Formation Of Nickel Sulfide Research Articles

Investigation of the characteristics of sulfurized electrochromic Ni(OH)2-PVA films deposited on transparent substrates

Obtaining new types of composite coatings for various purposes is the most important direction in chemistry. The synthesis of composite hydroxide-sulfide compounds can be useful in various areas of applied electrochemistry. Using a simple two-step method, thin films composed of nickel hydroxide sulfide-polyvinyl alcohol were formed. The production of nickel hydroxide sulfide-polyvinyl alcohol composite was carried out by holding the nickel hydroxide-polyvinyl alcohol composite coating formed on the glass electrode with an electrically conductive substrate in a solution of 0.03 M Na2S for 10 minutes. The formation of nickel sulfide on the surface of nickel hydroxide was shown indirectly. It was shown that there were no changes in morphology after the treatment of the electrode in sodium sulfide solution. As a result of the treatment, the electrochemical and electrochromic characteristics changed. There was some deterioration in the average coloration depth from 55 % to 49 % for the electrode containing nickel sulfide. The electrochemical characteristics also deteriorated slightly after the formation of the sulfide film, namely, the specific capacitance, which went to the passage of anodic and cathodic processes. However, the capacitance efficiency increased from 83 % to 87 % for the sulfide-treated film. Despite this, this simple method is considered to be potentially promising for the formation of electrodes for use in other electrochemical devices. In addition, due to the treatment in a sodium sulfide solution, it became possible to roughly determine the size of the nickel hydroxide clusters in the nickel hydroxide-polyvinyl alcohol composite coating. These clusters did not exceed 430 nm in size, which was almost equal to the lower limit of the wavelength of the visible spectrum.

Microextrusion printing of gas-sensitive planar anisotropic NiO nanostructures and their surface modification in an H2S atmosphere

The formation of NiO nanosheets (average CSR size is 10.4 nm) through the hydrothermal method using a heteroligand complex of composition [Ni(C5H7O2)2-x(C4H9O)x] as a precursor was studied. Using the obtained oxide nanopowder and pneumatic microextrusion printing, NiO coating was applied to the surface of a specialized Pt/Al2O3/Pt chip, and chemosensor properties were investigated in the detection of various gases. It was determined that when CO, NH3, H2, and NO2 were detected, the conductivity of the NiO coating changed from p- to n-type with increasing temperature. Using XPS, XRD, and Raman spectroscopy, it was found that upon exposure to H2S, the surface of NiO coating partially undergoes irreversible chemical modification with the formation of nickel sulfide, resulting in a significant change in the sensory properties of the coating. It was shown that the formed receptor material exhibits the greatest response when detecting H2S, and the proposed approach, combining hydrothermal synthesis and printing technology, is promising for the creation of modern components of resistive gas sensors.

Degradation behavior of Ni-YSZ anode-supported solid oxide fuel cell (SOFC) as a function of H2S concentration

This study investigated the effect of H2S concentration (5, 10 and 50 ppm) on the degradation and performance of Ni-YSZ anode supported solid oxide fuel cells. When supplied with hydrogen fuel containing H2S, the cell voltage dropped rapidly, and with increasing H2S concentration, voltage drop % increased (due to higher sulfur coverage on the Ni surface) and saturated more rapidly. A high concentration (50 ppm) of H2S led to an additional, slow rate voltage loss. In all cases, cell performance did not completely recover even after being supplied with H2S-free hydrogen fuel, because of the incomplete desorption of sulfur from the Ni surface. After the performance tests, nickel sulfides were detected on the Ni surface by Raman spectra, which were produced by the reaction of the remaining adsorbed sulfur with Ni during the cooling process. This indicates that the formation of nickel sulfides was not responsible for the secondary voltage drop. SEM/EDS analyses combined with FIB revealed that the reason for the additional 2nd drop was Ni oxidation; at a high sulfur coverage ratio (50 ppm), the outer layer of the Ni particle was oxidized by oxygen ions transported from the electrolyte. This indicates that H2S concentration as well as current density is a critical factor for Ni oxidation, and gives rise to the second voltage drop (irreversible cell degradation). The present work showed that the degradation behavior and phenomenon can differ significantly depending on the concentration of H2S, i.e., permanent changes may or may not occur on the anode (such as Ni oxidation) depending upon H2S concentration.

Synthesis, structural studies and antimicrobial activities of manganese, nickel and copper complexes of two new tridentate 2‑formylpyridine thiosemicarbazone ligands

Two new thiosemicarbazone ligands {HL1 = 4‑(2‑chlorophenyl)‑1‑((pyridin‑2‑yl)methylene)thiosemicarbazide and HL2 = 4‑(2‑methoxyphenyl)‑1‑((pyridin‑2‑yl)methylene)thiosemicarbazide} were synthesized. With Mn2+, Ni2+ and Cu2+, the metal complexes [Mn(L1)2] 1, [Ni(L1)Cl] 2, [Cu(L1)Cl] 3, [Mn(L2)2] 4, [Ni(L2)Cl] 5 and [Cu(L2)Cl] 6 have been isolated and their structures were assigned based on their CHNS contents, magnetic moments, spectral (IR, UV–Vis) data and DMF solution molar conductivities. The complexes are of varied structures, spanning from octahedral manganese complexes to square planar nickel and copper complexes or even square pyramidal geometries and adopt different topologies, such as monomers or dimers. Further studies on complex 2 and 3 were performed; single crystals of 2 and 3 were grown and analyzed by XRD technique. Additionally the thermal degradation mechanism of 2 in nitrogen atmosphere has been studied, being observed the formation of nickel sulfide as a final product at temperature of around 700 °C. All ligands and complexes have been tested against fungal and bacterial cultures and, in many cases, the biological activity of the free ligands is enhanced upon coordination.

Effect of Current Collector on Performance of Li‐S Batteries

Efficient, scalable energy storage systems such as lithium‐sulfur batteries have become a technological bottleneck for the growing energy demands in automotive sector. To realize the ultimate performance of such batteries, the effect of all structural components of the batteries has to be considered. Nowadays the effect of current collectors appears to be less explored in the battery research field. Therefore, this report draws attention to exploit different current collectors such as, copper, aluminum, platinum, and nickel. It is found that nickel has a profound effect on the performance of the lithium‐sulfur batteries by direct involvement in electrochemical reaction with soluble polysulfides leading to the formation of nickel sulfide. The formation of such unwanted species can be reduced dramatically by silane‐surface modification. Aluminum and platinum, on the other hand, have been found to be the most inert collector toward the cycle performance because of nonreactivity within the potential window.

Long term performance degradation analysis and optimization of anode supported solid oxide fuel cell stacks

The main objective of this work is minimizing the cost of electricity of solid oxide fuel cell stacks by decelerating degradation mechanisms rate in long term operation for stationary power generation applications. The degradation mechanisms in solid oxide fuel cells are caused by microstructural changes, reactions between lanthanum strontium manganite and electrolyte, poisoning by chromium, carburization on nickel particles, formation of nickel sulfide, nickel coarsening, nickel oxidation, loss of conductivity and crack formation in the electrolyte. The rate of degradation mechanisms depends on the cell operating conditions (cell voltage and fuel utilization). In this study, the degradation based optimization framework is developed which determines optimum operating conditions to achieve a minimum cost of electricity. To show the effectiveness of the developed framework, optimization results are compared with the case that system operates at its design point. Results illustrate optimum operating conditions decrease the cost of electricity by 7.12%. The performed study indicates that degradation based optimization is a beneficial concept for long term performance degradation analysis of energy conversion systems.

Template-free synthesis of nickel sulfides hollow spheres and their application in dye-sensitized solar cells

NiS and NiS2 hollow spheres were synthesized simultaneously by a facile solvothermal route without the help of any template or surfactant. The Ni/S molar ratio in the reactants plays a significant role in the formation of nickel sulfides with different stoichiometric ratio. The microstructures and morphologies of the NiS and NiS2 were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption isotherm measurements. In addition, the electrochemical performances of dye-sensitized solar cells based on these two types of nickel sulfides counter electrodes (CEs) were investigated in detail. It is found that NiS2 CE exhibit higher electrocatalytic activity than NiS CE for the reduction of triiodide. As a consequence, the DSSC with NiS2 CE generates higher power conversion efficiency (7.13%) than that with NiS CE (6.49%).

Stability and resistance of nickel catalysts for hydrodeoxygenation: carbon deposition and effects of sulfur, potassium, and chlorine in the feed

The long term stability and resistance toward carbon deposition, sulfur, chlorine, and potassium of Ni/ZrO2 as a catalyst for the hydrodeoxygenation (HDO) of guaiacol in 1-octanol (as a model compound system for bio-oil) has been investigated at 250 °C and 100 bar in a trickle bed reactor setup. Without impurities in the feed good stability of the Ni/ZrO2 catalyst could be achieved over more than 100 h of operation, particularly for a sample prepared with small Ni particles, which minimized carbon deposition. Exposing the catalyst to 0.05 wt% sulfur in the feed resulted in rapid deactivation with complete loss of activity due to the formation of nickel sulfide. Exposing Ni/ZrO2 to chlorine-containing compounds (at a concentration of 0.05 wt% Cl) on-stream led to a steady decrease in activity over 40 h of exposure. Removal of the chlorine species from the feed led to the regaining of activity. Analysis of the spent catalyst revealed that the adsorption of chlorine on the catalyst was completely reversible, but chlorine had caused sintering of nickel particles. In two experiments, potassium, as either KCl or KNO3, was impregnated on the catalyst prior to testing. In both cases deactivation was persistent over more than 20 h of testing and severely decreased the deoxygenation activity while the hydrogenation of guaiacol was unaffected. Overall, sulfur was found to be the worst poison, followed by potassium and then chlorine. Thus, removal/limitation of these species from bio-oil is a requirement before long term operation can be achieved with this catalyst.

Nickel-Indium Sulphide Core-Shell Nanostructures obtained by Spray-ILGAR Deposition

®depositions of thin indium sulphide films. The effect of deposition temperature was also investigated. For low number of deposition cycles, results showed complete and uniform covering of metal over the entire length of NWs, with formation of Ni - In2S3 core-shell structures. However, with increasing number of deposition cycles films became uneven and crusty, especially at higher temperatures, owing to the simultaneous formation of nickel sulfide. This drawback was almost eliminated doubling the duration of the spray step.

Sulfur poisoning of Rh–Ni catalysts during steam reforming of sulfur-containing liquid fuels

Sulfur poisoning during steam reforming is considered a significant barrier to synthesizing an active and stable catalyst. The present study investigates the mechanism of sulfur poisoning on a rhodium promoted nickel catalyst surface and uses the results to demonstrate how rhodium addition improves sulfur tolerance. Catalysts containing Ni and/or Rh supported on γ-alumina were synthesized and evaluated in a fixed-bed tubular reactor at a steam to carbon ratio of 3, 1000 ppm of sulfur, a temperature of 800 °C and atmospheric pressure. Hydrogen yield was used to evaluate catalyst activity while H2S in the effluent was monitored to determine the amount of sulfur trapped on the catalyst surface. In order to understand the mechanism of sulfur poisoning, fresh and used catalysts were characterized using pulse chemisorption, BET surface area analysis, transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Visual probing of the catalyst microstructure using TEM coupled with EDS revealed preferential adsorption of sulfur on nickel particles as multiple surface adlayers. There was no bulk nickel sulfide formation. Using pulse chemisorption studies and sulfur yields, it was shown that addition of rhodium to the nickel catalyst helps in lowering the amount of sulfur adlayers on the catalyst surface, thereby leading to improved sulfur tolerance, and this phenomenon was attributed to the close interaction of rhodium with nickel including the possibility of Rh–Ni alloy formation.

Unsupported NiMoW sulfide catalysts for hydrodesulfurization of dibenzothiophene by thermal decomposition of thiosalts

A family of unsupported NiMoW sulfide catalysts have been prepared by thermal decomposition of mechanically ground tetramethylammonium thiomolybdotungstate and Ni(NO 3) 2 for hydrodesulfurization of dibenzothiophene. The materials were characterized by Fourier transformation infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, X-ray diffraction, N 2 physorption, scanning electron microscopy, and transmission electron microscopy. The results showed that structures and properties of unsupported NiMoW sulfides depend on nickel content and decomposition condition. XRD revealed a decrease in the stacking along the c direction of the MoS 2 and/or WS 2 crystalline structures as the nickel content was increased, consistent with a higher dispersion of the metal sulfides observed by electron microscopy. The low nickel content in Ni 0.5MoWS y catalyst gave a positive effect on the hydrodesulfurization of dibenzothiophene, as indicated by the greatly increased specific catalytic activity per unit surface area. In contrast, the high nickel content in Ni 1.5MoWS y catalyst showed a negative effect due to the formation of nickel sulfides. Ni 0.5MoWS y catalyst showed the highest activity in the hydrodesulfurization reaction compared to other samples. The results further suggest that unsupported NiMoW sulfide catalysts may be promising candidates for wide application in hydrotreating of fuel oil.

ChemInform Abstract: Synthesis of Nickel Sulfide Powders by Thioacetamide in the Presence of Urea.

Additions of urea were found to increase the yield of nickel sulfide formation from acidic solutions of thioacetamide. Two precipitation mechanisms were identified : hydrolysis and direct reaction between nickel and thioacetamide. Hydrolysis-controlled precipitation is evident with low initial pH. The direct reaction is dominant at high initial pH. Nucleation proceeds by a direct reaction between nickel and thioacetamide. The role of urea in precipitation of nickel was found to be twofold. Urea increases the rate of thioacetamide decomposition, thus increasing the concentration of H 2 S form. Secondly, decomposition increases the pH of the solution, which in turn increases the relative concentration of S = ions. Agglomeration of particles was more evident in the powders obtained in the presence of urea.

Nickel sulfide formation at low temperature: initial precipitates, solubility and transformation products

Environmental context Remediation technologies often rely on manipulation of redox conditions or natural redox processes to favour microbial sulfate-reduction and mineral sulfide formation for treatment of inorganic contaminants in groundwater, including nickel. However, few data are available on the structural properties, solubility and mineral transformation processes involving nickel sulfides. These data are needed in order to constrain the long term performance of groundwater remediation efforts. Abstract The formation of nickel sulfides has been examined experimentally over the temperature range from 25 to 60°C. At all conditions studied, hexagonal (α-NiS) was the initial precipitate from solution containing Ni2+ and dissolved sulfide. Freshly precipitated nickel sulfide possesses significant residual Ni–O coordination as revealed by X-ray absorption spectroscopy. With progressive aging, residual Ni–O coordination is replaced by Ni–S coordination. The formation of millerite (β-NiS, rhombohedral) was not detected in any of the synthesis experiments. In the presence of elemental sulfur, hexagonal NiS converted to polydymite (Ni3S4) and vaesite (NiS2). Thus, conversion of nickel monosulfide to thiospinel and disulfide structures appears to be redox dependent, analogous to aging and transformation processes of iron sulfides. In the absence of elemental sulfur or with only hydrogen sulfide or bisulfide present, transformation of hexagonal NiS was not observed after 1680 h at 60°C. Low-pH solubility experiments yielded a solubility product for hexagonal NiS of log Ks0 = –2.69 ± 0.26. Solubility data at pH > 3 suggest that Ni–bisulfide complexation is important in controlling the solubility of Ni in sulfidic solutions.

Influence of Fuel Contaminants on SOFC Operation: Effect on Performance and Degradation Mechanisms

SOFCs can be operated with biosyngas, but this fuel contains inorganic species, which act as contaminants for SOFCs. One of the most active is H2S, but salts like KCl can also affect SOFCs. Experiments have been performed to evaluate the interaction between SOFC anode material and these species. A synthetic gas representative of biosyngas containing H2S and KCl was circulating over Ni-YSZ pellets at 800{degree sign}C. It is shown that both H2S and KCl affect the Ni-YSZ anode by forming surface deposits. When KCl is present, K is detected at the surface. In the case of H2S, nickel sulfides are locally formed. In addition SOFCs have been operated with hydrogen containing H2S. The electrochemical behaviour of the SOFC confirms an effect of H2S, showing degradation even for the lowest H2S level tested. This degradation is partly irreversible, which is consistent with the formation of nickel sulfides.

Study of Sulfur-Nickel Interactions Using Raman Spectroscopy

Ni-YSZ cermet and NiO-YSZ composite are exposed to hydrogen containing different concentrations of H 2 S to identify the phases formed under various conditions using Raman spectroscopy and x-ray diffraction (XRD). For samples exposed to hydrogen containing 100 ppm H 2 S at 727°C for 5 days, XRD analysis was unable to detect any changes but several new vibration modes were detected using Raman spectroscopy. These vibration modes are most likely associated with either the adsorption of H 2 S on the surfaces of these materials or the formation of nickel sulfides, suggesting that Raman spectroscopy could be a powerful tool for in-situ study of sulfur poisoning of SOFC anodes. For NiO-YSZ composite samples exposed to hydrogen containing 10% H 2 S at 950°C for 5 days, all NiO particles were converted to nickel sulfide, and vibration modes of NiS were detected using Raman spectroscopy.

Amperometric determination of sulfide at a pre-oxidised nickel electrode in acidic media.

The electrochemical response of a pre-oxidised nickel electrode to increasing additions of sulfide has been examined and shown to produce a stripping-like voltammetric wave. A mechanism is described based on the formation of nickel sulfide at the electrode surface from a non-electroactive nickel oxide layer. The analytical utility of the approach has been examined and a linear range from 1 to 140 microM and a limit of detection of 0.8 microM is achievable, depending on the accumulation time.

Re Os ISOTOPIC STUDY OF KOMATIITIC VOLCANISM AND MAGMATIC SULFIDE FORMATION IN THE SOUTHERN ABITIBI GREENSTONE BELT, ONTARIO, CANADA

We have investigated the Re–Os isotope geochemistry of 2.7-Ga metakomatiitic flows and associated Ni–Cu sulfide deposits from Alexo, Texmont and Hart in the Abitibi greenstone belt of Ontario in order to refine the thermal erosion model and evaluate the superimposed effects of metamorphism and hydrothermal alteration on ore environments and non-ore environments. Although the geochemical characteristics of these komatiites have led to the belief that these lavas were uncontaminated, radiogenic Os isotopic compositions (γOs = +20.2 and +33.2) obtained from well-preserved komatiites and olivine separates suggest that the Alexo flow has been contaminated by crust-derived material. These data are compatible with the trace-element enrichment observed in melt inclusions trapped within olivine. Redistribution of Os and Re did occur at least at the mineral scale and most likely during the Grenville orogeny. Hydrothermal fluids were channeled along the contact between the komatiites and their basement, and were responsible for the remobilization of Re or Os (or both) within the sulfides at Alexo and Hart. Matrix and disseminated sulfides from Texmont are located within the pile of cumulates and seem to have escaped this localized alteration. Although the Abitibi sulfides have experienced various degrees of metamorphism (from prehnite–pumpellyite to low amphibolite facies), the initial Re–Os isotopic composition of the flows appears to have been preserved at the whole-rock scale. Re–Os isotopic heterogeneity of the Abitibi sulfides is best explained by variable R -factor of the sulfides. Re and Os concentrations and Os isotopic heterogeneity of the Abitibi sulfides are consistent with the current model of nickel sulfide formation, which implies that the assimilation of sulfidic sedimentary rocks was the trigger for sulfide saturation.

Evidence for the Existence of a Late-Metal Terminal Sulfido Complex

The transition-metal-sulfur bond is an important linkage in both biological systems1 and industrial catalysts.2 Nickel sulfides, in particular, are key components of natural hydrogenases3 and are active promoters in current hydrotreating catalysts.2 Understanding the nature of the metal-sulfur linkages at active sites can offer insight on ways to improve catalysis and provide a better understanding of cluster formation and cluster interconversion reactions in general. Scheme 1 shows three possible binding modes of a sulfur atom to supported nickel. While numerous examples of binding modes A4 and B5 can be found throughout the literature, there exists no sound evidence for a terminal sulfido complex such as C in the solution phase.6 Additionally, there have been only a few cases for the group 9 and 10 metals where the intermediacy of a terminal sulfido complex has been postulated,7 and there has been no experimental evidence to support the existence of such a species. Terminal sulfido complexes of the earlier transition-metals are well-known, and display a wide range of reactivity.8 Late-metal analogues might then be anticipated to afford similarly rich chemistry. Raney nickel, and homogeneous nickel complexes,9 have been found to desulfurize a variety of organosulfur substrates. The fate of the sulfur atom in these reactions is usually nickel sulfide, thereby preventing catalysis under traditional laboratory conditions. A number of recent reports from our group,10 however, indicate that sulfur can be extracted from organic compounds without the formation of nickel sulfide. These results prompted us to further explore the mechanism of these unique desulfurizations, and to systematically investigate the intermediacy of the three possible binding modes of a sulfur atom to nickel (Scheme 1). In these efforts we have found kinetic and structural evidence that support the chemical feasibility of binding mode C, namely a terminal sulfido complex at nickel. Initial studies were directed toward finding an efficient way to prepare a nickel sulfido complex. Bergman has reported routes to transient [Cp2TidS] and [Cp2ZrdS] using Cp2Ti(SH)H and Cp2Zr(SH)I, respectively. The synthetic strategy that we found to be successful with nickel was based on two very different but related findings. It was discovered by Bergman and co-workers that thermolysis of Cp*2Zr(OH)(Ph) led to the loss of benzene and formation of the terminal oxo complex, which was subsequently trapped by a variety of substrates.12,13 Additionally, Osakada and co-workers found that thermolysis of trans-Ni(Ar)(SH)(PEt3)2 (Ar ) aryl ligand) led to decomposition of the metal with formation of Ar-H and SdPEt3. Curiously, no Ar-SH was formed.14 We wondered whether the loss of arene in this instance was concomitant with the formation of a transient terminal sulfido complex, mimicking the zirconium-oxo chemistry. We therefore prepared a nickel complex containing chelating phosphines and cis-(Ar)(SH) groups to examine if elimination of arene would readily occur. Chelating phosphines were used since recent reports have shown that [L2M(μ-S)]2 complexes (where L2 is a chelating ligand) are thermally quite stable.10b,15 Li2Ni(SH)(Ph) (1a and 1b) [L2 ) dippe (1,2-bis(diisopropylphosphino)ethane) (1a) and dcpe (1,2-bis(dicyclohexylphosphino)ethane) (1b)] were prepared and their thermolysis behavior was studied in solution. Nickel thiols of type 1 were synthesized by the addition of NaSH to L2Ni(Cl)(Ph). It was found that mild heating of 1 in THF solutions led to loss of benzene (1 equiv observed by 1H NMR spectroscopy) and production of the bridged sulfido dimers 2 in quantitative yields by NMR spectroscopy (eq 1). Complex

Re-Os Isotopic Study of Komatiitic Volcanism and Magmatic Sulphide Formation in the Southern Abitibi Greenstone Belt, Canada

We have investigated the Re–Os isotope geochemistry of 2.7-Ga metakomatiitic flows and associated Ni–Cu sulfide deposits from Alexo, Texmont and Hart in the Abitibi greenstone belt of Ontario in order to refine the thermal erosion model and evaluat e the superimposed effects of metamorphism and hydrothermal alteration on ore environments and non-ore environments. Although the geochemical characteristics of these komatiites have led to the belief that these lavas were uncontaminated, radioge nic Os isotopic compositions (Os = +20.2 and +33.2) obtained from well-preserved komatiites and olivine separates suggest that the Alexo flow has been contaminated by crust-derived material. These data are compatible with the trace-element enrichment observed in melt inclusions trapped within olivine. Redistribution of Os and Re did occur at least at the mineral scale and most likely during the Grenville orogeny. Hydrothermal fluids were channeled along the contact between the komatiites and their basement, and were responsible for the remobilization of Re or Os (or both) within the sulfides at Alexo and Hart. Matrix and disseminate d sulfides from Texmont are located within the pile of cumulates and seem to have escaped this localized alteration. Although the Abitibi sulfides have experienced various degrees of metamorphism (from prehnite–pumpellyite to low amphibolite facies), the initial Re–Os isotopic composition of the flows appears to have been preserved at the whole-rock scale. Re–Os isotopic heterogeneity of the Abitibi sulfides is best explained by variable R-factor of the sulfides. Re and Os concentrations and Os isotopic heterogeneity of the Abitibi sulfides are consistent with the current model of nickel sulfide formation, which implies that the assimilation of sulfidic sedimentary rocks was the trigger for sulfide saturation.

Synthesis of Nickel Sulfide Powders by Thioacetamide in the Presence of Urea

Additions of urea were found to increase the yield of nickel sulfide formation from acidic solutions of thioacetamide. Two precipitation mechanisms were identified: hydrolysis and direct reaction between nickel and thioacetamide. Hydrolysis‐controlled precipitation is evident with low initial pH. The direct reaction is dominant at high initial pH. Nucleation proceeds by a direct reaction between nickel and thioacetamide. The role of urea in precipitation of nickel was found to be twofold. Urea increases the rate of thioacetamide decomposition, thus increasing the concentration of H2S form. Secondly, decomposition increases the pH of the solution, which in turn increases the relative concentration of S= ions. Agglomeration of particles was more evident in the powders obtained in the presence of urea.