Institute of Mineralogy and Crystallography

Sofia, Bulgaria

Institute of Mineralogy and Crystallography

Sofia, Bulgaria
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Hamciuc E.,Petru Poni Institute of Macromolecular Chemistry | Ignat M.,Romanian National Institute for Research and Development in Electrical Engineering | Hamciuc C.,Petru Poni Institute of Macromolecular Chemistry | Stoica I.,Petru Poni Institute of Macromolecular Chemistry | And 3 more authors.
High Performance Polymers | Year: 2015

Polyimide composite films were prepared by casting solutions resulting from direct mixing of a poly(amic acid) and titanium dioxide (TiO2) nanotubes (TNTs) onto glass plates, followed by thermal imidization. TNTs with outer diameters of approximately 10-12 nm and length of several hundreds of nanometers were synthesized by the hydrothermal method. The morphology of the nanotubes was investigated by using high-resolution transmission electron microscopy. The influence of TNTs content on structural, thermal, and electromechanical properties of pure polyimide and composite films was studied. The scanning electron microscopy and atomic force microscopy showed good compatibility between TNTs filler and polyimide matrix. The value of average roughness of film surface increases with increasing the content of TNTs. The films were flexible, tough, and exhibited high thermal stability. A study of microelectromechanical properties of these films was performed. The films showed nanometric displacements in the range of 250-800 nm when an electric voltage of 500 V was applied on their surface. © SAGE Publications.

Hamciuc E.,Petru Poni Institute of Macromolecular Chemistry | Hamciuc C.,Petru Poni Institute of Macromolecular Chemistry | Musteata V.E.,Petru Poni Institute of Macromolecular Chemistry | Kalvachev Y.,Institute of Mineralogy and Crystallography | Wolinska-Grabczyk A.,Polish Academy of Sciences
High Performance Polymers | Year: 2014

New polyimide (PI) films containing zeolite L and/or silica, having a thickness of tens of micrometers, were prepared using a PI matrix with pendant carboxylic groups. The influence of various ratios of inorganic filler on thermal stability, dielectric behavior, and gas transport properties of the films was studied with respect to their structure. The surface morphology was investigated by scanning electron microscopy. The films were flexible, tough, and showed good thermal properties with a glass transition temperature in the range of 187-218 C. The dielectric spectroscopy revealed γ and β subglass transitions having the corresponding relaxation activation energy in the range of 44.7-51.4 kJ mol-1 and 65.1-121.6 kJ mol-1, respectively. At temperatures above 200 C, a conductivity relaxation process was evidenced. Gas permeation tests using small molecules (O2, N2 and CO2), at 6 atm and 30 C, indicated that the PI films containing higher amount of zeolite showed the highest permeability for all gases. © The Author(s) 2013.

Kerekov S.,NIPTIAT Ltd. | Gospodinova N.,University of Ruse | Dimitrov L.,Institute of Mineralogy and Crystallography | Nikolov M.,University of Ruse
Journal of the Balkan Tribological Association | Year: 2015

The aim of the study is MGO samples to be synthesised by means of two different solid heterogeneous catalysts at esterification of glycerol with oleic acid; as well as, their anti-wear performance to be investigated on four-ball machine as friction modifiers. The anti-wear properties of MGO samples as oil additives are tested on a four-ball machine. MGO samples were previously characterised by thin layer chromatography and IR-spectroscopy. Chemical syntheses have been carried out for preparation of two MGO samples in the presence of the catalysts FAU/Al2O3 and Zn acetate-succinate/aluminosilicate. The influence of MGO on the oils' anti-wear properties has been demonstrated. The proper MGO content has been established. Two MGO samples have been compared. MGO as a friction modifier reduces the wear, the wear scar diameter decreases by 10-13%.

Lilkov V.,Sofia University | Rostovsky I.,University of Architecture, Civil Engineering and Geodesy | Petrov O.,Institute of Mineralogy and Crystallography | Tzvetanova Y.,Institute of Mineralogy and Crystallography | Savov P.,Sofia University
Construction and Building Materials | Year: 2014

The hydration products in cements with individual addition of SF and two types of FA from TEPS and mixtures of FA and SF are studied. The phase transformations are followed in a 4-year period. Fly ashes from TEPS "Bobov Dol" and TEPS "Pernik", silica fume from the metallurgical plant "Kremikovtsi", and their mixed product Pozzolit are suitable pozzolanic additions to cement as they participate actively in the processes of formation of hardened cement paste. The above additives stimulate the formation of hydrate products with temperature of dehydration above 600 C, more clearly expressed after the 48th day of hydration. © 2014 Elsevier Ltd. All rights reserved.

Mihaylov L.,Sofia University | Lyubenova L.,Sofia University | Gerdjikov T.,Sofia University | Nihtianova D.,Sofia University | And 2 more authors.
Corrosion Science | Year: 2015

Amorphous Zr-Ni-Cu-Al ribbons were dealloyed by electrochemical selective dissolution. As a result three-dimensional microporous structures were obtained at different conditions (electrochemical potential, temperature, dissolution time). The smallest porous were obtained at low temperatures and potentials. To study the effect of precursor microstructure on the porous structure the as-cast alloys were annealed at two different temperatures - above Tg to cause structural relaxation of the amorphous material and at temperature above Tx to produce crystalline alloy. It is shown that only the entirely amorphous (as-cast and low-temperature annealed) alloys form homogeneous microporous structures as a result of the selective dissolution. © 2015 Elsevier Ltd.

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