Mihail Ionescu - Academia.edu (original) (raw)

Papers by Mihail Ionescu

Cubic silicon carbide (3C-SiC) is being investigated for two third generation photovoltaic (PV) d... more Cubic silicon carbide (3C-SiC) is being investigated for two third generation photovoltaic (PV) devices - the impurity photovoltaic (IPV) solar cell, and a silicon carbide/silicon superlattice structure for the upper cell in a tandem solar cell.

Journal of Macromolecular Science: Part A - Chemistry, 1985

A new principle for improving the catalytic activity of the classical complexes CuCl2-aliphatic a... more A new principle for improving the catalytic activity of the classical complexes CuCl2-aliphatic amines used for the oxidative coupling of 2,6-dimethylphenol (DMP) is presented. It is based on the “trans” effect, typical of the substitution reactions of ligands in the square planar complexes of platinum(II). Thus, by replacing a Cl anion with a strong “trans” effect-giving ligand such as NO2

ECS Journal of Solid State Science and Technology, 2014

Crystal Research and Technology, 2002

Tungsten trioxide is one of the potential semiconducting materials used for sensing NH 3 , CO, CH... more Tungsten trioxide is one of the potential semiconducting materials used for sensing NH 3 , CO, CH 4 and acetaldehyde gases. The current research aims at development, microstructural characterization and gas sensing properties of thin films of Tungsten trioxide (WO 3 ). In this paper, we intend to present the microstructural characterization of these films as a function of post annealing heat treatment. Microstructural and elemental analysis of electron beam evaporated WO 3 thin films and iron doped WO 3 films (WO 3 :Fe) have been carried out using analytical techniques such as Transmission electron microscopy, Rutherford Backscattered Spectroscopy and XPS analysis. TEM analysis revealed that annealing at 300 o C for 1 hour improves cyrstallinity of WO 3 film. Both WO 3 and WO 3 :Fe films had uniform thickness and the values corresponded to those measured during deposition. RBS results show a fairly high concentration of oxygen at the film surface as well as in the bulk for both films, which might be due to adsorption of oxygen from atmosphere or lattice oxygen vacancy inherent in WO 3 structure. XPS results indicate that tungsten exists in 4d electronic state on the surface but at a depth of 10 nm, both 4d and 4f electronic states were observed. Atomic force microscopy reveals nanosize particles and porous structure of the film. This study shows e-beam evaporation technique produces nanoaparticles and porous WO 3 films suitable for gas sensing applications and doping with iron decreases the porosity and particle size which can help improve the gas selectivity.

Biomaterials, 2007

Recent trials on diamond-like carbon (DLC) coated medical devices have indicated promise for bloo... more Recent trials on diamond-like carbon (DLC) coated medical devices have indicated promise for blood interfacing applications. The literature is sparse regarding structural and compositional effects of DLC on cellular response. An important goal in optimizing bloodinterfacing implants is minimal macrophage attachment, and maximal albumin:fibrinogen adsorption ratio. DLC coatings deposited by PACVD and FAD, were analysed with respect to sp 3 content (EELS), hydrogen content (ERDA), surface composition (XPS), surface roughness (AFM), surface energy, albumin:fibrinogen adsorption ratio, and macrophage viability and attachment. We found that increasing surface roughness and surface energy enhanced the macrophage viability and the albumin:fibrinogen adsorption ratio. We also found that the higher the hydrogen content for a-C:Hs deposited by PACVD, the lower the albumin:fibrinogen adsorption ratio, and macrophage attachment. This suggests that hydrogen content may be an important factor for influencing the biological response of DLC surfaces. Macrophage cells spread well on all DLC surfaces, and the surface results indicated the non-toxic nature of the surfaces on the cells at the time points tested. r

Journal of Polymers and the Environment, 2015

A novel bio based Mannich polyol using limonene was synthesized. Mannich polyols are a group of a... more A novel bio based Mannich polyol using limonene was synthesized. Mannich polyols are a group of amino polyols with aromatic structure which provide fire resistance, good thermal and superior physico-mechanical properties. The synthesized Mannich polyol was structurally characterized using wet methods (hydroxyl number, acid value and viscosity), gel permeation chromatography, and FT-IR spectroscopy. The Mannich polyol was successfully used for preparation of rigid polyurethane foams. Thermal analysis of the rigid polyurethane foams indicated that they were thermally stable up to 250°C. Studies based on dynamic mechanical analyses indicated that these rigid polyurethane foams have high glass transition temperature (~200°C). These foams have also high compressive strength and very regular cell structure with uniform size distribution. The closed cell content of these foams was higher than 90 %. The synthesized Mannich polyol based on limonene was very reactive, indicating that it is very suitable for preparation of rigid polyurethane foams using "spray" process.

Concerns about sustainability, ecology and needs for responsible management of our resources are ... more Concerns about sustainability, ecology and needs for responsible management of our resources are driving forces for greater utilization of biobased products. In this work we are describing new family of polyester polyols obtained partially or completely from renewable raw materials, and their application in cast polyurethanes. While hybrid polyether polyols are preferred in foam industry due to similarity in technology, polyester polyols may have advantages in special applications where higher oxidative stability and higher strength of polyurethanes is desired. Polyester polyols from castor oil, adipic acid and ethylene glycols were synthesized earlier and their application in polyurethanes discussed.

European Polymer Journal, 2015

A range of vegetable oil derivatives with hydroxyl, amine, isocyanate, isothiocyanate, epoxy and ... more A range of vegetable oil derivatives with hydroxyl, amine, isocyanate, isothiocyanate, epoxy and silane terminal groups, useful for making new bio-based polymers, were synthesized from mercaptanized oils and different allyl organic compounds by thiol-ene reaction. All products were low viscosity liquids of light yellow color except amine containing oil, which was a low melting solid. Novel functionalized oils had 3-6 functional groups per mole and were suitable for rigid and flexible polymer products.

Journal of Renewable Materials, 2013

This paper reviews a part of the rich fi eld of oleochemicals, their synthesis and applications a... more This paper reviews a part of the rich fi eld of oleochemicals, their synthesis and applications as precursors for polymers by referring to published data rather than discussing details of different reactions. The hope is to help readers in fi nding leads in the vast research area carried out over a long period of time, to avoid traps and to inspire new ideas for oil-based products and processes.

Journal of Cellular Plastics

Polyglycerol (PGL) is a polyhydroxyl compound obtained by selfcondensation of glycerol in the pre... more Polyglycerol (PGL) is a polyhydroxyl compound obtained by selfcondensation of glycerol in the presence of alkaline catalysts. It is a very attractive polyol as a starter for the synthesis of polyether polyols for rigid polyurethane foams. It is liquid, easy to handle and has a very high average functionality of 4-20 (or more) hydroxyl groups/mol. By propoxylation of PGL or PGL-sucrose mixtures, we obtained new polyether polyols with very high functionalities, which are very difficult or impossible to obtain by other methods. A new technology for PGL-based polyether polyols preparation was investigated. In the first step the self-polycondensation of glycerol to PGL in the presence of potassium hydroxide or potassium methoxide as a catalyst was carried out. In the second step, the crude alkaline PGL was alkoxylated with PO without removing the catalyst, followed by purification of the resulting polyether polyols. Rigid polyurethane foams prepared from the synthesized PGL-based polyether polyols and crude MDI displayed good physical and mechanical properties, excellent dimensional stability, and low friability.

Journal of Applied Polymer Science

Completely bio-based polyols, suitable for the preparation of rigid polyurethanes were synthesize... more Completely bio-based polyols, suitable for the preparation of rigid polyurethanes were synthesized from polyglycerol, lactic acid and fatty acids. Lactic units were introduced into the polyol structure by the ring opening addition of L-lactide to hydroxyl groups, in the presence of the titanium(IV) isopropoxide catalyst. To address the incompatibility issue of simple lactide–(poly)glycerol polyols with isocyanates, vegetable oil-based fatty acids were introduced into the polyol structure. Cast thermosetting polyurethane resins were prepared by reacting polyols with diphenylmethane diisocyanate. Polyurethanes were crosslinked glassy amorphous materials with tensile strength of ~ 60 MPa, flexural modulus of 0.9 - 2.3 GPa and notched Izod impact resistance of 30 - 80 J/m. These polyurethanes are potentially biodegradable.

Metallurgical and Materials Transactions E, 2014

ABSTRACT The effect of non-ionic surface active agents (surfactants) Triton X-100 (TX-100) and Tw... more ABSTRACT The effect of non-ionic surface active agents (surfactants) Triton X-100 (TX-100) and Tween 20 (Tw-20) and their role in potassium intercalation in electrolytic manganese dioxide (EMD) produced from manganese cake has been investigated. Electrosynthesis of MnO2 in the absence or presence of surfactant was carried out from acidic MnSO4 solution obtained from manganese cake under optimized conditions. A range of characterization techniques, including field emission scanning electron microscopy, transmission electron microscopy (TEM), Rutherford back scattering (RBS), and BET surface area/porosity studies, was carried out to determine the structural and chemical characteristics of the EMD. Galvanostatic (discharge) and potentiostatic (cyclic voltammetric) studies were employed to evaluate the suitability of EMD in combination with KOH electrolyte for alkaline battery applications. The presence of surfactant played an important role in modifying the physicochemical properties of the EMD by increasing the surface area of the material and hence, enhancing its electrochemical performance. The TEM and RBS analyses of the discharged EMD (-MnO2) material showed clear evidence of potassium intercalation or at least the formation of a film on the MnO2 surface. The extent of intercalation was greater for EMD deposited in the presence of TX-100. Discharged MnO2 showed products of Mn2+ intermediates such as MnOOH and Mn3O4.

Journal of Applied Polymer Science, 2015

ABSTRACT Novel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate... more ABSTRACT Novel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate route using dicyclic carbonates as precursors for both soft and hard segments. The hard segment was prepared from the dicyclic carbonate of bisphenol A and m-xylylenediamine as chain extender. The soft segment was poly(tetramethylene ether) glycol of molecular weight 1000. Three polyurethanes with different morphologies were made with soft segment concentration of 70, 50, and 30%. Method of synthesis consisted in preparation of dicyclic carbonate of bisphenol A from a commercial epoxy resin and carbon dioxide, while dicyclic carbonate of poly(tetramethylene ether) glycol (PTMEG) was made from previously prepared diglycidyl ether of PTMEG and carbon dioxide. Polymers were prepared by reacting dicyclic carbonates with m-xylylenediamine by one-pot process. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, differential scanning chromatography, thermogravimetric analysis, 1H NMR, 13C NMR, scanning electron microscopy, and mechanical measurements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42492.

The thin-film electrodes of LiNi0.8Co0.2O2 were deposited by pulsed laser ablation. The average t... more The thin-film electrodes of LiNi0.8Co0.2O2 were deposited by pulsed laser ablation. The average thickness of these thin-films was measured by AFM to be approximately 0.62μm. The electrochemical properties of LiNi0.8Co0.2O2 thin-films as working electrode in lithium cells were characterized by galvanostatic charge/discharge, cyclic voltammetry and ac impedance spectroscopy. The average capacity of these thin-film electrodes is about 60–62.5μA/cm2μm. The Li+

ECS Transactions, 2009

ABSTRACT In this paper, we review and present the results of carbon nanotubes syntheses using var... more ABSTRACT In this paper, we review and present the results of carbon nanotubes syntheses using variety of CVD and PECVD techniques that are available in our laboratories. The techniques included Joule-heating CVD, floating catalyst CVD, conventional thermal CVD, aerosol-assisted CVD, spray pyrolysis CVD, radio frequency plasma enhanced CVD (PECVD) and microwave plasma enhanced CVD. Influences of synthesis methods on the CNTs growth have been compared and discussed. The synthesized CNTs have been characterized by various techniques, including Raman Spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These studies are expected to pave the way to develop strategies for controlled synthesis of CNTs tailored for specific applications, including sensors and nanodevices.

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Journal of Superconductivity, 1994

High-quality single crystals are well suited to the investigation of some intrinsic material prop... more High-quality single crystals are well suited to the investigation of some intrinsic material properties. A modified Bridgman method using a sharp temperature gradient (approximately 300 C cm) was used to grow Bi[sub 2]Sr[sub 2]Ca[sub 1]Cu[sub 2]O[sub 8+x] single crystals. Although the samples was contained in alumina ampoules, no aluminium contamination of the samples was detected. Blade-shaped crystals up to [approximately]

Journal of Cellular Plastics, 2014

ABSTRACT This paper examines the feasibility of using polyols from vegetable oils as base polyols... more ABSTRACT This paper examines the feasibility of using polyols from vegetable oils as base polyols (i.e. with 50% or more in a blend with petrochemical polyols) for flexible molded polyurethane foams. A series of hyperbranched (HB) polyols were synthesized by transesterification of hydroxy fatty acid methyl esters and different modifiers to control viscosity, hydrophilicity, molecular weight, and functionality. All HB polyols had hydroxyl numbers around 85 mg KOH/g, with the exception of one which was 105 mg KOH/g. When mixed with petrochemical polyols with OH numbers 35 and 28 mg KOH/g, the HB polyols acted primarily as high molecular weight crosslinkers that increased the stiffness of the polymeric network and the load-bearing properties but decreased the tensile strength, elongation, and tear strength. However, most of the foams met the targeted tensile and tear strength values while some of the foam formulations provided satisfactory elongation. The best mechanical properties were obtained from foams with phthalic anhydride-modified HB polyols. It was demonstrated that flexible molded foams with satisfactory properties can be obtained with 50% and 65% of HB soy polyols in a blend with PPO polyols.