jAD

66-67

DEVELOPMENT OF AN IMPROVED RINSE SOLUT;ON

N •FOR PHOSPHATE COATINGS THROUGH

0 ADDITION OF ORGANIC ACIDSC2)

CLEARIN4H ~OUSNEA ,.F R FrS 7 , 17" A_'NDD. C. ,D]•L . ... -,"rE~ -?: y, :;' , ... - ,'• .

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TECHNICAL REPORTBy

W. 0. Crawford

Januury 1966

U. S. ARMY WEAPONS COMMAND

ROCK ISLAND ARSENAL

RESEARCH & ENGINEERING DIVISION

Distribution of this document is unlimited.

AD

U. S. ARMY WEAPONS COLMAND

ROCK ISLANkD ARSEIAL

RESEARCH & ENGINEERING DIVISION

TECHNICAL REPORT

66-67

DEVELOPMENT OF AN IMPROVED RINSE SOLUTIONFOR PHOSPHATE COATINGS THROUGH ADDITION OF ORGANIC ACIDS

By

W. 0. CrawfordLaboratory Branch

January 1966

DA # IC024401A328 AMS Code 5025.11.294

Distribution of this document is unlimited.

3.

ABSTRACT

This work was undertaken in order to improve the saltspray resistance capabilities of phosphate coatings throughinnovatioas in tho post treatment of the phosphate coatingsand. specifically through improvements in the supplementaryrinse solutions,

Various compounds, both organic and inorganic, weretested In solution, both by themselves and in combinationwith each other and with the existing chromic acid rinseuolution, as possible rinses for phosphate coatings.

It was found that four different 1-4 and 1-5 dicar-boxylic acids, when used in the proper concentration withthe-existing 0.6 gm/liter (0.08 oz,/gal.) chromic acidrinse increased the salt spray life of a phosphate coatingby at least one hour over the salt spray life of a coatingtreated in the standard 0.6 gm/1 chromic acid rinse. Thesefour acids are: citric acid, glutaric acid, maleic acidand succinic acid.

It was also found that one aromatic dicarboxylic acidtested phthalic acid, had the same effect on the saltspray life as the above mentioned aliphatic acids.

2

FOREWORD

This work was authorized under DA Number ICO-24401-Al10. The problem title is "Supplementary TreatmentsFor Plated And Conversion Coatings," under subtask title,"Protective and Packaging Materials," which is underproject, "Materials For Army Weapons and Combat Mobility."

The part played by phosphate coatings in the Armycorrosion prevention program is well known. This workwill attempt to produce a post-phosphating rinse solutionof superior quality which will increase the protectiveusefulness of phosphate coatings.

3

1-

TABLE OF CONTENTS

Page No.

Title Page 1

Abstract 2

Foreword 3

Table of Contents 4

Problem 5

Background - 5

Approach and Results 6

Testing of Miscellaneous Proprietary 6Materials

Screening of Inorganic and Organic Additives 8

Testing for Optimum Concentration of 8Organic Acids

Testing for Optimum Concentration of 14

Chromic Acid

Stability Tests and Trivalent Chrome Analysis 16

Discussion 16

Conclusions 20

Recomm, udations 20

Literature Cited 21

Distribution 23

DD Form 1473 (Document Control Data - R&D) 30

4

PROBLEM

The aim of this work was to increase the salt sprayresistance of phosphate coating systems through improve-ment of the post treatment operation by innovations inthe chromic acid rinse solution.

BACKGROUND

It is generally known and accepted that a phosphatecoating on metallic surfaces contains pores or pinholeswhich expose the basis metal; it is at these points inthe coating where initial corrosion of a specimen starts.(1)Therefore, parts are often rinsed in dilute chromic acidsolutions after phoaphating. Rinsing in these chromicacid solutions have be n found to aid in hindering thisinitial corrosion.31

In the field of chlromic acid rinse pslutions, workhas been carried out by Eisler and Doss(3) using taggedchromic acid rinse solutions on heavy manganese and zincbased phosphate coatings to determine optimum chromicacid concentrations to be incorporlted in the rinsesolutions. Further work by Doss(4J using chromic acidrinse solutions indicated that specimens rinsed in thechromic acid solutions exhibited less corrosion after thesalt spray test. Tests conducted by McHenry and Doss(5)showed that as the concentration of chromic acid inrinse solutions increased, the phosphate loss from thecoatings also increased.

Some success had been demonstrated by other workersusing citric acid solutions in both the pretreatment andpost treatment of phosphate coatings.(7,9)

At the present time, MIL-HDBK-205 "Phosphatizingand Black Oxide Coating of Ferrous Metals" recommendsthat an 0.6 g/1 (0.08 ounce per gallon) chromic acidsolution be employed as a rinse solution for phosphatecoatings. However, difficulty has been experiencedupon occasion in obtaining coatings that will meet theminimum salt spray requirements when phosphating withthe room temperature phosphating bath; even when employingthe chromic acid rinse solutions. It was decided, therefore,to try to improve the quality of the rinse solution inorder to thereby improve the corrosion resistant qualitiesof the phosphate coating systems on which the rinsesolutions are used.

5

APPROACH AND RESULTS

The investigation was programmed to cover thefollowing specific areas.

A testing of miscellaneous proprietary rinsesolutions was carried out in order to see what otherinvestigators in this area had found and how other rinsesolutions effected the salt spray resistance capabilitiesof a phosphate coating.

Various inorganic and organic additives were screenedin order to determine what general direction the bulk ofthe work should follow.

Based on the results of the screening tests, testswere carried out in order to find the optimum concentrationof organic acids that could be used in combinations withthe standard 0.6 gm/1 chromic acid rinse solution.

Tests were then run to determine the optimum levelof chromic acid to be used in the rinse solution.

Lastly tests were run to determine the stability ofthe rinse solution developed during this work.

Testing of Miscellaneous Proprietary Materials

In this portion of the testing program, a number ofcommercially available products were evaluated as shownin Table I. These products were labeled A, B and C.Product A seems to be a thermosetting plastic suspensionin water, product B is a chromic acid type rinse andproduct C is a combination chromic acid-organic typer inse.

In these tests panels were phosphated in sets offsur and rinsed in accordance with the instructions suppliedby the companies unless indicated otherwise in Table I.The control referred to in Table I is the 0.6 grams perliter (0.08 oz/gal) chromic acid rinse described in MIL-HDBK-205. All of the panels were subjected to the saltspray test conforming to the test recommended in MIL-P-16232B "Phosphate Coatings, Heavy, Manganese or ZincBase (For Ferrous Metals)."

It can be seen from the results given in Table Ith;t,. of the materials tested only C was as good as theco.ntrol and B and A were inferior to the control,

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APPROACH AND RESULTS

The investigation was programmed to cover thefollowing specific areas.

A testing of miscellaneous proprietary rinsesolutions was carried out in order to see what otherinvestigators in this area had found and how other rinsesolutions elfected the salt spray resistance capabilitiesof a phosphate coating.

Various inorganic and organic additives were screenedin order to determine what general direction the bulk ofthe work should follow.

Based on the results of the screening tests, testswere carried out in order to find the optimum concentrationof organic acids that could be used in combinations withthe standard 0.6 gm/1 chromic acid rinse solution.

Tests were then run to determine the optimum levelof chromic acid to be used in the rinse solution.

Lastly tests were run to determine the stability ofthe rinse solution developed during this work.

Testing of Miscellaneous Proprietary Materials

In this portion of the testing program, a number ofcommercially available products were evaluated as shownin Table I. These products were labeled A, B and C.Product A seems to be a thermosetting plastic suspensionin water, product B is a chromic acid type rinse andproduct C is a combination chromic acid-organic typerinse.

In these tests panels were phosphated in sets offour and rinsed in accordance with the instructions suppliedby the companies unless indicated otherwise in Table I.The control referred to in Table I is the 0.6 grams perliter (0.08 oz/gal) chromic acid rinse described in MIL-HDBK-205. All of the panels were subjected to the saltspray test conforming to the test recommended in MIL-P-16232B "Phosphate Coatings, Heavy, Manganese or ZincBase (For Ferrous Metals)."

It can be seen from the results given in Table Ithat, of the materials tested only C was as good as thecontrol and B and A were inferior to the control.

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1171CT OF CONCENTRATION OF SALT SPRAY RESISTANCE

CoatingSalt Spray Weights inGroup Set Variable Concentration Results in Hrs. Ugs. Per

No. No. Component of Var. Component Passed Failed Sq. Ft.

I1 None 2 3 2870

2 Succinic acid 1 gram/liter 3 4 3400

3 .. . 5 grams per liter 1 2 3520

4 " ' 10 .. . " 0 3560

5 None 2 3 2450

II1 " 2 3 2960

2 Tartaric acid 1 gram per liter 2 3 2960

3 " 5 " " 0 2900

4 " 10 " " " 0 1800

5 None 2 3 2900

III

1 None 5 6 2500

2 Phthalic acid 1 gram per liter 6 7 2670

3 " 5 .. .. . 4 5 2690

4 " 10 " " " 3 4 2820

5 None 5 6 2600

IV1 None 2 3 1840

2 Citric acid 1 gram per liter 3 4 1850

3 " " 5 " " " 2 3 1930

4 " " 10 " " " 0 2040

5 None 2 3 1840

V1 None 4 5 1630

2 Glutarlc acid 1 gram per liter 5 6 1680

3 " " 5 grams per liter 4 5 2000

4 " " 10" " " 4 5 1730

5 None 4 5 1560

VI1 None 3 4 1420

2 Maleic acid 1 gram per liter 4 5 1430

3 " " 5 " " 0 1450

4 " 10" " " 0 1470

5 None 3 4 1390

11

EFFECT OF CO.NCENTRATJON OF 'ALT SPRAY RESXSTANCS

Coat ngSal-t Spray W*eights in

Group Set Vtrlable Conceutzation Results in Hre. MUs. PerNo. NO. Coiuonent Z V~r.•Cojnnt issed Fled . Ft.

1 Norc- 2 3 1400

2 Glutarlc acid 0.5 gram.- per litei 2 3 1580

3 " " 1.6 " " " 3 4 1590

4 I I 2.5 " " " 2 3 1630

5 None 2 3 1510

ViiiI W~one 2 3 1350

2 Sucninic acid 0.5 grams per liter 2 3 l140

3 " " 1.0 " " " 3 • 1970

4 ' " 2.5 1" " 2 2050

5 Norse 2 3 ,34)

Ix1 None 4 5 166G

2 Phthalic acid 0.5 grame per liter 4 5 1780

3 i i 1.0 .. . " 5 6 1860

4 I " " 2.5 " " " 4 900

5 Nove 4 5 1660

1 None 5 6 2000

2 £artaric acid 0.5 grams per liter 3 4 2120

3 " " 1.0 t " " 2 3 2150

4 if Is 2.5 " " " 1 2 2160

5 None 5 6 1890

XI1 None 2 3 2350

2 Citric acid 0.5 grams per liter 2 3 2400

3 " " 1.0 " " " 3 4 2510

4 f " 2.5 " " " 2 3 2540

5 None 2 3 2300

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"Once again the 0.08 oz/gal. 0.6 g/). chromic acidrinse was used as a control. As only thiý effect of theorganic acids is being tested the other variables were

% •canceled out during this test, that is the rinse timewas 30 seconds for all sets, the rinse temperature wasmaintained at 160-1650 F for all sets, and the second-component in each rinse solution, chromic acid, wasmaintained at 0.6 gm/l. Each group of sets representsa different day of phosphating. A 0.6 gm/l chromicacid rinse control solution was run at the beginningand end of each group to'assure that no breakdown of thephosphate coating solution took place during the day ofthe groups processing.

It can be seen from the results shown in Table IIIthat a solution of citric, or maleic, or glutaric, orsuccinic, or phthalic acid at a concentration of one gramper liter in combination with chromic acid at a con-centration of 0.6 gm/i will increase the salt spray lifeof a phosphated panel by one hour over a panel rinsed inthe 0.6 gm/1 chromic acid control solution, where theother factors of rinsing, time and temperature, are 30aeconds and 160-165°F respectively. Adipic and tartaricacids showed some promise in the screening tests, seeTable 7I, but subsequent tests, Table III, using theseacids did not equal the initial results, Table II.Table III shows that as the concentrations of organicacid in the rinse solution is raised there is an increasein the coating weights obtained on the panels.

Testing for Optimum Concentration of Chromic Acid

In the following tests, Table IV, the optimum levelof chromic acid to use with the one gram per literorganic acid will be found. In these tests, the othervariables, organic acid concentration, rinse time, andrinse temperature, were kept constant at 1 g/l, 30seconds and, 160-1650 F. Once again a 0.6 gm/l chromicacid control rinse was run at the beginning and the endof each group.

The tests outlined in Table IV show that as theconcentration of chromic acid in the rinse solutionincreases the coating weights decrease and that thereis a tendency toward shorter salt spray resistances.Therefore, the concentration of 0.6 gm/l seems to be thebest concentration to use.

14

TABLE IV

EFFECT OF VARYING CHROMIC ACID CONCENTRATION

Salt Spray CoatingGroup No. and Set Chromic Acid Results in Hours Weights In Mgs.

Organic Acid Type No. Concentration Passed Failed Per Sq. Ft.

I Adipic acid1 0.6 gm/i 3 4 2460

(.08 oz/gal)

2 1 gm/liter 3 4 2230

3 5 gms/liter 3 4 218C

4 10 gms/liter 3 4 2190

5 0.6 gm/i 3 4 2350

II Succinic acid1 0.6 gm/l 2 3 1650

2 0.5 gm/liter 3 4 1720

3 1 gms/liter 3 4 1610

4 2.5 gms/liter 1 2 1780

5 0.6 gm/i 2 3 1700

III Phthalic acid1 0.6 gm/l 3 4 1650

2 0.5 gm/liter 4 5 1850

3 1 gm/liter 4 5 1700

4 2.5 gms/liter 2 3 1320

5 0.6 gm/1 3 4 1630

IV Citric acid

1 0.6 gm/l 2 3 1830

2 0.5 gm/liter 3 4 2240

3 1.0 gm/liter 3 4 2210

4 2.5 gms/liter 2 3 1920

5 0.6 gm/i 2 3 1680

V Glutari" acid1 0.6 gm/i 2 3 2600

2 0.5 gm/liter 3 4 3000

3 1.0 gm/liter 3 4 2760

4 2.5 gms/liter 3 4 2660

5 0.6 gm/i 2 3 2490

VI Maleic acid1 0.6 gm/i 2 3 2300

2 0.5 gms/liter 3 4 2460

3 1.0 gm/liter 3 4 2660

4 2.5 gas/liter 3 4 2170

5 0.6 gm/l 2 3 2890

15

Stability Tests and Trivalent Chrome Analysis

In these tests, all of the organic-chromic acidrinse solutions that have been found superior to the0.6 gm/1 (0.08 oz/gal) control were prepared and used onthree groups of panels on three different days, as therinse solution production are prepared fresh every daythis test proves that the new solutions are stable enoughto use in production. In all the rinses the chromicacid concentration is 0.6 g/l, the organic acid con-centration is 1 g/l, the rinse time is 30 secs., andthe rinse temperature is 160-1650 F. In all the previoustests each group was rinsed in fresh solutions.

The last two groups, II and III, of seven sets ofpanels were processed three days apart and rinsed inorganic acid-chromic acid solutions that had been heldover the three days. All of the other groups in allof the phases were rinsed in solutions that had beenfreshly prepared on the days that the groups werephosphated.

DISCUSSION

None of the inorganics initially tested producedany increase in the salt spray resistance qualities ofthe phosphate coatings so a detailed study of inorganicadditives to rinse solutions was not carried out.

The organics tested in this work were, citric acid,succinic acid, maleic acid, glutaric acid, malic acid,tartaric acid, oxalic acid, acetic acid and phthalic acid.Of these, the first four and the last one mentioned hadthe effect of improving the salt spray resistance ofphosphate coatings when the coatings were treated insolutions containing these organic acids in the properconcentrations in the existing 0.6 gm/1 (0.08 oz/gal.)chromic acid rinse solution.

It can be seen from the results of the workdescribed in this report; that five supplementary rinsesolutions have been developed that will increase thesalt spray resistance of a phosphate coating- by at leastone hour over the salt spray resistance of a phosphatecoating treated with the 0.6 gm/l (0.08 oz/galo) chromicacid rinse solution. The solutions are, a one gram perliter citric, 0.6 g/l chromic acid solutJon, a one gramper liter glutaric acid-0.6 g/l chromic acid solution,a one gram per liter maleic acid-0.6 g/l chromic acidsolution, a one gram per liter succinic acid-0.6 g/lchromic acid solution, and a one gram per liter phthalicacid-0.6 g/l chromic acid solution.

16

TABLE V

EIFECT OF RINSE SOLUTION AGE ONSALT SPRAY RESISTANCE

Salt Spray CoatingGroup Set Results in Hours Weights in Mgm.

No. No. Organic Acid Passed Failed Per Sq. Ft.

I1 None 2 3 1320

2 Citric 3 4 1330

3 Succinic 3 4 1330

4 Glutaric 3 4 1570

5 maleic 3 4 1550

6 Phthalic 3 4 1410

7 None 2 3 1310

II1 None 2 3 1240

2 Citric 3 4 1920

3 Succinic 3 4 2280

4 Glutaric 3 4 1780

5 maleic 3 4 1600

6 Phthalic 3 4 1400

7 None 2 3 1190

III1 None 2 3 1000

2 Citric 3 4 1180

3 Succinic 3 4 1330

4 Glutaric 3 4 1190

5 Maleic 3 4 1300

6 Phthalic 3 4 1240

7 None 2 3 1060

17

On considering the possible explanations of themechanisms by which the addition of such a small amountof organic acid to the standard 0.6 gm/i chromic acidrinse solution could increase the salt spray resistanceof a phosphated panel treated in the solution by anadditional hour over the salt spray resistance of panelstreated in the standard solution; three possibilitiesarise.

Based on the Baeyer strain theory,(9,10) the carboxylgroups of the four aliphatic acids found to be effectivein the supplementary rinse solutions are in close proximityto one another; this fact indicates that there is arelatively strong partial negative charge pres3nt in thevicinity of these carboxyl groups. By the same Baeyerstrain theory, the carbon atom in each of the aliphaticacids furr a loop. It is possible that, when the freshlyphosphated panels are rinsed in the solutions containingthe organic acids, the partial negative charge aroundthe two closely oriented carboxyl groups is attracted toa positive charge present on the phosphate crystallattice and attaches the organic acid loosely to thesurface of the phosphate coating by much the same mechanismas the varfous organic inhibitors used in steel picklingsolutions. llI If this reaction does take place, thenthe loop of carbon atoms would undoubtedly cover some ofthe pinholes in the phosphate coating where initial

-corrosion of the phosphated piece takes place. In thecase of the aromatic acid found to be of value in therinse solutions. The same theory would apply, exceptfor the fact that there is no need to use the Baeyerstrain theory as the carbon atoms in phthalic .acid areactually present in a ring formation. The above tentativeexplanation of the mechanism by which the organic acidsused enhance the salt spray resistance of a phosphatecoating would seem to be the most logical one.

There is another possible explanation that can beput forward as to the increased salt spray resistance ofcoatings treated with the organic acid-chromic acid rinsesolutions over coatings treated with the standard chromicacid rinse solution. The theory of trivalent chromiumprecipitation on coatings(1,2) is that trivalent chromiumis attracted to weak and/or bare spots in the coatings,precipitate on the weak spots, and set up a partialbarrier at the aforesaid weak spots. (2) As the organicacids(used are capable of forming complexes with metalions, (12 it is possible that the organic acids formcomplexes with the trivalent chromium ions present inthe solution, and in this way facilitate the transferof the trivalent chromium ions from the solution to thephosphate coating; thus giving a greater density of

18

trivalent chromium ions on the weak spots in the coating.

A third possible explanation of the improved saltspray resistance of the panels treated in the organic acid-chromic acid rinse solutions, is that phosphate coatingsare not smooth but consist of peaks and valleys or highand low spots. It is possible that the organic acids,which have low ionization constants and are not highlypolar settle in the low spots on the phosphate coatingswhereas the highly ionic and polar chromic acid attacksthe high spots setting up an active passive differentialin the same manner as in a solution of oxalic acMid andsulfuric acid that is used in tumble deburring.AI)This pheuomenon of having an organic acid coating protectingthe low, or thin, spots on the coating while the panel isimmersed in the rinse solution would prevent etching ofthe low spots of the coating thus increasing the salt sprayresistance of the coatings.

All of the three theories mentioned above would alsotend to explain the increase in coating weights obtainedwhen using the chromic acid-organic acid rinse solutionsrather than the standard chromic acid rinse solutions.

A logical explanation as to why a concentration of0.1 per cent of the organic acids used increases the saltspray resistance of the phosphate coatings when used inthe chromic acid rinse solutions while concentrations of0.25% and above seem to be detrimental to th. salt sprayresistance capabilities of the coatings is that the orgAnicacids used are oxidizable,(9) and in the presence of thestrong oxidizing agent, chromic acid, the advantageouseffect gained by the presence of a small amount of theorganic acid in the solution is offset when enough organicacid is added to reduce an appreciable amount of thechromic acid present.

There would appear to be no problems involved in theuse of the organic acids in a shop production situation.There are several chemical companies that produce citricacid and/or maleic acid and/or succinic acid on a commercialbasis at a reasonable price. Maintenance of the level oforganic acid concentration needed in the rinse solutionwould be no problem as the rinse solution is discarded anda fresh solution prepared every day.(18) The phase fourtests showed that the solutions developed are stable forat least three days.

19

CONCLUSIONS

It can be seen that the organic acid-chromic acidrinse solutions developed are superior to the 0.6 gm/lchromic acid rinse solution recommended for use withphosphate coatings by MIL-HfBK-205.

In the phase wo �tests, in every case, the solutionscontaining the five organic acids found to be beneficialto the rinse solutions showed the following characteristic.As the concentration of organic acid in the rinse solutionwas increased the coating weights obtained increased.However, only at the concentration of one gram per literdid the organic acids show any tendency to increase thesalt spray resistance capabilities of. the phosphatecoatings. At the one gram per liter concentration oforganic acid the salt spray resistance capabilities ofthe phosphate coatings treated were increased to the pointwhere each coating treated lasted one hour longer than thecoatings treated with the 0.6 gm/i rinse solution; thiswas true in all of the tests in all of the phases.

The concentration of chromic acid that should be usedin combination with the one gram per liter organic acidis 0.6 gm/i chromic acid. The phase three tests showedthat at concentrations significantly higher than thisthe salt spray resistant capabilities of the phosphatecoatings treated are decreased rather than increased.

RECOMMENDATIONS

It is recommended that one of the following organicacids, citric, succinic, glutaric, maleic, orphtbalic, beIn corporazed into the 0.6 gm/1 chromic acid rinse solutionat an installation and compared with the standard rinsesolution in use at the same installation on phosphatedwork processed at the installation in order to verify theresults obtained from the tests described in this report.

After the above pilot tests are completed, and theconclusions drawn in this report verified as sound whenapplied to shop procedures and practices; it is recommendedthat the addition of the organic acids tested be incorporatedinto the existing 0.6 gm/l chromic acid rinse solutionrecommended in MIL-HDBK-205 at a level of one gram perliter of solution.

20

LITERATURE CITED

1. "Metallic Corrosion, Passivity and Protection,"Evans, U. R., 1946, Longmans, Green and Co., New York.

2. "The Corrosion Handbook," edited by Uhlig, Herbert H.,1948, John Wiley and Sons, Inc., New York.

3. "Radiometric Evaluation of the Effectiveness of theChromic Acid Rinse Treatment for Phosphated Work,"Eisler, S. and Doss, J., December, 1952, Metal Finishing,Vol. 50, No. 12, pp. 54-59.

4. "The Effect of Chromic and Chromic-Phosphoric AcidRinse Solutions On the Durability of Paint Coatings,"Doss, J., June, 1955, Organic Finishing, Vol. 16,No. 6, pp. 7-13.

5. "Phosphate Loss From Phosphate Coatings As A Resultof the Chromic Acid Rinse," Doss, Jodie and McHenry,W. Dennis, March 5, 1956, Rock Island Arsenal TechnicalReport Number 56-660.

6. "Comparative Corrosion Resistance Tests On PhosphateCoatings," Doss, Jodie, July 15, 1958, Rock IslandArsenal Technical Report Number 58-1842.

7. "Method and Composition for Increasing the CorrosionResistance of Phosphate-Type Chemical ConversionCoatings On Metal Surfaces," Schneider, George,Amchem Products Inc., Feb. 26, 1963, United StatesPatent Office, Patent No. 3,079,288.

8. "Method of Pretreating and Phosphatizing a MetalSurface for Siccative Coatings," Ross, Jr., Wilford H.and Maloney, James E., Detrex Chemical Industries Inc.,Detroit, Michigan, Jan. 21, 1964, United States PatentOffice, Patent No. 3,118,793.

9. "Organic Chemistry,." Brewster, Ray Z., June 1954,Prentice-Hall Inc., Second Edition, pp. 329-331.

10. "Advanced Organic Chemistry," Wheland, 1948, John Wileyand Sons Inc., New York, pp. 365-375.

11. "Corrosion and Corrosion Control," Uhlig, Herbert H.,1963, John Wiley and Sons Inc., New York, pp. 233-236.

21

.LAD. V LAM MWIIA~.L %.ot$LA%#1 ýUM1UpUUM)b ~re.and Calvin, Sept. 1953, Prentice Hall Inc., pp. 194-196, 138-139.

13. "The Scientific Approach to Deburring," Saxby, George,Feb. 1962, Metal Finishing. Vol. 60, No. 2, pp. 41-47.

14. "Text.•b-k of Organic Chemistry," Wertheim, 1947, TheBl',okistc'ns Co., Phila, pp. 254-255.

15. "Effects of Chror.1, Chromic-Phosphoric Acid RinsesOn Performance o.f Phosphate Coatings," Reed, A. B.,Dec. 5, 1955, Development and Proof Services,Aberdeen Proving Ground, Maryland, EngineeringLaboratories Report No. 8.

16. "Electroplating Engineering Handbook," Graham, 1962,Reinhold Publishing Corporation, New York.

17. "Chemistry of Chromimum and Its Compounds," Udy,Marvin J., 1956, Reinhold Publishing Corp., New York,Vol. 1, pp. .79-181.

18. "Phosphatizing and Black Oxide Coating of FerrousMetals," 11 June 1957, Military Handbook 205, p. 48.

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