Influence of phosphorus diffusion modes on the formation of defects in an oxide

Using optical microscopy, SEM, atomic force microscope and profilometer, the shape, size and impurity composition of local defects occurring in the silicon dioxide layer during phosphorus diffusion were determined. The reason for the formation of defects in the passivating oxide during phosphorus diffusion is the local melting of SiO2 in interaction with liquid drops of phosphoric-silicate glass. A decrease in the temperature of the phosphorus deposition process and the concentration of POCL3 in the gas stream leads to a decrease in the density of oxide defects.

Defects of diamond crystal structure as an indicator of crystallogenesis

Based on the study of a representative collections of diamonds from diamondiferous formations of the Urals and deposits of the Arkhangelsk and Yakutian diamond provinces, we established patterns of zonal and sectoral distribution of crystal structure defects in crystals of different morphological types, identified the specifics of crystals formed at different stages of crystallogenesis and performed a comprehensive analysis of constitutional and population diversity of diamonds in different formations. We identified three stages in the crystallogenesis cycle, which correspond to normal and tangential mechanisms of growth and the stage of changing crystal habit shape. At the stage of changing crystal habit shape, insufficient carbon supersaturation obstructs normal growth mechanism, and the facets develop from existing surfaces. Due to the absent stage of growth layer nucleation, formation of new {111} surfaces occurs much faster compared to tangential growth mechanism. This effect allows to explain the absence of cuboids with highly transformed nitrogen defects at the A-B1 stage: they have all been refaceted by a regenerative mechanism. Based on the revealed patterns, a model of diamond crystallogenesis was developed, which takes into account the regularities of growth evolution, thermal history and morphological diversity of the crystals. The model implies the possibility of a multiply repetitive crystallization cycle and the existence of an intermediate chamber; it allows to explain the sequence of changes in morphology and defect-impurity composition of crystals, as well as a combination of constitutional and population diversity of diamonds from different geological formations.

Growth-sector dependence of morphological, structural and optical features in boron-doped HPHT diamond crystals

Semiconducting boron-doped diamond single crystals of cubo-octahedral habit with prevalent development of octahedron {111} faces and insignificant area of cube {001}, rhombo-dodecahedron {110} and tetragon-trioctahedron {311} faces were obtained using solution-melt crystallization at high pressure 6.5 GPa and temperatures 1380…1420 °C. Using the Fe-Al solvent, which allows controlled incorporation of boron dopant between 2·10–4…10–2 at.% made it possible to vary the electro-physical properties of the crystals. Methods of micro-photogrammetry, atomic force microscopy, and micro-Raman spectroscopy were applied to reveal sectorial inhomogeneity of impurity composition and morphology of different crystal faces. The obtained crystals were shown to have high structural perfection and boron concentration ranging approximately from 1·1017 up to 7·1018 cm–3. An increase in boron concentration increases the area of {111} faces relatively to the total crystal area. Nanoscale morphological features like growth terraces, step-bunching, dendrite-like nanostructures, columnar substructures, negative growth pyramids on different crystal faces are shown to reflect peculiarities of carbon dissolution at high pressures and temperatures. The changes in the crystals’ habit and surface morphology are discussed in relation to inhomogeneous variation of thermodynamic conditions of crystal growth and dissolution at different boron concentrations.

An analysis of geochemical features of crystallization of emeralds as an approach to determine the deposit of them

Relevance. It is known that minerals differ in morphology, features of the internal structure of crystals, chemical composition, etc., depending on the conditions of their formation and existence. These geochemical features of the gems crystallization are an important criterion for determining their deposit. In this paper, the impurity composition of the samples of emeralds from the deposits of Brazil, China, Zambia, Russia, Afghanistan, Colombia, and Tanzania was investigated by X-ray fluorescent analysis. The study of the impurity composition of emeralds by a non-destructive method and the construction of analytical dependences can be used as an additional way for determining the deposit of emeralds. Purpose of the work is the study of chemical composition of emeralds by X-ray fluorescent analysis to establish the relationship between the content of the main impurity elements and the deposit. Results. The data on the impurity composition of emeralds obtained by X-ray fluorescent analysis show that the content of impurities of Na, K, Rb, Cs, Mg, Fe, V, Cr differs from one deposit to another. The content of impurities of alkali metals and magnesium is higher in the samples from the shale-type deposits compared to the samples from deposits of the Colombian type. Thus, at the first stage, the type of deposit can be assumed. Further, the dependences plotted in the coordinate planes {Cr, V}, {Cs, Cr}, {Fe, Cr} show separate areas, delimited by the impurity ratios, which are typical for the samples from deposits in China, Colombia, Zambia, Afghanistan, and Tanzania. Conclusion. X-ray fluorescent analysis, as a non-destructive method for studying emeralds, is considered to be a promising approach to identifying their deposit, but as an additional method.

Sorption Extraction of Rare Earth Metals from Wet-Process Phosphoric Acid

When apatites and phosphorites are processed, up to 30% of rare earth metals are converted into wet-process phosphoric acid. Wet-process phosphoric acid from the phosphorite treatment process differs from apatite one by impurity composition, i.e. the iron content is by 3.5 times, and calcium is by 5.0 times more. The complex composition of the wet-process phosphoric acid from the phosphorite treatment process requires additional researches to select optimal ion exchangers and technological parameters of sorption. Various aspects of sorption have been studied to select the optimal ion exchangers and technological parameters, and technological modes for desorption of rare earth metals from a cation exchanger to obtain a concentrate of rare earth metals have been completed. The method enables to extract rare earth metals without changing the composition of commercial wet-process phosphoric acid directly in the production process of the enterprises engaged in the phosphorite treatment process.

GAS CHROMATOGRAPHIC ANALYSIS OF THE CHEMICAL COMPOSITION OF ETHYL ALCOHOL OBTAINED FROM PLANTS OF THE GENUS ASTERACEAE

In recent years, serious attention has been paid around the world to the chemical and biotechnological processing of biomass of easily renewable plant raw materials. One of the most mass-produced aliphatic alcohols is ethyl alcohol. The aim of this work was gas chromatographic analysis of the chemical composition of ethyl alcohol obtained from plants of the genus Asteraceae (dahlia and jerusalem artichoke tubers, chicory and big burdock roots) growing on the territory of Kazakhstan. The article discusses the methods of obtaining and application of ethyl alcohol. The results of the analysis of the chemical composition of ethyl alcohol obtained from plants of the genus Asteraceae are presented. As a result of the study, alcohols were obtained in different concentrations. The chemical composition of ethyl alcohol was determined by gas chromatography. The impurity composition of ethyl alcohol obtained from various types of raw materials is also shown. The composition of impurities in various samples of ethanol and alcohol-containing products is considered in detail. The results of the study were discussed, and the peculiarities of using the gas chromatography method were shown.

Extractive separation of selenium for atomic-absorption determination in purified sulfur

The expanding use of sulfur in medicine, science and technology has tightened the requirements for the impurity composition, including the content of selenium in sulfur. Combined extraction-atomic absorption methods have been developed to determine selenium in purified sulfur. The possibility of using thiourea derivatives such as sodium diethyldithiocarbamate and diphenylthiocarbazone for the extraction of microgram amounts of selenium from sulfuric acid solutions was studied. Optimal conditions for the extraction of selenium from sulfate solutions are determined. Two procedures for selenium separation are proposed: extraction of selenium diethyldithiocarbamate with ethyl acetate from a solution of sulfuric acid with pH 3 or extraction of selenium dithizonate with chloroform from a 5.25 – 6.0 M sulfuric acid solution. The results of the extraction-atomic absorption determination of selenium in sulfur are compared for both procedures of selenium separation. The accuracy of the selenium determination in purified sulfur is confirmed by the method of varying sample weight. The optimal temperature-time parameters for the electrothermal atomic absorption determination of selenium are determined. The limit of selenium determination is 1 × 10–5 % wt. The values of sr in the range of selenium content 2 × 10–5 — 1 × 10–4 % wt. change from 0.10 to 0.12.

Lutetium oxide analysis by direct arc atomic emission spectrometry

The requirements for the composition of initial oxides for the lutetium orthosilicate crystals are quite stringent: the content of the basic substance Lu2O3 is 99.999 wt%. Critical are coloring impurities: Fe, Ni, Cr, Co, Cu, V, Mn, the content of each should be no more than 0.0005 - 0.0010 wt%, Pr, Nd, Sm, Er, Tb, Yb no more than 0.0005 wt% for each one. It is also necessary to control the content of Al, As, Bi, Cd, Mg, Mo, Pb, Sb, Si, Sn, Ti, Zn, Y, La, Ce, Sc, Eu, Gd, Dy, Ho, Tm. To determine the impurity composition of lutetium oxide, one of the promising methods of analysis is direct arc atomic emission spectroscopy (DC Arc). The advantages of this method are the determination of the chemical composition without sample dissolution, a wide range of concentrations (10-6 - 10-1% wt%), a large number of determined elements. To realize the potential analytical capabilities of the method, the experimental conditions were studied: the interelectrode distance, the shape and size of graphite electrodes, the ratio of Lu2O3 to the spectral buffer, the type of carriers and operating modes of the generator. For most elements, the limits of determination are n ∙ 10-6 - n ∙ 10-4 wt%, that is significantly lower than in the current methods of DC Arc. The trueness of results is controlled by ICP-MS. The complex application of new approaches and modern capabilities of spectral equipment made it possible to develop a method with improved metrological characteristics.