CA1126497A - Method for the prevention of fouling and corrosion utilizing technetium-99 - Google Patents

Abstract

S P E C I F I C A T I O N

INVENTOR: CARL WOOTTEN
TITLE: METHOD FOR THE PREVENTION OF FOULING AND

ABSTRACT

A method for the protection of substrates subject biological fouling or corrosion in fluid environments is disclosed. Technetium metal, alloys or compounds are imbedded in, or cast, sprayed, electroplated, sputtered or otherwise coated onto the surface OF substrates or included in the s?
layer of the substrate exposed to said fluid environments, ?
varying concentration levels. The growth of bio-organisms on ?.
surface or near such surfaces is prevented and corrosion of substrates is simultaneously inhibited.

Description

li~649i' S Field of the Invention ~ This invention relates to the prevention of biological 6 fouling of substrates in fluid environments and simul-taneous corrosion inhibition by the application of or incorporation 8 into the surface of the substrate of Technetium-99, its compounds 9 or alloys.

11 Description of the Prior Art 1~ . I
13 Substrates exposed to various fluid environments are 14 continually subject to biological fouling and/or corrosion.
1~ ll 16 Considering air as a fluid, examples are the oxidation 17 of various metallic surfaces exposed to atmospheric environMen~s ~8 resulting in discoloration, flaking and structural weakening e.g.
19 the oxidation of the surfaces of alumln~, iron and steel.
Organic fluids.support various biological growths which foul the 21 function of associated mechanisms or pollute the product. It is 22 known that specific organisms live within the fuel tanks of jet 23 aircraft or fuel storage tanks digesting the jet fuel. Their 24 growth causes clogged fuel lines or other malfunctions in fuel handling mechanisms.

27 In both fresh and ocean water environments undersirable 28 and damaging biological fouling and corrosion are co~nonplace~
29 Marine organisms, e.g. algae, bacterial sludge, sea worms, plantc., 31 barnacles, crustacea, etc., cause millions of dollars damage ~ ch year to substrates exposed to underwater environmen~s such a~
32 instrument transducers and o~her underwater instrulllentation, huoy~, __ 6~7 :
submarine ballast tanks, water gura~s, underwater sonar, and the like, by forming growths of the organisms on the surfaces. Eventually undesirable and damaging fouling results which, at the least is expensive and time consuming to remove and at the worst totally destroys the usefulness of the device.

Instrumentation having moving parts which must operate in a fluid environment such as transducers of the flexible diaphragm type or fluid level measuring devices utilizing a sliding rod become totally inoperative when fouled by organisms or damaged by corrosion~

Boat hulls, anchors, lines, propellors and drive shafts are constantly subject to such fouling and corrosion.

Boiler plates and tubes, heat exchangers, steam lines and cooling towers each have specific biological fouling and corrosive problems peculiar to the compressed steam, hot water or cold water side or other particular Eluid environments.

The prior art has developed numerous approaches to the solution of these problems.

One approach has been to attempt to alter the composition of the substrates; the other to apply some coating which will increase the resistance of the substrate to biological fouling or chemical corrosion.

Although the first approach has produced a host of alloys and materials with improved resistance to biological fouling and corrosion, the problem remains one which results in billions of dollars in damage and maintenance costs annually.

~ 49 7 1 ¦ Numerous anti-fouling and anti-corrosive coaLings for 21 application to substrates in fluid environments have been develop~l 31 However, these coatings eventually peel or wear off the surface l during use and have but a limited life expectancy requiring 51 costly shutdowns and reapplication. In the case of stainless 61 steel, titanium and other special alloys these coatings fail ~o q¦ adhere satisfactorily. Also such coatings often require relativel~ji 81 thick applications which are subject to small cracks or crazing l permiting corrosive fluids to reach the surface of the substrate.
10¦ Even minute cracks can result in damage to coated devices, I
1~¦ Anti-fouling or anti-corrosive coatings have an additional dis-1~¦ advantage in that they can be relatively easily scrapped or 13 ¦scratched off the surface. Toxic substances are often used in 14 ¦anti-fouling coatings which create a health hazard to non-harmrul 15 ¦organisms and even humans, and also which loose their toxic 1~ ¦compounds or toxic effect in a short time period by either dissolv-¦in~, in the fluid environment or reaction with compounds present 18 lin that environment.
19 l 20 ¦ Thus it can be seen tha~ the problem of keeping ¦substrates exposed to fluid environments free from fouling 22 ¦organisms and corrosion has heretofore remained unsolved.
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3 These and other failings of prior art to provide a

4 satisfactory solution to the problem of biological fouling and corrosion are overcome according to the present invention by 6 applying an effective coating of Technetium-99 or Technetium-99 containing compounds or alloys to the substrate to be protected.

9 According to the present invention, Technetium-99 is applied to the basic substrate to be protected by any suitable 11 means well known in the prior art. Coatings can be formulated, 12 which incorporate Technetium-99 or its compounds, that contain 13 film formers which do not block the passage of the beta particles 14 but permit their effect at the fluid-substrate interface.
Because of the presence of Technetium-99, the coatings can be 16 applied in relatively thin layers which avoid the cracking and 1~ crazing problems of non-Technetium-9g protective coatings. The 18 material can be cast, deposited by sputtering or via an 19 electro-plating,metal spraying, ~lame spraying, chemical vapor deposition or ~acuum vapor deposition process in varying -thick-21 nesses to achieve the desired result. In addition, during the 22 manufacturing of the material to be protected, the inclusion of ~3 the Technetium-99 in the basic material can also be effective, 24 provided the Technetium is present in the base material close enough to the surface and in the appropriate parts per million to 26 allow the radiation to be effective at the surface of the 27 material.

29 Thus, according to the present invention, in~the-fluid instruments can be plated or coated to varying thicknesses wich 31 Technetium-99 metal to prevent harmful biological growths, and 3æ the movable portions o~ such items as transducer diaphragms coulcl

-5-be manufactured by including a thin layer of Technetium close to the outer sur-face of such active portions.
Through the controlled variations of either the parts per million in-cluded in a basic material, or the thickness of the Technetium plating or coating on material, which is not susceptible to plating, the dose rate can be adjusted such that organisms will be unable to grow on such surfaces. The dose rate at the surface can be adjusted up to a maximum by variation of the thick-ness of the layer of Technetium applied to the surface of the subject material, present in the compound or incorporated close to the surface of the material.
Therefore, the present invention provides a method for preventing the growth of organisms on substrates in a variety of adverse fluid environments by providing a Technetium treatment on the substrates. Also in accordance with this invention Technetium treated substrates are used in fluid environ-ments, such substrates being substantially free of corrosion and biological fouling as a result of the Technetium treating operation. The adverse fluid environments to whlch the treated substrates can be exposed include preferably temperatures of less than 2,200 C., environmental pressures above 1 atmosphere and in the range of 716 x 10 ~I Hg to 1.4 x 10 14 ~I Hg can be accommodated although the invention is not so limited.
The element Technetium of atomic weight 99 and atomic number 43 is not found in nature but is formed as a fission product. The principal method for obtaining Technetium from such products is by separation of basic purex waste supernate utilizing ion exchange techniques. While initially a laboratory curiosity, recent procedures developed by the U.S. Energy Resources Development Agency, have allowed this metal and its compounds to become available in economically attractive quantities.

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llZ64~

l Technetium-99 i.s known to have a half-life of 2.1 x 105 2 years. Significantly, Technetium-99 emits only a beta particle, I
3 having a maximum energy of O . 29 M.E.V. and an average energy oE
4 100 K.E.V. Therefore, as noted in more detail below Technetium (Tc) can be handled and applied with relative ease and safety.

7 The use of Technetium as a component for preventing 8 corrosion of metal substrates has been long known. In particular,, 9 the prior art has shown that the presence of the per~echnetate ion, Tc04-, in mild steels significantly reduces corrosion in 11 aqueous systems. (J. Am. Chem. Soc. Vol. 77, p. 2658 (1955) ) 12 Experiments have shown that these materials may be effectively 13 protected by as little as from 5-50 ppm -of the pertechnetate 14 ion when subjected to temperatures of up to at least 250C in aerated distilled water. Indeed, certain specimens have been l6 observed for two years with no evidence of attack. Further l studies have revealed that corrosion inhibition occurs without 18 depositing more than 3 x 1012 atoms of Technetium per square l9 centimeter of substrate.

~6 3 _7_ 1 DESCRIPTION OF THE PREFF.RRED EM~ODI~NT
3 In order to utilize Technetium-99 for the prevention of 4 fouling caused by biological organisms growth and simultaneous corrosion inhibition of metallic substrates, it is necessary lo

6 have the isotope present in such a concentration that the objective'

7. of the present invention can be obtained.
9 For example, it has been found that one gram of Techne-tium, having a density of 11.2 grans/cc, will coat 14.06 cm2 of ll substrate at a thickness of 2.5 mils. Alternately, a plating of 12 0.5 mil thickness could coat an area of 70.3 cm2, with the addi- ~i 13 tional advantage of providing an increased dose rate to the 14 biological organisms due to the lower self-adsorption of beta particles in the coating.

lq Technetium concentrations of this order can easily be 18 obtained by standard techniques of electrodeposition, as has been 19 previously demonstrated using the ammonium pertechnetate salt (ORNL Report ~PM 748). Sputtering techniques, also standard in 21 industry, can provide much thinner Technetium coatings. Thus, 22 the thickness of the Technetium coating can easily be adjusted 23 down to a monoatomic layer, both on metallic and non-metallic substrates, to provide the necessary anti-organism growth prevention treatment.

2~ In order to provide the necessary anti-corrosion effect 28 on metal substrates, concentrations as low as 5-50 ppm can 29 effectively be applied by already developed metal spraying tech-niques like sputtering or via an elec~ro-plating,metal spraying, 3~ flame spra-ying, chemical vapor deposition or vacuum vapor 3 deposition process.

64g7 l ¦ The metal spraying technique uses an oxyacetylene wire 2 ¦ and powder gun and is partic~llarly suited for applying hard, 31 corrosion resistant metals such as Technetium to other substrates, 41 including both large and small work pieces. By mixing the 51 Technetium metal powder in appropriate quantities with the 61 metallic powder of the substrate, the composite can be "metal ~1 sprayed" on the substrate using the above technique. The result 81 is an outer layer of the desired thickness containing the desired 9¦ composition of Tc in the base metal to inhibit corrosion.
~1 111 Other techniques for applying an effective Technetium-12¦ 99 coating for biological growth prevention would include va~or 13¦ deposition and chemical vapor deposition in which the Tc would 141 diffuse into the substrate, preferably iron based.

16¦ Of course, the Technetium coating can be applied to non-~71 metallic substrates1 e.g., wood, plexiglass, ~iberglass, plastics, 181 etc., as w~ll as non-ferrous metallic substrates, e.g., aluminum, l9¦ silver, copper, etc.
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1 As discussed above, there is no corrosive effect of 221 aqueous fluid environments on Technetium-trea~ed substrates. In 231 this respect, the lack of corrosion indicates a lack of ability 241 to attack and dissolve compositions con~aining the Technetium 251 metal. Since experiments have demonstra~ed that the Technetium 261 remains insoluble even a~ter l,OOO hours in simulated sea water 271 at 9UC, it is evident that the amount of Technetium passing into 28¦ aqueous ~luid environment would be substantially zero. It would 291 be anticipated then that Technetium concentrations in aqueous 301 environments would be substantially unchanged from present level~
3~1 and ingestion by marine creatures and any subsequent eEfects in 32 ¦ the ~ood chain would be entirely absent thereby ~aking this I _g_ 11~6~9'7 1 ¦ heretofore unrecognized application of radioactive Technetium-99 2 ¦ entirely practical from a safety standpoint.

41 While the metal itself does not appear to offer any 5¦ problem concerning solubility in aqueous solutions, i.e., is 61 non-soluble in water, a further consideration must be directed ~¦ at radiation levels generated by any corrosion inhibiting/

8¦ antifouling Technetium-treated substrate. From a radiation

9¦ standpoint, it can be shown that the dose rate emit~ed by the

10 ¦ Tc coating can provide the required inhibition of marine organism

11¦ growth on the treated substrate without polluting the marine 1~¦ environment.

14 ¦ For example, the specific activity of a 2.5 mil Tc 15 ¦plating can be calculated by the following equation:
16 j Specific Activity = N x 1 873 x 10-18 ¦ N = Avogadros No = 6 09 x lQ

T 1/2 = half-life 20 I .
21 ¦ Using 2.1 x 10 years for the half-life of Technetium-99, 22 ¦ the specific activity per square centimeter is found to be 4.54 x 23 ¦ 107 disintegrations per second.

25 ¦ As noted earlier, the average beta energy of Technetium-~
26 ¦ 99 is 100 K.E.V. (1 x 105 electron volts (ev) ) and would result 27 ¦ in a total energy emitted by a 1 gram sample of 4.54 x 107 times 28 ¦ 1 x 105, or 4.54 x 1012 ev/sec-cm2. Assuming that all of the 29 ¦ energy is absorbed in 0.1 centimeter of water, the dose rate 30 ~ from a 2.5 mil plating can be determined to be 260 rad/hr-cm2, 31 ¦ neglecting self-absorption. Assuming ~or example, a 23V/o self-32 absorptio ractor, the dose rate would ~hen be 200 rads/hr-cm2 ~126497 1 For a 0.5 mil plating, it is estimated that the self-absorption 2 would be in the order of 10.8%, with a resulting dose rate of 3 242 rad/hr-cm2.

5 It is well known that complex organisms react more 6 dramatically to certain levels of radiation than do those 7 lower down on the evolutionary scale. The exposure of the whole body of an animal to alpha, beta, gamma or X-rays results in a radiation effect that is found to be a function of the lO dose and the dose rate during the exposure period. The values ll needed to estimate the biological effects from chronic exposure

12 of higher animals to radiation can readily be calculated by f

13 one of ordinary skill in this art.
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15 From the standpoint of biological research, estimates of 16 the r~sponse of living organisms to chronic whole body radiation 17 treatments must be regarded as relatively crude except in certain, 18 highly studied species. It is possible to generalize, howe~er, 19 and it has been determined that for a typical human a dose of 500 20 rads will gen~rally be lethal while some viruses may survive 21 10,000,000 rads. Other living creatures fall in hetween, dependin~
22 on their molecular complexity.

24 For example,-it has been shown that the reaction of 25 mammalian skin to massive doses of external beta rays follows 26 essentially the same pattern of development as subjecting 27 mammalian skin to thermal burns, the important difference being 28 that thermal exposure results in a penetration of the skin much 29 more than that occurring from beta radiation. However, lethal 30 doses of beta radiation can be found and are attributed to 3 extensive destruction of the skin surface.
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1 ¦ As suggested above, no definitive studies are known to 2 ¦ applicants that show specific dose requirements to de-activate 31 the many varieties and species of marine organisms causing 41 fouling, but for any particular species the specific dose can 51 be readily determined. It can be stated, however, that any 6¦ organism attempting to attach itself to the beta-emitting q.¦ Technetium would eventually receive a lethal dose of radiation 8¦ and additionally, would probably be unable to continue its 9¦ attachment even before a lethal dose was reached.

~ For example, it has been long known that Pseudomonas A., .` ¦ the bacterial strain responsible for the formation of sludge 131 in jet fuel and the fouling and corrosion of wing tanks in jet

14¦ aircraft, can be~effectively eliminated with radiation. In this ¦ case, doses in the range of 10,000 rads provide a reduction 161 factor of 99% (AEC Report KLX-1872 of 7-15-65) 181 In general, the dose required to prevent fouling caused 19¦ by micro-organisms can be determined by the formula:
20¦ N/No.= e~br, where N/No is the fractional survival, b is 211 the exponential decay constant for the particular strain, and r is 221 the dose in rads.

241 For higher order marine organisms, lower doses will be 251 expected to de-activa~e them to the point where they are incapable 26¦ of adhering themselves to the ~reated surface.

28¦ As noted above, a dose rate of 242 rads/hr per square 291 centimeter would be expected from a 0.5 mil plating of Technetium.
3~¦ As also noted above, thinner platings would provide correspond-31¦ ingly higher dose rates.up to the point where self-absorption 32 ¦ is negligable. Any marine creatures attempting to a~tach l ll 1 ¦ themselves to such Tec~metium-plated substrates would be exposed 2 ¦ to this amount of radiation for every hour of attachment.
31 Lethal and/or de-activating doses would accumulate in periods of 41 24-48 hours Eor most species.
~1 61 Physical measurements and calculations show that the 7¦ absorption of beta particles from any source, including the 81 Technetium coatings discussed herein, is dependent upon the ¦ energy of the emitted beta particles, and can be generally 10 ¦ described for particles with a maximum energy (E) from .01 to 11¦ 2.5 MEV as follows:
12 ¦ R = 412 El-256 _ .0954 ln E; where 13 ¦ R = range in milligrams per cm2 and 14 ¦ E = maximum beta energy in MEV.

16 ¦ From available standard tables, the effective range of 1~ ¦ beta particles for a variety of absorbing mediums can be 18 ¦ determined. The range of the maximum energy beta from Tc 19 ¦ (0.29 MEV) in water (or tissue) and air is as follows:
20 ¦ Wate~ = 0,03 inches = .0762 cm.
21 ¦ Air = 18.0 inches = 45.7 cm.
22 l li 23 ¦ Therefore, in the application of the Technetium metal 24 ¦ the dry material can be handled in a standard glove box using 25 ¦ lead impregnated gloves for hand protection, and, in plating 26 ¦ solutions the liquid would effectively shield the activity~

28 ¦ For use in the present invention, the Technetium coating 2~ will be effective at a thickness as small as one atomic layer and preferably within the range of from about 500 angs~rom units ~7hil~
31 the upper liTnit o the coating thickness for practical use is 32 about 5.0 mil.

~ lZ64g7 l The present invention will now be described by the 2 following non-limiting example.

6 Using the apparatus and procedure of W. D. Box, 'IElectro-deposition of 99Tc Metal'l, Nuclear Applications, Vol 1/2, 8 April, 1965, a stainless steel diaphragm of an underwater transduc~
9 can be coated with Technetium metal having a thic~ness of 0.1 -2.5 mil.

12 A stainless steel diaphragm to be used as the active 13 element in a sonar device is used as the cathode. Platinum gauze 14 is used as an anode.

16 The electrolyte solution in which sufficient ammonium 17 pertechnetate is dissolved is a saturated solution of ammonium 18 oxylate (0.7M) adjusted to a pH of 1.0 by the addition of sulfuric 19 acid (1.411M). A current density of 1,3 amp/cm2 is used. The Technetium is ideposited as metal on the stainless steel diaphragm i 21 to give a thickness of about 0.633 mil (18 mg/cm2) whlch is 22 strongly adherent to the substrate.

24 When such a Technetium-99 treated diaphragm is utilized 2~ in an underwater transducer, no fouling by growth of marine 26 organisms will occur and corrosion will simultaneously be inhibite~

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Claims (15)

I CLAIM:

1. A method for the prevention of biological fouling and chemical corrosion on substrates exposed to fluid environments containing biological fouling organisms and corrosive environments which comprises treating said surfaces with Technetium-99, its alloys or compounds prior to exposure of said substrates to said environments in an amount effective to prevent the growth of said organisms and simultaneously effective to inhibit corrosion of said substrate and exposing said substrate to the adverse fluid environment.

2. The method of claim 1, wherein the substrate is treated with Technetium-99 in a thickness from that of a monoatomic layer to about 5 mils.

3. The method of claim 1, in which the substrate is coated with an alloy or compound containing concentrations of Technetium-99 sufficient to produce a dose rate at the fluid-substrate interface sufficient to prevent bio-fouling and corrosion.

4. The method of claim 2, in which the Technetium-99 is deposited by an electroplating process on the surface of the substrate.

5. The method of claim 2, in which the Technetium-99 is deposited by sputtering on the surface of the substrate.

6, The method of claim 2, in which the Technetium-99 is deposited using a vacuum vapor deposition process on the surface of the substrate.

7. The method of claim 2, in which the Technetium-99 is deposited utilizing metal spraying techniques in the surface of the substrate.

8. The method of claim 1, in which the Technetium-99 is embedded near the surface of said substrate.

9. The method of claim 1, wherein said adverse environment is an aqueous fluid environment.

10. The method of claim 9, in which the aqueous fluid environment is a marine or fresh water environment.

11. The method of claim 1, wherein said adverse environment is an organic fluid environment.

12. The method of claim 1, wherein the adverse environment contains substrate corrosive materials.

13. The method of claim 1, in which the adverse environment is at temperatures less than 2,200°C.

14. The method of claim 1, in which the adverse environment contains pressures in excess of 1 atmosphere.

15. The method of claim 1, in which the adverse environment contains pressures of from 716 x 102 MM Hg to 1.4 x 10-14 MM HG.