O. Yu. Chernova

Highly Sensitive Determination of Carbon- and Hydrogen-Containing Impurities in Silicon Tetrachloride by Gas Chromatography

Procedures were developed for the direct gas-chromatographic determination of impurities of organochlorine substances, chlorosilane, and alkylchlorosilane in silicon tetrachloride and for the gas-chromatographic analysis with matrix subtraction by preliminary hydrolysis of silicon tetrachloride and subsequent extraction of organochlorine impurities with an organic solvent. It was found that the major impurities in high-purity silicon tetrachloride obtained by the rectification of the by-product in the production of trichlorosilane are trichlorosilane, methyltrichlorosilane, methyldichlorosilane, chloroform, and carbon tetrachloride. Detection limits of impurities are 10–5–10–7wt %, which is lower than those reported in the literature by 1–2 orders of magnitude.

Ultrapurification of 76Ge-enriched GeH4 by distillation

Abstract76Ge-enriched germane has been ultrapurified by low-temperature distillation. The nature and concentration of molecular impurities in the germane samples were determined by gas chromatography/mass spectrometry, high-resolution Fourier transform IR spectroscopy, and gas chromatography. The distillate contains no more than 10−5 mol % hydrocarbons, 10−4 mol % carbon dioxide, 10−3 to 10−1 mol % digermane and trigermane, and <3 × 10−5 mol % other impurities. A distinctive feature of the impurity composition of the isotopically enriched germane samples is the presence of silicon tetrafluoride and sulfur hexafluoride impurities.

Molecular analysis of isotopically enriched 28SiF4 and 28SiH4 prepared from it

We have developed analytical techniques for the determination of impurities in isotopically enriched 28SiH4 and 28SiF4. The impurities in SiF4 were first determined by IR spectroscopy, and those in SiH4, by gas chromatography/mass spectrometry. High-sensitivity determination of organic impurities in SiH4 and SiF4 was performed by gas chromatography. SiF4 was found to contain C1–C4 hydrocarbons, hexafluorodisiloxane (Si2F6O), hydrogen fluoride, trifluorosilanol (SiF3OH), fluorosilanes, water, and carbon oxides. The impurities identified in SiH4 include C1–C4 hydrocarbons, disilane (Si2H6), inorganic hydrides, Si2H6O, alkylsilanes, and fluorinated and chlorinated organics. The detection limits of IR spectroscopy were 3 × 10−3 to 5 × 10−5 mol %, those of gas chromatography/mass spectrometry were 8 × 10−6 to 10−8 mol %, and those of gas chromatography were 6 × 10-6 to 2 × 10−7 mol %.

Preparation of weakly agglomerated yttrium aluminum garnet powders by burning a mixture of yttrium aluminum hydroxynitrates, urea, and acetic acid

We have optimized the composition of a mixture of aluminum yttrium hydroxynitrates, urea, and acetic acid for the self-propagating high-temperature synthesis of yttrium aluminum garnet (YAG) powder. The powder prepared in this way offers a low degree of agglomeration, and the ceramic produced from it has a low carbon content. A technique has been proposed for carbon determination in YAG ceramics through gas chromatographic analysis of the gaseous products of carbide hydrolysis after the dissolution of the ceramic in pyrophosphoric acid.

Hydrocarbon impurities in SiF4 and SiH4 prepared from it

Using gas chromatography and high-resolution Fourier-transform IR spectroscopy, we have determined the concentrations of C1–C4 hydrocarbon impurities in isotopically unmodified silicon tetrafluoride before and after fine purification and in 28Si-enriched SiF4. The concentrations of C1–C4 hydrocarbon impurities in silicon tetrafluoride for SiH4 synthesis have been shown to correlate with those in the synthesized silane.

Gas–Adsorption Chromatography of Reactive Compounds on Open-Tubular Columns with Poly(trimethylsilylpropyne)

The possibility of using a new poly(trimethylsilylpropyne) adsorbent for the separation of volatile inorganic hydrides and chlorinated organic compounds in capillary gas chromatography has been studied. Excellent separation properties of columns with the proposed adsorbent have been demonstrated.

Impurity composition of high-purity isotopically enriched monosilane and monogermane

The impurity composition of 28SiH4, 29SiH4, and 30SiH4 silanes and 72GeH4, 73GeH4, 74GeH4, and 76GeH4 germanes isotopically enriched to above 99.9 at % has been studied by gas chromatography/mass spectrometry using capillary adsorption columns. Impurities have been identified by comparing their mass spectra with NIST data and information available in the literature, and by inferring their structure from fragment ions and retention times. We have identified 53 impurity substances in silanes and 42 in germanes: permanent gases; saturated, unsaturated, halogen-containing, and aromatic C1–C9 hydrocarbons; their homologues; alkyl derivatives of silane and germane; chlorogermane; siloxanes; fluorosiloxanes; sulfur compounds; and dioxane. The silicon- and germanium-containing impurities have been shown to be isotopically enriched, as the major component. The detection limits of the impurities are 5 × 10–8 to 3 × 10–5 vol %, comparing well with the best results in the literature.

Composition of molecular impurities in high-pure germane

The impurity composition of germane has been studied by gas chromatography/mass spectrometry. We have determined permanent gases, C1–C9 hydrocarbons, fluorine- and chlorine-containing and aromatic hydrocarbons, ethers, hydrogen sulfide, germane homologs, alkyl derivatives of germane, and chlorogermane. The content of some impurities in high-pure germane is 2 × 10–6 to 1 × 10–3 vol %. The detection limits for impurities lie in the range 4 × 10–8 to 5 × 10–5 vol %.

Determination of Inorganic Fluorine in High-Purity Silane

A method was proposed for determining inorganic fluorine in high-purity silane. The method is based on the hydrolytic extraction of fluorine as fluorides to the aqueous phase, followed by the analysis of the extract by ion chromatography with a conductometric detector. The detection limit for inorganic fluorine was 1 × 10–5mass %.

Gas chromatographic determination of benzothiophenes in high-purity sulfur

A procedure is developed for the determination of benzothiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene in high-purity sulfur, including liquid-phase microextraction preconcentration, identification by gas chromatography−mass spectrometry, and gas chromatographic determination with flame photometric detection. The rate of microextraction recovery was from 16 to 78%. The limits of detection were 8 × 10–5 wt % for benzophiophene and 2 × 10–5 wt % for dibenzothiophene and 4,6-dimethyldibenzothiophene.