Wyniki wyszukiwania - BazTech

1

Enhanced thermal conductivity of graphene nanoplatelets epoxy composites

Jarosinski L., Rybak A., Gaska K., Kmita G., Porebska R., Kapusta C.

Materials Science Poland

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2017

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Vol. 35, No. 2

382--389

EN

Efficient heat dissipation from modern electronic devices is a key issue for their proper performance. An important role in the assembly of electronic devices is played by polymers, due to their simple application and easiness of processing. The thermal conductivity of pure polymers is relatively low and addition of thermally conductive particles into polymer matrix is the method to enhance the overall thermal conductivity of the composite. The aim of the presented work is to examine a possibility of increasing the thermal conductivity of the filled epoxy resin systems, applicable for electrical insulation, by the use of composites filled with graphene nanoplatelets. It is remarkable that the addition of only 4 wt.% of graphene could lead to 132 % increase in thermal conductivity. In this study, several new aspects of graphene composites such as sedimentation effects or temperature dependence of thermal conductivity have been presented. The thermal conductivity results were also compared with the newest model. The obtained results show potential for application of the graphene nanocomposites for electrical insulation with enhanced thermal conductivity. This paper also presents and discusses the unique temperature dependencies of thermal conductivity in a wide temperature range, significant for full understanding thermal transport mechanisms.

2

Processing And Properties Of MAX Phases – Based Materials Using SHS Technique

Chlubny L., Lis J., Chabior K., Chachlowska P., Kapusta C.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2A

859--863

EN

Authors present results of works on the interesting new group of advanced ceramics called MAX phases – Ti-based ternary carbides and nitrides. They have an original layered structure involved highly anisotropic properties laying between ceramics and metals, with high elastic modulus, low hardness, very high fracture toughness and high electrical and heat conductivity. Using Self-Propagating High-Temperature Synthesis (SHS) in the combustion regime it is possible to prepare MAX phases-rich powders that can be used as the precursors for preparation of dense MAX polycrystals by presureless sintering or hot-pressing. Different novel Ti-based phases with layered structures, namely: Ti3AlC2 and Ti2AlC have been synthesized in a combustion regime. The possibility of controlling of combustion phenomena for obtaining near single-phase products is discussed in details as well as some of properties of the materials tested as structure and functional ceramics.

PL

Autorzy przedstawiają wyniki badań nad nową interesującą grupą zaawansowanych materiałów ceramicznych nazywanych fazami MAX – potrójnymi węglikami i azotkami tytanowymi. Posiadają one oryginalną strukturę warstwową, z której wynikają silnie anizotropowe właściwości (wysokie moduły sprężystości, niska twardość, bardzo wysoka odporność na kruche pękanie, dobre właściwości elektryczne i cieplne) umiejscawiające je pomiędzy ceramiką a metalami. Dzięki zastosowaniu Samorozwijającej się Syntezy Wysokotemperaturowej SHS możliwe było otrzymywanie bogatych w fazy MAX proszków, mogących służyć jako prekursory w preparatyce gęstych polikryształów za pomocą spiekania pod ciśnieniem lub swobodnego. Przeprowadzone zostały syntezy dwóch materiałów warstwowych: Ti3AlC2 i Ti2AlC. W artykule przedstawiono możliwości kontrolowania procesu spalania w celu uzyskania niemal jednofazowych produktów a także przedstawiono niektóre właściwości badanych materiałów pod kątem zastosowania jako materiały funkcjonalne i strukturalne.

3

Structural, magnetic, and Mössbauer effect studies of bornite

Przewoźnik J., Żukrowski J., Gondek Ł., Lemański A., Kapusta C., Piestrzyński A.

Nukleonika

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2013

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Vol. 58, No. 1

43-46

EN

The results of a combined study of bornite with Mossbauer spectroscopy, X-ray diffraction and DC magnetometry are reported. The orthorhombic crystallographic structure of the mineral is observed at 15 K and 300 K. It exhibits an increase of the orthorhombic distortion with decreasing temperature. Magnetic susceptibility shows a Curie-Weiss like behaviour between 230 K and 380 K corresponding to the effective magnetic moment of 7.2(3) mi B per formula unit. The material undergoes a transition to an antiferromagnetic-like state at 75 K. Mossbauer spectra at the paramagnetic range are doublets with a small quadrupole splitting and the isomer shift corresponding to a high spin Fe3+ state. Upon magnetic ordering, a coexistence of the paramagnetic doublet with a broadened magnetic sextet is observed indicating an inhomogeneous character of the magnetic transition. The hyperfine field of 350 kOe at 4.2 K is much lower than that observed for a high spin Fe3+ in oxides (510 kOe) which is attributed to covalence effects and a possible copper contribution to the effective magnetic moment of the compound.

4

Hyperfine interactions and irreversible magnetic behavior in multiferroic Aurivillius compounds

Jartych E., Gąska K., Przewoźnik J., Kapusta C., Lisińska-Czekaj A., Czekaj D., Surowiec Z.

Nukleonika

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2013

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Vol. 58, No. 1

47-51

EN

In this work investigations of structure and magnetic properties of conventionally sintered Bim+1Ti3Fem.3O3m+3 compounds with 4 less-than or equal to m less-than or equal to 8 were performed using X-ray diffraction, Mossbauer spectroscopy and vibrating sample magnetometry. Room-temperature Mossbauer spectra of the compounds correspond to a paramagnetic state, however, low temperature measurements (80 K) reveal the antiferromagnetic state with a residual paramagnetic phase. Temperature dependencies of magnetic susceptibility,chi sigma(T), provided magnetic ordering temperatures and revealed an irreversibility in Aurivillius compounds with m greater-than or equal to 5. In the case of Bi5Ti3FeO15 compound the chi sigma(T) dependence shows a paramagnetic behavior down to 2 K. The Bi6Ti3Fe2O18 compound reveals a magnetic ordering at 11 K. The compounds with m = 6-8 show a magnetic ordering at temperatures higher than 200 K. Highly irreversible character of their temperature dependencies of chi sigma indicates a spin-glass type disordered magnetism with frustration due to a random distribution of Fe on Ti at their sites.

5

EXAFS study of iron nanoparticles with oxide shell

Onyszko A., Kapusta C., Sieniawski J.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 10

597-600

EN

Purpose: The aim of this work is to present the results of the study of the local structure of iron nanoparticles with oxide shell which uses EXAFS method that apply synchrotronic radiation. Design/methodology/approach: The samples used in the carried out analysis were as follows: pure iron powder, pure iron powder containing nanoparticles and pure iron powder containing nanoparticles subjected to 224 hours of grinding. Findings: The local structure of iron nanoparticles with oxide shell were found. Research limitations/implications: It wa s not enough time to measure O:K edge. Practical implications: The analysis of spectra does not reveal any iron oxides in samples. More accurate results would be obtained at oxygen K edge. Originality/value: It was proved that iron nanoparticles with oxide shell samples had the local structure characteristic for metallic iron.