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Related Concept Videos

Phase Diagram01:19

Phase Diagram

6.2K
The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).
6.2K
Phase Transitions: Sublimation and Deposition02:33

Phase Transitions: Sublimation and Deposition

18.3K
Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and standard pressure, a piece of dry ice (solid CO2) sublimes, appearing to gradually disappear without ever forming any liquid. Snow and ice sublimate at temperatures below the melting point of water, a slow process that may be accelerated by winds and the reduced atmospheric pressures at high altitudes. When solid iodine is warmed, the solid sublimes...
18.3K
Alkali Metals03:06

Alkali Metals

21.6K
Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the alkali metals are unusually low for metals and decrease going down the group, while the density increases going down the group with the exception of potassium (Table 1).
Table 1: Properties of the alkali metals
21.6K
Solubility Equilibria: Overview01:09

Solubility Equilibria: Overview

960
When a substance such as sodium chloride is added to water, it dissolves, forming an aqueous solution. The extent of dissolution is called solubility. The process of dissolution can exist in equilibrium, just like other chemical processes. Solubility equilibria are also called precipitation equilibria because the process of solubility can be reversible. The reverse of the solubility process is called precipitation.
Solubility is important in biological and environmental processes. A notable...
960
Extraction: Advanced Methods00:56

Extraction: Advanced Methods

564
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is...
564
Phase Transitions02:31

Phase Transitions

20.6K
Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to...
20.6K

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Synthesis and Microdiffraction at Extreme Pressures and Temperatures
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Synthesis and Microdiffraction at Extreme Pressures and Temperatures

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K+ extraction induced phase evolution of KFeO2.

Shiyu Zhang1,2, Jian Sun1,2, Jianghui Gao1

  • 1Key Laboratory of Interfacial Physics and Technology, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China. wangjianqiang@sinap.ac.cn.

Physical Chemistry Chemical Physics : PCCP
|February 8, 2022
PubMed
Summary

Orthorhombic KFeO2 degrades due to potassium ion (K+) extraction when exposed to air or water. Reinserting K+ via high-temperature calcination offers potential for catalyst reactivation and rechargeable batteries.

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Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles
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Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles
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Area of Science:

  • Materials Science
  • Solid-state Chemistry
  • Catalysis

Background:

  • Orthorhombic KFeO2 exhibits a unique structure enabling potassium ion (K+) mobility, making it suitable for catalysis and energy storage.
  • KFeO2 is susceptible to degradation from moisture and carbon dioxide, leading to performance deterioration.
  • Understanding the phase evolution of KFeO2 under environmental exposure is crucial for its practical application.

Purpose of the Study:

  • To investigate the phase evolution of KFeO2 upon exposure to ambient air and water.
  • To elucidate the mechanisms behind K+ extraction and its impact on the KFeO2 structure.
  • To explore the possibility of reversing K+ extraction for material restoration.

Main Methods:

  • Experimental analysis of KFeO2 samples exposed to different conditions (fresh, air-exposed, water-immersed).
  • Ab initio molecular dynamics simulations to study K+ behavior and interactions with water.
  • High-temperature calcination to attempt K+ reinsertion.

Main Results:

  • K+ extraction was identified as the primary cause of phase evolution in KFeO2.
  • Exposure to air resulted in K+ extraction, K2CO3·1.5 H2O formation, and lattice expansion.
  • Water molecules were found to be critical for K+ extraction, as confirmed by simulations.
  • Successful reinsertion of K+ into the expanded KFeO2 lattice was achieved through high-temperature calcination at 900 °C.

Conclusions:

  • The phase evolution of KFeO2 is driven by K+ extraction, influenced by environmental factors like moisture.
  • The reversible K+ extraction-insertion process demonstrates potential for regenerating degraded KFeO2.
  • This reversibility opens avenues for applications in catalyst reactivation and rechargeable high-temperature batteries.