Electrical properties of ZnO varistors prepared by direct mixing of constituent phases

Varistor samples containing different amounts of constituent phases were prepared by direct mixing of constituent phases. Detailed electrical characterization was performed to explain the influence of minor phases (spinel and intergranular phases) on overall properties. Characterization included investigation of the non-linear coefficients (alpha), breakdown electric field (E-B), leakage currents (J(L)), grain boundary barrier hight (Phi(B)) and constant beta from current-voltage characteristics, as well as calculation of activation energies for conduction (E-A) from ac impedance spectroscopy in the temperature interval 30-410 degrees C. Varistors sintered at 1100 degrees C for 1 h showed pronounced differences in electrical properties depending on relative molar ratios of the phases. Results were discussed in the sense of possible reduction of the content of minor phases in ZnO varistors

Electrical properties of mechanically activated zinc oxide

Microstructural properties of a commercial zinc oxide powder were modified by mechanical activation in a high-energy vibro-mill. The obtained powders were dry pressed and sintered at 1100 degrees C for 2 h. The electrical properties of grain boundaries of obtained ZnO ceramics were studied using an ac impedance analyzer. For that purpose, the ac electrical response was measured in the temperature range from 23 to 240 degrees C in order to determine the resistance and capacitance of grain boundaries. The activation energies of conduction were obtained using an Arrhenius equation. Donor densities were calculated from Mott-Schottky measurements. The influence of microstructure, types and concentrations of defects on electrical properties was discussed

Chemical stability and electrical properties of Nb doped BaCe0.9Y0.1O3-b

BaCe0.9-xNbxY0.1O3-δ (where x = 0.01, 0.03 and 0.05) fine powders were synthesized by auto-combustion reaction to investigate the influence of Nb concentration on chemical stability and electrical properties of BaCe0.9Y0.1O3-δ. The dense electrolyte pellets were formed from powders after being uniaxially pressed and sintered at 1600ºC for 5h. Chemical stability in a CO2 atmosphere at 750ºC was determined by X-ray powder diffraction. Conductivities of the sintered samples have been measured within the temperature range of 500-750ºC in different atmospheres (dry and wet argon, wet hydrogen). The highest conductivities were obtained at 750ºC in wet hydrogen reaching the value of 3,26.10-3Sm.cm-1

Development of a new system of solid ionic conductors based on multi-doped ceria for application in IT-SOFCs

Nanosized multi-doped ceria with composition Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ (CNSGDY) as perspective solid ionic conductor was obtained by modified glycine-nitrate procedure (MGNP) and room temperature self-propagating reaction (SPRT). The pressed pellets of both powders were sintered at 1550°C for 2 h in an air atmosphere. The obtained sintered samples were characterized by XRPD, Raman spectroscopy, FESEM, EDS and EIS methods. Despite a high temperature of sintering, XRPD and FESEM analyses of the samples confirmed appropriate dimensions of grains with fluorite structure. Overall concentration of introduced dopants (x = 0.2) in the structure of CeO2 after the sintering process was confirmed by EDS analysis. After sintering, Raman spectroscopy confirmed retention of the oxygen vacancies in the ceria lattice, which is in accordance with the improvement of ionic conductivity of solid ionic conductors. The highest value of total conductivity was obtained for the sintered MGNP sample at 700°C (4.22 × 10−2 S cm−1), with the corresponding activation energy of 0.26 eV

Fungicidi u zaštiti vinove loze od prouzrokovača plamenjače (Plasmopara viticola), pepelnice (Erysiphe necator) i sive truleži (Botrytis cinerea) i antirezistentna strategija

Economically the most important diseases that occur on grapevine are causal agent of downy mildew (Plasmopara viticola ((Berk. &. Curt.) Berl. & de Toni), causal agent of powdery mildew (Erysiphe necator (Schw.) Burrill) and causal agent of gray decay (Botrytis cinerea Pers.). A large number of registered fungicides for control of these phytopathogens in Serbia is at the same time an indicator of their spread and harmfulness. For the control of downy mildew in Serbia are registered 121 preparation based 36 active ingredients, while for the control of powdery mildew are registered 56 preparations based on 25 active ingredients, and for the suppression of gray mold 14 preparations based on 9 active ingredients. The aim of this study was to display the registered fungicides for suppression of before mentioned, economically important pathogens of grapevine (downy mildew, powdery mildew and gray mold), as well as the basic measures for anti-resistant strategies, considering that all three pathogens, as well as most fungicides used for their suppression, belong to groups of high risk for resistance developement.Ekonomski najznačajnije bolesti koje se javljaju na vinovoj lozi su plamenjača (prouzrokovač Plasmopara viticola ((Berk. & Curt.) Berl. & de Toni), pepelnica (prouzrokovač Erysiphe necator (Schw.) Burrill) i siva trulež (prouzrokovač Botrytis cinerea Pers.). Veliki broj fungicida registrovanih kod nas za suzbijanje pomenutih fitopatogenih gljiva je ujedno i pokazatelj njihove rasprostanjenosti i štetnosti. Za suzbijanje prouzrokovača plamenjače u Republici Srbiji je registrovano 121 preparat na bazi 36 aktivnih supstanci, dok je za suzbijanje prouzrokovača pepelnice registrovano 56 preparata na bazi 25 aktivnih supstanci, a za suzbijanje prouzrokovača sive truleži 14 preparata na bazi 9 aktivnih supstanci. Cilj ovog rada je bio da se za pomenute, ekonomski najznačajnije patogene vinove loze (prouzrokovače plamenjače, pepelnice i sive truleži), prikažu registrovani fungicidi za njihovo suzbijanje, kao i osnovne mere antirezistentne strategije, s obzirom da sva tri patogena, kao i većina fungicida koji se koriste za njihovo suzbijnaje, pripadaju grupama sa visokim rizikom od nastanka rezistentnosti

Prikladni alati za procjenu kronične boli u kliničkoj praksi

The aim of the study was to show the role of tools in the evaluation of chronic pain (CP) in general practitioner (GP) everyday clinical practice. The study was done by analyzing electronic database of the first visits of 1090 CP patients referred to the Pain Clinic of the Karlovac General Hospital, Karlovac, Croatia, by their GPs. All patient records were analyzed according to the cause of CP, strongest pain a week before the examination, quality of sleep, and the Patients’ Global Impression of Change scale. All statistical analyses were done using the IBM SPSS Statistics version 19.0.0.1 (www.spss.com). CP predominantly occurs in older age group. Patients with musculoskeletal pain accounted for the highest percentage (n=316; 29%), followed by those with neuropathic pain (n=253; 23.20%) and those with low back pain (n=225; 20.60%). The mean pain intensity rating scale score was 8.3±1.8 a week before the examination and the mean quality of sleep score was 6.8±1.9. Moderate and severe sleep quality disorder was significantly present in patients over 65 years of age (p=0.007), patients with musculoskeletal and neuropathic pain, back pain, and those having rated Patients’ Global Impression of Change scale as worsening (p=0.001). The severity of pain and poor quality of sleep are the leading causes of deterioration of the Patients’ Global Impression of Change scale in patients suffering from musculoskeletal and neuropathic pain. In order to treat CP comprehensively, it is important for GPs to evaluate the outcomes of clinical treatment using tools for CP assessment.Cilj istraživanja bio je pokazati ulogu alata za procjenu kronične boli u svakodnevnoj kliničkoj praksi obiteljskog liječnika. Istraživanje je provedeno analizom elektroničke baze podataka prvog pregleda 1090 bolesnika s kroničnom boli upućenih od obiteljskog liječnika u Ambulantu za bol Opće bolnice Karlovac, Karlovac, Hrvatska. Za sve bolesnike analizirani su uzrok kronične boli, najjača bol tjedan dana prije pregleda, kvaliteta sna i ljestvica općeg dojma bolesnika o promjeni. Statistička analiza je učinjena pomoću programa IBM SPSS Statistics ver. 19.0.0.1 (www.spss.com). Kronična bol se pretežito javlja u starijoj dobnoj skupini. Najzastupljeniji su bili bolesnici s mišićno-koštanom boli (n=316; 29%), potom oni s neuropatskom boli (n=253; 23,20%) i oni s bolnim leđima (n=225; 20,60%). Srednja najjača bol (Pain Intensity Rating Scale, PI-NRS) tjedan dana prije pregleda bila je 8,3±1,8, a kvaliteta sna 6,8±1,9. Srednje jaki i jaki poremećaj kvalitete sna značajnije je prisutan kod bolesnika iznad 65 godina starosti (p=0,007), bolesnika s mišićno-koštanom, neuropatskom boli i bolnim leđima te onih koji su prema ljestvici općeg dojma bolesnika o promjeni ocijenili kao pogoršanje (p=0,001). Jačina boli i loša kvaliteta sna bili su vodeći uzrok pogoršanja prema ljestvici općeg dojma bolesnika o promjeni za bolesnike koji boluju od mišićno-koštane i neuropatske boli. Radi sveobuhvatnog liječenja važno je da obiteljski liječnici procijene ishode kliničkog liječenja alatima za procjenu kronične boli

Highly efficient TiO2/Ppy photocatalysts

Titanium dioxide is the most suitable semiconductor for photocatalytic application due to its high efficiency, increased stability, low-cost, and non-toxicity. However, it is possible to enhance the photocatalytic activity of TiO2 by homogenizing it with conductive polymers. One of the most attractive conductive polymers is polypyrrole (PPy) owing to its stability, low-cost, and special redox properties. The aim of this work was to obtain the TiO2/PPy nanocomposites with a higher photocatalytic activity compared to TiO2. In order to determine the optimal content of PPy, four TiO2/x%PPy samples (x = 0, 1, 3, and 5 wt.%) were synthesized and characterized by XRD and TG/DSC analyses. The photocatalytic activity was examined towards the degradation of toxic textile azo dye Reactive Orange 16. It was observed that an increase in PPy content led to better adsorption capacity of the synthesized nanocomposites. Samples TiO2/1%PPy and TiO2/5%PPy demonstrated better photocatalytic activity than TiO2, while TiO2/3%PPy showed very similar photocatalytic activity to TiO2. Near complete degradation of the dye (98 %) was reached in 75 min by using TiO2/1%PPy, comparing to pure TiO2, which degraded the same amount of the dye in 120 min. Considering all the obtained results, the optimal content of PPy in the composite for degradation of Reactive Orange 16 is 1 wt.%

Synthesis and characterization of anodic substrates for IT-SOFCs based on proton conductors

Cermet anode substrates based on high temperature proton conductors Ni-BaCe0.9Y0.1O3- δ (Ni-BCY10) were prepared using wet chemical method. The microstructural properties of sintered pellets were investigated using X-ray diffraction analysis and field emission scanning electron microscopy. Impedance spectroscopy measurements were used for evaluation of electrical properties of the anode pellets. The high conductivity values of reduced anodes confirmed the percolation through Ni particles even for anode with reduced amount of nickel. Fuel cell tests were carried out and fuel cells with the cermet anode showed higher power output comparing to the fuel cells with platinum electrode

Effect of dopants on anatase structure

It is well known that TiO2-based Degussa P-25 is the mostly used comer-cial photocatalyst and that TiO2 exists in three crystalline modifications: tetragonal anatase (I41/amd) and rutile (P42/mnm) and orthorhombic brookite (Pbca). On heating, anatase and brookite, as metastable phases, can be transformed to rutile. The aim of this work was to investigate the effect of different dopants on anatase-rutile phase transition and thus on their photocatalytic behavior. For that matter, samples TiO2 M (M = Cu, Mn and V) having 5 at.% of dopants were prepared by 30 minutes hand-mixing of anatase and corresponding oxide (CuO, MnO2 and V2O5) powders in an agate mortar following by heat treatment at 700 °C for 3 h. The powder of pure anatase phase was also treated at same conditions. TG/DTA was used to define thermal treatment, and the obtained samples were characterized by powder XRD method in order to reach phase compositions, unit cell parameters and crystallite sizes. Since in the case of undoped anatase only 3 wt.% of rutile was formed, the presence of dopants accelerated phase transition: 26 and 76 wt.% of rutile was obtained beside anatase in TiO2 Mn and TiO2 V, respectively, while complete anatase to rutile phase transition occured in TiO2-Cu. The least rutile quantity in TiO2-Mn is related to the isovalency of Ti4+ and Мn4+ meaning that the incorporation of Мn4+ in TiO2 is not followed by the formation of new defects, which are driving force for phase transition, as in the case of TiO2 Cu. About 5 wt.% of the unreacted CuO was found in TiO2 Cu, which is almost all introduced quantity of CuO. This can be related to the fact that the ionic radius of Cu2+ for octahedral environment (0.870 Å) is larger than that of Ti4+ (0.745 Å). As a result, Cu2+ ions can hardly be incorporated in TiO2 comparing to smaller Мn4+ (0.670 Å) and V5+ (0.680 Å) although a small amount of Cu2+ surely was necessary to cause phase transition. Since no residues of initial oxides were found in TiO2 Mn and TiO2 V, it can be concluded that these metal ions were incorporated into anatase lattice. By comparing the calculated unit cell parameters of anatase mutually, the shrinkage along c-axis was revealed meaning the shortening of bond distances between М–Оapical. The photocatalytic activity of all synthesized samples will be tested since nanocrystalline samples were obtained according to determined crystallite sizes (55–90 nm).Degussa P-25 је фотокатализатор на бази титан(IV)-оксида, који се најчешће користи у индустрији. TiO2 се јавља у три полиморфне модификације: тетрагоналним анатасу (I41/amd) и рутилу (P42/mnm) и ромбичном брукиту (Pbca). Анатас и брукит, као метастабилне фазе, приликом загревања прелазе у рутил. Циљ овог истраживања је испитивање утицаја различитих допаната на фазни прелаз анатаса у рутил као и на фотокаталитичка својства. Узорци TiO2-M (M = Cu, Mn и V), који садрже 5 at.% допанта, припремљени су термохемијском реакцијом на 700 °C током 3 h између хомогенизованих прахова анатаса и одговарајућих оксида (CuO, MnO2 и V2O5). Ради поређења, прах чистог анатаса је термички третиран под истим условима. Помоћу ТГ/ДТ анализе дефинисани су услови термичког третмана, док су добијени узорци окарактерисани рендгенском дифракцијом на поликристалном материјалу да би се одредио фазни састав, параметри јединичних ћелија и величина кристалита. У случају недопираног анатаса настало је свега 3 mas.% рутила, 26 и 76 mas.% рутила добијено је у TiO2 Mn и TiO2 V, редом, док се потпуни фазни прелаз анатас–рутил одиграо у TiO2 Cu. Ово значи да присуство допанта убрзава фазну трансформацију. Најмања количина рутила у TiO2 Mn може се објаснити изовалентним Ti4+ и Мn4+, тј. да уградња Мn4+ у TiO2 није праћена настанком нових дефеката који представљају вучну силу за одигравање фазног прелаза, као што је то случај код TiO2 Cu. Око 5 mas.% непрореаговалог CuO (готово почетна количина) заостало је у TiO2 Cu, зато што се Cu2+-јони теже уграђују у решетку TiO2 због већег радијуса Cu2+ у октаедарском окружењу (0,870 Å) од радијуса Ti4+ (0,745 Å), за разлику од мањих Мn4+ (0,670 Å) и V5+ (0,680 Å). Ипак, сигурно је мала количина Cu2+-јона била неопходна како би иницирала фазни прелаз. Како у TiO2 Mn и TiO2 V нису присутни остаци полазних оксида, може се закључити да су се ови јони метала уградили у решетку анатаса. Међусобним поређењем параметара јединичне ћелије анатаса, уочено је скраћење дуж c-осе, што указује на скраћење дужина веза М–Оапикални. Израчуната величина кристалита (55–90 nm) показала је да су сви добијени узорци нанокристални, па ће њихова фотокаталитичка својства бити испитана

TiO2/PPy nanocomposites for photocatalytic application

Titan(IV)-oksid je jedan od najčešće korišćenih fotokatalizatora, dok za polipirol (PPy) postoje potvrde da je pogodan za ovu primenu. Cilj ovog rada bio je dobijanje kompozita TiO2/PPy sa boljom fotokatalitičkom aktivnosti u odnosu na TiO2. Kako bi se optimizovao sadržaj PPy u kompozitu, sintetisani su uzorci TiO2/x%PPy (x = 0, 0,5, 1, 1,5, 3, 5 mas.%), koji su okarakterisani TG/DTA, XRD, FTIR, FESEM i UV-Vis metodama, dok su njihova fotokatalitička svojstva ispitana kroz razgradnju tekstilne boje RO16. Nanokristalni TiO2 je dobijen u obliku anatasa veličine kristalita oko 2 nm, dok su izračunati parametri jedinične ćelije potvrdili da je kristalna struktura anatasa ostala nepromenjena nakon dodatka PPy. Gotovo svi uzorci (izuzev TiO2/3%PPy) su fotokatalitički aktivniji od TiO2, dok je TiO2/1%PPy pokazao najizraženiju fotokatalitičku aktivnost razgradivši 9 % boje nakon 75 min.Titanium(IV) oxide is one of the most used photocatalysts while polypyrrole (PPy) is a promising material for photocatalytic application. The aim of this work was to obtain TiO2/PPy composites exhibiting higher photocatalytic activity than TiO2. In order to determine the optimal PPy content in a composite, TiO2/x%PPy (x = 0, 0.5, 1, 1.5, 3, 5 wt.%) samples were synthesized and characterized by TG/DTA, XRD, FTIR, FESEM and UV-Vis methods, while the photocatalytic behavior was examined towards the degradation of the textile dye RO16. Nanocrystalline TiO2 was obtained in anatase form with crystallite size around 26 nm and preserved anatase crystal structure despite the addition of PPy according to the calculated unit cell parameters. Almost all samples (except TiO2/3%PPy) showed better photocatalytic activity than TiO2 while the best photocatalytic activity was demonstrated by TiO2/1%PPy which degraded 98 % of the dye after 75 min