Todorokite is a common manganese oxide mineral, with a tunnel structure, found in Earth surface environments, and is easily synthesized from layered birnessite. The aim of the current study was to prepare birnessites with different average manganese oxidation states (AOS) by controlling the ${\text{MnO}}_4^{-}{\text{/Mn}}^{2+}$\$\end{document} ratio in concentrated NaOH or KOH. A series of (Na,K)-birnessites, Na-birnessites, and K-birnessites with different AOS was synthesized successfully in strongly alkaline media. The (Na,K)-birnessites and Na-birnessites prepared in NaOH clearly contained both large (500–1000 nm) and small (40–400 nm), plate-shaped crystallites. The K-birnessites prepared in KOH media consisted mostly of irregular (100–200 nm), plate-shaped crystallites. The degree of transformation of birnessite to todorokite at atmospheric pressure decreased as the AOS values of (Na,K)-birnessites and Na-birnessites increased from 3.51 to 3.80. No todorokite was present when a Na-birnessite with an AOS value of 3.87 was used as the precursor. Pyrophosphate, which is known to form strong complexes with Mn3+ at a pH range of 1–8, was added to a suspension of (Na,K)-birnessites in order to sequester the available Mn3+ in (Na,K)-birnessites. Removal of Mn3+ from birnessite MnO6 layers by pyrophosphate restricted transformation to todorokite — no (Na,K)-birnessite transformed to todorokite after pyrophosphate treatment. The interlayer K+ initially within (Na,K)-birnessites could not be completely ion-exchanged with Mg2+ to form todorokite at atmospheric pressure. No todorokite was forthcoming from K-birnessites even from those with small AOS values (3.50).

Significant developments in micro-electrical-mechanical systems (MEMS)-based devices have led to the commercialization of windowed gas cells that now enable atomic-resolution scanning transmission electron microscopy (STEM) observation of phenomena occurring during gas-solid interactions at atmospheric pressure. An in situ atmospheric STEM study provides information that is beneficial to correlating the structure-properties relationship of catalytic nanomaterials, particularly under realistic gaseous reaction conditions. In this article, we illustrate the advantages of this tool as applied to our study of two important systems: (1) the CO-induced Pt nanoparticle surface reconstruction at saturation coverage and (2) the ordering and Pt surface enrichment in supported Pt3Co nanoparticles.

Runaway electrons preionized diffuse discharge (REP DD) could generate volume non-thermal plasmas at atmospheric pressure, thus is widely used for surface modification. In this paper, two pulsed generators are used to produce REP DD for modifying copper (Cu) foil in atmospheric air. One generator produces repetitive pulses with a peak voltage of 40 kV and a rise time of 150 ns. The other generator produces single pulse with a peak voltage of 280 kV and a rise time of 0.5 ns. After the treatment, the modification results for including the macro topography, chemical composition and microhardness in different depths of the Cu surface are analyzed. In order to estimate the modification results in different areas of the Cu foil, several points from the center to the edge of the Cu sample are selected. It could be observed that the maximal modification effect usually appears in the area where the density of the diffuse discharge plasma is highest. The experimental results show REP DD treatment could significantly decrease the water contact angle and increase surface energy of the Cu foil. Meanwhile, it could decrease the carbon concentration and increase oxygen concentration in the near-surface layer of the Cu sample, and enhance the microhardness in different depths of the Cu foil.

This paper reports on the properties of a supershort avalanche electron beam generated in the air or other gases under atmospheric pressure and gives the analysis of a generation mechanism of supershort avalanche electron beam, as well as methods of such electron beams registration. It is reported that in the air under the pressure of 1 atm, a supershort (<100 ps) avalanche electron beam is formed in the solid angle more than 2π steradian. The electron beam has been obtained behind a 45 µm thick Al-Be foil in SF6 and Xe under the pressure of 2 atm, and in He, under the pressure of about 15 atm. It is shown that in SF6 under the high pressure (>1 atm) duration (full width at half maximum) of supershort avalanche electron beam pulse is about 150 ps.

This article reports on experimental studies of subnanosecond electron beams formed in air under atmospheric pressure. An electron beam with an amplitude of ∼170 A with a duration at FWHM of ∼0.3 ns has been obtained. Based on beam temporal characteristics and discharge spatial characteristics, the critical fields were supposed to be reached at plasma approach to anode. Simultaneously, the sharp high-energy pulse of e-beam current is generated. Of critical importance is the cathode type and occurrence on the cathode of plasma protrusions. It is shown that to get maximum amplitude of the electron beam in the gas diode, the discharge in the gas diode should be volumetric.