Delia Patroi

Thermo-mechanical and tribological properties of phenolic polymers composites and C-C composites

Formaldehyde resin-based composites have been an inaugural step in obtaining and using composite materials and they have grown rapidly because of their multiple uses, especially in electrical and aeronautical field. Phenolic matrix composites represent a preliminary study to obtain mezophase carbon-carbon composites for advanced materials as potential solutions for reentry shields of cosmic vehicles and launch subsystems, as elements of modern braking systems in aircraft or as potential solutions for the components of the combustion chamber of rockets and also as hypersonic transport solutions for the future. Both phenolic matrix laminated composites and C-C mezophase matrix C-C composites were obtained. This paper presents an evaluation of the mechanical and tribological behavior of the obtained composites.

Some Considerations Concerning the Obtaining of Some Ag-SnO2 Sintered Electrical Contacts for Low Voltage Power Engineering Switching Devices

The paper presents some considerations concerning the obtaining and characterisation of some new electrical contact pieces of Ag-SnO2-MeO type, where the MeO is an additive chose from the series of metallic oxides WO3, Bi2O3 and CuO. These have a SnO2 content of 9.5 wt. %, a MeO content of 0.5 wt. %, the balance being Ag. The electrical contact materials were manufactured by powder metallurgy techniques using a new type of powder mixtures obtained from SnO2 and MeO powders which were wet mixed, simultaneously with “in situ” Ag synthesis. These present a very uniform and fine dispersion, which in turn leads to improved functional characteristics of the final electrical contact pieces in comparison to the dry mechanical powders mixtures. The new products were designed for low voltage power engineering switching devices working in air at In = 40, 125 and 200 A.

PAN/ZnO composite electrospun fibers for UV shielding applications

The aim of the presented work in this paper is to chemical synthesis of ZnO nanoparticles for PAN/ZnO electrospun composite fiber with UV shielding. During this work was study the influence of temperature of chemical synthesized on ZnO nanostructures structural and morphological properties. Composite fibers were electrospun using a PAN/ZnO solution in dimethylformamide (DMF). The effects of composition of polymer solutions on the morphological characteristics and UV shielding of fibers was investigated.

Biocorrosion and biodeterioration of some materials used in electrical engineering

Based on recent bibliographical data, representative actions of microorganisms on materials used in electrical engineering have been analyzed. The analysis undertaken have been revealed that the microorganisms, especially filamentous molds, have an important role in biocorrosion of metallic materials - in their presence the corrosion rate can increase up to 10 times. Biofilm formation on the surface of magnets has as effect the increasing of corrosion rate of approx. 7 times and degradation of magnetic characteristics. Microorganisms, especially filamentous molds have an important role in aging of the underground power cables insulation by initiating degradation of external polymeric jackets. On the other hand the microorganisms have a beneficial contribution in the biodegradation of insulating oils reached in the environment accidentally, in soil remediation and surface water pollution, respectively. It is noted that the biochemical processes of some microorganisms are stimulated by exposing of cultures to 50 ± 0.2Hz electric field, where the biocorrosion and biodeterioration processes are substantially accelerated / amplified.

Some Aspects Regarding the Complex Alloying of the Ni3Al Intermetallic Compound with Substitutional and Interstitial Elements

Research results focussed on the combined influence of iron and boron, in proportions of 0.5 and up to 10 wt.% respectively, in complex alloyed Ni3Al synthesised by Self Propagating High Temperature Synthesis (SHS) in the thermo-explosion mode at two ignition temperatures, 950 and 1150 oC, are presented. By XRD and Mössbauer spectroscopy it was established that for 950 oC ignition temperature, the evolved heat is not high enough for the added Fe to be fully incorporated into the synthesised Ni3Al phase, a temperature of 1150 oC being required. For this temperature, the density of the synthesised alloys, their capacity to be cold deformed by re-pressing, hardness and bending strength variations as a function of B and Fe contents, proved their cumulative effects of the ductility and mechanical properties of complex alloyed Ni3Al enhancing.

Obtaining of Ni Base Intermetallic Alloys by Solidification Control

Directional solidification techniques have been applied to produce Ni based intermetallic alloys with preferentially oriented columnar crystals extended along the complete length and parallel to the solidification direction. Enhanced ductility is expected from such alloys. In this paper we present the research results concerning the application of this technique to some complex Ni3Al- Fe-B alloys obtained from compacted mixtures of elemental powders. The corresponding master alloys have been obtained in a vacuum induction furnace by the known Exo-Melt process [1]. The directional solidification of these alloys was subsequently performed on cylindrical samples, at two solidification rates, 30 and 15 mm/h. The influence of the rate and composition used on the dimensional variations, densities, microstructure, constituent phases and lattice parameters, as well as on the surface chemical composition have been documented and are presented in the paper.