ZAŠTITA MATERIJALA 2011 52(2) 73-79 Scientific paper [PDF]
SLAVKO BERNIK1,2, MATEJKA PODLOGAR1,2, NINA DANEU1,2, ALEKSANDER REČNIK1,2 1Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia, 2Center of Excellence NAMASTE, Jamova cesta 39, 1000 Ljubljana, Slovenia
A novel approach to tailoring the microstructure and electrical characteristics of ZnO-based varistor ceramics via inversion-boundary (IB) induced grain growth Abstract: ZnO-based varistors with exceptional current-voltage (I-U) nonlinearity are widely used in the over-voltage protection of electrical equipment and devices at voltages ranging from a few volts to several hundred kilovolts. Their breakdown voltage is strongly influenced by the average ZnO grain size: a coarse-grained microstructure results in a low breakdown voltage for the ceramics, while a fine-grained microstructure is required for a high breakdown voltage. The grain size in high-voltage varistor ceramics is controlled by the addition of a spinel-forming additive, typically Sb2O3. The concept of grain-growth inhibition due to the reduced grain-boundary mobility caused by the pinning effect of the spinel particles largely defines the composition of the ZnO-based varistor ceramics with additions of 7 to 10 wt.% of varistor dopants to the ZnO. Spinel-forming dopants such as Sb2O3, TiO2 and SnO2 also result in the formation of inversion boundaries (IBs) in the ZnO grains. We have identified an IB-induced grain-growth mechanism which primarily controls the microstructure development, while the role of the spinel is subordinated. This understanding enabled us to prepare varistor ceramics with excellent I-U nonlinearity and breakdown voltages, ranging from 120 V/mm to 350 V/mm with the amount of varistor dopants added to the ZnO reduced to only about 3 wt.%.
ZAŠTITA MATERIJALA 2011 52(2) 80-84 Scientific paper [PDF]
S. NINEVA, TS. DOBROVOLSKA, I. KRASTEV Institute of Physical Chemistry, Bulgarian Academy of Sciences, ul. Akad. G. Bonchev, 11 Sofia 1113, Bulgaria Electrodeposition of Sb-In, Sb-Co and In-Co alloys
Abstract: In the present work an attempt was made, to investigate the Sb-In, Sb-Co and In-Co alloy deposition from one basic citrate electrolyte depending on the current density. The conclusions were made, that the used di-ammonium hydrogen citrate electrolyte is appropriate for the deposition of Sb-In, Sb-Co and In-Co alloys with good quality. During electrodeposition of Sb-Co and In-Co alloy coatings a wide range of alloying metal percentages could be reached, depending on the applied current density. The electrodeposited Sb-In alloy coatings are antimony-rich with constant percentage independent of the applied current density. Most probably, the metal content in the solution should be varied and the indium concentration increased. The electrodeposited coatings could be used for the further investigation of their physicochemical and mechanical properties. The observed spatio-temporal structures onto the surface of Sb-Co (initial stage) and In-Co alloys and the big variety of the pattern are a very appropriate object for the studies of self-organization phenomena during electrodeposition of alloys.
ZAŠTITA MATERIJALA 2011 52(2) 85-89 Scientific paper [PDF]
S. RAJENDRAN1,6, T.S. MUTHUMEGALA1, M. PANDIARAJAN1, P. NITHYA DEVI1, A. KRISHNAVENI2, J. JEYASUNDARI3, B. NARAYANA SAMY4, N. HAJARA BEEVI5
1Corrosion Research Centre, Post Graduate and Research Department of Chemistry, GTN Arts College, Dindigul-624 005, Tamilnadu, India
2Department of Chemistry, Yadava College, Madurai, India
3Department of Chemistry, SVN College, Madurai, India
4Department of Che-mistry, Thiagarajar College of Engineering, Madurai, India
5Department of Chemistry, B.S. Abdur Rahman University, Vandalur, Chennai, 600 048, India
6Department of Physical Sciences, Servite College of Education for Women, Thogamalai-621313, India
Corrosion resistance of SS316L in simulated concrete pore solution in presence of trisodium citrate
Abstract: The corrosion resistance of SS 316L in simulated concrete pore solution, namely, saturated calcium hydroxide solution, in the absence and presence of 100 ppm of trisodium citrate (TSC) has been evaluated by electrochemical studies such as polarization study and AC impedance spectra. Polarization study reveals that in presence of TSC, the corrosion resistance of SS 316L in simulated concrete pore solution decreases. AC impedance spectra reveal that in the presence of TSC, the corrosion resistance of SS 316L in simulated concrete solution decreases.
ZAŠTITA MATERIJALA 2011 52(2) 90-94 Scientific paper [PDF]
KATARINA MARUŠIĆ
Faculty of Chemical engineering and Technology, University of Zagreb, Croatia
Protection of CuSn6 bronze from atmospheric corrosion by an imidazole based corrosion inhibitor
Abstract: The CuSn6 bronze is a copper alloy with good corrosion resistance and strength properties. It is wear-resistant and well solderable and it is good for cold forming. Springs of all kinds, especially for the electrical industry, are made of this bronze. It is used in paper, pulp and chemical industries, shipbuilding and mechanical engineering. When exposed to urban atmospheres copper and its alloys are endangered from corroding with time. Thus additional protection is needed. One possibility of protection is the use of corrosion inhibitors. Previous investigations have shown that imidazole derivatives offer good protection in different media. Potentiodynamic measurements and electrochemical impedance spectroscopy (EIS) were applied to evaluate the inhibitive efficiency of 1-H-benzimidazole (BZI) as a corrosion inhibitor for CuSn6 bronze in a Na2SO4/NaHCO3 solution which simulates an urban atmosphere. The investigations have shown that BZI is a mixed corrosion inhibitor with good protective properties. The interaction between the inhibitors and the bronze surface is a combination of physisoption and chemical adsorption. However, after long immersion (over 1 month) the surface colour of bronze changes into a brown-reddish colour. Therefore, this inhibitor cannot be applied at present time to protect objects of which the appereance should not be changed.
ZAŠTITA MATERIJALA 2011 52(2) 95-100 Scientific paper [PDF]
VLADIMIR D. JOVIĆ
Institute for Multidisciplinary Research, Kneza Višeslava 1, 11030 Belgrade, Serbia
Composite materials based on non-noble metals as the cathodes in industrial electrolysis
Abstract: Almost all cathodes in the industrial processes of hydrogen evolution, particularly for chlor-alkali electrolysis, are based on coatings containing noble metals (Pt, Ru, Ir, etc.). Based on the theory of electrocatalysis of hydrogen evolution reaction (HER), in this work an attempt was made to produce Ni based cathode coatings containing MoO3 or MoO2 particles and investigate their behavior as cathodes for HER in concentrated NaOH solution. It is shown that it is possible to obtain coatings possessing the same overvoltage for HER as the one for commercial cathodes under the conditions of industrial electrolysis. In order to find optimal conditions for their electrodeposition all coatings were investigated by SEM, EDS and XRD analysis.
ZAŠTITA MATERIJALA 2011 52(2) 101-108 Scientific paper [PDF]
A. SAHAYA RAJA1, S. RAJENDRAN1, J. SATHIYABAMA1, T.S. MUTHUMEGALA1, A. KRISHNAVENI2, N. PALANISWAMY3, P. PRABHAKAR4
1Corrosion Research Centre, Department of Chemistry, G.T.N Arts College, Dindigul-624005, Tamil Nadu, India
2Department of Chemistry, Yadava College, Madurai, India
3Corrosion Protection Division, Central Electrochemical Research Institute, Karaikudi, India
4APA College of Arts and Culture, Palani, India
Corrosion inhibition by arginine–Zn2+ system
Abstract: The inhibition efficiency of arginine in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl–, has been evaluated by weight loss method in the absence and presence of Zn2+. Weight loss study reveals that the formulation consisting of 250 ppm Arginine and 50 ppm of Zn2+ has 80% inhibition efficiency in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl–. Synergism parameters suggest that a synergistic effect exists between Arginine and Zn2+. Polarization study reveals that this system functions as mixed type inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protection film consists of Fe2+-arginine complex. As the amount of Zn2+ ion available for transport of the ligand increases, the inhibition efficiency increases.
ZAŠTITA MATERIJALA 2011 52(2) 109-114 Originalni naučni rad [PDF]
JAGODA RADOSEVIC1, RATKO MIMICA1, SANJA-SLAVICA MATEŠIĆ2, IGOR JANJATOVIC3
1FESB, Department of Mechanical Technology, Split, Croatia
2Head of Enviromental protection office at Šibensko-Kninska county, Croatia
3NEXE Group d.d., Našice, Croatia
Inhibicija korozije CuNiFe slitine pomoću gensitinske i p-kumarinske kiseline izolirane iz vodenog ekstrakta ružmarina
Izvod: Ispitana je mogućnost inhibicije korozije CuNiFe slitine u 0,5 mol/dm3 NaCl otopini pri 250 °C pomoću gensitinske i p-kumarinske kiseline. Prisustvo ovih kiselina ustanovljeno je u prvoj kiseloj podfrakciji vodenog ekstrakta lišća ružmarina (Rosmarius officinalis L). Potenciodinamičkom polarizacijskom metodom i metodom linearne polarizacije određeni su elektrokemijski parametri koji ukazuju na ponašanje CuNiFe slitine u neinhibiranim i inhibiranim NaCl otopinama. Iz dobivenih rezultata izračunata je prekrivenost površine, djelotvornost inhibicije te standardna slobodna energija adsorpcije. Rezultati ispitivanja također su pokazali da se ispitivani spojevi adsorbiraju na površini slitine prema Freundlichovoj adsorpcijskoj izotermi, a dobivene vrijednosti standardne slobodne energije adsorpcije ukazuju na fizikalnu adsorpciju. Iz polarizacijskih krivulja može se zaključiti da ispitivane fenolne kiseline djeluju kao katodni tip inhibitora korozije CuNiFe slitine.
ZAŠTITA MATERIJALA 2011 52(2) 115-122 Originalni naučni rad [PDF]
DUŠAN GAVANSKI1, VERICA MILANKO1, SLOBODAN KRNJETIN2
1Visoka tehnička škola strukovnih studija, Novi Sad
2Fakultet tehničkih nauka, Novi Sad
Implementacija ocene sprovedenih mera zaštite od požara u Akt o proceni rizika za zatvoreni tip skladišta drvene građe
Izvod: Sistem bezbednosti u Republici Srbiji zasnovan je na Direktivi Saveta 89/391/EEC, Zakonu o bezbednosti i zdravlju na radu i važećim podzakonskim aktima. Zakonom o bezbednosti i zdravlju na radu promoviše se princip prevencije profesionalnog rizika na radnom mestu i reguliše obaveza poslodavca da donese Akt o proceni rizika u pisanoj formi. Da bi skladište drvene građe bilo požarno bezbedno neophodno je primeniti odgovarajuće mere zaštite od požara što podrazumeva da se pre svega mora izvršiti pravilna procena rizika od požara. Cilj istraživanja je da se u postupak izrade Akta o proceni rizika za skladište drvene građe implementira i oblast zaštite od požara, odnosno procena rizika
ZAŠTITA MATERIJALA 2011 52(2) 123-126 Stručni rad [PDF]
NENAD MARKOVIĆ
Student Fakulteta za ekologiju i zaštitu životne sredine Univerzitet Union, Beograd
Upravljanje otpadnim CRT monitorima i TV aparatima
Izvod: Na kraju svog životnog veka monitori i TV aparati postaju opasan ee-otpad. Dosadašnja praksa bila je da ovi uređaji završavaju zajedno sa komunalnim otpadom na deponiju i tako predstavljaju opasnost da se životna sredina zagati teškim metalima. U ovom radu predstavljen je proces upravljanja odbačenim CRT monitorima i TV aparatima propisan zakonskom regulativom Republike Srbije.
ZAŠTITA MATERIJALA 2011 52(2) 127-133 Stručni rad [PDF]
ALEKSANDER STOJANOV1, DRAGAN UGRINOV2
1Direkcija za građevinsko zemljište i izgradnju Beograd, J.P., Beograd
2Zavod za javno zdravlje, Pančevo
Istorijski pregled u tretmanu otpadnih voda
Izvod: U radu je dat istorijski pregled problematike sa otpadnim vodama u Velikoj Britaniji i Nemačkoj, gde se mogu videti početni koraci u identifikaciji uzročnika bolesti, kao i začetci postupaka za detekciju i tretman otpadnih voda (industrijskih i komunalnih).Sredinom 19.-og veka postojala su pitanja na koja je trebalo dati adekvatne odgovore: Koliko je prljava otpadna voda u odnosu na specifična jedinjenja ili ukupne parametre; i kako mogu izmeriti ove parametre ili koncentraciju ovih specifičnih jedinjenja? Gde je najbolje mesto za uzimanje uzorka za analizu iz reke ili iz postrojenja za tretman otpadnih voda?…
