Nor Azrina Resali

Study of Alloys Addition to the Electrodeposited Nanocrystalline Cobalt

Cobalt and its alloy have been identified as potential candidates for replacing hexavalent Chromium plating in corrosion resistant coating in acidic environment. In this study, the effect of alloys addition towards elemental composition, crystallographic structure characterization, surface morphology, hardness and potentiodynamic polarization of the cobalt alloys coatings is reported. Addition of Nickel (Ni) and Iron (Fe) to the Cobalt (Co) coatings are deposited on stainless steel substrate by electrodeposition method. The deposition is performed at acidic environment of pH 3. The granule sizes of cobalt alloys prepared by electrodepositionmethod are in the range of 34.95 nm72.08 nm. The microhardness of CoNiFe is the highest (267.8 HV) compared to Co and CoFe. CoNiFeperforms the smallest corrosion rate with 1.322 mmpy. It is found thatthe addition of Ni and Fe into pure cobaltimproves the hardness and corrosion behavior.

The Physical and Magnetic Properties of Electrodeposited Co-Fe Nanocoating with Different Deposition Times

Using the electrodeposition process, cobalt-iron (Co-Fe) nanocrystalline coatings were successfully synthesized onto stainless steel in deposition times of 30, 60, and 90 minutes. The temperature used throughout the process was 50°C in an acidic environment of pH 3. By changing the deposition time, physical properties such as phase and crystallographic structure, surface morphology, grain size, microhardness, and magnetic properties of Co-Fe coatings were examined. FESEM micrographs showed that the grain sizes of the coatings were in the range from 57.9 nm to 70.2 nm. Dendrite and irregular shapes were found in the microstructure of Co-Fe nanocoating. The Co-Fe nanocrystalline coating prepared in a deposition time of 90 minutes achieved the highest microhardness of 339 HVN. The magnetic properties associated with Co-Fe nanocoating at longer deposition times show greater coercivity, , and saturation magnetization, , values of 56.43 Oe and 70.45 eμ/g, respectively. The M-H curves for all the Co-Fe coatings exhibited soft ferromagnetic behaviour with narrow hysteresis loops. It was found that increasing the deposition time also improved the microhardness and magnetic properties of Co-Fe nanocoating, which is much needed for long-life high-coercivity magnetic strip card applications.

The Effect of Bath Ph on the Phase Formation of Ternary Co-Ni-Fe Nano-Coatings

This study describes how the control of bath pH allows different types of phase formation in the ternary Co-Ni-Fe nanocoating. The acidity of the plating bath has been known as a main factor to the properties of coatings. The Co-Ni-Fe coating was fabricated using a commercial electrodepostion process. Several pH solutions (3, 7 and 9) were employed to determine the optimum condition for Co-Ni-Fe synthesis. The bath pH was varied by using sodium hydroxide (NaOH) and sulphuric acid (H2SO4). Other parameters such as temperature, electrolyte composition, deposition time and current density were kept constant. The experiment was performed at 50°C. This temperature is commonly used in the industrial plating process. XRD analysis indicated the presence of both phases: body centred cubic (BCC) and face centred cubic (FCC) dependent on the pH value. Co-Ni-Fe nanocoatings obtained from the electrolyte of low pH showed the fine-grain morphology. The hardness of the Co-Ni-Fe nanocoatings was closely related to the obtained morphology.

Effect of Time Depositions on Electrodeposited Cobalt-Iron Nanocoating

Cobalt-Iron (CoFe) nanocrystalline coatings are successfully prepared in 30, 60 and 90 minutes time depositions using electrodeposition method. The effect of time deposition towards crystallographic structure, elemental composition, surface morphology, microhardness and corrosion behaviour of CoFe coatings were investigated. The CoFe nanocrystalline coatings were deposited on stainless steel substrate at pH 3 environment. The grain sizes of the coatings are in the range of 57.88 to 70.18 nm. The CoFe nanocrystalline coating prepared at 90 minutes deposition achieves the highest microhardness of 290 HV. This coating also exhibits the lowest corrosion rate with 1.086 mpy. It is found that the increment of time deposition improves the microhardness and corrosion behavior of CoFe nanocrystalline coatings.

The Influence of Bath Concentration on Particle Size of Cobalt Nanoparticles

Cobalt nanoparticles have been widely used in magnetic storage media application. This study reports the characteristic and properties of Cobalt (Co) nanoparticles due to the effect of different bath concentrations. The Co nanoparticles were coated on the stainless steel substrate using different molar concentrations (M) of 0.05 M, 0.075 M and 0.1 M, respectively. The coating was done using electrodeposition method. Interestingly, the sphere particles surrounded by flakes were only found in the Co nanoparticles prepared in 0.075 M. This structure exhibited the smallest particles size, which is 83 nm. Besides, the nanoparticles also had the highest microhardness if compared to the Co nanoparticles prepared in 0.05 M and 0.1 M. The Co nanoparticles prepared in other concentrations were irregular structure without flakes. The polarization curves for all the nanoparticles showed the active behaviour without any distinctive to passivation. However, the corrosion rate of the sample prepared in 0.075 M was the lowest; 42.51 mpy compared to the other samples prepared in 0.05 M and 0.1 M, which were 176 mpy and 223.3 mpy, respectively. Hence, it was found that the bath concentrations affect the particle size of as-synthesized Co nanoparticles and finally changed the properties of final product.

Corrosion Behavior of Electrodeposited CoNiFe Nanoparticles Immersed in Different Environments

Replacement or repair of corrosion damaged equipment is the largest maintenance requirement for the industry. One technique for reducing the corrosion of metals is to coat them with thin layers of less reactive metals or alloys. Unfortunately, most metallic coatings are inherently porous and historically have been of little value as barriers against corrosion. Recently, with the development of new alternative material such as electrodeposited CoNiFe, these problems have largely been overcome. This paper investigated the effects of different aggressive environments on the corrosion behavior of electrodeposited CoNiFe. Interestingly, the mixed morphologies with spherical and dendritic structure were found in the neutral and alkaline environment. This morphology exhibited the smallest particle size with less percentage of oxygen elements. Besides, alkaline environment experienced the slowest corrosion rate due to the mixed morphology. It was found that spherical and dendritic refinement provides higher corrosion resistance. The corrosion rate of the sample prepared in alkaline environment was the lowest compared to the others due to the reduction of particle size.

Morphological studies of electrodeposited cobalt based coatings: Effect of alloying elements

Electrodeposition is known as a simple and low-cost method to synthesize good-quality coating with excellent hardness. In this work, the morphology changes on Cobalt coating with the addition of iron and nickel elements were investigated. Co (Cobalt) and Co-based alloy coatings were prepared by electrodeposition technique using sulfate-based electrolytes. The process was conducted at 50°C temperature in an acidic environment (pH 3). The pure Co coating shows the tendency to form snowflake-like morphology structure. The dendritic morphology appeared in the Co-Fe coatings. However, the dendritic morphology was totally disappeared in the Co-Ni-Fe morphology and replaced by spherical morphology. The crystal structure of Co-Ni-Fe coating changed from bcc into mixed bcc+fcc structure with the addition of Ni element in Co-Fe composition. The Ni element which had been introduced in the Co-Fe composition improved the surface morphology and reduced the average particle size. The surface morphologies in the coatings affect the particles size and hardness property. This may due to the formation of full, compact coatings morphology and introduction of particles boundaries interphase. The Co-Ni-Fe coating with smaller particle size, less void formation and mixed crystal structure of bcc+fcc was roughly two times harder than pure Co.

Co-Fe Nanoparticles Coated on Copper Substrate: Effect of Different Deposition Times

Electrodeposition method has been effectively applied to the synthesis of the Cobalt-Iron (Co-Fe) nanoparticles on Copper (Cu) substrate. The electrodeposition was conducted in acidic environment at controlled temperature of 50°C±0.5°C. The influence of deposition times (30, 60 and 90 min) towards the characteristics and properties such as phase and crystallographic structure, surface morphologies, particle size and magnetic properties of Co-Fe nanoparticles were studied. The Co-Fe phase showed the Body Centered Cubic (BCC) crystal structure. Dendritic structure was visible in the Co-Fe nanoparticles prepared at 30 minutes deposition. Meanwhile, irregular particles surrounded by flakes were found in the sample prepared at 90 min deposition. The particle sizes were reduced from 61.6 nm to 54.8 nm when the deposition time was increased. The best soft ferromagnetic properties with higher saturation magnetization, Ms and lower coercivity, Hc were achieved by Co-Fe nanoparticles deposited at 90 min.

Electrodeposited cobalt and its alloys nanocoating: A brief review

Nanocrystalline materials have gained importance to be developed due to their significantly enhanced properties compared to the polycrystalline materials. Electrodeposition has a special role in synthesizing the nanocrystalline materials. In current review, the superiority of electrodeposition technique in producing various nanocyrstalline materials that exhibit improved characteristics compared to materials produced by conventional techniques are discussed. The nanocrystalline cobalt and its alloys have been recognized as one of the capable materials to replace the hard chrome coating. This coating is known to be carcinogenic on the tissue and toxic to human beings, plants and animals. The approaches taken in designing the efficient nanocrystalline cobalt and its alloys coatings which provide superior resistance to corrosion are outlined. The mechanical properties of various nanostructured coating materials using the nanoindentation testing are also described. The understanding obtained from the review will offer guidelines for future researches, thus providing new structured coatings which can be utilized in various applications such as corrosion and wear resistance applications.