Utjecaj brzine naprezanja na svojstva mikrolegiranog čelika S-MC gradacije

The influence of strain rate on properties of microalloyed steel for cold drawing of S 315 MC and S 460 MC gra-des was analysed. It has been shown by testing these steel that strain rates in the range from 10-3 up to 1 s-1 do not influence the mechanical properties significantly. Significant strengthening started at strain rates exceeding 2 s-1. It has been shown also that the basic mechanical properties of the coldworked tested steel by 5 to 25 % were not influenced by prestrain at 10-3 to 103 s-1 strain rates. It is supposed according to the results, that the susceptibility to cold work of these steel was not influenced significantly by the strain rates usually used at coldwork (less than 1 s-1) and that the products after coldwork maintain their mechanical properties.Analiziran je utjecaj brzine naprezanja na svojstva mikrolegiranog čelika za hladno izvlačenje gradacije S 315 MC i S 460 MC. Pokazano je testiranjem tih čelika da brzine naprezanja u opsegu 10-3 do 1 s-1 ne utječu značajno na mehanička svojstva. Značajno očvršćivanje započinje kod brzina naprezanja iznad 2 s-1. Također je pokazano da osnovna mehanička svojstva hladno obrađenih čelika testiranih pri 5 do 25% ne zavise o prednaprezanju pri 10-3 do 103 s-1 brzinama naprezanja. Pretpostavljeno je na osnovi rezultata, da osjetljivost na hladnu preradu tih čelika ne zavisi značajno o brzinama naprezanja, koje se uobičajeno koriste pri hladnoj preradi (manje od 1 s-1) i da produkti zadržavaju svoja mehanička svojstva nakon hladne prerade

Characteristics of Silver Nanoparticles in Different pH Values

Stability of silver nanoparticles strongly influences the potential of their application. The literature shows wide possibilities of nanoparticles preparation, which has significantly impact on their properties. Therefore, the improvement of AgNPs preparation plays a key role in the case of their practical use. The pH values of the environment are one of the important factors, which directly influences stability of AgNPs. We present a comparing study of the silver nanoparticles prepared by „bottom-up“ methods over by chemical synthesis and biosynthesis using AgNO3 (0.29 mM) solution. For the biosynthesis of the silver nanoparticles, the green freshwater algae Parachlorella kessleri and Citrus limon extracts were used as reducing and stabilizing agents. Chemically synthesized AgNPs were performed using sodium citrate (0.5%) as a capping agent and 0.01% gelatine as a reducing agent. The formation and long term stability of those silver nanoparticles synthesized either biologically and chemically were clearly observed by solution colour changes and confirmed by UV-vis spectroscopy. The pH values of formed nanoparticle solutions were 3 and 5.8 for biosynthesized AgNPs using extract of Citrus limon and Parachlorella kessleri, respectively and 7.2 for chemically prepared AgNPs solution using citrate. The SEM as a surface imaging method was used for the characterization of nanoparticle shapes, size distribution and also for resolving different particle sizes. These micrographs confirmed the presence of dispersed and aggregated AgNPs with various shapes and sizes