ALUMINUM FINISHING .,},.\~,~~:~

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Thermally Conductive Coatings forAluminum Hardware*by George HradilCovofinish Co. Inc., Harmony, R.I.

A n alternative coating to the currently usedType III hard anodize finish is being investi­gated for use on the steam condenser section

of the MK-50 torpedo and other underwater vehi­cles. The 2-mil thick hard anodize coating normallyused to provide scratch resistance and corrosionprotection to the 6061-T6 aluminum external shellsof torpedoes is not thermally conductive enough toallow normal operation of the MK-50. To remedythis problem the thickness of the hard anodize coat­ing has been reduced from 2 mils to 0.5 mil. 1 Con­denser sections with the 0.5-mil coating operatesatisfactorily with respect to heat transfer; however,the reduction in the coating thickness has reducedthe scratch resistance of the finish. Additionally,some underwater vehicles currently being developedmay require coating with even higher thermal con­ductivities than the MK-50.

Electroless nickel (EN) has been investigated as apossible coating for applications requiring high ther­mal conductivities and marine corrosion resistance.Studies of high phosphorus (high P) content electro­less nickel coatings applied to 6061-T6 aluminumhave demonstrated that the coating can withstand1,000 hours of neutral salt spray (B 117) with min­imal corrosion.2 Phosphorus-containing EN has athermal conductivity an order of magnitude largerthan Type III hard anodize and is an extremelyhard, tough coating. Additionally, it can be appliedusing commercial processes at a reasonable cost.These properties make EN an excellent candidatefor an alternative coating for the MK-50 condenser.An EN coating should significantly enhance the heattransfer of the condenser as well as increase thescratch resistance and extend the condenser servicelife.

Although EN shows considerable promise the ap­plication of the EN coating over aluminum alsopresents some challenges. Aluminum has a rapidlyforming stubborn oxide layer. This oxide layer isresponsible for aluminum's relatively good corrosionresistance despite its position in the electropotentialseries; however, the oxide layer interferes with nor-

·Final Report on Contract N66001-94-C-7701

12

mal plating practices so special procedures must beused to prepare the aluminum for plating.3 Addi­tionally, since aluminum is less noble than nickel, ifthe coating is damaged, the aluminum will corrodesacrificially with respect to the nickel; therefore, theprotection of the substrate aluminum is dependenton complete and perfect encapsulation by the nickel.The EN coating must be pore-free and ofa very highquality

The Phase I effort focused on evaluating coatingstrategies and plating procedures for applying EN to6061-T6 aluminum. Studies of corrosion resistanceof EN coatings report large variations in perfor­mance between samples provided by different ven­dors. 2,4 It was not clear whether this was due to theformulation of the EN plating solution, the platingprocedures used, or both. The Phase I effort wasaimed at establishing preplating and plating proce­dures, which consistently produce EN coatings ableto withstand 2,000 hr of B 117 with minimal or nocorrosion, the benchmark established for this coat­ing by the Navy.

PLA~ 01' ...-__

The basic steps for applying EN to aluminum are asfollows:

1. Cleaning: The aluminum is cleaned of all soilsand greases using either a vapor degreaser or anaqueous soak cleaner.

2. Etching: The cleaned aluminum part is immersedin an etching bath, which removes some alumi­num stock, revealing a fresh aluminum surface.

3. Desmut: A concentrated acid mixture is used toremove alloying metals and silicon left on thesurface from the etching step.

4. Immersion coating: An alkaline bath containingeither zinc or tin is used to remove the aluminumoxide layer from the aluminum surface and de­posit a thin immersion layer of metal to preventthe reformation of the oxide lyer.

5. EN plating: The part, protected by the immer­sion coating, is placed in an EN bath where thenickel-phosphorus alloy is autocatalytically de­posited from solution via reduction by sodiumhypophosphite.

MR.I F1n....lng

Teble I. Test Penel Metrix

Panel # Chemical Polish Etch Preplate EN Topcoat2, 3 Yes No Zincate 1.5 Vendor B No5,6,7 No Acid Zincate 1.5 Vendor B No8, 9, 1 No Alkaline Zincate 1.5 Vendor B No24-32 Yes Acid Zincate 4 Vendor A No33,34,35 Yes Acid Zincate 4 Vendor A No36,38,39 No Acid Zincate 4 Vendor A No42,43,44 Yes Acid Zincate 2 Vendor A No51,.52,53 Yes Acid Zincate 2 Vendor A 0.8 Bright EN48, 50, 54 Yes Acid Zincate 2 Vendor A Zn-NilCr57, 58, 60 Yes Acid Zincate 2.0 Vendor B No61,62,64 Yes Acid Zincate 2.0 Vendor B 0.8 Semibright EN59,63,65 Yes Acid Zincate 2.0 Vendor B Zn-NilCr66,67,69 Yes Acid Zincate 2.0 Vendor B Zn-Ni68, 70, 71 Yes Acid Zincate 2.0 Vendor B Passivate72, 73, 74 Yes Acid Zincate 2.0 Vendor B 0.8 Bright EN75, 76, 77 Yes Acid Zincate 4.0 Vendor B No78, 79, 80 Yes Acid Stannate 2 Vendor A No

LlnllATU... SDJICIIA literature search was conducted to establish themost important factors in preparing a quality ENcoating with high marine corrosion resistance. Thefollowing factors have been identified as signifi­cantly affecting EN quality and marine corrosionperformance.

1. Phosphorus content: A coating of 11% phospho­rus or more is highly desirable for maximumcorrosion resistance. 1.4,5.6

2. Deposit thickness: Corrosion resistance improvessignificantly with increasing coating thickness upto a thickness of 1.5 mil; beyond that, coatingperformance increases more slowly.l,4,5

3. Test panel supplier: EN-coated samples suppliedby some vendors or finishing shops significantlyoutperform others. It is not clear whether this isdue to the sample preparation, the EN bathchemistry, or both.2,4

4. Smoothness of the substrate: EN coatings appliedto rough surfaces perform poorly in comparisonwith equivalent coatings applied to a smooth sur­face. 4

5. Preplating procedure: The cleaning and etch pro­cedures used prior to plating can have a greatinfluence on the EN corrosion resistance.1,3,6,7

Some studies indicate that acid etches are supe­rior to alkaline etches. The type of immersioncoating (zincate, stannate) can also have a greatinfluence on coating quality. Alloy zincate bathshave been shown to be superior to pure zincformulations. a,fl,9 A process, which uses a tin im­mersion coating followed by a bronze strike bath,produces a finish that demonstrates less lateralcorrosion at defects than a zincate process!,lO

14

TaTP.-_....The following matrix of panels was developed to testthe most promising coating strategies:

• Panel smoothness:1. APJ received 606l-T62. Chemically polished (2 min., loo·C)

• Aluminum etch:1. Acid etch (two types)2. Alkaline etch (two types)3. No etch

• Undercoating:1. Alloy double zincate2. Stannate immersion followed by electrolyticbronze strike

• EN process:1. Vendor A2. Vendor B

• EN thickness:1. 4 mil2.2 mil

• Topcoats:1. Electrolytic zinc-nickel alloy2. Zinc-nickel with chromate conversion coating3. Semibright medium phosphorus EN4. Bright medium phosphorus EN5. Acid chromate passivate

With 80 many variables a complete matrix isimpractical; therefore, the panel matrix was de­signed so that each single variable could be testedagainst a baseline panel.

The panels were prepared in sets of three. Insome sets an intentional scribe through to the alu­minum substrate was made on one of the panels. Alist of panels is provided in Table I. The generalized

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Table II. Panel Prep....tlon Procedure Tablem. B 117 Salt Spray Test Results

1. a. Chemical polish (2 min at 100'C) Panel # Edge Defects Face Defects ComersRinse 2 3 0 2Desmut (30 sec) 3 6 0 0Rinse 5 1 0 2

b. No chemical polish, go to step 3 6 0 0 12. Electrocleaner (1 min) 7 0 0 1

Rinse 8 0 0 23. Etch a. Acid etch 9 11 0 2

b. Alkaline etch 1 7 0 24. Rinse 24 0 0 05. Desmut (30 sec) 25 0 0 16. 15% sulfuric acid rinse (2 min at 70'C) 26 0 0 07. Rinse 30 0 0 08. Desmut (30 sec) 31 1 0 09. Rinse 32 1 0 0

10. a. Zincate (1 min at 30'C) 33 1 0 0Rinse 34 1 0 150% nitric acid (dissolve all zincate) 35 1 0 1Zincate (30 sec at 30'C) 36 0 1 0Rinse 38 1 0 0Al-strike EN nickel strike (10 min at 43'C) 39 1 2 0

b. Stannate (40 sec at 30'C) 42 1 0 1Rinse 43 1 1 1Desmut 44 1 0 1Rinse 46 0 0 0Stannate (20 sec at 30'C) 47 2 0 0Bronze strike (4 min, 30'C, 4 A), immerse 48 0 0 0

under current 50 0 0 0Rinse 54 0 0 0

11. EN a. Vendor A (l90'F) 51 0 0 1b. Vendor B (l90'F) 52 1 0 0

12. Rinse 53 0 1 013. Topcoatings or posttreatments 57 0 0 0

58 0 0 060 0 0 161 0 0 0

procedure for preparation of the samples is given in 62 0 0 0Table II. 64 0 0 1

59 0 0 063 0 0 0

....TSIDIKUS_ 65 0 0 066 0 0 0

General Remarks 67 0 0 0The panels in the previously described matrix were 69 0 0 0prepared and placed in an Erichsen Model 608 cor- 68 0 0

rosion testing chamber and subjected to 2,000 hours 70 0 1 071 1 0 0

of B 117 neutral salt spray. The performance of the 72 0 0 0panels is reported in Table III. The panels were 73 0 0 0rated by the total number of defects on the face, 74 0 0 0edges, and bottom comers. It should be noted, how- 75 0 0 0

ever, that due to the design ofthe sample holder the 76 0 0 077 0 0 0

comers are often exposed to corrosion products and 78 0 0 0may not be representative of the true coating per- 79 0 0 1formance. Additionally, it should be noted that the 80 0 0 1average defects per panel will be reported, but thatin most cases there were very few defects (zero, one,or two) and only three panels. This means care must Chemical Polishing of the Substratebe taken in drawing conclusions from the results, Aluminumsince the average will not be statistically meaning- It has been reported that the corrosion resistance offui. This issue is discussed by Bayes.1 EN coatings applied over rough ground steel is poor

December 1... l'

compared to the same coating applied over smoothstee1.6 Additionally, it is well known that defects inEN coatings over aluminum occur predominantly atedges and knurled or threaded surfaces;1.6 there­fore, it is reasonable that it would be advantageousto have the aluminum substrate as smooth as pos­sible before EN plating. This can be accomplishedduring the manufacturing of the part and alsothrough chemical means. Chemical and electrolyticpolishing of aluminum are processes, which can en­hance the smoothness of an aluminum surface andremove burrs and sharp edges. The primary ingre­dient in these solutions is phosphoric acid. In theelectrolytic process the aluminum is made anodicand a DC current is passed, while in the chemicalpolishing process the part is simply immersed in theheated chemical polish solution.11

Test panels were immersed in a chemical polish­ing solution (composition in Table IV) at 95°C for 2minutes. The panel was then rinsed and immersedin a triacid desmut (composition given in Table IV).This treatment increased the reflectivity of the pan­els; however, no improvement was found in thecorrosion resistance. Panels 33 to 35 were chemi­cally polished while panels 36, 38, and 39 were not;they were plated using the same procedure. Bothsets ofpanels had an average of 1.7 defects per panelafter 2,000 hours of salt spray testing.

Aluminum Etch TypeTwo types of etches are commonly used to p'reparealuminum for plating-alkaline and acid. Alkaline

Table IV. Nonproprietary Solution Formulations

Mild Alkaline Etch: Tripotassiumphosphate

Sodium carbonateAcid Etch #1: Nitric acid

Hydrofluoric acidAcid Etch #2: Phosphoric acid

Sulfuric acidHydrochloric acidCitric acidAmmonium bifluoride

Desmut: Nitric acidSulfuric acidAmmonium bifluoride

Chemical Polishing: Phosphoric acidNitric acidSulfuric acidAluminumCopperIronWater

Nitric Acid / ChromatePassivate: Nitric acid

Sodium dichromate

30z/gal30z/gal10%10%15%4%0.05%3oz/gal80z/gal70%25%40z/gal73%4.7%13.8%35 gIL2 gIL0.48 gIL8%

2%20z/gal

Table V. Defects Found for Various Etching Proc....s

Process Panel # DefectsQ

Chemical polish, no etching 2, 3 4.5Mild alkaline etch (l50'F, 1 min) 9 13Mild alkaline etch (l50'F, 3 min) 1 9Proprietary etch (l50', 1 min) 8 2Acid etch #1 (70°F, 1 min) 5, 6, 7 1.7Acid etch #2 (lIO'F, 1 min) 57, 58, 60 0.3°Average defects per panel after 2,000 hr B 117.

etches remove aluminum stock quickly and alsohave very good cleaning properties. Acid-type etchesattack the aluminum more slowly, leaving a fine­grained uniform surface. Additionally, the etchingrate in an acid is not strongly influenced by theconcentration of dissolved aluminum in the etch,making the process easier to operate.5 Both of theseprocesses are used successfully in commercial plat­ing operations. Some studies have indicated im­proved corrosion resistance using acid etches versusalkaline etches.1.3•6 It has been reported, however,that acid etches do not clean as well as alkalineetches and, therefore, the parts must be cleanedextremely well before the etching stepS.2

Two alkaline and two acid formulations weretested (formulations given in Table IV). Addition­ally, samples using only the chemical polish with noetching were tested. The results are shown in TableV.

Acid etch #2 showed the best performance, whilethe mild alkaline etch produced the worst results.The proprietary etch, an alkaline etch, demon­strated fair performance. Satisfactory results can beachieved using either acid or alkaline etch; however,the etch composition, temperature, and immersiontime must be tailored to the specific alloy and appli­cation at hand. Acid-type etches do seem to have anadvantage over alkaline etches in terms of perfor­mance and ease of use, as long as the parts are wellcleaned prior to the etching step. Acid etch #2 wasfound most suitable for the current application andwas used to prepare most ofthe panels in this study.

Immersion CoatingThe most widely used immersion coating is an alka­line alloy zincate. These zincate solutions provide athinner, more uniform deposit than the pure zincsolutions used in the past.8•9 An alternate to zincat­ing is an immersion coating of tin applied from astannate solution, immediately followed by an elec­trolytic bronze strike. It has been reported that thistreatment is superior to zincate and that less lateralcorrosion is experienced at damaged areas in the·coating.7•10

Two immersion processes were tested in this

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work: the alloy zincate process and the stannateprocess. A double zincate procedure was used withthe first immersion time being 1 min and the secondimmersion being 30 sec. The immersion time in thestannate process was 30 sec in the stannate bathgoing immediately into the electrolytic bronze bathwithout rinsing and under current. The panel wasplated in the bronze bath for 4 min at a currentdensity of 20 AJft2.

The tin immersion layer is extremely fragile andthe transfer time from the stannate solution to thebronze bath must not exceed 30 sec. Some difficul­ties with blistering and poor adhesion were encoun­tered while using the stannate process; no suchdifficulties were encountered using the zincate pro­cess. The panels prepared using the stannate pro­cess (78, 79, 80) had only 0.7 average defect perpanel after 2,000 hours of B 117. The equivalentpanels using the zincate process (42,43,44) showedslightly worse performance, with 2.3 average defectsper panel. Although the stannate process may havemarginally better corrosion performance, it was feltthat the added complication of an electrolytic strike,the limitations on transfer times between the stan­nate and the bronze bath, and the difficulty in ob­taining consistent results, outweigh the advantagesof the process for this application.

Use of an EN StrikeMost of the zinc deposited in the zincate treatmentis subsequently dissolved when the part is immersedin the EN bath, eventually causing zinc contamina­tion of the EN bath. It has also been posited that thedissolution of the zinc layer is detrimental to the ENsubstrate bond.6 • An alklaine EN strike bath may beused prior to the EN bath to deposit a thin layer ofEN, preventing dissolution of the zincate layer andcontamination of the EN bath. It has also beenclaimed that the use of an EN strike bath increasesdeposit quality and corrosion resistance.6

Our own study shows that although EN strikebaths are effective and convenient to use, the use ofan EN strike has little effect on the corrosion resis­tance of the EN deposit., Panels 30, 31, and 32 wereprepared without an EN strike, while equivalentpanels 24, 25, and 26 were prepared using a propri­etary EN strike bath. These panels show nearlyidentical corrosion resistance, 0.7 and 0.2 defect perpanel respectively. Thus the use of an EN strikebath had no effect on the corrosion resistance of thedeposit in our experiments. Additionally, the usefullife of an EN bath for high-performance coatings isonly 3 to 4 turnovers of the nickel content of thebath. If large thicknesses of EN are being deposited

18

it is unlikely that zinc contamination of the EN bathwill be a problem during its useful life; therefore, theuse of an EN strike bath will be largely unnecessaryfor such an application.

EN Bath CompositionStudies of EN corrosion resistance have reportedlarge variations in performance of samples preparedby different vendors.2

•4 It has been shown that cor­

rosion resistance is strongly dependent on the ENphosphorus content, but even samples with similarphosphorus content provided by different vendorsshow marked differences in corrosion resistance. Itis possible that certain bath formulations may yielda deposit, which is less porous than that of otherformulations, thus providing better corrosion protec­tion; however, the preplating procedures can alsohave a significant effect on the corrosion resistanceof the EN coating and could explain the difference inperformance between panels provided by differentvendors.

Vendor A's high-phosphorus EN bath has beenidentified as a process that provides superior corro­sion protection in marine environments. Sampleswere prepared using Vendor A's process and forcomparison Vendor B's high-phosphorus process.Both baths produced EN deposits with excellentcorrosion resistance properties, with Vendor B's per­haps performing slightly better. In any case thelarge variation in corrosion resistance reported inother studies was not found between these two for­mulations. From this we conclude that either bothformulations offer exceptional performance or thatthe sample preparation procedures are responsiblefor some of the difference in performance observed inother studies, or perhaps both. In any case coatingswith excellent corrosion resistance can be obtainedusing either of these baths.

EN Coating ThicknessStudies have shown that the corrosion resistance ofEN coating improves rapidly as the EN thicknessincreases up to 1.5 mil, after which smaller improve­ments are realized. 1.4.5 We tested two thicknesses ofEN, 4 mils. The panels with 2 mils of high-phospho­rus EN bath had 2.3 defects per panel after 2,000hours of B 117, while panels with 4 mils had 1.1defects per panel. Vendor B samples with 4 mils hadodefects per panel while panels with 2 mils had 0.3defect per panel. The increase in thickness improvedthe performance of the Vendor A coating more thanthat of Vendor B, which had excellent corrosionresistance with only 2 mils of EN.

Metel Finishing

Posttreatments and Topcoats

EN Passivation TreatmentIt has been demonstrated that a chromate passiva­tion treatment improves the short-term (less than100 hours) corrosion resistance of EN-coated electri­cal connectors.1.l; To investigate whether long-termcorrosion resistance would also be enhanced, freshlyprepared EN-coated panels (68, 70, 71) were im­mersed in a nitric acid and sodium dichromate so­lution (composition given in Table IV) for 15 minutesand then rinsed and dried at 140"F for 10 minutes.These panels showed reduced corrosion at the scribeduring the first 72 hours of salt spray. This coatingalso reduced EN discoloration, which sometimes oc­curs during salt spray testing; however, this treat­ment did not significantly improve the long-termcorrosion resistance of the EN.

Medium-Phosphorus EN TopcoatIt has been reported that a composite coating of highP EN with a topcoat of medium P EN has bettercorrosion resistance than high P EN alone. Panelswere prepared with 2 mils of Vendor B's processwith 0.8 mil of either semibright medium P EN (61,62, 64) or bright medium P EN (panels 72, 73, 74).These panels performed as well as the panel with 2mils of Vendor B alone (57, 58, 60) at 0.3 defect perpanel. Panels with 0.8 mil of bright medium P ENapplied over 2 mils of Vendor A (51,52,53) showedbetter performance than panels with 2 mils of Ven­dor A alone (42, 43, 44), with 1 and 2.3 defects perpanel respectively. No significant improvement wasfound with this approach for EN coating with excel­lent performance, although this approach could im­prove the corrosion performance of high P EN withpoor corrosion resistance.. ~igh P EN passivates very quickly in air, makingIt dIfficult to apply additional coatings; therefore,the medium P coating was applied immediately af­ter removal from the high P EN bath. An effort wasmade to apply a medium P EN over an aged high Pdeposit by using an electrolytic nickel chloridestrike; however, these panels had poor adhesion ofthe topcoat and were prone to peeling. The nickelchloride strike was also used to apply zinc-nickelalloy to aged high P EN with similar results (48, 50,54).

EN/Zinc-NickellChromate Conversion CoatingsIt has been suggested that a coating, such as zinc

or cadmium, applied over the EN would provideele~trolytic protection to the EN and aluminum byactmg a sacrificial coating.2 In order to investigatethis possibility panels were prepared with a 0.35-mil

December 1999

thick coating of electroplated zinc-nickel alloy on topof the EN coating. One set of panels was tested as isand another set was treated with an iridescent chro­mate conversion coating to protect the zinc-nickel.Zinc-nickel alloy coatings have better corrosion re­sistance than pure zinc and are gaining acceptanceas a substitute for cadmium plating. I2 The panelswith the zinc-nickel topcoat did in fact provide elec­trolytic protection to the EN and aluminum sub­strate. Panels with intentionally scribed coatingwith the zinc-nickel topcoat showed no corrosion ofthe aluminum after 2,000 hours, while panels withonly EN show aluminum corrosion at the scribeafter only 24 hours.

Panels with the zinc-nickel topcoat without thechromate conversion coating applied over 2 mils ofVendor A (66, 67, 69) showed no corrosion of thealuminum but did have considerable white corrosionof the zinc-nickel alloy. This would not be an accept­able coating for marine service. Panels with 2 mils ofVendor B, 0.35 mil of zinc-nickel, and an iridescentchromate conversion coating (59, 63, 65) not onlyshowed no aluminum corrosion at the scribe butshowed no corrosion of any kind over the 2,000-hr B117 test. This coating strategy is considered the bestcandidate for an alternative coating for the MK-50condenser section.

COIlICLUSIOIISIt has been demonstrated that high-phosphorus ENapplied over 6061-T6 aluminum can withstand2,000 hours of neutral salt spray with minimal or nocorrosion.

The etching procedure was found to have a strongeffect on the corrosion resistance of the EN deposit.Acid etches have advantages over alkaline etchesbut either formulation may be successfully used ifthe etchant composition, temperature, and immer­sion time is suited to the alloy being plated. An acidetch containing ammonium bifluoride, phosphoricacid, citric acid, sulfuric acid, and hydrochloric acidwas found to be effective for the well-cleaned6061-T6 aluminum used in this study.

It was found that the corrosion resistance of theEN coating could be improved by using a 0.35-milelectroplated topcoat of zinc-nickel alloy (l0~ NOwith a chromate conversion coating. B 117 tests ofintentionally damaged EN-coated panels (coatingscribed to the substrate aluminum) showed signifi­cant corrosion of the aluminum after only 24 hours.Panels coated with the ENlZn-Ni/chromate coatingshow no corrosion after 2,000 hours. The zinc-nickeltopcoat provides cathodic protection to the substratealuminum and EN. This is similar to the way zinc

19

acts in galvanized steel. When a defect in the ENcoating exists the zinc-nickel, EN, and aluminumform a galvanic cell. The electrical potential of zinc­nickel is lower than that of EN or aluminum so asmall amount ofcurrent flows from the zinc-nickel tothe aluminum. This prevents the corrosion of thealuminum while the zinc-nickel is sacrificially oxi­dized. As a result the EN coating no longer needs toperfectly encapsulate the aluminum in order to pre­vent corrosion. In fact, even if the coating is dam­aged, the aluminum will still be protected from cor­rosion. This coating should be ideal for the MK-50condenser and other applications where marine cor­rosion resistance, scratch resistance, and high ther­mal conductivity are required.

1. Bayes, M. and R. Ellis, "Corrosion Performance Op­timization of Electroless Nickel Plating on Alumi­num Substrates," Electroless Nickel '91 Conference;1991

2. Ogden, T.R., "Conductive Coatings for Marine Ther-

mal Propulsion Systems: Metal Plating Alternativesto MIL-A-8625D, Type III Anodized Aluminum Coat­ings," NRAD Technical Report 1598; March 1993

3. Blackwood, A.W. et aI., "Effects of Surface Prepara­tion on Electroless Nickel Plating ofAluminum," Elec­troles Nickel '91 Conference; 1991

4. DiBari, G.A., Plating and Surface Finishing, 64(5):68;1977

5. Riedel, W., "Electroless Nickel Plating," ASM Interna­tionaVFinishing Publications, Metals Park, Ohio!Stevenage, England; 1991

6. Zitko, M. and P. Vignati, "Advances in ElectrolessNickel and Post Treatments for Enhanced CorrosionProtection of Aluminum Connectors," ElectrolessNickel '91 Conference; 1991

7. DiBari, G.A., Plating and Surface Finishing, 64(5):68;1977

8. Monteiro, F.J. et ai., Metal Finishing, 87( 10):49; 19899. Monteiro, F.J., Plating and Surface Finishing, 76(6):

86; 198910. DiBari, GA, Metal Finishing, 7517):17; 197711. Fern, D. et ai., Metal Finishing, 84(7):55; 198612. Zaki, N., Metal Finishing, 87/6):57; 1989 MF

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Colorimetric Analysis of MetalFinishing & Metal Working

Solutions & Effluentsby A. Knowles 190 pages $85.00

This new book provides 140 methods of colori­metric analysis from A to Z (aluminum to zirco­nium). The accomplished ,tuthor presents appli­cllions, basis of method. equipment ,md reagentsrequired, procedures. c1lculations, and literaturecit,ltions for e.lCh of the 140 methods. Included,1re those for the primary metallic ,md anionicconstituents, additives, ,md impurities of platingh.ahs and related solutions, and also for the deter­min.aion of m,m)' species of effluents.

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20 Metal Finishing