INDUSTRIAL A N D ENGINEERING CHEMISTRY
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1I-Bertrand, Brocq-Rousseau, and Dassonville, “Influence of Temperature and Other Physical Agents upon the Insecticidal Power of Chloropicrin,” Comfit. rend., 169, 1059 (1919); C. A , , 14, 588 (1920). 12-Bertrand, Brocq-Rousseau, and Dassonville, “Comparative Action of Chloropicrin on Weevil and on Tribolium,” Ibid., 169, 1428 (1919); C. A . , 14, 1404 (19201. 13-Bertrand, Brocq-Rousseau, and Dassonville, “Extermination of Rats by Chloropicrin,” I b i d . , 170, 345 (1920) ; C.A . , 14, 2046 (1920). 14-Bertrand and Rosenblatt, “Action of Chloropicrin on Certain Bacterial Fermentations,” I b i d . , 170, 1468 (1920); C.A . , 14, 2676 (1920). 15-Guerin and Lormaod, “Action of Chlorine and Various Vapors (Including Chloropicrin) upon Plants,” Ibid., 170, 401 (1920); C. A , , 14, 3415 (1920). 16-Piiitti, “Action of Chloropicrin on Parasites of Wheat and on Rats,” I b i d . , 170, 864 (1920); C. A . , 15, 1593 (1921). 17-Piutti and Mango, “Employment of Chloropicrin in Disinfection of Cereals,” Giorn. chim. i n d . afiplicafa,2 , 677 (1920); C. A , 15, 2523 (1921). 1s-Bertrand, “Action of Chloropicrin on Higher Plants,” Comfit. rend., 170, 858 (1920); C. A , , 16, 1593 (1921). 19-Feytaud, “Destruction of Termites,” Ibid., 171, 440 (192Oj; C. A . 14, 3746 (19201. 20-Burkhardt, “Experiments with Chloropicrin as a Means for Combating Parasites,” Deut. Zandw. Presse, 47, 447 (1920). 21-Neifert and Garrison, “Experiments on the Toxic Action of Certain Gases on Insects, Seeds, and Fungi,” U. S . Dept. Agr., Bull. 893 (1920). 22-Tattersfield and Roberts, “Influence of Chemical Constitution on the Toxicity of Organic Compounds to Wireworms,” J . Agr. Sci., 10, 199 (1920); C. A . , 15, 141 (1921). 23-Miege, “Effect of Chloropicrin on the Germinating Power of Seeds,” Comfit. rend., 172, 170 (1921); C. A , , 16, 1371 (1921). 24--Remy, “Action of Vapors of Chloropicrin on AYgas rcjlexus Fabr.,” Zbid., 172, 1619 (1921); C. A , , 15, 3337 (1921).
Vol. 19, No. 4
25--Wille, “Chloropicrin a s a n Insecticide, Especially for Combating the Grain Weevil (CUlQndYQ granaria),” 2. angew. Entomol., 7, 296 (1921); C. A . , 16, 2962 (1922). 2 G M a t r u c h o t and Sec, “Action of Chloropicrin on Various Fungi,” Compl. rend. SOL. biol., 83, 170 (1920); C. A . , 16, 4003 (1922). 27-Randier, “Chloropicrin,” Arch. med. fiharm. nauales, 122 (JanuaryFebruary, 1922), 22 pp.; Tech. sonit. munic., 17, 226 (1922); C. A . , 17, 1682 (1923). 28-Yamamoto, “Insecticidal Use of Chloropicrin,”Rikwaqaku K e n k r u j o Iho, 1, 1 (1922); C.A . , 17, 2341 (1923). 29-Delassus, “Chloropicrin and I t s Use for the Destruction of Insects,” Rev. agr. afrique nard., 20, 78 (1922). 30-Matthews, “Partial Sterilization of Soil by Antiseptics,” J . Agr. S c i . , 14, 1 (1923); C.A . , 18, 1543 (1924). al-Bertranc), “Suffocation of the Silkworm Cocoon by Chloropicrin,” Comfit. rend., 178, 1656 (1924); C. A . , 18, 2608 (1924). 32-Piedallu, “Destruction of Parasites in Stored Cereals,” Chimie b industrie, Spec. No., 740-2 (May, 1924); C. A . , 18, 3248 (19241. 34-Neifert, Cook, Roark, Toulsin, Back, and Cotton, “Fumigation against Grain Weevils with Various Organic Compounds,” U . S. Dept. A g r . , Bull. 1313 (1926). 3%McDonnell, “Recent Progress in Insecticides and Fungicides,” I n d . E n g . Chem., 16, 1007 (1924). 36-Chapman, “Fumigation Mixture,” U. S. Patent 1,502,174 (July 22, 1924); C. A , , 18, 2937 (1924). 37-Chapman and Johnson, “Possibilities and Limitations of Chloropicrin as a Fumigant for Cereal Products.” J . A g r . Research, 31, 745 (1925). 38-Strand, “Preliminary Experiments on the Use of Chloropicrin as an Insect Fumigant in Flour and Cereal Mills,” J . Econ. Entomol., 19, 504 (1926). 39-Roark, “Chemistry Bibliography No. 1. Chloropicrin,” U. S. Defit. Agr., Bur. Chemistry, 1926.
Influence of Rust-Film Thickness upon the Rate of Corrosion of Steels’ By E. L. Chappell RESEARCH LABORATORY
OF
APPLIEDCHEMISTRY, MASSACHUSETTS INSTITUTE
OF
TECHNOLOGY, CAMBRIDGE,
?YIASS.
In the absence of rust films different commercial relations have been sought steels corrode in water or in the atmosphere at characbetween corrosion films on a given c o m m e r c i a l steel is commonly obteristic rates determined by the chemical properties of steels and their corrosion rates their surfaces. Copper-bearing steels, for example, under ordinary conditions of served to be dependent upon surrounding conditions, such tend to be more resistant than non-copper-bearing exposure. This paper preas moisture, temperature, etc. steels under any circumstances where a thick rust sents data which indicate the It is almost equally agreed film does not form. conditions under which the that different steels may show The natural course of atmospheric corrosion does not rust films on steels seem to quite different resistances to lead to the formation of heavy rust films, so copperdetermine the corrosion rate corrosion under a given set of bearing steels have been shown by experience to be quantitatively, external facconditions. The recognition superior for this service. Underwater corrosion genertors being constant. ally leads to the formation of a heavy rust film, and of the factors which enter little difference has been found in the corrosion rates Texture of Films in Atmosinto such varying behavior pheric Corrosion of steels under water. Under conditions where some may be hoped to allow the e f f e c t i v e a p p l i c a t i o n of cause, such as abrasion, prevents the formation of a I t h a s b e e n frequently methods of corrosion retardafilm in underwater service, copper-bearing steels would noted that the appearance of tion and to prevent misleadprobably be superior to non-copper-bearing steels. Lhe rust on a highly resistant There is a quantitative decrease in corrosion rate steel exposed to the atmosing conclusions from being about proportional to increases of rust-film thickness. phere differs from that upon drawn in regard to the behavior of steels in tests of a less resistant one. This has led to the belief that resistant steels, such as copper steels, corrosion resistance. The effect of rust-film thickness upon the corrosion of steels build upon themselves a protective rust film. As this theory has been qualitatively recognized.2 The quantitative effects might be advanced as an objection to the suggestions which of oxide-film thickness in high-temperature corrosion394 will be made later in this paper, it will be discussed here. and in the natural corrosion of copper and zincs have been Data previously published from this laboratory6show that the studied. However, it seems that heretofore no quantitative relative rates of corrosion in the atmosphere of resistant and mn-resistant steels may be predicted frorn tests extending 1 presented before the ~ i ~of Industrial i ~ i and ~ Engineering ~ ChemOver Only a few days. I n these rapid tests the steels were istry a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 t o 11, 1926. entirely free from rust when first exposed and the more re2 Speller, “Corrosion,” p. 152, McGraw-Hill Book Co , 1926. sistant ones were frequently only partially covered with rust a Tamman, Rec. frav. chim., 42, 547 (1923). a t the end of the test, while the steels which corroded the 4 Pillings and Bedworth, THISJOURNAL, 17, 372 (1926).
HE rate of corrosion of
T
6
Vernon, Trans. Faraday Soc., 19, 839 (1924).
Whitman and Chappell, THISJOURNAL, 18, 533 (1926).
INDUSTRI.4L A N D ENGINEERISG CHEMISTRY
April, 1927
most rapidly were covered with more complete films of rust. At the end of the tests the samples were coated with a thin, bright red, fairly loose rust characteristic of bare steel which has been exposed to rusting for only a few days. The appearance of the samples from these rapid tests was quite different from that of similar samples which had been exposed for a period of years, the latter samples being covered with a thin, dark red, waxy, closely adherent film. I n no case was this so-called protective film observed in the rapid tests, and yet the ratio between corrosion rates of resistant and nonresistant steels was the same in both the rapid and long-time tests. I n view of these observations it seems necessary to conclude that the differences in corrosion rate of the commercial steels are due to properties of the metal surfaces themselves, and that differences in rust texture are a result and not a cause of differences in corrosion rate. Experimental
The ordinary exposure of steels under water leads to thick rust films, while in the atmosphere the film is commonly quite thin (see below), so that the classification of Table I may be adopted. I n order to study the effect of rust-film thickness a comparison has been made of the corrosion rate under known conditions of a representative group of five steels when exposed with and without rust films and under different thicknesses of an inert film of filter paper. Table I-Rust Films on Steels EXPOSURE U S U A L FILM UNUSUAL FILM Under water as water Thick, due to long exThin, due to either pipes, etc. posure short period of exposure or mechanical removal of rust In the atmosphere, Thin, due to drying and Thick, due to continusheet steels, etc. scaling ous wetting or artificial coverings CONDITION O F
The corrosion rates of these steels were determined in the laboratory under the following conditions: (1) I n the atmosphere sprayed with water (to duplicate ordinary exposure). ( 2 ) In the atmosphere sprayed with water covered with artificially thick films (to study the effect of film thickness). (3) Clean metal submerged in water for short time-no film a t start-only ihin film built up (initial corrosion under water). These materials have also been subjected to long-time tests both under water and in the atmosphere by the American Society for Testing Materials and data from their tests are available for comparissn and are included in the tables.
465
surface. Such films do not form naturally and therefore, as a substitute for a rust film, a n inert film of filter paper was placed around the samples and the corrosion rate determined as for the other rapid atmospheric tests.' These data are given in the last 4 columns of Table 11. The checks between duplicate samples were generally within 5 per cent, which was better than the aaeement between duplicate bare steels exposed under similar conditions. UNDERWATER(THIN FILMS)-TOdetermine the corrosion rates of the steels when exposed bare or with a thin film in water, clean samples were suspended in a glass tube in a water stream. The corrosion rate was determined by loss of weight a t the end of 3 days a t which time only a thin film of rust had formed. The data are given in Table 11, column 5. The more rapid appearance of corrosion products on the surface of the 0 and A samples was very noticeable in this and other experiments in which the bare samples were allowed to corrode in water. SUBMERGED IN RIVER-LONG-TIME TEST(THICK FILMS)Samples of these steels were exposed by the American Society for Testing Materials t o the action of the water of the Severn River at Washington, D. C., for two and a half years.' The number of months until a hole appeared in the sheet was recorded. These data and the original thickness of the plate were used in calculating the penetration rates of Table 11, column 6. The published report gives no information as to the thickness of the rust film present on the plates during this test, but experience in other tests makes it seem probable that the rust films were quite thick. EXPOSED TO ATMOSPHERE-LONG-TIME TEST(THINFILMS)The behavior of these materials in long-time exposure tests in the atmosphere has been recorded by the American Society for Testing Materials.7 The rates were calculated as for the underwater tests.
Discussion of Results
The data of Table I1 show that these five samples of steel vary widely among themselves in corrosion rate when exposed bare or with a thin film in the atmosphere or under water. However, when exposed in the air with a thick film the corrosion rates under a given film are practically the same for all five samples and in the American Society for Testing Materials underwater test in the River Severn over a two and a half year period, when the usual thick underwater film was presumably formed, there is little difference between the various steels. As shown in Figure 1, the corrosion rate for these steels decreases with increasing film thickness in a regular manner. It is seen that for films over 0.02 cm. thick the rate of corrosion is approximately inversely proportional to the film thickness. Data on the rust-film thickness on the sheets exposed under water by the American Society of Testing Materials are not available, so it is not possible to plot these
Table 11-Corrosion Rates of Steels (In centimeters per year) ~
1 A. S. T. hl. SAMPLE
0-31 A-37 '2-13
"-36 (2-20
I
THINFILMS (BARE) ATMOSPHERE
hf A T E R I A L
1
A. S. T.M. Pittsburgh Open hearth steel Bessemer steel Pdre iron Basic open hearth steel P,ire iron
,
~~~~~d
g:fz
3 days
days
I
~~~~
THICKFILMS Under water A. S. T. M. River Severn 2'/n years
0.036
0.0166 0.0164 0.0169
ATMOSPHERB, FILTER-PAPBR 0.020 cm.a
0.0317 0.0315 0.0287 0.0305 0.0297
FILY,
3 TO 5
DAYS
0.25 cm."
0.060 cm.O
0.14 cm."
0.0141 0.0146 0.0154 0.0156 0.0161
0.0098 0.0106 0.0113
0.0055
0.0108
0.0060
Thickness of filter-paper film.
A summary of the data is given in Table 11. Analyses of the materials are given in Table 111. The methods of obtaining these data were as follows: RAPID TESTSIN THE ATMOSPHERE (THINFILMs)-The metals
were exposed to a water spray and the corrosion rate was determined by loss in weight. The experimental method has been previously described.O The data for the five metals studied are given in Table 11, column 4. ATMOSPHERIC EXPOSUREWITH THICK FILMs-It was desired t o expose the steels in the atmosphere with a thick film upon the
rates in Figure 1. As shown below, however, i t has been possible to check these film thicknesses against the corrosion rates for certain long-time tests. The apparent increase of corrosion rates of the high-copper when covered with a filter-paper is possibly due to corrosion being induced over the entire metal surface by the covering. When the copper steels were exposed bare in the rapid tests, corrosion started a t isolated spots and fre7
Proc. A m .SOC.Tcsling Materials, 1914 to 1924.
INBLXTRIAL AAVDENGINEERING CHEMISTRY
466
quently did not spread over the entire surface before the end of the test period. Comparison w i t h D a t a Observed in Practice Having shown that for a small group of steels and irons in the atmosphere and under water there is a distinct dependence of corrosion rate upon the film thickness, and having obtained quantitative data as to the relation, it now remains to compare these data with the relations between film thickness and corrosion as observed in corrosion under water and for other cases in practice, both from laboratory and service data. Table 111-Analysis of Samples (Figures in per cent) SAMPLE 0-31 A-37 ‘2-13 ”-36
MATERIAL
Open hearth steel Bessemer steel Pure iron Basic ouen hearth steel Pure iron
C-20 a
Cu IN AVERAGE ANALYSIS POP GROUP^ TEST SAMPLE C Mn P S Si 0.016 0.008 0.214
0.22
0.121 0.038 0.015 0.074
0.536 0.386 0.028 0.373
0.008 0.089 0.006 0.011
0.030 0.040 0.036 0.026
0.249 0.007 0.003 0.004
0.140
0.01
0.028
0.002
0.027
0 002
Proc. A m . SOC.Tcsfing Materials, 23, 150 (1923).
ATMOSPHERIC FILm-In order to make comparisons with Figure 1 it is necessary to have data as to the film thicknesses actually found in practice. A careful examination (with a micrometer microscope) of the rust films on a number of different steels after 6 years’ exposure to the air* ahowed all to be about 0.0005 cm. thick. The samples examined included sheet irons badly corroded and copper steels that were almost full weight. Flakes of loose scale were not included in the measurements of the film on one badly corroded steel. I n the rapid atmospheric tests6 (Table I) the rust films developed were less than 0.0008 cm. These film thicknesses would be indicated by Figure 1 to have little influence 0.080
1,
I ~
OF A E L s UNDER INERT FILMS
t O R R A O N RAT;
1 I
T*ol. 19, xo. 4
exposed iron work. The surface may be irregular, but scratching the surface shows the real rust film (aside from occasional flakes) to be as thin as a coat of paint. RUSTFILMS UNDER WATER-Steels under water frequently form thick rust films, and in this case the rates are quantitatively comparable with the rates given in Table I1 for corrosion under a thick, inert film in the air with water spray. The corrosion rate in a ZOO-foot length of 3/rinch pipe after 2 months of constant flow of Cambridge water was determined by the oxygen drop method. The pipe was then sawed open and the average thickness of rust film estimated. Corrosion rate (oxygen drop method) = 00006 inch per year per cc. oxygen per liter Corrosion rate in oxygen-saturated water a t 20” C = 00039 inch per year = 0.0098 cm. per year Average rust film thickness = 0.15 cm. From Figure 1 corrosion rate = 0.0095 cm. per year
I n general, there is no record of rust-film thickness in reports of corrosion tests, so it is not possible to interpret the results in terms of the film thicknesses formed. The recognition of the part played by rust-film thickness, however, makes it probable that long runs upon submerged corrosion of steels become measures only of the effect of the film thickness. This can be shown qualitatively in several cases.9 DIFFUSIONOF OXYGENIN FILM-Rust films show a thin layer of dark rust (ferrous) next the metal surface, the rest of the film being red and presumably ferric. -4similar thin layer of dark rust (ferrous) was found next to the steel under 0.139 cm. of filter paper. Apparently, the oxygen penetrates both films to within a millimeter of the metal surface, where entire corrosion reaction occurs within a small zone. PoRoSITY-The porosities of the films used, both rust and filter paper, seem to have been about the same. Experiments in which the corrosion rate was determined by the oxygen drop method indicated that loose calcium carbonate films behave in the same manner. The films formed by alkalies and silicates, however, are much less porous than the filter paper or ordinary rust, though probably the same principles apply. PROPERTIES OF WATER-It is, of course, necessary to include specific properties of the water or rain as factors if the absolute value of the corrosion rates is to be calculated. The atmospheric tests of the A. S. T. lLr. show numerically about twice the rate of corrosion in the atmosphere a t Pittsburgh as at Fort Sheridan. Similarly, the time until failure of submerged plates was three times as long when in Severn River water as in acid mine water. Atmospheric tests must be calculated on the basis of the time the plates are wet, rather than total time, when comparing with submerged tests. However, the data from Figure 1 are for the same steels in the same water and under generally comparable conditions. Conclusion
FILM THICKNESS -CM. Figure 1
on the corrosion rates (which would then depend on properties of the metal itself). This observation as to the thinness of films on iron or steel exposed to the atmosphere has been frequently verified for 8
Test by American Sheet & Tin Plate Comnsny.
It is seen that a very thick film is required to decrease appreciably the corrosion rate of the copper steels, and that the more easily corroded steels have a rruch longer life when protected by even a thin film of corrosion product. This indicates the conditions under which copper-bearing steels under water would not be superior to ordinary steelnamely, where thick films are formed. On the other hand, where the rust film is removed, as by mechanical means, copper-bearing steels are likely to be more resistant. In addition, it must be concluded that the common practice of cleaning the rust accumulations from iron surfaces, such as inside water heaters and tanks, is likely greatly to increase the attack on the metal. The importance of rust-film thickness is recognized in practice, when, for example, it is pointed out that a n Friend, “The Corrosion cf Iron,” Carnegie Scholarship Memoirs, p 154 (1922)
I.\-DCSTRI.iL
April, 1927
AND ENGI,+rEERING CHEMISTRY
tubular condenser will last longer if not cleaned of rust. I n cases of heavy metals such as cast iron, a thick film may be allowed to build u p and corrosion practically stopped.I0 The effect of films of corrosion product must be carefully considered where tests of corrosion resistance are made, as '0
Friend. "The Corrosion of Iron," Carnegie Scholarship Memoirs, p 79
(1922)
467
neglect of this factor may lead to conditions which are not comparable to those of practice. Acknowledgment
This study was made possible by a fellowship grant from the Sational Tube Company.
Potash from Greensand' 11-Adsorption from the Vapor Phase by Glaucosil By C. W. Whittaker and E. J. Fox B P R E A UOF SOILS, W A S H I N F T O S , D. C
LAUCOSIL was firpt
Measurements have been made of the ability of glauageb when the greenband from cosil to adsorb vapors of benzene, xylene, carbon tetrawhich it is derived was formed. described by Turrenchloride, and water. The values obtained show the It is simply the silica skeleton tine, Whittaker, and high activity and adsorption capacity of this new inof the greensand granule, the FOX,^ and later in more dedustrial reagent as compared with other materials. surfaces of which, both inner tail by Whittaker and Fox.3 The use of glaucosil for solvent recovery is strongly and outer, have been cleared I n these papers the use of indicated both by its good mechanical condition and off and left in a highly actire glaucosil in the refining of its ability to adsorb various vapors. state by the action of the acid. m i n e r a l and vegetable oils It is never in solution, coland in the recovery of used cylinder oil was discussed. The present paper gives the re- loidal or otherwise, during its manufacture. Chemically it sults of some experiments designed to test the efficiency of is quite active, much more so than any crystalline silica. It dissolves readily in dilute caustic by simply warming. Acids glaucosil as an adsorbent from the vapor phase. Glaucosil, it will be recalled, is the siliceous residue ob- apparently leave it entirely unattacked. Unignited glaucosil is grayish in color. The gray color tained by extracting greensand with mineral acids, preferably sulfuric acid. The acid leach is treated to recover may be the effect of small amounts of a humus-like material which is removed by roasting, leaving a perfectly white product. The particle size is roughly that of the original greensand particles, the extreme limits being 10- to 200-mesh material and finer. The bulk of the material consists of particles between 20- and 100-mesh. When portions of any particular size are desired they are readily obtained by screening. Glaucosil is easily ground to pass 200 mesh and yet is strong enough to withstand handling and use without undue crumbling.
G
Experimental
Figure 1-Adsorption
Apparatus
potassium salts, iron and aluminum oxides, and fuming sulfuric acid. Glaucosil is thus obtained simultaneously with other products and is, in short, a by-product of the manufacture of potash and other materials from greensand. The siliceous residue as obtained in the process contains only such salts as are present in the mother liquor and these are easily removed by mashing. The washing is best acconiplished by using first cold and then hot water. If the hot water is used first the iron salts hydrolyze and ferric hydroxide is deposited in and on the glaucosil, which is undesirable. Washing is usually continued to neutrality. Glaucosil is practically pure silica. It differs from artificial active silica in that it has never been through the gel stage, unless perhaps it went through such a stage in the geological Presented under the title "Potash from Greensand. 11-Glaucosil as an Adsorbent in the Vapor Phase" before the Division of Industtlal and Engineering Chemistry at the 72nd Meeting of the American Chemtcal Society, Philadelphia, Pa., September 5 to 11, 1926. *THISJOURNAL, 17, 1177 (1925). "Glaucosil--A New Siliceous Adsorbent," a paper read before the Division of Industrial and Engineering Chemistry at the 70th Meeting of the i\merican Chemical Society, Los Angeles, Calif., August 3 to 8, 1925
-1dynamic method was employed for all measurements. The apparatus is shown in Figure 1. A stream of air was passed through a purification train (not shown) to reniove I
-
j
\I
I
l0
T/M€
m,mUTEs
Figure 2-Benzene Adsorption by Glaucosil Total amount adsorbed-40.5 per cent by weight
water vapor and carbon dioxide. This stream was measured by a flowmeter, f, and the rate of flow maintained constant by allowing a small excess t o bubble through a suitable adjustable seal. A uniform rate of 50 cc. of air per minute was used throughout. All apparatus following the flowmeter was immersed in a water thermostat carefully controlled a t 25" C. The gas stream after leaving the flowmeter
