Electrocrystallization Mechanism of Tungsten in Molten KF-B_2O_3-K_2WO_4

The electrocrystallization mechanism of tungsten in KF-B_2O_3K_2WO_4 melt has been investigated onthe platinum electrode at 795℃ by using cyclic voltammetric and chronoamperometric methods. The resultsshow that the electrocrystallization of tungsten is the process of progressive and three dimensionalhemispherical nucleation with nuclei growth controlled by diffusion of tungsten ions in the melt.

Electrocrystallizations of copper on glassy carbon in CuCl_2 silica sol and aqueous solutions

Electrocrystallizations of copper from both CuCl_2 silica sol and aqueous solutions were studied by the chronoamperometry technique.It was found that current density contributions of the double-layer charging（iDL） in current-time transients（CTTs） from both of the solutions were large.An adsorption-nucleation based model was proposed to analyze quantitatively the CTTs,by which copper electrocrystallization mechanism was characterized as progressive nucleation with 3D growth（3DP） under diffusion control.The diffusion coefficient of copper ions and the AN_∞products in aqueous solutions were larger than that in silica sols, which indicated that copper nucleation was inhibited in sol solution.The large iDL may be resulted from the adsorption of chloride ions on the electrode surface.

Electrochemical behavior of tungsten in(NaCl–KCl–NaF–WO_3)molten salt

Abstract The electrochemical reaction mechanism and electrocrystaUization process of tungsten in the NaCl- KCl-NaF-WO3 molten salt were investigated at 973 K （700℃） by means of cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques. The results show that the electrochemical reaction process of tungsten in the NaCl-KCl-NaF-WO3 molten salt system is a quasireversible process mix-controlled by ion diffusion rate and electron transport rate. Tungsten ion in this system is reduced to W（0） in two steps. The electrocrystallization process of tungsten is found to be an instantaneous, hemispheroid three-dimensional nucleation process and the tungsten ion diffusion coefficient of 2.361 × 10^-4 cm2.s^-1 is obtained at experimental conditions.

Potentiostatic deposition of differently shaped Pt and PtBi nanoparticles

This article presents a comparative study of the deposition behaviors of Pt and PtBi nanoparticles on glassy carbon. Sea-urchin-like Pt nanoparticles and spherical PtBi nanoparticles were produced by potentiostatic deposition. Chronoamperometric characterizations show that the Pt electrodeposition corresponds to the mechanism for 3D progressive nucleation and growth. The sea-urchin-like morphology can be attributed to the effect of applied potential and the electroadsorption of hydrogen and trace Cl^-. The PtBi electrodeposition fits well to the mechanism for 2D progressive nucleation at t/tmax 〈 1.5, and there is a transition from 2D adlayer to 3D clusters at t/tmax 〉 1.5. The spherical PtBi nanoparticles result from the three effects caused by bismuth co-electrodeposition： higher overpoten-tial, strengthened affinity to Cl^-, and improved hydrogen evolution. These results suggest that the adsorption of solution anions and cations on the deposit surface can be used to change the morphologies of the deposits.

Novel Nanostructured MnO_2 Prepared by Pulse Electrodeposition:Characterization and Electrokinetics

Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcMD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFM）. SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current （dcMD）. Higher distortion of MnO6 octahedral environment of dcMD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.

Effect of 2-butyne-1, 4-diol on silver electrodeposition from 5, 5-dimethyl hydantoin solutions

The effect of 2-butyne-1, 4-diol on silver electrodeposition process from 5, 5-dimethyl hydantoin solutions was investigated by means of cyclic voltammetric measurement, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cyclic voltammetric studies indicate that the reduction process of silver electrodeposition is influenced by adding 2-butyne-1, 4-diol. Owing to its adsorption on the electrode surface, 2-butyne-1, 4-diol moderately hinders the mass transfer of the silver complexed ions from the bulk solution to the outer limit of the electrode double layer and affects the electrocrystallization step. Scanning electron microscopy analysis reveals that the presence of 2-butyne-1, 4-diol in the electrolyte is beneficial and the silver deposits obtained are smoother, more compact and more leveled. X-ray diffraction analysis of the silver deposits obtained at 0.5 g·L-1 2-butyne-1, 4-diol indicated that the (110) plane is the most preferred plane and is not affected by the presence of 2-butyne-1, 4-diol in the electrolyte.

CRYSTALLIZATION OF SODIUM TUNGSTEN BRONZE USING ELECTROLYSIS WITHREVERSE CURRENT~＋

Utilizing the technique of electrolysis with reverse current,sodium tungsten bronze (Na_xWO_3) crystals were prepared from a molten mixture of sodium tungstate (Na_2WO_4 ) and tungstic trioxide (WO_3) at 800℃. Crystal structure, lattice parameter, and s

Controlled Growth Morphology of Porous Nanocrystal Iron Oxide by Electrodeposition

Fe（Ⅱ） was deposited into the bottom of the mesopores of highly ordered large caged cubic mesoporous silica by electrodeposition. And the deposited Fe mesoporous silica thin film was treated by 1%---4% HF to remove the SiO2 template and then calcined. It was found that nanowire bundles, dendritic plates of porous iron oxide, dense parallel backbones of porous iron oxide were obtained at -1.4-- -1.6 V and 0.08--0.1 mol/L electrolyte concentration after calcinations; the dendritic pattern of porous iron oxide film templated by the SBA-16 film was obtained in macrostructure at a higher absolute value of cathode potential（-1.7-- -1.8 V） and a lower electrolyte concentration（0.02-0.05 mol/L）, the dendritic pattern of porous iron oxide film could copy the microstructure of SBA-16 film; Fe（II） nanowires grew and formed in one dimension（1D） and two-dimension（2D） electrocrystallization at a potential of-l.6-- -1.7 V and an electrolyte concentration of 0.05 mol/L, and the shape of the ID or 2D crystalline iron oxide nanowires calcined was similar to the original shape of the SBA-16 channels. The desired morphology and size of porous nanocrystal iron oxide can be obtained by adjusting the applied potential value and electrolyte concentration, and all kinds of morphologies of porous nanostructure crystal iron oxide can be prepared.

STUDY THE INFLUENCE OF H_(3)BO_(3)ON THE ZINC ELECTROPLATING USING ELECTROCHEMICAL NOISE TECHNIQUE

The influence of H3BO3 on the zinc electroplating was studied using electrochemical noise technique, cyclic voltammetry and steady-state polarization method. The results showed that, under the experimental conditions, the deposition of zinc followed the mechanism of two-dimensional nucleation and subsequent grain growth. The addition of H3BO3 into the electroplating solution prominently changes the nucleation and growth kinetics of zinc deposits, which is directly related to the features of electrocrystallization noise and the corresponding structure of the electrodeposits. The results also shown that the electrochemical noise (EN) technique can give more information about the electrodeposits structure and electroplating mechanism than other normal electrochemical measurements can give, such as steady-state polarization method and cyclic voltammetry technique.

Electrodeposition of Molybdenum in Molten KF-B_2O_3-K_2MoO_4

The electrocrystallization mechanism of molybdenum was studied on platinum electrode bychronoamperometric method. The results show that the relationship between current and time remains agood linearity indicating that the electrodeposition of molybdenum is a process of three dimensionalhemispherical and progressive nucleation with growth of the nuclei controlled by diffusion. Thetechnological conditions of electroplating of molybdenum on nickel and copper substrates were also studiedand discussed.

Synthesis and Crystal Structure of 〔EDA〕〔Ni（dmit）2〕3

The crystal structure of the compound EDA Ni(dmit) 2 3 (EDA=2 diethylamino 1,3 dithioanylium; dmit=1,3 dithiole 2 thione 4,5 dithiolate)C 25 H 14 NNi 3S 32 , has been determined by single crystal X ray diffraction at 300K. The crystal is triclinic with space group P1, a=11.252, b=12.192(2), c=20.055(6) , α=108.127(2), β=106.287(8), γ=90.005(9)°; V=2498.3(3) 3, Z=2, M r=1530.38, D c =2.03(2) g/cm 3. Final R and R w values were 0.0603 and 0.0704, respectively. The structure consists of thick layers of stacked Ni(dmit) 2 entities separated by EDA cations. This salt shows semiconducting behaviour with room temperature conductivity of 0.2 Scm -1 and activation energy of 0.11 eV.

Electrochemical behavior of Cu in the (NaCl-KCl-CuCl) molten salt

The electrochemical reaction mechanism and electrocrystallization process of Cu on copper electrode in the eutectic NaC1-KC1-CuC1 molten salt were investigated by means of cyclic voltammetry, chronopotentiometry and chronoamperometry tech-nique at 710℃. The results show that the electrochemical reaction process of Cu is a quasi-reversible process mix-controlled by Cu＋ diffusion rate and electron transport rate;the electrochemical reduction mechanism is Cu＋e→Cu;the electrocrystallization process of copper is an instantaneous hemispheroid three-dimensional nucleation process; the Cu diffusino coefficient is 4.3×10^-4cm^2·s^-1 under the experimental conditions.

Controllable phase transformation and improved thermal stability of nickel on tungsten substrate by electrodeposition

Present study reports a controllable phase transformation of nickel(Ni) from amorphous to cubic crystal structures on tungsten(W) substrate by electrodeposition. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy were used to characterize the microstructure, micro-constituents and surface morphology of as-prepared Ni. The microstructure of Ni was strongly affected by the applied overpotential and deposition time. It is demonstrated that by controlling these two parameters either amorphous or cubic crystal structure of Ni on the W substrate could be obtained. The crystallization mechanism is discussed based on Gibbs crystal growth theory and Ostwald’s rule. It is concluded that W substrate, acting as a heat sink, can effectively promote the thermal stability of amorphous Ni, based on the data from differential scanning calorimetry and Kissinger’s model. This work contributes to the elucidation of the crystallization mechanism of Ni on W powder substrates, and proves that, better than alloying with other elements, incorporating powder substrates will significantly improve the crystallization temperature, hence the thermostability of amorphous Ni.