ExxonMobil

About: ExxonMobil is a company organization based out in Irving, Texas, United States. It is known for research contribution in the topics: Catalysis & Polymer. The organization has 16969 authors who have published 23758 publications receiving 535713 citations. The organization is also known as: Exxon Mobil Corporation & Exxon Mobil Corp..

Effective-medium theories for two-phase dielectric media

Abstract: Two different effective‐medium theories for two‐phase dielectric composites are considered. They are the effective medium approximation (EMA) and the differential effective medium approximation (DEM). Both theories correspond to realizable microgeometries in which the composite is built up incrementally through a process of homogenization. The grains are assumed to be similar ellipsoids randomly oriented, for which the microgeometry of EMA is symmetric. The microgeometry of DEM is always unsymmetric in that one phase acts as a backbone. It is shown that both EMA and DEM give effective dielectric constants that satisfy the Hashin–Shtrikman bounds. A new realization of the Hashin–Shtrikman bounds is presented in terms of DEM. The general solution to the DEM equation is obtained and the percolation properties of both theories are considered. EMA always has a percolation threshold, unless the grains are needle shaped. In contrast, DEM with the conductor as backbone always percolates. However, the threshold in EMA can be avoided by allowing the grain shape to vary with volume fraction. The grains must become needlelike as the conducting phase vanishes in order to maintain a finite conductivity. Specifically, the grain‐shape history for which EMA reproduces DEM is found. The grain shapes are oblate for low‐volume fractions of insulator. As the volume fraction increases, the shape does not vary much, until at some critical volume fraction there is a discontinuous transition in grain shape from oblate to prolate. In general, it is not always possible to map DEM onto an equivalent EMA, and even when it is, the mapping is not preserved under the interchange of the two phases. This is because DEM is inherently unsymmetric between the two phases.

Elastic blends comprising crystalline polymer and crystallizable polymers of propylene

Abstract: Improved thermoplastic polymer blend compositions comprising an isotactic polypropylene component and an alpha-olefin and propylene copolymer component, said copolymer comprising crystallizable alpha-olefin sequences. In a preferred embodiment, improved thermoplastic polymer blends are provided comprising from about 35% to about 85% isotactic polypropylene and from about 30% to about 70% of an ethylene and propylene copolymer, wherein said copolymer comprises isotactically crystallizable propylene sequences and is predominately propylene. The resultant blends manifest unexpected compatibility characteristics, increased tensile strength, and improved process characteristics, e.g., a single melting point.

Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary.

Abstract: The Triassic/Jurassic boundary, 208 million years ago, is associated with widespread extinctions in both the marine and terrestrial biota. The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province. This volcanic event is thought to have released significant amounts of CO2 into the atmosphere, which could have led to catastrophic greenhouse warming, but the evidence for CO2-induced extinction remains equivocal. Here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations, spanning a 20-Myr period across the Triassic/Jurassic boundary. Using a standard diffusion model, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000-4,000 p.p.m. increase. The relative stability of atmospheric CO2 across this boundary suggests that environmental degradation and extinctions during the Early Jurassic were not caused by volcanic outgassing of CO2. Other volcanic effects-such as the release of atmospheric aerosols or tectonically driven sea-level change-may have been responsible for this event.

High silica crystalline zeolites and processes for their preparation

Abstract: CRYSTALLINE ALUMINOSILICATE ZEOLITES HAVING SILICA TO ALUMINA MOLE RATIOS SUBSTANTIALLY HIGHER THAN PRIOR ART ZEOLITES ARE PREPARED BY A PROCESS WHEREIN A CONVENTIONAL CRYATALLINE ALUMINOSILICATE ZEOLITE IS CONTACTED WITH WATER AT AN ELEVATED TEMPERATURE AND THEN TREATED TO REMOVE ALUMINA FROM THE CRYSTAL LATTICE. THE WATER TREATMENT CAN BE ACCOMPLISHED BY CONTACTING THE CRYSTALLINE ALUMINOSILICATE ZEOLITE WITH A GAS CONTAINING AT LEAST 2% WATER AT A TEMPERATURE BETWEEN 800 AND 1500*F. HIGHER CONCENTRATIONS OF WATER ARE PREFERRED, AND, IN A PREFERRED EMBODIMENT, THE WATER TREATMENT IS ACCOMPLISHED IN TWO STEPS; VIZ, BY AFIRST TREATING THE CRYSTALLINE ZEOLITE WITH A GAS CONTAINING AT LEAST 2% WATER, FOLLOWED BY TREATMENT WITH PURE STEAM. FOLLOWING THE WATER TREATMENT, AMOPHOUS ALUMINA MAY BE REMOVED FROM THE ZEOLITE MATERIAL BY CONTACTING WITH A DILUTE MINERAL ACID OR AN ORGANIC ACID CHELATING AGENT.