ABSTRACT
Today, Ni-Cr steel is used for advanced applications in the high-temperature and electrical industries, medical equipment, food industry, agriculture and is applied in food and beverage packaging and kitchenware, automotive or mesh. A study of input steel powder from various stages of the recycling process intended for 3D printing was conducted. In addition to the precise evaluation of the morphology, particle size and composition of the powders used for laser 3D printing, special testing and evaluation of the heat-treated powders were carried out. Heat treatment up to 950 °C in an air atmosphere revealed the properties of powders that can appear during laser sintering. The powders in the oxidizing atmosphere change the phase composition and the original FeNiCr stainless steel changes to a two-phase system of Fe3Ni and Cr2O3, as evaluated by X-ray diffraction analysis. Observation of the morphology showed the separation of the oxidic phase in the sense of a brittle shell. The inner part of the powder particle is a porous compact core. The particle size is generally reduced due to the peeling of the oxide shell. This effect can be critical to 3D printing processing, causing defects on the printed parts, as well as reducing the usability of the precursor powder and can also change the properties of the printed part.
ABSTRACT
Recently, tailored synthesis of solid electrolytes satisfy multiple challenges, i.e. high ionic conductivity and wide (electro)chemical stability window is of great interest. Although both oxide- and sulfide-based solid electrolytes have distinguished merits for meeting such concerns separately, a new solid electrolyte having the excellent aspects of both materials is pursued. Herein, we report the synthesis of a sulfur-doped Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte with a NASICON crystal structure that combines elevated ionic conductivity with intrinsic stability against an ambient atmosphere. Sulfur doping was carried out using sulfur-amine chemistry and the system was characterized by XRD, Raman, XPS, ICP-OES, and EDS analyses. Bader charge analysis was carried out with the aid of density functional theory calculations to characterize charge accumulation in the local environment of the bare and sulfur doped LATP structures. Our results indicate that the partial replacement of oxygen with sulfur yields higher ionic conductivity due to the lower electronegativity of sulfur compared to oxygen, which reduces the attraction of lithium ions. The enhanced ionic conductivity of LATP is attributed to a decreased lithium ion diffusion activation energy barrier upon sulfur doping. Compared to bare LATP, the as-prepared sulfur doped LATP powders were shown to decrease the activation energy barrier by 10.1%. Moreover, an ionic conductivity of 5.21 × 10-4 S cm-1 was obtained for the sulfur doped LATP powders, whereas bare LATP had an ionic conductivity of 1.02 × 10-4 S cm-1 at 40 °C.
ABSTRACT
Different polymorphs of MnO2 (α-, ß-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers' method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge-discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm-2 using CR2016 coin cells. The initial specific capacity of graphene/α-, ß-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg-1, 198 mAhg-1, and 251 mAhg-1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg-1 after 200 cycles with 72% capacity retention.
