A. Yu. Sozin

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 %.

Fine purification of monoisotopic 32S and 34S

We have proposed and tested a combined process for ultrapurification of monoisotopic 32S and 34S sulfur, which comprises thermochemical treatment of sulfur vapor on silica and ceria packing, melting with aluminum, and distillation. The impurity composition of the purified sulfur has been determined by atomic emission and IR spectroscopy. We have obtained monoisotopic 32S and 34S sulfur samples comparable in chemical purity to high-purity sulfur of natural isotopic composition.

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 impurities in high-purity carbon tetrachloride by gas chromatography-mass spectrometry

The impurities in high-purity carbon tetrachloride (CCl4) were determined by gas chromatography-mass spectrometry (GC-MS). The use of chromatography of near-saturated vapors allowed the injection of samples up to 1 μL into a capillary column and to achieve specific column efficiency in an isothermal mode of 221,000 t.p./m. The detection limits for impurities were 1 × 10−1 to 1 × 10−8 wt %.

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.

Molecular composition of organic impurities in extrapure sulfur

We have determined the molecular composition of organic impurities in extrapure sulfur obtained by the distillation purification of sulfur recovered from gaseous hydrocarbons. Using vacuum extraction, we obtained a concentrate of impurities highly volatile compared to the major component. Gas chromatography/ mass spectrometry analysis indicated the presence of impurities in the form of hydrocarbons with up to eight carbon atoms and their thio, oxy, and nitro derivatives. The detection of this group of impurities accounts for the distinctive features of the preparation of sulfur with low carbon and oxygen contents through ultrapurification of gas-derived sulfur.

Ultrapurification of iron pentacarbonyl by distillation techniques

Volatile impurities have been removed from iron pentacarbonyl of natural isotopic composition by vacuum pumping. We have examined the behavior of impurities in the course of fractional distillation of iron pentacarbonyl. As a result of simple distillation, we have obtained an iron pentacarbonyl sample containing on the order of 10–4 mol % C3–C6 hydrocarbon impurities, 10–3 mol % C7–C8 hydrocarbons, and 10–8 to 10–6 wt % metallic impurities. We have estimated the effective separation factor at a distillation rate of 0.021 kg/(m2 s) for a number of impurities in Fe(CO)5.

Formation of impurity Si2OH6 in silane synthesized from silicon tetrafluoride

The possibility of the reduction of hexafluorodisiloxane by calcium hydride in the synthesis of silane from silicon tetrafluoride has been studied. This reaction is shown to be not decisive for oxygen contamination of silane. The most likely reason for the appearance of impurity Si2OH6 in “fluoride” silane is the Ca(OH)2-catalyzed reaction of silane with trace water. The concentration of impurity Si2OH6 in silane at the stage of synthesis may be efficiently decreased by the preliminary purging of calcium hydride with a hydrogen (grade A) flow.