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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%.


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.


Ignat M.,Romanian National Institute for Research and Development in Electrical Engineering | Ovezea D.,Romanian National Institute for Research and Development in Electrical Engineering | Hamciuc E.,Petru Poni Institute of Macromolecular Chemistry | Hamciuc C.,Petru Poni Institute of Macromolecular Chemistry | Dimitrov L.,Institute of Mineralogy and Crystallography
Journal of Polymer Research | Year: 2014

New polyimide composite membranes were prepared by physical incorporation of different amounts of TiO2 nanotubes (TNTs) and carbon nanotubes (CNTs) into a poly(amic acid) solution, followed by film casting and thermal imidization. The poly(amic acid) was synthesized by polycondensation reaction of 4,4-(1,3-phenylenedioxy)dianiline with 4,4-oxydiphthalic anhydride, in N-methyl-2-pyrrolidone as solvent. TNTs having outer diameters of approximately 10-12 nm and length of several hundred of nanometers were obtained by hydrothermal method. Their surface was modified by treating with 3-aminopropyltriethoxysilane to enhance organic-inorganic compatibility and to avoid agglomeration. A study of microelectromechanical properties of these membranes was performed. The influence of filler content on nanometric displacements when an electric voltage is applied on the membrane surface was determined. Also, theoretical aspects on the combined effects thermal and electrostrictive actuation are presented. The longitudinal microactuation included only electrothermal effect. The microactuation including electrostrictive effect as well as electrothermal effect was remarkable to the small electric field intensity and to small temperature domain. © 2014 Springer Science+Business Media Dordrecht.


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.


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.

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