Search Results (4)

The research aim was to optimize post-weld heat-treatment (PWHT) modes for a laser-welded joint of the Al–Cu–Li alloy and improve their respective strength properties. As a result, the ultimate tensile strength, yield point, and elongation of the joint were enhanced up to 95%, 94%, and 38%, respectively, of those inherent in the base metal. Before and after PWHT, both microstructures and phase compositions have been examined by optical and scanning electron microscopy, as well as synchrotron X-ray diffractometry. In the as-welded metal, the α-Al and T₁(Al₂CuLi) phases were found, along with the θ′(Al₂Cu) and S′(Al₂CuMg) phases localized at the grain boundaries, significantly reducing the mechanical properties of the joint. Upon quenching, the agglomerates dissolved at the grain boundaries, the solid solution was homogenized, and both Guinier–Preston zones and precipitates of the intermediate metastable θ″ phase were formed. After subsequent optimal artificial aging, the (predominant) hardening θ′ and (partial) T₁(Al₂CuLi) phases were observed in the weld metal, which contributed to the improvement of the strength properties of the joint. Full article

The results of the research of a composite based on multi-walled carbon nanotubes (MWCNTs) decorated with CuO/Cu₂O/Cu nanoparticles deposited by the cupric formate pyrolysis are discussed. The study used a complementary set of methods, including scanning and transmission electron microscopy, X-ray diffractometry, Raman, and ultrasoft X-ray spectroscopy. The investigation results show the good adhesion between the copper nanoparticles coating and the MWCNT surface through the oxygen atom bridge formation between the carbon atoms of the MWCNT outer graphene layer and the oxygen atoms of CuO and Cu₂O oxides. The formation of the Cu–O–C bond between the coating layer and the outer nanotube surface is clearly confirmed by the results of the O 1s near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) of the Cu/MWCNTs nanocomposite. The XPS measurements were performed using a laboratory spectrometer with sample charge compensation, and the NEXAFS studies were carried out using the synchrotron radiation of the Russian–German dipole beamline at BESSY-II (Berlin, Germany) and the NanoPES station at the Kurchatov Center for Synchrotron Radiation and Nanotechnology (Moscow, Russia). Full article

This paper reports the precise analysis of the eutectic mixing behavior of 1,3-distearoyl-2-oleoyl-sn-glycerol (SOS) and trilaurin (LLL), as a typical model case of the mixture of cocoa butter (CB) and cocoa butter substitute (CBS). SOS was mixed with LLL at several mass fractions of LLL (w_LLL); the mixtures obtained were analyzed for polymorphic phase behavior using differential scanning calorimetry (DSC) and synchrotron radiation X-ray diffractometry (SR-XRD). In melt crystallization with constant-rate cooling, SOS and LLL formed eutectics in their metastable polymorphs, allowing the occurrence of a compatible solid solution at w_LLL ≥ 0.925. With subsequent heating, the resultant crystals transformed toward more stable polymorphs, then melted in a eutectic manner. For mixtures aged at 25 °C after melt crystallization, eutectics were found in the extended w_LLL region, even at w_LLL = 0.975. These results indicate that phase separation between SOS and LLL progressed in their solid solution under stabilization. The crystal growth of the separated SOS fraction may cause fat-bloom formation in compound chocolate containing CB and CBS. To solve this problem, the development of retardation techniques against phase separation is expected. Full article

Currently, X-ray photoelectron spectroscopy (XPS) is widely used to characterize the nanostructured material surface. The ability to determine the atom distribution and chemical state with depth without the sample destruction is important for studying the internal structure of the coating layer several nanometers thick, and makes XPS the preferable tool for the non-destructive testing of nanostructured systems. In this work, ultra-soft X-ray spectroscopy methods are used to study hidden layers and interfaces of pyrolytic tungsten carbide nanoscale coatings on the multi-walled carbon nanotube (MWCNT) surfaces. XPS measurements were performed using laboratory spectrometers with sample charge compensation, and Near Edge X-ray Absorption Fine Structure (NEXAFS) studies using the Russian–German dipole beamline (RGBL) synchrotron radiation at BESSY-II. The studied samples were tested by scanning and transmission electron microscopy, X-ray diffractometry, Raman scattering and NEXAFS spectroscopy. It was shown that the interface between MWCNT and the pyrolytic coating of tungsten carbide has a three-layer structure: (i) an interface layer consisting of the outer graphene layer carbon atoms, forming bonds with oxygen atoms from the oxides adsorbed on the MWCNT surface, and tungsten atoms from the coating layer; (ii) a non-stoichiometric tungsten carbide WC_1-x nanoscale particles layer; (iii) a 3.3 nm thick non-stoichiometric tungsten oxide WO_3-x layer on the WC_1-x/MWCNT nanocomposite outer surface, formed in air. The tungsten carbide nanosized particle’s adhesion to the nanotube outer surface is ensured by the formation of a chemical bond between the carbon atoms from the MWCNT upper layer and the tungsten atoms from the coating layer. Full article