Specifičnosti elektrohemijskog taloženja i morfologija Zn-Mn prevlaka dobijenih iz pirofosfatnog elektrolita

The first successful attempt to electrodeposit Zn-Mn alloy coatings from alkaline bath was made only a few years ago. In this kind of solution, potassium pyrophosphate (K4P2O7) serves both as a complexing agent and as the basic electrolyte. The aim of this work was to study the electrodeposition process and properties of Zn-Mn alloy coatings deposited from pyrophosphate solution, with a new kind of alkaline pyrophosphate bath. Namely, chloride salts were used as the source of metal ions and ascorbic acid was used as reducing agent. The composition of the plating solution was as follows: 1 mol dm-3 K4P2O7 + 0.017 mol dm-3 ascorbic acid + 0.05 mol dm-3 ZnCl2 + 0.05 mol dm-3 MnCl2·4H2O. Cathodic processes during the alloy electrodeposition were investigated using linear voltammetry. The influence of addition of small amounts of ascorbic acid on the cathodic processes was established. It was shown that this substance inhibits hydrogen evolution and increases the current efficiency of alloy deposition. The current efficiency in the plating bath examined was in the range of 25 and 30%, which was quite higher as compared to the results reported in the literature for electrodeposition of Zn-Mn alloy from pyrophosphate bath. Electrodeposition of Zn-Mn alloys was performed galvanostatically on steel panels, at current densities of 20?120 mA cm-2. The coatings with the best appearance were obtained at current densities between 30 and 80 mA cm-2. The surface morphology studies, based on atomic force microscopy measurements, showed that morphology of the deposits is highly influenced by deposition current density. Zn-Mn coating deposited at 30 mA cm-2 was more compact and possessed more homogeneous structure (more uniform agglomeration size) than the coating deposited at 80 mA cm-2. Such dependence of morphology on the current density could be explained by the high rate of hydrogen evolution reaction during the electrodeposition process.U proteklih nekoliko godina pokazano je da se alkalni pirofosfatni elektrolit može primeniti za elektrohemijsko taloženje prevlaka Zn-Mn legura na čeliku. U ovom radu je ispitana zavisnost morfologije i hemijskog sastava Zn-Mn prevlaka od primenjene gustine struje taloženja. Karakterizacija prevlaka vršena je mikroskopijom atomskih sila i energetskom disperzionom atomskom analizom. Metodom linearne voltametrije ispitan je uticaj dodatka, askorbinske kiseline, na katodne procese. Utvrđeno je da se iz alkalnog rastvora mogu dobiti prevlake zadovoljavajućeg kvaliteta, ali da gustina struje ima veliki uticaj na homogenost i hrapavost površine Zn-Mn prevlaka. Askorbinska kiselina inhibira redukciju vodonika i povećava iskorišćenje struje za taloženje legure

van der Waals Interactions in Material Modelling

Van der Waals (vdW) interactions stem from electronic zero-point fluctuations and are often critical for the correct description of structure, stability, and response properties of molecules and materials, including biomolecules, nanomaterials, and material interfaces. Here, we give a conceptual as well as mathematical overview of the current state of modeling vdW interactions,focusing in particular on the consequences of different approximations for practical applications. We present a systematic classification of approximate first-principles models based on the adiabatic-connection fluctuation-dissipation theorem, namely the nonlocal density functionals, interatomic methods, and methods based on the random-phase approximation. The applicability of these methods to different types of materials and material properties is discussed in connection with availability of theoretical and experimental benchmarks. We conclude with a roadmap of the open problems that remain to be solved to construct a universal, efficient, and accurate vdW model for realistic material modeling

Progress in imaging techniques for characterization of polyelectrolyte complex microcapsules as encapsulation matrice for biocatalysts

Polyelectrolyte complex microcapsules showed to be an univerzal encapsulation matrice for wide range of biocatalysts including viable, native and recombinant bacterial cells, non-viable bacterial cells as well as enzymes. Developed continuous encapsulation protocol based on the polyelectrolyte complexation of oppositely charged polymers enabled production of uniform microcapsules with a controlled shape, size, membrane thickness, permeability and mechanical resistance. The characterisation and control of the microcapsule properties including the inner structure and surface properties was inevitable to determine their proper function and predictability in important applications such as the stabilisation and reuse of encapsulated biocatalysts for more efficient production of valuable compounds. Recent utilisation of unique environmental scanning electron microscope enabled an innovative observation and characterization of capsule morphology in native and fully hydrated state. Achieved results and comparison with previously used conventional microscopic techniques will be presented

The Electrodeposition and characterization of protective Zn-Mn alloy coatings

Ispitivan je uticaj vrste i sastava rastvora za taloženje i gustine struje taloženja na svojstva elektrohemijski dobijenih prevlaka Zn-Mn legura na čeliku. Korišćeni su rastvori gde su kao izvor jona metala bili hloridi (hloridni rastvori), sulfati (sulfatni rastvori) i hloridi uz visoku koncentraciju kalijum-pirofosfata kao kompleksirajućeg reagensa (pirofosfatni rastvori). Prevlake su bile taložene gustinama struje u opsegu između 20 i 300 mA cm-2. Uticaj parametara taloženja na hemijski sastav Zn-Mn legura je ispitan atomskom apsorpcionom spektroskopijom i energetskom disperzionom atomskom analizom, fazni sastav legura je određen rendgenskom difrakcijom, dok je morfologija površine prevlaka ispitana optičkom, elektronskom i mikroskopijom atomskih sila. Koroziona postojanost prevlaka Zn-Mn legura je ispitivana u slanoj komori kao i u 0,5 mol dm-3 rastvoru NaCl, pomoću više elektrohemijskih tehnika. Pokazano je kako rastvor za taloženje i gustina struje taloženja imaju veliki uticaj na svojstva i koroziono ponašanje Zn-Mn legura. Sadržaj Mn u prevlaci raste sa porastom gustine struje taloženja, i najveći sadržaj Mn (36 at.%) je postignut taloženjem iz hloridnog rastvora. Rendgenskom difrakcijom je potvrđeno prisustvo tri kristalne faze, i to η, ε- ili β1 faze, zavisno od uslova taloženja legure. Ispitan je uticaj dva specifična dodatka za taloženje iz grupe aromatičnih aldehida, i utvrđeno je da ove supstance inhibiraju izdvajanje vodonika na katodi i rast dendrita u prevlaci, i povećavaju sadržaj Mn u Zn-Mn legurama. Utvrđeno je da za svaki od tri vrste rastvora za taloženje (hloridni, sulfatni i pirofosfatni) postoji optimalna oblast gustina struje taloženja u kojoj se dobijaju koroziono najpostojanije prevlake. To su gustine struje koje daju prevlake sa dovoljnim sadržajem Mn koji omogućava stvaranje kompaktnog pasivnog sloja na korodirajućoj površini, ali istovremeno prevlake taložene tim gustinama struje imaju homogenu morfologiju površine. Optimalni opseg gustina struje je: za hloridni rastvor 20 – 80 mA cm-2, za sulfatni 20 – 40 mA cm-2 i za pirofosfatni 30 – 60 mA cm-2...The influence of a solution type and composition, as well as deposition current density, on the properties of electrodeposited Zn-Mn alloys on steel was investigated. Three solution types were used, where the source of metal ions were chlorides (chloride solutions), sulphates (sulphate solutions), and chlorides with a high concentration of potassium pyrophosphate, used as complexing agent (pyrophosphate solutions). The deposition current densities were ranging from 20 to 300 mA cm-2. The chemical composition of Zn-Mn alloys was investigated by atomic absorption spectrometry and energy dispersive X-ray analysis, the phase composition was determined by X-ray diffraction, while the coating morphology was investigated by optical, scanning electron, and atomic force microscopy. The corrosion behaviour of the Zn-Mn coatings was investigated in the salt spray chamber and in 0,5 mol dm-3 NaCl solution, by using several electrochemical techniques. The solution type and the deposition current density show high influence on the properties and corrosion behaviour of the Zn-Mn deposits. The Mn content increases with the current density increase, and the highest content of 36 at.% Mn can be achieved by the deposition from chloride solution. Three crystalline phases were identified by X-ray diffraction, namely η, ε or β1 phases, depending on the deposition conditions. The influence of the two brightening agents, which belong to the aromatic aldehydes, was also investigated, and it was shown that they not only inhibit hydrogen evolution reaction and dendrite growth, but also increase the Mn content in the Zn-Mn alloys. For each of the solution types (chloride, sulphate or pyrophosphate), there is an optimal deposition current density range which enables the formation of the Zn-Mn coatings with the highest corrosion stability. In this current density range, the obtained coatings possess enough Mn to enable the formation of passive layer on the corroding surface, and at the same time, the coatings obtained in this current density range are with homogeneous surface morphology. The optimal current density range is 20 – 80 mA cm-2 in chloride, 20 – 40 mA cm-2 in sulphate, and 30 – 60 mA cm-2 in pyrophosphate solution..

Krótka historia Wydziału Lekarskiego Historycznego Uniwersytetu Trnawskiego: 375-lecie Uniwersytetu Trnawskiego (Słowacja)

Trnava, a town in Slovakia, declared 2010 the "Year of Trnava University," in honor of the 375th anniversary of the university's founding. It was originally called "Universitas Tyrnaviensis", established in 1635 under the guidance of Cardinal Pázmány. The university was initially founded by the Jesuit Order and continues to exemplify traditional Christian values in its teaching and research activities. In 1777, Universitas Tyrnaviensis was officially closed and moved to present day Budapest, and the university doors did not open again until the foundation of the Slovak state in 1993 which prompted the reinstatement of the older college. The present day university builds on the rich heritage passed down by previous generations. The current day Faculty of Health Care and Social Work builds on the heritage and achievements of the School of Medicine, founded in 1769, which bore numerous esteemed scholars and practitioners. The current day university continues the legacies as established within the ethos of Universitas Tyrnaviensis, such as rekindling the focus on humanitarian activities, attaining high teaching standards in education and high levels in scientific research. Without doubt, the rich history and scholarly achievements of Trnava University constitute an important part of national Slovak history.Trnawa, miasto na Słowacji, rok 2010 ogłosiło "Rokiem Uniwersytetu Trnawskiego", aby tym samym uczcić 375 rocznicę założenia uczelni. Utworzona w roku 1635 pod kierownictwem kardynała Pázmány, pierwotnie nazywana ona była "Universitas Tyrnaviensis". Uniwersytet ten został założony przez Towarzystwo Jezusowe i nadal stara się w swojej działalności pedagogicznej i badawczej egzemplifikować tradycyjne wartości chrześcijańskie. W roku 1777 Universitas Tyrnaviensis został oficjalnie zamknięty i przeniesiony do Budapesztu, a drzwi uczelni zostały ponownie otwarte dopiero w momencie powstania Państwa słowackiego w 1993 roku, co pozwoliło na wznowienie funkcjonowania działalności. Dzisiejszy uniwersytet opiera się na bogatym dziedzictwie przekazanym przez poprzednie pokolenia. Obecny Wydział Nauk o Zdrowiu i Pracy Socjalnej rozwija się w oparciu o dorobek i osiągnięcia Szkoły Medycznej, założonej w 1769 roku, które wykształciła wielu wielkich uczonych i ekspertów-praktyków. Obecny Uniwersytet kontynuuje spuściznę Universitas Tyrnaviensis, opierając się na wartościach takich jak przywracanie zainteresowania działalnością humanitarną oraz osiąganie wysokich standardów nauczania w zakresie edukacji i badań naukowych. Bez wątpienia, ze względu na bogatą historię i osiągnięcia naukowe, historia Uniwersytetu Trnawskiego jest ważną częścią historii Słowacji

Корозиона стабилност превлака Zn-Mn легура добијених електрохемијским путем

Zinc alloy coatings electrochemically deposited on steel from electrolytes with different components differ in their composition, homogeneity, porosity, structure and other characteristics that affect their corrosion resistance. Manganese is characterized by a very negative electrochemical potential and very high strength, prompting many researchers to study Zn-Mn alloys for the anti-corrosion purposes in the industry, especially automotive. In this work it was examined the influence of the type of the electrolyte deposition on the current efficiency during electrodeposition of Zn-Mn alloys. Zn-Mn alloys were deposited on steel from chloride, sulphate and pyrophosphate plating baths at different current densities. We have examined the influence of deposition current density on the current efficiency during electrodeposition, appearance of alloy coatings, as well as their corrosion stability. It was shown that Zn-Mn alloys with the best corrosion properties, among all examined ones, were obtained from chloride plating bath at 2 A dm-2.Превлаке легура цинка електрохемијски добијене из електролита са различитим компонентама имају разлике у свом саставу, хомогености, порозности, структури и другим карактеристикама које утичу на њихову корозиону отпорност. Манган се одликује јако негативним електрохемијским потенцијалом и јако великом чврстоћом, што је навело многе истраживаче на испитивања легуре Zn-Mn у антикорозионе сврхе, за потребе у индустрији, нарочито аутомобилској. У овом раду испитиван је утицај врсте електролита на таложење Zn-Mn легура, као и на искоришћење струје приликом електрохемијског таложења. Легуре су таложене на челику из хлоридног, сулфатног и пирофосфатног електролита различитим густинама струје. При задатим условима таложења испитиван је хемијски састав, храпавост, изглед превлака легура, и њиховa корозиона стабилност. Показано је да највећу корозиону стабилност имају легуре добијене таложењем из хлоридног електролита густином струје од 2 A dm-2

Influence of ionic strength on the rheological properties of hydroxypropylmethyl cellulose-sodium dodecylsulfate mixtures

Mixtures of polymers and surfactants are commonly found in a range of products of pharmaceutical, cosmetic, and food industry. Interaction between polymers and surfactants influences different properties of these products, e.g. stability, flow properties, phase behavior, etc. It is known from previous work that an interaction in binary mixtures of hydroxypropylmethyl cellulose (HPMC) and sodium dodecylsulfate (SDS) takes place when SDS concentration (CSDS.) is higher than the critical association concentration (CAC) and lower than the polymer saturation point (PSP). The interaction results in the formation of an HPMC-SDS complex. The objective of this work was to study the effect of the ionic strength on the HPMC-SDS complex formation by rheological investigation. The HPMC/SDS mixtures composed of 0.70 % wt. HPMC, and 0.00 % to 2.50 % wt. SDS were prepared in deionized water, 0.01M and 0.05M NaCl solution. It was found that an increase in the ionic strength influences the HPMC-SDS complex formation by increasing the zero shear viscosity of the mixtures in the interaction region (CAC<CSDS<PSP), while a decrease in the viscosity is observed for CSDS>PSP. The HPMC/SDS mixtures showed a shear thinning or a shear thickening flow properties depending on CSDS. The flow properties were influenced by the ionic strength of the mixtures.[Projekat Ministarstva nauke Republike Srbije, br. III46010

Mathematical model for temperature change of a journal bearing

In this work, a representative mathematical model has been developed, which reliably describes the heating and cooling of a journal bearing as a result of its malfunctioning, and the model has been further confirmed on a test bench. The bearing model was validated by using analytical modeling methods, i. e. the experimental results were compared to the data obtained by analytical calculations. The regression and variance analysis techniques were applied to process the recorded data, to test the mathematical model and to define mathematical functions for the heating/cooling of the journal bearing. This investigation shows that a representative model may reliably indicate the change in the thermal field, which may be a consequence of journal bearing damage

Dissociative iodomethane adsorption on Ag-MOR and the formation of AgI clusters: An ab initio molecular dynamics study

International audience1 Radioactive iodine species belong to the most dangerous components of nuclear effluents and waste produced by nuclear facilities and this fact motivates a significant effort in development of technologies for their efficient trapping. In this work we use computer simulations at the periodic DFT level to investigate dissociative adsorption of iodomethane on silver exchanged mordenite, which is among the most effective sorbents of iodine species available as of today. The structure, energetics, and mobility of complexes Ag-(CH 3 I) and Ag-(CH 3 I) 2 formed upon adsorption of iodomethane on Ag + sites are investigated using the ab-initio MD approach. The free-energy profiles for the reaction CH 3 I + Ag-MOR → AgI + CH 3-MOR are determined using the blue moon ensemble technique. The AgI species formed as a product of dissociative adsorption are shown to combine spontaneously into small clusters (AgI) n with the dimensions restricted by the size and geometry of confining void. The structure and energetics of the (AgI) n species are analysed in detail and compared with the available experimental and theoretical data. The internal energy of formation of clusters in mordenite is shown to contribute significantly to the shift of equilibrium from undissociated to dissociated form of adsorbed CH 3 I

Functional properties of pumpkin (Cucurbita pepo) seed protein isolate and hydrolysate

Pumpkin seed protein isolate (PSPI) was enzymatically hydrolysed by pepsin to obtain pumpkin seed protein hydrolysate, PSPH. Investigation on solubility, interfacial and emulsifying properties of both PSPI and PSPH was conducted under different conditions of pH (3-8) and ionic strength (0-1 mol/dm3 NaCl). PSPI had the lowest solubility, i.e. isoelectric point (pI), at pH 5. PSPH had higher solubility than PSPI over whole range of pH and ionic strengths tested. Decrease in surface and interfacial tension evidenced that both PSPI and PSPH adsorb at air/protein solution and oil/protein solution interface. Emulsions (20 % oil in water) stabilized by 1 g/100cm3 PSPI or PSPH solution were prepared at pH 3, 5 and 8 and ionic strength of 0 and 0.5 mol/dm3 NaCl. PSPH stabilized emulsions from coalescence at all pH and ionic strengths tested. PSPI was able to stabilize emulsions at pH 3 and 0 mol/dm3 NaCl, and at pH 8 regardless of ionic strength, while emulsions at pH 5 and both 0 and 0.5 mol/dm3 NaCl and at pH 3 when ionic strength was increased separated to oil and serum layer immediately after preparation. All emulsions were susceptible to creaming instability. [Projekat Ministarstva nauke Republike Srbije, br. III 46010