Comparison of properties of silver-metal oxide electrical contact materials

Changes in physical properties such as density, porosity, hardness and electrical conductivity of the Ag-SnO2 and Ag-SnO2In2O3 electrical contact materials induced by introduction of metal oxide nanoparticles were investigated. Properties of the obtained silver-metal oxide nanoparticle composites are discussed and presented in comparison to their counterparts with the micro metal oxide particles as well as comparable Ag-SnO2WO3 and Ag-ZnO contact materials. Studied silvermetal oxide composites were produced by powder metallurgy method from very fine pure silver and micro- and nanoparticle metal oxide powders. Very uniform microstructures were obtained for all investigated composites and they exhibited physical properties that are comparable with relevant properties of equivalent commercial silver based electrical contact materials. Both Ag-SnO2 and Ag- SnO2In2O3 composites with metal oxide nanoparticles were found to have lower porosity, higher density and hardness than their respective counterparts which can be attributed to better dispersion hardening i.e. higher degree of dispersion of metal oxide in silver matrix

The effect of structural changes on magnetic permeability of amorphous powder Ni80Co20

The structural changes of Ni80Co20 amorphous powder were tested during heating. The alloy was obtained by electrolysis from ammonia solution sulfate of cobalt and nickel on the titanium cathode. The differential scanning calorimetry (DSC) method was used to detect that the crystallization process of powder occurred in two stages with crystallization peaks temperatures of the first stage at 690 K and of the second stage at 790 K. The effect of structural relaxation and crystallization of powder on magnetic properties was predicted by measurement of the relative magnetic permeability change in isothermal and nonisothermal conditions. On the basis of the time change of relative magnetic permeability at a defined temperature in the temperature range of the first and second crystallization peak on the thermogram, the kinetics of crystallization was defined. It was predicted, that in the initial time interval, in the range of the first crystallization peak, the rate of crystallization is determined by the rate of nucleation of the amorphous part of the powder. However, in the second time interval, the crystallization rate is determined by the rate of diffusion. In the range of the second peak, in the beginning the rate of crystal growth is determined by activation energy of the atom pass from smaller to bigger crystal grain. In second time interval, the rate of crystal grain growth is determined by the diffusion rate of atoms to the location of integration into bigger crystal grains. For all processes which determine the rate of crystallization in temperature ranges of both crystallization peaks, the Arrhenius temperature dependence of rate for those processes is obtained. The relative magnetic permeability of crystallized powder at 873 K, is smaller for about 30 % than the relative magnetic permeability of fresh powder at room temperature. However, structurally relaxed powder at 573 K has an about 22 % larger magnetic permeability than the same fresh powder at room temperature

Cerium oxide based nanometric powders: synthesis and characterization

Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re=Yb, Gd and Sm) were added to ceria in total concentration of x= 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure

Some Aspects of Isokinetic Law and Compensation Effect in Organophosphorus Compounds. Part II. Correlation Analysis of O-Alkyl-S-2-Dimethylaminoethyl Methylphosphonothiolates and Their Tetraalkylammonio Derivatives

The correlation analysis of alkaline hydrolysis and inhihibition of BuChE with O-alkyl-S-2-dimethylaminoethyl methyl phosphonothiolates and their tetraalkylammonio derivatives are described. The logarithm dependence of the rate constants of tQ.ese reactions at two different temperatures confirms that reactions of oH- ion and of BuChE with these esters show isokinetic functions i. e. these esters form isokinetic series. The correlation analysis with different Hammets constants showed that alkoxy groups bonded to phosphours1v have somewhat greater resonance effect (a. = 1.21) in comparison to the inductive effect in alkaline h ydrolysis reaction

Hydrolysis of Some Organophosphorus Compounds. Part I. Reactions in Alkaline Solution

The alkaline hydrolysis series of compounds derived from O-alkyl-S-2-dimethylaminoethyl methylphosphonothiolate, O-alkyl- S-2-trimethylammonioethyl methylphosphonothiolate methyl sulfato, and 0,0-diethyl-S-2-dimethylaminoethyl phosphorothiolate are studied in order to show substituent effects in these reactions. The influence of structural change of alkyl radical in RO group as well as electrophilic characteristic of phosphorus atom and charge effects on nitrogen atom on the hydrolysis rate are discussed

German travelogues about Montenegro during the reign of Petar II Petrović Njegoš ; Немецкие записи путешествий о Черногории во время правления Петра II Петровичa Негоша

Analiza poznatih, manje poznatih i domaćoj ĉitalaĉkoj publici gotovo nepoznatih putopisa o Crnoj Gori, napisanih ili objavljenih na njemaĉkom jeziku za vrijeme vladavine Petra II Petrovića Njegoša kao rezultat interesovanja za liĉnost ovog crnogorskog vladara i njegovu zemlju, tema su ovog rada. Kriterijume za odabir i metodologiju za obradu korpusa iz oblasti našeg interesovanja, a koji se odnosi na navedeni istorijski period, utvrdili smo na osnovu obuhvatnijeg istorijsko-teorijskog okvira, pri ĉemu smo se osvrnuli na istorijat, ali i na savremene teorije koje se tiĉu putopisa kao knjiţevne vrste. U radu smo, prije svega, predstavili kulturne posrednike koji su uticali na buĊenje interesovanja javnosti njemaĉkog govornog podruĉja za Crnu Goru i Crnogorce, kao i opšti društveno-politiĉki i kulturni okvir u kome su putopisi ovog perioda nastali. Da bismo rasvijetlili odreĊeni naĉin prikazivanja i shvatanja ove juţnoslovenske zemlje u zemljama njemaĉkog govornog podruĉja naroĉito smo skrenuli paţnju na presudne razloge interesovanja njemaĉkih putopisaca, odnosno putopisaca koji su pisali na njemaĉkom jeziku. Analizirajući prikupljenu graĊu, hronološki smo prikazali autore koji su putopisno opisali Crnu Goru Njegoševog vremena, naveli smo kada su njihova djela nastala, gdje su objavljena i kako je ova zemlja njihovim perom opisana, imajući u vidu splet svih kulturnih, društveno-politiĉkih i ekonomskih okolnosti koji su neizbjeţno uticali na percepciju i predstave o tadašnjem crnogorskom društvu. U putopisima koji su nastali izvorno na njemaĉkom jeziku ili su na njemaĉki prevedeni sa drugih stranih jezika, analizom su se, u pogledu autora ovih putopisnih djela, izdvojile najznaĉajnije teme i motivi, vladajući diskurs i pristup odreĊenim pojavama u crnogorskom društvu Njegoševog doba.The thesis aims at the analysis of travelogues about Montenegro written or published in German during the reign of Petar II Petrović Njegoš, which were the result of interest in the personality of this Montenegrin ruler and his country. The travelogues were well-known, less known, and almost unknown to our readership. Criteria for selection and methodology for processing the corpus in the field of our interest, which refers to the historical period, have been based on a more comprehensive historical-theoretical framework, referring to history, as well as contemporary theories concerning travelogues as a literary genre. The author of the paper has presented the cultural mediators who influenced the arousal of the German-speaking public's interest in Montenegro and Montenegrins, as well as the general socio-political and cultural framework in which the travelogues were created during this period. The author make clear to the crucial reasons for the interest of German travel writers, as well as those who wrote in German, to shed light on a specific way of presenting and understanding this South Slavic country in the German-speaking countries. Having analyzed the collected material, the author has chronologically presented the writers who described the Montenegro of Njegoš's time, stated when their works were created, when and where they were published and how this country was described by their quill, having in mind the intertwining of all cultural, socio-political and economic circumstances that inevitably influenced the perception and the notion of the Montenegrin society during that period. The analysis highlighted the most important themes and motives, the prevailing discourse and approach to certain phenomena in the Montenegrin society of Njegoš's time found in the travelogues that were originally written in German or translated into German from other foreign languages

Investigation of solidification behavior of the Sn-rich ternary Sn-Bi-Zn alloys

Solidification properties and microstructure of six as-cast Sn-Bi-Zn alloys with 80 at.% of Sn and variable contents of Bi and Zn were experimentally investigated using the scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and differential scanning calorimetry (DSC). The experimentally obtained results were compared with predicted phase equilibria according to the calculation of phase diagram (CALPHAD) method and by the Scheil solidification simulation.

The Influence of Milling Conditions on Mechanochemical Synthesis and Sintering of Zinc Titanate

The aim of this work was an investigation of experimental conditions for mechanochemical synthesis and sintering of spinel zinc titanate (Zn2TiO4). Starting powder mixtures of zinc oxide and titan dioxide in the molar ratio, in accordance with the stoichiometrics of spinel zinc titanate, were mechanically activated by grinding in a planetary ball mill for various periods of time in the interval of 0 to 300 minutes. Changes of physico-chemical characteristics and microstructure parameters in the ZnO—TiO2 system after grinding were followed using specific surface area analysis and X-ray powder diffraction, while thermal behavior was examined by differential thermal analysis and dilatometry. The beginning of zinc titanate formation was noticed after 30 minutes of milling, and prolonged milling led to the formation of spinel zinc titanate as the major phase with an insignificant amount of unreacted zinc oxide and titan dioxide. The main conclusions based on this analysis are that Zn2TiO4 ceramics could be obtained by mechanical activation after a certain time without additional thermal treatment and that sintering temperature as well as the formation temperatures of zinc-titanate are significantly lowered using mechanical treatment

Characterization of the natural mineral form from the PbS-Sb2S3 system

This paper presents the results of experimental investigations of natural mineral form from the PbS - Sb2S3 system. Investigated sulfosalt appears in nature in the form of nanowires with diameters ranging from 200 to 500 nm and its length can reach up to 150 mm. In most cases these nanowires are arranged like bundles, which were inspected with scanning electron microscopy (SEM). The chemical composition of this material was analyzed and its stoichiometry responded to 'plumosite'. Crystal structure was analyzed using XRD analyses and compared to available literature data. Investigated samples were subjected to thermal analyses and resulting mechanism of oxidation was concluded. Also, kinetic parameters were calculated for the process of oxidation

Synthesis of novel multi-functionalized pyrrolidines by [3 + 2] dipolar cycloaddition of azomethine ylides and vinyl ketones

© 2019, Springer-Verlag GmbH Austria, part of Springer Nature. Abstract: An efficient and easy synthetic route to substituted pyrrolidine derivatives has been established through [3 + 2] dipolar cycloaddition of vinyl ketones and azomethine ylides. The reactions proceed smoothly, under mild conditions, affording moderate to high isolated yields (up to 88%) of the products, within a short reaction time (15–45 min), providing a series of novel potentially bioactive compounds. Mechanistic considerations revealed that this cycloaddition exclusively proceeds following endo-pathway which enables access to the cis-derivatives. The products that contain acetyl group at C4 easily undergo isomerization, as it was confirmed by monitoring of the reaction kinetics and DFT calculations. Graphical abstract: [Figure not available: see fulltext.]