Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Journal of Thermal Analysis and Calorimetry - In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu2O2 (SCO) having possible applications...     

Driver gas contaminationin a detonation-driven reflected-shock tunnel

A computational study has been carried out to examine the effects of driver gas contamination in the NASA HYPULSE facility at GASL when operating with a detonation driver in reflected-shock tunnel mode. Unlike high-enthalpy shock tunnels which use helium as a driver gas, the driver gas in a detonation driver consists of a mixture of water vapour and argon, which has very different chemical and thermodynamic properties than those of helium. The purpose of the present work is to quantitatively evaluate the effects of driver gas contamination on the flow properties in the test section. Two computational analyses have been performed. The first analysis examined the nozzle flow under the influence of a prescribed level of driver gas contamination. In the second analysis, the transient development of the driver gas leakage in the reflected-shock region in the shock tube is studied. The unique flow features brought about by the detonation-driver gas and the method for detecting the contamination are discussed.Received: 6 August 2002, Revised: 22 September 2003, Published online: 10 February 2004Correspondence to: R.S.M. ChueAn abridged version of this paper was presented at the 23rd International Symposium on Shock Waves at Fort Worth, Texas, July 23 to 27, 2001     

Deposition of platinum monolayers on gold

Deposition of small amount of Pt is reported onto polycrystalline Au from H₂PtCl₆-containing solutions. Spontaneous deposition, yielding about 5% of a full-packed monolayer, has been found at the steady-state open circuit potential. Formation of a somewhat more dense, but still a partial monolayer could be observed at potentials between the steady-state open circuit potential and that of the onset of bulk deposition. A specific difference of monolayer and bulk deposition is that Pt surface area levels off with time and keeps increasing for the former and latter types of deposition, respectively. Pt monolayers with quite high coverages can be formed in a rather narrow, 20–30 mV potential region only. The surface areas of Pt and of the Pt-free Au have been simultaneously measured as cyclic voltammetry peak charges. From these measurements, the site requirement of the Pt atoms was determined to be around four; that is, each Pt atom blocks the oxidation of about four underlying/neighbouring Au atoms, implying their distant positions. Based on the results, Au surfaces coated with monoatomic Pt layers of quite high coverages can be prepared.

     

Synthesis and Structure of Some 1,3,2-Oxazaphospholenes

Abstract

The reaction of trialkyl phosphites and phosphines with o-quinones result in the formation of oxyphosphoranes [1]. In an effort to prepare o-quinone monoimine metal complexes with amine [2] and phosphine ligands it has been found that in the reaction either of o-quinones (1) with phosphines in the presence of ammonia or of o-quinone monoimines (2) with phosphines 1,3,2-oxazaphospholenes (3) are formed in good yields.     

A New Route to 16-Methylene-17-ketosteroids

A new, high-yield preparation of 16-methylene-17-ketosteroids by the methylenation of trimethylsilyl enol ethers is described.     

Palladium Deposition on Pt Surface by Reduction of Pd2+ Ions with Organic Substances

It has been demonstrated that Pd²⁺ ions can be reduced onto Pt surface in the presence of organic materials but only at a very low Cl^– ion activity. Unlike rhenium deposition, Pd deposition may proceed after the formation of an adsorbed Pd monolayer and bulk deposits are formed on the Pt surface.     

Occlusion of hydrogen in electrodeposited platinum layers

Occlusion of hydrogen in platinized platinum electrodes has been studied in 1 mol/dm³ H₂SO₄ electrolyte. It has been found that the amount of hydrogen dissolved in the platinum layer depends on the structure of the Pt deposit, which is determined by the parameters of electrodeposition. Composition of the platinizing solution as well as the potential of Pt deposition are decisive parameters. On the basis of experimental results it is assumed that occlusion of hydrogen takes place in special structural elements of the platinum layer which are formed in the course of Pt deposition. Hydrogen dissolution versus H-deposition potential, H-deposition time and Pt layer thickness relationships are also presented. Received: 2 March 1999 / Accepted: 25 May 1999     

Primary coolant circuit characterization related to starting up the WWER-440 unit

Neutron activation analysis, gamma-ray spectrometry, particle sizing and photography of the corrosion products were used to qualify the constructional materials and primary coolants. The investigations related to: characterization of the construction materials of the primary circuit, circulated washing, hot conditioning, physical and energetic start up. The aim of the measurements was to study the cleanness of the primary circuit from assembling up to energetic start up and to follow closely the variation in the amount and the removing of the mechanical contaminants and corrosion products depending on the technological parameters.Presented at IAEA Specialist's Meeting on The Influence of Water Chemistry on Fuel Element Cladding Behaviour in Water Cooloed Power Reactor, 6–10 June 1983, Leningrad, USSR.     

Aggregation Properties of Sodium Hyaluronate with Alkanediyl-alpha,omega-bis(dimethylalkylammonium Bromide) Surfactants in Aqueous Sodium Chloride Solution

Lysine, which is an amino acid with a basic side group, is present in biological fluids and its role in the biological calcification process was investigated. It was found to inhibit the crystal growth rate of hydroxyapatite (HAP), in solutions supersaturated only with respect to this calcium phosphate salt and this rate reduction was attributed to adsorption and further blocking of the active growth sites on the crystal surface. The crystallization kinetics were interpreted in terms of the Langmuir adsorption model. The apparent order of the crystallization reaction was found to be n=2, suggesting a surface diffusion controlled spiral growth mechanism. Kinetic results of HAP crystallization were obtained using the constant composition method where the concentration of the reactants is kept constant during the course of the crystal growth experiment. Copyright 2000 Academic Press.