September, 1932
I N D U S T R I A 1, A N D E N G I N E E R I N G C H E M I S T R Y
993
exposures, summer and winter exposures, window glass and other light-filtering media, and rate of cure and compounding. TABLE11. THICKNESS OF DESTROYED SURFACE COMPOUKD A (zinc oxide, 20 volumes) B (zinc oxide, 6 volumes) C (lithopone, 18 volumes; ainc oxide, 2 volumes) Oct. 7, 1930-April 7, 1931. b April 7, 1931-Oct. 7, 1931.
26 WEEKSO Inch (mm.) 0.015 ( 0 . 3 8 ) 0.040 ( 1 . 0 2 )
Inch ( m m . ) 0 . 0 2 8 (0.71) 0 . 0 5 8 (1.47)
0.020 (0.61)
0 . 0 3 2 (0.81)
52
WEEKSb
(1
ACKXOWLEDGMENT The data contained in this paper were obtained while the author was on the research staff of the New Jersey Zinc FIGURE4. DECREASE IN TENSILESTRENGTH FOR SHEETS Company, and he wishes to acknowledge their permission to 0.02 TO 0.08 INCH(0.51 TO 2.03 MM.) THICK,EXPOSED TO use it. SUNLIGHT I
b
TIME
Or
bCINC I N DAYS
I
that the amount and kind of pigment have a considerable influence on the depth of the oxidized layer; a n increase in the amount of pignient increases the protection. This method can be applied with advantage to a measurement of surface oxidation as affected by northern and southern
LITERATURE CITED (1) Van Rossem and Tslen, Kautschuk, 7, 79-86, 115-17 (1931). (2) Williams, IND.Eso. CHEY.,18, 367 (1926). RECEIVED April 15, 1932.
Diffusion of Sulfur, Manganese, Phosphorus, Silicon, and Carbon through Molten Iron W. F. HOLBROOK, C. C . FURNAS, AND T. L. JOSEPH North Central Experiment Station, U. S. Bureau of Mines, Minneapolis, Minn.
I
K STUDYI-UG the desulfurization of iron by means of
linear, and that the rate is directly proportional to the differslags, it was desirable to know the part played by dif- ence in concentration between the two points considered, fusion. Owing to the negligible solubility in iron of the This is analogous to the transfer of heat which is directly constituents of slag (e. g., lime) to which desulfurizing is proportional to difference in temperature. The equation which covers this case may be written: usually attributed, it appears that any reaction by which sulfur is removed directly by them occurs mainly a,t the interface between the slag and the metal. Disregarding the quese = eo (1 e - B 2 ,B) (1) tion of what the interface and its properties are, and assuming that there is no convection, bubbling, or other form of XdE stirring present, any transfer of ferrous sulfide from the body where Q = __ (2) 2dE of the metal to the reacting zone must be by diffusion. Also, in order that the r e a c t & n may not bee = concn. of desired element at any point eo = concn. of desired element in body of diminished by the accumulation of calcium bath from which diffusion takes sulfide in the slag adjacent to the interplace face, diffusion must remove the calcium sulz = distance from bath from which diffuThermocouple md fide as formed to the reservoir of slag above sion is taking place, ern. (graphite) the interface. I n the experiments to be D = sp. gr. of metal Coupling sleeve described, no interface such as that bet = time from beginning of diffusion period, sec. tween two immiscible fluids exists. They K = coefficient of diffusion, grams/sec./sq. are intended to show whether diffusion itcrn./per cent concn. difference/cm. self has an important bearing on desulB = function of distance x and timet, which furization. need not be defined Rate measurements were made on sulfur diffusing through iron. iit the suggesThe solution for the coefficient is quite simtion of C. H. Herty, Jr., measurements est metal column mere also made on manganese, silicon, phosple. Valuesofthequantity, e-B1 d B , phorus, and carbon to test the reliability of the method. for different values of q may b e obtained t metal container The diffusion of these elements through from t a b l e s r e p o r t e d by Ingersoll and a fluid was considered analogous to heat Zobel ( 2 ) . For instance, f r o m t h e table transfer, and a coefficient of transfer by it is found t h a t , w h e n e/& = 0.5 (that diffusion was evaluated by equations used is, the concentration of the desired element in heat flow work ( 2 ) . The solution is at some point in the diffusion column is FIGURE 1. DIAGRAM OF DIFbased on the assumption that diffusion is 0.5 of the concentration in the main bath), FUSION APPARATUS
5
ik
:;.f
INDUSTRIAL AND ENGINEERING CHEMISTRY
994
Vol. 24, No. 9
from electrode graphite because of its ability to withstand high temperature and because of the ease with which it can be worked. As a result of its use, the metal under test was always saturated with carbon. I n the tests with carbon and a few special cases, porcelain and alumina tubes were used. Metals containing manganese attacked the porcelain a t temperatures required to melt them. Although Armco iron did a 2 not attack the porcelain a t a temperature of 1550' C., when 3 per cent of carbon was present the attack was rapid a t that 1 temperature. The presence of carbon, however, lowered the melting point sufficiently so that a test could be made a t a temperature a t which the attack on the porcelain was very 16 0 2 4 6 8 LO 11 I4 Ifi I18 R M DISTAhCE FROM BATH COVTCT, MILLIMETEFS slow. Alumina tubes were used in the measurement of FIGURE2. TYPICAL DISTRIBUTION CURVEFOR MANGANESE carbon diffusion rates. (DIFFUSION OF 30 MINUTESAT 1624" C.)
s
1W
must be approximately 0.48. and substituting, Q
By rearranging Equation 2
p = 0.48 1.085 xi2D t
83
K = x, t
=
distance from main bath where e/eo
(3) =
= time of diffusion, sec.
0.5
0
4
:60
The distance z1is best determined by drawing a smooth curve, such as is shown in Figure 2, in which concentration is plotted against distance down the column. Such computations are based on the assumption that the molecular diffusion is analogous to the conduction of heat along an insulated rod. For the most part the data obtained justify this assumption.
22 su
g
s
:40 s
e
EXPERIMENTAL PROCEDURE The method consisted essentially in submerging a small tube containing material of one analysis in a bath of another analysis, holding the system a t a known temperature for a measured length of time, removing, quickly chilling, and subsequently analyzing sections of the solidified material in the small tube. Contact was made between the top surface of a column of metal, 2 to 4 mm. in diameter and 5 em. deep, and a bath of metal containing varying percentages of the element under investigation. The apparatus is shown diagrammatically in Figure 1. I n most cases the apparatus was constructed
I
30
0
10
2
4 6 8 1U 12 DIITA\CE FRO% POlUT OF CO\TICT \IILLI+IETERS
11
FIGCRE4. MAVGANESECONCENTRATION GRADIENTS
All tests were made in an induction furnace. Heat was developed in a graphite sleeve extending throughout the length of the furnace coil. Temperatures were observed by the use of a tungsten-graphite thermocouple which was kept immersed in the bath. This thermocouple was frequently checked against an optical pyrometer and occasionally against a noble metal thermocouple in a porcelain protection tube, which in turn was protected by a graphite tube. The graphite crucible containing the bath metal was supported midway between the top and bottom of the furnace where the temperature was uniform, to guard against thermal convection. T A B L E I. DIFFTJHOX OF hfASGAXESE THROCGH I R O N SECTION DIFFCSION Mn SECTION DIFFCSIOX Mn M m % Mm % 30 MIVUTPES A T 1624' ~~
Bath 1 2 3
...
Bath 1 2 3
...
2.1 2.2 4.8 K = 0.00056
2.8 3.2 3.5 K = 0.00045
...
Bath 1 2 9
4
K
-
2.0 3.5 3 5 3.0 0.00046
~~
4.83 4.03 2.80 1.23 30 M I N U T E 8 A T 1440'
8.17 5.70 3.34 1.04
4 84
1.52
5.4 6.7 12.0
6.0
0.14 0.10 0.10 0.10
3.7 8.1 11.8
0.32 0.15 0.15
3.5 3.5 3.5 4.4
0.51 0.26 0.21 0.24
C.
4 5 6
30 M I N U T E S A T 1415'
42.8 No sample 9.79
C.
4 5 6 7
5 6 7
8
0.
>cp1crtrbcr, 1932
INDUSTRIAL AN
L)
E N G 1 R :E 83 1%I N G C H E M 1 5 T H Y
T u b e s o f 2- t o .l-mni. bore were generally used. Small t u b e s a r e a n a i d
against convection. This was found to he a consiicrat i o n of minor importance owing to the quiet state wliich always prevailed in tire bath melts. Because of t h e q u a n t i t y of sample necessary for analysis, la.rge limes would have been desirable Were it not lor th
