CATHODIC PROCESS AND WEAR RESISTANCE OF ELECTRO-DEPOSITED RE-Ni-W-P-SiC COMPOSITE COATING

Cathodic deposition current density of the composite coatings increases when SiC par-ticles and rare earth (RE) were added in the bath, which is profitable for Ni- W-P alloy to deposit in the cathod, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composite coatings. On the contrary, the addition of PTFE in the bath decreases cathodic deposition current density of the coatings. The current density increases a little when the amount of RE is 7-9g/l; however, the current density increases greatly when the amount of RE is increased to 11-13g/l. Bui ij the amount of RE is raised further, the current density decreases. Hardness and wear resistance of RE-Ni-W-P-SiC composite coating have been studied, and the results show that the hardness and wear resistance of RE-Ni-W-P-SiC composite coating increase with increasing heat treatment tempera-ture, which reach peak values at 400℃; while the hardness and wear resistance of the coating decrease with the rise of heat treated temperature continuously.

Cathodic process of nickel electrodeposition from ammonia-ammonium chloride solutions

Mechanism of cathodic process on nickel electrodeposition from ammonia-ammonium chloride solutions was studied by Tafel polarization curves,linear sweep voltammetry(LSV),cyclic voltammograms(CV)and chronopotentiometry(CE)technologies.In the electrolyte with 1.0 mol·L^(-1) NiCl_(2)·6H_(2)O,4.0 mol·L^(-1) NH_(3)·H_(2)O and2.5 mol·L^(-1) NH4Cl,nickel ion mainly complexed with ammonia and almost no free nickel ion could be found.It is confirmed that the dominant form of nickel ammonia complex ion in the system is Ni(NH_(3))_(4)^(2+)by measuring the equilibrium potential of the electrode at various concentrations of ammonia.The species of Ni(NH_(3))42+turns into Ni(NH_(3))_(2)^(2+)during pre-chemical reaction step before discharging reduction reaction.Then,Ni(NH_(3))_(2)^(2+)discharges at the cathodic interface to form metal nickel deposit directly.Nucleation process is involved during nickel electrodeposition according to CV results.The reduction reaction of Ni(NH_(3))_(2)^(2+)is irreversible which is controlled by diffusion step.Other processes are also accompanied during the electrodeposition process,except for the diffusioncontrolled process.

Mechanism of Cathode Process of B(Ⅲ) in LiF-NaF-KBF_4 Meltby Electrochemical Titration Technique

The mechanism of cathode process of B(Ⅲ) at molybdenum and platinum electrodes in LiF-NaF-KBF4melt was studied and the transferred electron number of the reaction was calculated by means of cyclic voltammetry.The effect of adsorption of electroactive component on the electrochemical response (e. g., the voltammetric i─Ecurves) was analyzed and discussed. The 'electrochemical spectra' for linear sweep voltammetry was used to elucidate the electrode reaction accompanied by a following transform process. The results show that the reduction ofB(Ⅲ) to B(0) proceeds in reversible one step three-electron reaction and the cathode process of B(Ⅲ) is affected byproduct adsorbed strongly at the electrode surface. It is assumed that the reduction and deposition of B(Ⅲ) at molybdenum and platinum electrodes proceed in two kinds of mechanism： (1) B(Ⅲ)＋ 3e = Bads→ B (surface diffusiondeposition mechanism) and (2) B(Ⅲ) ＋ 3e = B (direct deposition mechanism).

Reduction behavior of cerium(Ⅲ) ions in NaCl-2CsCl melt

The cathodic process of cerium(III) ions in NaCl-2CsCl melt was studied bycyclic voltammetry and square wave voltammetry with tungsten and gold electrodes at 873 K. The twoelectroanalytical methods yield similar results. The cathodic process of cerium(III) ions consistsof two reversible steps: Ce^(3+)+ e^-= Ce^(2+) and Ce^(2+) + 2e^-= Ce. The half wave potentials ofCe^(3+)/Ce^(2+) and Ce^(2+)/Ce were determined as -2.525 V vs. Cl_2/Cl^- and -2.975 V vs. Cl_2/Cl^-,respectively. The diffusion coefficient of Ce^(3+) was also determined as 5.5 X 10^(-5) cm^2 centredot s^(-1).

Enhanced electrochemical oxidation of phenol by introducing ferric ions and UV radiation

The mineralization of phenol in aerated electrochemical oxidation has been investigated.The results show that a cathodic Fenton process can occur when the Ti-0.3Mo-0.8Ni alloy material is used as cathode in solution containing ferric or ferrous ions; moreover,the reinforcement of cathodic Fenton process on the total organic carbon (TOC) removal rate of phenol is quite distinct.Among the metallic ions investigated,the ferric ion is the best catalyst for the electrochemical mineralization of phenol at initial...