Browsing by Author "Sandu A.V."

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    Assessment of Persistence of Gunshot Residues Produced by Firearms from Criminal Cases in the Republic of Kosovo
    (2022-10-01) Tahirukaj M.; Surleva A.; Vizureanu P.; Olluri B.; Sandu A.V.
    Gunshot residue (GSR) is a material formed during firearm discharge with a specific spheroidal/noncrystalline morphology and chemical composition. The examination of gunshot residue by SEM/EDS is an important tool in forensic studies and presents supporting evidence in criminal investigations. This study is aimed at exploring the number of particles characteristic of GSR identified by SEM/EDS as a function of time, gun caliber, the number of shots, and weather conditions. Firearms typically used in criminal cases in Kosovo were studied, and the experiments were conducted outdoors in the summer and winter seasons. Nine people made different numbers of shots from one to nine and followed a common office routine. An optimized and validated SEM/EDS protocol was applied with a sensitivity of 95%, a bias of −5%, a repeatability of 2% (RSD), a within-lab reproducibility of 2% (RSD), and an expanded uncertainty of the number of GSR particles of 6% at coverage factor k = 2. The results showed that GSR particles could be identified by SEM/EDS five to seven hours after shooting, depending on the weapon used and number of produced shots. The results will benefit forensic scientists by providing a supportive tool for hypothesizing the time interval between firearm discharge and GSR sampling.
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    Characterization of Bulgarian Copper Mine Tailing as a Precursor for Obtaining Geopolymers
    (2024-02-01) Ilieva D.; Angelova L.; Radoykova T.; Surleva A.; Chernev G.; Vizureanu P.; Burduhos-Nergis D.D.; Sandu A.V.
    Valorization of high-volume mine tailings could be achieved by the development of new geopolymers with a low CO2 footprint. Materials rich in aluminum and silicon with appropriate solubility in an alkaline medium can be used to obtain a geopolymer. This paper presents a study of copper mine tailings from Bulgaria as precursors for geopolymers. Particle size distribution, chemical and mineralogical composition, as well as alkaline reactivity, acidity and electroconductivity of aqueous slurry are studied. The heavy metal content and their mobility are studied by leaching tests. Sequential extraction was applied to determine the geochemical phase distribution of heavy metals. The studied samples were characterized by high alkalinity, which could favor the geopolymerization process. The water-soluble sulphates were less than 4%. The Si/Al ratio in mine tailing was found to be 3. The alkaline reactivity depended more so on the time of extraction than on the concentration of NaOH solution. The main part of the heavy metals was found in the residual fraction; hence, in high alkaline medium during the geopolymerization process, they will stay fixed. Thus, the obtained geopolymers could be expected to exert low environmental impact. The presented results revealed that studied copper mine tailing is a suitable precursor for geopolymerization.
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    Improvement of the turbine blade surface phase structure recovered by plasma spraying
    (2020-01-01) Savinkin V.V.; Vizureanu P.; Sandu A.V.; Ratushnaya T.Y.; Ivanischev A.A.; Surleva A.
    This paper presents the results of research on the construction, technological parameters and criteria that control the process of formation of optimal phase structure of austenitic-and martensitic-class material for steam turbine blades. The hypothesis that the established correlation could increase the quality of blade recovery and its resistance against dynamic and vibrational loads was proved. The efficiency of the developed implantation method for the recovery of steam turbine blades was demonstrated. The optimal technological parameters of the process of laser plasma recovery were established empirically, allowing the development of the system for the fine tuning of the phase composition of austenitic-and martensitic-class steel.