Silver powders produced by both electrochemical (galvanostatic (DC) and potentiostatic (POT) regimes of electrolysis) and chemical processes were examined by scanning electron microscope, and ...particle size distribution (PSD) of the obtained particles was done. In the DC regime, the current densities of ?14.4 mA cm-2 for the nitrate (NIT; powder denoted with DC(NIT)) and ?13.05 mA cm-2 for the ammonium (AM; DC(AM)) electrolytes were applied. In the POT regime, the used overpotentials were ?90 mV (NIT(90)) and ?150 mV (NIT(150)) for the nitrate, and ?625 mV (AM(625)) and ?925 mV (AM(925)) for the ammonium electrolytes. Reduction with hydrazine was used for chemical synthesis (powder denoted with HYD). On the basis of SEM and PSD analysis, Ag powders were grouped into three groups. In the first group DC(AM), AM(925) and HYD powders with the (8.4?8.9 %) volume ratios were placed. In the second group were AM(625) and DC(NIT) powders with the (6.5?6.6 %) volume ratios. NIT(90) and NIT(150) powders with the volume ratios of (5.2?5.7 %) made the third group. The obtained volume ratios were correlated with the morphology of synthesized particles in order to perceive advantages and lacks of powder production via electrochemical and chemical routes.
nema
In this book, recent progress in batteries is firstly reviewed by researchers in three leading Japanese battery companies, SONY, Matsushita and Sanyo, and then the future problems in battery ...development are stated. Then, recent development of solid state ionics for batteries, including lithium ion battery, metal-hydride battery, and fuel cells, are reviewed. A battery comprises essentially three components: positive electrode, negative electrode, and electrolyte. Each component is discussed for the construction of all-solid-state Batteries. Theoretical understanding of properties of battery materials by using molecular orbital calculations is also introduced.
The aim of this study was to assess to which extent modernisation of an aluminium production complex reduced occupational noise hazard for jobs with the highest potential of exposure. Periodical ...measurements of noise level were taken at the same workplaces using the same method, before and after modernisation of all plants. The results were compared with the recommended standard. After modernisation, the noise was significantly reduced in all sections of all plants. The greatest reduction was measured in the foundry. After modernisation, the portion of workplaces with excessive noise level dropped significantly (chisquare=21.315; p<0.0001) from 78.4% to 13%. Noise remained a problem in ingot casting and dross skimming section. In the anode plant, noise remained a problem in the green mill section where noise intensities generated by mills and vibrocompactors varied from 95 dB(A) to 102 dB(A). In the electrolysis plant, the portion of workplaces with extensive noise dropped from 77.8% to 39.3% after modernisation (p=0.0019). Noise remains to be a problem at the anode covering section where levels rise up to 100 dB(A). The modernisation of the factory has considerably reduced the noise level in the working environment of all plants, but it can not be reduced completely.
Cilj je rada procijeniti utjecaj modernizacije tehnološkog procesa proizvodnje aluminija na prisutnost i razinu buke štetne za zdravlje radnika u radnom okolišu. U tu svrhu uspoređivani su rezultati periodičkih mjerenja razine buke prije i nakon modernizacije. Mjerenja intenziteta buke provedena su na istim radnim mjestima i istom metodom tijekom radnih smjena i uspoređeni s važećim nacionalnim standardom. Nakon modernizacije tvornice u svim odjelima proizvodnih pogona značajno se smanjila razina buke, kao i broj radnih mjesta na kojima su radnici izloženi prekomjernoj buci. Najbolji rezultati postignuti su u ljevaonici, gdje se broj radnih mjesta s prekomjernom razinom buke, tj. razinom buke višom od 90 dB(A) smanjio sa 78.4 % na 13 %. Na radnim mjestima gdje se izlijevaju ingoti i skida šljaka buka je i dalje prekomjerna. U pogonu anoda prekomjerna je buka i dalje prisutna pri proizvodnji sirovih anoda, gdje razina buke zbog rada mlinova i vibrokompresora varira od 95 dB(A) do 102 dB(A). U pogonu elektrolize buka viša od 100 dB(A) izmjerena je pri zasipanju anoda. Iako je modernizacijom tvornice i unaprjeđenjem tehnološkog procesa značajno reducirana razina buke, nije ju moguće u cijelosti ukloniti.
Provider: - Institution: - Data provided by Europeana Collections- Tritium (3H), a radioactive isotope of hydrogen, which reached in the nature
in the sixties, by nuclear explosions and nuclear ...industries, increased the
natural abundance of this radionuclide in the atmosphere and in the water
from the environment. The reason for studying the tritium content in natural
waters is a risk of water pollution by this radionuclide. Precipitation is
the main route for the elimination of tritium from the atmosphere, whether it
is natural origin or made artificially. Tritium enters in the surface water
by precipitation. Environmental monitoring of tritium began, in a systematic
way, in 1976 in the Institute of Nuclear Sciences "Vinča" in Belgrade, with
sampling and measurements of precipitation and surface waters. Because of the
existence of the heavy research reactors in the Institute as potential
emitters of tritium, it is necessary to monitor the distribution of tritium
in precipitation in the Institute, as well as at the other reference
meteorological stations (Zeleno Brdo and Usek). Due to possible contamination
of the Sava and Danube rivers by tritium because of a number of nuclear power
plants on the banks of the river upstream, it is important to examine its
contents, particularly since Belgrade is supplied with drinking water from
the Sava and Danube. Investigation of tritium in the creek Mlaka, which
starts within the Institute Vinča is significant to detect any unsuspected
change in local discharge, because it flows along the heavy reactor boundary
in the Institute into the Danube River (Vinča), across the river Bolečice. In
all samples of natural water that have been analyzed in this PhD thesis,
distribution of tritium concentration was followed for the long-term time
period (1985 - 2009). Given the fact that the concentration of tritium in
natural water is low (0,6 Bq l-1 - 1,19 Bq l-1), all samples were
electrolytically enriched in order to increase the concentration and, as
such, were measured by liquid scintillation detector LKB Wallac 1219
RackBeta. The parameters that define the process of electrolysis, the
separation factor, enrichment parameter and enrichment factor were
determined. The seasonal variations of 3H could also be analyzed by seasonal
indices. Monthly and quarterly seasonal indices were calculated and they
indicate the occurrence of the maximum and minimum values of tritium
concentration in the season. Based on the amount of precipitation and the
concentration of tritium at the examined meteorological stations, one can
predict the tritium deposition to the earth's surface. Since the water
samples were taken at different locations, determining linear correlation
coefficients (r), a direct linear relationship was shown, i.e. the trends
change in tritium concentration with time were the same. Symmetrical index as
a mathematical parameter is applied the first time in this paper to identify
the value of tritium concentrations in precipitation and surface waters at
different locations. It has been shown that the symmetrical index is a good
parameter which could describe the changes in the value of tritium
concentrations over time and it does not take into account the physical
parameters which influence on these changes. The obtained results for the
concentration of tritium in the Danube and Sava rivers were used to assess
the health risk and to calculate the annual effective dose due to tritium
intake by ingestion.- Tritijum (3H), radioaktivni izotop vodonika, koji je dospeo u prirodu 60-tih
godina veštačkim putem iz nuklearnih eksplozija i nuklearne industrije,
povećao je prirodni sadržaj ovog radionuklida u atmosferi i u vodama iz
životne sredine. Opasnost od zagađenja voda i potreba da se kontroliše stepen
tog zagađenja bio je i danas je sve više jedan od najvećih razloga
proučavanja količine i načina dolaženja 3H u vode. Padavine predstavljaju
glavni put za eliminaciju tritijuma iz atmosfere, bilo da je stvoren
prirodnim ili veštačkim putem. Putem padavina, tritijum dospeva u površinske
vode. U Beogradu se, u Institutu za nuklearne nauke Vinča, od 1976. god. vrši
ispitivanje sadržaja tritijuma u sakupljenim uzorcima padavina i površinskih
voda. Zbog postojanja teškovodnih istraživačkih reaktora u Institutu za
nuklearne nauke "Vinča" kao potencijalnih emitera tritijuma, potrebno je
pratiti distribuciju tritijuma u padavinama u samom Institiutu, a takođe i na
drugim referentnim meteorološkim stanicama (Zeleno Brdo i Usek). Usled moguće
kontaminacije reka Save i Dunava tritijumom zbog niza nuklearnih elektrana na
uzvodnim obalama ovih reka, važno je ispitivati njegov sadržaj, naročito zbog
toga što se Beograd snabdeva vodom za piće iz Save i Dunava. Ispitivanje
sadržaja tritijuma u potoku Mlaka, koji izvire u krugu Instituta Vinča je
značajno, jer se potok uliva u Dunav (u Vinči), preko reke Bolečice. Potok
protiče pored istraživačkog reaktora u Institutu Vinča, tako da može doći do
kontaminacije Dunava. U svim uzorcima voda koji su analizirani u ovoj
doktorskoj disertaciji, praćena je vremenska promena koncentracije tritijuma
u dugom vremenskom intervalu od 1985 - 2009. godine. S obzirom na činjenicu
da se srednja koncentracija tritijuma u padavinama i u površinskim vodama na
severnoj hemisferi kreće se od 0,6 Bq l-1 do 1,19 Bq l-1, svi uzorci su
elektrolitički obogaćeni u cilju povećanja koncentracije i kao takvi su
mereni na tečnom scintilacionom detektoru LKB Wallac 1219 RackBeta. Određeni
su parametri koji definišu sam proces elektrolize, separacioni faktor,
parametar obogaćenja i faktor obogaćenja. Izračunati su mesečni i kvartalni
sezonski indeksi koji ukazuju na pojavu maksimalnih i minimalnih vrednosti
koncentracije tritijuma u godišnjim dobima. Poznavanjem količine padavina i
vrednosti koncentracija tritijuma na ispitivanim meteorološkim stanicama,
može se predvideti depozicija tritijuma na zemljinu površinu. S obzirom na
činjenicu da se uzorci voda u kojima se ispituje sadržaj tritijuma uzorkovani
na različitim lokacijama, određivanjem linearnih koeficijenata korelacije
(r), pokazana je direktna linearna povezanost, odnosno da su trendovi promene
vrednosti koncentracije tritijuma sa vremenom isti. Indeks simetrije kao
matematički parametar je primenjen prvi put u ovom radu da utvrdi veličine
koncentracije tritijuma u padavinama i površinskim vodama na različitim
lokacijama. Dokazano je da je indeks simetrije dobar parametar koji može da
opiše promene u vrednosti koncentracije tritijuma tokom vremena i da ne uzima
u obzir fizičke parametre koji utiču na ove promene. Dobijeni rezultati za
koncentraciju tritijuma u Savi i Dunavu upotrebljeni su za procenu faktora
radijacionog rizika tj. za računanje godišnje efektivne doze usled unosa
tritijuma ingestijom.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Provider: - Institution: - Data provided by Europeana Collections- Fossil fuels, as currently the world's primary energy source, are depleting. In addition, their use is accompanied by greenhouse gas ...emission, primarily carbon dioxide, pollution and global warming. As the world demands for energy grow, intensive efforts are put into development of energy systems based on the socalled renewable energy sources (solar, wind, biomass, etc.). The use of these energy sources raises a question of medium for storage, transport and efficient use of energy on the locations significantly distant from these so-called primary energy sources. Hydrogen is currently the best candidate for such a medium in all future energy concepts. The future of hydrogen-based economy largely depends on the price of hydrogen in the world market, i.e. of its low-cost, fast and efficient production. Over 90% of hydrogen is currently produced from fossil fuels, mainly by steam-reforming of petroleum. As an environmentally friendly alternative to this process alkaline water electrolysis is being developed and commercialized. In addition, it gives a possibility to use renewable energy sources for hydrogen production. Alkaline water electrolysis requires the use of electricity and therefore is expensive, inefficient (about 40% in respect to the primary energy) and slow method for hydrogen production. One of the methods to increase the efficiency of this process is the development of new electrocatalytic materials which could lower the electrode overvoltage. The electrodes of commercially available alkaline electrolysers are usually made of Ni plated stainless steel or pure nickel. Brewer intermetallic bonding theory predicts a synergistic effect on the catalytic activity for hydrogen evolution, when combining two d-metals. Alloys of this type may exhibit better activity than the individual metals, and in some cases over exceed the activity of precious metals which have proven to be the best catalysts for this reaction. Doktorska disertacija Gvozden Tasić viii This thesis examines the possibility of using alloys based on a combination of transition metals Ni-W, Co-W and Ni-MoO2 as cathodes for alkaline electrolysis, as well as the method of in situ activation of alkaline electrolysis by using Ni-Mo and Co - W ionic activators. Special attention was paid to the influence of the microwave field on the electrochemical codeposition of Co-W alloys, their morphology, chemical composition and catalytic activity. It was found that the application of ionic activators can significantly reduce energy consumption in the process of alkaline electrolysis. In some cases, this reduction goes up to 20%. Electrodes obtained by electrochemical codeposition are catalytically more active for hydrogen evolution reaction compared to pure nickel. The activity of these electrodes depends on the conditions of electrodeposition (type of electrodeposition bath, concentration of electroactive species, pH and deposition current density). Application of the microwave field in the process of electrochemical codeposition, significantly affects the morphology and chemical composition of obtained electrodes, which show a slight improvement in catalytic activity for hydrogen evolution reaction.- Fosilnih goriva, trenutno osnovnog svetskog energenta, ima sve manje. Pored toga, njihova upotreba je praćena emisijom gasova staklene bašte, pre svega ugljen dioksidom, zagađenjem životne sredine i pojavom globalnog zagrevanja. Kako su potrebe za energijom sve veće, u svetu se intenzivno radi na razvoju energetskih sistema zasnovanih na tzv. obnovljivim izvorima energije (Sunce, vetar, biomasa, itd). Upotreba ovih energenata postavlja pitanje medijuma za skladištenje energije, transport i efikasnu upotrebu na mestima značajno udaljenim od ovih tzv. primarnih izvora energije. Vodonik je trenutno najbolji kandidat za funkciju ovakvog medijuma u svim budućim enegretskim konceptima. Budućnost ekonomije zasnovane na vodoniku u velikoj meri zavisi od cene vodonika na svetskom tržištu, tj. od njegove jeftine, efikasne i dovoljno brze proizvodnje. Trenutno se preko 90% vodonika dobija iz fosilnih goriva, pre svega procesom reforminga zemnog gasa vodenom parom. Kao pandan ovom procesu sve više se razvijaju i komercijalizuju metode elektrolize vode, među kojima prednjači alkalna elektroliza, kao ekološki prihvatljive alternative koja omogućava upotrebu obnovljivih izvora u procesu proizvodnje ovog energenta. Alkalna elektroliza zahteva upotrebu električne energije te je stoga skupa, neefikasna (oko 40% u odnosu na primarnu energiju) i spora metoda dobijanja vodonika. Jedan od načina za povećanje efikasnosti ovog procesa je razvoj novih elektrokatalitičkih materijala čijom bi se upotrebom smanjio nadnapon na elektrodama. Komercijalno dostupni alkalni elektrolizeri obično imaju elektrode od niklovanog nerđajućeg čelika ili čistog nikla. Brojerova teorija intermetalnih veza predviđa sinergetski efekat na katalitičku aktivnost za reakciju izdvajanja vodonika, kada se kombinuju dva d-metala. Legure ovog tipa mogu da pokažu aktivnost veću u odnosu na pojedinačne metale a u nekim Doktorska disertacija Gvozden Tasić vi slučajevima i veću u odnosu na aktivnost plemenitih metala, koji su se pokazali kao najbolji katalizatori za ovu reakciju. U okviru ove doktorske disertacije ispitana je mogućnost upotrebe legura na bazi kombinacije prelaznih metala Ni-W, Co-W i Ni-MoO2 kao katoda za alkalnu elektrolizu, kao i metoda in situ aktivacije alkalne elektrolize jonskim aktivatorima na bazi Ni-Mo, i Co-W. Posebna pažnja je posvećena ispitivanju uticaja mikrotalasnog polja na proces elektrohemijskog kotaloženja Co-W legura, njihovu morfologiju, elementarni sastav i katalitičku aktivnost. Utvrđeno je da se primenom pomenutih jonskih aktivatora može značajno smanjiti potrošnja električne energije u procesu alkalne elektrolize. U pojedinim slučajevima i do 20 %. Elektrode dobijene elektrohemijskim kotaloženjem pokazuju veću aktivnost za reakciju izdvajanja vodonika u odnosu na čiste niklene elektrode, a utvrđeno je da aktivnost ovih elektroda zavisi od uslova elektrohemijskog taloženja (izbora taložnog kupatila, koncentracije elektroaktivnih vrsta, pH vrednosti i gustine struje taloženja). Primena mikrotalasnog polja u toku elektrohemijskog kotaloženja, značajno utiče na morfologiju i elementarni sastav dobijenih elektroda, koje pokazuju neznatno poboljšanje katalitičke aktivnosti za reakciju izdvajanja vodonika.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Provider: - Institution: - Data provided by Europeana Collections- data publikacji: 1989-10-31- data zgłoszenia: 1984-08-03- numer publikacji: PL 142199- numer zgłoszenia: 249113- All metadata ...published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Provider: - Institution: - Data provided by Europeana Collections- data publikacji: 1996-02-29- data zgłoszenia: 1992-07-21- numer publikacji: PL 168451- numer zgłoszenia: 295378- All metadata ...published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Cilj je rada procijeniti utjecaj modernizacije tehnološkog procesa proizvodnje aluminija na prisutnost i razinu buke štetne za zdravlje radnika u radnom okolišu. U tu svrhu uspoređivani su rezultati ...periodičkih mjerenja razine buke prije i nakon modernizacije. Mjerenja intenziteta buke provedena su na istim radnim mjestima i istom metodom tijekom radnih smjena i uspoređeni s važećim nacionalnim standardom. Nakon modernizacije tvornice u svim odjelima proizvodnih pogona značajno se smanjila razina buke, kao i broj radnih mjesta na kojima su radnici izloženi prekomjernoj buci. Najbolji rezultati postignuti su u ljevaonici, gdje se broj radnih mjesta s prekomjernom razinom buke, tj. razinom buke višom od 90 dB(A) smanjio sa 78.4 % na 13 %. Na radnim mjestima gdje se izlijevaju ingoti i skida šljaka buka je i dalje prekomjerna. U pogonu anoda prekomjerna je buka i dalje prisutna pri proizvodnji sirovih anoda, gdje razina buke zbog rada mlinova i vibrokompresora varira od 95 dB(A) do 102 dB(A). U pogonu elektrolize buka viša od 100
dB(A) izmjerena je pri zasipanju anoda. Iako je modernizacijom tvornice i unaprjeđenjem tehnološkog procesa značajno reducirana razina buke, nije ju moguće u cijelosti ukloniti.
Autor opisuje konzervatorsko-restauratorske postupke na željeznom topu izlivenom na prijelazu XvII. u XvIII. st., izvađenom iz mora u luci Starog grada na
otoku Hvaru. Opisani su i postupci ...rekonstrukcije drvenog nosača („lafeta“) za top, izrađenog prema analogijama i opisima izrade takvih nosača.
Provider: - Institution: - Data provided by Europeana Collections- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain ...Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
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