Substoichiometric Precipitation Research Articles

The relationship between phase composition and conditions of sintering seawater derived magnesium oxide

This study has focused on the favourable effect of the TiO2 addition (1, 2 and 5 wt%) on the reduction of B2O3 content during activated sintering of magnesium oxide from seawater at temperatures of 1400, 1500 and 1700°C for the duration of 1, 2 and 4 h. A mathematical model of dependence between the B2O3 mass fraction in the sintered sample, the temperature of isothermal sintering, the isothermal sintering time and the mass fraction of TiO2 added have been proposed. Magnesium oxide was obtained from seawater by substoichiometric precipitation, with the addition of 80% of dolomite lime as the precipitation agent. New phases formed in magnesium oxide samples were examined by the XRD and SEM/EDS analysis. The results indicate that during activated sintering of seawater-derived magnesium oxide with a TiO2 addition, reactions of formation of Ca2B2O5, CaTiO3 and Mg2TiO4 took place simultaneously. The thermodynamics analysis of experimental results, based on the Onsager reciprocity relations (symmetry relations), was applied and phenomenological coefficients were calculated to describe the interference of these three irreversible processes.

Microstructural characteristics of low-temperature (1400°C) sintered MgO obtained from seawater

The purpose of this study was to investigate the influence of a rinsing of Mg(OH)2 precipitated from seawater by substoichiometric precipitation (80% precipitation) and the addition of TiO2 on microstructural characteristics of the MgO obtained by sintering at low temperature (1400?C). The results of examination indicate that the method of rinsing of the magnesium hydroxide precipitate in the technological process of obtaining MgO from seawater significantly affects the chemical composition of samples, primarily with regard to the CaO and B2O3 content. The samples were doped with TiO2 to improve the evaporation of B2O3 and sintering of MgO samples that were characterized by XRD and SEM/EDS. These techniques confirmed the high purity of MgO samples obtained and the formation of secondary compounds in very small quantities that have a positive effect on the densification.

Alpha-activation analysis of nitrogen in boron-doped silicon single crystal

The rapid dissolution of silicon and the substoichiometric separation of18F were studied in order to determine nitrogen in a boron-doped silicon single crystal by α activation analysis via15N(α,n)18F. The silicon dissolution method was developed by using a nitric acid-based solution containing a known amount of ammonium fluoride, instead of hydrofluoric acid, as the18F carrier. The silicon could be dissolved to a depth of 100 μm with a 10 mm O in 9 minutes. The conditions for18F steam distillation and substoichiometric precipitation as lanthanum fluoride were improved. 50% of the fluorine could be separated substoichiometrically even though the carrier amount was increased from 6–12 mmol to more than 16 mmol in order to add it to the dissolving solution. This dissolution method and improved substoichiometric separation were used to determine nitrogen in a boron-doped silicon single crystal. The nitrogen concentration was found to be less than the detection limit (50 ppb).

Determination of nanogram levels of lanthanoids in a marine macro-alga by neutron activation analysis combined with separation by selective precipitation

Preseparation of lanthanoids by substoichiometric precipitation of calcium oxalate and simple radiochemical separation of lanthanoids by lanthanum oxalate have been developed. They were combined with neutron activation analysis of a marine macro-alga (Laminaria religiosa, brown alga) sample. Quantitative recovery of lanthanoids throughout the procedure was examined by radiotracer technique. Eleven lanthanoids, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb and Lu, at 0.7–140 ng g−1 were determined with a relative standard deviation of 1–7% (n=3). Concentrations of lanthanoids in the marine macro-alga were compared with land plant and sea water.

Selective preconcentration of rare earth elements by substoichiometric precipitation of calcium oxalate and its application to the neutron activation analysis of biological material

A preconcentration method for trace amounts of rare earth elements (REs) based on the substoichiometric precipitation of calcium oxalate was developed. RE(III) was quantitatively coprecipitated with calcium oxalate which had been precipitated from the calcium of a macrocomponent in a biological sample by addition of a substoichiometric amount of oxalate. In this way high selectivity for RE(III) from other elements was achieved. The method was applied to the neutron activation analysis of a biological sample (NBS SRM 1572 Citrus Leaves), and Sc, La, Ce, Pf, Nd, Sm, Eu, Th, Dy, Ho, Yb and Lu were determined with a relative standard deviation of less than 5%.

Deuteron activation analysis of carbon in gallium arsenide using substoichiometric precipitation

Ultra trace carbon in gallium arsenide has been determined by deuteron activation analysis. It consists of steam distillation of nitrogen as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It is confirmed that nitrogen is precipitated substoichiometrically as ammonium tetraphenylborate in spite of the various chemical species of13N. The procedure developed was applied to the deuteron activation analysis of carbon in carbon-doped and undoped gallium arsenides. It took 30 minutes from the end of irradiation to the start of the radioactivity measurement. The detection limit of carbon in gallium arsenide was as low as 1 ppb.

Substoichiometric precipitation of nitrogen as ammonium tetraphenylborate for deutron activation analysis

The radiochemical separation of nitrogen was studied for the determination of ultra trace carbon in gallium arsenide by deutron activation analysis using the12C/d, n/13N reaction. It is based on steam distillation as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It was found that the decontamination factors of coexistent elements such as72Ga,76As and11Co to13N are enough large to determine carbon as low as 1 ppb in gallium arsenide.

Substoichiometric precipitation of silicon as barium fluorosilicate

Distillation and substoichimetric precipitation for silicon have been developed for the determination of trace amounts of silicon. It is based on substoichiometric precipitation as barium fluorosilicate and the distillation of silicon tetrafluoride. The separation has been applied for the determination of silicon in gallium arsenide and NBS steel as standard reference material.

Determination of oxygen in gallium arsenide by3He activation analysis using substoichiometric precipitation

Distillation of fluoride as fluorosilicic acid and substoichiometric precipitation as lanthanum fluoride was studied for the determination of oxygen in gallium arsenide by3He activation analysis. Fluoride could be separated substoichiometrically with a good reproducibility by two distillations and successive precipitation with lanthanum. The oxygen concentration in gallium arsenide prepared by the horizontal Bridgman technique was 10 to 36 ppb and increased a little along the front, middle and tail portions in the crystal.

Substoichiometric precipitation of fluoride with lanthanum

The substoichiometric precipitation of fluoride with lanthanum was studied by using18F and140La tracers and it was found that fluoride could be precipitated substoichiometrically with lanthanum and the reaction ratio between fluoride and lanthanum was 3∶1. The pH range at which fluoride can be separated substoichiometrically with lanthanum is between 2 and 8. Barium and indium interfere in the precipitation of fluoride, sodium, copper and manganese, however, not. Fluorosilicate can also be precipitated substoichiometrically by using lanthanum as a precipitant and the reaction ratio between fluorosilicate and lanthanum was 1∶2. This separation was applied for the determination of oxygen in silicon crystals. The concentration of oxygen measured in some silicon crystals was between 5 and 27 ppm and in good agreement with those by non-destructive method and infrared spectrophotometry.

Substoichiometric Isotope Dilution Analysis of Sulphur in coal

Abstract Substoichiometric radioisotope dilution analysis has been applied to the determination of sulfur in coal. The experimental procedure involved the combustion of coal samples labelled with 35S as sodium sulfate in a flowing oxýgen stream, collection of the combustion gases in hydrogen peroxide and substoichiometric precipitation of barium sulfate. Samples of 0.2–10.0% sulfur were accurately determined with ±2% RSD by measuring the activity of the precipitates thus obtained and with comparison to standard samples carried through the same procedure. Analysis times of 15 minutes per sample were typical.

Neutron activation analysis of iodine in blood serum or other biological materials by substoichiometric precipitation of iodine as silver iodide

Several modifications are proposed of the established methods of iodine determination in serum. Prior to the actual analysis, the serum is lyophilized. This preliminary treatment permits the use of large samples. Through lyophilization human blood serum samples can easily be reduced to one-tenth of the original weight. Reduction is even more dramatic with materials from other than human origin. After irradiation the samples are subjected to chemical treatment in the presence of an iodine carrier and131I-labelled thyoxine. This procedure has been adopted for the determination of the iodine content and the chemical yield in one and the same radioactive measurement. The analysis technique itself consists of an open system Schoniger combustion. The open combustion allows the use of large samples; the gases evolved are absorbed upon their subsequent passage through potassium hydroxide and hydrochloric acid; the mineralization requires less than two minutes. After the addition of a substochiometric amount of silver nitrate, silver iodide is precipitated from an ammoniacal solution as a flat sample, which has been found ideally suited for high efficiency counting with a Ge(Li) detector. The spectrum gives evidence of an excellent decontamination from the38Cl,80Br and82Br activities. The iodine content can be calculated from the ratio of the photopeak areas at 364.5 keV and 442.7 keV corresponding to131I and128I, respectively. The chemical procedure requires a mere 15 min, and the recording of the γ-ray spectrum takes no longer than 30 min. The technique is not limited to serum only. It proved well suited for the analysis of many other types of biological material, e.g. human skin tissues.