INDUSTRIAL AND ENGINEERING CHEMISTRY
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tures, or whether there might be an actual change in behavior a t different temperatures. Acknowledgment Thanks are due the R. T. Vanderbilt Company for their kindness in permitting the use of their machine for the compression tests, and to L. A. Edland, of the same company, for valuable assistance in making these tests.
Vol. 23, No. 6
Literature Cited (1) Boggs and Blake, IND.END.CHEM, 15, 224 (1926). ( 2 ) Ingmanson and Gray, I n d i a Rubber W o r l d , 83, 53 (1930).
i:;
~ ~ ~ ~ ~ ~ a ~ ~ e ~ ~ ~ ( 5 ) Scott, I n d i a Rubber I ~ s ~6,95 . , (1929). ( 8 ) Williams and Kemp, J . Franklin Inst., 209,35 (1927). (7) Winkelmann and Croakman, IND.ENG. CHEM.,22, 1367 (1930).
~
The Ammonium Carbonate Treatment of Polyhalite' John R. Hill and J. R. Adams FERTILIZER AND FIXEDNITROGEN INVESTIGATIONS, BUREAUOF CHEMISTRY A N D SOILS, WASHINGTON, D.
c.
The discovery of extensive deposits of the potash and give a solution containsaline mineral polyhalite, a triple sulfate of potassium, eral, polyhalite, is a ing the potassium sulfate, tocalcium, and magnesium, in recent explorations in triple salt, 2CaS04gether with considerable amTexas and New Mexico establishes that mineral as an MgSOa.KzS04.2Hz0,containmonium sulfate.and any unimportant potential source of agricultural potash. ing in the pure state 45.2 per precipitated m a g n e s i u m as While theoretically it should be possible to extract the cent CaS04, 19.9 MgS04,28.9 magnesium sulfate. The prepotash from this mineral by leaching with water, in Kz804, and 6Hz0. It usually cipitated magnesium would practice this is not possible without special heat treatcontains, however, sodium occur as a normal carbonate, ments, owing to the presence of the calcium sulfate. and small amounts of iron, basic carbonate, or d o u b l e The elimination of this contaminant is therefore dealuminum, and silica as imsalt with ammonium carbonsuable, and it has been shown in the Bureau of Chemispurities. ate, depending upon the relatry and Soils, that if the polyhalite is leached with Attention has been drawn tive concentrations of carwater solution of ammonia and carbon dioxide, not to polyhalite as a commercial bon dioxide and ammonia. only is the calcium eliminated but also the magnesium, source of potash by the disThe magnesium carbonates yielding a concentrated solution of potassium sulfate. covery of apparently extenare rather soluble, especially The calcium and the magnesium being precipitated sivedeposits in the southin the presence of ammonium as the carbonates, there remain in solution the correwestern oil fields, particularly salts. Thus, from the chemisponding amounts of ammonium sulfate. The prodin western Texas and southcal side, the problem is one ucts are therefore two well-known fertilizer ingredients, eastern New Mexico. These of determining the conditions potassium and ammonium sulfates. for the minimum solubility of deposits are found a t depths ranging from 700 to 2200 feet these magnesium carbonates. The material used in these experiments, obtained through and are interspersed with recurring strata of halite (NaCl) and anhydrite (CaS04). The salt beds were discovered inciden- the courtesy of the Bureau of Mines, was light red and gave tally in drilling for oil in this region, and most of the informa- the following analysis. The theoretical composition of the tion concerning them has been obtained by analyses of brines compound is given for comparison. from the wells and samples from core drillings. Exploratory ANALYSIS THEORETICAL work in this field is being carried out jointly by the United % % States Bureau of Mines and Geological Survey. CaO. . . . . , . . . , 17 29 18.6 M g O . . . . . . . . . 6.28 6.6 The Bureau of Mines (3) has developed a process for the K?O.. . . . . . . . . 11.66 15.6 SOS., . . . . . . . . . 51.47 53.2 treatment of polyhalite based on calcination a t 44C-450' C. H2O.. . . . . . . . . 4.82 6.0 followed by leaching with water and the subsequent recovery Na2O.. . . . . . . , .. 4.60 96.12 100.0 of potassium and magnesium sulfates. When mixed with water without any previous treatment, polyhalite is dissolved slowly and with difficulty because of its high percentage of The sample also contained small amounts of iron, aluminum, calcium sulfate, which is only slightly soluble. Moreover, and silica. part of the calcium sulfate going into solution a t the beginning Solubility of Magnesium Sulfate of the operation subsequently recrystallizes as gypsum on the The following factors were found to affect the completeness surface of the undissolved material, and this coating increases further the difficulty of solution. Thus, while the potash in of the reaction: time of stirring, size of material, and conpolyhalite is theoretically water-soluble, actually special centration of carbon dioxide and ammonia. The data given treatment is required to obtain it in solution. In working in this paper are for experiments all of which were made at out the process mentioned above, the Bureau of h h e s has room temperature. The procedure used was to add to a found that after calcination the calcium sulfate no longer weighed sample, usually 1 gram, of pulverized polyhalite a interferes and the rest of the material dissolves very readily. measured volume of the ammonium carbonate solution. The object of the present work was to investigate the The mixture was then agitated on a motor-driven stirrer for a possibility of using a solution of ammonium carbonate for definite length of time and filtered through a dry filter paper. extracting potash from polyhalite. This reagent should A measured portion of the filtrate was taken for analysis. remove the calcium and some of the magnesium as carbonates This method had the advantage of not requiring any washing of the precipitate. 1 Received September 22, 1930: revised paper received April 1, 1931. Table I shows the variation in apparent solubility with time Presented before the Division of Fertilizer Chemistry at the 80th Meeting of of stirring for several ranges of particle size, as indicated by the the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930.
HE potash saline min-
T
~
,
2
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
June, 1931
quantity of sulfate present in the filtrates from the reaction mixtures. Since all the sulfate ion must come from the polyhalite, these figures are a measure of the extent of reaction or apparent solubility. The solution used in the extraction was 1.3 molal and was made from commercial ammonium carbonate. The results show that the reaction proceeds very slowly after 3 hours, when a little more than 90 per cent of the sulfate has dissolved. Table I1 shows similar data for samples of different sizes of particles. During the first half hour of shaking the unscreened material dissolves more rapidly than the material ground to pass a 70-mesh sieve. This is due to the presence of fines in the unscreened material. Table I-Variation i n Apparent Solubility with Time TIWE 70 MESH 150 MESH UNSCREEUED Hours % % % 80 6 63 0 '/4 51 8 73 5 71 9 84 0 I/¶ 1 87 1 85 3 84 0
2 3 4
87 4 93 1 93 5
89 8 90 7 92 3
87 6 91 1 91 5
Table 11-Variation
i n Apparent Solubility with Sizes of Grains Time, 1/2 hour SIZEOF GRAINS SOLUBILITY Mtshes p e r rnch %
71:9 72.0 78.1 84.0 73.5
In Table I11 the magnesium sulfate content after extraction is given for solutions of various initial concentrations of ammonium carbonate. The filtrate from the reaction mixture was first boiled to remove the excess ammonia and ammonium carbonate, and magnesium was determined as the pyrophosphate. These figures show that ammonium carbonate alone precipitates only a small amount of magnesium. But it will be seen from Tables IV, V, and VI that the addition of ammonia aids greatly in making the precipitation more complete. Table 111-Effect of Concentration of A m m o n i u m Carbonate Time of extracting, 3 hours; weight of sample, 1,000gram; total volume of solution, 100 cc. MgSO4 MgSO4 REMAINING ("4) nCOr SOLUBILITY I N SOLN. Grams/lOO cc. Gram/100 cc. % of cola1
10.6 2.67 1.10 0.86 0.71 0.63 0.55 0.24 Table IV-Effect
0,125 0.106 0.104 0.113 0.115 0.119 0.118 0.141
66.6 56.5 55 4 60.3 61.3 63.5 62.9 75.2
of A m m o n i a Concentration
Total volume of solution, 50 cc.; (NHI)ZCOJ,10 cc. (1.34M ) ; weight of sample, 1.000 gram; time of extracting, 3 hours MgSOd MgSOd REMAINING a"
Grams 0 2 5 5 0 75 10 0
SOLu BILI TY
Gram/100 cc. 0 0945 0 0658
0 0739 0 0662 0 0656
IN
SOLN.
% of total 22 5 17 5 19 6 17 7 17 5
The system magnesia-carbon dioxide-ammonia-water has been studied by Lafontaine (1). He has determined the composition of various equilibrium mixtures and the solid phases in contact with them at 30" C. From his data the basic salt 4MgC03.Mg(OH)2.4H~0appears to be the least soluble of the magnesium carbonate compounds. But it was found that magnesium is not removed very effectively from the polyhalite extracts with the concentrations of ammonia and carbon dioxide given for the point of minimum solubility of the basic carbonate. This is undoubtedly due to the presence of other compounds, especially ammonium salts. The double salt MgCO~.(NH4)&03.4Hz0 also has a low
659
solubility. Lafontaine's data show that its lowest solubility is reached when the four components, in the order named above, have the mol ratio 0.006 : 1.593 : 10.38 : 100, respectively. And from this ratio, 0.006 mol magnesia to 100 mols water, the solubility is calculated to be 0.0400 gram magnesium sulfate per 100 grams water. Under the same conditions at room temperature (20-25" C.) the solubility will be somewhat lower. The equations for the probable reaction of ammonium carbonate on polyhalite in aqueous solution are: Cas04 (NH4)zCOs +CaC03 (NH&SO4 MgSOi 2(?SH4)2C03 4Hr0 +MgC03.(NHa)zCOa.4HzO+ ("4)zSOd Therefore, 1 gram of polyhalite which contains 0.00309 mol of calcium oxide and 0.00157 mol of magnesium oxide will require 0.00623 mol of carbon dioxide for complete reaction. This is equivalent to 0.489 gram of the compound SH4HCOsSH4C02NH2. Lafontaine's data show that the solubility of the magnesium ammonium carbonate is lowest in the presence of a solution containing 7.6 grams of ammonia and 6.94 grams of ammonium carbonate carbamate (NH4HCO3.NH4COZNH2)per 100 cc. of solution. This excess is added to the 0.489 gram required for the reaction.
++
+
+
Table V-Solubility of Magnesium Sulfate from Polyhalite in A m m o n i u m Carbonate Solutions Time of shaking, 1 hour, total volume of solution, 50 cc. MgSOi WT. OF MgSOd REMAINING (NH4)zCOa NHs SAMPLE SOLUBILITY IN SOLN. Grams Grams Grams M g . / l 0 0 cc. % of total
3.00 3.95 4.50 5.00 4.00 4.00 4.00 4.00 4.00 4.00 4.00
3.8 3.8 3.8 3.8 2.5 3.8 5.0 6.3 3.8 3.8 3.8
1,000 1.000 1,000 1,000 1.000 1,000 1.000 1.000 4.00 7.00 10.00
14.3 11.5 10.5 11.0 11 0 8.6 7.8 8.0 8.0 10.6 15.3
3.8 3.1 2.8 2.9 2.9 2.3 2.1 2.1 0.5 0.4 0.4
Table V presents the results of the runs made on the basis of the figures given above and shows the effect of varying the amount of ammonium carbonate and ammonium hydroxide used in the extraction. In both cases it is seen that the calculated amounts are most practicable in the elimination of magnesium from the solution. Increasing the amount of ammonia above 4 grams decreases the solubility of magnesium sulfate slightly, but not sufficiently to be of any value because the presence of ammonia also decreases the solubility of potassium sulfate. Also, small variations in the solubility of magnesium sulfate are not very significant because of the comparatively low accuracy in the quantitative determination of such small amounts and because of variations in room temperature. Recovery of Potash
AMMONICM C A R B O N A T E - ~ ~ ~ ~ M O NTREATMENT-hne IA experiments were also made to determine whether solutions shaken with polyhalite would approach saturation with respect to potassium sulfate. For this purpose a solution containing amounts of ammonium hydroxide, ammonium carbonate, and ammonium sulfate corresponding to those resulting from an actual extraction was saturated with potassium sulfate, after which it contained 5.43 grams potassium sulfate per 100 cc. Portions of this solution were then diluted by varying amounts, as shown in column 1 of Table VI. These solutions were shaken with an excess of polyhalite and then analyzed. Potassium was determined by the perchlorate method. After 2 hours' shaking the solution, 70 per cent saturated, approached very close to saturation while the two, 80 and 90 per cent saturated, dissolved an amount in excess of that contained in the original saturated
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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solution. The cause of this peak was not examined, but the same phenomenon was observed in triplicate experiments. However, the figures show definitely that the solutions used in the treatment of polyhalite can be saturated readily by shaking. Table VI-Treatment with Concentrated Solutions Time of shaking, 2 hours. weight of polyhalite, 5 grams; volume of solution, 50 cc SATURATION &SO4 CONCENTRATION WITH KISO~ Before shaking After shaking % GramsllOO cc. Grams/lOO cc. 70 3.80 5,34 80 4 34 5.76 4.89 90 5.83 5 43 100 5.43 Table VII-Variation i n Time of Shaking Sample of polyhalite, 10.000 grams; solution, 4 . 0 grams ammonia and 8 . 3 grams ammonium carbonate made up to 80 cc. TIME KzSO4 RECOVEHED (NH4)zSOd RECOVERED Hours Grams % Grams
Table VI1 shows the variation in potash recovery with time of shaking. Between 1.5 and 2.0 hours' shaking there is an increase of only 0.4 per cent in the recovery of potassium sulfate. From 2.0 to 2.5 hours there is no increase and the recovery is 90.2 per cent of the available potash. Increasing the temperature would hasten the solution of potassium sulfate, but this is found to increase considerably the solubility of magnesium sulfate. Therefore, the optimum time of shaking would appear to be about 1.5 hours a t room temperature. I n order to gain some information concerning the crystallization of solutions containing potassium and ammonium sulfate, some runs were made on a larger scale. Because of the limited supply of the natural polyhalite available, these experiments were made with a synthetic product2 which was formed by fusion of the theoretical amounts of the three salts. This product was ground to pass a 70-mesh sieve and 200 grams were stirred for 1 hour with 1000 cc. of solution containing 125 grams of ammonia and 200 grams of am-
ase
I
Vol. 23, S o . 6
Ammonium and potassium sulfate form mixed crystals, but since the first fractions contain most of the potassium it is possible to separate part of the large amount of ammonium sulfate into a fraction containing only a small proportion of potassium sulfate. Figure 1 shows the relation between the two sulfates in successive crystallizations. As an example consider that the solution is evaporated until half of the salts is crystallized. I n Figure 1 it is observed that the ordinate at 50 per cent intersects the curve showing the composition of the solid phase a t 57 and meets the other curve a t 85. This means that the solid fraction is a mixture of 57 per cent potassium sulfate and 43 per cent ammonium sulfate. But this amount of potassium sulfate represents 85 per cent of the total amount of available potash. The curve for the composition of the solid phase is only accurate for a solution containing 33.6 per cent of potassium. The solutions from natural polyhalite would usually be slightly lower in potash content, but the curves would be similar in shape, as indicated by the broken line. Table VIII-Potash EXPT. 1 Weight of sample, grams.. . . . . . 5 . 0 0 0 Time of stirring, hours. . . . . . . . . 1 . 0
Recovery EXPT.2 5.000 1.5
3 10.000 1.0
EXPT.
EXPT.4
10.000 1.5
SALTS RECOVERED
&SO4 . . . . . . . . . . . . . . . . . . . . . . . . 0 . 9 4 8 (NH4)zSO4. . . . . . . . . . . . . . . . . . . . 2 . 6 0 MgSO, . . . . . . . . . . . . . . . . . . . . . . 0 , 0 1 4 NasSO4 (by d i f f . ) ,. . . . . . . . . . . . . 0 , 3 5 1
--
Total . . . . . . . . . . . . . . . . . . . . . . . . 3 . 9 1 3 24.2 KBOI, %....................
0.970 2.85 0.012 0.320
3.952 24.5
1.911 4.805 0.024 0.899
-
1.940 5,000
0.022 1.020
--
7.639 25.0
7.982 24.3
1.032
1.047
1.166 88.8 0 773
1.166 89.8 0 868
POTASH BALANCE
Kz0: Recovered . . . . . . . . . . . . . . . 0 . 5 1 2 5 In residue.. . . . . . . . . . . . . . . 0 . 0 6 4 Total . . . . . . . . . . . . . . . . . . . . 0.577 Available . . . . . . . . . . . . . . . . . . 0 . 5 8 3 Recovered. L7, . . . . . . . . . . . . . 8 8 . 0 NH: in restdue, gram 0 488
.
0.5240 0.064 0.588 0.583 89.9 0 480
.... ....
....
....
Table VI11 gives the results of a more complete analysis of the extraction process. Two 5-gram and two 10-gram samples were each shaken with 50 cc. of solution which was made up according to the calculations given in the previous section. The potassium sulfate from a 10-gram sample is sufficient to make 50 cc. of solution about 85 per cent saturated. For this reason it might be expected that the recovery would be higher with a 5-gram sample, but the table shows that the extraction proceeds just as rapidly with the larger samples. Increasing the time of shaking from 1 to 1.5 hours gives an average increase of 1.6 per cent in potash recovery, but further shaking does not increase the quantity of potash in the extract, as shown by the results given in Table VII. Part of the 10 per cent of unrecovered potash which is left in the filter cake is lost because of the method of filtering. The precipitate could not be washed because of the solubility of the magnesium carbonate; consequently, some potash is retained by the solution held in the pores of the filter cake. In commercial practice this precaution would not be necessary, because the wash water could be returned to the extraction system and the magnesium reprecipitated. The filter cake resulting from such a process would contain ammonia, the recovery of which would be desirable. This is present partly in the compound MgCOr(NH&C03.4H20 and partly as ammonium compounds in the solution absorbed by the filter cake, All the ammonia can be removed by washing with hot water. In fact, the double magnesium salt decomposes on standing in the air, and in practical work the ammonia so combined could be recovered very effectively by forcing steam or hot water through the filter cake. AMMONIUM CARBONATE TREATMENlLEXtraCtiOn Of polyhalite with a solution containing ammonium carbonate and an excess of ammonia removes the greater part of the potash,
.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1931
but even under the most favorable conditions the resulting solution has a very low concentration of potassium sulfate. This increases the cost of processing by greatly increasing the quantities of solution to be handled and the subsequent expenses of evaporation. The main advantage in this leaching process is the almost complete separation of magnesium from the potash. In modern fertilizer practice the complete elimination of magnesium from fertilizer mixtures has not been found entirely advisable. This fact allows some leeway in the extraction process, and it was believed to be possible to increase the concentration of the resulting leaching solution in respect to potassium sulfate to the possible detriment of the elimination of magnesium.
4
2
4
6
Conch
8
IO
12
14
16
18 20 22 24 26
ZB 3 '
of ex fracf h q so/. gms ("4),C03/100 m.
Figure 2-Solubility of P o t a s s i u m a n d M a g n e s i u m Sulfates f r o m Polyhalite i n A m m o n i u m Carbonate Solution
Table IX gives the results obtained by eliminating the excess ammonia in the leaching solution and increasing the concentration of the ammonium carbonate. Amounts of polyhalite in excess of that required t o saturate 50 cc. of water were shaken with 50 cc. of ammonium carbonate solutions for 3 hours a t room temperature. The resulting solutions were sampled in the usual manner and analyzed for both potash and magnesium. Table IX-Effect of Concentration of A m m o n i u m Carbonate on t h e Solubility of P o t a s s i u m Sulfate f r o m Po15halite Total volume, 50 cc.; weight of sample, 25 000 grams, time of extracting, 3 hours &SO4
("4)PCOI G r a m d l 0 0 cc.
SOLUBILITY Grams/lOO cc 3.972 3.638 3.615 6.842 9.501 10.28 10.51 10.17 :.646 I ,708 0.235
hIgS04
SOLVBILITY GiamsllOO cc 2 855 2 416 1 851 2 460 4 751 4 560 3 ,512 2 926 2 210 1 729 0 039
The graphical representation of these data (Figure 2) shows that the best results are obtained with an extracting solution containing 16 t o 22 grams of ammonium carbonate per 100 cc. After leaching 100 cc. of the resulting solution contain 10 grams or more of potassium sulfate. When a solution containing 16 grams of ammonium carbonate per 100 cc. is used for extracting, the concentration of magnesium sulfate after extraction is found t o be 4.7 grams per 100 cc., but as the concentration of the extracting solution increases the concentration of magnesium sulfate drops to 3.5 grams per 100 cc. for a 22 per cent solution of ammonium carbonate. The extreme condition of extracting the polyhalite with a
661
solution containing solid ammonium carbonate throughout the extraction is also included. While the concentration of magnesium sulfate in the final solution is cut down to 0.039 gram per 100 cc., there is a much greater drop in the potassium sulfate extraction. The concentration of the solution after extraction in respect to potassium sulfate is only 0.236 gram per 100 cc. Conclusions
Ammonium carbonate can be used in the extraction of potash from polyhalite either with or without an excess of ammonia depending on the desirability of obtaining a magnesium-free salt. The ammonium carbonate-ammonia treatment of polyhalite gives a product which contains potash and ammonia in the ratio of about 1:I and 0.1 per cent or less of magnesia. The potash recovery reached 90 per cent in l l / z hours' shaking, and this should be increased to a t least 95 per cent by a countercurrent system. The potash content of the mixture can be increased by fractional crystallization. However, there is no need of this because the two sulfates are already present in a proportion suitable for direct application as a concentrated fertilizer. The treatment of polyhalite with a saturated ammonium carbonate solution is carried out in a manner similar to that used when there is an excess of ammonia. The recovered potash solution is much more concentrated in respect to potash than that obtained from, the previous method, but it also has a larger concentration of magnesia. KO figures are given on the potash recovery owing to a limited supply of polyhalite, but this would probably be fully as satisfactory as that found in the ammonium carbonate-ammonia extraction. From the foregoing data it would appear that these methods form two feasible commercial operations for the recovery of potash from polyhalite. The processes would operate on material ground to pass 150 mesh and at ordinary room temperatures. Acknowledgments
The authors wish to acknowledge their indebtedness to
J. R. Turrentine, whose suggestions have greatly facilitated the progress of this work, and to Miss E. Z. Kibbe for her valuable aid in the necessary analytical work. Literature Cited (1) Lafontaine, Comfit. rend., 180, 2045 (1926). (2) Storch, IND. ENG.CHEM.,22, 934-41 (1930) (3) Wroth, Bur Mines, Bull. 316 (1930).
List of Alloys Revised In 1922, Committee B-2 on non-ferrous metals and alloys of the American Society for Testing Materials prepared and published a list of alloys, the work being headed by William Campbell, of Columbia University. This list was of great utility and parts of it have been reprinted. Under the same auspices the list has now been revised and amplified, and is made available in two bindings: in paper, $1.50; bound in cloth, 62.00 per copy. The list is primarily one of non-ferrous alloys, but there are included a few iron alloys in which the properties are dependent on the added elements. More than 2500 alloys are listed and for these the trade name, typical chemical analysis, and in many instances a statement of physical properties are given. They are arranged by alloys and alphabetically under each subdivision. The list comprises some 65 pages. Orders should be sent to the American Society for Testing Materials, 1315 Spruce St., Philadelphia, Pa.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 23. No. 6
Influence of Antioxidants on the Rate of Oxidation of Linseed Oil 11-Phenols and Aromatic Amines' A. M. Wagner2 and J. C. Brier DEPARTMENT OF C H E M I C A L ENGINEERING. UNIVERSITY
The influence on the rate of oxidation of linseed oil a t 100" C. of each of five phenols and five aromatic amines
has been studied. Data were obtained by blowing samples with conditioned air and ascertaining the state of oxidation by iodine-number and refractive-index determinations. Four phenols and two aromatic amines were found to be effective antioxidants for linseed oil under the experimental conditions. The comparative effectiveness of the phenols in prolonging the induction period of linseed oil oxidation was found to be a s follows: hydroquinone 100, pyrogallol 70, a-naphthol 40, and resorcinol 4. Meta- and p-phenylenediamine were slightly more effective than a n equal concentration of hydroquinone. The rate of oxidation following the termination of the induction period was the Bame a s t h a t of pure linseed oil a t the same state of oxidation for four of the six antioxidants found to be effective. A t 100" C. pyrogallol and a-naphthylamine, like hydroquinone, did not influence the rate of oxidation of linseed
HE useful life of paint and varnish films depends in large part upon the ability of the linseed or kindred
T
vegetable-oil vehicle to retain the optimum physical properties that exist soon after the drying of the film. The deterioration of these physical properties is caused indirectly by the very agencies for which the vegetable-oil film is used as protection against decomposition. It is noteworthy that these agencies, principally light, heat, and moisture, are controlling factors in almost all chemical reactions and hence are of a nature that would promote chemical change within the organic compounds that exist in the film. It is logical to assume, therefore, that chemical changes within the film are the direct cause for the ultimate destruction of oleoresinous finishes, and that the useful life of the film is limited chiefly by the intensity and potency of the destructive agencies. Accordingly, it would appear that the proper method for prolonging the life of paint and varnish finishes should involve some means for preventing, arresting, or retarding chemical action within the film. I n a previous paper (6) the authors indicated that the destructive chemical action within a finish film is a continuation of the same chemical change that is essential to the gelation of the film-namely, oxidation. They suggested that the useful life of oleoresinous finishes would be prolonged by the use of suitable antioxidants, but emphasized the fact that to be satisfactory the antioxidants would be obliged to function by interrupting the oxidation process when the optimum physical properties of the film 1Received March 11, 1931. Part of a thesis submitted by A. M. Wagner in partial fulfilment of the requirements for the degree of doctor of philosophy in the Graduate School of the University of Michigan. 2 Holder of the Thomas Berry Memorial Fellowship for the study of organic protective coatings. Present address, Western Electric Co., Chicago, Ill.
OF MICHIGAN, ANN
ARBOR,M I C R .
oil when added after the conclusion of the induction period. Meta- and p-phenylenediamine, on the other hand, interrupted the oxidation of linseed oil under the same conditions. A t 30" C., however, p-phenylenediamine was not able to inhibit the oxidation of linseed oil, whereas hydroquinone did so very effectively. This fact, together with the peculiar behavior of the phenylenediamines during the experimental work, indicates t h a t it is their decomposition products, and not the phenylenediamines themselves, t h a t exercise the antioxygenic influence a t 100" C. The antioxidants appear to lose their effectiveness in controlling the rate of linseed oil oxidation as the velocity of the oxidation reaction increases and to become ineffective after a critical velocity has been exceeded. This critical velocity varies, but seems t o be governed by the nature of the antioxidant. From the results reported in this paper and in a previous one (6) it is concluded t h a t further investigation of antioxidants with the possibility of utilizing t h e m to prolong the useful life of oleoresinous finishes is warranted.
had been obtained, without, however, interfering with the early stages of the process which occur during the transition of the drying oil from the liquid to a solid state. In connection with this suggestion an extensive preliminary investigation of a known antioxidant was reported. This preliminary investigation involved a study of the behavior of hydroquinone in a linseed oil system. The experimental method employed consisted essentially of blowing hydroquinone-treated samples of linseed oil with an unvarying quantity of conditioned air and measuring the state of oxidation by frequent iodine-number determinations supplemented by refractive-index determinations made a t 30" C . During the period of air blowing the samples were maintained a t a constant temperature, both 100" and 30" C. being employed. The investigation reported in the present paper supplements the one conducted with hydroquinone and deals with four related phenols: pyrogallol, resorcinol, a-naphthol, and @-naphthol; and five aromatic amines: diphenylamine, a-naphthylamine, phenyl-&naphthylamine, m-phenylenediamine and p-phenylenediamine. The experimental work was not carried out with the same completeness that characterized the investigation of hydroquinone, because it was believed that an extensive study of each antioxidant would not contribute more toward solution of the problem of prolonging the life of oleoresinous finishes than would a comparatively brief investigation directed specifically toward this end. Experimental Procedure The conditions that prevailed and the procedure that was followed were identical for both the hydroquinone and the present supplementary investigations. All samples were blown with 1.5 liters of conditioned air per minute and were
