Microgravimetric Study Research Articles

In-situ microgravimetric studies of passive alloys: potential sweep and potential step experiments with Fe–25Cr and Fe–17Cr–33Mo in acid and alkaline solution

The quartz crystal microbalance (QCM) has been applied to the measurement of weight changes taking place during potential sweep and potential step experiments in the passive potential region in an acidic and a basic electrolyte. The alloys Fe–25Cr and Fe–17Cr–33Mo were studied as well as pure chromium and iron. The metal and alloy films used were prepared by magnetron sputter deposition on an AT cut quartz crystal. The composition of passive films after anodic polarization was determined by X-ray photoelectron spectroscopy (XPS) depth profiling. In 0.1 M H 2SO 4+0.4 M Na 2SO 4 solution, both alloys exhibited a mass decrease when the potential was increased in the passive region. The mass decrease resulted from preferential dissolution of iron and led to an enrichment of the passive film in chromium oxide. The Fe–17Cr–33Mo alloy exhibited a higher dissolution rate in the passive region that the Fe–25Cr alloy. Below the potential for transpassive dissolution passive chromium, contrary to the alloys, showed a mass increase with increasing potential. In 0.1M NaOH passive Fe–25Cr exhibited a mass gain when the potential was increased. XPS showed that iron cations accumulated in the outer part of the passive film because iron oxide does not dissolve in alkaline solutions.

New Evidence of Azimuthal Variations at Campi Flegrei: Attenuation and Predominant Frequency

—In this paper we have determined apparent Q from body-wave dispersion and a spectral ratio method for the Campi Flegrei area. A contour map of azimuthal variations of apparent Q (ranging from Q = 4 to Q = 40) reveals that the lower Q (higher attenuation) corresponds to an area that includes the Solfatara Crater (with active fumaroles), near the site of maximum uplift produced during the bradyseismic crisis of 1984, and just over the site evidencing the presence of a magmatic body. A strong azimuthal variation of the predominant frequency of the first pulse of the P wave has been found and is interpreted in terms of a vertical travel time in a surficial resonant layer (∼ 1 km thick) over a halfspace. The attenuation maps, the interpretation of the resonant frequencies, and the additional information provided by the P-wave velocity suggest the presence of a circular structure in the area. Not only does the distribution of the thickness of the resonant layer (obtained through the estimation of the contribution of different harmonics) show the circular structure, but it also agrees with the presence of a thin layer of lighter sediments, determined by means of a microgravimetric study, and with the total magnetic map, previously obtained for this area. The results of the azimuthal variation provide new evidence of the structure that can be used to improve the knowledge of the area.

In Situ Quartz Crystal Microgravimetric Studies of Molecular Adsorbates Containing Thiol and Hydroquinone Moieties Bound to Au(111) Surfaces in Aqueous Electrolytes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIn Situ Quartz Crystal Microgravimetric Studies of Molecular Adsorbates Containing Thiol and Hydroquinone Moieties Bound to Au(111) Surfaces in Aqueous ElectrolytesYibo Mo, Marnita Sandifer, Chaim Sukenik, Raul J. Barriga, Manuel P. Soriaga, and Daniel SchersonCite this: Langmuir 1995, 11, 12, 4626–4628Publication Date (Print):December 1, 1995Publication History Published online1 May 2002Published inissue 1 December 1995https://doi.org/10.1021/la00012a007RIGHTS & PERMISSIONSArticle Views102Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (335 KB) Get e-Alerts Get e-Alerts

Ultraviolet irradiation induced brain oedema in rats. A microgravimetric study.

The cerebral cortex of 36 anaesthetized Wistar rats were exposed to ultraviolet irradiation (UV-I) for 6 min through a 2 x 2 mm left parietal craniotomy. Animals were killed at different times and brains were removed immediately after death. Three consecutive coronal sections were obtained and sampled for gravimetric study. The density of the samples was measured using a continuous gradient of organic solvents. Gravimetric results showed significant differences between brain samples. The irradiated left hemisphere was less dense than the right one, and maximum differences in density were found in the medial coronal section. Grey and white matter oedema in the non-irradiated hemisphere was compared with the irradiated hemisphere. Early and delayed onset of odema was observed in both hemispheres but it was more marked in the irradiated hemisphere. In conclusion, brain oedema induced by ultraviolet irradiation in various animals is also reproducible in rats with all the advantages involved in the use of these experimental animals. Microgravimetric study correlated with topographical analysis using this model may lead to an understanding of some of the dynamic aspects of cerebral oedema.

Microgravimetric study on the interaction of nickel powders with nitrous oxide and dioxygen

The interaction of nickel powders with dioxygen and nitrous oxide was gravimetrically studied. The dioxygen proved relatively reactive toward the surface of nickel. The O/Ni s ratio obtained for this interaction increased with temperature but leveled off with a stoichiometry of 2.2 around 200 K. Nitrous oxide was a milder oxidant than dioxygen. The extent of nickel oxidation with nitrous oxide also increased with temperature. A stoichiometry of O/Ni s = 0.60 ± 0.03 was obtained from the oxidation at 195 K < T < 232 K. These two stoichiometries suggested that weight gain on the nickel samples upon oxidation by dioxygen or nitrous oxide may be coupled with dihydrogen chemisorption to estimate the specific surface area of nickel samples.

Reduction kinetics of thin and thick cupric oxide films at room temperature by hydrazine

Reduction of cupric oxide films by hydrazine has been monitored using in situ X-ray photoelectron spectroscopy (XPS) and microgravimetry to discern how the idiosyncrasies of this system can be used to prepare copper films with unique properties. Results from in situ XPS studies, in the topmost 5.0 nm at 0.8 Pa of hydrazine from 295–381 K, follow pseudo-first-order kinetics during the removal of CuO with an activation energy of 35 ± 4 kJ mol−1 and a pre-exponential factor of 103.3±0.7s−1. The measured pre-exponential factor is close to the collision frequency of hydrazine with the surface (i.e. 2100s−1) and is in a regime suggestive of adsorption control. Results from microgravimetric studies, of films 18.5–69.5 nm thick at hydrazine pressures of 80–1462 Pa and temperatures of 273–373 K, provide evidence for three different reduction mechanisms. These three regimes involve (i) an induction period during the first 0%–5% of the oxygen removal, (ii) a deceleratory regime from 5%–85% of the total weight loss and (iii) a period of much slower reduction during the final 80%–95% of the oxygen removal. Reduction kinetics in regime (ii) are well fitted by a parabolic rate law and are insensitive to the hydrazine partial pressure, indicative of counter current diffusion control within the porous network being formed. The activation energy measured in regime (ii) is ca. 32±2 kJ mol−1 with a pre-exponential factor of ca. 32±4 s−1, also suggestive of diffusion control. Since all films are observed to be reduced during nearly equivalent time periods, regardless of initial thickness, intragrain diffusion control has been postulated to limit the overall rate of reduction.

Étude cinétique par microgravimétrie de l'oxydation d'échantillons polycristallins et de cristaux de niobium dans le domaine de formation des films minces interférentiels

A microgravimetric study of the oxidation of niobium was carried out with polycrystalline and monocrystalline samples. The pressure and temperature conditions and the orientations of the single crystals were the following: 75 Torr oxygen; 300–450 °C; (100), (110), (111), (211), (321). Under these conditions the kinetics followed a parabolic law and, during this process, the formation of a thin oxide film and the dissolution of oxygen in the metal were observed. The activation energies obtained for polycrystalline samples and single crystals were between 26.8 kcal mol −1 for (100) and 36.8 kcal mol −1 for (321). We found, at 350 °C for example, for the kinetics of the various orientations and for the polycrystalline samples: (111) > (110) > (211) > (321) > polycrystalline > (100). In the temperature range studied the single crystal with the orientation (100) exhibited the slowest kinetics. These results give only the global kinetics and will be complemented by other methods.

Transport of caesium through a nuclear graphite. part I. Microgravimetric studies and electron probe microanalysis

Adsorption of caesium (≈40 mg/g maximum) on a gilsonite graphite at 473 K and subsequent desorption in the range 973–1373 K have been followed in a vacuum microbalance and caesium concentration profiles in the graphites have been measured by electron probe microanalysis at stages in the adsorption-desorption programme. An analysis is developed which enables apparent diffusion coefficients, D, to be determined from desorption rates. Electron probe microanalysis provides evidence for two-phase or multi-phase diffusion of caesium in the graphites during adsorption and desorption and there is evidence that diffusion of caesium is sensitive to the thermal history of graphite. The variation of all reported values of D (m 2/s) with temperature is log D = −6.34 − 5450 T . The limitations of the method of analysis due to nonuniform caesium concentrations, finite surface exit resistance and multi-phase diffusion are also considered.

Optical transmittance and microgravimetric studies of the oxidation of 〈100〉 single crystal films of copper

Thin single crystal copper films have been grown and oxidized on (100) faces of cleaved sodium chloride discs suspended from a vacuum ultramicrobalance. Optical transmittance measurements between 400–800 nm and electron microscopic investigations were also used to characterize the oxidation process. Polycrystalline copper films grown at room temperature are substantially the same as those grown previously on glass substrates. Single crystalline growth at 325 ° C on rock salt produces a characteristic transmittance curve due to the “island” nature of the films. These curves compare favorably with other previously published results. Single crystal copper films oxidized to CuO0.67 at temperatures of 117–159°C in 100 Torr of oxygen for films less than 500 A thick. For films 378 to 1000 Å thick, compositions of CuO0.52 to CuO0.62 were obtained between 123–176°C. The oxidation to less than CuO0.67 is attributed to the existence of islands in these films which are thicker than the average film thickness, and require higher temperatures or thinner films to permit oxidation to CuO0.67 before the nucleation of CuO sets in.

A Quantitative Study of Nucleation and Growth of Copper I—Oxide on Copper Single Crystals

A microgravimetric study shows that the rate of oxidation of the (100) face of copper is convenient for the observation of the different steps of the process: induction, nucleation, and growth of the oxide particles. The rate of those steps and the number of nuclei depend upon crystallographic orientation of the metal, temperature of reaction, and pressure of oxygen. Sticking probabilities and activation energies of the different steps have been determined. Our results show under which conditions Rhead's theoretical scheme founded on surface diffusion remains valid.