Kinetics Of Physicochemical Processes Research Articles

Stabilization of non‐native polymorphs for electrocatalysis and energy storage systems

AbstractEvolution in material centric devices like batteries and electrocatalytic reactors have predominantly been made possible via the exploitation of the thermodynamic ground state of pristine or defective bulk crystal, referred to as the “Native polymorph” (NP) here. A significant increase in the material search space is possible by utilizing “Non‐Native polymorphs (NNP),” which are materials that have different translational symmetry with respect to NP. As the NNP have a distinct coordination structure from that of the NP, critical material properties can be anticipated to be different, making NNP a potential substitute material for the aforementioned applications, which are the focus of this review. To obtain a structure–function relationship, systematic approaches to the synthesis of NNP has been demonstrated. Following certain generalities behind NNP, we classify synthesis techniques into few categories with the hope of rationalizing the underlying mechanism of these synthesis and stabilization strategies. We discuss the utility of NNPs in the context of electrochemical water electrocatalytic reactions. Typically, the NNPs have more open volume space enabling lower lithium‐ion diffusion barrier, higher lithium‐ion binding energies, thereby making NNP efficient in the context of energy storage material. However, NNP have lesser stability than the NP and methods to calibrate and improve the stability of NNP are important. Overall, the discussion of polymorphic materials by demarcating them as NP and NNP provides a systematic approach towards modulating material properties as a trade‐off between thermodynamics and kinetics of physicochemical processes. Finally, the challenges and perspectives in this emerging field are discussed.This article is categorized under: Fuel Cells and Hydrogen > Science and Materials Energy Research & Innovation > Science and Materials Energy and Development > Science and Materials

A lumped parameter model of electrochemical reprocessing of spent nuclear fuel

A lumped parameter model was developed for describing electrochemical processes. The model describes the kinetics of physicochemical processes occurring in the electrolyzer in the course of spent nuclear fuel (SNF) reprocessing, variation of the electrode material composition with time, component concentrations in definite regions of the electrolyzer, and partial reaction currents. The calculation results qualitatively agree with the expected relationships for both simple and complex (multicomponent) systems. The calculation for the setting similar to the experiment performed at the Argonne National Laboratory was presented as an example.

Application of Laser Videographic Cryoscopic Micro Osmometry in Measurements of Temperature Depression in Petroleum Products

This paper describes using the familiar MT-2 platform to build an instrument capable of supporting dynamic observations and recording of the kinetics of physicochemical processes during cryoscopic osmometry of crude oil media and refined petroleum products in automatic mode. Modifications of the MT-2 design generally include introduction of a laser source, a videographic speckle recording system, a digitizing board for the speckle recording signal, a stepper motor control module and redesigned micromechanics controllable by it, which via signals supplied by the computer (the nature of which is controlled by specially written software) alters the movement of the analytical head. As a result of the modification, the MT-2 with digital speckle recording, laser module, and microcamera allows us: to determine the transition to irreversible aggregation of the asphaltenes, characterized by their deposition on the walls of the measuring bath (after desorption of the resins); to do realtime classification of crude oil by speckle morphometry methods; to observe and identify the emulsion properties of the crude oil, including formation of “carpenter’s level” bubble inclusions and coacervate droplets; to carry out a rheological falling-drop experiment with thermographic monitoring; to make rheogoniometric observations while rotating the measuring instrument or thin cuvet; to observe wavy perturbations on the surface of the medium while the drop is falling, with delayed relaxation (dissipation) due to viscoelastic properties.

Kinetics of physico-chemical processes during intensive mechanical processing of ZnO–MnO 2 powder mixture

Experimental results of electron paramagnetic resonance spectra, X-ray diffraction, scanning electron microscopy and infrared spectroscopy demonstrate that the kinetic of the physical and chemical processes that takes place during prolonged intensive mechanical processing (MP, 0 < t MP > 3120 min ) of powder mixtures of 50%wt ZnO+50%wt MnO 2 can be described as a three stage process. (1) 0 < t MP > 30 min , particles destruction, formation of superficial defects, fast increment of sample average temperature (from 290 to ∼ 600 K ) and annealing of defects with the lowest energy of activation E ac . (2) 30 < t MP > 390 min , further particle destruction, slow increment of sample average temperature (from ∼ 600 to ∼ 700 K ), formation and growth of a very disordered layer of β ‐ MnO 2 around ZnO particles, dehydration of MnO 2, formation of solid solution of Mn 2+ ions in ZnO, formation of nano-quasiamorphous states in the ZnO–MnO 2 mixture and onset of the formation of the ZnMnO 3 phase. (3) 390 < t MP > 3120 min , the sample average temperature remains constant ( ∼ 700 K ), the reaction is completed and the spinel ZnMnO 3 phase with a unit cell a=8.431(1) Å and space group Fd 3 ¯ m is the only phase present in the sample. No ferromagnetism at room temperature was detected in this study.

Practical aspects of physicochemical kinetics using thermal techniques

AbstractA number of studies on the kinetics of physicochemical processes are described. The methods used are shown to be potentially useful for making time‐temperature predictions and for optimizing process variables. Examples described include (1) the long‐term prediction of the performance of a plasticized polyvinyl chloride and doped polyacetylenes; (2) the polymerization of a monomer and the optimization of time, temperature, and initiator concentration variables; (3) analysis of an order/disorder transition in a thermochromic polymer; (4) the crystallization of polymers and the effect of a nucleating agent; and (5) the crystallization of an amorphous metallic glass. The theoretical background, significance, scope, and limitations of these measurements are also discussed.

The inhomogeneous temperature field of the specimen as a factor in kinetic investigations by the nonisothermal method

To increase the precision of the results of an analysis of the kinetics of physicochemical processes by nonisothermal techniques the measured process temperature must be corrected to allow for the inhomogeneity of the temperature field of the specimen. Alternatively, the dimensions and heating conditions of the specimen must be such that this inhomogeneity does not exceed given permitted limits.

Calculation of nonisothermal kinetics of physicochemical processes

General methods have been developed for calculating the kinetics of physicochemical processes under nonisothermal conditions; existing solutions follow as special cases from the relationships obtained in this work.