Influences Of Technological Parameters On Microtructure Of Electrodeposited Nickel In The Mixed Acid Electrical System

Since the nickel has good thermal conductivity properties and good corrosion resistance, plastic workability and weldability, which is widely used in electrical and electronic component parts, petrochemical industry, food industry, aerospace and military industry and other fields. Currently anode diaphragm electrolysis nickel sulfide is the most important process for the production of electrolytic nickel, electrolytic nickel produced by this method more than 90% of nickel production. Due to the different electrolysis system and process parameters, so the microtructure of electrodeposited nickel would be different.First, the single factor experiment studied the cathodic current density, electrolyte temperature, p H and concentration of nickel and other electrodeposited parameters on the microtructure of electrodeposited nickel, and using XRD, SEM and other analytical tools for preferred orientation, changes in grain size, structure parameters and surface morphology of electrodeposited nickel were characterized.It was found that when the cathode current density is 190~310 A/m~2, the preferred orientation of electrodeposited nickel has a preferred growth plane of(111) crystal face. With cathode current density increasing, TC(220) increases gradually and TC(111) decreases. The size of grains and surface of the particles also increase.The electrodeposited nickel has a preferred growth plane of(220) when the bath temperature is 35 ℃, but changes to(111) when the bath temperature increases to 45~75℃. With increasing bath temperature, the grain size increases gradually. When the bath temperature is 45℃, the surface morphology of electrodeposited nickel is fine and uniform truncated octahedron "pyramid" shaped cluster structure, but changes to messy needles when the bath temperature increases to 55℃, and when the bath temperature increases to above 65℃, the surface morphology is the size of non-uniform and intertwined cellular clusters.With nickel ion concentration increasing, the preferred orientation of electrodeposited nickel transits from(200) crystal face to(111) crystal face, and the grain size decreases, the uniformity of surface particle improved.When the electrolyte p H value is 1.2 ~ 6.0, the electrodeposited nickel has(111) preferred orientation. With p H increasing,(111) diffraction peak intensity slowly increases, the grain size ranges from 28 nm to 42 nm. When the p H is 1.2 and 2.4, the electrolytic nickel surface fine particulate evenly distributed; when the p H is increased to 3.6 and 4.8 rear surface of the particle size becomes uneven; when the p H is 6.0, the surface becomes relatively smooth, but there will be cracks appear. Electrodeposited parameter changes will cause lattice distortion occurs, resulting in the presence of stress within the deposited layer.Secondly, effect of deposition time on preferential growth direction,grain size,surface morphology and cross-sectional microstructure of electrodeposited nickel was investigated by means of XRD and SEM.The results show that with increasing of deposition time, the preferred orientation of electrodeposited nickel transits initially from(111)(200) crystal face to(220) crystal face after 16 h; the surface morphology changes slowly from pyramid shape to cellular, the growth mechanism changes from screw dislocation growth mechanism to cumulative growth mechanism. The cross-sectional microstructure of electrodeposited nickel shows that the deposited layer is non-uniform and mostly grains are columnar and perpendicular to the sheet. The distribution of grain size follows stepwise distribution along the thickness.Finally, the cross section of two different thickness electrodeposited nickel was analysised by the electron backscatter diffraction(EBSD) technique. The results show that the electrodeposited nickel is made of fine crystal grains and coarse grain area; coarse grains area is the columnar crystals and perpendicular to starting sheet, the grain size is stepped distribution along the thickness of the deposited layer. Angle grain boundary is related to grain size, whereas the coincidence lattice(CSL) is related to preferred orientation. Therefore electrodeposited nickel grain boundary misorientation is 15° or more main high angle grain boundaries and coincidence lattice Σ3 appears highest frequency.