IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. OE-4, NO.3, JULY 1979 Electrodeposition of Minerals in Sea Water: Experiments and Applications
WOLF H. HILBERTZ
AbllT17CI_By establishing :a direcl eleclric:al current belween elec TABLE I trodes in an eleclrolyle like sea water, caldum urbontes. magne$.ium EleCTROC~leMICAL REACTIONS hydroxides, and hydrogen are precipilUed U the calhode, while the :anode produces oxygen :and chlorine. Recenl experiments have demon. t ANODE ~rHODE strated in pan the feuibilily of using lhe electrodeposited mineJais as building materials for :a wide variely of purposes, including the con. INoCIJ struction of arlificial reefs. Several of these experiments are described and some implicalions for maline building technology ale discussed.
I. INTRODUCTION EA WATER contains nine major elements: sodium, mag Snesium, calcium, potassium, strontium, chlorine, sulfur. bromine, and carbon. These elements comprise more than 99.9 percent of the total dissolved salts in the ocean (1)-[4). The conSlancy of the ratios of the major elements throughout the oceans has long been well known [5 J. In 1837. following the work of Davy on the protection of iron by zinc anodes. Mallet demonstrated that zinc so used became covered with a thick JeOwQW.2gvc:roge layer of zinc oxide and calciferous crystals which blocked the reducll()tl zinc surface (6), [7). In 1940 and 1947. G. C. Cox was issued .,,,."" U.S. Patents No.2 200 469 and No.2 417 064. outlining methods of cathodic cleaning and protection of metallic sur. II. EXPERIM ENTS faces submerged in sea water by means of a direct electrical current. During the cleaning process, a coating is also formed Large-scale studies with galvanized iron mesh cathodes and cathodically. consisting of magnesium and calcium salts [8]. If iron/lead anodes immersed in sea water have prOVided evidence this coating is hard and continuous, it affords a considerable for the role of electrochemical processes in the accretion of degree ofcorrosion protection to the enclosed metal [9] , [I OJ. minerals (18]. A preliminary qualitative model for these proc. Lower marine organisms utilize the minerals in solution sur. esses has been proposed (Table I). rounding them to build structural formations. Mollusk shells, In order to devise methods which would allow the solid ac for instance, are generally composed of calcium carbonate cretion of a three-dimensional cathode, the "onion" experi crystals enclosed in an organic matrix. A significant propor· ment was devised. This cathodic cube consisted of seven insu tion of the soluble protein of the matrix is composed of a lated layers of t" galvanized hardware doth. Immersed in sea repeating sequence ofaspartic acid, separated by either glycine water containing a.lead anode, layer I was connected to the or serine (II]. power supply. Afte; sufficient accretion thickness was achieved, This sequence, comprising regular repeating negative layer 2 was connected. and so fonlt. A solidly accreted cube 2 was obtained (lSI. charges, could bind Ca + ions and thus perform an important function in mineralization of the template (II J. Parts of beach sand volumes, between electrodes, contained Although impressed current produced CaCOa/Mg(OHh in 10-gal tanks and saturated with sea water. were solidified. formations were precipitated since the 1940's, these were The results were cemented sheets of sand after nushing of never thought oras possible building components until recently. loose sand particles. The water/sand mixtures were kept at a Consequently, only few publications outline structural testing temperature ranging from 78 to St'F. Power was supplied for of these materials, describe experiments and techniques using 720 h at a rate of 5 Y, 300 rnA. During the experiments, fresh the electrodeposited material for a wide variety of structural sea water was added to replace water lost through evaporation purposes, and report on the possible suitability of the material and electrolysis. as a substrate for biological growth in mariculture facilities and Since all previous mineral accretion experiments were per. as a primary construction material for same [12) -[221. formed in water depths not exceeding 15', an experiment was devised to accrete on a 15 em by 15 cm t" galvanized Manu!i\;ript received November 28, 1978; revised April 25, 1979. hardware cloth cathode with a I /l1l11 X 15 mm X 30 mOl lead Thc 0364·9059/79/07()().()()94S00.75 © 1979 IEEE HILBERTZ, ELECTHODEI-'OSITlON OF MINERALS IN SEA WATER ,"--""1~ II V "ATn,,,,' PLYWOOD l'AQ: '>lFLATFI' TI'IlF. -A'i( "n" P()WER cA"U' "opt' AW," " l'OWFll ('AIlL>; ·0 III IfAlll....'ARr. (LOTH, "'T"O"F ",,~, , ",,,,, u:... u A"')IJ~: 1m"" ),m. l~,m ~'"' Fig. I. Deep water accretion experimenUn $1. Croix. Fig. 2, Accreted material on ," hardware cloth cathode. and time span was performed at a depth of I' in Tague Bay, sample was obtained in the Port Aransas ship channel at a St. Croix. Identical accretion thickness was achieved in both depth of ±2 m,. The clearly discernable "rings" might reflect experiments (Fig. I). The current was supplied by a car battery periods of time under electric power and without power. It and measured 12.25 V/I.65 A at the beginning of the experi cannot be precluded, however, that seasonal changes also ment, and 3.8 V/l70 rnA at the termination, might be reflected. A typical section of accreted material on a r' galvanized A neutron activation quantitative analysis of this material hardware cloth cathode is shown in Fig. 2. The two dark areas performed in 1976 at the Nuclear Reactor Laboratory at the within the material mark the sections of the wiremesh. This University of Texas at Austin 'l. TABLE II QUANTITATIVE NEUTRON ACTIV ATION ANALYSIS Chemical Composition Element , Error' Mq 32.1.4 4.5_ V 3.4xl0 6.9xl0.5 Al .9 1.9xlO 3 Ca 11.16 .72 I'In .005 .001 Cl .118 .004 Na 1.56 .01 ,, --'.~,,'__ ~/_ _=__c·~,~, _ PLAN A1 i / 2' 2' 4' " .'-0' i i - > - .. ..TIIOOC '" '--I· 0.0. sn:EL ANODC '-TCSTSTRIP I(~M l.1CSlt ~I CO:->:S. ,(~L LlCO;,; , '-SILICON SEAL SEAL r2~~ \\'000 "HA~I£ 00.~:>I. I I 0 ..AI TEST STRIP POSlTlOloICD BY N'/LOloI U:>E ALL NAlL llEAD5 SlUCONED 9-TC5'T STRI 11 :::=i"~-3'~.l SECTION A E. Fig. 3. Test strip I. In order to determine accretion rate and composition of electrodeposited material as a function of proximity of elec trodes, location of negative pole cable connections, and gas evolution. the following experiments were devised: A. Test Strip 1 (St. Croix) A steel anode was positioned 2" opposile the narrOw side of a 2" X 72" galvanized t" wire mesh strip with a surface area of I £12 (Fig. 3). The cathode wire was connected to the narrOw end of the strip farthest from the anode. The supportive wood frame measured 2'3" X 2'2" X 8'0". All bare nail heads in the wood frame were covered with silicone. The cathode was fastened with t\" nylon string in the frame. Direct electrical Fig. 4. Consumption of electricity. teu strip J. current was delivered by a regulated power supply. Both anode and cathode wires were 8AWG multistrand insulated copper The test strip was submerged and under power for 52 h. wire with a length of 15'ON each. All electrical connections Consumption of electricity is shown in Fig. 4. After submer were insulated with dear silicon. The frame was submerged in sion. the electrodeposited strip was divided into 12 sections 12'0" of water in Tague Bay. Ambient water temperature was measuring 6" each. At these sections, thickness of electro 85~F. t' deposited material was det~rmined with a steel caliper (Fig. 5). HILBERTZ: ELECTRODEPOSITION OF MINERALS IN SEA WATER 1 3 4 ,, , 9 '0 " to "g to " ...... t ....;- $ ~ ~ "cZ, OZ ~8 " """" " 6'-0·"" " " " " • ~§ ,.#(j "• , 1 3 4 , , , 9 , 13 POS. • . " Fig. 5. Test strip I (below), test strip 2 (above)." TABLE III TABLE IV CHEMICAL COMPOSITION OF ACCRETED MINERALS, TEST CHEMICAL COMPOSITION OF ACCRETI::D MINERALS, TEST STRIP I STRIP 2 D...cdpt\on ~i.... I'n,,,,,i,,,, COlcil~ ...li.... Q.>!rt. Deocriptlon Il J '" lV:' .- ' Fig. 6, Consumption of electricity. test strip 2. Fig. 7. Consumption of electricity, test strip 3. At positions 1. 7, and 13. material samples were taken (54, The frame was submerged in 2'0" of water in a concrete 60, 66) and analyzed using a Philips X-ray diffractometer, tank with a flow rate of 3-! gal/min of sea water from a set involving an error factor of tlO percent (Table III). tling tank. Ambient water temperature was 74"F. The test strip was submerged and under power for 52 h. B. Test Strip 2 (St. Croix) Consumption of electricity is shown in Fig. 7. After sub The arrangement was identical to that used for test strip 1. mersion, the electrodeposited'strip was divided into 12 sec except that the cathode wire was connected to the narrow end tions measuring 6" each (Fig. 8). At positions 1.7, and 13. of the strip closest to the anode (Fig. 5). material samples were taken (98, 99, 1(0) and analyzed The test strip was submerged and under power for 52 h. (Table y). Consumption of electricity is shown in Fig. 6. After sub" mersion the electrodeposited strip was divided into 12 sections D. Test Square 1 (St. Croix) measuring 6" each (Fig. 5). At these sections, thickness of A steel anode was positioned 6'0" opposite at" 1 ft 2 electrodeposited material was determined with a steel caliper. galvanized wire mesh anode. The supportive wood frame meas At positions I, 7, and 13 material samples were taken (67,73, ured 2'3" X 2'2" X 8'0" (Fig. 9). 79) and analyzed using a Philips X-ray diffractometer, in· The cathode was fastened. with .fg" nylon string in the volvingan error factor of±IO percent (Table IV). frame. Direct electrical current was delivered by a regulated power supply. Both anode and cathode wires were 8AWG e. Test Strip 3 (Port AranSlls) multistrand insulated copper wire with a length of 15'0" each. The arrangement was identical to that used for test strip All electrical connections were insulated with clear silicone. I. The cathode wire was connected to the narrow end of the The frame was submerged in ±2'O" of water in Tague Bay. strip [arrhest from the anode. Ambient w;lter temperature was 85"F. IEEE JOURNAL ON OCEANIC ENGINEERING. VOL. OE-4. NO.3, JULY 1919 .' I .' I .' I .' I .' .' .' .' .' ." 6'-0'.' .' , 3 4 5 • • 10 II Fig. 8. Test strip 3. " TABLE V CHEMICAL COMPOSITION OF ACCRETED MINERALS. TEST STRIP 3 IYI _ o. .. II • n- It ...... ,... m ,. •II ,~" 1T I Anal. '" " "~" .' PLAN CATllOOE lr-- SUo.ICOS SEAL COl'!\'ECTIO I~ 0.0. STEEL AI'OOE I/t" JolESH ! $Q.fT. _. + ASODE • CO;.l!\,. 2' 2' 4' 6'-0' f.~·WOOD F"RA~\E a I ,- ALL NAIL }lEADS SILICOl>ED ~ j 1'-0' t _","'N~~ ... '0 .., , -" " GCATllODE COSNECTIOS 51. SECTION A 2'- 3' I Fig. 9. Tuuquare I. Before submersion, the I (t2 t ~ wire mesh cathode weighed 96,2 g. The test frame was submerged and under power for ;;T:~~ 42 h. Consumption ofelectricity is shown in Fig, 10. v :"I:'!::!I': One material sample (37) was taken after 42 h and anal n:' ••• 1 , yzed (Table VI). After electrodeposition, the cathode was dried for 22 h at 200°F. Weight of the cathode was 184.5 g. •.•• a: ..... Thus 88.3 g of material was precipitated with an electric input .. .""t'i";,.,. of approximately 46 W, giVing the approximate value of 1.9 kg of accreted mass per 1 kWexpended. Fig. 10. Consumption of electricity, test square I. HILBERTZ: ELECTRODEPOSITION OF MINERALS IN SEA WATER TABLE VI . 6) It is evident in all cases that the greatest percentage of CHEMICAL COMI'OSITION OF ACCRETED MINERALS, TEST sample material is brucite (Mg(OH)2)' It was found in two of SOUARE I its three distinct forms: the platy or foliate type. and massive _'_ 0..:.....,._ material. Brucite, in its foliate fonn, is harder than talc and gypsum, and not elastic; in its massive material form it has a "soapy" appearance. It is possible that some small percentages of the composition consist of portlandite (Ca(OHh), which is The composition of the accreted material on test square I isostructural with brucite, but not as yet detected through is very similar to the material at the center sample position of X·ray diffraction. This is due to concentration and availability test strips 1,2, and 3 (Tables III-V, Samples 60, 73,99) that of the (OH..) and (eOa--) anions at a pH greater than 9.00 at is, greater amounts of aragonite and less noncrystalline matter which point brucite is known to precipitate. Fast precipitation are evidenl. of compounds from sea water usually results in brucite of the Since the location of the cathode connection is at the top massive material form; slow precipit3tion and phasing usually of the test square, the concentration gradient caused by dif result in brucite with the platy or foliate crystalline structure. ferent temperature/resistance factors would be less at the bot During 1977, the construction of a cathodic hull for a boat tom and the accreted matter would exhibit properties like was completed [191. The frame consists of I.t" X 1t n yellow Samples 60, 73, and 99 of the test strips. It is hypothesized pine to which the double-layered til galvanized hardware that, during the electrochemical process, there are three meth· cloth is stapled. Spacing between layers is f'. The hull is ods by which material can be accreted: I) concentration grad· being accreted at the present, consuming dc at 12 Vand 1.5 A. ient; 2) ionic at traction; and 3) electrical migration. The former is the most likely to be the cause of these findings. From com III. ARTIFICIAL REEFS parative analyses of X-ray diffraction tests (Tables III-VI),the It has long been evident that substrates to which marine or· following preliminary conclusions can be drawn: ganisms can attach themselves and/or find shelter within, at I) Positioning of the anode and cathode connections rela tract fish populations. tive to the cathode surface area has a definite effect on the The oldest recorded establishement of artificial reefs dates composition of material accreted in their vicinity and deter back to the early 1800's [23J. Since the early 1950's American mines the amount of noncrystalline matter enveloped in the marine fishery interests have been investigating the possibility accretion matrix. of using artificial reefs as management tools for manipulation 2} Since the position farthest from either anode or cathode of fish populations (24], [25J. Calculations of fish popula cable connection reached the maximum amount of aragonite, tions on artificial reefs as compared with control areas or be it seems that the greatest electrochemical circuit resistance is fore reef placement showed increases of between 3 to 16 times developed near the anode and cathode cable connections. If (26] -(28]. Since the choice of material determines to a large the resistance is greater at these connections, temperature will extent transportation, construction, and maintenance cost of increase and as a function of temperature, the pH will rise. artificial reefs and their design, this factor becomes very im· Thus less favorable conditions to precipitate CaC03 exist. portant. 3) Conversely, evolution of O2 at the anode may decrease Preliminary investigations indicate that the mineral accre the pH to an unfavorable state for the precipitation of CaC03, tion process produces a vtry suitable substrate for marine having overcome the initial tendency for temperature/resist growth and, at the same time, a strong primary building ance to incre3se the pH. material (18], (19.]. Accreted wire mesh components also 4) Peak intensities and breadths from X-ray diffraction present a reduced profile, compared to solid components, analysis reveal very few "perfect" crystals formed. Broaden which reduces resistance to water currents, thus increasing ing of the reflections occurs due to the mosaic structure of the stability while offering open volumes and entrances for shelter mineral crystals, i.e., they are composed of smaller differently to marine organisms. oriented blocks of crystals. This broadening could also occur Placement of steel mats or wire mesh as an artificial sub from lack of chemical homogeneity in the specimen. These strate in areas predominated by soft, fine-grained sediments results would support the conclusion that loosely bound crys· has been suggested [29J. Accordingly, the use of accreted wire talline structure is precipitated through physicochemical re mesh may be particularly well suited for these areas. actions ofconcentration gradients. Two artificial reefs were constructed and placed in Tague 5) Considering Fig_ 5, it seems that electric migration Bay, St. Croix, in August 1976. These constructions were built and/or ionic attraction are also significant at the anode/cathode to determine the parameters of the electrodeposition process connections. Relative thicknesses (in mm) are shown at6" in onto large surfaces as substrate for marine growth, and to sup tervals along test strip I and 2. Test strip I displayed a curve port the hypothesis that wire mesh formations covered by from anode end to cathode connection end: greater thicknesses electrodeposited minerals can support marine communities at both ends and the least in the center. Test strip 2 displayed that are usually found inhabiting natural reef formations (181. another characteristic due to the position of the cathode con· Both of these reef components were placed in shallow waten nection: thicknesses decreased with more distance from the approximately 8' deep, on relatively barren and sandy IUb electrical activity at the anode end. strate with small amounts of seagrass .crhalauill) present. IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. 01::-4, NO. J. JUL Y 1979 ELEVATION 88°F. The anode consisted of a cast iron 7" OD met:!l pipe I/i _ ,'_ 0' with a length of9'2", and was placed parallel to the cathode at a distance of 4'0" on sandy ground. A moderale input of electrical power provided a mineral subSirate that allowed rapid diatomatious and blue-green algae growth which, possibly in connection with the availability of protected spaces, attracted various fish populations. The elec· tric field between anode and cathode did not negatively affect algae growth, as was clearly established by the observation of • an electrodeposited control sample without electric field under L e 2 f'l J '7i2 ' AIOODt identical conditions. l" O. D. tD+ 001<0"1'1. 1,." M~AL ~D' Inhabiting fish populations visibly were not affected nega 12' -,' tively by the electric field; individual animals moved freely in and around the structure. CATltODt CONNtCTIOl< Preliminary conclusions from X-ray diffraction analysis show, that, after the phasing sequence, the crystalline structure of tli'e accretion matrix becomes more apparent. Peak intensities and breadths indicate more well-ordered crystals and less non crystalline material. 8 Reef 2 consists of identically folded wire mesh formations of two dirrerent gauges with a total surface area of 144 ft2. Overall dimension are 7.5' X 7.5' X 6'. The anode consisted of a.• cast iron 6i" 00 pipe with a SU~I'ACt ARtA length of 7'3" and was placed under the reef. )~.2~ MtSH 101)/4 SQ. 1'. Fifteen hours after submersion while accreted material was )/2" MESH ~ll/0 SQ.I'. visible on all surfaces of the structure. Seventy-two hours after I/o" MESH nil) SQ. F. 1/1" MtSH 11'/0 SQ. F. submersion the same growth as on Reef I was observed covering the entire structure and reaching a length of 8 cm, 190 h after Fig. II. Artificial Reef I. submersion. Schools of small fish were observed graZing off the growth and inhabiting the structure. Direct electric current was supplied intermiltantly to the reef Consumption of electricity is shown in Fig. 14. One material components by an unregulated power supply in the range of sample was taken 413 h after submersion (Table VIII, Sample 3-16 Vj10-40 A. 32). Mineral deposition thickness on the I" X 2" wire mesh Reef I consists of an assembly of regular and irregular measured 6.2 mm (diameter of metal wire 1.75 mm) after shapes constructed with wire mesh of different gauges 485.5 h ofelectrodeposition. a total surface area of 253 ft 2 (Fig. 11). Overall dimensions of Fish censuses performed 4,. months and 16t months after the reef 3re 4' X 12.67' X 3'. Average accretion thickness placement indicated 92 individuals (6 species) and 142 in· on the wire mesh isf with thickness in some areas up to dividuals (14 species), respectively. Again, the fish population 3 in (Fig. 12). Fish censuses performed 4,. months and J5 was dominated by grunts, parrot fish, and damsel fish. months after placement indicated J27 individuals (5 species), Artificial Reefs 3A and 3B were built to determine to what and 483 individuals (J 9 species), respectively. The most degree the electrodeposited minerals on wire mesh formations dominant fishes were medium-sized grunts, parrot fish, and enhance the development of marine communities, and to what damsel fish. degree the wire mesh formation simply acts as an attractant. TwenlY hours after submersion white accreted material was Two reef components were constructed and submerged in visible on all surfaces of the structure. Sevenly-two hours after August 1977, in Tague Bay. Both components are identical in submersion diatomatious and blue.green algae growth was ob size and construction, each consisting of folded plate tIt gal. served on the ouler surface of the structure, gradually covered vanized wire mesh formations on a wood frame, having a total all surfaces, and had reached a length of 8 cm, 280 h after mesh surface area of 192 ft 2 and overall dimension of ap inhabiling the structure. The first sample of the elecuodepos· prOXimately 19.5' X 5' X 4.5' in height (Fig. IS). ited material was taken 437 h after the start ofeleclrodeposi Both components are situated in a water depth of ±IS' on tion (Table VII, Sample 33); the second sample was taken relatively barren, sandy bottom with a smail amount of seagrass 1991 h after the start of electrodeposi!ion and 1508 h after (77raIassia) present. One component (Reef 3A) is supplied with the power supply was disconnected (Table VII, Sample 95). dc from an unregulated power supply in the range of 6-12 Mineral deposition thickness on I" X 2" mesh measured 5.4 VjlO-20 A; the other component, Reef 38, is not under mm (diameter of metal wire = 1.75 mm) after 480 h of power, thus acting as a control since no e1ectrodeposition oc electrodeposi!ion, consumption of electricity is shown in Fig. cun, and is situated 265' from Reef 3A. Floral and faunal 13. The temperature of the electrolyte ranged between 82 and censuses are taken every 6 weeks at both the accreting reef and HILBERTZ: ELECTltODEI'OSITION OF' MINERALS IN SEA WATER Fig. 12. Detail of artificial Reef I ancr aCCletion. TABLE VII TABLE VlII CHEMICAL COMPOSITION OF ACCRETED MINERALS. CHEMICAL COMPOSITION OF ACCRETED MINERALS. ARTIFICIAL REEF I ARTIFICIAl- REEf 2 o-rlptioft 8r"\ICite ....."'f?'i.. calcl.. "'lite Q.>!ot>: O...cnp""" -,~ ...... ,...... COle...... ht., 9>&'"" ~- n U~. taMn en 11..-. aftc •• " " -"' " ",,,...1,,«1 ~ ,. w. " lSOS hrs a!t.... u~" u~ u~" " -~'"""'"..-...ot "' " • 10:-"'.. BjgggfS;tSC9iHo,±,±,±,*H i ...... Fi&. 13. Consumption ofelectricity. artificial Reef I. Fig. 14. Consumption of elecUicity. artificial Red 2. IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. 01::-4, NO.3, JULY \9'9 ~nl.IOI;l) IIAJlIIWi\IW Cl.Q~ '"ON~TIl1I("'O~ PLAN ~, CONTROl.. n~:t::F 11 l~ lPl;:-l'lR·AI. I;Xt"r.PT FOR ANO\)I0:.~ AND AN ll~: I ('ATUOlll': f AH1.~;S "'OOD~'HAMI(, t. '" FIR NAll.~:n..... "'.'ill FA<;TI':".:n WITH NAll..S , - .- " "< ". "> -. ~ ~ 1/1G' x It.!f IXAD Amm o UN"llON J'x i'WOf1l !iTHfrr , I,I I 114_1·0 ~'. r-- ---j o 10' ,r , -. Fig. 16. Artificial Reefs 4 and 5. -. on the site. In addition, the initial layer of electrodeposited l/lb'~ G', ,,' I.I':A!) AmlW material presents corrosion of the wire mesh template. ~'. t' '<"(lOU ~1"IWT----" lI: I I Fig. 17. Anificial Reef 4 assembled on land. ·1 ...... " ... ,... ~:~j; .; .1" Fig. 18. Consumption of electricity, dlum I. TABLE IX CIlU.lICAI. COMPOSITION OF ACCRETED MATERIALS, DRUM I Dncnp<."" .....,.ce 1¥!'P"U Cdc.... ''''1.',.. 2'"u. .... ~ liN/'!. m n n n' " !'>&I'd _,...1 '" ...... ava ,. n n ... " fluffy _'....1 " IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. OE'4, NO, 3, JULY 1979 - .----• ...;",J- Fig. 19. Circle segment before submersion. The circle segment (Port Aransas) consisted of a double , .. I , :1 layered .;." galvanized wire mesh construction separated by t" :i :.:.:)" I plastic spacers. It was suspended from a floating rig (Fig. 19). I I 1 Total mesh area measured 112 ft2. The structure was sub· 1 merged for 480 h. DireCl current was supplied by an unregu· lated power supply. The inner layer of the mesh '01lstruction I I i T I 1 performed :IS anode for 264 h, while the outer layer performed , .. :1I, I i as cathode. Both anode and cathode cables consisted of 6 --,,'~ , "'."f' ..". I Awe multistrand insulated copper cable with a length of bO i·,·,,;-...,- 30'0". All connections were insulated with clear silicon. . Electrical power consumption of the structure is shown in , Fig. 20. After 240 h, an electrodeposited mineral 1:Iyer of4.5 mm had formed on the cathode (outer mesh). The inner mesh, »--j.''':'': :::::: '-~r-;·, _~ performing as (he anode, was significantly oxidized and col· ! .. ):". lapsed over an area measuring 6.5 ft 2. After polarity was reo · A· ·1- .,,' - o -- 1'<'II'i! ·1·· . versed for 216 h, an e1ectrodeposited layer of 3 mm had I 40 -- :"::':,'\t-.:..:.. : ...... ,. ':1 ::; formed on the cathode (inner mesh). 3.2 ft 2 of the anode ...." (outer mesh) had fallen off. Sporadic marine growth was ob Fig. 20. ConSl,lmplion of e1eclrlclly, Circle segment. served on both layers. The concept of a sacrificial anode, when embedded in mineral layer with the capability to keep the integrity of the mineral precipitate, is an intriguing one and can offer many structure has formed. Then, polarity reversal on the solidly em· advantages. But, in the case of this experiment, anode corrosion bedded electrodes can be undertaken. Iron or steel is a rapidly data for galvanized wire mesh were not available, and the rela oxidizing anode material; once embedded in a mineral the tionship between iron mass (anode) and oxidation rate was in metal oxide will be integrated into the mineral. Thus it is sufficient. hypolhesized that longer lasting anode surfaces can be pro· For an experiment with sacrificial anodes to be repeated it vided using this method. Additionally, former cathodes could is proposed to treat both layers initially as cathodes until a be lIsed to perform as anodes. This could be of imporlance HILBERTZ: ELECTRODEPOSITION OF MINERALS IN SEA WATER nn Fig.21. Catenaries 1 and 2. during the mineral electrodeposition process of larger compo nents and during the phased construction of walls or shells with very thick sections. The catenaries 1 and 2 (Port Aransas) were identical in materials and dimensions. They consisted of i" galvanized wir~ mesh suspended from a floating rig, each with a surface area of 32 ft 2 (Fig. 21). Both catenaries were submerged in the boat basin on The University of Texas Marine Science Institute for 2664 h, the first 1896 h under dc delivered by an unregulated power sup ply. Six spherical-segment lead anodes were positioned above each catenary formation. Both cathode and anode cables were 6 AWe multistrand insulated copper wire with a length of Fig. 22. Consumption of electricity, catenaries 1 and 2. 15'0" each. All connections were insulated with clear silicon. Electrical power consumption is given in Fig. 22. TABLE X After 1896 h an electrodeposited mineral layer of 7.5 CHEMICAL COMPOSITION OF ACCRETED MINERALS, mm had formed on both catenaries. The first material sample CATENARIES 1 AND 2 was taken after 1896 h of operations (Table X, Sample 88). o....,<"if>ti The second sample was taken 768 h after power cutoff (Sample ~"' "' di~' u_ 92). The electrodeposited material then was densely populated Uk"" n ,~nn,_ r-+-'-:F'Pt~e-t2iT** , Fig. 24. Consumption of electricity. t circle. Fig. 23. Consumption of electricity, t circle. TABLE XI CHEMICAL. COMPOSITION OF ACCRETED MINERALS, tCiRCL.E o..,dptjan llNei... M! '" 200 v.' WI:-"DClllV(;:-: Cf"F:RArOIl'<: " ,-,' t ---.L-*,cr---r-Dc"~';'O~'~·------:-c,---- CAau: ,\we; hi I I ROP~; Fig. 25. Circular column and wind driven generators. ,,;~ ;In. Calenarv formation before accrclion. IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. OE·4, NO.3, JULY 1979 Fig. 27. Catenary formation after accretion. Observations made on previous test components showed '11 TABLE Xlii that phasing appeared to alter the properties of the electrode· CHEMICAL COMPOSITION OF PHASED ACCRETED MINERALS posited material. There'fore, controlled series of phasing tests Deocdpt!on B<\lo:ite Arogon.ile Cole!'e ""liu O~ were performed in S1. Croix in order to verify these observa· Typi.col le.' ,. ~ " c_ before fh..iNJ ". " " tions. ,. Mlet 7 OTEC 8 S.UII"I..I: I C\M.1U1ft I tno 1'.5. I. 2 tno 3 U30 t ~3!>O 3 tllO , tOtO iii 1 tl~O o 50m 100m e H3~ 8 HOO Fig. 29. Proposed cold water pipe for OTEC plant, horizontal section. LO tlS0 II t~30 11 5100 U t260 14 3~90 ere ted selectively in order to effectively withstand changing IS U60 II 3930 and unpredictably occurring forces (e.g., changing current IT JUg I' Jt;O patterns). I~ 3UO In case of slowly or suddenly occurring damage to the to J9JO wall section, tIle tube can be repaired by placing an anode in If>t!>O: to . ~ P.S.I. AVf:RAGF. the vicinity of the damaged portion, thus facilitating, for in TY.S'T ~IATE:ItIAL.S IN('"l.UI)F.I) ACOl£TIONS stance, cementation of cracks, replacement of lost materials. ~'RO~ PORT ARANSA!lJTEXAS ANn ST. CItOIXIU.S.V.I. and reinforcement of previously deposited mineral layers. The OTEC plant could be moured at an accreted gravity anchor Fig. 28. Compressive strcn,th of acaete obtained in Port Aransas and block and could move with preVailing currents (Fig. 30). SI. Croix waters. Aside from converting ocean thermal energy into elec· tricity, the plant can also produce hydrogen, ammonia, and at the cathode surface, occurring when electrical current is Mg(OH)2 as a byproduct of P1e electrolysis process used to discontinued. These two situations may be occurring simul provide uplift ofcold water in the deep water pipes (Fig. 31). taneously" or one may be entirely responsible. Further data Through the application of heat, brucite can be directly must be collected to be conclusive. reduced to the mineral periclase (MgO). Thus th~ plant can produce refractory magnesia, the raw material for magnesium VI. TESTING OF MECHANCIAL PROPERTIES production.The CI1 gas, resulting from electrolysis, can also be utilized. While building a considerable, but not yet calcu Twenty samples of electrodeposited minerals obtained on lated head, the upwelled water/gas mixture can drive turbines. i· galvanized hardware cloth in Port Aransas and St. Croix" The nutrient rich deep water can be utilized at the ocean sur· were prepared and tested at The University ofTexas Structural face as a mariculture medium. Testing Laboratory. Following standard procedures for con· crele testing" compression forces were recorded at the point of VIII. SUMMARY AND CONCLUSIONS breakage {2S]. Individual and averaged test results reflecting psi strength are shown in Fig. 28. For comparison, concrete EJectrochemical accretion of minerals in sea water and that is typically used for stairs and steps, sidewalks, driveways, other media (e.g., blood serum = internalized ocean in mam slabs on grade" and basement wall construction (probable 28th mals) appears to be as old as life itself and seems to have day strength" nonnal Portland cement Type I, 15 percent less proven its worth during evolutionary time. Construction, than recommended by ACI Joint Committee) breaks at about maintenance, and destruction technologies as used at the pres 3500 po [30J. ent, are mainly brain children of the first industrial revolution with built-in limits (12). Example given: A concrete or steel element in sea water, once broken or decayed, is useless be VII. OTEC FACIUTY PROPOSAL cause it cannot meet its design specifications unless it is re The mineral accretion process potentially can contribute paired. In most cases repair necessitates removal from the site significantly to the solution of fonnidable engineering tasks and repositioning, thus incurring unreasonably high cost. which will be undertaken in the oceans" like the construction An element produced by electrodeposition, however, can of Ocean Thermal Energy Conversion (OTEC) plants. It is evi· be repaired or reconditioned in situ after failure. With renewed dent" for example, that the use of traditional engineering electrical power input the same conditions and resources materials like steel or fiber reinforced concrete, tubular steel which formed the element initially can be utilized again. This or reinforced plastics for the construction of OTEC systems characteristic. is not found in any commonly used construction cold water supply pipes will produce enormous costs because method or material. Conversely, when, for instance, a rein· the system wm have to be overdesigned in respect to unknown forced concrete volume is cured and has left the form, its or only vaguely defined parameters. Quite to the contrary, a structural and formal characteristics can be altered only by relatively light aquadynamic cathodic tube configuration (Fig_ major operations. Thus strict limits con~erning the element's 29), which permits assembly on the plant on·site" can be ac- adaptability to changing conditions in situ are enforced. IEEE JOURNAL ON OCEANIC ENGINEERING, VOL. OE·4. NO. 3,lUl.Y 1979 OlEC 8 MAI.CULTURE SOD ", 1000 rn 1100_ 2000 ... "00 ... )000 m Fig. 30. Proposed multifunctional OTEC plant. Structures, while accreting, can double as artificial reefs. oncs : .. ,: ,: :,: '.:' Thus a combination of aquaculture facilities and building ::.:~.::'--.: component plants is envisioned. Building components can be accreted at greater depths and 111 • :" ." , . '., be designed and calibrated in such a way, that, when surfaces ~>', .. .., '." ~. ''.., are closed by the electrodeposited materials, accumulated ,~ ..;_: .:.'-.~ .'.~'~ ,:,' hydrogen, oxygen, or chlorine gas provides uplift and "malure" ",0, components can be harvested at the water sllrface. In a similar .,~. '{t~!~;~f way bUilding processes can be designd that allow structures to "grow" out of the electrolyte (Fig. 33). Moveable articulated form generators can be designed to ..:-iJ? produce a variety of configurations continuously by unspool· ClU.NINO_-I'~~ ing or weaving of cathodic material formations. These devices C"''''oo" p can "ride" on the generated profiles of pipes (Fig. 34). Anodes can be integrated in the generator or positioned independently Fig. 33. Structures "growing" out of the ocean. Skirrow, Eds. London, England: Academic Press, 1965, vol. 1, pp. 163-196. [51 W. Dittmar, "Report on re$t!arches into the composition of ocean water collected by H.M.S. Challenger. 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