Aleksandar Grujic

MECHANICAL AND MAGNETIC PROPERTIES OF COMPOSITE MATERIALS WITH POLYMER MATRIX

Many of modern technologies require materials with unusual combinations of properties that cannot be met by the conventional metal alloys, ceramics, and polymeric materials. Material property combinations and ranges have been extended by the development of composite materials. Development of Nd-Fe-B/polymer composite magnetic materials has significantly increased interest in research and development of bonded magnets, since particles of Nd-Fe-B alloys are proved to be very suitable for their production. This study investigates the mechanical and magnetic properties of compression molded Nd-Fe-B magnets with different content of magnetic powder in epoxy matrix. Mechanical properties were investigated at ambient temperature according to ASTM standard D 3039-00. The obtained results show that tensile strength and elongation decrease with an increase of Nd-Fe-B particles content in epoxy matrix. The modulus of elasticity increases, which means that in exploitation material with higher magnetic powder content, subjected to the same level of stress, undergoes 2 to 3.5 times smaller deformation. Scanning Electron Microscopy (SEM) was used to examine the morphology of sample surfaces and fracture surfaces caused by the tensile strength tests. The results of SQUID magnetic measurements show an increase of magnetic properties of the investigated composites with increasing content of Nd-Fe-B particles.

Complexation of amidated pectin with poly(itaconic acid) as a polycarboxylic polymer model compound

Complexes based on amidated pectin (AP) and poly(itaconic acid) (PIA) were prepared by casting films from solutions of AP and PIA in different ratios with the pectin amount ranging from 10% to 90% by mass. The complexes were investigated by elemental analysis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetry (TG). In all investigated ratios of AP/PIA glassy transparent films with a uniform structure were obtained. The results of elemental analysis confirmed the composition of the complexes, and FTIR spectroscopy has shown carboxylic and amide peak shifting, indicating complex formation between AP and PIA. Comparison of thermograms of AP/PIA films with different ratios of AP indicated that the increase of the amount of AP increases the thermal stability of the films by retarding the onset of the main degradation processes.

Magnetic and Dynamic Mechanical Properties of Nd-Fe-B Composite Materials with Polymer Matrix

At the end of the last century whole variety of technical-technological achievements occurred. Cars overflow the streets, air-conditions coated the facades, everyday life became unimaginable without computers and cell phones; kitchens are filled with assorted appliances, and industry has been improved and enforced by high technology in order to achieve higher manufacturing products, with less energy and manpower consumption. If a deeper look is taken, behind modern design exteriors, inside all of these appliances, it is noticeable that one of the key roles in their performance is engaged by permanent magnets. These materials have very important role as functional components within the wider spectra of contemporary devices in different industrial branches, as well as in the wider consumption. One of the most important applications of the permanent magnets are: spare parts in AC and DC engines production (Slusarek & Dudzikowski, 2002), as well as synchronized motors, transformers, actuators, magnetic buffers, stationary fields, etc. (Gutfleisch et al., 2011). Information storage (hard discs), communications, medical appliances and scanners, automobile and aircrafts industries, could also be emphasized as important applications (Matsuura, 2006; Brown et al., 2002). The nanocrystalline Nd-Fe-B alloys are one of the most superior magnetic materials with high value of maximum energy production (app 50 MGOe) (Herbst, 1991). Besides their high values of the remanence and coercivity, as well as relatively high Curie temperatures (app 312 °C) (Sagawa et al., 1984) this type of magnetic alloys are identified suitable for research and further development of magnetic composite materials with polymer matrix, so called bonded magnets (Brown et al., 2006; Ma et al., 2002). Contemporary research in the field of magnetic composite materials on the basis of Nd-Fe-B alloys are directed into four basic directions: increase of magnetic energy, meaning optimisation of magnetic capacities; improving corrosion resistance; optimisation production process of process parameters; and reduction of the subtle rare earth content (Nd), targeting decreasing the price of the final magnetic material, keeping high values of the maximum magnetic energy. Application of

Phase diagram investigation and characterisation of ternary Sn?In?Me (Me = Ag, Cu) lead-free solder systems

The Sn?In?Me (Me = Ag, Cu) systems belong to the group of potential candidates for lead-free solder materials. Samples, representing two vertical sections: with In : Ag = 7 : 3 from Sn?In?Ag ternary system and with Cu : In = 1 : 9 from Sn?In?Cu ternary system, were measured with Differential Scanning Calorimetry (DSC). The experimental transformation temperatures were compared with CALPHAD-type calculation results based on thermodynamic parameter values from COST531 database. The characterisation of investigated samples was done using Scanning Electron Microscopy with Energy Dispersive X-ray (SEM?EDX), Light Optical Microscopy (LOM), electroconductivity and microhardness measurements.

Synthesis of NiFe2O4 nanofibers by joint sol-gel and electrospinning technique

In this study, electrospinning combined with sol-gel technique is applied in order to produce magnetic nickel ferrite (Ni-ferrite) nanofibers. The prepared Ni-ferrite gel was mixed with poly(vinylpyrrolidone) (PVP) solution which was used as a spinning aid to enable spinnability of the mixture. Structural and morphological characteristics of the as-spun ferrite gel/PVP composite web structure and calcinated Ni-ferrite nanofibers were analyzed using scanning electron microscopy (SEM). Phase composition analysis was carried out by Fourier-transform infrared (FT-IR) spectroscopy, X-Ray diffraction analysis (XRD) and 57 Fe Mossbauer spectroscopy (MS). The obtained results suggest that the pure nanocrystalline NiFe 2 O 4 dense mat to the almost coral-like structure of fibers with diameters ranging from hundreds of nanometers to few micrometers was obtained. The results of MS analysis revealed the existence of a crystallite size distribution within the material as well as the existence of a superparamagnetic fraction with very small crystallite sizes (<13nm). Magnetic behavior of the obtained material at elevated temperatures was also scrutinized using thermomagnetic measurements (TM) up to 800 °C.

Targeting and Design of Organic Rankine Cycle Systems for Multiple Heat Sources with Simultaneous Working Fluid Selection

Abstract We propose a systematic model for the optimum design of Organic Rankine Cycles (ORC) used for power generation from multiple heat sources available at different temperatures. The model enables the automated generation of inclusive and flexible ORC cascades and is optimized using a global optimization algorithm. Design parameters include the number of ORC cascades, the shared structure of the heat exchanger network, the operating conditions and the working fluid used in each cascade in order to identify an overall ORC structure that maximizes the power output. Results indicate significant operating improvements from using a double ORC cascade with different working fluids.

Design of Multi-pressure Organic Rankine Cycles for Waste Heat Recovery in Site Utility Systems

This work addresses the design of Organic Rankine Cycle (ORC) processes used for power generation from low-grade heat available in site utility systems. The Exergy Composite Curves approach is used within a systemic optimization framework to explore various complex ORC configurations. The method facilitates interconnectivity at several temperature and pressure levels, considering different types and numbers of turbines as design decision parameters simultaneously with other operating ORC features. It is employed to investigate the performance of two generic ORC configurations, namely one considering independent pressure loops with expansion turbines and the other considering pressure loops contacted through induction turbines. To optimize the number of pressure levels, ORC structural configuration, and operating parameters an inclusive objective function is used considering thermodynamic criteria. The application of the method is demonstrated by a case study on waste heat recovery and reuse in a utility plant.

Nanocrystalline Nd-Fe-B Alloys for Polymer-Bonded Magnets Production

This study presents how different nanostructures of starting Nd-Fe-B particles have influence on magnetic properties of polymer-bonded Nd-Fe-B materials. Two types of nanocrystalline Nd-Fe-B alloys were used for polymer composite production by compression molding technique. The particles with low neodymium content (Nd-low) have nanocomposite structure with small exchange coupling effect between hard and soft magnetic phase. In other hand, practically monophase hard magnetic structure of Nd-Fe-B particles with stoichiometric neodymium content (Nd-stoich) shows improved magnetic properties. With increasing concentration of polymer matrix, the coercivity (Hcb), remanence (Br), and maximum energy product ((BH)max) decrease more prominenty for composites with stoichiometric Nd-Fe-B content.