The effect of strontium on the electrical resistivity and conductivity of aluminum-silicon alloys

Metallurgical and Materials Transactions A - Electrical conductivity and resistivity measurements have been conducted on Al-Si and Al-Si-Sr alloys containing up to 12.6 wt pct silicon and 0.035 wt...     

Microstructures,mechanical properties,and electrical resistivity of rapidly quenched Fe-Cr-Al alloys

By the rapid quenching technique, ductile supersaturated ferrite solid solution with high hardness and strength as well as unusual electrical properties has been found in Fe-Cr-Al ternary system. This formation range is limited to less than about 35 at. pct Cr and 23 at. pct Al. The ferrite phase has fine grains of about 10 μm in diameter. Their hardness, yield strength, and tensile fracture strength increase with increase in the amounts of chromium and aluminum, and the highest values reach about 290 DPN, 720 MPa, and 740 MPa. These alloys are so ductile that no cracks are observed even after closely contacted bending test. The good strength and ductility remain almost unchanged on tempering for one hour until heated to about 923 K where a large amount of Cr₂Al compound begins to precipitate preferentially along the grain boundaries of the ferrite phase. The room-temperature resistivity increases with increasing chromium and aluminum contents and reaches as high as 1.86 μ Ώ m for Fe₅₀Cr₃₀Al₂₀ alloy. Also, the temperature coefficient of resistivity in the temperature range between room temperature and 773 K decreases with increasing chromium and aluminum contents and becomes zero in the vicinity of 20 to 30 at. pct Cr and 15 at. pct Al. Thus, the present alloys may be attractive as fine gauge high-resistance and/or standard-resistance wires and plates because of the unusual electrical properties combined with high strength and good ductility. formerly with the Research Staff of Tohoku University formerly Graduate Student of Tohoku University,     

Electrical resistivity of V-H alloys

The electrical resistivity has been determined at temperatures between 120° and 500°K for V-H alloys with hydrogen concentrations from 0 to 42.1 at. pct. A plot of the hydrogen solubility limit in vanadium shows that it increases from 0.5 at. pct at 227°K to 26.4 at. pct at 436°K. X-ray diffraction powder patterns indicated that alloys containing between 33.8 and 42.1 at. pct H were single-phase, bet, β-V hydride at room temperature. The resistivity of the 33.8 at. pct alloy closely approximated that of hydrogen-free vanadium, but the room temperature resistivity increased with increasing hydrogen concentration at the rate of 1.7 microhm-cm per at. pet H. These β alloys underwent one transformation at temperatures below 224°K and two more transformations near 450°K. The rationale has been based on increasing disorder of hydrogen in the interstices of the lattice with increasing temperature.     

Evaluation of the electrical resistivity of steels

Literature data on the physical properties of steels have been collected and put into a database. The resistivity of steels has been analyzed as a function of composition and microstructure. An overview over former studies is given. The steels have been investigated in two groups, ferritic steels and austenitic steels. A thermodynamic analysis with ThermoCalc has been performed. Regression analysis on the influence of composition on the resistivity was then carried out. The results for ferritic steels are: Si and Al have the highest elemental resistivity, followed by Mn, Cu, Ni, Mo, and Cr. C precipitated in cementite shows a high coefficient in the analysis when the amount of Fe bound in cementite is not considered separately. C in solution with ferrite shows no significant effect. Cr bound in cementite shows a significant effect but Mn, though present in cementite in comparable amounts, has no significant effect on the resistivity. N and C have the highest elemental resistivity in austenite, followed by the substitutional solutes Nb, Si, Ti, Cu, Ni, Mo, and Cr. The carbides NbC and TiC appear with a higher coefficient in the regression model than can be explained by phase‐mixture models providing upper and lower bounds for the resistivity of two‐phase alloys. Cr₂₃C₆ shows no significant effect. The regression results can be used to predict the resistivity of steels with known composition. The model predicts the resistivity of ferritic steels with a maximum deviation between experimental and computed value of 12 nōm and a standard deviation of 5.6 nōm. For austenitic steels, the model prediction shows a maximum deviation of 52 μōcm and a standard deviation of 20 nōm.     

The electrical resistivity of cytoplasm

The apparent cytoplasmic resistivity of two different giant cells has been measured using an extension of a previously developed single microelectrode technique. Each cell is penetrated by a metal microelectrode whose complex impedance is measured as a function of frequency between 500 kHz and 5.7 MHz. By plotting the measured impedance data on the complex Z plane and extrapolating the data to infinite frequency, the substantial effects of electrode polarization can be overcome. For Aplysia giant neurons and muscle fibers of the giant barnacle, the extrapolated cytoplasmic specific resistivities are 40 and 74 omega-cm, respectively, at infinite frequency. The barnacle data are in excellent agreement with sarcoplasmic resistivity values derived from the measured cable properties of other marine organisms, and from high frequency conductivity cell measurements in intact barnacle muscle tissue. In the Aplysia neurons, the frequency-dependent part of the electrode impedance is larger when the electrode is in a cell than when it is in an electrolyte solution with the same specific resistivity as the aqueous cytoplasm; however, the phase angle of the frequency-dependent component of the electrode impedance is the same in both cases. This suggests that the high apparent values of cytoplasmic resistivity found using the single microelectrode technique at lower frequencies probably reflect an artifact caused by reduction of the effective surface area of the electrode by intracellular membranes, with a corresponding increase in its polarization impedance.     

Crystal structure and electrical resistivity of MoS2-NbS2 alloys produced by self-propagating high-temperature synthesis

Conclusions Replacing Mo by Nb atoms in MoS₂ brings about a sharp fall in the latter's electrical resistivity because Nb is an acceptor impurity for MoS₂. The substitution of 5% Nb lowers to (1–2)·10^–3 ·cm, i.e., to the electrical resistivity level of graphite. The SHS method enables substituted Mo_1–XNb_XS₂ compounds (solid solutions) to be obtained directly froma mixture of the elements (without the need to prepare Mo-Nb alloys), which results in higher productivity and lower power consumption. Admixture of a substituted compound as a means of lowering the reaction temperature makes it possible to obtain a product whose electrical resistivity is fairly evenly distributed over the ingot (cake) cross section and, in addition, is appreciably lower than that obtained with the admixture of MoS₂. The formation of solid solutions during SHS occurs mainly in those places where the charge melts, i.e., at distances from the reaction cake surface greater than 5–7 mm.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 56–59, October, 1982.