DTIC ADA427268: Instrumentation for the Rapid Discovery and Mechanistic Understanding of Non-Chromate Inhibitors

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A Multi-Disciplinary University Research Initiat!ve (grant merniber F49602-01-1-0352) was initiated in.
May 2001 t develop the seicutife basis for a multicfmetionsl zomspace coming using nezo-enginocng
anehods. Cerra fo this MURI iy he idenifcasim aren envroumensally niga component replace
<Srcmate-basedinhibitive pigments used in uesent day aetospase primes. Management of cheomate-hised
‘materials vepresetsa significant action ofthe $1 to $3 billion steers! malntentce cost spat by the Ac
Fore each yea

‘Nemerous compounds have Been examined ough the years with he hops of providing a chromate
epheoment. Tre comport inchs mlyodalin?, vanadiuny- based compound, borum-hased vompvuds™,
avd rare eatth salts, among vihas. Maury of these compounds fave been examined cecently for inhibitor
efficacy on sorospace alloys. However, io date o sige eammponnet has demonstated a concsion inkibition
power (officiency at specified concentration) comparable to chromate.

"A proitsingaleretve to thease ofa single inhibitor species is tha of using synergistic combinations
‘of two or more compounds, Syne-gy oocums when the ibibitive propery ofthe corabiaston exceeds the
seimetie sum oF the invidalcammponents, Syiteriste conbiuatious of ahiitan have esn examined
‘extensively for steel in acidified™™ and neutral” aqueous onviroments, as well as for copper in neutral
‘nquecnn envious" Numerons theoren for synergy have emerg dependinicom whether active
anions", cations?3"*5 oy organic spacias™™" arc omployed. However, a common theme throahout
the lat is tha one species aeorbs inially wl ridges oF faites, he adsopson of te other spores to
froduce a comples or yered barter sructure, These explanations conte to remain as thei. Mote
‘germane to paints, synergistic combinations of paint additives have beca explored since the late 1970's".
FReamples include phnephake rates, vine phsphue~ zine nieophhaale+ ne axe, and more recently,
zing molybdate | zine Phosphate | a zine salt of benzo aid, This laste comination bas heen used tn the
oP se priming topcoat, which has unforumately repute in poor aGhesion after limited sores. This pois
ot yet another hidden advantage of chromate pigments. In addtion ta having the aporopriatebalanet of
inhibiive power and solubility, an inhibitive pigmert mvs not interfere wilh in-service sdbsion, a property
thal is uctually sugmented by chromate pigments?

“Roce studios have examined syreipstc combinatious ofthe previousy dessibod tae earth and
‘yunsition metal salts'*", Although these preliminary experiments haye only examined {:1 ratios of those
‘material tote concentrion, synergistic elfects have een observed ws both electrochemical und pt
amombology analyses. irs almost ceain thot the opdiman rato is something other tar 1], and that a
Sign fear ati of sition experiments is nat ident the proper metrials and ato, Unfortunately,
{he predictive ables and faalemental understanding oF molecular systems will more than (wa or Ube
diferent atomic species cesiains extremely Hid, eo that one is cod wit a tormous atx of expen Lo
‘identify the optimum inhibiter combination under a wide range of lest conditions (6.8. pH. 'L).

‘One spprosch fo increase the ale of marin] dEsovery ' throt-h combtorial approaches
‘Combinatorics, initially utilized in electronic materials developnient™, has heen ore éommonty asaociated.
‘with automated syntesis and high doughpnt screening for pharmaceutical eteorch. in che combinatorial
process, large says of material or chmod! variabies can be prised ad serceno to ide the optima
process oe condition of nine. Creation ofthe combinaoria Hbrares i ypieally saightforwant. However
the ideniffeation of usp and dependabléasay dat can senstive'y detect nies in the celevan paremeter is
sotto be essmsed and i often the ate lniting procest in rapid dissow

‘The corrosion protootion propaics af inhibitors can be =leclrochowicatly quantfiod in many differem
ways, however there no atcepied elestrackeririeal parameters that cant he acquired rap (Le, mints) in te

laboratory to predict long-term (ie. yeara) corrosion protection. Ye, the desi is to screen Piousunds
‘chemical corapounds with an infiaite rumbat 0! combinations in 3 vast number of envicoumental conditions
Gemperature, pH, concentration, st).

TOSAESAB RS DISTRIBUTION STATEMENT A
‘Approved for Public Release
Distribution Unlimited
Cherival and electrochemical tests for high roughpat weeen'tg af corrasion inhibitor pertonmarcé
Ihave best: identtied Zor atunimum alloy AA2024, These mets have heen shown t Cuplicte beuchmatke
long-term (11 day) rest data acquired sing eloctrochctnical impedance specunscopy. Thus, a pathway has been
created for the use of combinatarial approaches for pid discovery of ervieonmentally benign corrosion
inhhitors an wel identi lication of sincrgistie combinations

‘Thc efficacious production ofthe central needs of this MUR r2quires dedicated instrumentation that
‘wil fuelitate high throughput testing of corrosion inhibitors. More imparrantly, the eduestional wissiou to
understand the sructure-property relaianships of inhibitor adsorption and function will require rurbiee analysis
instesmentation capable of analyzing the sequencing of events aad orientetion of componnds tative 0 the
surface. This knowledge will help further focos the seleution of effective inhititor compounds

UL Status nf Program

‘The putchase ofthis cquipmsnt wes delayed, however all equipment was ordered in late spring and has
snow béon delivered, Itcm D arrived in September, hence the delay in report eubmisrion. The following
eqwipmocpl was purchased under this orn

‘AL Miultiple-Microelectrode Analyzer (Seribuer Associates).

Thrigh the use af eamveitional reaction framce fitted with the anpropriaie eléctrode configuration iis
nvicipated that 96 experimcuts car be performed simoftareously. This Wil inereasc the throughput of
elecuorhemical experimentation by a fuctor a ea. 100 ata aisizmum,

Emtimated service lle: greater han 19 years

B. Plate Reader (Molecular Devices)
‘Reaction fms used for the chemical detection of alumiaum and other mat jon release can be read by
an antomiated plate reader, This ple reader allows the soqucntiel spectrometric nalyeis of x 96 well reaction
‘fame in legs time than has bocn usod to analyze onc sample up to 10m.
“Estimated service life: greater chan 10 yours

C. Blectrachemteal Quaréx Crystal Microbatanee (CH Instruononts)

Fleslmchensical experiments will provide a extain level af performance and mechanistic undecstanding,
However, to significantly advance tho educational process of understanding the mechanisin of inbibitor
porfonnanes, two additional pizces oF equipment ate cequestod, The surface adeorption charasteristicn of
{nhibitecs a8 a fuetion of the elecrochemical status of the interface is essential ro fully widerstand both the
‘mechanism and houndaries of performance of a given iabihit compound. Adserplion haracleristies
smogolayers or less can be assessed very effectively with un electrochemical quartz crystal microbalance
(EQCM). The EQCM will be very crucial to understanding the sequence of stops involved with tic adsonption,
bridging aad performane of synergistic combinations of inhibitor species"? *,

‘Estimated service life: greater chan 20 years

D, Raman Spectrometer (Digilab)

Further insight into the mechanism of inhibitor adserplion and orientation of the inkibitor species to the
substrate surface will be aquired via Raman Spectrasenpy with surface eabuncement. Reman Spectroscopy is
Valuable tool for the characterization of materials due to its extrome scnsitivity to the mologulsr environmcat
of the species of interes, ands of particular importance to surface and npar-surface apecice” such as ceerosion
inhihitos™®.

‘Molecular vibratious that produce Raman ecaltcring must alter de polarizability af the molecule and
complements the chaugo in dipole mornsat desecwet by TR spectroscopy. This makes Ramen Spectroscopy
‘sefil inthe avalysis of metal oxides.

Au advantage of Ramm spectroscapy is ite'arcessibtity to the low frequency of the spectrum (1041 ar),
‘his Law froquensy deta is impurtan! in dhe complete vibrational analysis of surface specics, especially fo the
investigation of “he nsiure of chemical inierastine of a surface species with tae mdatsicg surface. Again, this
intial ht init cum be investigated in stu without the concern fo trong scattering as experience in IR
specironsy.

"in addition, the weak Raman scetcring of water mnie the Raman analysis of adsorbed species on
ectode surfaces ard polymers in aqueous media wf particwer impor‘ance. This wall assist m the annlssis of
polycaerie costing rsins im another AFOSR funded project that sccks identify fon channels in polyeneric,
coating resin

Estimated service fe: arate than 10 years

IL E@ucational Renefit

‘Theprocess ol ihibitar discovory has historically aecuered.exnprially, ue ty The comglevty of howe
inhibitors fanetion, this process coutinaos, although tere ia more insight new with thease of modem surface
‘alysis metiods sech f Raraan and EQOM. The educational mission of tis research seks to embrace the
‘emplrca process init highest at, high iroughpat screening, to identify candidate compounis. More focused
Inethods, Raman ipesinsaupy dd EQCM, wil den be used to clade the mosKanism of inhibitor fnetion
‘These methods wil be even more eesti for fe underatenling OF synerg, @ phenomenon thal wil key hs 4
requisite for fulire chromate replacements

These eth il Find extensive uly inothoracas of eocac in those laboratories, For cxampls,
‘Rnan specroscopy wil alo aid in te invostigntion of costing resin dewraalion as «fonction of
evironmental expose de tothe weak fami ealleving hy wate. This wil provide data in the investigation
of eavizonpental degradation mechanisns in organic coatings that is complementary io the epcal
enochenical dara acquired in these laboratories.

‘This squiprent wil provide invaluable skills and wainig for graduate stuns on copies relevant the
‘Departmen of Defense and evilian society, Resoarch is presently under way.

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