7 research outputs found
Unusual Protonation of the Hydroxylammonium Cation Leading to the Low Thermal Stability of Hydroxylammonium-Based Salts
Energetic ionic salts
(EISs) are a class of thriving and promising
energetic materials (EMs) that can possess excellent properties and
performances comparable to common conventional EMs composed of neutral
molecules. As EMs, their response mechanisms to external stimuli are
strongly responsible for their safety and thus are highly concerned
about. Nevertheless, insight into these mechanisms remains still lacking.
We find in the present work a bimolecular reaction between two same
sign charged ions during heating dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate
(TKX-50), a typical EIS that are attracting increasing attention with
a high potential of practical applications. That is, the protonation
of NH<sub>3</sub>OH<sup>+</sup>, or a reaction between two cations,
occurs and serves as a dominant initial step in the thermal decay
of TKX-50. This is a rare case as a bimolecular reaction can usually
hardly take place between two ions with same sign charges (two anions
or two cations), due to their electrostatic repulsion preventing their
sufficient approaching each other to induce the reaction. The protonation
proceeds by a H<sup>+</sup> transfer from a NH<sub>3</sub>OH<sup>+</sup> to its neighboring one, and subsequently decompose NH<sub>3</sub>OH<sup>+</sup> to the final stable products of NH<sub>3</sub> and
H<sub>2</sub>O simultaneously to collapse the crystal lattice of TKX-50.
This new finding can well explain the experimental observations of
the prior decay of NH<sub>3</sub>OH<sup>+</sup> to the bistetrazole-1,1′-diolate
anion when TKX-50 heated at a constant temperature of 190 °C
and the relatively low thermal stability of NH<sub>3</sub>OH<sup>+</sup> based EISs relative to others. Thereby, we propose a strategy to
avoid a ready proton transfer and subsequent decomposition to enhance
the thermal stability of EISs. This work is hopefully to richen the
insight into both the decay mechanism of EISs and the mechanism of
the reactions between same sign charged ions
Environmental influences on indoor walking behaviours of assisted living residents
<div><p>Regular walking behaviours can improve older people's physical, psychological and social health. This project examined the relationships between assisted living facilities’ design features and residents’ indoor walking behaviours through surveys and field evaluations. Surveys were conducted in 18 assisted living facilities in the US state of Texas. Researchers gathered information from 343 residents about their walking behaviours, participation in other activities, health and demographic status, and perceptions of the environment. Field evaluations were conducted to collect objective physical environment measures. Facility information was provided by the administrators. Multivariate hierarchical regression analysis showed significant influences of physical environments on indoor walking behaviours. Indoor recreational walking was related negatively to the number of stories of the building and positively to the perception of looped corridors. Different types of utilitarian walking, such as ‘walk to other activities’, ‘walk to front entry' and ‘walk to mailbox' were influenced by specific design features. The number of utilitarian walking types was marginally influenced by the number of stories of the building. These findings will help inform the design of activity-friendly assisted living facilities and the creation of health promotion programmes for frail older people.</p></div
Enhanced Intermolecular Hydrogen Bonds Facilitating the Highly Dense Packing of Energetic Hydroxylammonium Salts
The energy and performance
of energetic materials can be improved
by increasing their crystal packing density. Thus, we propose a strategy
involving salification with hydroxylammonium cations (HA<sup>+</sup>) to increase the packing coefficients (PCs) and packing densities
of energetic ionic salts (EISs). Structural analyses and theoretical
calculations of the observed EISs indicate that the strong intermolecular
hydrogen bonds (HBs) between HA<sup>+</sup> and anions are primarily
responsible for the increase in EIS density. Such strong HBs usually
exist in HA<sup>+</sup>-based energetic salts and rarely in other
EISs but are absent in energetic crystals with neutral molecules.
Such HBs induce high PCs and relatively high crystal packing densities
by compensating for the relatively lower molecular density of HA<sup>+</sup> compared with other cations. Moreover, in combination with
HBs in common explosives, we find a simple dependence showing that
the shorter the strongest HB corresponds to the higher PC, suggesting
that the strongest HB can be regarded as a simple indicator of PC.
This study proposes that enhancing intermolecular HBs is the main
strategy to increase compactness because H atoms usually exist in
currently available energetic materials
Mechanical Anisotropy of the Energetic Crystal of 1,1-Diamino-2,2-dinitroethylene (FOX-7): A Study by Nanoindentation Experiments and Density Functional Theory Calculations
The mechanical anisotropy of the
wavelike π-stacked energetic
crystal of 1,1-diamino-2,2-dinitroethylene (FOX-7) is investigated
by nanoindentation experiments and density functional theory (DFT)
calculations. The FOX-7 crystal exhibits distinct mechanical anisotropy
when indented on different faces. The elastic modulus and hardness
of the (020), (−101), and (002) faces change in a decreasing
order. The indentation on the (020) face induces the largest depth
and the highest pile-up around all three edges of the indenter without
causing crack formation. By contrast, the indentations on the (−101)
and (002) faces are similar and induce a small indentation depth,
low pile-up with a small distribution, and crack formation. Mechanical
anisotropy is essentially determined by the wavelike π stacking
of FOX-7 along the (020) face with the support of intermolecular hydrogen
bonds; i.e., the molecular orientations and intermolecular spaces
along different faces vary distinctly. This is also supported by the
DFT calculations on uniaxial compression and shear sliding. In this
work, the nature of the wavelike π stacking responsible for
the low impact sensitivity of FOX-7 is discussed and compared with
that of other explosives with different packing structures
Interface Engineering of Anchored Ultrathin TiO<sub>2</sub>/MoS<sub>2</sub> Heterolayers for Highly-Efficient Electrochemical Hydrogen Production
An
efficient self-standing hydrogen evolution electrode was prepared
by in situ growth of stacked ultrathin TiO<sub>2</sub>/MoS<sub>2</sub> heterolayers on carbon paper (CP@TiO<sub>2</sub>@MoS<sub>2</sub>). Owing to the high overall conductivity, large electrochemical
surface area and abundant active sites, this novel electrode exhibits
an excellent performance for hydrogen evolution reaction (HER). Remarkably,
the composite electrode shows a low Tafel slope of 41.7 mV/dec, and
an ultrahigh cathodic current density of 550 mA/cm<sup>2</sup> at
a very low overpotential of 0.25 V. This work presents a new universal
strategy for the construction of effective, durable, scalable, and
inexpensive electrodes that can be extended to other electrocatalytic
systems
Interface Engineering of Anchored Ultrathin TiO<sub>2</sub>/MoS<sub>2</sub> Heterolayers for Highly-Efficient Electrochemical Hydrogen Production
An
efficient self-standing hydrogen evolution electrode was prepared
by in situ growth of stacked ultrathin TiO<sub>2</sub>/MoS<sub>2</sub> heterolayers on carbon paper (CP@TiO<sub>2</sub>@MoS<sub>2</sub>). Owing to the high overall conductivity, large electrochemical
surface area and abundant active sites, this novel electrode exhibits
an excellent performance for hydrogen evolution reaction (HER). Remarkably,
the composite electrode shows a low Tafel slope of 41.7 mV/dec, and
an ultrahigh cathodic current density of 550 mA/cm<sup>2</sup> at
a very low overpotential of 0.25 V. This work presents a new universal
strategy for the construction of effective, durable, scalable, and
inexpensive electrodes that can be extended to other electrocatalytic
systems
All-Inorganic Perovskite Solar Cells
The
research field on perovskite solar cells (PSCs) is seeing frequent
record breaking in the power conversion efficiency (PCE). However,
organic–inorganic hybrid halide perovskites and organic additives
in common hole-transport materials (HTMs) exhibit poor stability against
moisture and heat. Here we report the successful fabrication of all-inorganic
PSCs without any labile or expensive organic components. The entire
fabrication process can be operated in ambient environment without
humidity control (e.g., a glovebox). Even without encapsulation, the
all-inorganic PSCs present no performance degradation in humid air
(90–95% relative humidity, 25 °C) for over 3 months (2640
h) and can endure extreme temperatures (100 and −22 °C).
Moreover, by elimination of expensive HTMs and noble-metal electrodes,
the cost was significantly reduced. The highest PCE of the first-generation
all-inorganic PSCs reached 6.7%. This study opens the door for next-generation
PSCs with long-term stability under harsh conditions, making practical
application of PSCs a real possibility