• Journal of the Korean Chemical Society
• /
• v.28 no.5
• /
• pp.271-278
• /
• 1984

Ellipsometric and reflectance measurements were made with magneto-optically self-nulling ellipsometer on the iron surface being passivated. The passivation was induced by abruptly changing potential of the mechanically polished high purity iron from the reduction potential to the oxidation potential in basic solutions. From the differences in the optical paramates(${\Delta},\;{\psi}$) and reflectance (R) between the reduced (film-free) and oxidized (film-covered) states, the thickness(${\tau}$) and optical constants (n, k) of the film in the early stage of its formation were computed as functions of pH and time. From the computed values, it was deduced that the properties of the anodic film did not undergo a drastic change with time which would indicate a transformation of the film before effective passivity is attained, and that the film reached its stady state within a few second. The thickness of anodic film was $14\;{\sim}\;23{\AA}$. The anodic films also seemed to have small values of optical absorption coefficient. The film formed in high pH environments had thinner and denser structure than that formed in low pH.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.33 no.2
• /
• pp.114-117
• /
• 2020

In this study, we performed the deposition of Al thin film using a DC magnetron sputtering method. To evaluate electrical and structural properties, the growth conditions were changed in terms of two functions, namely, sputtering power ranging from 41.6 to 216 W and film growth rate ranging from 5.35 to 26.39 nm/min. The growth rate and the microstructure were characterized by a scanning electron microscopy and X-ray diffraction analysis. The plane of crystalline growth showed that the preferential (111) direction and defects due to the grain boundary increased with DC power. The resistivity of the Al film over 50 nm showed a constant value by horizontal grain growth. Our results can be applicable for the preparation of nano-templates for anodic aluminum oxide.

• Journal of Biomedical Engineering Research
• /
• v.14 no.4
• /
• pp.333-340
• /
• 1993

The high biocompatibility of titanium is connected with the high corrosion resistance of the surface oxide, its high dielectric constant, and some other specific biochemical properties of the oxide. The corrosion resistance of titanium can be improved with the formation of passive film by anodic oxidation. In other to characterize the titantium oxlde film formed by anodic oxidation, titanium plates were anodized in 0.5M $H_3SO_4$ electrolyte at voltages between 5V and 100v. The oxide film was examined by an X-Ray Diffractometer(XRD) and a Scanning Electron Microscope(SEM). In addition, the corrosion resistance of oxide film was tested by dipping in physiological NaCl,5% HCI,5% $H_3PO_4$ and its biocompatability was evaluated by the fibroblast-like cell culture. The results obtained are as follows : 1. The thickness of surface oxide and micropore are increased with the increase of electrode potential and formed deeply along the grain boundary. 2. The solubilities of titanium in electrolyte solution shows that the anodized titanium has more corrosion resistance than the untreated pure titanium. 3. The biocomatibility of anodized titanium is superior to untreated pure titanium.

• Journal of the Korean Chemical Society
• /
• v.56 no.5
• /
• pp.542-547
• /
• 2012

We have investigated the electronic properties of the oxide film and anodic oxidation mechanism. Iron was oxidized by two reaction pathways depending on pH. The oxide film has showed the electronic properties of n-type semiconductor based on the Mott-Schottky equation.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2017.05a
• /
• pp.96.1-96.1
• /
• 2017

This presentation introduces anodizing science of typical valve metals of Al, Mg and Ti, based on the ionic transport through the andic oxide films in various electrolyte compositions. Depending on the electrolyte composition, metal ions and anions can migrate through the andic oxide film without its dielectric breakdown when point defects are present within the anodic oxide films under high applied electric field. On the other hand, if anodic oxide films are broken by local joule heating due to ionic migration, metal ions and anions can migrate through the broken sites and meet together to form new anodic films, known as plasma electrolytic oxidation (PEO) treatment. In this presentation, basics of conventional anodizing and PEO methods are introduced in detail, based on the ionic migration and movement mechanism through anodic oxide films by point defects and by local dielectric breakdown of anodic oxide films.

• Corrosion Science and Technology
• /
• v.7 no.3
• /
• pp.168-172
• /
• 2008

A new type of electrochemical random signal (electrochemical noise) analysis technique was applied to localized corrosion of anodic oxide film formed 1100 aluminum alloy in $0.5kmol/m^3$ $H_3BO_4/0.05kmol/m^3$ $Na_2B_4O_7$ with $0.01kmol/m^3$ NaCl. The effect of anodic oxide film structure, barrier type, porous type, and composite type on galvanic corrosion resistance was also examined. Before localized corrosion started, incubation period for pitting corrosion, both current and potential slightly change as initial value with time. The incubation period of porous type anodic oxide specimens are longer than that of barrier type anodic oxide specimens. While pitting corrosion, the current and potential were changed with fluctuations and the potential and the current fluctuations show a good correlation. The records of the current and potential were processed by calculating the power spectrum density (PSD) by the Fast Fourier Transform (FFT) method. The potential and current PSD decrease with increasing frequency, and the slopes are steeper than or equal to minus one (-1). This technique allows observation of electrochemical impedance changes during localized corrosion.

• Journal of the Korean institute of surface engineering
• /
• v.57 no.1
• /
• pp.8-13
• /
• 2024

Anodizing of Al6061 alloy was conducted in two different electrolytes of 20% sulfuric acid and 8% sulfuric acid + 3 % oxalic acid solutions at a constant current or decreasing current density conditions, and its dielectric breakdown voltage was measured. The surface morphology of anodic oxide films was observed by TEM and thermal treatment was carried out at 400 ℃ for 2 h to evaluate the resistance of the anodic oxide films to crack initiation. The anodic oxide film formed in 8% sulfuric acid + 3 % oxalic acid solution showed higher dielectric breakdown voltage and better resistance to crack initiation at 400 ℃ than that formed in 20% sulfuric acid solution. The dielectric breakdown voltage increased 6 ~12% by applying decreasing current density comparing with a constant current density.

• Journal of the Korean institute of surface engineering
• /
• v.49 no.3
• /
• pp.225-230
• /
• 2016

The present work was conducted to investigate the effects of NaF concentration in phosphate and silicate-containing alkaline electrolyte on the morphology, thickness, surface roughness and hardness of anodic oxide films formed on AZ31 Mg alloy by plasma electrolytic oxidation (PEO) method. The PEO films showed flat surface morphology with pores in the absence of NaF in the electrolyte, but nodular features appeared on the PEO film surface prepared in NaF-containing electrolyte. Numerous pores ranging from 1 to $20{\mu}m$ in size were observed in the PEO films and the size of pores decreased with increasing NaF concentration in the electrolyte. Surface roughness and thickness of PEO films showed increases with increasing NaF concentration. Hardness of the PEO films also increased with increasing NaF concentration. It was noticed that hardness of inner part of the PEO films is lower than that of outer part of them, irrespective of the concentration of NaF. The low hardness of PEO films was explained by the presence of a number of small size pores less than $2{\mu}m$ near the PEO film/substrate interface.

• Corrosion Science and Technology
• /
• v.6 no.6
• /
• pp.311-315
• /
• 2007

The anodic polarization behavior of equiatomic TiNi shape memory alloy with pure titanium as a reference material was investigated by means of open circuit potential measurement and potentiodynamic polarization technique. And the structure of passive films on TiNi intermetallic compounds was also conducted using AES and ESCA. While the dissolved Ni(II) ion did not affect the dissolution rate and passivation of TiNi alloy, the dissolved Ti(III) ion was oxidated to Ti(IV) ion on passivated TiNi surface at passivation potential. It has also been found that the Ti(IV) ion increases the steady state potential, and passivates TiNi alloy at a limited concentration of Ti(IV) ion. The analysis by AES showed that passive film of TiNi alloy was composed of titanium oxide and nickel oxide, and the content of titanium was three times higher than that of nickel in outer side of passive film. According to the ESCA analysis, the passive film was composed of $TiO_2$ and NiO. It seems reasonable to suppose that NiO could act as unstabilizer to the oxide film and could be dissolved preferentially. Therefore, nickel oxide contained in the passive film may promote the dissolution of the film, and it could be explained the reason of higher pitting susceptibility of TiNi alloy than pure Ti.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.347-350
• /
• 2001

A typical Mold method is to form a gate electrode, a gate oxide, and emitter tip after fabrication of mold shape using wet-etching of Si substrate. In this study, however, new Mold method using a side wall space structure is used in order to make sharper emitter tip with a gate electrode. Using LPCVD(low pressure chemical vapor deposition), a gate oxide and electrode layer are formed on a Si substrate, and then BPSG(Boro phospher silicate glass) thin film is deposited. After, the BPSG thin film is flowed into a mold as high temperature in order to form a sharp mold structure. Next TiN thin film is deposited as a emitter tip substance. The unfinished device with a glass substrate is bonded by anodic bonding techniques to transfer the emitters to a glass substrate, and Si substrate is etched using KOH-deionized water solution. Finally, we made sharp field emitter array with gate electrode on the glass substrate.