INDUSTRIAL AND ENGINEERING CHEMISTRY
358
the per cent reduction in corrosion on iron in the vapor phase is about 60 as compared with 75 in the liquid phase. T a b l e IV-Analyses of Alloys METAL Calite casting Iron (obsolete formula) Nickel Chromium Aluminium Carbon, etc. ALLOY
Cyclops metal (nickel-chromium stainless steel)
McGill metal
Aterite
Nickel Chromium Iron
P E R CENT
56.6 31.89 4.34 6.93 0.24
18 8 Remainder
Tin Lead Copper Iron Nickel
Trace Trace 88
Nickel Iron Copper Zinc Lead
35
4.5
6.94
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then cleaned with acid, washed, and dried, and the results at 393.3' C. (740' F.) obtained (Figure 4). It will be noted that the initial rate of corrosion of the clean metal was very high, but that it drops off rapidly during the first hour and more slowly during the next 2 hours. The runs were then repeated several times to determine whether or not a steady rate was obtained, no cleaning being done between runs. The iron tubes were evacuated between the runs to prevent the formation of hydrogen during the heating and cooling periods. Considering the results as shown in Figure 4, it appears that (a) the coating of ferrous sulfide slows down the rate of corrosion to a small fraction of that on clean metal, but never entirely stops the corrosion; (b) heating and cooling between runs loosens or scales off some of the protective layer and gives a higher initial rate of corrosion, though not so high as for
15
40 1.5 5
Ascoloy
Chromium Iron
Hills-McCanna No. 45
Copper Aluminium Iron
88 10.5
Stainless steel (Firth-Sterling)
Carbon Chromium Iron
0.30 13:O Remainder
14 Remainder except for accidental impurities
1.5
Measurement of Rate of Corrosion of I r o n by Hydrogen Sulfide
.
A few experiments were carried out to throw some light on the main factors affecting the rate of corrosion by hydrogen sulfide a t elevated temperatures. A measured quantity of this gas was passed through iron tubes held in a lead bath a t a predetermined and regulated temperature. The exit gas was then passed through sodium hydroxide solution and the residual gas measured in a gas buret. This, corrected for the alkali-insoluble impurities in the original hydrogen sulfide, gave the volume of hydrogen liberated by the reaction of hydrogen sulfide and iron. I n the later runs these impurities averaged about 0.25 per cent. This gas was made by the absorption of an impure gas in magnesium oxide suspended in water. After considerable gas had been absorbed the solution was boiled and the first few liters of gas discarded, after which the gas reservoirs were filled. A diagram of the apparatus is shown in Figure 2.
clean metal; the rate varies from run to run, probably on account of variation in the scaling off between runs; (c) the rate a t 393.3' C. (740' F.) is several times as fast as a t 315.6' C. (600' F.), thus confirming observations on pressure still equipment; (d) the apparently steady rate of 1.3 cc. of hydrogen per minute corresponds to a corrosion rate of 15.7 mg. of iron per square centimeter per run, about four and'a half times that observed on the pressure still strips where the partial pressure of hydrogen sulfide was, of course, much less. Acknowledgment
The writers take this opportunity to acknowledge the work of E. P. Brown and C. C. Miller on the effect of lime on the rate of corrosion in pressure stills, and of H. G. Schnetzler on the rate of corrosion of iron by hydrogen sulfide.
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Runs a t 68.9' C. (200' F.) and 204.4' C. (400' F.) showed no appreciable reaction. The curve in Figure 3 shows the results a t 315.6' C. (600' F.), plotting both the total cubic centimeters of hydrogen as observed, and the rate of hydrogen formation determined from this smooth curve. The tube was
University of Alabama, Tuscaloosa, Ala. University of Arizona, Tucson, Ariz. Carnegie Institute of Technology, Pittsburgh, Pa. University of Missouri, Rolla, Mo. Ohio State University, Columbus, Ohio University of Utah, Salt Lake City, Utah University of Washington, Seattle, Wash. University of Idaho, Moscow, Idaho
Detailed information in regard to the terms of these various fellowships may be obtained from the Bureau of Mines, Washington, D. C., or from the different institutions named.
