Abstract
1. In the present work a method was developed for the measurement of the diffusion and the solubility of sulfur in rubber. Values of the diffusion coefficient and the solubility were obtained for a broad range of temperatures. It is shown that the free sulfur in rubber dissolves and diffuses in the form of S8 molecules. 2. The kinetics of sulfur combination with rubber in the presence of an accelerator was investigated. It is shown that at low sulfur concentrations the kinetics is of the first order. The rate constants of sulfur combination were determined, as well as the activation energy (U=23,000 cal./mole) of the process. 3. A study was made of the kinetics of the isotope exchange reaction between elemental sulfur and tetramethylthiuram disulfide in an inert solvent. The experiment showed that the rate constant of the isotope exchange and the rate constant of the combination of sulfur with rubber are equal to one another at all the temperatures investigated (120°–150° C). 4. The conclusion is drawn that the first stage of vulcanization, which governs the overall rate, and likewise the first stage of the isotope exchange reaction, consist in the decomposition of thiuram into radicals, with the diatomic biradical S2 being split off. 5. It is shown that, with an increase in the sulfur concentration, the kinetics of the sulfur combination with rubber ceases to conform to a linear equation. A secondary sulfur combination reaction, taking place at the point where the primary bonding of sulfur to rubber occurred, was discovered. A hypothesis is put forward as to the radical character of the primary sulfur combination, and regarding the union of polysulfide chains with the radicals in polymer chains, radicals which were formed by means of the primary action of sulfur upon the hydrocarbon.
Interfacial Kinetics of Nitrogen Dissolution in Molten Fe–Mn–C Alloys Using 15N–14N Isotope Exchange Reaction
