Wyniki wyszukiwania - Biblioteka Nauki

1

The effect of thermal treatments on the mechanical and electrical properties of nickel-coated carbon fibre composites

100%

Pierozynski B.

Polish Journal of Chemical Technology

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2011

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tom 13

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nr 1

16-19

EN

Nickel-coated carbon fibre (NiCCF) composites may find technological applications within many industrial sectors, including: laptop computers, automotive and military industries. Typically, these applications require that NiCCF be subjected to extensive material processing; thus, optimization of mechanical (and electrical) properties for this material at the stage of its production is of significant importance. The present paper reports the application of specific, high-temperature heat treatments to laboratory-produced 12K50 NiCCF material, carried-out in order to improve the ductility and interfacial adhesion of electrodeposited Ni coating to the surface of carbon fibre substrate.

2

Changes proposed for the IEC 93 standard concerning measurements of the volume and surface resistivites of solid dielectrics

100%

Lisowski M. , Skopec A. , Kacprzyk R.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

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2004

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tom Vol. 40, nr 15

147-152

EN

The IEC93 Standard, prepared by the International Electrotechnical Commission in 1980, sets up methods of measurements, determination and calculation of volume and surface resistivities of solid dielectrics. The document contains some editorial mistakes as well as content-related inaccuracies that require revision. Besides corrections of obvious editorial mistakes it is suggested to introduce some content-related improvements. The most important remarks given in the paper are associated with the following problems: 1) shunting of the current meter by the resitance between guarding and guarded electrodes; 2) significant influence of the electrodes made of conducting rubber on volume resistivity measurements results; 3) errors associated with application of simplified expressions tor resistivities calculations (volume resistivity for tubular samples, surface resistivity for samples with circular electrodes); 4) measuring electrode used for cylindrical samples; 5) increase of the effective surface of the measuring electrode (margin width determination and consideration). Finally, proposals of alterations of particular clauses of the standard, supplemented with appropriate justifications, were given in the paper.

3

Frequency domain electromagnetic and electrical resistivity geophysical investigation of tar sands deposits in the Ijebu Waterside area, Eastern Dahomey Basin, southwestern Nigeria

100%

Osinowo O. O. , Okechukwu I.

Geology, Geophysics and Environment

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2021

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tom Vol. 47, no. 4

217--226

EN

The use of electromagnetic conductivity and electrical resistivity geophysical techniques has been employed in this study to investigate the occurrence, thickness, and spatial distribution of bitumen deposit around Makun-Omi in the Ijebu Waterside area of southwestern Nigeria. Subsurface apparent conductivity distribution data obtained using Geonic 34-3 equipment along fifteen traverses which sounded from different depths of 7.5, 15, 30 and 60 m at inter-coil separation of 10, 20 and 40 m in vertical and horizontal coupling modes and ground resistivity distribution measurements, obtained using Geopulse Tiger Allied resistivity meter at fourteen Vertical Electrical Sounding (VES) stations, were processed and employed to characterize the subsurface in terms of tar sands distribution. The conductivity and resistivity distribution in the form of a 3D earth model, iso-depth maps, 2D sections generated from the processed conductivity and resistivity data indicate relatively low conductivity <20 mS/m and high resistivity >1300 Ωm values around tar/bitumen impregnated sands which mostly occurred in the southern part of the study area. Clearly defined conductivity and resistivity anomalies which delineate the lateral and vertical occurrence of tar impregnated sands underscore the efficacy of integrating electromagnetic and electrical resistivity geophysical techniques to identify occurrence of economic deposits of tar sands in parts of southwestern Nigeria.

4

Synthesis of mono layer graphene oxide from sonicated graphite flakes and their Hall effect measurements

100%

Siyar M. , Maqsood A. , Khan S. B.

Materials Science Poland

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2014

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tom Vol. 32, No. 2

292--296

EN

Graphene, a single atom thick sheet is considered a key candidate for the future nanotechnology, due to its unique extraordinary properties. Researchers are trying to synthesize bulk graphene via chemical route from graphene oxide precursor. In the present work, we investigated a safe and efficient way of monolayer graphene oxide synthesis. To get a high degree of oxidation, we sonicated the graphite flakes before oxidation. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results confirmed graphene oxide formation and high degree of oxidation. Raman spectroscopy and atomic force microscopy (AFM) results revealed a monolayer of graphene oxide (GO) flakes. The sheet like morphology of the GO flakes was further confirmed by scanning electron microscopy (SEM). The Hall effect measurements were performed on the GO film on a silica substrate to investigate its electrical properties. The results obtained, revealed that the GO film is perfectly insulating, having electrical resistivity up to 8.4 × 108 (W_cm) at room temperature.

5

Charakterystyka rezystancyjna wilgotnej masy formierskiej

100%

Szmigielski T.

Archiwum Odlewnictwa

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2004

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tom R. 4, nr 14

508-513

PL

W pracy opisano sposób wyznaczenia krzywej wzorcowej dla wybranej masy formierskiej wyrażającej przebieg oporności elektrycznej masy w funkcji zawartości wilgoci. Stwierdzono, że charakterystyki rezystancji w funkcji wilgotności można opisać zależnością dla modelu wykładniczego: y = [...] dla W>2%. Wykazano, że odległość pomiędzy parą elektrod w badanym zakresie x =10 do 30 mm ma wpływ na uzyskiwane wartości rezystancji badanej masy.

EN

The paper describes a method of determining an analytical curve for a chosen moulding sand presenting a run of (electric) conductivity of the moulding sand in a dampness content function. It was found out that the characteristics of conductivity in the dampness function can be described by the following dependence y = [...] for W>2%. It was proved that the distance between a pair of eIectrodes in the range in question x =10 to 30mm has much less influence on the achieved values of the tested moulding sand resistance than it had been assumed.

6

Properties of GdFeAl ternary compound in two crystallographic structures

100%

Klimczak M. , Talik E. , Jarosz J. , Mydlarz T.

Materials Science Poland

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2008

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tom Vol. 26, No. 4

954--958

EN

Properties of the GdFeAl compound which crystallized in the cubic MgCu2-type structure as well as in hexagonal MgZn2-type structure were compared. The electrical resistivity, AC susceptibility and magnetization as a function of temperature revealed relatively high magnetic ordering temperature about 200 K. The differences in magnetization were observed for samples crystallizing in two different crystallographic structures. The magnetic moments measured at 4.2 K and up to140 kOe are very far from the magnetic moment value for free Gd ion. The magnetic moment values of cubic and hexagonal phases are 1.1 μB and 1.7μB, respectively.

7

Electronic structure and electric properties of Gd(In1-xSnx)3 compounds

100%

Kwiecień M. , Chełkowska G. , Betlińska A.

Materials Science Poland

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2007

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tom Vol. 25, No. 2

411--416

EN

Results of measurements of the electrical resistivity, crystal and electronic structure of Gd(In1-xSnx)3 compounds are reported. All these compounds crystallize in the cubic AuCu3 type structure. The effect of partial substitution of In by Sn atoms is reflected in a linear increase of the unit cell volume. The temperature dependence of the electrical resistivity ?strongly depends on the composition. For compounds with x ??0.1, the ??(T) behavior, observed at low temperatures, is untypical of metals. The electronic structure of all systems was studied by using X-ray photoelectron spectroscopy. The chemical shift of the 4f Gd peak to higher binding energy with the increase of Sn concentration was detected. The valence band near the Fermi level is dominated by hybridized 5d Gd and 5p In/Sn states.

8

Validation of joint inversion of direct current and electromagnetic measurements

100%

Bała J. , Pięta A.

Acta Geophysica

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2010

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tom Vol. 58, no. 1

114-125

EN

One of the ways to improve the information content of a set of field data is that of combining the interpretation of disparate data sets. Electromagnetic and direct current resistivity methods suffer from inherent equivalence problem. Application of joint inversion for these measurements can overcome the problem of equivalence very well. In the present work, synthetic data from vertical electrical sounding (VES) and horizontal coplanar low-frequency induction sounding (EMHD) are inverted individually and jointly over different types of 1D earth structures. Global optimization with Monte Carlo Multistart algorithm was used in the calculations. The results obtained from the inversions of synthetic data indicate that the joint inversion significantly improves the solution reducing the ambiguity of the models.

9

Silicon Carbide Fabrication by Infiltration of Molten Fe-Si Alloy Through Two-Step Reaction Sintering

88%

Hanada Y. , Xiao Y. , Sonoda A. , Kang H.-G. , Nagayoshi H. , Yamamoto A. , Tokunaga T.

Archives of Metallurgy and Materials

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2019

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tom Vol. 64, iss. 4

1645--1652

EN

Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.

10

Deposition of Au, Au-V and Au-VOx on Si wafers by co-sputtering technique

88%

Narksitipan S. , Bannuru T. , Brown W. L. , Vinci R. P. , Thongtem S.

Materials Science Poland

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2009

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tom Vol. 27, No. 2

484--491

EN

Au, Au-V and Au-VOx thin films were deposited on Si wafers by a co-sputtering technique. A fourpoint probe shows that the electrical resistivity of pure Au thin film on Si wafer without annealing is 7.2 m?ocm. The resistivities of thin films deposited on Si wafers, with or without annealing, tended to increase with the increase in the V and VOx concentrations, and were attributable to the inhibited drift mobility of charge carriers within the films. By using the nanoindentation technique, the hardness in all cases also tended to increase with the increase in the V and VOx concentrations. The hardness of pure Au, without annealing, was 2.52 GPa. It decreased to 1.80 GPa and 1.75 GPa after annealing at 200 °C and 400 °C, respectively. SEM and TEM analyses revealed the presence of nanosized particles on the surfaces of the thin films. XRD analysis of Au-4.00% VOx film deposited on Si wafer detected the presence of Au, VO and Si. However, SAED analysis only detected the presence of Au on the film.

11

Geoelectric method applied in correlation between physical characteristics and electrical properties of the soil

88%

Filho A. M. S. , Silva C. L. B. , Oliveira M. A. A. , Pires T. G. , Alves A. J. , Calixto W. P. , Narciso M. G.

Transactions on Environment and Electrical Engineering

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2017

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tom Vol. 2, No. 2

37--44

EN

This paper presents the study of the relationship between electrical properties and physical characteristics of the soil. Measures of apparent electrical resistivity of the soil were made for different types of soil, varying moisture content gradually while maintaining a constant compaction, and then varying the compaction and relating it to a constant humidity. Development of a correlation surface is proposed in order to identify granulometry of the soil from moisture and compaction measurements. For the study of spatial variability, two areas were chosen to allow the change of moisture content and compaction in order to verify the measurement capacity of apparent electrical resistivity of the soil as methodology to identify change in soil dynamics. Results obtained show correlations among apparent electrical resistivity of the soil, moisture, soil compaction and clay content.

12

Prediction of Microstructure of Grey Cast Irons by Electrical Resistivity Measurements

88%

Petrič M. , Mrvar P. , Kastelic S.

Archives of Metallurgy and Materials

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2019

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tom Vol. 64, iss. 1

365--369

EN

The paper describes the influence of graphite shape, size and amount to electrical properties of different cast irons. Experiments of electrical resistivity measurements were conducted during solidification of four different melts in different time intervals from melt treatment by inoculation and nodularization. Metallographic analyses were made in order to determine the shape, size, distribution and amount of graphite and correlate results with electrical resistivity measurements. It was found out that nodular graphite is giving the lowest electrical resistivity and is decreased during solidification. Electrical resistivity of lamellar cast iron is increased during solidification since lamellas interrupt metal matrix severely. There is no significant difference in resistivity of vermicular cast iron from nodular cast iron. Smaller size of graphite and lower amount of graphite and higher amount of metal matrix also decrease resistivity.

13

Effect of MgB2 additives on structure, electrical and thermal properties of Eu1Ba2Cu3O7

88%

Akduran N.

Materials Science Poland

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2018

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tom Vol. 36, No. 4

609--615

EN

The effect of MgB2 addition on the Eu1Ba2Cu3O7 (EBCO) ceramics was systematically studied. Series of Eu1Ba2Cu3O7 + x(MgB2) samples (x = 0 wt.%, 0.05 wt.%, 0.1 wt.%, 1 wt.%, 3 wt.%) were prepared using traditional solid state method. X-ray powder diffraction measurements were used for phase identification. The lattice parameters and orthorombicity decreased with MgB2 addition. A standard four point measurement method was used to determine transition temperatures Tc of superconducting samples. Tc values of the samples were decreasing with MgB2 concentration. TGA results indicate thermal stability of doped samples.

14

Feed forward neural network and interpolation function models to predict the soil and subsurface sediments distribution in Bam, Iran

88%

Rezaei K. , Guest B. , Friedrich A. , Fayazi F. , Nakhaei M. , Beitollahi A. , Fatemi Aghda S.

Acta Geophysica

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2009

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tom Vol. 57, no. 2

271-293

EN

An application of the artificial neural network (ANN) approach for predicting mean grain size using electric resistivity data from Bam city is presented. A feed forward back propagation network was developed employing 45 sets of input data. The input variables in the ANN model are the electrical resistivity, water table as a Boolean value and depth; the output is the mean grain size. To demonstrate the authenticity of this approach, the network predictions are compared with those from interpolation methods and the same data. This comparison shows that the ANN approach performs better results. The predicted and observed mean grain size values were compared and show high correlation coefficients. The ANN approach maps show a high degree of correlation with well data based grain size maps and can therefore be used conservatively to better understand the influence of input parameters on sedimentological predictions.

15

Magnetic phase transitions from the point of view of macroscopic and microscopic methods

88%

Szytuła A.

Materials Science Poland

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2007

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tom Vol. 25, No. 2

313--320

EN

Magnetic phase transitions in some rare earth compounds are discussed from the point of view of different experimental methods. The discussion concentrates on the determination of phase transitions in magnetically ordered states. The data presented in this work suggest that the "classical" method, namely the specific heat method, does not yield information on phase transitions between commensurate and incommensurate magnetic structures.

16

Enhanced thermal conductivity of graphene nanoplatelets epoxy composites

88%

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

Materials Science Poland

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2017

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tom 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.

17

Chemically-modified polyaniline as a new conducting filler for polymer composites

75%

Kolasinska E. , Mazurek B.

Informatyka, Automatyka, Pomiary w Gospodarce i Ochronie Środowiska

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2014

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tom nr 4

94--97

EN

Polyaniline (PANI) is a potential filler in polymer composites with antistatic properties. As an intrinsic conducting polymer, PANI may be an alternative for carbons and metals. It is lighter than metals and shows better chemical affinity to traditional polymers than carbon allotropes. After modification, it may be incorporated into the matrix and thus helps to avoid the accumulation of static electricity in insulating polymers. In this research, insulating epoxy resin was filled with chemically-modified polyaniline and compared with classical fillers. Measurements of resistivity, thermal analysis and SEM observations were also conducted.

PL

Polianilina to (PANI) to potencjalny wypełniacz do kompozytów polimerowych o właściwościach elektrostatycznych. PANI, jako samoistnie przewodzący polimer, może stanowić alternatywę dla wypełniaczy węglowych i metalicznych. Jako polimer, polianilina jest lżejsza niż metale i wykazuje lepsze powinowactwo chemiczne do tradycyjnych polimerów niż węglowe. Po odpowiedniej modyfikacji, może być wprowadzona w matrycę w celu zapobiegania akumulacji ładunku w dielektrykach polimerowych. W poniższej pracy, wykorzystano chemicznie modyfikowaną polianilinę jako wypełniacz do żywicy epoksydowej i porównano jej działanie z tradycyjnymi dodatkami. Przedstawiono wyniki pomiarów rezystywności,analizy termicznej i obserwacji SEM.

18

Multifunctionality of cement based composite with electrostatic self-assembled CNT/NCB composite filler

75%

Zhang L. , Han B. , Ouyang J. , Yu X. , Sun S. , Ou J.

Archives of Civil and Mechanical Engineering

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2017

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tom Vol. 17, no. 2

354--364

EN

In this paper, electrostatic self-assembled carbon nanotube (CNT)/nanocarbon black (NCB) composite is employed as filler for developing multifunctional cement-based composites. The performances of the composites with different content of filler are investigated. The electrochemical impedance spectroscopy and equivalent circuit are used to explore the conductive and mechanical mechanisms of the composites. Experimental results indicate that the compressive strength and elasticity modulus of the composites sharply decrease when the filler content exceeds 0.77 vol.%. The percolation threshold zone of the electrical conductivity of the composites ranges from 0.39 vol.% to 1.52 vol.%. The piezoresistive properties of the composites with 2.40 vol.% filler are stable and sensitive, and the maximum fractional change of electrical resistivity is 25.4% when the stress amplitude is 10 MPa. The composites feature sensitive and linear thermal resistance effect when the filler content is 0.77 vol.%. Electromagnetic shielding effectiveness of the composites with 2.40 vol.% filler at 18 GHz is 5.0 dB, which is 2.2 times of that of the control samples. The composites exhibit high absorbing electromagnetic wave performances in the frequency range of 2–18 GHz, and the minimum reflectivity reaches −23.08 dB with 0.77 vol.% filler.

19

Phase equilibria in the Zr-Cu-Sn system and crystal structure of ZrCuSn and ZrCuSn2

75%

Romaka L. P. , Koblyuk N. O. , Stadnyk Y. V. , Frankevych D. P. , Skolozdra R. V.

Polish Journal of Chemistry

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1998

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tom Vol. 72, nr 7

1154-1159

EN

The isothermal section of the phase diagram of the Zr-Cu-Sn system has been constructed at 770 and 670 K. Two new ternary compounds were obtained and their crystal structure was determined. The ZrCuSn stannide crystallized with the TiNiSi structure type (space group Pnma, a=6.6279(1) A, b=4.3679(9) A, c=7.6791(2) A), the ZrCuSn2 structure belongs to the HfCuSi2 structure type (space group P4/nmm, a= 4.1350(7) A, c=9.225(3) A). Electrical resistivity and magnetic susceptibility of these compounds have been measured.

20

Electrical resistivity of disordered monolayer metallic films

75%

Jarguz P. , Paja A.

Materials Science Poland

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2006

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tom Vol. 24, No. 3

633--637

EN

Electron transport through a disordered two-dimensional array of potentials is investigated. The resistivity is calculated according to the Faber-Ziman diffraction model suitably modified for two-dimensional electron gas. The structure factor is obtained by means of numerical simulations. The pseudopotentials are assumed to be the Shaw potentials with appropriate screening. The resistivities of disordered monolayers of alkali metals have been calculated in this model using the parameters which allowed us to explain well the experimental data for the bulk materials.