Chemical stability | EPFL Graph Search

In chemistry, chemical stability is the thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibrium in which individual atoms or molecules change form, but their overall number in a particular form is conserved. This type of chemical thermodynamic equilibrium will persist indefinitely unless the system is changed. Chemical systems might undergo changes in the phase of matter or a set of chemical reactions. State A is said to be more thermodynamically stable than state B if the Gibbs free energy of the change from A to B is positive. Thermodynamic stability applies to a particular system. The reactivity of a chemical substance is a description of how it might react across a variety of potential chemical systems and, for a given system, how fast such a reaction could proceed. Chemical substances or states can persist indefinitely even though they are not in their lowest energy state if they experience metastability - a state which is stable only if not disturbed too much. A substance (or state) might also be termed "kinetically persistent" if it is changing relatively slowly (and thus is not at thermodynamic equilibrium, but is observed anyway). Metastable and kinetically persistent species or systems are not considered truly stable in chemistry. Therefore, the term chemically stable should not be used by chemists as a synonym of unreactive because it confuses thermodynamic and kinetic concepts. On the other hand, highly chemically unstable species tend to undergo exothermic unimolar decompositions at high rates. Thus, high chemical instability may sometimes parallel unimolar decompositions at high rates. In everyday language, and often in materials science, a chemical substance is said to be "stable" if it is not particularly reactive in the environment or during normal use, and retains its useful properties on the timescale of its expected usefulness.

Experimental Method to Distinguish between a Solution and a Suspension

Francesco Stellacci, Paulo Henrique Jacob Silva, Quy Ong Khac, Xufeng Xu, Ting Mao

Dispersion of objects in a fluid phase can be classified as solutions (Gibbs free energy of mixing, Delta G(mix) < 0) or suspensions (Delta G(mix) > 0) depending on their thermodynamic stability. Small objects tend to form solutions, larger ones suspensions, e.g., molecules versus micrometer-sized colloids. Proteins and nanomaterials fall between these two size regimes. The long-standing issue of whether proteins and nanoparticles are dissolved or suspended remains an important research question. Here, a simple, versatile, and experimentally robust method, based on sedimentation equilibrium analytical ultracentrifugation (SE-AUC), which can determine whether proteins, nanoparticles, or polymers form solutions or suspensions, is presented. SE-AUC determines the osmotic pressure profile for a dispersion. Such a profile for solutions (equilibrium one-phase systems) is independent of the initial and the operating conditions. The opposite is true for suspensions that are nonequilibrium two-phase systems. This study proves that bovine serum albumin and lysozyme form solutions while ferritin and apoferritin form suspensions.

WILEY2022

Theory-guided design of high-strength, high-melting point, ductile, low-density, single-phase BCC high entropy alloys

William Curtin, Christian Leinenbach, Carolina Baruffi, You Rao

The search for new high-temperature alloys that can enable higher-efficiency/lower-emissions power generation has accelerated with the discovery of body-centered cubic (bcc) refractory High Entropy Alloys (HEAs). These many-component, non-dilute alloys in the Cr-Mo-W-V-Nb-Ta-Ti-Zr-Hf-Al family hold the potential for combining high strength and thermodynamic stability at high temperature with low density and room-temperature ductility, but searching the immense compositional space is daunting. Here, very recent theories and expanded thermodynamic tools are used to guide the discovery of new alloys satisfying the required suite of properties. The search and discovery method is first demonstrated for 5-component equicomposition alloys, identifying HfMoNbTaTi as the one alloy satisfying many constraints, with predicted properties agreeing with experiments. The design process then discovers new quinary and quarternary alloys in the Hf-Mo-Nb-Ta-Ti space having even better overall properties. One new quinary alloy is fabricated and shown to be single phase with high room temperature hardness, high melting point, and low density. More broadly, the new design process can further be used to explore millions of alloys with other desired multi-dimensional performance requirements. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc.

PERGAMON-ELSEVIER SCIENCE LTD2022

Synthesis and characterization of iron-clathrochelates and their applications in materials science

José Luis Bila

This thesis focuses on the design and the synthesis of mono- and dinuclear iron clathrochelate complexes and their applications in materials science. Dinuclear iron clathrochelate complexes can be synthesized in different oxidation states: i. as negatively charged FeII-FeII complexes or ii. as neutral FeII-FeIII complexes. These compounds display interesting magnetic properties. The negatively FeII-FeII complexes are antiferromagnetic, whereas the neutral FeII-FeIII complexes are paramagnetic. In addition, an interconversion between the two redox states can be achieved, both chemically and electrochemically. The functionalization of clathrochelate complexes with electron-donating groups was found to stabilize the higher oxidation states (FeIII-FeIII), which was evidenced electrochemically. However, the deliberate preparation and isolation of FeIII-FeIII complexes was not achieved. Dinuclear iron clathrochelate complexes were successfully employed as redox-active compounds for redox flow batteries, and they displayed high battery voltages and Coulombic efficiencies. Iron clathrochelate complexes are stable under the harsh conditions of metal-catalyzed coupling reactions (e.g. Suzuki or Sonogashira reactions). The high stability makes them suitable building blocks for the preparation of networks displaying permanent porosity. Both mononuclear and dinuclear iron clathrochelate-based networks displayed apparent BET surface areas between 235 and 593 m2g 1. Moreover, all clathrochelateâbased porous networks displayed high thermal and chemical stabilities. Mononuclear iron clathrochelate building blocks can be decorated with chiral ligands, resulting in homochiral porous networks with apparent BET surface areas up to 548 m2g-1. Such materials were found to selectively adsorb D-tryptophan from water. Porous networks based on iron clathrochelates can also be synthesized via polycondensation reactions. This synthetic strategy involves the combination of an iron salt, a dioxime ligand, and a capping boronic acid. The resulting Fe-templated condensation reactions give networks with apparent BET surface areas up to 927 m2g-1. Similarly, these materials display high chemical and thermal stabilities. Additionally, they were found to efficiently adsorb chromium (VI) from water.

EPFL2020

Synthesis and characterization of iron-clathrochelates and their applications in materials science

José Luis Bila

EPFL2020