458
T H E JOCRi‘\7A4L OF I,YDC-STRIAL A K D E S G I S E E R I - Y G CHELVISTRY.
less, because of the existence of a large number of grains that did not run all the way through. The increase a t 800’ C. is unusual, because in most metals the resistivity is lowered by annealing. If we consider the results entirely from a point of view of the number of grain boundaries along the length of the wire, we would expect a slight rise in resistivity, owing t o the fact that in the unannealed state the grains are drawn out, and so present fewer boundary lines along the length of the wire than when subsequently annealed. If the change in resistivity were due wholly to the presence or absence of the amorphous phase then we would expect the usual decrease in resistivity after the first anneal. When heated in a high vacuum the cement apbarently volatilizes more rapidly than the metal grains, and leaves deep fissures between the grains. Such a n experiment, using pure silver, is given by Rosenhain and Ewen a s proof that the cement was amorphous silver, but it is readily conceivable that any foreign substance present may also have a lower vapor pressure and give the same result. We also obtained like results with wrought tungsten. Although the facts seemingly indicate that carbon, either free or combined, is the cementing material, all attempts to etch out the Fe,C from a cementitic steel b y electrolyzing in chromate have failed. A piece of “burned” steel containing a smaller proportion of cementite, similarly treated, separated nicely on the grain boundaries. Commercially pure ingot iron is not attacked, while iron containing a high percentage of free carbon is rapidly dissolved. Analyses were made of samples from a bar: ( I ) as rolled, ( 2 ) fired in hydrogen to 1 3 2 j O C. to a partially granular fracture, (3) fired t o 1425’ t o a complete granular fracture, and ( 4 ) refired in hydrogen over hydrocarbon till it reverted to a cleavage fracture. The results gave no indication that any of the impurities (S, P, C or Mn) had been removed or reduced b y any of these treatments, with the exception of carbon, which was reduced from 0.065 per cent to 0.013 per cent on the first heating in hydrogen. The carbon content, however, did not go up again on heating with dilute hydrocarbon vapor. The proof that this material is carbide or any other of these impurities is still indirect, but on the other hand the assumption that the cement is only the amorphous phase of either metal or of the solid solution is in view of these experiments insufficient. If we assume that this is the case, we would expect this amorphous material to exist in all samples, and moreover, once destroyed by heat we would hardly expect i t t o be restored on reheating t o the same temperature in a slightly different atmosphere, and this change reversible indefinitely without the least change in size or shape of the grains. On the other hand, the assumption that these boundary lines hold certain impurities explains most of the facts observed, for then the action of the hydrogen partakes of a chemical nature, and the reversing of the physical state is due t o the addition or subtraction of some specific element whose presence or absence determines
Vol. j, NO. 6
the strength of the junction. The experiments with samples of cast metals also strengthen this view, and when the metal is fused in pure hydrogen the old grain boundaries vanish, while the new ones are not attacked by the chromic acid, owing to the removal of the impurity. These experiments, i t will be remembered, have all been performed upon a product having only a commercial degree of purity, and the existence of sufficient impurity in highly purified metals may be questioned, but the amount required is so small t h a t it would be difficult t o obtain a metal sufficiently pure. S U M M 4 RY
It has been shown that the intergranular cement in a 4 per cent silicon-iron alloy may be completely removed by making the alloy the anode in a solution of potassium dichromate, and also by firing in hydrogen to a temperature just below the melting point. I t is again replaced in the latter case b y firing in a dilute hydrocarbon vapor. I t is shown t h a t in the unannealed cast metal impurities exist throughout the mass of the grain, and not only a t the boundaries, while after annealing these impurities have passed t o the boundaries. Resistance measurements on large and small grain wires show that the “cement” has a higher resistance than the crystalline metal. . I n view of the facts it does not seem sufficient t o say that the intergranular cement is composed entirely of the grain substance in the amorphous phase, b u t rather that it consists of the metal in combination with certain impurities which have been rejected by the crystalline grains. I t is not the purpose of this paper to deny any existing theory regarding the composition of the intergranular cement in metals, for the author realizes its limited scope, but it is hoped that the facts observed may aid somewhat in the general investigation of this subject. RESEARCH
LABORATORY
GENERALELECTRIC COMPANY SCHENECTADY
INFLUENCE OF VARIOUS ELEMENTS ON THE CORRODIBILITY OF IRON’ B y CHARLESF.
BURGESS
AND JAMES
ASTON
Incidental t o a n extensive investigation on electrolytic iron and alloys produced therefrom, as carried out under a grant made a number of years ago by the Carnegie Institution, tests were made upon the corrodibility of a number of alloys. Acknowledgment is made t o Mr. B. F. Bennett for his assistance on this particular phase of the work. The electrolytic iron which has been used as a basis for the alloys, when compared t o materials commercially available, may be taken as essentially pure and in making up the alloys care was taken to exclude impurities as far as possible. The method of preparing the test samples consisted, first in melting the electrolytic iron or the electrolytic iron alloy in closed graphite magnesia-lined crucibles heated in an elec1 Paper presented at the Eighth International Congress of Applied Chemistry, New York, September, 1912.
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June, 1913
T H E JOL-RIVAL OF I S D C ‘ S T R I A L A.YD ESGI-YEERIA-G C H E J I I S T R Y .
trical resistor furnace. Upon cooling down the small ingots weighing from one to two pounds were forged ATMOSPHERIC CORROSION ACIDC O R R O S I ~ K,-----Lbs. per K g . per Percentages Electrolytic iron. . . Aluminum. . . . . . . .
..
0.067 1.333 0.292 Arsenic. . . . . . . . . . . 0.430 0.915 1,810 .3 862 4,141 3.562 1.035 Cobalt 2.000 4.055 5 ,052 0.089 Copper. , , . . , . . 0.202 0.422 0.592 0.804 1.006 1,510 2.005 3.990 5 ,070 6.160 7.050 0.061 Lead . . . . . . . . . . . . . 0.505 Manganese. . . . . . . . 1.000 2.000 3.000 10 419 0.270 Sickel 0.560 1 070 1.930 i ,050 8 . 170 10.200 11.290 1 2 .OiO 13.010 19.210 22.110 25.200 26.400 28 , 4 2 0 35 ,090 47 , 0 8 0 7 5 ,060 , 0.017 Selenium. . . . . . . . . . 0.233 Silicon. . . . . . . . . . . .. . . 1.190 1.033 1.897 2 826 Silver. . . . . . . . . . . . . 0.281 0.492 0.581 0.691 Tin, . . . . . . . . . . . . . . . . 0.288 0.342 0.686 1.568 Tungsten. , . . , . , , , . 0.406 0.925 2.334 3.553 5.982 9 849 13.641 23.866
Gram pet
sq. d m . 1.300 0.628 0.760 0.448 0.815 0.405 0.131 0.086 0.102 0.144 0.705 1.020 0.356 0.257 0.178 0.095 0.059 0.112 0.104 0.067 0.147 0.091 0.093 0.087 0.143 0.186 1.300 0.560 0.520 0.725 1 110 0 352 0.6330 0 5470 0,5070 0.1920 0.2260 0.1250 0.0910 0.1230 0.0s40 0.2370 0.0720 0.0254 0.0540 0.5540 0,1550 0.1830 0.1600 0.0490 0.190 1.630 1.190 0.850 0,800 1.270 1.020 1.760 1.340 1.170 0.284 0.350 0.386 1.030 0.363 0.085 0.086 0.332 0 304 0.398 0.365 0.153
sq. i t . per year
sq. m e t e r per year
0.1025 0.110 0.080 0.0830 0.0703 0.0870 0.0720 0.0640 0.0740 0.0630 0.049 0.070 0.042 0.042 0.052 0.039 0.055 0.050 0.053 0.046 0.046 0.051 0.035 0.031 0.041 0.033 0.056 0.055 0.080 0.062 0.067 0.089 0.059 0.071 0.058 0.023 0.038 0.029 0.027 0.027 0.024 0.031 0.018 0.020 0.023 0.021 0.021 0.018 0.012
