V. I. Saldin

Spectroscopic Study of Modified Polytetrafluoroethylene

The effect of thermal gas dynamic destruction of polytetrafluoroethylene on its microscopic and supramolecular structure and dynamic properties is investigated by IR and 19F NMR spectroscopy. It is demonstrated that thermal gas dynamic dispersing changes the structure of polytetrafluoroethylene molecules. One of the possible mechanisms of PTFE depolymerization is the formation of oligomers with terminal –CF3 and –C=CF2 groups. This forms macromolecular packing with higher ordering and with dynamic characteristics other than those inherent in standard PTFE.

The thermal decomposition of hexamethylenetetraammonium dodecahydro-closo-dodecaborate

The kinetics and products of the thermal decomposition of hexamethylenetetraammonium dodecahydro-closo-dodecaborate in air, argon, and a vacuum were studied using thermogravimetry, volumetry, mass spectrometry, and IR spectroscopy. According to the nonisothermal kinetic data, noticeable rates of the formation of volatile products were observed at temperatures higher than 150°C. The thermal decomposition of the salt occurred in stages. At 160–200°C, the thermal decomposition of hexamethylenetetraammonium dodecahydro-closo-dodecaborate could not be described by simple kinetic equations. The dependence of the initial reaction rates on inverse temperature (lnV0−1/K) was linear, which showed that the thermal decomposition of the salt obeyed the Arrhenius equation V0 = 109.4 ± 0.6exp[(−20500 ± 1800)/RT], %/min. The obtained temperature dependences of the kinetic parameters of thermolysis were used to predict the time of salt storage and the conditions of work with it. A comparison of the kinetics of the thermolysis of hexamethylenetetraammonium dodecahydro-closo-dodecaborate and free hexamethylenetetraamine in open and closed reaction systems showed that the thermolysis of hexamethylenetetraammonium dodecahydro-closo-dodecaborate was not accompanied by salt dissociation to hexamethylenetetraamine and dodecahydro-closo-dodecaborate acid. The products of its thermolysis volatile under normal conditions were trimethylamine with a small admixture of nitrogen. The solid residue after thermolysis was a high-porosity insoluble product, whose volume was 6–8 times larger than the volume of the initial sample. An analysis of the IR spectra of the solid thermolysis product showed that it had a well-defined salt character. The special features of the IR spectra of initial hexamethylenetetraammonium dodecahydro-closo-dodecaborate and the product of its thermolysis led us to suggest that an acid-base equilibrium of the type [R3N-H+] + A ↔ [R3N… H+…A] occurred in it and, probably, in the initial salt. Here, R3N is the tertiary amino group, and A is the borohydride acid residue. Indications of amorphization allowed us to suggest that polymer structures were formed as a result of intramolecular interaction between the borohydride anion and onium cation.

Hexamethylenetetrammonium dodecahydro-closo-dodecaborate: Synthesis and study

The reaction of dodecahydro-closo-dodecaboric acid with hexamethylenetetramine (urotropin) was studied by potentiometric titration, chemical and X-ray diffraction analyses, thermogravimetry, and IR and X-ray photoelectron spectroscopy. The donor-acceptor bond with acid H+ cations involves only one of the nitrogen donor atoms of hexamethylenetetramine. The product (C6H12N4H)2B12H12 is isolated as a finely crystalline, easily filterable, and poorly soluble precipitate. A saturated solution of the product contains no more than 0.4 g of the salt per 100 g.

Thermodynamic properties of chitosan dodecahydro-closo-dodecaborate

Combustion enthalpies of chitosan dodecahydro-closo-dodecaborate corresponding to −13194 kJ/mol are measured via combustion in an AKS-3M automatic calorimeter. The standard enthalpy of formation corresponding to −5223 kJ/mol is calculated from the resulting experimental data.

Thermal conversions of chitosanium dodecahydro-closo-dodecaborate

The thermal behavior of chitosanium dodecahydro-closo-dodecaborate, (C6O4H9NH3)2B12H12, was studied by thermal analysis, X-ray diffraction, and IR and X-ray photoelectron spectroscopy. As this compound is heated at a rate above 10–20 K/min, it ignites at a temperature of about 300°C. As the compound is heated to 1000°C at a rate below 10 K/min in an inert atmosphere, it yields a mixture of carbon and amorphous boron and/or boron carbides. The presence of a small amount of boron oxide in the product is explained by the formation of a partially oxidized hydroborate anion at the early stages of (C6O4H9NH3)2B12H12 decomposition via the interaction between oxygen of the chitosanium cation and the B12H122− anion. Heating the initial compound in air at a rate below 10 K/min yields carbon and boron oxide as the main products. Molten boron oxide protects boron and/or boron carbides and boron nitride forming in small amounts in the particle bulk from oxidation.

Thermal studies of sodium tetrahydroborate–potassium tetrafluoroborate mixtures

The results of DSC studies of NaBH4–KBF4 mixtures are presented. It is shown by chemical analysis, XRD analysis, IR spectroscopy, and 11B and 9F MAS NMR that the decomposition of the mixtures starts at ~563 K to yield polyhedral borohydride compounds (predominantly B12H122-) in the solid residue. This temperature is much lower than the decomposition temperature of pure NaBH4 (749 K). The mechanism of formation of the B12H122- anion has been proposed and confirmed. According to this mechanism, boron atoms from KBF4 are involved in the formation of this anion.

Isolation of the dodecahydro-closo-dodecaborate anion with chitosan from aqueous solutions

The possibility of isolating the dodecahydro-closo-dodecaborate anion from aqueous solutions using chitosan in the form of chitosanium dodecahydro-closo-dodecaborate (C6O4H9NH4)2B12H12 was studied. The optimum conditions for the precipitation of this scarcely soluble, readily filterable salt and its decomposition with alkaline reagents were found. The new technique was tested with real aqueous salt solutions for leaching the products of the high-temperature synthesis of the B12H122− anion.

Thermodynamic Properties of Hexamethylenetetrammonium Dodecahydro-closo-dodecaborate

The enthalpy of combustion of hexamethylenetetrammonium dodecahydro-closo-dodecaborate is determined via combustion in a KL-5 calorimeter and is found to be‒17660 kJ/mol. Its standard enthalpy of formation is calculated using the obtained experimental data (−538 kJ/mol).

Thermal studies of potassium tetrahydroborate−sodium tetrafluoroborate mixtures

The KBH4−NaBF4 mixture was studied by thermal analysis (differential scanning calorimetry). Chemical analysis, X-ray powder diffraction analysis, IR spectroscopy, and 11B and 19F MAS NMR spectroscopy showed that the primary stage of the complex pyrolysis process is a metathesis reaction between components to form a new mixture, NaBH4−KBF4, the decomposition of which with the release of gaseous products and the formation of polyhedral borohydride compounds (mainly B12H122-) in the solid residue begins at a temperature of about 563 K. At a certain ratio between reactants in the initial mixture KBH4−NaBF4, the B12H122- anion can form with the material participation of the BF4- anion.

Micromechanical properties of intercalated compounds of graphite oxide with dodecahydro- closо -dodecaboric acid

The micromechanical properties (Young’s modulus, deformation, and adhesion) of the intercalated compound of graphite oxide with dodecahydro-closo-dodecaboric acid were studied by atomic force microscopy, transmission electron microscopy, and Raman spectroscopy and compared with the same characteristics of the starting graphite oxide. The significant difference in the micromechanical properties of the materials under study is dictated by differences in the topography and properties of their film surface, which, in turn, can be determined by their chemical composition. The introduction of dodecahydro-closo-dodecaboric acid in the interplanar space of graphite oxide affects the structuring of the latter. A considerable increase in the adhesion of the intercalated compound relative to that of oxide graphite is explained by high adhesive properties of the introduced acid, the Young’s modulus of graphite oxide being higher than that of the intercalated compound. This was attributed to the high hydrophilicity of dodecahydro-closo-dodecaboric acid and the difficulty of water removal from the interplanar space; water plasticizes the material, which becomes softer than graphite oxide. The difference in the structure of the coating of the intercalated compounds and the starting graphite oxide was found to be also reflected by their Raman spectra, namely, by the increased intensity of the D line with the preserved position of the G line, which points to the impurity nature of the intercalate and the unchanged hexagonal lattice of graphite.