Thermodynamic Methods and Models to Study Flexible Metal–Organic Frameworks

Much attention has recently been focused on a fascinating subclass of metal‐organic frameworks that behave in a remarkable stimuli‐responsive fashion. These soft porous crystals feature dynamic crystalline frameworks displaying reversible, large‐amplitude structural deformations under external physical constraints such as temperature, electric field or gas exposure. The number of reported syntheses of such materials is rapidly growing and they are promising for practical applications, such as gas capture, purification and fluid separation. Herein, we summarize the recently developed thermodynamic tools that can help understand the process of fluid adsorption and fluid mixture coadsorption in these flexible nanoporous materials. These tools, which include both molecular simulation methods and analytical models, can help rationalize experimental results and predict adsorption properties over a wide range of thermodynamic conditions. A particular focus is given on how these methods can guide the experimental exploration of a large number of materials and working conditions (temperature, pressure, composition) to help design efficient processes relying on fluid adsorption in soft porous crystals.     

High-Lying Rotational Levels of Water: Comparison of Calculated and Experimental Energy Levels for (000) and (010) up to J = 25 and 21

Emission spectra of methane-oxygen low-pressure flames have been recorded at a resolution of 0.02 cm-1 with an infrared Fourier transform spectrometer in the spectral ranges 780-1370 and 1800-5000 cm-1. The flame temperature was about 1850 K and a large number of transitions involving J values as high as 34 for an extended set of vibrational states could be assigned. Combined with already published data sets on H2O, our line position analysis yielded rotational energy levels for many of these states, but only the results relevant to the ground and the (010) states are presented here. The experimental energies for these two states have been fitted with the help of the bending-rotation Hamiltonian approach [L. H. Coudert, J. Mol. Spectrosc. 181, 246-273 (1997)], and for each rotational level, the calculated energy along with its uncertainty is reported and compared with the observed value. Comparisons with other available energy level data sets for the ground and (010) states are also presented. Copyright 1999 Academic Press.     

Kinetic modelling of the reduction of SiCl4 in an arc heater for the production of silicon

The conversion of SiCl₄ into Si has been achieved from reduction by a hydrogen plasma produced in an arc heater. As the results (conversion yield about 60%) are far from chemical equilibrium predictions, a kinetic model is proposed using the few kinetic data available in the literature and a temperature history of the reactants deduced from measurements of the temperatures and velocities of the flowing chemical mixture.     

Velocity Measurements for Arc Jets Produced by a DC Plasma Spray Torch

An optical method was used to determine the axial velocity of plasma jets produced by a DC plasma spray torch. Different experimental conditions were tested in order to systematically study the influence of the working parameters on the plasma velocity. In this way, the arc current ranged between 200 and 600 A, the gas flow rate between 30 and 80 slm, and the internal nozzle diameter between 6 and 10 mm; the plasma gases were either an Ar–H ₂ mixture or N ₂ . Rather well defined tendencies were observed and at the same time it appeared that the arc stability greatly influenced the fluctuations of the velocity.     

Synthesis of 2-oxazolidinones from (1S,2S)-2-amino-1-(4-nitrophenyl)-1,3-propanediol

A series of isomeric 2-oxazolidinones has been synthesized from (1S, 2S)-2-amino-1-(4-nitrophenyl)-1,3-propanediol. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 579–584, April, 2006.     

Modeling and experimental study of a transferred arc stabilized with argon and flowing in a controlled-atmosphere chamber filled with argon at atmospheric pressure

For a transferred arc with a flat anode working at atmospheric pressure in an argon atmosphere, the influence of the gas injector design close to the cathode tip has been systematically studied for arc currents below 300 A, gas flowrates between 5 and 60 slm, and anode-cathode distances between 10 and 46 mm. Two types of injector configurations hare been studied: a cylindrical one with its wall parallel to the cathode axis and a conical one with the same cone angle as that of the cathode tip. The arc temperature was measured using flit, absolute intensity of ArI and ArII lines. Beside the roltagc and arc current, the losses at the cathode and at the anode were continuously recorded. An elliptic model was used to calculate the flow velocity, the temperature, and the current density close to the cathode and in the arc column. This model was either laminar or turbulent (K - ), with the empirical constants being functions of the Reynolds nunther of turbulence. A cathode sheath with nonequilibrium conditions was used to obtain accurate cathode boundary conditions. Experiments and modeling hart shown the benefits of using conical injectors which constrict drasfically the plasma_ flow and enhance the gas velocity and the current density, thus increasing the heat flux to the anode. With the cylindrical injector, recirculations close to the cathode lip modify deeply its heating and reduce the plasma jet constriction: velocities and temperatures are lower when the recirculation velocity is higher. This results in lower heat fluxes to the anode compared to the conical injector.     

Behavior study of polyvinyl alcohol aqueous solution in presence of short chain micelle-forming polyols

Interactions in aqueous solution between polyvinyl alcohol (PVA) and various short chain nonionic polyols surfactants having six to nine carbon atoms and two to three hydroxyl groups are investigated using tensiometry, viscosity, and dynamic laser light scattering techniques. Despite the fact that weak interactions are noticed, they begin to occur at surfactant concentrations far lower than the Critical Micellar Concentration. Partition coefficients of the surfactants between water and the PVA macromolecules are determined, and the contributions of the surfactant alkyl chain length on one hand and of the hydroxyl groups on the other hand to the PVA interactions with monomer surfactants are discussed in terms of thermodynamic contributions.