Literatura académica sobre el tema "Iron-cobalt alloys. Alloy plating. Citrates"

Iron-chromium-phosphorus (Fe–Cr–P) alloys were prepared by electrodeposition from an acidic citrate electrolyte using sodium hypophosphite as the source of phosphorus. These alloys form a passive oxide layer when exposed to air and are useful as protective coatings on steel. The current efficiency of the plating process reaches a maximum of 20% at a current density of 100 mA/cm2 where the alloy has 10% Cr and 19% P. X-ray diffraction patterns and TEM analysis show that the alloy is amorphous. TEM results also indicate that small oxide particles (5–20 nm) are dispersed in the amorphous structure. Besides Fe, Cr, and P, the alloys contain a low level of oxygen (4–7%) in the form of mixed iron and chromium oxides, as confirmed by AES analysis. When heated, the amorphous structure transforms into a mixture of Fe3P and Cr3P, along with α–Fe–Cr grains. This phase transformation occurs in the temperature range of 450–460 °C for alloys with 19% P.

Cr-Co-P alloy coating was prepared from trivalent chromium bath and the appearance and performances of the coating were characterized. The Cr-Co-P alloy electroplating bath was prepared through orderly adding cobalt chloride, sodium hypophosphite monohydrate, urea, sodium format, ammonium citrate tribasic, boric acid, and ammonium brome into distilled water. Optimum plating crafts were determined as follows: pH value 1.5~3.0, temperature 25~45°C, plating time 1~15 minutes, and current density 5~25A·cm-2. Reticulate iridium dioxide coating electrode or highly pure graphite electrode were adopted as anode. And electro deposition experiments were carried out with air disturbance. The surfaces of deposited coatings are silvery white, bright and smooth. The Cr-Co-P alloy coatings were characterized by scanning electronic microscope (SEM). The results proved that P is favour to the improvement of deposit corrosion resistance. In addition, Cobalt atoms are in favor of enhancing throwing power and cover power of plating baths. Via adjusting plating bath, the electro-deposition rate could reach at 1.0~1.3μm·min-1, and the contents of P and Co could be controlled in 15~25% and 10~65%.

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.

Thesis (M. Sc.)--University of Alberta, 2009.
Title from pdf file main screen (viewed on Sept. 2, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Materials Engineering, Department of Chemical and Materials Engineering, University of Alberta." Includes bibliographical references.

Iron-cobalt alloys have been extensively studied as potential hard disk drive write head materials due to their potentially high saturation flux densities (~2.4T), low coercivities and ease of deposition. Iron-cobalt plating solutions have, however, been shown to have stability issues, necessitating that they be used at low pH or that a stabilizing agent be added to the solution. The purpose of this thesis is to evaluate the stability of a dibasic ammonium citrate plating solution and to characterize the deposits which result from its use. The plating solutions are found to be less stable than previously claimed. The solutions are oxidized by dissolved oxygen, which leads to a valence change in the iron ions and eventually the formation of iron oxide/hydroxide precipitates. These effects are exacerbated by heating or the application of a voltage across the solution. Deposits plated from the solution are fine grained (<40nm) and compact through their thickness. While normally deposited as the equilibrium BCC phase, metastable phases are deposited at elevated temperatures, high pH or in the absence of a stabilizing agent. A metastable phase which is isomorphous to α-Mn is deposited at elevated temperatures. This phase transforms to the BCC phase when annealed at >174ºC and is highly textured. Its presence is detrimental to deposit coercivity.
Materials Engineering