The new nickel/layered silicate nanocomposites were electrodeposited from different pHs to study the influence on the metal ions/layered silicate plating solution and on the properties of the deposited films. Nickel/layered silicate nanocomposites were fabricated from citrate bath atacidic pHs (1.6−3.0), from Watts’ type solution (pH ~4-5), and from citrate bath at basic pH (~9). Additionally, the new nickel/molybdenum/layered silicate nanocomposites were electrodeposited from citrate bath at pH 9.5. The silicate, montmorillonite (MMT), was exfoliated by stirring in aqueous solution over 24 hours. The plating solutions were analyzed for zeta potential, particle size, viscosity, and conductivity to investigate the effects of the composition at various pHs. The preferred crystalline orientation and the crystalline size of nickel, nickel/layered silicate, nickel/molybdenum, and nickel/molybdenum/layered silicate films were examined by X-ray diffraction. The microstructure of the coatings and the surface roughness was investigated by scanning electron microscopy and atomic force microscopy. Nickel/molybdenum/layered silicate nanocomposites containing low content of layered silicate (1.0 g/L) had increase 32 % hardness and 22 % Young’s modulus values over the pure nickel/molybdenum alloy films. The potentiodynamic polarization and electrochemical impedance measurements showed that the nickel/molybdenum/layered silicate nanocomposite layers have higher corrosion resistance in 3.5% NaCl compared to the pure alloy films. The corrosion current density of the nickel/molybdenum/layered silicate nanocomposite composed of 0.5 g/L MMT is 0.63 µA·cm-2 as compare to a nickel/molybdenum alloy which is 2.00 µA·cm-2.

No description available.

No description available.

A study of the nucleation, growth and final microstructure of vacuum deposited nickel films has been performed using scanning tunneling microscopy (STM) as the primary research instrument. Typical nucleation conditions are reported for nickel films grown on partially shadowed highly-oriented pyrolytic graphite (HOPG), and techniques are developed for using the STM to catalog film islands instead of more conventional electron microscopes. Values for the activation energy of surface diffusion, critical nucleus size, changes in the saturation nucleation density with temperature, and spatial variations in the nucleation rate are included. Roughening and microstructure changes observed with STM are reported as functions of substrate temperature and deposition angle for nickel films grown on highly-oriented pyrolytic graphite and fused silica. Conventional film RMS roughness values are compared to microRMS values derived from STM data and STM images of film microstructure are compared with SEM and optical microscope photographs.

published_or_final_version / Physics / Master / Master of Science

published_or_final_version / Dentistry / Master / Master of Dental Surgery

published_or_final_version / Physics / Master / Master of Science

<p>Chlorite is a ferrous silicate mineral occurring as afracture filling mineral in the Swedish granite bedrock thatsurrounds the area of the candidate Swedish geologicalrepositories for nuclear waste.</p><p>To investigate the importance of chlorites as a naturalbarrier for radionuclide migration sorption of Ni(II) onto anatural chlorite was chosen as the studied system. The sorptionbehaviour was studied using batch technique under differentexperimental conditions by varying the concentration ofbackground electrolyte, pH and initial nickel concentration.Our experiments showed that sorption is dependent of pH; belowpH 4 no sorption occurs and in the pH range 7-11 the sorptionmaxima was found. The sorption shows no dependence of ionicstrength in our experiments and together with pH dependency weconclude that the sorption of nickel to chlorite is mostlyoccurring through surface complexation. The distributioncoefficient, K<i>d</i>, was determined for our results and in the range formaximal sorption the K<i>d</i>is approximately 10³cm³/g.</p><p>Our experimental data were described using a diffuse doublelayer model, including strong and weak surface sites, in thesoftware PHREECQ and the results obtained from PHREEQC werealso used for a fit of the data in the software FITEQL. Thesurface complexes that dominate the sorption of nickel tochlorite from our model are Chl_ONi⁺(weak) and for pH above 9 Chl_ONi(OH)^-(weak). Flow-through technique was used in ourinvestigations regarding the dissolution rate of a naturalchlorite and the experimental results show that the dissolutionrate of chlorite is strongly pH dependent and at pH 2 thehighest dissolution rate (R_Si) could be determined to 7• 10^-11mol/(m²s) based on silica data.</p><p><b>Keywords:</b>chlorite, nickel, sorption, surfacecomplexation, dissolution rate.</p>

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No description available.