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NOTICE: When government or other drawings, speci-fications or other data are used for any purposeother than in connection with a definitely relatedgovernment procurement operation, the U. S.Government thereby incurs no responsibility, nor anyobligation whatsoever; and the fact that the Govern-ment may have formulated, furnished, or in any waysupplied the said drawings, specifications, or otherdata is not to be regarded by implication or other-wise as in any manner licensing the holder or anyother person or corporation, or conveying any rightsor permission to manufacture, use or sell anypatented invention that may in any way be relatedthereto.

.,+" CIIIII I DI

III4U~ ~ o.GENERAL DYNAMICS J CONVAIR

0..,. ..

C) Material - Finishes and Coatings - Primer Pigments

,J Salt Spray Corrosion Resistance,.d2

y A.

L. A. Mappus, R. H. Whidden W. M. Sutherland

(t-

27 December 1956

Published and Distributed

Nunder T"j!

Contract AF3j571-8926 C'rii' qm

- lY - JUN-P. 1STISIA D

Post Office Box 1950, San Diego 12, California 296-6611

Material Post Office Box 2071 273-8000 Accounting Post Office Box 510

GIIIIIIIIDGENERAL DYNAMICS I CONVAIR

MODEL PAGERTE REPORT NO.

Report No. 8926-167

Material - Finishes and Coatings - Primer Pigments

Salt Spray Corrosion Resistance

\Abstract:

Five pigments, potassium zinc chromate; calcium chromate; strontium chromate;barium chromate; and zinc tetroxychromate, were incorporated with twodifferent paint vehicles, an alkyd resin and a coumarone - indene resinvehicle, suitable driers and solvents, and applied to clad 7075-T6 aluminumalloy, AZ31, Condition H magnesium alloy, normalized 4130 steel, and annealedType 321 stainless steel. The several samples were exposed to 20 t0:salt spray exposure for 1500 hours to observe weight losses resulting fromthe corrosion exposure. The weight loss data showed the effectiveness ofthe five pigments when applied to steel and magnesium alloy ranked in theorder they are mentioned above. Those primers formulated with alkyd resinvehicle performed better when applied to alloy steel and magnesium alloythan those formulated with the cumarone - indene resin.

Reference: Mappus, L. A., Whidden, R. H., Sutherland, W. M."Chromate Pigments - Relative Efficiency in AircraftPrimers of," General Dynamics/Convair Report MP 56-264,San Diego, California, 27 December 1956. (Reference

attached).

FORM 1Il2 CASYIl/SI)

CO0N VAI R REPORT. 5-6

A DIVISION OF GENERIAL DYNAMICS CORPORATION DATE 12-27-56

SAN DIEGOMOE

TITLE

iiEFORT NO. 56-264CHROMATE PIGPIEtTS -

RELaTIVE EFFICIENCY L%IR~CRaFT i-RI',LRS OF

MuiEL MRS 56-185

PREPARED BYO("-C 22fjm GROUPI,"TERIh.W tk PRUCEi ES L- 6L.A. Mappult vd

REFERENCECHECKED BY R.I.Wh~e

CHECKED BY )APPROVED BW. M. Sutherland, z.' . StrongGroup Engineer Chief, Enginee ng

NO. OF PAGES 15..JL............ Test L, 'ooratories

NO. OF DIAGRAMSJS 10.........

REVISIONS

No. DATE BY CHANGE PAGES AFFECTED

FORM ,SIZA-4

ANALYUIS C 0 N V A I R PAGEPREPARED MY Mppus/Whidden A cMue eW eUM OVIAMU 6e0Mfee RErPORT NO. 56-264CHECKED MY W. M. Suth~erland MODEL 1IRS 56-185RWEVISD by DATE 12-27-56

REPORT NO. 56-264ChRO ATE PIGMENTS -

RELATIVE EFFICIENCY IB AIRCRAFT tRIMUAS OF

INTRODUCTION:

Potassium zinc chromate has been used exclusively as a corrosion inhibitivepigment in the aircraft industry. A literature search revealed that otherchromate pigments might be more satisfactory, especially under conditionsof high heat or in acid environments. These conditions are being encounteredon today's fighter type aircraft due to high speeds and missile exhaust gases.The most recent comprehensive comparison of the efficiencies of variouschromate pigments is that of H. G. Cole (Reference 1.).

This work was intended to be a purtial replicate of the work done by Mr. Cole.Originally, it was planned to include an alkaline pigment, especially formagnesium and steel protection, and barium potassium chromate (Pigment E).However, a supplier could not be located for these two pigments. The followingfive chromate pigments were selected for evaluation: potassium zinc chromate;strontium chromate; calcium chromate; barium chromate; and zinc tetroxy-chromate. These pigments were formulated into priming paints using a coumarone-indene vehicle and also an alkyd vehicle similar to that used in specificationMIL-P-8585 primer. The primers were applied to a clad aluminum alloy, amagnesium alloy, a chromium-molybdenum alloy steel, and a stainless steel.Test conditions for evaluation were the standard 20% salt spray cabinet andan exterior exposure with two daily sprays of sea water.

This report covers the results obtained after 1500 hours salt spray ex-posure on the magnesium and 4hromium-molybdennm alloy steel specimens.Addendum reports will be issued on the other specimens as soon as theresults become significant.

OBJECT:

To determine the relative efficiency of five different chromate pigmentsas corrosion inhibitors in primer formulations, using a couimarone-indeneresin vehicle and also the MIL-P-8585 alkyd vehicle, on four typical air-craft construction metals.

CoM CLUSIONS:

1. The relative overall performance of the five pigments tested after 1500hours salt spray exposure on magnesium and 4130 steel specimens was asfollows, in the order of decreasing effectiveness:

(a) Potassium zinc chromate(b) Calcium chromate(c) Strontium chromate(d) Barium chromate(e) Zinc tetroxychromate

lFnM Ill.A

ANALYSIS C 0 N V A I R PAGE2

PREPARED mY Mappus/Whidden a a,*UU.U.mi n ALYnmSAI.eU REPORT NO. 56-264CHECKED mY W. M. Suthtrland sA 0to MODEL NBS 56-185REVISED my DATE 12-27-56

CONCLUSIONS. (Cont'd.)

2. As a group, the primers formulated with the alkyd resin vehicle per-formed better than those formulated with the coumarone-indene resinvehicle on magnesium and steel specimens after 1500 hours salt sprayexposure.

MATERIALS:

Metals -

Clad 7075T6 aluminum alloy, QQ-A-287Magnesium alloY, QQ-M-44, AZ 31, Cond. H4130 steel, AN-QQ-3-685, normalized18-8 stainless steel, MIL-S-6721, Type 321, annealed

Pigments -

Potassium zinc chromate, Reichhold Chemicals # 1425Strontium chromate, Mineral Pigments Corp. # 1365Calcium chromate, Mineral Pigments Corp. # 1376Barium chromate, Mineral Pigments Corp. # 1355

Zinc tetroxychromate, Reichhold Chemicals # 1430

Vehicles -

Coumarone-Indene, Neville Chem. Co. # R-12-ALinseed oil, 900 poise, Archer-Daniels-MidlandMaleic anhydride, Barrett Chemical Co.Phenol aldehyde, Bakelite # BKS 3962Alkyd resin, Reichhold Chemicals # P-372

Driers -

Manganese drier, 6% solids, NuodexCobalt drier, 6% solids, NuodexLead drier, 24% solids, Nuodex

Solvents -

Naphtha (12-15% aliphatic), heville Chem. Co. # 250WXylol, McGuire Chemical Co.Butyl Alcohol, Union Carbide Corp.

TEST SPE CIMEN PREPARATION'

Metal substrates- The composition of the alloys selected for test is shown

in Table I. Specimens for each alloy were cut from a single sheet of materialto assure uniformity of composition. Representative samples of each sheet

were analyzed by the Chemical Laboratory. All specimens were .064 x 3 x Ainches. The edges and corners of the specimens were rounded by filing.

F'OU ISlA

ANALYSIS C O N V A I R PAGE 3PREPARED BY appus/Whidden A UI, eF GEKA EUSW CoWeA., REOwr NO. 56-264CHECKED MY W. M. Sutherland N loMODEL MRS 56-185REVISED BY OATS 12-27

TEST SPECIMEN P.EPARATION. (Cont'd.)

Metal substrates. (Cont'd.) -

The aluminum alloy specimens were solvent wiped with n thyl ethyl ketone,vapor degruased with t richoroethylene, alkaline cleaned and chromic acidanodized per MIL-A-8625, Type I.

Magnesium alloy specimens were vapor degreased, alkaline cleaned and di-chromate treated in accordance with MIL-M-3171, Type III.

The 4130 steel specimens were sandblasted and solvent wiped prior topainting.

Stainless steel specimens were vapor degreased and passivated with nitricacid.

Paint formulation - All of the experimental primers were formulatej forthis test by the U. S. Paint and Chemical Co., 1133 Mariposa Street, SanFrancisco, California. Details of the formulations are shown in Tables IIIand IV. Unlike the Cole report, no final adjustment was made for glossafter manufacture. Details on the pigments used for formulations are

shown in Table II.

Paint apolication - All of the primers were thinned with toluene to aZahn # 1 viscosity of 40 at 771F. prior to application. 6fecimens receivingthe same primers were sprayed in the same batch to assure a Uniform coaton the various substrates. Primers were applied within 24 hours after the

metals were surface treated. After priming with one 8ood cover coat, the

specimens were allowed to cure at least 24 hours ,-nd then all specimens were

top coated with MIL-L-7178 lacquer, color no. 514 black. The specimenswere allowed to cure for two weeks prior t6exposure.

Controls - Unpainted surface treated specimens of each alloy were usedas controls.

TEST PROCEDURE:

Salt spray cabinet exposure - Specimens were exposed in quadruplic-te to

20% salt spray in accordance with 4i-M-151A. Abll specimens were mountedat an angle of 20 degrees from the vertical in a single rack (see Figure 1.).Each of the quadrupicate specimens was exposed at a different level on therack. Specimens of each of the four alloys were sub-grouped together.Control specimens were placed between those painted with couarone-indenevehicle primers and those p.Ainted with the alkyd vehicle primers.

Exterior exoosure - Quadruplicate specimens mounted at an angle of 45degrees were exposed on a rack facing sout (see Figure 2.). The rack was -located ap~.roximately 1/2 mile inland from San Diego Bay. The specimens

were attached to the rack with wooden pegs. Twice every working d ay, thespecimens were sprayed with sea water hich had been collecteA in the neigh-borhood of the whistle buoy at the entrance to San Diego harbor.

FORM 1812-A

ANALYIS C O N V A I R PAGU4PREPARED BY Mappus/ghidden A"'e ff G110 "11" "TO- RIEPORT NO. 56-264CHCiKEID my W. M. Sutherland dan DO, mOOL MRS 56-185REVISED my DATE 12-27-56

TEST PROCURE. (Cont'd.)

Evaluation procedure - Corrosion was evaluated by weight loss, expressedas grams per square decimeter per ounce of paint applied per square yrdof surface. All specimens were weighed to the nearest tenth of - milli-gram at the following intervals:

(1) After surface treatment(2) After priming(3) After top coating(4) After exposure (paint and corrosion products removed)

A paint stripper conforming to MIL-R-8633 was used to remove paint fromthe specimens.

Corrosion products were removed from the m:gnesium alloy specimens byimmersing overnight in a cold 10% solution of ammonium chromate throughwhich a stream of air was bubbled.

Lorayne Rust Remover, a proprietary material manufactured by Kruse Prod-ucts Co. of LaMesa, Californi.a, was used to de-rust the 4130 steelspecimens. This product was selected because of its negligible etchingeffect on 4130 steel (Reference TN 8811).

In addition to the weight loss evalu-tion, the m gnesium and 4130 steelspecimens were visually exajined hnd rated after 1500 hours salt sprayexposure prior to the removal of paint and corrosion products.

RESULTS:

These results are based on 1500 hours exposure to salt spray on magnesiumand 4130 steel specimens only. Results are tabulated in Tables V, VI,VII, and VIII.

Performance of the potassium zinc clromate pigment was relatively rood inboth vehicles on magnesium and 4130 steel specimens.

There is no significant difference oetween the performance of the strontiumchromate and the potassium zinc chromute in the alkyd vehicle on eithermagnesium or 4130 steel specimens.

The overall 1 ~rformance of calcium chromate was almost as food as thepotassium zinc chromite.

Efficiency of the aarium chrom,te w!;s poor comp .red to tLe above t reeI~igments but much better th-n the zinc t troxychro', te except in t.ealkyd vehicle on 4130 stel s ,ecimnens.

Perforiance of zinc tetroxychro-m-te -j.Ls significantly poor in both Vehicleson magnesium alloy siecimens.

@1

FeOUM I*.IIA

ANALYsIs C 0 N V A I R PAGE 5PREPARED BY M4±us/ihidden A. OON, DAUU , REPORT NO. 56-264

CHECKED BY W. M. Sutherland SAN 01900 MODEL S -RIM'SED mY DATE 14-27-56

DISCUSSIO1. GF iUSbL'S:

in drawing conclusions from this data, it must be remembered that onlytwo alloys under an artificial exposure condition, namely ona-gnesim anid4130 steel alloys after 1500 hours salt spray exposure, are being considered.Results will be more significant after the completion of the exteriorexposure test.

Performances of the strontiw chrom.-te and calcium chromate were notexceptional enough on the tests completed to date to warrant substitution

Ifor potassium zinc chromnate in all primer formulations. Parhaps thesepigments may be used advantageously under conditions of high tempe.rature,acidic environment, or in cases wh re potassium zinc chromate is incom-pataole with the vehicle, such as in a-mine catalyzed epoxy primers.

a

Corrosion on the magnesium specimens coated with zinc tetroxychromatepigmented primers was of the concentrated cell type, indicating that therelative insoluble nature of this pigment may have something to do with itspoor performance. Zinc tetroxychronate is currently used in MilitarySpecificotion wash primers. The Paint Research Department of the Sherwin-Williams Company has found that substitution of strontium chromate,andsilicon dioxide as the pi.-mentation in -JL-C-15328A wash primer improved itsperformance on magnesium (Reference 2.).

RECOMbERNDAT IONS :

It is recommended that this study be continued until the exteriortxposuretst results become significant.

EFERFNXES:

1. "Tests on the Relative Efficiency of Chrotfte Pigments in iinticorrosivePrimers", by H. G. Cole, J. Appl. Chem., 5 May 1955.

2. "Protective Coatings for 1'gnesium", The Sherwin=Williams Company,WADC Technical Report 54-373.

NOTE: The data from which this report was prepared may be found inEngineering Test Laboratories Data Book # 979.

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ANALYSIS C 0 N V A I R PAGE 14PREPARED BYMppus/Whicdden A fIlIiON OY GINIRAL DYNAMICS CORPORATION REPORT NO. 56.-264CHECKED BY W. M. Sutherland SAN 01900 MODEL MRS 56-185REVISED BY DATE 12-27-50

w {lm -l

FIGURE L

SPECIMENS PLACED IN SALT SPRAY EXPOSURE RACK

ANALYSIS C 0 N V A I R PAGE 15PREPARED B Mappus/Whidden A DIVISION OF GINENRAL DYNAMICS CORPORATION REPORT NO. 56-264CHECKED BY W. M. Sutherland SAN DIEGO MODEL MS 56-185REVISED BY DATE 12-27-56

IMP,

-~~ ~ -- W_____________

FIGUe. 2

SPECAViS MOUNTED ON EXTERIOR EXPCSURE RACK

PORIM 1911-A