Jerome Kruger

Optical Constants of Iron in the Visible Region

The optical constants of clean iron single-crystal surfaces maintained in an ultrahigh vacuum were determined. An ellipsometric technique was used to determine values of the optical constants as a function of wavelength in the region of 3600–7000 A. A maximum at 4900 A in the conductivity versus wavelength curve indicates the presence of an interband transition.

Studies of passive film breakdown by detection and analysis of electrochemical noise

Abstract Random fluctuations in the passive current of electrodes under potentiostatic conditions have been measured on aluminum in boric acid: borate solution and on a Fe-Cr-Ni alloy, both in the amorphous and in the crystalline state, in sulfuric acid. The onset of pitting can be detected by thc large increase in current noise. The noise level is different in the amorphous and crystalline Fe-Cr-Ni alloy, indicating that the breakdown of the passive film differs in the two conditions. Thc experimental aspects involved in carrying out meaningful noise measurements in electrochemical systems are also discussed.

Optical Studies of the Formation and Breakdown of Passive Films Formed on Iron Single Crystal Surfaces in Inorganic Inhibitor Solutions

Polarized light was used to measure the thickness and optical properties of passive films as they were forming while simultaneous electrochemical measurements were being made. The film formation studies showed that a change in film thickness of 15–20Aa was associated with the onset of a passive potential. A direct, logarithmic‐type law governed the growth of a semiconductor film with crystallographic orientation of the substrate having little effect.When iron surfaces prepared in an ultrahigh vacuum (a vacuum of the 10−9 Torr order of magnitude), were passivated a 20Aa film formed instantaneously on the introduction of an air‐saturated . This film then dissolved and a new film commenced to grow. A passive potential coincided with a film 15Aa thick. No such initial dissolution occurred when the solution contained only dissolved oxygen, the instantaneously formed film continuing to grow and a passive potential occurring after the growth of around 40Aa. When the solution contained no dissolved gases, the instantaneous film did not form.Film breakdown studies revealed that only the 20–30Aa film next to the metal was responsible for passivity even if thicker films were initially present. Studies of the sites of film breakdown showed that the number of sites was highest for films on {110} iron surfaces and that these sites were not related to points where dislocations intersected the surface. These studies support the oxide film theory of passivity.

Optical Measurements on Thin Films of Condensed Gases at Low Temperatures

A determination of the refractive indices of thin films of oxygen, nitrogen, carbon dioxide, water, argon, neon, and krypton condensed at 4.2°K was made. These were obtained for the 5461 A line of Hg with an ellipsometer. Similar measurements were also made on films of these gases condensed after passage through a microwave discharge. With the exception of N2 and Kr, measurable differences in refractive indices were observed between films condensed from discharged and undischarged gases.

Structure of passive films on iron using a new surface-EXAFS technique

Abstract There exists considerable controversy about the structure, the bonding, and the composition of the passive films that form on iron surfaces in aqueous electrolytes. A major problem is that most of the surface analytical techniques used to characterize the passive film require exposure to vacua, which can alter the structure of the passive film. This study seeks to overcome this problem through the application of a new surface-EXAFS (extended X-ray absorption fine structure) technique that is both extremely sensitive to structural and bonding changes in the 2 to 3 nm passive film and does not require the use of a vacuum environment. Near edge and extended X-ray absorption fine structure spectra from passive films on iron were measured and compared with those from pure iron and a polycrystalline iron oxide of known structure. The EXAFS data provide a measure of the structures of the passive films, and they were used to derive bond lengths for the iron-to-oxygen and the iron-to-iron coordination shells. It was found that there was greater local disorder in a chromate formed film than in a nitrite formed film. The iron-to-oxygen bond lengths were within the usual range for the crystalline iron oxides but the preliminary iron-to-iron distances corresponded to none of the known structures. The near-edge data reveal differences in the electronic configurations of passive film samples formed in different aqueous electrolytes.

Use of Ellipsometry in the Study off Corrosion

Abstract Because corrosion processes are strongly affected by the presence of thin films, ellipsometry is an especially valuable tool in corrosion research because it allows observation of film formation, dissolution, or property changes while these phenomena actually are occurring on a metal surface immersed in any transparent environment. Experimentally the use of ellipsometry requires that light be reflected from the corroding or passive metal surface under study. Thus it allows other techniques such as electrochemical ones to be carried out simultaneously along with ellipsometric measurements. The following specific examples serve as a small sampling of the many ways in which ellipsometry has been applied to corrosion studies: (1) Determination of the nature and rate of growth of passive films on iron in inorganic inhibitor solutions* (2) Separation of different stages in the early growth process of films formed by potentiostatic anodic polarization on iron in neutral solutions. (3) Determination of t...

Electrochemical Studies of the Mechanism of the Formation of Metal‐TCNQ Charge‐Transfer Complex Film

Switching and memory storage thin films constructed from metallorganic charge-transfer complexes, such as Cu + TCNQ - , can be prepared by reacting metals directly with organic acceptors in an acetonitrile solution. SEM and electrochemical methods were used to study the formation process of Cu + TCNQ - films on Cu substrates in a TCNQ/acetonitrile solution. These studies show that the Cu + TCNQ - films are formed via a localized corrosion-crystallization process, and the electrode system of Cu/Cu + TCNQ - , TCNQ 0 (CH 3 CN) is an active-passive system corroding under diffusion control

A qualitative ellipsometric-electrochemical approach to the study of film growth under organic coatings

Abstract A study was made to determine if qualitative ellipsometry could be used together with electrochemical pH and potential measurements as a technique for the study of metal substrates protected by transparent organic coatings. The objective was to gain a deeper understanding of the mechanisms governing the corrosion protective actions of paints on metal surfaces. Computer modeling and experiments with collodion coatings on iron substrates indicated that changes in the ellipsometric parameter Δ could, for the most part, be safely interpreted as thickness alterations in the substrate oxide film. Experiments with the Fe-collodion system in dilute chloride solutions exhibited three sequential stages of activity, two of which could be interpreted in terms of corrosion mechanisms using the optical and electrochemical measurements. Chromate ion as a corrosion inhibitor in coatings was also studied using this technique, and was shown to have significant effects upon the development of the subcoating processes.

Ellipsometric-spectroscopy of films formed on metals in solution

Abstract The computational problems involved in the analysis of “ellipsometric-spectroscopic” data are considered, including the existence of multiple values of the optical constants for a single wavelength. Suggestions are made for eliminating the extra values. Examples of pertinent experiments to study corrosion processes are given for passive films grown on single crystals of iron in sodium borate-boric acid solution.

STRUCTURAL STUDIES OF PASSIVE FILMS USING SURFACE EXAFS

ABSTRACT Iron K-absorption edge spectra were obtained from the passive films on iron for the dried films in air ( ex situ ) and for the films in the passivating solutions ( in situ ). The ex situ results demonstrate that, while the structures of the films are more disordered than the spinel-like iron oxides (e.g. γ-Fe203), they are nevertheless closely related to these crystalline oxides. The in situ data shows evidence of a quite different structure, which may be due to the accommodation of hydrogen containing species into the structure.