The equilibrium phase of cesium lead iodide (CsPbI3) at room temperature is yellow and optically inactive due
to its indirect band gap. The metastable black phase of CsPbI3 on the other hand exhibits optical properties that are suitable
for photovoltaic and light-emitting devices. Here, we examine the
stability of the black phase of ligand-stabilized CsPbI3 nanocrystals heated in humid air. Water vapor is known to catalyze
the transition of CsPbI3 from the black phase to the yellow
phase. Uniform nanocrystals with cube shape were synthesized with
capping ligand mixtures of oleylamine and oleic acid or diisooctylphosphinic
acid, assembled into superlattices with preferred crystal orientation,
and studied using grazing incidence small- and wide-angle X-ray scattering
with in situ heating. The black-phase nanocrystals are found to inhabit
the γ-orthorhombic phase and do not revert to the equilibrium
yellow δ-orthorhombic phase until reaching a relatively high
temperature, between 170 and 200 °C, coinciding with superlattice
degradation.
Conspectus
Colloidal nanoparticles have
unique attributes
that can be used
to synthesize materials with exotic properties, but leveraging these
properties requires fine control over the particles’ interactions
with one another and their surrounding environment. Small molecules
adsorbed on a nanoparticle’s surface have traditionally served
as ligands to govern these interactions, providing a means of ensuring
colloidal stability and dictating the particles’ assembly behavior.
Alternatively, nanoscience is increasingly interested in instead using
macromolecular ligands that form well-defined polymer brushes, as
these brushes provide a much more tailorable surface ligand with significantly
greater versatility in both composition and ligand size. While initial
research in this area is promising, synthesizing macromolecules that
can appropriately form brush architectures remains a barrier to their
more widespread use and limits understanding of the fundamental chemical
and physical principles that influence brush-grafted particles’
ability to form functional materials. Therefore, enhancing the capabilities
of polymer-grafted nanoparticles as tools for materials synthesis
requires a multidisciplinary effort, with specific focus on both developing
new synthetic routes to polymer-brush-coated nanoparticles and investigating
the structure–property relationships the brush enables.
In this Account, we describe our recent work in developing polymer
brush coatings for nanoparticles, which we use to modulate particle
behavior on demand, select specific nanoscopic architectures to form,
and bolster traditional bulk polymers to form stronger materials by
design. Distinguished by the polymer type and capabilities, three
classes of nanoparticles are discussed here: nanocomposite tectons
(NCTs), which use synthetic polymers end-functionalized with supramolecular
recognition groups capable of directing their assembly; programmable
atom equivalents (PAEs) containing brushes of synthetic DNA that employ
Watson–Crick base pairing to encode particle binding interactions;
and cross-linkable nanoparticles (XNPs) that can both stabilize nanoparticles
in solution and polymer matrices and subsequently form multivalent
cross-links to strengthen polymer composites. We describe the formation
of these brushes through “grafting-from” and “grafting-to”
strategies and illustrate aspects that are important for future advancement.
We also examine the new capabilities brushes provide, looking closely
at dynamic polymer processes that provide control over the assembly
state of particles. Finally, we provide a brief overview of the technological
applications of nanoparticles with polymer brushes, focusing on the
integration of nanoparticles into traditional materials and the processing
of nanoparticles into bulk solids.
One of the main failure mechanisms of pressurized water reactors (PWR) is primary water stress corrosion cracking (PWSCC), which occurs in alloy 600 (75Ni-15Cr-9Fe) and weld metals such as alloy 182 (70Ni-14Cr-9Fe), and alloy 82 (73Ni-19Cr-2Fe). Corrosion cracking is due, for example, in reactor nozzles welded dissimilarly with alloys 182/82 between ASTM A-508 G3 steel and AISI316L stainless steel. Corrosion cracks can cause problems reducing nuclear installations safety and reliability. Hydrogen dissolved into primary water to prevent radiolysis, also may enhance PWSCC growth. This article begins from a study by Lima et al. (2011) based on experimental data from the CDTN-Brazilian Nuclear Technology Development Center, and related to a slow strain rate test (SSRT). This was prepared and used for testing welds in the laboratory, similar to the dissimilar weld in pressurizer relief nozzles operating at the Brazilian Angra Unit 1 nuclear power plant. It was simulated for tests, primary water at 325°C and 12.5 MPa containing four levels of dissolved hydrogen. Our objective in this article is to clarify, and discuss adequate modeling based on the SSRT experimental results, and to compare them with those from another database and modeling, of the PWSCC growth rate based on levels of dissolved hydrogen.
Dissimilar welds (DW) are normally used in many components junctions in structural project of PWR (Pressurized Water Reactors) in Nuclear Plants. One had been departed of a DW of a nozzle located at a Reactor Pressure Vessel (RPV) of a PWR reactor, that joins the structural vessel material with an A316 stainless steel safe end. This weld is basically done with Inconel/Alloy 182 with a weld buttering of Inconel/Alloy 82. It had been prepared some axial cylindrical specimens retired from the Alloy 182/A316 weld end to be tested in the slow strain rate test machine located at CDTN laboratory. Based in these stress corrosion susceptibility results, it was done a preliminary semi-empiric modeling application to study the failure initiation time evolution of these specimens. The used model is composed by a deterministic part, and a probabilistic part according to the Weibull distribution. It had been constructed a specific Microsoft Excel worksheet to do the model application of input data. The obtained results had been discussed according with literature and also the model application limits.
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