Identification of patterns of crystal-chemical transformations in historical artifacts made of metals

The theoretical substantiation of the process of elimination of individual chemical elements from crystal lattices of metals in the process of the crystal-chemical transformations taking place during the long history of artifact existence was given. To confirm the theoretical conclusions, five ancient gold items from different historical periods (from the IV century B.C. to the XVIII century A.D.) with approximately the same contents of gold, silver, copper, and iron in the alloy body were studied. The conducted studies will promote more exact attribution of historical artifacts made of metals and revealing the signs of forgery or restoration. The chemical composition of items was determined immediately under patina and in the alloy body using a scanning electron microscope equipped with an energy dispersion spectrometer. The results have shown a much lower gold content inside the alloy than in the item surface. At the same time, the undamaged surface cleansed of mineral crusts contained significantly fewer impurities than the polished surface which did not have contact with the environment. Therefore, the study of the chemical composition of gold artifacts cannot be conducted solely based on surface studies. The studies have resulted in establishing a dependence of the concentration of the main component (gold) of the alloy in the artifact surface on the item age in thousands of years. Equations for predicting the age of the items that are chemically belonging to the described item group were also presented. Studies of peculiarities of crystal-chemical processes are very important in practice to prove the historical artifact authenticity, adjust artifact dating, identify signs of forgery or profound changes caused by restoration

Oxidation behavior of Cr-coated zirconium alloy cladding in high-temperature steam above 1200 °C

Dense, uniform, and well-adhered chromium (Cr) coatings were deposited on zirconium (Zr) alloy claddings by using physical vapor deposition (PVD). The Cr-coated samples were tested at 1200 oC and 1300 oC, respectively, for different exposure time in water steam environment. Microstructures and compositions of the coating/substrate system after oxidation were characterized by X-ray diffraction, scanning electronic microscopy, and energy dispersion spectrometer. The microstructural results clearly demonstrated that Cr2O3 layer has been produced on the coating surface, acting as an oxygen diffusion barrier and concomitantly reducing the oxidation rate. The experimental results on weight gains soundly supported the microstructural findings that the Cr coatings could protect the Zr substrate from high-temperature steam oxidation, even at a temperature up to 1300 oC. Finally, the oxidation kinetics was theoretically analyzed and the underlying oxidation mechanism was also clarified.

Study of gold nanoparticles’ preparation through ultrasonic spray pyrolysis and lyophilisation for possible use as markers in LFIA tests

To monitor the progress and prevent the spread of the COVID-19 pandemic in real time and outside laboratories, it is essential to develop effective tests that can ensure rapid, selective, and reliable diagnosis of infected persons in different environments. Key in this regard is the lateral flow immunoassays (LFIAs) that can detect the presence of the SARS-CoV-2 virus quickly, with the aid of nanoparticles (NPs) and specific proteins. We report the use of gold (Au) NPs AuNPs synthesised from a gold(iii) chloride tetrahydrate precursor in a USP device and collected in a suspension composed of deionised water with polyvinylpyrrolidone as a stabiliser and cryoprotectant. In combination with freeze-drying of the AuNPs’ suspension to achieve water elimination, improved stability, and the target concentration, they exhibit the necessary properties for use as markers in LFIA rapid diagnostic tests. This was confirmed by complementary characterisation determined by using the techniques including inductively coupled plasma-optical emission spectrometry, dynamic light scattering method and zeta-potential, ultraviolet-visible spectroscopy, X-ray diffraction, scanning electron microscopy with energy dispersion spectrometer, and transmission electron microscopy, as well as with the preparation of a prototype LFIA test strip with AuNPs. Thus, such AuNPs, as well as the USP method, show promise for the development of new markers for use in LFIA.

Physicochemical and Mechanical Characterization of Raffia vinifera Pith

In this paper, the physicochemical and mechanical properties of Raffia vinifera pith (RVP) are discussed. Microscopic observations have shown that the structure of the RVP is similar to that of a composite consisting of natural fibers. The effective area ratio of Raffia vinifera (RV) fibers was evaluated along the raffia stem using ImageJ software, and it decreases from the periphery to the center. Energy dispersion spectrometer (EDS) analysis shows that RVP is essentially composed of carbon and oxygen. Densities of RVP and its matrix were determined using Archimedes’ principle and law of mixtures, respectively; from the results obtained, they can be considered as one of the lightest materials. Young’s modulus of RVP has been obtained from tensile and bending tests, while that of matrix has been obtained using the law of mixtures during tensile tests. RVP has better specific properties, and the results of the matrix properties show that we can easily select another matrix which has better properties than the case studied during the elaboration of composites.

Preparation and Activity Evaluation of the Novel Cu/TiO2 Nanometer Photocatalytic Materials

In this paper, the Cu/TiO2 thin film catalysts were prepared by alcoholthermal method with copper sheet as the carrier. In order to improve the degradation rate of antibiotic (cefazolin sodium), the synthesis conditions of Cu/TiO2 thin films were optimized. The physicochemical properties and activity were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray energy dispersion spectrometer (EDX), infrared spectrometer (FTIR), X-ray photoelectron spectrometer (XPS), high performance liquid chromatography (HPLC), chemical oxygen demand (COD) and spectrophotometry. The results show that the Cu/TiO2 catalyst had a uniform thickness of ∼200 nm and the particle size was about 0.4 nm, and the heterojunction between copper and anatase titanium dioxide has was successfully prepared. It can be found that when the dosage of TiF4 was 0.016 g, the tertiary butyl alcohol was 40 ml, the oven temperature was 130 °C, the oven reaction time was 24 h, the calcination temperature was 180 °C, and the calcination time was 2 h, the formed Cu/TiO2 catalyst can reach 58.1% for 3 h under visible light, with the photocatalytic degradation of 20 μg · mL–1 cefazolin sodium aqueous solution.

Analysis of Chemical Composition Homogeneity in the Cross-section of the Rods Produced from Alloys of 6xxx Group

The alloys from Al–Mg–Si system provide an excellent combination of mechanical properties, heat treatment at extrusion temperature, good weldability, good corrosion resistance and formability. Owing to the high casting speed of rods or slabs, the solidification is rather non-equilibrium, resulting in defects in the material, such as crystalline segregations, the formation of low-melting eutectics, the unfavourable shape of intermetallic phases and the non-homogeneously distributed alloying elements in the cross-section of the rods or slabs and in the entire microstructure. The inhomogeneity of the chemical composition and the solid solution negatively affects the strength, the formability in the warm and the corrosion resistance, and can lead to the formation of undesired phases due to segregation in the material. In this experimental investigation, the cross-sections of the rods from two different alloys of the 6xxx group were investigated. From the cross-sections of the rods, samples for differential scanning calorimetry (DSC) at three different positions (edge, D/4 and middle) were taken to determine the influence of inhomogeneity on the course of DSC curve. Metallographic sample preparation was used for microstructure analysis, whereas the actual chemical composition was analysed using a scanning electron microscope (SEM) and an energy dispersion spectrometer (EDS).

Effects of Homogenization Conditions on the Microstructure Evolution of Aluminium Alloy EN AW 8006

The industrial production of products, such as foil and aluminium alloy strips, begins with the production of semi-finished products in the form of slabs. These are produced by the continuous casting process, which is quick and does not allow the equilibrium conditions of solidification. Non-homogeneity—such as micro and macro segregation, non-equilibrium phases and microstructural constituents, as well as stresses arising during non-equilibrium solidification—are eliminated by means of homogenization annealing. In this way, a number of technological difficulties in the further processing of semi-finished products can be avoided. The aim of this research was the optimization of the homogenization annealing of the EN AW 8006 alloy. With the Thermo-Calc software, a thermodynamic simulation of equilibrium and non-equilibrium solidification was performed. Differential scanning calorimetry (DSC) was performed on selected samples in as-cast state and after various regimes of homogenization annealing and was used for the simulation of homogenization annealing. Using an optical microscope (OM), a scanning electron microscope (SEM) and an energy dispersion spectrometer (EDS), the microstructure of the samples was examined. Based on the results, it was concluded that homogenization annealing has already taken place after 8 h at 580 °C to the extent, that the material is then suitable for further processing.

Studi Metode Pendinginan Super Cepat untuk Pembentukan Bulk Metallic Glasses pada Paduan Cu45Zr45Al5Ag5

Bulk Metallic Glass (BMG) memiliki sifat mekanik, magnetik, kimia dan fisik yang berbeda dengan paduan polikristalin karena susunan internal atomnya yang tidak teratur. Sehingga, BMG memiliki kekuatan mekanik yang baik, kekerasan yang tinggi, ketahanan terhadap aus dan korosi yang tinggi, dan kehalusan permukaan yang baik. Berdasarkan sifat tersebut, BMG memiliki kelayakan yang menjanjikan di bidang industry. Dalam penelitian ini, metode pengecoran cetakan di tembaga digunakan untuk menyiapkan BMG paduan Cu45Zr45Al5Ag5. Paduan dileburkan ulang dengan pendinginan super cepat menggunakan mesin pendingin di bawah temperatur -25 oC. Dengan metode pengecoran cetakan di tembaga, sampel ukuran besar berbentuk batang dipotong dengan diameter 2 mm hingga 4 mm dan panjang 30 mm. Batang kemudian dipotong lagi menjadi spesimen berbentuk cakram. Untuk memastikan apakah sampel adalah BMG atau tidak, sampel dievaluasi dengan Scanning Electron Microscopy (SEM), Energy Dispersion Spectrometer (EDS), Differential Scanning Calorimetry (DSC), Electron Probe X-ray Micro Analyzer (EPMA), dan X -ray Difraction (XRD). Hasilnya dibahas dalam penelitian ini. Kata Kunci: Bulk Metallic Glasses, Cu45Zr45Al5Ag5, Pengecoran Cetakan di Tembaga.

The Study of Conditions for the Silicon Carbide Crystals Formation in the Complex Composition Metal Melt

The results of thermodynamic modeling and experimental studies are presented in this article. The aim of this work is to determine the conditions of silicon carbide crystals synthesis in the complex composition metal melts. The "FactSage" software was used for thermodynamic modeling. The phase diagrams, in the form of liquidus surfaces, allow determining the metal composition with minimum melting temperature and presenting the ranges of concentrations and temperatures for which the equilibrium product of the interaction between the components of the metal melt is silicon carbide. The results of experimental research confirmed the possibility of growing silicon carbide crystals in the complex metal melts at low temperatures. The results of the obtained sample of complex alloy examination (conducted with the scanning electron microscope JEOL JSM–6460LV with a energy dispersion spectrometer by "Oxford Instruments" used for performing qualitative and quantitative microprobe analysis) helped to reveal the crystals corresponding to SiC composition.

Characterization of natural and chemically modified kaolinite from Mako (Senegal) to remove lead from aqueous solutions

The chemical and sorption properties of clay minerals from the Mako area, Senegal, were investigated using FTIR spectroscopy, X-ray diffraction, scanning electron microscopy equipped with an X-ray energy dispersion spectrometer, thermal analysis and chemical analysis. The clay sample is essentially dominated by kaolinite and quartz as also shown by treatment with ethylene glycol and dimethylsulfoxide (DMSO). The clay fraction of this natural clay was organically modified by grafting with 3-aminopropyltriethoxysilane (APTES) in order to improve significantly its retention ability of heavy metals. The silane groups of the APTES reagent were partly grafted on the surface of platy kaolinite particles and the remaining ethoxy groups could be hydrolysed by aqueous treatment. The natural clay, its clay fraction and the organo-functionalized clay (with APTES) were investigated as adsorbents for the removal of Pb(II) from aqueous solutions. Evidence for an organic grafting has been demonstrated by comparing the spectroscopic characteristics of the natural clay and those of its chemically modified derivatives. The effects of different parameters (i.e. initial Pb(II) concentration and contact time) on the adsorption efficiency were studied. For an initial concentration of 10 mg L−1Pb(II), the adsorption was maximized after 30 min contact time both for the raw material and its clay fraction and after 90 min for the APTES grafted clay. Although the maximum of sorption for the APTES grafted clay is reached with slower kinetics, this maximum amount of Pb(II) uptake at room temperature (Xmax) is significantly higher since it is 0.99 mg g−1for the raw clay, 1.46 mg g−1for its clay fraction and 3.02 mg g−1for the organically modified clay, i.e. three times greater than the raw clay.