A DSC study of curative interactions. II. The interaction of 2,2′-dibenzothiazole with ZnO,sulfur, and stearic acid

The interaction of combinations of sulfur, 2,2′-dibenzothiazole (MBTS), ZnO, and stearic acid were studied by differential scanning calorimetry. A MBTS/stearic acid interaction was indicated as evidenced by the effect the MBTS/stearic acid combination had on the melting of sulfur, the S_α → S_β transition being suppressed in favor of a S_α → S_γ transition. The dissolution/interaction of MBTS in molten sulfur was also delayed by the MBTS/stearic acid interaction, which, it is proposed, involved protonation of the N atom in MBTS by stearic acid. MBTS did not affect the formation of zinc stearate from ZnO and stearic acid, but when sulfure was added to the mixture, the ZnO/stearic acid reaction did not go to completion. No direct evidence for the formation of 2,2′-dibenzothiazole polysulphides was found, but the absence of the S_γ → S_μ transition in sulfur/MBTS mixes was interpreted as indirect evidence of a reaction between these curatives. There was no evidence for the formation of a sulfur/MBTS/ZnO compound of the type generally attributed the role of an active sulfurating agent in accelerated sulfur vulcanization.     

Strain-Induced Deformation in Magnesia–Alumina Layered Composites

Ceramic beams are induced in situ to form complex shapes at elevated temperature without the application of an external stress. This process has been demonstrated for thin alumina substrates coated with a layer of magnesia. The internal strain causing the substrates to deform at elevated temperature arises as a consequence of strain mismatch accompanying the penetration of the coating into the substrate. The magnitude of the deformation depends on the amount of coating applied, on the thickness of the substrate, on the density of the substrate, and on the temperature. During exposure of the beams to elevated temperature, the magnesia coating reacts with the alumina substrate to form the spinel phase; the resulting volume change accompanying the phase transformation is likely the predominant driving force for deformation.     

Programmed cooling crystallization of potassium sulphate solutions

The crystal size distribution from a batch cooling crystallizer is predicted by the numerical solution of a mathematical model which uses empirical kinetics of nucleation and crystal growth. The predictions clearly point out the potential advantages of controlled cooling at a constant nucleation rate for improving the product crystal size over that obtained by either natural or linear cooling.Experimental runs following programmed cooling curves for seeded potassium sulphate solutions showed reasonable agreement with the theoretical predictions. A size dispersion of the crystals was observed which contributes to a slight deviation from theory. Nevertheless, controlled cooling significantly reduced the quantity of nuclei formed and improved the product crystal size distribution.     

On the mechanism of transfer enhancement by eddy promoters

Mass transfer rates in a rectangular duct of low aspect ratio containing semicircular cylindrical inserts attached alternately on opposite walls and perpendicular to the flow direction were measured with the electrochemical diffusion-limited current technique. Local and average mass transfer coefficients determined with arrays of strip electrodes indicate the existence of at least two transfer regimes. In the laminar regime the exponent on the Reynolds number depends on the eddy promoter spacing. In the turbulent regime the data correlate well according to j_D = 0.57 Re^?0.35(d_h/p)^0.40.The local transfer distributions reveal the existence of separated flow regions downstream of, as well as opposite to, turbulence promoters. The flow in the reattachment region is very unstable and this results in earlier transition to turbulence.The local transfer distributions also suggest that boundary layer disruption at, and redevelopment downstream of, separated regions is the dominant mechanism of transfer enhancement in the turbulent regime. An idealized model based on this assumption, and making use, of results obtained for turbulent transfer to a flat plate in an infinite medium predicts a relationship in approximate agreement with the experimental correlation given above.The mass transfer results for fully developed turbulent flow also correlate well according to a mass transfer similarity law.     

Airborne differences in odors emitted byRattus norvegicus in response to reward and nonreward

To test the hypothesis that rats (Rattus norvegicus) emit airborne, differential odors in response to reward and nonreward, donor rats received random sequences of rewarded and nonrewarded placements in small compartments and an airstream transported odors from these compartments to test rats in a separate chamber. When donors remained in the compartments during, or were removed just prior to, air transport, test rats utilized transported odors as discriminative cues signaling their own reward and nonreward for a lever-press response. When the airstream was passed through a clean compartment containing paper flooring extracted from donor compartments, test rats were not able to discriminate. Test trials to assess for control by food odors suggest that donor-produced odors, rather than food odors per se, provided the discriminative signals for test rats. Results confirm the existence of somewhat volatile, although apparently stable, odors emitted in response to reward and nonreward, and implicate a differential in amount and/or type of odor produced by donors to these two events as the source of discriminative control.     

Performance relationships in PVC–plasticizer dry blending

The phenomenon of plasticizer acceptance by poly(vinyl chloride) (PVC) in hotprocess dry blending is examined via scanning electron microscopy, mercury intrusion porosimetry, and torque rheometer measurements. The effects of granule porosity, resin molecular weight, and synthesis recipe in PVC manufacture by the suspension process are related to the rate of plasticizer acceptance. For a PVC resin to dry blend, i.e., to become a free-flowing powder when mixed with plasticizer under hot-processing conditions, the resin granules must be porous. Porosity arises from interstices between primary PVC particles. At a given granule porosity, an increase in primary particle agglomeration adversely affects dry blend performance. At constant molecular weight and for resins manufactured by a given recipe, dry-blend performance is quantitatively described by granule porosity. With an increase in resin molecular weight, a greater granule porosity is required to maintain an equivalent dry-blend time (DBT). Accordingly, for most suspending agent recipes, DBT is dependent directly upon granule porosity and inversely upon molecular weight. However, if the suspending agent used in resin manufacture is an excessively rapid film former, dry-blend performance with molecular weight variation is dependent upon the suspending agent's concentration, not upon granule porosity, which must be adequate, nor upon the resin's molecular weight. An interfacial film-forming suspending agent enhances fusion of primary PVC particles at the suspension granule—water interface, increasing the granule's “pericellular membrane” thickness. This membrane, a PVC skin, does not significantly influence dry-blend performance with low- or intermediate-viscosity plasticizers. The particle skin does impede dry-blend rates with high-viscosity, poorly solvating plasticizers, but this effect can be negated in part by increasing the diameter of pore openings in the topographical skin. Dry blending occurs below the glass transition temperature (T_g) of PVC with low-viscosity plasticizers and above the T_g with high-viscosity, poorly solvating modifiers. The influence of resin and plasticizer variables indicates the dry-blend phenomenon to be a diffusion-controlled process. The rate of dry blending is dependent upon two mechanisms: (1) the rate of pore penetration—which exposes the plasticizer to a much greater surface area than if it remained exterior, encapsulating the granule—and (2) the rate of plasticizer diffusion into the PVC matrix.     

Oxidation of Thin Sheet Reaction-Sintered Silicon Nitride

Oxidation of reaction-sintered silicon nitride was studied in damp air. The formation of "passive" silica films was investigated at 1 atm and 700 to 1100°C and some limited work on weight loss behavior was performed in vacuo of 10⁻⁸ to 10⁻⁵ atm at 1050 to 1200°C. Passive behavior was dominated by reaction in the pore network. Oxidation was extensive at 900 to 1000° but slight at 700 to 800°C. At 1100°C a protective skin limited reaction. Weight loss in vacuo was slight at 1050°C. The vacuum pressure required to suppress the weight loss increased from 4 to 5 × 10⁻⁷ atm at 1050° to 1.5 to 2.5 × 10⁻⁵ atm at 1200°C.     

Continuous solvent extraction of sunflower,seed, groundnuts,palmkernels, rapeseed,and copra

In principle, the oil milling process is straightforward. The wide variety of equipment in use reflects, however, a multiparametric process. The main limiting parameters are kind of seed, oil content, particle strength, particle structure, temperature, moisture, particle size, residence time, mechanical forces, etc. Additionally, the seed specific parameters vary not only between kinds of seed but also for the same seed, due to different conditions in climate, soil, and harvesting. Therefore, equipment design must be widely based on statistical averages of the limiting parameters. In other words, exact precalculation of the single technological steps is impossible. As a consequence, for more than 5,000 years, the oil milling process has been in the stage of being optimized. The acutal technical standard is very satisfying, but there is still a strong need for further research and development. Currently, as in the past, the oil milling process seems to be not so much a science as an art.