Visokoenergetski nanokristalni Nd-Fe-B magnetni materijali - sinteza, karakterizacija, primena

Permanentni magnetni materijali na bazi Nd-Fe-B legura su jedna od najznačajnijih grupa visokoenergetskih nanokristalnih magnetnih materijala. Savremena istraživanja u razvoju ove grupe magetnih materijala su usmerena u tri glavna pravca: povećanje magnetne energije, poboljšanje otpornosti na koroziju i redukovanje sadržaja retke zemlje (Nd) u cilju sniženja cene finalnog magnetnog materijala, ali uz zadržavanje visokih vrednosti magnetne energije. Direktna zavisnost mikrostukture i magnetnih svojstava Nd-Fe-B legura od sadržaja Nd je iskorišćena za razvoj tri osnovna tipa magnetnih nanokristalnih materijala: sa stehiometrijskim sadržajem Nd, sa obogaćenim sadržajem Nd (dekuplovani) i sa redukovanim sadržajem Nd (nanokompoziti). U radu je dat kratak opis svakog tipa materijala, prikaz metoda dobijanja i neki od primera visokotehnološke primene. Za dabranu metodu sinteze dati su procesni uslovi za optimizaciju magnetnih svojstava na bazi dobijenih eksperimetalnih rezultata istraživanja, primenom savremenih i visokorezolutivnih metoda karakterizacije. Dat je takoĎe kratak osvrt na trendove i izazove u daljem razvoju magnetnih nanomaterijala.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

Electrical Conductivity of Lignocellulose Composites Loaded with Electrodeposited Copper Powders

Composites based on polymers with conductive fillers have been gaining more and more significant roles in a variety of technological domains and are in the research focus of numerous studies as a part of growing research trend. Natural polymers based on renewable materials with addition of chosen materials can be directly used as contemporary materials by electrochemical methods. This article is concerned with the preparation characterization of the basic components: electrodeposited copper powder and lignocellulose as well as composite materials prepared by the compression molding of lignocellulose and galvanostatically obtained copper powder mixtures. Analysis of the most significant properties of individual components and prepared composites included quantitative structural analysis, morphological analysis, determination of density and porosity and measurements of electrical conductivity. Different investigation techniques including SEM, TGA, DSC, X-ray, FTIR, particle size distribution and conductivity measurements were used. The electrical conductivity of the composites is LT 10(-15) MS/m, unless the metal content reaches the percolation threshold of 14.4% (v/v), beyond which the conductivity increases markedly by as much as 14 orders of magnitude. It was found that this transition occurs at lower volume fractions than stated in the literature which can be due to the filler with high specific area

Oksidacioni procesi pri zagrevanju praha intermetalnog jedinjenja SmCo5

Understanding of the thermal stability of intermetallic SmCo5 powder is essential for designing the working atmosphere in all phases of the technological procedure in the production of sintered SmCo5 magnets to obtain maximal magnetic properties. The thermal stability of the SmCo5 powder with defined chemical composition and particle size was investigated in the interval from 20 to 900*C. It was found by thermogravimetic analysis (TGA) that up to 240*C, the oxidation of SmCo5 does not occur. X-Ray diffraction of the thermogravimetric experimental residue of the SmCo5 powder, heated at 240*C, yielded only the presence of the SmCo5 phase. By X-ray diffraction analysis different crystal forms were identified depending on the maximal heating temperature. The following phases were identified: Sm2O3, Co, CoO, Co3O4 and SmCoO3. According to TG and X-ray results, for each of the investigated temperatures, the corresponding chemical reactions were established. The experimental data from both the thermal and X-ray investigations confirm that the phases of pressing and aligning the SmCo5 powder, in the process of producing sintered SmCo5 magnets, may be performed without a protective atmosphere

Uticaj uslova mlevenja na svojstva intermetalnog jedinjenja SmCo5

The dependence of magnetic properties of sintered magnetic materials, demands the quantification of the milling conditions. In this paper the part of the results of the investigation of the phase of milling of SmCo5 powder in investigated technological procedure for production of sintered SmCo5 magnets are presented. The dependence of particle size of SmCo5 powder and oxygen pick-of milling time has been investigated. By X-ray diffraction the occurrence of magnetic SmCo5 phase has been observed. According to experimental data, the optimal milling time has been established, obtaining the required SmCo5 powder particle size and having the allowed oxygen content.Зависност магнетних својстава синтерованих магнетних материјала захтева квантификацију услова глодања. У овом раду су представљени део резултата испитивања фазе млевења SmCO5 праха у истраженом технолошком поступку за производњу синтерованих SmCo5 магнета. Истражена је зависност величине честица SmCO5 праха и времена млевења при одабирању кисеоника. Дифракцијом Кс-зрака примећена је појава магнетне SmCO5 фазе. Према експерименталним подацима, успостављено је оптимално време млевења, добиjањем потребне величине честица праха SmCO5 и дозвољеним садржајем кисеоника

Modeling of coating optical fibers with polymer-magnetic powder composite coating

A mathematical model of forming a composite coating on optical fiber was established. The model is based on existing mathematical models for coating optical fibers with polymer coating and experimentally defined rheological behavior of the investigated dispersed system. The model was developed for a dispersed system consisting of poly(ethylene-co-vinyl acetate) - EVA in a form of toluene solution and powders of magnetic materials (BaFe12O19 and SmCo5). The influence of the die diameter, diameter of the original optical fiber, concentration of EVA and magnetic powders on the thickness of composite coating was investigated. The model shows good agreement with experimental data.Postavljen je matematički model formiranja kompozitne prevlake na optičkom vlaknu. Model je zasnovan na postojećim matematičkim modelima prevlačenja vlakana polimernom prevlakom i eksperimentalno utvrđenom reološkom ponašanju ispitivanog dispeznog sistema. Model je razvijen za disperzni sistem koji čine rastvor poli(etilen-ko-vinil acetat) EVA u toluenu i prahovi permanentnih magnetnih materijala (BaFe12O19 i SmCo5). Ispitivan je uticaj prečnika dizne, prečnika osnovnog vlakna, koncentarcije EVA i magnetnih prahova na debljinu kompozitne prevlake. Model pokazuje dobro slaganje sa eksperimentalnim podacima

The influence of protective atmosphere on oxidation of sintered SmCo5 magnetic materials

Understanding of the thermal stability of intermetallic SmCo5 powder is essential for designing the working atmosphere in all phases of the technological procedure in the production of sintered SmCo5 magnets to obtain maximal magnetic properties. The thermal stability of the SmCo5 powder with defined chemical composition and particle size was investigated in the interval from 20 to 900*C. Commercial SmCo5 powder was used in this experiment. The powder was milled in anhydrous toluene in an agate mortar to fine powder of quality used in the production of sintered magnets. All the experiments were carried out with powder of an average particle size of 7.23*m, established by SEM. The thermal stability of the SmCo5 powder in static air atmosphere was investigated by thermogravimetric analysis (TGA) using a DuPont Thermal Analyzer. Investigation of the behavior of SmCo5 powder during heating was carried out using new samples of SmCo5 powder for each of the investigated temperature cycles. It was found by TGA that up to 200*C, the oxidation of SmCo5 was negligible. X-Ray diffraction of the thermogravimetric experimental residue of the SmCo5 powder, heated at 240*C, yielded only the presence of the SmCo5 phase. By X-ray diffraction different crystal forms were identified depending on the maximal heating temperature. The following phases were identified: Sm2O3, Co, CoO, Co3O4 and SmCoO3. According to TG and X-ray results, for each of the investigated temperatures, the corresponding chemical reactions were established. The experimental data from both the thermal and X-ray investigations confirm that the phases of pressing and aligning the SmCo5 powder, in the process of producing sintered SmCo5 magnets, may be performed without a protective atmosphere.Истражена је могућност коришћења вакуума на граници између ниског и високог (10-3-10-4 bar) као заштитне атмосфере у фазама синтеровања и термичке обраде SmCo5 магнета. Испитан је утицај заштитне атмосфере на структурне промене SmCo5 магнета за различите температурне и временске интервале синтеровања, а за константну температуру и у време термичке обраде. Присуство оксидних и других инклузија у било ком делу синтерованих SmCo5 узорака, осим у површинском слоју, није доказано. Сканирајућом електронском микроскопијом (СЕМ), коришћењем Texture Analysis System-a ( TAS´+) мерена је дебљина оскидне зоне. Утврђен је регресиони модел према коме дебљина оксидне зоне расте са квадратом температуре синтеровања, а линеарно са временом синтеровања, за дефинисану температуру термичке обраде

Methods of characterization of multiphase Nd-Fe-B melt-spun alloys

Nanocomposite permanent magnetic materials based on Nd-Fe-B alloys with a low Nd content are a new type of permanent magnetic material. The microstructure of these nanocomposite permanent magnets is composed of a mixture of magnetically soft and hard phases providing the so called exchange coupling effect. Beside the optimization process parameters, methods of characterization have a very important role in the design of an optimal magnetic matrix of multiphase melt-spun Nd-Fe-B alloys. Different methods and techniques of characterization were used for observation and study of the microstructure evolution during crystallization. A summary results of measurements using different methods of characterization are presented to enable a better insight into relations between the microstructure and magnetic properties of the investigated melt-spun Nd-Fe-B alloys. .Nanokompozitni permanentni magnetni materijali zasnovani na Nd-Fe B legurama sa niskim sadržajem neodijuma predstavljaju novi tip permanentnih magnetnih materijala. Mikrostruktura ovih nanokompozitnih permanentnih magneta sastoji se iz smeše magnetno meke i magnetno tvrde faze između kojih se javlja "exchange coupling" efekat. Osim optimizacije procesnih parametara, metode karakterizacije imaju veoma veliku ulogu u dizajniranju optimalnog magnetnog matriksa višefaznih melt-spun Nd-Fe-B legura. Različite metode i tehnike karakterizacije korišćene su za posmatranje i proučavanje evolucije miktrostrukture tokom kristalizacije. Sumarni rezultati merenja, dobijeni primenom različitih metoda karakterizacije, prikazani su radi boljeg uvida u povezanost između miktrostrukture i magnetnih svojstava istraživane melt-spun Nd-Fe-B legure.

NdFeB permanent magnets with various Nd content

Three kinds of commercial Nd-Fe-B based materials were compared using 57Fe Mössbauer spectroscopy and X-ray analysis: near the Nd 2Fe14B stoichiometry and with both lowered and raised Nd content. Magnetically hard Nd2Fe14B is present in all three materials. In the Nd-low material it is accompanied with the magnetically soft Fe3B phase, building the nanocomposite structure. In the Nd-rich sample the overstoichiometric Nd atoms seem to build separate phase of Fe-Nd solid solution. None of the materials contain significant content of phases degrading magnetic characteristics, with except of minor Nd1.1Fe 4B4 one

Processing and properties of silver-metal oxide electrical contact materials

The presented study gives a brief overview of the experimental results of investigations of different production technologies of silver-metal oxide electrical contact materials in relation: processing method - properties. The two most common routes of production, i.e. internal oxidation/ingot metallurgy and powder metallurgy are demonstrated on the example of Ag-CdO and Ag-ZnO materials. For illustration of alternative processing routes that provide higher dispersion of metal-oxide particles in silver matrix more environmentally friendly Ag-SnO2 contact materials are used. Processing of electrical contact materials by mechanical mixing of starting powders in high energy ball mill is presented. The obtained experimental results of application of different methods of introduction of SnO2 nanoparticles in the silver matrix such as conventional powder metallurgy mixing and template method are given and discussed in terms of their influence on microstructure and physical properties (density, hardness and electrical conductivity) of the prepared Ag-SnO2 electrical contact materials

Electrical Conductivity of Lignocellulose Composites Loaded with Electrodeposited Copper Powders. Part III. Influence of Particle Morphology on Appearance of Electrical Conductive Layers

The electrical conductivity of the system based on lignocellulose (LC) biopolymer matrix filled with electrodeposited copper powder has been studied. Galvanostatically produced copper powder, having highly porous, highly dendritic particles with high values of specific area was used as filler. Volume fraction of the electrodeposited copper powder was varied from 2.0-29.8 vol%. Analysis of the most significant properties of prepared composites and its components included measurements of electrical conductivity, impedance spectroscopy (IS) behavior, structural and morphological analysis. The composite preparation conditions allowed the formation of a random distribution of metallic particles in the polymer matrix volume. It was shown that percolation threshold depends on both particle shape and type of spatial distribution. IS measurements have shown that particle morphology having pronounced grain boundaries has great effect on appearance of electric conductive layers, i.e.. movement. of percolation threshold towards lower filler volume fractions. IS response of the composites showed existence of electrical conductive layers, each having different resistivity which increases towards interior of the composite