The influence of activation and relaxation time on the synthesis of cordierite ceramics

Due to its properties, cordierite, 2MgO·2Al2O3·5SiO2, is nowadays an attractive ceramic material for various applications.Mechanochemical activation of the initial componentswas used in order to decrease the sintering temperature. Changes in the specific surface area of the activated componentswere determined by the BETmethod. The TG andDTAmethods were used to monitor the temperature induced changes in the analyzed three-component system. The influence of the relaxation time on the activated components was analyzed by FTIR spectroscopy of both the initial components and the activated mixture after 24 h and 24 months relaxation periods

Effect of temperature on the electrodeposition of disperse copper deposits

The effect of temperature on the electrodeposition of copper at overpotentials belonging to the plateau of the limiting diffusion current density and higher was examined by the determination of the average current efficiency of hydrogen evolution and by scanning electron microscopic (SEM) analysis of the morphology of the formed copper deposits. Increasing the temperature of the solution led to a shift of both the beginning and the end of the plateau of the limiting diffusion current density towards lower electrodeposition overpotentials. Also, higher temperatures led to the formation of morphological forms of copper deposits characteristic for electrodeposition of copper at some higher overpotentials. The unexpected trend in the development of copper structures electrodeposited at an overpotential of 800 mV is discussed in terms of the effect of temperature on the viscosity and surface tension of the electroplating solution.Uticaj temperature na elektrohemijsko taloženje bakra na prenapetostima koje pripadaju platoima granične difuzione gustine struje, kao i na višim prenapetostima je ispitan određivanjem srednjeg iskorišćenja struje reakcije izdvajanja vodonika i analizom morfologija taloga bakra tehnikom skenirajuće elektronske mikroskopije. Povećanje temperature rastvora dovelo je do pomeranja i početka i kraja platoa granične difuzione gustine struje ka nižim prenapetostima. Takođe, povećanje temperature dovelo je do formiranja morfoloških formi taloga bakra karakterističnih za elektrohemijsko taloženje na nekim višim prenapetostima. Neočekivani trend u razvoju struktura bakra dobijenih na prenapetosti od 800 mV je bio diskutovan na osnovu uticaja temperature na viskoznost i površinski napon rastvora za elektrohemijsko taloženje bakra

Electrodeposition of Fe powder from acid electrolytes

Polarization characteristics of the electrodeposition processes of Fe powders from sulfate and chloride electrolytes and the morphology of the obtained powders were investigated. The morphology depended on the anion pre sence in the electrolyte but not on the current density in the investigated range. A characteristic feature of the dendritic powder with cauliflower endings obtained from sulfate electrolyte is the presence of cone-like cavities and the crystallite morphology of the powders surface. On the other hand, Fe powders electrodeposited from chloride electrolyte appear in the form of agglomerates. A soap solution treatment applied as a method of washing and drying provides good protection from oxidation of the powders.U ovom radu prikazani su rezultati ispitivanja polarizacionih karakteristika procesa taloženja Fe prahova iz sulfatnih i hloridnih elektrolita, kao i morfologija dobijenog praha. Utvrđeno je da morfologija čestica zavisi od vrste anjona prisutnih u elektrolitu, ali ne i od primenjene gustine struje u ispitivanom opsegu. Karakteristično za čestice koje su istaložene iz sulfatnih elektrolita je da su one dendritične sa karfiolastim, kristaliničnim završecima i da poseduju kupaste šupljine. Kod Fe prahova istaloženih iz hloridnih elektrolita uočeni su aglomerati. Korišćenje rastvora sapuna u procesu pranja i sušenja prahova pokazao se kao dobar metod zaštite praha od oksidacije

The effect of the particle shape and structure on the flowability of electrolytic copper powder. II. The experimental verification of the model of the representative powder particle

An analysis of the effects of the shape, surface structure and size distribution of particles on the flowability of the copper powder was performed. It is shown that the most important property of the particles of a powder, regarding the flowability of the powder, is the surface structure of the particles

Electrodeposition of Fe powder from acid electrolytes

Polarization characteristics of the electrodeposition processes of Fe powders from sulfate and chloride electrolytes and the morphology of the obtained powders were investigated. The morphology depended on the anion presence in the electrolyte but not on the current density in the investigated range. A characteristic feature of the dendritic powder with cauliflower endings obtained from sulfate electrolyte is the presence of cone-like cavities and the crystallite morphology of the powders surface. On the other hand, Fe powders electrodeposited from chloride electrolyte appear in the form of agglomerates. A soap solution treatment applied as a method of washing and drying provides good protection from oxidation of the powders

The microstructure and properties of as-cast Sn-Zn-Bi solder alloys

U radu su prikazani rezultati ispitivanja strukturnih i mehaničkih karakteristika bezolovnih lemnih legura u sistemu kalaj-cink-bizmut. Nakon dobijanja legura u indukcionoj peći sa zaštitnom atmosferom, trostrukim pretapanjem odmerene količine čistih metala, izvršena su ispitivanja strukture tako dobijenih uzoraka legura optičkom i skenirajućom electronskom mikroskopijom (SEM). Energetskom disperzivnom spektroskopijom (EDS) određen je hemijski sastav faza prisutnih u strukturi legura. Izvršena su merenja tvrdoće, i zatezne čvrstoće ispitivanih legura. Sva istraživanja su sprovedena sa ciljem boljeg upoznavanja osobina legura u sistemu Sn-Zn-Bi, koji se smatra odgovarajućom zamenom olovnih lemnih legura.Research on the lead-free solders has attracted wide attention, mostly as the result of the implementation of the Directive on the Restriction of the Use of Hazardous Substances in Electrical and Electronic Equipment. The Sn-Zn solder alloys have been considered to be one of the most attractive lead-free solders due to its ability to easily replace Sn-Pb eutectic alloy without increasing the soldering temperature. Furthermore, the mechanical properties are comparable or even superior to those of Sn-Pb solder. However, other problems still persist. The solution to overcoming these drawbacks is to add a small amount of alloying elements (Bi, Ag, Cr, Cu and Sb) to the Sn-Zn alloys. Microstructure, tensile strength, and hardness of the selected Sn-Zn-Bi ternary alloys have been investigated in this study. The SEM-EDS was used for the identification of co-existing phases in the samples. The specimens' microstructures are composed of three phases: Sn-rich solid solution as the matrix, Bi-phase and Zn-rich phase. The Bi precipitates are formed around the Sn-dendrit grains as well as around the Zn-rich phase. The amount of Bi segregation increases with the increase of Bi content. The Sn-Zn-Bi alloys exhibit the high tensile strength and hardness, but the values of these mechanical properties decrease with the increase of Bi content, as well as the reduction of Zn content. The results presented in this paper may offer further knowledge of the effects various parameters have on the properties of lead-free Sn-Zn-Bi solders

Consistent force field for metalloporphyrins

Molecular mechanics (MM) calculations to analyze the puckering of metalloporphyrins isolated and adsorbed on a graphite layer (0001) as a function of metal ion size and the peripheral substitution are presented. The Consistent Force Field (CFF) program was used with new parameters for metalloporphyrins, which included an out-of-plane bending function. Normal-coordinate structural decomposition (NSD) analysis was performed on the equilibrium structures obtained by the MM calculations. The conformers were also stereo-chemically characterized and compared with available experimental data and with conformers obtained in a previous MM study.Konzistentno polje sila (CFF) za molekulsko modeliranje metaloporfirina, koje uključuje novouvedenu out-of-plane funkciju, parametrizovano je na osnovu kristalnih struktura Ni(II)-porfirina, nikal(II)-mono-tercbutilporfirina, nikal(II)-di-tercbutilporfirina, nikal(II)-tetrafenilporfirina i nikal(II)-oktaetil-tetrafenilporfirina. Ono je upotrebljeno za proučavanje uticaja veličine centralnog metalnog jona, periferne supstitucije kao i uticaja prisutnog supstrata na konformacije porfirinskog jezgra kod okta- i tetrahalogeno-tetrafenilporfirina sa Ni(II) i Tb(III). Jedinstvene ravnotežne strukture, dobijene na osnovu molekulsko-mehaničkih proračuna velikog broja početnih struktura, pokazuju dobro slaganje sa kristalnim strukturama, kao i sa prethodno publikovanim rezultatima, ne samo u metričkim podacima, već i u načinu nabiranja porfirinskog jezgra. Metod normalne-koordinatne strukturne dekompozicije (NSD) omogućava da se na jednoznačan način opiše svaka optimizovana konformacija dobijena molekulsko-mehaničkim proračunima

Antioxidative enzymes in irradiated rat brain-indicators of different regional radiosensitivity

Purpose Previously, we examined manganese superoxide dismutase (MnSOD), copper-zinc superoxide dismutase (CuZnSOD), and catalase (CAT) activities in rat brain irradiated with 2 or 3 Gy of gamma-rays. The results indicated that lower MnSOD activity and inducibility found in hippocampus might explain higher radiosensitivity of this brain region. Thus, in this study, we wanted to determine changes of MnSOD, CuZnSOD, and CAT activities after dose of 5 Gy and to find out if differences in MnSOD activity are caused by changes in its expression. Heads of 4-day-old female rats were irradiated with gamma-rays, using Co-60. Animals were sacrificed 1/24 h after exposure. Hippocampus and cortex tissues were prepared for enzyme activity measurements and Western blot analysis. One hour after exposure, gamma-rays significantly decreased MnSOD activity in both examined brain regions. Twenty-four hours later, MnSOD recovery showed dose and regional dependence. It was weaker at higher doses and in hippocampal region. MnSOD expression changed in the similar manner as MnSOD activity only at lower doses of gamma-rays. In both examined brain regions, gamma radiation significantly decreased CuZnSOD activity and did not change activity of CAT. Our results confirmed that MnSOD plays an important role in different regional radiosensitivity but also showed that depending on dose, radiation affects MnSOD level by utterly different mechanisms. Postradiation changes of CuZnSOD and CAT are not regionally specific and therefore, cannot account for the different radiosensitivity of the hippocampus and cortex.Ministry of Education, Science and Technological Development {[}41027, 41022