m abou~ 30 minuteC to 1 hou~ Xt was ound ~ha~ below
1000C the pla~inum black does not ~dhere to t]l~ ta~alum
e~ectTode and a~ ~e~perature~ higher tl-an about 1200C
the;platinum ~lack bu}n~ off.. '~he ll~nace ls ~nai~talned
at a vacuu~ of 10-6 mm of mereury to pTevent oxidation
- of plat~num or tantalu~, bue ~Tacu~ms ~utside thi9 ra~ge
are also satisfactory. If desl~ed an Inert atDos~he~e
could also be us~d during ehe hea~ ~reatl~g .step.
Superior qu~lity of the platini~ed and hea~ 1rRated
electrode ~ver platinum plated ~leetr~des is f1lrther
conirmed by the followi~g ~es~t based on the galvanic
cell pr~nciple. The electrode consit~lting the posltive
lead i8 attached ~o one elld of a 0~1 mA a~meter and a
piece of tan~alum co~stituti~g the ~ega~ive lead ls
attached to ~he other end of said ammeter. The e~ectrode
arLd tantaluLI are placed in a beaker ~ontaining ~ Cl
~ater s;olueiorl and the rea~ on t~le a~meter ls ~soted.r
This re~ding i~; knoe~n as a nc~ aull: readi~g~ The electrode
25 and tantalun are allowed to re~ain in place for o~e week.
Af ter the one wee~c period a pt ece of iron is connec~ed
to the tantalum and ill~roduced into the ~Cl solution.
This simula~es the fault situa~ ion ~hen the gIass lining
of the vessel is damaged and l:he con~ents are exposed
30 to the metal. A reacling is ~:alcen which lndicates higher
current flow. In the simula~ed faul~c situation, l:he
tests have consis~ently shown higher current readings
for platinized and heat ~reated tantaluL~ electrodes than
for platinum plated electrodes. The hi~her readings
35 ~ignify higher sensitiv~ ty of the platini~ed and heat
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treated ele~tr~des to the plated electrodes. One ~ueh
exa~ple shoued the readin~s as follo~s:
F It Gu.-e---mA
~o ~ault Aft~r o~e After one
5 ElectrodeC~rr~ne =A ~ week 10 nin.
Conventio~al
Plaeinum Plsted
Ta 0.00 1.8~ 1~29
Plati~i~ed and ~eat
Trea~ed Ta . 0~00 -5.46 3021
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/ ~hus, i~ should be appreciated ~hat the present
inven~ion of platini~ing and h~a~ ~reating tantalum
produces electrodes which ~easure a fault in a glass
~ined Yessel on a continued basis far mcre precisely
than conventional platinum plated electrode~ even thnugh
. the plated platinum coating ~g ehicker than the platinized
~d heat treated pla~num layer. Further~ th~ superior
¦-. p2rformance of t~e platini~ed a~d heat treated platinum
~: : layer is arhieved at a much lower cost than that of ~he
2~ platinum plating~ ,
~: Although partic~lar e~bodiments o the present i~ven-
:~: tion ha~e been dlsclos~d herei~ ~or purposes o~ explana-
. tion, further ~odif ications or variatious thereof will
be appare~t to those skilled in the art to which this
invention pereains.
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