Ion exchange separations in the analysis of bismuth base alloys : Binary alloys with uranium and thorium

Procedures are described for the determination of uranium (0.001–10%) and thorium (0.05–10%) in binary mixtures with bismuth. A preliminary separation of the bismuth is effected by the passage of a hydrochloric acid solution of the sample through a column of Deacidite FF For thorium contents greater than 1%, the determination is completed volumetrically with EDTA using pyrocatechol violet as indicator, smaller amounts are determined absorptiometrically with thoronol Similarly the higher uranium contents are determined volumetrically after reduction to the tetravalent state with a lead reductor, and an absorptiometric method based on the coloured complex formed by tetravalent uranium with thoronol is used for the smaller amounts.     

The micro volumetric determination of uranium with application to bismuth base alloy analysis

The macro volumetric method for the determination of uranium by titration against standard ceric sulphate after reduction on a lead column has been successfully applied on the micro scale Microgram amounts of uranium can be determined by this method, the lowest amount determinable being about 1 microgram. The procedure is accurate to within ±1% at the 100 μg level of uranium Although bismuth and iron cause difficulty, there is no interference from zirconium or thorium.This method for uranium has been applied to the analysis of bismuth base alloys containing uranium in concentrations from 0.005 to 0.1% by weight.     

The determination of zirconium in fluoride-containing solutions

In the recommended procedure the zirconium is first precipitated from solution as the insoluble barium fluozirconate. After separation, the precipitate is dissolved in a mixture of nitric and boric acids and the zirconium is then precipitated as its hydroxide. This precipitate is separated, dissolved in hydrochloric acid and this solution is evaporated to fumes of perchloric acid to remove completely fluoride ions. The zirconium content is then determined volumetrically by adding a slight excess of a standard solution of ethylenediaminetetra-acetic acid and back titrating with a standard iron solution at pH 2.3 using potassium benzohydroxamate as indicator and the photometric technique for end-point detection. This method is applicable to the determination of milligram amounts of zirconium in fluoride-containing nitric or hydrochloric acid solutions provided that the concentration of these acids is below 3N. It is also suitable for the determination of zirconium in the presence of any of the following elements - uranium, titanium, niobium, tantalum, molybdenum, tungsten, lead, iron, copper and tin.     

On the width of ordered sets and Boolean algebras

Thewidth (chain number) of a partial order P, < is the smallest cardinal such that ¦A¦< 1 + whenever A is an antichain (chain) in P. We prove that, if a partial order (P, <) has width and cf()=, then P contains antichains A_n (n<) such that ¦A ₀¦<¦A₁¦ <...<={¦A_n¦: n < < } and either A₀1 A₂< ... or A₀>A₁ >A₂> ... A similar structure result is obtained for partial orders with chain number if cf()=. As an application we solve a problem of van Douwen, Monk and Rubin [1] by showing that if a Boolean algebra has width , thencf() .This work has been partially supported by NATO grant No. 339/84.Presented by Bjarni Jonsson.     

Electroreductive Radical Borylation of Unactivated (Hetero)Aryl Chlorides Without Light by Using Cumulene-Based Redox Mediators**

Single-electron transfer (SET) plays a critical role in many chemical processes, from organic synthesis to environmental remediation. However, the selective reduction of inert substrates (E_p/2<−2 V vs Fc/Fc⁺), such as ubiquitous electron-neutral and electron-rich (hetero)aryl chlorides, remains a major challenge. Current approaches largely rely on catalyst photoexcitation to reach the necessary deeply reducing potentials or suffer from limited substrate scopes. Herein, we demonstrate that cumulenes–organic molecules with multiple consecutive double bonds–can function as catalytic redox mediators for the electroreductive radical borylation of (hetero)aryl chlorides at relatively mild cathodic potentials (approximately −1.9 V vs. Ag/AgCl) without the need for photoirradiation. Electrochemical, spectroscopic, and computational studies support that step-wise electron transfer from reduced cumulenes to electron-neutral chloroarenes is followed by thermodynamically favorable mesolytic cleavage of the aryl radical anion to generate the desired aryl radical intermediate. Our findings will guide the development of other sustainable, purely electroreductive radical transformations of inert molecules using organic redox mediators.     

Heating of an Atomic Force Microscope tip by femtosecond laser pulses

During the 18th Egyptian dynasty (1570–1292 B.C.), opaque white, blue and turquoise glasses were opacified by calcium antimonate crystals dispersed in a vitreous matrix. The technological processes as well as the antimony sources used to manufacture these crystals remain unknown. Our results shed a new light on glassmaking history: contrary to what was thought, we demonstrate that Egyptian glassmakers did not use in situ crystallization but first synthesized calcium antimonate opacifiers, which do not exist in nature, and then added them to a glass. Furthermore, using transmission electron microscopy (TEM) for the first time in the study of Egyptian opaque glasses, we show that these opacifiers were nano-crystals. Prior to this research, such a process for glassmaking has not been suggested for any kind of ancient opaque glass production. Studying various preparation methods for calcium antimonate, we propose that Egyptian craftsmen could have produced Ca₂Sb₂O₇ by using mixtures of Sb₂O₃ or Sb₂O₅ with calcium carbonates (atomic ratio Sb/Ca=1) heat treated between 1000 and 1100°C. We developed an original strategy focused on the investigation of the crystals and the vitreous matrices using an appropriate suite of high-sensitivity and high-resolution micro- and nano-analytical techniques (scanning electron microscopy (SEM), X-ray diffraction (XRD), TEM). Synchrotron-based micro X-ray absorption near edge spectroscopy (μ-XANES) proved to be very well suited to the selective measure of the antimony oxidation state in the vitreous matrix. This work is the starting point for a complete reassessment not only of ancient Egyptian glass studies but more generally of high-temperature technologies used throughout antiquity.     

Coherent THz synchrotron radiation from a storage ring with high-frequency RF system

The generation of brilliant, stable, and broadband coherent synchrotron radiation (CSR) in electron storage rings depends strongly on ring rf system properties such as frequency and gap voltage. We have observed intense coherent radiation at frequencies approaching the THz regime produced by the MIT-Bates South Hall Ring, which employs a high-frequency S-band rf system. The measured CSR spectral intensity enhancement with 2 mA stored current was up to 10,000 times above background for wave numbers near 3 cm(-1). The measurements also uncovered strong beam instabilities that must be suppressed if such a very high rf frequency electron storage ring is to become a viable coherent THz source.