Vladimir Katovic

Collection-efficient, axisymmetric vacuum sublimation module for the purification of solid materials

A vacuum sublimation module of axisymmetric geometry was developed and employed to purify solid-phase materials. The module provides certain practical advantages and it comprises: a metering valve, glass collector, glass lower body, main seal, threaded bushing, and glass internal cartridge (the latter to contain starting material). A complementary process was developed to de-solvate, sublime, weigh, and collect solid chemical materials exemplified by oxalic acid, ferrocene, pentachlorobenzene, chrysene, and urea. The oxalic acid sublimate was analyzed by titration, melting range, Fourier Transform Infrared (FT-IR) Spectroscopy, cyclic voltammetry, and its (aqueous phase) electrolytically generated gas. The analytical data were consistent with a high-purity, anhydrous oxalic acid sublimate. Cyclic voltammograms of 0.11 mol. % oxalic acid in water displayed a 2.1 V window on glassy carbon electrode beyond which electrolytic decomposition occurs. During module testing, fifteen relatively pure materials were sublimed with (energy efficient) passive cooling and the solid-phase recovery averaged 95 mass %. Key module design features include: compact vertical geometry, low-angle conical collector, uniformly compressed main seal, modest power consumption, transparency, glovebox compatibility, cooling options, and preferential conductive heat transfer. To help evaluate the structural (module) heat transfer, vertical temperature profiles along the dynamically evacuated lower body were measured versus electric heater power: for example, an input of 18.6 W generated a temperature 443-K at the bottom. Experimental results and engineering calculations indicate that during sublimation, solid conduction is the primary mode of heat transfer to the starting material.

Electrochemical Studies of Triangular Niobium Cluster, Nb3O2(SO4)6 · 3H2O5−, in Sulfuric Acid

The electrochemical properties of Nb3O2(SO4)6 · 3H2O5− cluster anion in 9 M sulfuric acid were investigated using DC polarography, cyclic voltammetry, spectroelectrochemistry, and constant potential electrolysis. It was found that Nb3O2(SO4)6 · 3H2O5− in 9 M H2SO4 displays a reduction wave at E = −1.30 V vs. Hg/Hg2 SO4 electrode, and a large irreversible oxidation wave at Epa = −0.30 V. Cyclic voltammetry indicates that the reduction wave involves a reversible one-electron process. Controlled potential electrolysis at E = −1.4 V produces a green Nb(3.33) anion, Nb3O2(SO4)6 · 3H2O6− which is stable on the time scale of bulk electrolysis. Electrochemical reoxidation of Nb(3.33) anion Nb3O2(SO4)6 · 3H2O6− at E = −0.75 V consumes 1 mol e/ mol Nb3 cluster and regenerates the red Nb(3.66) Nb3O2(SO4)6 · 3H2O5− anion. Further oxidation at −0.2 V involves an irreversible four electron process to form Nb(V) species.