Surface Deterioration of Rubber HARLAN A. D b ~ e wAmerican , Zinc Sales Company, Columbus, Ohio
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which had hardened but had XPERIMENTS made by A method has been developedfor measuring the checked very little or none in 6 Williams (2) and by Van &ickness of the oridired layer that forms on the Rossem and Talen (1) months. In time, however, the sucfaee Of rubber It surface nrould check rather than have indicated that the deep been found (hat this byer becomes thicker with crack, as shown in Figure 1; cracks which form rapidly when time, but at a decreasing rate, the deteriorated this checkinp. however. is only a rubber is stretched and exnosed visible sign of the deterioration to weather are caused by &one. surface offerin0 some &&on. The kind and In addition to the cracking, m ~ a ~ &fluenee depth of that has occurred previously. Therubber sheets used in these Williams has pointed out that deterwralion. tests were made with thickliaht and oxvpen will form an nesses of 0.02, 0.04, 0.06, and oGdised film- Gn the surface of rubber. He stated that this film may protect the rubber 0.08 inch (0.51 to 2.03 nim). After aging periods of 26 and against ozone; Van Rossem also found this protective action. 52 weeks, tensile testa were made. These data are shown in The present investiration wm directed to the measurement Figures 2 and 3, using the compounds shown in Table I. of the bxidized layer,-and a method was developed for deterTABLEI. COMP~UXDS INVESTIQATED" mining its thickness as follows: A thin slieet of rubber, 5 X 6 " . , I/ incheb(12.7 x 15.2 cm.), was placed on a board and covered Parts by rmght with paper toweling of the same size. A second rubber sheet pale crBuB in0 100 100
of p;iment
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Sullur 3 M a r o a p t ~ b e ~ ~ " ~ h i s ~ " 1 ~ 0.5 1 122
Stearic seid Zinc oxideb
...
1,lthnnnnab
3
0.5 1
31
...
3 0.5 1
I2 82
100 100 ino Rubber Zinc oxide& 20 5 2 Lithoponel, ... 18 Cure 25 minii~eiat 153" C . ti The sine oxide used in thia work was XX Red. The I ~ t l i v p o i l ewss Ulaek Label Alhaiith.
...
An example of the method for calculating the thickness of the deteriorated layer is as follows: If a rubber sheet, 0.04 inch (1.02 mm.) thick, developed a tensile strength of 3000 pounds per square inch (211.5 kg. per sq. om.) in the dark (covered) and 1500 pounds (105.5 kg.) exposed to the sunlight, the thickness of the deteriorated surface would be half of the total, or 0.02 inch (0.51 mm.). If the tensile strength had been 2250 pounds (158.2 kg.) instead of 1500 pounds (105.5 kg.), the deteriorated layer would have been only onefourth of the thickness, or 0.01 inch (0.25 mm.). Using the thicknascs of the deteriorated layers given in Table 11, curves were drawn to compare the calculated tensile strengths for the range of thicknesses (see dotted lines in Figures 2 and 3) with those actually found, and these curves cheeked fairly well. of the snme dimensions was placed over ihe first, and tire edges were covered and held tight by placing adhesive tape along them so that the nibbar was under [io sbmin. The
NOTE: Althouph the tensile8 01 the unaged nieoss over the unliaually large range oi thickoases were not 8 8 oonatnnt as might lisve been wiahed, theae irregularities do riot &Sect the memurement 01 the deteriorated Isyei. The C G U o~f the irregularity m a y lie in difficulty in gaging the *oft thin sheets.
board was then set in position outdoors so that the rubber surface would present a 45' sontliern exposure. Examination of the rubber sheets showed that there was little deterioration e s c q t on the surface exposed to the sun,
The data in Figure 4, as well as in Table 11, show that the deterioration continues with time of exposure, but at a decreasing rate, bhe oxidized film exerting a protective action. The calculated thicknesses of the deteriorated layers show
....
or AGINGFOR 52 WEEKS,USINC SLABS OF Tmum 2. F~FFECTOP AGING POH 26 WEEKS, USINGS ~ a w s ikunr: 3. EFFECT OF D~FFERENT THICKNF:~SES DIFFERENT TNICKNESSE~ 992
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
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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 f r o m 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
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