O. Yu. Troshin

Preparation and Fine Purification of SiF4 and 28SiH4

Silicon tetrafluoride was obtained by the thermal decomposition of pure-grade sodium hexafluorosilicate and purified by low-temperature distillation. Next, SiF4 was 28Si-enriched by centrifugation and converted to silane by calcium hydride reduction. To remove hydrocarbons, the silane was distilled.

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.

Synthesis of High-Purity Calcium Hydride

A procedure for synthesizing high-purity calcium hydride in high yield was suggested. The admixture composition of the resulting CaH2 was determined by laser mass spectrometry.

Fine Purification of Monoisotopic Silanes 28SiH4 , 29SiH4 , and 30SiH4 via Distillation

High-purity isotopically enriched (99.98% 28Si, 99.57% 29Si, and 99.83% 30Si) silane samples are prepared for the first time. The total hydrocarbon content of the samples is no higher than 0.1–0.3 ppm. The concentration of electroactive impurities in the silicon prepared from the purified monoisotopic silane is below 1015 cm–3.

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.

Liquid-vapor equilibria in GeF4-A (A = C1-C4 alkane impurity) systems

The liquid–vapor separation factors in dilute solutions of methane, ethane, propane, n-butane, and isobutane in germanium tetrafluoride have been determined experimentally at 295 K by statically balancing phases. The measured temperature-dependent saturated vapor pressure over liquid germanium tetrafluoride in the range 260–300 K can be represented by the Antoine equation: log P (atm) = 5.2–1200/T. We have calculated the enthalpies of vaporization and fusion of germanium tetrafluoride:ΔHv0= 22.9 kJ/mol and ΔHm0(GeF4) = 8.0 kJ/mol.

Mechanically activated synthesis of monosilane by the reaction of calcium hydride with silicon tetrafluoride

Possibility of performing a mechanically activated synthesis of pure monosilane by the reaction of calcium hydride with silicon tetrafluoride in a rotating flow-through reactor containing milling bodies was analyzed. A number of operation parameters of the grinding reactor were theoretically evaluated and experimentally determined.

Reaction of silicon tetrafluoride with calcium hydride as a propagating wave

The synthesis of silane by reacting silicon tetrafluoride and calcium hydride is shown to proceed as a propagating wave. The main parameters of the process, namely, the propagation velocity, the reaction front temperature, and calcium conversion, are determined. The mathematical model of wave propagation for an exothermic reaction in a porous medium with purging a gaseous oxidant describes qualitatively the major laws of the process.

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.

Liquid–Vapor Equilibria in the SiCl4–A (A = SiCl4–nFn (n = 1–4) Impurity) Systems

The vapor–liquid separation factors of SiCl4–A (A = SiCl4–nFn (n = 1–4) silicon fluorochloride impurities in silicon tetrachloride have been determined experimentally at 298 K by statically balancing phases. The values obtained for the SiCl4–SiCl3F, SiCl4–SiCl2F2, SiCl4–SiClF3, and SiCl4–SiF4 systems are 4.9 ± 0.8, 8.2 ± 1.2, 29.8 ± 6.1, and 42.0 ± 7.5, respectively. In the SiCl4–SiCl3F system, the vapor–liquid separation factor has also been determined by the Rayleigh distillation method: α = 5.0. The experimental data agree with the vapor–liquid separation factors estimated in conformal solution theory using parameters of the Lennard- Jones potential.