Determination of the zinc and cadmium contents in low-alloyed tin

The method of anodic linear sweep voltammetry (ALSV) has been used to determine the content of Zn and Cd (up to 4% w/w) in eutectic type binary alloys with Sn. The alloy samples were prepared by casting. The effect of the type and the pH of the electrolyte, as well as of the sweep-rate on the dissolution of Zn and Cd from the alloy during an anodic potentinal-sweep was investigated. It was shown that ALSV is sensitive to low concentrations of both Zn and Cd in the investigated alloys, as well-defined peaks of the dissolution of the two metals were recorded before the massive dissolution of Sn commenced. Well-defined linear dependencies between the quantities of electricity under the dissolution peaks of Zn (Qzn) or Cd (Qcd) and the respective contents of the metals in the alloys were found. Intercepts at the abscissa were found in both investigated systems indicating the formation of solid solutions from which neither Zn nor Cd could be eluted. In both alloys, the smallest amount of the alloying component which could be detected was 0.25% (w/w). The application of the ALSV method has several advantages over other analytical methods: it is non-destructive as the dissolution involves only a very thin layer of the alloy; it requires simple and cheap instrumentation; it is fast and relatively sensitive. These make it suitable for routine analysis

Elektrohemijsko taloženje i fazna struktura legura Ni-W

The induced deposition of W in the presence of iron-group metals has been known for a long time without a proper understanding of the mechanism of codeposition. Hints were made by several authors, concerning primarily a similar case of codeposition of Mo, which were not sufficiently substantiated by proper kinetic investigation as the research was oriented mainly toward practical aims. In the present investigation induced deposition of W with Ni was studied primarily from the point of view of the composition and phase structure of the resulting Ni-W alloy. The method of anodic linear sweep voltammetry was used to analyze deposits obtained at a rotating disc electrode, as it was proven to be a good tool for analysis of thin-layered deposits. The polarisation diagram was found to exhibit a sharp current maximum and a subsequent decay at potentials at which Ni deposition starts. As some W oxide is found to deposit at less negative potential the sharp rise of current and the maximum are ascribed to catalytic effect of the oxide for hydrogen evolution, larger than that of depositing Ni-W alloy. The deposit was found to exhibit two peaks upon anodic dissolution, both at significantly more positive potentials than that of Ni dissolution. The first peak is of limited quantity of electricity independent of the amount of the deposit, the increase of the latter being reflected in the second peak only. An aging effect was found rendering an alloy requiring much more positive potentials for dissolution than those for dissolution of freshly deposited alloys.Taloženje volframa u prisustvu metala grupe gvožđa, indukovano taloženje, je fenomemen koji je odavno poznat. Međutim, mehanizam kodepozicije nije razjašnjen. Dosadašnja istraživanja indukovanog taloženja ( i to najčešće molibdena ) prvenstveno su bila usmerena ka primeni u praksi, a nedovoljno praćena odgovarajućim kinetičkim ispitivanjima. U ovom radu ispitivano je indukovano taloženje W sa Ni prvenstveno sa stanovišta sastava i fazne strukture dobijenih Ni-W legura. Metoda anodne linearne promene potencijala (ALSV) upotrebljena je za analizu prevlaka dobijenih na rotirajućoj disk elektrodi. Na katodnim polarizacionim dijagramima taloženja nađen je oštar strujni maksimum na potencijalu koji odgovara početku taloženja Ni. Pad struje se može pripisati sporijem izdvajanju vodonika na leguri Ni-W, nego na oksidu volframa koji je se dobija pri manje negativnim potencijalima. Na anodnim voltamogamima rastvaranja javljaju se dva karakteristična strujna vrha, oba na potencijalima znatno pozitivnijim od onih koji odgovaraju rastvaranju čistog Ni. Količina naelektrisanja koja odgovara prvom strujnom vrhu je ograničena odnosno, povećanje količine naelektrisanja pri taloženju odražava se u odgovarajućem porastu naelektrisanja drugog anodnog strujnog vrha. Nađeno je da se legure, koje su stajale na sobnoj temperaturi u toku nekoliko časova posle taloženja, rastvaraju na znatno pozitivnijim potencijalim od onih koje su ispitivane neposredno posle taloženja, što ukazuje na stabilizaciju procesom u čvrsoj fazi

Karakterizacija i korozione karakteristike elektrohemijski taložene legure Ni-W

Ni-W alloys electrodeposited from citrate solution consist of three different phases, which are all present in high W-content alloys: a solid solution of W in a Ni matrix; an intermetallic compound Ni4W, as well as another solid solution of W in Ni with a W content higher than 20 mol. %. XPS analysis revealed that the alloys were covered with a surface layer of complex structure containing the pure metals Ni and W, Ni(OH)2 andWO3, on the very surface as well as some partially reduced oxideWO2.72 (most probably a solid solution ofWO2.72 in Ni) and tungsten carbide in the layer underneath. It is highly likely that some of the oxide species in the layer act as intermediates in the cathodic deposition process. Identifying these species should be the clue to a more detailed understanding of the mechanism of induced deposition of W than has been achieved so far. Corrosion of Ni-W alloys in sulfuric acid solution at OCP, occurs by the preferential dissolution of nickel from the surface layer. The longer the corrosion process lasts, the more the surface behaves like pure W. The lowest initial corrosion rates were recorded with alloys rich in W, but after aging at OCP the lowest corrosion c.d. was found for the Ni-W alloy with the most homogenous phase structure, consisting of the solid solution only.Elektrohemijski taložene legure Ni-W iz citratnog rastvora sadrže tri različite faze, koje su prisutne pri visokom sadržaju W u leguri: čvrst rastvor W u Ni; intermetalno jedinjenje Ni4Wi čvrst rastvor Wu Ni sa sadržajem W većim od 20 mol %. XPS analizom je pokazano da su legure pokrivene slojem složene strukture. Ovaj sloj sadrži čiste metale Ni i W, Ni(OH)2 i WO3, na samoj površini. U sloju ispod same površine nađeni su i delimično redukovan oksid WO2,72 (najverovatnije čvrst rastvor WO2,72 u Ni) i volfram-karbid. Vrlo je verovatno da neka od oksidnih vrsta u sloju učestvuje kao intermedijer u procesu katodnog taloženja. Identifikacija te vrste mogla bi doprineti boljem razumevanju mehanizma indukovanog taloženja volframa. Na potencijalu otvorenog kola u sumpornoj kiselini korozioni proces se odigrava tako što se preferencijalno rastvara Ni iz površinskog sloja legure. Ukoliko korozioni proces traje duže utoliko korozione karakteristike postaju sve sličnije onima za čist W. Niže početne brzine korozije dobijene su za legure sa većim sadržajem W. Međutim, nakon stajanja na potencijalu otvorenog kola niže korozione struje su dobijene za Ni-W leguru homogene fazne strukture koja sadrži samo čvrst rastvor

Karakteristike legura Ni-W elektrohemijski taloženih konstantnom i pulsirajućom strujom

The Ni-W alloys were electrochemically deposited from a ammonia-citrate electrolyte on rotation disc electrode with a replaceable steel disc, by direct and pulsed current. The aim of the paper is investigations of parameters of deposition, structure of alloys and temperature treatment on morphology and micro hardness of alloys.Prevlake legure Ni-W su elektrohemijski taložene iz amonijačno-citratnog elektrolita, na rotirajuću disk elektrodu od čelika, konstantnom i pulsirajućom strujom. Cilj rada je ispitivanje uticaja parametara taloženja sastava legure i termičkog tretmana na morfologiju i mikrotvrdoću dobijenih prevlaka

The enhancement of energy gain of solar collectors and photovoltaic panels by the reflection of solar beams

The use of reflecting panels for increasing energy gain, as demonstrated by use in greenhouses, was applied to conventional solar (thermal) collectors and photovoltaic panels. Several types of reflectors were considered in order of increasing sophistication, cost and enhancement coefficients. Calculations showed that the increase in energy gain ranged from 20 to 250%, depending on the type of equipment and season

Catalytic effect of metal adatoms deposited at underpotential

Electrochemical deposition of up to a monolayer of metal on foreign substrates at potentials positive to the reversible one (underpotential deposition) has been known for some time. 1,2 It appeared interesting to see if an electrochemically deposited layer of these adatoms, with partial ionic character, 3,4 would affect the kinetics of some electrochemical process compared to that at a bare electrode surface

Electrochemical activation of the electroless deposition of Ni–P alloy and phase structure characterization of the deposit. Part I: Dual bath system

A typical low temperature alkaline bath was chosen for the investigation of the effect of electrochemical activation on the efficiency of the electroless deposition of Ni and on the phase structure of the Ni–P alloys obtained. Electrochemical deposition was separated from chemical deposition by employing a two bath sequence, the first (i.e., the bath for electrochemical activation) being free of reducing agent. It was found that an activation current density, as well as an amount of precursors at the surface larger than a critical value (0.5mA cm−2 and 8 mC cm−2, respectively) are required for the electroless process to take place. The phenomenon was explained in terms of nucleation theory. Anodic linear sweep voltammetry (ALSV) of the Ni–P alloys obtained after electrochemical activation, as well as of those obtained after chemical (Sn–Pd) activation, indicated the presence of two dominant phases, that is, a solid solution of P in Ni, and a nickel phosphide compound, most probably Ni2P. It was also shown that changes in the phase structure of the electroless Ni–P deposit upon thermal treatment may be followed by employing (ALSV)

Electrochemical activation of the electroless deposition of Ni–P alloy and phase structure characterization of the deposit Part II: Single bath system

The process of electroless Ni plating (EP) was activated by the cathodic deposition of precursors of Ni in the same bath in which EP takes place. The current density (c.d.), duration of cathodic activation, as well as the duration of subsequent EP were varied and the effect of these parameters on the phase composition of the resulting Ni–P deposits was determined by anodic linear sweep voltammetry (ALSV). It was found that electrochemical activation can be achieved with relatively low c.d. and short current pulses, to run at rates comparable to EP activated in other ways. The rate of EP alone was found to be in the range between 1 and 5 mC cm−2 s−1, regardless of the activation c.d. or the amount of electrochemically deposited Ni precursors. A synergistic effect was obtained in cases when a little low c.d. cathodic current was passed simultaneously with the EP. The alloys were found to consist of a solid solution of P in Ni, as well as of some phosphide compounds and pure Ni (at increasing activation c.d.). During EP, however, only the solid solution was deposited. The phase structure of the deposit can be varied to a certain extent by the activation c.d

Deposition of zinc of foreign substrates

Initial stage of deposition of zinc from buffered zinc sulphate solution (pH = 3.55) was studied using platinum, gold and graphite as substrates. The phenomenon of underpotential deposition, noted by recording potential sweep voltammograms (PSV), was taken as a criterion of the existence and strength of interaction between a substrate and the depositing metal. Strong adhesive interactions (including alloy formation) were found in the case of platinum and gold with indication of the existence of multiple states of zinc atoms at the surface. Graphite exhibited no notable interaction and at cathodic overpotentials a characteristic surface growth loop was recorded in the PSV. The later was submitted to a semiquantitative interpretation assuming instantaneous 3-D nucleation and growth with overlap of growing centres. Kinetics of deposition was investigated under the same conditions using a specially design potential pulse sequence enabling separate estimate of zinc deposition and hydrogen evolution partial currents. Recorded current responses were in line with the hypothesis that the deposition at substrates exhibiting strong interactions proceeds without notable nucleation effects. In the absence of such interactions phenomena typical of three-dimensional nucleation and growth are observed

Anodic deposition of colloidal gold

Colloidal gold solutions were prepared following classical recipes. When electrolysed between graphite electrodes, gold was found to deposit at the anode. The rate of deposition was dependent on the anode potential, on the concentration of gold in the solution, and on the particle size. Deposition seems to be controlled by slow discharge.Dedicated to the memory of Professor Dr. Dr. h. c. Kurt Schwabe