Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FORMING A METAL COATING
This lnvention relates to a method of form~ng a single metal
or mixed-metals coating on a surface, to a metallic palllt, to a
method of paintlng and to a method of spray-forming powders uslng
the pa~nt.
05 Metalllc palnts are known whlch comprlse metal (e.g. z1nc or
alum~n~ùm) partlcles suspended ln b~nder, plgment and volatlle
solvent. Such pa~nts are easy to apply but cannot g~ve a
seamless coherent metal coat~ng, wh~ch can be requlred ~n
demandlng and advanced technlcal appllcat~ons.
Accordlng to the present lnventlon, a metalllc pa~nt
comprlses a compound between the metal or each o~ the ~etals of
the palnt and a polydentate reagent, sald compound~s) belng
dlssolved ln a palntable solvent.
'' An ob~ect ls palnted, accordlng to the lnventlon~ by apply1ng
15 thereto a palnt as set ~orth above, allowlng the solYent to ?evaporate, and'applyln~ a gaseous or vo~atlle substance whlch can
decompose sald compound(s) to release sald metal(s). Metal
powder may be made by atomlslng the palnt and applylng a sald
gaseous compo~nd.
ZO Accord~ng to another aspect of the 1nventlon, the method of
formlng mlxed-metal coatings on a surface comprlses decompos1ng
at the surface a flu~d e.g. vapour comprls1ng:
a f1rst preferably volat~le compound between a first metal
and a polydentate reagent, and a second preferably volat~le
compound between a second metal and the same or another
polydentate reagent, wherein the reagent(s) is/are volatile,
whereby the metals are co-deposited on the surface. The
reagent(s) and the compounds are preferably stable in alr. The
decomposltlon preferably y~elds the reagent(s) d~rectly, whlch
accordingly may be recovered for re-use.
Transport o~ the 'bulk' complex ~n vapour phase and I
reactlon on the heated substrate can ln certa~n cases result ~n
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lnteractlons between the regenerating ligand and substrate
material, i.e. removal of surface oxide, or the formatlon of a
volatile intermedlate whlch itself ls reduced later. This would
particularly be enhanced where the chelat~ng llgands are
o5 e~tremely actlve toward the base material. Thus, ln one
optlon, the satd second metal ls the surface and the sald second
volat~le compound is formed from reagent llberated upon
decomposltlon o~ the flrst volatlle compound. By thls technlque,
~nterpenetratlon of metals can be achleved at lower temperatures
than if, say, dlffuslon was belng relled upon.
Preferably the decompositlon of the polydentate reagent(s) to
metal ls by reductlon. Preferably the reduction ls performed by
a gas or gases.
Preferably the donor atoms o~ the sald reagent~s) are any
selectlon from N, O and S. Pre~Qrably the sald reagent (or one
o~ sa~d reagents) ls a Schl~f base or a ~-dlketone. Both thes~
are alr~stable and non-tox~c, unllkQ ~or example metal alkyls and
metal carbonyls.
Where the reagents ar~ dlfferent ~or the two metals, at least
ZO one may comprlse ballastlng substttuents. Thus, by exploltlng
the resultlng dlf~erentlal volatllltles o~ the two compounds,
thelr relatlve vapour pressures can be varled so as to ad~ust the
composlt~on of the resultlng metal mixture 1f other ways of
alter1ng the vapour compos1t~on are not avallable.
One of the metals may be copper and the other may be nickel.
The substrate may be a metal or glass or ceramic (e.g. alum1na)
or a membrane requiring to be ~etallised.
UK Patent GB 2135984B, the disclosure of which is imported by
reference, clalms a method of winning metal from ore, and
d1scloses for that purpose compounds wh1ch may f1nd use 1n th1s
~nvent~on, such as, in the case of Cu(II), tetradentate Schlff
base reagents.
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~ -diketones wh~ch may be used include for example 2,2,6,6
tetramethyl 3,5 heptadione (trivilally called tert-butyl acetyl
acetone), two molecules of which complex each copper atom:
05 C ~ / CH3
CH~ C - C ~ C - C - C ~ CH 3
11 ~ 11 \
CH3 0~ ,0 CH3
`'Cu~
The removal of surface ox'ide, mentloned earller, takes place
as ~ollows.
Complex ML ~ Decomposlng agent say H2
~ DeposltQd metal M ~ polydQntatQ reagQnt LH2
Regenerated ~Hz ~ Sur~ac~ oxlde M0
~ ~120 vapour ~ ML
Note that sur~ace oxlde can be removed at low temperature
(e.g. 300C), below the onset of rapid diffus~on. Thls feature
lmproves the adheslon of deposlted metal.
The inventlon wlll now be descr~bed by way of example.
The co-deposition of metals, e.g. nickel and copper on
varlous substrates, was carrled out using physically mixed
'powdered' proportions of respective metal complexes. A range of `-
metallic complex mixtures was prepared by physical m'ixing, and
each m1xture was shaken and volatillised prior to reduction and
deposltilon. ~he volatilisation temperatures were dependent upon
the 'mixtures' used, generally iin the region of 180-200C for
~diketonoate complexes, and around 250C for Schiff's base
. 30 complexes. The relative percentage of respective metals iln t ~ ~,
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deposlt depends as mentioned on the relative volatlllt~es of the
complexes. Thus a mixture of nickel and copper
2,2,6,6-tetramethyl-3,5-heptandioate complexes ~n the proportions
Nl 70:Cu 30 gave a deposit containing the same ratio of metals.
05 With a mixture of the same ratio, but 2,4-pentandione as the
chelate, a higher proportlon of copper was detected.
In the following examples, deposltlon temperatures of between
350 ~ ~50 ~ lO~C and total gas flow ~carrler and reductant) o~
75 ~ 5 cm3/m1n were used.
Prlor to any deposltlon all substrates were washed ln 0.1 M
HCl, followed by an acetone rinse.
EXAMPLE 1: NiCu alloy ~s deposlted on mlld steel.
A physlcally mlxed composltlon of Nl/Cu ~heptandloate)2
complex mentloned above, ~n the metals ratlo 70:30, was welghed
~n a sample boat and placed ~n a volatlllzatlon zone. ~Total
complex 0.4273g; Nl 0.0415g; Cu O.Ol9g). The system was
lnltlally ~lush~d wlth nl~rogen. Then hydrogen ~15 ~ 5 cm3/mln)
was tntroduced lnto th~ system. The substrate, mounted on a
heatlng probe, was brought to a steady state temperature ~400 ~
10C) before the complex mlxture was heated to its volatlli~atlon
temperature o~ 180~C and held for a perlod of 1 hr.
Poroslty o~ the resulting NlCu alloy deposlt on the mlld
steel substrate was determlned using a chemical stalnlng
technique, lncorporat1ng a sens1tlv1ty test for the substrate
metal. A p~ece of f~lter paper was d~pped lnto a solution of
hexacyanoferrate (III), then- pressed l~ghtly on to the thln
depos~t. hlthough a quantit~ve result was not obtained from the
test, it gave an indication as to the poroslty of the deposit, in
that any holes in the de~os1t resu)ted in a blue stain on the
3V filter paper.
EXAMPLE 2: NiFe alloy is deposited on mlld steel by depositlng
Ni and relylng on the freshly liberated ligand to react w~th the
substrate 1ron, the lron complex then be~ng decomposed alongside
the nlckel complex.
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In this case, the nickel complex used was nlckel bis
1,1,1-trifluoro-2,4-pentanedioate, Ni(tfa)2 for short. Ni(tfa)2,
0.4344 g, was weighed in a sample boat and placed in a
volatlzation zone. The system was lnitlally flushed with
oS nitrogen. Then hydrogen (10 ~ 5 cm3/min) was introduced into the
system. The mlld steel substrate, mounted on a heat~ng probe,
was heated to 400 ~ 10C before the complex was vapourlsed over a
perlod of 1 hr at a temperature o~ 190C.
Cross-sect~onal analysls of the coated substrate, uslng an
energy dispersive X-ray analyser, showed interpenetratton of the
base metal (steel) into the coating (nickel). Quantit~ve results
have lndlcated the migratlon of lron to the nickel to be as hlgh
as 11% ln cases where the coating has been bullt-up durlng a
number of separate runs.
EXAMPLES 3 - S: NiCu alloy ls deposited on stllca glass/on
alumina/on aluminium.
In each case a thln yet non-porous coh~rcnt and adhcrent ~llm
of alloy was achleved, a~ a temperature low enough not to damage
the substrate, even wlth substrates havlng awkward grooves and
undercuts; that is, the method has good throwing power.
In Example 5 (alumlnlum substrate) ln partlcular, the
operat~ng condltlons were ldentlcal to Example 1.
In~tial mlcrohardness measurements of cross-sectional pieces
of coated substrate ~mounted in plastlcs) have indicated that the
deposlt in some cases is harder than the substrate. However,
these results are tentattve where the depos~t ls extremely thin,
such as 10 ~m.
EXAMPLE 6: Coating powder particles can radically alter their
propert~es. The coatings may only be a few atoms thick - less
than 1% of the weight of the powder, yet be effectlve. In this
example, metallic copper is deposited on supermagnetic flakes,
` Y,mm x Y,mm x /~omm for example, of iron neodymlum borlde Fel4NdB,
known as Magnequench-, or equally successfully on S-mlcr~n Fel4NdB
powder known as B14.
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This copper provides a non-magnetic insulation ; on
compressing the flakes (or powder particles), a small-domain
highly magnetic material is obtained. This task would be
difficult to achleve us~ng conventional metal paint, and is
oS conventionally performed by tumbling the flakes with copper
powder ln a process known as tumble-co-milling , which cannot
yield the same unlformlty of magne~lc lnsulatlon without greater
volumetrlc dllut~on of the supermagnet~c matérlal.
A copper complex conslsting of the compound
10 2,Z,6,6~tetramethyl-3,5-heptadlone described above, two molecules
of which complex each copper atom, was used.
B14 ls very pyrophor1c and ls therefore stored under
cyclohexane. The copper complex ls dissolved dlrectly lnto thls,
~n an amount dependlng on the ~hlckness of copper coatlng
lS requlred after calculat~ng the partlcle surface area: for
magnetlc purposes the coatlng thlckness should be the mlnlmum
whlch wlll survlve compresslon wlthout rupturlng. In thls
example, the complex was calculated to amount to 1% ~based on
copper) by mass of the B14. The same procedure, uslng
cyclohexane, was also used wlth Magnequench. The mlxture was
shaken thoroughly at room ~emperature. The solvent cyclohexane
was evaporated under nltrogen at 100C before lncreaslng the
temperature of the system and chan~ing to a hydrogen atmosphere
to deposit the copper on the Fel4NdB at operatlng temperatures of
2S 210C for 1 hour. At much lower temperatures, the complex wtll
not give up the copper at an ade~uate speed, while at much higher
temperatures, the liberated dione may attack and extract the
substrate Fel4NdB.
Good coverage of the Fel4NdB with copper was established by
vtsual ~nspectlon, and by noting in the case of B14 that the
product was ~ç~ pyrophoric. In some cases lt may be advantageous
as a final step to dry tumble the coated mater~al to assist good
overall coverage.
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The hydrogen gas reduces the complex, yielding elemental
solid metal and liberating, in the gas phase, the initial
chelating ligand. Inlt~al n.m.r. and i.r. studles on the
collected products have shown that whllst a number of ligands can
OS be regenerated to some purity , especlally straight cha~n alkane
~-dlketones, their fluorinated derivatives are prone to some
decomposltion.
EXAMPIE 7:
In other appl~catlons, the copper complex of Example 6
dlssolved ln cyclohexane or d1ethyl ether was brush palnted onto
a substrate, whlch was heated to 210C for 1 hour ~n hydrogen. A
contlnuous copper coatlng was left on the substrate, and the
liberated 11gand could be recycled to make further palnt.
EXAMPLE 8:
In another appllcatlon, the copper complex of Example 6 ln
solutlon was ~etted, through an atomtslng nozzle, as a ~lne spray
tn~o a chambèr con~aln~ng hydrogen a~ 250~C. Copper powder was
rQcovered ~rom the chambQr~ Th~ llberated llgand could be
recycled. Care must be taken to avold an undue proportlon of the
complex from decomposing on the chamber walls and slmply plat~ng
them, for example a cyclonlc gas flow path may be establlshed
wlth~n the chamber so that the cc~plex does not contact the
chamber wall.
A mixture of such compounds may be used, ln the same or
separate sprays, to yield a mixture of liberated metals, in
precalculated volumetric proportions of liquid to yleld the
metals in the desired ratios.
Preferably the metal ~s one or more of a m~xture of copper
and n~ckel.
A mlxture of such metal powders may permit alloys to be made
by pressure-sintering wh~ch would otherwise be unobtalnable or
only obtainable by extraordinary techniques such as 1mplantation
by nuclear bombardment.
