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91.
In order to simultaneously improve the conductivity and stabilize the contact resistance of electrically conductive adhesives (ECAs) containing silver flakes, different types of aminoaldehydes as multifunctional additives, N, N-dimethyl-4-aminobenzaldehyde (DABA), benzaldehyde (BA) as a comparison, and formamide (FA), were introduced into ECAs formulations. The results showed that when the optimal levels of FA, BA, and DABA were individually added into ECAs, the decrease in the resistivities of the ECAs were 34.8%, 67.2%, and 41.7%, respectively, compared to the control sample. This is because, during the curing process, the aldehyde acts as a reducing agent and reduces the oxidized silver flakes. Furthermore, the ECAs with FA or DABA had better contact resistance stability than that of the control sample under the condition of 85°C/85% relative humidity, but ECAs with BA could not stabilize the contact resistance on tin finish, The results indicate that FA and DABA can be adsorbed onto the tin surface and inhibit the occurrence of the galvanic corrosion on the interface between ECA and tin finish. The rheological results showed the processability of ECAs with FA, BA, and DABA were better than that of the control sample. However, the shear strength of ECAs with BA and DABA slightly declined.  相似文献   
92.
Abstract

High pressure electrical measurements were conducted in the antiferromagnetic insulator CoI, using a miniature Diamond Anvil Cell (DAC). The existence of a Mott Transition predicted from high pressure 129I Mgssbauer Spectroscopy (MS)1 has been verified. At about 8 GPa the system becomes metal1ic as evidenced by the temperature behavior of the conductivity. The conductivity at room temperature, however, still increases with increasing pressure, leveling off at 11 GPa. The metallic behavior in the 8 -11 GPa is explained by coexistence of metallic and insulating clusters via a percolating process. Above 11 GPa the material is completely metallic. This mechanism is consistent with the MS findings.  相似文献   
93.
Abstract

The temperature dependences of the resistivity of La0.7Ca0.3Mn1?xFexO3 and La0.7Ca0.3Mn1?xFexO3 (0 < × < 0.04) mixed crystals were studied under hydrostatic pressures up to 15kbar. The substitution of Fe for Mn results in an increase of the resistivity and a continuous decrease of the metal-insulator transition temperature Tmi while the substitution of Ge for Mn leads to a more complicated Tmi(x)-curve. In all cases Tmi shifts under pressure with a rate between 1.6 and 2.9K/kbar and a correlation between Tmi and its pressure derivative dTmi/dP is observed which is in accordance with the general trend of dTmi/dP versus Tmi as derived for other manganites and is discussed in terns of a competition between superexchange and double exchange.  相似文献   
94.
Normal state resistivity and Hall effect are shown to be successfully modeled by a two-band model of holes and electrons that is applied self-consistently to (i) dc transport data reported for eight bulk-crystal and six oriented-film specimens of YBa2Cu3O7?δ, and (ii) far-infrared Hall angle data reported for YBa2Cu3O7?δ and Bi2Sr2CaCu2O8+δ. The electron band exhibits extremely strong scattering; the extrapolated dc residual resistivity of the electronic component is shown to be consistent with the previously observed excess thermal conductivity and excess electrodynamic conductivity at low temperature. Two-band hole–electron analysis of Hall angle data suggests that the electrons possess the greater effective mass.  相似文献   
95.
ABSTRACT

The evolution of dislocations during shape-change of metal forms results from microstructural shear mechanism that is essential to enhance ductility. However, at room temperatures for face-centred cubic metals, this evolution results in the generation of vacancies that tend to form nano-voids, the growth of which leads to ductile failure. The correlated occurrence of dislocations and vacancies may be differentiated using the change of resistivity with plastic strain at 4.2?K, because resistivity is very sensitive to single vacancies compared to the formation of stacking faulted defects and dislocations. In order to assess the microstructure, the specific resistivity of these defect species was measured at 4.2?K, whereby thermal recovery processes are non-existent. The resistivity per dislocation line-length per volume was determined to be 1.87?×?10?25?Ωm3 for super-pure aluminium. The change in resistivity directly correlated to the shear flow stress squared. Vacancy-like defects formed during plastic flow were correlated to the recoverable resistivity after 298?K anneal and the derived volume fraction (CV) from mechanical data. The magnitude could be expressed as 12.9?×?10?9?Ωm per CV in % or as 1.21?×?10?25?Ωm3 in terms of line-length of vacancies per volume. The choice of representation depends on the presumed vacancy distribution. However, the recoverable flow stress upon 298?K anneal only appear to be proportional to √ CV at low strains; that is, at high strains the generated vacancies had transformed to defects that give rise to a small decrease in resistivity but a more notable increase in the flow stress. The possible mechanisms for this transformation are discussed.  相似文献   
96.
Antistatic poly(vinyl chloride)/quaternary ammonium salt based ion-conductive acrylate copolymer (PVC/QASI) composites were successfully prepared in a Haake torque rheometer. The surface resistivity of the PVC/QASI composites could be reduced to 107 Ω sq?1 order of magnitude when the QASI content reached 20 phr (parts per hundreds of resin). The surface resistivity of the composites was slightly sensitive to the relative humidity (RH), showing a good antistatic ability under an RH of 12%. Mechanical properties tests, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were also used to investigate the tensile strength, elongation at break, thermal properties, and morphology of the PVC/QASI composites, respectively.  相似文献   
97.
98.
99.
The calculations of electrical resistivity of Sn–Pb liquid metallic alloys/solutions are investigated by self-consistent approach. We employ modified empty-core pseudopotential to represent electron–ion interaction, while partial structure factors are calculated using Aschroft–Langreth scheme with hard sphere reference system. The potential parameters for elemental metals were optimised to structural data in our previous paper. Computed results for resistivity as a function of temperature and concentration are discussed with other such results. Overall good agreement confirms the applicability of the present model potential for computing the electrical properties, including thermal conductivity and thermoelectric power for liquid metallic alloys.  相似文献   
100.
Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63–6300 Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1 kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1 kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45 dB cm−1 to 3.77 dB cm−1 for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and −6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.  相似文献   
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