Showing papers by "ExxonMobil published in 1984"

Limiting efficiency of silicon solar cells

Abstract: The detailed balance method for calculating the radiative recombination limit to the performance of solar cells has been extended to include free carrier absorption and Auger recombination in addition to radiative losses. This method has been applied to crystalline silicon solar cells where the limiting efficiency is found to be 29.8 percent under AM1.5, based on the measured optical absorption spectrum and published values of the Auger and free carrier absorption coefficients. The silicon is assumed to be textured for maximum benefit from light-trapping effects.

Charge renormalization, osmotic pressure, and bulk modulus of colloidal crystals: Theory

Abstract: The interactions between charged colloidal particles with sufficient strength to cause crystallization are shown to be describable in terms of the usual Debye–Huckel approximation, but with a renormalized charge. The effective charge in general is smaller than the actual charge. We calculate the relationship between the actual charge and the renormalized charge by solving the Boltzmann–Poisson equation numerically in a spherical Wigner–Seitz cell. We then relate the numerical solutions and the effective charge to the osmotic pressure and the bulk modulus of the crystal. Our calculations also reveal that the renormalization of the added electrolyte concentration is negligible, so that the effective charge computations are useful even in the presence of salts.

Process and catalyst for producing reactor blend polyolefins

Abstract: Polyolefin reactor blends obtained by polymerization of ethylene and higher alpha-olefins in the presence of a catalyst system comprising two or more metallocenes and alumoxane.

Elastic Properties of Random Percolating Systems

Abstract: We study the macroscopic elastic moduli of an elastic percolating network in the critical region. A microscopic elastic Hamiltonian is used, which contains a bending energy term. We find that the rigidity threshold of this system is identical to the percolation threshold ${p}_{c}$. By considering the elastic properties of elements of the infinite percolation cluster we calculate the critical exponent $\ensuremath{\tau}$ which describes the behavior of the elastic stiffness near ${p}_{c}$ for $d=6$ and obtain a lower bound on $\ensuremath{\tau}$ for $dl6$. $\ensuremath{\tau}$ is considerably higher than the conductivity exponent $t$, suggesting that the elastic problem belongs to a different universality class.

Structure of three-component microemulsions in the critical region determined by small-angle neutron scattering

Abstract: The intensity distribution of the critical scattering from sodium di-2-ethylhexylsulfosuccinate $\mathrm{AOT}\ensuremath{-}{\mathrm{D}}_{2}\mathrm{O}\ensuremath{-}n$-alkane water-in-oil (W/O) microemulsions has been measured over an extensive range of droplet volume fractions (3-30 vol%) and temperatures (22 to 43\ifmmode^\circ\else\textdegree\fi{}C) in the critical region. The water/surfactant molar ratio of the microemulsion was kept at a constant value of 40.8, for which previous experiments on the temperature variation have been well documented. A structural model of W/O microemulsions based on well-defined surfactant-coated water droplets is firmly established up to a volume fraction of about 20 vol% for all temperatures studied. Data analysis assumes that the cloud points and subsequent phase separation are caused by concentration fluctuations of polydisperse droplets. The major conclusions drawn from the analysis are as follows. (1) The order parameter of the critical phenomenon can be taken to be the volume fraction of the dispersed droplets. (2) The size and polydispersity of the droplets remain essentially constant in the vicinity of the critical point (for a fixed water/surfactant ratio). (3) The critical phenomenon is driven by an increased attraction between the droplets as the critical point is approached. (4) The critical point can be approached by either raising the temperature at fixed volume fraction or by varying the carbon number of the oil solvent at fixed volume fraction and temperature. (5) The nature of the droplets does not change upon a phase separation into two coexisting microemulsions. The data also gives some evidence that the droplet picture of the microemulsion breaks down at sufficiently high concentrations of water and surfactant.

Fundamental Studies of Transition Metal Sulfide Hydrodesulfurization Catalysts

Abstract: Hydroprocessing catalysts based upon the transition metal sulfides have been widely used for over 60 years and catalysts such as Co/Mo/Al2O3 remain the industry “workhorses” in hydroprocessing of petroleum-based feedstocks [1]. Such applications include sulfur removal (hydrodesulfurization), nitrogen removal (hydrogenitrogenation), and product quality improvement (hydrotreating, hydroconversion). Original interest (prior to World War II) in these catalysts centered on their activityin the hydrogenation of coal liquids which contain considerable amounts of sulfur, thus maintaining the transition metal in the sulfided state. It was quickly discovered that Co, Ni, Mo, and W sulfides and their mixtures were the most active and least expensive of the transition metal sulfides [2]. Later (post-World War II) their major uses shifted to hydroprocessing of sulfur- and nitrogen-containing petroleum-based feedstocks with Co- and Ni-promoted Mo and W catalysts usually supported on Al2O3. However, as petroleu...

Near-edge X-ray-absorption fine-structure studies of chemisorbed hydrocarbons: bond lengths with a ruler

Abstract: Starting from an established correlation between the $\ensuremath{\sigma}$ shape resonance position in nearedge x-ray-absorption fine-structure spectra and the intramolecular C-C bond length for gas-phase hydrocarbons, we derive a similar relation for chemisorbed molecules. The linear relation obtained allows us to determine the C-C bond length for chemisorbed molecules from near-edge x-ray-absorption fine-structure spectra with a ruler to an accuracy of 0.04 \AA{}. Examples are given for bonding and bond-length changes of ${\mathrm{C}}_{2}$${\mathrm{H}}_{2}$ and ${\mathrm{C}}_{2}$${\mathrm{H}}_{4}$ on Pt(111).

Narrow MWD alpha-olefin copolymers

Abstract: The present invention relates to novel copolymers of alpha-olefins comprised of intramolecularly heterogeneous and intermolecularly homogeneous copolymer chains.

Torque and drag in directional wells-prediction and measurement

Abstract: A computer model has been developed to predict drillstring torque and drag, and a versatile rotary torque meter has been built to use in calibrating the model. The principle of the predictive model is that torque and drag forces in a directional wellbore are primarily caused by sliding friction. Sliding friction force is calculated by multiplying the sidewall contact force by a friction coefficient. Realistic sliding friction coefficients were determined from field data by using the same predictive computer model. These field data were gathered using novel torque and hookload indicators that are accurate, portable, and easily installed. Good agreement between friction coefficients calculated from different loads in the same well, as well as agreement between those for different wells, indicates the validity of the predictive drillstring model. Sliding friction is concluded to be the major source of torque and drag in directional wells. For waterbase mud systems, typical friction coefficients range from 0.25 to 0.40.

Attractive Interactions in Micelles and Microemulsions

Abstract: We have used small-angle neutron scattering to study surfactant interactions in an inverted micellar and a related microemulsion system. The structure-factor fits imply an attractive interaction between micelles with a short-ranged potential due to the overlapping of the surfactant hydrocarbon tails. The linear increase in this interaction with size accounts for the critical transition observed in the microemulsion. This analysis is confirmed by Monte Carlo simulations.

Procedure for fabrication of microstructures over large areas using physical replication

Abstract: The present invention is an improved replication process which copies a master pattern onto an intermediate transfer mask which is then used to form a lithographic mask on the surface of a substrate. A pattern derived from the original master pattern is then produced in the substrate by an etching process.

Drill Pipe Buckling in Inclined Holes

Abstract: Etude theorique montrant que les tiges de forage peuvent supporter des charges de compression sans flambage dans les forages a forte inclinaison

The Characteristics of Alumina Scales Formed on Fe‐Based Yttria‐Dispersed Alloys

Abstract: L'alliage etudie comporte 20% Cr, 4,5% Al, 0,5% Ti et 0,5% Y 2 O 3 . La cinetique d'oxydation de l'alliage a ete etablie a diverses pressions partielles d'oxygene, dans le domaine de temperature 1000-1200°C

Cobalt catalysts for the conversion of methanol to hydrocarbons and for Fischer-Tropsch synthesis

Abstract: A rhenium promoted cobalt catalyst, especially a rhenium and thoria promoted cobalt catalyst, and process for the conversion of methanol to hydrocarbons. Methanol is contacted, preferably with added hydrogen, over said catalyst, or synthesis gas is contacted over said catalyst to produce, at reaction conditions, an admixture of C 10 + linear paraffins and olefins. These hydrocarbons can be further refined to high quality middle distillate fuels, and other valuable products such as mogas, diesel fuel, jet fuel, lubes and speciality solvents, particularly premium middle distillate fuels of carbon number ranging from about C 10 to about C 20 .

Desulfurization and Structural Transformation of Thiophene on the Pt(111) Surface

Abstract: The temperature dependence of near-edge x-ray-absorption fine-structure spectra above the C $K$ edge and S ${L}_{2,3}$ edge for thiophene (${\mathrm{C}}_{4}$${\mathrm{H}}_{4}$S) on Pt(111) reveals changes in the chemisorption geometry and the cleavage of the carbon-sulfur bond. Our results suggest the formation of a metallocycle intermediate after desulfurization with the S atom replaced by a Pt surface atom. The near-edge x-ray-absorption fine-structure results are corroborated by thermal-desorption, x-ray photoemission, and electron-energy-loss data.

Ethylene copolymer viscosity index improver-dispersant additive useful in oil compositions

Abstract: Oil soluble viscosity index improving ethylene copolymers, such as copolymers of ethylene and propylene; and ethylene, propylene and diolefin; etc., are reacted or grafted with ethylenically unsaturated carboxylic acid moieties, preferably maleic anhydride moieties, and reacted with polyamines having two or more primary amine groups and a carboxylic acid component, preferably alkylene polyamine and alkenyl succinic anhydride such as polyisobutenyl succinic anhydride. Or the grafted ethylene copolymer can be reacted with already formed salts, amides, imides, etc. of said polyamine and acid component, preferably imides of alkylene polyamine and alkenyl succinic anhydride. These reactions can permit the incorporation of varnish inhibition and dispersancy into the ethylene copolymer while inhibiting cross-linking with resulting viscosity increase, haze or gelling. The aforesaid grafting reaction may be carried out thermally, or more preferably with a free radical initiator such as a peroxide in a mineral lubricating oil, in which case the acid component, preferably also acts to solubilize insoluble compounds formed by side reactions, such as maleic anhydride grafted oil molecules reacted with amine, to thereby inhibit haze formation, particularly when preparing oil concentrates of the V.I.-dispersant additive for later addition to lubricating oils. The invention also includes preferred methods of grafting maleic anhydride onto the ethylene copolymer by periodic or continuous addition of maleic anhydride and initiator charge, so as to maintain the maleic anhydride in solution during the grafting reaction.

Target annihilation by random walkers.

Abstract: We study the target annihilation through random walkers on regular lattices, and for it we derive, based on the generating functions' formalism, an exact expression. Extensions to continuous time and to random walks on fractals are given. Using numerical simulations we compare the results to those which obtain for the trapping problem.

Cylindrical microemulsions: a polymer-like phase ?

Abstract: The regions of stability of spherical, cylindrical, and lamellar phases of microemulsions are calculated within mean-field theory. In the cylindrical phase, thermal fluctuations determine a temperature dependent persistence length below which the cylinders are rigid (rod-like) and above which the cylinders are flexible (polymer-like). The length of the polymer-like chains depends on concentration and temperature. The radii of gyration of these flexible microemulsions are also calculated.

First-principles linear combination of atomic orbitals method for the cohesive and structural properties of solids: Application to diamond

Abstract: We present a new method for the ab initio calculation of the cohesive and structural properties of solids. The method is based upon a linear combination of atomiclike orbitals (LCAO). Thus it possesses the physical appeal of traditional LCAO approaches. The method is a "first principles" one in the sense that no adjustable parameters enter the calculation. The required overlap integrals are calculated directly in real space. The one-electron potentials are derived from atomic properties and correspond to "ab initio" pseudopotentials. Another aspect of the method is that it does not involve a fully-self-consistent-field solution of the Schr\"odinger equation. Rather, the total energy of the system is obtained by using a noniterative approach based explicitly on the variational principle in the density-functional formalism. The method is applied to an archtypical covalent system: the diamond crystal. Several ground-state properties---including the cohesive energy, lattice constant, the bulk modulus, and the derivative of the bulk modulus with pressure---are computed. The computed lattice constant and bulk modulus are within 1-2% of the experimental values and the computed cohesive energy is within 10% of the experimental value. Also, we present a frozen-phonon calculation for the optical phonons at the Brillouin-zone center and obtain agreement to within 1% of the experimental value.

Chapter 2 The Optical Absorption Edge of a-Si: H

Abstract: Publisher Summary This chapter explores the effect of temperature, isochronal annealing, and preparation conditions on the optical absorption edge of a-Si:H x films The chapter describes the Tauc, Abe, and Toyazawa models The Tauc model defines the absorption edge of an amorphous semiconductor through the concept of a nondirect optical transition in which electron momentum is not conserved (total disorder) By utilizing the random phase approximation and parabolic bands, Tauc defined an optical gap E G that is widely used by experimentalists to define the position and the shape of the high-energy side of the absorption edge for a-Si:H x and other amorphous semiconductors The quantity E G is not a significant feature of the absorption edge but can be successfully correlated with the magnitude of the mobility gap deduced from transport measurements Abe and Toyazawa generalized the Tauc model to include a variable degree of Gaussian site disorder on the basis of the coherent potential approximation From this generalization, the Tauc optical gap E G becomes an additive function of structural and thermal disorder, in agreement with experiment

Method and apparatus for separating carbon dioxide and other acid gases from methane by the use of distillation and a controlled freezing zone

Abstract: The invention relates to method and apparatus for separating carbon dioxide and other acid gases from methane by treating the feedstream in at least one distillation zone and a controlled freezing zone. The freezing zone produces a carbon dioxide slush which is melted and fed into a distillation section. The apparatus used to practice the process is preferably in a single vessel.

Critical Properties of an Elastic Fractal

Abstract: Some solvable fractal models of the percolating backbone are used to investigate the critical behavior of a random, $d$-dimensional, isotropic, elastic medium. The critical exponent $T$ for the elastic moduli is found to be appreciably greater than the conductivity exponent $t$, and the ratio of bulk to shear modulus is found to have the universal value $\frac{4}{d}$. A comparison with the effective-medium and the Clausius-Mossotti-type approximations leads to the conjecture that the result $\frac{4}{d}$ is in fact exact.