Anticorrosive Primers PIGMENTS AND VEHICLES APPLICABLE TO MAGNESIUM ALLEN L. ALEXANDER, HAROLD J. E. SEGRAVE, RODGER FRERIKS', AND J. E. COWLING Naval Research Laboratory, Washington, D. C.
T
HE rapid corrosion of magnesium in marine environments, together with a few lesser limitations, precludes the use of
this metal and its alloys for many possible structural parts, particularly hulls in naval aircraft. Possessing a much more favorable strength-weight ratio than aluminum, magnesium is potentially a n attractive structural metal. Much effort has been expended in the past t o increase the corrosion resistance of the light metal alloys to render them more suitable for such uses. The current investigation concerns the further development and adaptation of organic coating systems for impeding the corrosion of magnesium alloys. This paper describes the formulation and evaluation of a number of primers, gives data on t h e solubility of certain pigments in sea water, and discusses the effectiveness of these solutions as inhibitors of corrosion in magnesium alloys. Chemical surface treatments have increased t h e applicability of magnesium alloys, but developments in this direction have not yet reached a point where the application of organic coatings for additional protection is not imperative. Extensive improvements have been claimed through the use of certain anodic treatments (1, 2, 6, Y, IO) which deposit or cause t o be formed tightly adhering, insoluble compounds of magnesium on the metal surface. More recently, a spectacular development in this field has been announced by Frankford Arsenal ( 4 ) and is known as the RAE process. A hard, tightly adhering film is formed on the surface of the metal while the magnesium is suspended as the anode in a chemical bath. This film is fairly porous and requires the additional application of an organic material for optimum protection. Usually, organic coatings adhere better t o surface-treated alloys than t o the untreated metal. Although the prime coat aids adhesion of the finishing films, a major function is to provide a supply of inhibitive pigment near the surface subject to corrosive attack. Any pigment acting either chemically or physically t o improve the corrosion resistance of the metal may be regarded as inhibitive though the term is more commonly applied t o those pigments whose action is chemical. A popular conception of the mode of action is t h a t the inhibitor dissolves and, by its action from solution, prevents or moderates t h e resultant corrosive process. On the basis of such a concept, the gradual dissolution of the inhibitive pigment should leave void spaces in the matrix which should tend to accelerate the entire process. Practically, therefore, the life of the primer is limited b y its reservoir of corrosion inhibitor. Since complete exclusion of the corrosive medium from the metal surface has never been attained even with the most nearly impermeable organic materials, the inhibitive primer inevitably assumes a prominent role in combating the corrosion of magnesium and its alloys,
total chromate determined similarly, a measure of the chromate available t o sea water extraction was obtained. For these experiments a synthetic sea water was employed which has been proposed by May and Alexander (9). The concentrations of chromate ion developed in saturated sea-water solutions of the pigment, and the percentage of chromate ion in each of the pigments which is available t o extraction by sea water, are shown in Table I. Should the inhibitive action of chromate primers be ascribed t o this available chromate ion content, then those pigments making available the largest supply of inhibitive ion should prove the most protective. However, this does not always follow. Therefore, the process of inhibition is governed appreciably by other factors. I n order t o explore the protective qualities of these pigments, saturated solutions were prepared from them in sea water which, in turn, was used as a corrosion medium for chrome-pickled magnesium strips. This pickling treatment is the normal preparation prior t o coating with organic films. Panels of magnesium alloy J1H were prepared of such size that they could be coated on the edges and back to provide a n unencumbered surface on one side 1 X 3 inches in area. For each setof datain the accompanying tables, panels were exposed in triplicate and the values given are the average of three observations. For determining weight loss the panels were immersed in the solutions for the periods indicated, removed, and cleaned with solvents t o remove the wax coating. Next, they were boiled in 20% chromic acid t o remove corrosion products, washed, dried, weighed, and finally discarded. Blanks were run on panels not subjected t o corrosion in order t o correct for normal losses during the treatment. Therefore, for the lower values some discrepancies appear which in fact are not intolerable among data of this nature. The results of this experiment are listed in Table 11.
TABLEI. SOLUBILITYCHARACTERISTICS OF CHROMATE PIGMENTS IN SEAWATER
Pigment Barium chromate Barium potassium chromate Calcium chromate Strontium ohromate Zinc chromate Zinc chromium selenate Zinc tetroxychromate
1
Available Chromate (Ext.) of Pigment Total UnavailAvailchromate, able, able,
%
%
%
43.5 50.3 72.3 48.5 52.1 46.5 20.3
36.4 7.1 Nil 0.6 0.4 3.9 2.6
7.1 43.2 72.3 47.9 51.7 42.6 17.7
TABLE 11. CORROSION OF MAGNESIUM ALLQY
EXPERIMENTAL
PIGWENT SOLUBILITIES. The solubilities of selected chromate pigments in sea water were determined by shaking an excem of each pigment with sea water at 26" C. and determining the concentration of t h e chromate ion (Cr04--) b y means of a polarograph (8). Extractions of the pigment with sea water until the extracts were chromate-free, yielded residues whose chromate contents, determined by conventional titrimetric analysis, were reported as unavailable chromate. When subtracted from the
CrOd-Conon. in fjatd. Sea Water Grams) Liter 0.50 15.9 21.0 4.18 2.04 4.50 0.24
(In sea-water solutions of pigments-saturated pigment solutions) Days Exposure 5 12 21 27 41 Pigment Calcium chromate Barium potassium ohromate Strontium chromate Zinc tetroxychromate Zinc chromate Barium chromate Zino chromium selenate
Present address, Rimhed Mason Co., Detroit, Mich.
2409
10 15
17 23 25 29 58
Weight loss, mg. 17
20
45 79 64 36 235
30 23 56 110 121 69 412
21 26 69 88 148 178 519
18 57 115 169 183 298 67 6
Figure 1. Comparison of Alloys
after
Salt-Spray
Exposure Phenolic prime series
By comparing these data with Table I, it may be seen readily that n-hile calcium chromate caontains the largest percentage of available chromate ion and offers the greatest inhibitive action in solution, a similar relationship does not hold for all of the remaining pigments. Evidently factors other than chromate ion concentration are involved. I n these solutions, however, it was realized t h a t a wide variance in chromate ion concentration existed. Therefore, it appeared logical to dilute the saturated
TABLE 111.
C O R R O S I O X O F k~~4GNESIUR.I ALLOY
(In sea-water solutions of pigments-diluted pigment solutionea) Days Exposure ~5 12 21 32 Pigment Weight loss, mg. ~Barium chromate 16 51 95 70 120 17 39 73 Strontium chromate 142 27 39 Calcium chromate 67 156 133 99 38 Zinc chromate 164 44 96 Zinc chromium selenate 77 71 170 Zinc tetroxychromate 54 88 193 55 27 74 Barium potassium chromate 24s 47 136 188 None a
Vol. 44, No. 10
INDUSTRIAL AND ENGINEERING CHEMISTRY
2410
Chromate-ion concentration, 0.26 gram/litpr.
TABLE IV. TYPES OF C O R R O S ICAYSED O ~ ~ B Y SEA-WATER SOLUTIONS OF PIGPIEATS Multiple Perforations
Pigment
Large Spreading Anodic Pits
A. Saturated Pigment Calcium chromate Barium potassium chromate Strontium chromate .X. Zinc te troxyc hroma te X Zinc chromate X Barium chromate X Zinc chromium selenate X No pigment X B.
Solutions X X X X X
Diluted Pigment Solutionsa
Barium chromate X X Strontium chromate X Calcium chromate X Zinc chromate X Zinc chromium selenate X X Zinc tetroxychromate X X Barium potassium chromate X X a Chromate-ion concentration, 0.26 gram/liter
Attack on Face
Undermining Back or Edge Wax
solutions to contain similar concentrations of chromate ion, and t o re-examine their inhibitive tendencies in a similar fashion. The resuhs of this experiment are presented in Table 111. The types of corrosive at.tack and failure occurring in each instance are shon-n in Table IV. It is fairly interesting to note the relative high position of the chromates of calcium, barium, and Etront8ium followed quite closely by zinc. I n an experiment of this nature the values for each salt are so close relatively as to indicate little difference in their protective value. Therefore, all t'hree would appear as interesting possibilities in comparison to zinc yellow and zinc tetroxychromate, well established inhibitive pigments for the light metals, Referring to Table IV, the observation is significant, perhaps, that a t higher salt concentrations no undermining or removal of the wax backing on the panels was noted except in the case of zinc tetroxychromate and barium chromate which contain, by far, the loIvest available (soluble) chromate (Table I ) of the >severalpigments. This phenomenon might be explained by the observations of Kittleberger and Elm (6) that osmotic pressure is a factor in the remov-a1 of an organic film. Significantly, in the lower half of Table IV, involving the more dilute solutions, and therefore higher osmotic pressures, the wax coating was impaired in every instance. Should these observations prove difficult to correlate with service performance of primers prepared from them, it would indicate that the effect of the pigment cation cannot be discounted as evinced by the differences in corrosion rates observed when the chromate pigments were used as inhibitors a t equal chromate concentration in sea-lyater solution. The composition of the electrolytic medium which has penetrated the primer will usually determine the degree of corrosion of the magnesium alloy. To investigate this composit.ion seems a profitable, though difficult, project leading t o a comparison of inhibitive pigments under conditions approaching those in service. CORROSIOS RATEvs. ALLOYCOMPOSITIOS.It was recognized that even slight variations in the alloying constituents of the test panels could produce resu1t.s easily construed as differences in the protective qualities of the primers. Therefore, a. selected group of experimental formulations was evaluated, initially, over metal from three sources of slightly varying composition. This magnesium sheet conformed t o Navy specification 47M2 and i j usually designated FS-1H. The chemical composition and prior treatment, of t,he alloy is sho>T-nin Table Fi. From these analyses it is apparent, that source C provided increased amounts of several alloying elements. Possible significance of these differences may be observed from the data of Table VI, which lists performance results a t t'ide level for a series of primers based on alkyd resins applied on the t.hree alloys. Table VI1 lists data obtained from a series of phenolic primers exposed t o 20% salt spray for 28 weeks. In recording the rate of degradation of the film and panel, a system was used as proposed by Young ( I f ) in which a perfect panel rates 10, and one completely failed is rated zero. This same system is employed for subsequent data. The results of the
X
TABLEV.
X
X X X X
X X
X X
Recd. condition Designation Aluminum, % Zinc % nlaiganese, % Silicon, 55 Copper, 5 '0 Iron % Chrdrnium, % Nickel 3' % Magne'siuni. %
COMPOSITIOX OF ALLOYS
A Oiled FS-lh
2.78 1.11 0.47 0.01 0.008
0.002 None None Balance
B Chrome-4NC-52S pickleda 2.72 0.97 0.23 0 01
0 008 0.002 0 03 None Balance
C Oiled
FS-111 2.72 1.25 1.16 0.01 0.014 0.001 0.001 None Balance
a Boiledin potassium hydroxide aoiution, then given regularsealed chromepickle.
2411
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1952
35 and 60% in increments of 5%. Pigmentation was with zinc yellow and asbestine. Panels were finished with both Months Exposure Rfonthe E u o x u r e gloss lacquer and enamel and Panel 1 2 3 4 5 6 Final 1 2 3 4 5 6 Final Alloy No. Corrosion General appearancea exposed t o salt spray, tide 9 9 8 8 8 9 8 7 6 6 6 6 1 0 1 0 A 25-1 level, and Miami weather. 9 9 8 8 8 8 7 7 6 6 6 5 1 0 1 0 B 25-2 8 8 6 b 5 8 7 7 6 5 5 4 10 9 C 25-3 Few or no differences were 8 8 2 0 0 9 8 7 6 2 0 0 10 9 A 29-1 discovered from the atmos9 8 7 5 3 8 8 7 7 7 4 3 9 9 B 29-2 pheric exposures. The results 4 4 0 0 0 8 7 4 4 0 0 0 9 6 C 29-3 from the salt spray are listed 9 9 8 8 9 8 8 8 7 7 7 A 33-1 1 0 1 0 1 0 9 9 9 9 9 8 8 7 7 7 7 10 9 9 B 33-2 in Table VIII, and for tide 8 7 5 5 9 8 8 7 7 4 4 10 9 9 C 33-3 level in Table IX. 9 9 8 8 8 9 8 7 7 7 7 7 10 9 A 37-1 9 9 9 9 9 9 8 7 6 6 6 7 10 9 B 37-2 With reference t o P-V rela8 8 7 6 5 8 8 7 7 7 5 4 9 8 C 37-3 tionship, the only conclusion 1 0 1 0 9 9 9 9 8 9 8 7 7 7 7 7 A 41-1 that can be drawn is t h a t there 1 0 1 0 1 0 1 0 9 9 9 9 8 7 7 7 7 7 B 41-2 10 9 9 9 8 7 7 9 8 7 7 7 6 6 C 41-3 are no practical effects between 9 9 8 7 7 7 7 7 A 45-1 1 0 1 0 1 0 1 0 9 9 the limits investigated. The 1 0 1 0 1 0 1 0 9 9 9 9 8 7 7 7 7 7 B 45-2 4 8 8 7 6 5 b 4 C 45-3 9 8 7 7 6 b salt spray data, however, india Perfect panel rated 10. Completely failed panel rated zero. cate a decided preference for Removed from exposure racks because of signs of excessive corrosion. Top ooat, AN-E-3. a n enamel top coat over lacquer, whereas a slight trend in favor of lacquer is indicated salt spray test are augmented by Figure 1 in which the letters in the tide-level tests. In subsequent experiments no further A , B , and C refer to the three alloys. Figure 2 is a photograph attention was devoted to the pigment-volume relationship. of the panels removed from the tide level. It is obvious that VEHICLESTUDIES. I n addition to matrix studies already mentioned, a series of formulations wae prepared, based primarily comparable results may be obtained in using alloys A and B, on phenolic resins, in order t o study any minute differences in although some slight difference may exist in favor of B. From performance which might prove attributable t o inherent qualiTable V, it may be observed that alloy C contains appreciably ties resulting from variations in the substituent groups of thephegreater quantities of copper, manganese, andzinc, which obviously affect the alloy's corrosion resistance to a considerably greater nolic polymer. Similarly, other qualities such as variable oil degree than is obtained by wide variances in the quality of any length of the varnishes could be observed. I n the interest of of the applied organic coatings. On the basis of these data, maintaining the fast-drying feature, some phenolic dispersion alloy B was selected for future use in coatings-evaluation, PRIMERFORMULATION. The widely recognized quality of corrosion inhibition associated with the presence of chromate ion, and the possible influence of certain cations suggested a number of inhibitive pigments and salts, which in addition to those previously discussed, include magnesium sulfate, magnesium chromate, lead chromate, and lead sulfate. Previously, ferrous ammonium sulfate ( 5 ) had been proposed for similar application and was included for purposes of reference. In continuing experiments, soluble magnesium salts were investigated for use as additives or replacements, for the normally specified inhibitive pigment. Similarly, attention was directed to other factors such as selection of resin and pigment-volume relationships. Experiments were planned with a view toward studying each factor as it influences the role of the primer in the complete finish system. For purposes of evaluation, panels with the experimental formulations were exposed t o 20% salt spray a t 95' F. and a t tide level in Biscayne Bay, Fla. I n recording the rate of degradation, the system described above was used, augmented by photographic evidence. PIQMENT-VOLUME RELATIOKSHIP. In order to study the reFigure 2. Comparison of Alloys afeer Tide-Level Exposure lation of pigment to volume, a series of primers was prepared in a tert-butylphenolic vehicle in which the P-V ratio varied between Alkyd primer series OF ALKYDSERIES TABLE VI. ALLOYCOMPARISON
Tide-Level Exposure
OF PHENOLIC SERIES TABLEVII. ALLOYCOMPARISOPI'
Salt Spray E x p o s u ~ Panel NO.
Top Coat
P-2 P-8 P-24 E-3 P-30 P-31 E-3 P-35 E-3 E-3 P-36 Average final reading
4
8
12
10 10
10 10 10
8 9 9 10 8 9 9
10 10 10
10
10 10
10
10 10
16 20 Alloy A
24
28
Weeks Exposure 4 8 12 10 10 10
10
10 10 10 5.8
10 10 10 10 10 10 10
16 Alloy B 10 9 10 9 9 9 9 10 9 10 10 10 10 10
20
24
28
4
8
10 10
10
10 10 10 10
10 7.5
7 9
10 10
10 10
12
16 20 Alloy C
24 5
2
5 6 4 4 5
28 5
0 2 5 0 0 0
1.7
VOl. 44, No. 10
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2412
Salt-mrav and tide-level ex~" posure developed little or no discernible difference among Salt-Spray Corrosion Weeks Exposure Weekc Exposure the alkyd primers. The Pigment8 12 16 20 24 28 pane] 4 8 12 16 20 24 Panel Volume, over-all resistance of the alkyd NO. % Lacquer top coat __ NO. Enamel top coat primers used under high-alkyd PP-38 10 10 ..8 .. 10 10 35 PP-16 resin lacquer and alkyd resin 39 6 10 10 10 10 17 40 6 40 10 10 8 10 10 18 45 enamel was somewhat superior, 41 5 10 10 10 5 10 19 50 42 4 IO 10 7 10 10 20 55 indicating that alkyd top coats 10 6 43 10 8 10 10 60 21 are perhaps substantially more compatible than when applied TABLEIX. PIGMENT-VOLUMESTUDY over phenolic primers. Tide-Level Corrosion ________ Experience has indicated Months Exposure PigmentMonths Exposure__ that, in addition to the influpanel Volume, 1 2 3 4 5 6 Finala panel I 2 3 4 5 6 Final' KO. % Lacquer top coat NO. Enamel top coat __ ence of a n inhibitive ion, the 35 10 10 10 10 10 9 9 38 10 10 9 9 9 8 8 role of the cation cannot be 10 10 9 9 9 8 8 10 9 9 39 10 10 10 10 40 17 l6 ignored. T h e r e f o r e , i t a p 9 40 10 9 Y 9 9 8 8 10 9 10 10 10 10 45 18 1 0 1 0 9 9 9 9 8 10 9 9 41 10 10 10 10 50 19 peared logical t o prepare a 9 42 10 10 10 9 9 8 7 9 9 9 9 55 20 10 10 8 43 10 10 I0 10 10 9 9 9 8 10 10 9 9 60 21 number of formulations to a Panel rated upon return t o laboratory. which soluble salts had been added, to replace, on a volunre basis, part of the usual inhibitive pigment. The formuh for the basic primer is shown in the table below: resin was included in most cases. A series of pure and modified alkyd vehicles was formulated, in which some dispersion resin Constituent VoIume Weight W&B retained. Formulation data for these primers are shown in Zinc chromate 1.00 604 Tables X and XI. A number of vinyl and acrylic primers were Asbestine 0.21 90 also prepared and evaluated without the additional treatment Phenolic varnish 2.19 600 with wash primer now considered imperative for use with vinyls. Dispersion resin 0 55 212 Aluminum stearate (10% gel) 72 These results were disappointing. Cobalt drier 0 1:3 The results from the salt-spray test of phenolic primers are Lead drier 1 .I listed in Table XII. Although these data might show some slight Xylene *isrequired advantage in favor of the 25-gallon p-phenylphenol varnish, they In the formulations given in Tables XIT' and XV, the mngneare not conclusive. However, phenolic vehicles do compare sium salts replaced an equivalent volume of zinc yellon-. All favorably with existing standards which, of necessity, contain panels were finiqhed with light-gray nitrocellulose lacquer (AXconsiderable amounts of fast-drying alkyds. Similar data for 2~21)as top coats. The standard primer served as control. tide level exposure, Table XIII, show some advantage for the These tide-range data indicate a very slight advantage in the phenolic vehicle even though the difference is slight. The use of pigmentations containing some added magnesiumchromate. matrix, based on tert-butylphenolic vehicle, was considered to The higher numerical ratings shown in the case of magncsiuni possess sufficient merit t o warrant further study, and subsequent pyrophosphate and magnesium fluoride may be due in part to experiments have substantiated this view.
TABLE VITI. PIGMENT-VOLUME STUDY
I -
~~
T.4BLE
o r PRIMERS, PHENOLIC SERIES TABLE X. COAXPOSITIOS 15-Gal.
Panel No.
PP-1 2 3 4
5 6 7
8 9 10
11 12 13 14 15
16
17
18
19 20 21 22 23
Zinc Yellow or Other Yellow Pigments, Grams Control 550 588 590 576 660 692 601d 580e 644d
625e 3151 345d,/ 5508
286h 629 698 753 814
872 900 465 i Control
p-Phenylphenol 25 gal. * tmt-Butylphenoi, 25 gal. a-PhenulDhenol. 15 gal. C
d 6
Strontium chromate; Zinc tetroxychromate.
Panel
trrt._-
Butyl Phenol Resin (Or as Excepted), Grams
Asbestine, Grams
..98
so.
PA-1 DisperRion Resin, Grams
640 634 624
632 632 654
96
319
Liz
614 587 483 442 380 324 633
125 135 145 156
161 111
J'
2 3 4
..
6
3
(81 196 197 192 437 442 181 180 197 194 178 178 181
e'i4 660a 634 664C ,290 061 654
105 106 103 118 124 98 96 105 103 95 95 98
10% Alummum Stearate, Grams
178 157 137 118 105 90 175
..
78 84 84 82 94 100 78 77 84 83 76
76 78 0.5i 90 100 108 116 125 129 84
Plus 138 grams Impedex. Zinc chromium selenate. Zinc dust 72 grams zinc oxide. i Manganese naphthenate. 1 Zinc yellow 109 grams eino oxide.
0
h
+
+
8 9 10
11
XI. COMPOSITION O F PRIMERS, ALKYDSCRlEb Inhibitive Pigment, Grams 448Q 483C
492; 451 464G
507
464;
467 461a 504c
13 14
407; 461 4Wa 533c
16
526d
12
16 17 18
4886 516: 564
19
20
542d 5168
21 22
448"s i 464
24
488
23
461
25-27 Control a Zinc yellow .\fed. Con& mod. a l k y d Strontium chromate. d Ziac tetroxychromate e Zinc chromium selenate.
Bsbestine, Grams 80 80 82 80 83 83 83 83 82 82 82 82 87 87 87 87 08 95 92 95 80 83
Alkyd Resin, Grams 702 70 2 715 70 2 7041' 704 704 70 4
9220 822
822 822 788h 788 788 788
656 L 6j6 641 656 702 704f 8220
82
778h
87
lo!% Dispersion Alummuin Resin, Stearate, Grama Grams 161 64 161
163 161 166 166 166 166 165 165 165 165 175 175 175 175 190 190 185 190 161 166 165 113
64
65 64 66
66 66 66
66 66
66 66
70 70 ?O
70
76
76 74
76 64 66 66 70
f Med. oil plus phenol mod. alkyd.
Med. short alkyd. Phenol mod. short oil alkyd. Linseed nhort oil mod. alkyd. i Contains 1.6 grams maleic acid.
@
tb
i
October 1952 the presence of slightly greater film thicknesses. Particularly surprising, however, was the relative performance of magnesium chloride and sulfate, in view of the well-recognized effects of chloride and sulfate when present as impurities in zinc yellow. In general, these phenolic primers, including the blank (no soluble salt added), compare favorably with the controls (AN-TT-P-656). Based on the salt-spray data, the experimental primers all show some merit, and the addition of all salts, with the exception of magnesium sulfate, provided either equivalent or improved performance compared with the control. While no attempts have been made to explain the mechanism of the action of these salts, i t is tempting to speculate that magnesium chromate supplies a h i g h e r c o n c e n t r a t i o n of chromate ion, although its action is not overwhelmingly superior to other magnesium salts which provide no inhibitiveions. If some reaction between the magnesium metal and the corrosive solution occurs, perhaps the prior presence of magnesium ion in solution would tend to retard this action. A d d i t i o n a l e x p e r i ments are planned to elucidate these interesting observations. CONCLUSIONS
During the course of investigating anticorrosive primers for magnesium, the solubilities of a number of inhibitive pigments in sea water were explored, and their inhibitive properties toward the c o r r o s i o n of m a g n e s i u m studied. The chromates of calcium, barium, and strontium rate highly and compare favorably with zinc yellow and zinc tetroxychromate in this application. Evidence is presented t o indicate that slight metallurgical differences in magnesium-alloy composition vastly outweigh, and are capable of masking completely, difference arising from organic coatings of widely varying composition. Pigment-volume r e l a t i o n s h i p s over normal ranges, in the type of systems studied, are of little significance. All phenolic matrices
INDUSTRIAL AND ENGINEERING CHEMISTRY
2413
TABLE XII. SALT-SPRAY EXPOSURE OF PHENOLIC SERIES Panel No.
Primer Zinc chromate primer control 16-Gal. tert-butylphenolic vehicle 25-Gal. p-phenylphenolic vehicle 25-Gal. tert-butylphenolio vehicle 15-Gal. p-phenylphenolic vehicle As PP-2 with twice the disp. resin 4 s PP-4 with twice the disp. resin Zinc dust and zinc oxide in 15 gal. tert-butylphenolio vehicle Spec. AN-TT-P-655b control
4
P-1
Weeks Exposure 8 12 16 20 24 28 Panel Gloss lacquer top coat No.
10 10
9 8 8 8 7 7
8 7
P-2 P-3 P-4 P-5 P-6 P-7
10 10 10 10 10
P-15 P-46
Failed in 2 weeks 10 9 8 8 8 8
9
10
7
7
10 10 9 8 8 7 8 9 9 9
9 10 10 10
8 8 9 9
8 8 6 8 8 7 9 9 8 9 9 6 7
4
8 12 16 20 24 28 Gloss enamel top coat
10 10 10
9 9 9 9 9 9 8 8 8 5 7
P-23 P-24 P-25 P-26 P-27 P-28 P-29
10 10 10 10 9 8 8 10 10 9 8 8 10 10 9 7 6 6 10 8 8 7 10 9 8
P-37 P-45
Failed in 3 weeks 10 10 9 8 8
10
9
10
8
.. 7 7
6
7 2 7 8
TABLE XIII. TIDE-LEVELEXPOSURE OF PHENOLIC SERIES. CORROSION Panel No.
Primer
Control zinc chromate primer P- 1 15-Gal. tert-butylphenolic vehicle P-2 25-Gal. p-phenolic vehicle P-3 25-Gal. tert-butylphenolic veP-4 hicle 15-Gal. p-phenolic vehicle P-5 As PP-2 with twice the disp. resin P-6 As PP-4 with twice the disp. P-7 resin Zinc dust and zinc oxide in 15 tert-butylphenolic veP-15 DuPont spec. AN-TT-P-65613 P-46
g;Le
1
Months Exposure 2 3 4 5 6 Final" Gloss lacquer top coat
Panel No.
1
Months Exposure ~ i 2 3 4 5 6 n a l Gloss enamel top coat
9
P-23
10
10
9
9
9
10 9 9 10 10 9
P-24 P-25
10 10 10 10 10 10 10 10
9 10
9 9
9 9
10 10 10 10 9 10 10 10 10 9
P-26 P-27
10 10 10 10
10 10
10 9
10 9
10 8
P-28
10
9
9
8
10 10 10 10 10 10
10 10 10
9
9
9 9
5 2 0 10 10 10
9
9
9
10
10
10 10
10 10 10
9
P-29
10 10 10 10
0 0 9 9
P-37 P-45
5 2 10 10
9
0 10
0 9
10 10 10 0 9
0 9
0 9
TABLE XIV. TIDE-RANGE EXPOSURE RATINGS O F MAGNESIUM SALT SERIES NO. MS1 S
v
2 MS3 MS4 MS5 MS6 MS7 MS8 MS9 MSlO MSll MS12 MS13 MS14 MS15 MS16 MS17 MS18 MSl9 MS20 MS21 MS22 MS23 MS24
MS25 MS26 MS27 MS28 MS29 MS30 MS31 MS32 MS33 MS34 MS35 MS36 MS37 MS38
Salt Replacing Pigment None Magnesium chromate
Magnesium-chloride Magnesium sulfate Magnesium ammonium phosphate Magnesium oxide Magnesium carbonate
Ma nesium paate
Magnesium fluoride
Magnesium silicofluoride Magnesium ammonium chromate
MSC AN-TT-P-656b a
pyrophos-
1 3 5 10 15 20 25 1 3 5 1 3 5
Primer Thickness Mils' 0.5 0.5 0.6 0.6 0.6 0.7 0.7 0.8 0.7 0.7 0.7 0.5 0.5 0.5
5 10 20 5 10 20 5 10 20
0.6 0.5 0.6 0.6 0.6 0.7 0.6 0.9 1.1
8.5 8.5 8
5 10 20 5 10 20 30 40 50
0.9 0.9 0.9 0.9 0.8 0.8 0.9 0.7
9 8.5 7.5 8 8.5 8 8.5 8.5 7.5a
1 3 5
0.8 0.7 0.8
1 3 6
0.9
Added Salt Vol.
%
..
0.9
1.0 0.6
2 8.5 8.6 9 9 9 9 9 8.5 80 9 9 9 8.5
Months Exposed (Average of Duplicates) 4 6 8 10 12 Final 8.5 8 8 8 8 7.5 7 7.5 7.5 7.5 8 8.5 8 8 8 9 9 9 8 8 8.5 8.5 9 9 7.5 8 8 8.5 9 9 8 8 8 8 9 8.5 7.5 8 8 8 8.5 9 7.5 8 8 8 8 8.5 7.5 7.5 7a 6.5 6.5 6.5 8.5 8.5 8 8 7.5 7.5 8 6.5 6 6 5.5 5.5
9
7.5 7a 7"
7"
8.5 8.5 8 8.5 8 8.5 7 9 9
7.5 85 8 8 8 8 7 8.5 8.5
7;s 7 7.5 7.5 8 7.5 7 7.5 8
7 8 7.5 7a 7.5 7.5
9 8 7 7.5 8.5 8 8.5 6.5a
9 8 7 7a 8 8 7.5a 8.5 6.5"
8 7.5 6 6.5" 7.5 7 7" 8 6.5=
7.5 755 6 54 7.5 7 7" 8 6.5'
8.5 8.5 8.5
8.5 8.5 8.5
8.5 8s
7.5 7.5 7.5
7.5 7.5 7.5
6
8"
9 8.5 8 6.5a
9 8.5 8" 6a
8.5 8 7" 6"
7 7.5 6" 6"
6a
7 7.5
6.5 7 5.5a 5
8.5 8 8.5 7.5 9 9
sa
Numerical ratin of duplicate panels differed by two o r more units. Exposure racks 8estroyed in hurricane; panels recovered for final rating.
5a
6.5 6.5
6 7
7 Baa
b
6 5.5a 7 6 6 6'
7 7.5
7 7.5 5.5 4.5 7.5 7 6a 7 6.50 7 6.5
INDUSTRIAL AND ENGINEERING CHEMISTRY
2414 TABLE XV.
RATINGS OF
SAL'I'-SPRrlT
Added Salt ,
NO.
MS1 M 52 M 53
Salt Replacing Pigment Xone Xlagnesinm chromate
LIS4 AIS5 MS6 MS7
AIS16 LIS17
MS18 MS19 MS20 hlS21 MS22
LIS26 MS27 hIS28 LIS29 MS30 MS31 LIS32 LIS33 hIS34 NS35 MS36 MS37 MS38
1 3 .5 IO
15 Magnesium chloride Magnesium sulfate Magnesium ammonium phosphate Magnesium oxide Magnesium carbonate Magnesium pyrophosphate Magnesium fluoride
0.6 0.6 0.6
1
0.5
3 .5 10 20 5 10 20 >
5
0.8 0.8 0.9 0.7
10 20 J
10
40
.in 1
3 5 1
3 5
MSC AN-TT-P-656b
0.7 0.5 0.6 0.6 0.7 0.6
0'.9
30
Magnesium atnmoniurn chromate
0.6 0.5
10 20
PO
Magnesium silicofluoride
0 5 0.3 0.7 0.6 0.8 0.8 9.5
1 3 5
3
MS23 MS24 LIS25
..
20 25
>IS8
MS9 LIS10 MSll MS12 nisi3 MS14 RE315
5%
Val.
Primer Thickness, Mils 0.6
1.0
0.7 0.7 0.8 0.8 0.7
havior of inhibitive primers for magnesium
hlAGNBSITJY SALT SERIES
4CKNOWLEDGMENT
Weeks Exposed (Average of Duplicates) 8 16 24 28 Final
4
8.5 7 3 9 9 9
9.n 8.5 9.5
8 10
9.5 8.5 6.5
8
9.5 8.5 8 8.5 9.5 1 0
7.5 7.5 8 8 8 8.6 8 5 8 8 9.5 9.5 8.5
0.8 0.8 0.9
0.5 9.5
0'.a n.9
8.5 9 7.ba
0.5
7.5
9
8
7
8 7.5
8 7 7.5
6" 5.5a 7a 7.5 5 7' 6.5 7
8
7 7
8 9 9
8.5 8
6.5 8.5 8
8
6
6
8
!a5
8.5 8.5 8 7.5 8.5 9 8
8.ja 8 8 9,s ga 9.5 8;s 8.~5~ 8 10 8a 9.5 8 9 9 Sa 8.ja 9.5 9 10 9.5 8.Sa
8.5 9.5
6' 5.5Q
9.5
;:! 9" 8.5 8 7.5 8.5
7.5 7"
7
$ 8'L
7a
6,s 5.5 5.5
5.5 1
5.5
7.5 7 8 7 8.5 9
7.5
6 6.5
6.5
7 6
6a
8"
8.5a
6a
7 7.6
Sn
7.5 7 7.5
6
1.5
7 7.5 7.5 7 7.5 6.5 7.5
6.5 ii5
ha,> 8 7.5 7 8"
6
8.5 8
Sa
8.5 Sn 7.5 8.5
8 7.5 7 8"
8.5 8.5 7R 6
7.5 8 7a 6
7 7.5 6a 5
.
7.5
7.5 7
7 8 7.5 7.5 7.5 7.5 7
€ia
6 5 4" 6"
4"
6 5 6.5 6"
Vol. 44, No. 10
!..?
7" 7 5 7
7 6 7.5
6,s i.Sa 8 8
7.5 7
7 5
7 7.5
6 5
E"
Ea
5
sa
7
Numerioal rating of duplicat,e panels differed b y two or more unit-.
~
The authors are particularly grateful t o Fred Arndt and J. Allan Suther for their suggcstions and contributions in preparing a number of the E o r 1x1 u 1 a t 1o n P and exposure panels in the course of the work. LITERATURE CITED
(1) Buzzard, R. W., U. 5. Patent 2,414,090 (Jan. 14, 1947). (2) Delong, FI. K., Can. Patent 441,879 (June 3, 1947). ( 3 ) Erskine, A. hl., et al., INU. ENG. CHEM., 36, 456 (1944). (4) Evangelides, H. A , , 0 ~ g . Finishing, 10, 17 (1951). (5) Frasch, ,I:, Brit. Patent 571,271 (Aug. 17, 1945). (6) Kittleberger, W. TV., and Elm, A. C., IND.ENQ. Cami., 39, 876 (1947). ( 7 ) Kohl, A. L., and Watermail, E., I w n Age, 161, 50--5 (1948). ( 8 ) Kolthoff, I . M . , a n d Lingane. J. J.. "Polaroxrnphy,"' p. 292, New York, Intersoience Publishers, 1941. (9) May, T. P., and Alexander, A. L., Am. Soc. Testing Materials, Proc., 50, 1131
(1950). (10) Waterman, H., U. 8. Patent
perhape have mnie advantage over currently specified vehicles but their use is limited by drying requirenient,a. An investigamagnesium saltsJ particularly the Of the "le Of chromatep, appears promising for further elucidating tlhe be-
2,426,254 (Aug. 26,1947). (11) young, G . H., at nl., IND. ENG.CHX~LI., 39, 876 (1944). RECEIVED for review January 2 6 , 1952. ACCEPTED M a y 15, 1952. Presented before the Division of Paint, Varnish and Plastics Chemistry the m i s t hfeeting of the ANERICAV CHEXICAL SOCIETY, Milwaukee, Wir.
li
e
W, A, HARRIS, L. W. NORMAN, J. H. TURNER, H. F. H-kKEY, IYD R. €I. C O W O N Holly Sugar Corp., Colorado, Springs, Colo.
URIXG a study on the recoveiy of crystalline sumow from the juice of the stalk of the sorgo plant (Sorghum vulgare, Pers.) a negative correlation was observed between ease of boiling and the concentration of akoho~-insolublematerial in the boiling stock (6). Sherwood ( l a ) and Willaman and Davison (18) have sho-m that starch is the principal constituent of the so-called gums n-hich inhibit crystallization of sorgo juicee. Furthei more when a defecated, concentrated sorgo juice was difficult to boil, the enzymatic hydrolysis developed by TTdton and Ventre (16) effectively incremed the ease of crystallization or "boiling" while resulting in a lowering of the concentration of methanolinsoluble material in the juice. The present study indicates that the offending ciystnllization inhibitor, in thip case, n-as not
starch alone but, also another gum. A somewhat similar y u i u was isolated from a sample of beet molasses. Vork in this laboratory (6) on crystallization of sucrose from sorghum differed from earlier work (15)primarily because the juice was extracted from sliced chips from t'he stalk by diffusion rather than by conventional cane-crushing methods, though this was euggested as early as 1883 by X l e y ( 1 7 ) . With sorgo, crusliitig results in a high concentratJim of starch in the juice (several per cent); m-ith diffusion the concentration is low. I n the ca5c of beets the juice is, of course, obtained by diffusion, and thc guni tests negative for starch. Purposes of the preseut study m r e ( € ) to study further the effect of gums from sorgo and beets on sucrose crystallization rates; ( 2 ) to examine the effects of various enzymes on t,he gums
