Controlling the formation of sodium/black phosphorus intercalated compounds towards high sodium content

The solid-state synthesis of pure sodium-black phosphorus intercalation compounds (Na-BPICs) has been optimized in bulk for two stoichiometric ratios. Specifically, in-situ X-Ray diffraction (XRD) allowed the precise identification of the optimal temperature range for the formation of Na-BPICs: 94 °C–96 °C. Moreover, as the undesired formation of Na3P takes place at this very same range, we succeeded in introducing a new synthetic route based on a fast-thermal ball milling implementation that results in the bulk production of BPIC without Na3P in 9 out of 10 cases. Finally, by combining XRD, Raman spectroscopy, and DFT calculations we developed a new structural model for Na-based BPICs showing an increase of BP's unit cell with Na atoms incorporated in every second layer. These results will pave the way for the large-scale synthesis and application of pure BPICs, which are of great interest in fields such as optoelectronics or energy storage.PNICTOCHEM 804110 (G.A.)PID2019-111742-GA-I00CIDEGENT/2018/00

Effect of Tantalum Solid Solution Additions on the Mechanical Behavior of ZrB₂

Mechanical properties and microstructure were compared for zirconium diboride and two zirconium diboride solid solutions containing 3 and 6 at% tantalum diboride. X-ray diffraction indicated that the ceramics were nearly phase-pure and that tantalum dissolved into the ZrB2 lattice to form (Zr,Ta)B2 solid solutions. Microstructural analysis indicated that samples achieved nearly full relative density with average grain sizes that ranged from 3-5 μm. The three compositions had similar values of Young\u27s modulus (510-531 GPa), shear modulus (225-228 GPa), Vickers hardness (15.2-16.4 GPa), and flexural strength (391-452 MPa). Fracture toughness ranged from 2.6 to 3.7 MPa m1/2 and with increasing tantalum content, the fracture mode changed from predominantly intergranular to predominantly transgranular. Diboride solid solution materials had comparable properties to the single metal diboride, but differences in microstructure, secondary phases, and strain state among the three ceramics partially obscured the actual effects of the solid solution on fracture behavior

A Revised Relationship Between Fracture Toughness and Y2O3 Content in Modern Dental Zirconias

The relationship between fracture toughness and Yttria content in modern zirconia ceramics was revised. For that purpose, we evaluated here 10 modern Y2O3-stabilized zirconia (YSZ) materials currently used in biomedical applications, namely prosthetic and implant dentistry. The most relevant range between 2-5 mol% Y2O3 was addressed by selecting from conventional opaque 3 mol% YSZ up to more translucent compositions (4-5 mol% YSZs). A technical 2YSZ was used to extend the range of our evaluation. The bulk mol% Y2O3 concentration was measured by X-Ray Fluorescence Spectroscopy. Phase quantification by Rietveld refinement are supplied by considering only two tetragonal phases or an additional improbable cubic phase. A first-account of the fracture toughness (KIc) of the partly-sintered materials is given, which amounted to 0.4 – 0.7 MPaÖm. In the fully-densified state, an inverse power-law behavior was obtained between KIc and bulk mol% Y2O3 content, whether using only our measurements or including literature data, challenging some established relationships.</p

Exceptional strengthening of biodegradable Mg-Zn-Ca alloys through high pressure torsion and subsequent heat treatment

In this study, two biodegradable Mg-Zn-Ca alloys with alloy content of less than 1 wt % were strengthened via high pressure torsion (HPT). A subsequent heat treatment at temperatures of around 0.45 Tm led to an additional, sometimes even larger increase in both hardness and tensile strength. A hardness of more than 110 HV and tensile strength of more than 300 MPa were achieved in Mg-0.2Zn-0.5Ca by this procedure. Microstructural analyses were conducted by scanning and transmission electron microscopy (SEM and TEM, respectively) and atom probe tomography (APT) to reveal the origin of this strength increase. They indicated a grain size in the sub-micron range, Ca-rich precipitates, and segregation of the alloying elements at the grain boundaries after HPT-processing. While the grain size and segregation remained mostly unchanged during the heat treatment, the size and density of the precipitates increased slightly. However, estimates with an Orowan-type equation showed that precipitation hardening cannot account for the strength increase observed. Instead, the high concentration of vacancies after HPT-processing is thought to lead to the formation of vacancy agglomerates and dislocation loops in the basal plane, where they represent particularly strong obstacles to dislocation movement, thus, accounting for the considerable strength increase observed. This idea is substantiated by theoretical considerations and quenching experiments, which also show an increase in hardness when the same heat treatment is applied.ISSN:1996-194

Unifying Principles of the Reductive Covalent Graphene Functionalization

Covalently functionalized graphene derivatives were synthesized via benchmark reductive routes using graphite intercalation compounds (GICs), in particular KC₈. We have compared the graphene arylation and alkylation of the GIC using 4-<i>tert</i>-butylphenyldiazonium and bis­(4-(<i>tert</i>-butyl)­phenyl)­iodonium salts, as well as phenyl iodide, <i>n</i>-hexyl iodide, and <i>n</i>-dodecyl iodide, as electrophiles in model reactions. We have put a particular focus on the evaluation of the degree of addition and the bulk functionalization homogeneity (<i>H</i>_bulk). For this purpose, we have employed statistical Raman spectroscopy (SRS), and a forefront characterization tool using thermogravimetric analysis coupled with FT-IR, gas chromatography, and mass spectrometry (TGA/FT-IR/GC/MS). The present study unambiguously shows that the graphene functionalization using alkyl iodides leads to the best results, in terms of both the degree of addition and the <i>H</i>_bulk. Moreover, we have identified the reversible character of the covalent addition chemistry, even at temperatures below 200 °C. The thermally induced addend cleavage proceeds homolytically, which allows for the detection of dimeric cleavage products by TGA/FT-IR/GC/MS. This dimerization points to a certain degree of regioselectivity, leading to a low sheet homogeneity (<i>H</i>_sheet). Finally, we developed this concept by performing the reductive alkylation reaction in monolayer CVD graphene films. This work provides important insights into the understanding of basic principles of reductive graphene functionalization and will serve as a guide in the design of new graphene functionalization concepts

Cover. Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization

This cover illustrates how carbon nano-onions can be intercalated with potassium atoms through surface defects by means of thermal heating. This reductive route allows the efficient covalent functionalization with electrophiles such as alkyl iodides.PNICTOCHEM 804110 (G.A.)CIDEGENT/2018/001PID2019-111742-GA-I0

Lattice Opening upon Bulk Reductive Covalent Functionalization of Black Phosphorus

The chemical bulk reductive covalent functionalization of thin‐layer black phosphorus (BP) using BP intercalation compounds has been developed. Through effective reductive activation, covalent functionalization of the charged BP by reaction with organic alkyl halides is achieved. Functionalization was extensively demonstrated by means of several spectroscopic techniques and DFT calculations; the products showed higher functionalization degrees than those obtained by neutral route