INDUSTRIAL AND ENGINEERING CHEMISTRY
1292
result with pure platinum, and over three and a half times the loss from the 10 per cent rhodium alloy. Therefore, a gauze catalyst containing this amount of iridium would give only one-half the life of a pure platinum and less than one-third the length of service of a 90 per cent platinum-10 per cent rhodium catalyst. The 5 per cent rhenium alloy lost 3.34 ounces per 100,000 pounds of ammonia a t 900" C. as compared with the above. The alloy containing 3 per cent ruthenium was tested for loss a t only 84OOC. (1544OF.), and itIost 1.157ouncesper 100,000 pounds of ammonia as compared with 0.563 ounce for pure platinum a t this lower temperature. Such high losses obviously make these alloys unattractive. The use of a platinum or other platinum metal coating on an inert base, such as a refractory, has been proposed and tested (8, 21). While good results were often obtained a t the start, the volatilization of platinum from such a catalyst quickly removed the active material. Gauze catalysts, consisting of a refractory base metal alloy coated with platinum and coated with rhodium, were tried. The results were unsatisfactory, as the underlying metal quickly poisoned the coating. .~CKNOWLEDGMENT
Appreciation is expressed to Baker and Company and to
F.E. Carter for their valuable assistance in preparing the
Vol. 26, No. 12
alloys and gauze catalysts. Credit is also given to the many who assisted in carrying out this investigation. LITERATURE CITED dndrussow, L., 2.angew. Chem., 41,205 (1928). Bodenstein and Biittner, Ibid., 47, 364 (1934). Bosch, C., U. 9.Patents 1,207,706-8 (1916); 1,211,394 (1917); 1,379,387 (1921). Burgess and Sale, Bur. Standards, Sci. Paper 254 (1915). Burgess and Waltenberg, Ibid., 280 (1916). Crooks, William, Proc. Roy. SOC.(London), 86, 461 (1912). Davis, C.W., U. S. Patents 1,706,055(1929) and 1,860,316 (1932). Duparc, Wenger, and Urfer, H e h . Chim. Acta, 8, 609 (1925); 11, 337 (1928). Fauser, G., Chem. & Met. Eng., 37, 604 (1930). Foote, Fairchild, and Harrison, Bur. Standards, Tech. Paper 170, 114 (1921). Gaillard, D . P., J. IND.ESG. C H E X ,11, 745 (1919). Handforth and Kirst, C. S. Patent 1,919,216 (1933). Kausch, O., "Die Kontaktstoffe der katalytischen Herstellung von Schweflsaure, Ammoniak und Salpetersaure," Verlag von Wilhelm Knapp, Halle (Saale), 1931. Nagel, A. T', 2. Elektrochern., 36, 754 (1930). Pierce, J. N., J . Phys. Chem., 36, 2001 (1932). Raschig, F., 2. angew. Chem., 41, 207 (1928). Roberts, J. H . T., Phil. Mag., 25, 207 (1913). Scott and Leech, ISD. EKG.CHEX.,19, 170 (1927). Taylor, Chilton, and Handforth, I b i d . , 23, 860 (1931). Taylor, H . S.,J . Phys. Chem., 30, 145 (1926). Urfer and Wenger, 2.angew. Chem., 31-2, 395 (1918). RECEIVED October 29, 1934.
Thermal Properties of Rubber Compounds 11. Heat Generation of Pigmented Rubber Compounds C. E. BARNETT AND W. C. MATHEWS, The N e w Jersey Zinc Company, Palmerton, Pa.
T
HE first paper (1) of this
amount of offset may be varied Good correlation is shown to exist between within wide limits. With this series discussed thermal pendulum tests on rubber compounded with machine one may study either conductivity of rubber various types of zinc oxide and .flexing life as the temperature developed over and a number of compounding measured by the Firestone Jlexometer. The a period of flexing or the time ingredients which were measured effect of particle size of zinc oxide on the results required to compress the sample using the electric current as the a predetermined amount. source of heat. I n this article obtained in both tests is investigated and the Machines such as those just the fundamental factors conoptimum size found to vary greatly with changes described are open to the objectrolling the generation of heat in pigment loading. The Firestone jlexometer tion that no indication is oband the variations possible by measures the hysteresis effects in a rubber comtained of the work done on or pigmentation are being studied. pound whereas the thermal conductivity of the returned by the rubber. For Results obtained for pigmented example, when an integrating rubber in the pendulum and compound has no effect on its flexing life. Time xvattmeter was placed on the flexometer will be discussed and of failure in the flexomefer is a direct function flexing machine. it was found correlated. of the temperature attained in the test. that the power curve for the I n the writers' l a b o r a t o r y machine with the suecimen in two machines have been used extensively in studying the temperature developed in rubber place differed by only a very small amount fro; that obcompounds subjected to distortion by compressive forces. tained with the machine running empty, The energy reThe first of these is a flexometer described by Cooper ( 2 ) , quired to distort the rubber specimen was insignificant in and the second a compression machine in which a rubber comparison with that required to run the machine. Neither block 14 cm. (5.5 inches) in diameter and 9.53 cm. (3.75 the flexometer nor the compression machine is entirely inches) high is pounded with a definite load a specified satisfactory for a fundamental study because of the objecnumber of times per minute. The laboratory test block tions given above or for testing of compounds containing used in the flexometer is in the shape of a frustrum of a moderately low concentrations of pigment because of the rectangular pyramid, of which the base is 5.4 X 2.86 cm. length of time required to obtain satisfactory results. For these reasons a pendulum was constructed to measure (2.126 X 1.125 inches), the top 5.08 X 2.54 cm. (2 X 1 inches), and the altitude 3.81 cm. (1.5 inches). This block of the energy losses in rubber compounds under compressive rubber is compressed between two plates under definite forces. The properties determined directly by the pendulum load, one of the plates being stationary while the other are (a) resilience, or the percentage of the impact energy which travels in a circular motion of definite magnitude. After the is returned to the pendulum by the rubber, and (b) indentation sample has been placed in the machine, the moving plate is which is the depth of penetration of the hammer-shaped head set to one side of the center. Both the loading and the of the pendulum into the sample and is a measure of the
December, 1934
I X D U S T R I A L .\ND
ENGINEERING CHEMISTRY
0.001 inch and may be estimated to within 0.0005 inch.
seems to have been the first to recognize the pos*ibilities of the pendulum in rubber testing. H e found that b y the use of different pigments he could r e a l i z e the four possible conditions : high r e s i l i e n c e , lo^ hardnev; high resilience, high hardness; low r e s i l i e n c e , lorn h a r d n e s s ; a n d low resilience, high hardness. Williams (ii) used a rebound test in studying the traniformation of energy b y ram and v u l c a n i z e d r u b b e r , and the pendulum or similar device is commonly used in many rubber laboratories.
PHYSICAL CHARACTERISTICS OF THE PENDULUM The energy a t impact of
a pendulum, as well as that recovered in the rebound, i. given b y the equation : IC1
where w I
e
(1
FIGURE1. I'EXDCLU~IFOR
- cos 8 )
1293
= weight, in this case 4070 grams = length from axis to center of gravity, = angle through which pendulum falls
57.6 cm.
The formula for velocity at impact is ( 4 X~ r~ X arc)/P, where T is the radius (71 cm.), and P the period (1.7 seconds). A photograph of the machine, which was constructed after inspection and consultation with the Goodyear and Dunlop
(I
.___ -RESILIENCE
INDEUTATICh
Contact with the micrometer g a g e is m a d e by the lower hammer, and all readings are multiplied by the ratio of the distance from the axis to the upper and lower hammers, respectively. The r u b b e r test specimens are 5.08 cm. square and 2.54 cm. thick, and are held firmly against the anvil, t h e p e n d u l u m striking one of the large faces. The pendulum was found to lose between O . l O o and 0.15' in the first period for a drop from 25'. C o r r e c t i o n for this loss of energy due to friction in the roller bearings and air resistance would add only 0.8 per cent to the resilience a t the maximum with decreasing amounts as less energy was returned; it was not considered necessary to make the correction. The curves obtained by plotting per cent resilience and indentation against impact energy are shown in Figure 2. Since these curves show decreasing resilience and increasing indentation with increases in MEASURING E~VERGY LOSSES impact energy, it is necessary for-comparative work that the height from which the pendulum falls be kept constant. In all of the pendulum data shown in this paper the optimum cure for resilience has been used. The effect of cure in the pendulum test is about what would be expected, the opt,imumfor resilience being reached earlier than that for indentation. As the cure progresses, the compounds continue to harden until reversion commences and the indentation increases. Comparative tests with machines in use in other laboratories (all samples prepared in one laboratory) have agreed within 2 per cent for both resilience and indentation while two operators on the one machine have checked within 0.5 per cent for resilience and 1 per cent for indentation.
EXPERIJIEKTAL PROCEDURE Since it was planned to use the pendulum in a study of heat generation, the logical starting point mas to determine what correlation could be obtained betn-een the pendulum and other testing machines such as the flexometer. The
tz 1 2 0 4
8
2
I5 20 Z4 IMPACT ELIERSY K G M / C M S
28
I''
FIGURE 2 . REL\TIOR' BETWEEN I \ l P A C T ENEHGY, RESILIENCE,ASD INDEUTATIOU FOR 2- AND 20VOLUMEZIXC OXIDE COMPOUNDS
0 x w J
100
w
z
0 I-
80
w
laboratories, both of whom use similar instruments, is shown in Figure 1. The pendulum is a 2.22-cm. steel rod, 107 em. in length, and carries two hammers mounted, respectively, 71 and 85.4 cm. from the axis; the head of each hammer is a hemisphere of 1.11 cm. radius and the upper hammer, located at the center of percussion, strikes the rubber specimen. With the tn-o hammers located in these positions the perfect pendulum should have 70.87 halfperiods per minute. Using an electrical chronograph and a small swing of the pendulum, the number of half-periods per minute were determined for four consecutive minutes with the following results: 70.7, 70.8, 70.9, and 70.9. The rebound of the pendulum is measured by means of a pointer rrhich mag be ad-
a
L
w
60
I
2
4 @
z
z z 3 I
00
90
100
110 PE\IDULc10
123
130 I40 100-RES - 1 E Y C E
53
IhDELl~A~IOh
BETWEES FLEXING LIFE (PERCENT FIGURE 3. RELATIOK OF ST.IKD.IRD SIMPLE) AKD PEUDULUM TESTSAT 28 VOLUMES OF ZIYCOXIDE
1294
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 26, No. 12
resilience in the low volume loadings but that the coarser oxides are superior a t the high volume loadings. In the 40-volume loading, 9c for example, the extremely coarse oxide has :e5 about 13 per cent higher resilience than the w finest oxide, while at 2- and 5-volume loadings f 8 C the fine oxides are better by about 5 per cent. With the exception of the very coarse oxide, 5 75 the differences in resilience are small, below 30 U a volumes of pigment, but above this point the 70 slow-curing and fine fast-curing oxides lose resilience quite rapidly, the loss in the case of 05 the latter being in the inverse order of the particle size. With respect to hardness, this 60 series of zinc oxides showed onlv small differences with the exception of the fine experiFIGURE 4. EFFECT OF VARIATION IN ZINC OXIDE CONTENT ON RESILIESCE AT mental oxide and the oxide, the latter SEVERAL VOLUME LO.4DINGS being softer over the entire range of volume simplest way to do this was to take the compounds being loadings and the former showing greater hardness a t about 15 tested in routine work on the flexometer and determine their volumes of pigment. properties with the pendulum. It was soon found that, while Data for channel black, two soft blacks, lithopone, Dixie high resilience and indentation indicated low heat develop- clay, natural and precipitated whiting, and ground barytes ment in the flexometer, there were many results which were are shown in Figure 6 for resilience and Figure 7 for hardness. out of line owing to unusual results in one or the other of the The same base formula was used as in the work reported for properties determined with the pendulum. However, by Figures 4 and 5 and the data for the fast-curing zinc oxide of combining both of the pendulum measurements in one em- 0.35 micron size; particle size has been carried over for compirical factor, an excellent correlation was obtained. The parison. The channel black compounds decrease rapidly in ll.o resilience and increase factor a c t u a l l y used rapidly in hardness as was ratio of percentage ," the pigmentation is inof energy lost to indentation; although other E creased. Those with o.o the finer of the thermar e l a t i o n s h i p s would tomic blacks are very h a v e s e r v e d as well, close to the zinc oxide this one gave a factor o.o which varied inversely compounds, although p 7.0 somewhat less resilient with flexing life. In and harder in the higher Figure 3 flexing life is :6.0 volume loadings, while p l o t t e d a g a i n s t the those with the coarser pendulum results with both sets of data ex5.0 of t h e thermatomic V O L . 1 I IO VOL. I I 15 VOL. I I 2 0 V O L . 1 I 30 V O L . I/ 4 0 V O L . I I2VOL.I I 5 carbons show higher pressed as percentages r e s i l i e n c e s above 20 of a standard sample FIGURE5. EFFECT O F VARIATION IN ZINC OXIDE CONTENT ON h D E N T . 4 whose formula was as TION AT SEVERAL VOLUMELOADINGS volumes of p i g m e n t follows: and lower values for less pigmentation with softer stocks over the entire range. Channel black 9 Smoked sheet 100 Sulfur 4 Zinc oxide Variable The tests on the remaining pigments and fillers were from Diphenylgusnidine 2 10 volumes upwards, the lithopone compounds having the In this test the flexometer was operated a t 1200 r. p. m. with a most resilience and showing only a small decrease as the load of 250 kg. (550pound) and an offset of 1.4 cm. (0.55 inch), pigmentation was raised to 40 volumes. The natural whitand failure was taken as the time required to compress the ing and Dixie clay were practically equal in resilience a t sample t o a thickness of 0.76 cm. (0.3 inch). From the nature 10 and 20 volumes while a t 40 volumes the clay was somewhat of the comparison, the range covered by the test was not very I CHANNEL BLACK 6 DIXIE CLAY great, and for the shorter flexing times the data were ob( 2 GROUND BARYTES 7 NATURAL WHITING ~ n n3 T H E R M A T O M I C B L A C K NO.1 8 Z N O - F A S T C U R I N G , tained from special samples; consequently fewer tests were 4 THERMATOMIC BLACK N0.2 P. 5.,.35* made in this portion of the curve. The data are sufficient I S PRECIPITATED WHITING 9 LITHOPONE to establish a good degree of correlation between the flexomeu 90 z ter and pendulum tests over the range investigated. The =L 80 next step was to determine the properties of a large number of U widely different compounds in the latter test, to predict the 2 70 results which would be obtained in the flexometer, and finally J to determine the flexing times for the series of compounds. U i; 60 The data obtained over a series of volume loadings of zinc , oxide in the base formula (given above), with the black omit53 ted, are plotted for resilience in Figure 4 and for indentation in Figure 5. These data were obtained on zinc oxides covering a 40 range in particle size, in the fast-curing type, from a fine exDerimenta1 oxide to that of a highly calcined oxide of extremely coarse particle size and include one slow-curing zinc FIGURE 6. EFFECT OF 10, 2 0 , AND 40 VOLUMES OF VARIOUSPIGMENTS AND FILLERS ON RESILIENCE oxide. The data show that the fine oxides have the highest 9!
I PARTICLE SIZE . l a
Y
2
I""
v) .J
December, 1934
INDUSTRIAL AND
ENGINEERING
lower than the whiting. The precipitated whiting was equal in resilience to the zinc oxide a t 40 volumes of pigment and slightly lower at 10 volumes. Ground barytes was another filler which gave compounds showing only a small decrease in resilience a t 40 volumes from the lralue obtained with 10 volumes. However, a t the low loading the resilience was lower than for any of the powders except channel black, and at 40 volumes about equal to the Dixie clay compound. In Figures 8 and 9 the zinc oxides shown in Figures 4 and 5 hare been retested over a range of volume loadings and with a different formulation as follows: Pale crepe Smoked sheet Stearic acid
50 60
3
Sulfur Mercaptobenzothiazole Zinc oxide
3 1
v)
CHEMISTRY
I CHANNEL BLACK 2 THERMATOMIC BLACK N O I 3 DIXIE CLAY 4 ZNO-FAST CURING P . S . 35% 5 NATURAL WHITING 6 PRECIPITATED WHITING 10.0 7 THERMATOMIC BLACK N O 2
E+ g -i
