Simultaneous determination of nitrogen and carbon in silicon by photon activation

The analytical procedure includes irradiation by 30 MeV photons followed by a chemical separation by evolution from molten KOH. Two radiochemical states of nitrogen are observed: NH₃ and N₂. Finally all nitrogen is converted to N₂, which is absorbed on titanium sponge. Carbon is converted to CO₂, which is absorbed in a KOH solution. This procedure was applied to silicon samples of various purity. Detection limits of 0.01 g carbon and 0.1 g nitrogen were achieved.     

The use of neutron activation for routine analysis of pure iron and chromium

A method is presented for the routine analysis of high-purity iron and chromium by neutron activation analysis. The impurities determined are those which are significant in the control of the purification processes. Nine elements are determined in iron without separation; Co, Cr and Mo can also be determined after an anion-exchange separation. In chromium, a single elution on an anion exchanger allows the detection of nine significant impurities. For the determination of nickel a special method is used. All these methods were chosen to obtain the most comprehensive analytical procedure at the lowest cost.     

Utilisation des radioisotopes de courtes périodes pour le dosage d'éléments traces dans les métaux de haute pureté par activation neutronique

A complete study of high-purity metals must include the determination of some elements giving only short-lived radioisotopes by the (n, γ) reaction. In the case of elements giving also long-lived radioisotopes, the use of a short-lived isotope may be advantageous in two cases: possibility of a quick non-destructive analysis or better sensitivity. The determination of aluminium in iron, zirkonium and molybdenum and of cobalt in iron and nickel is described in detail. When necessary quick chemical separations have been developed. The determinations permit to follow the purification of the metals studied.     

Preparation, composition and structure of some nickel and zinc ferrocyanides: Experimental results

Several methods have been used for preparation of nickel and zinc ferrocyanides: precipitation, growth in a gel and a new method based on growth on a solid alkali-metal ferrocyanide. The granulometry, morphology, composition and structure of the compounds were studied. Only the last method of preparation gives products suitable for use as ion fixators in columns on a large scale. The nickel ferrocyanide compositions can be written as M(I)(2x)Ni(2-x)Fe(CN)(6).yH(2)O with M(I) Na, K, Cs, H and 0 < x < 0.8. They have a cubic lattice with a partial occupancy of iron sites. For zinc ferrocyanides, rhombohedral M(I)(2)Zn(3)[Fe(CN)(6)](2).xH(2)O, trigonal Zn(2)Fe(Cn)(6).2H(2)O and other cubic compounds were found. Products resulting from the fixation of caesium by ion-exchange were also studied.     

Morphology and surface heterogeneities in synthetic goethites

In the framework on a study of the acido-basic and sorption properties of iron oxides, a thorough characterization of two types of goethite powders was performed in several laboratories joined in a common project. Chemical analysis by ICPAES; high-resolution SEM, TEM, and AFM observations; XRD with line width analysis; and argon and nitrogen sorption isotherms were used for that purpose. The main crystallographic faces of goethite particles could be identified as {001}, {101}, and {121}, and their abundance correlated with the distribution of low-pressure argon adsorption local isotherms. These results will be very useful for further studies on the relationship between surface reactivity in aqueous solution and orientation of solid surfaces.     

Multielement analysis of aluminium by NAA and ICP/AES

The results of neutron activation analysis (NAA) and inductively coupled plasma atomic emission spectrometry (ICP/AES) are compared for aluminium samples in the purity range from 99.7 to 99.998%. The advantages of each method towards the determination of 25 elements is discussed.     

Morphology of RuO2-TiO2 coatings and TEM characterization of oxide sols used for their preparation

Characterization of RuO(2) and TiO(2) sols of different aging times, obtained by forced hydrolysis of appropriate chloride salts, was performed by transmission electron microscopy (TEM). The aging time of TiO(2) sols was observed to affect the size of particles as well as the crystallinity of the solid phase of the sols. The surface morphology of RuO(2)-TiO(2) coatings on titanium, obtained by the sol-gel procedure using TiO(2) sols of different aging times and RuO(2) sol of fixed aging time, was investigated by scanning tunneling microscopy (STM) at three different scan sizes. The STM data indicated uniform microdistribution of the coating material (small microroughness) and an increase in nanoroughness with the aging time of the TiO(2) sol. The observed increase in real coating surface area with increasing TiO(2) particle size confirms the earlier cyclic voltammetry results.     

Copper hexacyanoferrates: Preparation, composition and structure

A review on the chemistry of copper hexacyanoferrates during the period 1933-1993 with an emphasis on their compositions and structures in relation to the methods of preparation.     

Sorption of Selenite (SeO(3)(2-)) on Hydroxyapatite: An Exchange Process

The sorption of SeO(3)(2-) on hydroxyapatite surface was investigated in batch experiments over a range of pH and SeO(3)(2-) concentrations in the absence and presence of additional Ca and PO(4). The sorption is pH dependent with a maximum observed at pH values generally encountered in natural waters. While the presence of phosphate lowers SeO(3)(2-) sorption by direct competition, the presence of calcium enhances it. In order to identify the mechanism of sorption and the nature of the surface sites, microscopic observation and spectroscopic methods such as X-ray diffraction and X-ray photoelectron spectroscopy were used. Surface complexation, coprecipitation, and precipitation processes were ruled out. Localization of sorbed selenium in the crystallographic sites where phosphorus is normally located shows that selenite is sorbed on the apatite by an anionic exchange with phosphate groups. Although the exact equilibria involved could not be established, the stoichiometry of the exchange is close to 1 : 1. According to kinetics experiments and X-ray diffraction analyses, it seems that selenium is not exclusively located at the surface but diffuses slightly in a thickness of a few nanometers. Copyright 2000 Academic Press.