The growth kinetics of a film formed by the thermal decomposition of dimethyl disulfide on an iron foil are measured using a microbalance where the growth kinetics are parabolic (film thickness X varies with time as X 2 ∝ t) at high reaction temperatures and pressures, indicating that it is limited by diffusion through the film. The activation energy for this process is 54.5 ( 0.5 kcal/mol. The growth rate becomes linear as the reaction temperature and/or reactant pressure is lowered, indicating that, under these circumstances, the reaction rate is limited by thermal decomposition of dimethyl disulfide at the growing interface. The activation energy for thermal decomposition at the interface is found to be 37.6 ( 0.7 kcal/mol, and a half-order kinetics pressure dependence for the surface reaction rate is found consistent with a reaction limited by the rate of dimethyl disulfide dissociation. Analysis of the resulting film using Raman and X-ray photoelectron spectroscopies as well as X-ray diffraction reveal the formation of FeS, which may be slightly nonstoichiometric. This film is similar to that formed by methanethiol, suggesting that they may both initially form a surface thiolate species that further reacts to form FeS. The half-order reaction kinetics noted above are consistent with this. Measurement of dimethyl disulfide as an extreme-pressure (antiseizure) additive reveals a plateau at an applied load of ∼4000 N in the seizure load versus additive concentration curve. It has previously been suggested that the plateau corresponds to the load at which the interface reaches the melting point of the solid lubricant layer (in this case proposed to be FeS). Estimation of the interfacial temperature using a method developed previously yields an interfacial temperature of ∼1480 K, in good agreement with the melting point of FeS.
An attempt was made to melt incorporate ultra high molecular weight polyethylene, UHMWPE, into medium density polyethylene, MDPE. The behavior of the mixtures, containing up to 6 wt percent of UHMWPE, was examined using mechanical and rheological testing. The mechanical test results were found to contain large experimental errors, which makes interpretation very difficult. On the other hand, melt rheology studies, using dynamic and extensional deformations, gave direct insight into the extent and effect of blending. Degradation during the processing was evaluated by size exclusion chromatography. The degree of dispersion of the UHMWPE was examined under the optical microscope.
Following the ester‐amide interchange reaction in the poly(ethylene terephthalate)/poly(amide‐6, 6) (PET/PA) system in the presence of p‐toluenesulfonic acid (TsOH), samples were injection molded and tested in the tensile mode. A brittle fracture was observed for these unoriented specimens. To separate the influence of the crystallinity from that of the interphases, the samples were studied using differential scanning calorimetry (DSC). The DSC results indicated an increase of crystallinity in the blends caused by enhanced nucleation of PA (which crystallizes first) and that of the copolymer resulting from the esteramide interchange reaction. It has been independently verified that neat PET samples of comparable crystallinity to that existing in the PET/PA blends show a similar behavior.
Carbon tetrachloride thermally decomposes on iron in the temperature range 500-700 K to form films that consist predominantly of iron chloride. Two growth regimes are found: (1) parabolic, where the film thickness (X) varies as a function of time as X 2 ∼ t and where the growth rate is independent of pressure, and (2) a linear growth region (X ∼ t), where the growth kinetics are first order in CCl4 pressure. The kinetics are analyzed by a model which assumes that growth is controlled either by CCl4 thermally decomposing at the growing gas-film interface or by diffusion through the film. Analysis of the experimental data gives an activation energy for diffusion of 21.5 ( 0.3 kcal/mol and an activation energy for CCl4 decomposition of 18.3 ( 0.5 kcal/mol. In contrast to the behavior found for methylene chloride and chloroform, where small particles of carbon were identified in the film using Raman spectroscopy, no carbon particles are found in films formed from carbon tetrachloride decomposition below ∼700 K although carbon is found in the film using X-ray photoelectron spectroscopy. XPS results also suggest that, in addition to completely thermally decomposing to yield carbon and chlorine, a small portion of the CCl 4 can react to form adsorbed CCl2 species.
Extensional flow of mica-filled high density polyethylene was studied at 150°C in a Rheometrics elongational rheometer. The constant strain-rate mode at a rate of to 1.0 s-', and the constant stress mode were used. The mica content was 0, 25, 40, and 60 weight percent. In both testing modes, the steady state elongational viscosities were obtained; those for the filled samples were about ten to twenty times larger than the shear viscosity at corresponding (low) rates of deformation.
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