HIGH-ENERGY NANOCRYSTALLINE Nd-Fe-B MAGNETIC MATERIALS – SYNTHESIS, CHARACTERIZATION, APPLICATION

One of the most widely used high-energy nanocrystalline permanent magnetic materials are Nd-Fe-B alloys. Current R&D of Nd-Fe-B magnets is focused on three major topics: increase of magnetic energy, improvement of corrosion resistance and reduction of rare-earth content as a way of decreasing prices of final magnetic material with still significant magnetic energy. Utilizing the high sensitivity of microstructure and magnetic properties of Nd-Fe-B alloys to the Nd content, three distinctive types of nanocrystalline alloys have been developed: stoichiometric magnets, Ndrich (decoupled magnets) and magnets with reduced Nd content (nanocomposite magnets). In the presented paper a brief overview of each type of Nd-Fe-B alloy is given, processing methods are outlined and several high technology application examples are presented. Based on experimental results obtained using modern high resolution characterization techniques optimal processing conditions for the selected synthesis method are presented. Trends and challenges in future R&D of magnetic nanomaterials are discussed

Formation of magnetic microstructure of the nanosized NiFe2O4 synthesized via solid-state reaction

Magnetic NiFe2O4 structure formation was studied through structural, compositional and magnetic characterization of obtained reaction products of a simple, high yielding and low-cost solid-state reaction. Initial annealing of the starting oxides mixture at 700ºC did not allow us to observe formation of the desired magnetic phase. In contrast, subsequent thermomagnetic measurements up to 800ºC indicated the considerable increase of the magnetic moment, which can be reasonably assigned to the changes in phase composition and formation of magnetic NiFe2O4 structure during the heating cycle of measurements. Nanosized NiFe2O4 phase formation has been confirmed by the following XRD and MS phase analyses and its nanocrystalline structure by XRD and SEM/TEM techniques. The obtained hysteresis loop taken after TM measurements suggest the increased volume of magnetically active material and thus additionally support the previous findings

Study of Nd-Fe-B Alloys with Nonstoichiometric Nd Content in Optimal Magnetic State

Characterization of two rapid-quenched Nd-Fe-B alloys with nonstoichiometric Nd content in the optimized magnetic state was carried out using the X-ray diffractometry (XRD), (57)Fe Mossbauer spectroscopic phase analysis (MS), electron microscopy (TEM), high resolution TEM (HREM) and Superconducting Quantum Interference Device (SQUID) magnetometer. The experimental results demonstrate the fundamental difference in the structure and magnetic properties of the two investigated alloys in the optimized magnetic state. The Nd-Fe-B alloy with the reduced Nd content (Nd(4.5)Fe(77)B(18.5)) was found to have the nanocomposite structure of Fe(3)B/Nd(2)Fe(14)B and partly alpha-Fe/Nd(2)Fe(14)B, with mean grain size below 30 nm. On the other side, the overstoichiometric Nd(14)Fe(79)B(7) alloy has almost a monophase structure with the dominant content of the hard magnetic phase Nd(2)Fe(14)B (up to 95 wt. %) and a mean crystallite size about 60 nm, as determined by XRD and TEM analysis. The results of magnetic measurements on SQUID magnetometer also suggest the nanocomposite structure of the Nd-low alloy and nanocrystalline decoupled structure of the Nd-rich alloy after the optimal heat treatment.open

EFECTS OF CHEMICAL COMPOSITION ON THE MICROSTRUCTURE AND PROPERTIES OF THE CU-Ge-Sb ALLOYS

In the current study a ternary Cu-Ge-Sb system has been experimentally assessed. Chemical and phase compositions of the alloy samples from three vertical sections Cu-GeSb, Ge-CuSb and SbCuGe were studied using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and confirmed by X-ray diffraction analysis (XRD). Hardness of the alloys was measured by Brinell method while hardness of phases was measured using micro Vickers method. Electrical conductivity of the studied alloys was measured using eddy current instrument. Based on experimentally determined values iso-lines of hardness and electrical conductivity for the whole ternary system were calculated using assumed mathematical models

Polymer-Bonded Magnetic Materials with Various Nd-Fe-B Filler Content

One of the more important developments in magnetic materials, polymer bonded magnets, have opened a new world of application opportunities. The Nd-Fe-B/polymer composite materials offer an excellent combination of strong magnetic and dynamical-mechanical properties. However, the transition temperatures of filler and matrix should be selected carefully considering the future application. Uniform particle distribution and good adhesion between Nd-Fe-B powder particles and polymer are essential for the quality of the composite, while stiffness of polymer matrix is one of the influencing factors as well. The damping properties of Nd-Fe-B/polymer composites with 15 wt.%, 50 wt.% and 75 wt.% of Nd-Fe-B powder were studied by dynamic mechanical analysis and compared with a pure polymer sample. Thermal stability was analyzed using a simultaneous differential scanning calorimetric and thermogravimetric analysis technique.11th Annual Conference of the Materials-Research-Society-of-Serbia (YUCOMAT 2009), Aug 31-Sep 04, 2009, Herceg Novi, Montenegr

Changes of attitudes toward students with Down syndrome using the programs of indirect contact

Ефикасност програма индиректног контакта на развој позитивнијих ставова до сада је најчешће била проверавана у односу на припаднике мањинских етничких група. Иако је објављено неколико студија усмерених на промену ставова деце типичног развоја према вршњацима са интелектуалном ометеношћу применом појединих програма индиректног контакта, као што су десегрегација, међугрупни контакт и замишљени контакт, до сада није проверавана ефикасност ниједног програма индиректног контакта на промену ставова ученика типичног развоја према вршњацима са Дауновим синдрoмом. Приказано истраживање је спроведено са циљем да се утврди утицај програма проширеног контакта који обухвата моделе десегрегације, међугрупног контакта, заједничког унутаргрупног идентитета и двоструког идентитета, као и програма замишљеног контакта на промену ставова ученика типичног развоја према вршњацима са Дауновим синдромом. Поред тога, студија је била усмерена на утврђивање да ли се ови програми разликују у погледу ефикасности у промени ставова, као и да ли се промене ставова одржавају током времена. Такође, истраживање је имало за циљ да утврди да ли разлике међу испитаницима у погледу учесталости контакта са особама са Дауновим синдромом, знања о Дауновом синдрому, емпатије, тенденције давања социјално пожељних одговора и пола испитаника имају утицај на ефикасност примењених програма...The efficiency of programs of indirect contact on the development of positive attitudes has so far mostly been checked in relation to minority ethnic groups. Although several studies have been published aimed at changing the attitudes of typically development children towards peers with intellectual disabilities using certain programs of indirect contact, such as desegregation, intergroup contact and imagined contact, the effectiveness of any program of indirect contact on the change of typically development students' attitudes towards peers with Down syndrome has not been explored. The following research was conducted in order to determine the effect of the extended contact program, which includes models of desegregation, intergroup contact, common ingroup identity and dual identity, as well as the program of imagined contact on the change of attitudes of typically development students toward their peers with Down syndrome. In addition, the study was aimed at determining whether these programs differ in terms of effectiveness in changing attitudes, as well as whether the changes in attitudes held over time. Furthermore, the study was aimed at determining whether the differences among the respondents regarding the frequency of their contact with people with Down syndrome, knowledge about Down syndrome, empathy, tendency of giving socially desirable responses, and gender of the respondents have an impact on the effectiveness of the applied programs..

Changes of attitudes toward students with Down syndrome using the programs of indirect contact

Ефикасност програма индиректног контакта на развој позитивнијих ставова до сада је најчешће била проверавана у односу на припаднике мањинских етничких група. Иако је објављено неколико студија усмерених на промену ставова деце типичног развоја према вршњацима са интелектуалном ометеношћу применом појединих програма индиректног контакта, као што су десегрегација, међугрупни контакт и замишљени контакт, до сада није проверавана ефикасност ниједног програма индиректног контакта на промену ставова ученика типичног развоја према вршњацима са Дауновим синдрoмом. Приказано истраживање је спроведено са циљем да се утврди утицај програма проширеног контакта који обухвата моделе десегрегације, међугрупног контакта, заједничког унутаргрупног идентитета и двоструког идентитета, као и програма замишљеног контакта на промену ставова ученика типичног развоја према вршњацима са Дауновим синдромом. Поред тога, студија је била усмерена на утврђивање да ли се ови програми разликују у погледу ефикасности у промени ставова, као и да ли се промене ставова одржавају током времена. Такође, истраживање је имало за циљ да утврди да ли разлике међу испитаницима у погледу учесталости контакта са особама са Дауновим синдромом, знања о Дауновом синдрому, емпатије, тенденције давања социјално пожељних одговора и пола испитаника имају утицај на ефикасност примењених програма...The efficiency of programs of indirect contact on the development of positive attitudes has so far mostly been checked in relation to minority ethnic groups. Although several studies have been published aimed at changing the attitudes of typically development children towards peers with intellectual disabilities using certain programs of indirect contact, such as desegregation, intergroup contact and imagined contact, the effectiveness of any program of indirect contact on the change of typically development students' attitudes towards peers with Down syndrome has not been explored. The following research was conducted in order to determine the effect of the extended contact program, which includes models of desegregation, intergroup contact, common ingroup identity and dual identity, as well as the program of imagined contact on the change of attitudes of typically development students toward their peers with Down syndrome. In addition, the study was aimed at determining whether these programs differ in terms of effectiveness in changing attitudes, as well as whether the changes in attitudes held over time. Furthermore, the study was aimed at determining whether the differences among the respondents regarding the frequency of their contact with people with Down syndrome, knowledge about Down syndrome, empathy, tendency of giving socially desirable responses, and gender of the respondents have an impact on the effectiveness of the applied programs..

The Influence of Sintering Conditions on the Microstructure and Magnetic Properties of Sintered SmCo5 Magnets

Since the magnetic features of the magnet of Sm-Co type are in direct connection with microstructure, it is indispensable to achieve, in the procedure of synthesis of these materials, the microstructure which ensures the maximal values of the magnetic features.Proceedings of the Ninth World Round Table Conference on Sintering (IX WRTCS), held in Belgrade, Yugoslavia, September 1-4 199

The Impact of the Efficiency of the System for Vibrations Damping on the Efficiency of Vehicle Braking

This paper presents the plan and results of the research of the efficiency of the braking system depending on the condition of the shock absorbers and the velocity of the vehicle movement at the moment of braking. As expected, it has been proven that the braking efficiency decreases with decreasing efficiency of the system for damping vibrations. The interdependence of these two systems is also represented by a mathematical model that can serve for practical purposes in the analysis of traffic accidents