Index of content:
Volume 8, Issue 7, 01 July 1937
8(1937); http://dx.doi.org/10.1063/1.1710322View Description Hide Description
The Use of the A.S.T.M. Penetration Equipment for Estimating the Viscosities of Materials of High Consistency8(1937); http://dx.doi.org/10.1063/1.1710328View Description Hide Description
In a recent publication Thelen described experiments in which the standard penetrometer was used to determine the flow‐shear diagrams for a number of asphalts. On the basis of these diagrams Thelen calculated viscosities which are of different magnitude from those expected from Saal's formula. In the present paper certain fallacies in Thelen's deductions are pointed out. A new method for analyzing Thelen's experimental results is shown which makes it possible to calculate absolute viscosities from penetration readings for a series of successive time intervals. The method is based upon the determination of viscosity by axial displacement of concentric vertical cylinders. Since the conditions under which viscosity can be determined by axial displacement are only approximated in the penetration test the new method cannot be expected to have a high degree of accuracy. Nevertheless from successive penetration readings on a coal tar pitch (penetration 100 g, 5 sec. at 25°C) an average viscosity of 383,000 poises was calculated which closely agrees with the value of 380,000 determined by a capillary rise viscometer. The viscosity as calculated from the initial penetration reading by the Saal formula was 355,000 poises.
8(1937); http://dx.doi.org/10.1063/1.1710329View Description Hide Description
8(1937); http://dx.doi.org/10.1063/1.1710330View Description Hide Description
The absorptionspectrum of stretched rubber has been studied in the region between 2μ and 8μ. In the case of unilateral stretch transmission measurements indicate that the absorption bands near 3.3μ and 7μ become broader with increasing stretch while the general background absorption becomes more pronounced. Radial stretch was found to produce similar effects in the 3.3μ and 7μ regions while the bands near 6μ became less intense for both unilateral and radial stretch. In the spectrum of rubber stretched radially to approximately twelve times its original area a band was observed near 4.8μ in a region where there is no intense absorption in the unstretched material. Since both absorption and reflection are involved in transmission measurements, it was necessary to determine reflection and extinction coefficients. The results indicate that the reflection coefficient diminishes and the extinction coefficient increases with increasing stretch. The observed variations in the extinction coefficients are of greater magnitude than those to be expected from the known density changes which accompany stretching.
8(1937); http://dx.doi.org/10.1063/1.1710331View Description Hide Description
Eyring's reaction rate theory of the viscosity of simple and of non‐Newtonian liquids has been outlined. Mooney's data on the rheology of a sample of raw rubber have been shown to be in agreement with Eyring's theory. The data have been discussed from the viewpoint of the theory, and some conclusions have been drawn concerning the probable mechanism of viscous flow in raw rubber.