Determination Of Oxygen Content Research Articles

Simultaneous noninvasive determination of regional myocardial perfusion and oxygen content in rabbits: toward direct measurement of myocardial oxygen consumption at MR imaging.

To determine whether myocardial arterial perfusion and oxygen concentration can be quantified simultaneously from the same images by using spin labeling and the blood oxygenation level-dependent (BOLD) effect with fast spin-echo (SE) imaging. A T2-weighted fast SE pulse sequence was written to image isolated, arrested, blood-perfused rabbit hearts (n = 6) at 4.7 T. Perfusion images with intensity in units of milliliters per minute per gram that covered the entire left ventricle with 0.39 x 0.39 x 3.00-mm resolution were obtained in less than 15 minutes with a 32-fold reduction in imaging time from that of a previous study. Estimates of oxygen concentration were made from the same images acquired for calculation of perfusion images. Estimates of regional myocardial oxygen content could be made from the perfusion images; this demonstrated the feasibility of three-dimensional calculation of regional oxygen consumption, which requires concomitant measurement of both oxygen content and flow. Fast SE imaging was shown to be as sensitive to hemoglobin desaturation as standard SE imaging. Perfusion abnormalities and oxygen deficits were easily identified and verified qualitatively with gadopentetate dimeglumine on both perfusion and BOLD images obtained after coronary arterial ligation. T2-weighted fast SE imaging combined with perfusion-sensitive spin labeling can be used to measure myocardial arterial perfusion and oxygen concentration. This provides the groundwork for calculation of regional myocardial oxygen consumption.

Determination of lattice parameter, oxidation state, and composition of individual titanomagnetite/titanomaghemite grains by transmission electron microscopy

A transmission electron microscopy (TEM) method, higher‐order Laue zone (HOLZ) diffraction, has been applied to measurement of accurate lattice parameters of individual titanomagnetite and titanomaghemite grains. Lattice parameters and cation‐composition data are obtained with TEM/analytical electron microscopy (AEM) for individual grains smaller than 0.1 μm in diameter. A suite of Ocean Drilling Program/Deep Sea Drilling Project ocean‐floor basalts containing titanomagnetite‐titanomaghemite with a wide range of oxidation degree (z), were employed to establish the relationship between lattice parameter (a), z and Ti‐content (x) for naturally occurring samples. Standardization was accomplished with measurements on grains sufficiently large to allow the determination of absolute oxygen contents by electron microprobe analyses, which directly yielded z values. The probe data confirm that the maghemitization process in ocean‐floor basalts is one involving loss of iron and indicate a nearly linear relationship between lattice parameters and oxidation degrees for a given x value, except for the smallest and largest values of z. The standardized relation permits determination of z for individual submicrometer‐sized grains using only measured a‐values and cation compositions as determined by HOLZ diffraction and AEM.

Microgravimetric Investigations of High-Temperature Superconductors

It has been confirmed that, in oxide superconductors, the superconducting transition temperature Tc depends strongly on the oxygen content and oxygen ordering. The microgravimetric method is very useful in the analysis of oxide superconductors, because it allows investigations in vacuum and controlled environments in classical applications: thermogravimetric analysis, kinetics and thermodynamics of reaction, determination of oxygen contents in redox reactions, investigations of the correlation of the deviation from stoichiometry and carrier concentration and also the combined measurement of mass and additional parameters, e.g. evolved gas analysis, etc. Selected papers are reviewed.

Determination of Aluminum and Oxygen Contents in Liquid Iron in Equilibrium with .ALPHA.-Alumina and Hercynite.

The constitution of Al and O at 1873 K at the coexisting point, at which the Fe-Al-O system was in equilibrium with both of FeO·Al2O3 and α-Al2O3, was investigated, and the measured Al and O contents were found to be 0.072 mass% O and 0.0018 mass% Al. The O content of this point agrees well with other measured values. The Al content of this point is two orders of magnitude larger than the activity of Al but agrees fairly well with the Al content predicted by an associated solution model and that measured by Novokhatskiy et al. This result reveals that the equilibrium curve (E.C.), which indicates the Al and O contents in liquid Fe in equilibrium with α-Al2O3, is a concave curve in the low Al region that extends to the coexisting point. However, the E.C. calculated using the interaction parameters and deoxidation constant K is almost a straight line. This discrepancy indicates that the use of the interaction parameters reported for this system is probably inappropriate in the concave E.C. region. The interaction parameters and thermodynamics of this system should be reexamined.

Determination of oxygen content in nickel and cobalt powders: E.Grallath et al. (Max-Planck Inst., Stuttgart, Germany.) Powder Metall., vol 40, no 3, 1997, 214–218

Determination of oxygen content in nickel and cobalt powders: E.Grallath et al. (Max-Planck Inst., Stuttgart, Germany.) Powder Metall., vol 40, no 3, 1997, 214–218

Determination of oxygen in powders of refractory phosphides and phosphorus-containing alloys by the reduction extraction method

The conditions of determination of oxygen content in powders of different refractory phosphides phosphorus-containing alloys have been studied by the reduction extraction method. Phosphides of the second classification group and copper phosphides with a limited oxygen concentration have the least ability to sublimate the phosphorus under the analysis conditions. The use of metal flux, particular nickel, results in a satisfactory decrease in sublimate quantity. The reliability of results obtained has been checked through the method of additives and variation of weighted amounts. The metrological characteristics of measurements of oxygen mass fraction in the studied materials have been determined. The measuring errors follow the up-to-date standards for metal powders.

Adolf Fick (1829-1901), physiologist: a heritage for anesthesiology and critical care medicine.

Adolf Fick (1829-1901), physiologist: a heritage for anesthesiology and critical care medicine.

Determination of Stoichiometry and Oxygen Content in Platelike and Octahedral Oxygen Precipitates in Silicon with FT-IR Spectroscopy

Determination of Stoichiometry and Oxygen Content in Platelike and Octahedral Oxygen Precipitates in Silicon with FT-IR Spectroscopy

An accurate method of iodometric titration for determining oxygen content of superconducting cuprates

There are three problems existing in double iodometric titration. First, the calculating equation is too rough to obtain accurate results. Second, an error comes from iodine adsorbed by CuI. Third, when a sample is doped with iron-like elements, iron interferes with this method. The above problems were solved as following. We adopted a new equation, which may modify copper valence p by 4% and oxygen content by 0.02. To reduce the experimental error KSCN was added to displace the adsorbed iodine on the CuI. NH 4HF 2 was introduced to prevent the interference of Fe. Our experiment results show that by adding NH 4HF 2 the modification of oxygen content increases when Fe content increases.

A modified function of the formula of double iodometric titration

Double iodometric titration is the most useful method to determine oxygen content of high T c superconductors. Its traditional calculating formula is not accurate enough, and a new calculating formula has just been put forward. To understand which relationship of the traditional formula depends on the new one is an important problem. On studying the new formula, we find a modified function F relating the traditional formula to the new one, and also find that the value of F depends only on molar weight of the superconductor. For Y, Bi, and Hg systems, a group of curves of the modified function are put forward here. Since many results about average copper valence and oxygen content have been published, to correct those results one can modify them by means of the corresponding F. As a sample, we modify two published data of average copper valence and oxygen content of Y and Bi systems. After comparing the unmodified with the modified data, we find that it is necessary to modify the published data for quantitative research.

The influence of Ca doping on the crystal structure and superconductivity of orthorhombic

The changes of the chemical structure of and of the superconducting transition temperature associated with Ca doping have been investigated by means of neutron and x-ray powder diffraction, oxygen content determination and magnetic susceptibility measurements. In this work, we were able to show that the depression of superconductivity in Ca-substituted orthorhombic is related to essential structural changes. Using the cation - oxygen distances obtained by neutron diffraction at 1.5 K we calculated the bond valence sums of the cations. This allows us to estimate the charge distribution within the structure and yields a direct correlation between structural changes induced by Ca doping and . Our results show clearly that Ca doping leads to an overdoping of which cannot be reached by oxygen non-stoichiometry alone.

Spin dynamics by inelastic neutron scattering in YBCO

Key features of Inelastic neutron scattering experiments in YBCO-based cuprates are discussed. We underline the importance of precise oxygen content determination in samples having similar TC as well as the resolution configuration used. This may explain the apparent contradictory results recently obtained by different groups.

An improved procedure for determining oxygen content in high-T ccopper oxides

We present an improved double titration method for high-T c superconductors, in which the major step is adding KSCN as an indicator of the end point after the starch end point. By adding it, a greater amount of Na2S2O3 solution can be added after the starch end point, at least 0.12 ml. We found that adding KSCN can lead to precise measuring results and reduce the experimental error. The oxygen contents of two series of superconductors were determined by this approach. For YBa2Cu3O y , the errors are Δp∼0.003 and Δy∼0.005, which are lower than that of other reports.

Valence analysis of Pb and Cu and superconductivity of (Pb,Cu)(Sr,La) 2CuO y

The Pb 1201 phases, Pb 0.5Cu 0.5Sr 2− x La x CuO y , with x = 1.0–1.2 and Pb 0.6Cu 0.4Sr 2− x La x CuO y , with x = 0.9–1.2 have been prepared at 1010–1015°C for 1.7–2.0 hours in flowing oxygen. To evaluate the Cu valence in the CuO 2 sheet, the Pb valence is separately determined by K 2Cr 2O 7 titration, in addition to the oxygen content determination by iodometry. The T c (onset) rises as the oxygen content decreases due to release of the overdoping, but was not affected by La 3+ substitution for Sr 2+ and by the Pb content in the (Pb,Cu)O layer. The explanation is that the Cu valence in the CuO 2 sheet decreases as the oxygen content decreases, while the Pb valence is reduced by La 3+ substitution or the Pb content increases.

Catalytic decomposition and oxidation of CH 3Cl on Cr 2O 3-doped SnO 2

The adsorption, decomposition and oxidation of CH 3Cl have been investigated on pure and chromiadoped SnO 2 catalysts by means of infrared spectroscopy, mass spectrometric and gas chromatographic analysis. Catalyst samples have been characterized by X-ray photoelectron spectroscopy. It was found that the Cr 3+ ions incorporated in the surface layer of SnO 2 are oxidized to higher valent chromium ions. In harmony with the determination of active oxygen content, samples calcined at 873–973 K contained the largest concentration of higher valent chromium ions. Infrared spectroscopy showed that CH 3Cl interacts with the OH groups of SnO 2 at 200–300 K to form H-bridge-bonded alkyl chloride. The decomposition of CH 3Cl occurred slowly on pure SnO 2 above 573 K to give CH 4, H 2O, CO and HCl. The oxidation of CH 3Cl on SnO 2 proceeded at a measurable rate at 400–440 K. Incorporation of a small amount of chromium ions into the SnO 2 increased the rate of both the decomposition and the oxidation by a factor of 10–16. The enhanced activity of chromia-doped SnO 2 is attributed to the high reactivity of chromium ions in the surface layer of SnO 2.

Improved iodometric method for simultaneous determination of non-stoichiometric oxygen and total copper content in YBCO superconductors

Some improvements with regard to the iodometric method for the determination of the total copper and non-stoichiometric oxygen (or Cu 3+) content in YBa 2Cu 3O y superconductors were made. A potentiometric end-point determination with Pt wire electrode was introduced, and a higher concentration of KI was used in order to avoid precipitation of CuI. The two ways for calculating the oxygen coefficient γ and the possibility for detecting changes of the sample, with consequent differences in stoichiometry, were discussed.

Determination of oxygen content and cation valences in superconducting Tl-based cuprates by a wet chemical method.

A wet chemical route based on constant-potential electrolysis and different reactivities of ${\mathrm{Cu}}^{3+}$ and ${\mathrm{Tl}}^{3+}$ with water is proposed to distinguish the average valences of Cu and Tl in superconducting thallium cuprates. The validity of the method is demonstrated using ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{y}}$, ${\mathrm{Tl}}_{2}$${\mathrm{O}}_{3}$, and ${\mathrm{Tl}}_{2}$O as reference materials for ${\mathrm{Cu}}^{3+}$, ${\mathrm{Tl}}^{3+}$, and ${\mathrm{Tl}}^{+}$, respectively. Furthermore, the oxygen contents and the cation valences have been determined for various Tl-22(n-1)n phases (where n=1--4). With increasing n value the Cu valence is found to decrease, while the valence of thallium remains rather constant at ca. +3, regardless of the value of n. Based on these results, the possible carrier doping mechanisms in the Tl-22(n-1)n phases are discussed.

Determination of oxygen contents and cation valences in the superconducting bismuth and thallium cuprates

The oxygen contents and valences of cations in various superconducting cuprates such as Bi2Sr2(Ca, Y)Cu2Oy, Tl2Ba2Can−1CunOy, etc. which contain two kinds of multi-valence metals have been determined by novel wet chemical methods. The wet chemical methods are based on the differences in oxidation power of each cation and at the last step an electrochemical method is employed for measuring the amount of reducing agent, i.e., CuCl. For superconducting Bi-based cuprates, a modified constant-current coulometry has been developed. For the superconducting Tl-based cuprates a constant-potential electrolysis method which makes it easy to control the electrolysis potential has been applied. The results obtained for Bi2Sr2(Ca, Y)Cu2Oy have shown that both Bi- and Cu-valences decrease with increasing Y, which is consistent with the results of earlier works. The results obtained for the double Tl-O layer superconductors show that the Tl valence is about +3 in all the thallium cuprates and different from the value obtained from XPS measurements of earlier works. The reason for this discrepancy is discussed.

Superconducting La 1.5− xBa 1.5+ x−ySr yCu 3O z solid solutions. Stoichiometry, structure and properties

The stoichiometry range for Sr-doped La-123/336 solid solutions has been determined by means a phase diagram study at ∼950°C. The solid solutions have general formula La 1.5− x Ba 1.5+ x−y Sr y Cu 3O z and form over the entire range 0⩽ x⩽0.5 and 0⩽ y⩽0.5 apart from compositions with high x and y. The solid solutions are tetragonal under all conditions used; lattice parameters vary linearly with x and y. T c passes through a maximum of 65 K at x∼0.5, y∼0.3, which is ∼ 10 K higher th the previous maximum reported for this system. Oxygen content determinations by TGA indicate two mechanisms for increasing the hole concentration: with increasing x, the substitution La 3+⇔Ba 2++h + occurs, whereas with increasing y, the substitution mechanism is Ba⇔Sr+ mO 2−+2 mh +. Rietveld refinement of powder XRD data shows that Sr substitutes preferentially onto Ba sites, in contrast to Ca substitution where Ca occupies La sites.

ＹＢａ２Ｃｕ３Ｏ７−δ超伝導薄膜の酸素欠損と陽イオン秩序

Crystal structure and superconductivity of YBa2Cu3O7-δ thin films were investigated as functions of oxygen contents and growth temperatures. An effective method for the quantita-tive determination of oxygen content from X-ray diffraction intensity ratio was established through systematic studies on the structural change of the oxygen deficient films. Dependence of cation disorder and Tc on growth temperature, as well as post-annealing temperature has also been obtained. The results suggest an intrinsic relation existing between structure and superconductivity.