Silver 50 kopecks coins made by the metallurgist and the Mining Institute graduate Petr Latyshev

This paper continues a series of publications on the history of Russian silver 1 Rouble coins and the contribution of the Saint Petersburg münzmeisters, who graduated from the Mining University, to the coin business. The study focused on silver 50 Kopecks coins of the 1922–1924ss made by the former münzmeister of the Saint Petersburg Mint Petr Latyshev, who graduated from the Mining School. A study of archives confirmed his involvement in the minting of the first silver coins issued by the Soviet State in the 1920s at both the Leningrad Mint and the London Mint. The authors examined silver 50 Kopecks coins of the 1922–1925ss and established certain features of their production. By means of modern technology, the authors examined the distribution of chemical elements across the surface and defined the structure of the silver matrix. A relationship was established between certain elements and the hardness of different areas of the coin. All experiments were conducted using state-of-the-art equipment of specialized laboratories at the Saint Petersburg Mining University. The new approach to the study of historic artefacts enables to get a deeper insight into the production technology that was used. Vickers microhardness tests helped establish that the segregation can be primarily linked to such elements as nickel, copper and lead, which may affect the quality of the final product if their concentration is high. This research study was carried out as part of the preparation research work for the exhibition of the Coin Collection of the Saint Petersburg Mining University’s Museum of Mining, as well as in the framework of the cooperation agreement signed on 29/11/2019 between the Saint Petersburg Mining University and the Museum für Naturkunde at the Leibnitz Institute for Evolution and Biodiversity Science in Berlin, Germany.

Tribological behavior and microstructural evolution of lubricating film of silver matrix self-lubricating nanocomposite

The aim of this study is to fabricate the nanocomposite with low friction and high wear resistance using binary solid lubricant particles. The microstructure and tribological performance of the nanocomposite are evaluated, and the composition and film thickness of the lubricating film are observed and analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The nanocomposite exhibited improved tribological properties with a friction coefficient as low as 0.12 and a low wear rate of 2.17 × 10−6 mm3/(N·m) in high-purity nitrogen atmosphere. Decreasing sliding speed can increase lubricating film thickness, and the thickest lubricating film is approximately 125 nm. As the film thickness of the lubricating film exceeded 90 nm, the friction coefficient curves became smooth. In compared with WS2, MoS2 can be more effective in forming the transfer layer on the worn surfaces at the initial stage of the tribological process.

Effects of NiO content on the microstructure and mechanical properties of AgSnO2NiO composites

The AgSnO2NiO composites were prepared by internal oxidation method. The effects of different NiO content on the microstructure and mechanical properties of AgSnO2NiO composites were studied. The phase structure and surface morphology of the prepared AgSnO2NiO materials were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Metallographic Microscopy (MM). The results showed that the AgSnO2NiO composites with different NiO content can be obtained by the process of preoxidation of AgSn alloy powder and internal oxidation of ingot containing Ni. The agglomeration phenomenon of Ni in the silver matrix was serious, which led to the agglomeration of in-situ generated NiO particles after internal oxidation. After the multi-pass drawing, the SnO2 particles dispersedly distributed in the AgSnO2NiO composites and the NiO particles gradually dispersed from the agglomerated state of the sintered ingot billet. The hardness of the prepared AgSnO2NiO composites increased slightly with the increase of NiO content. The mechanical properties test showed that the introduction of NiO particles significantly improved the tensile strength and elongation of AgSnO2 materials to a certain degree. Adding proper amount of NiO is beneficial to improve the overall performance of AgSnO2 materials.