Evaluation of corrosion potential measurements as a means to monitor the storage and stabilization processes of archaeological copper-based artifacts

The focus of this study consists of examining how corrosion potential measurements can contribute in providing information on the effectiveness of storage and stabilization treatments of copper alloys in aqueous solutions. We report on the electrochemical behavior of artificial copper alloy coupons (covered or not with corrosion layers), simulating the behavior of real artifacts, immersed in sodium sesquicarbonate solutions. Particular attention is given to the transformation of the corrosion layer as a function of time. In addition, synchrotron radiation X-ray diffraction measurements are performed before and after the treatment in order to understand the reactions that take place during the immersion processes.     

From the grating scale monitor to the generalized seeing monitor

An instrument named the grating scale monitor for measuring the outer scale L0 from the angle-of-arrival (AA) fluctuations of a perturbed wave front was developed a few years ago at Nice University. The AA is detected with a 5-ms time resolution by modulation of the stellar image in a small telescope with a grating. One uses the normalized covariance of AA fluctuations to estimate L0. A new version of this instrument, the generalized seeing monitor (GSM) is described. It consists of four identical modules for measuring the AA at four locations on the wave front. A spatiotemporal analysis of these data leads to the determination of seeing epsilon0, outer scale L0, and the wave-front speed. In addition, isoplanatic angle theta0 is determined from scintillation, making the characterization of turbulence with the GSM almost complete. We describe the instrument and make a detailed analysis of its performance and accuracy. Several site-testing campaigns have been conducted with the GSM: at La Silla (Chile), Ouka?meden (Morocco), Maidanak (Uzbekistan), and Cerro Pachon and Cerro Paranal (Chile). The main results of these campaigns are presented and discussed.     

Capacitative dust monitor

Translated from Izmeritel'naya Tekhnika, No. 1, pp. 55–57, January, 1990.     

Press load monitor

The article describes the design and use of an instrument which displays the peak frame load during a single operating stroke of a press. It consists of a strain gauge link permanently bolted to the frame of each press to which a portable electronic unit is connected. The technique of using a strain gauge link eliminates the problems encountered when a load cell is used, or when a strain gauge system is bonded directly to the machine frame.     

The electrochemistry of corrosion beneath corrosion deposits

Based on the uniform corrosion mechanisms beneath corrosion deposits described in a preceding theoretical study, the present paper shows that certain deposits attain a steady state only at the free corrosion potential. Except for the natural corrosion potential, electrochemical investigation techniques can therefore only be used to study quasi-stationary states, where the electrochemical reactions and transport phenomena are in dynamic equilibrium with the instantaneous thickness of the deposit. The electrochemistry of a metal covered by soluble or anionic insoluble deposits is very close to that on bare metal (deposits transparent to the imposed polarization). Conversely, deposits of the insoluble cationic type compensate nearly integrally the effects of polarization, thus behaving as veritable passive layers. It is also shown that irreversibility effects are present in the growth regime control of deposits under imposed polarization. This may lead to multiple quasi-stationary states. For example, anodic or cathodic pulses can cause an insoluble deposit to change from cationic to anionic, or vice versa. A particular consequence is the existence of a pitting or general anodic depassivation potential for insoluble cationic deposits. Similarly, there is a protection or cathodic passivation potential for insoluble anionic deposits. Altogether, electrochemical methods shall be used, not only to measure corrosion rates, but also to study the intrinsic stability of the feature of observed deposits. This should enable us really to predict long-term corrosion rates.     

Mechanisms of uniform corrosion under corrosion deposits

The liquid-phase transport phenomena which occur at the surface of iron-base alloys during corrosion have been analysed. These mechanisms determine either the maintenance of bare metal or the precipitation of solid corrosion products, the build-up of a corrosion deposit and the control of its thickness, and finally, the kinetics of the electrochemical reactions under the deposit. Although it is shown that pure precipitation-redissolution or direct formation reactions are impossible, the only conceivable mechanisms are nevertheless closely related, because the transport of iron between the metal and the external corrosive medium occurs chiefly either via the solid phase of the deposit (for soluble deposits), or via the liquid phase permeating its porosities (for insoluble deposits). It is also shown that, depending on the precipitation conditions, any given solid compound Fe _n X₂ can lead to three types of deposit with quite different properties. (i) Soluble deposits: moderately protective, steady-state corrosion insensitive to potential, but highly sensitive to turbulence; (ii) Insoluble cationic deposits (controlled by the removal of Fe²⁺ cations by liquid-phase diffusion): highly protective, corrosion rate slightly sensitive to potential, and insensitive to turbulence. (iii) Insoluble anionic deposits (controlled by the diffusional supply of the precipitatable anion X ^n– : slightly or unprotective, corrosion slight or insensitive to the presence of the deposit; possibly profuse deposit if steady state corrosion is not attained. This theoretical analysis can retrospectively explain numerous experimental observations reported in the literature, such as the incubation time before the drop in corrosion rates, the multiple forms of CO₂ and H₂S corrosion, the role of Ca²⁺ ions, erosion-corrosion and bacterial corrosion. This analysis also paves the way for the reliable laboratory prediction of real corrosion rates under deposits.     

Thermal luminescence water monitor

A thermal luminescence (TL) spectroscopy method for detecting organic impurities in water solution is presented. Infrared emissions by the dissolved organic matter are measurable, once a thermal gradient between it and the water medium is established, at those TL frequencies that are absorbed by the contaminant, following irradiation by a pulsed microwave beam. This detection window of opportunity closes as the liquid reaches thermal equilibrium at elevated temperatures and on collapse of the gradient. TL radiance liberated by a suspected contaminated water sample is scanned interferometrically about the maximum thermal gradient event, where N interferograms are acquired and grouped into contiguous sets of two, with N/2 interferogram elements per set. The coadded averages of these sets enhance the sensitivity of measurement to a small variance in emissivity and are Fourier transformed, and the adjacent spectra are subtracted. The difference spectrum is preprocessed with linear baseline, noise filtration, scaling, and parity operators to reveal a clear emissions band signature of the solute of dimethylmethylphosphonate to concentrations of parts per 10(3) and less. An artificial neural network facilitates detection of the contaminant by pattern recognition of the contaminant's infrared band signature.     

Mechanism of local corrosion in corrosion cracking cracks

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 4, pp. 3–8, July–August, 1990.     

A non-intercepting current monitor

A non-intercepting current monitor has been installed on the beam course for radionuclide production in the NIRS cyclotron, and operates well with an adequate accuracy.     

A bistatic laser monitor

Technical Physics Letters - A prototype of a bistatic laser projection system employing copper bromide vapor based active media is presented that allows remote objects and high-speed processes to...     

An on-line tritium-in-water monitor

The paper describes the development and operation of a continuous on-line tritium-in-water monitor for the detection of heavy water leaks into the secondary coolant light water of a heavy water power reactor. The heart of the instrument is its plastic scintillator sponge detector, made from 5 μm thick plastic scintillator films. The sponge weighs only about 1 g and is in the form of disc of 48 mm diameter and 8 mm thickness. The total surface area of the films is about 3000 cm². In the coincidence mode of counting, the detector gives 1000 cps for the passage of 3.7 × 10⁴ Bq/cm³ (1 μCi/cm³) of tritiated water. The background in 6 cm thick lead shielding in the laboratory is 0.2 cps, and inside the reactor building it is below 1 cps. The monitor presently scans 18 sample lines in sequence for 5 min each and gives a printout for the activity in each line.     

Microcomputer-based real-time bearing monitor

Rolling element bearings form an important part of machine tools. Consequently, regular monitoring of their performance is essential to ensure manufacturing quality and operation safety. An effective approach is to measure the real-time load and temperature fluctuations inside the bearing against any potential danger of overloading and/or overheating. In this paper, the design, implementation, and testing of the measuring electronics are presented, to form the key part of the development of sensor-integrated “smart” bearings     

Two-dimensional beam image monitor

In this letter we describe a device useful in obtaining two-dimensional information from low intensity beams of ionizing radiation. It consists of an anode wire plane (to provide charge amplification), a gating plane (to control the flow of charge through the chamber), and a cathode plane for collecting charge. With a prototype chamber we have obtained 1 mm × 1 mm resolution with 48×48 pixels, and a sensitivity to single 6 keV X-ray events.