Eksperimentalna identifikacija uticaja geometrije alata na bočno razaranje materijala kod mikro rezanja mermera

Rad predstavlja eksperimentalnu analizu kod mikrorezanja mermera. Kod obrade krtih materijala na bazi kamena, moguće je postići obradu materijala u duktilnom režimu, čime se izbegava nekontrolisano razaranje materijala. Ukoliko se deo obrađuje u režimu krtog loma, postavlja se pitanje kako geometrijala alata utiče na intenzitet bočnog razaranja, i da li je moguće izbeći ili smanjiti, što je ujedno i tema ovog rada

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

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.

Design of PtSnZn Nanocatalysts for Anodic Reactions in Fuel Cells

In order to achieve widespread application of fuel cell technology, the development of an efficient and economical catalyst is a crucial step. Reducing the diameter of catalyst particles, producing particles with a specific orientation surface, and alloying noble metals with less expensive metals are possible approaches to improve catalyst performance. This study will be focused on novel ways for creating PtSnZn catalysts that are more effective for the anodic reactions in fuel cell such are methanol, ethanol and formic acid oxidation reactions. PtZn and PtSnZn nanoparticles were produced using the microwave assisted polyol method and were supported on high surface area carbon Vulcan XC-72R material. The electrochemical behavior of synthesized catalysts was investigated utilizing the cyclic voltammetry, chronoamperometric technique, and electro-oxidation of adsorbed CO. To determine the catalyst's physicochemical characteristics, X-ray diffraction (XRD), transmission electron microscopy analysis (TEM), and thermogravimetric analysis (TGA) were used. High catalytic activity of the PtSnZn/C catalysts was achieved thanks to the benefits of microwave synthesis and carefully adjusted metal alloying

Structure and magnetic properties of nanocrystalline NiFe2O 4 prepared via precipitation route

Nanocrystalline Ni-ferrite was synthesized by modified precipitation method in which soluble starch is used as dispersing agent and Na2CO 3 as a precipitating agent. NiSO4-6H2O and Fe(NO3)3-9H2O were used as precursors for nickel and ferric oxide, respectively. The obtained nanocrystalline Ni-ferrite was analysed and discussed through structural, compositional and magnetic characterization. Formation of pure NiFe2O4 phase with average crystallite size of 21 nm has been con rmed by X-ray di raction analysis (XRD). The determined phase composition was additionally supported by results of 57Fe Mössbauer phase (MS) analysis and material's nanocrystalline structure by field emission scanning electron microscopy (FE-SEM). Thermomagnetic behaviour was studied up to 800 C. The obtained room temperature magnetic hysteresis loop, recorded by means of a vibrating sample magnetometer (VSM), exhibits characteristic "S" shape of the soft magnetic material with the measured coercivity of about 10 kA/m and the specific moment up to 40 Am2/kg

Electrical Conductivity of Lignocellulose Composites Loaded with Electrodeposited Copper Powders. Part II. Influence of Particle Size on Percolation Threshold

This article is concerned with synthesis and characterization of electroconductive composite materials prepared by the compression molding of mixtures of lignocellulose and electrochemically deposited copper powder under different pressures, and investigation of the influence of particle size on conductivity and percolation threshold of obtained composites. Electrodeposited copper powder content was varied from 2.0-29.8 vol%. Analysis of the most significant properties of individual components and prepared composites included structural and morphological analysis and measurements of hardness and electrical conductivity. Hardness of the investigated composites, as expected, increased with the increase of the processing pressure, as well as lowering the particle size compared to previous work. The significant increase of the electrical conductivity can be observed as the copper powder content reaches the percolation threshold. The packaging effect and more pronounced interpartical contact with smaller, highly porous, highly dendritic particles with high values of specific area lead to "movement" of percolation threshold towards lower filler content, which for the particles LT 45 mu m and highest processing pressure of 27 MPa was 7.2% (v/v). In the investigated range of electrodeposited copper powder concentrations and applied pressures the increase of the electrical conductivity of composites is as much as fourteen 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

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

Influence of Electrolytic Copper Powder Particle Morphology on Electrical Conductivity of Lignocellulose Composites and Formation of Conductive Pathways

Composites based on polymers with conductive fillers have been gaining more significant roles in a variety of technological domains and they are getting in the research focus of numerous studies as a part of growing research trend. Galvanostatically produced copper powder with high values of specific area was used as filler for synthesis of electroconductive composite materials prepared by the compression molding of mixtures of lignocellulose and electrochemically deposited copper powder. This article is concerned with characterization of these composites. Analysis of the most significant properties of prepared composites and its components included measurements of electrical conductivity, impedance spectroscopy (IS) behavior and structural and morphological analysis. Volume fraction of the copper powder was varied from 2.0-29.8% (v/v). The significant increase of the electrical conductivity can be observed as the copper powder content reaches the percolation threshold (PT). It was shown that PT 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. The packaging effect and more pronounced interpartical contact with copper powder particles lead to "movement" of PT, which for the particles LT 45 mu m and highest processing pressure of 27 MPa was 7.2% (v/v). IS response of the composites showed existence of electrical conductive layers, each having different resistivity which increases towards interior of the composite

An overstoichiometric Nd–Fe–B hard magnetic material

A commercial Nd-rich Nd–Fe–B-based hard magnetic material was studied. The obtained results were compared before and after recording of the thermomagnetic curve up to 800 °C. The curve itself showed clearly besides Curie points of the Nd2Fe14B phase and α-Fe also another critical temperature. Mössbauer spectroscopic (MS) phase analysis and X-ray diffraction analysis (XRD) showed in addition to the commonly known phases Nd2Fe14B and NdFe4B4 also some paramagnetic and ferromagnetic iron atoms (MS) and Fe17Nd2 intermetallics (XRD). During the exerted thermal treatment, the content of the Nd2Fe14B and NdFe4B4 phases remained almost unchanged, while iron atoms from remnant minor phases built a separate α-Fe phase. The XRD pattern also showed the presence of some minor Nd phase. The results of Squid magnetic measurements suggest a nanocrystalline decoupled structure of the Nd-rich alloy in the optimized magnetic state. Measurement of the magnetization loop showed, in spite of small changes in the phase composition, that magnetic properties of the quality material deteriorated during the thermal treatment

Structural and mechanical properties of some aluminum-based binary alloys

The purpose of this study is to investigate structural and mechanical properties of some aluminum-based alloys. Microstructures of the Al-Sn and Al-Zn binary alloys were examined using optic microscopy. The mechanical properties - Vickers hardness and micro hardness tests were investigated according to standard procedure