Porous solids, such as zeolites and other molecular sieves, contain intracrystallite/framework cavities and channels that produce microporous (pore diameter, D < 2 nm), mesoporous (2 nm < D < 50 nm), and macroporous (D > 50 nm) structures, and have demonstrated excellent potential as materials for use in many separation and catalytic processes.[1] The pore sizes of these porous materials (especially the micropore sizes, which are close to molecular dimensions) may play a critical role in controlling separation and catalytic selectivity due to their shape and size selectivity. The production of materials with different microporosities has always been challenging. Natural and synthetic tunnel-structured manganese oxide octahedral molecular sieves (OMSs) make up a promising group of functional porous materials. They can exhibit various nanometer-scale tunnel sizes from 2.3 2.3 to 4.6 11.5 , which correspond to different micropore openings. As such, they constitute excellent model systems for studying the synthesis of materials with controlled microporosities. Moreover, the potential applications for synthetic manganese oxide OMS materials can be expanded by molecular modification or decoration of the tunnel structures.[2] There have been several attempts to synthesize manganese oxide OMSs with the same tunnel structures as those found in natural manganese oxides, or to create materials with new tunnel structures.[3±7]However, there has been very little work reported on the direct control of tunnel sizes. In this communication, we report the successful synthesis of manganese oxide OMS materials with controlled nanometer-scale tunnel sizes by controlling the pH of the hydrothermal transformation of layered manganese oxide precursors. Hydrothermal transformation of layered manganese oxide materials is one of the most effective methods of obtaining tunnel-structured manganese oxides. Due to the mixed-valent manganese framework, usually (+2, +3, and +4) or (+3 and +4), a small number of guest cations are usually required for charge balance in most layer-and tunnel-structured manganese oxides. These guest cations usually reside between the layers or inside the tunnels.[3±7] When layered manganese oxides are transformed into tunnel structures, the interlayer cations remain inside the tunnels. Therefore, the types and sizes of the guest cations in these layered manganese oxides might play critical roles as structure directors in templating different tunnel sizes during synthesis of tunnel structures. Since many cations are in hydrated form under aqueous/hydrothermal conditions, the template effect may actually result from the size of the hydrated cations rather than from that of the isolated cations. This is particularly intriguing since many cations can adopt different hydration states, and thus the sizes of the hydrated cations can be different. The corollary of this is that, if the sizes of hydrated cations can be controlled by varying the extent of hydration, it may be possible to synthesize materials with controlled tu...
The fusion power density produced in a tokamak is proportional to its magnetic field strength to the fourth power. Second-generation high temperature superconductor (2G HTS) wires demonstrate remarkable engineering current density (averaged over the full wire), JE, at very high magnetic fields, driving progress in fusion and other applications. The key challenge for HTS wires has been to offer an acceptable combination of high and consistent superconducting performance in high magnetic fields, high volume supply, and low price. Here we report a very high and reproducible JE in practical HTS wires based on a simple YBa2Cu3O7 (YBCO) superconductor formulation with Y2O3 nanoparticles, which have been delivered in just nine months to a commercial fusion customer in the largest-volume order the HTS industry has seen to date. We demonstrate a novel YBCO superconductor formulation without the c-axis correlated nano-columnar defects that are widely believed to be prerequisite for high in-field performance. The simplicity of this new formulation allows robust and scalable manufacturing, providing, for the first time, large volumes of consistently high performance wire, and the economies of scale necessary to lower HTS wire prices to a level acceptable for fusion and ultimately for the widespread commercial adoption of HTS.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.