Electrochemical deposition and characterization of Ni-W alloys

Kinеtikа еlеktrоhеmiјskоg tаlоžеnjа Ni-W lеgurа iz аmоniјаčnо-citrаtnоg еlеktrоlitа ispitivаnа је pоlаrizаciоnim mеrеnjimаnа rоtirајućој disk еlеktrоdi. Prisustvо i rеlаtivnа kоncеntrаciја rаzličitih kоmplеksnih vrstа је ispitivаnа еlеktrоnskоm аpsоrpciоnоm spеktrоfоtоmеtriјоm. Sаstаv lеgurа i iskоrišćеnjе struје tаlоžеnjа su ispitivаni u zаvisnоsti оd sаstаvа еlеktrоlitа, pH vrеdnоsti, hidrоdinаmičkih uslоvа, gustinе struје i pаrаmеtаrа pulsirајućе struје (frеkvеnciје i оdnоsа vrеmеnа pаuzе i pulsа). Rаzličiti kоmplеksni јоni su prisutni u еlеktrо-litu оd kојih su zа tаlоžеnjе lеgurе nајznаčајniјi prоtоnоvаni vоlfrаmаtnо-citrаtni kоmplеks i аmоniјаčnо-citrаtni kоmplеks niklа. Rеаkciја rеdukciје prоtоvаnih vоlfrаmаtnо-citrаtnih kоmplеksа је difuziоnо kоntrоlisаnа i tаlоžеnjе mеtаlа sе оdigrаvа sаmо u prisustvu аmоniјаčnо-citrаtnih kоmplеksа niklа. Тоkоm еlеktrо-hеmiјskоg tаlоžеnjа Ni-W lеgurа nikаl sе prvеnstvеnо tаlоži iz аmоniјаčnо-citrаtnih kоmplеksnih јоnа. Pri niskim pоlаrizаciјаmа rеdukciја је аktivаciоnо kоntrоlisаnа, а pri nеgаtivniјiјim pоtеnciјаlimа difuziоnо-rеаkci-оnо kоntrоlisаnа, pоštо је mаlа kоncеntrаciја rеdukuјućеg kоmplеksа i mаlа brzinа njеgоvоg stvаrаnjа iz drugih kоmplеksа. Моlski udео vоlfrаmа u dоbiјеnim lеgurаmа је оdrеđеn оdnоsоm brzinа dvе rеаkciје rеdukciје mеtаlnih kоmplеksа i iznоsi оd 0,06 dо 0,25. Uticај pаrаmеtаrа pulsirајućе struје nа mоrfоlоgiјu i udео vоlfrаmа u dоbiјеnim lеgurаmа prаti оpšti trеnd, prеtpоstаvlјеn tеоriјskim mоdеlоm nеstаciоnаrnе difuziје, аli i kоmplеksniје kаrаktеristikе.Еlеktrоhеmiјskо tаlоžеnjе Ni-W lеgurе је znаčајnо s оbzirоm nа spеcifičnе kаrаktеristikе i mоguću prаktičnu primеnu prеvlаkа. Lеgurе tаlоžеnе pulsirајućоm struјоm su rаvniје, vеćе tvrdоćе, pоsеbnо nаkоn tеrmičkоg trеtmаnа nа pоvišеnim tеmpеrаturаmа, u оdnоsu nа lеgurе tаlоžеnе kоnstаntnоm struјоm. Pоlаrizаciоnе krivе аnоdnоg rаstvаrаnjа i kаtоdnih rеаkciја snimlјеnе su u zаvisnоsti udеlа vоlfrаmа u еlеktrоhеmiјski tаlоžеnim lеgurаmа Ni-W, u sulfаtnim rаstvоrimа, pH vrеdnоsti оd 0 dо 14. Zаvisnоst kоrоziоnоg pоtеnciјаlа i dоbiјеnih struја оd mоlskоg udеlа vоlfrаmа i pH vrеdnоsti еlеktrоlitа ukаzuје dа sе nа pоvršini lеgurе, tоkоm stајаnjа nа pоtеnciјаlu оtvоrеnоg kоlа i tоkоm аnоdnе pоlаrizаciје u ispitivаnоm rаstvоru, stvаrа bаriјеrni slој kојi sprеčаvа dаlје rаstvаrаnjе lеgurе.Kinetics of the electrochemical deposition Ni-W alloys from ammonia-citrate electrolyte was studied by polarization measurements with a rotating disc electrode. Presence and relative concentrations of different complex species was employed by UV-VIS spectroscopy. The deposit composition and current efficiency were measured as a function composition of the electrolyte for deposition, pH, hydrodynamic condition, current density of deposition and the variables of pulsating current (frequency and ratio of off time to on time).Different complex species are found in the electrolyte, the most important for the alloy deposition process being the protonated tungstate-citrate complex and ammonia-citrate complex of nickel. The electrochemical reduction of the protonated tungsten-citrate complexes is diffusion controlled and the deposition of the metal occurs only in the presence of the ammonia-citrate complexes of nickel. During the electrochemical deposition of Ni-W alloys Ni is deposited primarily from the ammonia-citrate complex. At low overpotentials the reaction is activation controlled, while at more negative potentials diffusion/reaction control takes over, because of the low concentration of the electroactive species and low rate of its formation from other complexes. The composition of the alloy is determined by the ratio of the rates of the two reduction reactions of metallic ions, tungsten content were from 6 to 25 mol %. The effect of pulsating current parameters on the morphology of the alloy as well as on the tungsten content obtained in this work follow a general trend predicted by the non-steady state diffusion model, but show a some more complex behavior. Electrochemical deposition of Ni-W alloy is interesting for plating practice, because of some characteristic properties and possible practical applications of the deposit. The pulse deposited alloys were better smoothness, microhardness, especially after ageing at high temperatures, than alloy obtained by constant c.d. Polarization curves of anodic dissolution and cathodic reactions of electrodeposited Ni-W alloys, different content of tungsten, were determined in sulphate solutions, the pH values were varied from 0 to 14. The dependence of corrosion potential and obtained current on content of tungsten and pH indicated that at the alloy surface, during ageing and anodic polarization in employed solution, forming barrier layer, which to protected the alloy from dissolution

Oxidation of formic acid on bulk and nanosized Pt-Co alloys

Bulk Pt3Co and nanosized Pt3Co and PtCo alloys supported on XC-72 high area carbon were investigated as the electrocatalysts for the oxidation of formic acid. Cyclic voltammetry in 0.1 M HClO4 and stripping voltammetry of COads in the same electrolyte show a small difference in the potentials of Pt-oxide formation and reduction and COads oxidation. Based on these results, we concluded that electronic modification of Pt by Co atoms, which was theoretically predicted and experimentally proved on solid/gas interface, is exhibited in the electrochemical environment. Promotion of HCOOH oxidation rate on bimetallic Pt-Co surfaces with respect to pure Pt was found to be up to factor of eight in the case of PtCo/XC-72 catalyst. This moderate increase of the reaction rate is ascribed mostly to the ensemble effect, because partial leaching of Co increased Pt:Co ratio at the bimetallic surfaces, diminishing the efficiency of the ensemble effect.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3537

Electrochemical deposition and characterization of Ni-W alloys

Kinеtikа еlеktrоhеmiјskоg tаlоžеnjа Ni-W lеgurа iz аmоniјаčnо-citrаtnоg еlеktrоlitа ispitivаnа је pоlаrizаciоnim mеrеnjimаnа rоtirајućој disk еlеktrоdi. Prisustvо i rеlаtivnа kоncеntrаciја rаzličitih kоmplеksnih vrstа је ispitivаnа еlеktrоnskоm аpsоrpciоnоm spеktrоfоtоmеtriјоm. Sаstаv lеgurа i iskоrišćеnjе struје tаlоžеnjа su ispitivаni u zаvisnоsti оd sаstаvа еlеktrоlitа, pH vrеdnоsti, hidrоdinаmičkih uslоvа, gustinе struје i pаrаmеtаrа pulsirајućе struје (frеkvеnciје i оdnоsа vrеmеnа pаuzе i pulsа). Rаzličiti kоmplеksni јоni su prisutni u еlеktrо-litu оd kојih su zа tаlоžеnjе lеgurе nајznаčајniјi prоtоnоvаni vоlfrаmаtnо-citrаtni kоmplеks i аmоniјаčnо-citrаtni kоmplеks niklа. Rеаkciја rеdukciје prоtоvаnih vоlfrаmаtnо-citrаtnih kоmplеksа је difuziоnо kоntrоlisаnа i tаlоžеnjе mеtаlа sе оdigrаvа sаmо u prisustvu аmоniјаčnо-citrаtnih kоmplеksа niklа. Тоkоm еlеktrо-hеmiјskоg tаlоžеnjа Ni-W lеgurа nikаl sе prvеnstvеnо tаlоži iz аmоniјаčnо-citrаtnih kоmplеksnih јоnа. Pri niskim pоlаrizаciјаmа rеdukciја је аktivаciоnо kоntrоlisаnа, а pri nеgаtivniјiјim pоtеnciјаlimа difuziоnо-rеаkci-оnо kоntrоlisаnа, pоštо је mаlа kоncеntrаciја rеdukuјućеg kоmplеksа i mаlа brzinа njеgоvоg stvаrаnjа iz drugih kоmplеksа. Моlski udео vоlfrаmа u dоbiјеnim lеgurаmа је оdrеđеn оdnоsоm brzinа dvе rеаkciје rеdukciје mеtаlnih kоmplеksа i iznоsi оd 0,06 dо 0,25. Uticај pаrаmеtаrа pulsirајućе struје nа mоrfоlоgiјu i udео vоlfrаmа u dоbiјеnim lеgurаmа prаti оpšti trеnd, prеtpоstаvlјеn tеоriјskim mоdеlоm nеstаciоnаrnе difuziје, аli i kоmplеksniје kаrаktеristikе. Еlеktrоhеmiјskо tаlоžеnjе Ni-W lеgurе је znаčајnо s оbzirоm nа spеcifičnе kаrаktеristikе i mоguću prаktičnu primеnu prеvlаkа. Lеgurе tаlоžеnе pulsirајućоm struјоm su rаvniје, vеćе tvrdоćе, pоsеbnо nаkоn tеrmičkоg trеtmаnа nа pоvišеnim tеmpеrаturаmа, u оdnоsu nа lеgurе tаlоžеnе kоnstаntnоm struјоm. Pоlаrizаciоnе krivе аnоdnоg rаstvаrаnjа i kаtоdnih rеаkciја snimlјеnе su u zаvisnоsti udеlа vоlfrаmа u еlеktrоhеmiјski tаlоžеnim lеgurаmа Ni-W, u sulfаtnim rаstvоrimа, pH vrеdnоsti оd 0 dо 14. Zаvisnоst kоrоziоnоg pоtеnciјаlа i dоbiјеnih struја оd mоlskоg udеlа vоlfrаmа i pH vrеdnоsti еlеktrоlitа ukаzuје dа sе nа pоvršini lеgurе, tоkоm stајаnjа nа pоtеnciјаlu оtvоrеnоg kоlа i tоkоm аnоdnе pоlаrizаciје u ispitivаnоm rаstvоru, stvаrа bаriјеrni slој kојi sprеčаvа dаlје rаstvаrаnjе lеgurе.Kinetics of the electrochemical deposition Ni-W alloys from ammonia-citrate electrolyte was studied by polarization measurements with a rotating disc electrode. Presence and relative concentrations of different complex species was employed by UV-VIS spectroscopy. The deposit composition and current efficiency were measured as a function composition of the electrolyte for deposition, pH, hydrodynamic condition, current density of deposition and the variables of pulsating current (frequency and ratio of off time to on time). Different complex species are found in the electrolyte, the most important for the alloy deposition process being the protonated tungstate-citrate complex and ammonia-citrate complex of nickel. The electrochemical reduction of the protonated tungsten-citrate complexes is diffusion controlled and the deposition of the metal occurs only in the presence of the ammonia-citrate complexes of nickel. During the electrochemical deposition of Ni-W alloys Ni is deposited primarily from the ammonia-citrate complex. At low overpotentials the reaction is activation controlled, while at more negative potentials diffusion/reaction control takes over, because of the low concentration of the electroactive species and low rate of its formation from other complexes. The composition of the alloy is determined by the ratio of the rates of the two reduction reactions of metallic ions, tungsten content were from 6 to 25 mol %. The effect of pulsating current parameters on the morphology of the alloy as well as on the tungsten content obtained in this work follow a general trend predicted by the non-steady state diffusion model, but show a some more complex behavior. Electrochemical deposition of Ni-W alloy is interesting for plating practice, because of some characteristic properties and possible practical applications of the deposit. The pulse deposited alloys were better smoothness, microhardness, especially after ageing at high temperatures, than alloy obtained by constant c.d. Polarization curves of anodic dissolution and cathodic reactions of electrodeposited Ni-W alloys, different content of tungsten, were determined in sulphate solutions, the pH values were varied from 0 to 14. The dependence of corrosion potential and obtained current on content of tungsten and pH indicated that at the alloy surface, during ageing and anodic polarization in employed solution, forming barrier layer, which to protected the alloy from dissolution

Oxidation of formic acid on bulk and nanosized Pt-Co alloys

Bulk Pt3Co and nanosized Pt3Co and PtCo alloys supported on XC-72 high area carbon were investigated as the electrocatalysts for the oxidation of formic acid. Cyclic voltammetry in 0.1 M HClO4 and stripping voltammetry of COads in the same electrolyte show a small difference in the potentials of Pt-oxide formation and reduction and COads oxidation. Based on these results, we concluded that electronic modification of Pt by Co atoms, which was theoretically predicted and experimentally proved on solid/gas interface, is exhibited in the electrochemical environment. Promotion of HCOOH oxidation rate on bimetallic Pt-Co surfaces with respect to pure Pt was found to be up to factor of eight in the case of PtCo/XC-72 catalyst. This moderate increase of the reaction rate is ascribed mostly to the ensemble effect, because partial leaching of Co increased Pt:Co ratio at the bimetallic surfaces, diminishing the efficiency of the ensemble effect.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3537

Konceptualni model za istraživanje faktora koji utječu na dopiranje do glasa korisnika

Since the voice of the customer (VoC) could be of core importance for an organisation\u27s success, it is of high significance to identify the motivating and demotivating factors that influence the customers\u27 intention to provide or not to provide feedback on service quality. This study aims to observe how awareness on the issue of providing feedback, personal beliefs on the impact of feedback, expectations from the company, and organisational culture impact the customers\u27 decision to leave feedback. To explore the influence of the chosen factors an online survey was conducted and the Structural Equation Modeling (SEM) analysis was employed. The results show that awareness and organisational culture have a positive impact on the customers\u27 decision to provide feedback, while the expectations from the company have a negative impact on such customer behaviour. The presented conceptual model might provide novel viewpoints into the factors which impact customers\u27 behaviour regarding their decisions to provide feedback and initiate further studies on the topic of VoC.Budući da bi glas korisnika (VoC) mogao biti od presudne važnosti za organizacijski uspjeh, dragocjeno je za organizaciju da pravodobno identificira motivirajuće i demotivirajuće faktore koji utječu na volju korisnika da ostave ili ne ostave povratne informacije o kvaliteti usluge. Cilj je ovog istraživanja promatrati kako svijest o pružanju povratnih informacija, osobna uvjerenja o utjecaju povratnih informacija, očekivanja od kompanije i organizacijska kultura utječu na odluku korisnika da ostave povratne informacije o kvaliteti proizvoda ili usluge. Da bi se ispitao utjecaj odabranih četiriju faktora, provedena je online anketa i analiza modeliranja strukturne jednadžbe (SEM). Rezultati pokazuju da svijest i organizacijska kultura pozitivno utječu na odluku korisnika da ostavi povratnu informaciju, dok očekivanja od kompanije negativno utječu na takvo ponašanje korisnika. Predstavljeni konceptualni model mogao bi osigurati nova gledanja na faktore koji utječu na ponašanje korisnika u vezi s njihovim odlukama da ostave povratne informacije i pokrenuti nova istraživanja na temu glasa korisnika (VoC)

Prostorna interpretacija Hugelschaffer-ove konstrukcije jajaste krive

Konstrukcija jajaste kubne krive Hügelschäffer-ovom metodom, zasniva se na konstrukciji elipse metodom koncentričnih krugova različitih radijusa, a i b, koji odgovaraju parametrima elipse. Načinjen je pokušaj da se prostornom interpretacijom ovih krugova u bazise konusa I cilindra, objasni vrsta pravoizvodne površi koja bi kao ravan presek imala upravo ovako nastalu zatvorenu jajastu krivu. U pitanju je konoid koji kao jednu vodilju ima pravu, a kao drugu vodilju prostornu presečnu krivu ovih kvadrika.The construction of the ovoid cubic curve by the Hügelschäffer method is based on the construction of the ellipse by the method of concentric circles of different radii, a and b, which correspond to the parameters of the ellipse. An attempt was made to explain the type of rectilinear surface by the spatial interpretation of these circles into the bases of a cone and a cylinder, which, as a plane section, will have a closed egg curve formed in this way. the rectlinear surface is a conoid that has a straight line as a directrix, and a spatial cross-sectional curve of the above quadrics as the other directrix.http://mongeometrija.com/zbornici/2008/259-marija-obradovi-maja-petroviprostorna-interpretacija-hgelschffer-ove-konstrukcije-jajaste-kriv

Cu sub-monolayer decorated Pd/C and Pt/C as electrocatalyst for ethanol oxidation in alkaline solution

Easy storage and handling, high energy density, wide availability, and low toxicity are features that make ethanol attractive fuel cell liquid combustibles and the most promising among alternative power sources [1,2]. Unfortunately, the slow and incomplete ethanol oxidation reaction (EOR) occurs at the anode even on the best available catalysts known to date. Pure Pt and Pd are not capable of catalyzing the oxidation of ethanol through the total oxidation pathway [2]. However, Pt and Pd are necessary catalyst constituents to provide efficient adsorption of ethanol, which is the first reaction step in ethanol oxidation. The activity of Pd and Pt for alcohol oxidation can be enhanced by adding a co-catalytic element, mainly oxophilic metal (either d- or p-metals), or compounds such as oxides [3]. Therefore, in the present work, the influence of Cu sub-monolayers decoration of carbon-supported Pd and Pt nanoparticles was investigated for ethanol oxidation reaction (EOR) in the alkaline solution. Commercial Pt/C (E-TEK) and Pd/C catalyst synthesized by borohydride reduction method [4] were electrochemically characterized by cyclic voltammetry and COads stripping in acid and alkaline solutions. The onset potential and the peak potential of COads oxidation on Pd/C were more positive than those for Pt/C in both solutions, indicating lower oxophilicity and/or stronger bonding with COads in the case of Pd than Pt. Catalysts were decorated by underpotential deposition of Cu atoms (Cuupd) in acid solution with various surface coverages (up to 0.5). Electrochemically active surface area (ECSA) of undecorated catalysts was calculated from the charge of desorption of CO and Cuupd in acid solution, while ECSA of Cuupd decorated catalyst was calculated from the charge of CO desorption in alkaline solution. Cyclic voltammetry showed that on the Cuupd decorated surfaces the onset of CO desorption was negatively shifted. This indicates that Cuupd atoms provide oxygen-containing species at adjacent Pt or Pd sites at a lower potential than that achieved on pure metals. The influence of Cuupd decoration of the Pt/C and Pd/C catalysts on activity for EOR in 0.1 M KOH was investi¬gated under potentiodynamic conditions. Although the onset potential was the same, Pd/C was more active for EOR than Pt/C with the 1.5-fold enhancement of maximum current. Pd/C with Cuupd coverage of 0.30 exhibited lower onset potential and up to 2.5-fold increase in EOR activity with respect to Pd/C (calculated per Pd ECSA). However, with further increase in coverage the positive effect of Cuupd disappeared and activity even decreased. In the case of Pt/C the promotion effect of Cuupd was negligible, because only the catalyst with coverage of 0.11 showed lower onset potential and slightly higher current at low potentials. The higher EOR activity of Pd/C compared to Pt/C can be attributed to the optimum oxo¬philicity of Pd which provides ample space for adsorption of ethanol and still provides oxygen containing species for its oxidation. Decoration of Pd/C by 0.3 monolayer of Cuupd increases the amount of oxygen containing species that intensify ethanol oxidation rate on Pd

Constructing the Egg Curves Using the Golden Ratio of Pentagon

In the paper it is considered a construction of an egg curve obtained by continual joining of the circular arcs with three different centers. These three centers form sharp or flat triangles of the pentagon (sharp and flat triangles are the basic building shapes of Penrose tiling). They have many relationships with both the Fibonacci numbers and Phi. In such an egg curve, it is possible to inscribe two juxtaposed pentagons. We give also another construction which employs several, even infinite number of the pentagons. Those pentagons are forming a sequence related to Fibonacci sequence. The construction using the flat triangles will provide a curve which ratio between length of the perimeter and the sum of the length of its minor and major axes will give the coefficient Φ.http://mongeometrija.com/media/mongeometrija/2010/moNGeometrija%202010%20-%20PAGINACIJA.pd

MONITORING OF HONEY CONSUMPTION IN THE AREA OF THE CITY NAŠICE WITH REFERENCE TO THE HEALTH EFFECTS OF HONEY CONSUMPTION

There is a wide range of bee products on the market. The most famous and most accepted by consumers is honey. In Western European countries, the average consumption of honey per capita ranges from three to eight kilograms, while the average consumption of honey in Croatia is very low, 400 grams per capita. The European Union produces only 52% of honey for its own needs. The aim of the research was to study the availability of honey to potential consumers, honey consumption habits, ways of consuming honey, and knowledge of the properties of honey. A survey was conducted online. Respondents were of different genders and different age groups. The survey consisted of 20 questions, and 130 individuals (46% mean and 54% women) from the city of Našice were interviewed. The obtained data were analysed. After conducting research and processing the results, it can be concluded that honey is a product that is accepted by consumers of different age groups. Respondents believe that propolis has better healing properties than honey, but they rarely consume it. Honey is available and affordable to consumers

Solving the Situation of Airport Bled by Digital Terrain Modeling Using the Software Package Rinoceros

In the paper, we conducted an examination of topographical conditions of the airport Bled location, using the digital terrain modeling. A detailed analysis of the ambience around the airport is done in relation to natural and artificial obstacles (already built facilities). The ambience is defined by the imaginary surfaces (the taxiways, takeoff surface, the access surface, the internal horizontal surface, conical surface and transitional surface of the takeoff-landing track) through which can not or should not penetrate obstacles. Using the software package Rhinoceros, we modeled out the terrain at the foot of the mountain massif of the Savinjske Alps and the imaginary surfaces of the airport object, whereat possible obstacles were found. This method of 3D modeling gives a better visualization (display conditions on the ground) than previously applied methods of horizontal projection (2D) and methods of cross and transverse profileshttp://mongeometrija.com/media/mongeometrija/2010/moNGeometrija%202010%20-%20PAGINACIJA.pdf http://mongeometrija.com/zbornici/2010/165-petrovic-obradovic-solving-the-situation-of-airport-bled-by-digital-terrain---modeling-using-the