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Sept. 24; 1946.
Filed July 12, 1941
Jé'LE/V/DE 1744/
Arthur von Hippel, Weston, Mass., assignor to
Federal Telephone & Radio Corporation, a cor
poration of Delaware
Application July 12, 1941, Serial No. 402,103
10 Claims.
(Cl. 148-6)
In the single ?gure of the drawing is shown.
by way of example, a disc, partly broken away,
This invention relates to processes of treating
metal surfaces and products thereof, and it com
prises processes wherein metal surfaces are sub
iect to the action of selenidingagents to form a
film including a form of selenium, presumably a
metal selenium compound on the surface; it fur
ther comprises processes wherein such coated sur
faces are thereafter further coated with sele
nium, and it further comprises the products of
which may be considered as a selenium recti?er
disc or a photo-sensitive element made in ac
cordance with my invention. The dimensions of
the disc are exaggerated in order to more clearly
illustrate the component parts.
This comprises a metal disc I coated with a
?lm 2 of a metal selenium compound of the
10 metal. On the upper surface of the disc is shown
such processes.
a selenium layer 3.
The application of selenium to metals, such as
Thus my invention in part can be looked upon
- iron, nickel. and others, for the purpose of ' pre
as the formation of a metal-selenium ?lm on the
paring photoelectric cells, recti?ers, and the‘ like,
metal prior to the application of metallic sele
has hitherto presented many problems. Selenium
metal is customarily applied by spreading the 15 nium thereto with the metal "selenide” acting as
a bonding agent for bonding the metal to the
molten selenium on the metal surface or other
overlying selenium coating. This film also im
wise producing a smooth coating on one surface.
' proves the surface tension relationship so that
Selenimn, however, has a very high tension and
the metallic selenium more readily spreads
it is di?lcult to “wet” the metal surface with the
molten selenium. As a consequence the selenium 20 smoothly over the disc. Electronic diffraction
diagrams of metal surfaces “selenided” under dif
layer is not uniformly spread on the disc and
ferent conditions reveal different types of crys
does not adhere ?rmly thereto. The problem in
talline structures produced by compounds of the
volves at least two factors. The ?rst is that of
selenium and the metal plates.
so changing surface tension relationships be
Thin ?lms of metal-selenium compound can
~ tween molten selenium and the metal to be coated 25
be formed upon the metal surface in many di?er
that the selenium will spread evenly over the
, ent ways. One of the most convenient is that of
metal. This can be realized by thoroughly clean- .
ing the metal surface prior to applying the sele
nium. The second factor has to do with estab
dipping the metal, or otherwise treating its sur
face, with aqueous solutions of selenious acid or
lishing a ?rm bond of adhesion between the sele
30 a. selenate, to which in some cases nitric acid has
nium and the metal. The adherence of the ?lm
to the metal is of great importance in plates’ or
been added.
It has been previously found that an improved
bond could be obtained by roughing the surface of -
nitric acid.
For example, one suitable solution >
(for convenience called bath 1) consists of an
aqueous nitric acid solution containing, in each
discs to be used as recti?ers or light sensitive
liter, about 252 grams of nitric acid and about
cells, and hithertothere has been no satisfactory
way of improving the "bond" between the metal 35 105 grams of selenious acid expressed as $802.
Such a solution is approximately 4 normal in
and the selenium ?lm.
The metal surface on which a ?lm
of the selenide is to be formed is dipped or other
wise contacted with such a solution. The time
discs before applying selenium thereto. However,
even this rougheni'n'g does not secure a su?lciently 40 of dipping is not important, from two to ten
minutes is adequate. In such a solution the metal
close or ?rm bond. Moreover. it cannot be satis
of the surface undergoing treatment reacts with
factorily applied to base metal discs such as iron
or aluminum discs which have been plated with
another metal, such as nickel'or zinc, because the
roughening treatment will cut through the plat
ing exposing the plated metalto corrosion.
selenium ions to form a metal-selenium com
Theoretically, the reactions occurring are prob
matings on metal surfaces can be made to adhere .
ably as follows, using nickel as an example.
When the nickel, for example, a strip or disc
thereof, is immersed in the solution, the surface
dling, abrasion, and the like, so that the selenium
plates are not readily damaged in use.
My invention is based upon the discovery that
amount of nitrous oxide (NO) is also liberated
and the nitrous oxide reduces selenious acid
present to liberate divalent selenium ions. These
selenium metal adheres much more strongly to -
negative ions react with the positive nickel
I have now discovered ways by which selenium
of the nickel is attacked by the acid in the solu
tenaciously thereto and thus I am able to prepare
. selenium-coated metals which resist ro'ugh han 50 tion and nickel ions are formed. A certain
metal surfaces which have ?rst been “selenided.” 55 ions to form nickel selenide, NiSe. However, the
reactions actually occurring may be somewhat
Thatis to say, it adheres more tenaciously to sur
more complicated than this simple explanation
faces which have been provided with a thin ?lm
> would indicate. In any event, the nickel selenium
formed from a bath containing selenium, pre
sumably forming a metal selenium compound of
compound is deposited on the surfaces of the
the metal prior to applying the selenium metal 60 nickel strip or disc exposed to the solution. Then
the treated metal is withdrawn from the aqueous
solution. washed and dried. It can thereafter be
coated with molten selenium and the selenium
layer thus provided on the metal is uniform
throughout and adheres firmly to the base metal.
The temperature during the “selenidin8" oper
ation is not critical although I ?nd it advan
tageous to use moderately elevated temperatures
of about 50° C. to 60° C. when using the nitric
was generally preferable that selenates also are
I do not wish, however, to be limited to the
particular "seleniding” baths described above.
All of them will preferably contain selenium as
an acid or salt in solution, together with other
‘ constituents which will react with the metal to
form metal ions thereof so that these positive
ions can react with divalent negative selenium
the solution at 57° C. treatment must continue 10 ions to form a metal selenium compound. Cop
for a minimum time of about 10 minutes to pro
per, nickel, iron, zinc, tin, magnesium-aluminum
duce the desired result. If the treatment is con
alloys, steels of various kinds, and other metals
tinued too long, a pitting of the base metal re
can be selenided as described above.
Before “seleniding” the surface of the metal
If the above selenious acid solution is made up 15 it is advantageous to ?rst thoroughly clean it to
with 5 normal nitric acid (bath 2) instead of 4
free it of any solid particles, grease, rust, and the
normal then the temperature, for "seleniding”
like. While this canbe accomplished in any way,
nickel, can be reduced to about 45° C. for the
I find it advantageous to first wipe the metal
same time of treatment.
with a cloth to free it of any solid particles, dust,
These solutions are somewhat unstable due to 20 etc., then degrease the metal with any suitable
the formation of nitrous acid. This can be over
solvent for oils and fats, such as trichlorethylene,
come by the addition of sodium nitrite, in an
ethylene dichloride, and the like, then subject
amount of about 30 grams per liter, to the solu
the metal to an -electro-cleaning operation in
tion to form (bath 3). At the same time the
ways known to the art. Finally the thus treated
temperature during the seleniding operation can
metal can be washed in hot and cold water and
be reduced to about 29° C. for the ten minutes of
pickled in hydrochloric acid solutions, for ex
ample, to remove any rust and oxidation prod
If instead of 30 grams 60 grams of sodium ni
ucts. Metal surfaces so treated and ?nally
trite is added to the 4 normal HNOa solution
washed free of acid are quite readily wetted by
(bath 3A) two minutes treatment at about 29° C. 30 selenium so that homogeneous ?lms of metallic
is su?lcient for producing a ?lm to which the
selenium can be applied thereto but the selenium
selenium will ?rmly adhere.
does not adhere very strongly. But by selenium
acid-selenious acid solution just described. With
In the foregoing example I have illustrated
treating the surface of the metal prior to the
ways of practicing my invention for "selenidin8”
application of the selenium, as described above,
nickel prior to the application of metallic sele 35 I am able to obtain selenium-coated surfaces
nium coatings thereto. The same process is used
wherein the selenium metal has greatly improved
when iron is to be pretreated prior to coating
with selenium. Iron surfaces ordinarily require
Having thus described my invention, what I
a shorter dipping time than do nickel surfaces.
claim is:
As examples, it was found that iron when treated 40
1. In the coating of metal surfaces for the pro
with (bath 1) required only two minutes at 29°
duction of selenium coated plates the steps which
C. and with (bath 2) only three minutes at 22° C.
comprise treating the metal surface with a solu
Many other metals can be provided with a
tion containing a form of selenium to form a
coating of a metal-selenium compound in ex
metal-selenium compound thereon and there
actly the same way. For example, magnesium 45 after coating the treated surface with selenium.
aluminum alloys, such as that known as Dow
2. The process as in claim 1 wherein the surface
Metal, can be dipped in aqueous solutions con
to be coated is nickel.
taining selenious acid, thereafter washed and
dried, and ?nally coated with metallic selenium
3. The process as in claim 1 wherein the surface
to be coated is zinc.
in any convenient way. With this alloy a se 60
4. The process as in claim 1 wherein the surface
lenium compound having a gray color is formed
to be treated is a magnesium-aluminum alloy.
but the actual chemical composition of such com
5. The process of coating metal surfaces with
pound is not clearly understood. Dow-Metal is
destroyed by acids so for this metal the nitric
selenium which comprises the steps of treating
types of solution to give satisfactory ?lms are
lenium compound of the metal formed by sub
Jecting the surface of metal to an aqueous solu
the surface with an aqueous solution containing
acid is omitted. In tests it was found that a 55 nitric and selenious acid to form a metal selenium
60% S802 solution produced a satisfactory ?lm
compound on the surface and thereafter coating
with a two minute treatment at 21° C. and a
the treated surface with selenium.
10% S802 solution produced a satisfactory coat
6. The process as in claim 5 wherein the surface
ing in three minutes at 21° C.
to be coated 1s nickel.
Tests alsoéindicate that the same bene?cial 60
7. The process as in claim 5 wherein the surface
effects can be obtained with other metals, for
to be coated is zinc.
example, the results of treating zinc with three
8. A selenium-coated metal plate having a se
,tion of selenious acid underlying the selenium
'’ C’.
mseori-"i norm ‘HNOQ ......... - .
%%8e0|+2 norm BNO; .......... ..
1—1%NaSe04+2 norm BN0. ....... . .
9. Selenium-coated nickel having a nickel-se
lenium compound formed by subjecting the sur
face of the nickel to an aqueous solution of se
70 lenious acid underlying the selenium coating.
10. A process of treating galvanized iron sur
faces with selenious acid to form a zinc selenium
compound thereon.
It was found that while selenious acid (SeOa)
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