Mechanochemically assisted solid-state synthesis of Cu substituted thermoelectric sodium cobaltite

Polycrystalline samples of Cu substituted NaCo2-xCuxO4 (x=0, 0.01, 0.03, 0.05, 0.1) were prepared using mechanochemically assisted solid-state reaction method starting from the Na2CO3, Co3O4 and CuO powders. Each powder mixture was mechanically activated by grinding for 3 h in a planetary ball mill with ball to powder mixture ratio 20:1, at the basic disc rotation speed of 360 rpm. The asprepared powders were pressed into disc-shaped pellets and subsequently subjected to a heat treatment at 880 °C for 24 h in inert argon atmosphere. Changes in structural characteristics of the samples and particle morphology, caused by Co substitution by Cu, were characterized using X-ray diffraction and scanning electron microscopy, respectively. It should be emphasized that milling process reduced the time necessary for obtaining pure sodium cobaltite. From the results obtained in this study, observed changes in microstructure were correlated with changes in the lattice parameters, indicating the influence of Cu ion incorporation in NaCo2O4 crystal lattice

Hemijska stabilnost dopianog barijum-cerijum-oksida kao elektrolita za gorivne ćelije na bazi oksida u čvrstom stanju

Predmet ovog integralnog istraživanja je ispitivanje uticaja različitih količina Zr4+, Nb5+ i Ta5+ na hemijsku stabilnost, mikrostrukturna i električna svojstva BaCe0.9Y0.1O3–δ kao elektrolita za gorivne ćelije na bazi oksida u čvrstom stanju. Pored toga, izvršeno je poređenje tih materijala sa BaCe1–xInxO3–δ (x= 0.15; 0.20 i 0.25), a korišćene su i dve različite metode sinteze keramičkih prahova: metoda reakcije u čvrstom stanju i metoda samosagorevanja. Neporozni elektroliti su dobijeni sinterovanjem uniaksijalno presovanih keramičkih prahova BaCe0.9Y0.1O3–δ i BaCe0.9–xY0.1MxO3–δ (x= {0.01; 0.03; 0.05}, M= {Zr4+; Nb5+; Ta5+}) na 1550 °C u toku 5 h. S druge strane, BaCe1–xInxO3–δ su sinterovani na znatno nižoj temperaturi (1300 °C), na kojoj je izdvajanje BaO oksida praktično nemoguće, i to predstavlja glavnu prednost In kao dopanta. Električna karakterizacija sinterovanih uzoraka je izvršena elektrohemijskom impedansnom analizom. Ukupna provodljivost, merena u temperaturnom intervalu od 550–750 °C u atmosferi vlažnog vodonika, opadala je sa snižavanjem temperature i sa porastom koncentracije dopanata za BaCe0.9–xY0.1MxO3–δ (M= {Zr4+; Nb5+; Ta5+}), dok je kod BaCe1–xInxO3–δ primećen suprotan trend, ali su provodljivosti u slučaju dopiranja indijumom bile znatno manje. Hemijska stabilnost elektrolita je ispitana izlaganjem uzoraka atmosferi CO2 na 700 °C u toku 5 h. Svi elektroliti BaCe1–xInxO3–δ su bili postojani na uticaj CO2, kod BaCe0.85Y0.1Nb0.05O3–δ i BaCe0.85Y0.1Ta0.05O3–δ je primećena značajna stabilnost, dok je nestabinost ostalih uzoraka bila izraženija što je sadržaj Nb, Ta ili Zr bio manji. Elektrolit sastava BaCe0.75In0.25O3–δ (BCI25) je pokazao optimalna svojstva, pa je odabran za testiranje rada gorivne ćelije. Zahvaljujući velikoj specifičnoj površini praha BCI25, dobijenog metodom samosagorevanja, bilo je moguće njegovo procesiranje elektroforetskom depozicijom u kompaktan elektrolitni sloj od 10 μm. Izlazna snaga ćelije na 700 °C, sastava vodonik/Ni-BCI25//BCI25//La0.8Sr0.2Co0.2Fe0.8O3-BCI25/vazduh, iznosila je ~250 mW/cm2, čime je potvrđena funkcionalnost ovog elektrolita

Nanoindentation of nickel manganite ceramics obtained by complex polimerization method

Nickel manganite is very interesting NTC material due to its outstanding properties and wide field of applications mainly in microelectronics and optoelectronics and lately in the mobile phone industry. In this work, chemical synthesis of this material was performed by complex polymerization method (CPM). The presence of pure nickel manganite phase was confirmed by X-ray analysis. The obtained fine nanoscaled powders were uniaxially pressed and sintered at different temperatures: 1000 C -1200C for 2h. Microstructure development during sintering was observed by scanning electron microscope (SEM). Indentation experiments were carried out using a three sided pyramidal (Berkovich) diamond tip. Young’s modulus of elasticity at various indentation depths and hardness of NTC ceramics were calculated. It was found that the highest hardness and elastic modulus exhibit the ceramics sintered at highest temperature

Enhancement of thermoelectric properties induced by Cu substitution in NaCo2O4

In this work polycrystalline samples of NaCo2–xCuxO4 (x = 0, 0.01, 0.03, 0.05) were obtained from the powder precursors synthesized in two different ways: 1) by a mechanochemically assisted solid-state reaction method (MASSR) and 2) a citric acid complex method (CAC). Ceramic samples were prepared by pressing into discshaped pellets and subsequently sintered at 880 °C in inert argon atmosphere. The electrical resistivity (), the thermal conductivity () and the Seebeck coefficient (S) were measured simultaneously in the temperature range from 330 K to 830 K, and the effect of small concentrations of the dopant and syntheses procedures on the thermoelectric properties was observed. According to the temperature dependence of , all MASSR samples showed metal-insulator transition. The values of were lower for undoped samples in both syntheses. S increased with temperature and it was higher in all Cu doped samples, reaching 145 V/K at 830 K for the sample with 3 mol% of Cu prepared by the CAC method. High thermopower is the consequence of the strong electron correlation, present in this type of compounds. The CAC samples showed higher ZT compared with the MASSR samples of the same composition. The highest figure of merit (ZT = 0.056) was obtained for the sample with 5 mol% of Cu prepared by the CAC method, and it was 1.5 times higher than the highest value obtained for the MASSR sample (ZT (NCO3-MASSR) = 0.036). This result confirmed that, beside the dopant concentration, synthesis procedure considerably affected the thermoelectric properties of NaCo2O4

Dirofilariosis and Leishmaniasis in the Northern Region of Serbia

Research in the field of vector borne diseases and zoonozes became a topic of interest in Serbia, during the last decade. Climate changes as well as higher frequency of human and animal movement and travel, especially of dogs, is rising a threat of dirofilariosis and leismaniasis. The presence of native mosquito and sandfly vectors has already been confirmed in the country and some invasive/previously not detected were found. Dirofilariosis and leishmaniasis, which are found more or less often in dogs, cause clinical symptoms which are not obvious and therefore they represent a danger for public health with dogs acting as reservoirs of the infection

Wandering spleen-a possible cause of adrenal ”mass“-case report

Wandering spleen is a very rare clinical condition character-ized by spleen absence in the normal anatomical location in the upper left quadrant of the abdomen and its presence at another location in the abdomen or pelvis. The ectopic spleen is extremely rare in children, where its increased mobility is the result of a congenital disturbance of the fixation for the anterior wall due to the absence or weakness of the supporting ligaments. Wandering spleen is usually asymptomatic, but its torsion is possible, as well as infarction or rupture which demand an urgent diagnosis and surgical treatment. The diagnosis of wandering spleen can easily be overlooked due to low incidence and insufficient clinical experience, which multiplies patient's risk from life-threatening conditions. We present a case of wandering spleen in an 11-year-old girl with acute abdominal pain, which after ultrasound examination raised suspicion on the right adrenal gland tumor. Additional diagnostics verified an ectopic spleen in the right adrenal box, after which the recommended preventive splenopexy was seriously considered. Due to the fixation of the vital spleen in the new position, but also the negative attitude of the parents towards the surgical intervention, clinical monitoring was selected, with exclusion of intense physical activity that carries the risk of traumatization of the spleen. As the girl has been in good health for over 3 years and without symptoms, we consider that the selection of conservative access although difficult, was correct. We hope that our experience in treating wandering spleen in girls will increase the number of valid facts about this rare condition

Solvothermal synthesis of Ti doped ZnO

Titanium doped zinc oxide powders were synthesized by solvothermal method. Polycrystalline powders of ZnO with different amounts of Ti -Zn1-xTixO (x=0, 1, 2, 5, 7.5, 10 at%) were obtained from ethanolic solution of zinc acetate dihydrate in the presence of lithium hydroxide and titanium citrate. Reaction was conducted in autoclave at 225 0 C and 42 bar for 6 h. Detailed structural analysis was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on obtained results mechanism of Ti incorporation in ZnO lattice was discussed

Thermoelectric properties of Cu-doped sodium cobaltite ceramics

Layered cobalt oxide materials have lately been the subject of considerable fundamental and practical interest as potential candidates for thermoelectric application. The polycrystalline samples of NaCo2–xCuxO4 (x = 0, 0.01, 0.03, 0.05) were obtained by mechanochemically assisted solid-state reaction method (MASSR) and the citric acid complex method (CAC). Ceramic samples were prepared by pressing into disc-shaped pellets and subsequently sintered at 880 °C for 20 h in inert argon atmosphere. The electrical resistivity (ρ), the thermal conductivity (κ) and the Seebeck coefficient (S) were measured and observed in two temperature regions: low (from 0 to 300 K) and high (from 300 K to 800 K), and the effect of small concentrations of the dopant on the thermoelectric properties was observed. The values of κ were lower in higher temperature region, and almost independent of Cu concentration. S was positive above 25 K, and higher for Cu-doped samples, reaching the highest values for both syntheses for samples with x = 0.03(145 μV/K at 873 K for CAC sample). The highest figure of merit (ZT) at room temperature (0.022) was obtained for x = 0.01 while at high temperature region ZT were 0.050 and 0.034 for CAC and MASSR samples, respectively. ZT values for all samples were higher than in undoped samples, confirming that even small concentration of Cu significantly influences the thermoelectric properties of NaCo2O4. It was found that the samples synthesized by CAC method possess better thermoelectric properties, confirming the fact that this type of synthesis enables obtaining fine, homogeneous precursor powders with fine microstructures and small grains which presents prerequisite for obtaining material with good thermoelectric performances

THERMOELECTRIC PROPERTIES OF NaCo2–xCuxO4 (x = 0, 0.01, 0.03, 0.05) CERAMIC

Layered cobalt oxides have attracted great attention during past decade as potential candidates for thermoelectric application. However, the scientists are dealing with several problems concerning synthesis, Na evaporation, changes of the stoichiometry of the ceramic, etc. In order to reduce synthesis duration and temperature, prevent Na evaporation and improve mixing of the precursors we applied mechanochemically assisted solid state reaction and citric acid complex methods to obtain NaCo2–xCuxO4 (x = 0, 0.01, 0.03, 0.05) powders. Ceramic samples were prepared by pressing into disc-shaped pellets and subsequently sintered at 880 °C in inert argon atmosphere. The electrical resistivity (ρ), the thermal conductivity (κ) and the Seebeck coefficient (S) were measured simultaneously in the temperature range from 2 K to 830 K, and the effect of small concentrations of the dopant on the thermoelectric properties was observed. It was found that in the low temperature range ρ increased with temperature, indicating metallic behavior. The values of κ decreased as the temperature increased. S was higher in all Cu-doped samples, reaching 145 μV/K at 830 K for x = 0.03, and this suggested strong electron correlation in these systems. The highest figure of merit (ZT) at room temperature (0.022) was obtained for x = 0.01 prepared by the citric acid complex method and it was twice higher than in undoped sample. In the temperature region between 300 K and 830 K, higher ZT was also obtained for the samples prepared by citric acid complex method, reaching the value of 0.056 at 830 K for x = 0.05 and it was almost three times higher than in undoped sample. These results confirm that even small concentration of Cu significantly influences the thermoelectric properties of NaCo2O4

Hard Template Synthesis of Nanomaterials Based on Mesoporous Silica

Diverse hard template synthetic methodologies are being employed for the synthesis of mesostructured metal oxide and carbon nanomaterials, with the application of mesoporous silica as the hard template. We describe the main differences and advantages/disadvantages between the soft and hard templated synthetic routes, provide an overview of the synthesis and characteristics of different templating mesoporous silica nanomaterials and discuss on practical aspects of the hard template synthetic methodology for obtaining various metal-oxide and carbon-based mesostructured nanomaterials. Also, we cover various recent applications of thus constructed mesostructured metal oxide and carbon nanomaterials, such as sensing, energy storage, fuel cells, and catalysis, which demonstrate the highly promising character of the hard template methodology for the synthesis of a new generation of nanomaterials with broad application potential