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The morphology, phase and chemical composition of Ni-Co alloy powders electrodeposited from an ammonium sulfate-boric acid containing electrolyte with different ratio of Ni/Co ions were investigated. The ratios of NVCo ions were 1/1, 1/2 and 1/3. The morphology, chemical composition and phase composition of the electrodeposited alloy powders were investigated using AES, SEM, EDS and XRD analysis. Composition of the electrolyte, i.e. the ratio of Ni/Co concentrations was found to influence both, the alloy phase composition and the morphology of Ni-Co alloy powders. At the highest ratio of Ni/Co = 1/1 concentrations typical 2D fern-like dendritic particles were obtained. With a decrease of NVCo ions ratio among 2D fern-like dendrites, 3D dendrites and different agglomerates were obtained. X-ray diffraction studies showed that the alloy powders mainly consisted of the face-centered cubic alpha-nickel phase and hexagonal close-packed alpha-cobalt phase and minor proportions of face-centered cubic alpha-cobalt phase. The occurrence of the latter phase was observed only in the alloy powder with the higher cobalt concentration in electrolyte. The electrodeposition of Ni-Co powders occurred in an anomalous manner.

Electrodeposition of copper by pulsating overpotential (PO) regime in the range of hydrogen co-deposition was examined by scanning electron microscopy. It was found that the increase of the pause-to-pulse ratio produced a strong effect on the morphology of electrodeposited copper. Honeycomb-like copper structures were formed with the pause-to-pulse ratios up to 5. Up to this value of the pause-to-pulse ratio, the diameter of the holes formed by attached hydrogen bubbles was decreasing, while their number was increasing by the application of PO regime. The compactness of the formed honeycomb-like structures was also increasing with the increasing pause duration. The increase of the pause-to-pulse ratio suppressed a coalescence of neighboring hydrogen bubbles. Copper dendrites in the interior of the holes and at their shoulders were formed with the higher pause-to-pulse ratios. The size of the formed dendrites, as well as their number, increased with the increasing pause duration. Depth of holes was decreasing with the increasing pause duration. The increased compactness of the obtained structures was explained by the use of a set of equations describing the effect of square-wave PO on electrodeposition process.

Electrodeposition of copper by pulsating overpotential (PO) regime in the range of hydrogen co-deposition was examined by scanning electron microscopy. It was found that the increase of the pause-to-pulse ratio produced a strong effect on the morphology of electrodeposited copper. Honeycomb-like copper structures were formed with the pause-to-pulse ratios up to 5. Up to this value of the pause-to-pulse ratio, the diameter of the holes formed by attached hydrogen bubbles was decreasing, while their number was increasing by the application of PO regime. The compactness of the formed honeycomb-like structures was also increasing with the increasing pause duration. The increase of the pause-to-pulse ratio suppressed a coalescence of neighboring hydrogen bubbles. Copper dendrites in the interior of the holes and at their shoulders were formed with the higher pause-to-pulse ratios. The size of the formed dendrites, as well as their number, increased with the increasing pause duration. Depth of holes was decreasing with the increasing pause duration. The increased compactness of the obtained structures was explained by the use of a set of equations describing the effect of square-wave PO on electrodeposition process.

Cross-section analysis of copper deposits electrodeposited in the hydrogen co-deposition range at a constant overpotential and in a pulsating overpotential (PO) regime was performed. It was shown that a complete structural analysis of these technologically very important electrodes is impossible without an analysis of their internal structure. An insight into the compactness (or porosity) of the deposits, as well as into the depth of the holes, can only be obtained by this type of analysis.

Technological properties of powders depend on their granulometry and morphology. Very often one method is inadequate for characterization of powder particles. This article studied different methods intended for clear definition of the copper powder granulometric and morphological properties. Quantitative microstructural analysis, sieve analysis, and XRD analysis of copper powder as well as scanning electron microscopy analysis of the copper powder particles were performed. It was determined that selected stereological parameters, such as area, perimeter, and shape factor (roundness) show a linear decreasing dependence of current density, while the morphology was changed from massive to branched 3D dendrites. XRD analysis indicated that the crystallite sizes shows a linearly increasing dependence on current density. The shape factor could be a useful parameter for description of powder morphologies deposited by different regimes.

Polarization characteristics of the electrodeposition processes of Fe powders from sulfate and chloride electrolytes and the morphology of the obtained powders were investigated. The morphology depended on the anion presence in the electrolyte but not on the current density in the investigated range. A characteristic feature of the dendritic powder with cauliflower endings obtained from sulfate electrolyte is the presence of cone-like cavities and the crystallite morphology of the powders Surface. On the other hand, Fe powders electrodeposited from chloride electrolyte appear in the form of agglomerates. A soap solution treatment applied as a method of washing and drying provides good protection from oxidation of the powders.

The electrodeposition of the Ni-Mo-O alloy powders from ammonium chloride containing electrolytes for different Ni/Mo ions concentration ratios was investigated by the polarization measurements. The morphology, chemical composition and phase composition of the electrodeposited Ni-Mo-O alloy powders were investigated using DSC, TGA, SEM, EDS and XRD analysis. According to the EDS results, the powder composition depends on the Ni/Mo ions concentration ratio. However, some deviations in the composition of the as-deposited powders, as the result of the position of the EDS analysis, revealed that the composition of such powders is not homogeneous. The as-deposited alloy powders were nanocrystalline showing only one broad XRD peak around 44 degrees. Their morphology was found to depend on the Ni/Mo ions concentration ratio. After annealing of the Ni-Mo-O powders for 2 h in N-2 atmosphere at 600 degrees C, well-defined crystals for all powders were detected by SEM. The presence of the NiMoO4 phase only or NiMoO4 and MoO3 phases in these powders (XRD), depending on the Ni/Mo ions concentration ratio, was identified. The additional EDS analysis on different recrystallized grains revealed the influence of the annealing on a composition of the alloy powders. (c) 2008 Elsevier Ltd. All rights reserved.

The ionic equilibrium of the species in the CuSO4-H2SO4-H2O system was employed to systematize the conditions of copper electrodeposition leading to the formation of the honeycomb-like structure. The reason why CuSO4 concentrations higher than 0.15 M are unsuitable for the formation of honeycomb-like structures is shown. The range of H2SO4 concentrations enabling the formation of this type of structure was also determined. The conditions leading to the formation of the honeycomb-like structures are: electrodeposition from solutions with lower concentrations of Cu(II) ions (0.15 M CuSO4 and less) in a concentration range from 0.25 to 1.0 M H2SO4, at a temperature of 18.0 +/- 1.0 degrees C and at overpotentials outside the plateau of the limiting diffusion current density at which hydrogen evolution is vigorous enough to change the hydrodynamic conditions in the near-electrode layer.

Formation of irregular deposits by electrodeposition from acid sulfate solutions of various H2SO4 concentrations was examined by the determination of the average current efficiency of hydrogen evolution and by the scanning electron microscopic (SEM) analysis of the copper deposits morphology. Copper dendrites were the dominant morphological form obtained at overpotentials corresponding to the plateaus of the limiting diffusion current density. The number of the formed dendrites was increasing with the decreasing H2SO4 concentration. Holes formed due to the attached hydrogen bubbles were the basic morphological form of electrodeposited copper from all analyzed copper sulfate solutions at overpotentials outside the plateau of the limiting diffusion current density. The honeycomb-like structures (holes of the detached hydrogen bubbles with cauliflower-like agglomerates of copper grains between them) were formed if electrodepositions were performed from 0.15 M CuSO4 in both 0.250 M and 1.0 M H2SO4. On the other hand, aside from the holes and cauliflower-like forms, electrodeposition from 0.15 M CuSO4 in 0.125 M H2SO4 led to the formation of degenerated dendrites and dendritic particles inside channels formed of evolved hydrogen. Holes with shoulders of degenerated dendrites were also formed. The formation of different morphological forms under hydrogen co-deposition was discussed in the terms of hydrodynamic conditions in the near-electrode layer using the values for the break-off diameter of hydrogen bubbles.

The effect of overpotential pulsing and periodic current reversal on the morphology of silver powders was investigated using a scanning electron microscope (SEM). It is shown that the profile of pulses or current reversal determines the micromorphology of the electrodeposited silver particles. Generally, three forms of silver were detected: (1) dendrites, (2) equiaxial crystals (independent and/or agglomerates) and (3) rods. The shape of particle seems to be the result of an interplay between the surface energy and growth kinetics.

Polarization characteristics of the processes of Ni and Co powders and Ni-Co alloy powders electrodeposition from ammonium chloride containing supporting electrolyte and their morphologies are investigated as a function of Ni2+ and Co2+ ions concentrations. It is found that the shape of the polarization curves in all cases is practically defined by the shape of the polarization curve for hydrogen evolution. It is shown that correct polarization curves, as well as the morphology of electrodeposited powders are sensitive to the ratio of Ni2+/CO2+ ions concentration. Characteristic feature of powder particles obtained from chloride containing electrolytes is the presence of cone-shaped cavities. In the case of Ni powder cauliflower and spongy type particles are detected, while Co powder contains only spongy type particles. In all cases of alloy powder formation anomalous type of co-deposition is detected. (c) 2006 Elsevier Ltd. All rights reserved.

The effect of overpotential pulsing and periodic current reversal on the morphology of silver powders was investigated using a scanning electron microscope (SEM). It is shown that the profile of pulses or current reversal determines the micromorphology of the electrodeposited silver particles. Generally, three forms of silver were detected: (1) dendrites, (2) equiaxial crystals (independent and/or agglomerates) and (3) rods. The shape of particle seems to be the result of an interplay between the surface energy and growth kinetics.

In the course of the pasteurization treatment of milk and dairy products the temperature of the technological process is kept at a constant value. The regulation of the temperature is carried out by means of technological water that comes from certain pools cooled to the temperature of 5ºC. the water heated in the process of pasteurization is sent back through steel pipes to the pool where it is cooled to the working temperature. the pools for water cooling are fitted with a bundle of pipes made of plain carbon steel that corrode over the time. the protection of pipes against corrosion is possible to be performed in two ways: by use of inhibitors and by cathodic protection. The application of either method depends on a number of factors. It is cheaper to protect new pipes from corrosion using inhibitors, whereas pipes already attacked by corrosion are more efficiently protected against further corrosion by applying the cathodic protection., U toku postupka pasterizacije mleka i mlečnih proizvoda temperatura tehnološkog procesa održava se na konstantnoj temperaturi. Regulacija temperature se vrši pomoću tehnološke vode koja dolazi iz bazena rashlađena do temperature od 5°C. zagrejana voda iz procesa pasterizacije vraća se cevima u bazen gde se pomoću tečnog amonijaka hladi do radne temperature. U bazenima za hlađenje tehnološke vode nalazi se snop cevi od običnog čelika kroz koji prolazi tečni amonijak, a koje vremenom počinju da korodiraju. Zaštita cevi od korozije je moguća na dva načina: primenom određenih inhibitora korozije i primenom katodne zaštite. Koji će od ova dva načina da bude primenjen zavisi od više faktora. Za nove cevi je jeftinija zaštita od korozije primenom inhibitora. za cevi koje su već u upotrebi ili je kod njih počela korozija, primena katodne zaštite je efikasniji postupak dalje zaštite od korozije.

In this paper the morphology of Ni-Co powders electrodeposited from ammonium sulfate-boric acid containing electrolyte is investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni2+/CO2+ concentration is found to influence both, the alloy phase composition and the morphology of Ni-Co alloy powders. At the highest ratio of Ni2+/Co2+ ions concentration, typical 2D fern-like dendritic particles were obtained. With decrease of Ni2+/Co2+ ions ratio among 2D fern-like dendrites, 3D dendrites and different agglomerates of a size of about 100 mu m, being either compact (typical for pure Co powder) or composed of a large number of small 3D dendrites on their surface were obtained. According to the X-ray analysis, with decreasing Ni2+/Co2+ concentration ratio the amount of f.c.c. beta-Ni phase was found to decrease, while the amount of h.c.p. alpha-Co phase was found to increase being accompanied by the appearance of the f.c.c. Co phase at Ni2+/Co2+ = 0.33.

In this paper the morphology (SEM analysis), the internal structure (cross-section analysis) and the growth mechanism of Ni and Co powders electrodeposited from ammoniacal electrolyte are investigated. It is shown that morphology and the internal structure of those powders are quite different. For Ni powder, all particles are of the same morphology, cauliflower-like type. In the case of Co powder, generally two types of particles are detected: (1) dendrite particles and (2) different types of agglomerates, compact, spongy-like and ball-like ones. The growth mechanism for all agglomerates is based on the fact that with the time of growth the disperse (dendrite) agglomerate is branching in different directions and at the tip of each branch spherical diffusion takes over the planar one, providing conditions for the growth of compact deposit. After some time, these branches form compact deposit all over the agglomerate surface and the same agglomerate further grows as a compact one, until it falls off from the electrode surface. Characteristic of all agglomerates is the presence of deep cavities on their surface and the fern-like dendrites on the bottom for most of these cavities.

In this paper, the morphology and phase structure of Ni-Co powders electrodeposited from ammoniacal electrolyte are investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni(2+)/Co(2+) concentration is found to influence both, the phase structure and the morphology of Ni-Co alloy powders. It is shown that the current density practically does not influence the morphology of Ni-Co alloy powders as well as alloy powder composition. At the highest ratio of the Ni(2+)/Co(2+) ions typical spongy particles were obtained. With the decrease of the Ni(2+)/Co(2+) ions ratio agglomerates of the size of about 100 mu m, composed of a large number of fern-like dendrites on their surface were obtained. At the lowest Ni(2+)/Co(2+) concentration ratio, among more dendritic particles, agglomerates typical for pure Co powder deposition were detected. It is also shown that depending on the Ni(2+)/Co(2+) ratio different types of Ni and Co codeposition could be detected: anomalous and irregular. At the Ni(2+)/Co(2+) ions ratio higher than 1 only beta-Ni phase was detected, while at concentration ratios Ni(2+)/Co(2+) LT 1 h.c.p. alpha-Co phase together with beta-Ni phase was detected in the alloy powder deposit.

In this paper the morphology of Ni-Co powders electrodeposited from ammonium sulfate-boric acid containing electrolyte is investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni2+/CO2+ concentration is found to influence both, the alloy phase composition and the morphology of Ni-Co alloy powders. At the highest ratio of Ni2+/Co2+ ions concentration, typical 2D fern-like dendritic particles were obtained. With decrease of Ni2+/Co2+ ions ratio among 2D fern-like dendrites, 3D dendrites and different agglomerates of a size of about 100 mu m, being either compact (typical for pure Co powder) or composed of a large number of small 3D dendrites on their surface were obtained. According to the X-ray analysis, with decreasing Ni2+/Co2+ concentration ratio the amount of f.c.c. beta-Ni phase was found to decrease, while the amount of h.c.p. alpha-Co phase was found to increase being accompanied by the appearance of the f.c.c. Co phase at Ni2+/Co2+ = 0.33.

In this paper, the morphology and phase structure of Ni-Co powders electrodeposited from ammoniacal electrolyte are investigated as a function of alloy powder composition. Composition of the electrolyte, i.e. the ratio of Ni(2+)/Co(2+) concentration is found to influence both, the phase structure and the morphology of Ni-Co alloy powders. It is shown that the current density practically does not influence the morphology of Ni-Co alloy powders as well as alloy powder composition. At the highest ratio of the Ni(2+)/Co(2+) ions typical spongy particles were obtained. With the decrease of the Ni(2+)/Co(2+) ions ratio agglomerates of the size of about 100 mu m, composed of a large number of fern-like dendrites on their surface were obtained. At the lowest Ni(2+)/Co(2+) concentration ratio, among more dendritic particles, agglomerates typical for pure Co powder deposition were detected. It is also shown that depending on the Ni(2+)/Co(2+) ratio different types of Ni and Co codeposition could be detected: anomalous and irregular. At the Ni(2+)/Co(2+) ions ratio higher than 1 only beta-Ni phase was detected, while at concentration ratios Ni(2+)/Co(2+) LT 1 h.c.p. alpha-Co phase together with beta-Ni phase was detected in the alloy powder deposit.

The apparent density and flowability of copper powder are related to the structure of powder particles and the reversing current (RC) regimes. It was shown that the apparent density of the powders increases with the increase in the compactness of particles, hence with the increase in the frequency of RC and with the decrease in the cathodic to anodic time ratio.

The structure of powder particles was analysed by considering their cross sections. It was shown that the structure of powder particles of nonsieved flowing powders is sufficiently dense to produce a continuous surface, which does not allow the particles to jam and hence permits the free flow of nonsieved powder. It was also shown that the representative powder particle, the elementary cell of which can be presented by a 3D-cross, describes the properties of the powder relative to its flowability well.

The structure of powder particles was analysed by considering their cross sections. It was shown that the structure of powder particles of nonsieved flowing powders is sufficiently dense to produce a continuous surface, which does not allow the particles to jam and hence permits the free flow of nonsieved powder. It was also shown that the representative powder particle, the elementary cell of which can be presented by a 3D-cross, describes the properties of the powder relative to its flowability well.

The structure of the surface of copper powder particles is discussed and correlated with the lowest apparent density at which copper powder can still flow. It is shown that such structures can be easily obtained in the electrodeposition of powders in reversing current regimes., Razmatrana je struktura površine čestica bakarnog praha i korelisana s najmanjom nasipnom masom pri kojoj bakarni prah još uvek može da teče. Pokazano je da se takva struktura može lako dobiti elektrohemijskim taloženjem praha u režimu reversne struje.

An analysis of the effects of the shape, surface structure and size distribution of particles on the flow ability of the copper powder was performed. It is shown that the most important property of the particles of a powder, regarding the flow ability of the powder, is the surface structure of the particles., Izvedena je analiza uticaja oblika, površinske strukture i raspodele veličina čestica na tečljivost bakarnog praha. Pokazano je da površinska struktura predstavlja najvažnije svojstvo čestice praha u odnosu na njegovu tečljivost.

One of the most important properties of copper powder is its flow ability which depends on the shape and the structure of the powder particles. A procedure for the determination of a representative powder particle permitting the free flow of copper powder is proposed., Jedno od najvažnijih svojstava bakarnog praha je njegova tečljivost, koja zavisi od oblika i strukture čestica praha. Predložen je postupak za određivanje reprezentativne čestice praha koja obezbeđuje slobodno tečenje bakarnog praha.

The possibility of depositing copper powders with different apparent density by changing the shape of reversing current wave is shown. The morphology and crystallinity of powder particles can be varied considerably by changing shape of the reversing current wave and, hence, the apparent density of powders. The relation of apparent density with particle morphology and structure was illustrated., U radu je pokazana mogućnost dobijanja bakarnih prahova različitih nasipnih masa promenom oblika talasa reversne struje. Uspostavljena je zadovoljavajuća veza između morfologije i strukture čestica praha bakra i nasipne mase praha.

The preferred orientations of copper deposits obtained from acid sulfate solutions were examined. Mat deposits obtained in the absence of the additives and in the presence of disodium 2-naphthol-3,6-disulfonic acid possessed a weak (200) and (220) preferred orientation, respectively. Bright deposit obtained with thiourea only had (111)orientation, while the deposit obtained with mixture thiourea/disodium 2-naphthol-3,6-disulfonic acid exhibited predominant (111) orientation. Bright copper deposits had the preferred orientation in the closest-packed plane of f.c.c. copper lattice, i.e. in the (111)plane.

The role of defects on a substrate surface during the initial stages of nucleation and growth of Ag deposited electrochemically and physically on highly oriented pyrolytic graphite (HOPG) has been observed ex situ by scanning tunneling microscopy (STM). The silver was electrodeposited under current controlled electrochemical conditions at 26 mu A/cm(2), which corresponded to a deposition rate of 0.1 monolayers (ML) per second. For comparison, physical deposition of Ag on HOPG was performed by DC Ar+ ion sputtering, at the same deposition rate and for the same deposition times. In both cases, Ag grows in an island growth mode, but the distribution of the islands appears to be quite different. In physical deposition, the Ag islands are almost homogeneously distributed over the substrate surface and a slight accumulation of islands on steps does not contribute significantly to the overall morphology. This indicates the crucial role of point defects on the substrate in the initial stages of nucleation. In electrochemical deposition, more lined defects are observed after a flow of current, and their role in the beginning of the nucleation is more pronounced. Lined defects are responsible for the string-like shaped domains of deposited atoms. Also, the existence of string-like shaped nucleation exclusion zones is indicated. The problem of the formation of nucleation exclusion zones, which appear only in electrochemical deposition, has been reconsidered and a new explanaton of their formation is given. A mathematical model for the calculation of the radius of the nucleation exclusion zone has been developed., Uloga defekata na površini supstrata u početnim stadijumima nukleacije i rasta Ag deponovanog elektrohemijski i fizički na visoko orijentisani grafit (HOPG) je ispitivana ex situ tehnikom skanirajuće tunelirajuće mikroskopije (STM). Elektrodepozicija srebra je izvedena galvanostatski, sa gustinom struje od 26 µA/cm2 , što je odgovaralo brzini depozicije od 0,1 monosloja (ML) po sekundi. Poređenja radi, fizička depozicija Ag na HOPG je izvedena spaterovanjem sa DC Ar+ jonima, sa istom brzinom depozicije i za ista vremena depozicije. U oba slučaja je zapažen ostrvski rast Ag, ali se ispostavilo da je raspodela ostrva po površini sasvim različita. Nakon fizičke depozicije, ostrva srebra su skoro homogeno raspore|ena po površini, i slaba akumulacija ostrva na stepenicama ne doprinosi značajno ukupnoj morfologiji. Ovo ukazuje na presudan značaj tačkastih defekata na površini supstrata na početne stadijume nukleacije. Nakon elektrohemijske depozicije, primećeno je više linijskih defekata na samoj površini supstrata, i pokazano je da je njihova uloga u početku nukleacije mnogo izraženija. Linijski defekti su odgovorni za nastajawe trakastih oblasti sa deponovanim atomima. Takođe, ukazano je na postojanje trakastih zona isključenja. Problem zona isključenja u toku elektrohemijske depozicije je ponovo razmatran i ponu|eno je novo objašnjenje za njihovo nastajanje. Dat je matematički model za izračunavanje prečnika zone isključenja.

The initial stage of thin surface metal film formation on inert substrate is considered. The simultaneous action of both active centers and nucleation exclusion zones was taken into consideration when discussing the saturation nucleus density. The saturation nucleus density increases with increasing number of active centers and decreasing the radii of nucleation exclusion zones (enhancing the thin metal film formation). At one at the same deposition current density deposition overpotential increases with decreasing deposition process exchange current density, leading to the increase in the number of active centers and to decrease of crystallization overpotential and radii of nucleation exclusion zones. Because of this compact surface metal film will be formed at a lower quantity of electrodeposited metal with a decrease in exchange current density.

It is shown that the critical overpotential of dendritic growth initiation increases with increasing copper concentration under identical hydrodynamic conditions, as well as with increasing rotation speed to the rde (rotating disc electrode).

The effect of the shape of the current wave and frequency in silver deposition by pulsating and reversing currents on the morphology of powder particles were investigated. The possibility of obtaining particles with different properties, depending on conditions of electrolysis, was demonstrated.

It is well known that the deposition conditions such as bath composition, hydrodynamic regime, temperature, current density, exhibit a strong effect on the grain size and the morphology of electrodeposited metal powder particles [1, 2]. On the other hand it has been shown recently [3] that similar effects can be obtained by changing only the shape of the current overpotential waves in metal powder electrodeposition at a periodically changing rate with other conditions constant. This is in accordance with Ibl's observation [4] that, at one and the same average deposition rate (current density), it is possible to create a number of different deposition conditions in the pulsating regimes. In square-wave pulsating overpotential electrolysis the overpotential amplitude, frequency of pulsation and pause-to-pulse ratio can be varied independently. The purpose of this work is to discuss the effect of the last parameter on the morphology of electrodeposited metal powder particles on the basis of the existing experimental evidence.

Dеndritični rаst trеbа biti zаpоčеt pri istim uslоvimа i iz istih rаzlоgа kојi dоvоdе dо nеdеndritičnе аmplifikаciје bilо kоје pоvršinskе nеprаvilnоsti. Prinоs dеndritičnоg tаlоgа vаrirа sа prеnаpеtоšću dеpоziciје. Dеndriti sе nе fоrmirајu pri prеnаpеtоstimа mаnjim оd izvеsnе vrеdnоsti ηi. Pоvеćаnjе prеnаpеtоsti dоvоdi dо pоvеćаnjа prinоsа dеndritičnоg dеpоzitа svе dо prеnаpеtоsti pri kојој је sаv mеtаl dеpоnоvаn u оbliku dеndritа. Prеnаpеtоst ηc, pri kојој sе nе fоrmirа kоmpаktаn mеtаl, а dеndritični rаst zаpоčinjе bеz indukciоnоg vrеmеnа, dеfinisаnа је kао kritičnа prеnаpеtоst fоrmirаnjа prаhа. Pri pоtеnciоstаtskоm tаlоžеnju dvе kritičnе vrеdnоsti prеnаpеtоsti mоgu biti оdrеđеnе: kritičnа prеnаpеtоst zа pоčеtаk dеndritičnоg rаstа, ηi , i kritičnа prеnаpеtоst zа fоrmirаnjе prаhа, ηc. U istо vrеmе је pоkаzаnо dа sе dоbiјајu dеndritični tаlоzi pri svim prеnаpеtоstimа izmеđu ηi i ηc nаkоn dоvоlјnо dugоg indukciоnоg vrеmеnа. U оvој tеzi је istаknutо dа sе ηi mоžе оdrеditi iz I-t zаvisnоsti nа оsnоvu trаnsfоrmаciја mеhаnizmа rаstа unutаr difuzоnоg slоја; tаkоđе, mеtоd оdrеđivаnjа vrеmеnа, u kоmе аprоksimаciја δ>>h vаži, kао i mеtоd оdrеđivаnjа indukciоnоg vrеmеnа dеndritičnоg rаstа. S drugе strаnе, pri pоtеnciоstаtskim uslоvimа tаlоžеnjа, dеndritični i prаškаsti dеpоziti sе mоgu dоbiti pri gustinаmа struје nižim оd grаničnе difuziоnе struје pri dоvоlјnо dugim vrеmеnimа tаlоžеnjа. Оvо niје mоgućе u slučајu gаlvаnоstаtskоg tаlоžеnjа. Kоnаčnо, u оvој tеzi su оdrеđеnе: • Kritičnе prеnаpеtоsti i kritičnе gustinе struје zа pоčеtаk dеndritičnоg rаstа i fоrmirаnjе prаhа pri pоtеnciоstаtskim i gаlvаnоstаtskim uslоvimа tаlоžеnjа; • Indukciоnа vrеmеnа fоrmirаnjа dеndritičnоg rаstа pri pоtеnciоstаtskim i gаlvаnоstаtskim uslоvimа tаlоžеnjа; Меhаnizаm fоrmirаnjа prаhоvа mеtаlа, zаsnоvаn nа tеоriјаmа dеndritičnоg rаstа i nеdеndritičnоg pоvеćаnjа pоvršinskih nеprаvilnоsti pri pоtеnciоstаtskоm tаlоžеnju., Dendritic growth should be initiated under the sаme conditions and for the same reasons that lead to the nondendritic amplification of any surface irregularity. The yield of dendritic deposit varies with the overpoptential of deposition. Dendrites are not formed at overpotentials smaller than a certain value ηi. Increasing overpotential leads to an increase in the yield of dendritic deposit up to the overpotential at which all metal is deposited in the dendritic form. The overpotential ηc, at which compact metal is not formed and dendritic growth starts without an induction time, was defined as the critical overpotential of powder formation. In potentiostatic deposition two critical values of overpotential can be determined: critical overpotential for dendrite growth initiation, ηi., and critical overpotential for powder formation, ηc. It was shown in the same time, that dendritic deposits are obtained at all overpotentials between ηi and ηc after sufficiently long induction times. In this thesis it was pointed out that ηi can be determined from I-t dependences on the basis of the transformation of the growth mechanism inside the diffusion layer; also, the method of determination of the time, in which the approximation δ>>h is valid, as well as a method of determination of the induction time of dendritic growth. On the other hand, in potentiostatic deposition dendritic and powdered deposits can be obtained at current densities lower than limiting diffusion one at sufficiently long deposition times. This is not possible in the caseof galvanostatic deposition. Finally, in this work are determined: • Critical overpotentials and critical current densities for dendrite growth initiation and powder formation in potentiostatic and galvanostatic deposition; • Induction times of dendritic growth formation in potentiostatic and galvanostatic deposition; The mechanism for metal powder formation, based on the theories of dendritic growth and nondendritic surface roughness ampli

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.

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.