Logarithm Of Electrical Resistance Research Articles

Novel thermal‐sensitive properties of NBT‐BZT composite ceramics for high‐temperature NTC thermistors

AbstractWe found for the first time that (1 − x) Na0.5Bi0.5TiO3‐xBiZn0.5Ti0.5O3 (NBT–BZT) composite ceramics showed negative temperature coefficient (NTC) at a high temperature. The NBT–BZT nanopowders were successfully prepared by Pechini method. Their ceramics were sintered at 1100°C. The NBT–BZT ceramic exhibited a good linear relationship between logarithm of electrical resistivity (Inρ) and reciprocal of absolute temperature (1000/T) at 250°C–1050°C. The obtained ρ600, ρ900, and B600/900 constants of the NBT–ZBT NTC thermistors are approximately 5.92 × 106 to 3.01 × 104 Ω cm, 7.03 × 103 to 7.60 × 102 Ω cm and 2.3 × 104‐1.3 × 104 K, respectively. The electrical characteristics can be tuned to the desired value by changing the Na0.5Bi0.5TiO3 content in the compound. The electrical conductivity in these compounds is due to the electron jumps between Ti3+ and Ti4+ and oxygen‐ion conductivity. Results demonstrate a tremendous potential of the studied system for perovskite materials with NTC performance.

Electrical Resistivity of Cement Pastes Undergoing Cyclic Freeze-Thaw Action

AbstractThis study presents the electrical resistivity responses of saturated cement pastes undergoing cyclic freeze-thaw (F-T) action. An ordinary cement paste (OPC) and a blended paste (CS) containing ground granulated blast-furnace slag were used for the tests, and both pastes had water to binder ratios of 0.5. As the temperature decreases, the electrical resistivity increases. With increasing number of F-T cycles, the maximum electrical resistivity ρmax increases, revealing progressive frost damage. The pronounced frost damage has also been evidenced by the loss of compressive strength and the appearance of visible cracks for both OPC and CS samples. During freezing, discontinuities arise in the electrical resistivity versus temperature curves for both OPC and CS samples, implying the occurrence of ice nucleation. Moreover, the ice nucleation temperature θINT increases with F-T cycle number for all samples. The logarithm of electrical resistivity is a linear function of temperature after ice nucleatio...

FABRICATION AND CHARACTERIZATION OF Ni–Mn–Si–Al–O NTC THERMISTOR AND ITS APPLICATION AS TEMPERATURE WIRE SENSOR

A series of Al 2 O 3 substituted manganese oxide ceramic compounds, Ni 0.6 Si 0.2 Mn 2.2-x Al x O 4(0 ≤ x ≤ 0.6), were prepared by solid-state reaction route. The phase composition, microstructure, and electrical properties of compounds were studied. The results revealed that all the compounds were composed of cubic spinel structure without any other oxides. Besides they exhibited a linear relationship between logarithm of electrical resistivity (ln ρ) and reciprocal of absolute temperature (1/T) over a temperature ranging from room temperature to 300°C, which indicated a negative temperature coefficient (NTC) characteristic. The B25/85 constant was found to increase with the increase of Al 2 O 3 content. The B25/85 values of the NTC Ni 0.6 Si 0.2 Mn 2.2-x Al x O 4 thermistors for x = 0,0.1,0.2,0.3,0.4, and 0.6 were 4581, 4612, 4680, 4875, and 5089 K, respectively. Finally, a new method to produce one meter long continuous fire wire sensors was also proposed.

Patterns of pyrite oxidation by different microorganisms

The bacterial-chemical oxidation of natural pyrites with different physical, chemical, and electrophysical characteristics by bacteria Acidithiobacillus ferrooxidans, Sulfobacillus thermotolerans, and the archaeon Ferroplasma acidiphilum were studied. The electrophysical characteristics of three natural pyrites differed in the K thermoEMF value (pyrites 3, 4, hole conduction (p-type conductivity); pyrite 5, mixed type conductivity (n-p)) and in the logarithm of electric resistance. Chemical oxidation of pyrites 3 and 5 resulted in no changes of K thermoEMF. When pyrite 4 was oxidized chemically, the K thermoEMF values remained in the same range as in the initial sample, but the ratio of grains with different K thermoEMF values in the sample was changed: the number of grains with a higher K thermoEMF value increased. The same changes were also observed in the course of bacterio-chemical oxidation of pyrite 4. Of the three pyrites studied, an increase in the logarithm of resistance was observed only for chemical oxidation of pyrite 4 at 28°C. At higher experimental temperatures, the logarithm of resistance increased accordingly; more active bacterial-chemical oxidation resulted in a more pronounced increase in the logarithm of resistance than chemical oxidation. On bacterial-chemical oxidation of pyrites 3 and 5 by A. ferrooxidans and S. thermotolerans strains, iron was leached more actively than sulfur. Preferred bacterial-chemical oxidation of certain fractions from the pyrite samples was shown, namely of the pyrite 3 fraction with higher K thermoEMF values by the F. acidiphilum strain and of a fraction from the pyrite 5 sample with medium K thermoEMF values by the A. ferrooxidans and S. thermotolerans strains. The comparative assessment of bacterial-chemical pyrite oxidation by three types of microorganisms showed the direction of changes in the K thermoEMF values to be the same in the case of bacteria Acidithiobacillus ferrooxidans and Sulfobacillus thermotolerans and different in the case of the archaeon Ferroplasma acidiphilum.

A novel contamination sensor in solution: the response of the electric resistance of a composite based on crystalline polymer-grafted carbon black

The response of the electric resistance of the composite prepared from crystalline polymer-grafted carbon black as a function of the contamination in solution was investigated. The electric resistance of the composite prepared from poly(ε-caprolactone) (PCL)-grafted carbon black drastically increased in hexane, containing chloroform, trichloroethane, and ethanol and returned immediately to the initial resistance when it was transferred into pure hexane. The response of the electric resistance was highly reproducible. The logarithm of electric resistance was linearly proportional to the concentration of chloroform in hexane. Furthermore, the electric resistance of the composite prepared from crystalline poly(ethylene glycol) (PEG)-grafted and poly(ethylene adipate) (PEA)-grafted carbon black also drastically increased in hexane containing alcohol, which is a good solvent of the grafted chain (PEG and PEA). This is due to a widening of the gaps between the carbon black particles based on the absorption of solvent for these crystalline polymers.

Design and development of moisture meter for jaggery

Moisture is an important parameter, which determines the quality and storability of jaggery. The standard gravimetric method of moisture determination is tedious and time consuming as well. This paper deals with a new approach of moisture content determination which is quick and reliable. It has been found that the logarithm of electrical resistance of jaggery bears a linear relationship with its moisture content. Based on this information, an electronic moisture measurement system has been designed and developed. The system consisted of a resistive transducer (a pair of insulated steel electrodes which could be inserted in solid jaggery samples to desired depth), an impedance bridge, analog signal processing units and a digital display. The change in electrical resistance of the transducer, as a function of moisture content of the jaggery is processed by the measurement system to display moisture content on digital scale. The results obtained by using moisture meter were found to be in good agreement with those obtained by standard method of moisture determination of jaggery.

Carbon black/alumina gel composite: Preparation by sol-gel process in the presence of polymer-grafted carbon black and its electric properties

The preparation of a novel carbon black/alumina gel composite by sol-gel reaction of aluminum isopropoxide (AIP) was investigated. When sol-gel reaction of AIP was carried out in the presence of untreated carbon black, a thin film of alumina gel was hardly obtained, because of the presence of aggregated carbon blacks. On the contrary, in the presence of poly(N-vinyl-2-pyrrolidone)-grafted, poly(2-methyl-2-oxazoline)-grafted, and poly(N,N-diethylacrylamide)-grafted carbon black, a deep-black, thin film of alumina gel, in which carbon blacks were uniformly incorporated, was obtained. Carbon black was incorporated into an alumina gel matrix by the hydrogen bond between carbonyl groups of the grafted polymer and the residual hydroxyl groups in the alumina gel. Electric resistance of the polymer-grafted carbon black/alumina gel composite was very sensitive to the vapor of solvents of the grafted polymer chains on carbon black surface: the electric resistance of the composite drastically decreased in humidity and N,N-dimethylformamide vapor, but not in n-hexane vapor. The logarithm of electric resistance of polymer-grafted carbon black/alumina gel composite linearly decreased in proportion to relative humidity. In addition, the electric resistance of poly(N,N-diethylacrylamide)-grafted carbon black/alumina gel composite under humidity decreased drastically at 32°C. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3591–3597, 1999

A Novel Gas Sensor from Poly(ethylene glycol)-Grafted Carbon Black. Responsibility of Electric Resistance of Poly(ethylene glycol)- Grafted Carbon Black against Humidity and Solvent Vapor

Poly(ethylene glycol) (PEG) having different molecular weight was successfully grafted onto carbon black surface by direct condensation of terminal hydroxyl groups of PEG with carboxyl groups on the surface using N,N′-dicyclohexylcarbodiimide as a condensing agent. The electric resistance of a composite prepared from PEG and PEG-grafted carbon black drastically increased to 103–104 times of initial resistance in humidity and vapor of methanol, and ethanol, which are good solvent of PEG, and returned immediately to initial resistance when it was transferred in dry air. But the change of electric resistance of the composite was hardly observed in hexane and toluene vapor, which are poor solvent of PEG. The logarithm of electric resistance is linearly proportional to relative humidity. The sensitivity of electric resistance decreased with increasing molecular weight of PEG. In addition, the electric resistance of the composite from PEG-grafted carbon black lost the responsibility against solvent vapor above melting point of PEG. By crosslinking of the composite from PEG-grafted carbon black with triisocyanate, the responsibility against solvent vapor disappeared completely. These results indicated that the crystalline structure of PEG plays an important role on the responsibility of electric resistance of PEG-grafted carbon blacks against humidity and alcohol vapor.

Effect of elongation on electric resistance of carbon–polymer systems [I

Effects of elongation on the electric resistance of graphite–EVA(ethylene-acetate copolymer) systems were studied. It was found that a linear relation holds between the logarithm of electric resistance and elongation. We have made a simulation with tunneling junction-model. Namely, we have assumed that the system consists of many tunneling junctions which form series and parallel circuits through the system and that widths of tunneling potentials proportionally increase with elongation. The result of the simulation agrees with experiment: a linear relation holds between the logarithm of electric resistance and elongation. This implies that tunneling conduction plays an important role in carbon–polymer systems. However this result raises a new problem on the mechanism of switching which was thought to have been solved already.